Improvement of productivity on hot dip galvanising line

by decreasing strip vibrations in gas jets cooling systems

(Stripvibrations reduction)

Research and Innovation EUR 25317 EN

EUROPEAN COMMISSION Directorate-General for Research and Innovation Directorate G — Industrial Technologies Unit G.5 — Research Fund for Coal and Steel

E-mail: rtd-steel-coal@ec.europa.eu RTD-PUBLICATIONS@ec.europa.eu

Contact: RFCS Publications

European Commission B-1049 Brussels

European Commission

Research Fund for Coal and SteelImprovement of productivity on hot dip galvanising line

by decreasing strip vibrations in gas jets cooling systems

(Stripvibrations reduction)

K. BeaujardArcelorMittal Global Research and Development

Voie Romaine, 57283 Maizières-les-Metz, FRANCE

M. RenardDrever International

LiègeScience Park, allée des Noisetiers 15, 4031 Liège-Angleur, BELGIUM

K. WillemsArcelorMittal Gent

John Kennedylaan 51, 9042 Gent, BELGIUM

A. Cano ArcelorMittal Sagunto

Carretera de Acceso IV Planta, KM 3,9, 46520 Sagunto, SPAIN

Grant Agreement RFSP-CT-2007-00017 1 July 2007 to 30 June 2010

Final report

Directorate-General for Research and Innovation

2013 EUR 25317 EN

LEGAL NOTICE

Neither the European Commission nor any person acting on behalf of the Commission is responsible for the use which might be made of the following information.

The views expressed in this publication are the sole responsibility of the authors and do not necessarily reflect the views of the European Commission.

More information on the European Union is available on the Internet (http://europa.eu). Cataloguing data can be found at the end of this publication. Luxembourg: Publications Office of the European Union, 2013 ISBN 978-92-79-24828-3 doi:10.2777/92028 © European Union, 2013 Reproduction is authorised provided the source is acknowledged. Printed in Luxembourg Printed on white chlorine-free paper

Europe Direct is a service to help you find answers to your questions about the European Union

Freephone number (*):00 800 6 7 8 9 10 11

(*) Certain mobile telephone operators do not allow access to 00 800 numbers or these calls may be billed.

Table of contents

FINAL SUMMARY.................................................................................................................................................5

BACKGROUND .......................................................................................................................................................5 STAKES ..................................................................................................................................................................5 INITIAL OBJECTIVES .............................................................................................................................................5 CONCLUSION ..................................................................................................................................................11

Scientific and technical approach..................................................................................................................11 Innovative content ..........................................................................................................................................12 Industrial interest and scientific / technical prospects ..................................................................................14 Consistency of resources and quality of partnership.....................................................................................14 Community added value and contribution to EU policies .............................................................................14 Exploitation and impact of the research results ............................................................................................15

1. PROJECT TIME SCHEDULE....................................................................................................................17

2. SCIENTIFIC AND TECHNICAL DESCRIPTION OF THE RESULTS................................................19

2.1. OBJECTIVES OF THE PROJECT ....................................................................................................19 Introduction ....................................................................................................................................................19 Stakes ..............................................................................................................................................................19 Program ..........................................................................................................................................................19

2.2. COMPARISON OF INITIALLY PLANNED ACTIVITIES AND WORK ACCOMPLISHED ...22 2.3. DESCRIPTION OF ACTIVITIES AND DISCUSSION....................................................................23

2.3.1. WP 1 – Analysis of Strip vibrations on ArcelorMittal Ghent industrial line 3 ...........................23 2.3.1.1. Task 1.1 Installation of measuring system .............................................................................................23

o Strip vibrations measurement system in the cooling tower:............................................................................23 o Representativeness of the trials run: ...............................................................................................................24 o Presentation of results:....................................................................................................................................25

2.3.1.2. Task 1.3 Characterization of line process parameters ...............................................................................25 Effect of the line speed ...........................................................................................................................................25 Effect of the strip traction: analysis of the campaign database .........................................................................26 Effect of strip traction at given line speed and strip formats: ............................................................................28

2.3.1.3. Task 1.2 Characterization of blowing parameters ................................................................................29 2.3.1.4. Task 1.4 Synthesis ....................................................................................................................................31

2.3.2. WP 2 – Optimisation of the influent parameters on the experimental cooling device at ArcelorMittal Research site ............................................................................................................................32

2.3.2.1. Task 2.1 Design and manufacturing.......................................................................................................32 2.3.2.1.1. Representativeness of the pilot line...................................................................................................32 2.3.2.1.2. General technical characteristics of pilot line ..................................................................................35 2.3.2.1.3. Plenums front side design of pilot line .................................................................................................35 2.3.2.1.4. Geometrical characteristics ...............................................................................................................36 2.3.2.1.5. Measurement systems of pilot line ....................................................................................................36 2.3.2.1.6. Strip positioning measurement system .............................................................................................37 2.3.2.1.7. Product................................................................................................................................................38 2.3.2.1.8. Influent parameters detected on industrial line...............................................................................38

2.3.2.2. Task 2.2 Reproduction of vibrations phenomena on the experimental 2/3 scaled cooling device .............38 2.3.2.2.1. Initial tested configuration ................................................................................................................39 2.3.2.2.2. Reproducibility of industrial strip behaviour........................................................................................39 2.3.2.2.3. Reproducibility of vibrations phenomena observed at ArcelorMittal Ghent line .................................41 2.3.2.2.4. Reproducibility of the trials campaign .................................................................................................41

2.3.2.3. Task 2.3 Modification of the cooling design in accordance with the vibratory mechanism theoretical model 42

2.3.2.4. Construction and improvement of vibrations theoretical model ....................................................43 2.3.2.4.1. Observation: 3 major strip behaviours .................................................................................................43 2.3.2.4.2. Collaboration ArcelorMittal - LadHyX Laboratory .......................................................................46 2.3.2.4.3. Experimental validation of theoretical model ..................................................................................47 2.3.2.5. Task 2.4 Test and optimisation of the improved cooling device ......................................................47 2.3.2.5.1. Influence of line velocity ....................................................................................................................47 2.3.2.5.2. Influence of strip tension......................................................................................................................48 2.3.2.5.3. Influence of blowing boxes pressure equilibrium ................................................................................51 2.3.2.5.4. Influence of blowing width ................................................................................................................52 2.3.2.5.5. Influence of a pressure difference between the 2 plenums..............................................................52 2.3.2.5.6. Influence of nozzles length ..................................................................................................................53 2.3.2.5.7. Influence of staggered arrangement .................................................................................................54 2.3.2.5.8. Influence of PAD ................................................................................................................................55 2.3.2.5.9. Task 2.5 Synthesis ..............................................................................................................................62

3

2.3.3. WP3 - Installation and optimization of the improved proposed solution in industrial conditions on Sagunto line ...............................................................................................................................................64

2.3.3.1. Contractor change due to economical crisis (2009)...............................................................................64 2.3.3.2. Task 3.1 bis: Trials campaign at Sagunto to characterize the initial state before implementing the innovative technology .................................................................................................................................................64

2.3.3.2.1. Measurement system and Cooling tower configuration..................................................................64 2.3.3.2.2. Effect of blowing pressure of blowing box 1 ....................................................................................66 2.3.3.2.3. Effect of blowing pressure of blowing box 2 ....................................................................................68 2.3.3.2.4. Effect of line speed .............................................................................................................................69 2.3.3.2.5. Synthesis..............................................................................................................................................70

2.3.3.3. Task 3.1 design & manufacturing of the innovative technology implementation at ArcelorMittal Sagunto line .................................................................................................................................................................71 2.3.3.4. Task 3.2 - Assembly and adjustment of the improved cooling device in the industrial line ..............72 2.3.3.5. Task 3.3 - Preparation of industrial tests....................................................................................................75 2.3.3.6. Task 3.4 - Installation of vibrations online measuring systems .................................................................77 2.3.3.7. Task 3.5 - Tests on industrial lines ............................................................................................................77 2.3.3.8. Task 3.6: Optimisation of the industrial cooling device ............................................................................82 2.3.3.9. Task 3.7: Synthesis...................................................................................................................................91 2.3.3.10. Global synthesis: Transferability to others concerned lines.................................................................92

2.3.3.10.1. Transfer to cooling tower of other galvanizing lines .....................................................................92 2.3.3.10.2. Transfer to rapid cooling sections of other galvanizing lines and continuous annealing lines...94

3. CONCLUSION..............................................................................................................................................97

3.1. SCIENTIFIC AND TECHNICAL APPROACH ...............................................................................97 3.1.1. INDUSTRIAL APPROACH.....................................................................................................................97

3.1.2. Experimental approach.................................................................................................................97 3.1.3. Scientific and theoretical approach ..............................................................................................98 3.1.4. Innovative content .........................................................................................................................99 3.1.5. Industrial interest and scientific / technical prospects...............................................................100 3.1.6. Consistency of resources and quality of partnership .................................................................100 3.1.7. Community added value and contribution to EU policies .........................................................101 3.1.8. Exploitation and impact of the research results.........................................................................101

4. LIST OF FIGURES.....................................................................................................................................103

5. LIST OF REFERENCES............................................................................................................................107

6. LIST OF ACRONYMS AND ABBREVIATIONS ...................................................................................109

4

FINAL SUMMARY

Background

The high standard of hot dip galvanized coating quality for the automotive and industry markets and the needs for high productivity require a good stability (low vibration level) of the strip on galvanizing lines (scratch and strip breaking risk, production of low coating weights). This is particularly true in the cooling zone after the zinc bath and in the tower because, in these zones, the strip is “excited” by gas jets cooling equipments using a high blowing speed. Online observations show clearly that the more the productivity increases, the higher is the gas flow rate and the more the vibratory amplitudes increase.

Today, the only industrial solution is to limit, in critical situations, the cooling capacities and consequently the line speed (with loss of productivity). Taking into account the needs for productivity and quality increases, strip vibrations problems can impact in the future all industrial lines because the cooling systems will be used to the maximum of their capacities or will even have to be boosted.

There is rare information and studies on the vibratory behaviour of a strip in gas jets cooling equipments. The fluid-structure interactions, at the origin of the vibration problems, and the links between the design of the cooling equipments, the process parameters and the vibrations are very badly known. Studies conducted in 2003 by ArcelorMittal Research and Drever, the supplier of the cooling equipments of many galvanizing lines in Europe, revealed that the more the productivity increases, the more the capacities of the cooling devices are solicited and the more the vibratory amplitudes of the strip increase. The industrial consequences are the followings ones:

- Defects of the surface quality like scratches

- Production breaks due to strip breaking

- Bad homogeneity of the zinc thickness (wiping zone)

- Increase of the production costs due to the increase of the zinc coating weight.

Stakes

In the next years all the industrial lines will use the maximum of their capacities and the maximal capacities of the cooling systems too. The stakes of the strip vibrations reduction are consequently important and in progress:

- Stakes in terms of productivity: Considering the increase of the line speed, the expected gains are evaluated at 1 to 2 M per line per year. That represents a gain of 50 M per year considering that 25 galvanizing lines are concerned by the problem of strip vibrations in the cooling zone.

- Stakes in terms of quality: Considering the control of the zinc weight and the current price of zinc, the expected gains are evaluated at about 0.5 M per line per year. That represents a gain of about 12.5 M per year for the 25 galvani zing lines which are potentially interested (2006).

Initial objectives

The objective is not to work on external stabilizing actuators like the application of magnets or inductive actuators but to work directly on the design of the cooling equipment which is the “exciting source” of vibrations.

The present project will lead to an innovative industrial cooling device minimizing the strip vibrations in the cooling zone. The new solution will enhance the line productivity and increase the coating quality

5

of the strip. The transferability of the technological solution to other typical cooling devices will be supported by recommendations reported at the end of the project.

Comparison between initial work program and performed work

ArcelorMittal Research (as coordinator), Drever (as contractor), ArcelorMittal Ghent (as contractor until end 2008), ArcelorMittal Sagunto (as contractor since beginning 2009) and the LadHyX laboratory (as sub-contractor) took part to the project with complementary roles. The working program can be divided into three steps:

WP 1) Analysis of strip vibrations on ArcelorMittal Ghent #3 industrial line equipped with an experimental measures system of the strip-nozzles distance in the wiping zone

The distance between the strip and the blowing nozzles has been measured on many points across the strip width and on many positions along the strip length (at the wiping section and between the cooling boxes on the top of the tower). Those measurements represent the strip vibrations amplitudes. The trials campaigns allowed characterizing precisely the strip behaviour under various process conditions:

o a detailed parametric study and a statistical analysis of the strip-nozzles distance have been carried out with standard production parameters to characterize the vibrations phenomena at the starting point.

o We identified and characterized the major influent line and blowing parameters on the strip vibrations in the gas jets cooling equipment of the industrial ArcelorMittal Ghent line N°3:

- process parameters like the blowing power, the strip traction or the line speed effect:

o the standard deviation increases with blowing power and decreases with strip traction.

o The line speed effect did not clearly appear because it is combined with others process parameters like the strip tension:

- Product parameters like the strip format:

o the more the strip is large, the more standard deviation is high

We collected the input data required to reproduce the observed vibrations phenomena on the experimental 2/3 scale cooling device located at ArcelorMittal Maizières.

WP 2) Optimization of the influent parameters on the experimental cooling device

The observed and characterized vibration phenomena specific for the ArcelorMittal Ghent HDG line have been reproduced on the semi industrial pilot line (experimental 2/3 scale cooling device). This experimental device has been designed and developed in collaboration with Drever. The representativeness of the trials carried out on pilot line to industrial conditions has been validated (vibrations frequencies reproduced).

Mechanisms of strip instability, major influent process parameters (blowing pressure, impinging surface depending on the nozzles arrangement, strip-nozzles distance) and geometrical parameters (nozzles orientation) have been identified and characterized.

6

Regarding the complete trial plan carried out, the major results are:

o Influence of process parameters:

o Blowing pressure: major influent parameter, as well as the velocity homogeneity across the strip width

o Line velocity: no influence

o Heterogeneous strip tension: major influence on vibrations mode, especially twist positioning, but difficult to manage in industrial conditions

o Influence of geometrical parameters:

o Pressure balancing between blowing boxes: no influence

o Pressure balancing nozzle width-wise: influent

o Strip-Nozzles distance: influent

o Nozzle length: major influent parameter: a minimal nozzle length is required.

o Blowing width: this can be an influent parameter in the case of low strip width (when 2 opposite air jets meet on the strip edges).

o Staggered nozzles: major influent parameter, easy to implement in industrial conditions, very good benefits

o PAD sheet: major influent parameter. More especially a maximal PAD-Strip distance is required, and this is easy to implement in industrial conditions

Exhaustive trials tests have been carried out to determine the optimized cooling design and lead to improved design: staggered nozzles; close to strip PAD sheet.

Regarding the previous results obtained on semi-industrial configuration and taking into account the transposability of obtained results to industrial lines, the ideal technical solution could be:

o To stagger the blowing boxes with a ½ step

o To put closer to the strip the PAD sheet (~40 mm for industrial line)

An important additional result consists on the identification of the main strip instability mechanism under air jets. It is a dynamical instability due to aeraulic forces and pressure fluctuations on strip surface.

We succeed in building a theoretical model of instable and stable domains, based on non-dimensional parameters and in collaboration with the LadHyX laboratory. This is an innovation by itself. The model is based on a physical approach and has been validated at laboratory scale pilot facility. Then it has been extended to the 2/3 scale experimental pilot of Maizières.

The first recommendations have been done for an industrial application at the ArcelorMittal Ghent #3 line. The innovative technical solution selected for the industrial line consists in the following modifications, with respect to the present situation:

o Upward displacement of the right-side plenum by 200 mm, corresponding to a half nozzle pitch;

7

o Upward displacement by 200 mm of the duct connecting the plenum and the fan.

Consequence of 2009 economic crisis: change of contractor

However, one of the project contractors should have to withdraw because of the 2009 economic crisis.

The current financial crisis has affected the load of the galvanizing lines of ArcelorMittal to an unprecedented extend, and forced the company to take measures to reduce drastically production costs and working capital. The cost reduction includes total idling of a number of galvanizing lines in order to maintain the load of the running lines at an acceptable level. In this context, the site of ArcelorMittal Ghent wished to withdraw from the project and stopped to implement the new cooler design on its galvanizing line N°3. The demand for galvanized automotive steel sheet was expected to restart and exceed capacity first in South Europe. In this region, the galvanizing line of Sagunto has beneficiated in the past years of investments that have made the vibrations from the tower cooling emerge as the next bottleneck. The value of Sagunto as a pilot line is equal to #3 Ghent; both are among the best and highest capacity European galvanizing lines for exposed automotive steel sheet.

So, because of potential technical benefits of the project and the potential quality and productivity gains of industrial implementation of the new cooling system developed into the current RFCS project, in agreement with all the RFCS contractors, the coordinator proposed to conduct the industrial implementation at ArcelorMittal Sagunto and not at ArcelorMittal Ghent.

The proposal has been presented at the TGS 5 meeting on May 2009 and accepted.

The project was rescheduled has to consider the industrial line changes. An additional task has been integrated into the planning without extra costs: task 3.1 bis “exhaustive industrial campaign at ArcelorMittal Sagunto line to characterize the initial strip vibrations state before implementing the designed solution”.

WP 3) Installation and optimization of the improved proposed solution in industrial conditions

The last step is to transfer the new cooling technology to standard industrial conditions and ensure the good functioning. It requires:

o To adapt the design, to manufacture and to install the industrial innovative cooling device, based on the design of the 2/3 scale pilot.

o To test and to optimize the new cooling device in industrial standard conditions and to evaluate the benefits by comparison between the performances of the improved industrial cooling device and the initial performances described in the status report made at the end of the first step (WP1).

As the tasks of WP1, especially the characterization of the strip vibrations initial state have been done on the ArcelorMittal #3 Ghent line, we add to reiterate those complete trials at the ArcelorMittal Sagunto Galvanizing line.

The trial run campaign has been carried out in standard production conditions and is representative of current production of the CGL line of ArcelorMittal Sagunto.

8

The campaign gives the real state of the art of strip vibrations in the cooling tower:

- Standard deviation at the wiping zone: ~ 2 mm

- Standard deviation in the cooling boxes: ~ 4.5 mm

For maximal cooling capacities (40 mbar / 100% for each cooling box) = worth case:

- Peak-to-peak amplitudes in the wiping zone: max. 17 mm + a kind of twist / crossbow strip positioning

- Peak-to-peak amplitudes in blowing boxes: max. 37 mm + a kind of twist strip positioning + strip displacement on one plenum side

Process parameters can influence the vibration amplitudes:

- Standard deviation increase with blowing power of both boxes 1 and 2

- To avoid strip displacement on one preferential plenum side, it is important to balance as much as possible the pressures between the 2 plenums of one blowing box, whatever the blowing is.

- The line speed effect did not clearly appear because it is combined with others process parameters like strip traction or immerged rolls settings.

In conclusion, those analysis show high potential to decrease strip vibrations at the wiping zone as well as in the cooling boxes by optimizing the design of the current cooling system.

The expected gains for Sagunto are:

- Reduction of strip vibrations amplitudes in the blowing boxes: factor 4

- Reduction of strip vibrations amplitudes at the wiping zone

- Line speed enhancement

- Zinc savings thanks better control of transversal and longitudinal coating homogeneity due to the strip stabilization

The transferability of the new technological solution is ensured by a report of recommendations for transferability to others industrial lines and through the writing of industrial procedures.

Implementation of the innovative cooling technology

The new cooling technology has been especially designed for the cooling tower configuration of Sagunto line. Manufacturing and assembly have been done on due time. The implementation has been also conducted on due time. Optimisation tests occurred and a specific trials campaign has been conducted to measure the benefits in terms of strip stabilization at the wiping section and at the top of the cooling tower.

The new cooling technology consists in staggering the blowing nozzles with a half pitch in order to homogenize the impingement surface on the strip (stabilization factor). The PAD sheets have been removed. Pressure regulation has been modified to maintain a good pressure balance between two

9

opposite plenums. All those actions results from the experimental trials conducted on the semi-industrial pilot facility (WP2).

The measurement campaign carried out after the implementation and for standard production conditions shows only a slight improvement of the strip stabilization. This is in discrepancy with the expected results. Fifteen hypotheses have been verified to explain the difference between experimental and industrial approaches. Only one hypothesis could explain the phenomena: the industrial nozzles staggering could not respect the half pitch (200mm) because of mechanical reasons, so that a staggering pitch of 160 mm only could be applied. This dissymmetrical staggering could be theoretically an influencing factor.

Even if the implementation at Sagunto line is in discrepancy with the expected gains, the transposition to others industrial galvanizing lines started. Indeed, the results obtained in this study for the control of strip vibrations are integrated in the new design proposed by the partner Drever International for the galvanizing and annealing lines. The new design dedicated to rapid cooling sections working under protective atmospheres and with high cooling rates is called Ultra Fast Cooling. Taking into account the time required between the design and the industrial start of each line, 5 new lines (Greenfield projects) are equipped with the new cooling design proposed by the partner Drever:

o 2 galvanizing lines and 1 annealing line in ShunYi (Beijing) for Shougang Company

o 1 galvanizing line and 1 annealing line in Wuhan, for Wisco Company (Cold Rolling Mill 3).

In the after-pot cooling section, staggered nozzles (straight nozzles and PAD nozzles without PAD sheet) are used, as presented for the pilot line and as used in the modified Sagunto line. In the Shougang CGL, there are no rolls to stabilize the strip and no casing surrounding the plenums. The control of strip vibrations is very good. All the Final Acceptance Tests (FAT) have been successfully passed for this line.

Same good results in terms of control of vibrations are obtained for the Wisco galvanizing line with the same design.

Transfer to rapid cooling sections of other galvanizing lines and continuous annealing lines

If the implementation of the recommendations did not bring all satisfaction for the Sagunto configuration, the same recommendations have been implemented by the partner Drever on many new lines (Greenfield projects for Asiatic companies). Especially the principle of nozzles staggering by a half pitch is implemented in the many cooling towers: operators do not observe strip instabilities and are convinced by the benefits of the new technology.

The recommendations of the projects have been integrated in the new design Ultra Fast Cooling equipment by the internal R&D team of Drever. Many lines are currently equipped with the new technology:

o The Shougang continuous annealing line N°1 and the galvanizing line N°1 are equipped with the new Ultra Fast Cooling Technology. It is also the case for the new Wisco continuous annealing line. The CAL N°1 and CGL N°1 rapid cooling sections contain three zones, the two last zones having a shorter length than the first one. To get the highest cooling performances, only the two short-length zones are used. The cooling rate is expressed in °C/s for a strip thickness of 1 mm. The excellent cooling performances of the Ultra Fast Cooling System without vibrations show the success of the project’s recommendations:

o until 101.6 °C/s.mm for the continuous annealing line N°1

o until 112.4 °C/s.mm for the continuous galvanizing line N°1

10

This means that a very good control of strip vibrations is required for this technology using high gas speed and short plenum-strip distance. Straight nozzles in staggered configuration are used in the Ultra Fast Cooling system. No scratch on the strips is observed during our tests and by the lines managers, demonstrating the very good performances of the design in terms of strip vibrations control.

Same good results in terms of control of vibrations for the Ultra Fast Cooling technology are obtained for the Wisco galvanizing line and continuous annealing line with the same design. The transfer of the know-how stored up during the project by all partners is ensured.

CONCLUSION

Scientific and technical approach

The project has been divided in 3 approaches: Industrial approach, Scientific and theoretical approach and experimental approach.

o Industrial approach

Because we changed one contractor, we finally conducted strip vibrations characterization on two different industrial lines: Ghent #3 (WP1) and Sagunto (WP3) HDG lines. Both have been equipped with experimental measurements to analyse on long periods the strip vibrations in the cooling zone to connect the strip behaviour with some process parameters.

The identification and characterization of the major influent line and blow parameters has been done during the trials at Ghent and confirmed during the trials campaign at Sagunto:

• Order 1 effect of the blowing pressure and blowing velocity

• Effect of the pressure balance in the opposite blowing boxes

• Order 1 effect of the strip tension

• No effect of the line speed (if the blowing power regulation loop is de-correlated to the line speed)

The good understanding and dynamism between all the parties allow to collect the required data to design the experimental 2/3 scale cooling device able to reproduce the strip vibrations characterized on industrial conditions. The trial campaigns conducted on both lines were also the opportunity to collect database to validate and to fit the theoretical vibrations model.

To answer to the question: “How do the vibrations appear and how they can be minimized?”, two complementary approaches were proposed. The first one consists in using the experimental 2/3 scale cooling device to define a new cooling geometry reducing strip vibrations and the second approach consists in testing the new solutions with a theoretical model.

o Experimental approach

The 2/3 scale experimental pilot has been designed and optimised to reproduce the strip vibration phenomena observed on the industrial line; especially the vibration modes and frequencies, and the vibration amplitudes were reproduced. We developed a reliable experimental tool to investigate in controlled conditions (strip tension for example):

o The influence of the blowing parameters: Blowing distance, Blowing width

11

o The influence of the geometry parameters: Nozzle assembly geometry, Plenum geometry, PAD sheet

o The influence of the process parameters: Line velocity, Strip tension

o The influence of the product properties: Thickness and width, Grade

In addition, dedicated measurements have been developed and used to characterize the effect of the blowing and geometrical parameters. As an example, the “hot wire” technique has been used to characterize with high reliability the jets velocity at the exit of the nozzles.

Starting from the database of the measurements of strip vibrations done in the exhaustive trials on pilot facility and thanks to expert knowledge, we propose a theoretical model able to predictive the strip instabilities.

Further trial campaigns on the experimental pilot allowed to validate and to fit the model.

o Scientific and theoretical approach

In order to understand and predict the physical mechanisms of strip vibrations, a parallel theoretical approach is necessary. The questions to answer are: What are the physical mechanisms which control the vibratory behaviour in a gas jets cooling system? What type of interactions exists between fluid and structure?

To predict the strip instabilities, the theoretical model of strip vibrations has been developed in collaboration with a subcontractor of ArcelorMittal Research. The objective of this collaboration is to determine some major characteristics of the flow instability, like the Reynolds Number Re. Observations have been done on laboratory with a rigid plan mounted in such a way that it allows rotational and translational motions, with one or two air jets normal to the plan. It was possible to identify the configurations leading to instability.

Specific measures have been conducted to characterize the vibration eigenmodes (stiffness, frequency, damping). The strip vibration mechanisms under the gas jets cooling system have also been identified:

o Vibrations due to recirculation loops between jets

o Vibrations due to turbulent flows

o Vibrations due to aeroelastic forces coupling inducing dynamical instability

More specifically a physical model has been developed to predict the vibrations due to aeroeleastic forces because it is the most damaging instability mechanism (contact strip-nozzle).

The trials campaign conducted on the experimental pilot facility under controlled conditions allowed validating the stability / instability predictive model.

The combination of these two complementary approaches allowed defining the new cooling technology implemented on the production lines.

Innovative content

The innovative part of the project consists in improving the existing cooling device to achieve higher line speeds and higher competitiveness.

12

1. A first project innovation consists in a detailed analysis of the strip vibrations induced by industrial gas jets cooling equipments. The project provides an exhaustive characterization of the vibration amplitudes and frequencies due to the cooling boxes. The influence of the strip format and the major process parameters has been clearly identified. This task allows working later at the experimental device in very close conditions to industrial lines (strip size, line speed, strip tension, blowing pressure, etc.) including:

o The mastering of all process parameters,

o The possibility to test easily design modifications of the cooling equipment

o The measurement facilities (strip displacements at different points, gas flow analysis).

The transfer of phenomena characterized in industrial conditions to an experimental facility is an innovation by itself.

2. This project is innovative for a second reason: this is the first time that an asymmetrical slots cooling device is implemented on an ArcelorMittal line (Sagunto). The innovation is actually an improvement of the existing equipment and consists in breaking the symmetrical structure of the cooling device, which improves the distribution of the jets gas. It suppresses the coupling effect of opposite gas jets and reduces the vibrations phenomena.

The principles of nozzles staggering, PAD sheets removal, closer strip-to-nozzles distance, have been deployed and reinforced by the partner Drever through a new cooling equipment called “Ultra Fast Cooling”. This equipment is dedicated to the rapid cooling sections of HDG and CAL lines working under protective atmosphere (Cooling Rate of 118°C/s for a strip thickness of 1 mm). The Ultra Fast Cooling has been implemented on many new industrial lines around the world (Shougang, Wisco) reducing the vibrations and consequently improving the productivity and the coating high-quality. According to the Final Acceptance Tests report, the customers are very satisfied. In this sense, the proposed technology is a successful innovation.

3. At least, the major project innovation consists in understanding, identifying and modelling the mechanisms of strip vibration phenomena generated by the gas jets of the industrial cooling equipments. The previous work of transferability and reproducibility of the online observed vibrations to the semi-industrial experimental device makes those investigations possible.

For the first time it appears clearly that the strip instability phenomena can be classified in 3 families depending on the forces exerted on the structure:

o quasi periodical forces due to recirculation loops between jets

o turbulent flows forces

o forces due to aeroelastic coupling producing the strongest damages on the coating quality.

With the help of an expert team (sub-contractor), we built a physical model able to predict the strip stability / instability depending on the process conditions (gas pressure, nozzle design and nozzle configurations, strip-to-nozzles distance…). We validated the theoretical approach on the semi-industrial pilot facility. The results show very encouraging results: vibrations mode can be predicted, as well as vibration amplitudes. The approach of coupling phenomena between the gas pressure and the structure behaviour is a new approach on HDG lines. A physical model able to take into account the impact of the gas pressure field on the steel surface and the impact of strip reactions on the gas flows, on a weak way is an innovation.

The model has been reinforced by various industrial configurations (Ghent and Sagunto) and this is the first time that this theoretical approach is used for galvanizing lines. Publications

13

have been written and presented during conferences to communicate these achievements [1-4, 25-26].

Industrial interest and scientific / technical prospects

Two complementary approaches have been proposed. The first one consisted in using the experimental 2/3 scale cooling device to define a new cooling geometry reducing strip vibrations and the second approach consists in understanding the strip vibrations mechanism and building a theoretical model able to predict the strip vibrations in specific cooling configurations.

The fluid-structure interactions in such equipment was never been studied before this project.

Each of these steps aimed answering the fundamental question: how to reduce the strip vibrations in gas jets cooling equipments and consequently to increase line productivity and coating quality. That means to be able to answer to these basic questions, which are frequently asked on that problem and have no answer today:

o For existing cooling technology in hot dip galvanizing lines, what is the importance of the process and geometrical parameters on the vibratory behaviour of the strip? Is it possible to reduce the vibrations by actions on these parameters while preserving the cooling performances?

o With identical cooling performances, is there a blowing design, which makes it possible to strongly reduce the strip vibrations?

We answered to those questions with success.

Consistency of resources and quality of partnership

The project nature (pilot project) by itself leads to coordinate various competencies (technical and scientific experts) and approaches (industrial and experimental). Due to a closed partnership between the ArcelorMittal Ghent and Sagunto lines people, ArcelorMittal R & D team and Drever International, we succeed to conduct an exhaustive characterization of the strip vibration phenomena observed in the cooling sections and during production conditions (WP1). The WP2 was much more focused on the coordination between researchers (ArcelorMittal Maizières), university competencies (subcontractor), supplier knowledge (Drever International) and industrial background (ArcelorMittal Ghent). The WP3 consisted in coordinating the competencies of the line managers, the industrial people in charge of mechanical and electrical maintenance, the technology suppliers, and the ArcelorMittal researchers in charge of the measurements campaign. Because of the tasks diversity and because of the coordination of various competencies, the partnerships quality is very high. More especially, the industrial implementation of the new cooling technology has been done with success and on due time in spite of one contractor withdrawal and replacement, and in spite of the economical crisis occurred at the end of 2008, which leads to human resources restriction of the ArcelorMittal group.

Community added value and contribution to EU policies

The impact regarding preservation of natural resources, energy and environment had been reinforced considering the consequences of better controlled zinc coating on surface appearances of galvanized strips and on the painting / organic layers consumption of automotive suppliers. Even if we were not able to quantify those benefits on the Sagunto pilot line, the results obtained on the Chinese lines where the recommendations have been implemented shows that the strip vibrations could be mastered in

14

cooling sections, especially in the cooling tower, reducing the zinc consumption thanks a better mastering of the zinc coating homogeneity across the strip width as well as along the strip length. Those results could be easily reproduced on EU lines, on HDG lines as well on CAL lines.

Exploitation and impact of the research results

The first impact of the research results is the worldwide deployment of the recommendations coming from the WP2. Indeed the principle of staggering nozzles to reduce vibrations amplitudes, the removal of the PAD sheet, the optimisation of the nozzle-to-nozzle distances have been introduced within the innovative Ultra Fast Cooling developed in the Drever R&D department and commercialised by Drever International.

The second impact of the research results consists in the development of modelling tools able to predict the strip vibration amplitudes and modes for varied experimental and industrial configurations. Based on the theoretical approach of fluid-structure interaction done within the WP2 tasks, further numerical tools coupling computations of structural deformation and fluid mechanism have been developed at ArcelorMittal Maizières Research. Developments are still going on to make the strip vibrations prediction more robust, especially for industrial configuration taking into account the process parameter fluctuations.

15

I II III IV I II III IV I II III IVJ-S O-D J-M A-J J-S O-D J-M A-J J-S O-D J-M A-J

WP 1Analysis of strip vibrations on Arcelor Steel Belgium industrial line

Industrial reference Database

Task 1.1 Installation of measuring systemDisposal measuring system with process database connection

ArcelorMittal ResearchArcelorMIttal Ghent ok

Task 1.2 Characterisation of blowing parameters Test reportArcelorMittal ResearchDrever InternationalArcelorMIttal Ghent

ok

Task 1.3 Characterisation of line process parameters Test reportArcelorMittal ResearchDrever InternationalArcelorMIttal Ghent

ok

Task 1.4 SynthesisDatabaseSynthesis report

ArcelorMittal ResearchDrever InternationalArcelorMIttal Ghent

ok

WP 2Optimisation of the influent parameters on the experimental cooling device

Improved experimental cooling device

Task 2.1 Design and manufacturing Experimental 2/3 scaled cooling deviceArcelorMittal ResearchDrever International ok ok ok

Task 2.2Reproduction of vibration phenomena on experimental 2/3 scaled device

Experimental 2/3 scaled cooling devicereproducing the industrial strip vibration phenomena

ArcelorMittal ResearchDrever International ok ok ok

Task 2.3Modification of the cooling design in accordance with the previous developed theoretical model

Asymmetrical experimental improved cooling device valided by the vibrations theoretical model

ArcelorMittal ResearchDrever InternationalLadHyX (Subcontractor) ok ok

Task 2.4 Tests and optimisation Improved experimental cooling deviceArcelorMittal ResearchDrever International ok ok ok

Task 2.5 Synthesis Performances quantification ArcelorMittal ResearchDrever International

WP 3Installation and optimisation of the improved proposed solution in industrial conditions

Final industrial improved cooling device

Task 3.1 Design and manufacturing New / improved device Drever International

Task 3.1 BISAnalysis of strip vibrations on ArcelorMittal Sagunto industrial line

Industrial reference DatabaseArcelorMittal ResearchArcelorMIttal Sagunto

Task 3.2Assembly and adjustment of the improved cooling device in the industrial line

disposal cooling device(ready for use)

Drever InternationalArcelorMittal Sagunto

Task 3.3 Preparation of industrial tests Test proceduresArcelorMittal ResearchArcelorMittal Sagunto

Task 3.4 Installation of vibrations online measuring systems Industrial continuous control of strip vibrationsArcelorMittal ResearchArcelorMittal Sagunto

Task 3.5 Tests on industrial linesTrials planTest report

ArcelorMittal ResearchArcelorMittal SaguntoDrever International

Task 3.6 Optimisation of the industrial cooling device Final industrial improved cooling deviceArcelorMittal ResearchArcelorMittal SaguntoDrever International

Task 3.7 Synthesis

Industrial procedures Recommendations to transpose the solution to others industrial linesSynthesis report

ArcelorMittal ResearchArcelorMittal SaguntoDrever International

2nd year (08-09) 3rd year (09-10)ActorsWork

packagesWork packages’ title Deliverables 1st year (07-08)

1. PROJECT TIME SCHEDULE

NB: The contractor’s change of ArcelorMittal Ghent to ArcelorMittal Sagunto caused some delay on the technical program (WP3) due to the amendment signature procedure. We also had to add a task (Task 3.1 bis). However all the contractors succeed by hard work to follow the initial technical program before the end of the contract.

17

2. SCIENTIFIC AND TECHNICAL DESCRIPTION OF THE RESULTS

2.1. OBJECTIVES OF THE PROJECT

Introduction

The galvanized steel coils are intended on one hand for the automotive market, that requires a high quality in terms of surface aspect and on the other hand for the industry market, that requires enhancing productivity rates. In the two cases a very good stability of the strip is necessary during the complete process, especially in the cooling tower after the zinc pot.

Very little information and studies on the vibratory behaviour of a strip in gas jets cooling equipments are available. The fluid-structure interactions, at the origin of the vibrations problems, and the links between the design of the cooling equipments, the process parameters and the vibrations are very badly known. Studies conducted in 2003 by ArcelorMittal Research and Drever [1, 10,11], the supplier of the cooling equipments of many galvanizing lines in Europe, revealed that the more the productivity increases, the more the capacities of the cooling devices are solicited and the more the vibratory amplitudes of the strip increase [14, 15, 17, 18]. The industrial consequences are the followings ones:

-defects of the surface quality like scratches

-production breaks due to strip breaking

-bad homogeneity of the zinc thickness (wiping zone)

-Increase of the production costs due to the increase of the zinc coating weight.

Stakes

In the next years all the industrial lines will use the maximum of their capacities and the maximal capacities of the cooling systems too. The stakes of the strip vibrations reduction are consequently important and in progress:

-Stakes in terms of productivity: considering the increase of the line speed, the expected gains are evaluated at 1 to 2 M per line per year. That repr esents a gain of 50 M per year considering that 25 galvanizing lines are concerned by the problem of strip vibrations in the cooling zone.

-Stakes in terms of quality: considering the control of the zinc weight and the current price of zinc, the expected gains are evaluated at about 0.5 M per li ne per year. That represents a gain of about 12.5 M per year for the 25 galvanizing lines (2006) which are potentially interested [8, 23, 24].

Objectives

The objective is not to work on external stabilizing actuators like the application of magnet or inductive actuators but to work directly on the design of the cooling equipment which is the “exciting source” of vibrations.

The present project will lead to an innovative industrial cooling device minimizing the strip vibrations in the cooling zone. The new solution will enhance the line productivity and increase the coating quality of the strip. The transferability of the technological solution to others typical cooling devices used at industrial galvanizing lines will be assured with the recommendations report for industrial transferability realized at the end of the project.

19

ArcelorMittal Research (as coordinator), Drever, Arcelor Steel Belgium (at the project’s beginning) and ArcelorMittal Sagunto for the project second phases, are taking part in the proposal with complementary roles in three steps, which are briefly described as followed:

1-) Analysis of strip vibrations on ArcelorMittal Ghent industrial line equipped with an experimental measures system of the strip- blow nozzles distance in the wiping zone.

The distance strip-nozzles faithfully represent the strip vibrations amplitudes. The objectives are:

o To carry out a fine parametric study and a statistical analysis of the strip-nozzles distance with standard production parameters to characterize the vibrations phenomena at the starting point.

o To identify and characterize the major influent line and blow parameters on the strip vibrations in the gas jets cooling equipment of the industrial ArcelorMittal Ghent line N°3.

o To collect data in order to define and design the experimental 2/3 scaled cooling device planed at ArcelorMittal Research.

The success of the project is based on the good industrial analysis of the strip vibrations phenomena. The results coming from these parameters characterization are the determining factor for the next steps: the design of the experimental solution and the transfer to the industrial line. This first Work Package is the key link of the continuous processing improvement chain in which this pilot project belongs.

2-) Optimisation of the influent parameters on the experimental cooling device

An innovative technological solution to reduce even to cancel the strip vibrations in the cooling zone will be firstly defined on an experimental 2/3 scaled cooling device. This experimental device will be designed and developed in collaboration with Drever.

The characterization of the strip vibrations carried out in the first step on the industrial line is needed to reproduce faithfully the vibrations phenomena on the experimental cooling device.

Many key points are required to define the optimal innovative cooling technology which will minimize even cancel the strip vibrations on the experimental cooling device:

o To design and manufacture a faithful experimental cooling device reproducing the strip vibrations phenomena characterized in the first step of the pilot project.

o To propose and to test experimentally the innovative solutions as for example a new asymmetrical cooling device. The solutions will be evaluated by a theoretical model. The retained solution will be tested, optimised and finally designed for the experimental cooling device. The fact that the new cooling device is designed and optimised for a 2/3 scaled experimental device assure a good representativeness of the industrial reality and assure the good transferability of new designed solution to the industrial line.

3-) Installation and optimisation of the improved proposed solution in industrial conditions

In our approach of continuous improvement quality, applied to the industrial problem of strip vibrations, the last step is to transfer the new cooling technology to standard industrial conditions and ensure his good functioning. It requires:

Program

20

o To adapt the design, to manufacture and to install the industrial innovative cooling device, based on the design of the 2/3 scaled experimental cooling device.

o To install an industrial continuous measures system connected to the process control computer. This measures system should continuously measure the strip-nozzles distance and estimate the performance of the new solution in industrial standard conditions.

o To test and to optimise the new cooling device in industrial standard conditions.

This last step is the heaviest in terms of staff hours and costs and requires the good coordination of the interdisciplinary competences of all partners. His success depends on the quality of the two previous steps and will be evaluated by comparison between the performances of the improved industrial cooling device and the initial performances described in the status report made at the end of the first step (WP1). The continuous quality improvement chain is closed.

The transferability of the new technological solution is ensured by a report of recommendations for transferability to others industrial lines and through the writing of industrial procedures.

21

2.2. COMPARISON OF INITIALLY PLANNED ACTIVITIES AND WORK ACCOMPLISHED

The initial working program has been entirely accomplished on due time as the Figure 1 shows it:

Figure 1: comparison between initially planned activities and accomplished work

The lines in red show the impact of the industrial partner change in terms of time schedule, especial the impact on the deliverable deadline (1 year). It is important to underline that the table here above does not show the dates of the tasks starting. So the delay and time schedule difficulties encountered into the WP 3 do not appear clearly here. The delay of the tasks starting of WP3 is between 6 months and 1 year.

In spite of those difficulties, the respect of the initial foreseen time schedule has been ensured.

22

Top-roll

Blowingboxes 2

Blowingboxes 1

Wiping zone

Zinc

bath

Kaman sensors

Laser sensors

Top-roll

Blowingboxes 2

Blowingboxes 1

Wiping zone

Zinc

bath

Kaman sensors

Laser sensors

2.3. DESCRIPTION OF ACTIVITIES AND DISCUSSION

2.3.1. WP 1 – Analysis of Strip vibrations on ArcelorMittal Ghent industrial line 3

Objective:

o To identify and characterize the major influent line and blow parameters on the strip vibrations in the gas jets cooling equipment of the industrial Arcelor Steel Belgium line N°3.

o To collect data in order to define and design the experimental 2/3 scaled cooling device planed at Arcelor Research.

2.3.1.1. Task 1.1 Installation of measuring system

Objective:

- Measurements of the strip-nozzles distance in the wiping zone with experimental measures system connected to the process database. The distance strip-blow nozzle faithfully represents the strip vibrations amplitudes.

- Statistical analysis of the strip-nozzles distance measurements with standard production parameters

- Status report of industrial vibrations phenomena on line N°3 in Arcelor Steel Belgium plant.

o Strip vibrations measurement system in the cooling tower:

Strip vibrations are measured on two points:

- at the top of the cooling tower, between the cooling boxes, where vibrations are the most important - at the wiping zone, the most sensitive point of the production line to warranty the product quality

Experimental measurement systems:

- Between the cooling boxes; 3 Laser sensors are placed in front of the strip, strip width-wise

- At the wiping zone, 3 inductive sensors, called Kaman sensors, are placed in the front of the strip above the wiping nozzles.

The 3 width-wise sensors measure the strip position [9]. The vibrations amplitudes are obtained by calculating the standard deviation of the strip position. The 3 width-wise sensors give the vibrations amplitudes at the centre of the strip and at its 2 edges.

Figure 2: Configuration of the vibrations measurement system in the cooling tower

23

Positioning of the sensors:

For the Kaman sensors as well as for the Laser sensors, the positioning is organized in the following manner:

Figure 3: Positioning of three Kaman sensors across the strip (top view)

Figure 4: Three Kaman sensors across the strip

The distance between the Kaman sensors is about 500 mm, so that a large panel of strip width can be detected.

Process parameters observed:

- Line velocity

- Strip traction

- Blowing pressure Box 1

- Blowing pressure Box 2

- Strip section (Width x Thickness)

o Representativeness of the trials run:

The industrial trials campaign has been conducted for a high quantity of coils, about 400 coils. The campaign has been conducted in standard production conditions in order to identify the starting points characterizing the line, on which the design of the improved gas jets system will be based.

The totality of the sensors database has been worked and purified so that the transitory phases between two strips (line speed changes, traction changes and formats changes) do not appear: the results hereafter represent strip vibrations states by stable production conditions.

Kaman 1 Kaman 3Kaman 2

Center Edge 2Edge 1

Strip

24

o Presentation of results:

In following paragraphs, results will be shown firstly as a general overview of the influence of one parameter and in a second step results will be presented more in details in order to evaluate the influence of combined parameters.

2.3.1.2. Task 1.3 Characterization of line process parameters

Effect of the line speed

The effect of the line speed has been observed during the whole campaign whatever the strip format is. The results of the strip vibrations measures at the wiping zone as well as between the cooling boxes are shown hereafter (Figures 5 and 6):

Figure 5: Strip vibrations across the strip width at the wiping zone according to the line speed increase

25

Figure 6: Width-wise strip vibrations between the cooling boxes according to the line speed increase

Results:

The results shown in Figures 5 and 6, group together all the measured points during the trials run: all strip formats, all production parameters merged. It is an overview of all the results.

Whatever the line speed is, the strip vibrations at the wiping zone (Figure 5) are included in a range of ~ 2 mm in the strip centre as well as at the edges. There is a light tendency to see at the wiping zone: the standard deviation for the edges 1 and 2 are quite constant whereas the standard deviation at the centre is much more dispersed. It reveals a tendency of crossbow positioning for the strip.

On the contrary, the strip vibrations between the cooling boxes (Figure 6) increase according to the line speed. It must be stressed that the figure presents the complete data for the 400 coils, with various production conditions (e.g. various strip formats or various blowing pressure).

Regarding the maximal vibrations amplitudes at the wiping zone and between the cooling boxes, the ratio between amplitudes at the wiping zone and cooling boxes is about 3.5 whatever the line speed is.

The influence of the line speed on vibrations modes will be seen hereafter.

Effect of the strip traction: analysis of the campaign database

The effect of the strip traction has been investigated during the whole campaign whatever the strip format is. The strip traction takes into account the strip section (width [mm] x thickness [mm]). The results of all the measures are shown hereafter (Figures 7, 8 and 9):

There is no real tendency to observe for measures at the wiping zone, except one: for strip traction between 26 daN/mm² and 34 daN/mm², the standard deviation of edges 1 and 2 is more or less constant. On the contrary, the standard deviation of the strip centre is more dispersed. One possible interpretation is the so-called “long centre effect”.

26

Figure 7: Width-wise strip vibrations at the wiping zone according to the strip traction

The increase of the strip traction has not a real influence on vibrations between the cooling boxes (Figure 8): the standard deviation does not clearly change with the increase/decrease of the traction. It has to be taking into account that the previous figures include many strip formats, many line speeds, many blowing power in cooling boxes.

However there is no tendency to see according to the width-wise vibrations. It means the strip displacements measured by the edges sensors or by the centre sensor do not allow concluding on an influence of the strip traction on vibrations modes.

Figure 8: Width-wise strip vibrations between the cooling boxes according to the strip traction

27

Effect of strip traction at given line speed and strip formats:

The Figure 9 gives strip vibrations amplitudes according to the strip traction for 3 different strip formats and for 2 different line speeds.

Figure 9: Width-wise strip vibrations at the wiping zone and between the cooling boxes according to the strip traction and for 2 different line speeds: V=115 m/min and V= 140 m/min

Format 1:1650mm x 0,7mm

Format 2:1800mm x 0,7mm

Format 3:1750mm x 1,0mm

The whole results database is completely based on standard production conditions so that the strip traction did not vary so much.

However, the above results are very interesting because it is possible to confirm that:

o The increase of traction reduces vibrations amplitudes. For the same format (cf. format 1), the traction increase from 23 daN/mm² to 27 daN/mm² reduces amplitudes at the wiping zone as well as in the cooling system (factor 2).

o The strip thickness increase reduces vibrations amplitudes (cf. format 3)

However, those results show the influence of the strip width on vibrations. When we compare the formats 1 and 2, so two different widths, vibrations amplitudes at the wiping zone are quite in the same range whereas strip distortions are to be observed in the cooling system. For a strip traction of ~30.5 daN/mm², the laser sensor of the strip centre detected high vibrations amplitudes whereas the strip edges amplitudes varied less. It is to conclude that the strip shows distortion modes in the cooling boxes.

28

Indeed, many observations during measurements campaign highlighted those effects of strip distortion, especially strip “twist” positioning. It has not been possible to make measurements of this strip distortion during the trials run because the high strip displacement quasi induced strip-nozzles contact: on so short measurement range, the sensors are not able to deliver reliable results.

Figure 10: Width-wise strip vibrations at the wiping zone and between the cooling boxes according to the strip traction and for different strip formats (Line speed = constant)

The results presented by the Figure 10 are very interesting and complete the previous ones:

- For a constant line speed, the effect of strip traction on vibrations has been observed for 6 different formats.

Effect of strip width: Whatever the strip thickness, for low widths (1400 mm to 1500 mm), vibrations amplitudes at the wiping zone as well as in the cooling boxes are quite low whereas amplitudes in cooling boxes and for higher strip width are noticeably higher.

Effect of traction: for the formats 1650 mm x 0.8 mm and similar format 1650 mm x 0.84 mm, the effect of traction is quite clear: higher amplitudes (factor 2) at the cooling boxes zone for the lower traction.

Effect of traction combined with high thickness: for the format 1650 mm x 0.95 mm, a high strip traction does not have a real effect on vibrations amplitudes at the cooling zone.

2.3.1.3. Task 1.2 Characterization of blowing parameters

The Figure 11 presents the effect of blowing power of the fans in cooling zone 2 on the strip vibrations (the fan speed in cooling zone 2 being constant). These results – for all the coils data – do not show a clear tendency for the blowing power effect, except that the strip vibration amplitudes are generally higher at the cooling boxes level with respect to the wiping zone.

29

Figure 11: Width-wise strip vibrations at the wiping zone and between the cooling boxes according to blowing power of cooling box 2 (box 1 fixed)

Over a blowing power of 50%, the strip distortion effect, especially twist positioning in the cooling boxing is so high that it damages the product quality. Indeed in this twist position the strip edges can contact the blowing nozzles and induce scratches. Another consequence is knock-on effect at the wiping zone by propagation: the strip edges touch the wiping nozzles inducing inhomogeneous zinc coating weight and thus quality damages. That is the reason why blowing power does not exceed 50 %.

Figure 12: Width-wise strip vibrations at the wiping zone and between the cooling boxes according to blowing power of cooling box 2 (box 1 fixed) for line speed fixed.

In the Figure 12, the selected data for a same line speed of 135 m/min are given. In this case, a clear tendency can be observed: the vibration amplitude in the cooling zone is increasing linearly with the fan blowing power, whereas this amplitude remains constant in the wiping zone. The blowing power is

30

limited to 50% in the cooling zone 2 due to a strip-plenum contact above this 50% value, due to a strip twist shape which increases with the blowing power.

2.3.1.4. Task 1.4 Synthesis

The trial run campaign has been carried out in standard production conditions and is completely representative of current production of the HDG line of ArcelorMittal Ghent.

The campaign conducted gives the real state of the art of strip vibrations in the cooling tower:

o Standard deviation at the wiping zone: ~ 2 mm

o Standard deviation in the cooling boxes: ~ 9 mm

Process parameters can influence the vibrations amplitudes:

o Standard deviation increase with blowing power

o Standard deviation decrease with strip traction

The line speed effect did not clearly appear because it is combined with others process parameters like strip traction.

Process parameters can influence the vibrations amplitudes: the more the strip is large, the more standard deviation is high.

In conclusion, those analysis show high potential to decrease strip vibrations at the wiping zone as well as in the cooling boxes by optimising the design of the current cooling system.

31

2.3.2. WP 2 – Optimisation of the influent parameters on the experimental cooling device at ArcelorMittal Research site

Objectives

o To build at the ArcelorMittal Research site an experimental 2/3 scaled cooling device able to reproduce the strip vibrations detected and characterized on the industrial galvanizing line N°3 at ArcelorMittal Steel Belgium plant,

o To optimise this experimental cooling device adapted to the industrial situation of strip vibrations: definition of an innovative 2/3 scaled cooling device.

Program

o Optimisation of the influent parameters on the experimental cooling device:

o An innovative technological solution to reduce even to cancel the strip vibrations in the cooling zone will be firstly defined on an experimental 2/3 scaled cooling device. This experimental device will be designed and developed in collaboration with Drever.

The characterization of the strip vibrations carried out in the first step on the industrial line is needed to reproduce faithfully the vibrations phenomena on the experimental cooling device.

Many key points are required to define the optimal innovative cooling technology which will minimize even cancel the strip vibrations on the experimental cooling device:

- To design and manufacture a faithful experimental cooling device reproducing the strip vibrations phenomena characterized in the first step of the pilot project.

- To propose and to test experimentally the innovative solutions as for example a new asymmetrical cooling device. The solutions will be evaluated by a theoretical model. The retained solution will be tested, optimised and finally designed for the experimental cooling device. The fact that the new cooling device is designed and optimised for a 2/3 scaled experimental device assure a good representativeness of the industrial reality and assure the good transferability of new designed solution to the industrial line.

2.3.2.1. Task 2.1 Design and manufacturing

Objective

o Using of the industrial strip vibrations analysis carried out in the WP1, development and design of a 2/3 scaled experimental cooling device, representative to the industrial cooling device,

o Manufacturing of the 2/3 experimental cooling device,

o Cooling device assembly at the 2/3 scaled experimental plant

2.3.2.1.1. Representativeness of the pilot line

The experimental pilot at ArcelorMittal Maizières has been updated and equipped with the air blowing systems .

The design of this cooling equipment is very similar to the corresponding industrial devices installed by Drever International in ArcelorMittal galvanizing lines. Cooling devices consist of two movable plenums containing several slot nozzles.

32

The geometrical characteristics of a typical industrial plenum are the following: slot width 11 mm, pitch (distance between two nozzles) 400 mm, nozzle length 275 mm.

The reduced-scale cooling device in the pilot line is designed with these geometrical characteristics with a scale ratio of 2/3. The industrial distance between the nozzles and the strip is usually 100 mm in rapid cooling sections and 125 mm in towers. Movable plenums are designed for the cooling equipment in the pilot line, allowing to test the effect of nozzles-strip distance on strip vibration behaviour.

However the strip format and the strip tension have been chosen in order to reach similar vibrations amplitudes and frequencies as those observed on industrial lines [2,3].

Figure 13: Drever after pot cooling design at ArcelorMittal Ghent 3

Figure 14: ArcelorMittal Ghent #3

Top-Roll

Bain Zn

6 m

6 m

12

Wiping system

Blowing boxes are supplied with air from the back side

Blowing boxes are equilibrated from each other on 3 points

Hot air is evacuated on laterally

33

Figure 15: ArcelorMittal Ghent 3

Detailed schema of the after pot cooling design

Figure 16: Schematic overview of the experimental cooling device

Figure 17: Upper view of the equipped pilot line, with strip and guide-rolls

34

2.3.2.1.2. General technical characteristics of pilot line

Figure 18: Drawing of the equipped pilot line, with strip line pass (red line) and guide-rolls

2.3.2.1.3. Plenums front side design of pilot line

The geometrical characteristics of a typical industrial plenum are the following:

- slot width 11 mm,

- pitch (distance between two nozzles) 400 mm,

- nozzle length 275 mm.

The reduced-scale cooling device in the pilot line is designed with these geometrical characteristics with a scale ratio of 2/3.

Global geometry:

Distance between top-roll and bottom-roll: 9m

Dimensions of blowing boxes:

h = 2 000mm

w = 1 400mm

System flexibility:

Movable plenums

Movable guide-rolls

Flexible front side nozzles design

Distance between strip and nozzles: 25 to 125 mm

Air blowing system:

2 separate air supply systems for each blowing box

Blowing power: 2 x 28 000 Nm3/h

Blowing pressure: 2 x 0 to 100 mbar

Process parameters:

Strip tension: until 3000 kgf

Line velocity: 0-1000m/min

Product characteristics:

Steel product: Tin mini-coil

Width: until 1400 mm

Thickness: 0.05 until 1.2 mm

35

Figure 19: Different configurations of blowing plenum’s front side tested on pilot line. 1- 2 x 8 nozzles opposite to each others; 2- Variation of nozzles length; 3- Air PAD system

2.3.2.1.4. Geometrical characteristics

Slot width : 8 mm,

Pitch (distance between two nozzles): 267 mm,

Nozzle length : 184 mm,

Blowing width: 1400 mm (against 2000mm in industrial line),

Modularity of front side.

2.3.2.1.5. Measurement systems of pilot line

Continuous process parameters acquisition

Continuously acquired signals:

- Strip tension measurement (at 10 m): 2 points on strip edges

- Strip positioning measurement

- Strip velocity measurement at guiding rolls (S-Bloc…)

- Measurement of « dance » roll position

- Measurement of « centring » roll position

- Detection of weld path

- Measurement of motors intensity, couple…

- Pressure in each blowing box

36

- Fans rotation velocity

Figure 20: Control cabin of experimental pilot line

2.3.2.1.6. Strip positioning measurement system

Continuous strip position measurement:

- Strip position: at the 2 strip edges + strip centre

- Standard deviation

- Peak-to-peak

- Spectral analysis

- Acquisition frequencies: 64 Hz

Measurement range is 50-300 mm with a resolution of 0.2 mm. The sensors have been calibrated on specific installation at ArcelorMittal Research.

Figure 21: Strip positioning measurement system

Air flows characterizing:

- Hot wire measurement system

- Air velocity range: 0-150 m/s

Figure 22: Hot wire measurement system

37

2.3.2.1.7. Product

The tested strip format is typically 950 x 0.25 mm.

The low thickness has been chosen in order to favourite high strip vibrations amplitudes. Indeed two possibilities are identified: to reduce the specific strip tension or to reduce the strip thickness. Because of difficulties to transport the strip in dynamic conditions by very low tensions, it has been decided to reduce strip thickness even thought typical galvanized product is thicker. The strip width has been chosen based on a similar industrial ratio strip width / blowing width.

2.3.2.1.8. Influent parameters detected on industrial line

As shown in the previous 6-months technical report, influent parameters on strip vibrations amplitude increase have been identified during the industrial campaign:

- Standard deviation increase with blowing power

- Standard deviation decrease with strip tension

- The line speed effect did not clearly appear because it is combined with others process parameters like strip tension.

- Process parameters can influence the vibrations amplitudes: the more the strip is large, the more standard deviation is high.

The campaign conducted gives the real state of the art of strip vibrations in the cooling tower for standard production parameters:

- Standard deviation at the wiping zone: ~ 2 mm

- Standard deviation in the cooling boxes: ~ 9 mm

That is the reason why the effects of strip tension, line velocity and blowing power have to be investigated. The flexibility and representativeness of the reduced-scaled pilot allow to test those parameters.

2.3.2.2. Task 2.2 Reproduction of vibrations phenomena on the experimental 2/3 scaled cooling device

Objective

- Experimental validation of the 2/3 scaled experimental cooling device by comparison with the industrial database (WP1). The experimental device must be representative and faithful to the real industrial cooling device.

38

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35 40

blowing Pressure (mbar)

stri

p d

isp

lace

men

t R

MS

(m

m)

écart type centre

écart type rc

écart type rh

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40

blowing Pressure (mbar)

stri

p d

isp

lace

men

t p

eak

to p

eak

(mm

)

amplitude max centre

amplitude max rc

amplitude max rh

2.3.2.2.1. Initial tested configuration

- Distance between strip and nozzles is fixed at 67 mm (=100 mm in industrial line).

- Blowing width is 1400 mm

- Specific tension: 1.8 kg/mm2

- Line velocity: 0 m/min

- Blowing pressure: from 0 to 40 mbar

-

Figure 23: initial configuration: plenum nozzles configuration 4 straight nozzles + 1 PAD (aerodynamic stabilizer) per side

2.3.2.2.2. Reproducibility of industrial strip behaviour

The Figures 24 and 25 show the increase of vibrations amplitudes of strip displacement function of the blowing pressure increase. The behaviour is not linear. The maximal amplitudes are detected in the strip centre. A light gap between the 2 edges appears what can be induced, for example, by strip flatness defects or blowing pressure heterogeneity strip width-wise. It can be a case of edges fluttering phenomenon.

At 40 mbar, peak-to-peak measurements are more than 100mm what can induce strip-nozzles contacts.

To avoid destroying the strip, the blowing pressure has not been increase during the first trial run.

Figure 24: strip displacement as function of blowing pressure

Figure 25: peak to peak values as a function of blowing pressure

39

30

35

40

45

50

55

60

65

70

40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

time (s)

ral

ativ

e st

rip

po

siti

on

(m

m)

distance centre [mm]distance rive cabin [mm]distance rive halle [mm]theorical strip line pass

0

20

40

60

80

100

120

40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60time (s)

rela

tive

str

ip p

osi

tio

n (

mm

)

distance centre [mm]distance rive cabin [mm]distance rive halle [mm]

21/07/2004;10:27:12.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.

centre

50

45

40

35

30

25

20

15

10

5

0

21/07/2004;11:27:52.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.

centre

8000

7000

6000

5000

4000

3000

2000

1000

0

The Figures 26 and 27 give an idea about vibrations observed during a 20 s time for 2 different blowing pressures: 19 and 39 mbar. They are compared to the theoretical pass-line:

Two different strip behaviours are observed for the 2 cases:

- at 19 mbar : irregular vibrations with vibration power density spectrum from 0 to 2 Hz vibrations

- at 39 mbar : regular vibrations in the centre as well as at the edges with vibration power density spectrum concentrated around 2.4 Hz

Figure 26: evolution of the strip position with time at P=19 mbars => irregular strip vibrations

Figure 27: Evolution of the strip position with time at P=39 mbar => regular strip vibrations

Figure 28: power density vibratory spectrum P=19 mbar

Figure 29: power density vibratory spectrum P=39 mbar

40

The strip vibratory behaviour observed in the pilot line is very similar than the one observed on industrial lines (at the top of the cooling tower of ArcelorMittal Ghent for example): regular increase of strip vibrations until possible contact to nozzles (Figure 27: maximal strip displacement of 100 mm whereas the distance between two nozzles is 120 mm); twist positioning (Figure 26); low vibrations frequencies < 5 Hz (Figure 28).

The reproducibility of strip behaviour has been verified.

2.3.2.2.3. Reproducibility of vibrations phenomena observed at ArcelorMittal Ghent line

During the industrial vibrations characterization campaign, it has been often seen a strip twist shape increasing with the blowing pressure.

This phenomenon has been reproduced on the experimental pilot line as shown in Figure 30:

Figure 30: evolution of the strip position with time in a twist situation

The Figure 30 shows relative position of strip centre (blue curve) and strip edges (yellow and pink curves) during 80 minutes. The blowing pressure is not high: 30 mbar, what is representative of industrial conditions. The specific traction is 1kg/mm².

In those conditions, we clearly see that one strip edge and the strip centre are quasi at the same position: this is the phenomenon that we called “strip twist shape”. This mechanism takes place with a mechanism of buckling and is very spontaneous.

Intermediate conclusion:

Those observations are exactly similar to the strip behaviour observed on industrial lines. If it can be reproduced on experimental pilot line, the origins of this mechanism are not completely understood.

2.3.2.2.4. Reproducibility of the trials campaign

We verified the reproducibility of the strip behaviour for several trials time on experimental pilot. Four trials have been carried out in identical conditions and at different time periods. Those four trials are identified on the followings figures with number 1 to 4. Figure 31 presents the vibrations amplitude

0

20

40

60

80

100

120

140

160

180

200

0 10 20 30 40 50 60 70 80time (s)

rela

tive

str

ip p

osi

tio

n (

mm

)

distance centre [mm]distance rive cabin [mm]distance rive halle [mm] Twist

positioning

41

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60

Blowing Pressure [mbar]

RM

S C

entr

e [

A.U

.]

1

2

3

4

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60

Blowing Pressure [mbar]

Pea

k-P

eak

all

po

ints

[A

.U.]

1

2

3

4

depending on the blowing pressure in the cooling boxes. The values are RMS values for the central sensor and maximal values for the all three sensors. The curves show an excellent reproducibility of the trials, for the RMS values as well as the maximal vibrations amplitudes (peak-to-peak values).

Figure 31: RMS and peak-to-peak strip vibrations amplitudes as a function of the blowing pressure for tests performed at 4 different time periods

2.3.2.3. Task 2.3 Modification of the cooling design in accordance with the vibratory mechanism theoretical model

Objectives

- Improvement of a theoretical model of the strip vibrations phenomena providing the criteria of the vibrations starting point.

- Design of a new experimental 2/3 scaled cooling device minimizing the strip vibrations. Validation by the theoretical model.

- Tests of different complementary modifications of the cooling device configuration to decrease strip vibrations.

42

2.3.2.4. Construction and improvement of vibrations theoretical model

2.3.2.4.1. Observation: 3 major strip behaviours

The first trials conducted on the pilot line shown 3 major vibratory / instability behaviours:

Figure 32: RMS values as a function of time at 4 different time periods. Identification of 3 major strip behaviours:

- « irregular + centred » or a) mode in Figure 33

- « regular + centred » or c) mode in Figure 33

- « irregular + twist » or b) mode in Figure 33

30

35

40

45

50

55

60

65

70

40 41 42 43 44 45 46 47 48 49 50 51 52

time (s)

ral

ativ

e st

rip

po

siti

on

(m

m)

distance centre [mm]distance rive cabin [mm]distance rive halle [mm]theorical strip line pass

0

20

40

60

80

100

120

40 41 42 43 44 45 46 47 48 49 50 51 52time (s)

rela

tive

str

ip p

osi

tio

n (

mm

)

distance centre [mm]distance rive cabin [mm]distance rive halle [mm]

0

20

40

60

80

100

120

140

160

180

200

40 41 42 43 44 45 46 47 48 49 50 51time (s)

stri

p p

osi

tio

n (

mm

)

distance centre [mm]distance rive cabin [mm]distance rive halle [mm]

43

Figure 33: schematic view of the 3 major observed strip behaviours:

a) « irregular + centred » : several simultaneous modes

b) « irregular + twit »: several modes + strip instability type twist

c) « regular + centred »: vibrations with 1 mode

The hypothesis to explain this twist shape (Figures 32 and 33 b) is related to the fluid flows and especially to the pressure heterogeneity.

Pressure characterizations in the strip width direction and into the plenums have been conducted and show no heterogeneity. However the issue of strip vibrations under gas jets is a problematic of fluid-structure coupling, as shown is the following Figure:

Figure 34: Schema of interaction between gas jets fluid and the strip structure

There exist 3 types of unsteady forces coming from the flows and applied on the structure:

- Quasi periodical forces dues to vortex (recirculation cells)

- Forces due to turbulent flows

- Forces due to aeroelastic coupling

Wall jets

44

o Instability due to vortices (recirculation cells)

A simple calculation conducts to conclude that the frequency of vortex is around 10-40 kHz whereas the resonance frequency of the system {strip; blowing nozzles} is lower than 30 Hz. The factor 100 between the two frequencies leads to conclude that the instability of the strip does not come from the fluid vortex (Figure 35).

Figure 35: Illustration of vortex mechanism

o Instability due to turbulent flows:

The mechanism of forces fluctuations applied on the strip surface because of turbulent flows, is well known and plays a part in the instability mechanism but does not explain the suddenness of the phenomenon observed on line or on experimental pilot device.

Figure 36: Schema of strip vibrations amplitudes function of strip-nozzle distance

o Instability due to aeroelastic forces:

Aeroelastic forces are defined as the interaction between the aerodynamical forces coming from the fluid and the elastic reaction of the structure [20, 21, 22]. Those forces fluctuate in the neighbourhood of the strip surface and lead to stabilize or destabilize the strip movements and vibrations. The classical vibrations are disturbed by the aeroelastic force: it induces possible instabilities. There exist 2 kinds of instabilities:

- Static instability. The static instability is due to high pressure fluctuations and is easy to observe: it conducts the structure to the buckling phenomenon.

- Dynamical instability. The dynamic instability is due to fine pressure fluctuations and conducts the structure to the fluttering phenomena.

Vibrations amplitudes

Strip-Nozzle distance

Vibrations due to turbulences

Vibrations due to fluttering phenomena

���� Fluid-Structure

Interaction

45

Intermediate conclusion:

The comparison between theoretical approach and experimental approach on pilot line conduct to favour the hypothesis 3: aeroelastic coupling should be the key mechanism explaining the strip vibrations. In order to investigate this hypothesis ArcelorMittal Research built a collaboration with the LadHyX laboratory, with experts on fluid-structure coupling.

2.3.2.4.2. Collaboration ArcelorMittal - LadHyX Laboratory

Within the framework of this collaboration a simple installation composed of on reduced scaled nozzle and one 1-DDL -dimensionally stable sheet has been built. The aim of the laboratory experimental device is to understand the influence of geometrical aspect on vibrations amplitudes induced by spontaneous instability. Such a laboratory installation is very flexible and supports in a first time, a simplified approach.

Results:

Experiments were carried out to study the effect of strip-nozzle distance as well as the pressure, geometrical ratios and to identify the mechanism of strip instability.

The experimental approach allows determining:

o the stable and instable domains

The following curves (Figure 37) represent the strip damping function of the non-dimensional strip-nozzles distance and lead to determine an instable domain:

Figure 37: Strip damping function versus an adimentional strip-nozzle distance H

The strip damping is negative in the instable area whereas it is positive in the stable area. When the damping is negative, the air of wall jets (Figure 34) is continuously giving energy to the strip at each strip vibration cycle. This energy is transformed by the coupled fluid-structure system into vibrations amplitudes increase. This phenomenon is typically called “dynamical instability phenomena” [19].

46

o The major influent parameters

Laboratory experiments allow investigating the influence of the strip-nozzle distance, pressures, the nozzle opening section. They have been identified as order-1 parameters.

2.3.2.4.3. Experimental validation of theoretical model

The mechanism of strip vibrations has been identified and influent parameters have been investigated on laboratory installations with LadHyX. The next step aims at validating those observations and conclusions on semi-industrial configuration on reduced-scale experimental pilot device.

The tested configuration to validate the results coming from the LadHyX collaboration is made of 1 blowing nozzle per blowing box, classical geometrical parameters (blowing length, nozzles opening section…).

The preliminary tests show good correlation between laboratory trials at the LadHyX and trials on experimental pilot device at ArcelorMittal Maizières Research centre: same range of amplitudes, same major vibrations modes, emergence of instability at very low frequencies.

o influence of strip-nozzle distance

The strip nozzle distance has been made varied while the blowing pressure is kept constant. The objective is to investigate the influence of nozzle strip distance on dynamical instability phenomena. Indeed, the dynamical fluid-elastic instability has been observed (instantaneous instability and increasing amplitudes) for the following configuration on industrial pilot line:

- strip-nozzles distance: 20 mm

- Pressure: 20 mbar

Those results are consistent with the interpolation of the laboratory experimental pilot to the semi-industrial ArcelorMittal Maizières device: the instable domain has been reproduced.

2.3.2.5. Task 2.4 Test and optimisation of the improved cooling device

Objectives

- Optimisation of the improved cooling device in terms of gas flows, nozzles

- design, blowing characteristics to minimize or even cancel strip vibrations.

2.3.2.5.1. Influence of line velocity

Many trials were carried out to minimize the vibrations amplitudes. The first set of trials consisted in investigating the influence of the line speed. The semi-industrial pilot line is the ideal device to make vary the line speed from 0 to 200 m/min (usual line velocities range on HDG lines) under variable blowing pressures:

47

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40 45 50

blowing pressure (mbar)

stri

p d

isp

lace

men

t R

MS

(m

m)

RMS centre (T moy = 0.96 kg/mm2) RMS centre (T moy = 1.73 kg/mm2) RMS centre (T moy = 2.77 kg/mm2) E i l (RMS (T 0 96 k / 2) )

0

10

20

30

40

50

60

70

80

90

100

110

120

0 5 10 15 20 25 30 35 40 45 50

blowing pressure (mbar)

stri

p d

isp

lace

men

t p

eak

to p

eak

(mm

)

peak to peak centre (T moy = 0.96 kg/mm2) peak to peak centre (T moy = 1.73 kg/mm2) peak to peak centre (T moy = 2.77 kg/mm2) E i l ( k k (T 0 96 k / 2) )

The Figures 38 and 39 show the evolution of vibrations amplitudes (standard deviation and peak-to-peak values) as a function of line velocity and for different blowing pressures. Low variations of amplitudes can be observed but no specific strip behaviour is highlighted. Those results have been confirmed many times for further trials campaigns outside of this project.

As a conclusion, line velocity is not a major influent parameter on vibrations.

2.3.2.5.2. Influence of strip tension

o Effect of strip tension increase

The Figures 40 and 41 show the influence of blowing pressure on vibrations amplitudes (standard deviation or RMS and peak-to-peak values) and that, for 3 different specific tensions homogeneously distributed along the strip width:

- 0.96 kg/mm²

- 1.73 kg/mm²

- 2.77 kg/mm²

The curves are not linear and for a blowing pressure > 5 mbar, the curves seem to follow an exponential behaviour.

Figure 38: strip displacement (RMS) function of strip speed

Figure 39: peak-to-peak as a function of strip speed

Figure 40: strip displacement (RMS) function of blowing pressure

Figure 41: peak-to-peak values function of blowing pressure

0

20

40

60

80

100

120

0 50 100 150 200 250

line speed (m/min)

stri

p d

isp

lace

men

t p

eak

to p

eak

(mm

)

peak to peak centre (P blowing = 29 mbars - guide rolls open)

peak to peak centre (P blowing = 35 mbars - guide rolls open)

peak to peak centre (P blowing = 60 mbars - guide rolls 10 mm)

0

5

10

15

20

25

0 50 100 150 200 250

line speed (m/min)

stri

p d

isp

lace

men

t R

MS

(m

m)

RMS centre (P blowing = 29 mbars - guide rolls open)RMS centre (P blowing = 35 mbars - guide rolls open)RMS centre (P blowing = 60 mbars - guide rolls 10 mm)

48

When the specific tension is multiplied by a factor 2 for constant blowing pressures, the standard deviation and peak-to-peak values decrease by a factor 2.

Spectral analysis:

Whatever the specific tensions (0.96 kg/mm²; 1.73 kg/mm²; 2.77 kg/mm²), the observations are similar: the spectral analysis show irregular power density vibratory spectrum for low pressures and the power density vibratory spectrum is concentrated in a narrow range when the pressure increases.

Case of higher pressure (30, 40 and 50 mbar), the whole energy of the system {strip-air blowing jets} is concentrated around one specific frequency (see Figures 42, 43, 44; on the right side). However those specific frequencies increase with the blowing pressure increase.

One hypothesis to explain those observations is that vibrations are induced by air jet flows turbulence in case of lower pressures. Then vibrations are induced by turbulent flows. But the second observed phenomenon (concentration of energy around one frequency) is due to dynamic instability.

Figure 42: power density vibratory spectrum – T=0.96 kg/mm2 – P=19.4 mbar and P=29.3 mbar

x axis: Frequencies in [Hz] & y axis: Power Spectral Density

Figure 43: power density vibratory spectrum – T=1.73 kg/mm2 – P=29.3 mbar and P=39.2 mbar

x axis: Frequencies in [Hz] & y axis: Power Spectral Density

21/07/2004;10:11:26.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.

centre

3000

2500

2000

1500

1000

500

0

21/07/2004;10:00:40.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.

centre

400

350

300

250

200

150

100

50

0

« irregular » � « regular » strip vibrations when

blowing pressure increase

21/07/2004;11:27:52.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.

centre

8000

7000

6000

5000

4000

3000

2000

1000

0

21/07/2004;11:25:32.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.

centre

250

225

200

175

150

125

100

75

50

25

0

« irregular » � « regular » strip vibrations when blowing pressure increase

49

Figure 44: power density vibratory spectrum – T=2.77 kg/mm2 – P=39.2 mbar and P=49.7 mbar

x axis: Frequencies in [Hz] & y axis: Power Spectral Density

Intermediate conclusion:

- Strip tension plays a major part on vibration stabilization but this parameter is quite difficult to manage in industrial conditions. This conclusion coming from semi-industrial trials is in agreement with observations made during the industrial vibrations characterization campaign.

- The role of blowing pressure as vibrations mechanism selector has been identified:

The mechanism of vibrations during low blowing pressures is manifested by turbulent signals on a large range of frequencies whereas it is manifested by precised frequencies during high blowing pressures showing vibratory instability. Those observations are in accordance with the strip vibrations instability model which has been presented here above.

o Effect of heterogeneous strip tension across the width

The Figure 45 illustrates the influence of the heterogeneous strip tension across the width on vibrations amplitudes. A tension gap between the edges can be induced by a strip flatness defect or by a non-homogenous strip temperature across the strip width. On the left side graph, a small strip tension gap – 4% - is measured between edges.

Figure 45: Effect of difference between strip tension edges on strip vibration amplitude

For a blowing pressure of 40 mbar, the strip shows vibrations amplitude slightly higher on the strip centre than on the edges: the standard deviation average for the 3 sensors is 4.4 A.U. On the right side

21/07/2004;17:22:05.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.

centre

8000

7000

6000

5000

4000

3000

2000

1000

0

21/07/2004;17:19:51.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.

centre

150

125

100

75

50

25

0

« irregular » � « regular » strip vibrations when

blowing pressure increase

50

figure, the strip tension gap between the edges is higher: 17%. For the same blowing pressure (40 mbar), the strip’s behaviour is completely different. The global vibration amplitude increases: the standard deviation average is about 5.6 A.U., i.e. 28% higher than the case of low tension difference between the strip edges. However we can observe that the vibration amplitude increase is more important on the sensor located on the operator side (Cabin edge) than on the motor side (Hall edge). The heterogeneous width-wise strip tension favours the “twist” positioning.

Intermediate conclusion:

The heterogeneous strip tension across the strip width is a major influent parameter on vibrations. It plays a role on vibrations modes selector.

The heterogeneous strip tension across the width can be connected to industrial conditions like flatness defects or width-wise thermal heterogeneities, which induce tension heterogeneities.

2.3.2.5.3. Influence of blowing boxes pressure equilibrium

The industrial configuration of ArcelorMittal Ghent HDG line displays connections between two blowing boxes of each strip face (Figure 46). Those connections play the role of pressure balancing between the 2 blowing boxes in order to limit the propagation of pressure fluctuations from one strip side to the other one. In order to investigate the influence of this geometrical configuration, such connecting tube have been manufactured and implemented on the experimental pilot line. Measurements have been done only for one Laser sensor at the strip centre.

Results are shown on Figure 47.

Intermediate conclusion:

The connecting tubes do not affect significantly the vibrations amplitudes. However those trials have been also done with pressure differences from one blowing box compared to the other one. The conclusion is similar: no significant effect of the balancing tubes.

Figure 46: Connecting tubes between the two opposite blowing boxes

Figure 47: Influence of the connecting tubes between the opposite blowing boxes

0

5

10

15

20

25

30

0 10 20 30 40 50blowing pressure (mbars)

stri

p d

isp

lace

men

t st

and

ard

dev

iati

on

(m

m)

strip (center) standard deviation (mm)-d=67 mm-with tubes

strip (center) standard deviation (mm)-d=67 mm-without tubes

51

2.3.2.5.4. Influence of blowing width

One hypothesis to explain the fluttering phenomenon on strip edges is the interaction between two opposite air jets. In order to investigate the parameters different blowing widths are tested. The strip width is fixed and does not change during the trials run: 950 mm.

The tested blowing widths are: 800 mm, 900 mm, 1 000 mm, 1 100 mm, 1 200 mm, 1 400 mm. (Figures 48 and 49)

Figure 48: Effect of blowing width on vibrations amplitudes

Figure 49: Effect of blowing width on peak- to-peak values

Intermediate conclusion:

The strip stability is better when the strip blowing width is lower than the strip width (effect on strip vibrations and twist instabilities). The blowing width is a major influent parameter on vibrations. It is related to the fluttering phenomenon on strip edges.

2.3.2.5.5. Influence of a pressure difference between the 2 plenums

The Figure 50 presents the effect of a pressure difference between the two plenums on the strip vibration amplitude, for a plenum configuration containing 6 nozzles including a pressure PAD. The results show the very limited effect of a plenum pressure difference of 5%. Higher plenum pressure differences are not considered in this study because they are not realistic in industrial lines.

0

5

10

15

20

25

30

0 10 20 30 40 50 60blowing pressure (mbars)

stri

p d

isp

lace

men

t st

and

ard

dev

iati

on

(m

m)

strip (center) standard deviation (mm)-d=67 mm-straight nozzles-l=1400strip (center) standard deviation (mm)-d=67 mm-straight nozzles-l=1200strip (center) standard deviation (mm)-d=67 mm-straight nozzles-l=1100strip (center) standard deviation (mm)-d=67 mm-straight nozzles-l=1000strip (center) standard deviation (mm)-d=67 mm-straight nozzles-l=900strip (center) standard deviation (mm)-d=67 mm-straight nozzles-l=800

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60blowing pressure (mbars)

mea

n t

wis

t b

etw

een

str

ip e

dg

es (

mm

)

mean tw ist betw een strip edges (mm)-d=67 mm-straight nozzles-l=1400mean tw ist betw een strip edges (mm)-d=67 mm-straight nozzles-l=1200mean tw ist betw een strip edges (mm)-d=67 mm-straight nozzles-l=1100mean tw ist betw een strip edges (mm)-d=67 mm-straight nozzles-l=1000mean tw ist betw een strip edges (mm)-d=67 mm-straight nozzles-l=900mean tw ist betw een strip edges (mm)-d=67 mm-straight nozzles-l=800

blowing width > strip width

blowing width < strip

52

Figure 50: Effect of a delta pressure of 5 % between the 2 plenums for a configuration of 2 x 6 nozzles with and without PAD sheets

2.3.2.5.6. Influence of nozzles length

The geometrical parameter “nozzles length” has been investigated. Two different nozzles lengths have been tested: initial length = 275 mm and tested length = 55 mm (Figure 51).

Figure 51: Tested configuration equipped with shorter nozzles length (55 mm)

Figure 52: Influence of shorter nozzles length (55mm) on vibrations instability

0

5

10

15

20

25

0 20 40 60 80 100blowing pressure (mbars)

stri

p d

isp

lace

men

t st

and

ard

dev

iati

on

(m

m)

strip (center) standard deviation (mm)-d=67 mm-straight nozzles

strip (center) standard deviation (mm)-d=67 mm-straight short nozzles

strip (center) standard deviation (mm)-d=67 mm-nozzles in staggered row s

strip (center) standard deviation (mm)-d=67 mm-short nozzles in staggered row s

0 5

10 15 20 25 30 35 40 45 50

0 10 20 30 40 50 60 70 Blowing pressure [mbar]

strip (centre) standard deviation (mm)- delta(P1-P2) = 0%-with PADstrip (centre) standard deviation (mm)- delta(P1-P2) = 5%-with PADstrip (centre) standard deviation (mm)- delta(P1-P2) = 0%-without PADstrip (centre) standard deviation (mm)- delta(P1-P2) = 5%-without PAD

RMS [mm]

53

As shown on the pink and yellow curves on the Figure 52, the reduction of nozzles lengths has a negative impact on strip vibrations. However, two further major effects have been observed:

- The strip stability in terms of twist positioning is better due to the reduction of the air exhaust free volume.

- But with a lower exhaust volume in the nozzle zone, the vibration amplitudes increase

Intermediate conclusion:

The nozzle length seems to be a major influent parameter, easy to implement on industrial condition. As a recommendation, it is important to design sufficiently long nozzles (in the range of 200-250 mm).

2.3.2.5.7. Influence of staggered arrangement

As the blowing width has been identified as influent parameter on strip stability, a simple way to reduce the fluttering effect is to eliminate the opposite air jets by staggering the nozzles.

The Figure 54 shows the results of 4 different tested configurations (Figure 53):

- Initial configuration: classical nozzles arrangement with PAD sheet

- Classical nozzles arrangement without PAD sheet

- Straight nozzles

- Staggered straight nozzles

Indeed, the PAD sheet has been identified as negative influent parameter when the PAD-Strip distance is high.

Figure 53: 3 different tested configurations: a) straight nozzles b) staggered straight nozzles c) classical nozzles arrangement with PAD sheet

PAD sheet

54

Results:

Figure 54: Standard deviation and peak-to-peak measurements for the 4 different tested configurations

In this strip-nozzles distance, the staggering of straight nozzles has clearly a positive influence on strip stabilization (turquoise blue curve of Figure 54). The standard deviation is still < 3 mm whatever the blowing pressure is. The peak-to-peak measurements in that case increase lightly and continuously with the blowing pressure but is still very low compared to in initial configuration (yellow curve) and the other tested configurations. The strip stabilization allows performing the trials run until the maximal blowing pressure that can be delivered by the pilot fans: 100 mbar, without risk of strip-nozzles contact.

Intermediate conclusion:

The benefits of nozzle staggering are easy to calculate: for the blowing pressure of 40 mbar, the ratio between peak-to-peak values between the staggered configuration and the initial one is about 4. That means that vibrations maximal amplitudes can be decreased by a factor 4.

2.3.2.5.8. Influence of PAD

As the industrial cooling design of ArcelorMittal HDG line 3 includes the implementation of PAD sheets, the influence of this geometrical parameter has been investigated on the pilot line.

Indeed, the PAD sheet or AeroDynamical Bearings aims to form an air padding between the strip and the metallic sheet (Figure 55) in order to stabilize it [12,13].

The influence of the implementation of PAD sheet has been tested, as well as the staggering of the PAD sheets and the distance between the PAD sheet and the strip.

o Influence of PAD sheet:

Firstly, two different configurations have been tested (Figure 55):

- Initial design with staggered nozzles, and with staggered PAD nozzles with PAD metallic sheet (full red curve)

- Straight staggered nozzles without PAD (full yellow curve)

0

5

10

15

20

25

30

0 20 40 60 80 100blowing pressure (mbars)

stri

p d

isp

lace

men

t st

and

ard

dev

iati

on

(m

m)

strip (center) standard deviation (mm)-d=67 mm-straight nozzles

strip (center) standard deviation (mm)-d=67 mm-nozzles in staggered row s

strip (center) standard deviation (mm)-d=67 mm-w ith PAD sheet

strip (center) standard deviation (mm)-d=67 mm-w ithout PAD sheet

0

15

30

45

60

75

90

105

120

135

0 20 40 60 80 100blowing pressure (mbars)

stri

p d

isp

lace

men

t p

eak

to p

eak

(mm

)

strip (all points) peak to peak (mm)-d=67 mm-straight nozzles

strip (all points) peak to peak (mm)-d=67 mm-nozzles in staggered row s

strip (all points) peak to peak (mm)-d=67 mm-w ith PAD sheet

strip (all points) peak to peak (mm)-d=67 mm-w ithout PAD sheet

55

By the comparison between the full red curve and full yellow curve of the Figure 56, the PAD sheet does not play a major part on vibrations until a pressure of about 50 mbar. But for higher pressures (50-90 mbar) the peak-to-peak values of the full red curve (configuration with staggered PAD sheet) are lower than the yellow one.

Figure 55: Configuration on experimental pilot device with staggered straight nozzles and symmetrical PAD

Figure 56: Peak-to-peak value function of blowing pressure for 7 tested configurations

Intermediate conclusion:

The PAD seems to play its stabilization role for high blowing pressure.

o Influence of staggered PAD sheet:

Secondly, two different configurations have been tested (Figure 56):

- Straight staggered nozzles with symmetrical PAD nozzles with PAD metallic sheet (full dark blue curve)

- Initial design with staggered nozzles, and with staggered PAD nozzles with PAD metallic sheet (full red curve)

By the comparison between the full red curve and full dark blue curve, the symmetrical PAD sheet seems to play a negative role on vibrations as the peak-to-peak value increase continuously with the pressure. The PAD sheet should be symmetric in order to stabilize the strip.

Intermediate conclusion:

The current PAD sheet is not optimised and is more destabilizing than stabilizing.

o Influence of staggered PAD blowing nozzles without PAD sheets

We demonstrated the effect of staggered arrangement of the nozzles in the cooling device for the limitations of strip vibrations. In those conditions, it appears interesting to test configurations which can be used in industrial lines. The Figure 57 shows a standard plenum configuration containing PAD

Standard Nozzles design / staggered / without PAD sheetStandard Nozzles design / staggered / with PAD sheet

Straight nozzles / staggered

D =67 mm

0

10 20 30 40 50 60 70 80

0 20 40 60 80 100

Pressure [mbar]

Peak-Peak all points [mm]

Straight nozzles / Staggered / symmetrical PAD moved forward / without sheet, Straight Nozzles / Staggered / Symmetrical PAD sheet / with sheet

Straight Nozzles / Staggered / Symmetrical PAD sheet / without sheet

Straight nozzles / Staggered / symmetrical PAD moved forward / with sheet,

56

sheets, with staggered arrangement obtained by a displacement of half nozzle pitch for the entire nozzles set including the PAD sheet.

The Figure 58 presents the tests results obtained with this configuration, with and without the PAD sheets. A comparison with the standard design – i.e. non-staggered arrangement – with and without PAD sheets is also given in this figure. The distance between the nozzle and the strip – d = 85 mm – represents a classical distance generally used in galvanizing lines. The configuration with staggered nozzles arrangement and without the PAD sheets provides a very interesting solution for the control of strip vibrations in the after pot cooling section of galvanizing line.

Figure 57: Staggered standard design with staggered PAD

Figure 58: Peak-to-peak measurements for 4 different configurations:

- Staggered standard design with staggered PAD

- Staggered standard design with staggered PAD nozzles without PAD sheets

- Classical design with PAD

- Classical design without PAD sheets

o Influence of Strip - PAD sheet distance:

Thirdly the influence of strip-PAD distance has been investigated. As the PAD sheet seems to be efficient for higher pressure, one way to increase the efficiency if the PAD by lower pressures is to reduce the strip-PAD distance.

After Pot Cooling section (d=85 mm)

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100Pressure [mb]

Pea

k-P

eak

all

poin

ts [

mm

]

Staggered standard design, without PAD sheetStaggered standard design, with PAD sheetStandard design, without PAD sheetStandard design, with PAD sheet

57

Figure 59: Schematic configuration for the investigation on the effect of the strip-PAD distance on vibrations amplitudes

Two strip-PAD distances have been investigated:

- Initial distance: 67 mm (red curve with rhombuses)

- Advanced positioned PAD: 27 mm.

Figure 60: Effect of the strip-PAD distance for 3 different strip to blowing nozzles distances

The comparison between the 2 curves with same colours on the Figure 60 leads clearly to conclude that the PAD sheet is efficient as soon as the PAD-strip distance is reduced. For a strip-PAD distance of 25 mm, the peak-to-peak measurements stay in a range of 15-20 mm whatever the blowing pressure.

Intermediate conclusion:

The PAD sheet has been identified as a major geometrical parameter to stabilize the strip when it is positioned close to the strip. A 25 mm distance between the strip and the PAD sheet on the experimental pilot device (and strip-nozzles distance = 67 mm) corresponds to a distance of about 37.5 mm in industrial conditions (and strip-nozzles distance = 100mm) because of the scale of the experimental pilot.

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100blowing pressure (mbars)

strip

dis

plac

emen

t pea

k to

pea

k (m

m)

strip (all points) peak to peak (mm)-d=67 mm-nozzles in staggered row s + PAD in opposite(d strip=27 mm)strip (all points) peak to peak (mm)-d=67 mm-nozzles in staggered row s + PAD in oppositewithout PAD sheet (d strip=27 mm)strip (all points) peak to peak (mm)-d=85 mm-nozzles in staggered row s + PAD in opposite(d strip=45 mm)strip (all points) peak to peak (mm)-d=85 mm-nozzles in staggered row s + PAD in oppositewithout PAD sheet (d strip=45 mm)strip (all points) peak to peak (mm)-d=100 mm-nozzles in staggered rows + PAD inopposite (d strip=60 mm)strip (all points) peak to peak (mm)-d=100 mm-nozzles in staggered rows + PAD inopposite w ithout PAD sheet(d strip=60 mm)

0

10

20

30

40

50

60

0 20 40 60 80 100blowing pressure (mbars)

mea

n tw

ist b

etw

een

str

ip e

dges

(mm

)

mean tw ist betw een strip edges (mm)-d=67 mm-nozzles in staggered row s + PAD inopposite (d strip=27 mm)mean tw ist betw een strip edges (mm)-d=67 mm-nozzles in staggered row s + PAD inopposite w ithout PAD sheet (d strip=27 mm)mean tw ist betw een strip edges (mm)-d=85 mm-nozzles in staggered row s + PAD inopposite (d strip=45 mm)mean tw ist betw een strip edges (mm)-d=85 mm-nozzles in staggered row s + PAD inopposite w ithout PAD sheet (d strip=45 mm)mean tw ist betw een strip edges (mm)-d=100 mm-nozzles in staggered rows + PAD inopposite(d strip=60 mm)mean tw ist betw een strip edges (mm)-d=100 mm-nozzles in staggered rows + PAD inopposite w ithout PAD sheet(d strip=60 mm)

58

o Flow velocity characterization at the exit of blowing nozzles

Flow velocity characterizations have been realised with the 1 D hot wire equipment in order to detect potential flows velocity differentials between the blowing nozzle centre and its edges.

Tested configuration:

- 2 x 4 right nozzles without PAD sheet

- Strip-Nozzles distance: 85 mm

- Opening section of blowing nozzle: 8 mm

- Blowing pressures tested: from 0 to 100 mbar

- Spectral density analysis – conditions:

- Measures per sensor: 6553600

- Sample frequency for blow velocity: 2500 Hz

- Sample frequency for strip displacement sensors: 2500 Hz

- Acquisition time for spectral analysis: 44 min

- Frequency resolution: 0.0763 Hz

Flow velocity profiles from the nozzle to the strip at the nozzle centre:

Figure 61: Flow velocity profiles from the nozzle to the strip at the nozzle centre and for different blowing pressures. Legend : X is the distance between the nozzle and the strip; e is the nozzle opening section, Umax is

the flow velocity just at the exit of the nozzle, Umoy is the measured velocity at a distance X from the nozzle wall : Umoy = U(X,0)

Velocity profiles are presented in a non-dimensional form.

There is to see a perfect superposition of all velocity profiles whatever the blowing pressure is. As excepted the flow velocity is decreasing in the nozzle-strip direction.

59

Flow velocity profile from the nozzle to the strip at the nozzle edge:

Figure 62: Flow velocity profiles from the nozzle to the strip at the nozzle edges and for different blowing pressures. Legend : X is the distance between the nozzle and the strip; e is the nozzle opening section, Umax is

the flow velocity jus tat the exit of the nozzle, Umoy is the measured velocity at a distance X from the nozzle wall : Umoy = U(X,0)

There is a perfect superimposition of all velocity profiles whatever the blowing pressure is. By comparing the 2 previous graphs (Figures 61 and 62) there is a velocity gradient from the nozzle centre to the nozzle edge. The homogeneity is not completely ensured in the transversal direction and depends on the plenums air supply configuration. It could have an influence on strip vibrations behaviours, especially on twist positioning. Based on the symmetrical hypothesis, similar tests for the second strip edge have not been carried out.

Two Laser measurements across the width (strip centre « motor » edge) have been simultaneously realized in order to detect a potential connection between flow velocity frequencies and strip displacement frequencies.

The third Laser called « cabin Laser sensor » has not been analysed because the flow velocity measurement have been realized for a half strip (symmetry based on strip neutral line).

Common peaks are detected between 1Hz and 2.5 Hz, for the 2 Laser sensors and the velocities spectral analysis.

Spectral density analysis of flow velocity

Tested conditions: Blowing pressure = 30 (=30%), 40 (=40%) and 50 (=50%) mbar; Strip tension = 547 daN

60

Figure 63: The spectral density analysis of flow velocity signals show typical frequencies around 1-2,5 Hz ; 5-6 Hz and 18 Hz.

Superimposition of spectral density analysis of flow velocity and spectral density analysis of strip displacements:

Conditions: Blowing power: 50 mbar; strip tension: 547 daN

Figure 64: Superposition of spectral density analysis of flow velocity signal (black curve) and spectral density analysis of strip displacements(red, green and blue curves)

Conclusion:

The blowing velocity at the nozzle exit depends usually on blowing pressure, design of the plenum internal walls, air supply pipes geometry, nozzles design. The characterization of the jets velocity shows a dependency between the energy induced by the flow velocity (black curve on Figure 64) and the energy transferred to the strip (red, green and blue curves).

1 – 2.5 Hz 5 - 6 Hz

18 Hz

61

2.3.2.5.9. Task 2.5 Synthesis

Objectives

- Quantification of the improved designed cooling device performances

2.3.2.5.9.1. Summary of main results

Regarding the complete trial plan carried out, the main results are:

o Influence of process parameters:

- Blowing pressure: major influent parameter, as well as the velocity homogeneity across strip width

- Line velocity: no influence

- Heterogeneous strip tension: major influence but difficult to manage in industrial conditions; major influence on vibrations mode, especially twist positioning, but difficult to manage in industrial conditions

o Influence of geometrical parameters:

- Pressure balancing between blowing boxes: no influence

- Pressure balancing nozzle width wise: influent

- Strip-Nozzles distance: influent

- Nozzle length: major influent parameter: a minimal nozzle length is required.

- Blowing width: can be major influent in the case of narrow strip (opposite air jets on the strip edges).

- Staggered nozzles: major influent parameter, easy to implement in industrial conditions, very good benefits

- PAD sheet: major influent parameter especially the PAD-Strip distance, easy to implement in industrial conditions

2.3.2.5.9.2. Innovative technical solution

Regarding the previous results obtained on semi-industrial configuration and taking into account the application of obtained results to industrial lines, the ideal technical solution could be:

- To stagger the blowing boxes with a ½ step

- To put closer to the strip the PAD sheet (~40 mm for industrial line)

- To reduce the nozzle to nozzle distance with respect of global opening surface on one plenum

- To adapt the nozzles opening section

62

2.3.2.5.9.3. First recommendations for an industrial implementation

The first recommendations can be done for an industrial application.

The innovative technical solution selected for the industrial line – Ghent – consists in the following modifications, with respect to the present situation shown in Figure 65:

o Upward displacement of the right-side plenum by 200 mm, corresponding to a half nozzle pitch;

o Upward displacement by 200 mm of the duct connecting the plenum and the fan.

Figure 65: Current blowing technology implemented at ArcelorMittal Ghent Hot Dip Galvanizing line.

The results of these modifications are presented in Figure 66. Dedicated pieces will be manufactured in order to perform these modifications.

Figure 66: Proposed modifications at the blowing technology implemented at ArcelorMittal Ghent Hot Dip Galvanizing line.

63

2.3.3. WP3 - Installation and optimization of the improved proposed solution in industrial conditions on Sagunto line

2.3.3.1. Contractor change due to economical crisis (2009)

The economical crisis of 2008-2010 has affected the load of the galvanizing lines of ArcelorMittal to an unprecedented extend, and forced the company to take measures to reduce drastically production costs and working capital. The cost reduction measures include total idling of a number of galvanizing lines in order to maintain the load of the running lines at an acceptable level.

In this context, the site of ArcelorMittal Ghent wishes to retire from the project and not to implement the new cooler design on its galvanizing line N°3.

The demand for galvanized automotive steel sheet is expected to restart and exceed capacity first in South Europe. In this region, the galvanizing line of Sagunto has beneficiated in the past years of investments that have made the vibrations from the tower cooling emerge as the next bottleneck. The value of HDG Sagunto as a pilot line is equal to HDG3 Ghent; both are among the best and highest capacity European galvanizing lines for exposed automotive steel sheet.

So, because of potential technical benefits of the project and the potential quality and productivity gains of industrial implementation of the new cooling system developed into the current RFCS project, in agreement with all the RFCS contractors, the coordinator proposed to conduct the industrial implementation at ArcelorMittal Sagunto and not at ArcelorMittal Ghent.

The proposal has been presented at the TGS 5 meeting on May 2009 and accepted.

However an additional task (task 3.1 bis) has been introduced into the work program to evaluate the technical feasibility study to implement the innovative technology on ArcelorMittal Sagunto line

2.3.3.2. Task 3.1 bis: Trials campaign at Sagunto to characterize the initial state before implementing the innovative technology

An exhaustive strip vibrations characterization campaign has been conducted to evaluate the initial state of the Sagunto line before the technology implementation.

Identical work as the one done for the ArcelorMittal Line of Ghent #3 has been done for the Sagunto one.

2.3.3.2.1. Measurement system and Cooling tower configuration

The strip displacement measurement systems used to characterize vibrations at Sagunto line have identical as the ones used for Ghent line #3 characterization (§2.2.1):

Strip vibrations are measured on two points (Figure 67):

- at the top of the cooling tower, between the cooling boxes, where vibrations are the most important

- at the wiping zone, the most sensitive point of the production line to warranty the product quality

64

Experimental measurement systems:

- Between the cooling boxes; 3 Laser sensors are placed in front of the strip, strip width-wise

- At the wiping zone, 3 inductive sensors, called Kaman sensors, are placed in the front of the strip above the wiping nozzles.

The 3 width-wise sensors measure the strip position. The vibrations amplitudes are obtained by calculating the standard deviation of the strip position. The 3 width-wise sensors give the vibrations amplitudes at the centre of the strip and at its 2 edges.

Figure 67: Configuration of the Sagunto cooling tower and position of the measurement systems

Process parameter observed:

- Blowing pressure Box 1 (others process parameter kept stable and constant: Line speed : 150m/min; Strip format: 1440mm x 0.7mm )

- Blowing pressure Box 2 (others process parameter kept stable and constant)

- Line velocity

Product:

- Thickness: ~0.5 – 2.0 mm

- Width: ~750 to 1850 max

- Maximal blowing capacities (Box 1 and 2): 40 mbar = 100 %

Laser sensors position

Kaman sensors position

65

2.3.3.2.2. Effect of blowing pressure of blowing box 1

The effect of the blowing pressure of the cooling box 1 has been observed during the whole campaign whatever the strip format is. The results of the strip vibrations measurements at the wiping zone are shown hereafter (Figures 68 and 69) as well as at the top of the cooling tower (Figure 70):

Figure 68 & Figure 69: Standard deviation and peak to peak distance at the wiping zone (Kaman sensors measurements) on 3 points for different box 1 blowing pressures (%) and for stable other production parameters:

- blue curve: operator side

- pink curve: strip centre

- yellow curve: motor side

- black/grey curve: average trend

Figures 68 and 69 show a stabilizing effect measured at the wiping zone for a blowing pressure at the box 1 ~50 % whereas the blowing power of the box 2 has been kept constant at 20% =8 mbar.

Figure 70: Standard deviation and peak to peak distance at the top of the cooling tower (Laser sensors measurements) on 3 points for different box 1 blowing pressures (%) and for stable other production parameters:

- blue curve: peak to peak

- red curve: standard deviation

We do not see the same stabilizing effect on the measurement located at the top of the cooling tower. Figure 70 shows, on the contrary, that the standard deviation and peak to peak measures continuously increase with the blowing pressure.

Further trials have been conducted to explain the stabilization effect at 50 % observed at the wiping zone. This effect is explained by an unbalanced pressure between the plenums facing the strip into the cooling box 1. Indeed, a difference of ~1.3 mbar is observed between both plenums, especially for a power > 50 % (= 20 mbar).

Vibration amplitude at the Wiping zone

1.0

1.5

2.0

0 25 50 75 100

puissance caisson 1 (m/mn)

Sta

nd

ard

Dev

iati

on

(m

m)

Opér.

centre

moteur

Moy

Vibration amplitude at the Wiping zone

5

10

15

20

0 25 50 75 100puissance caisson 1 (m/mn)

Pic

àP

ic(m

m)

Opér.

centre

moteur

Moy

Vibration amplitudes in the tower

2.0

3.0

4.0

5.0

0 25 50 75 100 Blowing power box 1 (%)

Sta

nd

ard

Dev

iati

on

(mm

)

0

10

20

30

40

Pea

k to

pea

k (m

m)

66

A hypothesis is that the unbalanced pressure between the opposite plenums can induce a strip displacement regarding its initial pass line (Figures 71 and 72). As a consequence, the strip displacement induces tension increase. It has been previously shown that the strip tension is order-1 factor on strip stabilization.

At 75% of the Box 1 blowing power, a 1.4 mbar difference has been observed between the 2 plenums and a difference of 2.3 mbar at maximal fans power (=100%).

Figure 71 & Figure 72: Averaged strip displacement at the wiping zone (Kaman signals) and at the top of the cooling tower (Laser sensors) for different box 1 blowing power. Reference”0” is the averaged strip position at

minimal acceptable blowing power (10%)

Intermediate conclusion:

A stabilizing effect is observed for a blowing pressure ~50 %, probably due to local strip tension increase generated by the deviation of the strip from its pass-line. At higher pressures, vibrations amplitudes are increasing, as expected, until 35 mm (Figure 70, blue curve). As well, an important strip displacement has been observed on one plenum direction: 40 mm at 75 % blowing power (Figure 71).

D é placement de bande à

0.0

1.0

2.0

3.0

4.0

0 25 50 75 100 Puissance caisson 1 (%)

d é

placement

(mm)

Strip displacement at the wiping zone

0.0

1.0

2.0

3.0

4.0

0 25 50 75 100 Blowing power Box 1 (%)

Dis

pla

cem

ent

[m

m]

D é placement de bande dansla tour

0.0

20.0

40.0 60.0

0 25 50 75 100

Puissance caisson 1 (%)

d é

placement

(mm)

Strip displacement in the cooling tower

0.0

20.0

40.0 60.0

0 25 50 75 100

Blowing power Box 1 (%)

Dis

pla

cem

ent

[mm

]

Guarantied [mbar]

not gar. [mbar]

21.9 20.5 1.4 38 35.7 2.3 100

75

delta P

[mbar] Power

67

2.3.3.2.3. Effect of blowing pressure of blowing box 2

The effect of the blowing pressure of the cooling box 2 has been observed during the whole campaign whatever the strip format is. The results of the strip vibrations measures at the wiping zone are shown hereafter (Figures 73 and 74) as well as at the top of the cooling tower (Figure 75):

Figure 73 & Figure 74: Standard deviation and peak to peak distance at the wiping zone (Kaman sensors measurements) on 3 points for different box 2 blowing pressures (%) and for stable others production parameters:

- blue curve: operator side

- pink curve: strip centre

- yellow curve: motor side

- black/grey curve: average trend

Figure 75 Standard deviation and peak to peak distance at the top of the cooling tower (Laser sensors measurements) on 3 points for different box 2 blowing pressures (%) and for stable others production parameters:

- blue curve: peak to peak

- red curve: standard deviation

Figures 73, 74, 75 are clearly showing the increase of amplitudes with the blowing power. The effect of stabilization at 50 % is not observed. The blowing power of box 1 is kept constant = 20% = 8 mbar.

Strip displacement measurements have been done for various box 2 blowing pressures (Box 1 = 20% = 8 mbar) and results are presented hereafter:

2

2 2

Vibrations amplitudes in the tower

2.0 2.5 3.0 3.5 4.0 4.5 5.0

0 25 50 75 100 Blowing power Box 2 [%] )

Sta

nd

ard

Dev

iati

on

[m

m]

0 5 10 15 20 25 30 35 40

Pea

k to

pea

k [m

m]

)

Vibration amplitudes at the Wiping zone

5

10

15

20

0 25 50 75 100 Pea

k to

pea

k [m

m] Operator side .

Strip centre

Motor side

Average

Blowing power Box 2

Vibration amplitudes at the Wiping zone

1.3

1.6

1.8

2.1

2.3

0 25 50 75 100 Blowing power Box 2

Sta

nd

ard

Dev

iati

on

(mm

)

Operator side

Strip centre

Motor side

Average

68

Figure 76 & Figure 77: Averaged strip displacement at the wiping zone (Kaman signals) and at the top of the cooling tower (Laser sensors) for different box 2 blowing power. Reference”0” is the averaged strip position at

minimal acceptable blowing power (10%)

At 75% of the Box 2 blowing power, a 1 mbar difference has been observed between the 2 plenums and a difference of 3 mbar at maximal fans power (=100%).

Figures 76 and 77 show that the strip displacement at the top of the cooling tower is inversed compared to the blowing box 1 displacement effect. Indeed the unbalanced pressures between the 2 plenums of previous case induced a strip displacement in the opposite side of the Laser sensors (Figure 67) whereas Figure 75 shows negative figures. In the case of Box 2 trials, the strip displacement is done in the direction of the Laser sensors.

Intermediate conclusion:

Vibrations amplitudes at the top of the tower are very sensitive to pressure balance between 2 plenum of one cooling box.

2.3.3.2.4. Effect of line speed

The effect of the line speed has been observed during the whole campaign whatever the strip format is. The results of the strip vibrations measures at the wiping zone are shown hereafter (Figures 78 and 79):

Figure 78: Standard deviation at the wiping zone (Kaman sensors measurements) on 3 points for different line velocities and for identical others production parameters:

- blue curve: operator side

- yellow curve: motor side

- black curve: average trend

- pink curve: strip centre

Power guarantied

(mbars)

Not guar.

(mbars) delta P

10 2.1 0.6 1.5

25 4.4 3.2 1.2

50 11.4 11.1 0.3

75 22.8 23.8 -1

100 38 41 -3

Strip displacement at the wiping zone

0.0

1.0

2.0

3.0

4.0

0 25 50 75 100

Blowing power Box 2 [%]

Dis

pla

cem

ent

[mm

] Strip displacement in the cooling tower

-20.0

-10.0

0.0

10.0

0 25 50 75 100

Blowing power Box 2 [%]

Str

ip d

isp

lace

men

t [m

m]

Vibration amplitude at the wiping zone

1.0

1.21.4

1.6

1.82.0

2.2

100 115 130 145 160 Line velocity [m/mn]

Sta

nd

ard

Dev

iati

on

[m

m]

Operator side.

Strip centre

Motor side

Average

69

Figure 79: Peak to peak distance at the wiping zone (Kaman sensors measurements) on 3 points for different line velocities and for identical others production parameters:

- blue curve: operator side

- pink curve: strip centre

- yellow curve: motor side

- black curve: average trend

Intermediate conclusion:

For those standard production conditions, no significant effect of the line speed has been observed.

2.3.3.2.5. Synthesis

The trial run campaign has been carried out in standard production conditions and is representative of current production of the HDG line of ArcelorMittal Sagunto.

The campaign conducted gives the real state of the art of strip vibrations in the cooling tower:

- Standard deviation at the wiping zone: ~ 2 mm

- Standard deviation in the cooling boxes: ~ 4.5 mm

For maximal cooling capacities (40 mbar / 100% for each cooling box) = worth case:

- Peak-to-peak amplitudes at the wiping zone: max. 17 mm + a kind of twist / crossbow strip positioning

- Peak-to-peak amplitudes at blowing boxes: max. 37 mm + a kind of twist strip positioning + strip displacement on one plenum side

Process parameters can influence the vibrations amplitudes:

- Standard deviation increase with blowing power of both boxes 1 and 2

- To avoid strip displacement on one preferential plenum side, it is important to balance as much as possible the pressures between the 2 plenums of one blowing box, whatever the blowing is.

The line speed effect did not clearly appear because it is combined with others process parameters like strip traction or immerged rolls settings.

In conclusion, those analysis show high potential to decrease strip vibrations at the wiping zone as well as in the cooling boxes by optimising the design of the current cooling system.

Vibration amplitudes at the wiping zone

5

10

15

20

100 115 10 145 160

Line velocity [m/mn]

Pea

k to

Pea

k [m

m] Operator side

Strip centre

Motor side

Average

70

Expected gains for Sagunto:

- Reduction of strip vibrations amplitudes in the blowing boxes: factor 4

- Reduction of strip vibrations amplitudes at the wiping zone

- Line speed enhancement

- Zinc savings thanks better control of transversal and longitudinal coating homogeneity due to the strip stabilization

2.3.3.3. Task 3.1 design & manufacturing of the innovative technology implementation at ArcelorMittal Sagunto line

Objective:

o Using of the 2/3 scaled design’s characteristics of the new cooling device defined in the WP2, development and design of the final improved industrial cooling device taking considering the line constraints (bulk, free volumes)

o Manufacturing of the final improved industrial cooling device

Results:

Application of recommendations from tasks 2.3, 2.4, 2.5 to the Sagunto cooling tower configuration

o Removal of PAD sheet

As previously demonstrated on the experimental scaled facility, the PAD sheet is efficient only when it is positioned closed to the strip (~25 mm in experimental conditions, id est ~ 37.5 mm in industrial conditions). On the Sagunto configuration, the PAD sheets are positioned at ~ 125 mm to the strip. The recommendations to reduce strip vibrations are:

- to move the PAD sheets at a strip distance = 37.5 mm

or

- to remove the PAD sheets

The decision made by the line managers was to completely remove the PAD sheets, especially because the whole plenums could not be move closer to the strip.

o Nozzles staggering

The nozzles staggering has been identified as the major influent parameter and the easiest to implement in industrial conditions. The recommendations are:

- to stagger all the nozzles of one plenum

or

- to stagger the nozzles with a half pitch, so that the impacting jets are impacting the strip from one face to the opposite face on a symmetrical way

The decision has been made to stagger the 2 blowing boxes 1 & 2.

71

o Pressure balancing between 2 opposite plenums

As detected within the task 3.1 bis (additional industrial trials to characterize the current vibrations state on Sagunto line), a low pressure imbalance between 2 opposite plenums (until ~3 bar at 40 mbar, id est 7.5 %) can induce a constant strip displacement and could provoke the strip instability ignition. So that the negative effect of the opposite plenums imbalance can be multiplied if the same imbalance is observed into the second cooling box.

The recommendations are:

o to check the pressure balance between 2 opposite plenums, for both blowing box 1 and blowing box 2

o to adjust the regulation loop, the verify the measurement sensors if needed

o Final cooling design

Based on the common decision between all contractors, Drever has made the drawings of final cooling design.

The plenums modifications include:

o the complete removal of nozzles steel sheets on the plenum front,

o the dismantling / reassembly of the guiding rolls

o the dismantling / reassembly of the air inlet piping system

o the dismantling / reassembly of the air exhaust piping system

o the dismantling / reassembly of the fans motor support

o the assembly of additional pieces manufactured by Drever to warranty the nozzles staggering

o the reassembly of the nozzles and steel sheets on the plenum front

o the adjustments on the plenum front to warranty the air tightness

It is important to precise that the current cooling tower configuration of Sagunto is adapted for a galvannealed treatment, so that the blowing boxes are fully embodied into a closed casing, what makes the modifications more difficult (difficult access for the pieces manufacturing, for operators, for the pieces transport).

2.3.3.4. Task 3.2 - Assembly and adjustment of the improved cooling device in the industrial line

Objective:

o Cooling device assembly at the galvanizing line at ArcelorMittal Sagunto

o Adjustments until the new cooling device is ready to run

72

Results:

The implementation of the new cooling design has been prepared many weeks before the yearly stop line. The assembly of the new cooling technology took a few days and occurred with success. The Figure 80 shows the results: nozzles are staggered; PAD sheets are removed into the two blowing boxes.

Figure 80: the final configuration of the cooling tower at Sagunto

Encountered difficulties during engineering investigations due to the existing line configuration

One major issue encountered during the engineering study of the blowing boxes revamping consisted in respecting the staggering pitch of a half step. The distance between 2 nozzles is 400 mm, so that a half step means 200 mm. The recommendations of the previous experimental investigations are to respect a staggering step of 200 mm. In the specific case of Sagunto, because of non removable mechanical parts positioned in the top-roll area, the staggering pitch was limited on 160 mm instead of 200 mm, as the Figure 81 sums it up.

73

Figure 81: the final configuration of the cooling tower at Sagunto

Figure 82: Picture taking during the implementation of the innovative cooling technology on the Sagunto cooling tower: nozzles staggering, PAD removal.

Adjustment of blowing pressure regulation

Based on the results of the trials campaign conducted within the task 3.1 and showing the impact of a light imbalance between two opposite plenums at high blowing pressures, the pressure regulation loops have been controlled and adjusted.

Indeed the light pressure imbalance in blowing boxes 1 & 2, observed are not due to possible unsymmetrical air inlet pipes, what could induce differential pressure losses on one strip face compared to the other. This hypothesis has been verified:

o Both sides of fan inlet are symmetric (same design: duct length & size, elbow size, etc…).

o Both sides of fan outlet are symmetric (same design: duct length & size, elbow size, etc…).

o Fans are identical

Staggering pitch = 200 mm

RECOMMENDED INDUSTRIALIZATION

Staggering pitch = 160 mm

74

o Pressure taps of both sides are symmetric (same taps position and pressure transmitter located on tower platform at same altitude – atmospheric reference pressure).

On other emitted hypothesis consisted on possible deviation of the pressure sensors. But the pressure transmitters’ calibration shows no influence.

A cross-interlock has been introduced into the regulation software so that the pressure imbalance has been immediately corrected as the Figure 83 shows it:

Figure 83: Screenshot of the blowing pressure balance between plenums after regulation adjustments at Sagunto

Intermediate conclusion:

The pressure imbalance was not detected before the line speed increase (tests at 150 m/min). Now with the line speed increasing, both blowing boxes 1 & 2 are used at their full capacity. After adjustment of the cross-interlock within the regulation software, the pressure imbalance has been corrected (<< 0 mbar).

2.3.3.5. Task 3.3 - Preparation of industrial tests

Objective:

o Elaboration of online tests to evaluate the performances of the new industrial cooling device in standard conditions and in critical conditions (critical values of blowing and line process parameters defined in the WP1)

o Elaboration of the test procedures.

Results:

The trial plan has been built considering the previous characterization campaigns, in particular, the strip format, steel grades, process parameters have been kept as much as possible identical as the first trials campaign:

75

Figure 84: Identical product and process parameters during the trials campaigns on Sagunto line.

The trials have been conducted on standard production conditions for the strip formats: 1438 x 0.647 mm; 1829 x 0.636 mm and for 1561 x 0.79 mm whereas a specific strip format has been chosen to evaluate the strip vibrations under critical conditions. Indeed this strip format is well-known by the line operators to be very sensitive in terms of vibrations amplitudes.

The product and process parameters have been carefully chosen so that we aim to compare:

o the benefits of the pressure regulation adjustments (campaign 2009 versus first campaign 2010)

o the benefits of the new cooling design (campaign 2009 versus second campaign 2010)

The process parameters that we will make vary during the trials campaign will still be:

o the effect of the blowing pressure in blowing Box 1 (pressure in box 2 is kept constant),

o the effect of the blowing pressure in blowing Box 2 (pressure in box 1 is kept constant),

o the effect of combined blowing pressure in blowing Box 1 + 2

For each trial, the strip position, standard deviation (or RMS) and peak-to peak values are measured.

Intermediate conclusion:

The good preparation of the trials and the perfect coordination between all contractors ensures good reproducible conditions with the previous trials campaigns.

76

2.3.3.6. Task 3.4 - Installation of vibrations online measuring systems

Objective:

o Assembly of the industrial online measuring system of the strip vibrations. The control system will continuously measure the strip-nozzles distance in the wiping zone (similar principle as the experimental measuring system used for the analyses of the WP1). The industrial measuring system should resist at the standard industrial conditions and will be connected to the process control computer system.

o Tests and adjustments

Results:

As it has been done for the previous trials campaign, an identical strip vibrations measurement system has been installed at the wiping zone, just above the wiping nozzles. The system is still composed with 3 Kaman sensors across the strip width. The installation has been done with great care so that the Kaman alignment is warranted.

A similar measurement device has been implemented at the top of the tower just under the blowing nozzles.

The measurement devices positioning is kept identical as the one presented in the Figure 65.

2.3.3.7. Task 3.5 - Tests on industrial lines

Objective:

o Based on the previous trials plan, measurements of the strip vibrations by varying the blowing and process line parameters. Comparison with the results obtained with the experimental improved cooling device.

o Determination of the optimal industrial blowing and line process parameters (blowing velocity, pressure, cooling device positioning)

Results:

o Effect of blowing box 1

The effect of the blowing pressure of the cooling box 1 has been observed during the whole industrial campaign on 2 strip formats. Results will be presented for 1 format only (1438 x 0.647 mm), id est for 2 days of continuous production in normal conditions (no stop lines, no process incident, constant line velocity). The same tendencies have been observed for the second format (1829 x 0.636 mm). The results of the strip vibrations measures at the wiping zone are shown hereafter (Figure 85 a) and b)) as well as at the top of the cooling tower (Figure 86 a) and b)). The trial campaign after modification is presented in full curves.

The dotted curves represented the vibrations reference before modifications (trials campaign of 2008).

77

Figure 85: Effect of the blowing pressure on blowing box 1 (inferior) on strip vibrations at the wiping zone Sagunto line after modification (full curves). Comparison with the reference trials conducted on 2008 (dotted

curves).

a) Standard deviation; b) Peak to peak amplitudes

The blowing box 1 is generating more vibrations at the wiping zone after the modification of the cooling design than the reference case (campaign of 2008 on strip format 1438 x 0.647 mm). More especially, the increase of the blowing pressure makes increase the vibrations amplitudes on the strip edges (at cabin edge and at the motor edge) at the wiping zone whereas the vibrations at the strip centre are quite low and stable after modifications, whatever the blowing pressure is (Figure 85 a). The peak-to-peak measurements (Figure 85 b) show the same tendency: until a blowing pressure of 20 mbar, maximal vibrations amplitudes are quasi equivalent before and after the modification.

Figure 86: Effect of the blowing pressure on blowing box 1 (inferior) on strip vibrations at the top of the cooling tower on Sagunto line after modification (full curves). Comparison with the reference trials conducted on 2008

(dotted curves).

a) Standard deviation; b) Peak to peak amplitudes

We observe different phenomena at the top of the cooling tower (Figure 86 a) and b)). The standard deviation at the strip centre reduced after the modification, whatever the blowing pressure is. On the contrary, the standard deviations at the strip edges are continuously increasing with the blowing pressure: the standard deviation after modification is significantly higher on the strip edges than the initial state.

The Figure 83 b) shows the averaged peak-to-peak measurements between the 3 laser measurements. The curves show the same tendency: at high pressure (40 mbar), the maximal vibrations amplitudes

Vibration amplitude at the Wiping zoneeffect of box 1 - SD

0,5

1

1,5

2

2,5

0 10 20 30 40 50

pressure box 1 (mbars)

KAM ANET rive cabin 08KAM ANET centre 08

KAM ANET halle 08KAM ANET cabin 10KAM AN ET centre 10

KAM ANET hall 10

Vibration amplitude at the Wiping zoneeffect of box 1 - Peak-Peak

0,5

5,5

10,5

15,5

20,5

0 10 20 30 40 50

pressure box 1 (mbars)

KAM ANM ax PP 08

KAM ANmax PP 10

Vibration amplitude under cooling boxeseffect of box 1 - SD

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

0 10 20 30 40 50

pressure box 1 (mbars)

LASERET rive cabin 08LASERET centre 08

LASERET halle 08LASERET cabin 10LASER ET cent 10

KAM ANET hall 10

Vibration amplitude under cooling boxeseffect of box 1 - Peak-Peak

0,5

5,5

10,5

15,5

20,5

25,5

30,5

35,5

40,5

45,5

0 10 20 30 40 50

pressure box 1 (mbars)

LASERM ax PP 08

LASERmax PP 10

78

can reach 35.5 mm. Based on the confrontation of the 2 measurements (standard deviation on 3 points and averaged peak-to-peak), we can conclude that the strip edges generate high vibrations amplitudes on the top of the cooling tower.

Intermediate conclusion:

The averaged vibrations amplitudes are quasi equivalent before and after the modifications of the cooling technology. The strip edges seem to be very sensitive on the pressure of the blowing box 1 and generate high amplitudes also after the modification. On the contrary, the strip centre seems to be more stable after the modification.

o Effect of blowing box 2

The effect of the blowing pressure of the cooling box 2 has been observed during the whole industrial campaign on 2 strip formats. Results will be presented for 1 format only (1438 x 0.647 mm), id est for 2 days of continuous production in normal conditions (no stop lines, no process incident, constant line velocity). The same tendencies have been observed for the second format (1829 x 0.636 mm). The results of the strip vibrations measures at the wiping zone are shown hereafter (Figure 87 a) and b)) as well as at the top of the cooling tower (Figure 88 a) and b)). The trial campaign after modification is presented in full curves.

The dotted curves represented the vibrations reference before modifications (trials campaign of 2008).

Figure 87: Effect of the blowing pressure on blowing box 2 superior) on strip vibrations at the wiping zone Sagunto line after modification (full curves). Comparison with the reference trials conducted on 2008 (dotted

curves).

a) Standard deviation; b) Peak to peak amplitudes

The blowing box 2 is not generating more vibrations at the wiping zone after the modification of the cooling design than the reference case (campaign of 2008 on strip format 1438 x 0.647 mm). Whatever the blowing pressure is until 40 mbar, the standard deviations of the 3 Kaman measurements show a reduction of vibration of ~ 10 to 25 % between the initial state and the state after modifications. During the trial, a specific test has been conducted at the maximal fan power 45mbar. The standard deviations at this pressure are globally equivalent. The Figure 88 b) confirms the previous observations.

Vibration amplitude at the Wiping zoneeffect of box 2 - SD

0,5

1

1,5

2

2,5

0 10 20 30 40 50

pressure box 2 (mbars)

KAM ANET rive cabin 08KAM ANET centre 08

KAM ANET halle 08KAM ANET cabin 10KAM AN ET centre 10

KAM ANET hall 10

Vibration amplitude at the Wiping zoneeffect of box 2 - Peak-Peak

0,5

5,5

10,5

15,5

20,5

0 10 20 30 40 50

pressure box 2 (mbars)

KAM ANM ax PP 08

KAM ANmax PP 10

79

Figure 88: Effect of the blowing pressure on blowing box 2 (superior) on strip vibrations at top of the cooling tower at Sagunto line after modification (full curves). Comparison with the reference trials conducted on 2008

(dotted curves).

a) Standard deviation; b) Peak to peak amplitudes

We can observe similar phenomena at the top of the cooling tower. The laser measurements shows on Figure 88 a) an improvement of the strip centre vibrations whatever the pressure is, whereas the strip edges are more sensitive to vibrations after the modifications. Figure 88 b) shows a global improvement of the strip stability after the modifications excepted for the exceptional pressure of 45 mbar.

Intermediate conclusion:

The blowing box 2 is not generating vibrations. The modifications of the blowing design seem to have a positive effect on the strip stabilization, especially for the strip centre. The edges effect is still observed: the strip edges are very sensitive to vibrations even if we were careful to select the same steel grade and strip format for both trials campaigns.

o Effect of combined blowing boxes 1 + 2

The effect of the combined cooling box 1 and cooling box 2 has been observed in the same conditions. Please, note that the pressures in boxes 1 and 2 are increasing in identical proportions.

Figure 89: Effect of the combined blowing pressure on blowing box 1 (inferior) and box 2 (superior) on strip vibrations at the wiping zone on Sagunto line after modification (full curves). Comparison with the reference

trials conducted on 2008 (dotted curves).

a) Standard deviation; b) Peak to peak amplitudes

Vibration amplitude under cooling boxeseffect of box 2 - SD

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

0 10 20 30 40 50

pressure box 2 (mbars)

LASERET rive cabin 08LASERET centre 08

LASERET halle 08LASERET cabin 10LASER ET cent 10

KAM ANET hall 10

Vibration amplitude under cooling boxeseffect of box 2- Peak-Peak

0,5

5,5

10,5

15,5

20,5

25,5

30,5

35,5

40,5

45,5

0 10 20 30 40 50

pressure box 2 (mbars)

PP

(m

m)

LASERM ax PP 08

LASERmax PP 10

Vibration amplitude at the Wiping zoneeffect of boxes 1+2 - SD

0,5

1

1,5

2

2,5

0 10 20 30 40 50

pressure box 1 et 2 (mbars)

KAM ANET rive cabin 08KAM ANET centre 08

KAM ANET halle 08KAM ANET cabin 10KAM AN ET centre 10

KAM ANET hall 10

Vibration amplitude at the Wiping zoneeffect of box 1 + 2 - Peak-Peak

0,5

5,5

10,5

15,5

20,5

0 10 20 30 40 50

pressure box 1 & 2 (mbars)

KAM ANM ax PP 08

KAM ANmax PP 10

80

At the wiping zone, whatever the blowing pressure in both boxes 1 and 2 is, the standard deviation at the strip centre is improved after the cooling technology modifications (Figure 89 a) light green curve compared to the violin curve). The standard deviations on strip edges are lightly increasing after the modifications. One hypothesis could be the effect of existing long edges that we cannot easily detect on this industrial line.

Figure 90: Effect of the combined blowing pressure on blowing box 1 (inferior) and box 2 (superior) on strip vibrations at the top of the cooling tower on Sagunto line after modification (full curves). Comparison with the

reference trials conducted on 2008 (dotted curves).

a) Standard deviation; b) Peak to peak amplitudes

The Figure 90 b) shows the negative effect of the simultaneous increase of the blowing pressure in the both blowing boxes 1 and 2. At 40 mbar, the peak-to-peak amplitudes increased by 10 mm after the modifications.

However, the detailed measurements on the 3 lasers positioned across the strip show clearly the strip edges effect: the dark green (“hall side”) and kaki curves (“cabin side”) of Figure 90a) are systematically shifted by ~1 mm compared to the light green curve (“strip centre”).

Intermediate conclusion:

The pressure increase of combined blowing 1 and 2 generates light higher vibrations amplitudes after the modifications of the cooling design. One explanation could be the existing strip edges effect, which we observe at the wiping zone as well as at the top of the tower. If we focus the observation on the strip centre and the wiping zone only, the positive effect of the modification is more convincing: at 20 mbar, reduction of the standard deviation from 1.7 mm before the modification to 1.4 mm after the improvement.

o Conclusion of the trial campaign after the implementation of the cooling technology improvement

We took specific care in preparing the trials campaigns in the 3 past years (campaigns from 2008 to 2010:

o on selected product (steel grades and product properties, formats, zinc coating weight, product aspect and quality at the line entry),

o on process parameters (line speed, wiping parameters, bath material, strip tension)

o on measurement systems (Kaman sensors, laser sensors, acquisition system, frequent calibration, alignment).

Vibration amplitude under cooling boxeseffect of box 1 & 2 - SD

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

0 10 20 30 40 50

pressure box 1 & 2 (mbars)

LASERET rive cabin 08LASERET centre 08

LASERET halle 08LASERET cabin 10LASER ET cent 10

KAM ANET hall 10

Vibration amplitude under cooling boxeseffect of box 1 & 2- Peak-Peak

0,5

5,5

10,5

15,5

20,5

25,5

30,5

35,5

40,5

45,5

0 10 20 30 40 50

pressure box 1 & 2 (mbars)

LASERM ax PP 08

LASERmax PP 10

81

The trials conditions are reproducible, the measurement procedure is robust.

However, the comparison of the initial trials campaign before modification and the trials campaign after modification of the blowing technology shows disappointing results compared to the expectations from the experimental characterization campaign:

o The effect of the blowing box 1 is negative for high blowing pressures at the wiping zone as well as at the top of the cooling tower, whatever the pressure is. A light improvement is observed at the strip centre.

o The effect of blowing box 2 is more positive. The modifications of the blowing design seem to have a positive effect on the strip stabilization, especially for the strip centre. The edges effect is still observed: the strip edges are very sensitive to vibrations even if we were careful to select the same steel grade and strip format for both trials campaigns.

o The effect of combined blowing boxes 1 & 2 generates high vibrations amplitudes at the strip edges.

To explain the vibrations amplitudes at the strip edges, we can highlighted the hypothesis that the strips selected for the trials are impacted by an edges effect, what means that the strip edges are “elongated” compared to the strip centre. This unsymmetrical strip profiles is negative for the strip stabilization along the whole cooling tower due to the non-optimisation of the strip tension across its width.

More generally and even the strip edges effect, the vibrations amplitudes at the wiping zone as well at the top of the cooling tower are higher than the minimal expected benefits of the proposed innovative technology (§ 3.3.2.5.7 “influence of staggered arrangement). Indeed the nozzles staggering should have reduced the vibrations amplitudes (peak-to-peak) at the top of the cooling tower by a factor 4. This is not the case.

From the industrial point of view, if the vibrations amplitudes have not been significantly reduced (expected factor 4), the averaged vibrations amplitudes are quasi identical as the initial state (trials campaign of 2008, 2009 and 2010 before modifications). The modifications of the cooling technologies do damage neither the productivity nor the product quality.

However, we all together listed hypothesis to verify in order to explain the discrepancies between the experimental results conducted on the semi-experimental device and the industrial configurations (see the following task 3.6).

2.3.3.8. Task 3.6: Optimisation of the industrial cooling device

Objective:

o Optimisation of the improved cooling device in terms of blowing parameters to minimize or even cancel strip vibrations in standard industrial conditions.

82

Results:

Based on the results presented in the previous paragraph, all the contractors worked on establishing a list of hypothesis to be verified, in order to explain the discrepancies between expectations and real benefits and to be able to propose improvements.

2 work axes have been commonly defined:

- Axis 1: to verify the trials conditions and the modifications done

- Axis 2: to understand the discrepancies between experimental approach and industrial conditions.

Within the work axis 1, we defined 11 hypotheses that we verified. The following table (Figure 91) sums up the hypothesis and the checks that we carried out. When more investigations are needed the action plan is also mentioned.

Figure 91: list of hypotheses to be checked to explain the discrepancy between expected gains and real measurements

83

After verifying each hypothesis, we selected the three following probable hypotheses to be investigated more in details:

o Hypothesis N°1:

o the staggering pitch of a 1/2 step is not respected on industrial conditions (160 mm instead of 200 mm requested)

o Hypothesis N°3:

o the confinement due the galvannealed tower configuration influences the fluid flows in the strip neighbourhood and generates vibrations. In that case, the confinement would be an order 1 influencing parameter before the nozzles staggering.

o Hypothesis N°5:

o the orientation of the previous PAD nozzles influences the impinging flows on the strip surface and generates vibrations

To better understand why the modifications on the cooling equipment did not conduct to the reduction by a factor 4 of the strip vibrations amplitudes, we decided to conduct further trials on the experimental pilot facility.

o 1st additional trial campaign: Influence of the PAD nozzles orientation

Trials conditions:

As the previous trials campaign on the scaled guiding pilot, trials conditions are:

o Strip: 0.25 mm x 950 mm

o Distance between strip and nozzles: from 25 to 100 mm

o Blowing width is 1400 mm.

o Specific tension: 1.8 kg/mm²

o Line velocity: 0 m/min

o Blowing pressure: from 0 to 100 mbar

o Measurement: 3 laser across the strip width

o Acquisition time: 3 min

84

Tested configurations:

Figure 92: Four different configurations have been tested to determine the effect of the PAD Nozzles orientation:

a) initial design with oriented PAD nozzles but without PAD sheets; b) straight nozzles; c) the initial design” a)” is staggered; d) the design “b) straight nozzles” is staggered

The comparison between the configurations C) “staggered initial design with oriented PAD nozzles” and D) “classical straight nozzles” (Figure 92) will answer to the question: Do the oriented PAD nozzles influence the vibrations amplitudes?

The configuration A) is equivalent to the Sagunto design after removing all PAD sheets and configuration C) is equivalent to the Sagunto design after modification. The comparison between A) and C) will answer to the question: do the staggered oriented PAD nozzles increase the vibrations amplitudes ?

Results:

Figure 93: Example of averaged peak-to-peak measurements (for the 3 laser) for a strip-to-nozzle distance = 67 mm (= 100 mm for industrial conditions) and for 2 pressures: 40 and 60 mbar.

Configuration A

Configuration B

Configuration C

Configuration D

P = 40 mbar

50 mm 85 mm 30 mm 25 mm

P = 60 mbar

75 mm Out of measurement

range � amplitudes too

high

38 mm 35 mm

A CC DDBB

85

Figure 94: Example of the detailed curves of the averaged peak-to-peak measurements (for the 3 laser) and for 3 different strip-to-nozzle distances =25, 67, 100 mm on configurations C) = “staggered standard design without

PAD sheet” and D) = “staggered straight nozzles”

Based on the Figure 94, it is easy to conclude that the order 1 stabilizing parameter is the nozzles staggering, whatever the PAD nozzles are oriented or not. The comparison between C) and D) shows quasi no effect of the oriented nozzles at high pressure (60mbar). The comparison between A) and C) shows the staggering effect of the oriented nozzles: ~factor 2 on the peak-to-peak measurements at high pressure (60 mbar).

Intermediate conclusion:

On experimental conditions, the PAD nozzles orientation increases the strip stabilisation as well as the straight nozzles staggering. This hypothesis cannot be kept to explain the phenomena observed at Sagunto line.

o 2nd additional trials campaign: Influence of the confinement of the cooling technology due to galvannealed configuration

Trials conditions:

As the previous trials campaign on the scaled guiding pilot, trials conditions are:

o Strip: 0.25 mm x 950 mm

o Distance between strip and nozzles: 67 mm

o Blowing width is 1400 mm.

o Specific tension: 1.8 kg/mm2

o Line velocity: 0 m/min

86

o Blowing pressure: from 0 to 100 mbar

o Measurement: 3 laser across the strip width

o Acquisition time: 3 min

Tested configurations:

The following figure (Figure 95) describes the tested confined configuration. As much as possible, the confinement has been done to reproduce the closed galvannealed cooling tower.

Figure 95: Diagram of the tested confined configuration on the experimental facility. On the left, the diagram is from the top view; on the right from the side view.

Results:

Figure 96: Standard deviation of the strip displacement for configurations with and without confinement. Curves on the left show the standard deviation for the strip centre whereas the curves on the right show the standard

deviation for the strip edges.

On the Figure 96, the yellow, red and pink curves represent the trials carried out with the PAD sheets, whereas the blue and green curves represent trials without the PAD sheets. To quantify the effect of

Lateral air exhaust hole (open or closed)

Plenum (SIDE VIEW)

strip

Plenum (TOP VIEW)

Total confinement of the blowing boxes

Total confinement of the blowing

Lateral air exhaust hole (open or closed)

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80 90blowing pressure (mbars)

strip

dis

plac

emen

t sta

ndar

d de

viat

ion

(mm

strip (center) standard deviation (mm) - no confinement + PAD sheetstrip (center) standard deviation (mm) - no confinement + no PAD sheetstrip (center) standard deviation (mm) - conf inement + PAD sheetstrip (center) standard deviation (mm) - conf inement + no PAD sheetstrip (center) standard deviation (mm)- confinement total + PAD sheetstrip (center) standard deviation (mm) - conf inement total + no PAD sheet

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80 90blowing pressure (mbars)

strip

dis

plac

emen

t sta

ndar

d de

viat

ion

(mm

)

strip (cabin edge) standard deviation (mm) - no confinement + PAD sheet

strip (cabin edge) standard deviation (mm) - no confinement + no PAD sheet

strip (cabin edge) standard deviation (mm) - confinement + PAD sheet

strip (cabin edge) standard deviation (mm) - confinement + no PAD sheet

strip (cabin edge) standard deviation (mm)- conf inement total + PAD sheet

strip (cabin edge) standard deviation (mm) - confinement total + no PAD sheet

87

the confinement, we have to compare on both diagrams the yellow curve with the red one and the green curve with the blue one.

It is clear to see that the confinement has no effect on the strip stabilization.

Intermediate conclusion: the confinement has no effect on the strip stabilization

o 3rd additional trials campaign: Influence of the unsymmetrical nozzles staggering

Trials conditions:

On the contrary to the previous trials campaign on the scaled guiding pilot, trials conditions are:

o Shorter steel sheet ( ~2 m) instead of a strip (9 m)

o 0.25 mm x 950 mm

o Distance between strip and nozzles: from 50 mm to 100 mm

o Blowing width is 1400 mm.

o Specific tension: 40 kg/mm2

o Line velocity: 0 m/min

o Blowing pressure: from 0 to 70 mbar

o Measurement: 3 laser across the strip width

o Acquisition time: 3 min

Tested configurations:

Figure 97: 3 different tested configurations to evaluate the effect of the unsymmetrical nozzles staggering:

A) configuration of 2 x 2 facing straight nozzles

B) configuration of 2 x 2 staggered nozzles with a ½ pitch (= symmetrical nozzles staggering)

C) configuration of 2 x 2 staggered nozzles with a pitch < ½ pitch (= unsymmetrical nozzles staggering)

½ pitch< ½pitch

A CB

88

The configuration A) (Figure 97) corresponds to the initial configuration of Sagunto; the configuration B) corresponds to the recommended nozzles staggering, whereas the configuration C) corresponds to the implemented configuration at Sagunto cooling boxes. The comparison between the 3 trials should answer to the question: does the unsymmetrical nozzles staggering influence the strip stability?

Results:

The trials have been conducted within an internal ArcelorMittal research program, so that the trials have been done out of the contractual technical program (> July 2010).

Figure 98: Standard deviation of the strip position measured for the 3 configurations A) – B) –C). Average of the 5 laser signals measuring the strip position across the width. The blowing pressure is increasing from 20 to 70 mbar. 3 strip-to-nozzles distances have been tested: 50, 75 and 100 mm.

Moyenne Ecart-type - 2 buses quinconce // Dbb = 50-75-100 mm

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

0,50

0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00

[mbar]

[mm

] 50,00

75,00

100,00

B

Moyenne Ecart-type - 2 buses en vis-à-vis // Dbb = 50-75-100 mm

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

0,50

0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00

[mbar]

[mm

]

50,00

75,00

100,00

A

Moyenne Ecart-type - 2 buses en semi-quinconce // Dbb = 50-75-100 mm

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

0,50

0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00

[mbar]

[mm

]

50,00

75,00

100,00

C

89

Figure 99: Peak-to-peak measurements of the strip position measured for the 3 configurations A) – B) –C). Average of the 5 laser signals measuring the strip position across the width. The blowing pressure is increasing from 20 to 70 mbar. 3 strip-to-nozzles distances have been tested: 50, 75 and 100 mm.

The graphs 98 and 99 show respectively the standard deviation and the peak-to-peak amplitudes of the strip vibrations for the 3 configurations mentioned here above. The blowing pressure has been made varied from 20 to 70 mbar, whereas the strip –to nozzles distance has been made varied from 50 mm to 100 mm. The trials conditions are similar for the 3 tested geometrical blowing configurations.

The comparison of the 3 graphs does not show a clear effect of the unsymmetrical nozzles staggering on the strip vibrations.

Intermediate conclusion:

The unsymmetrical nozzle staggering has no clear effect on the strip vibration.

Moyenne Pic à Pic - 2 buses en vis-à-vis // Dbb = 50-75-100 mm

0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,00

8,00

9,00

10,00

0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00

[mbar]

[mm

]

50,00

75,00

100,00

A

Moyenne Pic à Pic - 2 buses quinconce / Dbb = 50-75-100 mm

0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,00

8,00

9,00

10,00

0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00

[mbar]

[mm

]

50,00

75,00

100,00

B

Moyenne Pic à Pic - 2 buses en semi-quinconce // Dbb = 50-75-100 mm

0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,00

8,00

9,00

10,00

0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00

[mbar]

[mm

] 50,00

75,00

100,00

C

90

2.3.3.9. Task 3.7: Synthesis

Objectives:

o Elaboration of the operating industrial procedures

o Quantification of the innovative cooling device performances in industrial conditions

o Elaboration of the recommendations to transpose the innovative cooling device to others typical cooling devices used at industrial galvanizing lines

o Global synthesis of the project

If the experimental approach conducted on a 2/3 scaled pilot facility allow us to design an improved cooling device reducing the strips vibrations by a factor 4, its adaptation on the industrial conditions of the Sagunto line appears disappointing.

Results:

o Operating industrial procedures

During the yearly line stop of the Sagunto line, the blowing boxes at the top of the cooling tower have been entirely removed after the galvannealed casing has been opened. This delicate procedure includes:

o the guiding removal to have an access to the blowing boxes

o the complete removal of the PAD sheets (unsoldering operations in extreme confined conditions)

o the complete removal of the plenums front sides composed with the nozzles

o the removal of the plenum to be staggered

o the removal of the ducts and pipes feeding the plenums

After the cleaning operations, the assembly operations can start, including following tasks:

o the assembly of the staggered plenums and nozzles taking into account the mechanical constraints due to existing platform and fans motors

o the assembly of the ducts and pipes

o the adaptation to warranty the plenums tightness

o the assembly of the guiding rolls

o the verification of the strip pass line

o the assembly of the casing

o the mechanical tests to ensure the structure holding

Re-start tests have been conducted with an incremental approach: from low blowing pressure to maximal, whereas the measurement systems have been implemented at the wiping zone and on the top of the tower.

91

o Quantification of the innovative cooling device performances in industrial conditions

Based on the trials campaigns conducted after the implementation, the innovative cooling technology does not show significant improvement in terms of strip stabilisation. Even if the strip centre seems to be more stable after the modification, the “long edges effect” remains on both strip edges, so that the global impression is neither optimistic nor pessimistic. The product qualities as well as the productivity have not been impacted by the implementation. No clear impact on the Zinc coating homogeneity at the wiping zone has been observed; so that the expected gains in terms of zinc saving could not be observed.

o Recommendations to transpose the innovative cooling device to others typical cooling devices used at industrial galvanizing lines

Even if the implementation at Sagunto line is in discrepancy with the expected gains, the transposition to others industrial galvanizing lines started.

2.3.3.10. Global synthesis: Transferability to others concerned lines

The results obtained in this study for the control of strip vibrations are progressively used in the new Drever International galvanizing and annealing lines. Taking into account the time required between the new cooling design and the industrial start of each line, 5 new lines have been started in China equipped with the new cooling design:

o 2 galvanizing lines and 1 annealing line in ShunYi (Beijing) for Shougang company

o 1 galvanizing line and 1 annealing line in Wuhan, for Wisco company (Cold Rolling Mill 3)

On a paralleled way, R&D studies are also performed by Drever International on detailed design improvements of multi-jets cooling equipments. These activities ensure Drever to develop optimised technology, the Ultra Fast Cooling (UFC) System, combining high cooling performances and control of strip vibrations.

To illustrate the performances of these new lines, the results obtained in the cooling zones in the tower of galvanizing lines and in the rapid cooling section of galvanizing and annealing lines are presented.

2.3.3.10.1. Transfer to cooling tower of other galvanizing lines

The Figure 100 shows one of the two Shougang ShunYi galvanizing lines.

The Shougang ShunYi CGL N°1 is equipped with a vertical annealing furnace, galvannealing soaking furnace, after pot cooling, final cooling and water tank. This line is designed to process cold rolled strips for the production of galvanized sheet for the automotive industry (steel qualities from CQ to DP-HSS 780 and TRIP-HSS 780, both GA and GI). The strip width range is 800 – 1870 mm and the thickness range is 0.4 – 2.5 mm. The maximum line speed is 180 m/min. The annual production is 475,000 tons.

In the after-pot cooling section, staggered nozzles (straight nozzles and PAD nozzles without PAD sheet) are used, as presented for the pilot line and as used in the modified Sagunto line. In the Shougang CGL, there are no rolls to stabilize the strip and no casing surrounding the plenums. So, the recommendations of the project are transferred to this industrial configuration.

92

Figure 100: Sketch of the Shougang ShuYi CGL N°1

No laser measurement could be performed in the Shougang after-pot cooling zone because of confidentiality reason.

The exploitation of the continuous coating thickness measurement could not be possible to quantify the effect of strip stabilization in terms of coating uniformity across the strip width as well along the strip length (waviness). As the Figure 101 shows it, we were able to collect only punctual pictures of the coating weight cartography across the strip width, what is not enough to conduct statistics.

Figure 101: Zinc coating weight repartition across the strip width at Wisco CGL

93

However, the visual control of strip vibrations is very good as the Final Acceptance Tests (FAT) have been successfully passed for this line.

The Ultra Fast Cooling system that equipped the Shougang CAL line is similar to the one installed into the Shougang CGL. The main lines and products characteristics are presented into the Figure 99.

The Final Acceptance Tests report of the Shougang CAL mentioned clearly that the cooling equipment is able to achieve high cooling rates at high blowing velocity by:

o Very low strip to nozzles distance (74 mm, 55 mm, 46 mm)

o Opened guiding rolls and high line speed (~ 200 m/min)

o By 20% H2 and high pressure (10kPa)

o Without vibrations.

Indeed the vibrations are recorded by a video camera located between 2 cooling boxes of the rapid cooling section (see Figure 100). In addition, the inspector (automatic marks detector) located at the exit of the line systematically did not detect any defects at the strip surface generated by potential strip to nozzles contacts due to high vibrations amplitudes. Those trials have been carried out on about 40 coils.

The tests of vibrations show that the strip processed through the furnace without touching the blowing nozzles by a maximal pressure of 11 kPa (= maximal pressure delivered by the blowing fan). No marks have been detected, what proves the efficiency of the innovative cooling technology in terms of strip stabilization in hard process conditions (confinement, high temperature range, low strip to nozzles distance, etc.).

Same good results in terms of control of vibrations are obtained for the Wisco galvanizing line with the same design.

2.3.3.10.2. Transfer to rapid cooling sections of other galvanizing lines and continuous annealing lines

As mentioned previously, the Shougang continuous annealing line N°1 (CAL N°1) and the Shougang galvanizing line N°1 (CGL N°1) are equipped with the new Ultra Fast Cooling Technology. It is also the case for the new Wisco continuous annealing line.

The Shougang CAL N°1 and CGL N°1 rapid cooling sections contain three zones, the two last zones having a shorter length than the first one. To get the highest cooling performances, only the two short-length zones are used. Figure 102 gives the characteristics of the production, the hydrogen content in the rapid cooling section, the cooling length and the strip cooling temperature range. The cooling rate is expressed in °C/s for a strip thickness of 1 mm. The table presents the excellent cooling performances of the Ultra Fast Cooling System: 101.6 °C/s.mm for the CAL N°1 and 112.4 °C/s.mm for the CGL N°1.

94

Figure 102: Ultra Fast Cooling performances for Shougang ShunYi CAL N°1 and CGL N°1

In order to get these excellent cooling rates, the Ultra Fast Cooling technology developed by Drever and based on the nozzles staggering by a half pitch uses the following features:

o high hydrogen content in the cooling zone,

o high plenum pressure (up to 10 kPa), i.e. high gas speed,

o short plenum-strip distance, e.g. 30-40 mm

This means that a very good control of strip vibrations is required for this technology using high gas speed and short plenum-strip distance. Straight nozzles in staggered configuration are used in the Ultra Fast Cooling system. No scratch on the strips is observed during our tests and by Shougang in these lines, demonstrating the very good performances of the design in terms of strip vibrations control.

Figure 103: Zoom of the Ultra Fast Cooling in Shougang CAL (from video camera records)

Same good results in terms of control of vibrations for the Ultra Fast Cooling technology are obtained for the Wisco galvanizing line and continuous annealing line with the same design.

Line CAL N°1 CGL N°1

Strip Thickness mm 1.8 1.48Strip width mm 1260 1253Steel grade DP 590 CQLine speed m/min 90 95Production T/h 96 83LSD mm*m/min 162.0 140.6RCS Hydrogen content % 22.0 20.0Cooling length m 10.6 5.35Entry Temperature °C 700 714Exit Temperature °C 301 457

Cooling rate for 1 mm thick °C/s 101.6 112.4

95

3. CONCLUSION

3.1. SCIENTIFIC AND TECHNICAL APPROACH

The project has been divided in 3 approaches: industrial approach, scientific and theoretical approach and experimental approach.

3.1.1. Industrial approach

Because we changed one contractor, we finally conducted strip vibrations characterization on two different industrial lines: Ghent #3 (WP1) and Sagunto (WP3) HDG lines. Both have been equipped with experimental measurements to analyse on long periods the strip vibrations in the cooling zone to connect the strip behaviour with some process parameters.

The identification and characterization of the major influent line and blow parameters have been done during the trials campaign at Ghent and confirmed during the trials campaign at Sagunto:

Order 1 effect of the blowing pressure and blowing velocity

• Effect of the pressure balance in the opposite blowing boxes

• Order 1 effect of the strip tension

• No effect of the line speed (if the blowing power regulation loop is de-correlated to the line speed)

The good understanding and dynamism between all the parties allow to collect the required data to design the experimental 2/3 scale cooling device able to reproduce the strip vibrations characterized on industrial conditions. The trial campaigns conducted on both lines were also the opportunity to collect database to validate and to fit the theoretical vibrations model.

To answer to the question: “How do the vibrations appear and how they can be minimized?”, two complementary approaches were proposed. The first one consists in using the experimental 2/3 scale cooling device to define a new cooling geometry reducing strip vibrations and the second approach consists in testing the new solutions with a theoretical model.

3.1.2. Experimental approach

The 2/3 scaled experimental pilot has been designed and optimised to reproduce the strip vibrations phenomena observed on the industrial line, especially the vibrations modes and frequencies, and the vibrations amplitudes could have been reproduced. We developed a reliable experimental tool to investigate in controlled conditions (strip tension for example):

o the influence of the blowing parameters:

� Blowing distance

� Blowing width;

97

� Nozzle assembly geometry

� Plenum geometry

� PAD sheet

o The influence of the process parameters:

� Line velocity

� Strip tension

o The influence of the product properties:

� Thickness and width

� Grade

In addition, dedicated measurements have been developed and used to characterize the effect of the blowing and geometrical parameters. As an example, the “hot wire” technique has been used to characterize with high reliability the jets velocity at the exit of the nozzles.

Starting from the database of the measurements of strip vibrations done in the exhaustive trials on pilot facility and thanks to expert knowledge, we propose a theoretical model able to predictive the strip instabilities.

Further trial campaigns on the experimental pilot allowed to validate and to fit the model.

3.1.3. Scientific and theoretical approach

In order to understand and predict the physical mechanisms of strip vibrations, a parallel theoretical approach is necessary. The questions to answer are: What are the physical mechanisms which control the vibratory behaviour in a gas jets cooling system? What type of interactions exists between fluid and structure?

To predict the strip instabilities, the theoretical model of strip vibrations has been developed in collaboration with a subcontractor of ArcelorMittal Research. The objective of this collaboration is to determine some major characteristics of the flow instability, like the Reynolds Number Re. Observations have been done on laboratory with a rigid plan mounted in such a way that it allows rotational and translational motions, with one or two air jets normal to the plan. It was possible to identify the configurations leading to instability.

Specific measures have been conducted to characterize the vibration eigenmodes (stiffness, frequency, damping). The strip vibration mechanisms under the gas jets cooling system have also been identified:

o Vibrations due to recirculation loops between jets

o Vibrations due to turbulent flows

o Vibrations due to aeroelastic forces coupling inducing dynamical instability

More specifically a physical model has been developed to predict the vibrations due to aeroeleastic forces because it is the most damaging instability mechanism (contact strip-nozzle).

o The influence of the geometry parameters:

98

The trials campaign conducted on the experimental pilot facility under controlled conditions allowed validating the stability / instability predictive model.

The combination of these two complementary approaches allowed defining the new cooling technology implemented on the production lines.

3.1.4. Innovative content

The innovative part of the project consists in improving the existing cooling device to achieve higher line speeds and higher competitiveness.

1. A first project innovation consists in a detailed analysis of the strip vibrations induced by industrial gas jets cooling equipments. The project provides an exhaustive characterization of the vibration amplitudes and frequencies due to the cooling boxes. The influence of the strip format and the major process parameters has been clearly identified. This task allows working later at the experimental device in very close conditions to industrial lines (strip size, line speed, strip tension, blowing pressure, etc.) including:

o The mastering of all process parameters,

o The possibility to test easily design modifications of the cooling equipment

o The measurement facilities (strip displacements at different points, gas flow analysis).

The transfer of phenomena characterized in industrial conditions to an experimental facility is an innovation by itself.

2. This project is innovative for a second reason: this is the first time that an asymmetrical slots cooling device is implemented on an ArcelorMittal line (Sagunto). The innovation is actually an improvement of the existing equipment and consists in breaking the symmetrical structure of the cooling device, which improves the distribution of the jets gas. It suppresses the coupling effect of opposite gas jets and reduces the vibrations phenomena.

The principles of nozzles staggering, PAD sheets removal, closer strip-to-nozzles distance, have been deployed and reinforced by the partner Drever through a new cooling equipment called “Ultra Fast Cooling”. This equipment is dedicated to the rapid cooling sections of HDG and CAL lines working under protective atmosphere (Cooling Rate of 118°C/s for a strip thickness of 1 mm). The Ultra Fast Cooling has been implemented on many new industrial lines around the world (Shougang, Wisco) reducing the vibrations and consequently improving the productivity and the coating high-quality. According to the Final Acceptance Tests report, the customers are very satisfied. In this sense, the proposed technology is a successful innovation.

3. At least, the major project innovation consists in understanding, identifying and modelling the mechanisms of strip vibration phenomena generated by the gas jets of the industrial cooling equipments. The previous work of transferability and reproducibility of the online observed vibrations to the semi-industrial experimental device makes those investigations possible.

For the first time it appears clearly that the strip instability phenomena can be classified in 3 families depending on the forces exerted on the structure:

o quasi periodical forces due to recirculation loops between jets

o turbulent flows forces

99

o forces due to aeroelastic coupling producing the strongest damages on the coating quality.

With the help of an expert team (sub-contractor), we built a physical model able to predict the strip stability / instability depending on the process conditions (gas pressure, nozzle design and nozzle configurations, strip-to-nozzles distance…). We validated the theoretical approach on the semi-industrial pilot facility. The results show very encouraging results: vibrations mode can be predicted, as well as vibration amplitudes. The approach of coupling phenomena between the gas pressure and the structure behaviour is a new approach on HDG lines. A physical model able to take into account the impact of the gas pressure field on the steel surface and the impact of strip reactions on the gas flows, on a weak way is an innovation.

The model has been reinforced by various industrial configurations (Ghent and Sagunto) and this is the first time that this theoretical approach is used for galvanizing lines. Publications have been written and presented during conferences to communicate these achievements [1-4, 25-26].

3.1.5. Industrial interest and scientific / technical prospects

Two complementary approaches have been proposed. The first one consisted in using the experimental 2/3 scale cooling device to define a new cooling geometry reducing strip vibrations and the second approach consists in understanding the strip vibrations mechanism and building a theoretical model able to predict the strip vibrations in specific cooling configurations.

The fluid-structure interactions in such equipment was never been studied before this project.

Each of these steps aimed answering the fundamental question: how to reduce the strip vibrations in gas jets cooling equipments and consequently to increase line productivity and coating quality. That means to be able to answer to these basic questions, which are frequently asked on that problem and have no answer today:

o For existing cooling technology in hot dip galvanizing lines, what is the importance of the process and geometrical parameters on the vibratory behaviour of the strip? Is it possible to reduce the vibrations by actions on these parameters while preserving the cooling performances?

o With identical cooling performances, is there a blowing design, which makes it possible to strongly reduce the strip vibrations?

We answered to those questions with success.

3.1.6. Consistency of resources and quality of partnership

The project nature (pilot project) by itself leads to coordinate various competencies (technical and scientific experts) and approaches (industrial and experimental). Due to a closed partnership between the ArcelorMittal Ghent and Sagunto lines people, ArcelorMittal R & D team and Drever International, we succeed to conduct an exhaustive characterization of the strip vibration phenomena observed in the cooling sections and during production conditions (WP1). The WP2 was much more focused on the coordination between researchers (ArcelorMittal Maizières), university competencies (subcontractor), supplier knowledge (Drever International) and industrial background (ArcelorMittal Ghent). The WP3 consisted in coordinating the competencies of the line managers, the industrial people in charge of mechanical and electrical maintenance, the technology suppliers, and the ArcelorMittal researchers in charge of the measurements campaign. Because of the tasks diversity and because of the coordination of various competencies, the partnerships quality is very high. More especially, the industrial implementation of the new cooling technology has been done with success and on due time in spite of one contractor withdrawal and replacement, and in spite of the economical crisis occurred at the end of 2008, which leads to human resources restriction of the ArcelorMittal group.

100

3.1.7. Community added value and contribution to EU policies

The impact regarding preservation of natural resources, energy and environment had been reinforced considering the consequences of better controlled zinc coating on surface appearances of galvanized strips and on the painting / organic layers consumption of automotive suppliers. Even if we were not able to quantify those benefits on the Sagunto pilot line, the results obtained on the Chinese lines where the recommendations have been implemented shows that the strip vibrations could be mastered in cooling sections, especially in the cooling tower, reducing the zinc consumption thanks a better mastering of the zinc coating homogeneity across the strip width as well as along the strip length. Those results could be easily reproduced on EU lines, on HDG lines as well on CAL lines.

3.1.8. Exploitation and impact of the research results

The first impact of the research results is the worldwide deployment of the recommendations coming from the WP2. Indeed the principle of staggering nozzles to reduce vibrations amplitudes, the removal of the PAD sheet, the optimisation of the nozzle-to-nozzle distances have been introduced within the innovative Ultra Fast Cooling developed in the Drever R&D department and commercialised by Drever International.

The second impact of the research results consists in the development of modelling tools able to predict the strip vibration amplitudes and modes for varied experimental and industrial configurations. Based on the theoretical approach of fluid-structure interaction done within the WP2 tasks, further numerical tools coupling computations of structural deformation and fluid mechanism have been developed at ArcelorMittal Maizières Research. Developments are still going on to make the strip vibrations prediction more robust, especially for industrial configuration taking into account the process parameter fluctuations.

101

4. List of Figures

Figure 1: comparison between initially planned activities and accomplished work ............................................ 22 Figure 2: Configuration of the vibrations measurement system in the cooling tower .......................................... 23 Figure 3: Positioning of three Kaman sensors across the strip (top view) ........................................................... 24 Figure 4: Three Kaman sensors across the strip .................................................................................................. 24 Figure 5: Strip vibrations across the strip width at the wiping zone according to the line speed increase.......... 25 Figure 6: Width-wise strip vibrations between the cooling boxes according to the line speed increase.............. 26 Figure 7: Width-wise strip vibrations at the wiping zone according to the strip traction .................................... 27 Figure 8: Width-wise strip vibrations between the cooling boxes according to the strip traction ....................... 27 Figure 9: Width-wise strip vibrations at the wiping zone and between the cooling boxes according to the strip traction and for 2 different line speeds: V=115 m/min and V= 140 m/min .......................................................... 28 Figure 10: Width-wise strip vibrations at the wiping zone and between the cooling boxes according to the strip traction and for different strip formats (Line speed = constant)........................................................................... 29 Figure 11: Width-wise strip vibrations at the wiping zone and between the cooling boxes according to blowing power of cooling box 2 (box 1 fixed)..................................................................................................................... 30 Figure 12: Width-wise strip vibrations at the wiping zone and between the cooling boxes according to blowing power of cooling box 2 (box 1 fixed) for line speed fixed. .................................................................................... 30 Figure 13: Drever after pot cooling design at ArcelorMittal Ghent 3.................................................................. 33 Figure 14: ArcelorMittal Ghent #3....................................................................................................................... 33 Figure 15: ArcelorMittal Ghent 3......................................................................................................................... 34 Figure 16: Schematic overview of the experimental cooling device ..................................................................... 34 Figure 17: Upper view of the equipped pilot line, with strip and guide-rolls....................................................... 34 Figure 18: Drawing of the equipped pilot line, with strip line pass (red line) and guide-rolls ............................ 35 Figure 19: Different configurations of blowing plenum’s front side tested on pilot line. 1- 2 x 8 nozzles opposite to each others; 2- Variation of nozzles length; 3- Air PAD system....................................................................... 36 Figure 20: Control cabin of experimental pilot line ............................................................................................. 37 Figure 21: Strip positioning measurement system ................................................................................................ 37 Figure 22: Hot wire measurement system............................................................................................................. 37 Figure 23: initial configuration: plenum nozzles configuration 4 straight nozzles + 1 PAD (aerodynamic stabilizer) per side................................................................................................................................................. 39 Figure 24: strip displacement as function of blowing pressure ............................................................................ 39 Figure 25: peak to peak values as a function of blowing pressure ....................................................................... 39 Figure 26: evolution of the strip position with time at P=19 mbars => irregular strip vibrations...................... 40 Figure 27: Evolution of the strip position with time at P=39 mbar => regular strip vibrations ......................... 40 Figure 28: power density vibratory spectrum P=19 mbar ................................................................................... 40 Figure 29: power density vibratory spectrum P=39 mbar ................................................................................... 40 Figure 30: evolution of the strip position with time in a twist situation ............................................................... 41 Figure 31: RMS and peak-to-peak strip vibrations amplitudes as a function of the blowing pressure for tests performed at 4 different time periods.................................................................................................................... 42 Figure 32: RMS values as a function of time at 4 different time periods. Identification of 3 major strip behaviours: ........................................................................................................................................................... 43 Figure 33: schematic view of the 3 major observed strip behaviours: ................................................................. 44 Figure 34: Schema of interaction between gas jets fluid and the strip structure.................................................. 44 Figure 35: Illustration of vortex mechanism......................................................................................................... 45 Figure 36: Schema of strip vibrations amplitudes function of strip-nozzle distance ............................................ 45 Figure 37: Strip damping function versus an adimentional strip-nozzle distance H ............................................ 46 Figure 38: strip displacement (RMS) function of strip speed ............................................................................... 48 Figure 39: peak-to-peak as a function of strip speed............................................................................................ 48 Figure 40: strip displacement (RMS) function of blowing pressure ..................................................................... 48 Figure 41: peak-to-peak values function of blowing pressure .............................................................................. 48 Figure 42: power density vibratory spectrum – T=0.96 kg/mm2 – P=19.4 mbar and P=29.3 mbar................... 49 Figure 43: power density vibratory spectrum – T=1.73 kg/mm2 – P=29.3 mbar and P=39.2 mbar................... 49 Figure 44: power density vibratory spectrum – T=2.77 kg/mm2 – P=39.2 mbar and P=49.7 mbar................... 50 Figure 45: Effect of difference between strip tension edges on strip vibration amplitude................................... 50 Figure 46: Connecting tubes between the two opposite blowing boxes................................................................ 51 Figure 47: Influence of the connecting tubes between the opposite blowing boxes.............................................. 51 Figure 48: Effect of blowing width on vibrations amplitudes ............................................................................... 52 Figure 49: Effect of blowing width on peak- to-peak values................................................................................. 52

103

Figure 50: Effect of a delta pressure of 5 % between the 2 plenums for a configuration of 2 x 6 nozzles with and without PAD sheets ............................................................................................................................................... 53 Figure 51: Tested configuration equipped with shorter nozzles length (55 mm).................................................. 53 Figure 52: Influence of shorter nozzles length (55mm) on vibrations instability ................................................. 53 Figure 53: 3 different tested configurations: a) straight nozzles b) staggered straight nozzles c) classical nozzles arrangement with PAD sheet ................................................................................................................................ 54 Figure 54: Standard deviation and peak-to-peak measurements for the 4 different tested configurations .......... 55 Figure 55: Configuration on experimental pilot device with staggered straight nozzles and symmetrical PAD . 56 Figure 56: Peak-to-peak value function of blowing pressure for 7 tested configurations .................................... 56 Figure 57: Staggered standard design with staggered PAD................................................................................. 57 Figure 58: Peak-to-peak measurements for 4 different configurations: ............................................................... 57 Figure 59: Schematic configuration for the investigation on the effect of the strip-PAD distance on vibrations amplitudes ............................................................................................................................................................. 58 Figure 60: Effect of the strip-PAD distance for 3 different strip to blowing nozzles distances ............................ 58 Figure 61: Flow velocity profiles from the nozzle to the strip at the nozzle centre and for different blowing pressures. Legend : X is the distance between the nozzle and the strip; e is the nozzle opening section, Umax is the flow velocity just at the exit of the nozzle, Umoy is the measured velocity at a distance X from the nozzle wall : Umoy = U(X,0) ........................................................................................................................................... 59 Figure 62: Flow velocity profiles from the nozzle to the strip at the nozzle edges and for different blowing pressures. Legend : X is the distance between the nozzle and the strip; e is the nozzle opening section, Umax is the flow velocity jus tat the exit of the nozzle, Umoy is the measured velocity at a distance X from the nozzle wall : Umoy = U(X,0) ........................................................................................................................................... 60 Figure 63: The spectral density analysis of flow velocity signals show typical frequencies around 1-2,5 Hz ; 5-6 Hz and 18 Hz......................................................................................................................................................... 61 Figure 64: Superposition of spectral density analysis of flow velocity signal (black curve) and spectral density analysis of strip displacements(red, green and blue curves) ................................................................................ 61 Figure 65: Current blowing technology implemented at ArcelorMittal Ghent Hot Dip Galvanizing line. .......... 63 Figure 66: Proposed modifications at the blowing technology implemented at ArcelorMittal Ghent Hot Dip Galvanizing line. ................................................................................................................................................... 63 Figure 67: Configuration of the Sagunto cooling tower and position of the measurement systems ..................... 65 Figure 68 & Figure 69: Standard deviation and peak to peak distance at the wiping zone (Kaman sensors measurements) on 3 points for different box 1 blowing pressures (%) and for stable other production parameters: ........................................................................................................................................................... 66 Figure 70: Standard deviation and peak to peak distance at the top of the cooling tower (Laser sensors measurements) on 3 points for different box 1 blowing pressures (%) and for stable other production parameters: ........................................................................................................................................................... 66 Figure 71 & Figure 72: Averaged strip displacement at the wiping zone (Kaman signals) and at the top of the cooling tower (Laser sensors) for different box 1 blowing power. Reference”0” is the averaged strip position at minimal acceptable blowing power (10%)............................................................................................................ 67 Figure 73 & Figure 74: Standard deviation and peak to peak distance at the wiping zone (Kaman sensors measurements) on 3 points for different box 2 blowing pressures (%) and for stable others production parameters: ........................................................................................................................................................... 68 Figure 75 Standard deviation and peak to peak distance at the top of the cooling tower (Laser sensors measurements) on 3 points for different box 2 blowing pressures (%) and for stable others production parameters: ........................................................................................................................................................... 68 Figure 76 & Figure 77: Averaged strip displacement at the wiping zone (Kaman signals) and at the top of the cooling tower (Laser sensors) for different box 2 blowing power. Reference”0” is the averaged strip position at minimal acceptable blowing power (10%)............................................................................................................ 69 Figure 78: Standard deviation at the wiping zone (Kaman sensors measurements) on 3 points for different line velocities and for identical others production parameters: .................................................................................. 69 Figure 79: Peak to peak distance at the wiping zone (Kaman sensors measurements) on 3 points for different line velocities and for identical others production parameters: ........................................................................... 70 Figure 80: the final configuration of the cooling tower at Sagunto...................................................................... 73 Figure 81: the final configuration of the cooling tower at Sagunto...................................................................... 74 Figure 82: Picture taking during the implementation of the innovative cooling technology on the Sagunto cooling tower: nozzles staggering, PAD removal. ................................................................................................ 74 Figure 83: Screenshot of the blowing pressure balance between plenums after regulation adjustments at Sagunto.............................................................................................................................................................................. 75 Figure 84: Identical product and process parameters during the trials campaigns on Sagunto line................... 76 Figure 85: Effect of the blowing pressure on blowing box 1 (inferior) on strip vibrations at the wiping zone Sagunto line after modification (full curves). Comparison with the reference trials conducted on 2008 (dotted curves)................................................................................................................................................................... 78

104

Figure 86: Effect of the blowing pressure on blowing box 1 (inferior) on strip vibrations at the top of the cooling tower on Sagunto line after modification (full curves). Comparison with the reference trials conducted on 2008 (dotted curves). ..................................................................................................................................................... 78 Figure 87: Effect of the blowing pressure on blowing box 2 superior) on strip vibrations at the wiping zone Sagunto line after modification (full curves). Comparison with the reference trials conducted on 2008 (dotted curves)................................................................................................................................................................... 79 Figure 88: Effect of the blowing pressure on blowing box 2 (superior) on strip vibrations at top of the cooling tower at Sagunto line after modification (full curves). Comparison with the reference trials conducted on 2008 (dotted curves). ..................................................................................................................................................... 80 Figure 89: Effect of the combined blowing pressure on blowing box 1 (inferior) and box 2 (superior) on strip vibrations at the wiping zone on Sagunto line after modification (full curves). Comparison with the reference trials conducted on 2008 (dotted curves). ............................................................................................................. 80 Figure 90: Effect of the combined blowing pressure on blowing box 1 (inferior) and box 2 (superior) on strip vibrations at the top of the cooling tower on Sagunto line after modification (full curves). Comparison with the reference trials conducted on 2008 (dotted curves). ............................................................................................. 81 Figure 91: list of hypotheses to be checked to explain the discrepancy between expected gains and real measurements........................................................................................................................................................ 83 Figure 92: Four different configurations have been tested to determine the effect of the PAD Nozzles orientation:.............................................................................................................................................................................. 85 Figure 93: Example of averaged peak-to-peak measurements (for the 3 laser) for a strip-to-nozzle distance = 67 mm (= 100 mm for industrial conditions) and for 2 pressures: 40 and 60 mbar.................................................. 85 Figure 94: Example of the detailed curves of the averaged peak-to-peak measurements (for the 3 laser) and for 3 different strip-to-nozzle distances =25, 67, 100 mm on configurations C) = “staggered standard design without PAD sheet” and D) = “staggered straight nozzles”............................................................................................. 86 Figure 95: Diagram of the tested confined configuration on the experimental facility. On the left, the diagram is from the top view; on the right from the side view. ............................................................................................... 87 Figure 96: Standard deviation of the strip displacement for configurations with and without confinement. Curves on the left show the standard deviation for the strip centre whereas the curves on the right show the standard deviation for the strip edges.................................................................................................................................. 87 Figure 97: 3 different tested configurations to evaluate the effect of the unsymmetrical nozzles staggering:...... 88 Figure 98: Standard deviation of the strip position measured for the 3 configurations A) – B) –C). Average of the 5 laser signals measuring the strip position across the width. The blowing pressure is increasing from 20 to 70 mbar. 3 strip-to-nozzles distances have been tested: 50, 75 and 100 mm............................................................. 89 Figure 99: Peak-to-peak measurements of the strip position measured for the 3 configurations A) – B) –C). Average of the 5 laser signals measuring the strip position across the width. The blowing pressure is increasing from 20 to 70 mbar. 3 strip-to-nozzles distances have been tested: 50, 75 and 100 mm. ..................................... 90 Figure 100: Sketch of the Shougang ShuYi CGL N°1 ........................................................................................... 93 Figure 101: Zinc coating weight repartition across the strip width at Wisco CGL.............................................. 93 Figure 102: Ultra Fast Cooling performances for Shougang ShunYi CAL N°1 and CGL N°1 ............................ 95 Figure 103: Zoom of the Ultra Fast Cooling in Shougang CAL (from video camera records) ............................ 95

105

5. List of References

[1] M. Renard, J. Muller, D. Van de Vyver, F. Gurniki, K. Beaujard , Control of strip vibrations in gas jets cooling areas, Proceedings of Galvatech’07, 7th International Conference on Zinc and Zinc Alloy Coated Sheet Steels, Osaka (Japan), November 18-22, 2007, pp. 57-62 [2] M. Renard, K. Beaujard Control of strip vibrations in cooling equipments of galvanizing lines; 5th China International Steel Congress, Shanghai (China), June 1-4, 2008 [3] M. Renard, K. Beaujard; Control of strip vibrations in cooling equipments of galvanizing lines, Revue de Métallurgie; March 2009; pp 118-123

[4] Michel Renard, Edgar Dosogne, Jean-Pierre Crutzen, Jean-Marc Raick, Ma jia ji , Lv jun and Ma bing zhi; improvement of Cooling Technology through Atmosphere Gas Management; Asia-Pacific Galvanizing Conference 2009, Korea, November 8-12, 2009

[5] C. Mu-Tsang and A. Ashraf, Computers & Structures, Vol. 66, No. 6, (1998) p. 785

[6] ABAQUS Inc, Abaqus 6.9 Theory Manual, version 6.5, 2004

[7] V. D. Pshenichnyi and L.R. Yablonik, Spectral characteristics of the pulsation effect of a plane turbulent jet on a solid surface (1975)

[8] European Steel Technology Platform, a vision of the future of the steel sector, March 2006 (see http://www.cordis.lu/coal-steel-rtd/steel/events_stp.htm)

[9] Bilimoria Y. – Strip shape measurement and control at Inland’s Hot Dip Galvanizing line, Galvanizers Association Meeting, Niagara Falls (1990)

[10] Dubois M. – Strip vibration and temperature at the top roll, Galvanizers Association Meeting, closed session, unpublished (1990)

[11] Gaignard S., Dubois M. – Characterization of strip vibration at the wiping nozzles, Galvatech 2004, Chicago, pp. 207-216

[12] Shimokawa Y., Ishikawa H., Sakai K., Nitto H. - Vibration prevention of a strip by air cushion method, ISJ International, 1983, pp. 1167-1174

[13] Shimokawa Y., Ishikawa H., Sakai K., Nitto H. - Studies of vibration prevention by the air cushion method for the application to commercial stripe lines, ISJ International, 1983, pp. 1175-1182

107

[14] Improved quality of galvanised products by controlled wiping, ECSC Steel RTD Programme, Contract number 7210-PR/281, CRM, Aceralia, CSM

[15] Hot dip galvanizing: stabilizing and cooling the strip in the wiping area, ECSC Steel RTD Programme, Contract number 7210-PR/282, CRM, Aceralia, BFI

[16] Renard M., Gouriet J.B., Planquart P., van Beek J., Buchlin J.M. – Thermal and dynamic study of rapid cooling in continuous galvanizing lines, Galvatech 2004, Chicago, pp. 449-456

[17] George S., Scott L. – New technologies for post-pot cooling equipment, Galvatech 2001, pp.461-468

[18] Kim, H S; Lee, M S - Instability of the flow field in a gas jet cooler, RIST Journal of R&D. Vol. 18, no. 3, pp. 218-224. Sept. 2004

[19] Price, M; Barker, H A; Evans, K J - Dynamic distributed parameter model of steel strip, Ironmaking and Steelmaking (UK). Vol. 24, no. 1, pp. 99-103. 1997

[20] Lemaitre C., de Langre E. ,Hémon P. - Instability of a long ribbon hanging in axial airflow - J. of Fluids and Structures, 2004

[21] E. de Langre. Fluides et Solides. Ecole polytechnique, 2001, diffusion Ellipse

[22] M. Païdoussis Fluid-structure interaction, vol II. Elsevier, 2003

[23] Base Metals Market Briefing February 2006, http://www.gfms-metalsconsulting.com/publications_BMMB.htm

[24] 10th Zinc & its Markets Seminar in Sheraton Park Lane Hotel - London - 24-26 May 2006

[25] Michel Renard, Edgar Dosogne, Jean-Pierre Crutzen, Jean-Marc Raick, Ma jia ji , Lv jun and Ma bing zhi; High cooling performances of Cooling Technology; Galvatech’ Conference 2011, Genoa (Italy), June 21-24, 2011

[26] Makhlouf Hamide, Karen Beaujard; Predictive model of strip vibrations in gas jets cooling scetions; Galvatech’ Conference 2011, Genoa (Italy), June 21-24, 2011

[27] Jean-Marc Raick, Jean-Pierre Crutzen, Edgard Dosogne, Michel Renard; Atmosphere control during continuous heat treatment of metal strips; WO 2004024959 (A1)

[28] Jérôme Muller, Akli Elias, Thierry Petesch, Ivan Santi, Paul Durighello, Karen Beaujard; Method and device for blowing a gas onto a moving strip; EP2100673 (B1)

108

6. List of acronyms and abbreviations

WP Work Package

e.g. Exempli gratia, for example

SD Standard Deviation

HDG Hot Dip Galvanizing

CAL Continuous Annealing Lines

PAD Pressure Aerodynamical Damper

RMS Root Mean Square

Vs Versus, compared with

Umoy averaged velocity

Umax maximal velocity

A.U. Arbitrary Unit

UFC Ultra Fast Cooling

mm millimetre

mpm meter per minute

mbar millibar

109

European Commission EUR 25317 — Improvement of productivity on hot dip galvanising line by decreasing strip vibrations

in gas jets cooling systems(Stripvibrations reduction) Luxembourg: Publications Office of the European Union 2013 — 109 pp. — 21 × 29.7 cm ISBN 978-92-79-24828-3doi:10.2777/92028

HOW TO OBTAIN EU PUBLICATIONS Free publications: • via EU Bookshop (http://bookshop.europa.eu);

• at the European Union’s representations or delegations. You can obtain their contact details on the Internet (http://ec.europa.eu) or by sending a fax to +352 2929-42758.

Priced publications: • via EU Bookshop (http://bookshop.europa.eu).

Priced subscriptions (e.g. annual series of the Official Journal of the European Union and reports of cases before the Court of Justice of the European Union): • via one of the sales agents of the Publications Office of the European Union

(http://publications.europa.eu/others/agents/index_en.htm).

doi:10.2777/92028

KI-NA-25317-EN

-N

The high quality standard of coated steels requires good stability of the strip, particularly in the cooling tower after the zinc bath, where the gas jets of the cooling equipment excite the strip.

The objective of the pilot project is to increase the line productivity and coating quality by decreasing the vibrations along the cooling path, not with external stabilising actuators but by the improvement of existing cooling technologies. We applied a methodology mixing industrial trials, experiments on a semi-industrial facility and a theoretical approach.

Despite the unforeseen withdrawal of the initial line due to financial difficulties in the European steel industry, we choose a newindustrial line.

Thus the major achievements are as follows.

— Actual state of vibration amplitudes under industrial conditions and the effect of the major process parameters.

— A model coupling physical and numerical approaches, able to predict the vibration amplitudes and frequencies for specific process parameters and configurations.

— A new cooling technology that significantly reducesstrip vibration amplitudes was designed and tested before being implemented on the chosen industrial line (revamping of existing cooling equipment).

— The principles of those findings extended by the partner Drever to a new efficient cooling equipment dedicated to fast cooling sections (protective atmosphere). Many new lines are equipped with this innovative equipment. Acceptance tests show significant benefits.

The project ended with success: the innovation has been implemented worldwide on many HDG lines. There are great benefits: strip stability, cooling efficiency and product quality. The results are shared with the community: six publications [1–4, 25–26] and two patents [27–28].

Studies and reports