Ladles & Slag Pots

LADLES & SLAG POTS

LADLES & SLAG POTS

Description

In the metallurgical and melting fields, a ladle is a vessel used to transport high temperature metal or pour out molten metals. Usually it has three different function types, for example, casting ladle, transfer ladle, treatment ladle. Ladles are normally rated by their working capacity rather than by their physical size

SLAG POT is a load-bearing vessel whose sole purpose is to collect molten or solid slag generated during metallurgical or chemical processes, to retain it during transport and to deposit it at a place of disposal.

Ladles and Slag pots are crucial items as they are part of lifting equipment and therefore undergo strict engineering design and national safety regulations.

Ladles and slag pots are uniquely designed to suit individual operations. This means that we can fine-tune the design to suit your specific requirements and finally give you the first class products.

Material:

In principle there are three sorts of materials available for the manufacture of ladles and slag pots.

Grey Cast Iron, Spheroidal Graphite (S.G.) Iron Cast Steel

Grey Cast Irons are with graphite in the form of flakes in a matrix of ferrite, nearly free from free-carbide phase. Due to this structure Grey Cast Irons have excellent thermal conductivity but exhibit poor tensile strength with low levels of elasticity and plastic deformation. Thus, on the one hand these materials are rather resistant against direct thermal attack of hot metal; on the other hand they are extremely sensitive to either thermal stresses or impact under operational conditions. Grey Cast Irons is often selected due to price effectiveness and is used on small pots in the light metal industry however this material is not suitable in the heavy metal industry.

Standard specifications of Grey Cast Irons may be found below

Grey Cast Iron

Standard Specifications for Grey Cast Iron

Country Specification Grade

United Kingdom BS 1452 150

USA ASTM A48-83 20A

Germany DIN 1691 GG15

France NF A32-101 FGL 200

Japan JIS G5501:1995 FC15

South Africa SABS 1034-1975 2

Europe EN 1561:1997 EN-GJL-150

International ISO 185:1988 15

Spheroidal Graphite (S.G.) Iron This material was developed to further improve the mechanical properties of the lower strength grey cast irons. Unlike grey cast irons, which contain free graphite in the form of flakes, spheroidal cast iron, with its greater plasticity, contains graphite in nodular form. This typical microstructure with stress patterns reducing internal stresses explains the superior mechanical properties of spheroidal graphite cast iron compared with grey cast irons.

Stress patterns in different types of cast iron

Grey cast iron with flake graphite.

SG cast iron with nodular graphite.

The material usually specified for ladle manufacture is defined with the following parameters

Chemistry

Total Carbon 3.75 - 3.95

Silicon 2.00 - 2.20

Manganese 0.5 max

Structure

Graphite Well defined spherules

Matrix

Containing approximately 80% ferrite free from massive free-carbide phase

To improve service life under high temperature conditions some ladles and slag pots manufacturers have modified the standard chemistry of ladles and slag pots material.

The Si content has often been decreased to a level of 1.55 to 1.6 % and the Mn content has been increased to about 0.6 % to improve heat conductivity and meet higher elongation values without changing basic strength characteristics. In some cases Cu (0.5-0.6 %), Ni (0.10-0.15 %) and Cr (0.20-0.25 %) have been added to increase ductile and tensile strength

The following are typically desired mechanical properties

Tensile strength MPa 240-390

Elongation % 20

For the manufacture of Steelwork ladle, SG iron has some remarkable advantages in comparison with grey cast irons and cast steel as well. Slag pots made of SG iron are renowned for their excellent shape stability under operational conditions. Also the slag does not adhere strongly to the sides of the slag pot walls due to favourable heat conductivity and can be easily removed.

In spite of these favourable properties SG iron has not replaced Cast steel as a popular material choice for slag pot ladles. Sg Iron selection for ladle material is predominately still being used in Europe and the Middle East

However from a strength point of view cast steel has a 50% higher tensile strength over SG Iron.

SG irons is also extremely section sensitive causing a loss of about 11 200 psi of tensile strength due to an increase of section thickness from 1 to 6 in. This means that ladles and

slag pots manufactured from SG iron are most vulnerable to cracking in areas where change of section occurs eg (bottom, trunnion seat, ribs, tilting lugs etc. ).

Once cracking occurs through thermal or mechanical impact, ladles and slag pots service life will diminish rapidly. Because SG irons are only weldable with great difficulties repair of cracks must be done with special welding techniques that never ensure long-lasting success.

SG irons with a melting point about 1300 degrees C is much lower temperature then molten Cast Steel may cause a breakthrough of slag pot wall or bottom when liquid steel should be carried over with slag during the tapping procedure. Material damages due to a breakthrough are in most cases not repairable.

Some preference still exists with SG Iron because of improved shape stability and less inherent molten metal sticking to the side walls as compared to cast steel ladles .

Standard specifications of SG Iron may be found below.

SG Cast Iron Standard Specifications for Spheroidal Graphite Cast Iron

Country Specification Grade

United Kingdom BS 2789:1985 400/18

USA ASTM A536-84(1999) 60-40-18

Germany DIN 1693 GGG 40

France NF-A32-201 FGS 400-12

Japan JIS G5502-1995 FCD 400-18

South Africa SABS 936/937 SG 38

Europe EN 1563: 1997 EN-GJS-400-18

International ISO 1083: 1987 400-12

China GB-T 1348-2009 400-15

Cast Steels with differing chemical compositions but defined mechanical properties play a dominant role in the manufacture of ladles and slag pots.

Standard specifications of Cast Steel for slag pots may be found below

Cast Steel

Standard Specifications for Cast Steel

Country Specification Grade

United Kingdom BS 3100:1991 425-A2

USA ASTM A 27 60-30

Germany DIN 17182 GS-16Mn5

Japan JIS G7821:2000 SC42

International ISO 3755:1991

The advantages of this material may be summarized as follows:

*Extraordinary resistance to impact load due to a high ductility with excellent elongation values.

*Considerable insensitiveness to excessive stresses caused by unequal heat load. Low cracking tendency because of high yield and tensile strength values.

*Reduced occurring of heat induced deformation of slag pot (narrowing). *A pot life history which, because of better material properties, will be three to four

times better compared to pots of other materials, as for example Cast Iron.

Excellent weld ability allowing the repair of cracks or other surface damages

The mechanical properties for Cast Steel slag pots as defined by manufacturers within the USA and Europe (especially Germany) are given below

USA Europe Tensile strength

psi >60000 >65000

MPa >414 >448

Yield strength

psi >30000 >35000

MPa >207 >241

Elongation

% >24,0 >35,0

Reduction of area % >35,0 >40,0

All ladles and slag pots coming into operation must withstand elevated temperatures, high temperature properties like creep resistance or creep strength are better suitable for characterizing casting ladle and slag pot materials.

Increase of tensile properties by a normalizing /annealing

Increase

Tensile strength about 2.0 %

Yield strength about 5.0 %

Elongation about 33 %

Reduction of area about 80 %

Charpy V-notch about 400 %

The prominent features of Cast Steel (CS) in comparison with SG Iron (SG) are given in the following table.

SG CS

Shape stability Better

Restrictions on design layout Better

Resistance to impact damage Better

Resistance to normal heat load Better

Resistance to direct hot metal attack Better

Maintenance and repair Better

Cost Better

Pot life Better

Cost efficiency Better

Design

The shape of a ladle or slag pot depends primarily on the operational conditions it has to withstand. Thus, the following design criteria must be taken into consideration:

Type of furnace that the slag pot will service, Quantity and type of slag generated, Method of handling and dumping the pot, Heat impact during operation, Dimensional restrictions, Pot maintenance procedures Ladles and slag pots designed by ISP comply with the requirements of structure dimensions, mechanical properties and guarantee by chemical composition, heat treatment, non-destructive testing and visual inspection against surface.

A ladle or slag pot essentially consists of the real container part as well as of the parts necessary for the handling of the pot.

Parts that are needed to handle ladles and slag pots are:

at least 2 trunnions to pick it up and move it wherever this should be necessary, the base to put it down onto the ground a mechanism to handle the pot by a ladle carrier, that is, using this mechanism, the pot

can be tipped to pour molten slag into slag pits for processing, at least one tilting lug either to tip the filled pot by a crane or to turn the empty pot in an

appropriate position for cooling down or for repair.

Multiple ladles and slag pots manufactured by ISP are as follows

Slag Pots, ladles, Convert Ladles, Ingot Mould, Cast Iron Ladles

A ladles and

Slag pots with all parts necessary for its handling must be designed to meet the following essentials:

The thermal expansion due to heat load during operation should be uniform all over the circumference of the slag pot body and should not be hindered by major section changes that cause heat sinks and higher stress levels leading to cracking occurring

Likewise a uniform contraction should be aimed at by a steered cooling after dumping.

Thus, there are rules of thumb in developing slag pot designs:

The bottom of the pot should not be in direct contact with the ground

As few ribs as possible should be placed on the outside of the slag pot

All these criteria aim at as good a stability or stiffness as possible to prevent excessive premature deformation and secure the best service life of the slag pot.

Section Modulus A significant measure of stiffness is section modulus, which is stiffness from shape or geometry. Unlike modulus of elasticity, it has nothing to do with the material.

Actually section modulus is an aspect of moment of inertia which is a function of a shape's cross-sectional area in combination with its height.

Stiffness from geometry of section modulus is a very powerful engineering tool. The knowledge of section modulus enables the engineer to create metal shapes that are much stiffer than the material itself could ever be.

The most significant observation that can be made about stiffness from geometry is that there is no other method besides metal casting that can offer so much geometry in the design and manufacture of component shapes. Because of this, parts to handle a slag pot such as the tilting lugs, are rather cast-on than welded in place.

Another significant observation is that design stress in a structural part is directly related to section modulus. In fact, it is a direct, inverse relationship in which increasing section modulus decreases stress.

We now see an important synergism between modulus of elasticity and section modulus. Modulus of elasticity determines how much stress a metal can safety carry before it begins to deform permanently and section modulus enables the engineer to use geometry to keep the stress within safe bounds. As we have got to know, creative use of section modulus enables relatively weaker metals to do the work of stronger ones.

Handling Cast Steel ladles and Slag Pots

Basic Premature break down of a slag pot will in most cases be caused by the direct impact upon the wall of a slag pot and stresses resulting from temperature difference between inner and outer surface of slag pot and stress levels exceeding the mechanical properties of slag pot material.

Steel carried over with slag will damage the wall of slag pot by erosion and even break-through often resulting in serious consequential damages, whereas temperature differences around the slag pot surface will cause formation of pronounced cracking mostly having its origin on the inner surface of the wall.

Slag Pot Operating Cycle

Slag pot operating cycle should be governed to meet a temperature of slag pot varying in a range between 55℃ and250℃ max immediately before the next slag will be tapped. Such operational conditions usually require a tap-to-tap cycle time of at least 60 to 80 minutes.

If a slag pot will not be emptied immediately after tapping heat absorption may cause a critical increase in temperature necessitating more extended cooling time before the next filling. Should a sufficient cooling time not be introduced and the slag pot be used again with a temperature of more than 250℃ then overheated wall areas may be deformed due to increased thermal stress load.

Preparing the Slag Pot before Filling Before filling with liquid slag the bottom of the slag pot should be protected against direct impact of slag stream. For this purpose different measures have been proved a success either separately or in combination.

A proven practice is to place some lumps of dry slag on the bottom of the pot before filling it with liquid slag. Usually a layer of about 10 to 20 in. will be introduced. It is imperative that the slag is dry, otherwise there is a danger of explosion.

Coating the inside with protective materials such as lime, graphite, fireclay, or some such may also considerably increase the slag pot service life. When pots are coated this should be done after emptying while the pot remains hot. The residual moisture, however, must be driven off before refilling with liquid slag.

Filling the Slag Pot

In order to avoid adherence to the wall or even breakthrough the slag stream should enter the middle of the pot and not be directed at the pot wall. To ensure this, the best location for the pot must be established and this position indicated in a way that it can always be found again. The pot should always be rapidly filled up with slag to its nominal volume with the lowest possible kinetic energy of the impacting slag stream.

Emptying the Slag Pot

Depending on the operational conditions of the plant the slag is emptied from the pot in the liquid or solid state.

If slag is still liquid the pot encounters the least loading because there is less heat absorption. Therefore, when filled the pot should immediately be transported to the slag dump and emptied.

Details about transport

If the pot is not tipped completely through 180o when emptying, problems can arise in the removal of residual slag. This may not only happen for solid but also for skin slag when tipped in the liquid state. Then the residual material can often be removed only by using impacting equipment. Impacting, however, can deform the slag pot making it difficult for the slag to slide out of the pot. In particular cases impacting may even cause the pot to be shattered and prematurely taken out of operation.

Manufacturing

All the ladles and slag pot are made to order. This means that we can fine-tune the design to suit your specific requirements. The main manufacturing steps are as followings:

Moulding

Each type of ladle has its own pattern. The moulding is individually carried out.

Trunnions

The trunnions – generally – are casting together with the pot body. But it becomes more and more popular to use a forged one.

Melting

The melting is carried out in the 50T Eccentricity Furnace, the ladle capacity allows a continuous bottom pouring process the speed of which is permanently controlled. The metal analysis is checked by using a computer linked spectrograph

.

Heat treatment Every pot undergoes a combined quality heat treatment (annealing) aiming both to grain refining and to stress relieving. Fettling and dressing

The inner surface is processed fit-for-purpose so that the surface discontinuities - which might cause some sticking of the slag - are extensively removed. Additionally, the castings are descaled by shot blasting and the outside is additionally coated for transportation.

Delivery

Reinforcement measure and security must be considered as a priority for transportation.

Maintenance and Repair

Temperature cycle

It is of greatest importance to keep and not exceed a certain temperature range with the circulation of slag pots.

General Inspection

If there are no adhering skulls and if the internal surface is still smooth and without washouts and undercuts due to spalling or deformation then the slag will slide out without any problems. But even without any specific problems preventive maintenance is always recommended. With a specified schedule pots should be regularly inspected. Stickers must be burned out and damage must be repaired immediately it occurs, otherwise the pot might prematurely fail.

Repair Work

In most cases the occurrence of cracks, penetrated walls, washouts, spalling, or narrowing of pots are the main cause for necessary repairs.

Depending on the material of the damaged slag pot there are different procedures available for the repair.

The most frequent applied procedures are:

Procedure Slag Pot Material Comments

Welding Cast Steel, SG Iron with restrictions

Riveting SG Iron, Grey Iron

Iron Stitching Cast Steel, SG Iron, Grey Iron

All repairs must be stress relieved to ensure a stress free repair.

Welding

The most commonly used welding procedures for the repair of ladles and slag pots are the arc-welding and the braze-welding process.

Braze welding is a procedure that makes use of the oxyacetylene flame and so it is very similar to fusion welding with the exception that the base metal is not melted.

Arc welding is a process utilizing the concentrated heat of an electric arc to join metal by fusion of the parent metal and the addition of metal to joint usually provided by a consumable electrode. Either direct or alternating current may be used for the arc, depending upon the material to be welded and the electrode used.

Electrodes for the repair of cast steel slag pots providing the desired operational features are:

Company Type of Electrode Country

ESAB Atom Arc 7018-1 USA

Weld Mould Company Polytrode H.D.515 USA

ESAB OK 55.10 Europe

Riveting

Cracks in Cast Iron slag pots are in most cases repaired by riveting a plate over the cracked area.

The main advantage of this technique is that only single-sided access is needed, the main disadvantage is that, in general, pre-drilled holes are required ensuring that holes of cracked area and overlapping plate will perfectly mate.

Most of the time the threaded holes are pre-drilled in the shop when riveting.

Before parts are joint mating surfaces should be cleaned, chips and burrs removed. Threaded bolts are then placed in the pre-drilled holes and plate with mating holes pushed over the bolts. Bolts are then welded to the plate and hot riveted.

Iron Stitching

Where there is the need to repair damaged production equipment, cold metal stitching - a special type of blind riveting - provides a fast and effective solution. This process is extremely versatile and can be used on any iron or steel casting of 6.35 thickness or greater.

The major advantages of the cold metal stitching process are that it can be carried out in-situ, and it does not involve the application of heat, thus removing the risk of distortion and misalignment.

If a damaged slag pot is part of a process where any delay would bring overall production to a standstill, cold metal stitching can get production up and running within a matter of hours instead of waiting for days for a welding or riveting repair.

Taking this factor into consideration, cold metal stitching is usually the most cost effective solution to the problem of cracked or damaged castings.

All above description is to introduce products and their application, if you require more information, please visit our website and or contact us.

We would like to take this opportunity to introduce you to other aspects of International Steel Products business. We also supply finished or proof machined steel products in the form of castings, forgings, profiled steel components and complete steel fabrications.

Our solution for you is to take out the complexities and risks involved in purchasing of shore by utilising our experience and knowledge of this area. We have a deep understanding of the products we bring into the country and are confident we will meet your needs. Our confidence comes from the disciplined quality processes we employ in our purchasing model. We re-enforce this by having strong business relationships with our chosen overseas partners and we have learned through experience who the quality suppliers are. Let us take the angst involved in overseas purchasing away from your business so you can focus on your customers more.

To find out more about how we can help your business contact ISP on +612 8801 9050

International Steel Products 9 – 11 Power Street St Marys NSW

+61 2 8801 9050