Colour Coated Steel

8/3/2019 Colour Coated Steel

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Colour coated sheets

industry in India:An overview

Perspective

- Sanjay Sengupta

he Indian producers of colour coated steel have introduced state-of-Tthe-art technology and are capable of producing high quality material ina cost-effective and eco-friendly manner. They should seriously considethe switchover to the use of chromate-free processes in pre-treatment andcoil coating paints. With construction and domestic appliances set to posrobust growths in future, the Indian colour coated steel industry is expectedto record a much better performance in the next few years

SEPTEMBER 201026


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Perspective

SEPTEMBER 201028

Steel is a versatile material. Theunique position of steel remainsunchallenged even today and lifewithout iron and steel remains almostunimaginable.Steel has a wide range ofapplications from the manufacturing asmall pen to automobile, railwaysystem, aircraft for both civil andmilitary operations, big engineeringand construction projects, nuclearpower stations, generation of power,housing, port construction, irrigationprojects and so on.During the last three decades or so,the world has seen many innovations inthe process of steelmaking and vasttechnological up-gradation to makesteel competitive. Steel producers allover the world are giving major thruston value addition to produce superiorquality of products in a cost effectiveand eco-friendly manner.Both long and flat steel productshave undergone remarkable orientationin product mix to suit high endapplications conforming to verystringent specifications as required bythe demanding end-users.In the flat product segment,galvanised steel in India has seen manynew applications in sectors likeconstruction (including housing),automobile, consumer durables etc.

One of the most remarkableachievements in the Indian galvanisedstee l industry has been thedevelopment of colour coated sheets.Colour Coated SheetsColour coating usually refers to theapplication of liquid paint coat over thesubstrate in an automatic continuousprocess after pretreatment. The pre-printed colour coated steel is a veryhigh value-added product thatcombines the best properties of thesubstrates and organic coatingadditionally, imparting it an aesthetic

finish, high degree of durability andhigh corrosion resistance capability.Basics of Coil CoatingCoil coatings, the continuouscoating of aluminium and steel coils, isa step in the manufacture of industrialsemi-finished products for use in

building facades, washing machinesand other white goods.Coatings provide corrosionresistance, colour and surface texture.Once the metal strip has been coated,the panels are cut, shaped and fitted,which after involves high complexprocessing stages such as deepdrawing and roll forming. The coatingsurfaces should be able to withstandmechanical damage, heat chemicalsand moisture.For instance, a building has towithstand the adverse effects of wind,

rain and sun attack and in the whitegoods sector, surfaces are exposed tovariety of abuses during use. Besidesthe above, there is a multiplicity ofapplications for coil coated materials.For each material and each step in thevarious production stages, there is anacknowledged state-of-the-art, whichrepresents current knowledge aboutthe material and its processing.ColourThe construction industry and whitegoods manufacturers have followed thecarmakers' trend towards metalliccolours for many years. While

historically these colours were onlyavailable in polyester, polyurethane orpolyvinylidene fluoride (PVDF)topcoats, a special formulation processnow permits brilliant metallic coloursa l s o t o b e p r o v i d e d f o rpolyvinylchloride (PVC) plastisols.

During the last three

decades or so, the worldhas seen many innovations

in the process of

steelmaking and vast

technological up-gradation

to make steel competitive


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SEPTEMBER 201029

SubstratesColour coating is done

on various substrates to

produce the most cost

effective, quality assured

products with top coat

c o m p a t i b l e w i t h

e n v i r o n m e n t . T h e

substrates usually used

are:

lhot dipper galvanised steel

lelectro-galvanised steel

lGalvalume

lGalbosheets

lAluminium

For selecting the right kind of

substrate, it is imperative to know that

each material used and each step taken

in various production stages. The

producer should possess a thorough

and in-depth knowledge about the

material and its processing.

PretreatmentPretreatment of the substrate is a

very important operation required for

better adhesion formability of the

preprinted steel sheets. Major

producers of colour coated sheets in

India have introduced No-Rinse

technology in place of phospating

(phosphate coat ing) over the

galvanised strip because of better bath

maintenance, uniform clear structure of

coating as well as to meet the demands

of end-users for more flexibility of

coated sheet.

No-Rinse coating pre-treatment is

a very thin layer of chemical treatment

that bonds the coating surface of steel

to the subsequently applied point toensure excellent point adhesion,

corrosion resistance and durability of

steel substrate.

PrimerAfter pre-treatment, the primer of

uniform layer is applied on the pre-

treated surface. The primer provide

flexibility to the paint system and help

corrosion resistance to a great exten

since it contains corrosion inhibitors

The primer is cured in the oven with

temperature control with greaprecision.

Various types of primers are

available based on different resins like

epoxy, polyester, polyurethane and

PVC. Epoxy primers are preferred fo

use in roofing as it contains chromate

pigment for better.

Chromate Coating andChromate - free Coil Coating

Historically, chromium compound

have been the key anti-corrosive

agents in coil coating paints and pre-

treatment. Normally, a two coat system

consisting of a top coat and a primer iapplied to pretreated metal substrate.

The vast majority of traditional coi

coating primers contains chromium

compounds such as strontium and zin

chromate to achieve the necessary

corrosion resistance of the fina

product. Hexavalent chromium

compounds (Chromium VI) serve as an

electro-chemical coupler that can

inhibit corrosive reactions on mos

surfaces.

However, hexavalent chromium

compounds widely used in industria

metal coatings are classified a

carcinogens (category 1 & 2) as well asbeing toxic and dangerous to

environment by Dangerous Substanceth

Directive by EEC, 9 Amendment, 28

adaptation to technical progress. It i

true that once the pigments are

embedded in the paint film, there are no

imminent health hazards. But in

considering the risks associated with

production of the materials at each

stage of their life and each process ha

to be taken into account.

The AlternativeUnder its sustainable developmen

and responsible care programmeBASF Coatings started to explore

options for replacing toxic chromate

pigments in the early 1980s. It wa

clear from the start that an alternative

to chromate containing primers had no

only to be chromate-free but had to

Perspective

Major producers of colour

coated sheets in India have

introduced No-Rinse

technology in place of

phospating (phosphate

coating) over the

galvanised strip because

of better bath maintenance,

uniform clear structure

of coating


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Perspective

SEPTEMBER 201030

match or surpass the overallperformance of its chromate-containing rivals. By the middle of1980s, these requirements were metfor household appl iances, asweathering and corrosion-resistantdemands of the indoor applications areless stringent than for outdoor panels.

By 1992, the first generationuniversal chromate-free primers forexterior applications were introducedand in 1995, there was a furtherdecisive breakthrough; BASF'schromate-free universal primer ongalvanised steel surfaces gavesuperior results over both chromate-free and chromate-contain ingpretreated coal. Continuous adaptationand optimization during the subsequentyears led to further improvements.The main resin system ofchromate-free primers consists of amixture of high molecular weightpolyester and epoxy resins, cross-linked in a system based on aminoresins. The pigment is also not onlychromate-free but also for free of anyother heavy metal or carcinogenicmaterials.Accord ing to experts , theconstruction industry is somewhatconservative and will need to haveconfirmation of the benefits and longlife performance advantages of using

chromate-free coatings. There will bea clear advantage for coil-coaters thatmake the switchover and establish aclear track record with the technologyof chromate-free coil coatings.TopcoatAfter pre-treatment, the primersurface is coated at uniformly coatedthickness and then cured in the oven.The top coat contains a combination ofcolour pigments and additives whichprovide the required colour of thecolour-coated sheets and infuse otherproperties like ultraviolet resistance.The coated product is then rigorouslytested before clearing for furtherapplications.Most of the roofing and constructionmarkets for colour coated sheets usetop coats which are based on polyester,polyvinylidene fluoride (PVDF), siliconmodified polyester (SMP) and

plastisols for cost effectiveness anddurability.Benefits of Paint Coating onGalvanised SteelWhen paint and galvanised steel are

used together, the corrosion controlprovided is superior to either systemused alone. The galvanised coatingprotects the base steel, supplyingcathodic and barrier protection and thepaint slows down the rate at which thezinc is consumed greatly extending thelife of the galvanised steel. Once thepaint has weathered down or damaged,the zinc is available to provide cathodicand barrier protection to avoid rustafter paint peels off.Because of this synergistic effectfor a duplex coating, it provides

corrosion protection 1.5 to 2.5 timeslonger than the sum of the lifetimes ofzinc and paint used individually. Forexample if the galvanised coating lifeon steel is expected to be 15 years andthe paint coating life on steel isexpected to be five years, thegalvanising and paint when usedtogether, gives a life of 35 years, whichis 1.7 times the sum of both systemsused individually.Textured SurfaceThe topography of the coating

The main resin system of

chromate-free primers

consists of a mixture of

high molecular weight

polyester and epoxy resins,

cross-linked in a system

based on amino resins


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Perspective

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surface is a significant design element.

Roll application of coating actually

results in a smooth surface in the coil

coating process. Thus when in 1980s,

the white goods inducting began using

pre-coated panels in combination withsprayed components, there was a

mismatch in surface appearances. The

coating process was required to look as

if it had been painted using spray

application including the typical orange

peel effect.

The challenge was met by the

introduction of special texture primer

which was over-coated with a top coat

adapted to the primers. However,

enormous efforts were needed initially

to achieve reproducible texture, but the

innovation that was launched as a result

became established by mid-1990s and

now represents the coil coatingstandard not only in Europe but in other

industrialized countries of the world.

In addition to its design aspects, the

textured coil surface offers advantages

in processing. The friction properties in

dies are lower than those of a

conventional smooth coating. Also the

surface is more robust and not so easily

damaged during the assembly process

and unevenness and flaws are

masked by the texture.

Ultimately, the surface

requires less care by

the consumer.

The advantages in the processing otextured coil surfaces can also beexploited with textures produced inother ways. Their appearance isdifferent, but they are easier to processand the more wear resistant thansmooth surfaces. For examplepolyamide in a fine particle distributioncan be incorporated into the colouringtopcoat. Roller blind elements veryoften use a surface of this kind wherethe flexible polyamide particles ensureenhanced wear resistance for thecoating to cope with the frequenopening and closing of the roller blinds.Colour Coated Steel Industryin India

India was a late starter in colourcoating business. The presenstructure of the industry is as follows:A : Number of units : 7Number of working units: 7Estimated capacity: 800,000 tonnesEstimated production in 2009-10680.000 tonnes

Construction sector

Including buildings

Domestic appliances

Including white goods

Others

TOTAL

40

55

5

100

B. Domestic DemandThe domestic demand for colou

coated sheets in India is steadily

increasing over the years. The

estimated demand in 2005-06 wa

85,000 tonnes which has gradually

increased to 215,000 tonnes in 2009-

10.

The details are furnished below

year-wise:

YearDomestic Demand

('000 tonnes)Y-O-Y growth

(%)

2005-062006-07

2007-08

2008-09

2009-10(e)

85110

140

175

215

29.41

27.27

25.00

22.86

(e) = estimated

Domestic Demand of Colour Coated Sheets In India

Consumption Pattern (%)

The coating process was

required to look as if it had

been painted using spray

application including the

typical orange peel effect.


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SEPTEMBER 201033

Producers of Colour CoatedSheets in India

Originally, Ispat Industries Ltd and

Shree Precoated Steels Ltd (SPSL)

were the only two producers of colour

coated sheets in India, each having acapacity of 50,000tpy. At present

Ispat's capacity is being expanded to

100,000tpy. SPSL, which has since

been acquired by Essar Steel Ltd, has a

present capacity of 400,000 tpy of its

colour coating line.

Bhushan Steel and Strips has

commissioned a 120,000tpy capacity

colour coating line at Khopoli in

Maharashtra.

Tata Bluescope joint venture on

50:50 basis has installed a metallic and

colour coating and painting facility at a

metallic and colour coating and paintingfacility at Bara near Jamshedpur in

Jharkhand with a capacity of 25,000 tpy

of premium zinc and aluminium coated

material called Zincalume (also called

Galvalume) and pre-painted zinc and

aluminium coated steel called

COLORBOND whose capacity is

150,000 tpy.

Uttam Galva Steels Ltd has set up

80,000 tpy capacity colour coating line

at Khopoli (Maharashtra).

Steel Corporation of Gujarat Ltd,

now owned by Essar Steel Ltd, has set

up a new colour coating line with a

capacity of 50,000 tpy.

Jindal Iron & Steel Co (JISCO) is

setting up a colour coating with an

annual capacity of 1,00,000 tonnes at

Tarapore.

In the PipelineBokaro Steel Ltd's New Cold

Roll MillAmong the features of Siemens VAI

for the major portion of the new 1.3

mtpy capacity cold rolling mill coming

up in SAIL's Bokaro Steel plant at

Jharkhand are Siroll CIS CM and PL

product line. The first link of the

production chain will be in tandem withcold mill coupled to a pickling line. The

state-of-the-art PLTCM will be first of

its kind in India equipped with heavy

gauge laser welder (LW 2 IH) pickling

section, horizontal looper and side

trimmer; 5 and 6 High cold mill and a

carrousel coiler.Bokaro's new CRmill will have a mostmodern colour coatingline of 50,000 tpy

capacity initially.ConclusionC o l o u r c o a t e dsheets are high value-added products thatcombines the bestproperties of thesubstrates and organic coatingadditionally importing it an aestheticfinish, high level of durability and stiffcorrosion resistance.While selecting a substrate, theproducers are required to know thebasic characteristics of the material to

be used. Textured coil surfacesprovide advantages in processing ofthe coil. The surface is more robust andnot so easily damaged during theassembly process.The Indian producers of colourcoated steel have introduced state-of-the-art technology and are capable ofproducing high quality material in acost-effective and eco-friendlymanner. They should seriouslyconsider the switchover to the use ofchromate-free processes in pre-treatment and coil coating paints.With construction and domesticappliances set to post robust growths infuture, the Indian colour coated steelindustry is expected to record a muchbetter performance in the next fewyears. With pre-fab construction trendbecoming increasingly popular in Indiacolour coated steel demand hasimproved significantly. The userindustries find these sheets more eco-friendly.Acknowledgments

1.`Innovative surface design with coil coating'by Lother Sandel of BASF, published in MillenniumSteel 2006.

2.Article in `Steel Times International,'January 2005 issue on chromate-free coil coatingprocess.

3.Various articles by L Pugazhenthy, ED,ILZDA

4.Article by G D Patange, Former GM, UttamGalva Steels Ltd, in `Steelworld' in January 2009issue

Textured coil surfaces

provide advantages in

processing of the coil.

The surface is more robustand not so easily damaged

during the assembly process.

Perspective

Documents

Colour Coated Steel