colour coated steel
TRANSCRIPT
-
8/3/2019 Colour Coated Steel
1/6
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
-
8/3/2019 Colour Coated Steel
2/6
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
-
8/3/2019 Colour Coated Steel
3/6
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
-
8/3/2019 Colour Coated Steel
4/6
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
-
8/3/2019 Colour Coated Steel
5/6
Perspective
SEPTEMBER 201032
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.
-
8/3/2019 Colour Coated Steel
6/6
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