Manufacturing Facilities -
Stages of Production
All tinplate originates as in
the steel-making furnace (Tata Steel), where the proper chemistry for
steel is obtained to meet the specific needs of the end user. All tin
mill products start their production process in a Basic Oxygen Furnace (Tata
Once the steel is produced, the continuous
casting process transforms molten steel into slabs in one continuous
operation. Continuous casting is a highly energy- and cost-efficient
process that produces a slab of excellent quality and consistency.
Continuous casting methods are now used in virtually all carbon steel
production facilities to produce products of consistent, high quality.
Next, the slab goes into the Hot Strip Mill (HSM) of Tata Steel where
its thickness is reduced and it is wound in a down coiler into coil
form. This is where the Hot Rolled Coil (HRC) is procured as the basic
raw material by TCIL from Tata Steel.
CRM Process Flow
To remove the scales adhering to the hot rolled
coils Tinplate Company uses its Push-Pull shallow bath Hydrochloric Acid
Pickling Line. The line has 3 pickling tanks and 5 rinse tanks. The
Pinch Roll # 1 in the entry section pushes the strip that is "paid off"
and the Pinch Roll # 3 in the delivery section pulls it thro the process
section of the line. The line has a cascading system for rinse water and
online trimming facility.
1. Incoming coils are checked for its shape
and steel composition.
2. Acid baths are checked for free acid
3. Rinse water is checked for chlorides
4. Pickled coils are checked for substrate
related defects such as rolled in scale, sliver and process related
pickling quality and surface finish.
If all checks conform to standards of delivery
to next process the coil is cleared for processing in cold rolling mill.
6 Hi Cold Rolling Mill
Tinplate, as a packaging
material, continues to be most preferred, both in packaging food
products like processed food, vanaspati, ghee, etc., and also where
criticality of application is important, as in the case of battery
jackets and pesticide cans, to name a few select areas.
Understanding the need of
increased indigenisation, TCIL commissioned its state-of-the-art 120,000
tonnes per annum Cold Rolling Mill having the benefit of synergy with
TATA STEEL, from where raw material is available in the form of Hot
Rolled Coils for the manufacture of TMBP coils.
The mother mill of the complex
is a 6 High, continuous variable crown-reversing mill. The pickled strip
is "paid off" from a Pay-Off Reel and fed into the cold rolling mill.
Depending on the input thickness, desired output gauge and pass schedule
designed by the mill operator, the hydraulic system sets the draught.
After the first pass that has run between the POR and Reversing Reel #
2, the tail end is fed into the Reversing Reel # 1. The strip is run
reverse and forward between RR1/ETR and RR2/DTR, thro the CR mill, with
the thickness being reduced in each pass. The thickness gauges at the
entry and the exit side of the mill gives real time feed back thro the
automation system to the mill's hydraulic system for online correction
of roll force and hence the thickness.
1. Shape of CR strip
2. Gauge tolerance or
3. Surface finish
4. Surface defects.Full
hard CR material from here is routed to Coil Preparation Line for
trimming or directly packed and sent to the customer.
Full hard material
Full hard steel is made without
the usual subsequent annealing step. The resulting product has a
particularly high stability. Due to the elimination of the grain
recrystallization process associated with annealing, the material
retains high internal stresses. Its deformability is therefore
restricted, i.e., very high forces must be employed in any downstream
metal forming process. Classic applications for this material include
products such as corrugated roofing sheet and some white goods
During the process of cold
rolling cooling oil is used to keep the temperature of the roll and the
strip within limits. This cooling oil mixed with water in an emulsion
has to be removed for further processing. This is achieved in the
Electrolytic Cleaning Line. The line uses alkaline dunk and ortho-silicate
electrolytic cleaning to remove the emulsion oil coating. The strip is
then scrubbed, rinsed, dried and rewound on a reel into coils. These
coils are then tilted 90o and taken for annealing.
Plate out on strip to check for the cleaning efficiency.
Annealing is done to relieve
the stresses that are built into it during the process of cold rolling
which makes the steel strip hard and brittle. Annealing is done using
the batch annealing process.
Degreased coils are stacked
four high on a base. An annealing cover is placed over this stack and
pure hydrogen is pumped in. Then the heating hood is placed and
programmed to heat the coils to predesigned temperatures. This follows a
heating - soaking - cooling cycle with cut off temperatures and times
depending on the hardness required by the customer. After the process
that takes 32 - 38 hours, the coils are discharged from the base.
1. In the base the
temperature and cycle of heating, soaking and cooling.
2. Annealed hardness of the
coil at the Temper Mill entry.
The mill is a four high
two-stand tandem mill with a facility to give a further reduction of
upto 30%. After the process of annealing the strip becomes soft. To put
it to further use the surface has to be given the proper finish and
hardness. For this purpose the strip is passed thro the temper mill.
Normally a skin pass is given (80% of product). This is dry temper
rolling; where the hardness and shape is controlled in the first stand
and the surface finish in the second stand. In the rest (20%) of cases a
post annealing secondary cold reduction of upto 30% is given by
controlling the draught in the first stand. This process is known as
Double Cold Reduction. This process also uses a cooling emulsion for
roll and strip cooling. This imparts higher hardness and strength to the
strip enabling thinner sections to be put to use in place of thicker
1. Shape of coil with
regard to bowness in the strip.
3. Surface finish and
4. Temper (hardness) for
SR/Proof stress for DR
Coil Preparation Line (CPL)
Full hard and / or tempered
coil before being tin plated has to be trimmed to the required width as
per the customer's order. For this purpose the coil is passed thro' the
CPL with edge trimming facility. The coil is "paid off" and passed thro'
the trimmer to cut off both sides to the ordered width of the end
product and then rewound. While rewinding the edge guide system thro a
continuous feedback process ensures that the two sides of the coil
winding is without any projected edges. This is done to facilitate
handling of the coils. The full hard cold rolled coils are packed and
shipped out of this mill to customers.
1. Shape of coil - edge
waviness and bow.
2. Edge burr on the strip.
3. Width tolerance (0 to +2
Electrolytic Tinplating Line
The unique properties of tin
provide a coating on the steel that protects the contents, while
providing the steel with an attractive appearance, corrosion resistance
and ease in bonding, welding and painting. Tin is applied to both sides
of the black plate coil through an electrolytic process. The thickness
of the tin coating (called coating weight) is dependent upon the end-use
application. Typical applications for electrolytic tinplate include food
and beverage containers, paint trays, battery tops and paint, varnish
and aerosol cans.
The Tinplate Company of India
Limited pioneered the Indian Industry when they put up the country's
first tinning line in 1922. The growth of TCIL has been a continuous
process of development and modernization to keep Indian Tinplate at par
with international standards.
The technological advances had
led to the introduction of Electrolytic Tinplate (ETP), while the
spiralling and prohibitive cost of tin resulted in the manufacture of a
suitable substitute, namely Tin Free Steel (TFS) or Electrolytic ally
Chromium coated steel(ECCS). To keep pace with these developments, TCIL
was the first to set up a combination line capable of producing both ETP
and TFS. The plant was commissioned in 1978 and has an installed
capacity of 179000 tonnes per annum. The line can be run upto a speed of
300 m/min and is capable of processing coils ranging from 0.14 mm to
0.60 mm in thickness and 600 mm to 965 mm in width.
Process flow Diagram of Electrolytic Tinplating plants
The Electrolytic Tinplating
line is the only one of its kind in India. It has a facility to coat the
line with tin or with chromium / chromium oxide (Tin Free Steel). The
ETP uses the FEROSTAN process, where in an acidic bath of Stannous
Sulphate is the electrolyte. The strip is "paid off" and passed thro the
looping tower - which stores material to enable the line to run
continuously, even while the entry is stopped for welding the tail end
of one coil to the head of the next. The strip then passes into the
cleaner solution to remove any remnant traces of oil or emulsion. Then
it goes thro the pickling bath where the Sulphuric acid removes any
oxide that may have formed in the CRM complex. This acid also etches the
plate, to prepare it for the electro-deposition of tin. After the
surface is fully prepared for plating it passes into the plating
section. Here the strip enters the bath with pure tin being used as
anode and the strip itself as the cathode. By passing the required
direct current - this is dependant on the coating weight required by the
customer - in the bath the plate is coated. Thereafter it passes into
the melting furnace where the deposited tin is melted to give it a
brighter finish and also make it adhere to the base material better.
After this the strip is chemically treated to reduce the action of
atmosphere on tin and then coated with oil to facilitate handling.
In case the order is for tin
free steel, the strip is passed directly from the pickling bath to the
chrome plating section. Here by using chromic acid bath and inert anodes
a layer each of chromium and chromium oxide is deposited on the strip.
Since this coated steel does not have any tin plating on its surface it
is called tin free steel.
The strip is then passed thro
the online inspection to segregate any sheet that falls outside the
acceptable range of thickness, sheets with pinholes in them and then cut
up as per order and piled into packets of about 1500 KGs. This is then
shipped out to customers in trucks or containers, the latter mainly for
1. Cut length and width of
2. Surface finish and
defects (Tin in Tinplate sheets and Cr in TFS)
3. Temper and other
physical properties of the sheet
Tin-free Steel/Electrolytic Chrome Coated Steels (ECCS)
Unlike the multiplicity of
coating weights with tin, only one standardized chromium-coated product
is manufactured. The chromium coating process was developed in the 1960s
as an alternative to tin coatings for packaging products
cost-effectively, with desirable material properties. Chromium offers
excellent lacquer adhesion, storage properties and strong resistance to
food corrosion with proper applications of lacquer. Chromium-coated
steels are most frequently used for can tops, screw and lug caps, snap
and press-on closures and shallow-drawn food cans. Packaging steels are
coated with different protective and decorative coatings, depending on
their intended use.