Corus Packaging Plus
The manufacturing route for tinplate products
From hot strip to tinplate
The basic raw material for the production of tinplate products is hot rolled
steel strip. The production process reduces this to the required thickness
by cold-rolling. This rolled strip is then coated with tin or chromium in an
electrolytic process. For some applications polymer coatings are applied
for additional protection of the metal.
Hot rolled strip The tandem mill has several stands the strip is passed through an alkaline
Hot rolled steel strip is the raw material equipped with a four high arrangement bath through which an electric current
for the production of tinplate. Large of rolls. At the bottom and top of each is passed.
coils of steel, measuring about 2 – 3mm stand are large back-up rolls with two
in thickness and weighing up to smaller working rolls in the centre Next the strip is scrubbed, rinsed,
25 tonnes, are supplied to the plant. through which the strip passes. By dried and rewound into coils.
passing the hot strip through these
1 Acid bath pickling rolls, the strip is reduced to less than 4 Continuous annealing
Processing begins with the pickling 10% of its original thickness. The strip Cold rolling makes the strip hard and
of the hot rolled strip in an acid bath and rolls require lubrication with an oil brittle and in this condition it is
to remove the iron oxide layer formed and water mixture. unsuitable for use as a packaging
during rolling. After the continuous material. The strip requires annealing
pickling process, the strip is rinsed, Water also provides essential cooling to restore its crystal structure and
dried, edge trimmed, oiled and of the rolls. Consumption of water is ductility. In continuous annealing the
rewound into coils. minimised through the use of a closed strip passes in vertical loops through
loop re-cycling system. a furnace in a controlled atmosphere
2 Cold rolling that prevents oxidation of its surface.
The tandem cold rolling mill takes the 3 Cleaning and degreasing
pickled hot rolled strip and rolls it to After cold rolling, the strip requires Strip annealed in a continuous furnace
achieve its final thickness of between degreasing. First it is cleaned of for approximately two minutes at up to
0.12 and 0.49 mm impurities and lubricant residue and 680°C is harder and more resilient than
then in an electrolytic degreasing cycle, batch-annealed material.
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5 Batch annealing 7 Double reduction rolling 10 Sheet cutting
An alternative option for restoring the Higher strength steels can be obtained After coating, the tinplate either remains
ductility of steel strip after cold rolling by giving the steel strip a stronger in a coil or is cut into sheets in various
is the batch-annealing method. reduction on a double reduction mill. cut-to-size formats for shipping to
Although this makes the steel less the processor.
This three-day process restores the deformable, the added strength is
crystal structure of the strip that was recognised and valued for making Sheets can be straight-edged for
changed during cold-rolling. As many very thin and lightweight packaging. rectangular sheet metal parts such
as four coils are stacked on top of each as body can sections or scroll-cut for
other and placed under a system of 8 Tin / chromium coating round sheet metal parts such as
inner protective and outer furnace Steel strip when coated becomes can ends or cups.
covers. The coils are heated to around tinplate. The steel is joined in an
600°C. Oxidation of the strip surface is endless strip by welding, and the 11 Coil inspection line
prevented by an oxygen-free controlled material is passed through an The sophisticated instrumentation
atmosphere. When compared with electrolytic strip coating line where system, together with advanced
the continuous annealing method, a thin layer of tin or chromium is temperature control and visual
batch annealing yields a product applied to its surface. inspection, ensures a final product with
of lower hardness. consistent adhesion, appearance and
9 Polymer coating structure.
6 Temper rolling Polymer coatings can be applied
For most applications, after annealing to the steel for specific applications. 12 Storage and despatch
the steel strip is too soft to handle and These coatings are made by either All products are carefully packed
lacks the required strength. Its strength applying a ready-made polymer film and stored before shipment. Our steel
is brought to the desired level by a light or by a direct extrusion process. products are transported to customers
reduction on a temper mill which also in any part of the world by rail, truck
gives the steel its required surface There are different sorts of polymer, or ship.
quality and flatness. the principle types being PET and PP,
available in a range of grades
At this stage, the product can be sold and colours.
as blackplate, mainly for applications
other than packaging. For packaging Polymer coatings are applied
purposes steel strip needs extra predominantly to chromium coated
protective coatings and this is when steel. Polymer-coated steel can be
it becomes known as tinplate. directly converted into cans and offers For further information please e-mail:
outstanding protection properties. packagingplus@corusgroup.com
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1 Pickling Line 2 Tandem Cold Rolling Mill
BA CA
3 Cleaning Line
Cleaning Section
4 Continuous Annealing Line
5 Batch Annealing
SR DR
6 Temper Mill 7 Double Reduction Mill
Coil Preparation Line 8 Coating Lines 9 Polymer Coating Lines
10 Shear Lines 11 Coil Inspection Line 12 Packaging Despatch
For further information please e-mail:
packagingplus@corusgroup.com
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