Tin free steel is a thin black sheet with two coats,
one of metal chrome film and the other of chromium oxide. Both the sides
of the sheet has beautiful lustrous metallic finish. Tin free steel
sheet is also known as packaging steel. Such a material is ideal for the
manufacturing of crown corks, tops etc. It is economical and is an
excellent replacement for Tinplate. Tin free steel sheet is produced by
the procedure known as electrolytic chromic acid treatment. Tin free
steel sheets are not only used in making containers but are also used in
electrical machinery parts and in other applications too. Tin free steel
is also known as Chromium coated steel and is a suitable substitute for
steel.
Features of TFS[Tin Free Steel]: Tin-free steel is a
chromium-coated, corrosion-resistant steel which, like tinplate, is used
for food and other packaging applications. It is correctly known as
electrolytic chromium coated steel (ECCS). The coating is applied to a
cold-rolled, low-carbon steel coil substrate in a continuous
electrolytic process using chromic acid. The result is a very thin layer
of chromium and chromium oxide. Apart from its packaging uses, it does
find other applications, such as in some electrical equipment. Compared
to tinplate, ECCS is easier to recycle because tin is a contaminant in
scrap.
Additional features of Tin free steel:
- Sulphur Blackening Resistance: - TFS has
metallic chromium which has sulphur resistance property while
canning protein-rich foodstuff. The under film corrosion is better
in the case of TFS than Electrolytic Tinplate.
- Filiform Rust Resistance: Filiform means the
continuous thread like deterioration of the lacquered and painted
metal due to the superficial corrosion of the base metal. TFS has a
good under film corrosion resistance which is better than
Electrolytic Tinplate.
- Coating: The coating in the tin free steel
sheet is not amphoteric [having the characteristic of an acid and a
base and has the capability to react chemically both as an acid or a
base]. This means that detergents and dispersion colors can be
packed easily.
- Resistance to Black Sulphide Stain: Fish cans
are ideally made out of such sheets due to this property of black
sulphide stain resistance.
- Heat Resistance: The high temperature baking
results neither discoloration nor in deterioration.
- Paint Adhesion: TFS possesses better paint
adhesion properties than tin plate sheet thus making it ideal for
DRD cans and adhesive bonded cans.
Points of Differentiation:
There are certain aspects wherein the differentiation between the Tin
plate and Tin free steel sheet lies, these are:
- Corrosion resistance: Painting of the sheet
makes it corrosions resistant and can be painted only on the
external side depending on the content of the tin.
- Solderability: Tin free steel sheet is not
suitable for soldering.
- Weldability: The weldibility of tin free steel
sheet is not as good as that of tin plate sheet. Though TFS can be
welded when the metallic coated layers are removed.
- Appearance: Both the sheets almost have a
similar appearance but the TFS has a unique luster due to the
presence of metallic chromium.
TFS-Manufacturing process
Tin-free steel sheets that have metallic chromium and hydrated chromium
oxide coatings are manufactured by placing a steel sheet in chromium
plating bath that contains an assistant to deposit and form metallic
chromium and hydrated chromium oxide coatings on the sheet surface. The
next step is that the sheet is subjected to reverse electrolysis in the
very same chromium plating bath in order to partially dissolve away the
metallic chromium oxide coating along with the anions that are
co-deposited in the hydrated chromium oxide coating. Then the the sheet
is rinsed with water and subjected to an electrolytic chromate treatment
in an electrolytic chromate treating bath.
Precautionary measures:
There are certain points which needs to be taken care of while using
Tin free steel sheet. The precautionary measures are mentioned below:
- While welding the metallic coating layer of sheet should be
removed as it has a high electrical resistance.
- Tin free steel is not ideal for DI forming and soldering but
once it is painted it can be used similarly as a Tin plate.
- The containers made of Tin free steel sheet should be painted on
the internal side as it is prone to corrosions, painting can be
avoided only if motor oil or cooking oil is stored in it.
- The Tin free steel sheets should be used immediately after
unpacking as the sheets tend to get rusted in humid conditions.
- The external surface of the Tin free sheet should be painted in
order to prevent corrosion.
- Tin free sheet does not have sacrificial properties like Tin
plate hence it has a tendency to get scratches on it's surface hence
they are handled with care.
Special Steel Sheet
Special steel sheets are made out of carbon steel that are used for
machine structural use, alloy steel for machine structural use, carbon
tool steel and alloy tool steel. These sheets are capable of responding
to diverse customer needs for homogeneous quality, high dimensional
accuracy/surface quality and a wide product line. The sheet goes
through numerous processes before the end product is produced, this
enables the product to be corrosion resistant. Special steel sheets are
produced according to the end usage requirements, mentioned below are
the specifications that are required for specific applications, like-:
- Abrasion resistant special steel sheet is manufactured for the
production of:
- Shovels
- Sieves
- Excavator
- Buckets
- Sprockets
- Crushers
- Feeders
- Edges
- Gears
- Conveyors
- Punch-shock resistant special steel sheet are also produced for
the manufacturing of:
- House-surfaces
- Cars, vehicles
