Steel Allied Products » Steel Sheets » Tin Free Steel Sheet

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