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Tin Free Steel (TFS) is also known as chromed steel, as it is obtained by coating the metal base (low-carbon steel) with an ultra-thin layer of metallic chrome and then with a chromium oxide layer. As a common practice Tin Free Steel is produced in bulk quantities over and above the actual requirements. Our prime interest lies in the excess production and non-prime quality TFS available in all shapes, forms and sizes.
Electrolytic Chromium Coated Black Plate This product, commonly referred to as tin-free steel or TFS, follows the same processing sequence as electrolytic tinplate. The coating lines are mechanically similar. During the electrolytic deposition process, chromium and chromium oxide are deposited. The metallic chromium coating on each surface is applied 5.0 milligrams (mg)/sq. ft. of area. The oxide film ranges from 0.7 to 2.0 milligrams (mg)/sq. ft., but is generally on the lower side of this range.
Unlike tin, the chromium layers cannot be reflowed, therefore a coating line dedicated to chromium coating will not have melting towers as used on the tin line to reflow the tin into a bright state.
The product is also electrostatically oiled before it exits the coating line. Historically, the industry used butyl stearate oil (BSO), which was developed for its lubricity to prevent scratching. In some instances, it has been determined that acetyl tributyl citrate (ATBC) oil used on electrolytic tinplate is more compatible with some specific lacquering and paint systems. In this case, ATBC has been preferred at the expense of the greater lubricity of the BSO.