Archive for Chromium plating

Apr
04

Type of Chromium Plating

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There are two type of Chromium Plating : Decorative Chromium Plating and Hard Chromium Plating. Decorative Chromium is thin coating serve as nontarnishing, corrosion resistance, and durable surface finish.

Hard Chromium Plating is heavy coating to take advantage of the properties of  chromium, like resistance to wear, heat, corrosion, abrasion, and low coefficient of friction.

Decorative Chromium Plating

The solution chromium plating for decorative purposes are used chromic acid with SO42- as catalyst. The actual concentration is not critical but the ratio of chromic acid : sulfuric acid is most important. Usually, this ratio is 100 : 1, and normally the concentration of chromic acid is within the range 150 – 550 g/l.

The throwing  power of chromium baths is notoriously poor, but the baths containing 250 – 300 g/l of chromic acid are the best in this respect.

Efficiency values over 12% are not readily obtainable from the chromic acid plus sulphuric acid solution. However, the presence of other anions in place off all or part of the sulphate, in particular the fluoride or similar ions, such as fluosilicate or fluoborate, has been found to produce higher efficiencies. These baths will give deposition at efficiencies up to 25 % without excessively high current densities.

Chromium electrodeposited from chromic acid baths of the aforementioned type is hard, britlle and has a high tensile stress.

Hard Chromium Plating

Hard chromium Plating used for engineering purpose like coating for paper machine roll, hydraulic roll, rohtogravure printing roll, and injection plastic mould.

The solution hard chromium plating is 150 – 300 g/l of CrO3, and containing fluoride type ions are frequently utilized because of their greater cathode efficiency.

Higher Temperature (over 50oC) and higher current densities (up to 80 A/dm2) are used than are employed for decorative chromium.

Fluoride ion is very dangerous for environment, so conducted research for replaced fluoride ion, and is available now.

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