November 14, 2008

Pickling Scale and Oxide Removal

It is essential that metal to be plated be free of scale and oxide for quality plating. Good shop practice can prevent or minimize scale problems. Such things as cleaning before heat treating, wearing gloves to keep fingerprints off metal surfaces, proper control of heat treat furnaces, and taking step to prevent rusting of steel parts pay for themselves. It is literally true that "an ounce of (scale) prevention is worth a pound of cure."

Every shop has methods of removing rust and scale. Both mechanical and chemical methods are employed. Acid pickling is one of the most widely used. It has been reported that scale and oxide removal consumes 5 % of all the sulfuric acid, 25% of the hydrochloric acid, most of the hydrochloric acid, and large quantities of nitric acid, most of the hydrofluoric acid, and large quantities of nitric acid and phosphoric acids.

Inorganic acids and acid salts used for scale removal are as follows:

Acids

Acid Salts

Sulfuric

Sodium acid sulfuric and ferric sulfate

Hydrochloric

Ferric Chloride

Nitric

Ammonium persulfate

Phosphoric

Acid phosphate

Hydrofluoric

Acid fluoride

Hydrofluosilicate

Acid Flousilicates

Flouboric

Acid flouborates

Chromic

Dichromic

Sulfamic

Ferric Chloride

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