Chrome plating is a finishing treatment utilizing the electrolytic deposition of chromium. The most common form of chrome plating is the thin, decorative bright chrome, which is typically a 10 µm layer over a underlying nickel plate. It imparts a mirror-like finish to items such as metal furniture frames and automotive trim. Thicker deposits, up to 1000 µm, are called hard chrome and are used in industrial equipment to reduce friction and wear and to restore the dimensions of equipment that has experienced wear.
Chromium Plating Solutions
There are two types of chromium plating solutions: hexavalent chromium baths whose main ingredient is chromic anhydride and trivalent chromium baths whose main ingredient is chromium sulphate or chromium chloride. Trivalent chromium baths are not yet common, due to restrictions concerning colour, brittleness, and plating thickness.
Typical Bath Composition and Operation of the Hexavalent Bath
Chromic acid (CrO3): 250–300 g/l
Sulphuric acid: 2.5–3.0 g/l
Operating Temperature: 45–60 °C
Plating current: 1.55–3.10 kilo amperes per square meter DC
Maximum superimposed AC ripple allowed is 18%, preferred ripple is 5% to 10%
Anodes: lead with up to 7% tin or antimony.
Chromium may be stripped anodically in an aqueous solution of sodium hydroxide.
The materials described herein are extremely hazardous. They are toxic, corrosive and damaging to the environment. Their use, storage, and disposal are governed by law in most jurisdictions. Personal safety equipment and proper containment facilities are considered mandatory.
Chrome plate shall be uniform in thickness on all surfaces, which can be touched by a sphere of 20 mm diameter. Plate shall be smooth, homogeneous and free from frosty areas, pin holes, pits, nodules, and other defects.