MaterialPedia

HARD CHROMIUM PLATING is produced by electrodeposition from a solution containing chromic acid (CrO3) and a
catalytic anion in proper proportion. The metal so produced is extremely hard and corrosion resistant. The process is used
for applications where excellent wear and/or corrosion resistance is required. This includes products such as piston rings,
shock absorbers, struts, brake pistons, engine valve stems, cylinder liners, and hydraulic rods. Other applications are for
aircraft landing gears, textile and gravure rolls, plastic rolls, and dies and molds. The rebuilding of mismachined or worn
parts comprises large segments of the industry. One specialized application is a thin chromium layer used as a lacquer
adhesive layer in the manufacture of "tin" cans.

Hard chromium plating is also known as industrial, functional, or engineering chromium plating. It differs from
decorative chromium plating in the following ways:

· Hard chromium deposits are intended primarily to increase the service life of functional parts by
providing a surface with a low coefficient of friction that resists galling, abrasive and lubricated wear,
and corrosion. Another major purpose is to restore dimensions of undersized parts.

· Hard chromium normally is deposited to thicknesses ranging from 2.5 to 500 μm (0.1 to 20 mils) and
for certain applications to considerably greater thicknesses, whereas decorative coatings seldom exceed
1.3 μm (0.05 mil).

· With certain exceptions, hard chromium is applied directly to the base metal; decorative chromium is applied over undercoats of nickel or of copper and nickel.