Electroplating is a widely utilized but little understood process, the fact that the average person is in contact with dozens of plated items daily without even being aware that they are electroplated is evidence of the success of the process, although a complete explanation of electrodeposition involves thermodynamics and modern theories of bonding and catalytic reactions, in its simplest form the process conforms to the following description.
Chromium is a metal with some very remarkable properties; but the full measure of the metal’s benefits as a coating is obtainable only with plating thicknesses greatly in excess of the hundred-thousandths of an inch that is present on the “bright” or decorative plating. Chromium which is plated to obtain the benefits of these additional properties is commonly called “hard” chrome plating, although it only seems harder because it is thicker. Thicknesses up to ten thousand times the thickness of “bright” chrome plating may be used/although thicknesses of two hundred to two thousand times are more common.
The techniques and procedures used to obtain good deposits and high bond strengths for these thicker coatings are different from those used for the ordinary plating thicknesses. First of all, hard chromium is normally applied directly to the base metal rather than over other deposits, as is the case for decorative plating, secondly, in order to obtain adequate adhesion special etching or activating processes are usually required, the actual etching process used depending on the qualities of the base metal and the thickness of chromium to be plated.
Hard chromium plating is employed in virtually every industry. The mining industry is no exception. Operating heavy, high production equipment under severe conditions of wear, abrasion and corrosion it is only natural that wide use would be made of hard chromium plating. During the past twenty years ever increasing use of chromium plating has been made to salvage worn parts on mining equipment. Typical of these parts are pump shafts and sleeves, armature shafts, crankshafts, cutter shafts, brake discs, brake cups, ball joints, and parts for hydraulic cylinders, valves and pumps, the proven success of the salvaging process, demonstrated by the fact that rebuilt parts usually provide several times the service life of unplated parts, has led to increasing use of new parts which are plated before they are initially placed in service.
