Saturday, July 18, 2009

Electroplating Operation and Control

It will be clear from the foregoing that in its simplest form an electroplating plant consists of degreasing, etching and rinsing tanks, separate plating tanks for each metal to plated, each with appropriate and adequate supply of continuous (or be directional) electric current. The articles to be plated are fastened to wires or suspension jigs, and these are then lifted intro and out of the appropriate tanks in sequence, the times and currents being adjusted at the judgment of the operator. Many electroplating plant are indeed operated in this way. For larger scale operation it is now, however, much more common to mechanize the whole process to a greater or lesser extent. The various tank are arranged in line a common width and depth, but with length in proportion to the relative time the articles will spend in them. Overhead mechanisms lift the work from tank to tank, and driving chains progress it laterally through the plant.

Not only does this save labour, which may even be reduced only to loading and unloading the machines, but it also ensures that each article receives the predetermined treatment without human judgement. Temperatures, current, pH values, etc. are automatically controlled and centrally indicated. Such machines are costly to install and maintain, and are uneconomic unless they can be kept fully loaded, but they have high capacity and above all they produce consistent result with a small labor force. This small force is used to supervise, control and inspect the operations and to maintain quality.

Where very large number of small parts such as nuts and bolts are to be electroplated a different type of process, called barrel plating, is used. The individual parts are not wired or jigged, but are put in mass into a perforated plastic cylinder which they about half fill. A main negative contact is fitted along the axis of this cylinder, which contacts some of the articles and they in turn contact the others. Thus current is conveyed from one to another throughout the mass. Means are provided for slowly rotating the barrel, which is then handled as a unit and progressed through the various tanks. As the barrel rotates the parts come successively to the surface of the mass and become plated.