September 19, 2012

Electroplating Process

Basic Process of Electroplating

Electroplating is the deposition of a metal onto a metallic surface from a solution by Electrolyses process. It is used for purpose of decoration and protection of the metal. Metals commonly use to plate surface are silver, chromium, cadmium, zinc, gold and copper. In the case of copper platting for example electroplating takes place by means of the reaction of Cu++ + 2e <====> Cu. Cu++ in this equation represent an ion that is carried to the metal surface to be plated, known as the CATHODE, from the source of the metal being plated, known as ANODE. The ion forced to the cathode by an external source such as a battery. The electrolytic solution is a salt of the metal being plated; in the case of copper plating. It is copper sulfate, CuSO4.5 H2O.

The appearance, adhesion, porosity, and protection value of electroplated coatings depends on several things, including the type of base metal be plated, the preparation of the metal to be plating, and the electrodepositing process itself.

Base Metal
It is not possible to apply high quality coatings to metals of poor quality. The composition of the base metal is usually known and controlled. The condition of the surface, including the degree and nature of the polishing processes, may also have a direct bearing on the characteristic and porosity of the coating.

Preparation for Plating
It is necessary to have the base metal surface chemically clean in order to secure good adhesion of deposits. The preparation usually involve cleaning that is, removal of grease and foreign particles and picking in the case of steel, or remove oxides or other compounds, and is some instances, to etch the surface. Because of a thin, natural oxide film, aluminum alloys do not usually respond to the cleaning and surface preparation treatments employed for other metals; special techniques must be used for such alloys.

In the plating process many variables are involved that are subject to control. The composition and temperature of the electrolytic bath itself must be closely maintained. Agitation of the bath often permits an increase in current density. Filtration, either continuous of intermittent, is often used to keep the solution free of suspended matter. The average current density should be kept within desired limits for the sake of uniformity in thickness and quality of coating.

Finally, the anodes should ordinarily be of such composition and structure as to maintain the metal concentration and the pH. Where insoluble anodes are used, the metal content is maintained by replenishment.
Most commercial plating with potentials of conducted with motor generator sets, usually with potentials of from 6 to 12 volts, and with current outputs, depending on the area of work to plated and the current density.

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