Electroplating design considerations

Satisfactory service of an electroplated article is not achieved, however, unless adequate care is given to the choice of deposited metal, its thickness, the technique of application, and the design of the article. The choice of metal deposit is primarily determined by the basis metal, i.e. the metal from which the article is made, and the actual conditions to which the plated article will be subjected during service. In addition, however, attractive appearance and reasonable cost are also important considerations. 

It will be seen that the design of articles to be electroplated can have a considerable effect on the corrosion resistance of the electrodeposited coating. The chief effects are the result of variations in deposit thickness, but also important are features which can influence the adhesion, porosity and physical properties of the deposit. Good design will also avoid features of the plated article capable of trapping liquids or solid contaminants which might cause more rapid corrosion. 

Anodes. There are two types of anodes soluble and insoluble. Most electroplating baths use one or the other specifically however, a few baths use either or both. Chromic acid plating baths use insoluble anodes alkaline zinc cyanide baths use both noncyanide alkaline zincs may use either. Soluble anodes are designed to dissolve efficiendy with current flow and preferably, not to dissolve when the system is idle. A plating solution having the anode efficiency close to the cathode efficiency provides a balanced process that has fewer control problems and is less cosdy. If the anode efficiency is much greater than the cathode efficiency and there are only small solution losses, the dissolved metal concentration rises until at some time the bath has to be diluted back or the excess metal has to be reduced by some other means. If the anode efficiency is less than the cathode efficiency, the dissolved metal decreases, pH decreases, and eventually metal salt additions and other solution corrections are required. Based on the cost of metal, it is usually considerably more economical to plate from the anode rather than add metal salt. Copper cyanide, for example, costs about twice as much to add than to dissolve a comparable amount of copper anode. Additionally, the anion added with the metal salt may build up in the plating solution. 

---