A practical method of nickel-plating is outlined and the various processes are described by which the Packard Motor Car Co. has been successful in producing a durable coating of nickel on automobile parts in general, and the radiator shells, the rim plates and the tire-carrier plates, in particular. These are the parts of greatest exposure, and for plating them a new system of moving-cathode tanks was installed.
The three problems to which special attention was devoted were rusting, pitting and peeling. No effort was made to secure a coating of any designated depth but reliance was placed solely on the results indicated by a 24-hr. salt-spray test, which was considered to be the equivalent of 2 years' exposure to the usual weather conditions. Peeling was overcome by thoroughly cleaning the parts before plating.
New equipment was purchased and laid out in accordance with the system decided upon, namely, copper-plating, buffing and nickel-plating. The complete process comprises the six stages of (a) polishing, (b) cleaning, (c) copper-plating, (d) buffing and cleaning, (e) nickel-plating and (f) buffing. Each of these steps is described in detail.
The advantage of the moving-cathode tank is said to lie in the fact that it has a definite time-cycle and in the ease with which the current can be controlled. The saving of solution that may be effected will depend largely on the volume of production. By having all the shells pass the same anodes, compensation is obtained for the wearing away of the anodes, and the slight agitation produced has a beneficial effect on pitting.
Although informed previously that a high current-density could not be used, the current was increased from 2 to 25 amp. As the cycle is 17 min., the total current consumption is about 425 amp-min. The effect has been that more copper is deposited and more quickly; the shells also withstand from four to five times as long a test as they endured under the old method of plating. Thorough buffing is said not only to improve the resistance to rust but to improve the appearance of the plating.
In the nickel-plating process, the solutions are contained in moving-cathode tanks, similar to those used in copper-plating, and the current was increased from 2 to 11 amp. During 40 min. the shells receive 440 amp-min. of current.
Solutions are not filtered but are kept clean by controlling the acid-content; sludge settles to the bottom of the tank and gives no trouble. A final washing and buffing completes the process.
The most important rules to be observed, in order to obtain successful results, are summarized under the heads of careful polishing, thorough cleaning, plenty of copper, buffing, another cleaning, plenty of nickel and accurate control of solutions.