Aluminum racks are preferred for plating aluminum alloys. It is recommended that 1100 alloy be used for the spines and 2024 alloys for the contacts. By increasing the cross sectional area of the spines by about 40%, a conductance equal of that of a copper rack is obtained. Where contact marks are not important, regular phosphor-bronze contact may be used. When phosphor-bronze contacts are used, however, the area adjacent to the contact may develop a small blister as a result of galvanic action in the zinc immersion bath. When nitric-hydrofluoric acids etch is used for conditioning, aluminum contacts should be used.
When aluminum is employed for the plating racks, the various deposits may be stripped from these racks by concentrated nitric acid of by an anodic treatment in 60% sulfuric acid solution. The thin oxide film remaining from the anodic treatment can be removed with light caustic acids.
Rinsing
Effective rinsing should follow every step in the plating procedure. The rinses must be reasonably clean and the rinsing thorough in order to prevent contamination of succeeding solutions. A combination of dip and spray rinsing is good yet economical. Since the zinc immersion solution is rather viscous. The subsequent rinsing operation is very important. A double rinse is needed to remove all of the zincates solution, and two combination "dip and rinse" rinses would be desirable.
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