Adherence of Paint on Chromium-Plated Zinc Die Castings 630169

After several alternative procedures were investigated for preparing chromium-plated zinc die castings for painting, one procedure proved best for contaminated chromium surfaces. This procedure included six steps: (1) alkaline spray cleaning, (2) electrolytic alkaline cleaning, (3) rinsing with high-purity water with a specific resistance of 500,000-700,000 ohm-cm, (4) immersing in chromic acid solution (0.05 oz/gal) at 150 F for 2 minutes, or treating cathodically in 0.7 oz/gal of sodium dichromate with a current density of 0.05 amp/sq ft for 30-60 sec, (5) rinsing with high-purity water, (6) forced-air drying with filtered air at 15 psi. Good adherence was obtained by following these procedures and painting with a single coat of acrylic or alkyd-resin paint. Other preparation procedures resulted in inferior paint adherence.


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