Metal Finishing Guide Book


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Table III. Automotive Standards 8-9 ��m of Zinc Plate with Hexavalent Chrome-Free Passivation and Sealer (NSS Test Requirements per ASTM B 117) Hrs���White Corrosion Auto Maker Hrs���Red Corrosion GM 3044 Clear/Blue/Black Yellow-Iridescent 120 120 240 360 Ford WSS-M12P17B1/B3 Clear/Silver white Clear/Silver white 96 72 384 360 Heat Treatment Required Conditions May be specified Daimler Chrysler PS 1207 - R Iridescent���Rack Iridescent���Barrel Irridescent���Rack No sealer Iridescent���Barrel No sealer 150OC/1 hr 150OC/1 hr No Yes 120OC/4 hrs May be specified 200 160 120 100 As of Aug. 2001 (Subject to change). 7. Dry (optional or as recommended) 8. Seal and/or topcoat 9. Dry PROCESS CONTROL Trivalent chromate conversion coatings are applied over acid or alkaline electroplated zinc and zinc alloys in conventional plating lines replacing existing hexavalent chrome tanks, with little or no modification to the line. Provisions for heating may be required along with proper ventilation. Postpassivation may be used in-line if it is compatible with the operation and space for extra stations is available. Organic topcoats, especially for barrel plating processes, are best applied off-line. The critical operating parameters are the chrome content, pH, and temperature. Analytical methods for trivalent chrome using spectrophotometric or simple titration techniques are commonly used and readily available. Chrome content affects the ultimate film thickness. Temperature and pH control the reaction kinetics, film strength, and adhesion. Fig. 6. Cr(3) passivation surpasses requirements for Ford. 497

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