Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 436 of 707

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 Auto Maker GM 3044 Clear/Blue/Black Yellow-Iridescent Ford WSS-M12P17B1/B3 Clear/Silver white Clear/Silver white Daimler Chrysler PS 1207 - R Iridescent—Rack Iridescent—Barrel Irridescent—Rack No sealer Iridescent—Barrel 200 160 120 100 No sealer 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. 96 72 384 360 No Yes May be specified 120O C/4 hrs 120 120 240 360 150O 150O C/1 hr C/1 hr Corrosion Hrs—Red Corrosion Heat Treatment Required May be specified Conditions Fig. 6. Cr(3) passivation surpasses requirements for Ford. 435 µ

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