Metal Finishing Guide Book

2012-2013

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Table III. Miscellaneous Requirements and Properties Acid Chloride Zinc Alkaline Noncyanide Zinc Cyanide Zinc Anode polarization Seldom Conductivity of the bath solution (higher conductivity lowers energy costs) Yes Yes Excellent LC-Poor, HC-Good Fair Agitation in rack operations Required Not required Not required Heating or cooling required Yes Yes Yes Filtration required Yes Yes Not normally pH adjustment required Yes No No Purifier needed to treat impurities No Yes Yes Chromate receptivity Good LC-fair, HC-excellent Excellent Waste treatment Simple Simple Complex Iron treatment by oxidation1 Yes No No LC, low chloride; HC, high chloride. 1 30 - 35% Hydrogen peroxide is most commonly used. When necessary, 400 ml/1,000 gal (~100 ml/1,000L) of bath is a typical addition. The addition should be diluted with water to a 10% solution before adding. Potassium permanganate may also be used; however this generates a greater amount of sludge, possibly creating filtration problems and iron precipitation/filtration problems. Table IV. Properties of Zinc Baths Acid Chloride Alkaline NonCyanide Zinc Cyanide Zinc LC Ductility1 at higher thicknesses HC LCN MCN HCN 1 3���4 4 4 4 1 (>0.5 mil) Bath efficiencies 95-97% Star-dusting Yes2 70-75% 70-95% 65-70% 70-75% No No No No 4���55 Plate distribution3 14 2���3 5 4���55 Commercial plating thickness requirements 5 2 4 2 2���3 75-70% No 4���55 3���4 HC, high chloride; LC, low chloride; LCN, low cyanide; MCN, mid cyanide; HCN, high cyanide. 1 Ductility is the ability of a materiality to be bent, molded, or formed without cracking, peeling, and/or chipping. 2 Newer chloride zinc systems are available which minimize or eliminate star-dusting. 3 Distribution or throwing power is the ratio of the amount of zinc deposited in the high current density to the amount of zinc deposited in the low current density. 4 Newer systems are available in barrel applications that exhibit distribution properties equal to or better than that of Low Chemistry Alkaline Non-Cyanide Zinc plating. 5 The plate distribution improves as the cyanide to zinc ratio increases. corrosive effect on tissue. Remember to follow all OSHA requirements, checking appropriate material safety data sheets prior to the handling and/or use of all chemicals, whether general or proprietary in nature. OTHER CONSIDERATIONS Operational requirements for the three types of baths are presented in Table III. Table IV gives a comparison of deposit properties. Troubleshooting is addressed in Table V. 369

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