Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 273 of 707

Table III. Miscellaneous Requirements and Properties Acid Chloride Zinc Anode polarization Conductivity of the bath solution (higher conductivity lowers energy costs) Agitation in rack operations Heating or cooling required Filtration required pH adjustment required Purifier needed to treat impurities Chromate receptivity Waste treatment Iron treatment by oxidation1 LC, low chloride; HC, high chloride. 1 Seldom Excellent Required Yes Yes Yes No Good Simple Yes Alkaline Non- cyanide Zinc Yes LC-Poor, HC-Good Not required Yes Yes No Yes Cyanide Zinc Yes Fair Not required Yes Not normally No Yes LC-fair, HC-excellent Excellent Simple No Complex No 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 LC Ductility1 at higher thicknesses Bath efficiencies Star-dusting Plate distribution3 Commercial plating thickness requirements 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. 2Newer chloride zinc systems are available which minimize or eliminate star-dusting. 3 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. 4 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 chem- icals, 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. 272 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. 1 (>0.5 mil) 95-97% Yes2 14 5 1 70-75% No 2–3 2 Alkaline Non- Cyanide Zinc HC 3–4 70-95% No 5 4 LCN 4 65-70% No 4–55 2 2–3 Cyanide Zinc MCN 4 70-75% No 4–55 3–4 HCN 4 75-70% No 4–55

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