Metal Finishing Guide Book


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Page 60 of 843

Table I. Current Density Ranges for Electrocleaning Substrate Current Density (A/ft2) Ferrous metals Copper metal and plate Brass alloys Zinc die castings Nickel plate Lead, lead alloys, and pewter 40-150 25-50 15-40 10-30 20-30 10-30 the desired results. Each metal is electrocleaned using a different current density range. The ranges for the particular metals are given in Table I. Cathodic Pickling Cathodic electrolytic pickling in an electroplating line is usually confined to the pickling of ferrous metals and activation of nickel-plated surfaces. Electrolytic pickling is another form of electrocleaning, but on the acid side. The principal functions of an acid solution in an electroplating cycle are removal of rust, scale, tarnish, light oxides, metal slivers, and in some cases, smut. Electrolytic pickling is usually restricted to difficult tasks where the soils are quite heavy or where the allotted pickling time is short. The pickling action, in an electrolytic process, is assisted by the evolution of hydrogen or oxygen on the work. These gases aid in prying off scale during pickling. Electrolytic pickling's advantages over chemical pickling can be stated as follows: 57

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