Metal Finishing Guide Book


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Table III. Electrocleaner Operating Parameters Current Density, A/ft2 Voltage Base Metal Cleaning Type Rack Barrel Rack Barrel Steel Anodic 50-100 10-20 4-8 8-2 Time (min) 1-5 Stainless steel Anodic 50-100 10-20 4-8 8-12 1-5 Brassa Anodic 15-30 5-10 6-9 9-13 1-3 Coppera Anodic 20-50 5-15 6-9 9-13 1-4 Zinc Anodic 10-20 5-10 6-9 9-13 1-4 White metal Cathodic 10-20 5-10 2-4 5-7 1-2 a Polished brass and copper may also be cathodically cleaned as per the speciļ¬cations given for white metal. function should be effective removal of metallic fines and oxide deposits. Oil and grease removal should be secondary since an effective soak cleaner removes these soils as a primary function. The electrocleaner concentrate can be either liquid or powder. The main ingredient is either sodium or potassium hydroxide as the source of solution conductivity. Desmutters, descalers, and water hardness conditioners are also present. Buffers and inhibitors control the surface action, moderate pH, and protect the base metal against the harmful effects of the process itself and buildup of solution bearing contaminants. Wetters and surfactants provide secondary cleaning to remove organic soils. They also form a light foam blanket to significantly suppress the effects of corrosive fumes during electrolyzing. The bath may also contain reducing agents to control certain contaminants such as hexavalent chromium. 2. Cathodic electrocleaning generates twice the volume of gas bubbles versus anodic electrocleaning. The scrubbing action on parts is essentially doubled. This method is preferred for highly buffed and polished nonferrous metals such as brass, other copper alloys, and white metal. It prevents oxidation, tarnish, and surface attack, which would mar or destroy the desired surface brightness, leveling, and luster. 3. Periodic reverse (PR) is a specialized treatment for descaling and derusting steel. This procedure uses a switch on the rectifier (automatic or manual) that changes polarity on the work between anodic and cathodic in specific time cycles for optimum cleaning. Parts usually exit the process bath anodic, deplating any metallic smuts deposited in the previous highly scrubbing cathodic mode. This oxidation/ reduction/oxidation surface treatment softens scales, rust, and oxides, permitting chelates and complexors to dissolve them. These electrocleaners are also referred to as alkaline descalers. 4. Combination soak/electrocleaners meet the requirements of soak and electrocleaning in one step, one tank, or in separate process tanks. In many applications this provides three advantages: simplifies prod142

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