Metal Finishing Guide Book

2013

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1. Moderately alkaline soak cleaner. 2. 5% v/v sulfuric acid dip. Neutralizes and conditions the surface. 3. Chemically polish in solution consisting of: hydrogen peroxide at 20-25% v/v and 0.3-0.5% v/v sulfuric acid at 90-11OF (32-43OC). Solution is wetted and specially inhibited. A golden-brown surface film must develop with minimal surface gassing to obtain desired surface polishing. 2-5 minute immersion should cover most cycle applications. 4. 5% v/v sulfuric acid dip for 10-15 seconds to dissolve the protective brown film. 5. Tarnish inhibit in dip application using either a soap (mechanical tarnish inhibit film) or a benzotriazole (active surface antioxidant). 6. Optionally lacquer (dip or electrolytic) or apply electrolytic chromate.or 1. Moderately alkaline soak cleaner. 2. 5% v/v sulfuric acid dip. Neutralizes and conditions the surface. 3. Chemically polish in 15-20% v/v sulfuric acid and 30-40% by wt of ferric sulfate at 100-140OF (38-60OC). Solution is wetted and specially inhibited. 4. Tarnish inhibit in dip application using either a soap (mechanical tarnish inhibit film) or a benzotriazole (active surface antioxidant). 5. Optionally lacquer (dip or electrolytic) or apply electrolytic chromate. If the scale is very heavy, the following mixed acid may be required. 1. Moderately alkaline soak cleaner. 2. Descale in a solution consisting of: 44% v/v of 66OBé sulfuric acid, 20% v/v of 42OBé nitric acid, balance water, containing 0.25 oz/gal of sodium chloride, 90-110OF (32-43OC). Monitor solution action to avoid etching, if a bright, polished finish is required. Descaling—Matte Finish 1. Moderately alkaline soak cleaner. 2. Immersion treatment in solution consisting of 2-3% v/v sulfuric acid and 2-4 oz/gal of sodium or ammonium persulfate, at 80-95OF (27-35OC).or 1. Moderately alkaline soak cleaner. 2. Immersion treatment in solution consisting of: 75% v/v of 85% phosphoric acid and 25% v/v of 42OBé nitric acid, 90-120OF (32-49OC). Cast Iron Standard alkaline soak clean, followed by alternate hot and cold rinsing to push solutions out of pores. Anodically electroclean in alkaline descaler. Parts exiting the electrocleaner should have a uniform light-yellow cast. Dip in 15 to 20% v/v hydrochloric acid or 5 to 10% v/v sulfuric acid to dissolve oxides, desmut, and form an active surface for plating. Control acid dip to avoid overtreatment. Cast iron has a low hydrogen overvoltage, which can reduce electroplating efficiency. Extended immersion in the acid will further reduce this efficiency. Mass finishing may be a better option to remove rust and scale. Gold and Gold Alloys Brightening 1. Alkaline soak clean. 2. Anodic treatment at 6-12 V in a solution consisting of 20 oz/gal sodium citrate and 5 oz/gal Rochelle salts, 80-90OF (27-32OC). 82

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