Metal Finishing Guide Book

2013

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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. High Strength Alloy Steels These materials retain a Rockwell C hardness of 38 or higher. Hydrogen embrittlement can be avoided by using the acid dip as mentioned previously. Baking at 50 to 75°F (10-24°C) below the tempering temperature, 800°F maximum (427°C) is recommended. Stainless Steel Standard soak and electrocleaning followed by acid dip or pickle is not sufficient if the material is to be plated. Surface passivity must be overcome. This is accomplished by a treatment in the Wood's nickel strike solution. (See Tables XX and XXI.) Beryllium Copper This copper alloy typically contains 2% beryllium with 0.25% cobalt and 0.36% nickel. Surface preparation cycle: 1. Alkaline soak clean to remove organic soils. Mild tarnish is acceptable. 2. Electroclean in a specially buffered blend (refer to suggested formula for copper), having moderate caustic at 20-40 A/ft2, anodic. 3. Activate in a mildly etching solution composed of peroxy derivatives, persulfates, or sulfuric acid with fluoride. Ex. 2% v/v of sulfuric acid and 4 oz/gal ammonium persulfate. 4. Rinse well,. proceed to plating bath. Cobalt Surface preparation similar to stainless steel. The Wood's nickel strike is very important to develop a sufficiently active surface to accept subsequent plated deposits. LEADED BRASS (0.35-4.00% LEAD) Red and Yellow Brasses Commercial Bronzes Surface preparation cycle: 1. Soak or ultrasonically clean to remove buffing and polishing compounds. 20-40 KHz/gal. Highly wetted, with solvents, soap optional. 2. Secondary soak clean. Moderate alkalinity, containing surfactants, some inhibition preferred. 3. Electroclean at 10-30 A/ft2, anodic. Buffered blend similar to application on copper alloys. 4. Activate. Sulfuric acid type containing fluorides, essential to dissolve lead smuts. 5. Rinse well, proceed to plating bath. Bright Dipping Brass 1. Mild to moderately alkaline soak cleaner. 2. 5% v/v sulfuric acid dip. Neutralizes and conditions the surface. 3. Chemically polish in either a peroxide-type or sulfuric acid/iron salts blend. Both solutions are wetted and specially inhibited. 152

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