Metal Finishing Guide Book

2013

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Table VIII. Operating Parameters for Electropolishing Different Metals and Alloys Temperature Metal/Alloy Aluminum Copper Nickel Stainless steels Carbon steels Titanium ° F 150-200 65-160 85-125 110-190 110-140 60-105 Anodic Current Density (A/ft2) 10-60 20-300 100-200 50-500 100-300 80-500 ° C 66-93 18-71 29-52 43-88 43-60 16-40 Voltage 10-30 6-18 10-18 6-18 10-18 3-10 Inhibitors are special amines, substituted ureas, and glycol-based organic compounds. Wetters may be anionic or nonionic types. Some wetters and inhibitors provide a filming action to inhibit attack on the base metal. Good rinsing is required to remove any films, or in a double cleaning cycle use an inhibited/wetted acid as the first acid, followed by a simple mineral acid as the second acid. Some modifications are made to cathodically remove heavy scales and rust. Acid dipped or pickled parts should be free of any organic soils, rust, scale, and smuts. This is the last process treatment bath before plating, painting, chromating, or final topcoat application. ADDITIONAL CLEANING OPERATIONS Electropolishing This is an electrolytic process by which the substrate's surface can be improved using a specific solution. Burrs, belt lines, scratches, scales, and other imperfections anywhere on the surface that is immersed and anodically charged will be polished and refined. Electropolishing is current-density specific. In this regard surface improvement occurs more readily than by mass finishing. A wide variety of common metals and alloys are successfully electropolished, Table IX. Liquid and Powder Spray Cleaner Operating Parameters Temperature Cleaner Type Liquid Powder a 22.5-45 g/L Concentration Range 2-5% v/v 3-6 oz/gala ° F 100-160 100-160 ° C 38-71 38-71 Time (min) 0.5-3 0.5-3 Agitation 15-35 psi 15-35 psi Table X. Spray Cleaner Operating Parameters—Bath Chemistry (oz/gal) Metal Caustic Silicate Complexor Phosphate Glycols Aluminum — 0.05-0.1 0.08-0.12 0.10-0.17 0.10-0.14 Steel 0.4-0.8 0.3-0.6 0.10-0.14 0.10-0.17 0.10-0.14 Stainless steel 0.4-0.8 0.3-0.6 0.10-0.14 0.10-0.17 0.10-0.14 Brass 0.0-0.06 0.3-0.6 0.12-0.17 0.2-0.4 0.10-0.14 Copper 0.0-0.17 0.15-0.3 0.12-0.17 0.2-0.4 0.10-0.14 Zinc — 0.3-0.6 0.12-0.17 0.1-0.2 0.10-0.14 White metal — 0.3-0.6 0.12-0.17 0.1-0.2 0.10-0.14 The cleanliness criteria are the same as described in the soak cleaning section. Wetters 0.06-0.09 0.06-0.09 0.06-0.09 0.06-0.09 0.06-0.09 0.06-0.09 0.06-0.09 145

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