Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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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 ° C 66-93 18-71 29-52 43-88 43-60 16-40 Anodic Current Density (A/ft2 ) 10-60 20-300 100-200 50-500 100-300 80-500 Voltage 10-30 6-18 10-18 6-18 10-18 3-10 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 imperfec- tions anywhere on the surface that is immersed and anodically charged will be pol- ished 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, especially the nickel-rich 300 series stainless steels. The electrolyte is typically a mixture of min- eral acids. Parts are predominantly racked. The ranges in the operating parameters shown in Table VIII reflect the use of more than one type of electrolyte. Table IX. Liquid and Powder Spray Cleaner Operating Parameters Temperature Cleaner Type Concentration Range Liquid Powder 2-5% v/v 3-6 oz/gala a 22.5-45 g/L Table X. Spray Cleaner Operating Parameters—Bath Chemistry (oz/gal) Metal Aluminum Steel Stainless steel Brass Copper Zinc White metal Caustic — 0.4-0.8 0.4-0.8 0.0-0.06 0.0-0.17 — — 0.15-0.3 0.3-0.6 0.3-0.6 0.08-0.12 0.10-0.14 0.10-0.14 0.12-0.17 0.12-0.17 0.12-0.17 0.12-0.17 0.10-0.17 0.10-0.17 0.10-0.17 0.2-0.4 0.2-0.4 0.1-0.2 0.1-0.2 Silicate Complexor Phosphate Glycols Wetters 0.05-0.1 0.3-0.6 0.3-0.6 0.3-0.6 ° F 100-160 100-160 ° C 38-71 38-71 Time (min) Agitation 0.5-3 0.5-3 15-35 psi 15-35 psi 0.10-0.14 0.06-0.09 0.10-0.14 0.06-0.09 0.10-0.14 0.06-0.09 0.10-0.14 0.06-0.09 0.10-0.14 0.06-0.09 0.10-0.14 0.06-0.09 0.10-0.14 0.06-0.09 The cleanliness criteria are the same as described in the soak cleaning section. 124

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