Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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coat in a dry, electrostatic spray followed by 350O F oven bake. Powder coats are not suitable for all parts. They work best on parts that have an open shape with few or shallow recessed areas and can be susceptible to the Faraday Cage Effect. This is com- monly seen with any electrostatic or electrolytic operation (including plating) and prevents deposition in deep recesses. Consequently, it is difficult to powder coat the inside surfaces of many parts. Electrophoretic Liquid Lacquers These products are not new but they are just now coming into popular use. They are liquid lacquers used as an electrophoretic immersion at the end of the plating line followed by an oven cure. Though not commonly used on parts that are high- lighted after coloring they do find use as a clear sealant over a solid black finish such as a black nickel. In this setting the part is racked and taken through the plating operation then black nickel and electrophoretic lacquer. Paste Wax and Oil Finishes Some parts do not require a permanent antique finish but are designed to allow the surface to age naturally in service. For example brass hand rails, building fascia panels, elevator panels, and other parts can be initially sealed with a temporary pro- tective film such as paste wax or oil. When installed they will be handled during nor- mal use and constantly "burnished" by this contact. Over time they will develop a nat- ural, soft patina that will ultimately be permanent because it is being constantly developed. TYPICAL PROCESS CYCLES Solid Copper or Brass (For example, a soldered light fixture assembly.) 1. Mild alkaline soak clean: 8-10 oz/gal mix; 150° tation. F; 4-6 minute soak with air agi- 2. Dragout rinse: nonflowing rinse to remove most of the cleaner residues. 3. Overflow rinse: treated by ion exchange. 4. Mild acid tarnish remover: 10% sulfuric acid; room temperature; 1-3 min- utes. 5. Overflow rinse: treated by ion exchange. 6. Oxidize: blacken or brown in room-temperature oxidizing solution; 1-3 minutes. 7. Overflow rinse: treated by ion exchange. 8. Final rinse: deionize water to minimize water staining during drying. Steel Stamping (For example, a rack-processed stamped lamp base.) 1. Heavy-duty alkaline soak clean: 10-12 oz/gal mix; 170-180° soak. 2. Alkaline electroclean; 12 oz/gal of high caustic formula, 160° ic current; 100-150 A/ft2 ; 2-4 minutes. 3. Rinse: clean tap water; 20 seconds. 4. Rinse: clean tap water; 20 seconds. 5. Acid pickle: hydrochloric acid; 30-40% by volume; room temperature; 2 minutes. 6. Rinse: clean tap water; 20 seconds. 7. Rinse: clean tap water; 20 seconds. 8. Copper strike: 75-120° 9. Brass plate: 90° F; 15-20 A/ft2 10. Rinse: clean tap water; 20 seconds. 390 ; 2 minutes. F; 6-10 V; 15-20 A/ft2 ; 15-30 minutes. F; 4-6 minute F; 6-12 V anod-

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