Metal Finishing Guide Book

2013

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Table XIII. Aluminum Soak Cleaner Operating Parameters—Bath Chemistry (oz/gal) Metal Aluminum Caustic Silicate Gluconate Phosphate Borates Wetters — — 0.15-0.30 0.8-1.2 3.0-5.0 0.4-0.8 The alkalinity level of the spray cleaner may range from near neutral (approximately 8) to high pH (14). This accommodates cleaning many metals (aluminum, brass, copper alloys, steel, stainless steel, and zinc). A desired or effective chemistry lifts soils. The concentration of surfactants and wetting agents can be low since mechanical action of spraying helps to dislodge soils. Displacement of oils and grease allows them to be collected in a side tank and removed by skimming or other separation device. This extends service life of the cleaner. It's a real benefit considering the heavy oil loading some incoming parts have. Removing displaced soils also prevents them from being sprayed on to parts that are to be cleaned. Water hardness conditioners in the spray cleaner are invaluable to prevent nozzle pluggage. Typical operating conditions shown in Tables IX and X. Mass Finishing This method helps with off-line capabilities. Cleaning, deburring, descaling, and burnishing are surface improvements accomplished by mass finishing. The base metal is conditioned prior to additional surface finishing. Critical areas are rounded out and burnishing can result in low rms value or high luster. The process combines mechanical energy and chemical action. The mechanical contribution is by tumbling in horizontal or oblique barrels or by using vibratory bowls. Specially blended chemicals are added in dilute-liquid form or lowconcentration powders. They wet and react with the surface of parts, allowing other parts or special media (e.g., plastic, ceramic, or stone) to work on the parts. (See Table XI.) Mass finishing is especially helpful to seal porosity of aluminum and zinc before transfer to the plating line. If parts are to be mass finished or if this is a feasible option, trial evaluations are recommended to determine best suited equipment, media, and optimum: media-to-parts ratio, flow rates, and cycle times. Table XIV. Alkaline Aluminum Etchant Operating Parameters—Bath Chemistry (oz/gal) Caustic 6-7 Complexor Conditioner Wetting Agent Defoamer 3-5 2-4 0.006-0.009 0.02-0.05 Table XV. Acidic Aluminum Etchant Operating Parameters Bath Chemistry (% v/v) Sulfuric Acid 5-7 Phosphoric Acid Complexor Wetting Agent 2-5 2.5-4.5a 0.006-0.009 a oz/gal Table XVI. Aluminum Desmutting Chemistry Depends on Alloying Elements Alloy Type Sulfuric Acid Nitric Acid Fluorides High silicon 10-25% v/v — 3.0-8.0 oz/gal — 15-25% v/v 1-3 oz/gal 10-25% v/v — — High copper Low alloys Note: Volume balance as water. Ammonium bifluoride suggested source of fluorides. 147

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