Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 127 of 707

Table XIII. Aluminum Soak Cleaner Operating Parameters—Bath Chemistry (oz/gal) Metal Aluminum Caustic — Silicate — Gluconate 0.15-0.30 Phosphate 0.8-1.2 Borates 3.0-5.0 Wetters 0.4-0.8 oils and grease allows them to be collected in a side tank and removed by skim- ming 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 pre- vent 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 con- tribution is by tumbling in horizontal or oblique barrels or by using vibratory bowls. Specially blended chemicals are added in dilute-liquid form or low-con- centration powders. They wet and react with the surface of parts, allowing oth- er 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. SURFACE PREPARATION FOR SPECIFIC METALS & ALLOYS The selection of specific working solutions should be determined by first eval- uating candidate baths to meet or exceed requirements while adhering to cycle and handling limitations. Information is given for the more commonly encoun- tered metals and alloys. Table XIV. Alkaline Aluminum Etchant Operating Parameters—Bath Chemistry (oz/gal) Caustic 6-7 Complexor 3-5 Conditioner 2-4 Phosphoric Acid 2-5 Wetting Agent 0.006-0.009 Complexor 2.5-4.5a Defoamer 0.02-0.05 Table XV. Acidic Aluminum Etchant Operating Parameters Bath Chemistry (% v/v) Sulfuric Acid 5-7 a oz/gal Table XVI. Aluminum Desmutting Chemistry Depends on Alloying Elements Alloy Type High silicon High copper Low alloys Sulfuric Acid 10-25% v/v — 10-25% v/v 126 Nitric Acid — 15-25% v/v — Note: Volume balance as water. Ammonium bifluoride suggested source of fluorides. Fluorides 3.0-8.0 oz/gal 1-3 oz/gal — Wetting Agent 0.006-0.009

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