Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 14 of 331

5.Composites: Mixtures of metals with other materials. CLEANER SELECTION AND OPERATING PARAMETERS Cleaner selection is codependent on the other aqueous cleaning factors discussed. Table I provides alkaline cleaner characteristics and the typical choice relationship. POSTCLEANING RINSING STAGES The purpose of rinsing is to remove or flush the remaining peptized soil, to neu- tralize the remaining alkaline salts, and to maintain a wet surface prior to entering the subsequent chemical stage. Initial rinsewater quality is very important as the part or product in question will only be as clean as the water is pure. Deion- ized or reverse osmosis treated water is used where a high degree of surface clean- liness is required. Part configuration, drain vestibules, and adequate time are important con- siderations in reducing overall water usage. Table II shows typical cleaner dragout that can be expected from various part configurations. Many improvements in rinse stages have been tested and employed to reduce the volumes of effluent to be treated. A common practice is the backflow rinses in a conventional five or more stage pretreatment system. The process is as follows: 1. Clean 2. Rinse 3. Phosphate 4. Rinse 5. Seal Finishing system organizations have introduced unique design improvements to utilize rinsewater more efficiently and to assist in maintaining rinse cleanli- ness. Counterflow rinsing provides the cleanest possible water as the last contact with the part, and allows for multiple use rinse effectiveness. The major control mechanisms for rinse tanks remain the control of pH and total dissolved solids (TDS). These tools have been automatically incorporated into washers, which allow sensing devices to either increase the overflow rate or reduce or drop TDS by automatic draining, thus maintaining consistency in water quality without regard to part shape, drag-in or drag-out. 13

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