Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 596 of 707

quick test of a representative sample with filter paper in a funnel will determine the nature and amount of solids present. This test will also indicate the most suit- able filter medium. Bagging of soluble anodes will materially reduce the amount of sludge entering the plating bath. Airborne dirt from ceiling blowers, motor fans, hoists, or nearby polishing or buffing operations may fall into the plating tank and cause defective plating. Good housekeeping and maintenance will, of course, reduce dirt load and contamination of the plating solution. Prevention of deposit roughness is perhaps the foremost reason for filtering plating solutions. Better covering power with less chance of burning is also achieved with a clean bath. In addition to suspended solids, the plater also has to contend with organic and inorganic (metallic) impurities, which are introduced into the solution primarily by drag-in. If this contamination is allowed to build up, it will affect deposit appearance. Continuous or periodic purification of the solution with activated carbon and/or low-current-density electrolysis (dummying) will often remove these impurities before a shutdown of the plating line becomes necessary. The trend of Environmental Protection Agency (EPA) regulations is to severely restrict the amount of suspended solids and dissolved metal impurities in wastewater discharged to sewers and streams. To comply, plating plants have had to resort to some chemical treatment of their effluents to precipitate the metals as hydroxides. The filtration of these hydrated sludges is difficult and requires special separation equipment. Closed-loop systems, recycling, and recovery are being employed and require greater attention to filtration and purification. Most filtration systems consist of a filter chamber containing the filter media and a motor-driven pump to transfer or circulate the solution from the plating RESERVE YOUR SPACE NOW FOR 2012/13 METAL FINISHING GUIDEBOOK & DIRECTORY Call for all the details. Arnie Hoffman 847-559-0909 • Dan Ramage 847-699-8680 • David Facinelli 727-866-9647 • 595

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