Metal Finishing Guide Book

2012-2013

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ALKALINE CLEANER CONTROL AND LIFE EXTENSION In the typical metal finishing process, the alkaline cleaning tanks are first in line and take the bulk of the dirt load. Whether the tanks are soak, ultrasonic, or electrocleaners, their purpose is to remove oils, grease, wax, polishing compound, particulates, and light oxides from the part surfaces. Depending on the detergent additives in these tanks, the tanks could build up surface oil, oil emulsions, suspended solids, or sludge at the bottom of the tank or any combination of these contaminant types. As with acids, the cleaning chemicals are consumed in the process of removing and preventing redeposition of the contaminants. First, there should be a procedure in place to monitor the alkaline cleaning strength of a bath. It may be as simple as measuring the pH. Typically the cleaning chemistry supplier can either do the testing or provide test kits or test methods to monitor and correct the cleaning chemistry as it ages. Second, the surface oils can be segregated and removed by a combination of surface sparging and the use of various oil skimmers available on the market. Third, the heavy particles that can settle on the bottom of the tank can be removed by bag filtration or some other simple filtration method. Finally, there are the emulsified oils and suspended solids. These are more difficult to remove by normal filtration methods. Ultrafiltration is a method that can often break the oil emulsions and remove the suspended solids without removing the active cleaning chemistry. Some of the commercially available ultrafiltration systems can handle pH from 2 to 11 and temperatures up to 160��F. One unique ultrafiltration system manufactured by Arbortech Corporation has filtration capability of a 1 to 14 pH range and temperature limits of over 200��F. Therefore, this system can easily filter hot alkaline cleaners without filter damage. By whatever ultrafiltration method used, the resulting filtered cleaning solution should have minimal loss of the cleaning chemistry and maximum removal of the suspended solids and emulsified oils such that the cleaning chemistry is ready to use again. Again, the economics of the cleaning process will drive the decision- making process. If the cleaning chemicals are inexpensive and easy to treat in wastewater treatment, and if tank life is already extended before contamination levels become excessive, then only the simplest and least expensive methods need to be used to provide acceptable cleaning chemistry maintenance. SUMMARY In conclusion, there is often a large opportunity for plating industries to reduce their costs, minimize their environmental footprint and remain competitive in their sector by various relatively simple and sometimes low- cost process changes. By developing a baseline for the energy use, chemical use, and water use for the process, a list of priority focus areas will be determined and the opportunities for cost savings will become evident. In regards to the finishing line, an essential first step is to develop a set of best practices for rinsing and rinse control for water use optimization, along with good process control for the acids and alkaline cleaners. By understanding the overall detailed costs of the metal finishing process, decisions can be made to determine where the major opportunities are and implement changes that financially benefit the bottom line. 673

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