Metal Finishing Guide Book


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system is the electricity used to run the exhaust blowers. The secondary cost will be very location-dependent and is the cost of reconditioning the make-up air either by heating, cooling, or both. As noted in the plating company example referenced above, the cost to run the blower was roughly four times the cost to heat the make-up air in the upstate New York climate. If the total exhaust requirements can be reduced, then the exhaust blower will be smaller and the make-up air costs will be proportionally smaller. Table 1 shows the total costs associated with various size exhaust systems as the system size changes. Average heating-degree days in Rochester, N.Y., were used to determine the heating costs. One method used to reduce the total exhaust requirements is with automatic tank covers and variable speed fan controls within the exhaust system. If only one tank requiring exhaust is open at a time, then the exhaust system size can be reduced to handle the full required CFMs for that tank and some small additional CFMs to provide fume extraction from under the closed tank covers. Unfortunately, the best time to implement this technique is on a new plating line. Retrofitting an existing line is sometimes possible depending on the type of the line, but is likely to be more expensive than incorporating this type of system into a new line. As can be seen from Table 1, the cost savings can be significant, even if the exhaust system is reduced by only 50%. ACID CLEANERS AND ACID ETCHANT LIFE EXTENSION The starting point for extending the life of an acid bath is having good process controls for the acid bath. Without good monitoring and acid addition methodology, an acid bath can be prematurely disposed of just because the acid strength was not kept at the proper level. If an acid tank is minimally managed, such as running a tank for a month and then disposing of it with no acid additions or titrations over that time period, then the tank effectiveness is variable and unknown. This could lead to plating or finishing defects as the tank ages. If the tank, in reality, was in good condition in that time period, then disposing of the tank is a needless waste of acid and an added cost to treat the acid waste. In another direct assistance project, the New York State Pollution Prevention Institute was able to reduce a 500-ton-per-year acid waste stream to a 250-tonper-year waste stream at a savings of almost $200,000 per year. Rigorous acid management practices were used to produce these savings. Good process control means that there is a routine sampling of each acid tank for chemical analysis. On a weekly basis, and in the case of high production lines, a daily titration of the acid baths may be necessary to properly control the acid strength. Then there should be equally regular acid additions to the acid tanks based on the titration results to bring the acid levels back to their original strengths. For large operations there are systems available that do the titrations and acid additions automatically, such as Scanacon titration and acid-dosing equipment. Second, and usually less frequently, each acid tank should be measured for dissolved metal content. These two tests, titration and metal analysis, are the basic requirements for the proper function of the acid process. The main reason to dispose of an acid tank and start with a fresh chemistry is due to dissolved metal concentrations being high enough to interfere with the acid-metal reaction. Therefore, a means of extending the bath life involves either removing the dissolved metal or converting the dissolved metal to a form that no longer interferes with the acid-metal reaction. 628

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