Metal Finishing Guide Book


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environmental controls WASTEWATER TREATMENT SYSTEMS FOR FINISHING OPERATIONS BY ALAN MONKEN One of the most common growing areas of concern in organic finishing operations is waste disposal. Where wastewater discharge into municipal sewers was once common place, greater and greater restrictions are being placed on any effluent from manufacturing operations, not only for obvious problem areas such as plating operations, but also for water once considered innocuous, such as spray washer rinse stage overflow. In some situations, it is possible to conserve water usage/discharge with filtration systems; it is also possible to find waste haulers to remove contaminated water from the plant. However, both can be costly and neither is a long-term answer to the ever-increasing regulations governing disposal of industrial waste. The best solution is to pursue installation of an in-plant treatment system, putting the control and reduction of contaminants in any effluent directly in the hands of the manufacturer. Before doing so, however, it is necessary to determine what types of materials may be entering your waste stream and the methods available to treat/remove them. SOURCES AND TYPES OF WASTE CONTAMINANTS The type of operation at each individual finishing shop largely determines the types of materials that will enter the waste stream, and the type of treatment that will be required for the resultant waste influent. The types of operations typically found include metal forming processes such as drawing, stamping, and bending, chemical treatment processes such as plating and phosphatizing, and coating processes such as painting. Metal Forming Operations In metal fabrication there are a number of processes that may been countered. One of the most common is drawing, the process by which sheet metal stock (or other material) is formed in a press into a cup like or box like shape. During this process lubricants known as drawing compounds are normally required to prevent scoring and damage from the metal-to-metal contact between the stock metal and the die.Coolants may be required for this process due to the heat of friction produced, which can reduce die life. These lubricants and coolants are normally oil-based compounds, either "natural" (i.e., petroleum or animal-fat derived) or synthetic. In addition, metal can be drilled, cut, forged, stamped, or cast, each of which may require additional coolants or lubricants. While these coolant and lubrication systems are typically closed (i.e., not directly tied to the wastewater stream), residue from these materials normally must be removed from the work in process. Paint Pretreatment Operations In metal fabrication operations the normal sequence of events in production is formation of raw metal stock into component parts, which are assembled and, most typically, painted. After the forming process it is necessary to go through several pretreatment steps prior to painting, including chemical or physical treatment to remove rust or other surface defects (such as mill scale) resulting 665

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