Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 29 of 331

The deionized rinse is the most widely used and successful over the widest range of paint coatings. Deionized rinses leave the least amount of potential contam- inants, which may reduce the life of the coating. The remaining two types of seal rinses fall into the nonchrome type or chromic acid type. Most honest seal rinse suppliers will claim that the chromic acid type of seal rinses provide the highest salt spray resistance over the widest range of paint formulations. Claims that some of the reactive nonchrome seal rinses are better than chrome can be agreed to with certain specific paint chemistries. The only effective way the metal finisher can protect himself from claims is through a qualified controlled evaluation of the substrate through the existing system and paint and then alternating the seal rinse choices. Testing and subsequent pro- duction duplication is the only way. Should your part quality dictate the use of a compounded chromic acid type of seal rinse, there are two methods for controlling the effluent (classified as a haz- ardous waste): conventional chemical reduction and proprietary ion exchange. The conventional reduction method reduces the total volume of waste.There are many different existing technologies and other metals and organics can be handled. The ion exchange method is simple, creates no hazardous waste, and re- turns all the water to process or drain. REFERENCES 1. "How to dramatically reduce your chemical and effluent costs with dry steam," by M. Compton. Canadian Finishing & Coatings Manufacturing. *Dry steam is defined as steam whose moisture content is so low that it evap- orates instantly. Dry steam is created in a steam generator by pressure. The amount of pressure the steam is under is directly proportional to the temperature of the steam. As the pressure inside the vessel increases, the temperature of the steam increases as well. In a typical steam boiler, the temperature of the steam is 328 degrees F whenthe pressure inside the boil- er is 85 psi. With the use of a dry steam generator, at these conditions, the amount of water and chemical mix used is only one gallon per minute. Un- der these conditions, time tests have shown that approximately 20 ft squared/minute of metal surface can be cleaned and phosphatized with dry steam. 28

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