Metal Finishing Guide Book


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disk is used in an enclosed omega shape loop (see Fig. 7) to coat the product. Disks may be mounted stationary and tilted (up to 45°) to coat small parts of 12 in. or less, or mounted on reciprocating arms to coat parts up to 40 ft. in height but generally no wider than 4 width. The disk produces transfer efficiencies in the 80 to 95% range. WATERBORNE ELECTROSTATICS Over the last several years, government regulations on VOC emissions coming from paint application facilities, have fueled the need for coating manufacturers to reduce the amount of VOC from their coating materials. Waterborne coatings have been around for many years,but due to tougher government regulations they are rapidly gaining more and more momentum in today's finishing industry. Many of current users of solvent borne coatings will be forced to make the switch to a more compliant coating in the future. And many of these manufacturers, in an effort to utilize as much of their existing finishing equipment possible, will make the move to waterborne coatings. Although the application of these waterborne coatings is basically the same as with solvent borne coatings, many factors must be taken into consideration. Are my system's components compatible with waterborne materials? Many alloys and metals will rust and corrode over time when coming in contact with waterborne materials; therefore, you must ensure that all components such as pumps, valves, piping and the atomizer itself are constructed of materials compatible with waterborne coatings such as 316 stainless steel or Teflon. A decision must be made as to how the system will be isolated from high voltage grounding out back through the to waterborne fluid supply. Water is a good conductor of electricity, and all components that come in contact with the waterborne material will be at high voltage. This includes all atomizers, fluid supply hoses, pumps, regulators, valves,and the fluid supply itself. In today's finishing environment waterborne materials must be safely isolated. This is accomplished by: (1) complete system isolation; (2) voltage blocking device; or (3) indirect charging of the coating material. Complete System Isolation Complete system isolation is the most commonly used method of isolating high voltage from the waterborne fluid supply. This low-tech approach has been around for decades. (See Fig. 3.) In an isolated system, any components that come in contact with the waterborne material must be kept isolated from any possible grounds.The fluid supply must be enclosed in a caged area with the supply bucket, drum, or tote on an isolation stand. The gates to these cages must be equipped with safety interlocks. When an operator opens the gate to enter the cage, a pneumatically operated ground rod must shortt he systems' high voltage to ground. This ensures that the operator will not come in contact with a charged waterborne fluid supply. In addition, one of the isolation stand's legs should have a 1,050 megohm bleed resistor installed inside it and attached to earth ground so that when the high voltage is turned off the voltage can bleed off to ground in a timely manner. Despite the fact that these properly confirmed waterborne systems may have safety interlocks and bleed resistors, never assume that all of the high voltage has been discharged to ground. Before approaching any of the wetted systems components, always take a secondary ground wire and touch it to all system components to make sure that the system is fully discharged. Failure to do so could result in a painful shock to the operator. Failure to keep the entire system properly isolated from ground can result in a 190

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