Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 136 of 331

Fig. 7. Typical bell-type installation. With automatic applicators such a rotary atomizers, a ring of probes (6-8) is placed around the applicator a few inches back and away from the rotary bell. This config- uration is often referred to as a "Copes" ring. Many U.S. automotive assembly plants have switched to waterborne basecoats and the Copes bells have become widely accepted in the automotive market. Utilizing Copes technology, color changes in the ten-sec- ond range can still be achieved. Unfortunately, of the three common methods of spraying waterbornes electro- statically, the external or indirect charging method is the least efficient. Voltage blocks and isolated systems have been proven to provide higher transfer efficiencies. Voltage Blocks In recent years, the application of waterborne coatings has become simpler and safer with the development of voltage blocking devices. Voltage blocking devices isolate the spray applicators from the grounded fluid supply. This prevents the high voltage from following the conductive path through the fluid lines back to the ground fluid supply and grounding (shorting) out the system high voltage. These devices can be used to feed both manual and automatic spray applicators. In a handgun situation, only one applicator can be fed from a single voltage block- ing device. Where as with an automatic applicator the voltage blocking device can feed multiple applications.This is due to the fact that any and all applicators will be charged back through their fluid lines when connected to one blocking device. Voltage blocking devices eliminate the need for safety cages and interlocks and protect the operator from coming in contact with a charged fluid supply. This elim- inates the need for isolation stands and the isolation of the fluid supply from ground. It is now a grounded fluid supply. This can lead to a significant amount of savings in floor space. 135

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