Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 139 of 331

$100 per gallon for these coatings. Considering this cost, it is crucial that the coat- ing is applied to the product as efficiently as possible. With a conventional air spray gun, roughly 15 to 40% of the paint sprayed from the gun is applied on the part. This is known as transfer efficiency. The remaining 60 to 85% is lost in the filters or left as overspray on the floor and walls. Conventional HVLP guns are more efficient than conventional air spray guns. HVLP guns will typically yield transfer efficiencies of 30-60%. Electrostatic guns can obtain even greater transfer efficiency. An electrostatic air spray gun is normally in the 40 to 80% transfer efficiency range. This means you can coat twice as many parts with an electrostatic air spray gun, compared to a nonelec- trostatic air spray gun given the same quantity of paint. As with nonelectrostatic guns, HVLP technology shows significant improvement in transfer efficiency.The same holds true with electrostatic HVLP technology as well. In some cases, electrostatic HVLP has obtained efficiencies as high as 90%. Typically, cost justification is obtained from paint cost savings alone. Its typical- ly enough to cost justify the purchase of the electrostatic applicator. Table II dis- plays the dollar figure in paint savings that can be achieved by slightly increasing transfer efficiency. VOC Reduction Another savings area is emission reduction. With federal and local regulations be- coming tougher by the day, VOC (volatile organic compound) emissions has become a major issue. We are constantly trying o reduce the amount of VOCs emitted into the atmosphere. By increasing transfer efficiency you lower VOC emission. (See Fig. 8.) This is a result of more paint being applied on the part and less paint being deposited into the booth filters or atmosphere. 138

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