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by Ron Joseph
June, 2009
Transfer Efficiency
Q. We are manufacturing hydraulic cylinders based at Bangalore, India. Our products are cylindrical in surface. What can be the Std. Transfer Efficiency for these surfaces thru HVLP Guns? Also how do we calculate Transfer Efficiency?
A. There is no standard transfer efficiency (TE) for painting cylinders, or any other object. TE is a function of many parameters, such as part size, part shape, distance of the HVLP spray gun from the cylinders, atomizing air pressure, fluid pressure, painting technique, type of coating, viscosity of the coating, and more.
T.E. is calculated by measuring the weight of solid paint that deposits on the cylinders and dividing this by the weight of solid paint sprayed from the spray gun. To calculate the weight of solid paint sprayed, you first need to perform a laboratory test to determine what percentage of liquid paint contains the solids; namely the resins, pigments, extender pigments and additives. ASTM D2369 provides the details and methodology of this test.
Suppose the paint has a solids content of 52%, then if you spray 1,000 grams of liquid paint from the HVLP gun, you will in fact have sprayed 0.52 * 1,000 = 520 grams of solid paint.
The test to determine the percent weight solids of the coating must be performed on the actual paint being used. For instance, if the painter adds thinners to the paint before using it, the percentage of solids will drop.
Regards,
Ron Joseph
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