Transfer Efficiency Study Revisited

Question:

work for a spray equipment supplier and have 16 years in the industry. My comment regards the questions about the transfer efficiency study that the student had in the February 2004 Painting Clinic (www.pfonline.com/articles/clinics/0204cl_paint5.html). It is false in question two to say that lowering the voltage on any applicator increases transfer efficiency. Whether it is a gun or rotary bell or disk, lowering the voltage will decrease the transfer efficiency. Lowering the voltage will increase penetration into recessed areas (Faraday Cage), but this will lower your overall transfer efficiency.

Correction to answer number three—Nonpolar solvents are often referred to as “dead” solvents. Polar solvents are referred to as “hot” solvents. A nonpolar solvent such as Xylene or Toluene has a higher resistivity on a resistivity meter than a polar solvent such as Acetone or MEK. Ketones are very low in resistivity. They often will cause applicators to short out or have much lower tip voltage thus causing a decrease in transfer efficiency. This offers another example of why decreasing paint resistivity often increases transfer efficiency and why slower drying solvents result in higher transfer efficiency. E.G.

Answer:

Thank you E. G. for clarifying and correcting the questions from P. P and my answers. About question two, P.P.’s statement didn’t sound right. However, since I didn’t have good references to back me up, I said I wasn’t sure. About question three, thanks for clarifying the relationships between polar solvents, nonpolar solvents and their resistivities. You sure can make a difficult subject sound easy.