Transfer Efficiency And Paint Spray Distribution

Q. Our facility has a paint application process using high solids solvent based paints. The system is an electrostatic disc application process. I’m trying to estimate particulate distribution for three areas; the metal parts (90%?), overspray to the surrounding plastic covered walls/floor and to the filter bank on the exhaust stack. I’m using 90% transfer efficiency for the application disc (do you think this is reasonable). My question is; what percent should be used for the particulate/solids being transferred to the walls/floor and what percent would be going through the filters to the exhaust stack? A. S.

 

A. I believe that 90% T.E. for a rotating disk is on the upper end of the range. That range is 80–90%. To really quantify the destination of the overspray, you would have to conduct a study. You can measure the weight of the paint on the metal parts and on the floor and walls. You can’t really measure the weight of the paint exhausted. It is important that you take into account the solids by weight of your coating. I suggest the following:

1. Cover the walls and floor of the spray booth with sheets of material such as paper or plastic and weigh them before and after spraying parts with a known volume of paint. The final weighing must be done after the solvents have evaporated. This will enable you to calculate the percentage of paint overspray that coats the walls and floor.
2. During step 1., weigh the parts before and after coating and calculate the percentage of paint sprayed that coats the parts. This is the T.E..
3. Add the percentage of paint on the parts to the percentage of paint on the walls and floor, subtract this sum from 100% to get the percentage of paint that coats the filters and goes up the stack.

In your calculations, remember to factor in the solids by weight of the paint.