The Reasons for Defects of Electrostatic Powder Spray
Electrostatic Spray is one of the application methods of the most common used soldermask - liquid photo imageable (LPI or LPISM). electrostatic_spray is sometimes Electrostatic Powder Spray. There are many advantages of electrostatic powder coating, meanwhile, there are several defects as well. This article will introduce some reasons surface defects of electrostatic powder spray.
LPI Soldermask Electrostatic Spray
1. Coating gloss deficiency: too long curing baking time, too high temperature, mixed with other harmful gases in the oven, too rough surface, inappropriate pretreatment method.
2. Coating color changes: repeatedly baking, mixed with other gases in the oven, excessive baking time.
3. Orange on coating surface: spray coating with uneven thickness, bad powder atomization, powder plot phenomenon in the spray gun, too low curing temperature, damp powder, too coarse powder particles, poor grounding of the work piece, too high baking temperature, too thin coating.
4. Coating recessed hole: improper treatment, residual grease, incomplete removal of grease and water with compressed air, non-flat surface, polluted by dust or other impurities.
5. Coating bubbles: After surface treatment, the water is not completely dried, leaving pre-treatment residue, incomplete degrease and rust removal, incomplete removal of underlying volatiles, bubbles on work piece surface, too thick powder coating.
6. Uniform coating: uniform powder spray, too close distance between spray gun and work piece, unstable high-voltage output.
7. Bad impact strength and adhesion of the coating: too thick phosphate coating, too low curing temperature, too short curing time, incomplete curing.
8. Pin hole: residual oil, too high gun voltage resulting in coating breakdown, too close distance between spray gun and work piece resulting in coating breakdown, too thin coating, incomplete curing.
9. Small sand on the surface: spray atomization and airflow blockage, poor spray atomization, residual powder drops, other impurities on surface.
10. Coating drop off: bad surface treatment, incomplete rust removal, insufficient voltage output of high-voltage electrostatic generator, bad grounding of work piece, too high air pressure.
11. Uneven powder supply: powder supply pipe or spray tube blockage resulting in powder adhesion hardening in the nozzle, insufficient air pressure, unstable pressure, air compressor mixed with oil or water, powder flow instability, too little powder in powder supply device, too long powder supply pipe, too high resistance of powder flow.
12. Powder flying, poor adsorption: insufficient high-voltage of electrostatic generator, poor work piece grounding, too high air pressure, recycling device jam.
13. Too little powder: insufficient air pressure, too high air pressure, too high ratio of air flow and powder mixture, air mixed with water and oil, blockage of spray gun.
14. Powder tube obstruction: powder attached to spray pipe walls, output tube gets heated causing powder caking, powder tube bending, powder mixed with impurities.
