“I have a question about an electrostatic gun’s behavior in a coating booth. We have a powder coil coating line for precoating galvanized & aluminium coils up to 48” wide. It is observed that the kV at guns tip drops to 50-60 level when guns are in installed conditions inside the coating booth made of 304 grade S.S. – compared to readings of 80-90KV when tested outside the booth. 6 nos corona type guns are normally used at a time in this booth.
To our mind this is one of the reasons for low transfer efficiency of around 60% as against expectation of 85-90% since object is flat strip. What steps could be taken to avoid / minimize kV drop?”
“KV’s (voltage) will drop as microamps (current) goes up. This is determined by the laws of physics. You are probably bleeding your corona field towards the booth, and definitely to the metal strip you are coating. Therefore, a drop in KV is very likely.
The important thing is to ensure that the KV’s are being directed toward the strip and not the booth. Check and adjust the position of the guns to be sure that the primary target is the strip and not the booth. Monitor the current (microamps) during spray and compare them to readings taken without powder spray. They should be higher when spraying. If all else fails, call your equipment supplier.”