“I work for a growing company in Saskatchewan, Canada. Currently we have two powder paint lines and one liquid paint line.
Our second line just came into operation last year and I have been on that line from the start. Lately we’ve been having problems with getting enough powder from the auto and manual guns. Some days there just isn’t any powder flowing and it’s hard to get good coverage on the parts. (We manufacture farm machinery.) We’ve checked the fluidizing and that seems good. We’ve cleaned out the hoses and the venturi pumps and the wearsleeves. Plus we’ve also checked out the stems going into the hopper. Everything seems good.
Something I’ve noticed is that when the manual guns are working fine there seems to be a lot of buildup on the tips. Then on the days they aren’t working well the tips are clean, no buildup at all on the tips. Could this be a sign that there is an electrical problem? Everything is clean, the powder is fine. We can’t seem to figure out why the guns don’t put out much powder some days.
We are using a Nordson reclaim booth…10 autoguns per side and two manual guns. Thanks for any information you may be able to offer.”
“Boy it seems that you looked at all the obvious areas of the powder feed system. I would have to assume that the transfer pumps are clean and operating properly, if you are refilling the feed hopper with reclaim powder at regular intervals. If this is not the case, then look at that.
Next, you should make sure that the feed rate is indeed changing or is the transfer efficiency (what ends up on the parts) is changing. The latter suggests that if the output for the guns is the same, then the powder isn’t charging properly or the part ground has gone away.
The easiest way to check powder charging is to check the output current of each gun. This is not the voltage reading that you normally check. To read current output, check your manual for instructions. Usually, you push a button or pull the voltage adjust knob, and the current reading is displayed on the voltage meter using a different scale. The current is a measurement of work for the charging mechanism of the gun. You can have voltage present without current. This means that the field exists, but the charge is not transferred to the powder particle. Current readings should read between 20 and 50 microamperes.
If this reading is OK, then check for proper ground on the part to be coated. There should be less than 1 megohm resistance to ground in the entire circuit (part, hanger, conveyor, etc.). If this is resistance is above 1 megohm, then clean the contact points along the entire circuit. Burn-off the hangers, clean the conveyor, etc.
The other area where transfer efficiency can be effected differently each day would be environmental conditions (temperature & humidity). These will effect the rate the powder is pumped and charged. Normal limits for these can be obtained from your powder supplier (65-85 degrees F & 40-60% RH).
If you are still having problems after checking these parameters, get back to us with more information.”