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Ask the Expert Question-and-Answer Archive

by Ron Joseph

November, 2008

Small Lumps on Powder-Coated Parts

Q. We are getting small lumps;- 0.5mm-3mm wide, 1-3mm high on powder coated sections. At first we thought this was swarf, or dust. It turns out these are powder lumps. We have checked the powder, its dry, clean, & brand new.
Please help!!!

A. My friend Mike Cravens sent me the following response:

The lumps that you are referring to are most likely due to accumulation of powder particles as a result problem(s) with the powder delivery system. The powder flow may be restricted by unusual ware in the feed hose, powder pump, the connector sleeves, or the deflector and electrode. These are areas where the powder will “hold up” due to a restriction somewhere in the feed system and eventually break free in “clumps” causing the accumulated particles to impact onto the substrate. You state that the powder is new and not the cause of the problem. I would screen the “new” powder through an 80 mesh and then a 120 mesh screen to see if there are any “large” particles of accumulation of particles that may be contributing to the problem.

Good Luck


Ron Joseph

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