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Small spots and craters on powdercoated material

2005

Dear Technical Whiz

Some of our powdercoated material has come out of the oven with spots and small craters.

Please advise whether this might be a metal treatment problem or powder application issue.

Bob Gordon
Powdercoating - Cape Town, South Africa

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2005

I'm not the whiz you're looking for, Bob, just the first to see your question.

Either could be the problem. A third cause is even possible (like bad powder), but we need more data (what is the substrate, what is the pretreatment, what is the powder). A picture of the problem would be great. Meanwhile, please start with these similar questions already posted--letters 834, 8523, 31579--and see if they help at all. Good luck, and hope to hear more info from you.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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Hi Ted

We are coating aluminium, using a chromate pre-treatment.

The surface blemishes are either small craters or round blemishes.

We have eliminated the water or oil in the air line factors and have reset spray guns' voltage. The whole pre-treatment system has also been checked thoroughly. Still a number of blemishes and craters visible.

Regards,

Bob Gordon
- Cape Town, South Africa
2005

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2005

Hi,

TGIC free powder can create blisters if heavily applied - this is due to water vapor that is evolved and trapped in the film during the cure. Another reason worth investigating is air entrapment - preheat the aluminium 80 °C (removes the air)and whilst still warm apply powder.
Let me know if there is any improvement.

Terry

Terry Hickling
Birmingham, United Kingdom

 Thanks for the pickup, Terry -- Ted.