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Metallic powder agglomerations

2001

I am coating a champagne metallic powder from a leading brand.

I have having problems that always one the edges / corners of the extrusion have agglomerations like a fillet weld. If it is a "U"-shaped channel the inside of one the lip gets the agglomerations along the line. For complex extrusions where there are several edges all are Ok except one edge / corner has all the metallic agglomerations like a continuous fillet weld along the edge.

The powder supplier says it is the grounding & the gun.

How important is grounding for metallic powder? Does it require more than the usual earthing? Must one use a metallic gun for metallics? Can a normal gun work? I notice that I get this when I do gold and champagne metallics only and not silver metallics.

Can anyone throw some light?

Rambo Puru
- Singapore

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2001

Dear Rambo,

The supplier is in part right, however all powder coatings require a good earth for a good coat. If you have insufficient earthing it will be much more noticeable in a metallic powder. I would suggest using clean hooks, jigs, etc. and make sure the track is also clean.

The problem you have could be caused by a number of aspects.

If you are applying the powder with an electrostatic gun try to turn down the kV to 30-50.

If you are reclaiming the powder the metallic may separate from the powder in the reclaim system and cause such an effect.

The spacing between the substrates may need to be widened.

One reason why the gold and champagne metallic only show this effect is that these product are more than likely to by dry blended and the silver is most probably bonded.

Hope this helps.

Drew Devlin
- Lincolnshire