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Rough powder coating after media blasting

July 30, 2009

We have been powder coating our products (railings,fences,etc) for almost two years now. Previous to that we have sent our work out to a local coater. For the past two years we have been steam cleaning prior to powder coating. Most recently we have added a media blasting room to blast our steel and aluminum products instead of steam cleaning. We think blasting was the way to go but have encountered a problem. Since we have started blasting prior to powder coating almost every time the surface has a gritty feel to it. The problem areas are so random we have not been able to determine the cause. After the blasting process we steam clean the items and prebaked them for 10 minutes @ 392 degrees. Still the problem exists. Our blasting material is G40 steel grit @ 90 psi.

Our gritty/roughness issue continues to haunt us. We have invested well over $50,000 for the blasting room and have not been able to use it, except to remove paint from old items. I am not sure the ideal grit size for powder coating e.g. 40, 60, 80 grit or if this could even be the issue.

Any ideas on what the problem might be or a solution would be greatly appreciated!

Michael Deck
Fabrication & Powder Coating Jobshop - Buffalo, New York

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First of two simultaneous responses --

90 grit before powder if you want good quality.

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
July 31, 2009

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Second of two simultaneous responses --

There are more qualified persons who will be able to help you than I. However, my thoughts are:
1) Shot blasting aluminium with steel shot must open up the surface of the Al and therefore the PC item is more prone to out gassing?
2) Using steel grit I would have thought was the wrong media. It is possible that the steel grit is embedding itself into the component and some of it stays behind even after the steam wash.
I am not sure, but I believe a blast material called aluminium oxide is a product you should evaluate. If the name is wrong an expert in this field will correct this.

Terry Hickling
Birmingham, United Kingdom
July 31, 2009