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Wet Coat Paint or Powder coating onto Zinc/yellow chromate finish

Q. We are a small company in New Dundee Ontario - and we are experiencing bondage problems and thought you may be able to help. We manufacture CRS racks for military applications. Our customer has requested that we Zinc plate with Yellow Chromate for paint adhesion. Then Vinyl wash primer and yellow zinc dust [on eBay or Amazon] , wet coat baking enamel. On small test samples we appears to achieve proper bondage. However, on actual racks, we loose bondage around bolt holes and pressure points."

 STOP!

At this point, you need to see if this coating system is reasonable. Ask to see the military specification or some other basis for this coating system. It can't be a list of mil specs for each individual coating, it must be for the system. Your vendors of coatings can help, but you have to work from the top coat backwards to the primer, then wash, then chromate. Unless you formulate your own paint, you can get a recommendation for compatible bottom coats.

  
Tom Pullizzi
Falls Township, Pennsylvania
1999

Q. We zinc plate .001" then yellow chromate a part for powder coating. The plate adhesion is good. However the powder coating supplier is having a bubbling problem. The bubbling is only the powder coat not the plate. Can the chromate cause a problem to the powder coater? The powder coater is concerned with the plate thickness in threaded areas as being the problem. Is there a minimum thickness required for zinc plate before powder coat?

Thanks,

A. Generally the chromates if properly applied over clean surfaces will provide excellent adhesion and no bubbling. Without actually putting the parts through a battery of tests myself, the only thing I can add is that a high percent of the failures that I have seen were caused by impurities in the plating, not the chromate. I also have found that you can usually see if the plating is bad if you see cloudiness or uneven coloring on the surface.

Just a shot to look at...good luck.

Bob Utech
Benson, Minnesota
2002

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