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Bonding powder paint to zinc plate.
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Further to our letter # 2922, we are still experiencing problems with bonding. We are now trying to coat over zinc plating with slightly better results, however not satisfactory. We've stopped using the Yellow Chromate over the zinc plating, as we found it was breaking bondage with the zinc when baking the powder paint at 400 deg. F.
We are using an iron phosphate wash after zinc plating and prior to powder painting. Should we be using a zinc phosphate wash? Is there a different plating process that could give us the same rust protection and increase paint bondage at the same time? Or is there an etch the platers could put parts in after plating to help with adhesion of the paint?
Gary A Ritzelectronics - New Dundee, Ontario, Canada
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"Our customer has requested that we Zinc plate with Yellow Chromate, Vinyl wash primer, yellow Zinc Chromate primer, 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. |
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Tom PullizziFalls Township, Pennsylvania |