Letter 2922

Wet Coat and Powder coating to Zinc/yellow chromate finish. 

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Ritz is 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 Chromate primer on top prior to 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. We have attempted to test with powder paint after the Yellow Chromate with no better results. In both cases, the yellow Chromate dip separates from the zinc plating and remains adhered to the paint flakes. Is temperature a concern when working with paint curing and yellow Chromate? Or time in the curing oven a factor? In all cases, we have let the plating sit for 1 week prior to painting. Is this an area of concern also?

Russ Godfrey
Ritz Electronics - New Dundee, Ontario, Canada

Dear Russ, After reading your problem you don't mention what pre-treatment you were using prior to your customer's suggestion. The treatment mostly used in the racking industry for steel substrates is iron phosphate prior to paint whether for powder or liquid. Is there a specification you are working to from your supplier.ie.Salt Spray,Chemical Resistance or Humidity etc? What type of curing process are you using? Please supply more information Regards John Underwood

john underwood
A.R.Monteith Inc - burlington Ontario