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Chromate coating for Zinc Diecast
Q. I've searched all sources for several years without positive results, perhaps you could provide an answer. I own and operate a shop that requires the process by which the yellow to drab chromate is applied to zinc diecast. The process is used most extensively for fuel delivery components. Any ideas?
Peter trotzuk- Burnaby, B.C. Canada
2002
A. What kind of "source" do you want? Products that apply yellow and/or olive drab chromate or an applicator job shop to do the work. Either way, the quality of the coating will vary as a function of the "crap" in the surface of the diecasting (which is about 7% aluminum). Such tramp metal in the surface is affected by the cooling rate of the die casting and is especially difficult to work with in the case of thin walls.
The only way to get a good chromate coating over bad diecast parts is to electroplate pure zinc over the die cast up to 0.0003 to 0.0005 thick - then chromate coat the pure zinc.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
2002
Q. After chromatization my zinc casting parts are becoming black while my concentration of chromatizing chemical is well in range and all other parameters like pH, temperature, are also as per standard. Please suggest!
Lalit Kumar- India
June 28, 2016
A. Hi Lalit. You have been successfully chromating these castings for a long time, then suddenly something went south? And you're sure it's not anything in your plating shop? Then the castings have changed. I can't see any other possibility unless I've misunderstood your posting.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 2016
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