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  for Metal Finishing since 1989
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Colored plating/conversion finishes for Zinc ZA-8

 

I am an Industrial Designer working for a design/engineering consultancy. Our company is designing a small part to be cast in zinc ZA-8. This part has very tight internal and external tolerances, so we are looking for a coating or plating that adds very little to the overall dimension. Additionally, we are interested in processes that can be done in a range of colors. From browsing the letters here, I have found that a black oxide treatment seems to be the best process for getting a consistent black finish with no added dimension, but I was wondering if there exists a similar process that produces, for example, a red finish, or blue, or mauve, in the ZA-8 alloy.

I was so happy when I found this website.

Thanks for all your help.

Sean Horita
IDE Inc. - Santa Cruz, California USA

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Chromate conversion coatings can be dyed. Tri-Valent coatings take the dye brighter than hex chromate. Castingalways leave a disuniform mottled finish as a function of the non-zinc (like 6% aluminum and other trash) left on the surface. Dyed chromate coatings may not be pretty enough for you application but are commonly used for color coding parts like bolts and nuts. To get the best finish you will electroplate pure zinc over the casting and then try-valent chromate thye pure zinc, then dye any color you like. Call me.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

 

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Firstly, dyes for conversion coatings whether directly on zinc die cast or plated zinc, are organic materials that vary in color from lot to lot much as paint or fabric or any other item that contains dyes. This said, now there is variation in the color brought about by operational variances that can not be controlled closely enough, unless being done on a very large scale, to get completely reproduceable results i.e. 98% reproduceabliltiy within the lot. Conversion coatings are available in colors such as yellow (iridescent), light blue, black and olive drab. These are generally used for corrosion resistance not cosmetics (except for sometimes the black). Although it is difficult to get an even finish due to casting defects (other metals, skinning, etc) a number of shops are able to get good quality reproduceable finishes without plating. Plating will give you the best finish, however it will add dimension to the parts and increase costs.

Gene Packman
process supplier - Great Neck, New York