Letter 41080

Zinc Yellow Vs Zinc Phosphate  

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We have been doing Zinc phosphate for valve parts. Material is 4130. Most of the parts have threads and many of those do not gauge properly after zinc phosphate. Sometimes, a layer of loose particles is stuck in the thread grooves which may be causing thread gauging problem. To avoid this, can we switch over to Zinc-yellow plating? Will there be any problem if one out of two mating parts is Zinc-yellow and other is Zinc Phosphate? If we know of the advantages and disadvantages of Zinc-yellow and Zinc Phosphate, it will help in making the decision.

Thanks,

AMAR SHELKE
MANUFACTURING - Pune, India

Lots of companies zinc plate fasteners. The threads have to have an allowance for the plate. I think that it works better with a thread that is also truncated, which lowers the extremely high current density on the sharp point.
It will require a cyanide zinc plating tank or a specially tweaked alkaline tank for best results.Barrel plating is common as it can use a low current density for a longer period to get the most even deposition.
For your phosphate, look into using a calcium modified zinc phosphate. It has much smaller crystals, and if you pay close attention to the operation of the tank, it produces a beautiful, uniform coating that holds oil very well.
All of the above is my opinion and I do not sell material.

James Watts
- Navarre, Florida

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