Letter 41080

Zinc Yellow Vs Zinc Phosphate [India] 

June 12, 2006

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
- FL

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