Metal finishing Q&As since 1989
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Excessive build up of yellow zinc in threaded holes
Q. I am the Buyer for a sheet metal job shop in Spingfield, OR. We have a production part that we have problems with from time to time. I would appreciate some help with gaining an understanding of what the causes are. The part is machined and then sent to be plated with yellow zinc. The problem we are having is with what appears to be excessive build up of zinc on the threads in the machined holes on this part.
My question is two fold; 1) What are the mechanics of the plating process, i.e., what factors determine how much material is deposited and where that material is deposited during the plating process, 2) There are two sizes of holes machined into these parts, 1/4-20 and 10-32. The failures we have had have been in the 10-32 hole and never with the 1/4-20 hole. Why would one hole be a problem while the other hole is not. The holes are being inspected by the machinist and we spot check them with Go-NoG0 gages before they are sent to the plater. The material is .250" x .500" cold finish flat bar.
I thank you in advance for your help.
Jay BuellSheet Metal - Spingfield, Oregon, United States
2004
A. Hello Mr Jay Buell,
An excellent question. A smaller hole will receive less plating and a larger hole will receive more plating thickness; thats why your 6mm hole will be ok and the 10 mm hole seems jammed up. The plater will not be able to effectively counter this unless you help him out with a greater go-nogo tolerance on the larger hole.
Khozem Vahaanwala
Saify Ind
Bengaluru, Karnataka, India
2004
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