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topic 53824

Why Pre-Bake before cadmium plating?

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A discussion started in 2009 but continuing through 2019

December 9, 2009

Q. I run a cadmium plating line where I plate aerospace fasteners. I was wondering if anyone could tell me the point of a four hour pre-bake on a part that will require a 23 hour bake after its plated.

John Roberts
plating shop employee - Kansas City, Missouri


December 11, 2009

A. John,

It is common to stress relieve after machining and prior to plating. This prevents distortion due to stress build up. The only thing that surprises me about the stoving before the plating in your case is the fact that the time is so short. If the de-embrittlement is 23 hours that would normally indicate a high tensile steel (probably >230ksi)so I would have expected a stoving time of nearer 18 hours than 4 hours.

Sometimes pre-plate stoving is done to aid with degassing the material, but this is more commonly associated with castings, where there may be some porosity.

Brian Terry
Aerospace - Yeovil, Somerset, UK


December 14, 2009

A. John, as Brian suggested, it is a stress relief operation. The concern is that heavily stressed high hardness steel parts can crack due to hydrogen embrittlement while they are being plated. The pre-plate bake helps to prevent that from happening.

The purpose of the post-plate bake is to diffuse the hydrogen to outside the part or to innocuous sites within the part, so long times are important. Twenty three hours was chosen since it makes it easy to put the parts into an oven and take them out the next day.

lee gearhart Lee Gearhart
metallurgist - E. Aurora, New York



Stress relieving parts then inventorying for plating in the future?

October 18, 2019

Q. Can you stress relieve parts and keep then in your inventory and do the cad plating later when you need it?

Thanks

Ermelo Pena
NHBB, Chatsworth - Chatsworth, California, USA


October 21, 2019

A. Hi Ermelo,

Absolutely no reason why you can't store parts after stress relieving and before plating. Make sure your parts are adequately protected against corrosion, especially if you are expecting to store them for a long time.

The reason stress relief tends to be done immediately before cadmium plating is convenience, the plating shop will usually stress relieve, cadmium plate and de-embrittle as one job lot.

Brian Terry
Aerospace - Yeovil, Somerset, UK

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