Plating a Brass Part 6

[tmech77]

What is the best plating for going over a brass part? This is an old part that was originally cadmium plated. We can no longer use cad plating so I need to find a different type of plating. I was wondering if zinc plating would work? Or would electroless nickel plating work? There are also #8-32-2B threads running thru the part.

 

[TVP]

Without any additional information on environment, I would say go with electroless nickel plating. Chromium plating of brass is also commonly done, but since there are threads, I would go with EN.

 

[israelkk]

Beware of EN coating thickness accumulation that will affect thread dimensions which is far more thick that Cadmium thickness to achieve same corrosion protection.

 

[tomwalz]

Not sure if you want to do it yourself or not.

If you want it done then figure out why and ask a couple professionals what they recommend.

EN is easy. You can do it on your desk in a mazon jar. Good EN is much trickier.

I believe israelkk is referring to what I was taught to call "edge effect". Edges plate differently than flat surfaces.





Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[israelkk]

Edge effect exists with electroplating while electro less coating doesn't have this problem. What I meant is that the coating thickness of EN comparable to 0.012 mm thick cadmium is 0.038 mm of EN coating to achieve same corrosion coating protection (Salt Bath test).

 

[IRstuff]

"Shiny" EN is stressy; we cracked some parts with a 1 micron coating of EN.

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[tbuelna]

What is the reason for plating the brass part? If it's just corrosion protection, I can't see that cad plating was the best choice.

EN on brass would definitely provide a beautiful finish, and you could mask any threaded holes if the plating thickness poses a problem. Zinc is cheap, but it is not pretty and provides little corrosion protection.

 

[tmech77]

I should have just asked,"Is it possible to zinc plate a brass part?" I thought that you could only do zinc plating on steel. I noticed that two well know screw and standoff companies offer zinc plating on their brass parts, so I assumed that it could be done, but wasn't quite sure. So at least now I believe that plating brass with zinc is an option. I am not concerned with the appearance. We are getting some steel parts zinc plated and I was hoping we could get the brass part zinc plated at the same facility. I specified Zinc per ASTM B633, Type II (yellow), FE/ZN 5, SC 1 (.0002"). I am guessing that the appearance will not be consistent over the entire part. I did not specify for the threads to be masked. Is that OK? The plating is only .0002" thick. The parts will be used indoors, inside a chassis in a controlled environment.

 

[israelkk]

0.002" thickness is the minimum as I recall. The edge effect can add 4 times the coating thickness to the thread dimensions while on the pitch diameter it will be twice. Depends on the thread size and class (2A,3A,2B,3B) and the combination between the internal and external threads. You need to calculate the maximum and minimum thread dimensions after coating to be sure there will be no interference between the external and internal threads.

 

[tmech77]

I think I will be OK because I just noticed on the drawing that there is a note which says, " Plated parts must fit gages and meet specified tolerances after plating." Thanks for your help everyone. I really appreciate it.

 

[KENAT]

Why was the part Cadmium plated originally?

On parts I've seen it was sometimes because of the nominally 'self lubricating' properties of Cad.

I think PTFE impregnated electroless nickel plating was developed for this kind of application.

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[tmech77]

I do not know why the part was cadmium plated. It is a very old part and no one has any history regarding it.

 

[ornerynorsk]

Israelkk, did you mean to say 0.0002 inch, or did you actually mean to say 0.002 inch? Most zinc electroplating is around 0.0002 to 0.0003. Barrel plating of fasteners is done very commonly, and rarely causes dimensional issues.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[israelkk]

ornerynorsk

You are correct, it should be 0.0002" (0.005 mm).