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"Porosity problem in sintered metal bearing liner"

An ongoing discussion beginning back in 2005 ...


Q. Sir,
I am plating sintered engine bearings which have sintered lining of Cu-Pb-Sn. I am doing Pb-Sn-Cu plating on these bearings, I am facing severe porosity problems -- please guide me to identify the cause of problem.

Shadab Khan
plating - Delhi, India

"Sintering: Densification, Grain Growth and Microstructure"
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"Sintered Metallic and Ceramic Materials"
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A. I'm not sure if I fully understand your question, Shadab, since my understanding is that sintered materials are always inherently porous, and probably cannot be properly plated without vacuum impregnation.

Are the bearing liners vacuum impregnated? If not, that is probably the problem. If they are vacuum impregnated, did you do it in house, or did you receive them already impregnated? Thanks, and good luckQ

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


A. You don't give too much detail of your process, but I suspect that the sintered bronze may not be adequately sintered and too porous. You must also make sure that no cleaning chemicals are trapped in the sinter; this will certainly cause you problems. Are you putting down a barrier layer before the Pb-Sn-Cu? If so, what -- copper or nickel? If not, why not? Engine bearings operate at high temperatures and the tin will migrate into the sinter. I also presume you are using a fluoborate bath for the Pb-Sn-Cu? I suggest you give more details of your process and your machining specification for the sinter.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

Porosity causes tiny blisters in plating

August 31, 2016

Q. We are facing problem of porosity in Cu-Pb-Sn Bearings during plating operation. Our product is sliding bearing therefore impregnation is not done -- it's machined and degreased, acid etch and Nickel barrier film is applied by nickel plating and further fluoboric bath is used for Cu-Pb-Sn plating. After plating we find tiny blisters and porosity on plated surface; surface examination shows no plating on the isolated site . Kindly guide us to resolve this issue. Is it machining or related with some chemical.

Sandeep Kumar
- Pune,Maharashtra,India

January 11, 2018 [2nd Request]

Q. Dear Sir,
I have a similar issue in our processing of Bronze bearings used for engine application. The plating bath is fluoborate. We apply Nickel barrier coat before Lead Tin Copper planting. After the coat, Tin Flashing is done. After coating we found many bearings show very tiny small blisters which under microscope shows micro porosity.
How can we avoid the generation of this porosity in the process? Kindly suggest?

Sandeep Sayikhindikar[Sandeep Kumar returning]
- India, Delhi

January 2018

Hi cousin Sandeep. It's best if you remember to always post with the same name on this site (you've used 4 variations) because it is easier for our readers to help you when they most fully understand your situation. Of course your earlier postings were back in 2009 and 2012, so this is more about the future :-)
Thanks and Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

January 11, 2018

A. I have seen this before. It may be caused by oils in the porosity. If the parts are vapor degreased and then baked at 300 °F for 1-2 hours, then this problem may be eliminated.

Lyle Kirman
Consultant - Cleveland Heights

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