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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Burnt Nuts after Cadmium plating?
Q. We are a nut mfg, providing Locknuts with Nylon inserts. We have Cad plated nuts for as long as I have been with the company, 23 years, and have never seen this situation. After plating the majority, not all, of the parts have the appearance of voids, dents in the material. It almost looks like they were beat up, or possibly acid washed ? We cannot figure out what went wrong with the process. Has anyone ever seen anything like this and can you shed any light on the situation ? Normally acid would also eat away the Nylon insert (Zytel 101) so we ruled that out. The coating company is telling us they had to receive them this way, but we manufacture these and would have seen this before sending out. Here is a pic of both good plated and ugly plated parts.
Thanks for any help you can provide.
Bob BaerBuyer - Wheeling, Illinois USA
December 30, 2015
A. Hi Bob. If I'm correctly seeing the situation from the photographs, it doesn't look like burning to me, it looks like mechanical damage or acid damage. It perhaps could have happened in transit, but my guess is that, due to some error, the plating shop left them churning in a plating barrel overnight or sitting in the acid tank overnight :-)
Please try to study the internal diameter, and the area under the castellations, to see if there is damage in areas that couldn't be caused by mechanical action.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 2015
Q. Well, we ruled out Acid because our experience has always been that acid would burn the nylon inserts, turning them White. Since there is no damage to the inserts, we didn't think that could be it.
What type of Mechanical damage are you thinking ? We were wondering if somehow the parts could have been burnt by the electrodes in the plating bath?
Plating company thought the parts may have had previous rust damage, been cleaned (pickled and oiled) before they received them ? But again, we would not have assembled and crimped the inserts into bad nuts.
- Wheeling, Illinois
December 30, 2015
A. Hi Bob. The possible mechanical damage I was thinking of was, as mentioned, allowing a plating barrel to churn overnight with the parts in it, so they keep banging into each other for hours. Please see our library article on Barrel Plating if you are not understanding what I'm talking about.
I can't necessarily disagree with the plating shop's theory that the parts could have been defective before they got them. Of your good parts, the 3rd from the left has a very obvious tear on it which doesn't look terribly different to me than the highly symmetrical defect lines on the bottom face of the bad parts. But you seem sure that you couldn't have shipped such parts to the plating shop, and you'll have to go by your own lights on that issue.
The cases of arcing & burning that I saw in almost 50 years of travel to plating shops were few and obvious, so I strongly doubt it.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 2016
A. My feeling is that the nuts are over pickled in HCl due to which over etching has taken place. As for the Nylon ring it is not affected as these nuts are not pickled/derusted for more that six to eight hours.
mahendra gargatti- BELGAUM.KARNATAKA INDIA
January 17, 2016
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Q. So if the nuts were overpickled in HCl, any idea on how the inside of the nuts (internal threads) were not affected at all? When we sectioned the parts and reviewed, the insides were still perfect. Locknuts - Wheeling, Illinois January 18, 2016 A. I agree with the guy from India. HCl does not attack nylon. Sulfuric acid dissolves nylon.  Robert H Probert Robert H Probert Technical Services  Garner, North Carolina  January 18, 2016 |
A. Good day Bob.
You seem to have quite a dilemma. The internal threads are not compromised, as you state, and you are confident that the material is not defective when you ship to plating. As I read this, the internal threads are masked with an insert.
I would hazard a guess as to what is the analysis of the the cad barrel solution? I am thinking this problem is related to the cleaning/prep of the nuts, and the condition of the solution itself.
Barrel plating operates at a very low amperes per square foot ratio, as compared to rack plating,(where the chemistry of the solution can provide some measure of cleaning due to high cyanides/and caustic) any TOC/organics can interfere with the cadmium deposition.
There is always the tried and true water break test for parts inspection before the actual plating.
I know this is long winded, but I hope this is food for thought.
Regards,
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada
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- Isle of Man, UK January 20, 2016 January 2016 Hi Mark. I was thinking the same after my bourbon last night. Had I served myself a third one, I'd have made your same posting. Alas I ran out. Regards, Ted Mooney, P.E. RET Striving to live Aloha finishing.com - Pine Beach, New Jersey January 21, 2016 When someone says bourbon here in the UK we think of a type of chocolate biscuit, sorry, cookie. So I was a bit confused as to the effect a chocolate biscuit might have on you. - Isle of Man UK January 22, 2016 Good day. Aerotek Mfg. Ltd. - Whitby, Ontario, Canada |
Burnt nuts after cadmium plating, I suggest he wears an apron and some trousers next time!!Over pickling leading to zinc plating issues?
Q. We recently ran some parts and didn't like the plating appearance -- so we stripped them in HCl (24 oz/gal) of 35% solution and replated. The issue is that the low density area inside the part came out gray (low coverage) and the inner lip was black.
After showing a colleague the parts he believes the metal was over-pickled due to too long in the HCl when stripping. Hw suggests running them through the cleaning stages again to try to stabilize the metal (raise the pH of the metal in a way). We are a trivalent shop. Any other suggestions?
Nico Cottone- Cincinnati Ohio USA
June 8, 2020
Perhaps you could tell us what the article is made from and what your process is?! You may then get some answers
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
June 8, 2020
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