Metal finishing Q&As since 1989
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Cadmium plating turning black
Q. We have a situation where Cadmium plated and chromate passivated parts are being rejected following short term storage due to black patches on the surface. This is not the white rust normally associated with corrosion of cadmium, could anyone help with advice on the possible causes.
(note - my research suggests that inadequate rinsing - aided by a porous coating - could produce this, could anyone confirm this or offer an alternative cause)
Regards
Nick Clark- Bristol, Avon, England
2003
A. Sounds like a sulfide. Check to see how they are stored. Many papers and cardboards have enough sulfur in them to spoil cad plating, even chromated. At the right temp, humidity and air movement, it does not take long. Solution-wrap the parts in crystal paper and store in plastic tote bins.
James Watts- Navarre, Florida
2003
A. Copper contamination in the cadmium plating solution.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
2003
A. Cadmium sulfide is yellow. I agree that porosity is likely the cause. Porosity in the basis metal most likely. I have found that plating porous metal, one can help the situation by a pre dip in clean hot water at a temperature above that of the alkaline cleaner. Water is drawn into the pores and usually stays there throughout the processing so that cleaner and acid cannot enter to later bleed out causing black spots. Also, alternate hot and cold rinsing is helpful after plating and before the chromate.
Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
2003
Cad plating turns black in a few days
2007Q. We are cadmium plating fasteners in a cyanide bath and we are finding that the finish is turning black after 4-6 days. Parts come out of he process more or less bright white.
After the cad plate we rinse and apply a chromate, rinse and dry.
We have been doing this for more than 20 years and sometimes the plated parts turn yellowish to brown, but never black.
I'm enclosing a picture so that you can se the magnitude of the black color, together with a freshly plated part. You can see one fastener is a little yellowish after a couple of weeks, but the others that are black, where plated only 4 days ago.
Can the brightener be the culprit? I've heard that to much Nickel in the brightener can cause this black spots.
Also, if we submerge a black stained part in a cyanide containing solution, we get a bright clear finish, so we think this stain is over the cad deposit.
Thank you for your help.
plating shop - Mexico City, DF, Mexico
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A. I never had the problem, so can not truly say. Typically, you have a sour rinse, probably with a high sulfide content or your packing containers have a high sulfide content (which is common in some cardboard and some paper)and you storage area is in slightly high humidity(IE: not air conditioned) Not that some plastic bags can cause problems also. James Watts- Navarre, Florida 2007 A. Off line in buckets, set up a 1/4%/vol nitric acid to neutralize the cyanide, then another bucket of fresh made chromate. Wait 5 days and let us know. I suspect your chromate pH is out of spec due to CN drag-in. So neutralize in nitric first, then chromate. Robert H Probert Robert H Probert Technical Services Garner, North Carolina 2007 A. I WOULD LIKE TO REQUEST TO YOU GET YOUR CAD BATH ANALYSED PROPERLY FOR IMPURITY CONTAMINATION -- SAY COPPER, IRON, ETC.  Ajay Raina Ludhiana, Punjab, India 2007 |
Q. We have some parts that we currently produce for a customer, the parts are Bright Cad plated. Once we get parts back from plater they look great, however over time they begin to show black spot through the Cadmium. we have had several labs look at this products and they say that it is due to the cleaning process, we have tried 3 different vendors and they all get the same results, are we missing something. We have had parts stripped and replated and same thing happens, material be used is a C1018. We have asked platter for titration results and they look ok from what we can tell. we have asked to have parts baked prior to plating and platter stated that they could not do it because they would rust as they do not have in line dryers. We are total lost as to what this could be any help would be great.
Thanks
Brian
- Jefferson, Ohio USA
June 21, 2013
Black stain in cadmium deposit after chromate
Q. We regularly, but not always, end up with parts having black or gray little stain all over after chromate conversion. It seems to be done at the plating stage as we have changed the chromate solution for a new one but the problem still occurs.
Pierre Legaultshop employee - Montréal, Québec, Canada
January 7, 2019
Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)
A. If the "stain" is in the low current density areas then we suspect copper contamination of the cadmium plating solution.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
January 9, 2019
January 17, 2019
Thank you for your comments!
I attach some photos that can help you understand our problem. Pierre
shop employee - Montréal, Québec, Canada
January 18, 2019
A. OK, so it is not the LCD area. so now I suspect the cyanide was not neutralized before going into the chromate.
Recommendation: Dip in 1/4 %/vol Nitric Acid before the chromate.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Q. Dear sir, we have cadmium plating and we are facing a problem of black spots after a few days. Base material that we do cadmium plating on is ms/brass.
We start by doing glass beading, magnetic before the process.
Also we confused whether this is corrosion or some other effect.
Please explain.
Regards
Ashutosh N
AI - Nashik, Maharashtra, India
June 5, 2019
A. Dear Mr Ashutosh,
The black spots in brass are on account of lead in the brass that shows up a few days after plating.
The black spots in MS are due to Carbon enrichment of the surface that initiates due to pickling.
You may also want to check the water used in the process.
These are possible causes, for confirmation of the same please post photographs.
Khozem Vahaanwala
Saify Ind
Bengaluru, India
June 15, 2019
Q. My question is that my 4130 tube is displaying small dark spots. The cad plating house is identifying it as 'cyanide bleed". Does anyone have information if this condition is non-complaint to AMSQQP416?
And what actually causes this condition?
Wilson FreireAerospace - Long Island, New York
February 3, 2020
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