Summary for painting over cadmium plating Discussion
painting over cadmium plating is the core issue in this thread, and the answers suggest the problem is usually not solved by simply cleaning and repainting. Chad Parkhill asked whether 4130 steel tubes that were cadmium plated, dichromate sealed, and painted could be lightly blasted, then phosphated instead of chromated for better paint adhesion without stripping and replating the cadmium. Don Baudrand replied that it would be difficult, though not impossible, to remove the paint and chromate without also removing the cadmium, and noted that if the chromate is being eliminated, it may be a good time to replace cadmium with zinc or zinc alloy plating instead. He also warned that phosphating can etch cadmium into the waste stream. In a later merged discussion, Mike Forbis reported poor primer adhesion on cad-plated, Iridited parts; James Watts suspected a thin oil film from vapor degreasing, and another reply recommended tack cloth after Scotch-Brite to remove cadmium dust. The thread shows differing troubleshooting ideas, but no simple universal fix.
Q. I am working on developing a re-lifeing process for 4130 Steel Tubes that have previously been Cadmium plated with a Di-Chromate seal and then painted. I would like to lightly plastic media blast the paint off and apply phosphate rather than chromate for paint adhesion purposes (ref AMSQQP416 ). Question is… In what condition should the tubes be in before I send them out to be Phosphate coated? I hope not to have to Strip and Replate the Cad but to simply just replace the Chromate with Phosphate.
Any input is greatly appreciated.
Chad Parkhill
– Phoenix, Arizona, USA
2004
2004
A. I think you’ll find it difficult — but not impossible — to remove the paint and the chromate without removing the cadmium plating–see letter 9406. However, these days the industry tends to not use cadmium for corrosion resistance, unless a combination of its properties is required (lubricity and freedom from gummy corrosion products, for example).
So, as long as you’re getting rid of the chromate, it may be a good time to substitute zinc or zinc alloy plating for the cadmium. Some of the cadmium is going to end up in the phosphatizer’s waste stream anyway from the etching that occurs during phosphatizing and they’re not likely to be pleased about that anyway. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
Painting Over Cadmium Bolts
Q. I have a customer requesting cadmium plating on ASTM A325 structural bolts to increase paint adhesion. Everything I have read seems to indicate just the opposite would occur. Does anyone have any experience that might help us make the most appropriate decision?
I would appreciate any help at all.
Thank you,
Beth Williams, Purchasing Mgr
– Valdosta, Georgia, USA
2003
A. I agree that painting over cadmium has potentially less adhesion of paint unless the cadmium has a yellow conversion coating. The conversion coating (chromate) acidifies and protects the surface allowing paint to adhere. If your client has trouble with paint adhesion on the steel it is likely because it was not prepared properly.
Don Baudrand
Consultant – Poulsbo, Washington
(Don is co-author of “Plating on Plastics”
and “Plating ABS Plastics” eBay
or
AbeBooks
affil links])
2003
Multiple threads merged: please forgive chronology errors and repetition 🙂
Q. We are have trouble getting primers to adhere to parts we have cad plated. Our cad is a cyanide bath and we are Iriditing the parts. We are applying a BMS 10-79 primer and then a topcoat. Our process is to clean with MEK and then prime. We have tried different batches of prime, different primers, wash primer, abrading the surface with scotch brite, with or without Iridite, all with no luck. Any ideas?
Mike Forbis
Paint shop manager – Denton, Texas, USA
April 17, 2010
 | A. Mike, Can you phosphate the Cadmium plating? If you have the facility then I would zinc phosphate straight onto the cadmium, don’t Iridite. I can’t see why a wash primer wouldn’t work, or indeed why Scotchbriting the surface isn’t improving the adhesion. The only thing with Scotchbrite is that you have to ensure the surface is cleaned very well, any residual dust will cause you adhesion problems. My personal way of painting cadmium is: cadmium plate, zinc phosphate, prime and then topcoat paint. Brian Terry A. We use a vapour degreaser to prep. our parts for painting after cad. Frank Dunleavy |
| | A. After plate and chromate conversion coating, why do you need to use the vapor degreaser? James Watts A. Hi Mike, what kind of paint-primer system is it and which temperatures (force drying and curing) are in use. How does parts present poor adhesion, by bending, after baking..etc? Cheers, Dominik Michalek A. After scotchbrite, use tack cloth ⇦[this on eBay or Amazon affil links]
April 23, 2010 |
A. Zinc phosphate will do the job
Sara Michaeli
Tel-Aviv-Yafo, Israel
April 27, 2010
Aluminized primer not sticking to cadmium plating
Q. Having issues with paint adhesion when applying it over cad plated steel.
Doc Holladay
– Paris, Texas USA
July 1, 2016
PAINTING OVER CADMIUM OVERPLATING?
Q. IS MIL-C-8514
[from DLA]
WASH PRIMER REQUIRED WHEN PAINTING OVER CADMIUM OVERPLATING?
I HAVE A REQUIREMENT TO EPOXY PRIME PER MIL-PRF-85582
[from DLA]
THEN TOP COATING PER MIL-PRF-85285 [link is to free spec spec at Defense Logistics Agency, dla.mil]
OVER ELECTROLESS NICKEL PLATE PER AMSC26074, CLASS 4, GRADE A, WITH CADMIUM ELECTRODEPOSITED OVERPLATING PER SAE AMSQQP416, TYPE 2, CLASS 1.
Randy Matuskey
– Scottsdale, AZ, USA
March 27, 2019