Summary for salt spray failures in zinc plating Discussion
Salt spray failures in zinc plating were raised by V.R. Sankar, who reported 12–17 microns of zinc yet red and white corrosion before 48 hours SST. Ted Mooney replied that the problem could not be diagnosed from thickness alone and said the best path is to retain a plating consultant or get on-site help from the supplier. He noted that many process details matter, including whether the parts are rack or barrel plated, whether the zinc process is acid or alkaline, what chromate is used, and what the substrate is. In a later question, Ratnadip Kadam asked how to reach 48 hours SST on MS rod and said he was only getting 9 hours with 8 microns. The thread suggests that 48 hours should be achievable, but only if the full process is checked, including possible thin coverage at thread roots and the quality of the trivalent chromate.
Q. V.R.Sankar
2006
We are doing zinc plating. our product is failing in salt spray test. Our materials have the good zinc thickness 12 – 17 microns but it is not pass 48 hrs SST. We are facing red & white corrosion. let me know how to avoid this problem.
A. Hello, Mr. Sankar. I think you’re going to need to retain a plating consultant or at least enlist on-site support from your supplier. To try to learn how to do zinc plating properly from an internet posting is only going to delay getting to a solution.
But if you want to persist, we’d need to start by knowing a lot of process details including whether you are rack plating or barrel plating, acid or alkali process, what type of chromates you are using, what is the substrate material, etc. Good luck.
Ted Mooney, P.E.
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2006
Q. Sankar
2006
Thank you for your response. I am using barrel plating. Plating parameters are Current-5 amps/sqft,Voltage, 7-10V, time-60 minutes. I am using trivalent blue passivation.
A. “Old style” trivalent blue passivation (from the days before RoHS) does not do 48 hours, and that may be a good part of the problem. A modern proprietary trivalent chromate, or switching to yellow hex chromate if color is not an issue, will bring you to the point where the process should pass if operated correctly. That’s a start.
Ted Mooney, P.E.
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2006
What is the procedure for Zinc electroplating for 48 hours salt spray
Q. Hello ,
What is procedure to attain SST of 48 hours for coating on 5.8 mm of MS rod ? I am currently getting 9 hours SST with 8 micron thickness of zinc on MS rods. IS there any alternative by which I can attain SST of 48 hours? Please help.
Ratnadip Kadam
October 3, 2017
A. Hi Ratnadip. 48 hours should not be especially difficult. Might it be possible that the plating at the root of the threads is substantially less than 8 microns? Barrel or rack plating? Acid or alkaline zinc plating? Are you using a trivalent chromate from a reputable vendor?
Regards,
Ted Mooney, P.E. RET
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October 2017
October 4, 2017
A. Hi Ratnadip,
As Ted says, it’s not difficult to achieve 48 hs of SST resistance. If you have to plate mild steel rods, I suppose you have a rack plating system. Just correct me if I’m wrong.
Do you have acid or alkaline zinc plating bath?
Are you sure of the 8 micron thickness? Is it homogeneous/uniform?
Are you using trivalent or hex chromate? I assume blue/clear color.
If you are using trivalent: Zinc content in chromate? pH? Concentration?
Please answer these questions and we may be able to help you in your problem.
Best regards!
Daniel Montañés