Duplex Nickel and Chrome Plating on Stainless Steel.
We are a high volume production, chrome plating company supplying into automotive industry. The automotive companies have increased quality standard. Our problem is with duplex nickel and chrome, plated onto stainless steel. Inconsistent adhesion of nickel to base metal. (plating peels off)All parts on flight bar peels, not just individual parts.
Our current process (excluding water rinses):
- 1/ soak clean
- 2/ electroclean
- 3/ cathodic sulphuric acid etch. 30% acid. 5 amp per square foot.
- 4/ semi bright nickel
- 5/ bright nickel
- 6/ chrome
When we add woods nickel strike operation, after acid etch, we solve peeling problem but experience roughness, which is now deemed unacceptable to auto industry. nickel strike operation is cathodic and we have bagged carbon anodes. solution is filtered continuously. It is our understanding that if process is correct, you should not require a etch and then a strike operation.(you should be able to use either one. I am asking if anyone has experienced the same problems and what would some suggest solutions be.Michael Hayward
- Adelaide, South Australia, Australia
First of two simultaneous responses(2000)
We acid etch and Wood's strike our stainless parts. Using the strike is insurance so to speak. You should not be getting roughness out of the strike, though. Keep in mind that a Wood's nickel, like other strikes, is relatively sacrificial and should be made up new relatively often. Are you putting a lot of grit blasted parts through the strike and introducing media to the solution? Also what pore size filters are you using? If they're too large, they're useless.
- Syracuse, New York
Second of two simultaneous responses(2000)
Keep your acid etch. Get rid of the carbon anodes. This is about the worst possible thing that you can put into a Woods strike tank.
Use rolled depolarized cast nickel anodes. McGean Rocho is one of the few companies that still cast them. Bag these and change the bag at least quarterly and every two months would be beneficial. Change your filter elements every couple of days until you do not show any more black stuff on them.
Personal preference is to run the HCl on the middle of the recommended and the nickel on the low end. Optimum adhesion is at 90 -100 ASF, but it falls like a rock at 110ASF, so I would use 80 -90ASF.
This tank system will generate nickel ions, so don't be cheap. Bail some out and replace the volume with an appropriate amount of HCl and water.
You should have absolutely no problem with peeling strike. Strike long enough to see color. That is all it takes.
If you do the above, you should not have any problem with roughness. If you do , increase the flow rate thru your filters rather than going to a finer filter media.
- Navarre, Florida
Hi Michael ,
The answer lies in the amount of time & current density used in the WOODS nickel Strike , as this process does not use any Brighteners , levelers if used for too long it develops what appears to be roughness but is actually nodulation . Cure is to check everything , Anodes , anode bags , they should be double or napped polypropylene , is the filter effectively filtering the solution , you are not just taking from & delivering to the same area of the tank are you ?
- Victoria Australia
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