HOME FAQs BOOKS JOBS: Help Wanted Suggestions you are here: Hotline/Forum => Letter 44089
Electropolish and Bead Blast?
+++++++
We recently reviewed routing sheets for a maker of 303 stainless steel components which are then electrodeposited with nickel plating per QQ-N-290 [link is to spec at TechStreet] specs. Routing sheets indicated a permaganate clean followed by an electropolishing step and then followed by a dry glass bead blast.
These components are seeing a high degree of plating adhesion problems recently even with the above cleaning regime. We reviewed other components which have similar cleaning processing/plating done to them without any plating adhesion problems. Those components are also made of 303 stainless.
We've went to copper strikes recently which has resulted in components where the nickel plating adheres but it is believed at this time that the root cause of the plating adhesion problems still not been identified?
Removal of Nickel plating from stainless steel surface is not an option. The engine manufacture wants the plating.
Aerospace - Buffalo, New York, USA
+++++++
I may have misunderstood your question, Daniel, but it sounds like you don't yet have any observations upon which to make a conjecture towards root cause except that a copper strike helps. If I understood, the parts are processed identically and the plating adheres to some and fails to adhere to others?
QQ-N-290 says it applies to steel (and copper materials) but it does not claim to apply to stainless steel, and I don't think it does. I think you need to do a Wood's Nickel Strike before the copper plating. Of course, the usual caveat applies that you can't process real parts except per the specifications.
|
 Ted Mooney, P.E. finishing.com Brick, New Jersey |
+++++++
My favorite subject, 303.
From several years in jobshop work, we rarely saw just plain 303. It almost always had a suffix something like S or Se or ? These make a world of difference as it is an additive to 303 to make it "free cutting" as in leaded brass.
That said, I have never seen such an aggressive preplate cycle.
The electropolish makes it difficult to plate because the surface is now very passive and has oxide films. The glass bead helps to reduce the passivation by roughing up the surface.
The solution to adhesion problems is a stronger acid activation step, one for whatever suffix SS you are working with. You have NOT mentioned what you are using. Without delay, go to a Woods Nickel strike. This is not a good place for a sulfamate nickel strike which is great in a few other places. Next is to not let the parts repassivate between the strike and the nickel plate (it only takes seconds). Keep the parts wet and proceed as rapidly as the line will go.
I do not remenber any Aerospace OEM spec that allowed a copper strike on 300 series alloy under a nickel plate.
- Navarre, Florida
First of two simultaneous responses -- +++++++
Hi;
It is 303 SE. It is plated with a low stress sulfamate Nickel plating. We did an SEM and found on the back of the plating (the part of the plating that is in contact with the stainless steel) Cadmium and Chromimum.
We have observed their processing and according to both the platters and connector maker these connectors are the only ones that have plating coming off. Plating a stainless steel connector with Nickel is kind of redunant but that is what they want. The connector itself is quald to MIL 83723/88N. That spec calls out QQ-N-290.
We have seen other parts that have everything the same (material, plating, no copper strike) and did not observe any plating coming off.
I am thinking it is in their cutting fluids, or pre plating processing which is not removing something that they are putting on.
Thanks
Dan
- Buffalo, New York, USA
Second of two simultaneous responses -- +++++++
I'd agree with the previous two submissions adding that the permanganate followed by electropolish pretreatment is what I would expect for heat treated or welded stainless that has an intense blue heat treat scale. Using an alkaline permanganate renders the blue, acid-resistant scale removable by acid (i.e. electropolish)treating. My firm does a ton of nickel plating on stainless, Invar, and other nickel bearing aerospace materials such that the parts can be brazed - we rarely encounted such adhesion woes - especially on something as basic as 303 (S or Se) stainless! Another possibility could be the cleaning - anodic cleaning of nickel bearing alloys can also render the surface more passive that it would be otherwise.
|
Milt Stevenson, Jr. Anoplate Corp  Syracuse, New York |
|
+++++++
Dear,
With all that cleaning and electropolishing, your are realising a perfectly clean and smooth surface. Why are you destroying/contaminating this smooth surface with the glassblasting?
In my experience, an electropolished surface is a perfect base for an electroplating.
On the other hand, the sequence and type of layers you have to apply are very important and are the problem/answer in your situation.
- Brugge, Belgium