Do roller swaging & proof load test remove passivation layer of outer surfaces of the bearing ra 1

The oxide layer on chromium steels forms on its own. Passivation is primarily to remove free iron that serves as a corrosion initiation site. If the surface was passivated to begin with then as long as tools are used that don't add iron back, it will be OK. A key is to use tools for use with stainless steel only with stainless steel.

This is different from anodizing aluminum where the surface is forced to convert to aluminum oxide to a far greater depth than the ordinary oxidation would manage.

Dave,

Thanks for the response, the race is made of 17-4PH. So, unless there is machining/grinding on the passivated surface, the pressure from swaging won't affect it much? The vendor is asking us to remove the passivation requirement on the race.

I am confused - what does the vendor do for you?

The swaging process will likely introduce iron to the surface, so your part will not be considered passivated after swaging. The grinding component can also introduce iron unless the machine is specifically used for stainless steel only.

Passivation should be the last step of the manufacturing process. Consider removing the passivation requirement to take the burden off the machine shop and perform the passivation at a specialist after final machining.

Dave
The vendor is producing the bearings for us, we are finalizing the engineering drawing.

Tugboat
Passivation for spherical bearings is typically done after swaging process? Seems to be difficult to clean the chemicals off after the swaging? Maybe the acid would damage the liner? that's probably why the vendor is asking to remove the requirement.

You're right, it would be very difficult to passivate the contacting surfaces of a spherical bearing. You may have just found that you have specified an impossible to meet requirement.

I would consider coating these surfaces with a material that is not subject to sensitization. First thought is electroless nickel but these coatings might be too brittle to survive the swaging process. You may have to swage to a near finished shape prior to coating.

Also, a stainless steel surface in contact with another surface may as well not be passivated. Anywhere contact is made such as inside of a spherical bearing, crevice corrosion will be the dominant failure mode and that will occur regardless of surface conditions. Using a less noble copper based alloy such as bronze will help prevent the crevice corrosion at the contact points.

Tugboat

Yes, the ball is going to be chrome plated, so the spherical ball is good without passivation, but it's the race that I was confused on why it cannot be passivated since it has no coating, it seems like the way the vendor applies the liner, the race outer surfaces will be somehow machined as well, no idea how and why, I guess 17-4ph should be fine without passivation?

I "feel" that the geometry of a stainless steel spherical bearing poses too many other corrosion sources which override any benefit of passivation.

Also note that hard chrome coatings have fissures in their surface so the base metal will still be exposed in places. This means pitting is still a possibility with hard chrome plating alone. Nickel plating is often used under hard chrome plating to prevent corrosion of the base metal.

What environment will this be exposed to? This combination of materials is fine for most terrestrial conditions with the exception of salt water/spray.

(Taking notes on nickel plating the ball...) It's going to be part of aircraft, non-pressurized.

I have given you what I can. I am an end user and see failures from material selection but am NOT an expert on material selection. 17-4 is an alloy that is highly resistant to atmospheric corrosion and generally acceptable without special consideration. I would not hesitate to use 17-4 without passivation for your application but I cannot say that with authority.

This is being mounted in an aluminum housing?

Yea I was told that the vendor will machine & clean the race surfaces, it should be fine. The housing is made of passivated stainless steel. Thank you for sharing your knowledge!