Curated with aloha by
Ted Mooney, P.E. RET

The authoritative public forum
  for Metal Finishing 1989-2025
  

Local / Swab / Spot Passivation for an Assembled and Laser Welded Part

www.finishing.com is made possible by supporting advertisers ...
this text gets replaced with bannerText

Q. Hello all,

I am required by my customer to perform spot passivation on a Laser welded assembled part made out of 17-4 and a plastic component. I have not performed spot passivation before and was looking for some advice. We have a Nitric 2 Passivation line currently, and are not approved for citric.

Does anyone have any advice on how to make this go smoothly? Any recommendations on what swabs to use, and how to test the parts after? Or what to look out for?

I'm concerned on how to test the parts as all of the test methods we currently use involve submerging or spraying the entire part.

Additionally, do i just walk the part down our normal clean line, but instead use a swab at every step instead of submerging the part? Or is general practice just to clean off the weld, swap passivation, and then clean again? Is there any need for neutralization?

Justin,
The typical procedure for spot passivation is to brush on a paste/thickened acid (or spray it on for a liquid), let it soak the amount of time called for by the standards for a room temperature treatment (i.e. at least 20 minutes for citric per ASTM A967), then rinse the acid off thoroughly and let it dry.

Testing can be per any of the methods provided for in the standard being used, though of course that's limited by the size of the item. Copper sulfate is generally fine, A967's wet cloth test would be the fallback from there.

When you say you are not approved for citric, that would be not approved by whom? The customer?

(Adv.) If you are in need of citric acid passivation products for this, my company can assist.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois