Where the
world gathers for metal finishing
Q&As since 1989

Passivation required on Chemical Etched / Laser Welded parts ?

I work for a medical device company designing class III devices. My question is regarding passivation of chemical etched parts.

In our device, there are 2 chemical etched parts that are laser welded to a needle that has been formed (bent/shaped) from annealed tubing. All parts are 304 SS. After laser welding, the entire assembly is electropolished.

This device is used for minimally invasive surgery inside the eyeball, so contamination is of high concern to us.

My question is: do I need to worry about passivation on the etched parts? These parts may sit on the shelf for a number of months before being assembled / laser welded / electropolished.

Also, even though the entire assembly is electro polished (considered by many to be superior to passivation), should I be concerned about the interior surfaces not being fully effected by the electropolish. In particular I am thinking about the surfaces inside the needle (needle ID = .033"), and between the laser welded parts (etched parts thickness = .004").

Thanks very much for your help!

If the parts are going to sit around for awhile before assembly and electropolishing it is a very good idea to passivate. You can also passivate after electropolishing to get the highest chrome oxide ratios and best corrosion resistance, but this is not normally necessary.

The only way you can get any passivation inside the tube is to flow the passivation liquid thru the needle.

The parts that will be waiting on the shelves require rinsing with dissolved baking soda [on eBay or Amazon] solution, then final rinse with de-ionized water, then hot air drying - in order to eliminate possible rusting.

The assembled device after electropolishing require the same type of treatment since electropolishing work like etching in the hard-to reach areas. Therefore you need to eliminate residue from acid electrolyte by neutralizing in dissolved baking soda [on eBay or Amazon] solution, de-ionized water final rinsing and complete drying.

I would say a simlpe passivation of the parts full dip in the citrisurf 2250 at 125 deg. for 10 min at a 7% water mix would do the trick. I have been cleaning stainless steel for many years now and for me citric acid is really great. cleaner and safer to use. Good luck

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