Passivation and laser etching of stainless steel

A. I would look at two other approaches. Check with Stellar Solutions [a finishing.com supporting advertiser]; possibly their citric based gel would be a more practical solution to the problem. Another approach would be to talk to the brush plating companies. At least one has a brush electropolish which looks like it would be a good way.

A. Gary, why the heck would these require passivation? The way to do assemblies, as you know, is to passivate the piece parts before you assemble. Unless there's machining on these parts, through which stray iron particles can get onto the surface of the 15-5, then the original passivation is still good.

When we have to machine assemblies, we use carbide tooling or grinding wheels dedicated to stainless steels, or some other such controls to make sure we don't need to passivate again. Mere laser marking will NOT affect the surface such that it'll require passivation again.

Does your company have evidence that laser marking WILL affect 15-5 corrosion resistance? I've never seen such, and we've been laser marking for decades...

A. Depending on the type and power of the laser you will normally destroy the properties of the steel due to the high heat of the laser etch. This is a major problem in the surgical and orthopedic industries which has been resolved with the products mentioned above. Many of these assemblies must be laser etched AFTER assembly, and then the laser mark will rust in autoclaving or other disinfecting processes, or in corrosive atmospheres. The weakest part of the device for corrosion will be the laser etch. This is why they use a paste on the laser etch area after assembly, but it must be a product that passivates the etch without totally removing the desired black color.

adv.
Let us know if we can help.

A. You could laser after passivation and thus avoid the problem altogether. Bear in mind, the laser process does not impart any foreign substance to the stainless which would promote corrosion, and passivation is the process used to dissolve ferrous metals from the surface of the stainless steel.

A. Laser etching areas on stainless steel are indeed more susceptible to corrosion, and passivation treatments do have the tendency to remove the laser mark. What is often done is a full length passivation treatment prior to the laser etch, then a reduced-time passivation treatment after the laser etch. This helps restore corrosion resistance around the laser mark but you can stop short of the point where the mark starts to fade.

Update:

I now boil my pieces in a solution of Alconox ⇨
and water, then sonic-clean in methanol ⇦ on eBay or Amazon [affil links] and sonic-clean in acetone ⇦ on eBay or Amazon [affil links] Warning! highly Flammable! . This seems to work better, but with all of the harsher sterilization procedures on the forefront, are there better ways to go about this laser marking preparatory procedure?

A. Ed,
Passivation is always, always, always, the final step in manufacturing or fabrication of a stainless steel item.

The sticky wicket with laser marks is that many marks are unable to endure the acid bath for the entire length of time needed for passivation. It's always better if the laser setting can be adjusted to produce a more resilient mark, of course, but the more common work-around is to perform a full-length passivation prior to marking, for the sake of the part as a whole, and then a shortened-length passivation after marking, for the sake of the mark itself.

A. Hi Fionn.

There are so many ways to blacken stainless steel (black oxide, black chrome plating, anodizing, and paint are a few), that it's hard to eliminate all but one and come up with a suggestion. But if you are talking about blackening just indicator marks, the fastest and easiest may be laser marking. For longest wear, it is preferable to machine indentations into the tubing where you want the markings, to reduce the wear on them and increase their longevity.

Regards,

A. Try stencil etching; you can use ac or dc current -- one of them should give you white etch, the other would give black etch. Good luck

A. I have used etching kits for years to mark 416 and 410 stainless gun barrels. The last couple of years I have been sending them over to a local engraving shop for laser engraving. The results are a million times better. They can make the etching as deep as I want and at the same time they can cut lines that are only a few thousandths of an inch wide. The diversity of pictures and fonts they can create is limited only by the software they have. They can even do custom images on demand. They simply scan them in and out they come. The best part is that it's dirt cheap.