Passivating stainless steel

[RedNeckGeek]

I got a feeling you used carbon steel filler metal, and C-25 gas.

Sheesh, I hope not :shocked:

But if that's the case it's probably time for a rattle can of Tijuana chrome. I bet you can teach that robot to apply a perfect coat. :laughing::laughing::laughing:

 

[Sodo]

I figured it out years, and years, and years ago, it is cheaper, and less frustrating to play by the rules.

It can be cheaper,,,,, if there's volume to support following 'the rules'. BTW good article on SS with a MIG, thanks for that link.

Just want to research this over the weekend and git'er done on Monday. Simply have to grind (60!) droopy robot-welds with minimum effort/cost and the buyer not noticing there was re-work.

 

[Shield Arc]

This is the perfect project for a Tig welder! Even a scratch start Tig rig would work great on those small stainless steel tubes.

 

[yomax4]

If you use abrasives designed for stainless you shouldn't have any rust issues. If you already stained the area you can use pickling past to bring it back to color match. You will have to neutralize the paste afterwards. Many fab shops that Tig SS have pickling past or the acid you are looking for to remove the rainbow next to the welds. maybe they will give you a small amount. It is nasty though. So much so that it can't be sent UPS.

 

[Sodo]

Not welding, just cleaning up after a slovenly robot. The tubing is 3/4" x .080 thick stainless. It has a beadblasted appearance and I was told the final process is called "electropolishing".

Heres the pic again from the top post, this is exactly the re-work I have to do. The weld has been ground flat with angle grinder then peened with a wire wheel. You can see the area where the wire wheel darkened the surface. I think this is OK, as long as it doesn't darken further over time, and look like a stain or even rust. Unknown if the wire wheel is stainless, but (if I don't come across any pickling paste) I will make sure the next brush is stainless. Appreciate all the help!

Still on the lookout for a passivating method but almost convinced I can get away without it. Thanks Gary, Steve I'll avoid Hydrofluoric acid.

Heres my plan.

1) Grind the offending weld bead with just enough pressure to avoid heat coloration beyond.
2) Polish it with a new clean flapper disk.
3) Peen it with a stainless steel wire wheel.

 

[Shield Arc]

Have you tired a Scotch Brite pad? The welding inspectors use to drive us crazy with our stainless steel. They would wrap their hand with toilet paper and wipe the weld zones, if the toilet paper snagged we had to hit the weld zone again. Seems as I remember the Scotch Brite pads really helped with the color of stainless steel.

 

[RedNeckGeek]

McMaster Carr carries a wide variety of abrasive pads, many of which can be powered with a die grinder. Two day delivery to my place but not the least expensive place to order. Something on this page may help you:

McMaster-Carr

 

[Sodo]

Got die grinder scotchbrite type too, forgot I had them. Diegrinder & pads at HF cost about the same as pads alone at McMaster. Not really, but I got an HF air grinder for $9.99 and pads for $4.99 for an earlier project.

Here's the discs



I like McM, they give you a lot of info, even the drawings with dimensions. McM is overnite to Seattle, not sure how they do it!

 

[Gary Fowler]

If I were using a flapper wheel, I would forgo the brushing afterward. Depending on the grit, a flap wheel can polish to a mirror or near mirror shine. Much better than a grinder as a little mishap as shown to the left of the weld in your photo doesn't do the damage like a grinder wheel

 

[BukitCase]

Polish?? Did somebody say POLISH???

Seriously tho, I'm with Gary on this one - most of what you've made fun of (in a loving way, of course :laughing was done with flap disks - and the ones I use most are 36 to 60 grit. If you were to go up to 120 or finer, and use a light touch, I doubt you'd even see any marks... Steve

Although for blending, you'd probably wanna use some STAINLESS scrap to "break it in" first - when new, the outer edge can be hard to control for blending. Once the square edge is worn off, they become easier to control...