Stainless rusting...

[weldguy]

Wow thats crazy! I have done TONS of 304 stainless work and have never had an issue even remotely close to that!

Does a magnet stick to this particular piece?

Do you have piece of scrap from that job that you have not surface finished? You could leave it outside and see what happens to determine if it is in fact your finishing or just the material itself?

[davek0974]

I'll have it back in a couple of days, can test it then.

I might still have the skeleton of the sheet outside, will check.

Edit...

Just checked and I have two skeletons from the same batch/order outside on the pile, been there maybe 8 weeks or more, no rusting just a couple of spots of brown.

Had some scraps in the bin from this job, one was finished where i tested the flap-disc and another just plain, I have put them outside to weather.

Could it be the flap disc maybe having ferrous abrasive content??
I used to finish these with a stainless wire brush but after a near-miss with the grinder/brush I won't do that again so changed to a flap-disc which was easier and far safer as the stainless brush was very "grabby" which is what caused the near-miss.

Is there a recommended abrasive for stainless?

Have been looking at a large (6") hand drum sander for the job but would need to know if its a good idea first?
https://www.ebay.co.uk/itm/Electric-Bur ... 3979520099

[weldguy]

[robertspark]

I did wonder about the flap discs and whether they were zirconium or aluminium oxide or something with steel in them...

use a stainless wire brush for SS + I believe zirconium flap disc

[davek0974]

I won't use a SS wire brush again, nearly killed myself with one, not going there again.

So zirconium and ALox is ok on SS ??

[davek0974]

Just had a look and the flap disc i used was marked zirconium and was blue as expected.

I am baffled now, the customer is in-land so its not salt etc.

The only thing i can think of doing with this part is to re-finish it with steel tools and then clear-coat it, cant use stainless tools as the rust will contaminate them i think.

As for future parts i have no idea at all but i either need to fix it or drop these parts and that means a sizeable loss of income.

[ben de lappe]

I took a minute and conferred with a good friend of mine in Florida who does the most amazing artwork with stainless and other alloys. Her first question was do you use a water table? Any piece she plasma cuts is coated with clear powder as she knows it'll rust. She warned also that any buffing, grinding or even wire brushing with ss brush creates friction building heat within the piece and actually pulls the carbon to the surface. If you can't repasivate the surface coat it with powder is her advice.

[davek0974]

Down-draught table here no water.

All my stuff is surface-worked so it sounds like the only option is clear-coat.

I have looked at passivating in citric acid but its just not practical at all on big stuff.

Thanks for that, appreciated.

[davek0974]

I have started clear-coating it.

It does look really good but darkens the sheen to a very pale straw hue, not the usual bright finish, but it does look really good.

[adbuch]

Could it be the flap disc maybe having ferrous abrasive content??

That was my first thought when I read this. Perhaps ferrous material being imbedded into the surface layer as a result of grinding with a flap disc that was previously used for grinding steel, etc. I know that I use a dedicated stainless steel wire brush for removing oxide from aluminum before tig welding - to avoid contamination of the aluminum with ferrous material.
David

[davek0974]

I think it was contamination, I was using cheap "stainless" cup brushes - my thoughts are that they were not really stainless and was contaminating the metal.

I now only use segregated tools - a grinder with flap disc, mini drum sander and thats it - both tools only ever touch stainless.

Since then all the samples i have out in the garden on the test bench seem quite happy and show no sign of corrosion, no more customer issues either.