How to clean stainless ?

[Hitch]

I use this. Gotta be honest, scares the hell out of me. You MUST use the neutralising paste. That stuff can drop on concrete and still be fizzing after 5 minutes.

I believe it's Nitric and Hydrofluoric Acid. It's the Hydrofluoric which is the proper nasty bit.

A spray is much better really because you get a uniform appearance rather than an obvious etched

A much safer but more expensive option is electro-passivating or electropolishing. Just uses harmless phosphoric acid and dc current.

They pedal it as harmless, but that tig brush fluid is nasty. It will melt through some stuff, like the backing on those day to day handling gloves and leave you with sore skin...
And the fume is hideous.

Have to admit, I'd sooner use antox paste any day.
Use it properly and there's no issues.

 

[Hitch]

These are the two for tig brushing, looks like the electrolyte is 75% phosphoric acid.

 

[Agroshield]

But whatever I do I need to avoid white staining.

Would the quality/hardness of your mains water have an influence on this?

It seems a lot easier these days to get bulk deionised water - I think a lot of window cleaners use it with their pole systems.

 

[Munkul]

Re "passivating" is your customer calling up something specific on that?

I retired some years ago, and it may well be the case that H&S and environmental factors have forced changes in the methods used to process stainless. But back in the day, we always thought in terms of three-step processing of most stainless steels;
>cleaning - invariably an alkaline cleaner
>pickling - a mixture of ~3% hydrofluoric acid and conc nitrc acid
>Passivating- conc nitric on its own.

-with lots of water washing between each stage.

Such treatment appreciably improved the corrosion resistance of 300 series steels and was beaten only by electro-polishing.

I never used phosphoric on stainless, nor did I ever become aware of anyone else using it, but Google now shows it's fairly standard practice and it's apparently biodegradable.

Yes, they're a food industry supplier so everything needs to be mint. Previously they've done all the passivating because its a faff and i didn't want to do it.

An electro passivating setup with phosphoric acid based solution cleans, pickles and passivates in one step. Then you just neutralise it.
You can use a few different milder acid solutions... Sulphuric gives a matte finish. Citric works too, but much slower. Elmer Wallace sell an "eco" balanced pH solution which just neutralises with water, again works a lot slower.

I'm a big fan of electro passivating, its far safer than pickling paste. With the right power source it's pretty much effortless. The Bymat has an AC mode which is literally double the speed of the DC modes, but not sure how it compares to other machines... isojet and cougartron with single DC mode were around the same speed, IIRC.

PPE wise, definitely use a proper organic filter mask or airfed respirator, the fumes are noxious and probably harmful. There isn't a lot of it, but it comes right up in your face. i haven't seen any concrete data on this but better safe than sorry. Also, acid splatters everywhere, and the Neutraliser solutions are medium strength caustics usually, so gloves etc unless you like the nip of the chemical burn.

We used a lot of electro passivating in my previous workplace, i actually set it up because the h2s fumes in some areas were attacking stainless welds from the outside (previously they just wire brushed the colour away). We used Elmer Wallace turboclean and mainclean.
I'm using Bymat electrolyte A which is basically the same as Turboclean but a bit weaker, looking at the msds.

 

[Munkul]

Would the quality/hardness of your mains water have an influence on this?

It seems a lot easier these days to get bulk deionised water - I think a lot of window cleaners use it with their pole systems.

No its just acid that carries on reacting with the stainless, basically it does the opposite of passivating it and it starts rusting after a while.

 

[Ross365]

If anyone is using hydrofluoric, you can get a special cream to treat HF burns as First Aid. It's full of calcium and the idea is the calcium reacts with the fluoride, unfortunately, I cannot recall the name of the product. I only recall one incident when some got a very small HF burn, but it was decided they had to go to the local A&E.

 

[Hitch]

Calcium Gluconate gel I think it is, got a tube of it on the side of the coshh cupboard that stores the acid.

 

[Anguz]

Calcium gluconate

 

[Anguz]

There's another supposedly better one...but I can't remember what's in it... we keep both at work, mind you we have 3000l of hydroflouosilic acid

 

[Ross365]

Yep, calcium gluconate gel. Some years ago the French brought out an aerosol that was supposed to be good for all acids including HF. Not sure about that and never used any.

When you see pictures of really bad HF burns, they really are scary enough to make you remember them forever and regard it with great caution!