[Josh646]

I welded up a bin out of some scrap stainless for practice and shop organization. I am going to try to finish the outside for practice as well.
My question is how to clean up the inside? Since it was a bin, I used a backer bar and it discolored.

[Toggatug]

Are you looking to grind down and blend the welds or just polish the heat tint off?

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[cj737]

A backer alone won’t prevent oxidation. It can help, but only an atmospheric purge will prevent it.

You can remove some of the tint with a stainless brush promptly after welding, but the sugaring will remain.

[Josh646]

Sorry.
I am not sure of a good way to clean up the backside of the weld joints(the inside of the bin). Is there a commonly used “pickling gel” (passivation agent?) that works for this type of thing?

This is totally a non-critical project. I am getting practice in anything I can.
Thanks in advance for any help you can provide.

Josh

[Josh646]

A backer alone won’t prevent oxidation. It can help, but only an atmospheric purge will prevent it.

For future reference, would a small backing purge box work for this type of thing, if I position it on the backside of each weld as I move along?

Thank you for your help.

[tweake]

pickling gell will clean it up fairly well but may not do much if its sugared.
backing plate can work really well, but it needs to be firmly attached and i found thin material can warp a bit and lift off the backing plate. the aim here is more about cooling than shielding. i think jody has a few videos on it.
a purging backing plate works the best.
you can also simply dam off the aera with tin foil.

[cj737]

A backer alone won’t prevent oxidation. It can help, but only an atmospheric purge will prevent it.

For future reference, would a small backing purge box work for this type of thing, if I position it on the backside of each weld as I move along?

Thank you for your help.

Sure will. For some practice, you can weld 2 pieces of ally angle iron together to make a long box. Seal both ends with flat piece. Then you can drill, mill or grind either lots of small holes (like 1/16-1/8) throughout one face. Drill a hole in one end to run a purge hose. This will make a crude but reasonably effective purge box for non-critical practice or pieces.

I’ve made several variations of this, each with a tapped hole for a quick connector. Some are flat and drilled, others are on the edge for inside or outside corners. Just use your imagination when making tools to help you weld or fabricate better.

[sbaker56]

Pickling gel can be some NASTY stuff, while you can use citric acid or something similar for very light heat tint, commercial passivation/pickling gel often is a wonderful combination of sulfuric, nitric and hydrofluoric acid. While sulfuric and nitric acid will generally just burn you, HF is EXTREMELY toxic and can do anything from eating away at your bones to stopping your heart.