Why does Oxy Acet crack sometimes?

Done a little MIG welding, and Arc, but never Oxy Acetylene. Had a go with some gear my friend has, and found that I often get a laud CRACK and this occasionally blows out the flame, its very similar to a small explosion.

why is this?

Is it because I am holding the flame too close to the weld?

Or is it to do with the mix of the gasses?

Any help offered most welcome.

Thanks all Deb

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Most likely getting the torch to the surface and causing a blowback.

Mix will have some effect on this, but distance to the surface is generally most of it.


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wrote: (clip) Mix will have some effect on this, but distance to the surface is generally most of it. ^^^^^^^^^^^^^ It can also be caused by running too low a gas flow for the tip, or by having a poor connection between the torch butt and the tip. Look for cracked O-rings or nicks on the metal surfaces.

Reply to
Leo Lichtman

That happens with the tip gets too hot. If the tip is black with carbon soot, polish the end. If the tip is to small for the job so you're too close to the work, that will also overheat the tip. Either way, the hot tip causes the oxy/fuel mix to explode inside the tip.

Do you have flashback arrestors at your torch? You should. Are you adjust> Done a little MIG welding, and Arc, but never Oxy Acetylene. Had a go

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Don't do that, it's a bad thing to have happening. In particular the more you do it, the more often it will happen.

Technically it's caused by the flame propagating backwards past the nozzle orifice, because you're no longer keeping the gas velocity forwards high enough to "blow the flame forward". When the gas burns faster than it's all travelling, the flame front migrates inside.

Lots of things cause it, some are technique, some are kit. Generally it's some variant of "too small a flame on too big a hole" which you can cause by:

- Setting the flame size too small by adjusting the gas down (switch to a smaller nozzle)

- Holding the nozzle too close and disturbing the gas flow (move back).

- Using a worn nozzle, particularly one that's oval or bell-mouthed (go easy with those prickers and change worn-out nozzles)

- Sticky regulators with creeping pressures and varying gas mixtures.

- Dirty kit, particularly a dirty mixer.

If you have such a backfire, then shut the gases off and let it all cool down before even thinking about re-lighting. A small pop should make you count to 10 first. A "screamer" where it actually burns inside the nozzle (you'll know it when it happens!) is an excuse for a cup of tea.

OK, so you're learning to weld so it'll be about positioning. No big deal, we all do it. Maybe try a smaller nozzle and faster gas flow though - it's easier to control.

REALLY don't re-light a hot nozzle or dirty nozzle. If the rig is making a habit of popping back, such that it's actually getting warm or sooty somewhere it shouldn't, then fix the problem before carrying on welding. This is the situation that leads to a flashback into the torch body or hoses, and you really don't want one of those.

Reply to
Andy Dingley

Lots of reasons, some equipment, some technique. One thing I haven't seen mentioned yet is to raise your acetylene pressure a bit and see if that helps. Often if I have a torch that is prone to "popping", I can give it another couple of pounds of gas pressure and it will settle down.


Reply to
Bill Marrs

Many thanks to you for your info. Have tried plying with the above, and not perfect, but getting much better.

Again thanks Deb

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Got a new set of welding tips, for those I thought too far gone, and got the correct tip files for the others. Have also played at adjusting the gas settings, and now feel that it was a combination of me too close, and the tip too dirty.

Many many thanks to all for the help


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