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I'm new to welding and am having a problem with gas welding: when using B.O. number 3 jet with 2 lb per sq inch pressure on both gases, I get a loud popping noise which often blows the molten metal clean away. What causes this?

Hi Popeye!

It's along time since I done any O/A welding, however this type of problem can be caused by wrong gas pressures, you could try upping them a bit!

Are you using a 'correct' flame? For welding steel, it should be an 'oxidising' flame.

Is the nozzle the correct size for the thickness of material being welded?

Is the metal clean?

As you can see, there are a lot of varibles involved!

2psi is too low. For normal welding you want them both on about 4psi and then keep the 'point' of the flame a short distance away from the workpiece.

Fire the Acytelene up first and turn it up until the black smoke stops, then bring in the Oxygen until you get the right flame!
. . . . . > Flame settings & Welding guide < . . . .
Thanks for your replies guys.
QUOTE (rodofgod @ Nov 27 2005, 08:40 PM)
Are you using a 'correct' flame? For welding steel, it should be an 'oxidising' flame.

Hi Rodofgod,
don't like to contradict you, but isn't an "oxidising flame" (very blue) not for brazing?
For steel a "carburising flame" (blue with a touch of red) should be used.

sorry Captain and Rodofgod but you both are wrong. The correct flame setting for welding steel is neutral.
A carburising flame will add carbon to the weld and increase the hardness and brittleness.
An oxidising flame will cause oxidation of the iron making the weld weak and brittle.

Popeyes problem is that the flame keeps backfiring ( intermittent retrogression of the flame back into the nozzle ). This may be caused by gas pressure too low, nozzle to close to the work, dirty nozzle or nozzle too hot.

The big problem is when a flashback occurs.


Hi Harweld!


Grr, thanks for keeping us on the straight and narrow! Sometimes my fingers go faster than my brain!


Hi Guys

Wow! this is a brilliant forum for getting to the heart of the matter - thanks for all the very helpful comments - even the contradictory opinions are of great help as they give me a deeper insight into the subject.
you're right, I completely forgot about the neutral flame.
Thanks for keeping me right!
Blob the Welder

Up your gas pressure to 3psi

nigel 42
hi all

believe a slight carburising flame can be used for bronze welding
and when gas welding stainless steel you start with a slight feather on the flame
as the nozzle warms up you adjust to a neutral flame

regards nigel 42
Poacher Turned Gamekeeper
Agree with Harweld.

Neutral flame for carbon steel.

As you are new to this I would bet (from experience as a welding tutor) that you either have a dirty (caused by being too close to the weld pool) or worn nozzle (constant cleaning) but most probably have an oxidising flame.

Try a new nozzle and when setting the flame, ignite acetylene first and turn up until the flame stops smoking (the flame should still be in contact with the end of the nozzle - if it isn't, your gas pressure is too high for the size of nozzle you are using, so turn it down). Open the oxygen valve and adjust until the white feathery cone disappers into the bright blue inner cone. You can tell a neutral flame by the blue halo around the end on the nozzle (this dissapears if you have too much oxygen). If you do have too much oxygen, the flame will hiss and the inner cone will become sharply pointed.

Hope this helps!
hi popeye, game keeperand hareweld are correct, but please remember , when you do have problems with the pressures you could have a "blow- back" make sure you have non returns fitted to your gas torch and your gauges , if not fitted you could get killed by you bottles exploding, so regardless whether you have them fitted or not allways "blow- off" when you out the torch, this means turning the gas off and blow a little oxygen through , allways turn thes bottles off completion . there has been many fatilities where the oxygen has been left on, when you light up again bang your gone, keep practicing your gas welding it can be very rewarding good luck . oddy
A slightly carborizing flame was reccommmmended for brazing when I used to do it.
jobber & nigel42,

The correct flame for both brazing and brazewelding (bronzewelding ) is oxidising.

This is used to supress the volatilisation of the zinc.

Regards. Harry
nigel 42

appologies you are correct

have now found out that a caburizing flame is only used for hard surfacing and stelliting purposes

this acccording to caxton press modern welding handbook 1961 edition
"a slightly oxidizing flame is useful for welding bronze while a definitley oxidising flame is esssential for brass.

regards nigel
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