Hi everyone, here's something that has been puzzling me for a long while. Why is it that when welding mild steel with an oxy-acetylene torch and the acetylene flow through the nozzle is slightly lower than optimum( I do not mean a carburising flame or a lean flame) then every so often the weld will pop and sometimes even extinguish the flame. The nozzle is not loose and the work is not dirty or oily. To clarify, I usually light up the acetylene and flare to a fox tail till there is no black smoke, I then run in the oxygen to a fine tip, so if I just open the acetylene 3/4 of where it should be I'll get the problem. I'd just like to know the reason that this happens. Any ideas? Thanks for your help in advance.

My experience with oxy/acetalene is limited. But, make sure your running the acetylene at 5psi, if your flame is too big, use a smaller tip. More than likely, sounds like just a lack of pressure.

BTW, what are you gas welding? Or are you brazing?

MC

My experience with oxy/acetalene is limited. But, make sure your running the acetylene at 5psi, if your flame is too big, use a smaller tip. More than likely, sounds like just a lack of pressure.

BTW, what are you gas welding? Or are you brazing?

MC

Thanks for the input MC. This problem never happens whist brazing or cutting just when welding mild steel. The pressures are set right and it doesn't matter whether I use a #50 tip or a #500 tip I still get the same thing happen given the same conditions. I know how to stop it happening , I'm just interested to know why this happens.

You mean "popping" as in little pops (noise) that sometimes create spatter while gas welding? That is the oxygen reacting with the steel. I thought you meant your flame was making a loud popping noise then going out.

MC

HI MC thanks for getting back to me. Yep, I mean just that, you are welding away and suddenly there is a loud bang and the flame goes out and the weld gets blown to the four corners of the workshop!!lol. It is a very similar sound to the popping when you turn the torch off and I have wondered if it is caused by the same set of circumstances. I understand that oxygen reacts strongly with red-hot steel as that is how a cutting torch works generating a super-heated area that is then so fluid the pressure in the central oxygen jet is enough to blow the material away. But why would it pop? What is really happening there? Maybe this is more of a physics question than a welding question. Thanks for your answers anyway.

That is just what happens when the flame goes lean. Same thing as you have your torch properly set-up for welding or cutting, and you turn the acetalyne off, BANG! Turn the oxygen off first, the acetalyne flame goes rich and smokes like hell, but no popping. I'm sure there are some physics or chemistry behind it, but simple answer, the results of a lean flame.

BTW, I'm no chemist or physics major, but a oxy torch works by rapid oxidation. Simple thought is the pre-heat flames heat up the base metal and the oxygen blows it out of the way. Not true, it's rapid oxidation that is actually cutting the steel. This is why oxy torches won't cut SS or aluminum, they can melt them and blow them out of the way, but I think you understand the difference.

Plasma on the other hand, was discovered by Union Carbide back in the 50's or 60's? They were playing around with TIG welding and tried using high pressure shielding gas and realized that the rapidly expanding gas increased the temperature of the arc, which lead to what we know today as Plasma cutting.

Plasma is by definition super-heated gas. The rapidly expanding gas, shop air in most cases, allows for the arc to generally hit temps around and above 25,000*F, in the case of Plasma cutting, yes, the base metal is simply heated then pushed out by the high pressure gas, weather it be shop air, nitrogen, argon, helium or a mixuture of those gasses.

MC

It sounds to me like your tip might be dirty, and possibly have to large of a hole for what you are doing with it. If you clean your tips too aggressively you can accidentally enlarge the hole in your tip.

Personally I prefer the Henrob 2000 (http://www.cut-like-plasma.com/):cool:.

I once had a flame that was only an inch and a half long, that I then held my hands as far apart as possible, and tried to see how hot the air was at that distance. Well what ended up happening is I burned the skin on my hand. Which would definitely not have happened with a normal torch, but the truly amazing part of it was that the burn was only an inch and a half in diameter, to have that size burn with a normal torch your hand would have to actually be in the flame.

If you go from a nice clean new standard torch, to a dirty old Henrob, you would still see how much better the Henrob is than any other standard torch.

One note about using the Henrob, use a smaller tip than what you would use in a normal torch, or you will be constantly blowing out your flame.

To see this torch in action watch this http://www.youtube.com/watch?v=6v1WJ6uPsaQ (not my video), especially watch to see how thin the flame is.