Basic questions on O-A

This should help with welding:

And this one's for cutting:

If those aren't correct for your equipment back up to here and see what you can find:

Best Regards, Keith Marshall snipped-for-privacy@progressivelogic.com

"I'm not grown up enough to be so old!"

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Re: Annoying welding problem

Here it is quoted again - seemed generally well-received.

Richard Smith

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My own addition (experience - UK City & Guilds training, plenty of use oxy-acet at work)

Nozzle size. You want a certain amount of heat, so you will try to put a certain mass per unit time of oxygen and acetylene through the nozzle, regardless of its size, so

- too small and the gas velocity is too high and it blows the molten metal away - as soon as the metal melts it sprays away on the far side, so you end up reducing the size of the object you are heating but never welding it, at the extreme

- too large and the gas velocity is lower than the flame velocity and you get light-backs into the inside of the nozzle, with noted bangs and the weld pool being thrown around, usually over you, especially in your hair.

The nozzle size if fairly critical. By that I mean, if the job rightly calls for a #3, you would be happy neither with a #2 nor a #4.

Another reason for "banging" is that the nozzle simply gets so hot that there is lighting of the mixed oxygen and acetylene in the inside of the nozzle. If you really do have to work for a long time in an awkward corner, it is OK to dip the nozzle of the torch in a bucket of water every now and again. Told flame will stay lit while you do this, but never tried it...!

Pressure at the regulator. I don't think it will have any effect on the lighting-back. The reason is the given-massflow argument regarding the amount of heat you need at the weld. If you raise the pressure out of the regulator, you would restrict back the flow in proportion with the valve on the torch. So the pressure in the nozzle will be exactly the same! (surely?). I tend to set pressure so that the torch valve is quite well open and a lot of movement makes a small adjustment. That gives you easy fine adjustment. For goodness sake, you can set the acetylene pressure at the regulator by setting the torch adjustment valve wide open and having the regulator set way low, light the acetylene and turn up the acetylene regulator pressure until the flame is a bit bigger then the flame you know you will need to weld. Then you restrict back on the torch valve to the correct flame. Same with oxygen. You will likely end up with pressures less that 8 and 8 (psi, that is). That will give you fine control in the range you want. This works because, burning acetylene only, you identify the range the nozzle will be correctly drive at because it is when, increasing the acetylene supply, the acetylene-only flame stops being smokey and becomes a clean roaring incandescent yellow/white. I have to admit the main reason I do this is to be a flash bastard and show off by operating the torch very rapidly wiht one hand, using only the fingers of the hand it is held in. You can "drive the nozzle hard" by increasing the acetylene supply beyond the point where the acetylene-only flame burns clean. With the oxygen on and a proper "neutral" flame, the gas velocity will be higher and you can actually use this. I found it helpful in some fillet joints, where you might drive a #2 hard rather than go to a #3 driven at normal rate, for the same heat.

Haven't used oxy-acet much for a while. Would have thought try #3. #2 would be too small for 1/8th inch, for sure (?).

BTW - filling technique - you know that "melting off the filler rod like sealing wax for a letter", with metal dripping into the melt pool, is definitely a defect in oxy-acet? You get an oversized uncontrolled overheated looking weld if you do this, compared to the controlled fine-looking weld with desired profile if you dip ("harpoon") the rod into the weld pool as needed far slightly afar.

I will gladly be stood corrected if any of the above is not correct.

Richard Smith