welding explosions (oxy acetalene)

[bawjaws]

went out today and got some 2.4mm gas welding rods (steel) so got home dug out dome 3mm sheet, cleaned it with grinder then set up the welding torch, number 10 nozzle i think and about 10 psi flow, so off i went and layed a lovely looking tig like weld on a bit of the plate, pleased with it i went to join 2 peices of the sheet together, went well for about 10mm then bang, big scary noise and the flame extinguishes, pood me pants!, i tried it several more times on a join or just on a piece of plate but same thing keeps happening, help please, it could turn dangerous

 

[Omniata]

Seems like too big a nozzle and not enough gas pressure, bang sounds like flashback into the torch...

I'm assuming the flashback arrestors are ok?

 

[bawjaws]

what size nozzle and pressure should i use for 3mm then?

er, how do you tell if theyre ok

 

[Hitch]

Not enough fuel gas, put a bit more red on before the blue.

 

[runnach]

No 5 nozzle is more than suffice for 3mm carbon, up it to a No 7 if laying doon fillet welds. For rule of thumb when using lower end No's nozzle is 1psi of each gas per No size.

When firing up fuel gas, make sure you burn off most of the carbon to only a small amount o black smoke, then add oxy till you achieve a neutral flame.....

Cheers.............

 

[bawjaws]

ahh cheers, ill give it another go, after chippy

 

[madkayaker]

hope the star fish has recovered

 

[Omniata]

Bangs can be a bit scary but it's when the hoses whistle you want to be really worried.....

 

[bawjaws]

had to think about that one for a couple of minutes before i got it

 

[Welderpaul]

One of the first times i used o/a (at about 15 i think!) it started blowing out the stringy black sooty sh1t. I never slept a wink that night, thinking it was going to blow up the shed!

 

[bawjaws]

first time i used it (last year (15)) i made the same sort of mistake, trying to cut through some thick flatbar i turned the acetalene on and tryed to heat the metal red hot with just that then came the downpour of all the soot from the roofand got the whole place mankey

 

[bawjaws]

anyway, been out today again, corrected the mistakes and had another ar5e aboot, its a slow job but quite satisfying at the end the fillet was a get though,not enough heat

 

[Weldingartisan]

Just don't wind up the acetylene pressure too much - above 15 psi it becomes very unstable ( which is why it is dissolved in acetone in the cylinder). W/A

 

[3Rs]

Setting up the right flame for Oxy-acetylene welding

1. Turn your actylene on untill the carbon smoke just disappears and NO more.
2. Turn your oxy on SLOWLY.
the flame will change color from a red to a slighty blue/white carry on
an inner color will now start to evolve it will be a pale blue, with the inner envlope a very light shade of white/blue. this is the flame to use for welding.

While turning the oxy valve you will here a harsh sound the flame will be short and the inner envlope will look very sharp this flame is called an oxidizing flame if this happens your oxy valve is open too much.

A neutral flame will have a slight noise to it, and will not see any carbon smoke comming of the flame. the flame will consist of an outer envelope middle and inner envelope. and this flame is used for welding carbon steels.

If you find your back firing, clean the metal with a grinder/file/wire brush. Also clean your nozzles, Have your pressure set at 2Bar square (ie 2bar for oxy and 2bar for your actylene). If your welding say 3 mm plate use a No3 (the bigger the hole the more heat your going to use)

 

[eil]

Or
http://tinmantech.com/html/meco_midget_torch_setting.php

 

[Omniata]

If you find your back firing, clean the metal with a grinder/file/wire brush. Also clean your nozzles, Have your pressure set at 2Bar square (ie 2bar for oxy and 2bar for your actylene). If your welding say 3 mm plate use a No3 (the bigger the hole the more heat your going to use)

Shouldn't that be 1 bar?? Operating at 2 bar is a little on the risky side isn't it??

 

[Paul.]

Actually it should be about 0.2 bar for a no 3 nozzle

 

[Omniata]

Makes sense now, typo hehe...

 

[irondarren]

get yourself a no 25 nozzle, you can near enough climb inside it lol.

 

[Tungsten Sharpener]

a balanced flame is what you are looking for, dont try to turn down to get a soft flame with a big nozzle, you can only run in the heat band that suits that nozzle.

Lots of years since i have gas welded but i use heating neck a lot, AHT100 3200deg with 10mm candles, just about warms the world and if you imbalance the flame it will pop and fart all over.

TS