Blow back from cutting torch

admin

How do I avoid hot metal from blowing back at me when using a cutting torch.  I usually have no problem with this, but the other day I had to cut some heavy plates, that were welded on some really heavy steel.  I had to cut them at the weld.  The position I was cutting them in was vertical, but slightly tilted back.  At a slightly higher level from my face.  Although I've used a cutting torch thousands of times, and mostly with no problems at all, I have to say, this was the sh*ttiest experience I've had with a cutting torch.  And considering that there were about 7 of these boogers I had to do, it wasn't no fun.Welders have bigger rods.Welders achieve deep penetration.Welders know how to fill a gap.Don't eat the yellow snow.
Reply:P.S.  To be more specific, I wasn't cutting through anything.  The plates were welded directly onto the heavier steel.  I was basically gouging the weld in order to be able to remove the plates.  There was a small gap between the plates and the heavier steel.  Once the flame hit the gap, it would blow back at me.  No matter how hard I tried, I would always hit the gap sooner or later.  What was I doing wrong, and how could avoid blow back in the future when doing this?Welders have bigger rods.Welders achieve deep penetration.Welders know how to fill a gap.Don't eat the yellow snow.
Reply:In that situation you will get blowback no matter what you do. Dress in lots of dead cow, that's all I can offer.
Reply:sounds like you need air arcR.T. Welding LLCOn Site ServiceColumbus, NJ
Reply:Originally Posted by 12V71In that situation you will get blowback no matter what you do. Dress in lots of dead cow, that's all I can offer.
Reply:Originally Posted by richTsounds like you need air arc
Reply:DeepPenetrationWith a regular cutting tip you will always experience some blow-back.A scarfing tip is designed to prevent this.  You can modify a worn-outtip to perform like a scarfing tip by simple drilling a shallow counterbore in the high pressure [center] orifice. Opus
Reply:Originally Posted by OPUS FERRODeepPenetrationWith a regular cutting tip you will always experience some blow-back.A scarfing tip is designed to prevent this.  You can modify a worn-outtip to perform like a scarfing tip by simple drilling a shallow counterbore in the high pressure [center] orifice. Opus
Reply:You can't really "cut" welds with O/A, it's more a matter of melting them, and removing the slag with the oxygen stream.Get the torch above the seam, use the preheat to melt the weld, then gently AND intermittently hit the oxygen to push the slag out of the way.  In this case the only function of the O2 lever is to apply something to move the slag, the preheat will do most of the work in a downhill position.  The gentle oxygen, and gravity, will make the slag run downhill, and it will be easy to remove with a chipping hammer where it adheres to the metal.An alternative is to start a cut in the intact plate, then wash the heat back into the weld, and blow it out that way.  It's destructive though.If you wind up scarfing the weld, be careful.  It's easy to start blowing out the weld, and then wind up digging into the parent metal with the O2 stream.  Scarfing requires some finesse."Any day above ground is a good day"http://www.farmersamm.com/
Reply:yes its a little easier with a 30* scarfing tip. lay it flat and blow the weld out. all I used before I got airarc on my truckR.T. Welding LLCOn Site ServiceColumbus, NJ
Reply:On technique I'm somewhere along Samm's #9 and richT's #10.Depends on weld quality. Good clean deposits can be burned as easily as base metal. Mostly I'd emphasize torch tip positioned almost flat (parallel, not perpendicular) to weld being cut. Heavy pre-heat and gentle "washing" of weld deposit by "dipping" the cutting jet's "side" (if you will) into preheated soon-to-vaporize weld.Try to keep a ramp or trough open so that the burn has an exit path. If the plate is being removed it's usually not necessary to completely cut the weld.Once a weld is "thinned" without going through it (thus avoiding accessing the burn-stopping,  blow-back causing, cavity) the plate can usually be easily raised and then the last bit of  weld simply fractures; follow with unobstructed clean-up with torch or grinder.Last edited by denrep; 07-15-2014 at 10:19 PM.