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O/A welding thicker metal - techniques?

chadillac

Hot Rolled
Joined
Apr 1, 2005
Location
Benson, AZ
Is Oxy/Acetylene welding of thicker metal where you separate the men from the boys?

I'm taking an O/A class; Been going along welding 3/16" and thinner plate for the most part. I've been slowly improving and am starting to produce acceptable welds with this stuff, though I struggle daily with trying to get a nice looking weld. Our class has victor torches with tip sizes from 0-3, but limited amount of #3 tips, so I normally use a #2 when welding on the 3/16" stuff.

Now for the welding test, the instructor has given us 1/4" cards to weld the various joints. I find my difficulty in producing a nice weld with good penetration seems to increase exponentially with the thickness of the material, making this test pretty difficult. Any suggestions?

I try to use a crescent pattern and wait for the "keyhole" to appear before dipping my 3/32" rod in the weld pool Is there any rules of thumb for how much of the base metal to heat while doing, say, a butt joint? For example, using 1/4" plate, should you do a 1/2"+ wide sweep pattern with the torch?

Chad
 
Other than just doing if for kicks no one welds more than about 1/8" steel with O/A that I know of. That is what stick welders and mig welders are for. I just don't know anyone who would waste that much gas to get 1/4" hot enough to weld. Brazing is a different matter.

I guess if your teacher is insisting you have to do it..... Sorry I can't really help you.
 
We had a big casting sent out to be repaired, i figured they would stick weld it. They brazed it and the gussets were over 2" thick. I was really impressed with the work. I have some big torch tips that are marked 1" plate, i never did anything that thick but it is possible. Keep practicing maybe those big jobs will come to you someday because you can do the lost art of torch welding...Bob
 
It might be wasteful and not used in the real world -- but I know it can be done -- my instructor manages to make beautiful welds with good penetration in the same stuff (1/4") he gives us.

Seems like my tip size may be a little too small -- I find with small tips and high volume (i.e. opening the valves more and/or higher pressure) that the gas tends to blow the molten weld pool around, making it difficult to make a nice uniform bead. Of course a good operator could probably make it work :)

I was reading in some literature about angling the tip in the direction of your completed weld (i.e. opposite your direction of travel) when welding thicker material, but it was never mentioned in class, and I just read about it last night, so haven't given it a try yet.

Chad
 
Chad,
O/A welding was used for much larger weldments that 1/4" prior to the widespread use of arc welders.

What kind of gap are you using? I'd have that gap pretty big 3/32 to 1/8" or more at the start and wider at the finish. You shold bevel if you can get a way with it. Victor recommends a #4 tip for 1/4" material.
 
Chad, as you noticed the flame can blow the pudle around. That is very usefull at times to keep the pudle where you want it especially in out of position work. What you are learning will help all your future welding skills. Lots of it is about heat and pudle control anyway. You most likely will do thick brazing in the future if you work on machines at all.
 
You shold bevel if you can get a way with it
Afraid not. My instructor said at the beginning of class that for this particular welding class, we were not to touch a grinder for anything - I think he understands the need to bevel, but wants us to learn how to get good penetration without it. Funny thing is, he doesn't stress cleaning of the joint before welding.

For me, in order to get good penetration in the thicker stuff, it almost seems like the plate is in a jello state in order to get 100% penetration. Like if I jabbed the filler rod in rather than dipping it would pierce right through.

My gap size was about 3/16". I'm having trouble with lap joints as well though. Mainly centered around not getting enough heat into joint. It seems like a pretty fine line between too much and not enough.

I too, noticed that a #4 tip was recommended for 1/4", but I'll wager a guess that the school isn't going to spring the $30-40 for it for me
This class is already a steal at $216 (including fees) for a semester long course of using their gas and metal. No way could I do this at home for that price -- even if I already had the equipment.
 
Chad,
Are you talking the whole plate? That's an indication of too small a tip. You have to heat it too long. If you're talking about the puddle, that's kinda sorta how you want it. You can't have full penetration without melting all the way through. Your keyhole should be larger than your gap, all the way to the bottom. I assume you're welding on firebricks so they should do a pretty good job of supporting the puddle on the backside.
 
Dave,
yeah, talking about the puddle, but also the material in very close vicinity to the puddle. In the flat position, the metal is supported on a piece of angle iron, but I'm doing these joints in the horizontal, vertical and overhead positions as well. Fun stuff :D Some nights, I just get so frustrated cuz I can't seem to control all the right variables to get the weld to turn out the way I want.

Thanks for the tip about the keyhole.

Chad
 








 
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