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Old 06-29-2004, 11:42 AM
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SlagKing SlagKing is offline
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Default O/A torch cutting

Lately, I have been cutting Angle Iron and I have experienced the slag welding itself back together behind the kerf. I have been using different tips with the recommended pressures, but at times this rewelding takes place. Sometimes the slag is truly just slag, maybe from rusty metal, and the parts I am cutting seperate easily or with just a light tapping. Other times, and less frequent, it is truly a reweld of the metal, and I have to recut. What am I doing wrong when that happens and what do I need to do to correct my errors. I have been cutting alot and 95% of the time, the cuts are clean and doesnt' need much dressing, but the other 5% is frustating. I'm posting this because I know I'll get help and maybe it will help someone else to..
Thanks guys
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Old 06-29-2004, 11:55 AM
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morpheus morpheus is offline
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I used to have this same problem ALL the time. There is a speed of travel that must be learned to have a clean cut, especially when the materiel is thick. A plasma cutter can have the same issues as well i've learned

From my most recent experiments on Sunday afternoon it seems to me that the appropriate rate of travel is when you can see the sparks/dross/etc shooting straight out the bottom of the work. Any angular direction to the sparks mean that the cut is not clean and if you move ahead the dross from the new cut materiel could even weld the kerf shut.
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Old 06-29-2004, 02:37 PM
Franz Franz is offline
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Slag, I believe your question contained its own answer, RUST.
Rust makes O/A cutting a sumbich, but doesn't seem to be much of a factor when cutting with propane or MAAP.
While I've never positioned myself to actually view what is happening, I have a hunch the rust on the back side of the cut acts as a dam and prevents the metal from burning clear thru, so the molten pool will resolidify.
Another consideration is that the actual fuel producing the cut once initially established is molten iron. Rust tends to burn differently from steel, so you loose a lot of heat.
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Old 06-29-2004, 02:50 PM
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wolfgangwelding wolfgangwelding is offline
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I would have to vote for speed of cut also. Are you getting your cleaner cuts on thicker material? That thicker stuff will absorbe your heat. Adjust your cutting speed for the diferent thicknes of the material you are cutting, and speed up on those thinner pices so you wont weld up behind yourself.
no you cant fix it with a hot pass
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Old 06-29-2004, 03:15 PM
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SlagKing SlagKing is offline
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I would have to say....yes the cuts on the thicker stuff is several times better.
Example:..on thinner angle iron, 1" by 1" and I guess 1/16 thick, with a 000 cutting tip, it will still sometimes, not everytime, weld back together. With a 0 tip, of course it just blows away, but it's a rougher cut. If I'm notching pipe, I don't have any problems at all, clean cut, piece I cut falls off without touching and no dressing is needed to weld. Only on angle iron am I having this trouble. Doesn't matter if I cut the flat part or the vertical or turn it as to cut from different angles. Like I said, it's not everytime, and it many have been a problem more so in the past, as I have learned to cut better, but it's a problem I think I need to clear up. Thanks so much for what you guys have said so far, sometimes it helps to see from different points of ideas. Thanks Franz for the rust points. Yeah this angle has some rust on it and if I remember correctly, the pipes or tubing I have cut, didn't have any. Could be the rust and also since it is thinner steel I'm having the most touble with, my travel speed needs to be exammed closer. I'll also pay more attention to how the sparks are exiting from below, and also watch for any "Damming" of slag.
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Old 06-29-2004, 08:39 PM
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Markopolo Markopolo is offline
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I'll cast my vote for travel speed also.
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Old 06-29-2004, 10:28 PM
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Arrow Something to try..........

On thin steel try cutting with the tip on about a 30 degree angle. (handle high pulling towards you)
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Old 06-30-2004, 12:04 AM
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boilerman boilerman is offline
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when i get into troublesome steel i try to angle the torch in the direction of travel as to help heat before i get there
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Old 06-30-2004, 12:29 AM
revpol revpol is offline
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SlagKing: Whenever you are cutting something thin, say 1/4in or thinner you are not really "cutting" but "slicing" the metal. If you hit rust it will usually pop back at you,blow a unwanted hole, mess up your tip or just make a mess. revpol
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