Flame Bending/Line Heating with Stick Welder and Carbon Electrode?

[Kelvin]

Hey, all,

I need to flame-bend some 3/16" thick mild steel that was made into a welding tabletop.

I bought the table used, and wanted to fill some holes that had been drilled in it, and after I'd welded plugs in the holes (from the top), I noticed that the tabletop had developed a "hollow" on top that catches rainwater (table is outdoors).

I tried flame-bending it to make the top convex instead of concave by heating the bottom of the tabletop with an O/A torch, and cooling the top surface with water, and I got some of the hollow out – but now I've run out of oxygen. It also seems to take FOREVER to do this with a torch, even a #4 torch.

I've done this before both with an O/A torch, and also by stick welding HOT on the side I want to shrink (and then grinding off the weld) but I don't want to do that in this case.

But I would like to use my stick welding power source, since that seems to put heat into the plate a hell of a lot faster than my O/A torch.

So my question is, could I do this (dump heat into the plate for "flame-bending" or "line heating") by using a carbon electrode and putting the welder on DCEN and then dumping heat from the electrode into the plate? I saw some carbon/graphite electrodes on ebay that were 10mm diameter by 100 mm long – would they work for this? (I also considered using 6010 or 6011 and long-arcing it, but didn't want to set the wooden shelf under the table on fire...)

Anyone done this? Any tips? Thanks--

P.S. If it works, I'm thinking that if I turn down the amperage on the welder, it might be good for shrinking sheet metal when doing auto body work, too...

[bent]

On thin material I have found strongbacks or other external forces are valuable. Can you put a jack under the center of the table? It may be able to be placed on the stretchers for the legs. Bend the table top about as far past where you want as it is in the wrong direction now.

My limited experience with carbons as you describe is to etch identification numbers. It leaves tracks that don't grind out as well as a weld bead.

[Meltedmetal]

You might want to build or buy a carbon arc torch rather than arcing to the table.
http://www.instructables.com/id/Make...volt-stick-we/
Google "Carbon Arc Torch" there is a fair amount of info out there.

I don't do shrink straightening but I would have thought that the top of the table would be the wrong side to apply the cooling to.??

[old jupiter]

I'm pretty sure you don't want a twin-carbon torch, not for this job, anyway; you want less total heat, but in a much more concentrated area. Heat-bending doesn't require red heat, but it does call for heating a small area quickly, and cooling it quickly (preferably also with some pressure applied, if possible). And those carbons you saw for sale are about 3/8" diameter, which is too big even for the single-carbon set-up you want to try. A stick-welding handpiece isn't designed to take the heat that a 3/8" carbon will put into it; carbon arc is a very hot process, and bright, so use the #12 darkness setting in your helmet. Get a few of the smallest diameter arc-gouging carbons and see how that works.

[CEP]

I tried flame-bending it to make the top convex instead of concave by heating the bottom of the tabletop with an O/A torch, and cooling the top surface with water,

I’m fairly new to heat shrinking, but that is opposite of how I was taught. I was taught to cool on the same side as the heat was applied.

[Kelvin]

[/U][/B]
I’m fairly new to heat shrinking, but that is opposite of how I was taught. I was taught to cool on the same side as the heat was applied.

Naw, you need to cool the side opposite the side you're heating to keep it "contracted" ... basically, when the hot side tries to expand linearally due to the heat, the cool side "holds it in place." The expansion has to go SOMEWHERE, so the metal that's being heated expands in thickness (since it can't expand in length). Then, when it contracts again, it contracts in length, causing the convex surface that you heated to become more concave/dished.

See discussion and diagrams beginning at:

https://books.google.com/books?id=UT...ending&f=false

It's used in shipbuilding a lot...they must use some godawful big heat sources!

[CEP]

I disagree 100%. I’ve been doing heat shrinking for over 40-years. I learned heat shrinking from one of the guys who help bend the legs on the Seattle Space Needle.

[knightbouy]

"I got some of the hollow out – but now I've run out of oxygen. It also seems to take FOREVER to do this with a torch, even a #4 torch. "
Do you suppose ... this took so long with o/a because you were running out of gas (oxygen)?

[Kelvin]

You can disagree all you want. For it to work depends on the surrounding metal remaining cool and constaining the heated metal. End of story.

See post here:

http://weldingweb.com/vbb/showthread.php...262#post446262

Misting the surrounding metal -- or the other side of the plate -- will help bend the metal faster because the cooler steel will restrain the hot steel and upset it faster. Quenching the heated metal itself, like shown in the pic above, doesn't accomplish anything except cool it so you can heat it and upset it again sooner.

[CEP]

Yeah, you keep believing that.

[welderj]

Yeah, you keep believing that.

I love it when someone asks for help, you offer it, then they tell you "no your wrong ". If they already know then why did they ask?

Jon

[CEP]

I love it when someone asks for help, you offer it, then they tell you "no your wrong ". If they already know then why did they ask?

Jon

Jon here is a good example. In the early 1980s we did a project at the Boeing Space Center in Kent Washington. We had to sheet an 80’ X 80’ X 70’ tall building with 4’ X 8’ sheets of 10-GA. The walls, and ceiling we could plug weld the sheets to the structural steel. The sheets laid on the concrete floor. Every sheet in the building was 100% welded. When the floor was welded, you had to be very careful walking on it. The sheets bowed almost a foot tall. Boeing would not allow us to anchor the sheets to the concrete floor. We took a large welding tip on an oxygen & acetylene torch, heated a line 6” on 12”. When the line was heated, and moved to the next line the heated line was sprayed with water. Now how do you suppose we sprayed water on the opposite side of the heated line with the sheets laying on a concrete floor? When we were done the sheets on the floor were as tight as the skin on a drum!

[Bonzoo]

OK CEP. But is it in a Google book ? !

[CEP]

OK CEP. But is it in a Google book ? !

I have no idea. I only know what I’ve done, and seen. I’ve straightened W-shapes up to 36” x 300#.
I got stuck building 200 of these Seattle Metro bus shelter. The legs had to be within 1/8” at the bottom. I think everybody knows how reactive square tube is to heat. Every bus shelter had to be heat shrank back within the 1/8” tolerance.

[Bonzoo]

Ya see man. Youz murkinz are doin' it wrong

[Kelvin]

I love it when someone asks for help, you offer it, then they tell you "no your wrong ". If they already know then why did they ask?

I don't need help with line heating or flame bending, got that covered, thanks.

The original question was about using carbon electrodes for heating. When in doubt, check the OP.

[Kelvin]

Now how do you suppose we sprayed water on the opposite side of the heated line with the sheets laying on a concrete floor? When we were done the sheets on the floor were as tight as the skin on a drum!

I didn't say it wouldn't work to spray the hot side. What I said was that the only way it will "help" is by cooling the plates faster so you can heat and upset them again sooner, if needed. In other words, in the situation described above, the heating did all the upsetting and bending; it still would have been bent whether or not you had sprayed the hot side. All you accomplished by spraying the hot side was, you cooled the metal a little faster than it would have cooled in the air, allowing you to handle it sooner.

On the other hand, if your heat source can't heat the plate up fast enough to cause upsetting (for example if your torch is too small or your plate is too thick), spraying the "cold" side with water will help it restrain the metal on the hot side such that it can be upset.

If you don't heat the metal fast enough, and there's not a big enough temperature differential between what you're trying to upset and the surrounding metal, flame bending won't work.

In a nutshell: Spraying the hot side won't shrink the metal...but spraying the cold side might help (if you have too small a heat source for the metal size).

Now: About those carbon electrodes for heating...

[Pavinsteelman]

We flame camber beams straighten plate girders to NYSSCM spec all the time 1200 deg max Harris Torch natural gas did 4" in W 44x 498 beams.

[welderj]

I have no idea. I only know what I’ve done, and seen. I’ve straightened W-shapes up to 36” x 300#.
I got stuck building 200 of these Seattle Metro bus shelter. The legs had to be within 1/8” at the bottom. I think everybody knows how reactive square tube is to heat. Every bus shelter had to be heat shrank back within the 1/8” tolerance.

It's all because your just a beginner at this, that's why they don't trust you. It's hard to trust someone's advice when they've only been doing something for 30 or 40 years and have only a couple hundred projects that are similar under their belt. Once you've been around a bit folks will start to listen to what you have to say.

Jon

[Econdron]

I didn't say it wouldn't work to spray the hot side. What I said was that the only way it will "help" is by cooling the plates faster so you can heat and upset them again sooner, if needed. In other words, in the situation described above, the heating did all the upsetting and bending; it still would have been bent whether or not you had sprayed the hot side. All you accomplished by spraying the hot side was, you cooled the metal a little faster than it would have cooled in the air, allowing you to handle it sooner.

On the other hand, if your heat source can't heat the plate up fast enough to cause upsetting (for example if your torch is too small or your plate is too thick), spraying the "cold" side with water will help it restrain the metal on the hot side such that it can be upset.

If you don't heat the metal fast enough, and there's not a big enough temperature differential between what you're trying to upset and the surrounding metal, flame bending won't work.

In a nutshell: Spraying the hot side won't shrink the metal...but spraying the cold side might help (if you have too small a heat source for the metal size).

Now: About those carbon electrodes for heating...

I understand where you're coming from, but in practicality I don't think it actually works. Heat shrinking works by rapidly heating and rapidly cooling. It's not about the temperature differential. You can temporarily simulate heat shrinking results by keeping one side cool and heating the other, but it will just go back to how it started once the temperatures are equalized. Did you try heating small sections with a cutting torch?

As for carbon arc, you can try it. I tried it once but wasn't happy with it. It was hard to tell how hot the metal was looking through the welding helmet. It should get hot enough if you have the amps to run it, but you may risk burning through the top. Is the table top welded to the frame? I bought two 5'x5'x5/8" plates for my tables and they came in bowl shaped. Really bad actually, like a 2" bow in the center. I built A nice solid frame out of 3x3x1/4" tubing and bolted the top down. I shimmed different sections and used flat head socket cap screws countersunk through the top and locknuts on the bottom and tightened the bolts until the top was flat. Still has some minor dips and bows in it, but nothing over 1/16". You could try something similar. That would allow future adjustment if you ever warp the top again.

[Sandy]

The applying of a cooling mist or damp rags to this side or that side at differing times during the process can assist the person in achieving their desired results. It all depends on what you want. There is no 'always do this'. When I see someone applying a damp rag I'd have to ask them why, each person could be doing it for various reasons. If done right at the right times it can dampen one effect or accelerate another, ya never know, it's in the mind of the doer.

I've been known to wrap a huge beach towel dripping wet fresh from a 5 gallon bucket around the whole section before, screaming "stop, stop, stop" seemed to help a little bit too ..

[Sandy]

The applying of a cooling mist or damp rags to this side or that side at differing times during the process can assist the person in achieving their desired results. It all depends on what you want. There is no 'always do this'. When I see someone applying a damp rag I'd have to ask them why, each person could be doing it for various reasons. If done right at the right times it can dampen one effect or accelerate another, ya never know, it's in the mind of the doer.

I've been known to wrap a huge beach towel dripping wet fresh from a 5 gallon bucket around the whole section before, screaming "stop, stop, stop" seemed to help a little bit too ..

[Pavinsteelman]

New York will not allow water to be used only air. There are formulas from Bethlehem Steel on heat curvature and camber . 1200 deg max or scrap the piece templesticks needed!

[M J D]

Cut the top off, scrap it. It's too light if it's bent up and warped. While you could make it better with lots of work, it will just bend and warp again.

[old jupiter]

CEP. did you get to meet Prof. Richard Holt, who did the engineering on exactly how to heat-bend the legs of the Space Needle?