Has anyone seen a publication be it a book or university paper that describes in detail how to heat metal for bending purposes.
I was just informed by the shop forman that the torch has to be moved in line with the stress the part is to carry, for example a beam would be heated by moving the torch back and forth along the long axis. In order for shrinking to take place.
If the torch is moved across the flange apparently the shrinking effect will not take place; due to the molecues in the metal by incorrectly aligned.
They even brought a photocopied paper showing the correct way to move the torch, But I did notice the top of the page was describing the method I was using but they do not have the previous page.
Apparently there are different recommendations of how to apply the heat to a beam for depending on its end use; staticly loaded or dynamically loaded structure.
So if anyone has seen a publication like this please send the info, I am not worried about the cost so long as it is available.
I am rolling on the floor with laughter. It is as good as when a foreman challenged me about how I could measure temperature with a magnet or that when you heat steel the water rises out onto the surface. I woud like to align some molecules myself... I might be up for a Nobel science award if I can do it right. Most code doesn't like heat shrinking beams and have quite low limits on how hot you can get the material. The problem is that you cannot get a good red heat with the limits required. If you e-mail me I might be pursuaded to send you my snail mail something I have found useful. (TWI stuff ) I hope the other stuff I send was siilarly so. Randy
Yes you are correct about the procedure handbook. I have a few of copies one even from back in the forties great reading.
The one thing missing is a picture showing the movement of the torch and the explanation that the molecules align with the torch movement and provide a greater shrinkage force.
Though the technique I was using has work before my supervisor claims it is impossible because they tried it and it failed.
One thing I did notice today was the difference in the stress lines formed in the mill scale of the beam. I plan on measuring this tomorrow if the shop is open to record the difference for future use. As I mentioned to Randy I plan on conducting a few experiments with a couple of six inch beams In order to have a comparison of methods, might prove interesting.
I have downloaded all the files on distortion from the TWI and saved them in word format if anyone would like a copy I will send it to them via email. I will transfer the format to plain text or pdf as needed.
Now back to searching for that elusive publication.
Have you got the TWI booklet Control of Distortion in Welded Fabrications? Mine is a 1982 reprint. I am sure there is a later edition. A classic mistake on large beams is to just heat the beam flange for a length of say six inches but not put any heat in the web. If you do shrink in this manner you will see the web buckle as the flange shortens. One really has to heat a full pie section which includes the flange and down the web to the opposite flange at least half way. Molecules don't align as you heat... they vibrate! We are dealing with expansive forces that cause plastic flow of the red areas. When those red areas go black they contract bending the beam. It is important to understand that when things take a bend yield point has been reached somewhere on the structure. People often do not heat a pie section concentrating on the beam flange. Little will happen if you only heat the flange since it would have to buckle the web which takes massive forces. I have seen buckles of 1/4 inch when a two foot square is put against the web. The beam was cambered but the web was buckled. If you are looking at stress lines forming on the mill scale I will bet dollars to doughnuts you are not heating the web???? I like flame shrinking beams but it is not very practical in dollar cost. A better way is to cut the beams to length, load them up and send them to a shop that cambers them with a press. Are you using a air /water spray, wet rags or just letting the unit cool in air? the most effective shrinking is done with two people, one on the torch and one with the spray. I cannot see how someone "aligns" molecules with a torch. Maybe change shape of the grain structure but not aligning molecules. Also if you don't know, heating with acetylene is best because the heat is so concentrated but there are always flow rate problems. MAAP gas is next best and then comes propane. I am always using oxy-propane but on the few occasions I used MAAP I noticed the difference. You could also e-mail the guys who put up that section on distortion control. they might have some additional ideas. There is a credit at the end. Randy
"John Noon" wrote in message news:6RUIe.159253$HI.116238@edtnps84...
I searched the TWI for the booklet you mention but I must be going blind as I cannot find it. Thanks for the info you provided at least now I know I am not out in left field. I did heat the web, first actually as they requested. Then the flange. This was the first time I ever noticed this type of stress line showing up in the area heated. Probably never see it again.
This shop will not allow the use of a cooling mist on the steel as they are worried about hardening the steel. Which makes for a very long process of cambering any beams.
Your right about the molecules as they are heated they move around more; but this area has a few old wives tails that are good for a laugh or two.
OLD WIVES TAILS For example the reason for preheating steel "is to remove the water that the steel has soaked up, Thicker section soak up more water hence require more preheat"
7018 cannot be used for open root welding
7018 is not suitable for vertical welding
7018 has to be pushed for max penetration Visual inspection of a weld tells you nothing Weave beads 2" wide are stronger than a stringer bead
100 amps with a 1/8" SMAW electrode gives you a 1/4" penetration, which is why slag removal is not that critical in multipass welding. Slag on the weld protects the weld from corrosion SMAW gets more penetration than GMAW of FCAW
1/8" tacks with porosity are best as the bubbles help mix the tack and the weld metals together.
6011 is stronger than 7018, which is why it is used it is used in root passes Selfshielded fluxcore wire cannot be used in building fabrication Metalcore wire cannot get porosity in the weld bead The older the welding machine the better it runs over thirty years is the best Its impossible to start a 7018 rod that is at room temperature Cast iron cannot be welded
He used rich text format which will be quarantined by the dropbox bot. I'm sure that when Steve gets a chance he'll check it out and place it in the dropbox (probably convert it to standard txt in the process). The reason for the restrictions is that people try to put viruses in the dropbox so Steve restricts automatic files to the safe varieties.
John (or anyone else), a plea for clarification on a couple of the old wives' tales -- there are a couple that I thought were true at least to some degree:
If they meant that the slag was supposed to stay on indefinitely to prevent corrosion -- sort of like an alternative to galvanizing -- then I certainly see that this is ridiculous. But in terms of the welding process itself, wouldn't it be correct to say that slag protects the molten metal from -- well, maybe corrosion is not the right word, but from the nitrogen/oxygen in the air that would otherwise result in a weaker/more brittle weld? If the former was meant, perhaps it could have started from a misunderstanding of the latter?
Okay, on this one I must have been taught the same old wives' tale -- in fact, I am pretty sure I read something like this here. Of course, it would have to be qualified: "all things being equal." Obviously one could do SMAW in a way that would give less penetration than another approach with GMAW. But I thought that, in general, SMAW could penetrate more than either GMAW or FCAW?? Or am I just confusing that with SMAW, especially 6010/6011, being more able to deal with rust & dirt?
Thanks to all for continuing my education ... just when I think I've learned something, I find out there's an exception or another way to look at it or ... !
(( Slag is for shielding the weld while it is in the molten state, once the weld has coolled below approx 900 deg then the slag can be removed. Thought the cooler the slag when being removed the better; nothing worse than hot slag rolling down the inside of your shirt. Especially if it makes it into your pants.
Slag left on a weld for the entire life of the weld actually traps moisture and along with its acidic nature helps speed up the corroding process))
((Amperage is more of a factor for penetration than the proccess; also the size and shape of the arc cone has an effect. When comparing directly, throw in a variety of shielding gases and things can take a twist. Some gases provide a wide bead with shallow penetration and others a narrower bead with deaper penetration. Best if seen in a book so side by side comparisons can be made. Pushing or pulling the electrode effects penetration PULL "slight increase" PUSHING " reduces penetration And of course the polarity affects penetration))
This is one of those things that many variables have to be taken into account For example I have been told many times that a 1/8" 7018 at 100 amps gets 1/4" penetration or double that of MIG "GMAW" even when in spray transfer even after blowing a hole through a 1/4" plate. His response was pushing doubles the penetration and accused me of cheating.
The best thing I found was to run several beads side by side with a couple kinds of electrodes and a couple of different processes all at the same amperage or at least the minimum amperage the electrode can run. For example
120 to 125 amps and select as many 1/8 electrodes you can find. Set you wire feeder up to run at 125 amps as well.
After running all the combinations you can saw the weld specimen into a couple pieces across the weld. Sand the welds to a nice smooth finish around 600 grit. Etch the ends of the plate with a mild acid; this will make the welds stand out. Now take a close look at the weld profiles with a magnifying glass or borrow a microscope 100x to 300x is more than enough. You can actually measure the weld penetration with a micrometer to see just how different each electrode is for penetration
With a 7018, the slag definitely protects the molten puddle 'till it freezes (and helps to support it too, particularly in vertical work). The slag on a 6010 doesn't do much at all to protect the puddle, if you look at it closely you'll see that it's pretty spread out with considerable exposed weld.
Could also be that someone just used the word "corrosion" when "contamination" might have been the better word.. and it could also be that a thought extension was made- "slag protects weld.. slag good, leave slag on weld.."
Regardless, it sounds funny, and funny sounding ideas are sometimes a pain to the new guy with good intentions..
All things being equal, a wire feed will give better penetration than a stick. Penetration is acheived with a fast and hot travel, the wirefeed naturally allows this better than the stick. "Go nice and slow to get good penetration" is a contradiction in terms which I've heard before..
You can build a special case for 6010, such as vertical work on a very heavy piece, but I think the same case could be built for the wirefeed.
Metalmangling Mike and I discussed penetration to some extent and I have come around to his view on some penetration issues; it's not that important and, no matter what, there's times when it's detrimental, sometimes you want minimal parent metal admixture in the weld.
I'm all for root pentration, it's possible to save time and material on, say, a lap or tee joint in 3/16" stock by getting good root penetration and depositing a narrower bead.. but if you're making multiple passes on a heavy piece you should worry more about joint preperation and fitting so that exceptional penetration is unnecessary.
Once you've made a good root, penetration is pretty much a waste because you're melting metal that's already been deposited or doesn't need to be melted, better to melt the minimal amount of what's already there and put the heat into what your depositing. If you don't need to use xx18 that's where a 7014 or 24 really shines, fairly shallow penetration with very high deposition rates.
That's pretty much how I look at penetration now- if you're single passing stuff that's thin enough that you can melt the root to a considerable fraction of the parent metal thickness then it's a good thing.. but on heavy work, after the root pass, it's a waste of heat that could have melted filler material.