Flame straightening, if you think it thru and do it carefully, can straighten angle iron. I was taught by oldtime ironworkers and boilermakers on jobsites when I was a young engineer- in the days when mechanics were supposed to be able to think a job through, and in the days before people got crazy about needing "approved procedures" to do anything. I have seen ironworkers camber a wideflange beam or straighten hot rolled steel structural shaped that simply distorted as a result of rolling/cooling stresses. I have seen old boilermakers flame straighten plate steel work after welding had things "pulled". Those oldtimers taught me.
The method I use is to first determine which way the bow or curve in a piece of steel is laying (which side is convex, which is concaved). Go to the "outer circumference"- the convex side, and that is the side which has been stretched. The way I was taught, I take some soapstone- the hard "chalk" steel fabricators, boilermakers and blacksmiths use to layout on steel. I divide the curved area into some equal parts drawing lines square to the outer edge running accorss the flange of the angle iron. I then sketch in triangles on each of these lines, the base of each triangle laying along the convex curved edge.
Next, I get into a darker area- you do not do flame straightening in broad daylight or in a well lit shop. You need dim or bad light. Take an oxyacetylene torch- the tip size will depend on the size/thickness of the stock to be straightened. For thinner angle iron of about 3/16" thick, a big brazing tip will probably work fine (no need to go broke fuelling a rosebud heating tip). For anything much heavier, get out the rosebud. Support the angle iron on a piece of steel plate if possible and have some C-Clamps handy. Start heating the flange on the side which has the curvature- this is curved "the hard way". The other flange is simbly curved "the easy way" and won;t take any real effort to straighten.
Heat each of the triangles, from the centermost outwards. All you need is a dull red in bad light. When you have them hot, quench the outermost edge at each triangle (along the convex curved side). A light spray of water from a hose nozzle works fine and you should move around and keep it uniform. You may find the nagle iron wants to twist a bit as a result of "locked in stresses" from the rolling mill and subsequent cooling at the mill where it was made. That is hwere the C-Clamps and plate come into play.
Take it slow and do not overdo the size/number of triangles or the amount of heat you put in. You can get things on the way to straight and repeat the exercise, doing it a little at a time rather than overdoing it. I flame straighten structural shapes & steel plate from time to time as well as sometimes flame straightening to take out post-weld distrotion on long running seam welds on fabricated jobs. I find it is a matter of a little thinking, perhaps some instinct and practice.
Recently, at the plant, two mechanics were directed to fabricate this heavy support for a new valve, in place, to fit onto an existing angled concrete foundation- a long story about a p-- poor design that wasn't my idea. They followed the other engineer's design and directions and welded the dickens out of some 1" steel plate cut to various shapes and welded to form this mounting bracket for this very heavy valve. When they got done, things were warped a good 3/4" in perhaps 18" on the 1" thick base plate of that valve mounting bracket. I wa sup in my office when the two mechanics popped in. One guy had been an apprentice when I ran the crew. The other guy also knew me pretty well. They appeared in my office and said: "Hey Joe.. we got a problem..." They explained another engineer had designed the job and been insistent as to how they put it together and now they had a mess on their hands. The other engineer thad told them to put some porta power jacks on things to cold-straighten it. With the amount of weld and thickness of the plate, the mechanics laughed the guy out of the area. They told him to take a hike, they would fix it. That is when they came and asked me to take a look. I got down to the work area and found one guy already had the rosebud and the other guy had a water hose rigged up. They grinned at me and said: "Joe- we figured you;d show us how to pull it straight with a rosebud and without getting someone killed". We stretched a string line to get some ideas as to how things curved, and laid out the heating triangles. It was in a dark area down in the powerplant, so we didn;t have to try too hard to see the dull red heat. It took us all of 45 minutes, no jacking needed. I told the two mechanics not to breathe a wrod to the pother engineer as he would likely pitch a fit about heating a weldment and spraying cold water on it.
They did dye penetrant check the welds to be sure nothing had cracked- it was fine.
Another flame straightening job happened back about 1985. I was sent to a vendor's shop to look over the final design and fabrication of these big bulkhead panels for use in unwatering a hydroelectric plant penstock ( a pipe that is stabbed thru a dam and big enough to drive a truck into). The panels had warped in fabrication, which was fully expected. The design called for machining the seating surfaces flat on a giant Ingersoll CNC Planer Mill. As the panels came thru the weld shop, despite good welding engineering, they had developed a bow on the order of 1/2 to 3/4" from flat in perhaps 25 feet.
There was enough mea ton the panels to allow for machining things flat and living with the bow in the structural members. A meeting was held and corporate engineers from my firm were driving the vendor nuts about the bowing. We were on a very tight deadline as the bulkhead panels were needed to unwater and a contractor was on standby at the dam site. I looked at the vendor's engineers and asked: "Do you have a blacksmith in your shops ?" They said they did, and I asked that they bring the smith into the meeting. The smith was, in truth, doing some very tricky welding jobs on (of all things) aluminum barrels for medical CAT Scan equipment that this same shop was making and machining as a subcontractor to G.E. The smith came into the meeting and was introduced. The corporate guys from my outfit were flipping out asking me what I was hoping to accomplish. I told them to sit tight. I explained the problem with the bulkhead panels and the bowing to the blacksmith. I then asked the smith if he had done any flame straightening. He said he had. I then asked him one question: "What time of the day would you take the bow out of our bulkhead panels ?" He grinned and said: "Tonite, after it is fully dark." I shook his hand and thanked him.
The corporate guys were now going nuts, and I told them I was a Professional Engineer and would not have a problem putting my own seal on that job even after it had been flame straightened. The corporate guys were asking loads of questions and making noises about stuff being calibrated, grain structures and so on. I told them this was mild carbon strcutrual steel- A-36 steel- and to leave it to us. After some more carryings on, the corporate guys from my outfit left to catch a plane. I told the vendor to go ahead and tell the smith to flame straightne our bulkhead panels. These things wer ehuge, made with deep wideflange steel beam sections run longitudinally, tee bars run laterally and thick skin plates as well as heavy steel bar continuously welded for the seatings surfaces and guides. Miles of running welds on each bulkhead. The fab shop foreman had the crew set the panels on heavy steel horses. I went to supper and got back about 8:00 at night. The blacksmith was there with three guys, all of who worked with him. All of the crew sported Harley tattoos. They had the cutting outfits and some BIG rosebuds. The smith and one guy stretched the stringlines and measured the bow, then laid out the triangles with the soapstone.
They turned out the lights in the bay of the shop, leaving only a little light from the next bay. They started heating. The smith told them where to heat and where to cool things down with the hoses. There were four such panels to be straightened. The crew got rolling and they worke dinto the wee hours of the morning. The string lines showed things were flat to better than 1/16" in 25' when that smith and the crew got done. They closed the bay doors to keep out drafts and left things to cool down slowly. We went out for steak and eggs and a few beers. By 8 AM, the first bulkhead panel was up on that big Ingersoll planer mill. Still a little warm, but OK to work on. It didn;t take much for that big Ingersoll planer mill to skim cut the seating surfaces flat and drill/tap hundreds of holes for neoprene "J" Seals. Within 72 hours, the panels were out of the vendor's shop and on their way to our dam- we sent them back after our job was done for sandblasting and painting. I was looked upon as a hero, but I never did tell the "suits" from corporate how we had picked up the time by flame straightening those big bulkhead panels.
As I wrote, flame straightening is something you think through. If you can "feel" or sense what the steel needs to do or how the shrinking/upsetting process will move it, you will do fine. Even that experienced blacksmith did NOT flame straighten those panels all in one rip. He had his crew heating the triangles a little at a time, then spray the water to them and check things with a stringline, blocks and a combination square. It took a few iterations on each panel as it is all too easy to overdo flame straightening. It is a good skill to have if you do any sort of fabrication work.
Joe Michaels
