#51
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US steel trade war
On Mon, 12 Mar 2018 16:17:18 +0100, Emanuel Berg
wrote: AMuzi wrote: In a closed figure, overall expansion/contraction is a real problem. When you see guys do aluminium tubes with MIG or TIG one gets the impression that the filler metal and gas/weld area sure is warm enough but for the whole structure to disalign from this isn't something I instantly think of... Firstly aluminum distorts more then steel at any given temperature. But as I said previously, a bicycle is two triangles and very small distortion of any part of a triangle will have large effects. I suppose the bicycle frame fixtures have clamps to allow just the right minimal play so that tubes don't suffer too much stress/strain while at the same time still remain in their right places with enough stability? -- Cheers, John B. |
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#52
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US steel trade war
On Mon, 12 Mar 2018 11:27:42 -0400, Frank Krygowski
wrote: On 3/12/2018 9:14 AM, Emanuel Berg wrote: John B. wrote: Sure. When you heat, or melt a metal it expands. If you bond two pieces of metal when they are hot, or molten, i.e. in it's expanded state when it cools and shrinks there has to distortion or if the parts are not free to move extreme stress will be imposed. See: https://tinyurl.com/y7feu33f Still, the area affected is local if we assume two long tubes being put into one so what is distorted is the intersection area (plus change) and by implication the angle or relative positions of the two tubes/tube parts? The very first welding project I ever did was back in the 1970s. I designed and built a little 4' wide, 6'long, 1' deep utility trailer to tow behind our car. The frame is steel angle. Visualize a two horizontal 4' x 6' rectangles of welded steel, with the upper one resting above the lower one on 1' tall vertical steel struts. So after a couple preliminary welding lessons, I welded up the two 4x6 rectangles flat on the workshop floor, then clamped them and the vertical struts together and, working late at night, hurried to weld the verticals. I rushed through the job, then left for home. When I returned the next day, I was very disappointed to see that the trailer "box" was no longer nicely square. The distortion from welding had sort of pulled a rear corner upward an inch or more. I didn't try to correct it, because the trailer was a rush job, and it's plenty strong. There's not much chance of dangerous residual stresses. The trailer's done lots of heavy hauling, and I still use it occasionally. But its not as pretty as I would have liked. We were making an aircraft work stand that required a 8' x 8' platform. we got a couple of 4' x 8' x 1/4" plate. Laid them out on the shop floor all nicely aligned, gaped one rod diameter and all and weighted them down with some scrap metal and told the newest apprentice to tack weld these together.... all the way. Do a 1 inch tack then move up about 6 inches and do another one... We went off to have a cuppa, or something, and when we came back the apprentice had decided to make a continuous weld.... much stronger he figured. He had gotten about a foot, maybe 18 inches, and the flat 4' X 8' plats had warped horizontally so that the far end of the joint was nearly 6 inches wide. -- Cheers, John B. |
#53
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US steel trade war
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