Regards,
Alan
At 02:06 PM 10/15/2003 -0400, you wrote:
Alan,
Just sat in a TT seminar in Austin and they claim, as they have for years now, that the weld is done without foreign material and is sort of "vibrated" together. I am sure they used that term for us laymen and it is somehow symbolic of the actual process. They say after the weld, it is almost impossible to detect. They then heat and forge the steps into the shaft and they say that this anneals the metal. I am not sure what that means and am not going to look it up, but they claim after the shaft has been stepped, it is impossible to detect the weld.
FWIW, they also check each shaft for straightness and have an elaborate bending machine that takes out any irregularities.
I also thought I heard them say that step less shafts are cold drawn.
Al
At 10:02 PM 10/13/2003, you wrote:Hi guys,
I did feel compelled to snip. I believe that shafts are drawn hot and it is probably the residual stresses due to the heating and cooling and the large amounts of strain associated with the drawing process that leaves residual stresses in the shaft and these are what produce the residual bend. I'm a long way from a metallurgist, but I find it highly unlikely that there will be a significant change in modulus due to welding. It also surprises me that the carbon content of the steel is actually reduced, in aggregate. Welding will definitely change the strength of the material and it changes the crystalline structure of the metal (which is why the strength changes) and carbon may migrate away from the weld zone, but the weld zone in RF welding is very small.
I believe the technique works by inducing circular currents in the metal and it is the high resistance across the un-welded gap that locally heats the metal and produces the weld (similar to spot welding). Once the metal fuses the resistance drops and the weld zone produces no more heat than the metal around it. Hence the heating occurs in a very narrow zone immediately around the weld, and the change in material properties in the shaft is limited to a very small volume of material. I believe that it is unlikely that there is sufficient change in a large enough volume to significantly change the properties of the shaft at all. Especially since these shafts are then reheated prior to the drawing process.
Regards,
Alan
At 08:38 PM 10/13/2003 -0400, you wrote:
* I posted a speculation -- admittedly and specifically a speculation -- that whatever process produces residual bend in a steel shaft also produces spine.
* Tom Wishon posted that this was not true; fair enough. He said that the seams of butt-welded tubing are very tightly dimensionally controlled, so it does not cause a significant spine.
* RK said that there is a big difference in carbon content in the steel near the seam and elsewhere in the tubing. TW concurred. So what does this have to do with spines?
* Lloyd said that it has nothing to do with spines. Spines have nothing to do with the hardness or strength of the steel, but with its elastic modulus. And the elastic modulus varies very little with carbon content. (I checked a few reference books, and found only a 4% variation in modulus over a very wide range of carbon content.)
Lloyd is clearly correct that hardness has nothing to do with spines. I tend to agree with Lloyd that the carbon content due to the welding won't change the modulus significantly, so it won't affect the spine significantly. RK is probably right about the change in carbon content, but I conclude that has nothing to do with spines.
