Dan_Bower%RPI-MTS.Mailnet@MIT-MULTICS.ARPA (09/19/85)
For shipping purposes, welded rail is usually in quarter mile lengths. Up until recently (the last decade or thereabouts) railroads would just bolt these sections together with standard joint bars. Now it is popular to weld the joints in the field. Since there are very few field welds to do, it isn't effective to bring in a mobile flash-butt unit. Field welding on a onesy-twosy basis is done with the alumino-thermic method. (This is where you align the two rails and clamp a crucible around the joint. A mixture of iron oxide and aluminum powder is put in the top, along with a magnesium filings. The magnesium is lit by a striker or a torch, which in turn lights off Al-FeO.. in a very hot reaction. The result is iron and aluminum oxide (as slag). The iron flows down around and between the rails, melting the ends. When it cools, you have a weld.) "Thermit" welding is cheap on a small time basis. It however is not a very high quality weld. Most railroads that use it will put a pair of joint bars around the weld just in case. I've noticed that lately Conrail has been welding *everything*. They weld frogs and switchpoints to stock rails even. This makes for as continuous welded rail as you can get (insulated joints notwithstanding). RE: rail anchors It is not true that some have decided that anchoring against thermal movement isn't necessary. Even in jointed track, some have used anchors, especially in turnouts. As I said in my earlier message, some fastenings serve also as anchors, making separate anchors unnecessary.