Regarding the pre-weld treatment, the iron oxide, floating rust and various impurities of the end face of the 40×60 crane rail flat bar should be thoroughly polished with a sander before the hoisting is in place. A heat-insulating tile should be placed between the 40×60 crane rail flat bar and the rubber pad to protect the pad from heat loss. A gap of 15mm to 20 mm is reserved for the adjacent two rails as a welding spacer. Since the base material has high carbon content, large rigidity, and large thickness, an alkaline low-hydrogen welding rod with high resistance to cold cracking, high thermal cracking resistance and the same strength level must be selected. Before use, the electrode will be placed in a 350°C to 400°C insulation tube. During welding process, we should select welding rods with diameters of 4mm and 5mm with a welding machine, and reverse the DC to reduce the splash of metal and the pores in the weld. Pre-welding preheating is the main measures for welding medium carbon steel. Due to the large tendency of the base material to harden, it is necessary to preheat to slow down the cooling rate, improve the microstructure of the joint, reduce the hardness and brittleness of the heat affected zone, and improve the plasticity to prevent the occurrence of cold cracks.
Before welding, preheat the range of 10cm to 15 cm on both sides of the 40×60 crane rail flat bar weld with oxyacetylene flame to 200°C – 250 °C. According to the cross-sectional shape of the rail and several sets of welding modules prepared before welding, the module comprises 1 bottom mold and 2 side molds, the material is electrolyte brass, the bottom mold is 8 mm thick, and the side mold is 10 mm thick. After the 40×60 crane rail flat bar is placed on the bottom mold, a steel gasket with the same width as the partition and the same length as the bottom of the rail and thickness of 3 mm is placed on the bottom mold at the bottom of the partition. The 40×60 crane rail flat bar is welded immediately after preheating, and the welding is continuously performed and can not be interrupted. First, we should use small current to melt the metal along the side of the steel gasket to ensure that the rail and steel gasket are completely fused together. After the first layer is welded, the slag should be removed immediately and the second layer is welded. The welding of the first layer can be carried out with small current, and the welding rod runs straightly. Starting from the second layer, the welding current is increased, and the welding rod is continuously moved forward while swinging in the lateral direction, and is sequentially performed until the bottom of the 40×60 crane rail flat bar is welded. After each layer is welded, the welding slag and the splash metal are removed and the next layer is welded. Each layer of the weld is kept to a thickness of 3mm to 4mm. After the bottom of the 40×60 crane rail flat bar is welded, the slag is cleaned, the side mold matching the curvature of the rail is installed in place, and a gap of 3mm-5 mm is reserved between the side mold and the rail for the slag to flow out. During welding process, we should adjust the current appropriately, and the electrode moves slowly forward while doing lateral movement to complete the welding of each layer. For each layer of welding, the welding slag must be cleaned until the deposited metal at the welding site is slightly higher than the top of the rail by 1mm-2 mm.