With the development of the crane industry technology, the whole crane rail square bar design of cranes at home and abroad has adopted more and more steel rail design schemes. The continuity of the whole rail provides more direct and fundamental optimization conditions for the smoothness of crane load operation, which overcomes the influence of the crane rail square bar butt joint error (crane rail square bar height difference, crane rail square bar side straightness) when the rail adopts straight edge or the 45° mitre cutting to invoid the vibration generated by the crane trolley load running to the rail interface and the large compressive stress phenomenon caused by bottom support of the rail interface. support. This optimization provides a new topic for the process level. Because the length of the standard rail is limited, to achieve the design requirements of the entire rail, the long welding of the rail is imperative. The crane rail square bar material is generally a kind of high-carbon and high-manganese rolled steel, which has large tendency to weld cracks, and its weldability is poor. If the welding process is improperly handled, the welding quality is difficult to ensure. In order to solve this new problem, the professional technicians gradually improved the welding method of the rail during the trial, practice and summary process.
Place the track indoors and use a 1 meter steel ruler to detect the sides of the track to make it straight. When both rails are long, they can be welded on the flat ground. Asbestos pads are used for insulation and post-weld insulation during orbital welding. When the track section is large, it should be 10mm high under the asbestos cloth at the track interface to correct the post-weld deformation. In order to ensure the welding quality of the rail and prevent the occurrence of weld cracks, it is important to select a suitable electrode. According to the characteristics of carbon and manganese in the rail material, it is most suitable to use low-hydrogen welding rod. The electrode has good plasticity and high toughness in the weld metal during welding. This meets the requirements at the rail interface. From the perspective of economy and use, the welding of the rails is realized in three layers using three low-hydrogen welding rods. During welding process, the rail must be preheated and slowly cooled. The rail is preheated by welding with oxygen-acetylene. The purpose of preheating is to prevent martensite hardened structure in the weld heat affected zone and cause crack at the rail interface. Preheating should ensure that the temperature is consistent throughout the preheat range. When the preheating temperature reaches 300 °C to 350 °C, the bottom should be welded and welded flat, and there should be no convex parts on both sides. Otherwise, when the middle layer is welded, the copper plates on both sides cannot be installed. After the rail is welded, the part has a certain welding deformation, which can be straightened by heating with an oxygen-acetylene flame. The outer surface of the rail joint is to be surfaced by a coloring method, and is qualified if there is no crack. If the quality defect is found after the inspection, the welding convex can be scraped off and repaired again.
In summary, the welding of the rail usually depends on the chemical composition, mechanical properties, crack resistance of the parent metal of the rail to select the type of welding rod, the size, shape, working conditions and welding equipment and parameters of the welding and take according to the welding object. Corresponding process measures, such as tire assist, pre-weld preheating, post-weld slow cooling, etc., especially temperature control, each step needs to be taken seriously to ensure the quality of the rail welding.