Butt Welding Process of 30x40mm Crane Rail Flat Steel

Butt Welding Process of 30x40mm Crane Rail Flat Steel

In the manufacturing process of the crane, the rails laid on the box-type main beam are often welded into a long rail without gaps by means of butt joints. We should select the welding consumable according to the material and surface hardness requirements of the rail. There are three types of crane trolley tracks, namely crane rails, such as QU70, QU80, etc., P-type rails, such as P24, P38, P43, etc., square steel, such as 30x40mm crane rail flat steel, 40x40mm and so on. The tops of the first two rails are convex, and the bottom is a flat plate with a certain width to increase the contact surface with the foundation. The cross section of the rail is I-shaped and has good bending strength, and its carbon content and high manganese content. The material of 30x40mm crane rail flat steel is usually S355 steel, and the top of the 30x40mm crane rail flat steel is straight.

The butt weld of the rail requires that the surface hardness of the rail be achieved without treatment. Below the 30x40mm crane rail flat steel head, E5061 electrodes should be used. Surfacing electrode D322 (chromium tungsten molybdenum vanadium cold die electrode) is used in the track head. This is both economical and practical, which not only can guarantee the quality and strength of the butt weld, but also can make the hardness of the surfacing layer (air cooling after welding) more than 55HRC. Due to the poor welding performance of the rails, the welding process is cumbersome. It is necessary to fix the 0℃ to 300 °C thermometer on the rails, and preheat the rail tops with 2 to 3 torches at a distance of 100 mm from both sides of the weld lines. When the rail temperature reaches 230℃ to 250°C, the E5016 electrode is first used to weld from the bottom of the rail while heating. The welding should be carried out intermittently, and the heat of the welding part should be minimized. When the orbital temperature is maintained at between 230℃ and 250 °C during the welding process, the E5016 welding rod is used to weld from the bottom of the rail while heating, and during welding to the track head, D322 is used again. The electrode is welded while being heated. The welding should be carried out intermittently to minimize the heat of the welded part, so that the orbital temperature is always maintained between 230℃ and 250 °C during the welding process. After all the welding is completed, the heating is continued to 250°C, and the rail is slowly cooled to an outdoor temperature (about 30 ° C) in the air for moret than 0.5 hours to prevent cracks. After welding, check the welds and the joints with the rails for obvious marks and post-weld hardness. Grinding with a pneumatic grinding wheel is necessary after welding, the weld seam of the rail head is kept in the same plane as the original rail surface, and has the same surface roughness.

Steel has different internal structure at different temperatures, and changes in internal structure will inevitably change the mechanical properties of steel. Before welding, the rail is preheated to 230℃ to 250°C, and a low temperature tempering treatment is performed to prevent the metal in the weld portion from being cracked after cooling. At this time, the structure of the hardened layer is changed from martensite to tempered martensite. The internal stress of the steel is partially eliminated, the toughness is increased, and the hardness is hardly reduced, and the rail is not deformed at the preheating temperature. If the preheating temperature is too high, the martensite structure of the original hardfacing layer is transformed into other tissues, such as sorbite, resulting in a decrease in the hardness of the rail. In the butt welding of the rail, as the welding temperature increases, the tempered martensite at the welded portion begins to transform to other structures. The welding should be intermittent, and the heat of the welding part should be minimized, so that the temperature of the rail is always maintained at 230℃ to 250 °C. Since the alloy and the track of the weld are slowly cooled to the outdoor temperature as a whole, the internal stress at the weld portion is reduced, and no crack is generated on the surface. In addition, after the hardness test, the top weld of the track reached the original hardness of the top surface of the track, indicating that the surface hardness also met the requirements.

The steel rails laid on the box-shaped main beam of the crane are welded into a seamless steel rail, which can greatly increase the rigidity of the box-shaped main beam of the crane, reduce the bending deformation of the main beam and reduce the noise of the crane car so that the car runs smoothly and the wheel pressure is even. In addition, the wheel wear of the trolley is reduced, the life of the wheel is prolonged, the service life of the crane is prolonged, the reliability is improved, the maintenance workload is reduced, the cost of the user is saved, and the user’s praise is received. This welding process is especially important for large tonnage, long span cranes.