Crane rail joint welding

crane rail joint welding

Preparation before welding

Before the crane rail joint is welded, the groove and nearby oil, rust, and other dirt should be carefully cleaned until the metallic luster is exposed. Welding consumables are matched with basic electrodes according to the principle of equal strength.

Control of orbital welding deformation

The pre-padded height of the rail end depends on the type, length, fixing condition, and ambient temperature of the rail. The pre-padded rail end is 30-40mm with a copper backing plate and a carbon steel plate. Connecting parts such as bolts and pressure plates, tighten the nuts to fix the rail on the track beam and set at least 4 fixing points near each rail joint.

After the bottom of the rail is welded, loosen the pressure plate, lower the raised part of the end of the rail to 20mm, and then tighten the nut of the pressure plate. When welding the rail waist part, gradually lower the backing plate height. When the rail waist part is welded, remove all the backing plates and loosen the pressure plate. At this time, there should be a small upturn at the rail joint. During the head process, it is decided whether to tighten the pressure plate nut according to the condition of the rail returning to straightness.

During the entire welding process, the deformation of the rail joint must be checked with a straight steel ruler at any time, and the height of the joint and the tight and loose pressure plate must be adjusted at any time to control the deformation of the rail joint. When fixing the rail joints before welding, the gap between the ends of the two rails is wide at the top and narrow at the bottom. The gap between the rail bottoms shall not be less than 12mm, and it should not be too wide. Generally, it shall be controlled within the range of 15-18mm. . When adjusting the joints of fixed rails, in addition to ensuring the size of the end gap, the ends of the two rails must also be aligned without distortion or staggering.

Before welding and during welding, it should be strictly checked to ensure that the centerlines of the two rails are on the same line, so as to prevent the rails from being bent and not straight when the rails are welded. For the rails fixed with hook bolts, when welding the rail joints, you can refer to the above method according to the specific situation, and set up temporary fixtures to fix the rails for welding.

Welding

The sequence of welding track joints is from bottom to top, first the bottom of the crane rail, then the waist of the rail, and the head of the rail, surfacing welding layer by layer, and finally repairing the surrounding area. The range of the ends of the two rails is 40mm each, and the preheating is carried out at the same time, and the temperature between the preheating and the layers is controlled from 300°C to 350°C. The first layer of welding (priming): the current is 120A ~ 130A to prevent the permanent carbon steel backing plate from burning through and melting the copper backing plate, thereby reducing the difficulty of removing the copper backing plate, shortening the air cooling time of the track, and maintaining the gap between layers. Temperature to prevent quenching; each layer can be used in the future (130±15)A and the welding slag must be removed after each layer is welded before continuing to weld;

Rail waist welding: current 130-140A, welding from the lower part of the waist upwards, pay attention to slag removal.
Rail head welding: the current is 130-140A. After installing the copper support plate, start welding. Pay attention to cleaning the slag once for each layer; finally, repair the unwelded full parts around the weld seam.

Precautions during orbital welding

When welding each layer of welding wave, especially when welding each layer of welding wave at the bottom of the rail, one welding rod should be used to complete the welding, and the welding rod should be avoided in the middle to break the arc. The welding direction of the front and rear two layers of welding waves should be opposite; The welding work of each rail joint should be carried out continuously so that the rail ends can be kept welded at a relatively high temperature (300°C to 350°C). After welding, before cooling after stress relief heat treatment, it must be protected from rainwater, etc.; the hot copper plate can be removed and dipped in water to cool it down so that it can be reused next time.

Stress relief heat treatment (flame heating method)

Stress-relief heat treatment of rail ends after welding is an important measure to improve welding quality. This measure must be adopted for rails that are welded at relatively low temperatures (such as winter construction); stress-relief heat treatment is used The gas welding nozzle is heated repeatedly around the rail head, rail waist, and rail bottom. The entire section of the rail should be heated evenly as much as possible, and special attention should be paid to the heating quality of the rail bottom. The heat treatment temperature for stress relief is 620°C to 650°C, and the range of stress relief heat treatment is 40 mm from the center of the weld on both sides; after the temperature of stress relief heat treatment reaches the temperature, the constant temperature heating must be kept at 20 to 30 minutes. Wrap the blanket with thermal insulation cotton, keep warm, and cool slowly until it reaches normal temperature.

Grinding treatment of track joints

After the welded joints of the rail have been heat-treated for stress relief and cooled to atmospheric temperature, the welds on the top surface and both sides of the rail are ground and smoothed. When the welding protrusion is too large, use a grinding wheel grinder to grind it until it is flush with the rail head, and finally polish the surface