Why Are Crane Tracks Prone To Problems? —— Welding

Why are crane tracks prone to problems? —— Welding

 

In engineering, the track installation of bridge cranes and gantry cranes is an engineering field between machinery and civil engineering.

 

The track installation is often installed by the plant construction party, while the crane is installed by a unit with crane installation qualifications, and the two are often out of touch.

 

The installation of rail track beams and crane rails in engineering construction is often completed by two majors (such as civil engineering and mechanical installation), and there is also a disconnect between the two majors.
 

Therefore, it is difficult to ensure the quality of crane rail installation.

 

The quality of the track installation of the 50 ton bridge crane directly affects the running quality of the crane. Only by grasping the quality control from the source can the quality of crane rail installation be guaranteed.

 

 

1. 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.

 

2. Control of rail welding deformation The pre-raised height of the rail end depends on the type, length, fixing condition of the rail and ambient temperature and other factors. In advance, the rail end is raised for 30 degrees with a copper backing plate and a carbon steel plate. ~40mm, use the prepared bolts and pressure plates and other connecting parts, 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.

 

3. Welding
 

The sequence of welding track joints is from bottom to top, first the bottom of the 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 at 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.

 

 

4. 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.

 

5. Stress relief heat treatment (flame heating method)
 

The stress relief heat treatment of the rail end after welding is an important measure to improve the welding quality. For the rails that are welded at relatively low temperatures (such as winter construction, etc.), must use
 

This measure; heat treatment for stress relief uses gas welding nozzles to heat 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 40mm from the center of the weld on both sides; after the temperature of stress relief heat treatment is reached, 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.

 

6. 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.

 

 

Treatment of track joints at factory building expansion joints
 

There are usually two types of treatment for track joints at the expansion joints of the plant:
 

One is connected by splints or fishplates, the track adopts 45° oblique joints, and the gap is 10mm;
 

The other is connected by splicing splints processed according to the shape of the rail head, with a gap of 50mm.