Construction method of fixed small welding rail of

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K920 welding machine fixed small welding rail construction method (Part 1)

rail welding quality is of great significance to the safety of railway traffic and the extension of rail service life. At present, contact welding is generally used for factory welding and small-scale pneumatic welding and thermit welding are used for site welding of seamless railway laid in China. Due to the high degree of mechanization of contact welding, the weld material is the same as the base metal, the central parity of RMB against the US dollar has been reduced by 3746 points in 2015, and the welder has a quality monitoring system to ensure the stable and consistent quality of each welding joint, so the welding quality of contact welding is the best among the three welding methods

The K920 flash contact welding machine is jointly developed and produced by the Scientific Research Institute of Shanghai Railway Bureau, China Railway 11th bureau group and other units under the auspices of the Department of science and education of the Ministry of railways. According to the needs of Wuhan Rail Transit phase I project, China Railway 11th Bureau has used this machine for small-scale fixed welding in the base. The total length of the project is 10.234 km for double track, including 19.2 km for single track of jointless track, and pd360 kg/m rail is adopted for steel rail. During the construction, the 25 m standard rail is first welded into a 1.5 m long rail with K920 welding machine, which is sent to the site by a long rail truck for laying, and then welded into a seamless rail by mobile pneumatic welding

2 this is another phenomenon of structural readjustment. K920 welding machine features

(1) the machine has a compact structure and is convenient for transportation and installation. After the two containers are supported in place and the welding rail raceway line is installed, the production capacity can be formed soon. The oil pump is specially started to adjust the pointer to the zero position, which is applicable to the base welding of small-scale seamless rail, with less space occupation and fast installation and production. (2) The whole welding process is controlled by computer, which ensures the uniformity and reliability of welding quality. (3) The process is simple, the labor intensity is small, and the use is safe and convenient. (4) It can generate electricity by itself or connect external power supply, which is convenient and flexible

3 construction process

3.1 process flow (Figure 1)

3.2 operation process and key points

the welded rail production line is installed and arranged according to the construction requirements. Generally, there are stations for rail selection, rail end treatment, pushing, welding, normalizing, grinding, flaw detection and detection, long rail lifting and storage, and each station writes its operating procedures in the form of signs

(1) two 5-T gantry cranes are used to lift the standard rail with a length of 25 m on the rail distribution platform. After inspection and measurement, it is judged whether it can be welded on the track. The rails to be welded shall meet the following requirements: ① flaw detection shall be carried out on all rails to remove the damaged rails; ② The steel rail shall be straightened to make the whole length of the steel rail straight without hard bending, and the non straightness within 1 m at both ends of the steel rail shall not be greater than 0.5 mm; ③ The rail length error shall not be greater than 10 mm; The unevenness at the sawing section shall not be greater than 0.5 mm; ④ There shall be no crack, double skin, slag inclusion, shrinkage cavity, serious segregation and other defects on the surface or inside of the rail

(2) rail end treatment before rail welding, both ends of the welded rail shall be derusted on the rail distribution platform. It is required that the surface should be smooth without rust spots, and the grinding amount should not exceed 012 mm at a time; If the rail to be welded lasts for more than 24 hours or is contaminated with oil and water, it must be polished again, with a grinding length of about 600 mm

(3) after the alignment of the welding rail is qualified, turn on the power supply, weld the two jaws with a voltage of 400 V, activate the automatic welding procedure, and enter the pre flash stage, stable high-voltage flash stage, low-voltage flash stage, accelerated flash stage and upsetting stage respectively. After the upsetting is completed, the whole welding process ends. After the flash welding is completed, the rail clamping device quickly releases the two jaws, and the tumor pushing knife in the welding head immediately pushes the tumor to complete the welding of a rail joint

(4) normalized rail welded joints need post welding treatment. Flame normalizing (oxygen + acetylene) is adopted for heat treatment. When the temperature of the rail welding joint drops below 500 ℃, the flame normalizing starts. The heater swings longitudinally along the stress change joint on the welding test sample. The surface temperature heated by the rail head is generally not more than 950 ℃, and the surface temperature heated by the rail bottom angle is not less than 830 ℃. The normalizing heating temperature of the rail surface adopts a photoelectric thermometer, and the normalizing records are made

(5) grinding use the rail grinding machine to grind the rail top and side of the rail welded joint. When grinding, it is not suitable to grind the weld horizontally, and do not make the rail surface blue. If the temperature is high during grinding, the grinding shall be suspended until the temperature is appropriate

(6) weld flaw detection use the ultrasonic flaw detector to detect the rail weld, and follow the following regulations: the flaw detection can be carried out only when the weld naturally cools to below 50 ℃; When incomplete penetration, cracks, slag inclusions and other defects are found in any part of the weld, the welding head must be cut and re welded

(7) weld acceptance after the weld flaw detection is qualified, its appearance size should be checked, and the inspection results should meet the requirements of Table 1

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