Qinghai-Tibet Railway runs through China's western Qinghai, Tibet, the two provinces, across the Qinghai-Tibet Plateau, the average across the board for more than 4 000 m altitude, frost heave in permafrost thaw, cold, snow and more, large diurnal temperature, light intensity and other natural roadbed and track conditions on the line to bring a lot of adverse effects. Laying of the Qinghai-Tibet line CWR for improving speed, reducing track maintenance, lower operating costs and achieve leapfrog development strategy railway, is of great significance.
Ministry of Railways major research projects "section of the Qinghai-Tibet grid lines look CWR test section --- Key Technology Research", at the Oasis to Jade Everest count 2318546 km between the three operative shop CWR test, which laid 50kgPm rail 1611442 km, laying 60 kgPm rail 71710 47 km, are used the temperature range of stress-type seamless line.
On-site welding and lock welding unit is currently used mainly domestic pressure Welding Wire and aluminum welding two kinds of heat welding process. Thermite weld strength is only about 70% of the base metal, weld cast the organization as the organization, often produced with casting defects and breakage rate, is not favored by experts. Pressure weld strength, breakage rate, but in special circumstances the Tibetan Plateau (average sea level air pressure is 60% to 70% oxygen in air than in sea level by 38 to 46%, the welding quality can be not meet the TBPT1632 -91 "welded rail
Joints technical conditions, "the technical requirements, to be in practice, further research and discussion.
2 traditional pressure welding pressure welding and CNC Performance Comparison
Mobile pressure welding equipment including: crimping machine (with push-convex device), heater, control box, water cooling, high pressure electric pump station and some auxiliary facilities, such as end mills, profiling grinding machine, piping systems, oxygen bottles, acetylene bottles and generators and so on.
2.1 The traditional pressure welding
Traditional welding are manual and pneumatic control, each operation (clamp, put the fire, gas flow and ratio, pressure conversion, etc.) control the process parameters of the low accuracy, poor stability parameters. Thus the joint quality is often affected by human factors, show a great volatility, breakage rate increased, the CWR potential safety hazard, endanger traffic safety.
2.2 new pressure welder CNC
Test section of the Qinghai-Tibet Railway CWR developed using the newest digital pressure welding equipment, welding the whole process to achieve the order of the closed-loop control and intelligent control. No manual welding process, welding process to ensure the stability and consistency, completely eliminating the human factor of the joint quality. Main features:
1) the order of the welding process control and flexible control: PLC as the core sequence of welding operations process control, high time, low time, upset the input parameters such as pressure time control program, the program automatically by the control and welding time Automatic conversion. Rail welding conditions according to the actual needs, but also can be adjusted in real-time manual intervention.
2) heat input control: the use of closed-loop control of welding parameters, put the fire from the heater control module, the ratio of the heating gas flow control module with the joint, put fire to achieve amplitude, frequency, size, flow, temperature of the flame characteristics associated with welding precise control of parameters.
3) extrusion welding control: welding the rail pressure "three-stage pressure" process solidified in the PLC control program, the use of pressure sensors, displacement sensors, closed-loop control method to achieve real-time control of welding pressure, flexible adjustment and automatic conversion and the top forging displacement of closed-loop control.
4) with welding parameters on-line detection, recording, storage.
3 high altitude of the main welding process
3.1 Oxygen, acetylene flow
Pressure welding of the welding flame is generally used oxygen - acetylene flame or oxygen - propane flame, in fact, most of the use of oxygen - acetylene welding. The flame structure and flame shape and temperature distribution is mainly determined by the combustion ratio.
Combustion than: β0 = VkPVa (Vk is the volume of oxygen; Va is the volume of acetylene).
Low-lying areas in the Mainland (altitude ≤ 1 000 m), pressure welding using a weak carbon flame, β0 is generally 0185 - 0195. However, in the Qinghai-Tibet line altitude> 3 000 m of the region, there is no mature experience to draw on the scene to determine the ratio of the combustion air pressure welding to the mainland in the past can not guarantee the quality of welding experience. To this end, we altitude 4 300 m stations were jade Everest trial, made a first-hand information, should be controlled burn in 0196 than the β0 ~ 111.
Pressure welding 60 kgPm U71Mn rail 15 through the drop test of the joint, the welding of oxygen, acetylene flow rate recorded in Table 1.
3.2 Heater
Pressure welding various parts of the flame of intensity heaters, directly affects the quality of Nickel Alloy Welding Electrodes. Fracture occurs on the spot, incomplete penetration and over-burning, if no other reason, is certainly the appropriate parts of the flame low or high power, need to debug on the heater fire hole. Low-lying areas in the Mainland (altitude ≤ 1000 m), pressure welding 60 kgPm U71Mn fire heater used rail hole pattern (38 × 2 = 76 holes) shown in Figure 1.
Figure 1 60 kgPm rail heater flame intensity can not meet the fire-hole under the conditions of the plateau pressure welding technology requirements. Similarly, we altitude 4 300 m stations were jade Everest trial, debugging, summed up a set for high altitude areas of the fire-hole configuration in Figure 2. The number of fire hole 39 × 2 = 78 holes.
4 results
Test section of the Qinghai-Tibet Railway CWR site used by the new welding pressure welding process, welding quality to fully meet its
TBPT1632 -91 "rail welding joint technical conditions," the technical requirements, pressure welding 60 kgPmU71Mn rail 15 drop test specimens are given in Table 2.
5 Conclusion
CWR test section of the Qinghai-Tibet Railway construction experience has fully proved that pressure welding pressure welding using advanced numerical control equipment, excluding man-made factors on the welding quality. At the same time, the welding process according to different environments, different altitude adjustment, optimization, summed up a world of experience welding pressure plateau railway scene, plateau for the future, seamless cold special circumstances to provide a reference line construction experience