Differences in welding process parameters of national standard rails
- What are the differences in flash butt welding parameters between 60kg/m and 50kg/m national standard rails?
The burning amount of 60kg/m rail flash butt welding is 15%-20% more than that of 50kg/m, usually 25-30mm, because the larger section requires more metal filling. In terms of upsetting force, 60kg/m rail needs to reach 350-400kN, and 50kg/m is 250-300kN to ensure tight combination of welds. The energization time of 60kg/m rail is 10%-15% longer than that of 50kg/m to ensure full fusion of the heat-affected zone. The holding time of 60kg/m rail after welding needs to be extended by 5-10 minutes to reduce internal stress.
- How does the welding current affect the joint quality of national standard rails?
If the current is too small (20% lower than the standard value), the welding will be insecure, and the joint strength is only 70%-80% of the base metal, which is prone to cold welding defects. If the current is too large, the width of the heat-affected zone will increase by 30%-40%, the grains will be coarse, the toughness of the joint will decrease, and the impact energy will decrease by more than 25%. The welding current of 60kg/m rail is usually controlled at 8000-10000A, and that of 50kg/m rail is 6000-8000A, which needs to be dynamically adjusted according to the actual temperature of the rail.
- What are the differences in the mechanical properties of national standard rail joints affected by different welding methods?
The tensile strength of flash butt welded joints can reach more than 95% of the base metal, and the impact energy is ≥40J, which is suitable for high-speed railways and heavy-haul railways. The strength of gas pressure welded joints is slightly lower, 90%-95% of the base metal, but the plasticity is better, and the elongation after fracture is 5%-10% higher than that of flash butt welding, which is suitable for ordinary railways. The performance of arc welded joints is the worst, with strength only 80%-85% of the base metal, which is only used for emergency repair, and the detection cycle needs to be shortened.
- What measures should be taken for national standard rail welding when the welding environment temperature is below 0℃?
The range of 100mm at both ends of the rail should be preheated to 80-120℃ to reduce the temperature gradient during welding. The welding current is 10%-15% higher than that at room temperature to compensate for heat loss at low temperatures. The upsetting force is appropriately increased by 5%-10% to ensure that the weld can still be tightly combined at low temperatures. After welding, the joint is immediately wrapped with thermal insulation cotton and slowly cooled to room temperature to avoid cracks caused by rapid cooling.
- How to check whether the quality of national standard rail welded joints is qualified?
The appearance inspection should ensure that the height difference at the joint is ≤0.3mm, the 错牙 is ≤0.2mm, and there are no obvious burns and cracks. Ultrasonic flaw detection is used to detect internal defects to ensure that there are no pores and slag inclusions with diameter ≥0.5mm. Tensile test is carried out, and the tensile strength of the joint should be ≥90% of the base metal, and the bending test should be 180° without cracks. For high-speed railway rails, fatigue test is also required, and there is no fracture under 2 million cycles of load.