Wear-resistant coating treatment and wheel-rail wear control for external standard rails
What are the core process parameters of laser cladding wear-resistant layer for foreign standard rails?
For the laser cladding wear-resistant layer of foreign standard rails, the laser power must first be controlled, usually set at 3-5kW. Too low power will lead to poor bonding of the cladding layer, while too high power will easily burn the rail matrix. The cladding powder is iron-based alloy powder, and the powder particle size is controlled at 50-150μm to ensure uniform melting of the powder and tight adhesion. The laser scanning speed needs to match the powder feeding rate, generally 0.5-1m/min, to ensure uniform thickness of the cladding layer, and the thickness of the finished wear-resistant layer must reach 1.5-2mm. Argon gas must be introduced as a protective gas during the cladding process, with a gas flow rate of 15-20L/min, to isolate air and prevent oxidation of the cladding layer. In addition, the clad rail needs to be subjected to low-temperature tempering treatment at 200℃ for 2 hours to eliminate the residual stress of the cladding layer and improve bonding stability.
What cost advantages does plasma spray welding wear-resistant layer have over laser cladding?
The equipment investment cost of plasma spray welding wear-resistant layer is much lower than that of laser cladding. The unit price of its spray welding equipment is only 1/3 of that of laser cladding equipment, which is more suitable for wear-resistant treatment of small and medium batch rails. The procurement cost of spray welding powder is lower. The price of iron-based spray welding powder with the same dosage is 20%-30% lower than that of laser cladding powder, which can reduce raw material expenses. The production efficiency of plasma spray welding is higher, and the processing time of a single rail is 40% shorter than that of laser cladding, which can increase production capacity and amortize unit processing costs. The consumable loss rate of this process is lower. The replacement cycle of vulnerable parts of the spray welding gun is 1000 rails, while that of the laser cladding head is only 500 rails, reducing equipment maintenance costs. In addition, plasma spray welding has low requirements for the operating environment and does not require a special dust-free workshop, which can save site renovation costs, and the comprehensive cost advantage is significant.
Why can wear-resistant layer rails adapt to heavy-haul lines in alpine regions?
The alloy composition of wear-resistant layer rails adds elements such as nickel and chromium, which can still maintain a hardness above HRC55 at -40℃ low temperature, and will not experience toughness degradation due to low temperature. The bonding strength between the wear-resistant layer and the rail matrix is ≥350MPa, which can resist the stress impact caused by freeze-thaw cycles in alpine regions and avoid peeling of the wear-resistant layer. The wheel-rail friction force of heavy-haul lines in alpine regions is greater, and the wear resistance of the wear-resistant layer is three times that of ordinary rails, which can reduce rail surface damage caused by rail wear. The dense structure of the wear-resistant layer surface can prevent melt water from snow and ice from penetrating into the rail, reducing the risk of low-temperature corrosion. At the same time, wear-resistant layer rails have better fatigue resistance. Under the dual effects of low temperature and heavy load, the fatigue crack growth rate is reduced by 50%, ensuring the long-term stability of alpine lines.
What is the correlation between wear-resistant layer thickness and rail service life?
There is a positive correlation between the thickness of the wear-resistant layer and the service life of the rail, but it is not the thicker the better, and it needs to be controlled within a reasonable range. A 1.5mm basic wear-resistant layer can extend the service life of the rail to twice that of ordinary rails, meeting the needs of conventional speed heavy-haul lines. A 2mm wear-resistant layer is suitable for high-speed heavy-haul lines, with a service life three times that of ordinary rails, and can maintain a good wheel-rail contact state. If the thickness of the wear-resistant layer is less than 1mm, its wear-resistant effect is limited, and the service life can only be increased by 30%, with low cost performance. If the thickness exceeds 2.5mm, it will cause a sudden change in the stiffness of the rail head, increase the wheel-rail impact load, and instead easily cause matrix cracking and shorten the overall life. Therefore, it is necessary to accurately match the wear-resistant layer thickness of 1.5-2mm according to the line axle load and speed to achieve a balance between life and safety.
What are the key points of on-site testing for wear-resistant layer rails?
The on-site testing of wear-resistant layer rails first needs to inspect the thickness of the wear-resistant layer. An ultrasonic thickness gauge must be used to test one measuring point per meter to ensure that the thickness deviation is ≤±0.2mm. Secondly, the hardness of the wear-resistant layer needs to be tested. A portable Rockwell hardness tester is used, and the measuring points cover the working surface of the rail head, and the hardness must meet the design standard of HRC58-62. The bonding state of the wear-resistant layer is the core of the test. Penetrant testing is required to check surface cracks, and ultrasonic testing is used to detect internal bonding defects to prevent delamination and slag inclusion. The surface roughness of the rail head also needs to be tested, and the roughness should be controlled at Ra1.6-3.2μm. Excessively high roughness will increase wheel-rail friction, while excessively low roughness will easily cause wheel-rail slippage. In addition, the wear amount of the wear-resistant layer is regularly tested. When the wear amount reaches 0.8mm, preventive grinding must be arranged to ensure the safety of line operation.