Oil resistance of rail pads and response to oily environments
- What are the oil resistance performance indicators of under - rail pads?
Volume change rate is a key indicator. After soaking in engine oil for 24 hours, the volume change must be ≤5%. If it exceeds 10%, the pad will deform and cannot fit with the rail. Chloroprene rubber pads perform excellently in this indicator. The weight change rate should be ≤3%. Excessive weight increase indicates that the pad absorbs oil seriously, which will lead to decreased elasticity. The weight change rate of natural rubber pads after soaking in diesel oil is usually 2% - 4%. Hardness change must be ≤±5 Shore A. Too high or too low hardness will affect the buffering performance. Nitrile rubber pads have good oil resistance, and the hardness change can be controlled within ±3 Shore A. Tensile strength retention rate ≥80%. Pads with poor oil resistance will have a significant decrease in tensile strength in oil, and even cracks may appear. The composite rubber pad can reach more than 85% in this indicator.
- What are the hazards of oil - contaminated environment to under - rail pads?
Oil contaminants will dissolve the plasticizer in the pad, leading to hardening and decreased elasticity of the pad. After one year, the elastic modulus may increase by 20% - 30%, the buffering performance will decrease, and the train vibration will increase. Pads after oil absorption are prone to swelling. Volume increase may lift the rail, and the gauge deviation exceeds ±1mm, affecting driving safety, especially in oil - contaminated areas such as locomotive depots. Long - term contact with oil will accelerate the aging of the pad, with cracks and chalking on the surface, and the service life will be shortened by 30% - 50%. The service life of ordinary rubber pads in oil - contaminated environment is only 3 - 4 years. Oil will reduce the friction between the pad and the rail, leading to increased lateral displacement of the rail, which is more obvious in curve sections, requiring frequent gauge adjustment.
- Which materials of under - rail pads have better oil resistance?
Nitrile rubber pads have the best oil resistance. They contain acrylonitrile groups and have strong resistance to mineral oil, diesel oil, etc. The volume change rate is ≤3%, which is suitable for areas with much oil pollution such as locomotive depots and freight stations. Chloroprene rubber pads have balanced oil resistance and weather resistance, with a volume change rate of 5% - 8%, and can be used in environments with both oil pollution and humidity, such as coastal freight railways. Polyurethane pads have good oil resistance, with a weight change rate of ≤2%, and fast elastic recovery, suitable for oil - contaminated sections of heavy - haul railways, but the cost is 20% - 30% higher than rubber pads. Composite rubber pads added with oil - resistant additives (such as rubber + polytetrafluoroethylene) have 40% - 50% better oil resistance than ordinary rubber, with high cost performance, and are widely used in oil - contaminated areas of ordinary railways.
- What are the maintenance measures for under - rail pads in oil - contaminated environment?
Regularly clean the oil on the surface of the pad, wipe it with a special cleaning agent (such as alkaline cleaning agent) at least once a month. After cleaning, dry the surface to avoid residual cleaning agent affecting the performance of the pad. Apply an oil - resistant coating (such as silicone coating) on the surface of the pad to form a protective film to prevent oil penetration. The coating thickness is controlled at 0.1 - 0.2mm, and re - coating is carried out every six months. Shorten the pad replacement cycle. The replacement cycle of pads in severely oil - contaminated areas is 30% - 40% shorter than that in normal environment. Nitrile rubber pads in locomotive depots are replaced every 2 - 3 years to ensure that the performance meets the standard. Install oil - proof baffles. Add baffles on both sides of the rail to reduce oil dripping onto the pad. The height of the baffle is ≥50mm, and the gap with the rail is ≤5mm, which is suitable for areas with fixed oil sources.
- How to detect the performance changes of under - rail pads in oil - contaminated environment?
Regularly sample for oil resistance test. Soak the pad sample in the actually used oil (such as a mixture of engine oil and diesel oil). Measure the volume and weight changes after 24 hours. If it exceeds the standard, the state of the pad in this area must be evaluated as a whole. Measure the elastic modulus of the pad on site. If it increases by more than 20% compared with the new pad, it indicates that the oil resistance has decreased, and maintenance measures must be taken. Ordinary railways are tested once a quarter. Observe the appearance of the pad. If there is swelling, cracks or discoloration on the surface, and the area exceeds 10%, it is judged that it is seriously eroded by oil, and needs to be replaced in time. High - speed railways have stricter requirements (replaced when the area exceeds 5%). Measure the friction between the pad and the rail with a tension meter. If it decreases by more than 15% compared with the initial value, it is necessary to clean the oil and add anti - skid measures.