Low temperature elasticity retention rate of spring bars
- What is the standard for the low-temperature elastic retention rate of Type Ⅰ elastic clips at -30℃?
The elastic retention rate of Type Ⅰ elastic clips at -30℃ must be ≥80%, that is, the clamping force is more than 80% of that at room temperature (20℃). During testing, the elastic clip is placed in a -30℃ environmental chamber for 4 hours, the clamping force is tested, and the retention rate is calculated by comparing with the room temperature value. If the retention rate is lower than 80%, the rail restraint will be insufficient and the gauge deviation will increase. In low-temperature areas (such as the three northeastern provinces), it must be replaced with Type Ⅱ elastic clips. In production, nickel (0.3%-0.5%) is added to improve low-temperature toughness to ensure the retention rate meets the standard. The proportion of low-temperature sampling inspection for each batch is not less than 3%, and if unqualified, the whole batch will be reworked.
- What is the difference in low-temperature elastic retention rate between Type Ⅱ and Type Ⅰ elastic clips?
Type Ⅱ elastic clips are made of 60Si2CrA material, with an elastic retention rate of ≥85% at -40℃, which is 10 percentage points higher than that of Type Ⅰ elastic clips (75% at the same temperature). Its low-temperature impact toughness reaches more than 12J/cm², which is 1.5 times that of Type Ⅰ elastic clips. Under the cyclic temperature of -40℃ to -5℃, the clamping force attenuation rate is 8%-10% lower than that of Type Ⅰ. Type Ⅱ elastic clips are suitable for extremely cold areas (such as Inner Mongolia and northern Xinjiang) and can reduce maintenance times caused by insufficient elasticity of elastic clips in winter.
- What are the reasons for the decrease in elastic retention rate of elastic clips in low-temperature environments?
Low temperature will reduce the atomic activity of the elastic clip material, hinder dislocation movement, and lead to a 3%-5% decrease in elastic modulus. Trace impurities (such as phosphorus and sulfur) in the material will form brittle phases at low temperatures, making the elastic clip prone to microcracks when stressed, reducing elastic recovery ability. When in an environment below -20℃ for a long time, the internal stress of the elastic clip will gradually accumulate, and after exceeding the yield limit, the elastic retention rate will decrease by 1%-2% per month.
- How to improve the elastic retention rate of elastic clips at extremely low temperatures?
Adopt low-temperature tempering process, keep the elastic clip at 280℃-320℃ for 4 hours to reduce internal stress and improve low-temperature toughness. Add chromium (0.8%-1.2%) and vanadium (0.08%-0.12%) to the material to refine grains, so that the elastic retention rate at -50℃ is still ≥80%. The surface is subjected to low-temperature nitriding treatment to form a 5-8μm hardened layer, reducing the impact of wear at low temperatures on elasticity. Pack in vacuum to avoid moisture and freezing during storage affecting performance.
- What track problems will elastic clips with unqualified low-temperature elastic retention rate cause?
It will cause insufficient rail clamping force, and the longitudinal displacement of the rail will exceed 10mm when the train passes, and the rail gap will exceed the standard, causing impact vibration. At low temperatures in winter, elastic clips with low elastic retention rate are prone to plastic deformation. If the number of deformed elastic clips per kilometer of track exceeds 5%, emergency maintenance is required. Long-term use will aggravate sleeper loosening, reduce track lateral stability by 20%-30%, and increase the risk of derailment, especially in curve sections.