The Material Hardness of the Ballast Plate and its Relationship with Sleeper Collapse Risk Prevention Mechanism
Why will the hardness of the pressure plate material exceeding HRC40 increase the risk of concrete sleeper crushing?
The compressive strength of concrete sleepers is usually C60-C80, corresponding to an allowable compressive stress of 30-40MPa. When the hardness of the pressure plate material exceeds HRC40, the surface hardness is high, the contact area with the sleeper is small, and the compressive stress per unit area will increase by 25%-30%, exceeding the allowable compressive stress of the sleeper. Under the action of high stress, the sleeper will produce local crushing, with cracks and spalling. Under long-term alternating loads, cracks will propagate rapidly, leading to sleeper fracture and affecting the overall track stability. In addition, pressure plates with excessively high hardness are easy to have hard contact with the sleeper, exacerbating sleeper wear and further increasing the risk of crushing.
Why do sleepers of ordinary-speed lines choose pressure plates with HRC35-38 instead of those with HRC40 or above?
The compressive strength of concrete sleepers of ordinary-speed lines is C60, and the allowable compressive stress is 30MPa. Pressure plates with HRC35-38 have moderate surface hardness, large contact area with the sleeper, and the compressive stress per unit area is controlled within 25MPa, lower than the allowable value. The pressure plates with this hardness have good wear resistance, are not easy to deform, and can effectively protect the sleeper from crushing. Pressure plates with HRC40 or above have excessively high hardness, and the unit compressive stress exceeds the standard, which is easy to cause sleeper crushing, not suitable for ordinary-speed lines. Therefore, ordinary-speed lines choose medium-hardness pressure plates, balancing clamping force and sleeper protection needs.
The risk of sleeper crushing is high in heavy-haul lines. How to prevent it through pressure plate material selection?
Heavy-haul lines have large axle loads, and the sleeper compressive stress can reach more than 50MPa. It is necessary to select quenched and tempered alloy steel pressure plates with HRC38-42. The hardness of this material is moderate. After carburizing treatment, the wear resistance is improved by 30%, and at the same time, the contact stress with the sleeper can be reduced. In addition, the contact area between the pressure plate and the sleeper can be increased to control the compressive stress per unit area within 35MPa, lower than the allowable compressive stress of the sleeper. At the same time, high-toughness pressure plate materials are selected to avoid pressure plate deformation caused by load impact, further reducing the risk of sleeper crushing.
What impact will the low hardness of the pressure plate material have on the overall performance of the track clamping system?
Pressure plates with low material hardness have weak ability to resist plastic deformation, and are prone to bending deformation under the action of train load. The deformed pressure plate cannot be close to the rail base, and the clamping force decreases by 20%-30%, leading to lateral displacement of the rail and increased gauge deviation. At the same time, the deformed pressure plate will form gaps with the sleeper, discontinuous stress transmission, exacerbating local stress on the sleeper and increasing the risk of crushing. In addition, the deformation of the pressure plate will cause uneven stress on the elastic clips, accelerating elastic fatigue and shortening the service life. Therefore, the hardness of the pressure plate material must meet the design requirements to avoid system performance degradation due to insufficient hardness.
How to test the hardness of the pressure plate material on-site to ensure it matches the compressive strength of the sleeper?
A Rockwell hardness tester can be used to test the surface hardness of the pressure plate on-site. For conventional speed lines, the pressure plate hardness needs to be controlled within HRC35-38, and for heavy-load lines, it should be HRC38-42. Simultaneously, it needs to be combined with sleeper compressive strength testing. If the sleeper is C60, the allowable compressive stress is 30MPa, and the pressure plate hardness should not exceed HRC38; if the sleeper is C80, the allowable compressive stress is 40MPa, and the pressure plate hardness can be increased to HRC42. In addition, a crush test can be conducted, applying the rated load to the pressure plate and observing whether the sleeper crushes, ensuring hardness matching. Only after passing the test can the track be put into use.