Bolted connections are widely used in rail vehicles. The reliable bolting connection of rail transit vehicles ensures the safe operation of trains, and TB/T 3246 is adopted, which provides a reliable theoretical basis for urban rail transit.
Under the influence of variable load, vibration, and even working temperature, the bolted connection will be deformed or creep, so that the bolt connection will be loosened due to the decrease of preload, so that the alternating stress in the bolt will be greatly increased than when it is not loosened, and the impact will occur during the force process, so that the thread of the bolted connection has fatigue damage.
In the design of rail transit vehicles, different anti-loosening measures are taken according to the different risk levels and tightening occasions of the bolted joints. At present, the commonly used anti-loosening forms mainly include friction relaxation, mechanical anti-loosening, riveting anti-loosening, and structural anti-loosening.
The surface treatment of the bolt can directly affect the reliability and service life of the connection function, and the torque coefficient K is composed of the friction coefficient between the internal and external threads, the friction coefficient of the bolt or nut support surface and the pressure-bearing surface of the fastened part in contact with the fastener; It is related to the surface treatment, tensile strength, shape and position tolerance, thread accuracy, roughness of the pressure surface of the fastened parts, stiffness and many other factors, of which surface treatment is a key factor. The torque coefficient of different surface treatments varies greatly, sometimes by nearly 1 times.
The most important corrosion of bolted connections is contact corrosion, and a surface coating with a controllable range should be selected. In some parts of the vehicle, due to daily maintenance reasons, such as the anti-roll torsion bar bolt under the vehicle, the bottom cover plate connection bolt Due to daily car washing, the cleaning fluid will stay on the bolts near the lower edge of the skirt plate on both sides, so that the bolt connection is often in a wet state; Or due to the extreme harsh operating environment, such as the connecting bolts on the vehicle bogie, the existing method of coating isolation grease, after the bolt installation reaches the specified pretension, the entire bolt connection is exposed around all coated with specific isolation grease to protect the bolted connection from the influence of the environment and ensure driving safety.