Knowledge of Anti-Loosening Design and Application of Fastening Systems
What are the main manifestations of the anti-loosening design of elastic bars?
The core of the anti-loosening design of elastic bars is to optimize the cross-sectional shape, adopting an arc or wave structure to increase the contact pressure with the rail and form a self-locking effect. High-elastic alloy steel is selected as the material, which maintains stable elasticity after quenching and tempering treatment and does not undergo permanent deformation under long-term stress. The fitting clearance between the elastic bar and the gauge block is controlled at 0.1-0.3mm to avoid relative displacement during vibration. A double elastic bar design is adopted in some heavy-load scenarios, and the double clamping force improves anti-loosening reliability. The clamping angle at both ends of the elastic bar is accurately calculated to ensure that the clamping force does not attenuate during train vibration and maintains the anti-loosening effect.
What are the applicable scenarios for common anti-loosening methods of bolts?
Spring washer anti-loosening has low cost and simple installation, suitable for scenarios with low vibration frequency such as conventional railways, generating preload through the elastic deformation of the washer. Lock nuts with built-in nylon rings or metal locking structures are suitable for high-frequency vibration scenarios such as urban rail transit, with long-lasting locking force and reusability. Thread locking adhesive fills the thread gap with anaerobic adhesive, forming a firm connection after curing, suitable for humid environments such as tunnels, and can prevent loosening caused by moisture erosion. The combination of cotter pins and slotted nuts has high safety for anti-loosening, used in key parts such as turnouts, and the state of cotter pins needs to be regularly inspected. Double nut anti-loosening offsets the impact of vibration through the interlocking of upper and lower nuts, suitable for heavy-haul railway bolts, which can withstand large load impacts.
How does temperature change affect the anti-loosening performance of the fastening system?
Sudden temperature rise will cause thermal expansion and elongation of bolts, resulting in decreased preload. If no temperature compensation design is adopted, loosening risk is likely to occur. Steel contracts in low-temperature environments, which may lead to attenuation of elastic bar elasticity and insufficient clamping force, affecting the anti-loosening effect. Repeated temperature cycles will cause fatigue stress on the connecting parts, accelerating thread wear or elastic bar aging, and reducing anti-loosening reliability. High-temperature and high-humidity environments will accelerate bolt corrosion, increase thread gaps, and damage the sealing performance of the anti-loosening structure. For areas with large temperature differences, materials with strong thermal stability should be selected, and the installation preload should be optimized to offset the impact of temperature changes.
What requirements must the anti-loosening grade of the fastening system for heavy-haul railways meet?
The fastening system for heavy-haul railways must pass 5 million fatigue vibration tests, after which the bolt preload attenuation does not exceed 15% and the elastic bar has no plastic deformation. The locking torque of the bolt must reach more than 1000N・m, and remain stable under the impact of 100-ton axle load without loosening. The clamping force of the elastic bar must be ≥180KN, and the clamping force loss after long-term use is ≤10% to ensure no rail displacement. The fastening system must be equipped with anti-corrosion and anti-loosening components, passing a 2000-hour salt spray test without obvious corrosion and functional failure. Multiple anti-loosening designs are adopted for key parts, such as the "elastic bar + lock nut + washer" combination, to improve anti-loosening reliability under extreme working conditions.
How to improve the anti-loosening effect of the fastening system through installation technology?
Before installation, it is necessary to clean impurities and oil stains on the thread and contact surface to ensure tight fit of the connecting surface and avoid gaps during vibration. Bolt tightening adopts the three-step method of "initial tightening - retightening - final tightening". The initial tightening torque is 50% of the final tightening torque, the fit degree is checked after retightening, and the final tightening is performed according to the standard torque. During the installation of elastic bars, it is necessary to ensure that the clamping is in place, closely fitting with the rail base without curling or hanging. The gap is detected by a feeler gauge to be ≤0.1mm. After installation, a vibration test is carried out to simulate train operation conditions, detect preload changes, and re-tighten if unqualified. Regular retightening maintenance is carried out: retightening once every 3 months for heavy-haul lines and once every 6 months for urban rail transit to timely supplement preload.