Anti-loosening structure and vibration stability of bolts
- What are the common types of anti - loosening structures for bolts?
Friction anti - loosening is a basic type, including double nuts and spring washers. Double nuts prevent loosening through friction after tightening, with a preload retention rate ≥80% (after 1 million vibrations), widely used in ordinary railways; spring washers generate elastic force after tightening, continuously applying friction, with low cost but general anti - loosening effect (retention rate 60% - 70%). Mechanical anti - loosening has high reliability, such as the cooperation of cotter pins and slotted nuts. Cotter pins pass through nut slots and bolt holes to prevent nut loosening, suitable for turnout areas with strong vibration, with a preload retention rate ≥90%, but complex installation. Permanent anti - loosening is achieved by damaging threads, such as spot welding nuts or applying glue, fixing nuts and bolts as a whole, with excellent anti - loosening effect (retention rate 100%), but non - detachable, only used for permanent connections, such as bridge track bolts. Deformation anti - loosening is aimed at the bolt tail, which is flattened or bent after tightening to form interference with the nut, with good anti - loosening effect (retention rate 85% - 90%), commonly used for fishplate bolts of heavy - haul railways.
- What impact do anti - loosening structures have on bolt vibration stability?
Effective anti - loosening structures (such as mechanical anti - loosening) can reduce the bolt preload attenuation rate by 50% - 60%. After 1 million vibrations, the preload loss ≤10%. Ordinary railways do not need retightening within half a year after using double nuts. Failure of anti - loosening structures will lead to rapid preload attenuation, with a loss of more than 30% after 100,000 vibrations, obvious bolt loosening, and gauge deviation exceeding ±1mm, requiring emergency maintenance. If the spring washer fails, the loosening risk increases by 40%. Complex anti - loosening structures (such as combined anti - loosening) can cope with broadband vibration, with preload fluctuation ≤5% at 5 - 50Hz vibration frequency. High - speed railway bolts adopt "double nuts + glue coating" combination, with 30% - 40% higher stability than single structures. Overly strong anti - loosening structures (such as permanent anti - loosening) will cause difficult disassembly, requiring bolt destruction during maintenance, increasing costs, only used in non - maintenance parts.
- What are the differences in the selection of bolt anti - loosening structures among different railway types?
High - speed railways prefer combined anti - loosening (double nuts + thread glue) with a preload retention rate ≥90% (after 2 million vibrations), able to cope with high - frequency vibration, ensuring gauge deviation ≤0.5mm, and extending the maintenance cycle to 1 - 2 years. Heavy - haul railways focus on mechanical anti - loosening (cotter pins + slotted nuts) combined with deformation anti - loosening, with a preload retention rate ≥85%, resisting low - frequency vibration caused by large axle loads. Turnout bolts must adopt this structure to avoid loosening leading to derailment. Ordinary railways choose economical anti - loosening (double nuts or spring washers) with a preload retention rate of 60% - 80%, meeting basic needs, 50% - 60% lower cost than high - speed railways, retightened every 3 - 6 months. Urban rail transit needs broadband anti - loosening, adopting "friction + mechanical" combination (such as disc springs + cotter pins) to adapt to broadband vibration caused by start - stop, with a preload retention rate ≥80%, reducing the impact of frequent maintenance on operation.
- How to detect the effectiveness of bolt anti - loosening structures?
Vibration testing is a core method. Place the bolt assembly on a vibration table (10 - 50Hz, acceleration 50m/s²). Measure the preload after 1 million vibrations. A retention rate ≥80% is qualified, and high - speed railways require ≥90%. Torque attenuation testing measures the torque before and after vibration with a torque wrench. An attenuation of ≤10% is effective, and ordinary railways allow ≤15%. If it exceeds, the anti - loosening structure must be replaced. Visually inspect the state of anti - loosening components: whether cotter pins are broken, spring washers are invalid, or glue is 脱落. Any abnormality is judged as anti - loosening failure. Turnout bolts must be inspected weekly. Long - term operation monitoring: count the bolt loosening rate. Ordinary railways with a monthly loosening rate ≤1% are qualified, high - speed railways ≤0.1%. Sections with excessive loosening rates need to replace anti - loosening structures.
- What are the maintenance measures for anti - loosening structures?
Regularly inspect anti - loosening components. Ordinary railways inspect spring washers for deformation and cotter pins for integrity every 3 months. Replace immediately if invalid to ensure normal anti - loosening function. For bolts with thread glue anti - loosening, remove old glue after disassembly, reapply glue (thickness 0.1 - 0.2mm), cure for ≥24 hours, then tighten to the specified torque. High - speed railway bolts must strictly follow this process. Mechanical anti - loosening components (such as cotter pins) must be replaced with new ones after each disassembly. Old cotter pins may have fatigue damage and cannot guarantee anti - loosening effect. Turnout bolts are replaced more frequently. For bolts in strongly vibrating sections, upgrade anti - loosening structures, such as changing spring washers to double nuts or adding thread glue, increasing the preload retention rate by 10% - 20%, commonly used in curve sections of heavy - haul railways.