Bolt Anti-Loosening Structure Design
- What are the common mechanical anti-loosening structures for railway bolts?
Common ones include double nut locking (thin nut below, thick nut above, thin nut reversed 1/4 turn after tightening), cotter pins with slotted nuts (for high-vibration parts, cotter pins must pass through nut slots and bolt holes), and lock washers (washer tabs bent against nut sides to prevent rotation). Double nut locking is suitable for ordinary railways with 90% reliability; cotter pin structures are used in high-speed railway turnouts with ≥95% reliability.
- What are the performance requirements for thread locking coatings?
Locking coatings (e.g., Loctite 243) must remain stable at -55℃ to 150℃, with coating thickness 5-10μm, uniformly covering thread surfaces. Breakaway torque after assembly should be ≥80% of preload torque, with no loosening after 1000 vibration cycles (10-500Hz). Coatings must resist oil and water immersion, with ≤10% loss of locking performance after 72 hours. Threads must be clean, oil-free, and rust-free during application; otherwise, coating adhesion decreases by 30%.
- How does bolt thread locking relate to ambient humidity?
Humid environments (relative humidity >85%) require moisture-curing lockers with curing time ≤24 hours to avoid moisture affecting curing. Dry environments can use general-purpose lockers with 12-hour curing. Coastal area bolts recommend "coating + mechanical anti-loosening" dual schemes, with salt spray-resistant lockers (500 hours rust-free) and stainless steel cotter pins for mechanical locking.
- What special requirements apply to anti-loosening structures for high-strength bolts (10.9 grade)?
10.9 grade bolts require increased friction locking: thread surfaces are phosphated (3-5μm film) with friction coefficient controlled at 0.12-0.16. Alternatively, Spiralock threads (60° thread angle with 30° wedge angle) provide 3x better locking than standard threads. Installation preload must reach 70%-80% of yield strength, combined with lock nuts to ensure no loosening under high loads.
- How to test the effectiveness of bolt anti-loosening structures?
Perform vibration tests: fix assembled bolt components on a vibration table, apply 1000N axial force and 50Hz lateral vibration for 2 hours. Check nut loosening angle after testing, which must not exceed 3°; preload loss should be ≤10%. For critical bolts, conduct temperature cycle tests (-40℃ to 80℃, 100 cycles); qualified if locking performance shows no significant decline.