Relationship between Anti-loosening Performance of Rail Bolts and Thread Pair Matching
Why do track bolts loosen easily under vibration?
Trains bring high-frequency repeated impact. Micro-movement reduces friction and preload gradually. Once loose, clearance increases and loosens faster. Bolts need special locking design and installation to stay tight.
How does thread accuracy affect anti-loosening?
High-precision threads engage evenly with less wear and better anti-loosening. Low-precision threads have bigger clearance and easier slippage. Track bolts usually use 6g/6H for good assembly and anti-loosening. Low accuracy shortens locking life.
Why does surface treatment influence anti-loosening?
Different coatings have different friction coefficients. Hot-dip galvanizing has high friction and stable locking. Black oxide or phosphating has low friction and tends to loosen. Torque must be adjusted accordingly to avoid failure.
Is lubrication good or bad for bolt anti-loosening?
Proper lubrication makes torque-to-preload more stable and uniform, helping anti-loosening. Excess lubrication lowers friction too much and causes loosening. Only specified lubrication in controlled amount is allowed.
What is the most practical on-site check method?
Retorque with a torque wrench; obvious drop means loosening. Check for gaps or rotation marks between nut, washer and plate. Use a marking line across parts; misalignment shows rotation. Retorque the whole section if many bolts are loose.