How to Calculate Bolt Torque
What is Bolt Torque?
Bolt torque relates to clamp force, preventing loosening and joint slippage. Proper torque specification is critical for safety.
Formula
Calculate: T = K × d × F where K is coefficient (0.15-0.2), d is diameter, F is clamp force
- T
- K × d × F where K is coefficient (0 — K × d × F where K is coefficient (0
- K
- K value — Variable used in the calculation
- F
- T / (K × d) — T / (K × d)
Step-by-Step Guide
- 1Calculate: T = K × d × F where K is coefficient (0.15-0.2), d is diameter, F is clamp force
- 2Or inverse: F = T / (K × d)
- 3Standard torque specifications follow ASME or ISO standards
Worked Examples
Input
M20 bolt (d=20mm), desired clamp F=100 kN, K=0.17
Result
Torque ≈ 340 N·m required
Use calibrated wrench
Common Mistakes to Avoid
- ✕Using dry bolt torque for lubricated conditions
- ✕Over-torquing and yielding bolts
Frequently Asked Questions
Why does torque vary by material?
Higher strength steel allows greater clamp force without yielding; coefficient K also varies with surface.
What happens with inadequate torque?
Joint relaxation and slippage; vibration causes eventual failure.
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