ボルト締付けとトルク仕様の完全ガイド。適切なトルク値、締付け方法、予緊張力計算について学びます。
Understanding Torque and Preload
Proper bolt tightening creates clamp force (preload) that holds the joint together: Torque Formula: T = K × F × d Where: - T = Torque (Nm or ft-lb) - K = Nut factor (typically 0.2) - F = Desired preload (N or lb) - d = Nominal bolt diameter (m or ft) Preload Requirements: - Joint design determines required preload - Too little: Joint may separate - Too much: Bolt may yield or fail Typical preload: 60-75% of bolt proof load
Metric Bolt Torque Values
Typical torque values for metric hex bolts: Grade 8.8 Bolts: - M8: 25-30 Nm - M10: 50-60 Nm - M12: 85-95 Nm - M16: 210-240 Nm - M20: 410-460 Nm - M24: 710-800 Nm Grade 10.9 Bolts: - M8: 35-40 Nm - M10: 70-80 Nm - M12: 120-135 Nm - M16: 295-330 Nm - M20: 580-650 Nm - M24: 1000-1100 Nm Note: Values are approximate and depend on lubrication condition.
| Bolt Size | Grade 8.8 Nm | Grade 10.9 Nm | Grade 12.9 Nm |
|---|---|---|---|
| M8 | 25-30 | 35-40 | 40-45 |
| M10 | 50-60 | 70-80 | 80-90 |
| M12 | 85-95 | 120-135 | 140-155 |
| M16 | 210-240 | 295-330 | 345-380 |
| M20 | 410-460 | 580-650 | 680-750 |
Tightening Methods
Different methods for achieving proper preload: 1. Torque Wrench Method: - Most common method - Direct torque measurement - Accuracy ±10-20% - Requires calibrated wrench 2. Angle Turn Method: - Turn bolt specific angle after snug - More accurate than torque - Requires experienced operator - Common: 60-90° after snug 3. Hydraulic Tensioner: - Uses hydraulic pressure - Very accurate preload - Used for large bolts (M36+) - Expensive equipment 4. Combined Method: - Torque to 50-60% of target - Angle turn remaining amount - Best accuracy and repeatability