What is Torque?
Measure of the rotational force applied on the obejects is known as the Torque. It is measured in Newton per meters (N m).
Refer the relation between tension and torque online!
Relationship Between Torque and Tension
Torque and Tension both are closely related to each other, if torque increases, tension in the joint also increases and vice versa. We can say that Grade 10.9 bolts threads convert rotational torque into linear tension.
Which factors affects Torque Calculation
There are several factors which affects the torque calculation listed below:
- Threads: Fine threads have more friction compared to coarse threads which affects the torque
- Coatings: Different coatings on Grade 12.9 bolts will increase its friction
- Material and grade: Hardness of material or grade will impact the friction
- Class of thread fit: Thread systems with tighter fit have more friction compare to looser fit which increases torque
- Lubrication: It also impacts friction.
Fastener torque calculation formula
The equation to calculate torque is below:
T = kDP
where:
T = Torque in (Nm)
k = Coefficient of friction
D = Diameter of the fastener in (mm)
P = The desired tension in kilonewtons (kN)
Bolt tightening torque table in nm
| Size (mm) | Recommended Maximum Tightening Torque (Nm) | ||
|---|---|---|---|
| Grade 12.9 | Grade 10.9 | Grade 8.8 | |
| M30 | 2774 | 2377 | 1719 |
| M24 | 1395 | 1195 | 865 |
| M20 | 809 | 690 | 500 |
| M16 | 413 | 354 | 248 |
| M12 | 167 | 143 | 99.8 |
| M10 | 95.7 | 81.8 | 57.3 |
| M8 | 48.3 | 41.3 | 28.8 |
| M6 | 19.9 | 17 | 11.8 |
| M5 | 11.7 | 10 | 7 |
What is Torque-Tension Testing?
To calculate bolt torque, we can run Torque-Tension Test. It is the measurement of the twisting force required to a bolt to reach a target level of tightness. Check above typical setup of Torque-Tension Testing which contains test bolt, nut and washer which is loosely fitted in the Skidmore fixture.
Nut is slowly rotated to achieve the target tension, this process elastically stretches the bolt, which generates a clamping force within the Skidmore fixture. Measure the torque necessary to drive the nut until it reaches the specified tension.
How to tighten bolts or nuts?
Below is the step by step guide to tighten bolts or nuts:
- Choose the Right Tool: Choose the right bolt tightening machine, a wrench or socket which fits on the head of nut or bolt.
- Positioning: Stabilize the bolt head with one hand or heavy duty bolt tightening machine and turn it clockwise with the other.
- Apply Force: Tighten the bolt slowly to avoid strain or damage.
- Secure It: Give a final small turn to ensure it’s snug. Do not overtight.