Torque = T
Force = F
Torque = force from turning or twisting
Tension = power from a straight pull (this differs from torque)
So Torque is used to create Tension
Why is Torque necessary?
Example A: threaded objects (example: bolts securing a motor in position)
Lack of torque (lightly tightened) = bolts will loosen over time, leading to displacement of the motor.
Over torque (strongly tightened) = impacts the security and longevity of the bolts, and any impact or changes in temperature could further impact this weakness, leading to breakage
Example B: unthreaded objects (example: connecting TV set to channel selector)
Lack of torque (lightly tightened) = unstable contact which impacts connection and impacts picture quality
Over torque (strongly tightened) = friction, difficulty of use, shortens lifespan of parts
What Torque is suitable?
This varies and you should check the guidelines specific to the products you are using; the below figures are a general guideline:
When Q = Suitable Torque and P = Breaking Torque
- When the joint will not be subjected to external force or vibration:
Q = (0.5 to 0.7) P
- When the joint is subjected to external force or vibration:
Q = (0.5 to 0.6) P
Bolt Tightening Method:
There are three ways to ensure that you have tightened correctly:
- Torque Control Method
Using a hand torque tool such as a wrench or screwdriver – or a power operated torque tool such as an electric screwdriver or nutrunner – to tighten screws, nuts and bolts.
- Part-Turn method
Where bolts are tightened until the surfaces of the joint are in close contact. At that point, just before the solid tightening starts, nut and protruding bolt threads are marked to show their relative positions then tightened correctly and completely by turning the nut ½ or 1/3 of a turn.
- Bolt elongation measuring method
This is when bolts are tightened at the same time and the elongation of the bolts is measured.
Units of Torque and Conversion Values.
In order to measure the tightening torque of a screw, kgf.cm = 0.098066N.m=0.098N.m
This now becomes N.m in terms of SI units. Therefore, their relationship is given as:
1 kgf.cm = 0.098066N.m=0.098N.m
1 N.m = 10.1972kgf.cm=10.2kgf.cm