What is the meaning of Torque in Bolt?


Torque in Bolt?

What is torque?

Torque or as also referred to as torque loading is the rotational equivalent of a linear force. In simpler terms, the application of force that acts at a radial distance which causes rotation. Essentially it is a twisting force measured force multiplied by its distance. It’s distance can be measured in either foot or inch pounds per usual in the US or as Newton-Metres across Europe. Typically the distance would be the length of the wrench, which in this instance could be, say 2 feet with your hand that is applying force i.e. a 2 foot wrench and 10 pounds of pressure would equal to about 20 foot pounds).

How does one calculate torque?

It is the outcome of multiplying the value of Force applied by the Distance from the point of the application of force. Hence torque of a bolt can be calculated by the below equation –
T = F x L
In this equation, the T stands for torque, while F corresponds to the applied force and L is the length/ distance of wrench or leaver. To illustrate, Let distance A be 1m and distance B is 2m. While the force applied at point A is 20 Newton, whereas the force applied at point B is 10 Newton. Using the equation to calculate the value for both point A and point B i.e. - 

Point A is 20N x 1m = 20 N.m
Point B is 10N x 2m = 20 N.m

The above illustration indicates that the same value can be achieved with the use of a lower force if the distance or in this case length from the nuts or bolts has been increased. This being said, most wrenches are dependent on the length, the implication of which is that the torque applied in actuality to the fastener could, however, vary if the position of the user’s hand on the wrench is changed, even with a pre-set wrench. This is incidental if the pivot point of the wrench mechanism does not coincide to the point of the application.

How is this applicable to Bolts Tension?

Since torque has been used to create tension, bolts are utilized to fasten two components in such a manner that they have the ability to resist forces such as tensile, or what is referred to as pulling apart as well as shearing or as referred to as sliding apart. Once the nut has been fixed onto the bolt, additional torque is what causes the nut to turn the bolt while stretching it. After the bolt has been stretched, it tends to resemble a solid spring, which in turn clamps the components together that is the nut and bolt. Bearing in mind that the clamp load is not to exceed the tensile load, these components i.e. nut and bolt shouldn’t be pulled apart. Material failure can be eliminated by the increased friction under shear loads, prevented by the relative motion of these components.

Determining the correct torque is dependent on two factors -

1. The material characteristics of the bolt, which means the alloy grade used to produce these bolts.
2. The purpose these bolts are to be used for.

Typically, a bolt that has been under torqued could deform. Hence, these deformed bolts will be unable to provide as much clamping force as required for a particular application. On the other hand, it is possible to break an over torqued bolt. Another part that aids the user in applying torque is not only the use but also maintenance of proper tools. Generally, wrenches used aids the user by measuring the appropriate amount of torque being applied. This is done either in an analogue format or a digital format. In order for these wrenches to function in a reliable fashion, they have to be treated with the utmost care. Unlike conventionally used instruments such as the hammer, or even a screwdriver, a torque wrench is an instrument that functions on precision. Therefore, wrenches have to be handled carefully in order to avoid costly recalibration.