Industry knowledge
There are many connection methods that are more reliable than bolts. Why do people in all walks of life like to use bolts?
Because it is easy to install, easy to disassemble (non-destructive and repeatable), efficient and low cost (money is actually the most important).
Then the tightening of the bolt is deformation. Specifically, it is to stretch the bolt or compress the connected parts by tightening the bolt. To put it bluntly, it is an elastic process.
How to determine whether it is tightened, or how to tighten it? The most commonly used is the torque method, which is to tighten the bolt to the torque specified in the design. The general operation process is to tighten the bolt with ordinary tools first (initial tightening), and then use a torque wrench to increase the force to the appropriate torque (final tightening).
In some occasions, the angle method is also used to tighten the bolt. The specific operation is to first use an ordinary wrench to tighten it until it cannot be tightened (initial tightening), and then use an extension wrench to continue to tighten it to a certain angle (final tightening). Depending on the material and design requirements, it is generally 120°-240°. For precision, some bolts are required to be tightened to a certain angle and then reversed by 60°. Please note that this reverse twisting at a certain angle will not cause loosening, because the set of bolts and the object being fixed can be combined and regarded as an elastic body.
For a certain bolt and nut, the angle of rotation of the nut fixation corresponds to the elongation of the bolt fixation, that is, the fixed axial force. This control method is relatively accurate, but the premise is that the properties of the bolt, nut and the fixed object must be stable.
