The bolt-nut connection is to rotate the nut relative to the bolt by applying torque, and the connected parts are compressed by using the influence of the thread rise angle, and the bolt itself is elongated to generate preload.
The rotation angle when the bolt is tightened is roughly proportional to the sum of the bolt elongation and the compression of the connected part, therefore, the purpose of tightening can be controlled according to the specified rotation angle.
Today, we will introduce the formula and curve of the torque angle method and explain the key points of using this tightening technique.
1. Rotation method formula and tightening curve
For torque angle method tightening, firstly, it is necessary to apply a starting torque to eliminate the gap between the clamped parts, warping, etc., so that the torque and the rotation angle are linear when it is tightened later, the pitch of the bolt is relatively accurate size, and the angle of rotation Q can be converted into the distance of the nut relative to the bolt, which is:
How much the bolt elongates depends on the stiffness ratio between it and the connected parts, so the relationship between the angle q and the bolt preload:
Torque-angle method tightening curve.
Second, the scope of application of the torque angle process
Torque angle process tightening parameters are applicable to the strength class of. 9 and 12Connection section of 9-grade metric threads.
The torque corner process should be divided into elastic zone (TAE) tightening and yield zone (TAY) tightening.
When the reinforced part is a thin plate (clamping thickness < 1d), the torque angle tightening process is not recommended.
The parts that need to be disassembled and repaired frequently after assembly are not suitable for the yield zone tightening process.
3. Explanation of terms
Fourth, the torque angle process parameters
The recommended yield value (tay), torque, rotation angle, process torque and preload parameter values commonly used in the yield zone torque and rotation angle process are shown in Table 1 and Figure 1.
Table 1 Axial Force Torque Parameters
Remarks:1Recommend 45 2Recommend 180
Figure 1 Process rotation WA at different clamping lengths
In addition to bolt strength, there are other variables that affect the final torque value, including the initial coefficient of friction and the friction radius of the head. Therefore the final torques given in the table are reference values and they are only available for GB T16674A small series of hexagonal flange bolts mentioned in 1.
When using the large head flange face bolts mentioned in GB T5789 5790, the final torque value is increased.
5. Calculation principle
Formula for calculating axial preload in the yield zone assembly:
Formula for calculating the final torque of the assembly in the yield zone:
The maximum preload occurs when the bolt strength is the largest and the thread friction coefficient is the smallest, and at the same time, the maximum torque occurs when the bolt strength is the largest and the friction coefficient is the largest.
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