In the process of grid processing, the assembly of unique positions and bolting are carried out under strict operation guidelines and specific instructions. There are often established standards for how much torque is released. After the bolts are tightened, in order to avoid loosening, an additional pre-tightening force should be released, so the pre-tightening force will be cleared after loosening half a circle. The grid bolts are in ductile deformation after tightening, especially at high temperature and vibration Under load conditions, continuous working pressure for a long time will cause stress loosening. After the bolt becomes plastically deformed, its compressive strength will be greatly reduced or even invalid.

Next, the editor of Jiangsu Huahai Steel Structure will introduce you the control plan for the tightening of grid bolts:


1. Torque control method

Definition: When the tightening torque exceeds a certain set operating torque, the tightening control measures are immediately terminated.

Advantages: The automatic control system is simple and immediate, and it is convenient to use torque or high-precision torque wrench to check the quality of tightening.

Disadvantages: The control accuracy is not high (pre-tightening force deviation ± 25%), and the development potential of raw materials cannot be used flexibly.

2. Torque-angle control method

Definition: First screw the anchor bolts to a not large torque, and then start to tighten a required corner control measure.

Advantages: The grid anchor bolts have a high radial preload accuracy (±15%), can receive a large radial preload, and the marked values can be concentrated around the average value.

Disadvantages: The automatic control system is complicated, and it is necessary to accurately measure the two main parameters of torque and rotation angle; and it is not easy for the quality inspection unit to find an appropriate way to inspect the tightening results.

3. Scope control method

Definition: A way to terminate the tightening after the anchor bolts of the grid are tightened to a certain extent.

Advantages: The tightening accuracy is very high, and the pre-tightening force deviation can be manipulated within ±8%; but the key to its accuracy lies in the tensile strength of the anchor bolt itself.

Disadvantages: The whole process of grid installation and tightening requires dynamic and continuous measurement and resolution of the slope of the torque and rotation angle curve. The practicability of the automatic control system and the calculation speed often have higher regulations.