Principle and Characteristic Analysis of Fastener Torque Test Method

Release time:

2022-09-19

Fastener torque is divided into two types: static torque and dynamic torque. Static torque: The instantaneous torque required to rotate a fastener in the tightening direction after it has been secured. Torque is measured after loading. Dynamic torque: The maximum peak value measured when the fastener is fixed again. Both torque wrenches and power tools can apply dynamic torque, which cannot be measured after the fastener has been tightened. Dynamic torque is measured online during loading. The detection torques of these two torques are the same. The main test methods for the torque of fasteners shared by the standard parts network are: tightening method (additional tightening method), marking method (scribing method) and loosening method.

The detection torques of these two torques are the same. The main test methods for the torque of fasteners shared by the standard parts network are: tightening method (additional tightening method), marking method (scribing method) and loosening method.

1. Tightening method (additional tightening method)

The principle of tightening method (increasing tightening method): the torque wrench of tightening method (increasing tightening method) gradually increases the torque with steady force (avoid impact). when the nut or bolt starts to produce slight rotation, its instantaneous torque value is the largest (due to overcoming static friction). if it continues to rotate, the torque value will fall back to a short-term stable state, and the torque value at this time is the torque obtained by inspection.

The advantages of tightening method (increasing screw method): simple operation, single must be skilled and experienced.

Disadvantages of tightening method (additional tightening method): A there is the possibility of secondary tightening; B it is difficult to determine when the bolt starts, and there are subjective factors. C when the bolt starts, the actual torque value should be about the torque value at the time of installation, so the test value is generally too large.

Static torque: This method is used to test the residual torque and is suitable for testing the tightening quality at the assembly site.

2. Marking method (scribing method)

Principle of marking method (scribing method): Before inspection, draw a line between the head of the bolt or nut to be inspected and the connected body to confirm the original position of each other. Then loosen the bolt or nut, and tighten the bolt or nut to the original position with a torque wrench (the line should be aligned at the scribed line). At this time, the maximum torque value is multiplied by 0.9~1.1 to obtain the torque obtained by inspection.

The advantages of marking method (scribing method): the technical level is not high, the operation is cumbersome, and it is not suitable for fasteners with anti-loosening function.

The disadvantage of the tightening method (increased screwing method): it is more precise than the tightening method (increased screwing method).

Dynamic torque: The torque given by the designer from the design point of view is the dynamic torque, so this method is recommended when dismantling the car.

3. Loosening method

Principle of loosening method: slowly move the torque wrench to the inspectedBoltOr apply torque to the nut to loosen it, read the instantaneous torque value when it starts to rotate, and multiply it by a coefficient according to test and experience: 1.1~1.2 is the inspection torque value.

The advantages of loosening method: simple operation, but must be skilled and experienced;

The disadvantage of loosening method: small torque.