There are two types of fastener torque: static torque and dynamic torque. Static Torque: The momentary torque required to continue rotating a fastener in the tightening direction after it has been secured. Torque is measured after loading. Dynamic Torque: The maximum peak value measured while the fastener is being re-tightened. Both torque wrenches and power tools can apply dynamic torque, which cannot be measured after the fastener has been tightened. Torque value obtained by online measurement during dynamic torque loading.
The detection torque of these two torques is the same. There are three main ways to test the torque of the fasteners: tightening method (increasing tightening method), marking method (scribing method) and loosening method.
1. Tightening method (increasing tightening method)
The principle of the tightening method (increasing tightening method): the torque wrench of the tightening method (increasing tightening method) gradually increases the torque with steady force (avoid impact). Static friction force), continue 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 the tightening method (increasing tightening method): the operation is simple, and the single must be skilled and experienced.
Disadvantages of the tightening method (increased tightening method): a. There is the possibility of secondary tightening; b. It is difficult to determine when the bolt starts to start, and there are subjective factors; c. When the bolt is started, the actual torque value should be approximately the torque at the time of installation value, so the test value is generally too large.
Static torque: This method is used to test the residual torque and is suitable for the detection of the tightening quality on the assembly site.
2. Marking method (scribing method)
The principle of the marking method (scribing method): before the inspection, draw a line on 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 use a torque wrench to tighten the bolt or nut to the original position (the line should be aligned at the scribed line), and the maximum torque value at this time is multiplied by 0.9~1.1 The value obtained is Check the resulting torque.
The advantages of the 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.
Disadvantages of the tightening method (increased tightening method): It is more precise than the tightening method (increased tightening method).
Dynamic torque: The torque given by the designer from the design point of view is the dynamic torque, so it is recommended to use this method when dismantling the car.
3. Release method
The principle of loosening method: slowly apply torque to the tested bolt or nut with a torque wrench to loosen it, read the instantaneous torque value when it starts to rotate, and multiply it by a factor according to test and experience: 1.1~1.2 To test the torque value.
The advantages of the loosening method: the operation is simple, but it must be skilled and experienced;
Disadvantages of the loosening method: the torque is too small.
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