Fastener torque is divided into two types: static torque and dynamic torque. Static torque: The instantaneous torque required to continue rotating a fastener in the tightening direction after it is fixed. Measure the torque after loading. Dynamic torque: The maximum peak value measured during the process of fixing the fastener again. Both torque wrenches and power tools can apply dynamic torque, which cannot be measured after the fasteners have been tightened. The torque value obtained through online measurement during dynamic torque loading.
The detection torque for these two types of torque is the same, and there are three main methods for testing fastener torque: tightening method (tightening method), marking method (marking method), and loosening method.
1. Tightening method (increased tightening method)
The principle of tightening method (incremental tightening method): The torque wrench of tightening method (incremental tightening method) gradually increases the torque with steady force (avoid impact). When the nut or bolt starts to rotate slightly, its instantaneous torque value is the maximum (because it needs to overcome static friction). Continuing 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 during inspection.
The advantages of tightening method (increasing tightening method): simple operation, single must be proficient and experienced.
The disadvantages of tightening method (increasing tightening method): (1) there is a possibility of secondary tightening; (2) It is difficult to determine when the bolt will start, and there are subjective factors involved; (3) When the bolt is started, the actual torque value should be around the torque value during installation, so the test value is generally higher.
Static torque: This method is used for testing residual torque and is suitable for inspecting the tightening quality on assembly sites.
2. Marking method (underlined method)
The principle of marking method (marking method): Before inspection, draw a line on the head of the inspected bolt or nut and the connected body to confirm their original positions. Then loosen the bolt or nut slightly and tighten it to its original position with a torque wrench (align the line at the marked area). Multiply the maximum torque value by 0.9~1 The value obtained from 1 is the torque obtained from the inspection.
The advantages of marking method (line drawing method) are: low technical level, complicated operation, and not suitable for fasteners with anti loosening function
The disadvantage of the tightening method (increasing tightening method) is that it is more precise compared to the tightening method (increasing tightening method).
Dynamic torque: The torque provided by the designer from a design perspective is called dynamic torque, so it is recommended to use this method when disassembling the vehicle.
3. Release method
The principle of loosening method: slowly apply torque to the inspected bolt or nut with a torque wrench to loosen it, read the instantaneous torque value at the beginning of rotation, and multiply it by a coefficient of 1.1-1.2 based on experiments and experience to obtain the inspection torque value.
The advantages of the loosening method: simple operation, but must be proficient and experienced;
The disadvantage of the loosening method is that the torque is too small.
