The pre-tightening force of the bolt is a key factor in ensuring the tightness of the connector and preventing the bolt from loosening or breaking while working. The following is a detailed explanation of the general value range, relevant standards and recommendations for bolt preload:
First, the general value range of bolt preload
The pre-tightening force of the bolt is generally recommended to be 60% to 70% of the yield point of its material. For example, for the commonly used M12 structural steel bolt, the 70% yield preload is about 38kN. This value range ensures the tightness of the connection while avoiding bolt damage or deformation of the connection due to excessive pretightening.
Second, relevant standards and recommendations
1. Definition of preload
The pretightening force of the bolt is the pretightening force along the axis line of the bolt generated between the bolt and the connected member under the action of tightening torque during the process of bolt screwing. Its size is related to the tightening torque of the bolt, the friction force between the bolt and the nut, and the friction force between the nut and the connected part.
2. Influencing factors
Bolt material: The yield limit of the bolt determines the maximum preload it can withstand.
Working requirements of connecting parts: different connecting parts have different requirements for preload, which need to be adjusted according to the actual situation.
Tightening torque: The tightening torque directly affects the size of the pre-tightening force and needs to be accurately controlled.
3. Measurement method
Torque method: The torque wrench is used to measure the tightening torque, so as to control the pre-tightening force. This is one of the most common methods.
Nut Angle method: Screw the nut until it is close to the connected part, and then rotate at a certain Angle to obtain the required pre-tightening force. This method is suitable for situations where precise control of the preload is required.
Bolt elongation method: by hydraulic, electric or steam heating, the bolt is pre-lengthened to the required deformation, and then the nut is tightened, and the bolt is shortened after cooling, that is, the connection is pre-tightened. This method is suitable for large bolts.
In addition, there are direct measurement methods (such as using a torque wrench or tension measuring instrument to directly measure the preload), diaphragm method (by measuring the deformation of the diaphragm to indirectly infer the preload of the bolt) and ultrasonic method (using the propagation characteristics of ultrasonic waves to infer the preload of the bolt).
Third, relevant technical documents or information support
The above information is based on the integration and analysis of multiple sources, including public information from authoritative sources such as Baidu Encyclopedia and Baidu Love Procurement. These data provide detailed information on the definition, calculation methods, influencing factors and measurement methods of bolt preload.
In summary, the preload of bolts is an important parameter that needs to be controlled accurately. When selecting the preload force, the bolt material, the working requirements of the connector and the tightening torque should be considered comprehensively, and the appropriate measurement method should be selected for accurate control.
