Under different working conditions, the correct method of pretightening bolts and nuts will be different. The following are several pre-tightening methods in general: Standard pre-tightening method: Use a torque wrench for pre-tightening operation. First, the appropriate standard torque value is selected based on thread diameter, material and lubrication. Then, use the torque wrench to turn the bolt or nut counterclockwise and gradually pre-tighten it to the set torque value. Angle control preload method: This method is suitable for connections requiring high precision. First, use a torque wrench to pre-tighten to the initial torque value. Next, the rotation Angle of the bolt or nut is measured by the Angle measuring instrument until the predetermined Angle is reached. Stretch control preload method: This method is suitable for connections that require higher safety and reliability. First, the tensile force requirements of the bolts are determined according to the requirements of the connectors and applications. The bolt is then stretched to a predetermined tensile force value using a tension device. Finally, add the nut and use the torque wrench for final torque pretightening. It should be noted that the actual conditions under different working conditions may vary, so it is recommended to carefully read the relevant specifications and instructions before the specific operation to ensure that the pre-tightening operation is performed in the correct way. For some special conditions, such as high temperature, low temperature, vibration environment, etc., special bolt and nut design may be required, or additional pre-tightening measures may be taken.
