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The tightening of high-strength bolts must be carried out twice. The first time is the initial tightening. The initial tightening is tightened to 60%-80% of the standard axial force of the bolt (that is, the tensile force). The torque value of the initial tightening shall not be less than the final tightening. 30% of the torque value. The second tightening is the final tightening. In order to make all the bolts in the bolt group evenly stressed, the initial tightening and final tightening should be done in strict accordance with the tightening sequence. Operate symmetrically according to the "meter" shape. So, what should be paid attention to when using electric torque wrench?
Check the electric torque wrench before operation, first confirm that the power is turned on, the switch is turned on, the motor sound is normal, then the wrench can be used.
Preheat the Air Impact Wrenches for at least 5 minutes (10 minutes in winter to a cold place), start with no load operation to obtain rated accuracy, select the maximum torque of the wrench to preheat.
The bolts that have been screwed at the beginning should be marked for confirmation to prevent leakage. The bolts installed on the same day should be finished on the same day. Do not install bolts in rainy weather, and the friction surface should be dry. The final tightening torque must be carried out according to the set value requirements.
For an electric torque wrench with a set torque, the bolt should be able to rotate at least 30° from pre-tightening to tightening. For bolts that have reached the set torque, do not use the electric wrench again, otherwise, the torque may be increased unintentionally, and the load of the bolt and the electric wrench will also increase or even damage the bolt and the wrench. For pressure vessels, if the pre-tightening force is too large, the bolts will be broken due to too much tension or the gasket seal will fail.
Strictly follow the electric torque wrench operating procedures. Be sure to reset the wrench to zero after each use to avoid metal fatigue of the spring. The torque value of the calibration wrench should be calibrated regularly with a deviation of no more than 5%.
It should be noted that when the electric wrench is working, the transition between the high-speed gear and the low-speed gear will not damage the wrench, but the torque values of the high-speed and low-speed gears are different. When the electric wrench is working, keep your hands away from the reaction arm.
Assuming that the torque or pre-tightening force of the solid bolt is accurate, but due to factors such as external force, temperature change, vibration, etc., the pre-loading force will still change after a period of time, and it still needs to be checked.
