What should I do if the large hexagonal head steel structure bolt rotates when it is finally tightened?

In the torque coefficient test, the nut is required to rotate while the bolt rod cannot rotate, so that the torque coefficient can be accurate. However, in actual engineering, "coaxial rotation" often occurs. When checking the final tightening torque, if this happens, the only solution is to fix the bolt first.

When the high bolt is finally tightened, the bolt head must be clamped with a "card-swimming" wrench to prevent the high bolt from rotating with the nut; after the high bolt is finally tightened, if only the mark line of the nut rotates, it can be confirmed that the final tightening is qualified, and only the mark line of the nut rotates after the final tightening.

In theory, the friction between the washer and the plate surface, the bolt head and the washer plate surface is greater than that between the nut and the washer, and only rotation will occur between them when tightening. However, when tightening the bolt, the bolt head or the washer under the nut often rotates due to insufficient counter-torque. If the bolt or the washer under the nut is not fixed, the torque applied is not required. Similarly, the bolt head cannot be tightened. This is the torque coefficient test data, which must be obtained by the reason that the bolt head is fixed and the washer does not rotate.

TN-21LP

If rotation occurs during construction or sampling, take measures to stop the rotation and do not need to replace it. As for the lack of space for tightening the nut due to design or bolt installation sequence, tightening the bolt head can only be an abnormal practice that is done out of necessity. At this time, the control level of preload force will be reduced.

Based on the above, we can give the following suggestions:

(1) When using the loosening method to check the final torque, it is necessary to ensure that the bolt does not rotate. A convenient way is to clamp the bolt head;

(2) In theory, it is possible to do so without clamping the bolt head. The bolt does not rotate during final tightening. However, in actual operation, it is sufficient to ensure that the bolt does not rotate. Whether to clamp the bolt head is up to the construction party.

(3) The quality of bolt tightening is related to the quality of steel structure processing and installation. Only by effectively improving the quality of steel structure processing and installation can the quality of bolt construction be ensured.

(4) The use of high-bolt information construction technology can identify over-tightening and under-tightening caused by bolt rotation, wrong washer placement, washer rotation and false tightening, and realize the digitization of bolt tightening.

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