The overlong bolt is usually constructed by the torque axial force method, which is divided into two stages of initial tightening and final tightening. The torque coefficient refers to the coefficient between the torque and the axial force of the bolt in the tightening process. Generally speaking, it has a great relationship with the friction coefficient of the friction surface and the geometric condition of the screw connection pair.
For a particular ideal screw connection pair, when the friction coefficient is determined, the torque coefficient is also determined, but the actual screw connection inevitably has manufacturing errors, sometimes even the thread has bumping, corrosion and other defects. At this time, even if the friction coefficient of a group of bolt connection pairs is kept constant, its torque coefficient will inevitably have some dispersion. Not a constant corresponding to friction.
In extreme cases, when an overlong bolt interferes, although the tightening torque is large enough, the bolt axial force may be small. In general, K value varies from 0.100 to 0.450 according to different thread connection mode, surface friction condition and thread manufacturing quality.
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