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Five tips for control bolt tightening force

BoltIs one of the commonly used in mechanical fastener, bolt preload and use properties of this close relationship, bolt preload relates to be close and the reliability of the connection, and too much or too little preload will have an impact on the quality of connections. Bolt tightening force is too large, Super twist occurs; bolt tightening force is too small, you can not guarantee the strength and quality.

Here we see the following control screw pretightening force method:

Method 1,Preload by tightening torque control

Screw and bolt tightening force is linear in, control the size of the tightening torque, can be obtained through experimental or theoretical calculation method of preload values. But in practice, due to the geometrical parameters of friction coefficient and deviation Influence under the certain tightening torque, preload is larger, it is controlled by tightening torque bolt tightening force of accuracy is not high, the error of about ± 25%, can be up to ± 40% in General, controlled tightening High torque accuracy measuring spanner for force moment is the tool and force-limiting wrench.

Method 2,By preload nut angle control

Calculated according to need to preload the nut angle tighten nut angle can achieve the objective of controlling preload. The easiest way to measure nuts corner is engraved a zero line, according to Lu turn nut angle is measured in the number of parties, nut angle measurement precision of control within 10 °-15 °.

Method 3,By preload bolt elongation control

Due to the elongation of the bolt and bolt stress related, you can eliminate the friction coefficient and contact deformation, influenced by variables such as deformation of the connection. So, through the preload bolt elongation control can obtain very high accuracy, this method is widely used in important occasions bolt preload control.

Method 4,By control hydraulic tensile preload

Use hydraulic bolt tensioners subjected to tension, elongation of bolts, and screw-nuts, remove the load, due to bolt contraction can be connected and equal to the tensile preload. This method can increase the preload Control accuracy. Hydraulic tensioner bolt preload is applied no friction, so the method can be used to any size of bolts, and put on a set of bolt and preload, uniform compression nut and washer will not Accurate control of the tilt effect of preload.

Method 5,Preload angle control

Tightening torque and angle control preload is to give bolts subjected to a certain amount of torque, then the nut turned a certain angle, check whether the final torque and angle meets, to avoid excessive lack of pretension or pretension.

Preload torque angle control method: first, tightening torque-controlled tightening processes until the tightening torque value is sufficient to ensure that nuts, bolts and real were snapping up, measured at this time can turn nut Angle, then the nut angle and tighten the torque-controlled tightening processes. This method is the use of tightening torque and nut angle gives information can accurately control the pre-tightening force of bolt and found that may occur during the installation of screw Tight or tightening the excess.

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