What are the fastening methods of large hexagonal head type high strength bolts?
Jan 12, 2021
Large hexagon head high strength bolt connecting pair comprises a bolt, a nut and two washers; The torsional shear type high strength bolt connecting pair comprises a bolt, a nut and a washer. The common tightening methods of large hexagon head high strength bolt pair include torque method, Angle method and tensioning method, etc.
A. torque method
The method of fastening high strength bolt pair by controlling construction torque value. Tightening to specified torque values using torque wrenches that directly display or control torque.
Tightening is divided into initial screw and final screw, and for large joints, it should be divided into initial screw, compound screw and final screw.
1) the initial twist, the purpose is to make the contact surface close, the initial twist torque is 50% of the final twist torque value. The high strength bolt after initial screw shall be color-marked on the nut.
2) Re-screw, the re-screw torque is 50% of the final torque value, and the high-strength bolt after re-screw shall be marked with color on the nut.
3) Finalizing the screw. Finalizing the screw according to the final screw value (construction torque value) calculated by the torque value of the connecting pair in this batch.
electric torque wrench is used for fastening large hexagonal high-strength bolts with digital display controller. The torque can be adjusted within a certain range of torque. When the machine reaches the set torque value, the machine automatically stops.
B. Angle method
The Angle method is to tighten the high strength bolt connecting pair by controlling the relative Angle of the bolt and the nut, that is, after the close contact between the plates and layers, the axial force of the bolt is controlled by controlling the elastic elongation of the screw with the rotation Angle of the nut. Tightening by Angle method is carried out in two steps: initial screw and final screw (double screw should be added if necessary).
(1) Initial screw, tighten the bolt with a fixed-moment wrench. The purpose is to make the contact surface of the connection close, the initial torque, for common bolts (M22, M24) set at 200~300N·m is more appropriate;
(3) Finally screw, use special wrench to tighten the nut at a certain Angle, so that the bolt axial force can reach the construction pre-tension. End twist Angle according to the table.
C. rafah
The tensioning method is to use the tensioner to directly tensioning the bolt, so that it reaches the specified pre-tension, and then tighten the nut to be fixed. The tension of the bolt can be displayed directly on the tensioner.
The quality inspection of large hexagonal head high strength bolts should be carried out after the end of twisting. The method is:
Tap the bolt with a small hammer to check whether the rotation Angle of the nut is sufficient; Use a 0.3mm thick test inserter to insert between the connecting plate layers to see if they are tight; Spot check 5% bolts with a more accurate torque wrench
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