Tightening Methods For High-Strength Bolts

High-strength bolts are critical fasteners widely used in steel structure engineering and mechanical assembly. The tightening process is a key procedure that determines connection performance and overall structural safety. Focusing on common industry questions including how to tighten high-strength bolts and what mainstream tightening methods are available, this article elaborates three standard tightening processes and corresponding construction precautions based on years of fastener manufacturing and construction experience.

1. Torque Method

This method follows the mechanical principle that tightening torque is directly proportional to bolt pre-tension force. During construction, firstly tighten the nuts preliminarily with ordinary wrenches to eliminate gaps between connected plates and make all plate layers fit closely. Then use a special torque wrench with torque display function to tighten nuts up to the standard torque specified in construction drawings and industrial codes, so as to accurately control the axial pre-tightening force of bolts. This method features simple operation and excellent on-site applicability.

3. Shear-Twisted Bolt Breaking Method

This method is exclusively applied to shear-twisted high-strength bolts, which are designed with a prefabricated fracture groove at the tail. A special shear-twisted wrench is adopted during construction, with inner and outer sleeves sleeving the bolt tail and nut respectively for reverse rotation. When the nut is tightened to the standard pre-tightening force, the preset torque will act on the fracture groove, and the bolt tail will be broken off automatically. The dimension of the fracture groove is designed to match standard torque and pre-tension force. The bolts reach the qualified pre-tension force instantly once the tail breaks. This method requires no torque detection, with simple operation and stable tightening accuracy.

Warm Tips

For friction-type connections of high-strength bolts, the friction coefficient of joint contact surfaces greatly affects the bearing capacity of structural joints. Tests show that the friction coefficient is directly affected by component material, contact surface roughness and clamping force, among which contact surface treatment mode and base material are the dominant influencing factors. To obtain a stable and qualified friction coefficient, rust and oxide scale on joint contact surfaces must be removed before construction. Common treatment methods include sand blasting and steel wire brush cleaning.