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What are the Causes of Loosening and Breaking of Screws?

Sep. 27, 2020

Under normal circumstances, the screw only bears axial tension, not radial shear stress. When the nut is loosened, the force of the screw changes from tensile force to shear stress. When the sudden increase in load exceeds its rated load, the screw will be sheared and broken. Screw fracture is a very dangerous matter. According to the knowledge of fastener screws, Rail Fishplate Manufacturer shares the reasons for loosening and fracture of screws, and effective preventive measures in addition to the quality of screws and nuts and the reasons for processing and processing.

High Strength Bolt

High Strength Bolt

Causes of loose and broken screws:

(1) The installation is not tightened according to the technical requirements, or the tightness of each nut has a large gap. Once the individual nut is loose and does not bear the load, the load of the other nuts is greatly increased.

(2) In tire maintenance and installation operations, many units use ordinary wind guns for disassembly and assembly instead of fixed-torsion wind guns for installation. Therefore, the upper limit of torque is often not controlled during installation. The repairman increased the tightening torque because he was worried that the tire screws were not tightened, so that the normal tightening torque of 550~650Nm (general coaches) was increased to 100ONm or even greater, and the tire screws were elongated during frequent disassembly and assembly. The tire nut is loose.

(3) The screw hole of the tire rim is worn or deformed, and the torque of the nut has reached the requirement, but the tire rim is not compressed.

(4) When bolts and nuts are used for a long time, the thread is damaged, the disc spring washer fails, or the flat washer is cracked and deformed, and the nut cannot play a good locking effect, and the nut is loose.

(5) The nut positioning ring is damaged or missing, or the inner hole of the steel ring is out of round due to the deformation of the screw hole. When installing the tire, the operation is simplified. The nut is not tightened diagonally, but is in place at a time, and tightened one by one. For bolts without a central positioning sleeve, this method of operation will cause the bolts to be positioned off-center. The nuts have been tightened during assembly, but due to the asymmetric arrangement of bolts and screw holes, the tire rotation radius is not equal, and the nut will loosen soon after the wheel rotates. .

(6) Pay more attention to use and neglect maintenance, and the driver and repairman have a weak sense of responsibility. They have not been inspected regularly as required by the regulations, and some have been inspected but are not serious.

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