Reasons For Tire Screw Fracture And Effective Preventive Measures

The function of tire screws is to firmly connect the car wheel hub and wheel into one unit. Under normal circumstances, screws only bear axial tension and do not bear radial shear stress. When the wheel hub nut of a car becomes loose, the force on the screw changes from tensile to shear stress. When the sudden increase in load exceeds its rated load, the screw will be sheared and broken. The breakage of screws is a very dangerous issue for cars. Below, we will share with you the reasons for loose and broken screws, as well as effective preventive measures, in addition to the quality and processing of screws and nuts.

1. Apart from the quality and processing of screws and nuts, the reasons for loose and broken screws
(1) If the installation is not tightened according to the technical requirements, or if there is a significant difference in the tightness of each nut, once some nuts become loose and do not bear the load, the load on other nuts will greatly increase.
(2) During tire maintenance and installation operations, many units use general air guns for disassembly and installation, rather than fixed torque air guns for installation. So the upper limit of torque is often not controlled during installation. The repairman increased the tightening torque due to concerns that the tire screws were not tightened, increasing the normal tightening torque of 550~650Nm (usually for large buses) to 100ONm or even greater. During frequent tire disassembly and assembly, the tire screws were stretched, causing the tire nuts to loosen.
(3) The tire rim screw hole is worn or deformed, and the nut torque has reached the required level, but the tire rim is not tightened.
(4) When the threads of bolts and nuts are damaged after long-term use, the disc spring washers fail, or the flat washers crack and deform, the nuts cannot play a good locking role, resulting in loose nuts.
(5) The positioning collar of the wheel hub nut is damaged or missing, or the inner hole of the steel rim is deformed due to screw hole compression, which simplifies the operation of tire installation. The wheel hub nut is not tightened diagonally, but is tightened one by one. For bolts without a central positioning sleeve, this operation method will cause the bolt to deviate from the center positioning. When assembling, the nut has been tightened, 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) Heavy use, light maintenance, and weak sense of responsibility among drivers and mechanics. Not conducting regular inspections as required by regulations, and some inspections are extremely careless.
2. Effective prevention measures should be taken from the following aspects to address the causes of tire screw breakage
(1) Drivers should check the technical condition of tires and wheel hub bolts before, during, and after driving. If any looseness is found, it should be reported for repair immediately. They must not drive with a problem.
(2) Mandatory maintenance operations shall be carried out according to technical requirements, and the maintenance interval mileage shall not be arbitrarily extended. Repair workers should follow the job specifications. During first level maintenance, it is necessary to check and tighten the wheel hub nuts. Secondary maintenance operations must clean and inspect the condition of bolts, nuts, and threads, clean and inspect the wear of steel ring screw holes, check the deformation of positioning sleeves, washers, steel rings, and steel ring inner rings, as well as the flatness of steel ring end faces. When replacing a new steel ring, check the thickness of the steel ring wall. For double wheels, be sure to tighten the inner wheel when disassembling and assembling the outer wheel.
(3) Before pre tightening the nut, it is necessary to check whether the center position of the wheel is aligned. The tightening operation must be completed diagonally in 2-3 turns, achieving a normal torque of 550~650Nm. The nut is subjected to uniform force. However, excessive torque can also cause premature damage to bolts and nuts. Failed spring washers, cracked flat washers, locating rings, and severely worn steel rings with screw holes should be replaced in a timely manner, and the deformation of the inner circle of the steel ring can be repaired. Thread damage exceeding 3 threads must be replaced to ensure the alignment and fastening of the vehicle wheels.
(4) After the qualified unit replaces the tire, it should be re tightened at the warranty factory after driving the vehicle for 50-100km to ensure the tightness of the tire screws.
(5) Choose high-quality wheel hub bolts and avoid purchasing inferior products at a low price. The air pump should be regularly maintained to remove water and oil from the reservoir and reduce the erosion of the steel rim and tire body by oil and water. At the same time, it is necessary to regularly check the technical performance of the tire dismantling machine to avoid insufficient torque. If possible, it is best to use pneumatic or electric torque tools to ensure even force distribution.
(6) If there is abnormal noise from the wheels or shaking of the vehicle while driving, it is necessary to stop and check to eliminate hidden dangers. If the wheel hub bolt breaks, do not forcefully turn the steering wheel or apply emergency braking. Instead, grasp the steering wheel, slowly slow down and stop the vehicle, and then take corresponding measures to deal with it.