Can car tire screws be disassembled and assembled many times? Is tighter the better?

The tire screw of the car is undoubtedly very strong, so this screw has been repeatedly disassembled and assembled (for example, 100 times), can it still be tightened like this? Will it be fatigued and aged? In fact, the tire screws of the car should not be disassembled and assembled 100 times, as long as they are disassembled and assembled more than 10 times, they must be replaced. The large dump truck of our unit, the tire screw can be used up to 3~4 times, and then it can no longer be tightened, and it must be replaced with a new one, otherwise the steel rim will be loose, resulting in the expansion of the threaded hole. If it is an ordinary passenger car, the tire screws will also be fatigued and aged after many disassembly, and if it is not replaced in time, it may cause the failure of poor tire tightening, which is undoubtedly very dangerous.

Why do tire screws age after multiple disassembly? First, let's look at how the tire screws are fastened and locked.

The tire screws of the car are generally made of high-strength steel, the strength is generally above 10.9, using ordinary triangular thread fastening, when the tire nut is twisted with the specified torque, the thread of the nut and the bolt is attached to each other, the bolt is elastically deformed, and the wheel is tightly fixed on the hub. This triangular thread can theoretically be automatically locked, and generally does not loosen under static load. However, under alternating loads, continuous shock and vibration loads, the connection may lose its self-locking effect and loosen. The wheels are precisely under such working conditions, so the tire screws must have a self-locking anti-loosening device. The vast majority of tire screws use friction self-locking anti-loosening device, that is, the front of the nut is made into a tapered shape, the screw hole of the wheel rim is also made into a matching cone, when the tire screw is tightened, the contact area between the two is large, and the friction can prevent the nut from loosening. In addition, some models use "inside and outside" tire screws to make the fastening direction of the threads consistent with the direction of wheel rotation, which will reduce the loosening torque caused by the tire screws when the speed of acceleration and deceleration changes of the wheel.

What happens if the tire screws are disassembled multiple times? As mentioned earlier, the tightening of tire screws is completed by relying on the thread bonding friction between the nut and the bolt. However, in the process of disassembling and installing tire screws, the thread will inevitably undergo a certain amount of deformation, repeated disassembly, the amount of deformation will become larger and larger, when this deformation exceeds a certain extent, the friction area between the threads will become smaller and smaller, and the friction will also decrease, until the friction is not enough to lock the nut, the tire nut will gradually loosen during driving. There is also repeated disassembly and assembly will also damage the thread, resulting in permanent deformation of the thread, or even cutting off the thread, and the failure of sliding teeth, at which time the tire screws are completely damaged.

In addition, each tire screw disassembly and assembly is a stretch of the bolt, long-term multiple tightening will lead to metal fatigue of the bolt, elasticity decrease, and the tightening force of the wheel will decrease; If the tightening torque is too large, it will cause the bolt to stretch to the yield limit, permanent plastic deformation will occur, the elasticity of the bolt will be greatly reduced, and the wheel will be difficult to tighten. Especially in some models, the tightening force of tire screws is particularly large, and even tightened to the yield point of tire bolts, such tire screws are only allowed to be used once, as long as they are disassembled and must be replaced. Such models are specifically stated in the car's workshop manual.

Therefore, the tire screws of the car are not allowed to be repeatedly disassembled and assembled. From a safety point of view, it is recommended to replace it after disassembling and assembling more than five times. If the tire screws of the car are loosened at high speed, it is very dangerous, and if the wheels fly out, it will even cause the tragedy of car destruction. A college girl of mine hit the road after a tire repair when the tire screws were not tightened, and the wheel almost flew out, which she said afterwards was "the aftermath of the disaster". In addition, we should tighten diagonally when tightening tire screws, and finally twist to the specified torque, it is best to use a torque wrench, do not use a wind cannon. Do not think that the tire screw is as tight as possible, too large torque force will damage the thread, lengthen the bolt, resulting in complete damage to the tire screw.