We analyze the fracture of stainless steel bolts from the following four aspects: bolt quality, pre-tightening torque, strength and bolt fatigue strength. In fact, most cases of bolt breakage are caused by loosening and being broken due to loosening. Because the situation of bolt loosening and breaking is roughly the same as the situation of fatigue fracture, in the end, we can always find the reason from the fatigue strength. In fact, the fatigue strength is too big for us to imagine, and the fatigue strength of the bolt is not used at all during the use process.
1. The bolt fracture is not due to the tensile strength of the bolt:
Take an M20×80 grade 8.8 high-strength bolt as an example. Its weight is only 0.2 kg, and its minimum tensile load is 20 tons, which is as high as 100,000 times its own weight. Under normal circumstances, we only use it to tighten Only one thousandth of its maximum capacity can be used for a solid 20 kg part. Even with the action of other forces in the equipment, it is impossible to break through a thousand times the weight of the component. Therefore, the tensile strength of the threaded fastener is sufficient, and it is impossible to damage the bolt due to the insufficient strength.
2. The fracture of the bolt is not due to the fatigue strength of the bolt:
Threaded fasteners can be loosened only one hundred times in the transverse vibration loosening test, but in the fatigue strength test, they need to be repeatedly vibrated one million times. In other words, threaded fasteners become loose when they use one ten-thousandth of their fatigue strength. We only use one ten-thousandth of its capacity. Therefore, the looseness of threaded fasteners is not due to bolt fatigue strength. .
Stainless steel bolt customization
3. The real cause of damage to threaded fasteners is looseness:
After the threaded fasteners are loosened, huge kinetic energy mv2 is generated. This huge kinetic energy directly acts on the fasteners and equipment, causing damage to the fasteners. After the fasteners are damaged, the equipment cannot work under normal conditions, which further leads to Equipment damage. For fasteners that are subjected to axial force, the threads are broken and the bolts are broken. For fasteners that are subjected to radial force, the bolts are cut, and the bolt holes are punched into an oval.
Fourth, the choice of the thread anti-loosening method with excellent anti-loosening effect is the fundamental solution to the problem:
When stainless steel bolts are broken, the easiest conclusion that people can draw is that the strength is not enough, so most methods of increasing the bolt diameter and strength grade are adopted. This method can increase the pre-tightening force of the bolt and its frictional force. Of course, the anti-loosening effect can also be improved, but this method is actually a non-professional method. It requires too much investment and too little profit. In short, the bolt is: "Don't loosen continuously, and break as soon as it is loosened."
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