Detailed explanation of the factors causing screw breakage

TIME：

2021-11-09

As we all know, all screws have grades. This grade is determined by the tensile strength and shear strength of the screw. If the stainless steel screw breaks, it is not a problem with the stainless steel screw itself, then the tensile force and shear force exceed the ultimate strength of the stainless steel screw. The reasons for the breakage of stainless steel screws are as follows:

First: the quality of the screw

Second: the strength of the screw

Third: the pre-tightening torque of the screw

Fourth: the fatigue strength of the screw. The material of the screw is unqualified, the heat treatment is unqualified, the product manufacturing process is unqualified, the selection of stainless steel screws is unreasonable, and the use environment is harsh. There are direct effects. Under the condition that these prerequisites are standardized, the majority of stainless steel screws break because of looseness. Because the situation of loosening and breaking of stainless steel screws is roughly the same as that of fatigue fracture, in the end, we can always find the reason from the fatigue strength. In fact, the fatigue strength is so great that we can't imagine that stainless steel screws don't use fatigue strength at all during use. The reason for screw damage is loosening: When threaded fasteners loosen, huge kinetic energy mv2 is generated. This huge kinetic energy directly acts on fasteners and equipment, causing damage to fasteners. After fasteners are damaged, the equipment cannot work in a normal state, further causing equipment damage. Fasteners subjected to axial force have their threads damaged and bolts pulled off. Fasteners subjected to radial force have their bolts sheared off and their bolt holes punched into ovals. Choosing a threaded anti-loosening method with excellent anti-loosening effect is the fundamental solution to the problem.

The loosening of screw fasteners has nothing to do with the fatigue strength of stainless steel screws: Threaded fasteners only need one hundred times to loosen in a transverse vibration loosening test, while they need to vibrate repeatedly one million times in a fatigue strength test. In other words, threaded fasteners loosen when using one ten-thousandth of their fatigue strength, and we only use one ten-thousandth of its maximum capacity, so the loosening of threaded fasteners is not due to the fatigue strength of the bolts.

Have you seen this? Most of the reasons for the breakage of stainless steel screws are caused by the strength of the screws and the loosening of the screws. When stainless steel screws are found to be broken, we can analyze the reasons from these two aspects.

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