First: the quality of the screws
Second: the strength of the screw
Third: the pre-tightening torque of the screw
Fourth: the fatigue strength of the screw. Unqualified screw material, unqualified heat treatment, unqualified product manufacturing process, unreasonable selection of stainless steel screws, harsh environment for use, etc. have a direct impact. When these premises are standardized, most cases of stainless steel screw fracture are caused by loosening. 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 it. Stainless steel screws do not need fatigue at all during the use process. strength.
The cause of screw damage is loosening: After the threaded fasteners are loosened, huge kinetic energy mv2 is generated. This huge kinetic energy directly acts on the fasteners and the equipment, causing the fasteners to be damaged. After the fasteners are damaged, the equipment cannot function normally. Working in the state of the device, further causing damage to the equipment. 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 ellipse. Selecting the thread anti-loosening method with excellent anti-loosening effect is the root of the problem.
The loosening of screw fasteners has nothing to do with the fatigue strength of stainless steel screws: threaded fasteners can be loosened only one hundred times in the transverse vibration loosening test, but need to vibrate repeatedly one million times in the fatigue strength test. In other words, threaded fasteners become loose when using one ten-thousandth of their fatigue strength. We only use one ten-thousandth of its maximum capacity. Therefore, the loosening of threaded fasteners is not due to bolt fatigue strength. .
Most of the reasons for the fracture of stainless steel screws are caused by the strength of the screws and the looseness of the screws. When stainless steel screws are found to be broken, we can analyze the reasons from these two aspects.