01、Quality problem

The quality of screws includes the quality of raw materials and the production process. If the quality of the raw material is not good, it contains a lot of residue and is not pure, it will cause insufficient hardness of the screw. Production process problems, such as improper heat treatment, can also cause screws to break.

02、Preload moment

If the pre-tightening torque of the screw is too large, the screw may break.

03、Strength and fatigue strength

The strength and fatigue strength of screws are also important factors affecting their fracture. If the strength and fatigue strength of the screw are insufficient, it may break during use.

04、corrosion

Physical or chemical reactions between screws and the service environment may result in failure and fracture.

05、Become loose

The screws gradually loosen under the circumstances of shock, vibration, variable load, and large temperature changes, generating kinetic energy, the bolts are damaged by axial force, the bolts are pulled off, the fasteners are cut by radial force, and the bolt holes are beaten into ellipses.

06、Usage problem

When the user uses the screw, if the force is too large, it may also cause the screw to break.

In fact, the vast majority of bolt breakage is due to loose and broken, is due to loose and broken, because the situation of bolt loosening break and fatigue fracture is about the same, we can always find the reason from the fatigue strength, in fact, the fatigue strength is so large that we can not imagine, the bolt in the use of the process simply do not use fatigue strength.

For example, M20×80 8.8 high strength bolt, its weight is only 0.2 kg, and its minimum tensile load is 20 tons, up to 100,000 times its own weight, under normal circumstances, we will only use it to tighten 20 kg parts, but also only use one thousandth of its maximum capacity.

Even if the role of other forces in the equipment, it is impossible to break through the weight of the parts thousands of times, so the tensile strength of the threaded fasteners is sufficient, and it is impossible to damage because of the insufficient strength of the bolts.

Threaded fasteners can be loosened only 100 times in the transverse vibration loosening experiment, and need to be repeatedly vibrated one million times in the fatigue strength experiment. In other words, threaded fasteners are loosened when they use 1/10,000 of their fatigue strength, and we only use 1/10,000 of their large capacity, so the loosening of threaded fasteners is not because of bolt fatigue strength.

After threaded fasteners are loosened, huge kinetic energy is generated, and this huge kinetic energy directly acts on fasteners and equipment, resulting in fastener damage. After the fastener is damaged, the equipment cannot work in the normal state, which further leads to the damage of the equipment.

Fasteners subjected to axial forces, the threads are broken, and the bolts are pulled.

For fasteners subjected to radial forces, the bolts are cut and the bolt holes are punched into ellipses.

When the bolt is broken, the most easy conclusion to draw is that the strength is not enough, so most of them use the method of increasing the bolt diameter strength grade. This method can increase the preload force of the bolt, and its friction is also increased.

Carbon steel screws are broken because of hydrogen embrittleness, when hydrogen molecules penetrate into the carbon steel screws, when the carbon steel screws face pressure, even if it is far below the tensile strength of carbon steel materials, there will be a broken head.

The hydrogen embrittlement of carbon steel screws is mostly internal hydrogen embrittlement. In general, atomic hydrogen penetrates into the carbon steel screw during pickling or electroplating, hydrogen embrittleness may occur, such as hydrogen stays in the carbon steel screw, hydrogen will gather to the highest pressure place and form a small gap, when the pressure becomes large, it will cause the head of the screw to suddenly break.

Environmental hydrogen embrittlement is one of the primary reasons for the breakage of carbon steel screws, and it is another hydrogen embrittlement condition caused by the infiltration of hydrogen into the screws when they are under pressure in the surrounding environment. The surface corrosion of carbon steel screws will also increase the chance of hydrogen infiltration into the screws, which is the least obvious hydrogen embrittleness situation, but also the most easily ignored by people, of course, is the most difficult to solve.