Analysis of the Reasons for Bolt Fracture
June 08,2022
Upset Threads Bolt, Anchor Fast Bolt, Metric Brass Bolts
In general, we analyze bolt fracture from the following four aspects:
1. Quality of bolts
2. Pre-tightening torque of bolts
3. Strength of bolts
4. Fatigue strength of bolts
In fact, the vast majority of Metric Brass Bolts fractures are broken due to loosening, and they are broken due to loosening.
Because Anchor Fast Bolt loosening and breaking is roughly the same as 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 the bolt does not need fatigue during use. strength.
1. Bolt fracture is not due to the tensile strength of the bolt
Take an M20×80 8.8-level high-strength Upset Threads 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 will only use It fastens 20kg of components and also uses only one thousandth of its maximum capacity.
Even with other forces in the equipment, it is impossible to exceed a thousand times the weight of the component, so the tensile strength of the threaded fastener is sufficient, and it is impossible to damage the bolt due to insufficient strength.
2. The fracture of Metric Brass Bolts is not due to the fatigue strength of the bolts
Threaded fasteners can be loosened only 100 times in the lateral vibration loosening test, while they need to be repeatedly vibrated one million times in the fatigue strength test. 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 maximum capacity, so the loosening of threaded fasteners is not due to the fatigue strength of bolts .
3. The real cause of damage to threaded fasteners is looseness
After the Anchor Fast Bolt fasteners are loosened, huge kinetic energy mv2 is generated, which directly acts on the fasteners and equipment, resulting in damage to the fasteners. After the fasteners are damaged, the equipment cannot work in a normal state, which further leads to equipment damage.
Fasteners subjected to axial force, the threads are damaged, and the bolts are pulled off.
Fasteners subjected to radial force, Metric Brass Bolts are sheared, and the bolt holes are ovalized.
4. Select the thread anti-loosening method with excellent anti-loosening effect
Solve the root of the problem
Take the hydraulic hammer as an example. The weight of the GT80 hydraulic hammer is 1.663 tons. The side plate bolts are 7 sets of 10.9 grade M42 bolts. The tensile force of each bolt is 110 tons. Ton. But the bolts will also break, and now I am going to change them to M48 bolts. The root cause is that the bolts cannot be prevented from loosening.
When the bolt is broken, the easiest conclusion that people can draw is that the strength is not enough, so most of them use the method of increasing the strength level of the diameter of the bolt. This method can increase the pre-tightening force of the bolt, and its friction force can also be increased. Of course, the anti-loosening effect can also be improved, but this method is actually a non-professional method. Its investment is too large and the benefit is too small.
In short, Upset Threads Bolt, Anchor Fast Bolt, Metric Brass Bolts are: "Don't loose and break, once loose."