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We subconsciously believe that the higher the strength of bolts, there will be no fracture. It is not. On the contrary, the fracture of High Tensile Allen Bolts is more common than in ordinary bolts. Why?

We need to understand a sentence: the higher the strength of the bolt, the higher the hardness, which is a direct ratio, while the higher the hardness, the worse the toughness, which is an inverse ratio. In other words, it does not have much elongation. If it is stressed too much, it will break directly, rather than a deformation process like an ordinary bolt. The logic is that the stress of a high-strength bolt must be relatively large, and it will exceed the stress range of its mechanical properties for a lot of time. If it is not too stressed, a high-strength bolt will not be used, which is why the fracture of a high-strength bolt is more common than the ordinary bolt.

The first factor is the reason for assembly.

When installing a High Tensile Allen Bolt, the bolt and thread are tightly connected by rotating and pressurizing the tail thread of the bolt. This torque has standard parameters. Generally, it is about 75% of the yield strength of the High Tensile Allen Bolt material. This torque can make the bolt produce some slight deformation under the condition of continuous cracking. In this deformation process, the reverse elasticity of the material is the locking force. If the torque range is exceeded, an overload fracture will occur.

How to control the installation torque is related to the design and installation tools on the installation site, and the operators can only take the post after formal training. Otherwise, it's a joke that they can't even understand the parameters on the torque plate. Generally, the tolerance range of the torque wrench fluctuates up and down by 20%. As long as the working power supply and steam pressure are stable, this tolerance will not have a fracturing effect on High Tensile Allen Bolts.

The second factor is the friction coefficient of High Tensile Allen Bolts.

In the mutual engagement of the two threads, the actual torque parameter values will be scattered, and the friction influence of the two threads will become more important. If the friction coefficient of the thread is not fully considered, it is wrong to look at the torque parameter completely. If the friction coefficient of the thread is large, the torque parameter value should be reduced, otherwise, the torque parameter should be increased. When is it easy to reduce the value of the friction coefficient? In some service environments, the bolt will be stained with talc powder first. At this time, the friction coefficient will become smaller due to the effect of lubrication, and this operation mode is common in many factories.

The third reason for high strength fracture is the fracture caused by fatigue use.

The High Tensile Allen Bolts in fatigue use can not see any problems before fracture, so it is difficult to protect them. Most of the locations of fatigue fracture occur at the intersection of the head and the screw, and will suddenly appear in the static state. Because the added value of High Tensile Allen Bolts is relatively high, to save costs, enterprises will repeatedly use High Tensile Allen Bolts indefinitely, and such problems will be caused when the use frequency exceeds its fatigue coefficient for some time. Therefore, it is rarely necessary to conduct comprehensive inspections on High Tensile Allen Bolts regularly.

The fourth is the fracture without tightening.

When the High Tensile Allen Bolts and nuts are not fully tightened, there will be a large space for movement. Let's take an example: two drill pipes are connected by High Tensile Allen Bolts, and then drill holes down on the ground. If the bolts are not tightened and the torque during drilling is very large, one drill pipe drives one drill pipe to rotate continuously. When this force is transmitted to one drill pipe, the bolts are not tightened and there is a lot of space for movement. All this empty force is transmitted to the bolts, and the bolts can not bear this excessive torque, It will break.

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