Eye Bolt supplier,Carriage Bolt With Mushroom Head supplier

In most cases, the strength of the tension bolt connection depends on the strength of the bolt. There are many factors that affect the bolt strength, such as material, structure, size parameters, manufacturing and assembly process, etc.

Here are some measures to improve the bolt strength.

Improve load distribution between threads

When the common nut is used, the axial load is unevenly distributed among the turns of the screw thread.

Theoretical analysis and experiments show that the more the number of turns, the more obvious the uneven load distribution. After the 8th to 10th turns, the thread is almost free of load.

Therefore, the use of thick nuts with a large number of turns can not improve the connection strength.

Avoid or reduce additional stress

Due to negligence in design, manufacture or installation, the bolt may be subject to additional bending stress, which has a great impact on the fatigue strength of the bolt, and should be avoided.

For example, when installing bolts on unmachined surfaces such as castings or forgings, bosses or countersunk seats are often used, and flat bearing surfaces can be obtained after machining.

Reduce stress concentration

There is stress concentration at the root of the thread, the joint between the bolt head and the bolt rod, which is a dangerous part of fracture. The stress concentration of the screw root has a great influence on the fatigue strength of the bolt.

Measures such as increasing the fillet radius of the thread root, increasing the fillet at the transition part of the bolt head or cutting the unloading groove can be taken to reduce the stress concentration.

Reduce stress amplitude

When the maximum stress of the bolt is constant, the smaller the stress amplitude is, the higher the fatigue strength is. Under the condition that the working load and residual pre tightening force remain unchanged, reducing the bolt stiffness or increasing the stiffness of the connected parts can achieve the purpose of reducing the stress amplitude, but the pre tightening force should be increased.

The measures to reduce the bolt stiffness are as follows: increase the bolt length properly; Partially reduce the diameter of the bolt rod or make it into a hollow structure, that is, flexible bolt. Installing an elastic element under the nut can also play the effect of a flexible bolt. The flexible bolt has large deformation and strong energy absorption when under stress, and is also suitable for bearing impact and vibration.

In order to increase the stiffness of the connected system, it is not suitable to use a gasket with small stiffness.

Improve manufacturing process

The manufacturing process has a great influence on the fatigue strength of bolts. It is more significant for high-strength steel bolts. When rolling thread is used, due to the effect of cold work hardening, there is residual compressive stress on the surface, the metal streamline is reasonable, and the fatigue strength of bolt is higher than that of turning. Carbonitriding, nitriding and shot peening can improve the fatigue strength of bolts.

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