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Why are the Bolts Loose?

Apr. 19, 2021

As a Rail Bolt Manufacturer, share with you. Bolts are the preferred fasteners in many industries and applications for the simple reason that they are easy to disassemble. However, this also makes them prone to loosening on their own and losing preload.

Track Bolt

Track Bolt

Depending on the application, loose bolts can have a profound effect. A loose bolt may bring the entire production plant to a standstill and cost the company thousands of dollars. In other applications, a loose bolt can cause serious safety hazards. So, what are the reasons for bolt loosening? Broadly speaking, there are two main reasons: spontaneous loosening and loosening.

"The main reasons and consequences of failure depend on the purpose of the bolt connection, the environment and generally in industry," said Georg Dinger of Siegenia-Aubi KG, who has studied the causes and effects of bolt self-loosing.

"Under the effect of the thread torque, the repeated relative displacement between the contact surfaces will cause the bolt or nut to gradually rotate under the influence of the tool holder torque," Dinger continued. "This can lead to loss of bolt preload, which leads to failure of the bolt connection. This effect is well known, but prevention is usually only done through experiments after a self-relaxation event."

In order to prevent spontaneous bolt loosening, it is necessary to eliminate the sliding between the connecting parts or at least reduce it below the critical level. This can be achieved by increasing the axial tension, increasing the friction between the clamping parts or reducing the cyclic load (for example, shock, vibration or cyclic thermal load).

Another common method is to increase the friction between bolt threads. There are many solutions to do this, and although some of them are effective, they also have their disadvantages. Glue or adhesives can be effective friction-based methods, but when it comes to disassembling and removing bolts, dry glue can be problematic. In addition, increasing the friction between threads will reduce the achievable preload at a certain torque level. Locking the line is a commonly used method in the aviation industry.

Our company also has Track Bolt on sale, welcome to contact us.