The Role of Thread Locking in Preventing Loosening

Analysis of Bolt Fracture Causes and Anti-loosening Solutions

Usually, the analysis of bolt fractures typically revolves around four aspects: the quality of the bolt, the preload torque, the strength, and the fatigue strength. However, most bolt fractures are actually caused by loosening rather than these factors.

Bolt Fracture is Not Due to Insufficient Tensile Strength

Take the M2080 8.8-grade high-strength bolt as an example, which weighs only 0.2 kg but has a minimum tensile load of 20 tons, which is 100,000 times its own weight. In practical applications, we usually use it to fasten components weighing only 20 kg, which is only one thousandth of its maximum capacity. Therefore, the tensile strength of the bolt is sufficient, and fractures are not caused by this.

Bolt Fracture is Not Due to Insufficient Fatigue Strength

In transverse vibration tests, threaded fasteners will loosen after just 100 vibrations, whereas in fatigue strength tests, one million vibrations are required. This indicates that during use, the bolt is far from reaching its fatigue strength, so loosening is not due to insufficient fatigue strength.

The True Cause of Threaded Fastener Damage is Loosening

Once the threaded fastener loosens, it generates significant kinetic energy, which directly acts on the fastener and equipment, leading to damage and affecting the normal operation of the equipment.

Adopting Effective Anti-loosening Measures is Key

For example, the bolts of the GT80 hydraulic hammer, despite having high tensile strength, can still fracture, mainly due to insufficient anti-loosening measures. Increasing the bolt diameter and strength grade is not a professional solution; the real solution lies in choosing the right anti-loosening method.

Analysis of Bolt Loosening Causes

Threaded connections do not self-loosen under static loads, but under conditions of impact, vibration, variable loads, and temperature changes, friction is reduced or momentarily lost, leading to gradual loosening of the bolt.

Introduction to Common Anti-loosening Methods

Bolt anti-loosening methods mainly include friction anti-loosening, mechanical anti-loosening, and permanent anti-loosening. Here are several common anti-loosening methods:

Friction Anti-loosening:
Spring Washer Anti-loosening
Counter Nut (Double Nut) Anti-loosening
Self-locking Nut Anti-loosening
Elastic Ring Nut Anti-loosening
Mechanical Anti-loosening:
Slot Nut and Split Pin Anti-loosening
Stop Washer
Tied Wire Anti-loosening
Permanent Anti-loosening:
Non-reversible methods such as spot welding, riveting, and bonding
Clinching Method Anti-loosening
Bonded Anti-loosening – Nut Locking Liquid
These methods can effectively prevent bolt loosening and ensure the stability of equipment and structures.