How to prevent fasteners from loosening and falling off?

How to prevent fasteners from loosening and falling off?

During the operation of mechanical equipment and the construction of building structures, the loosening and falling of fasteners are like potential "invisible killers", which may not only cause equipment failure and affect the quality of the project, but also bring serious safety hazards. In order to effectively avoid these problems, people have developed a variety of methods to prevent fasteners from loosening and falling. These methods start from different angles and use physical, chemical and mechanical principles to fully guarantee the stability of fasteners. The following will introduce them to you in detail.

1. Friction-proofing: increasing friction to stabilize the connection

Friction anti-loosening is to increase the friction between fasteners to prevent them from rotating relative to each other under external forces such as vibration and impact, thereby avoiding loosening. Spring washers are one of the common friction anti-loosening parts. They use their own elastic deformation to generate axial tension after the nut is tightened, increasing the friction between the nut and the connected parts. In the connection of ordinary mechanical equipment, such as fans and water pumps, spring washers can effectively resist the vibration generated during the operation of the equipment and prevent the nuts from loosening. However, when spring washers are used in some high-precision equipment, the elastic deformation may affect the assembly accuracy, so they need to be selected with caution.

Double nut anti-loosening is also a commonly used friction anti-loosening method. By installing two nuts on the screw in sequence, first tightening the main nut, and then tightening the auxiliary nut, the two nuts apply pressure to each other, so that the friction between the threads of the screw and the nut increases, thereby achieving an anti-loosening effect. This method is often used in low-speed, heavy-load and low-vibration situations, such as the base connection of large mechanical equipment. In addition, nylon ring locking nuts also use the friction anti-loosening principle. The nylon ring is embedded in the nut. When the nut is tightened, the nylon ring produces elastic deformation, tightens the screw, and increases the friction between the threads. It is widely used in the connection of components that are sensitive to vibration, such as automobile engines and motorcycles.

2. Mechanical anti-loosening: locking the position with the help of auxiliary parts

Mechanical anti-loosening is to use various auxiliary parts to mechanically fix the fastener and the connected parts together to prevent their relative movement. The use of split pins and hexagonal slotted nuts is a typical mechanical anti-loosening method. After the nut is tightened, the split pin is inserted into the slot of the nut and the hole of the screw, and then the tail of the split pin is broken open to fix it on both sides of the nut to prevent the nut from rotating. This method is often used in occasions with vibration and impact, such as the connection of agricultural machinery and railway locomotive components.

Lock washers are also commonly used mechanical anti-loosening parts. For example, when installing a lock washer for a round nut, first insert the inner tongue of the washer into the groove on the shaft, then tighten the round nut, and then bend the outer tongue of the washer and insert it into the groove of the nut to fix the nut to the shaft to prevent the nut from loosening. This method is widely used in parts that require reliable fixation, such as machine tool spindles and automobile transmission shafts. In addition, the series wire anti-loosening method is to use steel wire to pass through the holes of multiple bolt heads in sequence, connect the bolts in series, and use the restraining force of the steel wire to prevent the bolts from loosening. It is often used to connect components with extremely high reliability requirements such as aircraft engines.

3. Long-term anti-loosening: fixation by irreversible means

Long-term anti-loosening is to use irreversible methods such as welding, riveting, and bonding to make the fasteners and the connected parts become a whole to prevent loosening and falling off. Spot welding is a common form of welding anti-loosening. In the connection of thin plate structures, the contact parts of bolts, nuts and connected parts are spot welded to make the three firmly combined to prevent loosening. Once this method is implemented, the fasteners are difficult to disassemble. It is often used for some structural parts that do not need to be disassembled, such as partial connections of automobile body frames.

Riveting to prevent loosening is to use rivets to rivet the fasteners and connected parts together to form a permanent connection. In the field of aerospace, some parts with extremely high weight and strength requirements are often connected and prevented by rivets to ensure that the parts will not loosen under complex working conditions. Adhesive anti-loosening is to use high-strength thread locking glue, which is applied to the thread surface. After the glue is cured, the threaded connection parts are firmly bonded to increase the reliability of the connection. It is widely used in screw connections of small electronic equipment and precision instruments.

4. Reasonable design and correct installation and maintenance

In addition to adopting specific anti-loosening methods, reasonable design and correct installation and maintenance are also important links to prevent fasteners from loosening and falling off. During the design stage, the type, specification and material of the fasteners should be reasonably selected according to the use environment and stress conditions. For example, in high temperature and high corrosion environments, high temperature and corrosion resistant fastener materials should be selected, and suitable anti-loosening structures should be designed. During the installation process, it is necessary to strictly follow the specifications, control the tightening torque, ensure that the fasteners reach the specified pre-tightening force, avoid loosening due to insufficient pre-tightening force, or damage the fasteners due to excessive pre-tightening force. At the same time, during the use of the equipment, regular inspection and maintenance of the fasteners, timely detection and treatment of loosening, wear and other problems are also the key to ensuring the stability of the fasteners.

Preventing fasteners from loosening and falling off is a systematic project, which requires the comprehensive use of friction anti-loosening, mechanical anti-loosening, long-term anti-loosening and other methods, and pays attention to each link such as design, installation and maintenance. Only in this way can the reliability of fasteners be ensured, providing a solid guarantee for the safe operation of mechanical equipment and the stability of building structures.