What kind of bolts and nuts never loosen?

Many of the traditional thread locking devices are unable to maintain bolt tension and clamping forces resulting in premature failure and potentially, costly downtime.Bolts and nuts are the most common and common fastening parts in all kinds of equipment, but they are very critical in some situations. Once loosened and dropped, they may cause fatal damage to the equipment.

Why assemblies fail

Threaded assemblies generally fail because of a loss of bolt tension, the main causes of which are relaxation and self-loosening.

Relaxation results in a change in bolt tension which leads to reduced clamping forces. This effect is mostly triggered by settling – pressure-induced smoothing of the surface roughness – or creeping, the time-dependent yielding of substrates when loads exceed the compressive strength of the material; clamping gaskets are a typical example.

If the elastic capacity of the assembly is inadequate, for example, if bolts are too stiff or the wrong length to diameter ratio is selected, there can be no compensation for loss of bolt tension.

Self-loosening is caused by any type of dynamic load, such as vibration or changes in temperature, insufficient clamp load and poorly fitting parts, allowing relative movements to increase the risk of self-loosening.

These load changes lead to short-term frictionless situations where the bolt unwinds from the nut.

The sum of these very small movements ultimately results in the loosening of the threaded assembly.

How to prevent the loosening of bolts and nuts is a problem we often face. Ningbo Fuchun Precision Casting Co., Ltd. operates various fasteners all the year round, and summarizes some methods to prevent bolts and nuts from loosening.

Common methods of bolt loosening prevention：

Friction anti-loosening, Mechanical anti-loosening, and other methods.

Friction anti-loosening

It mainly includes twin nuts, spring washers, self-locking nuts (one end of the nut is made into a non-circular closure or radial closure after peak opening, the closure is opened after the nut is tightened, the elastic force of the closure is used to make the screw thread tighten), thread glue and other methods.

Mechanical anti-loosening

It mainly includes round nuts, slot nuts with finned washers, open pins, stop gaskets, anti-loosening nuts, etc.

The working principle of anti-loosening nut: it is permanent attachment of special engineering plastics to the thread, making the internal and external threads in the process of tightening, engineering plastics are extruded to produce strong reaction force, which greatly increases the friction between the internal and external threads, and provides absolute resistance to vibration. This resistance is completely distributed in the whole meshing section of the internal and external threads, and the friction force has nothing to do with the tightening pressure between the internal and external threads. Different from the previous stopping method, it relies on the friction force produced by the pressure after the screw tightening to stop the retreat. Once the screw is a little loose and the pressure decreases, the friction disappears rapidly and loses the stopping effect, resulting in the loosening of the screw. However, the shortcoming of plastic loosening prevention is that it can not meet the requirements of high temperature and severe cold because of the environmental impact.

Other methods

Mainly includes end riveting anti-loosening, punching point anti-loosening, spot welding anti-loosening, bonding anti-loosening, series steel wire anti-loosening, anti-loosening rubber anti-loosening.

Anti-loosening and anti-loosening glue is a common anti-loosening method, which can be divided into pre-coated chemical glue and dispensing glue according to its usage; anti-loosening glue, sealing glue and adjusting glue according to its usage; nylon glue and chemical glue according to reaction type. Loctite, ThreeBond, 3M, Nylok and so on are well-known foreign brands in the pine-proof glue industry.

Common methods of nut loosening prevention:

In order to prevent loosening of screw nuts, three mature methods of loosening prevention have been gradually formed after opening various brain holes: friction loosening prevention, mechanical loosening prevention and permanent loosening prevention.

Common mechanical anti-loosening methods include stop washer, open pin and so on. Common anti-loosening friction is generally used gaskets, self-locking, twin nuts and so.