"A thousand miles of dykes, destroyed in the ant nest", a small ant hole, can make a thousand dykes break. Screws are known as industrial rice, although small but not small, but historically, the incidents of catastrophic failure due to the neglect of screws are everywhere.
In response to the loosening of threaded fasteners, the technicians have taken various active and effective measures to inject new vitality into the development of threaded fasteners. There are many anti-loose techniques and anti-loose structures for threaded fasteners. The specific solutions are as follows: .
Control preload
Controlling the installation pre-tightening force is one of the cost-effective measures to prevent loosening of the threaded fasteners. This method utilizes the self-locking condition of the thread, does not require any modification to the bolt and nut structure, and prevents loosening by ensuring a suitable pre-tightening force. . For the occasions with extremely high installation control requirements, the direct control method is adopted to measure and control the pre-tightening force during the installation process. Under normal circumstances, direct control of the installation pre-tightening force requires the use of special equipment or specialized technology. Difficult to promote. In order to obtain a satisfactory pre-tightening force in an economical way, more methods of indirect measurement and control of the pre-tightening force, that is, a torque control method, are employed.
The torque control method converts the pre-tightening force into assembly torque by torque coefficient, uses assembly torque or torque measuring assembly machine or wrench to control assembly torque, or uses fastener structure to ensure tightening torque (such as torsion-type bolt connection pair), indirect The purpose of controlling the preload is achieved. In order to achieve the intended purpose, the torque coefficient of the connecting pair can be accurately determined in advance, and the torque coefficient dispersion of the same batch of parts is not large. For example, GB/T1231-1991 clearly stipulates that the average torque coefficient of the same batch of connecting pairs is 0.110-0.150, and the standard deviation of the torque coefficient should be less than or less than 0.001%. In engineering practice, control methods such as cornering method and yield point tightening method are also used.
Effective torque fastener
The effective torque type fastener is an effective torque part added to the structure of the ordinary fastener, and its function is to add a resistance torque which does not change with an external force in the connection pair.
The effective torque part is mainly added to the nut, and the product with the effective torque part on the external thread is relatively rare. All-metal effective torque type lock nut, one type is the deformation of the nut body after the threading of the nut body is completed, so that the thread is axially or radially deformed, causing local interference of internal and external threads during assembly to generate effective torque, due to deformation And the influence of deformation resistance and geometric precision of the blank before deformation, the processing requirements are high, and the effective torque control is difficult; the other is to reduce the effective torque part, close the mouth after closing or slotting, and currently it is mainly used in the military industry in China. The third type is to embed a metal elastic component in the nut body. When assembling, the external thread forces the elastic component to deform and generates an effective torque. Such a nut has high requirements on the elasticity of the elastic component and the position of the insert, and sometimes scratches the external thread. surface.
Use washer
The gaskets currently used mainly include flat rings, spring washers, and elastic washers.
The flat washer is mainly used to improve the contact state of the bearing surface, to ensure the stability of the friction coefficient of the bearing surface, and to have a certain effect on the anti-looseness; the spring washer uses its elasticity to generate the axial force to improve the elasticity of the connection, and the lateral vibration test results show that it Under the test condition, the anti-loose effect is poor; the twisted teeth of the elastic washer are flattened by the tightened nut, so that the threaded auxiliary shaft is pressed tightly, and the bearing surface is partially embedded, the elasticity is uniform, the anti-loose effect is good, and the scratch is scratched. The surface of the part. In some specific situations, it is desirable to scratch the surface of the part. For example, the terminal on the part painted on the surface can be scratched to ensure the conductivity.
Directly locked
Use a locking (stop) element to lock the nut and bolt after tightening the nut to prevent them from rotating relative to each other. The most common use is the use of split pins, series wires and stop washers. The split pin is used with the end hole bolt and the slotted nut to ensure reliable locking. Generally, the angle of the nut slotting is 60°. The slot must be aligned during installation and the assembly is inconvenient; use a low carbon steel wire to penetrate the bolt head or Inside the wire hole of the nut, several bolts or nuts are mutually restrained in series, and the lock is reliable. The retaining washer is plastically deformed by the washer to clamp the nut. When disassembling, the washer should be flattened and then loosened to loosen the nut. Heavy-duty, dynamic load connections that are often removed, such as flywheel nuts.
Destroy the relationship between sports
The punch is used to locally deform the threads of the bolt and the nut, and the original tooth profile is deviated from the original tooth profile, so that the local part cannot mesh with the normal thread, thereby destroying the movement relationship of the original motion pair, and forming a non-reusable connection. If it is to be disassembled, it must be used. Large torques screw out or break the nut, which is currently rarely used.
Bonding
Bonding is to bond bolts and nuts or to the connected parts to achieve the purpose of preventing loosening. Bonding bolts for mass production are generally applied to the parts by a anaerobic adhesive in a fastener manufacturer and dried to form microcapsules. The surface of the microcapsules is dry and has no stickiness. When assembled, micro The capsule is crushed and ruptured, the glue overflows, and the bolt and nut are firmly bonded. As long as sufficient torque is applied during disassembly, in general, it can be reused for a limited number of times within a certain period of time.
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