Talking about the anti-loose connection of threaded fasteners
1 Introduction
In machines or equipment, assembly of parts, fixing and locking of parts, positioning, etc. are commonly used for threaded fasteners. We commonly use bolts, studs, screws, nuts and washers, etc. Work or not will have a major impact on the normal operation of machinery and equipment. Due to its large connection force, easy assembly and disassembly, and reusable use, it is widely used in various industries. However, threaded fasteners also have shortcomings that can not be ignored. It may loosen during work, especially in the environment of multi-impact, high temperature difference and frequent vibration. It is easier to loosen and will fall off in severe cases, which will directly affect The normal operation of the equipment reduces the efficiency of the equipment and even leads to serious accidents. Therefore, for the reasons of the looseness of the threaded fasteners, taking effective and feasible anti-loose measures is of great significance in practical applications. In the following article, the reasons for the loosening of the threaded fastener connection will be analyzed in detail. On this basis, the common anti-loose measures for the connection of the threaded fasteners are analyzed and combed, and it is expected to have a certain enlightening effect on the reader.
2. Analysis of the reasons for loose connection of threaded fasteners
The threaded connection is pre-stressed by a pre-tightening force before it is subjected to the working load. The looseness of the threaded fastener means that the threaded connection is completely lost or partially lost. The reasons for the looseness of the threaded fastener connection are as follows.
(l) Initial loosening. After the threaded fastener is tightened, during the working process, for example, in a vibrating environment, the roughness of its various contact faces, including the thread profile, the bearing surface and the contact surface with the connected parts, will decrease due to continuous running-in. , resulting in a change in the fastening state, loss of pre-tightening force, and then loosening. In this case, after the threaded fastener is used for a period of time, it is checked for its fastening state, and it is tightened again to have a pre-tightening force.
(2) The bearing surface is crushed to cause looseness. When the bearing surface of the bolt or nut is subjected to too much pressure, the contact surface of the bolt or the nut and the contact surface of the connected part may be crushed and deformed. This deformation is a plastic deformation, and even if the pressure is removed, the original state cannot be restored. As a result, the pre-tightening force of the threaded fastener is reduced or even lost, and the connection is loose.
(3) Self-looseness of the threaded connection. Self-looseness of threaded connections is the most common cause of failure. We know that when an object is placed on a slope, it is subjected to downward gravity, perpendicular to the support force of the slope and the friction parallel to the slope. When the lateral component is greater than the friction, the object will slide down the slope. The same is true for bolts. The threads are equidistant spirals. Any one of the threads is a diagonal line. The pressure of the bolt is decomposed into axial force and lateral force. When the bolt is vibrated, the instantaneous lateral component is greater than the friction. The bolt will rotate along the slope, and if it does, it will loosen.
3. Common anti-loose measures for threaded fastener connections
(1) Increase the friction between the threaded fasteners. The threaded fastener can be prevented from loosening by increasing the friction between the threaded fasteners or the nut contact. It is not limited by space and can be used cyclically. It is the most widely used measure to date.
(2) Adopting welding, gluing or punching and riveting to destroy the thread movement relationship of the threaded fastener. This method destroys the original structure of the threaded fastener so that the threaded fastener cannot be reused. This method is mainly used on a single-use threaded connection.
(3) Add mechanical fasteners. The mechanical fasteners such as the retaining washers and the split pins can be used to fix and lock the threaded fasteners, and the anti-loose method is widely used at important joints, which can effectively prevent the loose connection of the threaded joints. However, the process of manufacturing and installing this method is cumbersome, and the weight of the threaded fasteners is also increased.
(4) Use double nut to prevent loosening. Replace the original single nut with two nuts of the same specification. This double nut assembly can first tighten the inner nut of the double nut with 80% of the assembly torque, and then use the 100% torque to lock the outer nut, which can effectively increase the two nuts and The fit of the thread on the bolt can significantly improve the frictional resistance of the threaded fastener. However, the same disadvantage of this method and the third method is that it increases the weight of the threaded fastener itself, and this method also has certain requirements on the installation space of the nut.
(5) Use a spring washer. The elastic washers mainly include spring elastic washers, wave elastic washers, saddle-shaped elastic washers and tooth-shaped elastic. The principle of using elastic washers is mainly to prevent the screw tightening by using the external elastic force of the spring or the friction of the tilting teeth. The firmware connection is loose, providing a certain locking effect for the threaded connection. The use of elastic washers is simple, low-cost, easy to install and use, and is one of the widely used anti-loose methods. However, it is worth noting that the elastic gasket material is easy to be hydrogen embrittled, and the anti-loose effect is general. It is not suitable to use the elastic pad to prevent loosening in areas with severe impact or vibration. The important thread connection cannot be used alone to prevent loosening.
(6) Use a self-locking nut. Self-locking nuts are classified according to their functions. They are fitted with a nylon ring, a neck with a neck, and a metal anti-loose device. They are all effective torque type locknuts and are widely used in a variety of important joints.
4. Practice of thread anti-loose
In practical applications, it is necessary to analyze the importance of the joints and the frequency of disassembly and assembly, and comprehensively select the anti-loose measures. For example, parts that are never removed can be connected by riveting, welding, gluing, and the like. Fast disconnect connectors are available for frequent removal. For the connection of important parts, the threaded fasteners must be replaced once they are removed, and a variety of anti-loose methods must be used at the same time to ensure the safety of the connection. The screw connection should ensure that the screw is on the top and the nut is on the bottom so that the connection can still be ensured after the nut is loosened.
5. Conclusion
In order to reasonably and effectively increase the fastening effect of the threaded fastener connection and prevent the threaded fastener connection from falling off during use, in addition to the several methods described above, the user needs to closely combine the specific situation of the use of the threaded fastener. Scientifically analyze the advantages and disadvantages of the anti-loose measures for the connection of various types of threaded fasteners, and correctly and reasonably select the anti-loose method of the connection of the threaded fasteners. In addition, it is necessary to continuously accumulate the anti-loose experience of the threaded fastener connection in the course of practice. For the production accidents caused by the loosening of the threaded fastener connection, it is necessary to find out the looseness of the threaded fastener connection. The root cause of the loosening of the threaded fastener connection is solved from the source.
references
[1] Zhang Weihong, Liu Min. Application of Thread Locking Technology for Motorcycle Engines [J]. Motorcycle Technology, 1998(12): 4-7.
[2] Cao Xiangquan, Chen Li, Wei Qing. Anti-loose Analysis of Threaded Fastener Connections[J]. China Science and Technology Expo, 2013(16):1 3:1 3.
[3] Zhang Zhanyuan. Discussion on the thickness of plating layer and the thread matching clearance of aircraft threaded joints [J] Aircraft Design, 2003,: 4015.
[4] Li Weirong, Zhu Jiacheng. Discussion on anti-loose technology of threaded fasteners [J]. Development and Innovation of Mechanical and Electrical Products, 2003 (2): 15-17878 Oriental Enterprise Culture.
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