The nut is an important connecting tool between the mechanical parts. Any mechanical thread connection will occur after the nut is loose, which will cause various losses of the parts, resulting in the machine not working properly. Especially for the mechanical equipment such as mining machines, since the mining machine is subjected to large fluctuation loads and vibrations in actual work, the looseness of the thread will cause serious damage to its normal work and service life, thus the thread can be seen. The problem of fastening connections is especially important. In view of the prominence of the problem, this paper takes the mining machine as an example to analyze the causes of loosening and loosening of the fasteners, and further combines some effective protective measures abroad to propose a method to effectively prevent the loosening of the fasteners. For the future analysis of the reasons for the vibration loosening of mining machinery fasteners and the adoption of measures to provide a corresponding reference.
1 Analysis of the reasons for loose fasteners
1.1 The selection and application of the method is not reliable
The key to solving the loosening problem of fasteners is prevention. At present, the following methods are often used in practical applications: adding nuts
Spring washers, inlaid nylon locknuts, lock-up nuts, etc., but the actual work tests found that these methods are more or less flawed, and their application effects are obviously insufficient, and the intended use effect cannot be achieved. .
1.2 insufficient pre-tightening force
According to scientific and technological progress, the yield point tightening method is the latest concept and theory in the design of bolted joints. That is, the preloading force of the bolt requires the bolt preload force to be the same or close to the yield strength of the material used for the bolt. However, in practical work applications, due to various factors such as working environment, technical application, and equipment use, the installation of bolts in the underground does not meet the expected installation requirements, resulting in insufficient bolt pre-tightening force.
1.3 The tightening torque during design and installation is not standardized, and the design is not flexible.
For the mining machinery independently developed and produced in China, there is no standardization requirement or even no requirement for the tightening torque during the installation process. This phenomenon is often generated during the operation of the vibration part using large diameter bolts. The pre-tightening force is insufficient and the nut loosening phenomenon occurs. The lack of elastic design is mainly due to the lack of elastic elongation force in the design process of the bolt, and the loosening of the nut occurs due to the mutual influence of the diameter of the bolt and the short length.
1.4 Support surface compression
For mining machines, the material of the motor, the drive housing and the bracket are significantly different from the bolts and nuts. The strength of the joint surface of the mining machine casing is lower than that of the bolt joint. The pre-tightening force of the screw is affected by vibration and plastic deformation of the casing. The contact surfaces of the mining machine are very rough. If there are debris in the installation process, serious local plastic deformation will occur, which will lead to stress drop and loose nut.
2 The effect of loose fasteners
2.1 The strength and rigidity of the floor frame are seriously frustrated
Due to the short distance between the bottom plate and the bottom bracket of the working surface, the long socket wrench cannot be used, resulting in insufficient pre-tightening force on the fastener, and finally the bolt on the bottom bracket is loose. During the actual working process of the mining machine, when the rigidity caused by the looseness of the bottom bracket disappears, the cross-section of the two ends will jump, and the loosening of the nut will occur, thereby causing serious accidents such as loose nuts or broken bolts between the components.
2.2 Bolt life is shortened
The service life of the bolt has a very important influence on the working life of the mining machine. If the bolt is loose during the working process of the mining machine, a gap will occur between the joint surfaces of the joint, resulting in uneven or change of the force of the bolt. This ultimately leads to a shortened bolt life.
2.3 Seal oil leakage
In each component of the mining machine, the motor, the transmission and the cutting part are connected to each other, and when the vibration occurs, the nut on the bolt is loosened, and the gap between the components is damaged, and the gear coupling is generated. The center of the device is forced to develop a certain degree of displacement, so that the high-speed seal is deformed, eventually leading to leakage of the seal.
2.4 Transmission component load increase
When the mining machine starts working, after the loosening of the nut between the tractor fixed box, the cutting part and the motor, the passive displacement of the gear coupling center and the uneven force of the tooth surface of the gear coupling are finally caused. This causes the friction on the tooth surface to increase, causing the gear coupling to be damaged by the impact load.
2.5 Case thread tripping
In the component configuration of the mining machine, the thread strength in the casing is smaller than that of the bolt, and the internal thread may trip after the connecting thread is loosened, resulting in an increase in load between the components, ultimately affecting the conveying device. The service life is reduced.
3 Countermeasures against the loosening of fastening hardware
3.1 Ensure the tightening torque
For domestic mining, design and production of mining machinery, there is no uniform industry standard for the tightening torque required by the machine, and even no clear requirements are made. Therefore, during the operation and use of the mining machinery, the large-diameter bolts in the vibration part tend to have insufficient pre-tightening force due to the operation of the staff, and the nut is loosened at the same time. At the same time, the pre-tightening force is too tight, which may lead to the failure of the connection of the components. Therefore, in order to ensure the reliable and safe connection between the components, the designer needs to accurately analyze the tightening torque required by the nut, select the appropriate thread and bolt, and the operator needs to master the correct operating procedure, and use the torque wrench to carry out the nut. Tightening, at the same time, the bolt pre-tightening torque is detected by the torque wrench in the direction of the nut tightening direction to ensure the correct tightening torque, thereby prolonging the service life of the machine.
3.2 Appropriately increase the elastic elongation during the bolting process
For mining machinery, the bolt length is affected by the thickness of the butt joint plate connected between the casings. Because of its limited thickness, the length of the bolts cannot be too long, so two in the actual design and installation process. A long sleeve is placed in the middle of the bolts at the ends of the connecting plate to increase the length of the bolt. In order to reduce the cross-sectional area of ​​the bolt without affecting the strength of the screw, thereby increasing the elastic elongation of the threaded solid part, generally speaking, the thread bottom is used as the diameter of the bolt interruption, so that the tightness can be prevented to some extent. The release of the firmware occurs.
3.3 Using new nuts and lock washers
The actual vibration of the mining machine will produce large vibration, and the general anti-loose gasket can not meet the anti-loose requirements in the vibration environment, and the anti-loose effect is not good. In order to effectively solve this problem, zigzag lock washers and nuts can be used. This new type of component has achieved good results in practical applications, effectively coping with the environment in which the mining machine vibrates under working conditions.
3.4 Appropriate application of adhesive on the surface of the thread
In the United States, there are relatively complete requirements and rules for the production, type and use of adhesives, which is of great significance for ensuring the effect of the binder and improving the pertinence of the binder. For the application of the adhesive on the surface of the thread, it will provide the minimum effective torque, and will not make it lower than the existing disassembly torque. In order to solve the problem that the domestic binder can not meet the technical requirements and can not meet the normal use effect, we can Drawing on foreign experience and technology, the bonding agent is divided into dry type and liquid type, which are different for different sizes. For larger operation, the effect of dry type anti-loose bonding agent is generally better.
4 Conclusion
Through the analysis of this paper, we can know that for the mining machine, the vibration loosening problem of the fastener is the main problem affecting its work efficiency, safety and mechanical service life. This paper focuses on the analysis of the actual work, causing mining. The machine produces the loosening of the fasteners, such as insufficient pre-tightening force, compression of the support surface, and the fact that the tightening torque during design and installation is not standardized, lack of elastic design, etc., and further analysis of the tightening of the mining machinery. The effects of loose vibrations, such as the strength and rigidity of the floor frame, severely frustrated, oil leakage from the seal, increased load on the transmission components, tripping of the casing threads, and shortened service life. In view of the common problems of fastener loosening, this paper introduces several effective methods to prevent the loosening of the fasteners by using the mining machine as an example, such as ensuring the tightening torque, increasing the elongation, and applying the adhesive. In the actual engineering application, the above several methods have been effectively applied and achieved good results. It can be seen from the analysis of the actual situation in this paper that several methods for effectively preventing the vibration loosening of mining machinery fasteners are proposed in this paper. Can be directly applied to large mining equipment,
See the literature:
[1]褚ä¸åº. The loosening of mining machinery fasteners and new methods of anti-loose [J]. Mining Machinery, 1994, 10.
[2]Wu Yifeng, Wang Binwu, Su Qingyong. Material selection and reinforcement of joint vibration mechanical bolts[J]. Forestry Machinery and Woodworking Equipment, 2OO4, (1)
[3]Zhang Yusheng. Calculation method of bolt connection using yield point tightening method[J]. Mechanical Design, 1989, (4)
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