Research On Loosening Process And Anti-loosening Device Of Threaded Connection Based On Transverse Excitation

The threaded connection has the advantages of simple structure,reliable connection,convenient disassembly and assembly,etc.,it has been widely used in aerospace,rail transit,rolling stock,construction,medical and other industries.In some security fields,once there are problems such as loosening,taking off,falling off,or cracking of the threaded connection,the result will be catastrophic.In many industrial applications,problems such as equipment failure,seal leakage and environmental noise caused by loose screw connections have been plagued by people.Threaded connection is prone to connection failure under the conditions of vibration and shock.The vibration excitation types that cause looseness are axial and transverse,but mainly caused by transverse vibration.Therefore,it is of great scientific significance to study the loosening process and anti-loose device of threaded connection under transverse vibration,it palys an important guiding role in industrial use and installation of threaded connection.In this paper,firstly,through three-dimensional modeling and the ANSYS workbench platform,the loosening processes under the conditions of different pre-tightening forces,different transverse vibration amplitudes,different vibration frequencies,different friction coefficients between threads and different friction coefficients between nut bearing surfaces is studied under transverse vibration.It is found that the threaded connection loosening process is divided into two stages.The first stage shows a rapid decay of the clamping force,while the second stage decays the clamping force at a relatively stable rate.At the same time,it is found that the magnitude of the pre-tightening force,the amplitude of transverse vibration,the coefficient of friction between different threads and the coefficient of friction between different nut bearing surfaces all affect the loosening law of the connection and the transverse vibration frequency is not the main reason for the loosening.Secondly,by using the Junker transverse vibration testing machine to study the loosening law of the threaded connection under transverse vibration,it is found that the two stages of loosening are consistent with the simulation analysis.At the same time,the influence of different pre-tightening force,transverse vibration amplitude,vibration frequency,surface coating,different metal substrates and different times of use on the loosening of threaded connections was studied and the surface morphology of the first three threads was analyzed.It is found that these initial conditions have different effects on the loosening process of threaded connections.In practical engineering applications,it is difficult to achieve the anti-loosening effect of threaded connections by changing the initial conditions.These parameters can only improve the anti-loosing effect within a certain range but cannot fundamentally solve the anti-loosening problem.Therefore,the method of using the anti-loose device to achieve the ideal anti-loose effect is the general method at present.This paper studies the spring washers with flat washers,eccentric locknuts,spring embedded locknuts,nylon embedded locknuts that are often used in rail transit at present.The pre-tightening force of the steel substrate and the aluminum substrate are 12 k N and 20 k N.it was found that they all showed different anti-loose effects under different conditions.Therefore,the use of the anti-loose device should be combined with the actual situation of the project.Finally,in view of the fact that the double-stack self-locking anti-loose device is an anti-loose method that uses pressure instead of friction,its feasibility and anti-loose performance have outstanding significance for the development of fasteners.In this paper,ANSYS finite element analysis is carried out,it is found that it has obvious anti-loosening effect under the conditions of low torque and large transverse vibration amplitude.However,when tested on the Junker transverse vibration testing machine,the device did not show a good anti-loose effect.Therefore,this paper proposes two optimization schemes.The first optimization scheme is to improve the damping performance of the large tooth surface by preparing thermoreversible repaired EPDM rubber and give it a certain shock and noise reduction performance.The preparation of this functional rubber is in The introduction of hydrogen bonds and metal coordination bonds on the MAH-g-EPDM elastomer,combined with the vulcanization characteristics,enhances the strength of the rubber matrix,at the same time enables the material to obtain a certain thermal reversible repair performance.The second optimization plan is to change the contact mode between the small tooth surface and the nut to ensure that the nut and the matching washer maintain consistent movement,to ensure that the double-stack self-locking anti-loosening washer has a good anti-loosening effect.These two optimizations schemes have shown good anti-loose effects in the transverse vibration experiment.