Assembly of threaded and adhesive-threaded joints with the application of ultrasonic vibrations

Introduction. The main problem in the use of threaded joints is the reduction of the preliminary force under the influence of workloads, which contribute to stress relaxation in the joint elements. The main directions of intensifying assembly operations in order to improve the performance properties of a threaded joint are improving the design of joints, using adhesive compositions that, after polymerization, prevent unscrewing. One of the ways to modernize the assembly is the use of ultrasonic vibrations, which makes it possible to influence the distribution of forces arising during assembly, as well as to process treat the adhesive to improve its properties. Research methodology. Experimental studies were carried out in three stages. At the first stage, the influence of shear ultrasonic vibrations on the threaded joint assembly process was assessed. As a complex indicator that determines the effectiveness of the impact, a relative unscrewing torque is proposed, which takes into account the change in the tightening torque under vibration conditions and the increase in the unscrewing torque after assembly. At the second stage, studies were carried out on the effect of ultrasonic treatment on the properties of epoxy adhesive in the liquid (viscosity) and polymerized state (submicrostructure, microhardness, shear stress). At the third stage, the adhesive threaded joint was assembled with the simultaneous addition of adhesive and the application of vibrations. Results and discussion. The application of shear ultrasonic vibrations with an amplitude from 5 to 9 μm leads to an increase in the relative unscrewing torque by 1.5 times, which is associated with the creation of an additional force that promotes tightening and a decrease in friction, which acquires the characteristics of quasi-viscous. At the same time, ultrasound increases the uniformity of load distribution along the thread turns, which is confirmed by the absence of its deformation at a higher tightening torque. Ultrasonic treatment of the adhesive at amplitudes of 8...12 μm leads to a decrease in viscosity to 70–80 % and an increase in strength to 24 %, which is explained by the action of cavitation and acoustic flows. The assembly of an adhesive threaded joint at vibration amplitude of 9 μm combines effects that promote tightening and increase the properties of the adhesive. As a result, such a connection has a relative unscrewing torque 1.95 times greater compared to the control one.