OBRABOTKAMETALLOV technology Vol. 26 No. 3 2024 One of the most common types of joints is threaded, which allows the assembly and disassembly of products without damaging it. Threaded joints make up about 70 % of all connections, which account for 25...30% of the labor intensity of assembly and 25...64 % of the labor intensity of disassembly work [1, 2]. According to various estimates, up to 15–20 % of equipment failures during operation are due to threaded joints. Accordingly, ensuring the assembly quality of threaded joints is one of the main tasks in production conditions [3, 4]. The reliability of a threaded joint is determined by the force interaction of its elements. During assembly, it is necessary to create stresses in the fasteners and jointed parts, leading to elastic and plastic deformations, to ensure the rigidity and strength of the joint, as well as to prevent its self-loosening. These stresses are determined by the tightening force of the thread, which standard values are found in accordance with [5]. During operation, stress relaxation occurs in the elements of the threaded joint under the influence of static and dynamic loads, which leads to a decrease in the pre-tightening force and loosening of the thread. This is related to one of the most common causes of failures of threaded joints [6, 7]. In order to reduce the likelihood of loosening the thread during operation, the joint is done using lock nuts, wedge lock washers, and locking washers, which provide additional grip on its support surfaces. However, these methods do not provide reliable locking under vibration and cyclic loads [8–9]. Another significant problem in the assembly of a threaded joint is the uneven distribution of forces along the turns of the thread, which is proved in [10]. Thus, more than 70 % of the load falls on the first three turns of the thread, which, with an increase in the tightening torque, can lead to thread failure on these turns [11]. In this regard, an increase in the strength of the joint is possible only by increasing the diameter of the threaded parts, and, accordingly, increasing its holes. The scope of using threaded joints and its importance in the assembly of products determines the relevance of research aimed at improving assembly operations and the operational properties of joints. A significant number of scientific research and design studies have been devoted to solving issues related to the assembly of threaded joints. A number of works are aimed at improving the elements of threaded joints or adding new ones [12–16]. The patent [12] proposes a solution to reduce the bending stresses that occur in a threaded joint when the bolt head is transversely displaced due to the force at the end of the tightening device. At high loads, these stresses lead to an increased likelihood of loosening the tightening. In order to reduce stresses, it is proposed to apply an antifriction coating on the spherical surface of the washer and a friction coating on the support surface. In this case, the friction force on the bottom surface of the washer will be greater than the friction force on the spherical surface of the bolt. The authors [13] proposed a method for redistributing the load along the turns of the thread, which implies cutting grooves in the bolt and then pressing plates of titanium nickelide into it. Next, the threaded parts are cooled to a temperature below -80 °C, which leads to superplasticity of the inserts, and assembly is done. After the temperature increases, the plates regain its elasticity, which allows the load to be distributed from the first turns to the rest. It is proposed to place a shrink cap on all fasteners of the joint, followed by heating it to the shrinkage temperature to increase the reliability of locking [14]. An additional effect is the corrosion protection of the joint. For the same purpose, ref. [15] proposed to place a thin-walled tube between the outer and inner threads, which deforms axially during assembly, providing resistance to thread loosening. The study [16] indicated that the most difficult load to loosen the nut was the load directed perpendicular to the axis of the bolt. In order to increase the reliability of the joint, a lock nut design with a spring inside has been developed, which further increases the axial force. A number of studies are devoted to the effect of ultrasonic vibrations on threaded joints titanium nickelide, which have proven itself well both during assembly and disassembly operations. Ultrasonic vibrations of various types superposed on the threaded joints significantly reduce friction in the thread elements during assembly and disassembly operations, which reduce the likelihood of surface
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