The article is aimed to perform a structural analysis of the main and auxiliary mechanisms of tube straightening machines, to identify structural and local redundant links in the mechanism schemes, and to offer recommendations on their rational design. Methodology. The solution is realized by means of the theory of mechanisms and machines using structural analysis of the mechanisms of tube straightening machines based on the universal structural theory of O.G. Ozol. Findings. The extended principle of the machine's mechanism formation, which provides inclusion to the mechanism not only невільних solid bodies, but also the deformed bodies, allows us to consider the structure of machines for pressure processing of metals, taking into account the plastically deformed workpiece. Therefore, such machines include in their composition a deformed workpiece as an integral part of the machine mechanism, whose deformation and addition of certain geometric parameters to it is the reason the tube straightener was created for. Defects in the machine structure are determined by the local and structural redundant links included in the kinematic chains of the mechanisms, which transform the mechanism into a statically undetermined system. Movement of the mechanism with defects in the structure is possible in the presence of gaps or due to deformation of the links. The main mechanism of the tube straightening machine is a mechanism of variable structure, therefore, an analysis for its two states is carried out: before the tube is caught by the rollers and during its straightening. For calculation of the number of mobilities of the outer «rolltube» pair, it was taken into consideration that most of the coordinates are overlaid with non-retentive links, which contain a fractional number of constraints. Fifteen redundant links were identified in the main mechanism and their amount in the auxiliary mechanisms of the tube straightening machine was established. Originality. The structural analysis of tube straightening machines with the search for redundant links was never performed. A structural analysis of the mechanisms of cross roll tube straightening machine was performed for the first time, taking into account the presence of external fractional links that are superimposed in the «roll-tube» pairs. Practical value. The practical recommendations for eliminating the harmful redundant links that were found in the structural analysis of the main and auxiliary mechanisms of the tube straightening machine were developed.

The paper presents the results of the vibrodiagnostics of a centering machine mechanism for holding piercing mill mandrel N1 of the pipe-rolling plant (PRP) 350. In the paper, it is established that vibration acceleration of a bearing roller lever of the centering machine mechanism for holding piercing mill mandrel during milling of an Æ282х50 mm shell, steel 20 reaches 5…12 m/s2, and of the upper roller’s vibration frequency is 33.3 Hz. The paper presents the results of the thickness measuring of the Æ282х50 shell, steel 20 after using the piercing mill N1 350. The results shows the distinctive influence of the dynamics of the milling holding mechanism rod. The system is put forth for calculating the energy-power parameters during the realization of the technical process for making shells of the required specifications in a piercing mill. The paper establishes the value of the milling axial resistance to the flow of the milled metal (taking the calibration values into account). The paper presents a refined system for making a dynamic model for the piercing bill milling holding mechanism rod with the milling calibration parameters taken fully included. A differential equation for the milling rod movement is made, specifically for the dynamic model of the PRP piercing mill mechanical system. The dynamic values of the mechanical system are refined, which is used as a starting point for solving the tasks dealing with the analysis of the PRP piercing mill milling rod’s vibroactivity state. In order to decrease rod vibroactivity levels, the paper recommends choosing rational milling calibration and to set the shell milling modes using mechanical system dynamics modelling during the corresponding stages of the design of technological processes. The paper pro-poses a scheme for modernization of the PRP 350 piercing bill exit side by switching the centering machine rod system holding bridges gear to proportional hydraulics. Keywords: piercing mill, vibration diagnostics, thickness measurement, piercing, sleeve; difference in wall thickness, energy-power parameters, calibration, mandrel, vibroactivity, dynamics, mandrel retention mechanism.

The results of the study of the dynamics of the mechanism for holding the mandrel of an automatic TPA mill are presented. The value of the axial force acting on the mandrel and the rod system of the mechanism of its holding is determined. Developed models of the mandrel retention mechanism have been developed, which made it possible to establish the nature of the development of dynamic processes on the output side of the automatic mill, taking into account the force parameters of the longitudinal rolling process of the sleeve and the parameters of the output side of the automatic mill. Mathematical models of the mandrel retention mechanism have been developed, taking into account the parameters of the technological process and the inertness of the rolled sleeve. The solution of the system of differential equations with variable coefficients is implemented numerically using the Runge-Kutta method for the corresponding dynamic models of the mandrel retention mechanism on the example of calculating the automatic mill TPA 350. The picture of the formation of dynamic processes in the mandrel retention mechanism during the implementation of the entire technological process of pipe production on an automatic mill has been clarified. taking into account the variable impact from the deformation zone and the change in the mass of the rolled sleeve. For various dynamic models, numerical solutions of problems were implemented, which made it possible to select the necessary technological and dynamic parameters of the mechanical system, to assign stable modes of rolling the sleeves on the automatic mill TPA 350. It is shown that the refined solution of the problem for three developed dynamic models of the mechanical system differs significantly from the previously known mathematical models. It has been established that the dynamics of the mechanism for holding the mandrel of the automatic TPA 350 mill is equivalent to the formation of the mechanism for the formation of different wall thickness of pipes. A mechanism for stabilizing the dynamics of the mandrel holding mechanism by separating the sections of the output side of the mill is proposed.