Hanush V. Estimation of the technical condition of the basic structures of the press-rolled equipment after long-term operation

Dissertation for obtaining the scientific degree of Candidate of Technical Sciences by specialty 05. 05. 08. “Machines for Metallurgical Production” – Ukrainian State University of Science and Technologies, Dnipro, 2023. The dissertation is devoted to the improvement of maintenance of the basic elements of mechanical systems that suffer from a combination of damaging processes, using the example of working rolling housings and hydraulic presses. The specified goal is achieved by developing diagnostic models that take into account the combined nature of the structure load. The actual scientific and technical task of assessing the technical condition after long-term operation of the basic structures of press-rolling equipment, which suffer from the action of combined load, has been solved, which in the end ensured increased safety and extension of the resource of the housings of the working cages of the pipe-rolling unit and the press for railway wheels production. The principle of finding probabilities of failure and non-failure by comparing the functions of the distribution of durability and earnings has been developed. A multiaxial fatigue longevity model was developed based on the rule of combining resource safety indices. In its format, a model of weighting coefficients for the combined action of tangential and normal stresses in the form of a second degree polynomial was found. Solved the problem of the relationship between the accumulated damage and the burden factor. It has been found that the risk function of stand of crack initiation can be represented by a linear dependence directly proportional to the build-up. To assess the technical condition of tube rolling mill unit 350 stand, a risk function was used, which, unlike the reliability function, is sensitive to earnings. The process of loss of load-bearing capacity of stand is represented by several stages, in which the risk increases with different intensity. A model of the guaranteed resource of the columns of heavy hydraulic presses has been developed, which takes into account the non-stationarity of the stamping process, variations in the coefficients of the uneven load of the columns, the tightening force of the thread, and its endurance limit. It was determined that a safe long-term operation of the columns is possible only under certain conditions - not exceeding the load unevenness coefficient of more than 15%, approaching the endurance limit in the thread zone to 30 MPa.