Shyfrin Y. The development of the theory and technologies of continuous plugless rolling of pipes based on the complex due regard for the factors influencing their quality

Thesis for competition of the scientific degree of the doctor in engineering sciences in the specialty 05.03.05. - Processes and machines for plastic metal forming. - The National metallurgical academy of Ukraine, Dnipro, 2018. The thesis is aimed at the solution of important scientific and technical problem, which consists in development of the complex of rational parameters for the process of continuous lengthwise plugless tube rolling in the mills of different type using theoretical and experimental investigations of the process of metal form changing taking into account the maximum possible number of factors influencing the stability of deformation process, what allows obtaining of tube products with strict characteristics of accuracy and quality, expanding the range of working assemblies and decreasing the metal content. The methods of analytic research in the form changing had been developed for calculating the rational roll pass designs and schedules of deformation in different type continuous mills of the lengthwise plugless rolling. Presented methods take into account the influence on technological potentialities of mills, on accuracy of diameter and tube wall thickness as well as metal expenditure on the part of such factors as technology of grooves cutting, number of rolls in the working stand, number of stands and their interaction on the process, type of motion, presence of non-stationary and stationary stages of the process, skidding of rolls on metal and so on. Results of investigations, which had been carried out served for development of the basis for creation of the rational roll pass designs, schedules of deformation and constructing the tables of rolling for lengthwise plugless mills of different types, what ensures assortment expanding and raising the competition capacity of tubes. Recommendations have been developed as to creation of the improved technological processes of grooving and reducing tubes for mills, which had been in exploitation for a long time and are not in the position to compete with modern tube rolling assemblies. The key words: continuous lengthwise plugless rolling, elastic deformation, tube wall thickness deviation, form changing, microstructure