Improving the methodology for calculating temperature stresses in the working rolls under non-stationary thermal conditions in a hot rolling mill

Introduction. A significant increase in productivity and intensification of the technological process require taking into account the temperature conditions of the rolls in hot rolling mills. In this regard, the calculation of temperature stresses becomes particularly important for selecting optimal design parameters and technological regimes during the operation of the rolls in modern mills. Study object. The solution to the problem of calculating the temperature stresses that occur in the working rolls of hot rolling mills can be achieved by improving the existing mathematical model for cold rolling mills, which is based on the analytical solution of the differential heat conduction equation, taking into account that their temperature field is axially symmetric. A special feature of the analytical solution is that it is not possible to set the graph of the change in the surface temperature of the rolls in advance, because it is a complex function of the rolling regimes. In advance, only the graph of the function is known, which is given in the form of a continuous angled line. In this paper, we consider an improved model based on a numerical and analytical solution of the problem of the temperature regime of the working rolls. The aim of the work is is to develop an improved method for calculating temperature stresses in the working rolls under a non-stationary thermal regime typical of continuous finishing groups of such mills, in order to assess their contact-fatigue strength. Material and methods of research. The study is based on the specified improved numerical-analytical model and equations for calculating temperature stresses for a specific layer of the working roll of an operating hot rolling mill in a cross-section, taking into account its design features and the physical and mechanical parameters of its material. Results and its discussion. The advantage of the improved method of calculating temperature stresses in terms of their determination at any given time during the roll work is shown. The results of the computational experiment are presented in the form of the calculation of equivalent stresses σeq using the classical and improved methods, and a comparative assessment of the contact-fatigue strength of the working rolls using the presented methods for the actual operating mode of the finishing group of the current mill is performed. Based on previous studies of the thermal regime of the finishing group of the 2000 hot rolling mill, it is recommended to turn off the cooling collectors during pauses between strips rolling.