The Roller Thermal Structure Coupling Analysis And Its Fatigue Life Study

Twin-roll continuous casting technology has become more and more important because of short process and good product qualities in the world. To the end of 2005,our country has 280 roll-casting machines. The roll shell is very important in twin-roll casting process as the roll-casting machine. The heat that the melted aluminum gives out in the course of cooling and solidification is mostly transferred to the roll shell, then is absorbed and taken out of by the cooling water. So, the roll shell is impacted by the periodic thermal load , it produces mechanical and thermal fatigue at the compositive effects of thermal stress, rolling stress and assembling stress , as a result, it induces the roll shell's invalidation. Besides normal abrasion invalidation, most of the roll shells early produce fatigue cracks and result its invalidation ahead of schedule, it is above 80% in the roll-casting process. The roll shell is very expensive, if it early ends it's lifetime, it adds the cost of production, so the research of improving the roll shell's lifetime has important significance.In this paper, based on analysis of the roll shell's lifetime at home and abroad , the ANSYS software was used to construct the thermal-structural coupling model of the roll shell and resolve it in the continuous roll-casting process. The most researchs were as following:(1) The mathematical and physical model of heat transfer in the roll shell was established, especially the problems about mass transfers and periodic rotational boundary condition were solved in the roll-casting process, and gained the distribution rule of the roll shell's thermal field;(2) Based on the analysis of the roll shell's thermal field, the research considered the compositive effects of thermal stress, rolling stress and assembling stress on the roll shell in the roll-casting process, and carried through the thermal-structural coupling analysis for the roll shell, then gained the distribution rule of the roll shell's stress field;(3) Through simulation getting the distribution rule of the roll shell's thermal and stress fields, the paper analysed the reasons of producing fatigue cracks of the roll shell. Based on metal cumulate damage theory and rupture mechanics theory, the paper studied the forming and extending rules of the roll shell's fatigue cracks, and established the estimating model of the roll shell's fatigue lifetime;(4) The paper comprehensively analysed the different roll-casting technical parameters, such as roll-casting velocity, length of roll-casting area, strength of cooling water, thickness of roll shell,, excess lengths of assemblage etc, and gained the distribution rules of roll shell's thermal and stress fields under the different conditions. Based on the research, the paper received the best matching parameters of prolonging the roll shell's lifetime. Then a practical example is given to calculate the roll shell's fatigue lifetime.(5) Factual testing surface temperatures of a roll shell was done in a factory, and the correlative datum were collected. The experiment basically proved the sameness of simulation and experiment. As a result, the experiment proved the reliability of model. Through the statistics of a roll shell's lifetime in practice, it had a conclusion that the practical lifetime of roll shell was basically equal the lifetime of estimating model, so it proved the reliability of roll shell's fatigue lifetime estimating model.