Abstract
In the rolling production, rolls with box passes are widely used, which is explained by the best gripping ability and high draw ratio. However, along with these advantages, there are significant drawbacks - the formation of an erosion net along the bottom of the pass and side cracks on the side outlets, since hot rolling of metals and alloys is accompanied by intense wear of the working rollers and welding fixtures, which happens due to exposure to high temperatures and stresses. Therefore, the task of elaboration of rational temperature regime to provide not only stable mill operation, but also high rollers endurance, is rather actual and requires its solution. It is very important to follow the today’s trend to increase continuous mills rolling speed, which will result in still heavier temperature conditions of rollers operation. Results of the study of the rolling process main technological parameters influence on the formation of erosion net across the bottom of the pass presented, as well as magnitude and nature of the distribution of thermal cyclic stresses along the surface layers of the bottom of pass. Study of the thermal state of roughing stands rollers of OJSC “Belorussky steel-works” 370/150 continuous wire-rod mill show, that comparing with intermediate and finished stands rollers they subject more to thermo-cyclic destruction of passes surface, but not to mechanical one. As a result of the computer simulation new data obtained on the character and peculiarities of dynamics of surface thermal state of rollers passes. The possibilities to reduce thermal cyclic stresses by improving the cooling regime of the rolls shown. Using the simulation by the finite elements method, the study of the dynamics of heating and stress state of the surface and subsurface layers of the pass bottom was accomplished. Based on the analysis results of numerical experiments and analytical calculations, isotherms of the surface layers of the bottom of the pass were compiled to select the optimal cooling mode. The data obtained can be used to control the cooling systems of roughing stands rollers of continuous section and pipe hot rolling mills.
Highlights
В поверхностных слоях калибров бочки валков возникают высокие контактные напряжения, близкие по величине к значениям пределов текучести и прочности
Rolls with box passes are widely used, which is explained by the best gripping ability and high draw ratio. Along with these advantages, there are significant drawbacks - the formation of an erosion net along the bottom of the pass and side cracks on the side outlets, since hot rolling of metals and alloys is accompanied by intense wear of the working rollers and welding fixtures, which happens due to exposure to high temperatures and stresses
As a result of the computer simulation new data obtained on the character and peculiarities of dynamics of surface thermal state of rollers passes
Summary
При горячей прокатке высоких полос в ящичных калибрах возникают характерные зоны очага деформации, отличные от прокатки на гладких валках. При дальнейшей работе стана в связи с тем, что отвод тепла осуществляется только снаружи, температура внутренних зон постепенно повышается, происходит выравнивание температур по сечению и, как следствие, уменьшается благоприятное воздействие сжимающих окружных и осевых напряжений в поверхностных слоях [5, 6]. Во время паузы между проходами, а также при внезапных остановках стана вследствие охлаждения валков эмульсией может оказаться, что температура их внутренней поверхности станет выше температуры поверхности бочки. При термических воздействиях прокатываемого металла на поверхности отбеленного слоя бочки валка появляется мелкая сетка трещин. Thermal state of a roller pass in the vertical stand No 3: На втором этапе исследования температуры рабочих валков применялась разработанная математическая модель прокатки полосы в клетях черновой группы стана 370/150. Математическая модель позволяет выполнять численное моделирование температурного поля в очаге деформации и может служить частью комплекса для моделирования и проектирования технологии прокатки сортовых профилей. Исходные данные для численного моделирования процесса прокатки в клетях No 1, 2, 3 представлены в табл. 1
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