Internal And External Forced Convection Effect Analysis Of Core Hole Roller Temperature-controlled By Flow Oil

Light-alloy such as Mg-alloy,Al-alloy are important basic materials for lightweighting of equipment structures.The method of cogging-finishing rolling is currently an efficient process for mass production of light-alloy.It is important to ensure stable of rolling deformation,optimum control of organisation,properties and shape of plate,which is all depend on the precise temperature control of roller.In the medium-heavy plates rolling process,the roller temperature will keep rising quickly due to the cumulative effect of large reduction in multi-pass.So cooling the roller down rapidly and uniformly during the rolling process can guarantee the quality of the plate forming.The application of the core hole roller temperature-controlled by flow oil can effectively improve the temperature uniformity of roller surface.But the roller design with multi-oil channel is difficult to satisfy the stiffness due to the huge rolling forces of the open billet.The single core-hole roller is more in line with the roller surface temperature control and rolling application requirements.But there is a significant delayed time in the temperature response of roller surface to oil temperature due to the distance of the cooling source from roller surface and the restricted thermal conductivity of the roller.It is essential to explore viable cooling methods for roller and study the behaviour of heat transfer and temperature response patterns.In this paper,based on the design and research of core hole roller temperature-controlled by flow oil,a combined method of fluid-structure interaction finite element and heat transfer theory analysis is used to study the temperature distribution state of roller and delay time characteristics of roller surface temperature under two forced convection cooling methods——the internal oil flow through the roller(oil temperature range of 200°C to 60°C,flow rate of oil from 2m~3/h to 5m~3/h)and its combination with external air cooling(wind temperature of 27°C,(-40)°C,oil flow rate 3m~3/h,5m~3/h,wind speed 26m/s,31.2m/s,50m/s).In order to provide a theoretical basis for rapid and uniform cooling of roller during the rolling process,it explores the influence of different cooling methods on roller surface temperature uniformity and delay time in the cooling process.The results of study show that:(1)Reduce the roller temperature will shorten the temperature difference between adjacent nodes on roller surface,then improve the axial temperature uniformity on roller surface;The heat transfer efficiency from the inner wall of roller to the roller surface is gradually reduced with the radial cooling process,then the temperature difference of roller is gradually reduced,so that the axial temperature of roller surface is more uniformity than the inner wall of roller.The temperature difference between oil and inner wall of roller reduces with the decreases of roller temperature,then the convective heat transfer capacity decreases,as well as the cooling efficiency,so the delay time of temperature drop of roller surface gradually increases with the reduction of roller surface temperature,and the increase rate is growing.(2)Comparing with the cooling method of roller temperature-controlled by flow oil,method of its combination with external air cooling roller will significantly charge temperature drop value of roller surface and temperature drop rate:Keep the same flow rate of oil and wind speed,reduce the wind temperature will enlarge temperature difference between wind and roller surface,then increase its coefficient of convective heat transfer,thus increasing temperature drop value of roller surface and rate of temperature drop;Keep the same flow rate of oil and wind temperature,increasing the wind speed will enhance the Reynolds number of convective heat transfer between wind and roller surface,thus enlarging the temperature drop value and temperature drop rate of roller surface.The reduction of wind temperature will directly lead the increase of temperature difference between roller surface and wind,then enhance the temperature gradient between nodes of roller surface,thus weaken the axial temperature uniformity of roller surface.