Basic Research On New Roll Constant Temperature Control In Magnesium Alloy Sheet Rolling

Magnesium alloy is poor at plastic forming ability in room temperature,its hot processing temperature range is narrow,so we usually product magnesium alloy sheet by warm-rolling or hot-rolling.The temperature of magnesium alloy in the rolling deformation zone changes dramatically,and the temperature of the roll is an important factor to affect the heat distribution in the rolling deformation zone and the hot roll profile of the roll.Therefore,it is of great significance to study the temperature field of the roll during the rolling process of magnesium alloy and accurately determine the control strategy of the roll temperature.Magnesium alloy sheet rolling has special requirements for the temperature control of the working roll.Based on the existing problems in the preheating and cooling process of the roll,our research group has proposed a new type of magnesium alloy temperature-controlled roll,in which the flow channels of heat conduction oil and cooling oil are distributed inside,and the temperature of roll can be controlled by changing the temperature and flow rate of the fluids.In order to achieve the purpose of constant temperature control of roll,this paper mainly studies it from two aspects,one is the preheating of roll and the other one is the cooling control of roll in the rolling process of magnesium alloy sheet.In the roll preheating stage,the temperature distribution and temperature rise curve of roll under different temperature and flow rate of heat conducting oil are studied from two angles of theoretical calculation and finite element numerical simulation in this paper,with the corresponding experimental verification,which provide theoretical guidance for the actual preheating of the roll and roll temperature compensation in rolling process.In the rolling stage of magnesium alloy sheet,when the rolling process is determined,it is also sure that the heat produced per unit time into the roll,the essence of studying the constant temperature control of roll is to study the effect of internal cooling oil on the temperature field of roll,that is,the roll temperature on the response of different cooling oil flow rate.Based on ABAQUS/Explicit finite element analysis software,thermo-mechanical coupled rolling model and equivalent heat transfer model are established in this paper.The rolling model is used to analyze the temperature distribution of magnesium sheet in rolling deformation zone,the average temperature of magnesium sheet after rolling and the surface temperature of roll under different rolling process parameters,which is complemented by the corresponding experimental verification;Equivalent heat transfer model is mainly used to analyze the thermal equilibrium temperature and the time of reaching the thermal equilibrium at different cooling heat transfer coefficients and initial temperature of roll,which effectiveness is verified by rolling model.The results show that:(1)The problem of non-uniform temperature distribution in the axial,circumferential and radial direction of the roll can be solved by heating the roll with the new roll temperature control device.At the same fluid temperature,the roll surface temperature increases with the increase of flow velocity,but the increase is not obvious,because the increase of flow velocity leads to the increase of convective heat transfer coefficient.Additionally,due to the small increase of flow rate,the increase of roll surface temperature is not significant;at the same flow rate,the roll surface temperature increases obviously with the increase of fluid temperature,because the increase of fluid temperature increases convective heat coefficient on the one hand and the temperature difference between fluids and solids on the other hand,which enhances the heat transfer effect between fluids and solids,showing that the roll surface temperature increases obviously.(2)The empirical formulas of average temperature and roll temperature,rolling speed,rolling reduction and plate thickness of AZ31 magnesium alloy plate after rolling based on thermo-mechanical coupled rolling model can predict the average temperature of magnesium plate after rolling.(3)The new roll temperature control device can have a better cooling effect on the roll,and the radial temperature gradient of the cooling roll is large.According to the temperature range,the roll can be divided into three areas: pre-temperature adjustment zone,transition zone and cooling zone.The higher the preheating temperature of the roll,the higher the heat balance temperature of the roll surface,the shorter the time to reach the heat balance temperature correspondingly;and the size of the cooling heat transfer coefficient directly affects the temperature of the roll surface,the temperature and range of the roll cooling zone indirectly affect the temperature and range of the pre-temperature-regulating zone;there is an optimal value of the cooling heat transfer coefficient,that is,when the cooling heat transfer coefficient is less than the optimal value,increasing the convective heat transfer coefficient can play a good cooling and cooling effect;when the cooling heat transfer coefficient is greater than the optimal value,the increase of the cooling heat transfer coefficient has no significant effect on the cooling and cooling effect of the roll.The research results of this paper have certain theoretical guidance for the research and application of heating technology and technology of roll before rolling magnesium alloy sheet,temperature control of roll during rolling magnesium alloy sheet and temperature prediction of magnesium sheet after rolling,and as part of the magnesium alloy plate rolling model,it is conducive to the isothermal control of the roller in the rolling process and realizing isothermal rolling control of magnesium alloy sheet.