Study Of The Coupling Mechanism And Regulation Between The Periodic Heat Transfer Boundary Condition And Temperature Distribution Inside Steel Billet(Slab)During Hotrolling

Iron and steel industry has characteristics of high energy consumption,high pollution,and over-capacity.In order to survive and develop,it is necessary to further develop products with high value and high quality.Microstructure and properties of slab affect the products quality,which is closely related to the temperature distribution,temperature level and temperature gradient.Further,the slab heat transfer boundary directly determines its temperature field distribution.Therefore,it is very significant to study the slab heat transfer boundary in hot rolling area.The hot rolling area mainly consists of reheating furnace,rolling and laminar cooling.The slab has experienced heating and multi-point cooling,which is a complex periodic heat transfer process,from reheating furnace to laminar cooling.However,this periodic heat transfer mechanism is vague at present.Therefore,this paper put forward the characterization method of boundary function through experimental test,theoretical analysis calculation and least square method.Therefore,it is proved that the heat transfer boundary has periodic characteristics in hot rolling area.From both the positive and negative side,coordination between periodic characteristic parameters and temperature field has been studied.Then,the influence of characteristic parameters on heat transfer has been achieved.Meanwhile,the coordination operation law has also been analyzed in-depth.In general,this study can provide basis for thermal operation optimization and reasonable arrangement of heating(cooling)production process.(1)The heat transfer boundary of each section has obvious periodicity,and the periodic functions are differentThe factors affecting the heat transfer boundary mainly includes furnace temperature and heat transfer coefficient,both of which have obvious periodic characteristics.In reheating furnace,furnace temperature can be superposed by trigonometric function and linear function.In rolling process,the heat transfer boundary mode is mainly‘Trapezoidal wave’or‘Rectangular wave’.In laminar cooling,the heat transfer boundary is a piecewise function composed of‘Half sine curve’centered on the nozzle.(2)The influence of sine amplitude and period on slab heat transfer is significantAlthough a single characteristic parameter has impact on the slab temperature field;nevertheless,there are differences in terms of way and effect.The sine amplitude reflects the rise and fall of temperature in the same region.Case study shows that the maximum increase of slab surface temperature is 1.22℃in reheating furnace,when the sine amplitude of furnace temperature increases by 1℃;the maximum decrease of slab surface temperature is 0.36℃in laminar cooling process,when the sine amplitude of heat transfer coefficient increase by 1W/(m~2·K).The sine period reflects the slab temperature distribution along the slab running direction or the cooling area.Case study shows that the larger the sine period in the reheating furnace,the more gentle the slab surface temperature,and the smaller the sine period in laminar cooling process,the worse the slab cooling effect.(3)The coordinated change of heat transfer boundary sine period and amplitude play a decisive role in the control of temperature target.And it has also an important influence on the production rhythm control in hot rolling area.The sine amplitude furnace temperature decreases exponentially with the increase of sine period(heating time)in normal production state.Case study shows that the fuel gas consumption intensity decreases with the heating time,but the effect is only effective in a certain time interval.Especially,the effect of the case reheating furnace is significant in the range of 150 min to 206 min.At the same time,the regional thermal efficiency of 170 min,190 min,210 min heating time is analyzed.The calculation results shows that the shorter the heating time is,the higher the regional thermal efficiency is,especially,in NO.1 heating region.The sine amplitude of heat transfer coefficient decreases linearly with the increases of sine period(cooling time)in laminar cooling section.The regulation of production rhythm is mainly the coordination of heat transfer boundary sine period(heating time,rolling time and cooling time)of each section in hot rolling area.Case study shows that the adjustable heating time is 4080s,the corresponding flue gas consumption regulation amount is0.58 GJ/t,and the adjustable cooling time is 10.76s.