单螺杆橡胶挤出机三维非等温流动数值模拟

Simulation of non-isothermal three-dimensional flow in the channel of a single-screw extruder for rubber material

为研究胶料在挤出过程中的流动模式,本文建立了具有复杂几何构型的主、副螺纹单螺杆螺槽内胶料三维非等温流动的有限元模型,采用Bird-Carreau模型和Arrhenius shear stress方程分别表征胶料黏度随剪切速率和温度的变化,并通过热力学估算确定了合理的机筒壁热学边界条件.在此基础上求解了20 r/min转速下的速度场、温度场和压力场,并将温度数值计算结果与实测结果进行了对比,两者吻合较好,这表明了模型的有效性.此外,通过模拟发现主、副螺纹构型的热喂料螺杆确实可以避免挤出过程中的"死区"并提供更强剪切作用;螺杆挤出段的副螺纹阻碍了胶料的流动,使得该处压力更大;由于受剪切时间更长、更强烈,胶料在挤出段温度最高.最后考察了不同转速下的压力和温度,结果发现挤出过程的最大压力与最高温度均随转速增大而升高,与此同时由于胶料自身的剪切变稀特性和温度依赖性,压力与温度上升的趋势会随着转速的升高而减缓.

In order to study the flow patterns in rubber extrusion process, a 3D finite element model of non- isothermal flow of the rubber material in the single screw channel of a complicated-geometry main/subsidiary screw was established. The viscosity of the rubber materials as a function of the shear rate and temperature is described by Bird-Carreau law and Arrhenius shear stress equation. The reasonable thermal boundary conditions of the barrel wall was thermodynamically estimated. Based on the foregoing model, the velocity field, temperature field and the pressure field at the screw speed of 20 r/min were elaborated. The simulation results agree well with the experiment ones, confirming the validity of the numerical model. Meanwhile, the numerical results of velocity field and shear rate field indicated that the hot-feeding extruders with the main/subsidiary threads configuration can avoid the formation of the ＂dead zone＂ and facilitate greater shear deformation. The subsidiary thread located at the extrusion region of the extruder can hinder the flow of the rubber material, causing a greater pressure. A long time and strong shearing results in the highest temperature of the rubber material in the extrusion region. Moreover, the pressure and the temperature were studied at different screw speeds. As the screw speed increases, both the highest pressure and the highest temperature increase. Meanwhile the upward trend of pressure and temperature slows down due to the shear-thinning property and the temperature dependence of the rubber material.