【作者】 朱敏； 彭炯； 陈晋南；

【Author】 ZHU Min,PENG Jiong,CHEN Jinnan (School of Chemical Engineering and Environment, Beijing Institute of Technology, Beijing 100081,China)

【机构】 北京理工大学化工与环境学院；

【摘要】 口模的设计是挤出成型加工的一个关键。工业生产中挤出口模的设计一直采用反复的修模和试模过程得以完成,导致绿色化学新产品研发试制周期长、成本高。随着计算机和计算技术的飞速发展,计算机辅助设计CAD和计算机辅助制造CAM应用于各行各业,大大地促进了工业生产的发展,使得人们能够在计算机上完成口模的优化设计,有利于绿色化学材料的研制和开发。本论文应用计算流体力学(CFD)软件POLYFLOW对异型材橡胶密封件的挤出口模进行了数字设计。根据所需产品截面的具体尺寸,初步绘出口模模型图,进行网格划分并设置边界条件进行计算。在计算机上进行了挤出实验和修模,根据流场分析进行逐步修模,经过5 6次的修模和计算,最终确定了口模的流道结构和尺寸。应用POLYFLOW软件包对数字设计的口模进行数值分析,给出了速度分布、压力分布和剪切速率分布。数值计算的结果表明,口模壁面速度为零,挤出后的流体速度均匀一致,已达到稳态;从口模的入口到出口压力逐渐下降,口模外部熔体的压力最低而且分布很均匀。这是因为口模壁面的剪切作用,压力降主要发生在口模内部。物料挤出口模后,由于不受外力而处于大气压下的自然状态,因而压力降较小且趋于0。由于壁面的束缚,壁面处的剪切速率最大,流体挤出口模后,脱离了壁面的束缚,剪切速率急剧下降,可降至为0。最大的剪切速率出现在口模壁面的沟槽位置处。对数字设计的口模进行挤出模拟,所得的挤出物截面图与产品截面图形状和尺寸大体一致,吻合较好,但变化较为剧烈的边角沟槽处与实际还有一定的差距,计算相对误差为9 87%。分析出现该误差的原因有三个方面:其一,对于复杂的口模,直流道是不能很好的满足设计需要的,若想弥补细小边角处形状不符的不足,须应用非直流道进行修正。其二,由于计算机内存的限制没有考虑壁面滑移、牵引速度等实际存在的因素,对计算模拟的结果有一定的影响。其三,实际生产中物料挤出后还要进行硫化、冷却等步骤,最终的产品与刚刚挤出口模的产品也是会有一定形状差异的。更多还原

【Abstract】 Die design is the key of extrusion A traditional method of die design entirely depends on "trial and error" method, which requires repeated modifications and tests of extrusion dies The process is very costly and time-consuming With the fast development of computer, CAD and CAM that approve the improving of the industry are applied in various fields It is available to optimize the dies on the computer, which is benefit to the development of green materials Digital design on extrusion die for rubber profile was carried out using the commercial computational fluid dynamics (CFD) package POLYFLOW in this paper According to the section of product needed, the geometry was drawn elementarily Then it was meshed and calculated On the bases of analysis of flow fields, the geometry of die was modified again and again After fifty-six times "trial and error", the structure of runner was confirmed at last Pressure, viscosity, shears rate distribution and extrusive profiles were derived with the package POLYFLOW The velocity of the wall is zero The velocity of the fluid is uniform after extrusion, which shows that it was steady From the inlet to outlet of the die, the pressure dropped gradually The pressure of exterior fluid of die is the lowest, and whose distribution is uniform As the reason is the role of shearing on the wall, the pressure drop was mainly occurred in the interior Without the outside force after extrusion, the pressure of materials tends to zero under the atmospheric pressure Because of the restriction of the wall, the shear rate of wall reaches maximum Shears rate descend rapidly after extrusion and tends to zero Maximum of shears rate occurs at the nooks of the wall Simulation on the die designed was carried out The section of simulation was compared with the real product The agreement is satisfactory There are some differences at nooks only The relative error is 9 87% Three aspects lead to relative error: Firstly, for the complex die, direct runner cannot meet the demand of die design better Non-direct runner is needed to revise it Secondly, discounts of wall-slip and draw velocity because of the limits of computer memory, which also can affect the results of simulation Thirdly, In fact, materiel is needed to pass through the processes like desulfurization and refrigeration after extrusion It will be the differences between the final product and extruded one更多还原