T型挤出模具平衡流道的设计

Design of Balance Flow Channel in T-type Extrusion Dies

T型挤出模具是一种广泛使用的平缝型模具。为提高熔体出口流率沿模具宽度方向的均匀性,采用现有设计方法设计流道时,通常采用增加歧管半径或减小阻流区厚度的方法,前者使熔体停留时间增加,后者使挤出压力急剧增加,工程中还需要采用其他措施才能满足使用要求。为此,文中提出采用厚度不同的两个阻流区,在满足熔体出口流率沿模具宽度方向均匀的条件下,利用流变学理论推导了两个阻流区的分界形状曲线;并将该方法与传统的T型模具设计方法进行了对比。结果表明:采用该设计方法,通过对歧管半径和两个阻流区厚度及其分界形状曲线的设计,能够显著降低熔体的停留时间,而其挤出压力能够根据工艺需求进行调整,可用于指导T型模具流道的设计。

T-type extrusion dies is a kind of widely-used slot die.According to the present design method for flow channel in die,increasing the radius of the manifold or reducing the thickness of the choke zone was generally adopted to improve the uniformity of the melt exit flow rate along die width direction.However,increasing the radius of manifold increases the residence time of the melt in die,and reducing the thickness of choke zone causes a sharp increase of extrusion pressure,so other measures are demanded to meet requirement in practice.Two choke zones with different thicknesses were adopted to solve the problem.Under the precondition that the melt exit flow rate is uniform along the die width direction,the demarcation carve between the two choke zones were deduced based on rheology.In addition,the traditional T-type dies designing method was compared with the method proposed.The results show that the residence time of the melt can be significantly reduced by using the proposed design method and the flow channel designed through proper selection of radius of manifold,the thickness of the two choke zones and demarcation curve between the two choke zones.,and the extrusion pressure can be adjusted according to the processing requirements.Therefore,the proposed design method can be used to guild the design of flow channel in T-type dies.