The Research On Flow Field Of Three-Layer Coextrusion Sheet Die

Multi-Material Coextrusion Molding has been widely used in construction, aerospace, optical, agriculture, medicine and other fields due to its advantage of banlancing the excellent features for various polymers. The coextrusion molding sheet is one of the coextrusion molding products, whose quality is determined by the design of die. The influence of three-layer coextrusion sheet die geometry parameters, material physical parameters and processing parameters on pressure field, the uniformity of velocity and interface shape and position of exit were studied in this paper.It was analyzed and summarized that the advantages and disadvantages among commonly used sheet die and coextrusion die. Combined with the main design points of the cross section shape and thickness ratio of three-layer composite coextrusion sheet, the three-layer composite sheet coextrusion die was preliminary designed. The finite element model of flow channel for the three-layer composite coextrusion sheet die was established by Senior meshing software ICEM CFD, and the flow field of the die was analyzed by software POLYFLOW.For the geometry parameters of the die, the influence of baffle length, sector zone angle, sector and damping zone height, die lip zone thickness on the pressure field, the uniformity of velocity and interface shape and position of exit was studied. The study indicated that the shorter the baffle length was, the greater the sector zone angle, the sector zone height, the die lip zone thickness and die lip zone length were, the more uniform the exit velocity became. The longer the baffle length was, the more stable the exit interface was.For the materials physical parameters, the influence of viscosity ratio and relaxation time ratio for the interlayer material on the pressure field, the uniformity of exit velocity and exit interface shape and position was studied. The results indicated that the smaller the material viscosity ratio was, the greater the relaxation time ratio was, the more uniform the exit velocity became. The greater the material viscosity ratio was, and the smaller the relaxation time ratio was, the more stable the exit interface was. When the differences of viscosity and relaxation time for the interlayer material were smaller, the interface position was closer to the ideal one.For the processing parameters, the influence of the inlet volumetric flow rate ratio and drawing velocity on the pressure distribution, the uniformity of exit velocity and interface shape and position of exit was studied. The study indicated that the exit velocity was more uniform and the interface was more unstable with the increase of the inlet volumetric flow rate ratio. The interface position shifted to the side of low viscosity melt and the interface was becoming more and more stable with the increase of drawing rate.