| Based on an understanding of design theory of coextrusion die, the3D solid model ofheart-shaped manifold was developed. The3D solid model was translated into2D geometricmodel, namely the coat-hanger die model. Then the main dimensions of the coextrusion diewere calculated, and the die was designed and manufactured.The solid model of the aforementioned coextrusion die channel was established accordingto its dimensions. The flow characteristics of the melt in the coextrusion die was investigatedvia finite element simulation. The simulated results showed that the pressure drop was high inthe slit zone. The melt velocity was increased gradually from the wall to center of the channel,and the velocity gradient was also increased. The shear rate of melt in manifold was muchlower than that in slit zone, the shear rate was very high in the junction of the manifold andthe slit. The exit interface of the coextruded sample was circular, its radius was the same asthat of the entrance interface. This meant that the interface along the coextrusion flowdirection was stabilized gradually. When volume flow rate ratio (Q1/Q2) of the outer layer(PA6) and core (PP) melt was1/4.5, the interface radius changed along the whole coextrusionflow channel. When entrance flow rate ratio was constant and entrance flow rate was changed,the coextrusion interface radius had the same variation along the flow direction.The shear viscosity and complex viscosity of PA6and PP were measured using the highpressure rheometer and dynamic rheometer, respectively. The required material parameters forsimulation were obtained by fitting the shear viscosity curve and the complex viscosity curve.The two-layer PA6/PP samples were coextruded using the designed die. The results showedthat when the mass flow rate ratio (m1/m2) of the outer and core melts was increased from1:9to1:1, the thickness of outer layer of coextruded samples was increased gradually and thecoextrusion interface radius was decreased gradually. |
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