Solution to Design Problem VI

The volumetric flow rate for each component is determined from the mass and density of each component and the hang time. 

The curvature in the die cross section is neglected, and it is treated as a parallel plate geometry. 

The design equations for coextrusion are used to determine the pressure gradient, G, and the position where the velocity profile passes through a maximum, a. 

The shear rate and viscosity are calculated at the interface to determine if the flow could be unstable. 

We first calculate the volumetric flow rate of each component where is Q for nylon 6 and Q for HDPE. The density of nylon 6 at 25 °C is 1132 kg/m while that for HDPE at 25 °C is 971 kg/m. Given the mass of the parison is 18 lb HDPE and 2 lb nylon 6 and time for hanging the parison is 5 s, we find 

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FIGURE 7.2 Exit face of the die used to produce the parison in Figure 7.1. The die opening is an elliptically shaped annulus of major axis a and minor axis b. The thickness, a, and b are determined in the solution to Design Problem VI. 

Section 7.6. Finally, in Section 7.7, the solution to Design Problem VI is presented. 

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