Extrusion Introduction An extruder is a common machine in industry ...

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Theory Theoretical Background In this lab, we are going to use an annular structured tubing die to produce tubes in different dimensions. When a polymer melt is extruded through an annular die and stretched under tension to a desired diameter, a hollow tube can be made. Although the overall process that involves die swell followed by draw down (or stretching) is rather complicated as indicated in Figure 5, analytic understanding of the process can be made under some simplifying assumptions. die exit die swell zone r z=0 z r = R o (z) r = R i (z) u = (u, w) draw down region z=L F, w L Figure 5. The diagram for analyzing polymer flow through the die.
In Figure 5., r and z are the radial and axial direction, respectively. R o (z) and R i (z) are the outer and inner radius at different z position, respectively. The polymer flowing velocity is defined as u, which including r-direction velocity u and z-direction velocity w. When a polymer melt flows out of the die exit, “die swell” occurs in that the polymer melt expands in the radial direction (i.e., swells) due to residual stress in the melt. Die swell is a very complicated phenomenon because it depends on the strain history (i.e., memory effect) in the die as well as the rheological properties (both viscous and viscoelastic) of the melt. Thus, prediction of it is very difficult. The die swell, however, is restricted to a very short region near the die exit and an analytic progress can be made by simply neglecting the die swell region and focusing on the draw-down region. The simplifying assumptions for the current analysis are a) Isothermal and axisymmetric flow b) Length of the draw-down region (L) is much longer than the radius of the exit hole of the die c) Viscous force is dominant and the viscoelastic force, inertia, gravity and surface tension are negligible. d) Newtonian fluid Although polymer melts are non-Newtonian and the viscoelasticity effects are often important, the current flow of interest is weakly extensional and slow. Furthermore, the shear strain is also very weak throughout the entire draw-down region for this free surface problem. Thus, the Newtonian assumption is not too restrictive. Considering that the viscosity of polymer melts are quite high, assumption (c) is also not very restrictive. As the draw-down region is typically exposed to the air, the temperature may decrease as it flows down due to the cooling by air. However, the temperature variation may not be very large unless air is blown against the polymer melt for forced convective cooling. We consider the cylindrical coordinates while determining the variables in the extruder process. Figure 6. is the figure of a standard cylindrical system.
Page 1 and 2: Extrusion Introduction An extruder
Page 3: Objectives for Extrusion 1. Determi
Page 7 and 8: R o 2 z p 1 u r 2 R
Page 9 and 10: 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0
Page 11 and 12: 1. Switch the main power from “OF
Page 13 and 14: These are the experimental dimensio
Page 15: 5. Calculate the inner diameter (Di

Extrusion Introduction An extruder is a common machine in industry ...

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