Down-channel extruder drag flow

Simple pressure/drag flow. Here we treat an idealization of the down-channel flow in a melt extruder, in which an incompressible viscous fluid constrained between two boundaries of infinite lateral extent (2). A positive pressure gradient is applied in the X-direction, and the upper boundary surface at y - H is displaced to the right at a velocity of u(H) - U this velocity is that of the barrel relative to the screw. This simple problem was solved by a 10x3 mesh of 4-node quadrilateral elements, as shown in Figure 1. 

Melt conveying is the forward motion of the molten polymer through the extruder, due to the pumping action of the rotating screw. This simple drag flow Md is proportional to melt density, down-channel velocity, and cross-sectional area of the screw channel. In most cases, however, there is also a pressure gradient as the melt moves downstream, either... 

Pressure flow is caused by pressure in the head of the extruder. If we assume that the screw is stationary, but that there is melt under pressure at the die, the screw channel will act like a long rectangular orifice. The melt, forced by the pressure in the die head, will travel backward down the helical screw channel. In actual operation, pressure flow is a reaction to drag flow, caused by the die restriction and the pressure developed in the die head. It is influenced by screw channel dimensions, barrel diameter, melt viscosity, and back pressure. If viscosity is assumed constant, then ... 

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