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Simplified Flow Theory for Screw Extruders The flow behavior of a viscous liquid in the channel of an extruder screw is shown to be similar to the flow behavior of viscous liquids between infinite parallel plates， one of which is station... Simplified Flow Theory for Screw Extruders The flow behavior of a viscous liquid in the channel of an extruder screw is shown to be similar to the flow behavior of viscous liquids between infinite parallel plates， one of which is stationary and the other moving. Assuming Newtonian behavior of the liquid， a differential equation was derived which relates the rate of extrusion and the die pressure to the screw and die geometry and to the operating variables. Integrated flow equations are given for the special case in which the viscosity of the liquid is constant throughout the screw channel (isothermal extrusion). Equations are also given for the case in which the dimensions of the screw channel are functions of their position along the length of the screw. IN THE preceding paper ( 1 )o f this symposium the literature pertaining to the problem of viscous flow in extruders was reviewed. In this paper the development of simplified but more useful flow equations is presented. The synibols and nomenclature used in this paper are defined in the preceding paper (1). The flow mechanism of the viscous liquid in the helical channel of the screw can be better understood if one imagines that the channel be unrolled and laid out on a flat surface. Figure 1 shows this concept of the screw channel. If the lower plate， representing the screw surface， is held stationary and the upper plate， representing the barrel surface， is moved in the direction of the arrow， the relative motions will be the same as those existing in an extruder where the barrel is stationary and the screw rotates. Assuming that the liquid wets both surfaces， the motion of the barrel drags the viscous liquid along with it， while the stationary plate exerts an equal and opposite drag. The velocity of the liquid， relative to the screw， is a maximum at the barrel surface and zero at the screw surface. There is also a directional factor involved， since the channel is inclined at angle p to the direction of motion. Therefore， in computing the flow rate in the channel we break up the velocity into two components: one of these acts directly down the channel， and the other acts at right angles to it. We call the component which acts down the channel drag velocity， and the component which acts at right angles to this transverse velocity. At the end of the channel there is generally a die or some other restriction to flow. This sets up a pressure gradient down the channel causing a flow in the reverse direction to the drag flon. There is one other flow that must be considered. Generally the screw does not fit perfectly inside the barrel. In other words， there is a clearance between the top of the screw threads and the barrel surface.