Intermeshing Counterrotating Extruders

In theory CICTR extruders are positive conveying devices where the maximum possible flow rate is given by 

FIGURE 8.25 Closely intermeshing counterrotating twin-screw extruder, (a) Cross-sectional view (end view), (b) Cross-sectional view through flights showing open region. 

Leakage through the gap between the flight and the barrel wall, which is called flight leakage, Qf. 

Leakage between the bottom of the channel of one screw and the flight of the other screw, which is called calender leakage, Qo. 

Leakage through the gap that goes from one screw to the other between the flanks of the flights of the two screws, which is referred to as leakage through the tetrahedron gap, Qt. 

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Fig. 10.14 The location of four gaps in fully intermeshing, counterrotating extruders though which leak flows can take place. [Reprinted by permission from A. J. van der Goot, O. Poorter, and L. P. B. M. Janssen, Determination of the Degree of Fill in a Counterrotating TSE, Polym. Eng. Set, 38, 1193 (1998).]...

Li and Manas-Zloczower (31) used the CFM commercial FIDAP FEM package to simulate the three-dimensional isothermal flow patterns and distributive mixing in three consecutive filled, closed C-shaped chambers of fully intermeshing, counterrotating extruders, having the dimensions of Leistritz 30.34 (30 denotes the centerline distance and 34 the barrel diameter in mm units). An equal pressure drop per C-shaped chamber was applied for the calculations. The melt was assumed to be Power Law above y() and Newtonian below it. The design, process, and material variables are given by the authors. 

Figure 13.15 Conversion as function of the throughput for BMA polymerization ( ) self-wiping corotating extruder (Z) = 40mm) and ( ) closely intermeshing counterrotating extruder (Z) = 50 mm).

Fig. 11. Schematic representation of intermeshing counterrotating twin-screw extruder.

Fig. 10.4 Hexalobal, intermeshing, counterrotating twin-screw mixing screw elements. [Reprinted by permission from W. C. Thiele, Counterrotating Intermeshing Twin Screw Extruders, in Plastics Compounding—Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998.]...

S. Lim and J. L. White, Flow Mechanisms, Material Distribution and Phase Morphology Development in a Modular Intermeshing Counterrotating Twin Screw Extruder of Leistritz Design, Int. Polym. Process., 9, 33—45 (1994). 

T. Sakai and N. Hashimoto, Application of Novel Counter-rotating Intermeshed Twin Extruder for Degassing Operation, SPE ANTEC Tech. Papers, 32, 860-863 (1986) also T. Sakai, N. Hashimoto, and N. Kobayashi, Experimental Comparison between Counterrotation and Co-rotation on the Twin Screw Extrusion Performance, SPE ANTEC Tech. Papers, 33, 146-151 (1987). 

The twin-screw injection molding extruder is an injection molding machine that is capable of both blending/compounding and extrusion in one step. Because it is a one step process, the fibers never go through the entire extrusion process as well as the pelletization that limits the fiber size, but are blended into the molten plastic before injection. The screw part of this machine is based on a non-intermeshing, counterrotating twin-screw extruder (Chapter 5). One of the screws in this machine is capable of axial movement and has a non-return valve on the end. This action enables the screw to inject and mold parts. 

A closer look at the two types of extruders shows that the closely intermeshing counterrotating twin-screw extruder has a better ability to build up pressures, even in an environment with low-viscosity liquids. This is due to the nearly closed C-shaped chambers, which provide a positive displacement action that enhances stability. Self-wiping extruders, on the other hand, are generally capable of much larger throughputs at comparable residence times. This leads to a preference of counterrotating extruders for... 

With counterrotating extruders, the screws at any common point have the same helix angle but are oppositely pitched. Some intermeshing types feature conical rather than parallel, constant-diameter screws. The large diameter of such screws at the feed end promotes heat transfer and allows greater... 

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