Self-wiping corotating twin-screw extruders

1 Self-wiping Corotating Twin-Screw Extruders 

We consider only the melt conveying section of the SWCOR type, because there are no theories available at present for describing the solids transport and melting zones. We first describe some general features of the flow regions in SWCOR types and then geometrical features that are required to understand the more quantitative aspects associated with flow. 

FIGURE 8.21 Cross section of a closely inlenneshing twin-screw extmder with donble-flighted screw elements (or paddle elements). The tip angle, [, the angle of intermesh, a, and the centerline distance are shown. 

FIGURE 8.22 Channel depth for a double-flighted corotatmg self-wiping twin-screw extruder, (a) Channel depth as a function of circumferential angle, (b) Channel depth as a function of distance across channel. 

We can now find the cross-channel depth profile along the x direction (note that this is the same as for the single-screw extrader where z is taken along the helical path or down channel direction and x is taken along the channel width) by substituting in the following coordinate transformation  

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The constraint that the tip of one screw element wipe the flank of its mate in self-wiping, corotating twin-screw extruders leads to a unique relationship for the shape of the screw channel (Booy, 1978,1980). Figure 13 is an isometric view of this channel and Fig. 14 is a cross section of the channel in a plane that is perpendicular to the plane which defines the helix angle. Figure 14 shows the actual shape of the channel, which is described by the following expressions ... 

C. D. Denson and B. K. Hwang, The Influence of the Axial Pressure Gradient on Flow Rate for Newtonian Liquids in a Self Wiping, Corotating Twin Screw Extruder, Polym. Eng. Sci., 20, 965 (1980). 

Twin-screw extruder Dimensionless calculations of throughput and pressure gradients for flow of non-Newtonian fluids in screw and kneading disk elements of a modular intermeshing self-wiping corotating twin-screw extruder, as well as the temperature rise. Chen and White, 1992, 1993... 

For reactive extrusion of butylmethacrylate the influence of the rotation rate of the screws and the throughput on the product were also investigated by Jongbloed et al. (11) in a self-wiping corotating twin-screw extruder. The inhibited monomer was mixed with a combination of two peroxide initiators with different half-life values. A combination of initiators was used to prevent a deficiency of radicals towards the end of the reactive extrusion process, where due to the reaction, the temperature increased significantly. The total initiator concentration was 0.07mol/l. The mixture of monomer and initiators was fed to the extruder at room temperature. 

Figure 15.10 Cross-sectional view of a three-tip screw in a self-wiping, corotating twin-screw extruder. (From Ref 20.)...

FIGURE 8.2 Self-wiping closely intermeshing corotating twin-screw extruder. Flow of material in double-flighted screw elements (left). Cross section of the barrel showing the pertinent dimensions (right). 

In this section we consider the essential features of two of the most common types of twin-screw extruders self-wiping corotating (SWCOR) twin-screw extruders and closely intermeshing counterrotating (CICTR) twin-screw extruders. As discussed in Section 8.1.2, there are a vast number of types of twin-screw extruders, and it is not possible to discuss all of these here. Further discussion of the technology and theory for twin-screw extruders is given elsewhere (Rauwendaal, 1986 White, 1990). 

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