Intermeshing/nonintermeshing twin-screw extruders

Finally, the effect of process variables, such as screw speed, differs with twin-screw extruders. Due to positive conveyance, the output of starve-fed twin-screw extruders (Fig. 5.36 b is independent of screw speed and, to some degree, head pressure. Head pressures and melt temperatures of intermeshing twin-screw extruders are also not as sensitive to screw speed as they are in single-screw extruders. In contrast, nonintermeshing twin-screw extruders exhibit output characteristics that are similar to those of single-screw extruders. A comparison of the characteristics of single and intermeshing twin-screw extruders is summarized in Table 5.9. 

Figure 12.28 Comparison of intermeshing and nonintermeshing twin-screw extruders schematic summarizing the different types of parallel twin-screw extruders and applications.

Counterrotating intermeshing twin-screw extmd-ers have the narrowest residence time distribution followed closely by co rotating intermeshing twin-screw extmders. Counter rotating nonintermeshing twin-screw extruders have the broadest residence time distribution. 

For a welding engineer counterrotating nonintermeshing twin-screw extruder, the barrel section does not appear radically different from the intermeshing barrels shown previously and the drive system components are similar. The only slight difference is the apex area of the barrel where the metal on top and bottom of the bore extend farther toward each other due to the larger screw center line separation distance. 

Since the screws do not intermesh, the nonintermeshing extruder is not subjected to some of the same mechanical tolerance constraints as the other twin-screw extruders. This enables the non-intermeshing machine to be built to an almost unlimited 1/d ratio. A 72 to 1 1/d unit was used for a number of devoli-talization experiments. The enhanced length capability provides a mechanism for the increased internal volume. 

Figure 5.30 Twin-screw extruders (a) counterrotating, fully intermeshing (6) corotating, fully intermeshing and (c) counterrotating, nonintermeshing. ...

Twin screw extruders can be operated with either counter- or corotating screws. Additionally, the screws can be fully intermeshing, partially intermeshing, or nonintermeshing. Figure 7-10 illustrates the various cases. 

Figure 5.14 Diagram showing the difference between (a) intermeshing and nonintermeshing as well as (b) co-rotating and contra-rotating or counter-rotating types of twin screw extruders. (Fteprinted from Ref. 20.)...

FIGURE 8.6 Various types of twin-screw extruders (a) counterrotating intermeshing elements, (b) corotating intermeshing elements, and (c) counterrotating nonintermeshing elements. 

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