Twin screw extruders types

The following table compares the single screw extruder with the main types of twin screw extruders. 

The same assumptions and equations used in developing an expression for kialob for single-screw extruders can be used to describe mass transfer rates in the type of corotating twin-screw extruder considered here. In this regard. Fig. 14 is relevant, and ki a/ob will be given by Eq. (53) ... 

The third type of compounding device is the extruder. Next to its use for fabrication (which will be dealt with in 11.4.2), it is applied as a mixer. In essence, it is a screw pump, in which the mass to be mixed is transported in a heated cylinder by a screw, or, with twin-screw extruders, by two parallel screws. During this transport melting and intensive mixing take place. At the end of the screw the blend is pressed through a number of openings and cooled down in most cases the strands thus obtained are on-line cut into granules. 

To break up agglomerates or disperse liquid droplets, flow forces that exceed a certain minimum value are required. In addition, the type of flow is crucial for the dispersion result, namely, the respective ratio of shear and extension. The shear and extension rates are not constant over the cross-section in an extruder. There are zones with more or less loading. In addition, there are zones with almost pure shear flow and zones where extensional flow dominates. The different zones in the cross-section of a twin screw extruder are shown in Fig. 9.15. 

This chapter provides an overview of the vast variety of screw elements developed and patented in the more than 60-year history of twin-screw extruders. For ease of identifying the various types, the patents are divided into six categories within which they are ordered with ascending number of flights. 

Different types of wear occur in the plastification zone, in the additive intake zone, or in the discharge zone of the twin screw extruder. These include ... 

The first twin-screw compounder (ZSK) went into production at Werner Pfleiderer in 1957, marking the beginning of a success story for this type of machine. The first major applications were in the chemical industry. Today, the machine is predominantly used in the plastics industry, e. g., in extrusion and compounding. These screw machines are therefore also known as extruders and the twin-screw is known as the twin-screw extruder. 

Highly viscous polymeric reactions (e.g., the hydrolytic polyamide reaction) are often carried out in a gear-pump reactor (Tadmore and Klein, 1970). This type of reactor is often difficult to operate because the clearance of the gear teeth is increased by wear caused by flow and the reaction process. For smaller viscosity of the melt, a screw reactor or a twin-screw extruder is often used. Sterbecek et al. (1987) used a twin-screw extruder (i.e., Wemer-Pfleiderer extruder ZSK 83) for studying fast ion-catalyzed polymerization (6-caprolactam) in a melt. They indicated that power input and quality of product in such a reactor depends on the slot width between reactor wall and impeller in a twin screw extruder. They provided an optimum design of a twin-screw reactor for a fast ion-catalyzed polymerization in a melt. 

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