Overview of Patented Screw Elements

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. 

Erdmenger Profiles (Section 13.1 - 13.5) Even today, most of the screw elements in use are based on the traditional, self-cleaning Erdmenger profiles. Chapter 5 provides a detailed derivation of these profiles. 

Eccentric Screw Profiles (Section 13.6-13.9) Elere, the screw profiles are arranged eccentrically on the shafts. These screw elements consume less energy because, except for one screw tip, all other tips feature an enlarged clearance to the barrel. The self-cleaning of the barrel is guaranteed by the one tightly intermeshing tip. 

General Screw Profiles (Section 13.10-13.15) Next to the traditional screw profiles, additional completely self-cleaning profiles have been developed in which the tip angles differ or which feature asymmetrical profiles. 

Transition Elements (Section 13.16-13.19) Generally, shims are inserted between elements with different numbers of flights to compensate for the axial clearance of the shafts. It is also possible to use transitional elements whose screw profiles alter continuously along the axis from o ne number of flights to another, while maintaining a complete self-cleaning function. 

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