Designing of extrusion lines

Abstract

AbstractThe design of extrusion lines deals with the extruder and the die as well as with the down stream equipment, especially the cooling section. This paper aids in the design of these three units, regarding different aspects. The scale‐up of extruders by means of the model theory is demonstrated in its practical use with examples. Emphasis is laid on the design of series of single screw extruders with mixing‐pins and of twin‐screw extruders (scale‐up). There the adequate selection of the necessary restrictions for the compilation of model laws is discussed in detail. This is an approach to the safe machine design on the basis of model theory.The present standard of the calculation of threedimensional flow patterns in extrusion dies by means of the finite‐element‐method (FEM) is shown in order to point out how design‐aids for the die‐designer are derived from these calculations. After a discussion of application‐criteria for the FEM, examples will show possible ways of using FEM‐results.For the shaping of Y‐branches in twin‐screw machines the FEM‐results point to possible plate‐out areas and to their avoidance by geometrical modifications. The calculation of a die for a T‐profile helps to design the passages between entry and exit sections. Finally, flow coefficients for the calculation of pressure losses in different cross sections are given.The design and optimization of cooling sections, as it can be done with the aid of the actual cooling models, is shown for some important extrusion processes. Heat transfer coefficients for practical cases (film‐sheet‐, pipe‐ and parison extrusion) are presented. Examples show, how diagrams for the design and optimization of cooling sections (for example the reduction of internal stresses and warping) can be made, using a microcomputer.