Design and Validation of a Cable Extrusion Tip with Spiral Channels

Abstract

Abstract Traditional cable extrusion dies employ a side-fed flow distribution system. In this case, the flow is split into two streams, resulting in the formation of a weld line. The weld line runs as a radial line through the cross section of the cable coating and has the least favorable orientation when the cable coating is exposed to circumferential stresses. Therefore, a new cable extrusion tip based on the principle of spiral mandrel dies was developed to change the orientation of the weld line from radial, that takes place when side-fed mandrel dies are used, to circumferential, when melt distribution resulting from the layering of the leakage flow in spiral mandrel dies occurs. The circumferential orientation of the weld line reduces the exposure of the weld line to circumferential stresses and thus improves the mechanical properties of the cable coating. This paper first outlines the design strategy for the new cable extrusion tip and further presents experimental results. The design strategy is based on two-dimensional flow networks. The network model is applied to calculate the flow channel geometry for a wanted distribution of the flow. Further, it should generate a better understanding of the correlation between the flow, pressure drop, and the flow channel geometry to facilitate the design of the tip. Three dimensional FEM simulations were used in this work to validate the flow network model in terms of pressure drop and velocity profile at the exit of the tip. The results of the calculations with the network model show good accordance with three dimensional FEM-simulations. For the experimental part a tensile test was conducted to compare the tensile strength in circumferential direction of a cable extruded with the new tip with a cable extruded with a conventional cable extrusion tip. The measurements showed an increase of the tensile strength in circumferential direction of 10% to 15% for the cable extruded with the new tip compared to the tensile strength at the location of the weld line in the cable extruded with the conventional tip.