Fiber orientation in multilayer tubes processed by a conical extruder

Abstract A new extruder design has been developed for the coextrusion of two‐layer annular sections. The extruder consists of a conical stator‐rotor‐stator assembly, which performs extrusion from each side of the rotor. Flow within this assembly is fully three‐dimensional, with helicoidal streamlines in the vicinity of the rotor and the die entry region. Fiber orientation is created in a circumferential direction by these helicoidal streamlines; close to the inner and outer surfaces of the tube, the fibers are parallel to the main extrusion direction, whereas in the mid‐thickness, they are oriented in the circumferential direction. It is demonstrated that the amount of orientation depends on rotor speed and die design. When using a short die and high rotor speed, an increased fraction of fibers are oriented in the circumferential direction. Polym. Compos. 25:331–341, 2004. © 2004 Society of Plastics Engineers.