OPTIMIZATION OF THE EXTRUSION PROCESS FOR GLASS-FIBER-REINFORCED TUBES

The resistance of short-fiber-reinforced thermoplastic tubes to intern al pressure is strongly related to fiber orientation. A new way to inc rease the degree of orientation in the hoop direction is presented. It consists of injecting a lubricant at the surface of a diverging die, A calculation of flow and fiber orientation in a lubricated die with a divergent final land shows that extensional deformations, which tend to orient the fibers perpendicular to the flow, take place on the enti re thickness; in contrast, without lubricant, shear deformations near the surface orient the fibers in the flow direction. Various dies are tested with a 30 wt% short-glass-fiber-reinforced polypropylene. Obser vations show that, with-the lubricated diverging die, the fibers are o riented mainly in the hoopwise direction throughout the tube thickness . Consequently, mechanical properties are increased in this direction, The resistance of the tube is increased by about 40%.