| A new high-efficiency mixing (HEM) section for single screws was developed to boost outputs of polyolefins with smooth or grooved feed sections. Kiefel Extrusion in Germany (U.S. office in Wrentham, Mass.), makes the HEM with a series of mixing rings perforated by holes in the direction of flow. Each ring starts at the root of the screw, tapers to a shear gap —like a land between the ring and barrel wall—then forces the melt to pass through a series of holes bored at an angle to exit near the barrel wall. Melt accelerates as it crosses the shear land and then again as it passes through the holes. The shear gap is typically 2% of the screw diameter. The mixer consists of four mixing rings 2D long, but more rings can be used. Kiefel says the benefits are simultaneous mixing and shearing for excellent dispersive and distributive mixing and homogenizing of melt temperature. The screw was also cut deeper to increase throughput while providing energy savings of 10% to 20%. (508) 384-1200 • www.kiefel-extrusion.com |
