Research Of Mixing Performance For Soft Shearing Twin-Screw Elements

The shear stress should be controlled when processing heat-sensitive or shear rate-sensitive polymer material. Flow field of five different kinds of soft shear screw configurations were simulated by polyflow. Pressure field, weighted average shear stress and weighted average shear speed were obtained by the simulation of five kinds of soft shear screw configurations.The results showed that the weighted average shear stress of the configuration of various clearance rotor(VCR) and FTX polygon was minimum, and the weighted average shear stress of the configuration of kneading disks and non-intermeshing kneading disks with a staggered angle of150°was maximum. The other three soft shear screw configurations, in order of the weighted average shear stress, from small to large were the configuration of S type element and FTX polygon, the configuration of kneading disks and non-intermeshing kneading disks with a staggered angle of90°and the configuration of kneading disks and non-intermeshing kneading disks with a staggered angle of30°. The five kinds of soft shear screw configurations, in order of the weighted average shear rate, from small to large were the configuration of VCR and FTX polygon, the configuration of S type element and FTX polygon, the configuration of kneading disks and non-intermeshing kneading disks with a staggered angle of90°,30°and150°. The configuration of kneading disks and non-intermeshing kneading disks with a staggered angle of30°had the most little differential pressure between exit and entrance, and the configuration of kneading disks and non-intermeshing kneading disks with a staggered angle of150°had the max differential pressure between exit and entrance. The weighted average shear stress of five kinds of soft shear screw configurations were smaller than normal screw element, so they could be used in soft shearing processing.The mixing performance for five kinds of soft shear screw configurations was verified by experiments. The results showed that the number average particle diameters of five kinds of soft shear screw configurations were all bigger than normal screw element, which suggested that the average shear stress of five kinds of soft shear screw configurations were smaller than normal screw element. The experimental data were in good agreements with the simulation results.