Knowledge You Should Know About Twin Screw Extruder
Twin screw extruder may be divided into different zones which are distinguished
. A melting zone, a mixing zone, a degassing zone and a discharge zone may be arranged in line from an extruder inlet to the outlet. As a rule, the screws have different configurations adapted to the particular zone, over their length. The screw turns may have different pitches and spacing in the zones and may be provided with interruptions, baffles or the like. The screw turns may be replaced by meshing toothed disks or kneading blocks particularly in the melting and/or the mixing zones in order to obtain a particularly intensive mixing of the powder in the melt and to homogenize the melt. The screws usually have continuous screw turns in the discharge zone which mesh with slight roll and flank clearances, thereby preventing any back flow of the melt and producing the necessary pressure for pressing the melt into a molding tool attached to the extruder.
It is an object of the invention to design a twin screw extruder so that it will deliver the melt at a temperature and viscosity largely uniform over the entire cross section area, to a closed tool. According to the invention the twin screw extruder is designed with an extruder housing having a dual cylinder shaped internal cross section. Two extruder screws are located in the housing configured to be driven in opposing directions. The screw turns and screw lands of the extruder screws and transport an extrusion material to an extruder outlet or a molding tool attached to the extruder. During transport the material is heated and plasticized.
While the aforedescribed embodiment of the invention concerns a twin screw extruder with axially parallel cylindrical extruder screws, the invention is also applicable to extruders with conical or doubly conical screws. In this case the cell rotors 9 must be designed as an extension of the extruder screws with the appropriate conicity and with converging axes.