GB1354146A - Mixing apparatus - Google Patents

Abstract

1354146 Mixing extruder STERLING EXTRUDER CORP 13 July 1971 [3 Sept 1970 26 Oct 1970] 32693/71 Heading B5A [Also in Division B1] Mixing apparatus for plastics materials has a coaxial rotor 1 and stator 2 with respective external and internal opposite screw threads 8, 9 including at least one "extensive" mixing section (with narrow lands and wide grooves in which the emphasis is on dispersal rather than shear coating) the depth of the opposite grooves varying at least once, the one from a minimum to a maximum and the other from a co-operating maximum to a minimum, the total depth of the two opposed grooves becoming progressively smaller towards the discharge end as indicated by the extension lines 18, 19. As shown there is a "charging" section, six "extensive" mixing sections with an intermediate venting section, and a final "intensive" mixing section 11, with lands wider than the grooves, where primarily shear working takes place. There are zone controlled heaters and cooling coils 14, 15 and the rotor has cooling channels 13. Extensive mixing.-In the charging section the stator is smooth and the rotor preferably has a single start thread of one diameter pitch. In Stage I both rotor and stator have a two-start thread, that of the rotor being of the same pitch as in the charging section. In Stage II the rotor has a single or double start thread of reduced pitch, the stator retaining a two-start thread. In Stage III the rotor has the same thread as in Stage II while the stator charges to a single start. In Stage IV the roror pitch is increased while that of the stator remains unchanged. Melting is completed in these first few stages and the material may then pass to a stage where it is vented to atmosphere or by a pump 12, the rotor groove depth being a maximum and the stator smooth. Stages V and VI follow. The relative depth of opposite stator and rotor grooves varies in each stage but the thread interface lies throughout on a cylinder 17. The material is cooled before entering an intensive mixing section which is tapered and may have a groove depth which varies twice between a minimum and a maximum in both rotor and stator, or they may both have smooth surfaces. The clearance in this section may be altered by axial adjustment of the rotor. There may be an extension die 10. The stator may be made up of separable portions corresponding to the respective stages.