Verfahren und Vorrichtung zur Steuerung der Stroemungsmittelfliessrate

1,262,285. Screw extruders. IMPERIAL CHEMICAL INDUSTRIES Ltd. 14 March, 1969 [28 March, 1968], No. 14964/68. Heading B5A. In a screw extruder, flow of material through nozzle 2, Fig. 4, is maintained substantially constant during temporary stoppages in the flow of material to the die from screw 4, e.g. during -the change of filters 5, by the provision of an accumulator 16 and the working therein of a piston 17 in timed relationship with the stoppage. As shown, material is transferred to accumulator 16 via valve 23, by-pass 22 and non-return valve 21 in piston 17. When a stoppage occurs valve 23 is closed and piston 17 is depressed. Baffles, (not shown), may be provided in connecting piece 13 to promote flow along by-pass 22. For a simplified arrangement, Figs. 1 and 2 (not shown), the by-pass arrangement is dispensed with, material flowing directly into the accumulator. In another embodiment, Fig. 3 (not shown), nozzle (12) is arranged telescopically with respect to connecting piece (20) and is moved towards the screw during a stoppage. In a further embodiment, Figs. 5 and 6 (not shown), a hydraulically operated piston (27) is situated within nozzle (26) and is moved towards the extrustion orifice during a stoppage. In a final embodiment, Fig. 8, a distensible member 34 encloses a recess 33. During a stoppage, hydraulic fluid is injected into the recess via a channel 35 to distend member 34 as shown. Extrudable material mentioned include rubbery materials and glues and in particular resins such as poly ethylene, polypropylene, polystyrene, P.V.C., polyamides and polyesters.