GB1434343A - Filtering - Google Patents

Abstract

1434343 Metering and filtering plastics P G KALMAN 19 April 1973 [19 April 1972] 48871/75 Divided out of 1433867 Heading B5B [Also in Division B1] Molten plastics is delivered through a filter 501 and a flow regulator 500-512 to a spinneret nozzle, the regulator comprising a chamber 502 whose volume is variable without resilience, volume variations being monitored and used to control the flow to or through the filter to stabilize the chamber volume and hence achieve a uniform flow to the nozzle, the chamber being located in a constant temperature bath. As shown chamber 502 is a ductile bellows on which a constant external pressure is maintained by weighted piston 510 pressurizing the liquid in bath 505. Movement of piston 510 detected by potentiometer 512 controls a delivery screw, variable restrictor or variably heated tube supplying plastics to filter 501. If filter 501 is of the movable ribbon type described in Specification 1,181,075, potentiometer 512 could control movement of the ribbon so that flow therethrough is restricted by clogging. Plastics leaves chamber 502 through a flexible capillary 503, which may have fins 504 and serves to reduce pressure fluctuations and to bring the plastics to the bath temperature. The bath contains oil and has a cooling coil 500, an electric heater 507 and a magnetic stirrer 508. Piston 510 may rotate to reduce axial drag. In Fig. 2 (not shown) the bath is open and the bellows 502 is pressurized by an external spring. The bellows volume is monitored by a differential transformer (517) or by recording the bath level, to control the flow. In Fig. 3 (not shown) plastics flows through two bellows-capillary units in series, located in separate baths pressurized by separate spring-loaded pistons, whose differential level is monitored to control the flow. In place of the bellows described, ductile tubes, diaphragms or hydraulic cylinders may be used. Capillaries may be replaced by collapsible tubes or variable orifices. The spinneret nozzle may be mounted directly on the bath to control the nozzle temperature.