Extruder for thermoplastic plastics has filter housing with piston having opening which aligns with screw and opening of filter housing when moved to servicing position

摘要

A filter housing(3) with melt outlet(15) mounted on the extruder barrel(2) has a piston(10) between the extruder outlet(9) and melt outlet. The piston has control sections(11.1,11.2,11.3), one(11.1) of which has a filter insert(12) and another(11.3) has a screw opening(14) through which the extruder screw(6) is guided. In a servicing position of the piston the screw opening is aligned and with an opening(19) in the filter housing and extruder outlet. A third control section(11.2) of the piston between the filter insert(12) and screw opening(14) has a solid cross-section which shuts-off the extruder outlet(9). The distance between the first control section(11.1) with filter insert(12) and third control section is such that the extruder outlet can be blocked off while the filter is exchanged outside the housing(3). A linear drive unit(21) moves the piston into either the extrusion, filter exchange or servicing position. An adjustable stop(31) holds the piston or linear drive in the servicing. The filter housing has a plug(18) which closes the servicing opening(19) and has a right angled melt channel(22) at the inner end. The melt channel connects the melt outlet with a chamber(17) in the piston holding the filter insert. A shut-off valve is assigned to the melt outlet in the filter housing. A second moving piston with a second filter insert may be located in the filter housing parallel to the first piston(10). During extrusion the second piston with filter insert in the extrusion position is connected to the extruder outlet and melt outlet via by pass channels.