Pumping section
It is, therefore, a general object of the present invention to provide a novel rotary screw extruder which minimizes or reduces problems of the type previously noted. It is another general object of the present invention to provide a novel method of extruding hygroscopic synthetic resinous material into a finished product without a preliminary dehumidification.
According to a preferred embodiment of the single screw extruder, a rotary screw extruder, intended to substantially accomplish the foregoing objects includes a barrel provided with at least two vent openings which are spaced apart axially of the barrel which receives a rotatably mounted screw. One end of the barrel is provided with a conventional die orifice and the other end is provided with an opening through which particulate materials may be supplied to the rotatable screw. The screw includes a first pumping section which receives the particulate material from the feed section and which plasticizes the particulate material and controls the rate of flow of the material through the extruder device.
The sheet production extruder includes a second pumping section downstream of the first pumping section which has a flow capacity greater than the flow capacity of the first pumping section. Between the first and second pumping sections is a vent section which communicates with one of the radial vent openings of the extruder barrel. Downstream of the second pumping section is a third pumping section which has a flow capacity that exceeds the flow capacity of the second pumping section. Between the second and third pumping sections a second vent section is provided which is aligned with the second radial vent opening of the extruder barrel. A reduced pressure source is connected with the radial vent openings of the extruder barrel and thus creates a reduced pressure section over a substantial length of the extruder barrel. Since the second pumping section's flow capacity is greater than the flow capacity of the first pumping section, the material being pumped through the second pumping section does not completely fill the channels of the screw. Accordingly, a continuous passage interconnects the two vent sections within the extruder barrel.