| 摘要 |
1,165,985. Screw extruders. NRM CORP. 7 Dec., 1967 [8 Dec., 1966], No. 55664/67. Heading B5A. A screw extruder comprises a screw having, in the downstream direction, feed, compression and metering zones 12, 15, 18 of a first stage, a transition zone 20, and feed, compression and metering zones 35, 38, 40 of a second stage, the transition zone 20 comprising a flight 21 which is a continuation of upstream flight 13 and a second flight 22 of greater pitch than flight 21 and which defines therewith a channel 25 of decreasing axial width and a channel 27 of increasing axial width, the changes being considered in the downstream direction. Furthermore, flight 22 is of lesser diameter than flight 21, has an inclined and rounded leading edge (60, 61), Fig. 3 (not shown), and provides a gap (29) between the flight and barrel (2). Screw core 23 within transition zone 20, Fig. 2, decreases in diameter downstream. Other diametral changes in the core are evident from the Figure. In a modification, Figs. 4, 5 (not shown), the second stage of the screw is also provided with a transition zone and comprises flights (13<SP>1</SP>) and (45). The core of the screw within zone (38<SP>1</SP>) as in zone 38, Fig. 2, increases in diameter downstream. The screw extruder may comprise a feed inlet (5), Fig. 1 (not shown), a gas outlet (62) to which vacuum may be applied, a breaker plate (7) and die (8). The extruder is particularly intended for use with low density polyethylene, elastomeric polyvinyl chloride and polystyrene. |
