Patent GB-963121-A (GB)
Title: Improvements in or relating to extruder dies
Inventor: EBERMAN AUGUSTUS HARVEY
IPC: B29C48/08
Filed: 1962-08-15
Abstract: 963,121. Extrusion dies. OSCAR MAYER & CO. Inc. Aug. 15, 1962, No. 31282/62. Headings B5A and B5B. An extrusion die for use in forming a continuous sheet or film from thermoplastic material comprises a generally cylindrical internal material delivery passageway closed at one end and arranged for communication at the other end thereof with material supply means which passageway is of decreasing diameter in a direction towards the closed end, and a sheet-forming slot extending from said passageway longitudinally thereof to a face of said die, said slot being in radially directed communication with said passageway at least substantially throughout the length of said passageway and opening outwardly of said face for extrusion of said material therethrough, the effective material flow area of said slot and of said material delivery passageway being related to maintain a virtually constant and equal extrusion time rate of flow of material upon entry thereof into said material delivery passageway to any point along the terminus of said slot along said face and through any portion of said passageway and said slot. The die may be provided with separate fluid circulating passageways through which a heating medium is passed. Preferably the internal material delivery passageway has a single longitudinal axis, the sheet forming slot extending radially from said passageway to a face of said die and said material delivery passageway in the direction of its closed end being angled throughout its single longitudinal axis towards said face. The slot may be of constant depth and of diminishing width in a direction towards the closed end of said passageway. As shown (Fig. 2) the die may comprise interconnected plates 16, 17, each of which in combined surfaces thereof is provided with a semicircular groove 18, 43, said grooves being combined to define a cylindrical internal material delivery passageway 26 closed at one end thereof (28, 45, Figs. 3 and 6) and arranged for communication at the other end thereof (25, 42) with material supply means, said passageway having a single longitudinal axis, and a triangularly shaped, relatively shallow recessed area (30, Figs. 2 and 6), said area being in communication with said passageway throughout an entire longitudinal margin thereof while further opening outwardly of an outer face of said die (31, Figs. 2 and 6), said passageway being angled toward said outer face in the direction of its closed end (28, 45). Separate heating fluid circulating passageways may be provided in each of said plates (37, 35, 32 in Fig. 3, and 47, 50, 52 in Fig. 6) including interconnecting passageways 39, 46 for delivery of heating fluid from one of said plates to the other. Alternatively (Figs. 7, 9), the internal material delivery passageway is forked (62, 63) and extends in generally Y-shaped outline, each of said forks having a single longitudinal axis, the forks of the passageway being of decreasing diameters 63, 64, 65 in a direction towards the closed ends thereof, and a sheet-forming slot 66 extending from and between said forks to a face of said die 67, said slot being in radially directed communication with said forks throughout the lengths thereof and being of uniform depth while opening outwardly of said face, the clearance in said slot and the diameters of said forks being related to maintain a virtually constant and equal extrusion time rate of flow of material upon entry thereof into said material delivery passageway to any point along the terminus of said slot and along said face and through any portions of said forks and said slot. The material delivery passageways 26, 27, 28, 42, 43, 44, 45 and 62, 63, 64, 65 may be continuously tapered instead of being stepped as shown. The apparatus is especially suitable for the extrusion of heat-sensitive thermoplastic materials, e.g. vinylidene chloride copolymers.