1348410 Casting composite articles; making extrusion dies MATCON Inc 19 April 1971 [11 March 1970] 23339/71 Headings B3A and B3F [Also in Divisions B4-B5] A die 200, Fig. 7, for the extrusion of plastics comprises, a liner 150, the inner wall whereof defines the extrusion passage including a transition portion T, which is configured exponentially (as in Fig. 9) in the axial direction, between an inlet opening 160 from the extruder and the commencement of a land portion L, so that a constant fractional area reduction is obtained of the cross-sectional area of the passage per unit distance towards the land portion L. The liner 150 is made to the configuration of a stretched elastomeric sleeve 72, Fig. 2, which is secured by clamps 76, 80 to a ring member 66 and a plug member 78, respectively defining the opening 160 and the opening of the land commencement, the member 78 being secured to the base 52 of a stretching frame 50, and the member 66 to a plate 62 which is upwardly displaced to effect the stretching by pressure on fittings 86, and is supported by nuts 60 on uprights 54. A cast 85, of meltable or water soluble material, e.g. plaster, is obtained of the inner or outer surface of the stretched membrane 72, preferably with the opposed surface thereof supported, e.g. within a tank, by a preferably liquid material of a specific gravity similar to that of the plaster. The liner 150 is then fabricated, e.g. by investment casting, or powder metallurgy techniques, or as in the described embodiment by coating the cast 85 and part of the member 78 with the liner material, effected by flame spraying a coating of a pure or alloy metal, which may be thicker in the region of the inlet 160 than in the land region L, on to the cast 85 (of the inner membrane surface) during rotation thereof whilst supported between chucks, Fig. 3 (not printed). After removal of the cast 85, e.g. by heat or dissolving thereof, and of the member 78, e.g. by melting, the liner is assembled within a steel housing shell 200 against a plate 180, together with surrounding heater elements 190, sensor elements 194 (and optionally cooling elements) connected to heating and sensor units 214, 212, and steel or concrete 220 is then cast within the shell around the liner 150 to complete the extrusion die. The concrete 220 may be introduced through a shell port 207 under pressure or vacuum and with vibration, with venting through port 209, to form the completed extrusion die after removal of plate 180. Where the coefficient of thermal expansion of the material 220 is low, the liner 150 can be pre-stressed to its extrusion operating temperature. The land portion L of the die liner may be made of constricting form intermediate its ends, by replacing the member 78 of Fig. 1 by spaced apart clamping members, Fig. 8 (not printed), between which the membrane is stretched to assume the required configuration which is then formed as part of the cast 85. Fig. 13 shows a cross-section through a die comprising a circular inlet from the extruder, with an L-shaped land 170. The die may be employed with a single screw extruder, the barrel whereof is provided with a venting means for moisture and condensation and a plurality of surrounding heating elements, and which discharges to the die via a breaker plate.
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