| 摘要 |
An improved apparatus for extruding an expandable thermoplastic composition onto an elongated article is disclosed comprising an extruder housing; a cylindrical extruder screw axially positioned within an extruder barrel within the housing; a device for heating the expandable thermoplastic composition passing through the hollow chamber; a gas input for supplying an inert gas into the extruder barrel; and a die head attached to the output end of the extruder housing through which an elongated article is passed for the extrusion thereon of the expandable thermoplastic composition. The cylindrical extruder screw which is of a conventional length, comprises a shaft portion from whose circumference extend in addition to the usual helically wound conveyor members, at least two shearing members whose surface configurations with respect to the surface of the hollow chamber in the housing, and longitudinal positions with respect to the gas input, provides a pressure retention chamber into which the inert gas is fed to elevate the pressure applied to the expandable thermoplastic composition for increasing the quantity of inert gas dissolved therein.
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