| 摘要 |
An annular extrusion die for extruding tubular thermoplastic materials, such as foamed thermoplastic, which incorporates an internal spider mandrel and a novel choke ring for eliminating striations in the extruded thermoplastic material while imparting an improved control over the uniformity in the gauge or thickness of the extruded plastic material. In order to more accurately control the uniformity in the gauge of the extruded plastic material, rather than varying the width of the gap or restriction in the die flow passageway formed by the choke ring which, in response to even minor changes in the gap width considerably changes the flow quantity, may overcompensate or overcontrol variations in the gauge thickness; there is varied the length of the land of the choke ring in the direction of material flow, in effect, in the machine direction, downstream of the spiders supporting the internal mandrel.
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