| 摘要 |
The technique uses an extruder for delivering a supply of softened thermoplastic resin material containing a foaming or expanding agent, the resin material being under pressure and therefore unexpanded in the extruder, but being delivered into an unconfined zone of lower pressure for partial expansion. The partially expanded resin material is drawn by a puller mechanism through a chilled shaping or sizing die of a cross sectional dimension smaller than that of the material in the unconfined zone. The material drawn into the sizing die continues its expansion in the interior of the profile with resultant development of porosity in the core of the profile while the surface layer is cooled and hardens as a substantially unexpanded structural shell.
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