METHOD OF MOLDING THERMOPLASTIC PRODUCT ORIENTED TO HIGH DEGREE

摘要

A method for forming deep drawn highly oriented thin-walled thermoplastic articles including the steps of planarly supporting a sheet of at least partially crystalline thermoplastic polymeric material and establishing at least one differentially heated area within the sheet. The differentially heated area is to include an outer cool zone having a temperature range generally below the crystalline melt point of the thermoplastic material, a hot zone disposed within the outer zone having a temperature range generally above the crystalline melt point but below the complete melt point of the thermoplastic material, and an inner cool zone located centrally of the hot zone having a temperature range generally below the crystalline melt point of the thermoplastic material. The heated sheet is placed between a female mold unit and a forming mandrel with the inner cool zone generally axially aligned therewith. The mandrel is driven against the inner cool zone of the heated sheet and into the female mold unit so that the thermoplastic material is drawn radially inwardly toward the inner cool zone and around the mandrel forming an elongated generally cylindrical shaped preform having a central cavity. The material is longitudinally stretched a distance sufficient to cause at least a portion of the walls of the preform to undergo strain hardening while the outer cool zone maintains tension control of the sheet material throughout the forming process. The central cavity of the elongated preform is then subjected to internal fluid pressure to radially expand the preform against the interior surface of the female mold cavity. The fluid pressure is maintained for a time sufficient to allow the expanded material to cool and set.