APPARATUS FOR PARISON EXTRUSION

摘要

A process and apparatus for programming the wall thickness of thermoplastic parison extrusions for subsequent conversion to blow-molded plastic articles. The apparatus for forming the parison includes a mandrel or core pin and a die assembly wherein the mandrel is made from a material having predictable and repeatable elastic properties and has enclosed therein a piston and piston rod. The piston rod extends the full length of the mandrel and is connected to the piston on the rod's opposite end. The piston is contained in a chamber that is connected to a hydraulic fluid source. The wall thickness of the formed parison is changed by varying the size of the extrusion orifice through expansion or contraction of the mandrel produced by the application or release of hydraulic pressure on the top of the piston. The die assembly is particularly suited for extrusion of parisons from heat sensitive thermoplastic material such as polyvinyl chloride since no sliding surfaces are utilized which are known to trap and cause degradation of heat sensitive thermal plastics.