METHOD OF FORMING MOLECULARLY ORIENTED PREFORMS

The invention relates to a method and apparatus for forming molecularly oriented plastic containers from generally cylindrical, hollow preforms with one open end formed by injection molding from a partially crystalline, molecularly orientable plastic for subsequent stretch blow molding. Melted material is injected into a preform mold at a predetermined fill rate controlled to minimize molecular flow orientation and further controlled to minimize residual stress which both are otherwise developed during injection. The preform is then reheated below the crystal melting point by radiant heat source to a temperature that intercrystalline structures are melted without melting the crystal nuclei. To avoid so-called edge effects resulting from the geometry of the heating zone, the preform decreases in thickness at both ends. The preform is then rapidly transferred to the mold in which it is stretched axially with a rod engaging its closed end and then rapidly quenched against a polished mold surface.