Method of blow molding and then exhausting hollow plastic articles

Claim 1

In a method of manufacturing a hollow plastic article of the type comprising the steps of extruding plastic material into a tube which is utilized to form unit parisons, accommodating each unit parison in a closed metal mold having a cavity therein, sealing the upper and lower ends of the unit parison accommodated in said metal mold, blowing pressurized gas into said sealed unit parison for blow molding the same in said metal mold, the improvements comprising the steps of: transversely inserting a blunt nozzle tube through said metal mold until the inner end of said nozzle protrudes into said cavity 2 to 5 mm, but not through the side wall of said unit parison after the upper and lower ends of the unit parison have been sealed; ejecting pressurized gas through said nozzle against the outside of the wall of said unit parison sealed in the metal mold, thereby forming a gas inlet opening through said side wall of the unit parison and inflating said unit parison against the inner wall of the cavity by the pressurized gas ejected into said unit parison through said inlet opening; providing a transverse exhaust opening for said metal mold at a position corresponding to a portion of the molded article to be cut away after the hollow article has been formed; providing a mold configuration at said transverse exhaust opening which will result in reduced stretching of the parison during said inflating and thereby forming that portion of the wall of the molded article at said transverse exhaust opening to be thicker than the rest of the wall of the molded article, said thicker portion being sufficiently thick to be sustained in a semi-solid state during blow molding of said article; forming an exhaust port through said thicker wall portion by raising the internal pressure within the molded article until said semi-solid thicker wall portion is forced open at said exhaust opening; retracting said blunt nozzle tube away from the molded article; and exhausting the pressurized gas from the molded article through said exhaust port and said transverse exhaust opening, thereby removing the gas from the molded article and enhancing the cooling thereof.