njection blow molding is part injection molding and part blow molding. Injection blow molding is generally suitable for smaller containers and absolutely no handles ware. Injection blow molding is often used for containers that have close tolerance threaded necks, wide mouth openings; solid handles, and highly styled shapes. Injection blown containers usually have a set gram weight which cannot be changed unless a whole new set of blow stems are built. Generally injection blow molded container’s material is distributed evenly throughout, and generally do not need any trimming or reaming. The air is injected into the plastic at a rate between 75 to 150 PSI.
• Injection molding can be broken down into three stages.
• The first stage is where the melted plastic is injected into a split steel mold cavity from the screw extruder.
• The mold produces a preform parison which resembles a test tube with a screw finish on the top.
• The preform is then transferred on a core rod to the second part of the injection blow molding stage. The preform is then placed inside another cold and usually aluminum blow mold cavity.
• Air is then injected through the core rod till the preform takes the shape of the cavity.
• While still on the core rod, the container is then transferred to a desired location for the third stage, where it is ejected from the machine.
Injection blow molding:
(1) parison is injection molded around a blowing rod;
(2) injection mold is opened and parison is transferred to a blow mold;
(3) soft polymer is inflated to conform to a blow mold; and
(4) blow mold is opened and blown product is removed.