Injection blow molding is a two stage process since the parison is produced in a separate operation. In the first process molten plastic is injected into a heated preform mold around a hollow mandrel blow tube or core rod. This is similar to insert injection molding. The workpiece for the second, blow molding, process is the preform-mandrel assembly. The preformed parison is placed in a larger mold cavity for blow molding. Between the preform production and blow blow molding processes a heated preform may be held in a temperature conditioning stage or a cooled preform re-heated. After blow molding the part is stripped from the core rod at an ejection station.
Raw Materials
- Polyethylene (Low Density) LDPE, LLDPE
- Polypropylene PP
- Polyethylene - Terephthalate PET
- Polyvinyl chloride PVC
- Polyethylene (High Density) HDPE
These factors are critical to this process:
- Shear & temperature dependent viscosity
- Temperature-dependent tensile strength on the pin
- Tensile elongation during inflation
- Crystallization kinetics on the core pin
- Crystallization kinetics during blowing and cooling
Examples of Application
- Bottles
- Jars
- Roll-on containers
Injection blow molding
The process of Injection Blow Molding (IBM) is used for the production of hollow glass and plasticbottles. The process is divided into three steps: injection, blowing and ejection. objects in large quantities. In the IBM process, the polymer is injection molded onto a core pin; then the core pin is rotated to a blow molding station to be inflated and cooled. This is the least-used of the three blow molding processes, and is typically used to make small medical and single serve
The injection blow molding machine is based on an extruder barrel and screw assembly which melts the polymer. The molten polymer is fed into a manifold where it is injected through nozzles into a hollow, heated preform mold. The preform mold forms the external shape and is clamped around a mandrel (the core rod) which forms the internal shape of the preform. The preform consists of a fully formed bottle/jar neck with a thick tube of polymer attached, which will form the body.
The preform mold opens and the core rod is rotated and clamped into the hollow, chilled blow mold. The core rod opens and allows compressed air into the preform, which inflates it to the finished article shape.
After a cooling period the blow mold opens and the core rod is rotated to the ejection position. The finished article is stripped off the core rod and leak-tested prior to packing. The preform and blow mold can have many cavities, typically three to sixteen depending on the article size and the required output. There are three sets of core rods, which allow concurrent preform injection, blow molding and ejection.
Another application of injection blow molding is in the production of soft elastic gelatin capsule for pharmaceutical applications. Two strips of gelatin are pressed together in a rotary die which cuts out the desired shape of capsule while the fill liquid is injected. Afterwards, they are cooled and dried to yield a firm, strong capsule.
Injection 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.
