The process of injection blow molding

The process of injection blow molding (IBM) is used for the production of hollow glass and plastic 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 bottles. The process is divided into three steps: injection, blowing and ejection.

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 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.

Common Bottle Types & Speeds

Common bottle types include tablet or pill bottles, liquid medicine, dropper bottles, injectables, jars, ovals, cylinders, Boston rounds, roll-on deodorant and mascara. Container resin types include HDPE, polypropylene and PET.

The process is ideal for small containers that require precise neck finishes. Blow molding rates typically range up to the 120 BPM range for the majority of applications. Bottles sizes become smaller as the molding speeds increase.

The SC Linear was originally designed with the standard Injection Blow Molded (IBM) container range in mind. This machine can typically handle the entire range of container sizes and speeds for IBM applications. A key part of the design was to consider the smallest end of the range i.e. vial or dropper bottles. SC Linear features include:

Flat profile conveyor chain with no gaps, to ensure small footprint containers remain stable

Vacuum conveyor with very small holes in its centerline, to allow precise stopping of indexing bottles at high speeds

Probe heads with standard diameters available down to 0.875” diameter

Small diameter rod reject cylinder to cleanly and positively reject small diameter containers

Reject and gate cylinders are built into the inboard conveyor rail for ease of setup

The side of the conveyor frame is flush to minimize the dead area for bottle side transfers to and from the leak tester

Integration of the SC Linear into the production line does require the setup of bottle transfers to and from the leak tester conveyor. For smaller containers, side transfers are recommended to minimize the dead space on which the bottles must travel. Care must be taken with the customer conveyor interface, and set up of the transfers, for the leak tester to operate efficiently. The Prime Sensor option is available to maintain a minimum backlog of containers across the upstream transfer.          

ALPS SST Linear Leak Tester with Integrated Takeout Conveyor

The ALPS SST Linear incorporates a blow molder takeout conveyor and indexing conveyor leak tester into an integrated system. The use of a common frame allows a quick and easy pushbutton adjustment for conveyor height changeovers; which are necessary on Injection Blow Molding lines where the bottle neck exit the blow molder at a fixed height.

The takeout conveyor section will accept a ‘pause’ input to index together with the bottle takeout function.

The takeout conveyor is driven by a frequency drive and controls are included to run in forward motion or reverse. An optional Counter/Diverter can be added to the end of the conveyor, to automatically count bottles into one of two boxes.