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January 2019
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Common Pet Preform Molding Method

There are several common molding methods for Pet Preform: extrusion blow molding (EMM), injection blow molding (IBM), stretch blow molding (SBM), etc.

Extrusion Blow Molding – In extrusion blow molding, a circular hollow tube or parison is formed by an extruder. A cavity consisting of two halves closes and pinches one end around the parison. The compressed air expands the parison to conform to the wall of the cold mold cavity. When fully cooled, the mold opens and the container is removed and trimmed of excess plastic or flash. When the parison is clamped off by the mold, the basic feature of extrusion blow molding is formed – the flash edge. Since most of the resin can be reprocessed, flashing is not wasted, but rather used as a “re-grinding” wall distribution, thickness and weight can be controlled by parison programming. When the parison is extruded, programmed changes in the relationship between the mandrel and the mold can be used to transfer material from a heavier, stronger area to a lighter, weaker area. This approach greatly helps maximize container performance and minimizes container weight and cost.

The injection blow molding-injection blow molding process (IBM) is used to produce hollow plastic articles. Injection blow molding is basically carried out in three stages. In the first stage, molten plastic is injected into the mold cavity to produce a preformed parison. The preform is shaped like a test tube but has a molded threaded opening at the top. The preform is then transferred to a second blow molding stage. Air is blown through the core pin to expand the preform against the cold mold cavity. The container is then transferred to a third station for discharge. There are two main types of processes:

One-step injection molding – the molten polymer is injected into the final shape of the container in a cold mold and then released.

Two-step injection molding – the first step in injecting molten plastic into a mold, resulting in the creation of a preform. The cold preform is then placed on another machine, enclosed in a mold, heated, stretched with a pin to the desired length, and then blown into the shape of the selected mold.

Stretch blow-stretch blow molding is based on injection molding or extrusion blow molding processes. In either case, the preform is molded and then transferred to the blow cavity. The parison is biaxially stretched during the blow molding process to orient and align the molecules. This orientation increases the gas barrier, hardness, clarity and impact strength of the container. As a result, the container can be lightened. Stretch blown resins include PET, PVC, and polypropylene. PET is by far the most commonly used in carbonated beverage containers.

Injection molded-injection containers can be straight or tapered, narrow or wide mouth shapes such as cans, buckets and vials. The material is injected into a cavity in which the pressure forces the resin to conform to the mold body. The container is able to maintain tighter dimensional tolerances and a more uniform wall distribution. A wide variety of resins can be processed by injection molding, the most popular being polypropylene, styrene and polyethylene.

Multi-Layer Bottles – Co-Extrusion – The latest blow molding machine technology, co-extruded multi-layer bottles bond various plastic resins and bonding layers together to produce barrier and thermal stability bottles for hot filling , sealed food. Currently EVOH (ethylene vinyl alcohol) is used as an intermediate layer due to its barrier properties. Polypropylene or polyethylene is used as the inner wall and the outer wall due to its heat resistance and transparency. The hot filling process creates a vacuum that draws in the side walls of the plastic container. In bottle design, this effect must be compensated, either by obscuring the notch, or by using stiffening ribs or panels in a round bottle design. Possible applications include: juice, sauce, jam, toppings, mayonnaise and pickles.

Choosing a reliable China Pet Bottle manufacturer allows you to get more reliable products at a lower cost, so what are you still hesitating? Come and contact us.