Blow Molding Process
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Blow molding is the process of forming hollow products by expanding a hot
plastic parison against the internal surfaces of a mold. Different blow
molding processes offer different advantages, based on the material used,
performance requirements, production quantity, and costs.
Plastics are used to fabricate a wide range of blow molded parts, including
small bottles for household products and personal care, dairy products and
carbonated drinks, small containers for industrial goods or chemicals, fuel
tanks, jerry cans, IBC, large tanks, drums, and car dashboards.
There are various kind of blow molding processes:
- Continuous extrusion blow molding: In the continuous process,
a stationary extruder plasticizes and pushes molten polymer through the
head to form a continuous parison. For large part blow molding,
accumulators are used to prevent sagging of the parison.
- Intermittent blow molding: In the intermittent process, the
melt is accumulated in the barrel and pushed out in one shot.
Intermittent blow molding is used in the fabrication of dairy bottles,
amongst other applications, because of its high production speed.
- Co-extrusion blow molding: Co-extrusion blow molding makes
it possible to combine materials with different properties to create a
finished product most suitable for a particular application. This
process can be used to fabricate products which contain several layers
in their wall structures. The various parts of the structure can be
optimized for the best balance between properties and cost.
- Injection blow molding: Injection blow molding starts with
an injection molded pre-form, which is then reheated, and blown into its
final shape in a mold.
- Injection stretch blow molding: Injection stretch blow
molding starts with an injection molded pre-form which is reheated, and
stretched with a pin while simultaneously being blown in a mold. This
conversion process is typically used to produce PET bottles.
- 3-D blow molding: 3-D blow molding is a recent development
in which a robot arm is used to position the parison in a
three-dimensional mold, prior to being blown. Advantages are low
trim-off, and the ability to produce complex shapes. It is typically
used to produce automotive parts.