Engineering Workshop Material Science

Blow Molding Process-Pressure Distribution, Applications, Differences etc.

Blow Molding: It is a manufacturing process by which hollow plastic parts are formed. It is also used for forming plastic containers, plastic buckets, bottles or other hollow shapes.

It is applicable for thermoplastics only.

Blow Molding Diagram:

The figure shown below illustrates the complete Blow Molding Process in A, B and C segments. It generally consists of

Blow Molding
Blow Molding
  1. The feed from the Extruder
  2. Melted Plastic
  3. Extruder Head
  4. Airtube
  5. Parison(Tubular shape of hot plastic)
  6. Mould
  7. Air Pressure
  8. End Product.

Blow Moulding Process-Pressure Distribution, Applications, Differences, etc:

The Feed from the Extruder is given as an input into the Blow Molding Machine. The feed acts as the melted plastic and it is to be passed through the extruder head section and forming it into a parison.

The parison is a tube-like piece of plastic with a hole at one end through which compressed air can pass. The parison is to be passed through the mold. The Cope and Drag portions of mold are to be pressed against each other and at the same time compressed air is to be passed from the air tube.

By blowing high-pressure air on the soft sheet(parison), it will bend according to the internal shape of the mold and deposits on the internal surface of the mold and achieve the shape of the component. By the cooling process, the sheet will regain its hardness.

This is how you can get the final product in the segment C as shown in the fig.

Pressure Distribution(P):

  • Water Bottles ;P<1 bar
  • Plastic Buckets;P=1-2 bar
  • Large Liquid Containers; P=2-5 bar

The simple analysis of the component can be produced with a good dimensional accuracy of the product

Note:

  • Difficult to produce Complex geometry of the components with good dimensional accuracy.
  • To produce high thickness plastic parts, high blowing pressure is required.
  • If the shape of the mold is complex that implies result distribution is non-uniform that implies compaction of the film is non-uniform and that implies thickness is nonuniform and that implies dimensional accuracy is low.

Blow Molding Products/Applications of Blow Molding:

The applications are as follows.

  • Water Bottles
  • Plastic Buckets
  • Liquid Containers
  • Plastic Cups
  • Mugs etc.

Difference between Injection Molding and Blow Molding:

blow molding is used to produce hollow singular containers, such as bottles. On the other hand, injection molding is used to produce solid pieces, such as plastic products.

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