What is Blow Molding of Plastics? (And how does it work?)

What is Blow Molding of Plastics

What is Blow Molding?
Definition: Blow molding of plastics is a manufacturing technique that is used to create hollow plastic parts by filling the heated plastic tube with air until it occupies a desired shape.

By using blow molding, the parts like bottles and containers with different shapes can be manufactured. 

Plastic blow molding is also used in manufacturing a wide range of small and large components like small water bottles, shampoo bottles, as well as large storage drums, tubes, etc.

Well, this was just a simple overview. Let’s see the entire plastic blow molding technique in detail using a schematic diagram.

Let’s dive right into it!

How does blow molding work?

how does blow molding work

Blow molding is a modification of the plastic extrusion process and injection molding process.

Generally, the raw material (or polymer) used in blow molding is a thermoplastic polymer.

First, the raw material is in the form of solid small pellets or granules and then it is melted down.

This molten polymer is then formed into a hollow tube, which is known as Parison.

The extruded tube diameter (diameter of parison) is smaller than the size of the mold cavity.

In blow molding, the parison can be made in many different ways.

This parison is clamped between the molds and then it is inflated by blowing hot pressurized air in it.

The air is blown until the parison takes the inner shape of mold cavity.

The pressure of the hot air can range between 350 kPa to 700 kPa.

After this, the blow molded plastic is allowed to cool down and then the molds are separated.

The solidified plastic is ejected out and in this way, the blow molded plastic is obtained.

Blow molding products/applications

Blow molding products or blow molding applications are mentioned below.

#1) Plastic containers of various shapes

Blow molding products

#2) Liquid soap bottles

Blow molding products

#3) Shampoo bottles

Blow molding products

#4) Milk bottles

Blow molding products

#5) Plastic drums

Blow molding products

#6) Plastic tubes

Blow molding products

#7) Storage tanks

Blow molding products

Besides these above mentioned products, many other products can be manufactured by using blow molding.

Blow molding materials

Generally the thermoplastic materials are used in Blow molding. These materials are listed below.

  1. Polypropylene
  2. Polyvinyl chloride
  3. Polyethylene terephthalate
  4. Low density polyethylene
  5. High density polyethylene


What is Parison in blow molding?
In blow molding, Parison is a heated hollow tube that is made by extruding the thermoplastic polymer. This hollow tube is inflated by passing a pressurized hot air until it fills the mold cavity and takes a desired shape.

What materials are used in blow molding?
Blow molding is used to form thermoplastic polymers like polypropylene, PVC, polyethylene terephthalate, etc.

What are the types of blow molding?
There are 3 types of blow molding techniques.

  1. Extrusion blow molding
  2. Injection blow molding
  3. Stretch blow molding

External links:
Blow molding: Image by Basant Nayak, CC BY-SA 4.0, via Wikimedia Commons
Plastic barrel: Image credits indiamart
Plastic storage tanks: Image credits Vikas tanks

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