Blow moulding

 How blow moulding works

Blow moulding is a process used together with either extrusion or injection moulding. Blow moulding is accomplished in two steps:

  • Creating a tube of molten plastic, called a parison (the same term as used in glass-blowing)

  • Inflating the tube to the desired final shape.

Forming the parison can be done by either extrusion (used for thicker plastic bottles) or injection moulding (as in the case for the thin see-through softdrink bottles).

Blow moulding only uses thermoplastics. Stiffer and stronger materials are often used so that the walls of the product can be thinner.

Extrusion blow moulding step by step

In most cases of extrusion blow moulding, the process is organised for very high production operation for making plastic bottles. The sequence is automated and usually integrated with downstream operations such as bottle filling and labelling. It is usually a requirement that the blown container be rigid, and rigidity depends on wall thickness among other factors.

 

Step 1

A parison is created through extrusion moulding and fed between 2 parts of a mould.

Step 2

The mould is closed around the parison sealing off its ends. The one end is also sealed off by a blow pin.

Step 3

Air is blown through the blow pin into the sealed parison forcing it into the shape of the mould.

Step 4

The mould is separated and the blow pin withdrawn, leaving the new plastic blown product behind.

Injection moulding step by step

A variation of this process – called stretch blow moulding – is often used to make soft drink bottles.

 

Step 1

A parison is injection moulded around a blowing rod; Sometimes this parison is called a preform.

Step 2

The injection mould is opened and the preform is transferred to a blow mould.

Step 3

The soft plastic is inflated to conform to a chilled blow mould

Step 4

The blow mould is opened and the blown product is removed.

 Uses for blow moulding

Mostly, blow moulding is used to produce disposable containers for packaging and liquids.

That said, it is also used to manufacture:

  • large shipping drums for liquids and powders

  • large storage tanks

  • car gasoline tanks

  • toys

  • hulls for sail boards and small boats

DemaPlasTech

 

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DemaPlasTech have a wealth of experience in the South African plastics manufacturing industry and can help your business with a range of customised solutions to meet your needs. Our areas of expertise include:


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If you are involved in plastics manufacturing, let’s see how we can help your business.