The process of moulding and shaping hollow plastic parts is known as blow moulding. The process of blow moulding can be broken down into three main styles. These are:
- Extrusion blow moulding
- Injection blow moulding
- Injection stretch blow moulding
All three of these blow moulding manufacturing processes involves heating the plastic to high temperatures so that it melts and becomes malleable. From here the plastic is formed into what is known as a parison. This is a piece of plastic which is tubular in shape. Air is able to pass through the parison via a small hole in one end of the tube.
In the case of injection moulding and injection stretch blow moulding (ISB) the plastic is shaped into what is known as a preform.
Extrusion Blow Moulding
Extrusion blow moulding (EBM) involves melting plastic into a parison. The parison is then sealed in a metal mould which has been pre-cooled. Air then passes through the parison, blowing the plastic through the tube and filling the metal mould. The mould can be a variety of shapes and sizes.
If you’ve ever wondered how hollow plastic bottles and containers are made, the manufacturing process usually involves EBM. Once the plastic has cooled, the mould is removed and the parison is removed. The result is a plastic bottle or container which accurately resembles the metal mould.
- Production rates are fast
- Low cost on tools and dyes
- Handles can be easily added to the design
- Complex parts can be moulded easily
- Designs are limited to hollow constructions
- These parts can break easily
- Multi-layered parisons are used in order to increase strength and barrier properties, however the use of a variety of materials prevents the structure from being recycled
Injection Blow Moulding (IBM)
Injection blow moulding is most commonly used to produce hollow glass or plastic products on a large scale. The process follows three steps, namely injection, blowing and ejection.
This process requires the use of a core pin. Polymer is then injected onto this pin which is rotated onto a blow moulding station. When the pin reaches the blow moulding station the polymer is inflated and then cooled, solidifying the desired shape.
IBM is the least used method of blow moulding. It is predominantly used to manufacture small medical supplies and bottles.
- The injection mould neck provides superior accuracy
- Due to the difficult nature of controlling the centre of the bottle during blowing, IBM is only suited to small capacity bottles
- The material is stretched biaxially which means that there is no increase in strength
- Handles cannot be included in the design
Injection Stretch Blow Moulding (ISB)
ISB can be broken up into 2 methods; single stage injection and the two-stage method.
Single stage injection requires the use of 3 or 4 station machines while the two-stage method involves the initial moulding of the plastic into a preform. Injection moulding is used to accomplish this quickly and efficiently. These preforms include most aspects of the finished product such as bottle necks and threads, for example. At this stage the preforms can be packaged and reheated in a stretch blow moulding machine at a later stage.
The ISB process is typically performed by heating the preforms to high temperatures and then, using metal blow moulds, high pressure air is blown into the bottles. The purpose of this is not for shaping but for stretching. The stretching process is made possible through the use of a core rod which centres the mould during the blowing process.
- This process enables high volumes of a particular mould to be produced
- There is very little restriction placed on the design of the bottle
- Preforms can also be sold to third parties who can blow the bottles themselves
- High cost
- Lots of floor space is required
- Only suitable for round bottles
At Big Boy Plastics we offer a wide variety of blow moulding services. No matter the job, we have the facilities to make it possible. Whether it’s a small job or a large contract, let Big Boy Plastics make your design a reality