Manufacturing Processes - Blow Moulding Process
Blow Moulding Process
The blow moulding process fits in the general manufacturing processes category of 'forming'. A heat softened hollow plastic blank, sometimes referred to as a 'parison' is clamped between two mould halves. Air is then blown in to force the parison into the shape of the mould. The mould is water cooled so that when the parison makes contact with the inner surface it is cooled to set the shape, so actually could almost be considered as a casting process.
The process is used primarily in the production of plastic containers, bottles and other hollow articles that require thin, uniform sections. The material used is thermoplastics such as polyalkenes and PET. Utilising the blow moulding technique removes the need for 2 halves to be produced and joined together .
Tooling costs tend to be expensive, as are the machines, especially if they are fully automated. There is however very little scrap material and setting up times are short. Surface texture is good and a significant amount of molecular orientation can be induced adding strength to the overall shape. Cycle times are dependent on the heating and cooling rates of the polymer.
Types of Blow Moulding
- Extrusion blow moulding, where plastic is melted and extruded into a hollow tube or parison which is captured between 2 halves of a mould. This process can be further categorized as continuous or intermittent blow moulding, which means the parison is either produced continuously and cropped by the mould or the parison is produced in measured amounts by controlling the screw or using an accumulator.
- Injection blow moulding, this process uses a preformed component which is then further processed to create the final product form. The series of events is first injection to create a preform, then the preform is moved from the preform mould to a final form mould. Then air is blown into the preform to make the final form and the finished component is ejected.
- Stretch blow moulding, this also uses a preform but this time the preformed component is allowed to cool before being re-heated and blown to its final form often aided by a core rod. The 2nd video below demonstrates this process.
Continuous Blow Moulding
Blow Moulding Plastics
The second edition of Principles of Polymer Engineering brings up-to-date coverage for undergraduates studying materials and polymer science.
Stretch Blow Moulding Using the Preform Method
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