Blow molding (also known as blow moulding or blow forming) is a manufacturing process by which hollow plastic parts are formed. In general, there are three main types of blow molding: extrusion blow molding, injection blow molding, and stretch blow molding. The blow molding process begins with melting down the plastic and forming it into a parison or preform. The parison is a tube-like piece of plastic with a hole in one end in which compressed air can pass through. The parison is then clamped into a mold and air is pumped into it. The air pressure then pushes the plastic out to match the mold. Once the plastic has cooled and hardened the mold opens up and the part is ejected.

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Rotational molding, also known as rotomolding, rotocasting or spin casting, is a molding process for creating many kinds of mostly hollow items, typically of plastic. A heated hollow mold is filled with a charge or shot weight of material, it is then slowly rotated (usually around two perpendicular axes) causing the softened material to disperse and stick to the walls of the mold. In order to maintain even thickness throughout the part, the mold continues to rotate at all times during the heating phase and to avoid sagging or deformation also during the cooling phase. The process was applied to plastics in the 1940s but in the early years was little used because it was a slow process restricted to a small number of plastics. Over the past two decades, improvements in process control and developments with plastic powders have resulted in a significant increase in usage.

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Polymers are materials composed of long molecular chains that are well-accepted for a wide variety of applications. This unit explores these materials in terms of their chemical composition, associated properties and processes of manufacture from petrochemicals. The unit also shows a range of products in which polymers are used and explains why they are chosen in preference to many conventional materials.
This particular section focuses on design in polymers, specifically the manufacturing and process methods including fabrication, rotationally moulding, vacuum forming, blow moulding and injection moulding.

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