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Reforming Polymers
Reforming Polymers
Plastic is perhaps the most commonly reformed material due to the ease with which it can be turned into a liquid and back to a solid at relatively low temperatures.
Injection Moulding
Injection Moulding
Injection Moulding is a manufacturing process for producing parts by injecting material into a mould. Injection moulding can be performed with a host of materials, including metals, glasses, elastomers, confectionary, and most commonly thermoplastic polymers. Material for the part is fed into a heated barrel, mixed, and forced into a mould cavity, where it cools and hardens to the configuration of the cavity. After a product is designed, moulds are made by a mould maker (or toolmaker) from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers which do not melt during the injection moulding of some lower temperature thermoplastics, can be used for some simple injection moulds.
This diagram shows how the Injection Moulding process works using thermoplastic polymers.
Rotational Moulding
Rotational Moulding
involves a heated hollow mould which is filled with a charge or set 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 mould. In order to maintain even thickness throughout the part, the mould 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 last few decades, improvements in process control and developments with plastic powders have resulted in a significant increase in usage. Unlike other types of moulding, the shape can be hollow yet have a very thick wall.
Extrusion;
Extrusion;
similar to Injection Moulding but without the use of a hydraulic ram as the polymer is continually pushed through the die.
Compression Moulding
Compression Moulding
Compression Moulding is the main process used to produce products using Thermosetting Polymers such as Urea Formaldehyde.
The moulding material, generally preheated, is first placed in an open, heated mould cavity. The mould is closed with a top force or plug member, pressure is applied to force the material into contact with all mould areas, while heat and pressure are maintained until the moulding material has cured.
The process employs thermosetting resins in a partially cured stage, either in the form of granules, putty-like masses, or preforms. Compression moulding is a high-volume, high-pressure method suitable for moulding complex, high-strength fiberglass reinforcements.
It is one of the lowest cost moulding methods and it wastes relatively little material, giving it an advantage when working with expensive compounds.
Resin and GRP Moulding
Resin and GRP Moulding
is not strictly a reforming process as it effectively involves using a liquid polymer (Resin) which is left to cure and set hard.
GRP (Glass Reinforced Plastic) is also combined with fine strips of glass to reinforce the resin when it sets. However as the resin changes form from liquid to solid. It is included in this section just for reference.
3D Printing - Filament
3D Printing - Filament
3D printing is an additive process where you start with nothing and add layers of plastic which build up to form a 3 Dimensional shape. As the plastic (PLA / ABS) is molten it is essentially a reformation process but it is a very new process and can print metal, wood, food and even body parts!
Summary
Summary
Redistribution is the movement of material in order to shape it. This can be done by deforming the material using heat and/or pressure or by turning the material into a liquid state then reforming it.
Reforming is used primarily with metal and plastics.
Wood can only be reformed into MDF, Chipboard and Maplex but it can be deformed by steam bending or laminating in a press.
Most complex plastic components are made by moulding techniques.
Plastic bottles are commonly made by deforming techniques.
The terms are not rigid so, 3D printing is additive but involves melting the polymer filament so could be considered reforming.
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