Moulding & working with plastic:

Rotational moulding:

Rotational moulding is a process in which mainly professes in making hollow-shaped products. This machine works with 3 seperate arms which rotate around a central point. They stop at different stages, otherwise known as processing points. Moulds are attached to these arms and are rotated throughout the moulding process. The only times in which they are not being rotated is the first stage (where the moulds are filled with plastic) and the final stage (where the mould is opened and the product is then removed).
Stages of roational moulding:
1. - Filling the mould with thermoplastic powder/granules.
2. - Transfer the mould into the oven chamber where the plastic is heated to take shape of the mould.
3. - While rotating with the heat, the mould is transferred to a cooling chamber in which it is cooled by air or water jets.
4. When the product has been cooled, the product is removed from the mould and the process may repeat.

 Extrusion moulding:

Extrusion moulding is a continuous process which produces hollow and solid products which have a constant cross section.
Process:
1. - Thermoplastic granules are fed into a hopper which then are fed through the machine by a reciprocating screw, which leads to the heating area where the thermoplastic granules are melted to be liquid.
2. - The thermoplastic granules are given a plasticiser after being compacted into a small area, which allows them to flow easier through the moulds.
3. - While the plastic flows through the mould, it is cooled by a water cooling system being a trough in order to solidify while it is continuously being produced and pushed further.
4. - There will be something such as a saw at the end of this cycle wich will cut the extrusion to a set length so that the product is cut to the same precise sizes.

 

Vaccum moulding:

Vaccum forming is a process which can produce a variety products made from thermoplastic materials.
Process:
1. - A mould is used for producing the desired product. It is attatched to a platen (otherwise known as a support plate).
2. - A thermoplastic sheet material is clamped to an airtight gasket and heated from above to soften.
3. - After the thermoplastic sheet material is heated and become softened enough, the air is blown to make the sheet rise ready to take the impact of the mould.
4. - The mould which is attatched to the platen is risen, forcing the plastic to take shape as the mould and plastic both meet and the plastic has then taken shape of the mould.
5. - The air between the platen and the thermoplastic sheet is removed by a vaccum pump, in order to reduce errors as the air may have the plastic change shape slightly.
6. - After the plastic sheet has been cooled enough to solidify, air is then released into the area between the mould and plastic to allow both to seperate without the plastic freezing to the mould. This is done quickly otherwise the plastic forming may grip to the mould, and then be pried off by the platen and mould being lowered down in which can damage the forming.