subject: Plastic Casting Methods And Its Uses [print this page] There are many methods of plastic casting as this process is defined as any method which does not require the presence of applied pressure. This is the significant characteristic of casting and can be used to create solid plastic objects from both liquid and powdered resin.
The most common plastic casting process is a moulding method utilised on a smaller scale and is used to produce smaller products such as toys, dolls, garage kits and model objects such as cars, trains etc. Casting is a 6000 year old process but this is a method initially developed for plastics in the early 70s at universities, mainly in Europe and America and was designed to create complex shapes that would be difficult to make by any other methods.
This is a process whereby liquid molten plastic resin mixed with a setting agent (a polymerisation catalyst) is poured into a mould containing the required shape and then left to cool and solidify at room temperature and pressure. It is the mixing of these to agents that causes an exothermic reaction enabling the plastic to harden in minutes. To ensure the plastic resin fills the entire cavity of the mould, risers are in place at the far corners of the mould to determine when the mould is full. This process is also known as surface casting or gated casting and is very similar to the machinery used when moulding metal in sand moulds. Once solidified, the plastic is then broken out of the mould to reveal the finalised shape and complete the casting process. The end product can then be sanded down into its final shape, cut and painted. For products such as model kits that are intended for the customer to assemble, the plastic is left unfinished, sometimes in its original cast.
Each time the mould is used the casing begins to break down slowly due to the aggressive nature of compounds used thus the mould loses details and begin to degrade. A typical mould can be used for between 25 100 castings therefore its use is limited and produce a very low volume of products.
This process is also used to create marble whereby a certain chemically-set plastic such as epoxy or polyester is mixed with powdered stones of multiple colours giving it that real-marble effect.
As well as the mould casting process there are many other casting processes such as film casting, slush or static powder casting. All of which are used on a small scale to produce detailed plastic products.
