Plastic material moulding
What plastic material moulding is?
In order to understand what the injection moulding of plastic materials is and how it works we ought to start from the understanding of what the raw material used for this type of process is and how it works.
Plastic materials are artificial materials with a macromolecular structure that under certain temperature and pressure conditions, undergo permanent changes in shape. They are divided into thermoplastics, thermosets and elastomers. Although having chemically and technologically a lot in common to do with plastics, rubber is not normally considered this way.
· Thermoplastics: they are so called, those plastics which have thermoplastic malleability, it is to say that they soften under action of heat.
In this phase they can be modeled or formed into finished products and then return to become rigid by cooling. This process, in theory, can be repeated several times depending on the quality of the different plastics.
· Thermosettings: those are a group of plastics that after an initial phase of softening due to heat, harden as a result of three-dimensional crosslinking; while during the softening stage they result to be formable under the combined effect of heat and pressure.
If these materials are heated after hardening they never come back to soften, instead they decompose charing.
· Elastomers: their main feature is the large deformation and elasticity, they can be either thermoplastic or thermosetting.
In chemistry, plastics are generally the result of polymerization of a number of basic molecules (monomers) in order to form even very long chains. We talk about homopolymers if there’s a unique monomer; copolymers, if the polymer is obtained from two or more different monomers; and polymer alloys, if the material is the result of mixing two monomers that polymerize without being chemically combined.
A plastic material is typically composed of polymer molecules of different lengths, so you ought to know the molecular weight distribution to determine the chemical and physical properties of the plastic material examined.
Plastics are obtained by petroleum processing.
Plastics are classified through an American system called SPI (Society of the Plastics Industry), which consists of a triangle (the recycling symbol) with a number inside (corresponding to a type of plastic material).