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Glossary of Moulding Terms

Abrasion Resistance: The ability of a material to withstand mechanical actions such as rubbing, scraping, or erosion, that tend progressively to remove material from its surface.

Aspect Ratio : Ratio of total flow length to average wall thickness.

Blow moulding : Method of fabrication in which a warm plastic hollow tube is placed between the two halves of a mould cavity and forced to assume the shape of that mould cavity by use of internal pressure. This process forms hollow articles such as bottles, tanks, etc.

Bulk-moulding compounds (BMC): Bulk-moulding compounds are used as a premix in composite manufacturing. A BMC consists of a mixture of resin, reinforcements, inert fillers, and other additives which form a puttylike preformed shape, rope or sheet.

Cavity: A depression, or a set of matching depressions, in a plastics-forming mould which forms the outer surfaces of the moulded articles.

Clamp: The part of an injection moulding machine incorporating the platens that provides the force necessary to hold the mould closed during injection of the molten resin and open the mould to eject the moulded part.

Clamping Area: The largest rated moulding area an injection press can hold closed under full moulding pressure. Clamping Force: The force applied to the mould to keep it closed, in opposition to the fluid pressure of the compressed moulding material within the mould cavity and the runner system.

Composite: A structural non-homogenous material consisting of a combination of materials. Typically, one of the materials is a strengthening agent, the other being a thermoset or thermoplastic resin.

Compound: A mixture of resin(s) and additives usually formed in a separate machine downstream forn the primary reactor. Compounding: The process required to mix polymer(s) with all of the additives that are necessary to provide the end user with a finished grade with suitable properties.

Compression moulding: A method of moulding in which the moulding material, generally preheated, is placed in an open heated mould cavity, the mould is closed with a top force, pressure is applied to force the material into contact with all mould areas.

Creep: Due to its viscoelastic nature, a plastic subjected to a load for a period of time tends to deform more than it would from the same load released immediately after application, and the degree of this deformation is dependent of the load duration.

Density: Mass per unit volume of a substance.

Elastic Memory: A characteristic of certain plastics evidenced by their tendency to revert to a previously existing shape or dimension.

Elasticity: The ability of a material to quickly recover its original dimensions after removal of a load that has caused deformation.

Injection moulding: The method of forming objects from granular or powdered plastics, most often of the thermoplastic type, in which the materials is fed from a hopper to a heated chamber in which it is softened, after which a ram or screw forces the material into a mould. Pressure is maintained until the mass has hardened sufficiently for removal from the mould.

Polymer: High-molecular-weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the mer: e.g. polyethylene, rubber, cellulose. If two or more monomers are involved, a copolymer is obtained.

Thermoplastic: material that will repeatedly soften when heated and harden when cooled.

Thermoset: A polymer that doesn’t melt when heated. Thermoset polymers “set” into a given shape when first made and afterwards do not flow or melt, but rather decompose upon heating. They are often highly cross-linked polymers, with properties similar to those of network covalent solids, i.e., hard and strong.

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