< MOULDMAKING HINTS
MOULDMAKING KEYWORDS
BLANKET MOULD: A mould formed by pouring or painting a flexible moulding compound directly over a master pattern surface. A plaster or resin case can be applied later to support the mould ‘skin’.
CURE: Usually applies to RTV rubbers – the period required to reach full strength and elastic properties after catalysation and application to a master pattern.
DIE: A rigid or semi-rigid mould usually formed in a rubber compound (as in jewellery casting), or a metal (as in die pressure/high precision wax casting).
DOGS: ‘U’ shaped metal clamps forced over the edges of adjoining mould cases to keep sections located and fixed.
CAST FILLER: Any material introduced into a reproduction mould to create a hard copy. The standard filler used for the lost wax process is a wax. Moulds may also be suitable for accepting alternative fillers such as plaster of Paris, resin, ciment fondue, concrete etc.
CATALYST: Compound, often metallic compound based (tin, lead, platinum etc), added into RTV base rubbers to initiate setting and curing.
KEY: A feature set into a mould to locate and retain individual mould elements (rubber skins or cases), in their correct position.
LOCK-IN: Where a moulding material (usually a rigid variety such as plaster) keys into a surface undercut on a master pattern preventing the mould from being later disengaged.
MOULD CASE: A jacket surrounding and supporting an underlying mould. The case helps to locate and maintain the rigidity of the contained rubber skin. Also used to restrain highly fluid moulding compounds in restrained case moulds.
PARTING LINE: The optimum moulding contour(s) taken over a three dimensional pattern to divide a pattern into two or more main sections for moulding. A simple parting line will usually divide a pattern in to two (roughly equal) halves.
PIECE PARTS: A series of individual, interlocking mould sections (usually refers to rigid plaster or sand moulds).
POUR MOULDS: Also called ‘drop moulds’. A moulding method in which the moulding compound is poured over a master pattern that has been contained in a clay or shuttered wall.
REPRODUCTION MOULD: A negative image impression of a master pattern formed either in a flexible rubber/plastic compound or rigid material like plaster of Paris. The reproduction mould enables wax or another filler material to be cast, creating a near exact copy of the original master pattern.
RESTRAINED CASE: A type of mould where the mould case is constructed over the master pattern before a fluid moulding compound is poured in.
RTV: (abbr.) Room Temperature Vulcanisation. A group of rubber elastomers used for reproduction moulding. These rubbers are capable of vulcanisation in ambient conditions.
THIXOTROPIC: A substance, usually a powder, added to RTV moulding compounds to increase their viscosity.
UNDERCUT: Any feature on a master pattern surface which can potentially key into and therefore lock in a supporting mould case.
VULCANISATION: Process of ‘fixing’ rubber compounds under heat and pressure. Vulcanisation is usually enabled by a ‘screw vulcaniser’ a device which applies an appropriate level of heat and pressure to the rubber mould.
WAXWORKING >
|
