REFRACTORY MOULDING KEYWORDS

BLOCK MOULD: A traditional type (plaster & grog/jewellery), refractory mould. A wax pattern assembly has a flask or temporary liner placed around it. Fluid refractory is poured into the container and sets into the classic cylindrical block form mould.

CERAMIC SHELL: A refractory moulding system for lost wax casting. A wax pattern assembly is coated with a ceramic slurry and dusted with fused silica grits. Successive layers are built up until the refractory mould reaches a sufficient thickness to allow wax removal and casting.

CHARGE: Quantity of molten metal alloy for pouring into a refractory mould.

CIRE PERDU: (Fr.) ‘Lost wax’.

COLLOID: Minute particles of electrically charged material (silica for lost wax casting), dispersed in a ‘sol’. Silica sol – a water based colloid, or ethyl sol – an alcohol based colloid, functions as a refractory binder.

CORE: A refractory mass suspended within a refractory lost wax (or sand) mould. After wax removal, the core maintains an air gap into which molten metal is run to enable a hollow cast to form.

CORE VENT: A tube set into the core interior which is extended through the outer refractory wall out the atmosphere, allowing evolved cavity gases to escape a mould during casting.

CORE PINS: Metal pins for locating and fixing a core in place relative to the outer refractory wall.

DE-WAX: See WAX/KILN BURNOUT.

DRAIN: An aperture in the refractory mould, placed on the wax pattern to allow wax to evacuate from the mould cavity during kiln burnout.

FACING (LAYER/COATING): Also PRIMARY COAT, the first refractory layers, in contact with the wax pattern. These layers should form a dense (but porous) matrix over the waxes surfaces to permit a faithful reproduction of the sculptures surfaces & forms.

FLASK: Metallic container sleeved over sprue trees etc to contain liquid refractory. May be perforated to assist the even application of a vacuum force.

FUSED SILICA: A fragmented refractory body of variable grit size used to build up of a wall thickness in ceramic shell refractories. Referred to as a STUCCO in the larger mesh sizes, FLOUR in the finest.

GREEN: An unfired refractory mould or material.

GROG: Crushed, fired and graded fireclay refractory.

HEAD: Typically, the top end or entrance into a mould.

HYBRID REFRACTORY MOULDING: A specialist method of lsot wax refractory mould construction, combining different moulding techniques and refractory systems, typically plaster & grog, ceramic shell and hard set sand.

INVESTMENT:   The refractory material or materials used to create a thermally resistant mould suitable for metal casting by the lost wax process. The word may also be used as a verb to describe the overall process of forming a mould.

INVESTMENT/REFRACTORY MOULD: Any mould which encases or ‘invests’ a lost wax type pattern in advance of casting.

JEWELLERY CASTING: The casting of (typically) small intricate wax patterns, usually vacuum or centrifuge assisted.

LUDO: Spent refractory material (typically plaster & grog), recycled for use in the next cycle of mould construction.

MESH SIZE: Scale for grading refractory and sand particulate etc. The larger the mesh number the smaller the grit size.

OPEN CORE: The omission of a solid core mass for layers of ceramic shell to create a hollow metal cast.

PLASTER OF PARIS: Calcium sulphate hemihydrate/gypsum, an important material both for pattern making, and as a foundry refractory/binder.

REFRACTORY: Materials (esp selected minerals) highly efficient at resisting the effects of severe thermal exposure.

REFRACTORY MOULD: A general term which may include both lost wax and sand moulds (or any mould with a heat resistant quality).

SLURRY: Refractory flour suspended in colloidal sol (ethyl or silica), plus modifying/stabilising additives, to create a fluid ceramic preparation.

WAX REMOVAL/KILN BURNOUT: Evacuation of wax from a refractory mould through the application of a heat source (ie by a kiln or autoclave), or occasionally by solvent washing.

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