< SAND CASTING SUMMARY
SAND CASTING KEYWORDS
BI-VALVE : A simple two part mould.
BREAKDOWN POWDER: A heat sensitive dextrose based additive. Assists in the degradation of the bond between sand and binder after casting allowing easy removal of waste sand (esp.cores).
CHAPLETS: Small metal spacers positioned in mould cavity between a sand core and outer mould. These help prevent core to mould surface contact and mis-runs.
CHILL: A device (often a conductive copper mass), placed adjacent to any part of a sand mould or welded joint, aids rapid cooling after heating.
CO2 SAND: Sand moulding system using silica sand with added sodium silicate binder and carbon dioxide gas catalyst. The most common art foundry sand moulding system.
CORE: An internal refractory mass, suspended within a [sand] mould on metal bars or else sand ‘prints’. The core provides an even air gap in the mould cavity, into which the charge flows to form a hollow cast.
DIE: A rigid or semi-rigid mould, usually formed either in vulcanised rubber (jewellery casting/electroforming), or metal (die gravity/pressure casting).
DRAW: The tapering of a master pattern’s sides towards an imaginary apex, allows for easy withdrawal of a moulded pattern from a sand box. Also known as a ‘draft’, the incline is usually between 5° and 15° off vertical.
DRESSING: Refractory coatings variously applied to EPS patterns, sand moulds and die moulds, to prevent fusion of cast alloy with the refractory sand or metal die tool.
EPS: (abbrv.) Expanded polystyrene, also sometimes referred to as ‘Foam’.
EVAPORATIVE CASTING: Lost pattern sand casting with a foam pattern, or other suitable material capable of dissolving on contact with an entering metal charge. Also referred to as ‘Lost Foam Casting’.
FEEDERS: Vents out off a sand mould which can also function as metal reservoirs for feeding the cast as it cools, thus counteracting any contraction in volume. Broadly equivalent to ‘risers’ in lost wax investments.
FLASK: Receptacle for containing a refractory mould, usually in sand, or jewellery investment. A sand flask normally consists of two interlocking boxes, the cope (upper part) and the drag (lower part). Gaggers are a grid of keyed bars set into large flasks to help keep large volumes of sand in a fixed position.
JOBBING FOUNDER: Alternative term for a general commercial (engineering or architectural) foundry operation.
GAS GUN: Device for delivering a pressurised gas trigger (such as CO2 ), into sand moulds.
GREEN SAND: Traditional sand moulding system, uses refined silica sand with a clay based binder. May be hardened by kiln baking (referred to as ‘Dry Sand Moulding’).
HEAD: Typically, top part of a mould or ‘head box’, contains runner access for the molten charge.
INGATE: Entrance point of the molten charge into the sand mould.(metal flow sequence: POURING BASIN > RUNNER/SPRUE > INGATE > MOULD).
LOCK-IN: Where a rigid outer mould (sand, plaster, metal die etc) penetrates a surface undercut on an encased design, preventing the mould or cast from being later disengaged.
LOST FOAM CASTING: See Evaporative Casting.
MASTER PATTERN: Artist’s, model, sculpture, template etc. The basis of any cast, the pattern usually supplied to the art foundry by the artist or designer as a complete design . May be in a modular form for commercial sand casting.
MESH SIZE: Scale for grading of ceramic, sand and other fine particulate.
PARTING POWDER: A fine ‘talc’ like lubricating powder, dusted over contacting sand pieces to prevent adherence [to adjoining pieces], allows easy breaking down of the mould (stripping), to remove the master pattern..
PATTERNMAKER: Craftsman specialising in the construction of patterns, primarily for commercial foundry work.
PERMANENT PATTERN: A master pattern used as a permanent template for cast reproduction. Unlike lost patterns, permanent patterns are not directly used in a refractory mould and therefore require intermediate processing (such as piece moulding in sand). Use of permanent patterns allows multiple casts to be created from a single pattern design.
PETROBOND: Oil bonded sand casting system.
PIECE PARTS: Individual, interlocking sections of a rigid piece mould (normally in sand or plaster), used primarily to accommodate undercuts and awkward features on a master pattern.
POURING BASIN: Similar to the lost wax pouring cup, can be designed to filter and regulate the flow of the moten charge into the mould's running system.
RAMMING UP: Compression of refractory sand medium around a master pattern or core box etc. Consolidates the sand grain to form a good quality moulding surface for the metal reproduction to form in.
REFRACTORY: Materials highly efficient at resisting thermal conditions. ‘Refractory Mould’: a general term which may include both investment and sand moulds.
RISERS: Integral system within refractory moulds, for venting gases to atmosphere and preventing ‘back pressure’ in the mould. In commercial sand moulding this feature is also termed a ‘Feeder’, when it serves as a metal reservoir to counteract the effects of contraction as the cast cools.
RUNNERS: Integral system within investment and sand refractory moulds, for the supply of a molten charge to remote areas of the cast. In commercial sand moulding this feature is often termed a ‘Gate’, ‘Ingate’ or sometimes ‘Sprue’.
SAND CASTING: Technique of metal casting where a refractory sand is mixed with a binder, then set hard to form a castable refractory mould. Each cast is normally formed in it’s own individual flask, using a master pattern as a template. Some (commercial) master patterns can be adapted to impress multiples of a design or component into each mould.
STRIPPING: Removal of the master pattern from the flask after surrounding sand mass has been moulded and set hard.
TOOLMAKER: Craftsman skilled in constructing casting dies and similar metal tooling.
UNDERCUT: A surface feature on a master pattern or mould, which forms a sharp overhang or deep pocket. The undercut may Lock-in to the surrounding mould, and must be allowed for in the construction of a sand or other rigid mould.
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