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THE METAL FEEDING & VENTING SYSTEM 

After the wax pattern has been cleaned up and approved by the artist for casting, the founder has to carry out a series of procedues that will allow metal to be 'run' freely into the casting or INVESTMENT MOULD. The type of investment mould used by the foundry determines the method of running used by the founder, however the following is a brief overview of some of the features that can be attached to wax patterns to enable casting.

CORE

A core is a solid mass of refractory used to fill a hollow wax's cavity. This feature allows metal to be run into a relatively thin air gap in the mould and form a lightweight and hollow cast. Some INVESTMENT processes like CERAMIC SHELL do not require the use of solid cores, instead the investment material is applied to all the wax pattern surfaces (inside and out), to form a thin walled/self contained mould.

CORE ATTACHMENTS

The lost wax founder will usually apply core attachments. These usually include CORE PINS (these hold the core in position in the investment mould once the wax pattern has been removed), and CORE VENTS these are hollow tubes or wax tapers with one end inserted into the core and the other exiting the mould; allowing gasses (created by the core's reaction to molten metal), to escape.

POURING CUP

The pouring cup is attached to the top of the running system [see below] has two primary functions, in the first instance the cup can be used as an exit route for evacuated wax during the KILN BURNOUT. Later, during casting, the cup forms the entrance into the REFRACTORY MOULD, allowing metal to enter and flow through the running system. Once poured metal cools in the mould, the resevoir of semi-molten metal held in the filled cup is drawn into the mould as the contained volume of cooling metal contracts. This helps prevent casting faults like SHRINKAGE and SHORT RUNNING.

RUNNERS & RISERS (RUNNING SYSTEM)

Known as a SPRUE SYSTEM in some regions, runners and risers direct metal into the mould and allow air and gases to vent as the mould fills with metal. The founder assesses each wax pattern and determines the best method and system for that particular job, attaching wax bars that run from the cup onto the wax pattern's surface for runners (also 'feeders'). Risers (also 'vents' & 'airs') are attached separately to runners and are usually placed towards the top of the wax (as poured) and on high points; these exit the mould near the cup and prevent trapped air arresting the flow of metal and allow gasses to vent the mould. Runners and risers are never connected to each other.

OTHER ITEMS

Founders may also add a variety of other features to waxes for casting, these can include CORE PRINTS (sections of wax cut out to form a direct connection between the core and outer mould). ARMATURES these are (usually steel) bars that are used to support wax patterns, cores and even running systems. DRAINS are additional wax stubs which act as a relief to allow wax to vacate the investment mould in the kin, they may be plugged before casting or have a flexible vent inserted (before being incased in set sand etc), thus functioning as a vent. CHILLS (DRAWS) these are large masses (wax or polystyrene) placed close by and connected to solid or heavy sections of wax pattern, burnt out with the wax pattern, these fill with metal and like the CUP (see above), feed localised areas of the casting that might otherwise be prone to shrinkage.

WAXWORKING SUMMARY >

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