Core (casting)

A core is a device used in casting and moulding processes to produce internal cavities and angles. The core is normally a disposable item that is destroyed to get it out of the piece. They are most commonly used in sand casting, but are also used in injection moulding.

An intriguing example of the use of cores is in the casting of engine blocks. For example, one of the GM V-8 engines requires 5 dry-sand cores for every casting.

Cores are useful for features that cannot tolerate draft or to provide detail that cannot otherwise be integrated into a core-less casting or mold.

The main disadvantage is the additional cost to incorporate cores.

There are seven requirements for core:

There are many types of cores available. The selection of the correct type of core depends on production quantity, production rate, required precision, required surface finish, and the type of metal being used. For example, certain metals are sensitive to gases that are given off by certain types of core sands; other metals have too low of a melting point to properly break down the binder for removal during the shakeout.

Green-sand cores makes casting long narrow features difficult or impossible. Even for long features that can be cast it still leave much material to be machined. A typical application is a through hole in a casting.

The most simple way to make dry-sand cores is in a dump core box, in which sand is packed into the box and scraped level with the top. A wood or metal plate is then placed over the box, and then the two are flipped over and the core segment falls out of the core box. The core segment is then baked or hardened. Multiple core segments are then hot glued together or attached by some other means. Any rough spots are filed or sanded down. Finally, the core is lightly coated with graphite, silica, or mica to give a smoother surface finish and greater resistance to heat.Single-piece cores do not need to be assembled because they are made in a split core box. A split core box, like it sounds, is made of two halves and has at least one hole for sand to be introduced. For simple cores that have constant cross-sections they can be created on special core-producing extruders. The extrusions are then just cut to the proper length and hardened. More complex single-piece cores can be made in a manner similar to injection moldings and die castings. Types of core

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