Core (manufacturing)

For example, cores define multiple passages inside cast engine blocks.

[1] 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.

[2] Green-sand cores makes casting long narrow features difficult or impossible.

Finally, the core is lightly coated with graphite, silica, or mica to give a smoother surface finish and greater resistance to heat.

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.

More complex single-piece cores can be made in a manner similar to injection moldings and die castings.

The binder that touches the hot surface of the core box begins to cure within 10 to 30 seconds.

In a similar vein, the cold-box process uses a binder that is hardened through the use of special gases.

The binder coated sand is packed into a core box and then sealed so that a curing gas can be introduced.

However, because high temperatures are not required the core box can be made from metal, wood, or plastic.

[4] For example, a cold-box sand casting core binder is sodium silicate which hardens on exposure to carbon dioxide.

This attribute is especially important for steel casting because a large amount of shrinkage occurs.

[6] It is usually more critical to ensure the upper chaplets are stronger than the lower ones because the core will tend to float upward in the molten metal.