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.

First, a core is made from a fusible alloy or low melting temperature polymer.

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

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.