lantern

A lantern is a perforated cylindrical or barrel-shaped core support used in metal casting to hold and position a sand core inside a mold cavity. It is most commonly encountered in casting operations where a hollow casting is required, such as the production of cylinder blocks, pump housings, or bell shapes. The lantern itself stays in place during pouring and helps the core resist buoyancy forces and hydrostatic pressure from the molten metal surrounding it.

The structure of a lantern consists of a metal (usually iron or steel) barrel with regularly spaced holes or slots running along its length. These apertures allow molten metal to flow past the lantern into the core cavity, while the barrel walls provide mechanical support to the sand core. The core is rammed or packed around the outside of the lantern during core assembly, gripping it firmly so that it cannot shift when the mold is inverted or vibrated.

Function and placement

The lantern performs two critical functions. First, it anchors the core axially within the cavity, preventing vertical displacement during pouring. Second, the holes reduce the effective thickness of the core itself by allowing metal to flow through the perforated support rather than requiring a thicker, more fragile core material. This design is especially valuable in tall or thin castings where a solid core would be prone to breaking under thermal stress or metal pressure. The lantern is typically positioned along the centerline or lengthwise axis of the cavity.

Material and hole size are matched to the specific casting. For iron castings, cast iron lanterns are common; for smaller or more precise work, steel versions with drilled holes may be used. Hole diameter typically ranges from 6 to 12 millimeters, spaced 25 to 40 millimeters apart, though these dimensions vary with the core size and metal pouring temperature. The lantern barrel wall itself is usually 4 to 6 millimeters thick to provide rigidity without excessive mass.

After casting and knockout, the lantern remains embedded in the casting and is either left in place or drilled out during secondary machining, depending on the design. In some cases, lanterns are designed to be removable from the casting, particularly if they would interfere with internal passages or finished dimensions. The term arises from the visual resemblance of the perforated barrel to the pierced metal sides of an old oil or candle lantern.