lance

In shell casting, a lance is a thin iron rod inserted vertically through the mold cavity to support and position the core at the correct height and location. The core, typically made of bonded sand, would otherwise sag or shift during pouring, causing dimensional defects or metal penetration into the sand. The lance transfers the core's weight to the mold structure itself, keeping it suspended in the cavity until the metal solidifies.

Lances are usually 6 to 12 millimeters in diameter, made from low-carbon mild steel, and long enough to span from the core's top surface through the mold wall to the back plate or flask. They must have sufficient stiffness to prevent deflection under the thermal stress and hydrostatic pressure of molten metal, yet small enough in diameter that their own metal imprint on the casting remains acceptable, typically ground smooth to minimize damage to the casting surface after ejection.

The lance is positioned through a hole drilled or cored through the shell mold during the mold-making stage. Multiple lances may be used for large cores, spaced to distribute support evenly. After casting solidifies and the mold is broken away, the lance remains embedded in the casting and must be removed, usually by grinding, burning, or chipping. In some cases, especially for internal cores in turbine blades or complex cavities, the lance hole becomes a necessary ancillary feature that must be managed during finishing.

Problems arise when lances are undersized, allowing cores to sag and distort the casting cavity, or when they are positioned poorly, creating stress concentrations that cause core fracture during pouring. Thermal shock can also cause lances to break or pull free if they contract too rapidly during cooling, leaving a loose core. The term itself comes from the spear-like appearance of the thin rod piercing vertically through the mold structure.

Lances are standard in high-volume investment casting and shell molding processes where repeatability and dimensional control are critical. They are essential for casting internal features such as cooling passages in superalloy components, intricate cavities in aerospace parts, and undercuts that cannot be shaped by the mold walls alone. Proper lance design, material specification, and positioning are part of the tooling specification for each casting program.