lancet

A lancet is a tapered iron bar, typically 1.5 to 2.5 meters long, used to pierce or clear the tap hole of a melting furnace, most commonly in iron and steel foundries. The tap hole is the opening through which molten metal drains from the furnace into a ladle or runner; over time it accumulates slag, solidified metal, and other debris that must be removed to restore flow. The lancet is driven through this blockage by hand or, in larger operations, by a pneumatic or hydraulic lance gun.

The working end of a lancet comes to a sharp point, hardened by heat treatment so it can penetrate frozen metal and slag without shattering. The handle end is usually slightly enlarged or wrapped to protect the operator's hands from radiant heat. Industrial lancets are made from low-carbon steel rod; the point hardens but the shaft remains tough enough to withstand repeated impact without becoming brittle.

Variants and Related Tools

A hollow lancet or tube lance has a small bore through its length, allowing compressed air or oxygen to be injected at the tip as it enters the tap hole. This speeds slag oxidation and blows the blockage clear rather than simply pushing it aside. Single-hole furnaces often use a solid lancet for daily maintenance; ladle and pit furnaces may use hollow lances for heavier blockages. The choice depends on the volume of metal being cast and the frequency of blockage.

Lancets fail chiefly by bending or breaking under impact, or by thermal shock if plunged into a cold furnace shortly after use. A bent lancet cannot re-enter a narrow tap hole and is salvaged for scrap. The term comes from the lancet arch in architecture, which has a similar pointed profile; medieval surgeons' lancets (small surgical blades) share the same pointed shape but bear no functional relation to the foundry tool.

In modern foundries, especially those casting gray or ductile iron, the lancet remains standard equipment despite advances in furnace design. Automatic tap-hole-clearing systems exist but are expensive; manual lancing is still faster and cheaper for small- to medium-volume shops. Operators learn quickly to judge tap-hole depth and the location of blockages by feel, adjusting lance angle and driving force to clear without damaging the refractory lining.