A crucible furnace consists essentially of a water-cooled induction coil wound around a refractory lining made of a ramming mixture which forms a crucible that holds the metal to be melted. The combined action of the magnetic field and the electric currents creates electro-magnetic forces which raise the metal temperature and stir the melted metal. The intensity of this stirring is inversely proportional to frequency. It greatly increases bath homogeneity, but results in rapid wearing of the refractory surfaces.
The furnaces are used in steel and iron foundries, but also are used for non-ferrous metals. Most precious metals are generally melted in medium-frequency induction furnaces using graphite crucibles. It should be noted that the crucible and the inductor may be placed in a vacuum chamber for special casting applications.