Induction Furnace

On the outside, a steel shell serves as the main structural support; inside it sits a multi-turn water-cooled copper coil, and inside the coil the refractory-lined crucible. Yokes made of magnetic silicon-steel strips are placed on the outside of the coil; these provide a return path for the magnetic flux, keeping the field contained and preventing the shell from heating up. Upper and lower Faraday rings also shield magnetic steel parts from the field.

The current passing through the coil both generates the magnetic field and heats the coil itself. To prevent overheating, the coil is water-cooled, with the water cooled in a cooling tower before recirculating through the circuit. The furnace has two separate electrical systems: one for cooling, tilting and instrumentation, and another for coil power.

In the 5 to 30 tonne range. DNL Mühendislik carries out the full design, engineering and manufacture, in two types: steel-shell and steel-frame. The steel-frame design makes maintenance access easier, while the steel-shell design gives higher mechanical strength.

Granular refractory material is rammed between the coil and a metal pattern placed inside it; the pattern melts away on the first heat, leaving the crucible itself behind. An acidic lining is widely used because it is both more economical and thermally more efficient. Investment cost is low and replacement is fast.

Lining life is measured by the number of heats it withstands before repair or replacement, and it ends early for two main reasons: thermal shock from rapid heating without adequate sintering or from sudden cooling, and chemical attack from aggressive slags. Field-measured examples show the scale of the difference: at one foundry where slag build-up was brought under control, lining life rose from 11 to 26 months; at another, from 4,500 to 7,500 tonnes per lining. DNL Mühendislik also manufactures the refractory for the induction furnaces it produces.