Induction Melting Furnace

Overview

A coreless induction melting furnace melts metal by electromagnetic induction rather than by burning fuel against the charge. A medium-frequency alternating current flows through a water-cooled copper coil wound around a refractory-lined crucible. The coil sets up an alternating magnetic field that passes through the crucible wall and induces circulating eddy currents in the metal inside. Those eddy currents heat the metal by its own electrical resistance, so the heat is generated within the charge itself. The same field stirs the molten bath, which gives a uniform composition and temperature without any mechanical agitation. Foundries use these furnaces to melt cast iron, carbon and alloy steel, copper, brass, aluminium and precious metals.

The furnace is built around a small number of high-stress subsystems. The Crucible and Refractory Lining holds the charge and isolates it from the live coil. The Induction Coil Assembly both carries the working current and cools itself. The Medium-Frequency Power Supply turns mains power into the medium-frequency current the coil needs, and the Capacitor Bank tunes the circuit to resonance so the supply only has to make up real losses.

How induction melting works

Mains power, typically three-phase at 400 V to 11 kV, enters the Isolation Transformer and then the Thyristor Rectifier, which produces a smoothed DC link. The Medium-Frequency Inverter chops that DC into an alternating current at the chosen working frequency, between 250 Hz for large furnaces and 10 kHz for small crucible units. Smaller charges need higher frequency because the depth that current penetrates into the metal, the skin depth, must stay smaller than the piece being melted for the induction to couple efficiently.

The coil and capacitors form a resonant tank circuit. At resonance the large reactive current circulates between coil and capacitors, and the converter only supplies the real power lost as heat in the charge and the coil. The Power Regulator continuously trims frequency and power to hold resonance as the charge changes from cold solid scrap to a fully molten bath, because the electrical properties of the load shift dramatically through the melt.

Crucible and refractory lining

The crucible is the consumable heart of the furnace. A welded Crucible Steel Shell carries an insulating Coil Grout Layer layer and then the working Refractory Lining. The lining is rammed in place as a dry granular refractory around a sacrificial steel Lining Former, then sintered hard by melting the first heat against it. Silica linings suit grey iron, alumina and magnesia suit steel and ductile iron. An Lining Leak Electrode electrode grid sits between lining and coil; if metal penetrates a worn lining the grid earths and trips the furnace before molten metal reaches the live coil. Lining life ranges from 50 heats for steel to several hundred for iron.

Coil and cooling

The Hollow Copper Conductor is hollow so cooling water can flow through the same copper that carries the current. Interturn Coil Interturn Insulation withstands the coil voltage and the radiant heat from the crucible. Laminated Magnetic Yoke bars around the outside return the magnetic flux and clamp the coil stack so it cannot move under the strong magnetic forces. The Cooling Water System runs a closed loop of deionised water, kept below 10 microsiemens per centimetre by a Deioniser Cartridge so it does not conduct between coil turns. A plate Plate Heat Exchanger passes that heat to a secondary loop and a cooling tower. Loss of cooling flow, sensed by a Cooling Flow Switch, instantly cuts power, because the coil would melt within seconds without water.

Tilting and pouring

When the melt is ready the whole furnace body tilts forward to pour. The Tilting Frame and Furnace Body pivots on two Trunnion Shaft shafts running in heavy bearings. Two Tilt Cylinder units, fed by the Hydraulic Power Pack, swing the furnace through up to 95 degrees so the Pouring Spout empties the bath into a ladle. A gas Hydraulic Accumulator holds the furnace at angle if power is lost mid-pour, so a full crucible never crashes back uncontrolled.

Control and safety

The Control and Instrumentation Panel carries the Furnace PLC, the operator touchscreen and the regulation electronics. An optical Optical Pyrometer reads bath temperature without contact. Interlocks chain together cooling flow, water conductivity, panel doors and the Emergency Stop buttons so that any fault drops the converter. At shutdown the Discharge Resistor safely bleeds the capacitor bank, which otherwise holds a lethal charge.

Operation and applications

Operators charge cold scrap, often topping up as the bath sinks, and the magnetic stirring blends alloy additions evenly. Power is run flat out for fast melting, then backed off to a holding level once temperature is reached. Because heat comes from inside the metal and not from a flame, melt loss and oxidation are low, alloying is precise, and the workplace stays cooler and cleaner than with a cupola or fuel-fired furnace. These furnaces serve job foundries, automotive casting plants, steel mini-mills and recycling operations, where fast batch melting and tight metallurgical control matter more than the lowest possible energy cost.