Induction Heating

Induction heating is a method of heating electrically conductive materials, usually metals, without direct contact between the heat source and the workpiece. An alternating current flows through a coil, often water-cooled and made of copper, which produces a rapidly changing magnetic field. When a conductive object is placed inside or near this field, the changing flux induces circulating electric currents within it. These induced currents are known as eddy currents.

The eddy currents encounter the electrical resistance of the material and dissipate energy as heat, so the workpiece heats itself from the inside rather than being warmed from an external flame or element. In ferromagnetic materials such as iron and steel, additional heat is generated by magnetic hysteresis losses below the Curie temperature. Because the heating is produced within the part, induction is fast, clean and easy to control, and it avoids combustion products. The frequency of the alternating current strongly affects how the heat is distributed: higher frequencies concentrate the induced currents near the surface through the skin effect, while lower frequencies allow deeper penetration.

Industrial applications take advantage of this controllability. Induction is widely used for surface hardening of gears and shafts, for brazing and soldering, for melting metals in induction furnaces, and for heating bars and billets before forging. Domestic induction cooktops use the same principle, generating a magnetic field beneath a glass surface that heats a ferrous pan directly while the cooktop itself stays relatively cool. The efficiency and precise local control of induction heating make it suitable for both mass production and delicate joining work.

Frequently asked questions

How does induction heating produce heat without flame?

An alternating magnetic field from a coil induces eddy currents inside the conductive workpiece. The material's resistance turns these currents into heat, so the part heats itself.

Why does an induction cooktop need a ferrous pan?

Ferromagnetic pans couple strongly to the magnetic field and add hysteresis losses, producing efficient heating. Non-magnetic cookware couples poorly and heats little or not at all.

What does frequency change in induction heating?

Higher frequencies concentrate the induced current near the surface for shallow, fast heating, while lower frequencies penetrate deeper into the material.