What is Induction Heating?
Induction heating involves passing an alternating current through a conductor coiled into a loop (typically a copper tube), which generates a magnetic field. When a metal object is placed within this magnetic field, the field penetrates the metal and induces eddy currents (also called Foucault currents) that flow in directions perpendicular to the magnetic field. Due to the electrical resistance of the metal, these eddy currents generate Joule heat, causing the temperature of the metal to rise. This process enables non-contact heating of metallic objects.
Basic Facts About Induction Heating:
Induction heating works only on electrically conductive and magnetic materials, such as steel and iron. Non-conductive materials like wood, plastic, or the human body cannot be heated by induction.
The heating efficiency varies depending on the material’s magnetic permeability and electrical conductivity. Ferrous metals (e.g., carbon steel and iron) have high magnetic permeability, resulting in stronger eddy currents and higher heating efficiency. Non-ferrous metals (e.g., stainless steel, copper, and aluminum) have lower or negligible magnetic permeability, leading to lower heating efficiency, though they can still be heated due to their electrical conductivity.
Working Principle of a Medium-Frequency Induction Furnace:
A medium-frequency induction furnace heats workpieces through electromagnetic energy conversion. The process involves three energy transformations:
Electrical energy → Magnetic energy
Magnetic energy → Electrical energy (eddy currents)
Electrical energy → Thermal energy (heat)
The system starts with standard 50 Hz AC power input. Inside the furnace:
The AC power first passes through a rectifier, converting it into DC power.
The DC power is then smoothed by a reactor (inductor) to filter out ripples and harmonics from the rectification process.
The smoothed DC is fed into an inverter section, where a control board generates pulse signals at a specific frequency, converting the DC back into AC—but now at a medium frequency (typically 1–10 kHz).
This medium-frequency AC is supplied to the induction coil (the load), creating a strong alternating magnetic field that induces eddy currents in the metal charge, thereby heating or melting it efficiently.
