Induction Heating Glossary
Plain-language definitions for the terms that come up when specifying induction heating equipment.
Induction Heating
A process that heats an electrically conductive material — usually metal — by inducing an electric current in it through an alternating electromagnetic field, without any physical contact between the coil and the part.
Skin Effect
The tendency of an alternating current to concentrate near the surface of a conductor rather than flow evenly through its cross-section. Higher frequency pushes the current closer to the surface, which is why frequency controls case depth in induction hardening.
Frequency
The rate of oscillation of the alternating current driving the induction coil, measured in Hz or kHz. Higher frequency produces a shallower, more concentrated heating effect; lower frequency penetrates deeper into the part.
Case Depth
The depth below a part's surface that reaches hardening temperature and is transformed by the quench. Case depth is controlled primarily by frequency, with power and heating time as secondary factors.
Coil (Inductor)
The shaped copper conductor that carries the alternating current and generates the electromagnetic field used to heat a part. Coils are typically custom-shaped to the geometry of the part being processed.
Quenching
Rapidly cooling a heated part, typically in water or a water-polymer solution, to lock in the hardened structure created by heating above the transformation temperature.
Static Hardening
An induction hardening method where the coil heats the entire target zone of a part at once, without moving. Faster per cycle, but requires a larger power supply and a coil built for that specific part.
Progressive (Scanning) Hardening
An induction hardening method where the coil and quench travel along the length of a part, heating it section by section. Needs less power than static hardening and can often handle a family of similar parts with one coil, but runs slower.
Case Hardening
Hardening only the outer surface layer of a part while leaving the core relatively soft and tough — the category of process induction hardening belongs to, as opposed to through-hardening the entire cross-section.
Curie Temperature
The temperature above which a ferromagnetic material (like steel) loses its magnetic properties. It affects how efficiently a part couples with an induction coil's field as it heats through that point.
Eddy Currents
The circulating electric currents induced inside a conductive part by a changing magnetic field. In induction heating, eddy currents flowing against the material's electrical resistance are what actually generate heat.
Tempering
A lower-temperature heat treatment applied after hardening that reduces brittleness and improves toughness, trading a small amount of hardness for a significant gain in the part's ability to withstand impact and fatigue.
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