What is the frequency classification of induction heating equipment?

Based on the frequency of the alternating current (AC) output by the equipment, induction heating technology can be classified into five categories by operating frequency: low-frequency induction heating, medium-frequency induction heating, super-audio frequency induction heating, high-frequency induction heating, and ultra-high-frequency induction heating. Due to the skin effect that occurs when alternating current flows through a conductor, the current tends to flow through the surface layer of the conductor as the current frequency increases.

It has the relatively highest frequency, with a frequency range generally above 200 kHz, which can be as high as several tens of MHz. The heating depth and thickness are the smallest, approximately 0.1–1 mm. It is mostly used for quenching and welding of local tiny parts or extremely thin bars, as well as surface quenching of small workpieces.

Its frequency range is generally 40 kHz to 200 kHz, with common frequencies ranging from 40 kHz to 80 kHz. The heating depth and thickness are approximately 1–2 mm. It is mostly used for deep heating, red forging, forging, annealing, tempering, quenching and tempering of small workpieces, surface quenching, heating and welding of medium-diameter pipes, hot assembly, and quenching of small gears.

Its frequency range is generally 20 kHz to 40 kHz (it is called “super-audio frequency” because the audio frequency ranges from 20 Hz to 20 kHz). The heating depth and thickness are approximately 2–3 mm. It is mostly used for deep heating of medium-diameter workpieces and heating of large-diameter thin-walled pipes. For example, it is applied in energy-saving transformation projects of plastic machinery (such as injection molding machines, wire drawing machines, granulators, extruders), food machinery, crude oil transportation, and other similar heating industries.

Its frequency range is generally 1 kHz to 15 kHz, with a typical value of around 8 kHz. The heating depth and thickness are approximately 3–10 mm. It is mostly used for heating, annealing, tempering, quenching and tempering, and surface quenching of large workpieces, large-diameter shafts, large-diameter thick-walled pipes, and large-modulus gears, as well as red forging and forging of small-diameter bars.

It has the lowest frequency, with a frequency range from power frequency (50 Hz) to approximately 1 kHz, and the commonly used frequency is mostly power frequency. The relative heating depth is the deepest, and the heating thickness is the largest, approximately 10–20 mm. It is mainly used for overall heating, annealing, tempering, and surface quenching of large workpieces.