Induction heating is a breakthrough technology to heat metals and electrically-conductive substances. It offers quick, consistent, and targeted heat. As a result, several industries have been using it.
The use of induction heating is common in metal brazing, surface hardening, preheating, etc.
Nevertheless, for each application, induction heating works on different frequencies.
Wondering why? Well, several factors influence induction heating frequency selection.
In this post, we will discuss those aspects. However, before that, let’s take a look at the history of induction heating frequencies.
Induction Heating Frequencies Over the Years
Induction heating is non-contact heating. It utilizes a certain degree of heating frequency to heat electrically conductive materials.
Today, induction heating equipment is a primary tool in manufacturing industries. However, this technology was not that efficient from the beginning.
Induction heating has come a long way since its invention. Michael Faraday, an English scientist, discovered the basics of induction heating in 1831. He introduced the concept of melting metals with the help of induction heating.
For the first time in 1935, induction heating became a topic of debate. At that time, there were only three sources of power generation. These were arch discharge generators, motor generators, and tube generators.
Arch generators were low-efficiency generators. On the other hand, motor generators could generate only 500 kW at a frequency of up to 10 kHz.
Tube oscillators were the only option for producing a high induction heating frequency. Unfortunately, the issues with tube oscillators were their large size and poor performance.
Thereafter, solid-state power supplies came into existence. It upgraded the induction heating technology several times.
Even today, SSP (solid-state power) supplies generate induction heating at MHz frequency. They can produce frequencies of more than 5 MHz.
Influencing Factors for Induction Heating Frequency Selection
Today, induction heating is used worldwide. It has become a popular choice for annealing, hardening, brazing, shrink fitting, soldering, and more. And for each application, induction heating works at different frequencies.
Several aspects influence induction heating frequency selection. We have put together some crucial ones below.
- Duration of heating and production rate
- The type of metal used
- Diameter of workpiece
- Depth of hardness and heat pattern control
- The efficiency of the inductor and its installation
- Electrodynamics forces
- Cost and size of equipment
Induction heating frequency (F) selection is achieved by keeping the heating power (P) and time (T) in mind.
Various experimental and theoretical studies provide recommendations for induction frequency selection.
Check out the induction heating frequency selection recommendations for different applications below.
Induction Heating Frequency Selection for Surface Hardening
Surface hardening involves metal treatment using induction heating. The process strengthens the hardness of a metal’s outer surface. However, the core remains soft.
Surface hardening is one of the most complex heating processes. The process includes various geometrics and heat-treatment specifications. As a result, it is difficult to make a general suggestion for its heating frequency selection.
Most experts suggest the following points for frequency selection for surface hardening.
- An operator must precisely calculate frequency, time, and power for hardening.
- The induction heating frequency should be in a narrow range depending on the tooth pitch. For small gears, the heating power must be high and rapid.
- Choose the induction heating frequency based on the requirements of your workpieces.
Some suitable induction heating frequency ranges for different surface hardening depths:
| Hardening Depth | Heating Machine Frequency |
|---|---|
| 0.8 – 1.2 mm | 200 – 400 kHz |
| 1 – 2 mm | 30 – 200 kHz |
| 2 – 4 mm | 5 – 30 kHz |
Induction Heating Frequency Selection for Brazing
Induction brazing is the process of joining two metals using induction heating. In many industries, people use it as an alternative to conventional flame-brazing.
Several factors influence induction heating frequency selection for brazing. These include the brazing material, welding depth, and thickness of the workpiece. However, the frequency range often stays between 15 and 300 kHz.
Induction Heating Frequency Selection for Melting
Induction melting is the process of melting a metal using an induction furnace. The furnace produces high heat until the metal reaches the melting point.
Generally, operators set the frequency of the induction melting machine between 3-30 kHz. But it all depends on the metal material and its melting capability. Every metal has distinct melting capacities.
Induction Heating Frequency Selection for Forging
Induction forging involves preheating metals using an induction heater. After that, they are deformed with the help of a hammer or press. The metal gets heated to a certain temperature so that it can deform.
The induction heater provides consistent heating. But the frequency of heating is determined by the diameter of the workpiece.
Recommendations for induction heating frequency selection for forging applications:
| Workpiece Diameter Induction | Heating Frequency Range |
|---|---|
| 20 – 30 mm | 15 – 30 kHz |
| 30 – 50 mm | 6 – 15 kHz |
| 50 – 80 mm | 2 – 5 kHz |
| 80 mm | 2 kHz |
Conclusion
Now you know that several factors affect induction heating frequency selection. And frequency selection is made based on application, metal type, depth, and diameter of the workpiece. If you are not sure about frequency, get recommendations from experts.
