About Induction Heating
What is Induction Heating?
About Induction Heating: Induction heating is a fast, efficient, precise, repeatable, non-contact method for heating metals or other electrically conductive materials.
An induction heating system includes an induction power supply that converts line power to an alternating current, delivers it to a worksheet, and works the coil creating an electromagnetic field within the coil.
The workpiece is placed in the coil where this field induces a current in the workpiece, which generates heat in the workpiece. The coil, which
is water-cooled and cool to the touch, is placed around or adjacent to the workpiece. It does not touch the workpiece, and the heat is only generated by the induced current flowing in the workpiece.
The material of the workpiece may be a metal such as steel, copper, aluminum, or brass or it can be a semiconductor such as carbon, graphite, or silicon carbide. To heat non-conductive materials such as plastics or glass, induction can heat an electrically conductive susceptor, typically graphite, which then transfers the heat to the non-conducting material.
Induction heating is used in processes where temperatures are as low as 100 ºC (212 °F) and as high as 3000 °C (5432 °F). It can be used in
brief heating processes that are on for less than half a second and in heating processes that are on for months.
How does induction heating work?
About Induction Heating; It helps to start with the basics to provide a little electrical understanding. Induction creates an electromagnetic field in a coil to transfer energy to the workpiece to be heated. When an electrical current passes along a wire a magnetic field is created around that wire.
About Induction Heating
Key Benefits of Induction:
• Rapid heating
• Precise, repeatable heating
• Efficient heating
• Safe heating since there is no flame
• Extended life of fixturing due to precise heating
Methods of Induction Heating
There are Two Methods of Heating When Using Induction:
1. Eddy current heating from the I²R losses from the resistivity of the work piece’s material.
2. Hysteretic heating in which energy is generated within the part by the alternating magnetic field created by the coil changing the magnetic polarity of the part. Hysteretic heating occurs in the part up to the Curie temperature when the material’s magnetic permeability reduces to 1 and hysteretic heating is minimized. The remaining induction heating effect is by eddy current heating.
When the electrical current changes direction (AC) the magnetic field created collapses and is created in the reverse direction, as the current
reverses direction. When a second wire is placed in that alternating magnetic field an alternating current is generated in the second wire.
The current in the second wire is proportional to the current in the first wire and the inverse of the square of the distance between them.
When we replace the wire in this model with a coil, the alternating current on the coil creates an electromagnetic field and while the workpiece to be heated is in the field, the workpiece corresponds to the second wire and an alternating current is generated workpiece. Heat is generated in the workpiece due to the I²R losses of the work piece’s material resistivity. This is called eddy current heating.
How Does an Induction Coil Work?
The work coil is used to transfer energy to the workpiece using an alternating electromagnetic field.
The alternating current flowing through the coil generates the electromagnetic field which induces a current flowing in the workpiece as a mirror image to the current flowing in the work coil.
The work coil, also known as the inductor, is the component in the induction heating system that defines how effectively and how efficiently the workpiece is heated.
Work coils range in complexity from a simple helical wound (or solenoid consisting of a number of turns of copper tube wound around a mandrel) to a coil precision-machined from solid copper and brazed together.
What is the ?
The operating frequency for an induction heating system is dictated by the workpiece to be heated and the material it is made from. It is important to use an induction system that delivers power over the range of frequencies appropriate for the application.
To help understand the reasons for different operating frequencies let’s look at a characteristic known as the “skin effect.” When the electromagnetic field induces a current in the part, it flows primarily at the surface of the part. The higher the operating frequency the shallower the skin depth; the lower the operating frequency the deeper the skin depth and the penetration of the heating effect.
The skin depth of penetrating depth is dependent on the operating frequency, material properties, and the temperature of the part. For example, in the table below, a 20 mm steel bar can be stress-relieved by heating it to 540 C (1000 °F) using a 3 kHz induction system. However, a 10 kHz system will be required to harden the same bar by heating it to 870 °C (1600 °F).
As a rule, heating smaller parts with induction requires higher operating frequencies (often greater than 50 kHz), and larger parts are more efficiently heated with lower operating frequencies.
With modern solid-state induction power supplies with embedded microprocessor control systems, repeatable and efficient heating processes are readily achievable as long as every part is placed in a consistent location within the coil.
What Makes Up an Induction Heating System?
An induction heating system consists of a power supply (or inverter) a tank circuit (or worked) and a work coil. In industrial applications, there is usually enough current flowing through the coil to require water cooling, so a typical installation includes a water cooling system.
The power supply converts the alternating current from the AC line to an alternating current that resonates with the combination of the capacitance in the workhead, the inductance of the coil, and the resistivity of the part.
Factors to Consider
• The material the workpiece is made from determines the heating rate and power required; steel and iron heat easily as they have higher resistivity whereas copper and aluminum require more power to heat due to their lower resistivity.
• Some steels are magnetic so both the metal’s resistivity and hysteretic properties are used when heated with induction. Above the Curie temperature (500 to 600 °C/1000 to 1150 °F) the steel loses the magnetic properties but eddy current heating provides the heating method for higher temperatures.
• The power required is determined by:
– The type of material
– The size of the workpiece
– The required temperature increase
– The time to temperature
The operating frequency of the induction heating system is a factor to consider based on the size of the workpiece to be heated. Smaller workpieces require a higher frequency (>50 kHz) for efficient heating, and larger workpieces benefit from a lower frequency (>10 kHz) and more penetration of the heat generated.
As the temperature of the heated workpiece rises, so do the heat losses from the workpiece. Radiation and convection losses from the workpiece become an increasingly important factor with higher temperatures.
Insulation techniques are often employed at high temperatures to minimize heat losses and to reduce the power required from the induction system.
Shahab Induction Company, founded in 1999, started its enterprise as a leading Iranian high-frequency induction welding and heating equipment manufacturer. Our innovations in the field include technological breakthroughs in tube induction welding, catheter tube tip forming, and surface hardening. In 2004 SIC obtained patent approval certification from the Iranian Research Organization for Science and Technology (IROST). The company has ever since continued on a steady course of developing research and optimizing products: in 2009 we were honored to receive the International Trophy for Quality from the Trade Leaders’ Club, and in 2013 we succeeded in getting our products certified to ISO (International Organization for Standardization). SIC received ISO 9001: 2008. ISO 14001: 2004, and OHSAS 18001: 2007. All rights to technical science, machine design, and manufacturing techniques of the products are reserved for the SIC.
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