(Electromagnetic) induction is a physical effect in which a changing magnetic field generates an electric field . This is the basic principle for all electrical machines, such as generators, transformers and electric motors, and thus the basis for the generation of electrical energy and its conversion and use. When an electrically-conducting structure is exposed to a time-varying magnetic field, a voltage is generated ("induced"), which can trigger a current flow.
According to a principle underlying many electrical machines, one machine part generates the magnetic field, inducing a voltage in another machine part. Usually both parts are mechanically separated so that the energy is transmitted contactless over an air gap. This separation allows degrees of freedom in the design of the machines, e.g. the rotation of the rotor in the electric motor or the heating of a pot on an induction cooker.
The gap is not necessarily filled by air, however, the medium in the gap should not unnecessarily disturbe the magnetic field. The magnetic field is typically generated by a flow of current in the first part of the machine. Here the current is enclosed, thus forming closed magnetic field lines. The magnetic field is at its largest at the direct location of the exciting current and decreases with increasing distance from it. It is therefore advantageous to select the smallest possible air gap so that the most of the magnetic field is right there where the current in the second machine part is to be induced.
In reality, an interaction occurs between the currents and fields of both currents, such that the induced current counteracts the exciting current. However, for understanding the principle, it is sufficient to imagine that the exciting current generates a magnetic field, which then causes an induced current
With regard to the induction effect, the important factor is that only a change in the magnetic field causes an induced current flow. For this reason, most electric machines are operated with alternating current. The alternating current in the first machine part gives rise to an alternating magnetic field in the air gap, which in turn generates the induced alternating current in the second machine part.
When comparing induction heating with furnace heating, one main difference is obvious: induction heating occurs within the actual workpiece. It is therefore not limited by the size or shape of the furnace, the ambient temperature or by heat transfer.
The power density can be significantly increased compared to furnace heating so that very fast heating is possible (red-hot in seconds). Temperature control is flexible. This makes it possible to realize any desired heating profiles and intermediate holding phases. Heating can also be set locally so that only a single area of a workpiece or several areas with different temperature profiles per area are heated.
On the other hand, holding a temperature over long periods (e.g. temperature control or keeping warm) is not optimal with induction. Holding chambers in combination with inductive preheating are ideal for this purpose.
The combination of induction and the conventional heating method using a furnace, is used to increase the output of existing lines as well as for new lines. This is called hybrid heating. The addition of upstream or downstream induction increases the throughput and extends the temperature range of the furnace. The furnace size is thus significantly reduced, which brings further advantages in terms of space requirements and energy consumption. Furthermore, changing production requirements can be dealt with flexibly within the shortest possible time, because the heating power can be switched „on and off at the push of a button“. The hybrid heating solution leads to a reduction of waste gases, which in turn allows our customers to take another important step towards CO2-free production.