We performed an engineering investigation on overheating issues in an induction furnace undergoing upgrades.
Induction heating is caused, as the name implies, by induced electric currents in a material. Just as electrical current can produce a magnetic field which ultimately can be used to power a motor, so can a magnetic field be used to produce secondary current in a material. The principle is exactly the same one used in constructing a voltage transformer whereby one AC voltage across the primary windings of a transformer will induce a different AC voltage (higher or lower) across the secondary windings. The voltage ratio of the transformer is solely dependent on the ratio of coil windings due to electromagnetic principles, although the frequency is the same for both AC voltages.
In a transformer, it is common to use a core of ferromagneric material to focus and direct a magnetic field and thereby maximize the efficiency of electromagnetic energy transfer between the primary and secondary circuits. This core is typically constructed of silicon iron and is fabricated by using multiple thin layers, laminated with electrically insulated barriers between layers of iron. The orientation of the layers parallels the magnetic field path or flux lines to minimize any undesirable eddy current heating of the core, and subsequent loss of transformer efficiency.
In the case of a “coreless” induction furnace, the metal to be heated becomes the “secondary” path. Shunts or “yokes” are used to focus the magnetic field back into the crucible/metal. These shunts are constructed similar to the transformer coils.
Problems with undesirable heating of furnace components (and loss of furnace efficiency) can result from fugitive magnetic fields which result from unshielded conductors and higher magnetic flux densities. The foundry upgrade project included an increase in power input, resulting in higher magnetic flux densities and a subsequent increase in fugitive field emissions – resulting in overheating.
O’Donnell Consulting Performs Thermal & Structural Analysis for Clients in Industries including Manufacturing, Petrochemical and Energy.