Channel induction furnace

In ferrous metal foundries, the channel induction furnace is mainly used as a holding furnace. It is the furnace of choice for duplex operation with the hot blast cupola. In this case, its function is either to hold or to homogenise the chemical composition of the metal, or to serve as a reservoir of the melted metal for the casting. The furnace s role is not to increase the metal temperature, but rather to prevent unwanted cooling. 

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The term channel induction furnace is appHed to those in which the energy for the process is produced in a channel of molten metal that forms the secondary circuit of an iron core transformer. The primary circuit consists of a copper cod which also encircles the core. This arrangement is quite similar to that used in a utdity transformer. Metal is heated within the loop by the passage of electric current and circulates to the hearth above to overcome the thermal losses of the furnace and provide power to melt additional metal as it is added. Figure 9 illustrates the simplest configuration of a single-channel induction melting furnace. Multiple inductors are also used for appHcations where additional power is required or increased rehabdity is necessary for continuous operation (11). 

Hearth. The hearth of a channel induction furnace must be designed to satisfy restraints that are imposed by the operating inductor, ie, the inductor channels must be full of metal when power is required, and it is also necessary to provide a sufficient level of metal above the channels to overcome the inward electromagnetic pressure on the metal in the channel when power is appHed. Once these requirements are satisfied, the hearth can then be tailored to the specific appHcation (13). Sizes range from stationary furnaces hoi ding a few hundred kilograms of aluminum to rotating dmm furnaces with a useful capacity of 1500 t of Hquid iron. 

The channel induction furnace consists of a big, thermally isolated bucket, equipped with an isolated top-lid for introduction of the charge (Figure 2.15). The bottom is equipped with one or more U-channels. Around these channels is a water-cooled induction coil, which heats and circulates the metal. The induction current has the frequency of the local electricity grid. The furnace is generally mounted in an hydrauUcally tiltable frame for tapping or maintenance operations. Pressurised and non-tilting furnaces are also in use. 

Figure 3.3 presents the energy consumptions of some representative channel induction furnaces. The consumption depends on process related parameters, such as the holding time. The graph shows that the consumption decreases with increasing annual tonnage. The extreme values are 80 and 20 kWh per tonne transferred. 

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