ITP Metal Casting: Advanced Melting Technologies: Energy Saving ...

elements, advanced coil insulation, and noise reduction. Wide-bodied furnaces for large capacity
operations allow loading of larger scrap and give better access for slag removal.
Furnace Covers: The use of furnace cover is critical to energy efficiency once the metal is
molten. The simplest system is to keep a slag on the molten metal, reducing radiation losses from
the top surface. Higher efficiency systems include furnace lids constructed from refractories or
ceramics with low thermal conductivity, which reduces conduction and radiation heat losses.
Harmonics Controls: Harmonics problem, or feedback of electrical equipment on the power
source, can be caused by the high power of the furnace power supplies. These power interface
problems include low-power factor, high-frequency harmonics, line voltage notching, and interharmonic
distortions. Special technologies and equipments have been developed to minimize the
negative influence of induction furnaces on the power supply. Computerized controls and
diagnostic systems are available to provide close control of the melting operation and reduce the
chances of accidental overheating. A typical control system uses information from load cells for
the weight of the furnace charge and thermocouple readings for melt control optimization.
Multiple-Output Power Supplies: Dual-output or “butterfly” operations utilize a single power
supply and two furnaces with mechanized or electronic switching. This results in continuous and
completely controllable power to two furnaces at the same time. Recently, multiple-output power
units with three or more outputs have been developed. These new systems are designed with
capacitive furnace isolation and include one or two AC rectifiers. Such systems are capable of
achieving the high volumes of metal production previously possible only with cupolas.
Refractories: Push-out lining systems use a large plug to quickly remove the old lining for easy
disposal. This system reduces time and cost for periodic lining changes, lowers refractory dust,
and is less likely to damage back-up lining than manual refractory removal. 31 In addition, lining
life has been improved to nearly 400 heats by optimizing melt parameters, lining compositions,
lining installation techniques and sintering procedures. 32 One of the major technical hurdles to
operating induction furnaces for extended periods is chemical erosion of the silica linings, one of
the main causes of lining failure.
4.1.6 Reverberatory Furnaces
Reverberatory furnaces melt aluminum with the heat that re-radiates from the hot refractory
heated by the burners mounted in the roof or in a sidewall of the furnace, as shown in Exhibit 15.
The molten metal is held inside the furnace at the required temperature before it is tapped out for
pouring or transferred to a holding furnace.
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