Melting furnaces are employed to overheat solid materials until they become liquefied. Typically, thermal processing equipment is utilized to change the internal characteristics or the surface of materials by elevating their temperature carefully.
In the instance of metals, this usually heightens ductility at the expense of both strength and hardness. So an industrial furnace with the ability to generate and maintain temperatures below that of the material’s melting point is needed.
By comparison, a melting furnace produces overhot temperatures which go above the metal’s melting point and cause decomposition of its physical structure which results in liquefaction. This phase transition is wholly dependent on both pressure and temperature. It is uncommon that metals can exist in a liquid state at ambient temperatures, with the exception of known eutectics like gallium-based (Ga-) alloys and mercury (Hg).
The melting furnace has to be capable of producing and maintaining the requisite temperatures over a prolonged period to achieve a homogeneous molten mixture. There are numerous melting furnace architectures which are capable of conducting this process.
Cupola Melting Furnaces
A cupola melting furnace is usually made up of a vertical heating chamber in a shaft-like arrangement, which is packed with layers of combustible matter such as limestone and coke. Inlets permit air into the chamber to facilitate combustion whilst a working door allows easy access to the lowest portion of the cupola. Here is where the raw materials are reduced to a molten mixture which can be extruded periodically through the drop-bottom spout.
Cupola furnaces are the favored aid for melting procedures in ferrous metal foundries. The architecture is robust and simple, but for safe venting and control of emissions, further considerations must be made. Usually, the top of the cupola shaft will be capped with an innovative filter which is designed to extract particulates from gaseous waste.
Operating on a radically different principle to the cupola version, induction melting furnaces utilize coiled heating elements embedded within a crucible or integrated into the walls of the heating chamber itself. These coiled heating elements convert electrical energy into heat which radiates through the material with outstanding degrees of thermal uniformity.
Restricting the utilization of combustible fuels in a facility, especially for routine melting applications, results in a safer daily operation for personnel and for components. Helically-wound induction coils which are made from refractory heating metals and ceramics enhance service longevity and allow good compatibility with extra controls.
Extra controls can be put in place and thermal cycling can be automated to decrease the production and emission of toxic metal vapors in metal melting furnaces.
This information has been sourced, reviewed and adapted from materials provided by Thermcraft, Inc.
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