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

EBM is distinguished by its refining capacity. However, electron beam technology is primarily
for melting refractory metals and laboratory-scale melts. One of the disadvantages of the electron
beam process is its high capital cost due to its requirement of vacuum pumps. In addition, the fit
up must be precise and locating the parts with respect to the beam must be perfect. 45 Therefore,
the technology is not applicable in typical foundry operations.
4.2.2 Immersion Heaters (High-Temperature Melting)
Immersion heaters, although well established for melting zinc, is currently not well-adapted for
melting metals with higher melting points. The protective ceramic coatings pose thermal barrier,
lowering the melting efficiency. Several ITP Metal Casting projects are currently focusing on
enabling this technology commercially.
One ITP-sponsored project addresses the critical need for advanced materials that are lighter,
stronger, and more corrosion-resistant than metals. 46 Work has been done to optimize the nitridebonded,
silicon-carbide-fiber-reinforced Continuous Fiber Ceramic Composite (CFCC)
immersion tube burners for application in aluminum and other light metal melting. The project
validated that CFCC materials are stable in molten aluminum and in combustion gas for long
periods. When tested at an industrial site, the immersion tube survived over 1,000 hours and 31
cycles in an aluminum casting furnace. In another testing, the immersion tube successfully
survived for 1,752 hours in the furnace.
ITP has also been supporting research effort in the development of intermetallic alloys that
possess improved or unique environmental resistance, which can result in efficiency benefits and
energy savings. 47 Recently, researchers developed Ni3Al alloy that can withstand service
temperatures of 100 to 150°C (180-270°F) higher than commercial Ni3Al alloys. Other alloys
under study are based on the intermetallic alloy FeAl. These alloys can resist carburization and
sulfidation that most commercial alloys cannot. In addition, alloys based on Ni3Si are being
developed. The Ni3Si alloys have good mechanical properties and excellent resistance to
oxidizing conditions, such as in sulfuric acid and seawater, and to ammonia at temperatures up to
900°C (1,650°F). These kinds of intermetallic alloys can be applied in immersion heater tubes to
withstand any wear from chemical reactions.
An ITP cost-shared project called “Isothermal Melting (ITM)” shows promise for developing
future models with in-plant thermal efficiencies of 97%. New materials and construction
techniques allow immersion heaters to be built with high heat flux (approximately 70,000 Btu/hrft
2 ) and external coatings that provide mechanical and chemical protection. These new heater
designs are based on a highly conductive, impact- resistant ceramic coating on a metallic sheath
and a highly thermally conductive, dielectric integral coupling medium between the sheath and
the heat-producing element. This allows heat transfer by conduction to be the dominant mode,
rather than particle-to-particle radiation heat transfer that prevails in conventional electric
immersion heaters with compacted powder coupling media. The composite refractory coating is
resistant to corrosive attack by the molten aluminum, yet sufficiently thin enough to provide a
high heat flux. High flux heaters incorporated into the ITM are practical for large-scale
applications. 48
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