efficiency by switching from gas to electric. While the majority of furnaces sold today are gas-fired, the most energy efficient (and more expensive in up-front purchase price) are electric. When comparing gas-fired and electric reverberatory furnaces, the following numbers can be used as rules of thumb: A well-designed, radiant roof-
fired natural gas reverb furnace with 10% cold metal charging will melt at 1,500 BTU/lb. for 33% efficiency. Te same furnace, with a super insulating package, a preheat hearth for sow and t-bar aluminum charge and molten metal circulation, will melt at 1,225 BTU/lb. for 41% efficiency. • Adding heat recuperation will provide 1,095-BTU/lb. for 46% efficiency.
• Adding regeneration, instead of recuperation, will bring melting efficiency to 900 BTU/lb. or 56%.
• High headroom, wall-fired reverbs will add 150-200 BTU/lb. To go electric:
• A new electric reverb melter melts 0.21 to 0.23 kWH/lb. with 100% cold metal charging for 65%-70% efficiency or 750 BTU/ lb. average.
• With molten metal circulation, efficiency reaches 660 BTU/lb. or 76% efficiency.
• With an immersion element with molten metal circulation, efficiency reaches 650 BTU/lb. or 77% efficiency. Gas-fired furnaces are popular in
part because of their affordability, so switching to electric or reconfigur- ing melting operations must make financial sense for the metalcasting facility. Some considerations for furnace
decisions when thinking about your return on investment include: • Superinsulating the lining can reduce a fixed 24/7 heat loss. The furnace linings available to today’s aluminum metalcaster shed the least amount of heat in history and save considerable BTU.
• Including the ability to preheat inexpensive aluminum such as sows or t-bars in a hearth gains 10%-12% energy reduction for a
Shown is a basic electric reverb furnace. August 2013 MODERN CASTING | 25
the right quantity, quality and temperature of metal as flawlessly as possible. Eliminating the trans- fer ladle between the melting and holding furnaces is one way to achieve this. Turbulent transfers are detrimental to casting quality and melt efficiency. Every time metal is trans-
High headroom, gas-fired reverb furnaces are more ef- ficient than low headroom furnaces.
20-24-month ROI.
• Circulating molten metal in the furnace gains 10%-15% energy reduction for a 24-28-month ROI.
• Preheated combustion air- through recuperators or regen- eration pick up 6%-8% efficiency, for a 24-month or 60-month ROI. Before purchasing a new
furnace, metalcasters also must ensure their plant has the energy capacity for a new furnace.
Reducing Turbulence An efficient aluminum
casting facility will deliver
ferred turbulently, approxi- mately half a percent of it is lost. So if you tap or pump mol- ten aluminum out of a central
furnace into a transfer ladle, then pour the metal from the ladle to the holding furnace, you have lost 1% of all the metal you have pur- chased. You have also deteriorated the quality of the metal through
An efficient aluminum
casting facility will deliver the right quantity, quality and temperature of metal as flawlessly as possible.
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