Taking Energy Cost Out of Nonferrous Melting
Cut your melting energy costs by improving metal yield and increasing your furnace’s efficiency.
Klaus Malpohl and Rudolf Hillen, StrikoWestofen GmbH, Wiehl-Bornig, Germany
so metal loss is an important cost factor. In an aluminum facility, a 1% loss of an annual melting output of 5,500 tons equals a loss of $128,000, assuming an ingot price of $2,565/metric ton. Given a 50% yield, this amount must be allocated to 2,750 tons of castings. Therefore, the lost metal means an extra $0.03-0.05 per 1 lb. of casting weight. Other factors affecting melting costs
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are energy consumption, maintenance-related is- sues, workplace efficiency and metal quality. Due to these factors, a universal answer for how melting and holding facilities in an aluminum high production plant should be designed does not exist. However, the rule, “fuel for melting, and electricity for holding,” remains valid for today’s operations. This rule takes into account the more fa- vorable costs of natural gas and mineral oil vs. electric-
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metalcaster’s operational costs are largely influenced by its melt shop efficiency. In nonferrous casting, the met- als processed are expensive,
ity and the high thermal energy demand of aluminum melting processes. Two main melting options are avail-
able to aluminum diecasters: crucible and reverberatory furnaces, which includes a subset of shaft, or stack furnaces. Crucible furnaces work well for small-batch, multiple alloy facili- ties, but for those facilities producing a higher volume of melt, including high production permanent mold facilities, an efficient shaft furnace system may be useful to provide the melt rates to meet the higher metal demand. This article explores the factors con-
tributing to melting costs and methods to reduce them.
Fit for Crucibles Aluminum diecasters typically use
a static type crucible furnace when melting up to 2,200 lbs. (1,000 kg) and a tiltable furnace when melting up to 3,306 lbs. (1,500 kg). Crucible furnaces are simple to operate and maintain and require a low capital investment. Metalcasters can produce different al- loys in small lots, with no restrictions on alloy type. The melt can be treated directly in the crucible, and the alloy can be exchanged quickly. The maximum melting
rates of electrically heated furnaces amount to ap- proximately 551 lbs. (250 kg) of aluminum per hour. Fuel-heated furnaces reach rates up to 882 lbs. (400 kg) of aluminum per hour. Gas-heated crucible fur-
Fig. 1. This schematic design depicts a gas-heated crucible furnace.
naces typically divert the heated combustion exhaust away form the melt and into the stack, leaving the workplace free from pollut- ants. The crucible should be equipped with a swiveling
MODERN CASTING / August 2010
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