Aluminum and brass crucible furnaces deliver a wide range of melt rates per installed kilowatt because the rate is set by metal specific enthalpy, charge starting temperature, and overall furnace efficiency, not by furnace nameplate capacity. Published electric aluminum crucible ratings run 110 to 660 lb/hr (50 to 300 kg/hr) across nine models in the 330 to 2,200 lb (150 to 1,000 kg) holding class [S1].
For a first-pass estimate, divide the metal's melting enthalpy by furnace efficiency and installed power; the figure shifts markedly with alloy and heating method, which is why two furnaces with identical kW ratings can produce different hourly throughputs on the same shop floor [S5].
Electric Aluminum Crucible: Published Model Range
The EM-A Series of stationary electric aluminum crucible furnaces documents a 6:1 spread in melt rate across the model line: 110 to 660 lb/hr (50 to 300 kg/hr) of clean aluminum, paired with holding capacities from 330 to 2,200 lb (150 to 1,000 kg) [S1]. A model rated 660 lb/hr at the top of the range typically pairs with the 2,200 lb holding size, which is the manufacturer-recommended balance for steady, low-dross foundry supply [S1].
Working back from those numbers, the largest units sit near 0.45 lb/hr per lb of installed power density when sized against a 660 lb/hr ceiling, while smaller bench-top electric crucibles used for gold and silver work finish a 1 to 15 kg charge in 2 to 20 minutes depending on the model (CDO-MT26 to CDO-MT31) [S6]. That 2 to 20 minute range maps to roughly 3 to 450 kg/hr effective melt rate for jewelry-scale equipment, a span that is wider than any single industrial class because the charge mass itself varies by an order of magnitude.
Gas-Fired Brass and Aluminum: Heat-Input Calculator Output
For a 25 kg brass charge heated with a 920 K rise in 25 minutes, a fixed-property calculator returns 102.6 kW average heat input, 7.96 kg/hr propane use, 60 kg/hr melt rate, and 8.93% assumed efficiency (cp 0.38 kJ/kg-K, latent heat 200 kJ/kg, propane LHV 46.4 MJ/kg) [S2]. The same calculator's published operating envelope covers average fuel power from about 0.317 kW up to 2,186.67 kW, which is the practical sizing range for gas crucible melting in light non-ferrous service [S2].
That 0.59 kg/hr per kW figure at 8.93% assumed efficiency should be read as a gas-side benchmark only: the calculator explicitly does not solve alloy-specific enthalpy, furnace warm-up, or the actual firing schedule, and the model assumes the chosen interval spans complete melting without checking a liquidus [S2]. Real installations usually show higher overall efficiency once refractory is hot, which is why gas crucible throughput can climb past the calculator's cold-charge default.
Induction Iron Melting: kWh/ton Baseline and Time Math
Cast iron (ingot) baseline energy demand is 560 kWh/ton, with cast scrap running slightly higher at 575 kWh/ton because of oxide and surface-area losses [S3]. At a 700 kW supply, melting 1,000 kg of cast iron ingot takes about 48 minutes, which works out to roughly 1,250 kg/hr effective rate at full power once the furnace is in steady-state melt [S3].
The classic ASM rule for coreless induction iron melting states 4.5 kg (10 lb) melted per hour for each square inch of crucible cross-section, or 3.2 to 3.3 Mg (3.5 to 3.7 short tons) per hour per megawatt of connected power for medium-frequency units [S4]. The CDO induction buyer guide repeats the warning: a 500 kg crucible does not automatically produce 500 kg/hr, because melt rate also depends on power, starting temperature, charge density, and the complete tapping cycle [S5]. Capacity is a vessel dimension, not a throughput promise.
Side-by-Side Comparison: Electric Aluminum, Gas Brass, Induction Iron
Three reference cases line up cleanly against the four selection criteria buyers actually use: (1) electric aluminum (EM-A top model) at roughly 0.45 to 0.50 kg/hr per lb of installed power density, 50 to 300 kg/hr across the line, alloy limited to aluminum, holding reserve 150 to 1,000 kg, dross loss the lowest of the three [S1]; (2) gas-fired brass on a tangential-burner crucible, 0.59 kg/hr per kW at the 8.93% cold-charge efficiency point, alloy flexible across copper alloys, but with a fired exhaust and combustion-air system to maintain [S2]; (3) induction cast iron, 575 kWh/ton for scrap, 1,250 kg/hr at 700 kW, fastest cold-charge start, but requires a heel-free coreless or maintained heel in a channel holding unit, plus transformer and cooling integration [S3][S4][S5].
The cleanest single takeaway from those three rows: induction wins on cold-charge iron by a wide margin, electric resistance wins on aluminum cleanliness and dross control, and gas crucible wins on capital cost and alloy flexibility at the cost of efficiency and emissions. For shops that need a side-by-side reference, the crucible furnace size chart by melt capacity lays out the same kg/hr numbers against nominal capacity for several model families.
Sizing Rules and What the kW Number Does Not Tell You
Crucible sizing must start from the metal, charge condition, batch versus hourly output, furnace body, and plant power, in that order; only then does the catalog kW rating become useful [S5]. A coreless induction melting furnace, a holding furnace, and a cupola furnace all carry a kW label, but the holding unit is sized for steady-temperature reserve and the cupola is sized for combustion airflow, so neither translates melt rate the way a melting crucible does.
Two engineering limits recur in published data: induction cast iron tops out near the 3.2 to 3.3 Mg/hr per MW rule from ASM, and the gas crucible calculator's 0.317 to 2,186.67 kW envelope is the practical sizing window for non-ferrous melting [S2][S4]. Outside that band, the equipment class changes: a gas aluminum melting furnace and an induction furnace follow different scaling laws than the generic crucible calculator, and the crucible furnace itself is a vessel geometry, not a power class, so specifying a kW rating requires naming the metal and the furnace family together.
Limitations and What the Research Does Not Pin Down
Published model numbers give clean anchors for aluminum, brass, and cast iron, but research on copper, bronze, zinc, and reactive alloys at matched kW ratings is thin; the gas calculator explicitly states it is not solving alloy-specific enthalpy and does not predict pour quality [S2]. A dual-chamber research setup for aluminum cans reported melt-rate variation across 4, 6, 8, and 10 kg charges but did not publish a kW-normalized figure, so it is useful for batch-time scaling and not for cross-alloy comparison [S7].
Two trackable signals to watch: tighter published kW-per-kg/hr curves on electric aluminum models above the current 660 lb/hr ceiling, and induction iron data released at the 575 kWh/ton scrap figure with explicit cold-start versus hot-hold split [S1][S3]. Either would meaningfully tighten the answer to the underlying question of how many kilograms per hour a given kW actually delivers on the shop floor.