Melt Furnace Energy per Heat and per Saleable Pound

It is the theoretical heat the metal absorbs, divided by the furnace's efficiency -- and then divided again by the casting yield, if the question is what the energy bill reflects. Both divisions are large and they multiply, so the figure a foundry actually pays for is a considerable multiple of the theoretical one. Melting point is not what melting costs, and that is the misconception worth correcting here. Aluminium melts at less than half the temperature of cast iron and takes substantially MORE energy per pound to melt, because its specific heat and its latent heat of fusion are both much higher. Foundry people know this and everyone else finds it surprising, and it is the reason an aluminium foundry's energy per pound bears no resemblance to an iron foundry's despite the lower temperature. Furnace type is the first multiplier and it is a large one. An induction furnace and a gas-fired furnace melting the same iron differ by a factor of two or more in input energy, and the difference is paid on every heat for the life of the furnace. It is also the number most often quoted optimistically, because efficiency depends on how the furnace is run -- holding time, lid discipline, charge preparation and the size of the heat relative to the furnace -- as much as on the equipment. THE CASTING YIELD IS THE SECOND MULTIPLIER AND IT IS THE ONE LEFT OUT. Only the portion of a heat that becomes saleable casting earns anything; the gating and risers are remelted, so their energy is spent again on the next heat. Counting the yield alongside the furnace efficiency is what turns a theoretical figure into the one on the bill, and it is why an energy reduction programme that ignores the methoding is working on the smaller of the two terms. This computes energy from entered figures. It does not supply the theoretical melt energy for any metal, the furnace efficiency, or the yield -- all three are entered, because they vary by alloy, by furnace, and by how the furnace is operated. It does not model holding energy (which on a furnace left up between pours can rival the melting energy), superheat above the pouring temperature as a separate term, melting loss and oxidation, the energy in sand handling, moulding, or heat treatment, or demand charges and time-of-use tariffs, which on an induction melt shop are frequently the larger part of the electricity bill. The foundry's own melt records and metering, and the furnace manufacturer's data, govern.

input energy = charge weight x theoretical melt energy / furnace efficiency, converted at 3,412.14 BTU per kWh; energy per saleable pound divides again by the casting yield.

Melt furnace energy accounting. The theoretical melt energy, the furnace efficiency and the casting yield are all ENTERED because they vary by alloy, by furnace and by how the furnace is operated.

Two divisions and one exact unit conversion.

Estimate. AHJ and licensed professional govern.

Field names used by the API: charge_weight_lb, theoretical_btu_lb, furnace_efficiency_pct, energy_cost_per_kwh, alt_efficiency_pct, alt_theoretical_btu_lb, casting_yield_pct, theoretical_mmbtu, input_mmbtu, input_kwh, cost_per_heat, alt_input_mmbtu, btu_per_saleable_lb

• Efficiency is entered depends on holding time, lid discipline and heat size as much as on the equipmentthe foundry's own metering
• No holding energy a furnace left up between pours can rival the melting energythe furnace manufacturer's data
• No demand charges time-of-use tariffs are often the larger part of an induction shop's billthe utility tariff