Charge
The Encyclopedia of Founding (1892)
The amount of metal, fuel, flux, etc., introduced into the furnace at one time, either as one of a number of charges to constitute a whole heat, as in a cupola, or, as the whole quantity charged at once, as in a reverberatory furnace. Too much intelligence cannot be brought to bear on the operation of charging the cupola, as not only may there be a substantial saving effected in the quantity of fuel used, but time in melting may be shortened, as well as hotter iron produced when the true proportions of fuel to iron has been once accurately determined. Commence with 9 pounds of iron to 1 of fuel above the bed-charge, and continue this for one day, noting well the length of time taken to melt the heat, as well as the temperature of the iron melted; then gradually decrease or increase the amount of fuel, as occasion demands, until the smallest percentage possible is reached, after which the whole labor of charging is reduced to a positive science, demanding only accurate weighing of the materials used every day to insure satisfactory results at every heat, providing the requisite blast-pressure is maintained on every occasion. See CUPOLA; RATIO OF FUEL TO IRON; CHARGING THE COMMON CUPOLA. Charging-doors are the doors used for closing the mouth of the cupola after the charge has been thrown therein. It is a great mistake to provide a too limited hole through which to charge the iron and fuel; when this occurs, the operations are sure to be faulty, as the cupola-man cannot place the alternate layers of fuel and iron with the regularity necessary for even melting. Very much of the irregularity in melting, so prevalent almost everywhere, could be prevented if a capacious aperture was provided with close-fitting doors, which latter should be kept closed after the charge is in. See CUPOLA; CHARGING THE COMMON CUPOLA.
What Has Changed in the Last Century
When this foundry dictionary was written in 1892, the cupola was effectively the only way to melt iron in quantity, and the writer's advice — start at 9 pounds of iron to 1 of coke above the bed-charge, then trim the fuel by trial — was the state of the art. Cupolas still run, now with water-cooled shells, divided or oxygen-enriched blast, continuous mechanical charging and weigh-hoppers rather than a man laying alternate layers by hand through a door, but since the mid-20th century the coreless electric induction furnace has taken over most iron melting, especially in smaller shops, because it burns no coke and is far easier to control for emissions. Air-quality rules from the 1970s onward closed many cupolas outright. What has not changed is the underlying logic of the entry: the charge is still a weighed recipe of metal, fuel and flux, and getting the proportions right still decides melt rate, iron temperature and cost.
Written for this edition, 2026.