Brass-furnace
The common method of erecting brass-furnaces for melting in crucibles is to build them on one side of the shop. The insides are formed within cast or wrought iron castings, from 18 to 20 inches diameter and about 36 inches high. These are ranged over the ash-pit, and the air is supplied through gratings set even with the foundry floor, through which the air finds its way to the pit below. Usually the tops of the furnaces stand about 9 inches above the floor and are covered while in operation with a cast-iron doomed door. The casings are fire-brick lined to a suitable diameter that will leave the requisite amount of fuel to surround the crucible. A small hole, about 6 inches square, is left near the top, which connects with the flue leading to the chimney. If a row of such furnaces are thus constructed, there should be a separate flue for each, so that one or more of them may be employed at any time without any interference with the draft. The chimney in all cases should be a tall one to encourage the draft. Portable brass-furnaces, round and square, are now supplied by the dealers. They are simply an iron casing, complete in all respects, except the lining; can be located at any part of the foundry, and connected with the chimney. The Gas-blast Melting Furnace manufactured by the American Gas Furnace Company is now extensively employed for all purposes of crucible melting. A positive air-pressure maintains perfect combustion of the gas, and cleanliness is secured by the entire absence of soot. The best results are attained in these furnaces by securing perfect combustion and by confining the space to be heated to the smallest possible limits consistent with convenience. These furnaces are made in sizes to suit Dixon's block crucibles from Nos. 0 to 200; special fire-bricks being made for every sized furnace (see GAS-BLAST FURNACE). Very frequently the eupola is employed when a large quantity of metal is wanted. A much better mode, however, is to provide a reverberatory or air-furnace in close proximity to the brass-foundry, or wherever it may be customary to cast heavy brass-work.
The Garrett Furnace, a fire-brick construction after the manner of an air-furnace, is described by the inventor as follows: "In a shop where any considerable amount of brass is melted, the method of melting in a crucible is wasteful and expensive. The Garrett Furnace not only saves the cost of crucibles, but is also economical of metal, fuel, and labor, besides reducing the time of melting a charge from one half to two thirds. This furnace was especially designed for full gas, but with a slight modification of details it could be used with soft coal or crude oil as a fuel.
There is a slant hole for charging coils of copper wire or material difficult to compress into a small space. Smaller pieces, bars, or plates are introduced through the charging door. The bosh for the molten metal is located below the melting-chamber, being 33 inches wide by 18 inches high from the bed to the top of the arch, which is composed as shown, and has filling above and between it and the bottom of the charging-chamber, made of fire-clay and sand. The bed of the bosh is undulated being composed of a mixture of fire-clay and sand, which makes it as hard as a crucible and will last from two to seven weeks without repair, according to the work required of it. Below the bosh gas-flues are provided, two 6-inch by 6-inch for gas and two the same size and adjacent for air. The gas is brought to the gas-flues by two 1/2 inch gas-pipes having valves for regulating the supply, and passes along the flues to a combustion-chamber, 12 inches wide, 36 inches long, where it mixes with air, ascends and passes over the bridge, and is divided into two flames, one larger than the other. The large flame passes over the bosh to the flue, and the other flame passes through the melting-chamber to the flue. Dampers are provided in the flues to regulate the supply of gas, or proportion it for either of the chambers as desired. One flue is 4 inches by 10 inches, and the other is 8 inches by 10 inches, both entering into a stack-flue 16 inches square.
A door is provided to give access to the combustion-chamber and bridge, and another door, gives access to the bosh. See BRASS; PORTABLE FURNACES.