Gas-blast Furnace
The only prerequisite demanded for the gas-blast furnace, manufactured by the American Gas Furnace Company, is a positive air-pressure. This obtained, it will confer an even and controllable temperature, more even distribution of heat in a given space, greater speed of operation, saving of space, greater convenience, and a substantial reduction in the cost of fuel over all other methods. Melting-furnace No. 5, which consumes 200 feet of gas per hour, is described as follows:
This furnace is used for melting metals in black-lead crucibles, Nos. 15 to 20. They are in use for gold, silver, copper, and brass, as also for making tests and smaller melts of iron, steel, glass, etc. The linings are heavy and durable, and firmly bound by iron bands drawn together by clamps. Every part of the furnace is interchangeable, and easily replaced. The combustion chamber consists of the bottom and the cylinder, both firmly secured to the distributing-ring. The burners penetrate the "bottom" lining, and are easily detached and replaced if necessary. The bottom is held in position by the iron platform, which is easily dropped down to replace the lining. The cylinder is secured to the distributing-ring by hinged bolts. The cover is hinged to the shafts, so as to lift clear of the furnace top when swung to either side. The "feed-hole" in cover is sufficiently large to give free access to the crucible without removing the cover, thus confining the heat while feeding the crucible. The small cover closes the feed-hole. The crucible stands upon a conical fire-brick support, which is easily repaired. A channel through the bottom of the chamber affords an outlet for the products of combustion, and in case of accident the metal runs out of it into a drip-pan. By means of outlets for the products of combustion, at both the bottom and top of the furnace, the greater heat can (in a measure) be made to act upon either the bottom or top of crucible. When the vent on top is tightly closed, the greatest heat will be below, while the partial opening of the cover will draw it upwards.
The air-supply pipe is laid close to the floor, or comes up to furnace from under the floor when practicable. This is a precaution against the intermixture of gas and air in the blast-pipe, when the blower is accidentally stopped.
The gas supply required is the size of "Union" G. The consumption of gas varies according to quality of gas and degrees of heat required. Taking ordinary city gas as a criterion, the No. 5 furnace will require from 200 to 250 feet of gas per hour and melt 40 lbs. pure copper in thirty minutes. See BRASS-FURNACE; PORTABLE FURNACES.