BRASS AND IRON FOUNDRY HAZARDS
Specially written for FIRE AND WATER ENGINEERING.
Working in iron and brass, including, of course, brass and iron-casting goes back to prehistoric times, Tubal Cain being recorded in the Scriptures as the father of those working in them. At first, apparently, each metal was used for household and ornamental purposes, and bronze was chiefly employed. Casting or foundry work is today carried on in one-story rectangular buildings of brick or frame construction, with pitch roof and monitors and floors, whose area varies according to the amount of work to be done in the case of either material. For reasons that will be seen farther on, the calling of an iron or brass founder is by no means unaccompanied with danger, and the work of melting either involves risks from fire that must not be overlooked by the owners of the foundries, the insurance companies, building inspectors, fire chiefs and fire marshals. Hence, as regards the foundry building, the better form of construction is a one-story building, with earth floor, brick or concrete walls, protected steel or concrete posts, and with an iron or concrete roof on protected steel trusses. For a casting a mould or pattern must he prepared; the metal must be melted and in a fluid state be introduced into the cavity of the mould and allowed to cool and solidify. Ingots of brass are cast in stone moulds, usually granite; iron and others, with high melting points, in sand or loam; easily fusible metals in plaster of Paris. The floors of foundries where heavy castings are made are generally covered with, or composed of moulding sand, whereby the danger of fire is reduced. The sand, especially for small cast pigs, must have sufficient gravity to admit of the escape of air and gases generated during the process of melting. In small articles a “flask” contains the sand for the mould. It is of wood, as a rule—sometimes of iron—and is in three parts. It is not hazardous. For very large castings the mould is made in large excavations in the foundry floor, and built up of firebrick suitably braced and supported and finished with loam. For hollow articles a core somewhat larger than the mould is made of sand and paste baked dry in a core-oven and placed on the axis of the hollow mould. This process involves risks, as the core-oven is heated with hard coal, fuel-oil or gas. All excessive moisture must be dried out of large moulds before pouring, lest an explosion should ensue. Sometimes temporary furnaces are used for this purpose, and danger lies in their use. The cupola is another source of danger. In one part of the main foundry room, usually at the side in alxnit the centre, stands this furnace for melting the metal. This may be an air-furnace, or that form of a blast-furnace known as the cupola—the latter being the most in use at the present time. Anthracite coal is used for fuel to a great extent in this country; but coke is better, and wood charcoal is best, as it contains no sulphur. Unlike the air-furnace, which depends upon the ascending column of air in the chimney for its draught, it is fed by a curtent of air forced in at the bottom by a blowing machine through tubes called tuyeres. The cupola is usually made of boiler-iron in the form of a cylinder, lined with fire-brick. It is from 10 to 16 ft. in height and from 3 to 6 ft. in internal diameter, and capable of melting from five to fifteen tons of metal per hour. The chimney may be of brick or boileriron lined with fire-brick, which is more common. A cupola is charged by placing a sufficient quantity of kindling wood upon the floor, and above this a layer of the best anthracite coal in large lumps and in sufficient quantity to fill the cupola to such a height that it will be several inches above the entrance of the tuyeres, after it has well settled and the wood has burned away. Upon the layer of coal one of pig iron is placed, and upon this another layer of coal is deposited—afterwards successive layers of iron and coal. The wood is usually ignited when the first layer of coal is added, and in from an hour to an hour and a half the furnace may be tapped. A reverberatory furnace has a dome that reflects the flame upon a vessel placed within it, so as to surround it. Charcoal is the fuel generally used. Cupolas are very rarely used for melting brass. When the quantity is not large, black lead crucibles are used, which are heated in a furnace placed beneath a platform raised a few feet above, or depressed a few feet into the floor for convenience in handling. The melting point of brass containing thirty-three per cent, of zinc is about 1,800° Fabr. The copper is usually melted first and the zinc added. Anthracite coal is used for heating the crucibles, and the surface of the alloy is covered with charcoal, which is consumed and adds to the heat at the same time that it prevents oxidation. The other processes for brass casting are the same as for iron casting. All moisture must be removed from the sand, or, when poured, the amount of steam formed, together with the expanding gases, would endanger the mould, the workmen, and, if the explosive were excessive, the building. These drying stoves are small, temporarily constructed brick ovens or sheet iron stoves which burn kindling wood or coal, and are not considered dangerous as no fire is known which can be attributed directly to this hazard. Indirectly under the heading of hazardous may be included core-baking ovens. These are generally constructed of brick and heated by hard coal fires. Fuel-oil and gas are also occasionally used to heat these ovens. Several fires are attributed to this hazard. To guard against fires, keen all wood work away from ovens and flues. Protect the woodwork in proximity to ovens and flues. Some flues at times are dangerously hot near the roof and cooler near the furnace; such flues should be extended, thus bringing the hottest portion above the roof. A flue or oven too hot to be touched by the hand is too hot for safety. Where a metal stack passes through the roof, make the roof all metal or tile or the equivalent for a large area and pass the stack through the centre. Do not protect woodwork by partial covering with sheet metal. Woodwork to be effectually protected by sheet metal must be entirely inclosed, as called for in the rules for standard fire-doors and shutters. Wire-lath and plaster and Portland cement can he employed plentifully. Cleaning the castings is accomplished by means of grinding with emery wheels, burnishing, buffing, polishing, painting and japanning. Some of these processes are accompanied with considerable friction; others, such as japanning, call for the application to be made while the stuff is exceedingly hot. The process, as well as those in which friction generating sparks is employed, needs considerable care to avoid fire. Fire may also arise from hot bearings or spontaneous combustion in the refuse of the finishing room, and of the twenty-two foundry fires of unknown origin doubtless some should be credited to the hazards under those processes. The chief hazard of importance under this heading is the drying of the mould. This is usually done with temporary stoves or furnaces either placed directly in the mould or with heat flues so arranged that the heat will be conducted to the interior surfaces of the mould. Excess moisture must be got rid of. The melting pattern is also a cause of fire. Ninety-two fires, directly or indirectly traceable to this source, occurred last year, from melting metal. Eleven of these started from sparks in the cupola lodging on, and setting fire to the foundry roof, and several from overheated woodwork near the cupola. All roofs, therefore, should be of non-inflammable material, and no unprotected material of that sort should be allowed near the cupola walls. Spark-arresters are useful, except that they are extremely liable to rapid deterioration. If fireproof roofs arc not used, the roofs should be well metaled or graveled, with no exposed wooden ventilators, frames or skylights. All cupola charging floors should be of brick, iron or concrete, and hand-hose should always be near to wet down, when the charge is dumped from the cupola, near which there should be no woodwork. In a well-constructed furnace the brass-melting hazard is not especially serious. Furnace, ashpit and flue should be of brick, with no wood near in walls, partitions or floor. Brick or fireproof floor should be insisted upon for all brass foundries. Before the molten metal is run into the ladles, small kindling wood fires are built in them to remove the chill, a practice which is not dangerous, if carefully done in a clear space in the foundry. During the pouring the wooden flasks often catch fire; but the fires are generally small and easily put out by throwing sand upon them. The hot molten metal, however, by coming accidentally in contact with unprotected woodwork has caused several foundry fires, which need not happen, if the floors are of earth and the foundry posts are protected.
Bovey, Minn., now has a waterworks system.