US2293332A - Open hearth furnace structure - Google Patents

Description

Aug. 18, 1942. s. lv..r Dow Erm. 2,293,332"

OPEN HEARTH FURNACE STRUCTURE l Filed June 23, 1939 ATTORNEYAS.

Patente-d Aug. 18, 1942 y ,n

OPEN HEARTH FURNACE vs'rnuc'rulnt George L. Dow, A'nn Arbor, Mich., and Charles ,Rt Fondersmith, Middletown, Ohio, assignors to The American Rolling Mill Company, Middletown, Ohio, a corporation of.0hio

Application June 23, 1939, Serial No. 280,852

2 Claims. CL 263-44) Our invention relates to animproved structure for open hearth or other heating or melting furnaces and has for its fundamental object the.

provision of a construction whereby the furnace is rendered more efcient and the life of its component parts usefully prolonged.

'I'he more specific objects of our invention will f be pointed out hereinafter or will'be apparent to one skilled in the art upon reading this specilication; and reference is now made to the draw# hearth 2 of suitable refractory supports the bath of molten iron or steel 3 whichI isbeing treated in the furnace. Above the hearth there is a roof 4 of refractory material suitably supported and generally arch shaped. The roof together with the hearth and such other walls as goto make up the furnace form an enclosure in which the hot metal is being treated as known in theart.

mains.

Certain problems arise in,connection with open` hearth furnaces which problems include thev c onservation of heat and preservation of the refractories. Attempts at insulating open hearth furnaces above the charging floor have met with lfailure oronly partial success. The `usual -method of attack has been to impede the flow of heat outwardly by the use of insulation on the outside .ofthe refractories. This results in increased refractory temperatures. In the open hearth furnace the heat release, the gas velocities and the surface temperature of the bath are so high that the problem must be met in a different manner. It is uneconomical'to cool the refractories for obvious reasons; but the bare addition of insulation, while it may contribute t0 the eillciencypf the furnace at any one time, is not helpful'in the long run and seriously reduces the life of the refractories especially in the roof of the furnace.

The problem in part is a problem of keeping the heat out of `the refractories.

Heat enters the refractories* by radiation from the hot metal bath and the flame, by convection f the temperature differential. Convection heating can be lessened by increasing the surface gas lins, but the serious problem of absorption reall of these problems could .be solved simultaneously.

It will be understood that the passage of gases outwardly through the brickwcrk minimizes any dead air effect on the inside of the brickwork. The brickwork, as we have pointed out, is heated by radiation and convection, but is also heated by the absorption of the hot gases in the furnace. The heat of the external surface of the roof causes a flow of air upward. This in turn produces a slight vacuum at the outer surface of lthe roof. The vacuum assists the internal pressure in the furnace in reducing such dead air films as might otherwise be formed; and it; increases the flow of gases through the brickwork.

In all cases where records are available, pressure has been found on the inside of the furnace roof. Such a pressure must indeed be present if a balanced pressure is to be maintained at the charging doors and on the bath surface to prevent the infiltration of cold air and to provide the best contact between the flame and the bath. The pressure is produced in part by the introduction of gases into the furnace but especially by the stack effect of the gases in the furnace.

In the practice of our invention we build up a counter pressure on the outside of the roof refractories and if desired on the wall refractories also.V This may be accomplished by enclosing the refractory surfaces to be protected by a housing or casing which is effectively gas tight, to

the extent that a pressure may be built up therein greater than the pressure of the gases against the same walls or roof on the inside of the furnace. drop through the roof of the furnace thus thickening the dead air films both internally and externally and producing preferably a condition of dead air or gas within the body of the refractory.

' The enclosing medium can be and preferably is provided with a reecting surface so that it may return to the wall and roof s o protected heat which-is radiated from the outside of the wall and roof.

It will be understood that by preventing the outward passage of the furnace gases through the roof or walls so protected heat is kept out of the refractories from withinv andalso the secondary effects of gas infiltration are prevented or minimized. 'I'hus the entrance into the brick An ideal situation would be attained if This reduces or eliminates the pressure work of calcium and iron oxides entrained in the furnace atmosphere is prevented or reduced.l This is of especial importance during the early life of the roof, say approximately the rst ten days or two weeks. Oxides of calcium and iron would, if allowed to penetrate the brickwork, reduce the melting point of the silica causing it to flux. By preventing this action, the silica as quartzite is allowed to change its crystal construction through the stages of tridymite and crystabolite without interference, and the brickwork will thus have a longer life and can withstand a higher working temperature. Thus the insulative effect inherent in our invention may be employed to increase the effciency of the furnace without endangering the life Iof the brick work.

In the practice of our invention we provide a housing over at least the roof of the furnace. This housing is shown as comprising a top portion 5 resting upon the usual tie rods 6 extending between the fra'me portions or otherwise supported as may be desired. Side pieces 1 and .are joined to the edges of the top piece 5 and extend downwardly making contact with the supports 9' and l0 to which the roof arch is attached. Similar arrangements are madeat the ends of the furnace. The metallic sheeting or other form of sheeting used to form the housing may be joined together in any suitable way as by riveting; or it may be welded. It is convenientl to form the top member 5 of corrugated metal for the sake of stiffness and to prevent sagging; but the casing or housing may be formed in a variety of ways and may be reinforced with ribs of angle or channel iron or the like as may be required. The metal employed may be suitable material including plain iron or steel or galvanized materials. Brightness and reflectivity may be increased through plating, through the use of stainless Asteel or otherwise. At a convenierit point in the casing an opening is made as at Il to which by means of a hood l2 and conduit I3 a fan I4, driven by a motor I5, may be attached. This is` a convenient construction but may be varied, as will be understood, by the use of other means for supplying air under pressure. The housing or casing as well as the hood and connecting .conduit are essentially gas tight in the sense that the fan or other source of air under pressure may be employed to build up within the casing and against the -roof or other wall of the furnace a pressure higher or at least as high as the pressure within the furnace, without substantial movement of air through the housing. By substantial movement of air through the housing we mean such air flow as would have a substantial cooling effect on the roof or other wall of the furnace. Our object is to build up against the roof or wall a dead air body which will not only have an insulating effect but also will be at a pressure Apreferably higher than the pressure gf the gases within the furnace against the otler side of the roof or wall.

While we have shown our invention applied to the roof of the furnace, the skilled worker in the artfrom the description which has been given above will be readily able to apply it to other walls of the furnace if desired by the construction of appropriate housings.

Since the pressure on the outside of the roof or wall is greater than the pressure within, inltration of the furnace gases into the brickwork is prevented as has been explained. We, however, do not attempt to cool the brickwork by forcing air from the outside of the furnace through the walls thereof toward the inside, nor do we employ pressures so high as to accomplish this. Our intention is to retain heat within the furnace and to provide a roof or wall which can be worked at higher temperatures. Were we attempting to cool the brickwork by a reverse passage of air, we would feel it advisable to use air pressures on the cooled surfaces of two inches of water or more with air velocities over the surface of say 400 feet per minute. This we do not do. On the contrary, we maintain a pressure of approximately .05 of an inch' of water, or such other pressure as may be suflicient to counteract the pressure Within the furnace and we provide no movement of air over the surface other than that which is necessary to overcome air leakage through the casing or'housing.

While our description and claims are based on the use of air, other gases or vapors may be used, Modifications may be made in our invention without departing from the spirit of it. Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

1. In an open hearth furnace, a supporting framework, a hearth, side walls, and a roof, said framework having tie members overlying said roof and a casing having a top portion overlying said roof and supported by said tie members, and depending portions joined substantially to the edges of said roof so as to form substantially an air tight casing exteriorly of said roof, means for forcing air into said casing, and a connection between said last mentioned means and said casing'whereby a blanket of substantially static airl may be built up within said casing, in contact with, and exterior to said roof, under a controlled pressure.

2. In an open hearth furnace, a supporting framework, a hearth, side walls, and a roof, said framework having tie members overlying said roof and a casing having a top portion overlying said roof and supported by said tie members, and depending portions joined substantially to the edges of said roof so as to form substantially an air tight casing exteriorly of said roof, means for forcing air into said casing, and a connectionA

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