US2023174A - Furnace construction - Google Patents

Description

Dec. 3, 1935.. K, HOFMANN 2,023,174

FURNACE CONSTRUCTION Filed Feb. 16, 1934 3 Sheets-Sheet 1 De@ 3, 1935. K. HoF-'MANN FURNCE CONSTRUCTION Filed Feb. 16, 1934 5 Sheets-Sheet 2' Dec.. 3, 1935. K. Hol-MANN FURNACE CONSTRUCTION 3 Sheets-Sheet 3 Filed Feb. 16, 1934 Patented Dec. 3, 1935 UNITED STATES PATENT OFFICE 16 Claims.

This invention relates to a furnace and to the form and method of constructing a furnace. In the form illustrated herewith it has particular application to the construction of open hearth furnaces although it is not of necessity limited to furnaces of that particular type.

The invention has for one object to provide a furnace in which the hearth wall may be built of basic materials such as magnesite, metal case magnesite brick, chrome ore brick or other basic or neutral ceramic material and in which the roof may be made of acid material such as silica. Another object of the invention is to provide a construction for a furnace in which, for a given hearth width, the size of the roof span may be reduced from that heretofore possible. Another object is to provide in a furnace construction a suitable joint between the walls of neutral or basic material and the roof of acid material, such as silica, to compensate for the difference in expansion or shrinkage of the two materials.

Other objects will appear from time to time in the specification and claims.

The invention is illustrated more or less diagrammatically in the accompanying drawings, wherein:-

Figure 1 is a vertical longitudinal section through a stationary open hearth furnace, illustrating in elevation the front wall and door arch construction which form an important feature of this invention;

Figure 2 is a transverse vertical section through a tilting open hearth furnace;

Figure 3 is a transverse vertical sectional detail on an enlarged scale, taken at line 3-3 of Figure 1 or Figure 4;

Figure 4 is an elevational view with parts broken away and on an enlarged scale, looking from within the furnace shown in Figure 1 and illustrating in detail the door arch construction;

Figure 5 is a transverse vertical section taken at line 5 5 of Figure 4;

Figure 6 is a transverse vertical sectional detail taken at line 6-6 of Figure 4;

Figure 7 is an elevation looking from within the furnace and showing the outer row of bricks of the door arch, before the inner row has been put in position.

It will be noticed that in the figures the furnace walls are indicated as being formed of brick and as sloping, at least on one side. Furnaces with sloping walls have been built before, but it has been customary where such sloping wall furnaces have been used to cover the bricks of which the walls are made with some protective material, such as granular dolomite or magnesite, which is sintered upon a wall of basic or neutral brick. Consequently the angle of inclination of the wall must be suiiicient to secure adequate adhesion of the dolomite, magnesite or 5 other mass upon the sloping wall and since this material may settle or shift, the angle of inclination of the wall must be equal or approach the angle of repose of the material which covers it. When this is done, without reducing the desired 10 width of the hearth, the distance across from the top of one Wall to the top of the other is inevitably increased, and consequently greatly increases the width of the arch spanning the distance between the walls.

In the present invention the rows of bricks preferably slope outward from the interior of the furnace and no coating is provided for the walls and there is no necessity, therefore, to provide an angle of inclination approaching the angle of repose of the dolomite, magnesite or any other coating, and the front and back Walls of the furnace are built of proper brick, without any covering and while the walls are preferably slightly inclined, their angle of inclination is infinitely less than would be necessary if they were provided with a coating'such as that described and consequently the span of the furnace roof is reduced. While in the earlier type of sloping wall furnaces the span of the furnace roof has been largely determined by the angle of repose of the rwall coating, such as dolomite or magnesite, in the present invention it is determined only by (a) the desired furnace or hearth width and (b) the setting of the brick. It is possible, therefore, to reduce the arch span of the furnace roof greatly for the same furnace or hearth size, i. e., Width.

The furnace walls may be built of magnesite brick or other basic or neutral material. Magnesite brick burnt at 1600 C- 2912 F.) will eX- pand about 2 per cent when it is thereafter heated in the furnace to 1500 C. @732 F.). Above 1500 C. 2732 F.) the magnesite brick may shrink somewhat and the occurrence of the shrinkage will coincide with the time of softening or deformation of the brick due to the heat and pressure within the furnace which may be about 1500 C. @732 FJ. This factor has been considered in the design of the furnace shown herewith to permit the use of. magnesite brick.

At the temperatures which will normally prevail in the use of the furnace and which will eX- ceed 1600 C. 2912 F.), heavy shrinkage and softening of the magnesite brick in the furnace wall facing the inside of the furnace will occur. This would, of course, weaken the wall and result in possible collapse if true vertical furnace walls were employed. To compensate for this condition and to avoid the danger of collapse the bricks of the wall are laid on a slight incline with respect to the horizontal and this angle of inclination of the brick joints with respect to the horizontal is such as to compensate for the shrinkage of the inner face of the wall at high temperatures.

As heretofore built, hearth furnaces, and particularly open hearth furnaces, have comprised rear walls of any suitable design and front walls with doors. The front walls have, therefore, been made up of piers bounding the doors, and between the piers door arches have been built. These arches were made as a part of the `piers so that the piers and the arches formed a unitary structure. The roof arch running across from the front to the rear wall has been supportedv against skew blocks or bricks which have been themselves positioned in a beam of channel or other suitable section. Thus the roof arch is separate from the wall but the door arches are unitary with the piers of the front wall. One disadvantage of this construction which is avoided in the structure of the present invention lies inthe fact that when the front wall must be repaired or rebuilt the door arches must also be repaired and since these are Vthe most difficult part of the wall to build, the

necessity for rebuilding or repairing them adds greatly to the cost of the operation.

In the present construction the door arches are entirely separate from the front wall and the piers and the door arches are made as a part of the roof arch so that they and the roof arch form a unitary structure, wholly separate from the front wall and from any part of it.' The particular details of construction of the rear Wall form no essential part of the present invention.

Thus in the present invention the door arches of refractory material and the furnace roof arch are constructed as one unit and the bricks of the door arches are built upto form skew blocks against which the roof arch is seated. This construction avoids the necessity of. rebuilding the door arches when repair or rebuilding of the front wall piers is necessary. The door arches, being built of refractory material, preferably of the same as the roof, have the same life as the furnace roof because they offer only a very small surface subject to the flame and gases within the furnace. Y

While for many purposes it is desirable to form the wall of a basic or neutral ceramic material, it might be formed of, an acid ceramic material and thus the wall of this invention is not limited to any particular material, although it will more frequently be formed of basic or neutral material.I

Whatever the material of the wall or of the roof arch, in the present invention the door arches are built into the roof and become a unit with it and thus the front wall in which the door arches are situated becomes in effect only a series of piers because the door arches which extend between the piers are separate from them and are in fact a part of the roof. The door arches while shown as arched or curved upwardly, might be fiat arches or of any desired shape. i In the invention as shown herewith metal members surround the door openings, but as will be described more in detail below, they serve mainly to preserve the door contour and to protect the door from physical injury or damage caused by the movement into or out of the door of charging boxes, tools or objects which might strike against and damage the door. The metal members are thus not weight-carrying members and do not support the roof nor the door arches and they may be of any suitable shape. They are pro- 5 tected from the llames within the furnace by the overlying bricks of the wall piers and by the overhanging bricks of the door arches.

Like parts are designated by like characters throughout the specification and drawings. 10 In Figure 1 an open hearth furnace is shown.

The invention is not limited to the application to an open hearth furnace nor in fact to any particular type of furnace and it is adaptable to furnaces of many different types. As shown, there- 15 fore, in Figure 1, a support A is carried on foundation'members A1. Beams A2 may rest upon the support A and they carry the furnace. In Figure l an outer insulating wall A3 is supported by the beams A2 and carries the inner wall A4 of the furnace which may be of fire brick or other suitable material. It may be lined with some material A5 which may be of any suitable nature and may be applied in any desirable manner. Frequently it will be basic or neutral material, such as 25 dolomite or magnesite. Frame members A6 are carried from any suitable foundation and may support longitudinal members A1. 'I'he details of these members and of the frame construction generally are not shown as they form no essential 30 part of the present invention,

As shown in Figure 2 the invention is applied to a tilting open hearth furnace. In that figure B is a foundation from which track-carrying members B1 extend upwardly to carry the track 35 B2, which is preferably curved on the arc of a circle. B3 is an arcuate cradle member or support. B1 are rollers of any suitable design resting upon the track B2 and supporting the cradle member B3. Frame members designated gen- 40 erally by the symbol B5 extend upwardly from the cradle B3 and surround and support the furnace. They need not be described in detail as their details form no essential part of the present invention. A rack member B6 is pivoted 45 to the frame B5 as at B7. It depends downwardly and engages a pinion B8 on the shaft B9.

A gear B1o on the shaft B9 engages a pinion B11 on the second shaft B12 which carries also a gear B13 which meshes with the pinion B14 on a 50 shaft B15 which is driven in any desired manner from any power source.

The furnace, in the form shown in Figure 2, comprises a layer C which may be of any suitable material and may be lined with a basic or neutral coating C1. The layer C is pierced by one or more tap connections C2, each of which communicates with a pouring spout C3. The furnace is provided with a back wall which may be identical in manner of construction with the front wall or which may differ from it as shown in Figure 2, in which Cf1 is the wall proper, usually of re brick, and C5 is a covering which may be the same as or integral with the covering C1.

The front wall is formed by a plurality of piers D. These, as above noted, will ordinarily be made of a basic or neutral material but may be of any material. As shown they are built up of brick.

Running longitudinally along the furnace on each side is a frame member E which may be of any suitable section. As shown in Figures 2 to 7, inclusive, it is of I-beam section but might be of any suitable section. There are ordinarily no doors in the back wall and a row of skew bricks E1 bears against and is received within the I-beam or frame member E, as shown at the right hand of Figure 2. Bearing against the skew bricks El is one edge of the roof arch E2 which is formed of bricks, preferably of acid ceramic material, such as silica brick. The other edge of the roof arch bears against the opposite frame member E. The details of this construction will now be described.

Since there must be doors in the front wall to permit material to be inserted into or withdrawn from the furnace, arches are formed over the doors. As pointed out above, these arches are structurally separate from the door or wall piers and are out of contact with them. About each door opening and positioned substantially on the outside of the furnace is a metal frame member F which is preferably hollow as at F1 to permit the circulation of water or other cooling medium. As shown particularly in the detailed Figures 3 to '7, inclusive, this door frame is preferably entirely out of contact with the piers D and with the channel or I-beam frame member E. The frame F might, however, be in contact with the I-beams and with the walls and the arch; in other words, it may be a loose or a tight t. Reinforcing members FZ may be applied to the I-beams where desired. As shown these reinforcing members bear against the web and stiifen it, to assist in resisting the thrust of the roof arch. Any part of the metal assembly or framework may be water cooled.

Bearing against the left hand frame member E, at the portion intermediate the door openings, are skew bricks G, which may be substantially the same as the skew bricks E1 on the opposite edge of the roof arch. In the door arches, however, skew bricks of different shape are necessary because the skew bricks which are positioned over the door openings must serve both to support the roof arch and to support and build up the door arches which are made integral with the roof. Such skew bricks appear generally in Figures 1, 4 and 7 and in greater detail in Figures 3 and 6. At each end of each door arch there is an irregularly shaped skew brick G1 which, as shown particularly in Figure 6, rests upon or bears against the inner edge of the left hand frame member E. Against these door and skew bricks Gl and extending across the door opening, is a series of skew bricks G2. As shown particularly in Figures l, 2 and 3, these bricks overlie the upper edge of the metal door frame member F. Inside the skew bricks G1 and G2 and spanning the door opening is a second set of door arch bricks. At each end of each door arch is an irregularly shaped brick G3 and extending across the arch between the end bricks G3 is a second or inner series of skew bricks G4. 'I'he roof arch bricks E2 bear directly against th-e skew bricks G4 as shown in detail in Figures 3 and 6. Bricks or other lling material G5 and G6 may be inserted as 6 above the skew bricks G1 and G3 and serve to round out the edge of the roof arch.

A door closure H of any suitable design may be mounted to close each of the door openings. The details of the door form no essential part of the present invention.

I have not described in detail the furnaces nor the means for heating them nor for introducing material into or removing it from them, as these features form no essential part of the present invention. My construction is applied mainly to shown in Figure the front wall of the furnace although it may also be applied to the back wall and it is independent from the particular details of furnace construction and of the means for heating the furnace, as well as the manner o-f charging and uncharging it.

It will be realized that whereas I have herewith shown and described a practical operative device, nevertheless many changes might be made in the size, shape, number and disposition of parts without departing from the spirit of my invention and I wish, therefore, that my showing be taken as in a sense diagrammatic.

In particular the details of the arch co-nstruction over the doors may be greatly varied. AsV

above noted the arch may be at or of any desired shape.V While I have shown two rows of bricks forming the door arch, such as the bricks G2 and G4, one row might be substituted, by the use of larger bricks or with the use of smaller bricks several' rows might be inserted instead of the two shown. Whatever the ar'- rangement of bricks in the door arches and in the skew bricks G which are placed intermediate the doors, it is preferable to arrange the skew bricks so that there is one continuous plane o-f bricks against which the roof arch is built and there is thus provided one continuous plane to receive the thrust' of the roof arch. The water cooled frame F may be of any desired shape and may be a loose or a tight fit. It need not project into the door arch as shown in Figures 2, 3 and 6.

While the two furnaces shown are described as open hearth furnaces, the invention is not limited to any particular type of furnace and might be embodied in and applied to a furnace of any other type.

Where in the specication and claims I have spoken of expansion of parts of the furnace and of the diierence in expansion between different parts of the furnace, it is important to recognize the fact that I am considering not merely differences in the coeflicients of expansion of different materials, but the difference in mass expansion of different parts of the furnace, because if the piers and the roof arch were made of identical material there still might be difference in mass expansion due to the different heating and cooling conditions and due to the difference in cross sections of the parts and due to other factors, and thus in the solution of the problem involved the furnace must be constructed not merely to provide for the use and expansion of materials of different coeiicients of expansion but to provide also for those diiferences in mass expansion which have just been described.

The use and operation of this invention are as follows:

No matter what the details of the furnace 1ining, this lining has a limited life and what may be generally called the brick work of a furnace from time to time must be renewed. The heat, the flames, the material treated in the furnace, the chemical reactions which take place, and other inuences, affect the furnace lining and gradually destroy it so that it must be renewed and it is one of the important objects of the present invention to build a furnace in such manner that the amount of reconstruction is reduced as far as possible and to build a furnace so that the reconstruction can be carried out as cheaply as possible', among other things by the elimination of the necessity of reconstructing parts which in themselves may not have been sufficiently eroded or worn to require their own replacing or reconstruction.

In practice in the past it has been found that in the use of many types of furnaces the front wall and the door arches require replacement several times during the life of one roof arch. In other words, the walls wear out more rapidly than the roof. The most diiicult part of the walls to rebuild/is the roof arch. Many ways have been tried to avoid this difculty and to give the walls as long life as the roof. One such arrangement is shown in Figure 2, in the right hand wall, in which the coating of magnesite or other ceramic material C5 is used. This, however, as there shown, is applied to the back wall.

In the present invention, to avoid, the diiiiculties mentioned and particularly to avoid a repeated reconstruction `-of the door archor arches, in case there are more than one, the door arches are built quite separately from the piers, as has been explained above, and the door arches are built as a unit with the roof arch, of the same material as the roof arch, and they have the same life, so that when the front wall requires reconstruction the door arches do not require reconstruction and remain until the roof arch, with which they form a unit, requires reconstruction.

As formed in the structure of the present invention, the roof arch is wholly supported in the I-beam shown. Skew back bricks are inserted in the I-beam and against one of its ilanges and the roof arch is supported directly on these. Certain of the skew back bricks are also given the shape necessary to enable them to be used to build door arches and they thus not only form the door arches but form the skew back bricks to receive the roof arch. Ihey thus carry out the dual purpose mentioned and are a unit with the roof arch and since the door arches are part of the roof they do not need to be rebuilt until the roof is rebuilt. They have the same life as the roof, among other reasons because they offer only a small surface to the attack of the flame and gases, being very flame and against them. This effect is shown in detail in Figures 3 and 6 particularly.

In constructing the furnace of the invention, the roof arch is ordinarily made of anacid material such as silica and the pier is ordinarily made of a basic or neutral material. Where this is the case it is important to keep the acid roof bricks or door arch bricks out of contact with the basic or neutral pier bricks. When heated, if the two are in contact, the reaction is such as to cause extremely rapid erosion or destruction of both contacting materials. This rapid erosion is further increased by the fact that the conditions of expansion and contraction of the acid and basic or neutral bricks are so different, and

in the present invention the construction is such" that the basic or neutral bricks of the piers are held out of contact with the acid bricksof the roof arch or of the door arch.

I claim:

l. In combination in a furnace, a wall structure formed of a plurality of separated piers, a roof arch for said furnace and a door arch spanning the distance between a pair of piers, said door arch and said roof arch forming an integral structure, the door arch being spaced away from the piers adjacent it.

2. In combination in a furnace, a wall structure largely shielded from the.v gases by the roof arch where it rests' formed' of a plurality of separated piers, a roof arch for said furnace and a door arch spanning the distance between a pair of piers, said door arch and said roof arch forming an integral structure, the door arch being spaced away from the piers adjacent it, and a liquid cooled frame for each door, said piers and said door arches overhanging said frame, whereby the latter is shielded from heat within the furnace.

3. In combination in a furnace, a wall structure formed of a plurality of separated, generally vertically extending piers, a roof arch for said furnace and door arches, one spanning the distance between each pair of piers, said door arches and said roof arch forming an integral structure, and means independent of said piers for supporting said door arches and said roof arch, the door arches being spaced vaway from the piers adjacent them, and a liquid cooled frame for each door, said piers and said door arches overhanging said frame, whereby the latter is shielded from heat within the furnace.

Ll. In combination in a furnace, a front wall and a back wall, a roof arch extending between the two, the front wall being formed of a plurality of piers, there being door spaces between pairs of piers, and an arch permanently built into position in each of said door spaces extending across between the pair of piers framing each door space, said door arches being supported independently of said piers.

5. In combination in a furnace, a front wall and a back wall, a roof arch extending between the two, the front wall being formed of a plurality of piers, there being door spaces between pairs of piers, and an arch in each of said door spaces extending across between the pair of piers framing each door space, said door arches being supported independently of said piers and being built integrally with said roof arch.

6. In combination in a furnace, a front wall and a back wall, a roof arch extending between the two, the front'wall being formed of a plurality of piers, there being door spaces between pairs of piers, and an arch in each of said door spaces extending across between the pair of piers framing each door space, said door arches being supported independently of said piers, being built integrally with said roof arch and being held out of Contact with said piers.

7. In combination in a furnace, a front wall and a back wall, a roof arch extending between the two, supported independently of them, the front wall being formed of a plurality of piers, there being door spaces between pairs of piers, and an arch in each of said door spaces extending across between the pair of piers framing each door space, said door arches being supported independently of said piers, and being built integrally with said roof arch.

8. In combination in a furnace, a front wall and a back wall, a roof arch extending between the two, supported independently of them and .held out of contact with them, the front wall being formed of a plurality of piers, there being door spaces between pairs of piers, and an arch in each of said door spaces extending across between the pair of piers framing each door space, said door arches being supported independently of said piers, being built integrally with said roof arch and being held out of contact with said piers.

9. In combination in a furnace, a front wall, a back wall and a roof arch spanning the distance between the two, the front wall being provided with wall portions and a door portion, there being an arch spanning the door, formed of a material of different coeicient of expansion from that of the wall portions, the said door arch being formed integrally with the roof arch and being spaced away from said wall portion, whereby differential expansion of the wall portion and the doonarch portion is permitted.

10. In combination in a furnace, a front wall, a back wall and a roof arch spanning the distance between the two, the front wall 4being provided with wall portions and a door portion, there being an arch spanning the door, formed of a material of different coelcient of expansion from that of the wall portions, the said door arch being formed integrally with the roof arch and supported separately from the wall portions, and held out of contact with them, whereby differential expansion of the.wall portion and the door arch portion is permitted.

11. In combination in a furnace, a front wall, and a back wall, a roof arch spanning the distance between the two, the front wall being provided with wall portions and a door portion, there being an arch spanning the door, formed of the same material as the roof arch and formed of a material of different coeicient of expansion from that of the wall portions, the said door arch being formed integrally with the roof arch and supported separately from the wall portions and held out of contact with them, whereby differential expansion of the wall portion and the door arch portion is permitted.

12. In combination in a furnace, a front wall, a back wall and a roof arch spanning the distance between the two, the front wall being formed with wall portions and a door portion, there being an arch spanning the door, said arch being separated from the wall portions and providing a support for the edge of the roof arch, and forming a unit with the roof arch.

13. In combination in an open hearth furnace,

front wall piers, a roof arch, a door arch extending between said front wall piers and being out of contact with them, said door arch formed of skew back bricks, which bricks simultaneously support the roof arch, the roof arch and the door arch forming a unit.

14. In combination in an open hearth furnace, front wall piers, a roof arch, a door arch extending between said front wall piers and being out of contact with them, said door arch formed of skew back bricks, which bricks simultaneously support the roof arch, the roof arch and the door arch forming a unit, the roof and door arches formed of refractory material and the wall piers formed of a different refractory material having a coeihcient of expansion diferent from that of the roof and door arches.

15. In combination in a furnace, a front wall, and a back wall, a roof arch spanning the distance between the two, the front wall being provided with wall portions and a door portion, there being an arch spanning the door, formed of the same material as the roof arch and having a different mass expansion from that of the Wall portions, the said door arch being formed integrally with the roof arch and supported separately from the wall portions and held out of contact with them, whereby differential expansion of the wall portion and the door arch portion is permitted.

16. In combination in a furnace, a front wall and a back wall, a roof arch extending between the two, the front wall being formed of a plurality of piers, there being a door space between a pair of piers a horizontal ceramic support and a self-supporting ceramic arch permanently built into position in said door space, spanning the distance between the piers framing each door space, said door arch being supported independently of said piers.

KONRAD HOFMANN.

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