US2508739A - Multiple-layer hearth structure for metallurgical furnaces - Google Patents

Description

2,508,739 May 23, 1950 H. L. ALLEN, JR.. EI'AL MULTIPLE-LAYER HEARTH STRUCTURE FOR METALLURGICAL FURNACES Filed Aug. 1, 1947 2 Sheets-Sheet 1 INVENTORS. HARRY L.A1.LEN,JR. y JAMESES \TH, D

ATTORNEY 2 Sheets-Sheet 2 JNVENTORS ALLEN, JR. E/SS ITH JR. EI'AL Hmn'ni STRUCTURE H. L. ALLEN LAYER.

HARRY L MULTIPLE- F 0R METALLURGICAL FURNACES May 23, 1950 Filed Aug. 1 1947 Patented May 23, 1950 MULTIPLE-LAYER HEARTH STRUCTURE FOR METALLURGICAL FURNACES Barry L. Allen, Jr., Garfield Heights, and James E. Smith, Cleveland Heights, Ohio Application August 1, 1947, Serial No. 765,460

6 Claims. (01. 266-43) Our invention relates to furnaces, and particularly to improvements in the hearth structures of open hearth furnaces.

It is well known to those versed in the art that quite often molten metal will break out of the refractory front or back banks'the ends or the bottom of the hearths of open hearth furnaces. These breaks may be due to carelessness of the furnace operators, or to conditions not within the control of the operators such as the presence of non-ferrous materials in the furnace charge.

These break-outs of the molten metal present great hazards to the personnel working about the furnace, cause considerable financial loss by reason of the metal lost, and take the furnace out of production until the damage can be repaired. The necessary repairs are oftentimes difficult to make and frequently cannot be entirely satisfactorily effected.

It is an object of our invention to provide an open hearth furnace having a hearth from the front and back banks, the ends or the bottom, of which, it will be practically impossible for the furnace charge to break out.

It is a further object of our invention to provide a furnace hearth having front and back banks, ends and a bottom, of a structuralnature that will provide a hard-surfaced, close-grained,

and basic mass, whereby very effectively to resist erosion due to the metal and slag contained in the furnace at high temperatures, which structure shall be of rigid character for supporting the contained weight in the furnace, and will retain high temperatures in order that the metallurgical reactions of the molten contained mass be not retarded.

To the above and related ends the improvements presented herein are directed, all as hereinafter fully explained, shown in the accompanying drawings, and claimed in the appended claims.

The annexed drawingsand the following description set forth in detail certain means illustrating our improvements in furnaces, the disclosed means constituting, however, only one of the various forms in which the improvements may be embodied.

In said annexed drawings:

Figure 1 is a broken central vertical longitudinal section of substantially one-half of an open hearth furnace structure in which our improvements are incorporated, the plane of the section being indicated by the line l-l, Figure 2;

Figure 2 is a broken transverse vertical section,

- 2 taken in the plane indicated by the line 2-2, Figure 1;

Figure 3 is a broken horizontal section, taken in the planes indicated by the line 3-3, Figure 1;

Figure 4 is a perspective of one of a multiplicity of carbon blocks which form a sub-base of an improved hearth structure forming part of our invention;

Figure 5 is a view similar to Figure 1 showing particularly, in longitudinal section, the design of the sloping top of the hearth structure forming part of our invention; and

Figure 6 is a view similar to Figure 2, taken slightly to the right of the plane indicated by the section line 2-2, Figure 1, this Figure 6 also showing the design of the hearth top, but in transverse vertical section and substantially in the plane of the axis of the tap hole of the furnace.

Referring to the annexed drawings in which the same parts are indicated by the same respective members in the several views, a showing of a conventional design of open hearth furnace is suggested by the figures, having front and back walls 6 of suitable construction such as chrome brick, a fire-brick roof 26, such as silica brick, furnace ends 21, such as chrome brick, of which the left-hand end only is shown, charging doors 24 in the front wall 6, and an inclined tap hole l3 formed in and centrally of the back of the furnace.

The furnace has a suitable foundation brick structure 5, such as fire brick, supported on structural metallic framework 25, and this foundation 5 supports an upper base ll of the furnace bottom and an intermediate formation or sub-base which will be hereinafter described in detail. It is well known practice to form the sub-base of chrome brick and to form the upper base ll 'of suitable protective and wear-resisting material such as sintered magnesite or any airhardening cold-rammed refractory. The top of this upper base ll forms the top of the furnace hearth. The mass to be heated is charged into the furnace chamber 9 and rests on the top of the upper base H.

The furnace hearth consists of the base I I and the sub-base and the foundation structure 5 and has a raised peripheral portion and a stepped formation which provides a dished structure draining toward the center of the furnace and into the mouth I: of the tap-hole lit for withdrawing the completed heat.

A furnace hearth is usually distinguished by certain terms as to its different portions and the 3 same terms will be herein used, and are a bottom, a front bank 2, a rear bank 3, and ends 4 (of which one is shown). All these different portions of the hearth are provided with our improvements.

This invention is directed to an improved hearth structure for open hearth furnaces, and particularly to the formation of the sub-base of the different portions thereof. We form this sub-base of carbon blocks I.

In thus making use of carbon, instead of chrome brick, for the sub-base, we form carbon blocks of rectangular cross-section and of about the following dimensions: 15 feet long, 30 inches wide, and 11% inches thick, although we do notlimit ourselves to even substantially these dimensions and shape and, in fact, use parts of such blocks, or special blocks, for suitably effecting the formation of certain parts of the hearth, all as hereinafter fully described and as, shown in the accompanying drawings. In these drawings, the blocks of substantially the dimensions and shape mentioned are indicated by the reference number I, and the other blocks, of different dimensions and shapes, for their several purposes, are indicated by distinguishing numbers.

Substantially one-half of a sub-base of a complete hearth is shown in the accompanying drawings and our improved formation thereof consists, in part, of eight carbon blocks I which are laid on one face on the foundation brick 5 crosswise of the furnace in staggered relation so that the same ends of alternate blocks I abut a binder layer I on the same side of the furnace, this binder layer 1 being interposed between the ends of the blocks I and the inside faces of the respective front and back walls 6. Each block I is materially shorter in length than the cross-dimension of the furnace and the remaining space between the layer 1 and the adjacent end of the block I is filled by staggered short blocks 8 one of the ends of each of which abuts the adjacent end of a block I and the other of whose ends abuts the inside face of the adiacent layer I. Actually, one of the two blocks I and one of the two blocks 8, nearest the end i of the furnace hearth, are somewhat shorter than the remaining seven blocks I and their cooperating seven blocks 8 since the centralportion of the furnace, on the back or tapping side, as is customary, has a somewhat expanded cross-dimension and the wall portion opposed to the ends of these shorter blocks I and 8 tapers inwardly so that one of the blocks I and one of the short blocks 8 are not only somewhat shorter but are also bevelled at their ends according to the taper of this portion of the back wall 6.

To provide for lateral expansion under heat, the adjacent sides of the opposed blocks I are laid in somewhat separated condition to provide an expansion space III of about inch between the sides of adjacent blocks I. Whatever slight lengthwise expansion of the carbon blocks may take place is taken up by the binder layers I.

The longitudinal dimension of the improved sub-base is completed, Figure 3, by a narrower block I 4 and its cooperating short block I 4 a sharply upwardly inclined block I5 and its cooperating short block I5 and a second similarly upwardly inclined and end block I6 and its cooperating short block I6 Figures 1 and 5. The adjacent sides of the blocks I4 and I5 are suitably bevelled, and the top side of the block I6 is so bevelled as to present a horizontal top face.

The brick foundation 5 increases in thickness 4 from the center toward the end of the furnace in stepped arrangement and has sharply upwardly directed endportions, so that, as illustrated in the accompanying drawings. four. of the blocks I, the inner blocks. occupy one level, the next two blocks I a substantially higher level, the outer two blocks I and the block ll a still higher level, and the full height of the ends of the sub-base is completed by the upward angle at which the blocks I8 and It are laid. The other half of the V hearth sub-base is laid correspondingly and in reverse relation. This formation provides for the longitudinal draining of the heat toward the center of the furnace when the heat i withdrawn from' the furnace. Of course, the bottom of the heated charge actually is in contact with the top surface of the upper base II, and not with the sub-base formed of the carbon blocks, and this top surface of the upper base II is also inclined toward the center of the furnace, as suggested in Figure 1, and as definitely appears in Figure 5.

Furthermore, the innermost block I is so mounted on the foundation brick structure 5, due to a top sloping formation of the fire-brick of the latter from the front of the furnace to the tap hole II, as to incline toward the tapping side of a the furnace, as appears in Figures 2 and 6. The short block 8 cooperating with the innermost inclined large block I is laid horizontally and at the lower level of the inclined block I. The heated charge is withdrawn through the tap hole I3 formed in the foundation brick work lying between the saidshort block 8 and an upper side block I I laid edgewise and longitudinally of the furnace as hereinafter described.

Opposed series of lengthwise blocks are laid on one of their sides on the ends of the aforedescribed crosswise blocks I8, I|--Il I5I5 and Iii-I6 such lengthwise bloclm being designated, on the charging side, 2|, 22, and 23, and on the tapping side, II, I8, I9, and 20. The blocks I1 and 2| are mounted on the lowermost series of blocks I and I; the blocks I8 and 22 are mounted on the intermediate series of blocks I and 8; the block 23, on the front side of the furnace, is cut to be mounted on the outermost blocks I and 8, the blocks II, I 5 and IS, in a manner clearly appearing in Figures 1 and 3; the block I9, on the rear side of the furnace, is mounted upon the two outermost blocks I and 8 and abuts on the block Il the inner end of the block 20, which latterblock also rests on the block I5 and the block I6 The top surfaces of the blocks I9 and 2B are in the same horizontal plane, somewhat below the plane of the top surface of the outer'end blocks II and I6 and these blocks are cut to be accommodated to each other and the respective top surfaces of the outermost blocks 8 and I, the narrow block Il and the inclined blocks I5 and I6 The magnesite or other suitable base II is formed on the top of all of the blocks heretofore mentioned with a longitudinal downward inclination such as shown in Figures 1 and 5 toward the center of the furnace, and an inclination crosswise of the furnace toward the mouth I2 of the tapping hole It such as shown in Figures 2 and 6.

The surfaces of the carbon blocks lend themselves to' accurate machine finishing so as to provide tight joints 2! between the abutting ends of the blocks and uniform expansion spaces III between the sides of adjacent blocks.

In addition to the objects of the invention hereinbefore stated, such as providing a hearth that is bard-surfaced. close-grained, and basic for resisting erosion, having rigidity for supporting a contained weight, and holding high temperatures, and preventing the breaking out of the molten mass, the aforedescribed structure is comprised of a very few pieces as compared with chrome brick previously utilized for hearth subbases; has a weight less than one-half the weight of chrome brick; presents a sub-base which does not melt, as compared to a melting of chrome brick at about 3900 F.; has substantially no linear expansion, as compared to substantially 2% expansion of chrome brick; has excellent resistance to spalling, and to loads at high temperature, whereas these characteristics of chrome brick are both poor; and avoids the characteristic of reversible expansion occurring in chrome brick at about 2100 F.

If the original wear and heat-resisting layer H does permit a break-through, due to lack of durability in itself, or due to the reforming of its character because of refractory materials (principally dolomite) added between heats combining with the original bottom, the carbon subbase, being impervious to metals, will not allow any steel to pass therethrough, and the period of direct contact between the steel and the carbon will not cause undue damage. Such a break through the base Ii will be discovered before the loss of any of the heat and repairs can be made in a normal manner. Under present practice, such breaks through the layer l I, even ii. discovered, necessitate repairs during a furnace campaign. If the damage holes are of undetermined depth, while a heat is in the furnace, and the judgment of the operators as to their character is wrong, a break-out of the heat through the chrome brick will frequently occur inasmuch as the latter will not support the metal load in the furnace. Furthermore, carbon blocks can be wired electrically to the furnace controls so that if any metal comes in contact with the carbon, an alarm would be sounded and the operators can take steps to tap the beat out of the furnace.

The invention is also applicable to tank linings, by using carbon as a substitute for the conventional clay brick used therefor, and to the linings against the metallic shells of hot metal mixers, insuring that no metal can break through the vessel regardless of the condition of the in ner or wearing lining.

What we claim is:

1. A hearth structure for an open-hearth furnace comprising a foundation and wall structure, and a compact carbon mass mounted therein and abutting and matched thereto, the carbon mass having an'upper basic refractory lining dish-shaped in cross-section and sealing the carbon mass in the foundation and wall structure. the lining having a hard wearing surface and being of density and thickness to withstand the physical effects of charging the furnace load and the temperatures of making the heat.

2. An improvement in a standard multiplelayer hearth structure of open-hearth furnaces having a top basic wearing and heat-resisting layer and a bottom refractory supporting layer. consisting of an intermediate layer which is comprised of a compact carbon mass abutting and matched to the top and bottom layers.

3. In a hearth structure for open-hearth furnaces, the combination with the refractory bottom and the peripheral walls of a hearth, and a hard basic refractory heat-resisting top lining dish-shaped in cross-section, having a draining top surface and forming the heating chamber base, of a sub-base abutting and between the top lining and the bottom and the walls, matched thereto, and formed of a compact mass of carbon blocks, a tap hole from the draining area of the lining surface being formed through the lining and sub-base.

4. A hearth structure for open-hearth furnaces, characterized as in claim 1, in which the compact carbon mass includes a series of crosswise carbon blocks of which each two longitudinally-adjacent blocks are slightly spaced, and lengthwise. hearth-side blocks mounted on the respective ends of the cross-wise series.

5. A hearth structure for open-hearth furnaces, characterized as in claim 1, in which the compact carbon mass includes a series of crosswise carbon -blocks of which each two longitudinally-adjacent blocks are slightly spaced, and lengthwise hearth-side carbon blocks mounted on the respective ends of the cross-wise series, and in which the cross-wise carbon block formations each consists of two end-abutting blocks, one comparatively long and one comparatively short, the long and short blocks alternating lengthwise of the hearth.

6. A hearth structure for open-hearth furnaces, characterized as in claim 1, in which the carbon mass is electrically wired to a signal system positioned exteriorly of the hearth structure.

HARRY L. ALLEN, JR. JAMES E. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHERREFERENCES "Carbon and Graphite Products," published October 1944, by National Carbon 00., Inc., New York.

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