US3448703A - Dome-shaped electric furnace roof construction - Google Patents

Description

Juile 10, 1969 WHANSEN ET AL 3,448,703

DOME-SHAPED ELECTRIC FURNACE ROOF CONSTRUCTION Filed Dec. 26. 1967 Sheet INVENTORS. AEWA/'T/I 1144 44 55 W/LLMMC 720201? v lrram/vzf m 1 R Z W 6 0 r. 2 mm m6 6 M June 10, 1969 K. w. HANSEN ETAl 3,448,703

DOME-SHAPED ELECTRIC FURNACE ROOF CONSTRUCTION Filed Dec. 26. 1967. Sheet of 2 INVENTORS'. mam 5mm #mvsew BYW/LL/AM c 74mm? MZIAflM ATTOAIVEY United States Patent 3,448,703 DOME-SHAPED ELECTRIC FURNACE ROOF CONSTRUCTION Kenneth W. Hansen, Bethel Park, and William C. Taylor, Pittsburgh, Pa., assiguors to Dresser Industries, Inc., Dallas, Tex., a corporation of Delaware Continuation-impart of application Ser. No. 533,725, Mar. 4, 1966. This application Dec. 26, 1967, Ser. No. 701,514

Int. Cl. F23m 5/02; H051) 7/18; F23d 1/00 U.S. Cl. 110-99 7 Claims ABSTRACT OF THE DISCLOSURE A dish-shaped dome type furnace roof comprising basic refractory shape arranged in concentric rings, a portion of which comprise metal encased shapes covered by a contour control structure and the remainder of which comprise shapes mortared together.

Related case This case is a continuation-in-part of our application Ser. No. 533,725, filed Mar. 4, 1966, having the same title, now abandoned. That application has been abandoned favor of this application.

Background A good treatise on the subject of electric furnaces, the construction of roofs therefor, and the like, is Electric Furnace Steelmaking, Volume 1, Design, Operation, and Practice, published by Interscience Publishers, a division of John Wiley & Sons, Inc., in 1962. It is a product of the Physical Chemistry of Stcelmaking Committee of The American Institute of Mining, Metallurgical, and Petroleum Engineers. The reader is directed thereto for a discussion of known prior art and, in particular, the section entitled Roof Construction, beginning on page 163. As this work points out, silica brick and, to a lesser extent, certain types of firebrick and high alumina brick have been the conventional refractories for the roofs of electric steelmaking furnaces. However, with increasingly severe and extended furnace campaigns becoming conventional, such brick are proving of insuflicient refractoriness. Basic brick would seem to provide the logical substitute, but usage thereof has been considered replete with difficulties. First, the very appreciable increase in density as one moves from silica (about 120 p.c.f.) or one of the more dense high alumina brick (for example, about 160 p.c.f.) to basic (180+ p.c.f.) brick so increases the total weight of a given roof that much existing roof lifting and moving equipment is insufficient. However, in now or refurbished shops (or, of course, in those with large enough moving equipment) this is overcome and, thus, it is an object of this invention to provide a basic refractory roof construction of the type used for electric furnaces and the like.

In United States Patent No. 2,814,476, there is illustrated one prior published suggestion of a possible construction for a basic electric arc furnace roof in which all of the brick between electrode mounts and what are termed abutment brick are suspended from a rather complicated arrangement of interconnected steel work to form a flat roof.

Others have also suggested a suspended flat-type roof construction for the electric arc furnace but, as far as we know, none has ever been installed and operated successfully. In any even, one problem with such flat roof construction is that when a furnace is tilted (and tilting to an angle of 40 is not out of the ordinary) this puts 3,448,703- Patented June 10, 1969 can cause a short circuit of the furnace. This can be, in I large part, mitigated by avoiding use of carbon steel anywhere within perhaps six feet of the center of the roof. Nonmagnetic stainless steel can be a useful device.

Brief description of the invention The present invention provides cooperating hold-down contour structure for a novel arrangement of basic refractory brick in a downwardly opening dome-shaped roof configuration. The arrangement overcomes the various prior art difiiculties outlined above. Briefly, a roof according to this invention is comprised of a plurality of abutting rings of basic brick contained Within a circular roof band in a downwardly opening domed configuration. A portion of the brick in the roof which are arranged in the rings between the band, but stopping short of the electrode ports, are metal cased brick; for example, of the type disclosed and claimed in United States Patent No. 3,180,744, the preferred embodiment described in column 5, beginning line 58. By a portion, I mean at least two rings of brick adjacent the band are metal encased. It is preferable if a majority of the brick in the roof are metal encased. The metal casing is preferably of the general type shown in United States Patent No. 2,736,187. The remainder of the brick in the roof can be of the same type but they are not metal cased. They are laid up with refractory mortar. A preferred mortar is comprised approximately of about 40% ball mill fine dead burned magnesite, about 50% pigment grade iron oxide, and about 10% of sodium silicate. Other refractory mortars comprising finely ground refractory aggregates such as calcined fire clay, calcined bauxite or chrome ore or magnesite and a suitable binder such as clay and sodiumsilicate may be used. Suitable binders for refractory mortars are described in Cementitious Bonding in Ceramic Fabrication, chapter 18, Ceramic Fabrication Processes, edited by W. D. Kinary (1958). The mortar is applied as a bed joint between adjacent rings, and as a dipped joint between brick in a common ring. The remainder of the center area about the electrode portion is rammed in place. We prefer a high alumina composition called Korundal Plastic, a high alumina ramming mix.

The metal cased brick are provided with means to allow expansion, as is discussed in more detail below. In addition, there is provided contoured hold-down structure arranged to prevent upward movement of the roof when it is heated. The roof is in compression when heated.

Detailed description A better understanding of the invention and other features and advantages thereof will become readily apparent from a study of the following detailed description, with reference to the appended drawings. In these drawings:

FIG. 1 is a sectional side elevation of the roof of FIG. 2, taken along the line AA;

FIG. 2 is a top view of a roof construction according to this invention;

FIG. 3 is an isometric view of one of the metal encased brick used in fabrication of the roof of FIGS. 1 and 2; and,

FIG. 4 is a schematic diagram of an alternative holddown structure design.

Before describing the drawings in detail, it should be understood they show but one manner of practicing this invention and thus are intended as exemplary only and not limiting since the true measure of the spirit and scope 3 of this invention is as defined in the hereafter appended claims.

In FIGS. 1 and 2 there is shown a plurality of rings, numbered 1 through 19, arranged circumferentially within the circular roof band 20. Rings 1 through 11, all of the full rings, are fabricated of metal encased brick of the type shown in FIG. 3. The remaining partial rings, 12 through 19, are of uncased brick. Sequential rings 12 through 19 are joined by approximately A of mortar. Each of the electrode ports 22, 23, and 24 are fabricated of a plurality of refractory arch brick; for example, of the type disclosed and claimed in United States Patent No. 3,210,206. These brick are also laid up with a & mortar join-t. Contoured hold-down members 25 extend across equidistant chords of the circle formed by the band 20 to hold down substantially all rings of the metal encased brick in those areas where distortion is most likely to occur. In FIG. 2, we have shown but three of these members. An even more satisfactory arrangement is shown in FIG. 4, which illustrates an intersecting arrangement of contour members 25A generally in the form of a sixpointed star. The ends of the reinforcing members 25 or 25A are suitably affixed at their respective ends to the retaining band 20. They can be spring-loaded to allow for some upward movement of the roof; for example, a spring of sufficient strength as to allow only about /2 rise in the roof. Alternatively, the contour member can be spaced about 1 or /2 above the cold roof, thus allowing for a /2 rise when the roof is heated. The center area 35 is of a rammed refractory monolith.

When the furnace is placed in service, adjacent metal cases in the metal encased brick rings oxidize and react with each other and adjacent brick forming a monolithic structure over the hot face. In the more central uncased rings the mortar likewise reacts with adjacent brick, whereby all of the brick in the roof are joined in a monolithic structure over the hot face. When an iron oxide containing mortar is used in the inner rings, joints of similar (predominantly magnesio-ferrite) chemical composition are formed over the entire roof between brick without the danger of inducing an electrical current through metal cases.

There is provision for both circumferential and radial expansion. As can be seen by reference to FIG. 3, each of the brick has an expansion crimp 50 formed on the flat side adjacent its hot face and an additional crimp 51 formed on one edge adjacent the hot face. A single crimp 52 is formed adjacent the cold face of one fiat side of each brick. It is preferable that the crimps 50 and 52 be on the same flat face to simplify bricklaying. This arrangement provides for both radial and circumferential expansion over the hot face and circumferential expansion over the cold face of each ring.

Also note that the three partial segments of ring 19 abut substantially centrally about the vertical axis of the roof. This arrangement provides increased strength until the roof is burned in and the rammed material acquires a ceramic bond therethrough.

The shapes of the respective brick of each ring are dictated by conventional practice as, for example, shown in page 507 of the book Modern Refractory Practice, 4th

edition, published by the Harbison-Walker Refractories Company in 1951.

Having thus described the invention in detail and with sufficient particularity as to enable those skilled in the art to practice it, what is desired to have protected by Letters Patent is set forth in the following claims:

We claim:

1. In an electric furnace or the like having a downwardly opening dish-shaped dome-type roof, said roof being fabricated of a plurality of basic refractory shapes contained in adjacent rings within a band, said shapes arranged in a series of concentric rings, a portion of the I brick forming adjacent rings and extending from said hand towards the center of said roof being metal encased basic refractory brick, the remainder of the brick forming the remainder of the rings being uncased basic refractory brick joined by a refractory mortar, said metal encased brick having means arranged to allow for expansion upon heatup of said roof, there being contour controlling hold-down structure over substantially all of said metal encased rings.

' 2. In an electric furnaceor the like having a downwardly opening dish-shaped dome-type roof, said roof being fabricated of a plurality of basic refractory shapes contained in adjacent rings within a band, said shapes arranged in a series of concentric rings, a major portion of the brick forming adjacent rings and extending from said band towards the center of said roof being metal encased basic refractory brick, the remainder of the brick forming the remainder of the rings being uncased basic refractory brick joined by a mortar characterized by a substantial proportion of iron oxide, there being sufficient iron oxide to react with adjacent basic brick to form a monolithic hot face, said metal encased brick having means arranged to allow for expansion upon heatup of said roof, there being contour controlling hold-down structure over substantialy all of said metal encased rings.

3. The roof of claim 1 in which said cased brick include means adjacent the cold face thereof allowing for circumferential expansion, and means adjacent the hot face thereof allowing for both radial and circumferential expansion. 4. The roof of claim 2 in which the means which allows for expansion at both the hot face and the cold face is comprised of expansion crimps formed from the metal of which the metal cases are made.

5. The roof of claim 1 in which the hold-down structure is comprised of a plurality of arched members extending across substantially equidistant chords of the band.

6. The roof of claim 5 in which the arched members are arranged to allow on the order of about A." rise in the roof upon heat-up.

7. The roof of claim 5 in which there are three of said arched members.

References Cited UNITED STATES PATENTS 2,304,170 12/ 1942 Heuer. 3,139,048 6/1964 Hall. 3,367,292 2/1968 Woodruif et al. -99

FREDERICK KETTERER, Primary Examiner.

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