US3356353A - Dome-shaped electric furnace roof construction - Google Patents

Description

De. 5, 1967 NALE EI'AL DOME-SHAPED ELECTRIC FURNACE ROOF CONSTRUCTION 3 Sheets-Sheet 1 Filed Feb. 14, 1966 IN ROBERT E /POBERT l4! 4 VENTORS /V4LE SS/DY ATTORNEY Dec. 5, 1967 R. F. NALE ETAL 3,356,353

FURNACE EOOF' CONSTRUCTION DOME- SHAPED ELECTRIC 3 Sheets-Sheet 2 Filed Feb. 14, 1966 F z'g. 4

ATTORNEY Dec. 5, 1967 R. F. NALE ETAL 3,356,353

' DOME-SHAPED ELECTRIC FURNACE ROOF CONSTRUCTION Filed Feb. 14, 1966 3 Sheets-Sheet 5 INVENTORS ROBERT/ 1v E f ROBERT M C SID) ad WM United States Patent 3,356,353 DOME-SHAPED ELECTRIC FURNACE ROOF CONSTRUCTION Robert F. Nale, 5141 Azalea Drive, Pittsburgh, Pa.

15236, and Robert W. Cassidy, 153 Clemson Road,

Bryn Mawr, Pa. 19010 Filed Feb. 14, 1966, Ser. No. 527,144 7 Claims. (Cl. 263-46) ABSTRACT OF THE DISCLOSURE In electric furnace construction the improvement comprising filling the delta area of the roof with a group of substantially identical refractory shapes, the shapes in addition forming a minor portion of each of the electrode port rings.

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 publication 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, the preponderant portion of the roof is made up of a group of concentric rings of refractory brick from an outer retaining band to a point just short of the three electrode ports. Partial rings extend a short distance between adjacent electrode ports, each of the ports thermselves being constructed of a circularly-arranged series of refractory arch brick. The remaining area substantially centrally of the roof between the complete and incomplete rings of brick and the ports is conventionally rammed in place.

This rammed section is perhaps the weakest section of the roof, particularly until the roof is burned-in and a ceramic bond formed through the rammed monolith. Obtaining uniform density centrally of the three electrode ports with a ramming mix is also difiicult. Yet further, that central area between the ports, sometimes referred to as the delta section of the roof, is a troublesome hot spot since hot gases and fumes issuing from the electrode openings or ports severely attack the refractory in this area; and stresses are induced because of superimposed water-cooled glands (in some instances). In addition, movement of the electrodes results in their sometimes hitting or bumping the refractories making up the electrode ports. There are, of course, the ever present stresses due to thermal expansion and contraction of the roof. All

of the foregoing factors have considerable influence on the refractory life of the center or delta area of the roof.

It is, therefore, an object of this invention to provide a superior construction for the delta area of an electric furnace roof. The improved construction is arranged to provide the greatest amount of fired refractory in the delta area with the fewest possible joints. This use of fired refractory assures substantially identical density through this area.

It is another object of the invention to provide a set of refractory shapes, said shapes being substantially identical, but arranged together cooperate to completely fill the delta area of the furnace and to additionally interlock with each other and with additional conventional refractory arch shapes or the like to form the three electrode port openings.

A better understanding and further features and advantages of the present invention will become readily appar cut to those skilled in the metallurgical and refractories arts from a'study of the following detailed description ICC of a preferred modified configuration of the shape of FIG. 2, schematically illustrating tongue and groove interlocking elements therefor;

FIG. 3 is a side elevation of the shape of FIG. 2;

FIG. 4 is illustrative of alternative shapes which can be used to fabricate the delta area of the roof of FIG. 1;

FIGS. 5 and 6 are still additional alternative arrangements for lining the delta area of an electric furnace roof;

FIG. 7 is still another alternative configuration. However, the construction of FIG. 7 requires use of a variety of arch shapes greater than the variety required for any of the other constructions of the previous drawings;

FIG. 8 is yet another alternative construction of the delta area of an electric furnace roof.

It should be understood that the attached drawings are but exemplary of the practice of this invention, and are presented for purposes of easier explanation only and not by way of limitation Applicants do not intend to be limited thereto but, rather, note that the true sprit and scope of the invention is as defined in the hereafter appended claims.

In preferred practice of the present invention, our design for the construction of the delta area of an electric furnace utilizes standard electrode port brick for approximately threefourths of the circumference of each electrode port ring, thereby keeping need for special shapes to a minimum. The units which We use to line or form the delta area are further arranged to comprise the remaining about one-fourth of respective adjacent electrode rings. Only one ype Of refractor shape is required to build this delta area. In the preferred practice, there are three of such pieces or shapes forming a set which together cooperate to form the delta and electrode port section, as just discussed. One of these shapes, in its installed at titude, cooperates with the other two members of the set in a very positive fit. This positive fit is the result of various forces. As is well known, electric furnace roofs are dome-shaped, i.e., of generally downwardly-opening concave or inverted dish shaped configuration. The dome shape is usually fabricated by laying concentric rings of brick on a dome-shaped wooden form or the like. When all brick have been installed, including those of the delta section, the completed roof is lifted from the form. Once the roof is lifted from its form, the brick elements making up the roof are placed in compression due to the inherent characteristics of lines of force through a dome-shaped construction of separate members such as one finds in the electric furnace roof. As will be better understood from the description hereafter, the three identical shapes used to form the electrode ports are tightly wedged against each other by these forces, and also tightly held as a part of the rigid group of shapes forming the respective electrode ports all without needing extraneous hold-up or holddown structure.

Our design incorporates the greatest amount of fired refractory in the delta area with the fewest possible joints or points of weakness. Our design helps to decrease the effect of preformed and fired refractory surfaces that can be subjected to difierential thermal expansion with adjacent monolithic ramming material or refractory plastic.

Referring now to the drawings: In FIG. 1, there is shown an electric furnace comprised of an outer furnace roof retaining ring (usually a steel structural memher-for example a channel, I beam, etc.) having a plurality of concentric rings of refractory brick 22 supported therewithin. These brick are of conventional shape as for example discussed on page 507 of Modern Refractory Practice, 4th edition, published in 1961 by the Harbison- Walker Refractories Company. As one approaches the electrode port rings 23, 24, and 25, partial rings of brick, such as 26 and 2'7, are present between the three equispaced ports. The port rings themselves are formed of a plurality of regular arch-shaped brick 30 which are used to form approximately three-fourths of the circle defining the electrode port opening. The remaining one-fourth of each of the rings forming the respective ports is formed by a complimentary portion of one of the special shapes 31.

FIGS. 2 and 3 represent an enlarged view of one of the special shapes 31. A top or bottom face may be, in general, characterized as defined by five sides. Two sides, 1 and 2, intersect to form an obtuse angle 3. An additional pair of sides, 4 and 5, intersect the sides 1 and 2 to form equal included acute angles 6 and 7. The remaining side 8 is arcuate. It forms an outwardly-opening or concave depression extending the vertical extent of the shapes. Installed, it is a part of the inner wall which forms one of the electrode ports. It is opposed to the obtuse angle 3 of the shape. Sides 1 and 2 are equal in length as are sides 4 and 5; and sides 4 and 5 are shorter than sides 1 and 2.

Referring to FIG. 1, respective adjacent long faces or sides 1 and 2 of each of the special shapes 31 abut against a side or face of equivalent dimension of another shape 31. The corners defining respective obtuse angles 3 abut at the center or vertical axis of the roof.

The shorter sides 4 and 5 lie on radii of electrode port rings. Note the respective shorter sides 4 and 5 are of greater length (as viewed from the top) as compared to abutting faces of adjacent arch brick which cooperate to form the remainder of the respective ports. This provides a larger and more easily rammed area 50. Of course, the remainder of the top of the roof is of rammed monolithic material 51.

FIGURE 4 is illustrative of an equally useful alternative embodiment of the present invention. In FIG. 4, there is shown a pair of shapes and 41. These two shapes are identical. They, together, form a shape equivalent to a shape 31. Thus, we again provide but one refractory shape, a plurality of which cooperate to fill the delta area and at least a portion of each of the rings forming the electrode ports. Of course, we prefer to keep the number of separate pieces in the set used to fabricate the delta section according to our invention to a minimum; but, in some instances, especially with much denser refractory, it is sometimes desirable to form shapes of less weight. For example, in an exemplary installation in which the shapes 31 are made of refractory according to United States Patent No. 3,067,050, each shape weighs on the order of 80 pounds. Some operators may prefer 40 pound shapes, since they would be easier to handle and the shapes 40 and 41 are the answer.

FIG. 5, it is seen, shows a set of three identical shapes which together occupy precisely the same volume or area as do the three shapes 31 in FIG. 1. The configuration of the individual shapes 60, however, is different. Each of them may be generally characterized, viewed from an upper (cold) or lower (hot) face, as forming a generally diamond shape, the opposed ends of which have been scalloped to form arcuate side faces 61, two of which together cooperate in a common electrode port ring. Further, each of the sides of the opposed two sets of straight sides forming the remainder of the generally diamond shape are equivalent to each other (in a common set) but not equivalent in length to the sides forming the opposed 4 set in order to provide the cooperating structure shown in FIG. 5.

FIG. 6 is yet another exemplary arrangement of three identical shapes which together cooperate to fill an area of the same configuration as the three shapes of FIG. 1. As the shapes 31 of FIG. 1 together cooperated to fill the delta area and form a part of adjacent electrode port rings, the shapes 60 and70 also do, and they are further constructed and arranged to wedge against each other. A comparison of any one of the shapes of FIGS. 2, 4, 5, and 6 indicates at least three-fold symmetry in the assembled delta-filling configuration.

The delta-filling configuration formed of a set of shapes of the various drawings above discussed can be described as a nine-sided figure. Six of the sides forming this figure are straight and of equallength and size. Three pairs of these equal-length sides are spaced apart by arcuate sides. The arcuate sides are also substantially equidimensioned. Each set of equal sides intersects to form an included obtuse angle between respective adjacent arcuate sides. The radius of each of the arcuate sides is equivalent to the radius of an electrode port in a roof in which the set is to be installed.

Shapes 31 are the preferred embodiment. They are preferred over the shapes of FIG. 4, since they represent a lesser number of shapes to fill the desired area. They are preferred over the shapes of FIGS. 5 and 6, because they are of less complicated configuration, as far as manufacture is concerned.

Still another alternative configuration for forming the delta area of electric furnace roofs is shown in FIG. 7. In FIG. 7, there is shown three identical shapes 80. These three shapes cooperate as did the shapes 31 and the others above discussed to fill the delta area, form a part of respective adjacent electrode port rings, wedge against each other about the vertical axis of the roof, etc. It will be noted the three shapes cooperated to form what may be described as an isosceles triangle, the three included angles of which have been scalloped to form three equispaced and equidimensioned concave surfaces. While the shapes 80 can be used satisfactorily, they are not preferred, because they leave an area 81 more difficult to ram than the area 513, for example, of FIG. 1.

FIG. 8 illustrates still another embodiment providing for use of two identical shapes together assembled in mirror-image relation to form the same delta-filling configuration as the set of three shapes 31 in FIG. 1. The shapes provide most of the benefits described in relation to the shapes 31. However, two shortcomings are: excessive weight when a large furnace or an extremely dense refractory is being used and they do not provide the degree of symmetrical distribution of forces about the central axis of the roof that the shapes 31 provide. This is, of course, the result of having but one long contiguous face 91 instead of the three planes of intersection found with the shapes 31 in FIG. 1.

In a preferred embodiment, all of the brick and the special shapes used to construct a furnace according to this invention are made of mullite-bonded high alumina refractory of the type disclosed and claimed in United States Patent No. 3,067,050. The ramming mix used to form the remainder of the roof is of a compatible high alumina refractory. We preferred the one called Korundal Plastic, sold by the Harbison-Walker Refractories Company. Further, in preferred construction, all shapes are laid-up with a mortar. We prefer the mortar of United States Patent No. 3,179,526.

Still further, in the preferred embodiment of the invention and as shown in FIGS. 2A and 23, some manner of interlocking tongue and groove arrangement or equivalent is provided for the shapes 31 to better lock them in position. Reference numeral 31A is indicative of a groove and 31B of a tongue formed integral with opposed faces of the shapes 31 which interlock with complementary structure of adjacent identical shapes 31 to form the desired 7 delta-filling configuration.

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 electric furnace construction in which three electrode ports are defined by three electrode port rings equispaced substantially centrally in the delta area of a domeshaped electric furnace roof the improvement comprising a set of equishaped substantially identical refractory pieces which together cooperate to fill the delta area of said furnace and form a minor portion of each of the electrode port rings, the remainder of each said port ring being of conventional refractory brick.

2. The roof of claim 1 in which there are at least three equispaced and equishaped refractory pieces filling said delta area which together cooperate in wedging reaction against each other.

3. The roof of claim 2 in which each of said shapes includes interlocking means on respective contiguous wedging faces to better interlock the respective pieces together.

4. The roof of claim 1 in which there are six identical equispaced pieces forming said delta area and a portion of respective adjacent electrode port rings.

5. The roof of claim 1 in which said equishaped pieces consist of two identical pieces arranged in mirror-image relation to each other.

6. The roof of claim 1 in which the equispaced pieces, as viewed from a top face, may be characterized as de-- fined by five sides, a first pair of said sides being equidimensional and intersecting each other to form an obtuse angle, a second pair of equidimens-ional sides spaced apart from each other and converging from intersection with one of the first set of sides to intersection with an outwardly opening arcuate side opposed to said obtuse angle, and each of said second pair of sides intersecting one of said first set of sides to form equal included acute angles.

7. The roof of claim 6 in which the arcuate side has a radius equal to the radius of an electrode port opening.

References Cited FREDERICK L. MAT'IESON, JR., Primary Examiner. JOHN J. CAMBY, Examiner.

Claims (1)

1. AN ELECTRIC FURNACE CONSTRUCTION IN WHICH THREE ELECTRODE PORTS ARE DEFINED BY THREE ELECTRODE PORT RINGS EQUISPACED SUBSTANTIALLY CENTRALLY IN THE DELTA AREA OF A DOMESHAPED ELECTRIC FURNACE ROOF THE IMPROVEMENT COMPRISING A SET OF EQUISHAPED SUBSTANTIALLY IDENTICAL REFRACTORY PIECES WHICH TOGETHER COOPERATE TO FILL THE DELTA AREA OF SAID FURNACE AND FORM A MINOR PORTION OF EACH OF THE ELECTRODE PORT RINGS, THE REMAINDER OF EACH SAID PORT RING BEING OF CONVENTIONAL REFRACTORY BRICK.

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