US3387575A

US3387575A - Basic roof construction for a metallurgical furnace

Info

Publication number: US3387575A
Application number: US396472A
Authority: US
Inventors: Ralph C Padfield
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1964-09-08
Filing date: 1964-09-08
Publication date: 1968-06-11
Anticipated expiration: 1985-06-11

Description

United States Patent O 3,387,575 BASIC ROOF CONSTRUCTION FOR A METALLURGICAL FURNACE Ralph C. Padfield, Bethlehem, Pa., assigner to Bethlehem Steel Company, a corporation of Pennsylvania Continuation-in-part of application Ser. No. 330,028, Dec. 12, 1963. This application Sept. 8, 1964, Ser. No. 395,472

13 Claims. (Cl. 11d-99) This is a continuation-in-part of my application Serial No. 330,028, filed December 12, 1963.

This invention relates to an improved all-basic roof for metallurgical furnaces, particularly roofs of open hearth steel furnaces.

For years it has been known that basic refractories, i.e. those made of chrome ore and magnesite, possess certain characteristics which are desirable for high temperature service. From a steelmakers viewpoint, the most important feature of basic brick is its ability to absorb large quantities of mo-lten iron oxide without substantial loss in refractoriness. Furthermore 'basic brick is more resistant than silica brick to cycling reducing-oxidizing atmospheres containing iron oxide at elevated temperatures. However, basic bricks cost more than the silica bricks generally used in open hearth roofs and have the additional -disadvantages of greater weight, higher reversible expansion, greater growth from iron oxide absorption and lower load bearing capacity at elevated temperatures.

In order to capitalize on the ability of basic bricks to withstand high temperatures, present all-basic roof construction requires an intricate steel structure to support the bricks yand to control the roof contour. In addition to the expense ofthe suspension steelwork, `a large amount of labor is needed to assemble this type of roof.

It is an object of the present invention to provide an all-basic brick furnace roof in which the suspension features heretofore thought necessary for lbasic bricks are eliminated.

Another object is to provide an all-basic brick furnace roof which can be rapidly assembled.

It is a further object to provide an all-basic brick furnace roof which will have a life equal to, but which will cost substantially 'less than, -all-basic furnace roofs now in service.

Contrary to the 'long held views of those skilled in the furnace art, I have discovered that it is possible to erect a fully sprung arch type allebasic brick furnace roof which does not require suspension means for the brick- Work and which will achieve a roof life equ-al to that of present all-basic roof designs. The all-basic roof of my invention has the bricks arranged in rows extending longitudinally of the furnace with overlapping transverse joints, i.e. 'bonded construction, and is held down by countour control beams but is not suspended. By 'bonding the `bricks in this fashion, each brick is partially supported by contiguous bricks and in like fashion partially supports them. The sprung arch and 'bonded arrangement of the brickwork in the basic brick roof of my invention eliminates the need for a suspension system to support the bricks, and therefore is considerably more economical than basic `roofs Ias presently constructed. ln addition to the savings obtained by the elimination of the suspension steelwork, there is a considerable reduction in the number of man hours required to lay the brickwork.

Other and additional features and advantages of the present invention will become apparent from-the following specification and the accompanying drawings, in which FIG. 1 is -a sectional view of a sprung arch roof in accordance with the present invention.

ice

FIG. 2 is a fragmentary plan view of the sprung arch roof of FIG. 1 with the beams and jacks omitted.

FIG. 3 is a fragmentary plan view of a different embodiment of my roof construction.

For purposes of illustration this invention will be described with particular relation to open hearth steelmaking furnaces, but it is not necessarily limited thereto.

Referring now to the drawing, there is shown in FIGURE 1 a furnace framework consisting of vertical buckstays 10, at the front and 'back of the furnace, connected at their tops by cross-channels 11 which span the roof transversely of the furnace. Heavy channels 12 extend longitudinally of the furnace and connect the upper ends of buckstays 1@ along the front an-d rear of the structure. Skewback beams 13, which are connected to buckst'ays 10, also extend longitudinally of the frame and support skewbrick 14. Springing from the skewbricks 14 and extending transversely of the furnace is `a sprung arch roo-f 15, built of basic refractory bricks 16 bonded together with joints staggered in a pattern which is hereinafter m-ore fully described.

In a fully sprung arch of bonded basic bricks the rise of the roof, ie. the number of inches the roof rises per foot of horizontal span between the skewbricks, should be not less than 2% inches. Contour control beams 17, which extend longitudinally of the furnace, rest on top of the roof. Hold-down jacks 18 preferably adjustable, extend radially of the arch and are connected to the cross channels 11 and the beams 17.

In constructing the roof of my invention, conventional arch forms are erected in the furnace and the individual bricks are laid dry on the forms in rows, as shown in FIGURE 2, which extend longitudinally of the furnace, as for example rows A, B, C `and D. One manner of erecting the roof is to lay the bricks starting at one end of the furnace and work toward the other end simultaneously from the lfront and back skewbacks to the crown. A convenient way of breaking the bond is t-o have the first brick 19 in alternate rows of bricks 50% wider in longitudinal cross-section than the bricks 16 which make up lthe remainder of the roof. By starting alternate rows in this manner with the oversize bricks 19 and then continuing the rows with the bricks 16, the joints extending transversely of the furnace between bricks in each row are offset with respect to the joints between bricks in the next adjacent rows, and the bricks `are bonded together with joints staggered. After the brickwork has been completed, the contour control beams 17 are set substantially parallel on top of the roof. lacks 18 are adjusted to hold the beams in position and restrain upward movement `of the roof. The arch forms are dismantled and removed from the furnace which is then slowly brought up to temperature and placed in operation according to the usual practice.

At times, particularly on furnaces which have warped steelwork and which have the front and rear walls out of line, it has been found convenient to modify the construction described above, as shown in FIGURE 3. The erection of the roof proceeds, as Valready described, from the skewbrick to the crown on the roof. At the crown, for the full length of the roof, a key section 20` is installed by means of which the roof is tightly wedged together at the upper surface. Key section 20 is made up of key bricks 21 arranged in rows extending transversely of the furnace, as for example, rows X, Y and Z as shown in FIGURE 3. The width of key section 20 is a matter of construction, which is determined by numerous factors including non-alignment which may exist between the front and rear walls of a furnace, an'd variations which exist in the size of the

bricks

16 and 19 that make up the remainder of the roof. As those skilled in the art know,

key bricks are made in standard sizes with various standard tapers. The number of key bricks 21, which make up the separate rows, such as rows X, Y and Z of the key section 20, may be a matter of design, but usually varies according to the size and taper of the key bricks 21 required to obtain the des-ired degree of tightness in the root` 15.

Naturally, in the roof of my invention the bricks must be laid up tightly, and provision must be made for thermal expansion of the refractory. Methods of compensating for thermal expansion are, of course, well known to those skilled in the art and include the use of insulating board spacers, asbestos spacers, etc. When the roof of my invention is made with unplated basic bricks expansion allowance of between approximately .5% and 1.75% of the total arc of the -roof should be provided at spaced intervals thereof between the rows of basic bricks. Contrary to the accepted way of providing expansion allowance in a basic roof, i.e. near the hot face only, the expansion allowance in such a roof should extend approximately the full thickness, i.e., at least '75% of the thickness, of the roof, and extend from the hot face toward the cold face. Thin sheets of insulation should be spaced between bricks about every foot across the arc of the roof to provide the desired amount of expansion allowance. Very thin spacers could be inserted in every brick joint, but this arrangement is somewhat impractical. Longitudinal expansion allowance should also be incorporated into the roof in a similar manner and should preferably be governed by the same speciiications, i.e. between approximately .5% `and 1.75%, but, as is well known to those skilled in the art, the provisions for longitudinal expansion of `a furnace roof are not as critical as those for expansion in a transverse direction across the arch.

The expansion allowance incorporated into a roof of this type made with metal encased Ibasic bricks can not be specified as accurately as that for a roof of unplated basic bricks. In addition to the expansion allowance of the refractory, the method of encasing the bricks, the thickness ofthe metal casing and the magnesium oxide (MgO) content of the bricks must all be taken into consideration when the expansion allowance is determined for a basic roof made with metal encased bricks. Different manufacturers use different thickness meta-l to encase their bricks, and the methods of applying the casing to the refractory are not standard. In addition, less expansion allowance must be incorporated into a roof with bricks having a high magnesium oxide content than for a roof with bricks having a lower magnesium oxide content. Basic bricks with a high magnesium oxide content can absorb more iron oxide from the steel of their casings as they oxidize than can bricks with a lower magnesium oxide content. Preferably a roof of metal encased 'basic bricks constructed in accordance with my invention should have an expansion -allowance of between approximately and 2% of the total arc of the roof depending upon the several features, described above, of the particular metal encased bricks that are used.

In a specific embodiment of this invention, a sprung arch open hearth roof was constructed of metal encased burned chrome-magnesia bricks. A hot face expansion allowance was incorporated in each brick by the manufacturer. This allowance took the form of a small tapered slightly raised surf-ace, approximately .020 high, at the hot face of one of the lplates of the metal casing. Roof bricks 16 were 3" x 3 x 12" keys or wedges; bricks 19, used to start alternate rows, were 3" x 41/2" wedges; and key bricks 21 were various sizes, available from the standard selection of key shapes produced by refractory manufacturers, as required for tightly keying the roof. Contour control beams were placed on the roof and set in place by hold-down jacks, the arch forms were dismantled and removed, and the furnace was slowly brought up to temperature `and placed in operation. The A.I.S.I. Unit .Roof Life of this roof, that is, the number of heats obtained per unit volume of bricks consumed in this roof, was equal to that of conventional basic roo-fs which had the bricks suspended and laid up in rings extending transversely of the furnace. In addition to the savings made by the elimination of the 'brick suspension means, there was a reduction of between 30% and 40% in the number of man hours required to lay the brickwork of this roof as compared to that required to construct a typical all-basic roof with suspension features.

In another specific example of this invention, a sprung arch roof of unplated basic bricks, 50% Mg() magnesitechrome commercially fired above 2950 F. to develop high hot strength, was installed on an open hearth furnace of ton capacity. The main roof section had three openings for oxygen lances and extended from knuckle to knuckle for a distance of 40 feet. The span of the roof, measured from toe to toe of the skewbricks, was 15 feet 5 inches, and the rise of the roof measured from the centerline of the crown was 36 inches. The roof was l3l/2 inches thick and was constructed of 131/2 x 3 x 3 inch series brick of conventional key shapes. The bricks were laid on conventional wooden forms shaped to an arch contour and having a rise as specied above. The brickwork was begun at the centerline of the furnace along both the front and back skews and proceeded toward both ends simultaneously. At the top of the arch a crown key, ve bricks wide, was installed. Standard wedge and key bricks were laid in ring construction to complete the crown key. To insure tightness of this type of construction it was necessary to tightly drive the last brick in the crown key and then to tightly drive additional keys, one brick wide, that had been provided midway between the crown and each skew. The purpose of this multiple keying was to insure that the roof was suicientiy tight to sustain its own weight and to insure that it would not sag when the forms were removed. Expansion allowance of 1.04% was provided for the full thickness of the roof by placing 1/s-inch thick asbestos board in every fourth brick joint across the arc of the arch and every l2 inches along the length of the arch. An additional l-inch expansion joint of Celotex was provided at the ends of the roof at each knuckle. Since the bricks were laid in longitudinal rows the expansion joints that ran longitudinally were made of asbestos board 12 inches wide and 48 inches long. For the short, broken joints that ran transversely of the roof smaller pieces 12 inches long and 21/2 inches wide were inserted between the bricks. Six longitudinal rows of 6-inch wide flange hold-down beams were placed on the roof and set in piace by hold-down jacks. The roof forms were dismantled and removed from the furnace which was thereafter slowly heated to operating temperature. Except for minor repairs to each of the three lance hole openings, this roof operated successfully for over 400 heats.

Although certain novel features of my invention have been shown and described, it will be understood that changes and modifications can be made therein without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. In a metallurgical furnace a sprung arch roof extending transversely of the furnace, said roof consisting of basic bricks, rows of said ibasic bricks extending longitudinally of the furnace and comprising a construction wherein the joints between bricks in each row are offset with respect to the joints between bricks in the next adjacent rows.

2. In a metallurgical furnace according to claim 1, said roof including at least one key section extending longitudinally of the furnace.

3. The metallurgical furnace roof of claim 1 in which the basic bricks are encased in metal.

4. The metallurgical furnace roof of claim 1 in which the bricks are burned basic brick.

5. The metallurgical furnace roof of claim 4 in which said arch has a rise of not less than approximately 21A inches per foot of span.

6. The metallurgical furnace roof of claim 4 in which there are provided expansion means equal to between approximately 0.5% and 1.75% of the total arc of said arch at spaced intervals thereof between said rows of basic bricks.

7. The lmetallurgical furnace roof of claim 6 in which the expansion means provided extends approximately the full thickness of the roof and extends from the hot face toward the cold face thereof.

8. In a metallurgical furnace having buckstays spaced along the front and back thereof (a) an overhead framework secured to said buckstays and spanning the roof transversely of the furnace,

(b) a sprung arch consisting of basic bricks extending transversely of the furnace,

(c) fixed skewbacks at opposite ends of said arch,

(d) rows of said basic bricks extending longitudinally of the furnace and comprising a construction wherein the joints between bricks in each row are offset with respect to the joints between bricks in the next adjacent rows,

(e) arch contour control means on said roof,

(f) means securing said arch contour control means to the overhead framework.

9. The metallurgical furnace roof of claim 8 in which the -bricks are burned, uncased high strength basic bricks.

10. The metallurgical furnace roof of claim 9 in which said arch has a rise of not less than approximately 21A inches per foot of span.

11. The metallurgical furnace roof of claim 9 in which there are provided expansion means equal to between approximately 0.5 and 1.75 of the total arc of said arch at spaced intervals thereof between said rows of basic bricks.

12. The metallurgical furnace roof of claim 11 in which the expansion means provided extends approximately the full thickness of the roof.

13. In a metallurgical furnace having buckstays spaced along the front and back thereof (a) an overhead framework secured to said buckstays and spanning the roof,

(b) a sprung arch consisting of high strength burned, uncased basic bricks and extending transversely of the furnace,

(c) said arch having a rise of not less than approximately 2% inches per foot of span,

(d) xed skewbacks at opposite ends of said arch,

(e) rows of said basic bricks extending longitudinally of the furnace and comprising a construction wherein the joints between bricks in each row are offset with respect to the joints between bricks in the next adjacent rows,

(f) expansion means equal to between approximately 0.5% and 1.75% of the total arc of said arch at spaced intervals thereof between said row of basic bricks and extending approximately the full thickness of the roof,

(g) arch contour control means on said roof, and

(h) means securing said arch contour control means to the overhead framework.

References Cited UNITED STATES PATENTS 2,236,920 4/ 1941 Robertson 110-99 2,901,990 9/ 1959 Hutter 110-99 3,005,422 10/ 1961 Heuer 11099 3,005,424 10/ 1961 Heuer 110-99 3,013,510 12/1961 Parker et al. 110-99 3,038,423 6/ 1962 Oswald 110-99 OTHER REFERENCES The All-Basic Open Hearth Furnace, General Refractories Co., 1956, pp. 9 and 10.

FREDERICK L. MATTESON, JR., Primary Examiner.

ROBERT A. DUA, Examiner.

ATENT OFFICE UNITED STATES P CERTIFICATE OF CORRECTION June ll, 1968 Patent No.

Ralph C. Padfield It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

to the printed specification, lines 4 and 5,

a corporation of In the heading m Steel Company,

by mesne assignments,

Bethlehe "assignor to should read assignor,

oration of Delaware Pennsylvania a corp to Bethlehem d sealed this lSth day o Steel Corporation,

f November 1969.

Signed an (SEAL) Attest: y

WILLIAM E. SCHUYLER, IR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

Claims

1. IN A METALLURGICAL FURNACE A SPRUNG ARCH ROOF EXTENDING TRANSVERSELY OF THE FURNACE, SAID ROOF CONSISTING OF BASIC BRICKS, ROWS OF SAID BASIC BRICKS EXTENDING LONGITUDINALLY OF THE FURNACE AND COMPRISING A CONSTRUCTION WHEREIN THE JOINTS BETWEEN BRICKS IN EACH ROW ARE OFFSET WITH RESPECT TO THE JOINTS BETWEEN BRICKS IN THE NEXT ADJACENT ROWS.