US3053237A - Furnace lining - Google Patents

Description

Sept. 11, 1962 F. H. N. CARTER FURNACE LINING 2 Sheets-Sheet Filed Nov. 2, 1959 6 Q IMM g INVENTOR F/?EDEE/ CK h'. M U k' 75? j ATTO Sept. 11, 1962 F. H..N. CARTER FURNACE LINING 2 Sheets-Sheet 2 Filed Nov. 2, 1959 jo 12 uni 21 INVENTOR FPEDE/?ICK f/.N. 654275? 3,053,237 FURNACE LINING Frederick H. N. Carter, New York, N.Y., assignor to Sunrod Manufacturing Corporation, New York, N.Y., a co'poraton of Delaware Filed Nov. 2, 1959, Ser. No. %0,206 7 Claims. (CI. 122-6) This invention relates to electrc arc steel furnaces and especially to a lining, such as a cover or -roof therefor, which will operate longer and more efficiently than covers presently in use.

Removable covers for steel furnaces are lined on the underside with refractory material put in place by casting or in the form of bricks. Building the lining from bricks is expensive, requiring care in shaping the lining in a domed shape and in fastening 'the bricks to the cover. Such linings are apt to be heavy and, therefore, diflicult to move.

A refractory known in the art as a high alumina castable may be -used to form the r-efractory layer in the cover. lt may be prepared as a liquid and spread over the surface of the cover after inverting the same, much as concrete is spread in a mold in constructing a floor. It is not necessary to cast such -refractories in a domed shape. Cast refractories are subject to deep cracking or crazing in use, however, and thereby may become separated into a fairly large number of irregular chunks or sections. It is desirable to hold the cast refractory in such a manner that these chunks will not fall from the cover into the molten metal.

Cast refractories are subject to fairly rapid erosion due to the high radiant temperature to which they are exposed. The temperature inside a steel furnace is in the neighborhood of 3,000 F., which is close to the breakdown temperature of the refractory lining of the cover. Cooling of the refractory layer is desirable, but excessive cooling spells a loss of power because what is taken out by the cooling medium must -be supplied by the arcs. Therefore, it is desirable to reduce radiant heat transfer to the cover by maintaining the surface of the refractory layer exposed to the molten metal at as high a temperature as possible without producing speedy disintegration.

Attempts have been made to cool covers with cooling pipes through which coolant is circulated. If these pipes are placed between the refractory material and the molten metal mass they absorb too much heat and cut down the efficiency of the furnace. Such an arrangement protects the refractory but requires a high current supply.

If the cooling pipes are placed above or imbedded in the refractory, due to the low conductivity thereof, they may be of little assistance to the bottom surface which is exposed to the high radiant heat from the arcs and mix contained in the bottom of the furnace.

The present invention has as an object the production of a cover which includes cooling pipes with heat conductivity studs imbedded in the refractory which mechanically support the refractory and cool the surface thereof only enough to prevent disintegration without removing so much heat as to make it necessary to supply excess current to the arcs.

Another object is to make a self compensating refractory surface which will automatically assume a satisfactory balance between minimum power loss at the arcs and long life for the refractory surface.

Another object is the provision of heat conducting studs which are so located relative to the cooling pipes and the cast refractory that even if deep cracks in the refractory occur the resulting chunks or sections will be held in place by the studs.

Another object is the provson of cooling studs which Patented Sept. 11, 1962 will bind the refractory to the cooling pipes without the necessity of leaving spaces between individual cooling pipes for fastening means extending from above the cooling pipes into the cast refractory.

A further object is to provide a relatively large area of contact between the refractory and the metal cooling coils and studs.

In tests cover sections constructed in accordance with the present invention have lasted three or four times as long as adjacent conventional cover sections and have done so without any increase in power consumption at the arcs.

Objects and advantages other than those above set forth will *be apparent from the following description of a preferred embodiment of the invention, when read in connection with the accompanying drawings thereof.

In the drawings:

FIG. 1 is a diagrammatic view in vertical cross section of an electrc arc steel furnace;

FIG. 2 is a -detail enlarged view of the right hand side of the cover or roof shown in FIG. l;

FIG. 3 is an enlarged partial section through 3-3 of FIG. 2;

FIG. 4 is a transverse sectional view through the cooling tubes of FIG. 2, showing the studs attached to the tubes and a layer of refractory material;

FIG. 5 is a plan 'view of a portion of the tubes and studs of the cover or roof before the refractory material is applied thereto; and

FIG. 6 is a view similar to FIG. 5 showing another type or form of stud.

Looking at the figures, F is an electrc arc steel furnace; 1 is the body thereof which is made of or at least lined with refractory material; 2 and 3 are electrodes projecting downwardly through the roof or cover into the interior of the furnace.

The present invention has to do with the design and Construction of the roof or cov er. The cover, as shown at C, consists of a supporting framework which includes a steel box member 5 adapted to rest on the upper wall 1 of the body of the furnace F. This frame member may be some other cross section such as a channel or I-beam. However, the boX Construction shown in FIGS. 1 and 2 has been found satisfactory. Resting on the box section member 5 are a plurality of I-beams 6. These support inverted short U-shaped members 7 which in turn support long inverted U-shaped members 8 arranged parallel to the I-beam member 6. Members 6, 7 and 8 are all welded together as shown in FIG. 3.

Members 8 support the cooling tubes shown at 10. These are arranged side by side to cover most of the area of the roof and as shown in FIGS. 1 and 2, may be arranged vertically, one on top of the other around the openings for the electrodes.

Due to the high temperatures involved, it is desirable to support the cooling tubes 1 1]` to allow for contraction and expansion. This is accomplished by welding U-shaped straps shown at 11, to the upper side of the tubes as the cover is arranged for furnace operation. Corresponding openings are furnished in the members 8, as shown at 12, which o-penings are designed to accommodate the straps 11 -so that they may pass'freely through the openings. Each strap with the attached tube is drawn snugly up against the member 8 by means of a Wedge 15, shown in FIGS. 2 and 3. In this manner the rows of cooling tubes are more or less flexibly supported on the members 8. The vertically arranged tubes around the openings for the electrodes may be supported on the horizontal rows of tubes or by a suitable vertical support attached to the members 8 or 6.

The design of the supporting members may be varied to accommodate the shape of the cover and the number of electrodes in use. It is necessary that the -supporting structure be strong enough to hold the cooling tubes so that undue strain will not be put -upon them when the cover is moved. At the same time sufficient flexibility should be provided so that various parts of the cover may expand and contract under the temperature changes.

Attached to the cooling tubes and depending therefrom when the cover is in use, are studs 20 which project downwardly from the tubes and are disposed at an angle to the vertical plane through the axis of the tube and preferably alternate studs project on alternate sides of this vertical plane, as shown in FIGS. 2, 4, and 6. In the pattern shown in FIGS. 5 and 6, the base of the studs where they join the tubes may be thought of as being located on some of the squares of a checkerboard in rows running from left to right and columns from top to bottom. Each tube has two rows of such an imaginary checkerboard. The basic pattern for the studs which is repeated over the whole area of the tubes (except the edges and where tubes bend, where extra studs .are displaced or added) contains sixteen squares or possible 'stud locations in `four rows and four columns. If the rows are numbered from one to four proceeding from the top down and the columns from one to four with the first column on the left, there is a stud located in row one, column four and slanted toward the top of the figure. A second stud, slanted toward the bottom of the figure, is in row two, column three, a third, slanted toward the top in row three, column one, and a fourth, slanted toward the bottom in row four, column two. The remaining twelve squares are empty. This arrangement of studs is repeated like a wallpaper pattern over much of the watercooled surface which is forrned by the tubes. The pattern allows all studs in a given row to slant in the same direction and those in adjacent rows to slant in opposite directions. By this construction an interlocking pattern is produced and yet all studs can be welded perpendicular to the surfaces of the circular tubes, as is most clearly shown in FIG. 4. It is desirable to have the base of the stud where it jons the cooling pipe or tube, of a larger cross section than the outer end of the stud, because the inner end of the stud against the tube normally carries a higher heat flow than the outer end of the stud.

FIG. 5 shows studs which have a more or less rectangular cross section but decreasing in cross sectional area from the tube to the outer end of the stud. FIG. 6 shows a slight modification wherein the studs have the sh-ape of truncated cones as shown at 21.

Studs 20 and 21 may be used in many different shapes and arrangements but should be designed and disposed in relation to the tubes and to each other so that they will function efficiently to 'transfer heat from the refractory layer to the coolant at such a rate as to produce a reasonably long life in the refractory without subtracting more heat than is necessary from the arcs and the melt in the furnace. Also, the studs should be arranged so to give the maximum mechanical support to the layer of refractory. The disposition shown in FIGS. 4, 5 and 6 has been found quite satisfactory and it can be seen -from FIG. 4 that the overlapping studs produce a criss cross arrangement which serves well to support the refractory.

The surface of the studs 20 and 21 may have an irregular shape; for instance, concentric ridges could be formed on the surface or a slightly bulbous or enlarged end could be used to further enhance the mechanical supporting function of the studs. However, the arrangement disclosed in `FIGS. 4, 5 and 6 operates efliciently and it produces an interlaced reinforcement which serves to hold together the refractory layer even after it is cracked in places due to the -severe service imposed -by the high temperatures.

With studs on the cooling tubes, the spacing between the tubes is not critical because the studs overlap one another and overlap the space .between the tubes. The tubes may be spaced very close together because there is no need to imbed them all the way in the refractory. They can also be spaced apart because the outer ends of the studs overlap each other and distribute the cooling effort throughout the layer of refractory material.

The cover carries a layer of refractory material, as shown .at 30 in FIGS. 2 and 4, and a cast type of refractory is desirable for the present invention. In order to install or replace a refractory layer the cover is removed from the furnace and turned upside down. The cast refractory is then poured into place as one might pour cement into a mould. It has been found that if the refractory is poured to a depth of about one inch above the outer ends of the studs, satisfactory operation will be obtained. It has also been found that cast refractory such as that known as high alumina castable can be used for the purpose of this invention. Such castable refractory `is supplied by the General Refractories Co., under the name Special High Alumina Castable and by the Babcock and Wilcox Co., under the name Kaocrete-32.

In renewing old refractory, it is found that after it has been subjected to the heat of the furnace for some time and then the cover removed and turned upside down, it is a relatively sirnple matter to break out the old refractory and cast a new layer.

After the refractory has hardened, the cover is ready to be replaced on the furnace and 'put to use.

In operation the studs serve to mechanically hold the refractory in place and even though it may become cracked in use it is unlikely that any substantial part of the refractory layer will actually drop ofi into the mix.

The studs also serve along with the cooling tubes to cool the refractory layer but the cooling tubes and studs do more than merely cool. They provide a structure along 'with the refractory layer which automatically maintains the optimum temperature for the refractory layer. This optimum temperature is a 'balance between too little cooling on one hand and too much on the other. If the layer is cooled too much, it absorbs the reflected heat from the arcs and the mix, which heat in turn must be supplied 'by the arcs with resulting inefficiency. If the refractory layer is not cooled enough, it will break down, soften, crack and fall off into the mix which, of course, requires frequent renewal and consequent shut downs of the furnace.

As a result, it is desirable to create :a condition where the refractory layer will come to a state of equilibrium whereby it will withdraw a minimum of reflected heat from the interier of the furnace compatible with reasonably long life.

In the present construction, this is accomplished with the aid of the studs attached to the cooling tubes which, as heretofore pointed out, serve the dual purpose of cooling the nterior of the refractory layer and mechanically supporting it. When the refractory layer is installed, it is made somewhat thicker than it will be after some little use in the furnace. In operation when a new cover or a new layer of refractory is installed and the furnace brought up to temperature, the outer layer of the refractory will have a tendency to b'urn off and decrease the space between the ends of the studs and the under surface of the refractory. As this space decreases, the cooling effect of the studs becomes greater on the lower surface of the refractory material and a balance is reached whereby the under surface of the refractory is cooled sufliciently by the studs so that it is not readily burned away. Erosion will, of course, continue at the very high temperature present but it will be slowed down to a point where the roof or cover will last three or four times longer than conventional roofs or covers. A cover of this type should last three or four months and yet it will not absorb heat from the furnace in such quantity as to produce an ineficient operation. In prior constructions the refractory layer broke down because of insuflicient cooling and, therefore, required frequent replacement, or where too much cooling was used, the efficiency of the furnace fell off.

In practice, water has been found to be a satisfactory coolant and it may be put under pressure to discourage the generation of steam within the cooling parts. This practice is known in the art and is not a part of the present invention.

What is claimed is:

1. In a furnace lining comprising rows of interconnected cooling tubes, studs projecting from said tubes toward the interior of the furnace when the lining is in Operating position and a layer of refractory material enclosing said studs and located between said tubes and the interior of said furnace, the improvement wherein said studs are long enough and so slanted from a plane at right angles to the layer of refractory material and passing through the longitudinal axis of the tube from which the stud projects as to overlap studs projecting in the opposite slanting direction from an adjacent tube, when viewed in a plane at right angles to the longitudinal axs of said tubes, to an extent so that the ends of overlapping studs project beyond each other and into the portions of said layer of refractory material surrounding the overlapping studs sufiiciently to lock said portions against sep aration from the rest of said layer of refractory material.

2. The furnace lining of claim 1, wherein the studs join the surface in an overall pattern, characte'ized by a repetition of a basic pattern, said basic pattern being of rectangular Outline and having sixteen possible stud positions arranged in four columns and four rows, the rows being parallel to one side of the rectangular Outline and the columns parallel to an adjacent side of the rectangular outline; the points of attachment of the studs to the surface being located only as follows: a first stud in the first row, fourth column; a second stud in the second row, third column; a third stud in the third row, first column; and a fourth stud in the fourth row, second column; the axis of the studs of a column lying in an imaginary plane, said imaginary plane being perpendicular to the surface and containing the column, the aXis of each stud being slanted out of a direction perpendicular to the surface, the first and third toward one end of the column and the second and fourth toward the other end of the column.

3. 'Ihe furnace lining of claim 1 wherein the studs join the tubes in an overall pattern, characterized by a repetition of a basic pattern, said basic pattern being of rectangular Outline and having sixteen possible stud position-s arranged in four columns and four rows, the rows being parallel to one side of the rectangular Outline and the columns parallel to an adjacent side of the rectangular Outline; the points of attachment of the studs to the tubes being located only as tollows: a first stud in the first row, fourth column; a second .stud in the second row, third column; a third stud in the third row, first column; and a *fourth stud in the fourth row, second column; the axis of the studs of -a column lying in an imaginary plane, said imaginary plane `being perpendicular to the longitudinal axis of the tubes and containing the column, the axis of each stud being slanted out of a direction perpendicular to the layer of refractory material, the first and third toward one end of the column and the second and fourth toward the other end of the column.

4. The rfurnace lining of claim 3 wherein the tubes are of circular cross section, the first and second rows being on a single tube and the third and fourth rows on an adjacent single tube.

5. In a furnace lining comprising rows of interconnected cooling tubes -arr anged in a single plane, studs projecting from said tubes toward the interior of the furnace when the lining is in Operating position and a layer of refractory material enclosing said studs and located between said tubes and the interior of said urnace, the improvement wherein said studs are long enough and so slanted from a plane at right angles to the layer of refractory material and passing through the longitudinal axis of the tube from which the stud projects as to overlap studs projecting in the opposite slanting direction from an adjacent tube, when viewed in a plane at right angles to the longitudinal -axis of said tubes, to an extent so that the ends of overlapping studs project beyond each other near ly to -a plane at right angles to the layer of refractory material and passing through the longitudinal axis of an adjacent .tube.

6. In a furnace lining comprising rows of interconnected cooling tubes, studs projecting from said tubes toward the interior of the furnace when the lining -is in Operating position and a layer of refractory material enclosing said studs and located between said studs and the interior of said furnace, the improvement wherein said studs are long enough and so slanted from a plane at right angles to the layer of refractory material and passing through the longitudinal axis of the tube from which the stud projects as to overlap studs projeoting in the opposite slanting direction from an adjacent tube, when viewed in a plane at right angles to the longitudinal axs of said tubes, to an extent so that the ends of overlapping studs project beyond each other and into the portions of said layer of refractory material surrounding the overlapping studs sufiiciently to lock said portions against sep-aration from the rest of said layer of refractory material, and wherein said studs each have a maximum cross-section where joined to said tube and minimum cross-section at the outer end of said stud.

7. In a furrace cover comprising rows of interconnected cooling tubes, studs projecting from said tubes toward the interior of the furnace when the cover is in Operating position and a layer of refractory material enclosing said studs and located between said tubes and the interior of said furnace, :the improvement wherein said studs are 'long enough and so slanted from a plane at right angles to the layer of refractory material and passing through the longitudinal axis of the tube from which the stud projects as to overlap studs projecting in the opposite slanting direction from an adjacent tube, when viewed in a plane at right angles to the longitudinal axis of said tube, to an extent so that the ends of overlapping studs project beyond each other and into the portions of said layer of refractory material surrounding the overlapping studs sufliciently to lock said portions against separaton from the rest of said layer of refractory material.

References Cited in the file of this patent UNITED STATES PATENTS 2,190,271 Powell Feb. 13, 1940 2,360,855 Dow et al Oct. 24, 1944 2,648,714 Williams et al Aug. 11, 1953 FOREIGN PATENTS 1,053,707 Germany Mar. 26, 1959 OTI-IER REFERENCES German application Serial No. =D16,444, printed December 27, 1956 (KL. 13a 8).

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