US2236920A - Open hearth furnace roof - Google Patents

Description

Filed Feb l0, 1959 .u m R o mw m f A E mm v Mw m uw BN ne. M

44 ATTORNEYS.

Patented Apr. 1, 1941 UNITED .STATES PATENT OFFICE OPEN HEARTH FURNACE ROOF Hugh S. Robertson, Coraopolis, Pa., assignor to Harbison-Walker Refractories Company, Pittsburgh, Pa., a corporation of Pennsylvania.

Application February 10, 1939, Serial No. 255,601

Claims.

high compressive stresses which must be sus tained at the elevated temperatures attained by open hearth furnace roofs.

Silica refractories possess the strength requisite to permit their use in open hearth sprung arch roofs, and since the mechanical strength of the furnace roof is of primary importance, it has been the invariable practice to construct such roofs wholly of silica refractory brick. Silica brick are, however, subject to certain disadvantages When used in the roofs of open hearth steel furnaces. For example, the lsilica refractory brick composing the roof react with iron oxide, lime, or'other basic materials contained in the dusts formed in the chamber, with formation of slags which drip off into the bath beneath. Not only is that objectionable, but also such corrosion naturally weakens the brick and materially shortens the eective life of the roof. mental are these effects that open hearth engineers have frequently resorted to the practice of thickening the 'roof in the shoulder regions and especially opposite the charging doors, where the attack of the brick is usually most severe.

Such dusts do not tend to react to any material extent with basic or neutral refractories such, for example, as those in which magnesia, dolomite, or chrome predominate, but they have not been used to construct open hearth sprung arch roofs because at the temperatures involved they have not been capable of withstanding the stresses created in such roofs. A certain degree of success has been indicated recently with an expensive type of chrome-magnesite brick in sprung arches, but this has required an elaborate and expensive steel structure to accommodate the marked rise or expansion of basic brick when used in this manner. Even with these expensive provisions the al1-basic roof is still regarded as unproved and highly experimental.

It is among the objects of this invention to provide, for basic open hearth steel furnaces, a sprung arch roof in which silica and basic refractory bricks are so combined that the roof possesses sufficient mechanical strength at working furnace temperatures and is resistant to material corrosion, whereby the advantages of silica and basic or neutral brick are obtained with repression of their disadvantages.

The invention has little connection with the architectural andvmechanical design of the furnace proper or the sprung arch roof, but rather is :applicable generally to all sizes, shapes, and

7 types of open hearth steel furnace construc- So detrition. Hence, the accompanying drawings with whichfthe invention is described serve merely to illustrate one of various types of sprung arch construction to which' the invention may be applied.

In these drawings, Fig. 1 is a vertical sectional View on a plane running transversely of the furnace; Fig. 2 is an interior perspective View of the furnace taken from near one of its ends; and Fig. 3 is a fragmentary view similar to Fig. 1 illustrating a modified embodiment of the invention.

buckstays 8. Each end of the chamber is bound# ed by and terminates in a suitable mixing chamber 9 composed of any lnormal combination of` throat, gas and air ports, etc., which need not be shown in detail.

Located at the top of front wlall 2 are skewbacks I0 which normally run the entire length of chamber I and are supported upon, for example, L-shaped members II, which are rigidly attached to buckstays 4, as is illustrated in Fig. 1, or directly upon the top of front wall 3, as is illustrated in Fig. 2. Similarly supported skew-backs I2 are located at the top of back wall 1.

springing from skew-backs I0 and I2 is an arch roof I3 normally built up of a plurality of individual refractory bricks, as is shown, these bricks being set in accordance with any common structural pattern for such purpose. Thus, they may be built up in individual ring arches, the roof I3 las a Whole being composed of a series of these arches set side by side, or the bricks may be bonded together in the checker pattern of the normal brick wall. Likewise, the bricks may be thickenedl in places forming ribs which strengthen the roof.

toward roof crown 2|.

When sprung arch roofs of the type thus briefly described are formed wholly of silica bricks corrosion of the inner face Il of roof Il, due to dust particles in the furnace gases, mainly occurs in the shoulder regions roughly indi- "cated at I5 and I8, although generally it ismost severe in the shoulder segment I6. Central arch segment I1 of inner face-I4, where the compressive stresses are lower than in the shoulders, is

attacked at a much lower rate.

I. have further found that, although sprung arch roofs of open hearth steel furnaces formed wholly of basic or neutral refractory bricks' are in almost all cases too weak to stand under working furnace temperatures, a satisfactorily strong roof isy obtained by substituting for the silica brick used heretofore basic or neutral refractories in the shoulder region I8, or in shoulder segments I8 and I9, while using the stronger silica refractories in the remainder, or crown, portion 20 of the roof.

The basic refractories are suiliciently strong to sustain the stresses within these shoulder portions of a sprung arch roof, and they are highly resistant to corrosion in the operation of the furnace. On the other hand, the silica brick occupy the region of maximum stress where corrosion is ordinarily not severe. In this manner. the benefits of each typeof brick are realized. As suggested hereinabove, the neutral or basic vrefractory bricks may be con'ned to one shoulder of arch roof I3, in which case only `one springing portion of the arch will be immune to corrosive attack by dust-particles. Thus, for example,` basic refractory might be used only in shoulder region I8 to reduce corrosion adjacent back wall 1, where corrosion is normally most severe.

Conversely, a sprung arch roof which is subs tantially immune to corrosion attack by dust particles in the furnace gases, or in which cor-- rosion is so reduced asnot to present a serious problem, may be formed compositely of silica and basic or neutral refractory brick occupying those segments of the roof whose vinner faces normally are subjected to material corrosion attacked by dust particles in the furnace gases, or, in other words, throughout shoulderv segments roughly indicated by I5l andI I8. Since these segments are adjacent skew-backs III and I2 and are spaced from crown portion 20, the roof, being made of good basic refractories, is mechanically strong.

Various neutral and basic refractory brick may be used, examples being chrome brick, magnesia brick, chrome-magnesio. brick, and the like. For so'me purposes brick encased in or carrying a sheath of metal, such as iron, are desirable because the bricks become integrated by oxidation of the metal in the use of the flu'nace, and similar results may be. had with metal plates supported between the faces of the bricks. Such roof and allows the brick to be extended further Fig. 3 illustrates one` being known in the art. But. other basic or neutral refractories of good quality may also be safely extended throughout the whole of segments I5 and I8.

For ease of reference in the claims both basic and neutral brick are termed non-acidic brick to distinguish them from silica. brick.

According to the provisions of the patent statutes I have explained the principle and construction of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as-specically illustrated and described.

I claim: A

l. In a` basic open hearth steel furnace, a sprung archroof having a section of the refractory arch built from silica brick and having at least one shoulder segment of the refractory arch exposed to the interior of the furnace having its full vertical cross section built from nonacidic brick which sustain the usual stresses in this portion of the arch and are resistant to material corrosion attack by dust particles in the furnace atmospheres.

2. In a basic open hearth steel furnace provided on one side with charging doors, a sprung arch'roof having a. section of the refractory arch built from silica brick and having the full vertical cross section of the exposed shoulder segv ment of the refractory arch opposite said charg ing doors built from non-acidic brick which sustain the usual stresses in this portion of the arch and are resistant to material corrosion attack by dust particles in the furnace atmospheres.

3. In a basic open hearth steel furnace, a sprung arch roof exposed to the interior of the furnace, the refractory arch being formed compositely of sections built from silica bricks and from non-acidic bricks, the crown of the refractory arch being composed of said silica bricks,

and said non-acidic bricks being confined to andy oxidiaable metallic spacer plates between certain of the non-acid refractory bricks.

5. A refractory brick sprung arch, 'l having a. center portion exposed to the furnace interior Vand consisting of acid refractory bricks and having shouldersexposed to the furnace interior on either side of the center portion consisting of nonacid refractory bricks, and oxidizable metallic spacer plates between non-acid refractory bricks of the shoulders, the non-acid refractory bricks andh the plates bearing the entire load of the arc HUGH s ROBERTSON.

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