US2961978A - Refractory roof and method of prolonging its life - Google Patents

Description

Nov. 29, 1960 A. H. SOMMER ETAIQ REFRACTORY ROOF' AND METHOD OF PROLONGING ITS LIFE Filed July 18. 195e zal United States Patent O REFRACTORY ROOF AND METHOD OF PROLONGING ITS LIFE Alviny H. Sommer, Peoria, Ill., and Francis P. Shonkwiler,

Pittsburgh, Pa., assignors to Harbison-Walker Refractories Company, a corporation of Pennsylvania Filed July 1s, 1956, ser. No. 598,682

1 Claim. (Cl. 11o-99) This invention relates to refractory roofs for industrial yfurnaces and to a method of prolonging the service life of vsuch a roof.

In the operation of industrial furnaces, such as open hearth steel furnaces, glass melting furnaces, and smelting and refining furnaces in the copper industry, conditions exist which consume or destroy the refractory bricks of4 which the roof is constructed. The temperatures in the furnace may be high enough to actually melt the refractories at Itheir lower exposed surfaces so that they dripvor run away and thus wear thin, resulting in an unstable roof. Sometimes holes are burned through the roof. In other cases, the refractories may be eroded due torslags or corrosive fumes or dusts present in the furnacel atmosphere. Spalling may occur from thermal or mechanical shock. In any case, the result is to produce costly delays or to entirely terminate the operation of the furnace until repairs can be made to the roof. Frequently, theseentail replacing the entire roo-f even though only a small area may be worn away.

It is among the objects of this invention to provide a way, of constructing a refractory roof which will prolong its service life, and which permits a roof to be strengthened without taking the furnace out of operation.

In accordance with this invention, a roof to which the invention applies is formed from a plurality of refractory bricks' disposed side by side in the usual manner, and in addition the roof has laterally spaced protuberances projecting upwardly. The protuberances may be longer bricks or they may be metal hangers by which the bricks are supported. Covering the top of that area of the roof which is subject to excessive wear from below, is a hardened mass of castable refractory material that is bonded to the top of the roof and to the sides of the adjoining protuberances. It is applied in plastic form, after the furnace has operated for a while, and allowed to set. This mass increases or restores the thickness of the roof in the area covered, so that the furnace can be used muc-h longer than heretofore before a major roof repair or reconstruction is needed.

The invention is illustrated in the accompanying drawings, in which Fig. 1 is a vertical cross section through la furnace provided with our roof;

Fig. 2 is an enlarged fragmentary section taken on the line II-Il of Fig. l;

Fig. 3 is a view, similar to Fig. 2, of a modification;

Fig. 4 is a fragmentary perspective view of a further embodiment of the invention;

Fig. 5 is a view, similar to Fig. 2, of another modication and Fig. 6 is a fragmentary vertical section of a further embodiment.

Referring to Fig. l of the drawings, an larched roof 1 is shown sprung between refractory buttresses 2. The roof is formed in the usual way from refractory bricks disposed side by side. In this particular case, some of the bricks are longer than others and project above the main body of the roof to form spaced parallel ribs 3 extending across it. The bottom of the roof inside the furnace is shown with a recess 4 which was caused by erosion of the refractory bricks in Vone way or another. Such erosion generally is most severe just above the tap hole 5, the bricks commonly wearing out and requiring replacement after about a month of furnace operation. With normal ribbed roof construction, although a hole may have Worn through the shorter bricks, the roof might maintain its stability due to the remaining three inches or more of brick in the rib arches. Nevertheless, the furnace had to be removed from the line, because it could not be operated with a hole through which heat escaped. Furthermore, the impaired stability militated against operation with safety to personnel. In the past, one way of treating such a situation was to make partial or total replacement of the roof. Another thing that had been done was to allow the furnace temperature to drop far enough to permit workmen to get on top of the furnace, Where they worked with considerable hazard and discomfort to accomplish a hot repair. Of course, both practices entaledloss of operating time with great expense.

These problems have been solved in accordance with this invention by applying to the top o-f the roof over the thin area above recess 4, castable or monolithic refractorymaterial. This is not applied until after the furnace has operated for a time, because it is then more evident as to what area of the roof is going to wear the fastest, and also the roof will have expanded under heat and assumed its final shape or rise so that the castable refractory will bond itself more firmly to the roof brick. The load bearing castable refractory 6 is applied over the eroded area between the rib arches '3. The material is applied several inches thick, and it is made certain that itfrmly `engages the sidesof the adjoining ribs. Asit hardens, the bond developed within the castable also produces adherence to the roof, including the ribs. Therefore, the hardened mass not `only increases or at least restores the thickness of the roof at that point, but it also serves Vto hold in place the underlying bricks after they have worn so thin that they otherwise would fall into the furnace. The castable refractory may merely lill the valleys between the ribs, or the mix can be applied still thicker and allowed to cover the tops of the ribs also, as shown in Fig. 2. Consequently, the height of the ribs does not limit the maximum thickness of the material that can be applied.

While the term castable, meaning in the trade a monolithic refractory material cast or poured into place, has been used herein, this invention is equally applicable to the same material used in other ways, such as by gunning, troweling or ramming. Refractory castables are made of refractory aggregate or grain, with plasticizers if necessary, and with a bonding ingredient. When mixed with water and applied, such a product hardens and bonds itself to the adjoining bricks. Selection of the type of refractory castable to be used is subject only to the normal considerations governing refractories. Thus, the product must be sufficiently refractory for the intended service, it must not shrink excessively, and it must be compatible with the other refractories that it engages. If the roof is formed of silica brick, a compatible castable might be one containing silica as an aggregate. Chrome ore castables are perhaps equally suitable for this purpose, and they may be applied also to basic bricks, which are commonly made of chrome ore or magnesia, or a combination of the two. The hardening or binding agent most commonly is calcium aluminate cement, and a typical refractory castable will generally contain about l5 percent of such material.

Since furnace roofs must bear stresses, it s necessary that the castable refractory disclosed herein be capable of contributing its share to the stability of the roof. This distinguishes it from monolithic layers that have been intended and suited only for insulation and not for producing a securely bonded section capable of renewing the roof itself. Of course, such "insulation is not load bearing. v'

Although the necessity for it has not yet been proved, it is believed to be good insurance against accidents that might possibly arise from applying a wet material directly to a hot brick roof, to iirst spread a dry layer of the castable over the brick work. This dry layer then is covered with the plastic mass, which wets the dry material so that all of its hardens together as a unitary mass.

In some cases, the roof has ribs 8 that run lengthwise of the roof, as well as ribs 9 that extend crosswise, so that rectangular areas bounded by the ribs are formed as shown in Fig. 4. This is'an excellent arrangement where our invention is to be used, because all sides of the applied castable refractory 10 are bonded to ribs.

In some instances, it may be advantageous to use brick shapes of special design to help hold the castable refractory in place. Thus, the ribs may have vertically inclined side surfaces. If the ribs are tapered upwardly in cross section, as shown in Fig. 2,V it is easier to place the material. If the ribs 13 are tapered downwardly, as shown in Fig. 3, they help hold the castable 14 in place by aring out over it.

Although ribs have been disclosed herein as projecting above the body of the roof, other types of protuberances also can be used. For example, individual bricks projecting above the roof at laterally spaced points will serve the purpose. The same thing is true of metallic elements extending above the brick work.

In some cases, it may be desirable to use steel reinforcing elements in the castable refractory. Thus, as shown in Fig. 5, wire screening 16 or the like can be suspended between the ribs 17 so that it will be embedded in the castable refractory 18. Or, a metal sheet can be laid on the roof before the plastic mass is applied. The heat will cause the metal to bond to the castable refractory and to the bricks, particularly if they are basic types.

This invention is equally applicable to ribless roofs, in which the bricks 20 are hung singly or in groups by metallic hangers Z1, as shown in Fig. 6. The hangers can be embedded to some extent in the castable refractory 22 to help hold it in place. Also, the slots 23 in the upper ends of tht bricks, where the hangers enter them, will serve to key the castable to the roof.

This invention is even applicable to electric arc furnaces, which suier early erosion of the refractory roof brick in the area around the electrodes. The life of the roof can be extended by applying refractory castable after some erosion has occurred, provided that protruding refractory or metallic elements are available for the castable to bond itself to.

It will be seen that with this invention the life of a furnace roof can be prolonged without shutting down the furnace or even allowing it to cool to any great extent. Consequently, a furnace campaign can be lengthened materially before a major repair is necessary.

According to the provisions of the patent statutes, we

have explained the principle of our invention and have` illustrated and described what we now consider to r`epresent its best embodiment. However, we desireto have it understood that, within the scope of theappendedclaim, the invention may be practiced otherwise than as "Specifically illustrated and described.

We claim:

A method of prolonging the service life of the refctory roof of an industrial furnace that has laterally spacd protuberances projecting above the main body 0f the roof, the method comprising applying while the furnace is hot and after the roof has expanded a plastic mass of castable refractory material to the top of that area of the roof subject to excessive wear from below and against the sides of the adjoining protuberances, said material being one that will bond strongly to the roof, and allowing the matcrial to harden. t

References Cited in the file of this patent UNITED STATES PATENTS 1,394,470 charles oct. 1s,A 1921 1,727,675 Ross et al. Sept. 10, 1929 2,717,564 Kreutzer Sept. 13, 1955 FOREIGN PATENTS 922,665 Germany Ian. 24, 1955 611,704 Great Britain Nov. 3, 1948

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