US2504185A

US2504185A - Method for making basic furnace bottoms

Info

Publication number: US2504185A
Application number: US590634A
Authority: US
Inventors: William S Debenham
Original assignee: Carnegie Illinois Steel Corp
Current assignee: Carnegie Illinois Steel Corp
Priority date: 1945-04-27
Filing date: 1945-04-27
Publication date: 1950-04-18
Anticipated expiration: 1967-04-18

Description

April 18, 1950 w. s. DEBENHAM 2,504,185

mz'mon FOR MAKING BASIC FURNACE BOTTOMS Filed April 27, 1945 2 Sheets-Sheet 1 INVENTOR M44 MMJT DEBENHA/Vl, 91 4, 5

April 18, 1950 w. s. DEBENHAM METHOD FOR MAKING BASIC FURNACE BOTTOMS 2 Sheets$heet 2 Filed April 27, 1945 fig.

Li Lml I] INVENTOR I W/L 4 MMS QEBENHAM,

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Patented Apr. 18, 1950 MAKING BASIC FURNACE BOTTOMS William S. Debenham,

Carnegie-Illinois Stee METHOD FOR tion oi New Jersey Chicago, Ill., assignor to i Corporation, a corpora- Application April 27, 1945, Serial No. 590,634

2 Claims. 1

This invention relates to a method of making basic furnace linings and bottoms, and more particularly, the linings and bottoms in furnaces such as basic open hearth furnaces and electric furnaces with basic linings.

The invention has among its objects an improved method of making basic linings or bottoms for furnaces whereby such linings or bottoms are characterized by being dense, strong, and completely burned. I

This and further objects of the invention will be more readily apparent in th following description.

The method of the present invention is applicable to and displays advantages in the making of linings or bottoms in various types of furnaces employing basic materials for such purpose, such as open hearth furnaces and electric furnaces, where the lining or bottom material is applied in granular form and is sintered in place. For the purposes of illustration, however, the invention will be particularly described in connection with the making of a bottom in a basic open hearth furnace wherein its advantages are particularly great. 7

The invention will be more readily understood by reference to the accompanying drawings, in which:

Figure 1 is a view in transverse vertical section through a typical basic open hearth furnace;

Figure 2 is a view in longitudinal vertical section through a portion of such furnace, said section being taken along the line IIII in Figure 1;

Figure 3 is a view in front elevation of a furnace bottom ramming or pressing device made in accordance with the present invention;

Figure 4 is a view in section through the presser shown in Figur 3, such section being taken along the line IV-IV in Figure 3; and

Figure 5 is a view in vertical section through such presser, the section being taken along the line V-V in Figure 4.

The open hearth furnace 2 which is shown in Figures 1 and 2 provides a covered hearth in the form of a large shallow receptacle in which the charge of metal is placed, such charge then being subjected to the action of flames directed over the top thereof alternately from either end of the furnace for the purpose of melting the charge to allow its purification and the addition of desired amounts of alloying ingredients. As a result of the high temperature to which the furnace is subjected, the lining is eroded by the bath, becoming progressively thinner in successive heats, and therefore frequently must be renewed.

As shown in Figures 1 and 2, furnace 2 is provided with a foundation 4 of insulation and/or fireclay brick, a layer of basic brick 6, usually chrome or chrome-magnesite brick, on top of such foundation, and a bottom 8, which, in a basic open hearth furnace, is composed largely of burned magnesite grain sintered in place on top of the basic brick. It is with the application of the furnace bottom 8, whether in a new furnace or in an old furnace upon relining thereof, with which the present invention is concerned. Bottom 8 includes beside that part of the lining actually in contact with the bath the curved front banks [0 shown in Figure 1 leading up to the charging doors I2 of the furnace and the inclined rearward portion I 4 which is termed the backwall.

Bottoms or hearths of basic open hearth furnaces ar currently prepared by applying high magnesia materials in granular form over a suitable foundation, such as the layer of brick 6 of the furnace shown, in either of the following ways:

1. The material, usually dead burned grain magnesite, is mixed with 10 to 25% basic open hearth slag and the mixture is gradually burnedin in successive layers approximately one inch thick until the desired thickness is obtained. As several hours of burning at about 2900 F. is taken for each layer, several days may be required to complete a bottom, but this method produces a well sintered bottom that has fairly satisfactorily stood the test of time in the industry.

2. The material, size-graded dead burned magnesite or dolomitic magnesite, to which special air setting bonds including dry sodium silicate has been added, is moistened and rammed cold to the desired thickness with pneumatic hammers, thus producing a dense monolithic bottom, after which the furnace is subjected to heat. This method has the advantage of considerable saving in time over the burning-in process, and has been largely adopted in recent years. Such rammed bottoms, however, do not sinter completely in service, and while some strength resides in the unsintered material due to the air setting bonds, these bottoms are frequently friable in the subsurface layers and have been found often more susceptible to penetration by steel, and consequently to steel breakouts than the burned-in bottom.

It is the opinion of many that with decreasing steel production rates, the burned-in bottoms will again return to general favor. The burnedin bottoms, however, as made in the prior practice are not ideal since the refractory properties and effectiveness are reduced. by the necessity of diluting burned magnesite grains with slag in order to allow the bottom to consolidate and make it dense.- This apparently homogeneous burned-in bottom employing burned magnesite grain and slag is in reality a mixture of refractory grains in a slag matrix which is quite soft at operating temperatures and renders the bottom more susceptible to erosion. Although it is thought by some that the slag has a certain mineralizing effect on the magnesia grains promoting their growth, it is more generally agreed that the higher the MgO content the better the bottom, and thus the slag cannot be considered other than a necessary evil.

The method of the present invention makes possible the use of high MgO content grain in the production of a sintered furnace bottom and produces a dense, strong, completely. burned lining or bottom. Ingeneral, the method consists in pressing the granular material in place while the furnace is heated, thereby securing the desired degree of packing of material while the grains are in condition to sinter and bond to each other. The rammer or presser which is the subject of divisional application Serial No. 650,176, filed February 26, 1946, now Patent No. 2,426,673, has proved to be advantageous in carrying out the present method. The rammer or presser is inserted within the furnace for subjecting the bottom to the desired amount of pressure, such presser being of such shape as to allow the furnace bottom to be pressed to the desired contours in different portions thereof.

The presser device consists of a curved form It, preferably made of cast iron, such form being roughly of a shape corresponding to half a right circular cylinder. One portion of the curved surface thereof, the front surface 20, may be made of circular cylindrical contour, but the rear curved surface 22 thereof, although it may be circular in'cross sectional shape, is preferably made of a longer radius than the front portion so that it conforms more closely to the surface of the backwall of the furnace. The presser is also provided with two end walls 2| and 23 which complete the structure.

presser adaptable to the different contours of the furnace bottom, it is provided on the front end thereof with three ram engaging sockets 2!, 26, and 28 and On the end wall'li with a ram engaging socket 30. Sockets :4, 26, 28 are formed by providing vertical slots in the upper edge of wall 20 to receive the portion of reduced diameter at the end of the charging machine ram,

and are completed by a plate 21 welded to the presser having cooperating recessed portions and a centrally located hole therethrough for the verticalreception of the flange 29 on the outer end of the charging machine ram and the slidable locking pin 3| through ram i5, respectively. Socket It on the end of the presser is similarly 4 formed, with the exceptionthat the plate 32 on the inner surface of the wall 2| contains only one recess for the reception of the flange on the ram.

It will be readily apparent that with the four sockets by which the presser may be mounted on the ram, the ram, which as is well-known, may be adjusted angularly in a vertical plane, may be adjusted longitudinally of the furnace, may be projected into the furnace through the charging door to variable extents, and may be rotated about its own axis. can present the form to the furnace bottom in such manner that the entire area of the bottom which may be reached through the charging doors can be covered and shaped to the desired contour.

In lining a basic open hearth furnace in accordance with the present invention, the hearth foundation is prepared in the usual manner and the grain burned magnesite, which is preferably straight grain burned magnesite of fine particle size. containing over MgO is shoveled over the bottom and burned as in making a regular burned-in bottom. When the bottom has been built up to a depth of approximately six inches and has attained a surface temperature of approximately 2900 F. or above, the fuel is shut off and the presser member quickly inserted by the charging machine through a charging door of the furnace, pushed against the backwall, dragged across the bottom, rolled against the ends, and pulled against the front banks, thereby pressing down the bottom and conforming it to the desired shape. Usually for commercial burned magnesite containing 80% Mg() and heated to 2900 F. a pressure of ten pounds per square inch between the presser and furnace bottom has been found adequate.

Manipulation of the presser through one furnace door to cover the area of the furnace bottom which can be reached through that door ordinarily requires one or two minutes. Such period of time is insufficient to heat the presser sufficiently to damage it. The presser is then withdrawn, and the furnace is again heated for onehalf hour to bring the bottom back to temperature, after which the same pressing operation is repeated from the next furnace door and so on until the whole bottom has been consolidated in this manner. Usually it is preferred to use two or three such complete pressings of the entire furnace bottom area, additional layers of burned magnesite about four inches thick being shoveled onto the furnace bottom between successive pressing operations. In some instances, it is necessary in order to reach areas behind the door jainbs or to press the curved boundary areas of the furnace bottom, to present the presser in varying relationships to the furnace bottom. This can be readily done as above described, either by rotating the ram of the charging machine, as shown in Figure 2, to make the presser conform to the area engaged or in some cases to withdraw the presser from the furnace, place it on a suitable support and to engage it at a different socket by the charging machine ram. Such operation may be quickly and easily accomplished and does not need entail undue cooling of thefurnace bottom. Although the presser has been described as merely being dragged over the furnace bottom, the charging machine upon which it is mounted makes possible, if desired,

, a tamping action by raising and lowering the MgO grain. it is obvious that the invention displays advantages when small amounts of fluxes, for example, up to 5% flux, are incorporated therein.

It is obvious that variations are possible in the method disclosed, and it is to be understood, therefore, that the scope of the invention is not limited to the disclosed embodiments thereof but is defined by the following claims.

Iclaim:

1. The method of making bottom in a basic furnace which comprises applying a layer of granular basic refractory material high in MgO to the inner bottom refractory surface of the furnace, heating the layer of material throughout to a sintering temperature, and subjecting the heated layer to pressure to compact the layer and shape it to the desired contour, said pressing operation being effected in successive localized areas by subjecting the layer in such areas to a pressure on the order of 10 lbs/in. in a direction generally downwardly against the layer of refractory thereunder.

2. The method of making bottom in a basic open hearth furnace which comprises applying a layer of granular basic refractory material composed substantially wholly of straight grain burned magnesite to the inner bottom refractory surface of the furnace, heating the layer of magnesite throughout to approximately 2900 F., and &

subjecting the heated layer to pressure applied to the top of the layer in a direction generally REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS