US2652793A - Refractory furnace roof brick resistant to spalling - Google Patents

Description

Sept. 22, 1953 R. P. HEUER ET AL 2,652,793

REFRACTORY FURNACE ROOF BRICK RESISTANT TO SPALLING Filed Oct. 50, 1948 I 6 Sheets-Sheet 1 I L l ZO -"Z0 INVENTORS Sept. 22, 1953 R. P. HEUER ET AL 2,652,793

REFRACTORY FURNACE ROOF BRICK RESISTANT TO SPALLING Fiied Oct. so, 1948 e Sheets-Sheet 2 Sept. 22, 1953 R. P. HEUER ET AL REFRACTORY FURNACE ROOF BRICK RESISTANT TO SPALLING 6 Sheets-Sheet 3 Filed Oct. 30, 1948 AME ' INVENTOR asseZJ f v'cefl w ATTORNEYS Sept. 22, 1953 R. P. HEUER ET AL REFRACTORY FURNACE ROOF BRICK RESISTANT TO SPALLING Filed Oct. 30, 1948 6 Sheets-Sheet 4 jgzz m, m lm w M 6 N -W ew REFRACTORY FURNACE ROOF BRICK RESISTANT TO SPALLING Filed Oct. 30, 1948 Sefif. 22, 1953 R. P. HEUER ET AL 6 Sheets-Sheet 5 INVENTO R6 Sept. 22, 1953 R. P. HEUER ET AL 2,652,793

REFRACTORY FURNACE ROOF BRICK RESISTANT TO SPALLING Filed Oct. 50, 1948 6 Sheets-Sheet 6 L//16 0 -----;U 44 L :5

INVENTORS Patented. Sept. 22, 1953 REFRACTORY FURNACE ROOF BRICK RESISTANT TO SPALLING Russell Pearce Heuer, Villa Nova, and Mervin Adrian Fay, Narberth, Pa., assignors to General Refractories Company, Philadelphia, ha, a corporation of Pennsylvania Application mmso, 1948, Serial No. 57,454

Claims. 1

The present invention relates to the manufacture of brick having unusually high resistance to spalling and particularly to such brick intended for use in suspended roofs or supported wall construction of furnaces.

This application has been divided, and claims on the process of molding a refractory brick have been inserted in co-pending application for Process of Molding Refractory Brick Having Spacer Plates Serial No. 375,094, flied August A purpose of our invention is to mould basic refractory brick under high forming pressure and concurrently'with the moulding to imbed in the, brick an oxidizable metallic spacer which effectively subdivides the brick internally in a direction which will resist spalling.

A further purpose is to imbed such anoxidizable metallic spacer in 'a plane parallel to the major axis of the brick and/or parallel to one of the longitudinal faces of the brick, thereby subdividing the brick into a plurality, suitably two, comoulded cells.

A further purpose is to provide cellular brick of this character with a socket or other engagement at one end of its major axis bywhich the brick can be hung or otherwise supported so that a temperature gradient in the brick cell exists along the major axis.

Further purposes appear in the specification and in the claims.

In the drawings we have chosen to illustrate a few only of the numerous embodiments in which our invention appears, choosing the forms shown from the standpoints of convenience in operation, satisfactory illustration and clear demonstration of the principles involved.

Figure 1 is a diagrammatic side elevation of a conventional brick intended for suspended arch use in vertical position, the lowermost edge of the brick in this view being exposed to high temperature.

Figure 2 is a diagrammatic illustration showing the length of the brick of Figure 1 plotted as ordinate and the temperature at any point when in furnace roof service plotted as abscissa to the left of the right hand edgeof the brick as shown. The curve thus gives temperature gradient.

Figure 3 is a diagrammatic side elevation similar to Figure 1 with the brick broken up into elements to illustrate the spalling behavior.

Figure 4 is a diagrammatic side elevation similar to Figure 3, in which the behavior of the laminae in Figure 3 is illustrated.

Figure 5 is a diagrammatic side elevation similar to Figure 1 showing the action of the brick in spalling.

Figure 6 is a central longitudinal section parallel to a side face showing the preferred brick made in accordance with the present invention.

Figure 7 is a side elevation similar to Figure 4 showing the spalling behavior of the brick of Figure 6.

Figure 8 is a perspective showing a brick according to the invention intended for suspended roof or supported wall construction, and having its principal side faces covered with metallic spacers, with a metallic spacer also imbedded in the brick.

Figure 9 is a top plan view of a U-shaped spacer and an internal cell separating spacer according to the invention.

Figure 10 is a front elevation of Figure 9.

Figure 11 is a side elevation of Figure 9.

Figure 12 is a side elevation of a spacer plate used on the side opposite to the base of the U-shaped spacer plate.

Figure 13 is a front elevation of Figure 12.

Figure 14 is a perspective of a brick according to the invention, having three cells.

Figure 15 is a perspective of a brick according to the invention having cells but without spacer lates on the lateral faces.

Figure 16 is a diagrammatic central vertical section showing a moulding press by which the brick of the invention is moulded and illustrating the method of moulding. The end portion of the mould box is removed to permit seeing the interior.

Figure 17 is a view similar to'Figure 16 showing the moulding press in closed position, whereas Figure 16 shows the moulding press in open position.

In the drawings like numerals refer to like parts throughout.

Describing in illustration but not in limitation, and referring to the drawings:

In the construction of many types of furnaces to be used at high temperatures, such as open hearth steel furnaces, it is desirable to form the roof of suspended refractory brick and to employ mechanically supported construction for certain downtake walls. The refractories used for this purpose consist of the various basic refractories, of which the most widely used are chrome ore, magnesite, chrome-magnesite and magnesitechroine. It is customary to lay the brick with oxidizable metallic spacers in the joints. Frequently such basic brick are used without previous kiln firing and in such cases the metallic spacers are desirably applied to the brick at the time of forming the brick.

In service of this character, failure of the refractory is primarily by spalling away of the brick at the hot end due to the temperature changes which the hottest part of the brick A an open hearth furnace roof will be understood more clearly by reference to Figures 1 to 5 inelusive.

Figure 1 shows a brick 20 having a lower face or hot end 2|, a side face 22, an edge face 13 anda cold end 24 provided with a hanger opening or other recess 25 for suspending the brick. The vertical or lateral faces of the brick are protected from the heat of the furnace by adjacent brick.v The lower or hot face 2| may exhibit a temperature of 3000 F. at the time the finished heat of steel is tapped from the open hearth furnace.

A thermal gradient then prevails along the lon-.

gitudinal axis of the brick as shown by the line ab in Figure 2, the temperature being indicated by the abscissa distance from the right hand edge of the brick. After the furnace is tapped, the furnace doors are opened, the fuel is shut off and a large quantity of cold charge is placed in the furnace. As a result the hot face of the brick cools rapidly and its temperature may fall 1000 F. or more. The line ch in Figure 2 represents schematically the new condition. Since the cooling is relatively rapid, most of the temperature change is confined to the hot end of the brick. At some interior point such as 26 there is relatively little loss in temperature.

After charge of the furnace is completed, the fuel is again supplied to the furnace and the hot face of the brick rises in temperature until the gradient shown by the line ab is again established. This operating cycle is repeated again and again. The brick are thus subjected to repeated strains and finally fractures develop and the hot faces of the brick spall off. The new hot faces thus formed are subjected to a similar treatment and gradually the brick are destroyed.

Figure 3 aids in understanding the mechanism by which these spalling cracks develop. In this figure the heated end of the brick shown in Figure 1 is represented as consisting of a number of elements of thickness S across the width of the brick. Each strip 21 thus represented will extend from one edge to the other of the brick amounts suflicient to compensate for the change Sc(T1-Tz).' This is accomplished in two ways.

Tensile stresses are set up across the hot face of the brick, which increase the thickness of the individual elements. In addition, the adherence of each element to its neighbor tends to conform the adjoining elements to each other. conformation plus the tensile strain tends to compensate for Se (Tl-T2). The resulting assembly of the strained elements is indicated at 28 in Figure 4.

The tensile stress acting across the hot face may rise to a value which the refractory material cannot stand, whereupon a crack 30 will result at about 90 degrees to the hot face as shown in Figure 5. The deformation of the elements at the edge of the brick may exceed the strain which the refractory is capable ofstanding, whereupon a crack 3| (Figure 5) will start and then gradually work its way across the brick. Cracks similar to 30 and II are commonly observed in actual practice. As a result of such cracks, portions such as 32 and 33 of the brick separate and fall off as spalls. Of the two types of cracks indicated, the cracks 3| are more destructive.

In the foregoing study, only the forces caused by cooling have been considered. Upon rapid heating, compressive forces are set up across the face of the brick. Deformation of the individual brick elements also occurs, but in an opposite direction to the deformation caused by cooling. If the compressive forces are large enough they may cause shearing stresses and consequent cracking of the refractory. In basic refractory roofs these shear cracks are seldom observed. However, the effect of deformation of the-brick elements upon heating supplement the destructive deformation caused by cooling and may therefore accelerate failure.

We have observed that the presence of metallic spacers attached to the sides of the brick during forming of the brick minimizes the tendency of cracks to form at the surface due to the strains set up by heating and cooling. The exact nature of the action of the metallic spacers in preventing crack formation is not entirely clear. It is, however, evident that the spacers exert a skin eifect in avoiding crack origin and propagation.

The spacers are usually made ofordinary low carbon steel, although they can be made of any oxidizable constructional material which will operate at the temperature at the hot end of the refractory. It will be evident of course that the spacers need not be oxidizable at room temperature as long as they oxidize at furnace temperature, and therefore stainless steel, such as the 18% chromium 8% nickel grade or the 16% chromium grade or other alloys of iron and chromium may be used.

The heat of the furnace oxidizes the spacer at the hottest part of the brick and the iron or actual/brick, however, each element 21 is firmly the individual elements must undergo strains in other metallic oxide formed reacts with the basic material present in the refractory, suitably magnesia or impurities in chrome ore. The resultant product welds together and forms a monolithic structure which definitely resists crack formation. 1

Our studies indicate that the strain set up at the surfaces of the brick due to heating and cooling are greater if the transverse dimensions of the brick are greater. This will be evident by reference to Figure 4. This is one reason why it is customary to limit the maximum dimensions of the brick to definite prescribed figures.

This

. metallic spacer plates which are placed in a plane or planes parallel to the major axis of the brick and preferably approximately parallel toone of the longitudinal faces of the brick, thereby subdividing the brick into co-moulded cells of smaller dimensions, which can be heated and cooled with less strain at the outer surface. The same mysterious action of the spacer plate which minimizes the crack formation when the plate is located at the edge of the brick likewise minimizes crack formation at the edges of the cells within the brick. Therefore, spalling resistance is decreased due to a combination of the cellular effect on account of reduced dimensions subjected to strain, and the skin effect exerted by the oxidizable metallic spacer subdividing the cells.

While the partition wall between the cells should extend a major portion of the distance across the brick at the hot end (and most desirably at least three quarters of such distance), it will be understood that there may be some remaining cross connection between the refractory where the partition does not fully extend across the brick. Likewise while the cell should run the major length of the brick, it will be understood that considerable benefit will be evident if the partition is located at the hot end and extends for a distance of even two or better three inches from the hot end. Naturally for best rekilograms per square centimeter), and preferably exceed 5000 pounds per square inch' 351.5 kilomm: per square centimeter) and will most desirably exceed 10,000 pounds per square inch (703 kilograms per'square centimeter).

Where reference is made herein to a brick it is intended to include the standard rectangular shape as well as any suitable block or other shape, provided with any suitable contour or attachment to engage a suitable hanger, or support if any. 1

A suitable brick according to the present invention is illustrated in Figure 6, provided with sults the cells should be separated for the major portion of the length of the brick beginning at the hot end.

In making up the brick, the brick mix employed may, for example, be magnesia or refractory materialhigh in magnesia, such as deadburned magnesite or electrically fused magnesia.

It is important that the refractory material be of a basic nature, since certain refractories such as silica would react with the metallic spacer when they oxidized and would form fusible slags, destroying the roof. Chromite may be used instead of material high in magnesia. For instance mixtures of chromite with magnesia, containing, for instance 75% of chromite and 25%' cells 34 and 35 separated by a metallic spacer plate partition 36. Metallic spacer plates 31 are provided at the lateral faces of the brick (Figure 6). The top of the hanger recess 25 is closed by the base of the U of an inverted U-shaped metallic support 38 comoulded in the brick.

- The behavior of the brick of Figure 6 after repeated reheating is indicated in Figure 7,

'of the brick in accordance with the invention.

The partition wall 36 between the cells has at one edge a flange 40 which is suitably attached as by welding to the base 4| of the U of the U- shaped oxidlzable metallic spacer plate 42, having sides 43 which extend along the edges of the brick. The sides 43 may diverge slightly from parallelism if desired, even in a rectangular brick. Interlocking tabs 44 are lanced or otherwise formed from the spacer plate and extended inwardly to imbed in the brick.

The sides of the U are desirably short enough so that a thin line of refractory 45 exists on the edges adjoining a spacer plate 46 which closes the open space of the U and extends over the portion of the side of the brick opposite to the base of the U below the hanger recess. Interlocking tabs 44 are also lanced or otherwise formed from the plate 46. It is usually not necessary to extend the plate 46 over the portion 41 of the brick adjoining opening.

It will be seen in Figures 8, 10 and 14 that the partition spacer desirably does not extend fully to the cold end of the brick, in order to avoid nesium sulphate, magnesium chloride, sodium v dichromate, sodium silicate and the like may be used. The amount of binder used should be sufficient to form a brick which is mechanically strong without kiln firing. Normally the binder interference with the hanger recess.

In-some cases it may be desirable to use more than two cells, and in Figure 14 a brick is shown having cells 34, 35 and 35' separated by spacer lateral faces. A broadened base 40' on the parti-' tion spacer is provided to hold it in the mould.

Figures 16 and l'lillustrate a desirable manner of mouldingthe brick. It is preferable to use a hydraulic press, although any other suitable press may be used. Th material need not be formed by a steady forming pressure but may be formed by repeated impacts or blows delivered by falling weights, pneumatic hammers or the like.

Figures 16 and 17 show a mould assembly hav ing a mould opening 41 of the desired brick size contained in the mould box 48. The opening is closed by upper and lower dies 50 and 5|. Both dies are desirably movable. The forming presthemouth of the hanger I 7 sure may be supplied as by ahydraulic cylinder acting on the upper die 50.

The brick is formed on its side with the 1.0!181-1 I is placed in the mould. The opposing spacer plate 46 is attached to the upper die 50 with the interlocking projections 44 downwardly directed. The spacer plate 46 is desirably" temporarily held in place on the upper die by a magnetic chuck 53,

although adhesive or any other suitable attachment may be employed. The upper die has a plug 54. which forms the hanger recess and desirably carries any metallic parts relating to hanging such as the U element '38 associated therewith. To mould the brick the dies are closed to the position shown in Figure 17. Thereupon the upper die 50 is withdrawn and the lower die is raised to eject the brick from the mould. The cycle is then ready for repeating.

The moulded brick are dried for about twentyfour hours, after which they are ready for use.

It will beevident that the spacer plates are secured to the brick by comoulding.

The spacers are desirably made of metallic 'sheet or plate of about 1 6 inch thickness, al-

though thinner or thicker spacers. may be used. Spacers thicker than inch are not recommended because of the tendency of the metal to melt out rather than oxidize. Spacers thinner than inch are not recommended.

In view of our invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art,'to obtain all or part of the benefits of our invention without copying the process and structure shown, and we, therefore, claim all such insofar. as they fall within the reasonable spirit and scope of our claims.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is;

1. A unitary basic refractory brick of elongated shape having support means adjacent one end and an oxidizable metallic spacer plate in comoulded relation to the refractory extending longitudinally through the interior of the brick for part only of the length of the brick and extending across th brick and partially separating the brick into refractory blocks on either side, there being refractory brick material extending unitarily across a transverse edge of the spacer plate between the blocks adjacent the end having the support means.

2. A unitary basic refractory brick of elongated shape having support means adjacent one end, an oxidizable metallic spacer plate in comoulded relation to the refractory extending longitudinally through the interior of the brick for part only of the length of'the brick and extending across the brick. and partially separating-the brick into refractory blocks on either side, there being refractory brick material extendingunitarily across a transverse edge of the spacer plate between the blocks adjacent the end having the support means, and an oxidizable metallic spacer plate on one of the lateral faces of the brick comoulded therewith. v

3. A unitary basic refractory brick of elongated shape having a hanger connection adjacent one end, and an oxidizable metallic spacer plate in comoulded' relation to the refractory extending longitudinally through the interior of the. brick for part only of the length of the brick and extending across the brick and-partiallyv separating the brick into refractory blocks on either side,

there being refractory brick material extending plate between the blocks adjacent the end having metallic spacer the support means. and a second oxidizable metallic spacer plate secured to the first plate, located on a lateral face of the brick and comolded with the brick.

5. A unitary basicrefractory brick of elongated shape having support means adjacent one end, a

first oxidizable metallic spacer plate in comolded relation to the refractory extending longitudinally through the interior of the brickfor. part only of the length of the brick and extending across the brick and partially separating the brick into RUSSELL PEARCE HEUER. mzavm spams FAY.

References Cited in the file of this patent V UNITED STATES PATENTS Number Name Date 2,187,669 Stewart Jan. 16, 1940 2,247,376 Heuer July 1,1941 2,465,170 Rochow Mar. 22, 1949

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