US3767375A

US3767375A - Refractory furnace tank walls

Info

Publication number: US3767375A
Application number: US00241055A
Authority: US
Inventors: E Brichard; J Declaye; J Autequitte
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 1968-10-30
Filing date: 1972-04-04
Publication date: 1973-10-23
Anticipated expiration: 1990-10-23
Also published as: JPS5233128B1; ES372961A1; IL33248A; CA954303A; BE740490A; IL33248A0; AT301082B; NO126613B; RO57033A; NL6916331A; GB1292158A; LU57194A1; FI50872C; BR6913734D0; IE33898B1; FI50872B; CH520627A; FR2021878A1; IE33898L; DE1954716A1

Abstract

A tank for containing a bath of molten metal in a float glass furnace has a wall formed by a plurality of juxtapositioned prefabricated refractory members. The joints between the members define interstices. Interstices are also being defined adjacent other faces of the blocks. Powdered carbon, alumina, chromium oxide, a carbide or nitride not wettable by molten metal at least partially fills these interstices to prevent the flow of molten metal therein so as to prevent raising of the blocks from their assembled positions by the flow of molten metal behind the blocks. These are in the interstices between the particles of the powder flow paths having restricted cross-sectional areas. The object of these restricted areas and the surface properties of the powder material is to prevent penetration by molten metal.

Description

United States Patent [1 1 Brichard et al.

[ 1 Oct. 23, 1973 REFRACTORY FURNACE TANK WALLS Inventors: Edgard Brichard, Jumet; Joseph Declaye; Jean Autequitte, both of Moustier/S/Sambre, all of Belgium Related U.S. Application Data Continuation-impart of Ser. No. 872,151, Oct. 29, 1969, abandoned.

Assignee:

Foreign Application Priority Data Oct. 30, 1968 Luxembourg 57,194

US. Cl 65/182 R, 65/347, 65/374 Int. Cl C03b 18/00 Field of Search 65/182 R, 99 A, 346,

References Cited UNITED STATES PATENTS 5/1970 Bacchiega et al 266/43 X 3,584,475 6/l97l Galey et al 65/374 X Primary ExaminerArthur D. Kellogg Attorney-Edmund M. Jaskiewicz [57] ABSTRACT A tank for containing a bath of molten metal in a float glass furnace has a wall formed by a plurality of juxtapositioned prefabricated refractory members. The joints between the members define interstices. Interstices are also being defined adjacent other faces of the blocks. Powdered carbon, alumina, chromium oxide, a carbide or nitride not wettable by molten metal at least partially fills these interstices to prevent the flow of molten metal therein so as to prevent raising of the blocks from their assembled positions by the flow of molten metal behind the blocks. These are in the interstices between the particles of the powder flow paths having restricted cross-sectional areas. The object of these restricted areas and the surface properties of the powder material is to prevent penetration by molten metal.

9 Claims, 10 Drawing Figures PAIENIEflumzs ms- 3761.375

SHEETlUF3 V V i Fig.1.

AN AUTEQUITTE ATTORBzY PAIENIEDUUZMBH' 3.767.375

SHEET 2 OF 3 INVENTORS EDGARD BRICHARD JOSEPH DECLAYE JEAN AUTEQ UITTE PATENIEBIIBI 23 ms 3.767; 375

SHEET 3 [IF 3 INVENTORS EDGARD BRICHARD JOSEPH DECL JEAN AUTEQ E ATTOR EY 1 REFRACTORY FURNACE TANK WALLS RELATED APPLICATION This application is a continuation-in-part of the copending application filed by the same-named applicants on Oct. 29, 1969 and having Ser. No. 872,151 now abandoned.

The present invention relates to refractory float glass furnaces of the type having a tank therein for containing a bath of molten metal, more particularly, to the construction of the refractory wall in order to prevent molten metal from penetrating behind refractory blocks constituting the wall.

Refractory walls for furnaces are generally formed by justzpositioning a plurality of prefabricated refractory members or blocks. When this wall is employed to support a bath of molten liquid some consideration must be given to sealing the joints between these refractory members against the flow of'the bath liquid. Such refractory walls have been made fluid tight merely by relying on the solidification of the molten liquid in the joints. However, this arrangement is not particularly effective especially where the temperature of the bath liquid is considerably above its melting point. Under these circumstances the bath liquid will solidify only at a considerably great distance from the interior face of the furnace wall so that the bath liquid is still able to penetrate a considerable distance into the wall. This penetration of the bath liquid into the wall is disadvantageous since there will be some bath liquid stationary in the wall joints. The liquid will bring about corrosion of the wall, the liquid will become polluted by the products of such corrosion, and the fioor blocks may be lifted when their density is less than that of the bath liquid and this liquid is'able to flow behind the block through a joint opening to the liquid bath. It is particularly important to prevent the penetration of the molten bath liquid through the refractory wall so that the liquid does not come in contact with the metallic elements positioned behind the refractory blocks. The strong corrosive action of the molten material on these metallic elements can be extremely destructive. It is therefore desirable to position some form of a barrier within the refractory wall to prevent the passage of the bath liquid through the wall. The position of the barrier may depend to a large extent upon the thickness of the furnace wall.

It is therefore the principal object of the present invention to provide a novel and improved refractory wall for a tank furnace containing a bath of molten metal.

It is another object of the present invention to provide simple and effective fluid tight joints between and behind the refractory members forming a furnace wall.

It is a further object of the present invention to provide a refractory wall of refractory blocks for supporting a liquid bath with restricted joints pervious to gas but tight to the liquid bath.

According to one aspect of the present invention a refractory furnace tank containing a bath of molten material such as molten tin may have a wall comprising a layer of justaposed prefabricated refractory members. This layer of refractory members is positioned on the interior surface of the tank wall and defines a thickness portion of the furnace wall. The joints between interior faces of the refractory members define flow paths extending from the interior of the furnace tank through at least a portion of the wall thickness. Means are provided in these paths for preventing the flow of bath liquid therethrough. These means may be positioned in at least portions of the joints so as to modify the cross sectional area of a flow path. The means form restricted cross section paths which also have surface properties which prevent the penetration of bath liquid along these paths through at least a portion of the wall thickness either in the joints between the members or elsewhere. The joints may be formed by various configurations of the opposing faces of adjacent refractory blocks or merely closely positioning these faces to each other. There may be disposed in the joints a loosely packed porous mass of material whose surface properties prevent the penetration of the bath liquid. The materials within the joints of this layer of refractory materials and the configurations and dimensions of these joints are determined so as to prevent the penetration of at least a portion of the wall thickness by the bath liquid.

Preventing of the raising or lifting of the refractory blocks from their assembled positions is thus obtained according to the present invention by providing a barrier of pulverulent material which is not wettable by the molten metal and which is situated under the blocks or the same barrier situated under or below the periphery of the only face of the block which is directed to the interior of the tank.

The present invention can eliminate or at least significantly reduce the amount of bath liquid which has solidified in the joints of the refractory wall after the operation of the furnace has been stopped. This solidified liquid represents an economic loss since it is not being used in the operation of the furnace and at the same time presents possible sources of corrosion of the wall members. By providing the presence of this liquid in the refractory walls the pollution of the bath liquid by dissolved or suspended bodies is significantly reduced and vitreous phases and gases which may result'from contact of the bath liquid and certain constituent materials of the refractory wall may be avoided or reduced.

It is known to construct a tank for retaining molten aluminium having a refractory wall comprising a plurality of refractory blocks with loose silicon carbide poured between the blocks. According to the present invention the interstices between fabricated refractory blocks forming a wall of the furnace tank arefilled with a pulverulent material, which is characterized by not being wettable by the molten metal, i.e., tin, in the furnace and the density of the pulverulent material is less than that of the molten tin. i

The non-wettability of the carbon prevents the-molten tin from penetrating the interstices and, in effect, isolates the granules of carbon so that as a result these carbon grains do not have any tendency to rise to the surface of the molten bath. The density of the carbon material between the refractory blocks ranges from 1.8 to 2.1 which is considerably less than the density of molten tin which is about 7.3. This relationship is contrary to that in known prior art where the density of this silicon carbide powder is greater than that of the molten aluminium in a furnace.

The use of a compacted material with a binder as disclosed in known prior art has the disadvantage that this compacted mass will crack because of any movements of the blocks of the refractory wall. The presence of such cracks will eventually become enlarged will per-' mit the molten metal to penetrate between the blocks and produce either a lifting of the blocks or a corrosion of the supporting structure for the blocks. A loosely packed pulverulent material in the joints between and adjacent the blocks has the advantage that the particles are able to slide over each other in the event of any movement of the blocks but the nonwettability of the particles will still prevent penetration by the molten metal.

Other objects and advantages of the present invention will be apparent from the accompanying description when taken in conjunction with the following drawings, which are exemplary, wherein;

FIG. 1 is a transverse vertical sectional view of a portion of a furnace wall which forms a tank for molten material according to a form of the present invention;

FIG. 2 is a transverse sectional view of a portion of a refractory furnace wall showing a modification thereof;

FIGS. 3-7 are similar to FIG. 2 and show further modifications according to a form of the present invention;

FIGS. 8 and 9 are top plan views of modifications in furnace walls according to a form of the present invention; and

FIG. 10 is a top plan view of another form of refractory furnace wall according to the present invention.

Proceeding next to the drawings wherein like reference symbols indicate the same parts throughout the various views a specific embodiment and modifications of the present invention will be described in detail.

As may be seen in FIG. 1 a refractory furnace tank incorporating the present invention has a floor and a side wall 22 which are both formed of

layers

24, 26 and 28. The layer 24, which is toward the interior of the furnace, is comprised of a plurality of slabs 30 with each slab comprising a body 31 of silico-argillic refractory, ceramic or of silicon carbide. Each body portion 31 has on its face 32 which is directed toward the interior of the furnace and on the four adjacent side faces 34 a compact coating 36 of carbon. The carbon coating is made adherent by means ofa binder of refractory cement. Adjacent faces between the slabs 30 define joints 38 which are not filled but which are fluid tight. Where the carbon coating 36 on the side faces is not accurate it may be necessary to trim this coating by a planing operation to insure that the joints 38 are sufficiently narrow. The joints 38 will be sufficiently tight with respect to the molten tin bath up to the operating temperatures of about 1,000C when the space in the joint ranges up to about 2mm. Up to this width the surface and interfacial tensions at the interfaces between the molten tin, carbon and gases present in the joints will prevent penetration of the liquid.

Where there is a possibility of the space in the joints 38 exceeding 2 mm. even in localized areas it may be preferred to subject the layer 24 to compression in one direction or even in both directions when viewing th layer in plan. Such compression may be obtained by means of adjustable clamps 40 which exert compressive forces against two vertical uprights 42 against cross-members 44 positioned against outer wall 46 of the furnace at the level of the layer 24. The tops of the uprights 42 are connected and may also be used for the construction of a known type of furnace crown which is not shown in the drawing.

The layer 24 contacts against layer 26 which is formed of silico-argillic blocks 50 which are shown in the art and are used particularly because of their thermal insulating properties. This layer 26 rests upon an outer wall or shell 28 of steel plate. The support framework for the furnace is not shown in the drawings for purpose of clarity. With this construction it is not necessary to provide any expensive or complicated anchoring structure for the ceramic blocks since the molten tin is unable to penetrate below the lower face of the blocks 50 and thus is not able to lift these blocks. When the bath liquid is a good conductor of heat or electricity it is particularly desirable to prevent this liquid from penetrating into the wall since preventing this penetration would reduce energy losses and the need to take any remedial measures.

According to the present invention the members constituting the layer may consist primarily of carbon at least along their surfaces forming joints with other members. The member may consist entirely of carbon or the carbon may be only at these joint surfaces. It is to be understood that carbonincludes graphite as well as amorphous carbon which may have suitable additives as well as certain impurities. Carbon is preferred since it is not wetted by the molten metals such as tins, used in the liquid bath or by various glasses.

When forming a layer of blocks it is preferable to use blocks of relatively large dimensions so as to limit the number of joints. A block according to the present invention also includes relatively large thin members which might better be described as slabs. The use of blocks of relatively large dimensions has the further advantage that the mere penetration, e.g., fortuitous, of liquid a short distance beneath its lateral edges will not cause the block to lift as quickly as would be the case when its dimensions are smaller.

By fitting the blocks 30 tightly together as described above the spaces in the joints will be so small that the bath liquid will not be able to penetrate between the joint surfaces. This arrangement is particularly advantageous where there are rapidly flowing currents of liquid which could entrain granular materials from the joints. Clamping of the blocks against each other by subjecting them to compressive forces which'are adjustable enables the width of the joints to be limited in spite of the thermal expansion due to fluctuations in furnace temperatures. Such variations are particularly likely to occur when the furnace is first being started up.

In FIG. 2 a powdered carbon 54 which is impermeable to molten tin is filled in the joints between the refractory blocks. The carbon grains are smaller than 1 mm. and preferably smaller than 0.1 mm. The refractory layer adjacent the interior of the surface comprises a plurality of slabs 56 of graphite with their joints 58 being filled with the powdered carbon 54. The slabs 56 are positioned on a relatively thick layer of powdered carbon 60 in which are embedded metallic tubes 62 through which may flow a thermal conditioning medium. Depending on the regions of the furnace floor these tubes may be used for heating or cooling with the thermal effect being achieved by means of water, cold air, hot air circulating as indicated by the arrows 63 or by the use of electrical resistors which are not shown in the drawing. Heat is readily transmitted from the liquid positioned on the slabs 56 to the thermal element or vice versa because of the good thermal conductivity of the powdered carbon 54 and the graphite slabs 56. The

layers

26 and 28 are substantially the same as the corresponding layers described in FIG. 1.

Analogous results have been found with powders of A1 Cr O carbides and nitrides not wettable by molten tin in the same conditions as carbon powder in the application according to FIG. 2 as in other applications wher powder is used.

In FIG. 3, there are formed joints 64 between slabs 66 of silicoargillic ceramic. Each joint 64 is formed by a projection 68 on a face 70 of one block positioned within a groove 72 on the adjacent face 74 of the next continguous block. The projection and groove have a sinuous configuration so that an inter-locking effect is achieved. The blocks rest upon a bottom bed 76 of powdered carbon. The joints 64 are also filled with powdered carbon and these joints together with the bottom bed 76 have a thickness ranging from 2-10mm.

In FIG. 4, a refractory insulating concrete 78 has been cast on the shell 28 so as to form a foundation surface with the top face of this surface having grooves 80 intersecting at right angles. Rectangular slabs 82 of graphite each have a recess 84 in their bottom face so as to define a downwardly projecting peripheral rib 86 on the slab bottom face. The peripheral ribs 86 of two adjacent slabs are seated together in a groove 80. The joints 88 between adjacent slabs are open and have a width of about 6mm. so that molten tin is able to penetrate into this joint. The molten tin, however, is stopped at the level of the ribs 86 by a carbon layer 90 which is positioned on the foundation layer and within the grooves 80. In certain cases grains from the carbon layer 90 may be entrained within the molten tin and flow upwardly through the joint 88 to float upon the tin, however, these would not float upwardly above the horizontal plane defined by the bottom faces 92 of the ribs 86. lnfact, the grains located above this plane cannot be entrained since they have a tendency to rise. In this manner, the major portion of each of the slabs 82 is protected against erosion of the subjacent layer with the result that raising of a slab is impossible. This measure is an additional precaution since the carbon powder located beneath the joint 88 is already extremely well protected from erosion because of its distance from the liquid mass of molten tin. The liquid-tight layer 90 is separated from the liquid bath by a layer of spaced blocks 82. In certain instances, a series of metallic plates, such as tungsten, may be placed on this liquid-tight floor of the blocks 82. These metal plates are not welded but are merely positioned-on the slabs, and are not shown in the drawings. It is also possible to provide a second layer of refractory slabspositioned on the layer of slabs 82 shown in the drawing. The second layer of slabs could have a greater density than that of the molten bath.

In the wall structure shown in FIG. there is provided a layer of graphite slabs 94 with the adjacent edges of successive slabs having a configuration to form a joint 96 having a pair of reverse bends therein. The

joint is provided with a region 98 which is located higher and further along the path of the joint as measured from the interior of the furnace than the region 100 which is lower and closer to the interior of the furnace. Thus if any grains of the carbon powder within the joint 96 were accidentally to escape toward the surface of the bath, such erosion of the joint would be arrested immediately after the lower region 100. The

graphite slabs 94 form a joint 102 between their rear faces and a layer of blocks 50 of silico-argillic ceramic. No material is interposed within the joint 102. In order to facilitate inserting of the powdered carbon in the joint 96 the powder may be tempered with the minimum quantity of water necessary to obtain a mortar having a consistency capable of being retained by adhesion on the ridge and groove defining the joint 96. This water is obviously rapidly eliminated by drying so that in operation the joint 96 if filled with loose powdered carbon.

Any gases which are evolved are able to escape through the pores of the joints. Since the escape of such gas bubbles into the bath of molten tin and particularly below the glass ribbon are disadvantageous, a suction may be provided with an aperture 103 connected by a conduit 104 to a pump which is not shown in the drawing. In order to collect the glass from as wide an area as possible an oblique cut-out 105 is formed in the corners of the blocks 150. An angle from 106 is positioned in the cut-out 105 and is welded at a number of points to the plate or shell 28. Since the quantity of the gases which are to be exhausted is relatively small these gases can readily circulate in the

joints

96, 102 and 108 and infiltrate between the angle iron 106 and the plate 28. The suction through the conduit 104 is established during the starting of the furnace but after a period of operation the evacuation of these gases can generally be discontinued.

The furnace wall structure shown in FIG. 6 combines the advantages of the joints shown in FIGS. 3 and 5. A joint 110 is formed between successive slabs 112 and 113 and has a lower region 100 or first zone and a high region 98 or second zone as in FIG. 5. However, the lower portion 114 of the joint is inclined to the vertical toward the lift-hand slab 112 as viewed in FIG. 6 so that a projecting portion 115 on the slab 1 12 is not only between the regions 1 l6 and 118 of the adjacent slab 113 which are located on the same horizontal plane but also between regions 120 and 122 of the same slab 113 located on a vertical plane which is perpendicular to a surface 124 of the face of the layer in contact with the molten tin bath. This arrangement not only provides for inter-locking of adjoining slabs but also a trapping of the powder in the joint 110 should accidental erosion occur. Preferably, the faces 126 and 128 forming the projection or tongue 115 define an acute angle toward the end of the projection in order to facilitate ,the positioning of the slabs. It is thus not necessary to position the slab 113 by moving the slab in a direction perpendicular to the plane of the drawing but a slab may be introduced in the direction indicated by the arrow .130. This angular insertion of the slab 113 insures the grip of the tempered powder for the joint during this opera-j tion.

In FIG. 7, a layer of graphite slabs 132 is positioned on several layers of granular materials having thermal insulating properties considerably superior to those of the usual refractory ceramic blocks'50. 0n the steel shell or wall 28, there are superimposed a layer of highly insulating mineral W001 134, a bed of Koalin fibers 136 having 43 percent alumina which is more refractory than mineral wool, a layer of powdered carbon 138 and finally the graphite slabs 132. The joints 140 between adjacent slabs are not filled and these slabs need not be positioned particularly close together. Fluid sealing is obtained in the upper portion of joint 140 by means of a groove 142 having with inclined slopes 144. A graphite strip 146 having a trapezoidal shape is inserted within groove 142. The faces 144 of the groove 142 and the faces and angles of strip 146 are accurately formed so as to minimize the thickness of the joints 148 between the strip and the groove walls. Should the spacing of joints 140 increase from deformations or other causes the strips 146 will be depressed under the forces exerted by the bath of molten tin so that the joints 148 will be very close and fluid tight. The layers of loose material used in the joint 107 may be either in powder or fiber form.

It is thus apparent that the joints illustrated in FIGS. 2-7 all function to stop the flow of bath liquid either between the refractory members or along the rear faces of the refractory members formed in a layer adjoining the interior of the furnace. Preventing the bath liquid from reaching the rear faces of the blocks eliminates the relatively expensive anchoring structures for these blocks. Sealing of the rear faces of the blocks is also a safety measure where there is any likelihood of the joints between the blocks opening because of deformations due to the effects of heat. Further, the resistance of these joints to the penetration of the bath liquid can be significantly increased at points positioned further from the liquid bath because of the temperature drop in a direction away from the bath. A further advantage of sealing of the joints at the rear faces of the blocks is that in the case of a floor structure the vertical joint is under greater stress than the horizontal joint beneath the blocks since in a vertical joint the weight of the molten bath tends toward a penetration of the bath liquid of the joint. Light solid or gaseous particles which might arrest this penetration are evacuated much more easily from the vertical joint.

A mutual interlocking of adjoining blocks in the layer decreases the likelihood of lifting of light blocks since one or more blocks which might be susceptible to such a lifting because of a deep penetration of the liquid would be retained in position because of the interlocking relationship. Thus, such blocks which are subjected to a lifting force would not be removed from the layer of blocks.

A liquid seal is attained in the spaces between the grains or particles of a powder filling a joint between slabs. Regardless of the dimensions of the grains the spaces between the grains are so small that the liquids which do not wet the grains will not penetrate into the spaces between them. It has been found that such a liquid seal is highly reliable and that the grains which are lighter than the liquid are not lifted and floated on the liquid when these grains are not wetted by the liquid. Such non-wettable powders are further advantageous since they can be subjected to internal movements without losing their tight seal. Such movements may occur when the dimensions between joints varies substantially because of the action of heat on the adjacent solid refractory blocks.

By filling the joints between successive blocks with powder it is thus necessary to provide only the amount of molten materials necessary to form the bath in the furnace. It is not necessary to allow an additional quantity of liquid for filling the joints as was the previous case. The quantity of powdered material which must be used to form the liquid tight seal depends on the volume of the spaces between the refractory blocks in the furnace wall. Under certain circumstances the refractory blocks may be made of a wettable material and non-wettable material is used in powder form to seal the joints between the blocks. It is also possible to cover the wettable material with a film of non-wettable material on those faces which are to be used in forming the joints. This can be done in such a way that a liquidtight seal is obtained only in the presence of a nonwettable material.

In forming the joints according to the present invention at least a portion of the powder in the joints is fixed in position by means of minimum amount of a binder which thus minimizes any erosion of the joints even when the joints are defined by plane surfaces of adjoining blocks. The use of binder also facilitates positioning the powder between the blocks particularly in vertical or thin joints. It is preferred that the binders be rich in carbon so that the binder itself is not wetted by the liquid contained in the furnace tank. Preferably the binder should be rich in carbon at least in the upper portion of the joints which comes into contact with the molten tin bath. This carbon in the binder will prevent the tin from coming into contact with materials other than carbon which may be used in forming the joints. Solutions containing sugar and heavy hydrocarbons may be used since when they are heated they leave a residue consisting essentially of carbon. Even when a binder is used it is preferred that the powder thus fixed in position be porous to insure ready evacuation of any gases which may be evolved. These gases should be evacuated in a direction away from the liquid and toward the exterior of the furnace. The gases include not only those which might be released during the operation of the furnace but also any gases which may be produced from the setting of the binder either during the temperatures encountered during the use of the furnace or during the initial heating-up of the furnace.

Differential conductivity in longitudinal and transverse directions of a furnace wall may be obtained between the blocks of a tight layer by the forming of the joints between blocks so that the joints in one direction have a different resistance to heat transmission than the joints in another direction. This arrangement will significantly limit the temperature gradient in one direction while producing a strong gradient in a perpendicular direction. Further, cooling or heating effects can be concentrated in particular areas. The differences in conductivity between joints can be readily obtained merely by forming the joints of varying thicknesses.

The joints between the blocks are then filled with a.

suitable material which may either be the bath liquid itself if it is an insulator. Materials of different conductivity may also be used to insulate joints to obtain such conductivity differentials. For example, the bath liquid may be in some joints and an insulating material may be positioned in other joints. Depending upon the materials, this arrangement permits greater flexibility for a wide range of adjustment of the conductivity differential.

Particular arrangements for obtaining thermal transmission differentials in the thickness of a layer of carbon slabs are illustrated in FIGS. 8-10. In FIGS. 8 and 9, a layer of refractory blocks is formed which is relatively insulating in a direction indicated by the arrow X but has good conductivity in a perpendicular direction as shown by the arrow Y. The joints or 151 in the direction X are formed to be conducting whereas the

joints

152 or 153 in the direction Y are formed to be insulating. In the conductive joints 151 the molten metal of the bath itself may be used. In the alternative, a filling of a conductive powder, such as carbon, with a preferably conductive binder may be used. In the insulating joints 153, a ceramic powder, such as Kaolin preferably without a hinder, or a liquid of the bath itself, if it is insulating, may be used. Joints filled with wettable powder may be made fluid-tight close to the inner surface of the wall by a local thin application of powdered carbon, with a binder if desired, or by reducing the dimension at that point of the joint between the slabs if they are non-wettable. The difference in conductivity may also be produced from the difference in the thickness from one group of joints 150 to another 152 as may be seen in FIG. 8.

In FIG. it is possible to vary the conductivity along axes other than straight lines. A layer of graphite slabs 56 is provided with a hot point 158 which can be insulated radially by means of wide circular insulating joints 160. At the same time circular conduction is enhanced by the relatively narrow joints 162.

Thus it can be seen that the present invention has disclosed in a float glass furnace the use of powdered carbon in spaces formed along faces of carbon blocks constituting a refractory wall of the furnace tank in order to prevent the flow of molten tin behind the blocks although the density of the pulverulent carbon between the refractory blocks is considerably less than the density of molten tin. The non-wettability of the carbon by the molten in prevents the molten tin from penetrating interstices between and adjacent the blocks forming the refractory wall and from flowing under a block and a substantial portion of the lower face of the block to prevent lifting of the block. The joints between refractory blocks which are filled with pulverulent material may be linear, sinuous or have some other configuration which would tend to restrict the flow path between or adjacent the blocks. The presence of the pulverulent material in linear joints between refractory blocks constitutes an effective barrier against molten tin. This barrier is achieved by the use of pulverulent material without a binder and the pulverulent material may be loosely packed in the interstices between and adjacent the refractory blocks.

It is to be born in mind that the present invention has many other applications other than the tank furnaces which contain a molten metal or molten glass as described above. The invention is particularly applicable to a furnace as used in the glass industry for treatment of glass by the float process in which at least a portion of the tank containing liquid must be tightly sealed to prevent escape of the liquid. The invention is particularly suitable to a wall which is sealed against tin and its alloys or for molten salts retained in a tank formed of carbon slabs. The carbon slabs and the powdered carbon between the slabs possess to a large degree the properties disclosed above according to the present invention. Further, the coating of carbon has the advantage of bettering the convection currents of liquid and of preventing adhesion of any molten glass which may come into contact with the walls of the tank. While the wall structure has been disclosed herein as comprising the floor of a tank it is to be understood that walls other than the floor may also incorporate the present invention.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions, and accordingly, it is desired to comprehended such modifications within this invention as may fall within the scope of the appended claims.

What is claimed is:

1. In a wall for a refractory furnace tank for making glass floating on a bath of molten metal, the combination of a plurality of juxtapositioned prefabricated refractory blocks defining at least a thickness portion of a refractory furnace tank wall, there being interstices in the joints between the interior faces of said blocks, said interstices being filled with a pulverulent material not wettable by the molten metal and whose density is less than that of the molten metal in order to prevent penetration of the metal into the interstices, and wherein said interstices have a sinuous groove configuration so that an interlocking effect at said joints between the interior faces of the blocks is achieved.

2. In a wall for a refractory furnace tank for making glass floating on a bath of molten metal, the combination of a plurality of juxtapositioned prefabricated refractory blocks defining at least a thickness portion of a refractory furnace tank wall, there being interstices in the joints between the interior faces of said blocks, said interstices being filled with a pulverulent material not wettable by the molten metal and whose density is less than of the molten metal in order to prevent penetration of the metal into the interstices, and wherein said interstices have a configuration to define a higher and a lower zone with said higher zone being further from the faces of the blocks toward the interior of the tank than said lower zone, the distances being measured along the said interstices.

3. In a wall as claimed in claim 1 wherein said pulverulent material is principally carbon.

4. In a wall as claimed in claim 1 wherein said interstices are also located along faces being behind the blocks from the interior of the refractory furnace tank.

5. In a wall as claimed in claim 3 wherein the grains of carbon are smaller than 0.1mm.

6. In a wall as claimed in claim 1 wherein said pulverulent material is loosely packed.

7. In a wall as claimed in claim 1 wherein said blocks have downwardly directed ribs around at least the major part of their bottom faces, means under said juxtaposed blocks for defining a foundation surface thereunder, there being recessed means in said foundation layer to receive said ribs, said pulverulent material being between said blocks and foundation surface, at least along the side faces of said ribs.

8. In a wall as claimed in claim 1 where said juxtapositioned blocks form at least one layer of a wall also comprising means in the interstices between the blocks for providing different resistances to heat transfer in different areas of the wall.

9. In a wall as claimed in claim 1 wherein said pulverulent material is A1 0 Cr O or carbides and nitrides not wettable by molten tin.

Claims

2. In a wall for a refractory furnace tank for making glass floating on a bath of molten metal, the combination of a plurality of juxtapositioned prefabricated refractory blocks defining at least a thickness portion of a refractory furnace tank wall, there being interstices in the joints between the interior faces of said blocks, said interstices being filled with a pulverulent material not wettable by the molten metal and whose density is less than of the molten metal in order to prevent penetration of the metal into the interstices, and wherein said interstices have a configuration to define a higher and a lower zone with said higher zone being further from the faces of the blocks toward the interior of the tank than said lower zone, the distances being measured along the said interstices.
3. In a wall as claimed in claim 1 wherein said pulverulent material is principally carbon.
4. In a wall as claimed in claim 1 wherein said interstices are also located along faces being behind the blocks from the interior of the refractory furnace tank.
5. In a wall as claimed in claim 3 wherein the grains of carbon are smaller than 0.1mm.
6. In a wall as claimed in claim 1 wherein said pulverulent material is loosely packed.
7. In a wall as claimed in claim 1 wherein said blocks have downwardly directed ribs around at least the major part of their bottom faces, means under said juxtaposed blocks for defining a foundation surface thereunder, there being recessed means in said foundation layer to receive said ribs, said pulverulent material being between said blocks and foundation surface, at least along the inner side faces of said ribs.
8. In a wall as claimed in claim 1 where said juxtapositioned blocks form at least one layer of a wall also comprising means in the interstices between the blocks for providing different resistances to heat transfEr in different areas of the wall.
9. In a wall as claimed in claim 1 wherein said pulverulent material is A12O3, Cr2O3, or carbides and nitrides not wettable by molten tin.