IL33248A - Furnace having a tank for holding molten material - Google Patents

Description

Furnace having a tank for holding molten mate ial •win imn ΠΡΤΠΓΡ n na The present invention relates to furnaces for holding a bath of molten material comprising at least one vail formed at least in part by juxtaposed prefabricated elements, there being paths along which gaseous fluid can flow extending from the interior of the tank through at least apart of the wall thickness via the joints between the interior faces of the eaid elements.

The fluid tightness of such refractory walls may be obtained more particularly by solidification of the molten liquid in the joints, but this solution is not always easy, particularly where the liquid is considerably above its melting point; in fact in this case the liquid can be solidified only at a fairly great distance from the front face of the furnace wall, so that the liquid penetrates deeply into the said wall; this may present a number of disadvantages : liquid remaining stationary in the joints of the wall, corrosion of the latter, pollution of the liquid by the products of such corrosion, raising of the floor blocks when their density is less than that of the liquid and the latter comes to flow into the joint beneath the block over a sufficient area of the said joint, etc... More particularly, the penetration of the molten material in contact with metal pieces situated behind the refractory blocks can be inadmissible because of the strong corrosive action of the molten material. It is therefore always necessary to dispose of a barrier preventing the passage of the liquid whichever the position of this barrier may be in relation to the thickness of the furnace wall.

The invention makes it possible to resolve or to minimise these disadvantages, and presents many advantages which will appear hereinbelow.

According to the invention, the paths are at least locally both restricted in cross-sectional size and delimited by materials which are, due to their surface properties, capable of preventing the penetration of the molten material of the bath through the paths restricted in cross-sectional size across at least a part of the wall thickness. There exists a layer formed by elements, it ie to say juxtaposed prefabricated elements and/or grains separated by joints and capable of being brought into contact with the bath, the layer being tight to the said bath by the effect of the dimensions of the joints between the elements and of the surface properties of the materials present - that is to say, of the bath, of the any gases present. The materials of the fluid-tight layer, and the dimensions of its joints are therefore chosen so as to obviate the penetration .

The invention thus makes it possible to reduce or to elimi-nate the unproductive investment represented by the stagnation of liquid in the joints and the loss, or difficult and incomplete recuperation, of the said liquid solidified in the wall after extinction of the furnace. It is therefore possible to provide hollow spaces in the walls where this is desirable. The corrosion of the wall elements by the liquid at points other than at the surface is largely obviated, which makes it possible to use materials which otherwise could not be used at those points. The contents of the furnace, and more particularly the liquid, are no longer polluted by the dissolved or suspended bodies, the gases, the vitreous exudations which may result from the contact between the liquid and certain constituent materials of the wall if they are no longer contacted by the liquid. On the other hand, where it is desired to modify totally or slightly the composition of the liquid, slow mixing with the stagnant liquid in the joints is obviated.

The Archimedean thrust which is exerted upon the wall elements when a sufficiently large proportion of the bottom surface of the elements is in contact with the liquid filling the joints is also obviated. This upward thrust upon the elements which are lighter than the liquid compels the constructor to adopt a number of more or less expensive measures which can be avoided by the invention .

Where the liquid is a good conductor of heat and/or of electricity, by preventing it from penetrating into the wall,the invention also makes it possible to eliminate energy losses and certain palliative measures which would be necessary as a result of this situation.

Advantageously, the elements of the layer are constituted principally of carbon at the joint positions; that is to say that the elements, the shapes and dimensions of which may be widely varied are made of carbon in the mass, or solely at the surface.

The term carbon is to be understood to embrace graphite as well as amorphus carbon, and the latter in no way excludes the presence of various impurities, or even of suitable additive substances. Carbon is used by virtue of the fact that it is not k Preferably, at least one layer constituted solely or princi pally of blocks is arranged in order to ensure fluid tightness. T significance of the term "block" here also embraces fairly large but relatively thin parts which are also called slabs. It has bee found advantageous to limit the number of joints - i.e., to use elements of large dimensions. In fact, when the liquid is able to enter a short distance beneath the lateral edges of a part, the sa part rises the more rapidly as its dimensions are smaller. Fluid-tightness between blocks may be obtained in the lateral joints which separate them, or else, by means of a layer coming into contact with the rear face of the blocks, the one which is opposite t the face directed towards the mass of the liquid in the furnace,.

According to one embodiment of the invention, joints betwee blocks are open - i.e., do not contain filling material - but they have at least on. a part of their surface, a smaller thickness than those which permit the flow of the liquid, for the material consti tuting the surface of the blocks. Provided that blocks having a sufficiently plane surface are used, the maximum distance between contiguous surfaces can be smaller than for which the liquid is able to penetrate between the surfaces. This solution is advantageous especially where fairly violent currents of liquid could entrain filling materials, and it obviates the difficulty of securing perfect filling of the joints.

Preferably, a clamping of the contiguous blocks against eac other under pressure is obtained in order to prevent the opening of the joints - for example, by the effect of a greater expansion of the metallic frame or structure than that of the blocks of the fluid-tight layer. By using adjustable cramps, the pressure of th joints can be adjusted according to the temperature variations, particularly when the ( furnace is ignited.

It is sometimes advantageous to prohibit the introduction o the liquid along the face of the blocks located at the rear of the latter, relatively to the mass of the liquid, by the effect of the surface tensions and of the dimensions of the joints extending along the said face. This sealing at the rear is necessary to obviate the expensive solution of anchorages where there is no fluid-tight joint between the blocks, and it is advantageous as a eafety measure where opening of the joints between the blocks is feared in the case of deformations which occur by the effect of heat Furtherm re the resistance of the oints to the enetratio of the liquid can be the more effective as points more remote from the mass of the liquid are considered, due to the temperature drop0 On the other hand, in the case of a floor, the vertical joint is more highly stressed than the horizontal joint beneath the blocks, 5 since in the vertical joint the effect of the weight is fully in favour of the penetration of the liquid, and also light solid or gaseous particles which might inhibit this penetration are evacuate much more easily in the vertical joint.

It is useful in some cases to provide on the periphery of 0 the blocks one or more protuberances projecting and capable of being housed in the cavity or cavities of the contiguous blocks. Mutual interlocking of the. blocks is obtained in this way. This interlocking also increases the warranty against lifting of light blocks, since one or more blocks which might accidentally be immer-5 sed in the liquid at all their faces would be retained by the interlocking, and therefore could not be extracted from the layer of blocks.

It is particularly advantageous to realise the tightness to the liquid in the open joints between the grains of a powder. In 0 fact, whatever the dimensions of the said grains, the dimension of the joints is very small so that liquids which do not wet the substance of the grains cannot penetrate into them. It has been found that such tightness is highly reliable, and that the grains lighter than the liquid do not tend to be lifted and float on the 5 liquid when the liquid does not wet them. Nori-wettable powders are further advantageous by the fact that they can undergo internal movements without losing their tightness - for example, they can adapt themselves to a space of which the dimensions vary substantially by the action of the heat on the adjacent solid bodies. 0 In particular, the said powder is arranged in joints between contiguous blocks; this arrangement makes it possible to create, by means of the blocks, a well-defined surface to limit the bath, so that, part icularly , it is thus possible to obviate the need to use quantities of liquid having no other purpose but to fill the 5 joints when the liquid is required to reach a predetermined level. On the other hand, the quantity of powder to be used is reduced to the volume of the joints to be filled. It is also possible to use as material of the blocks a wettable material, and to limit the use of the non-wettable material to the material in powder o f rm h t e is adv nta e in s doin It is also ossible to cover the wettable material with a film of non-wettable materia on the faces intended to form the joints, in such a way that tightness is obtained, preferably solely in the presence of non-wettable material. Lastly, the arrangement of the powder in the joints is a good precaution against the accidental raising of the grains which might be caused in certain circumstances - for example, where a solid body is moved in the upper part of a mass of light powder in contact with a denser liquid.

It may be useful or necessary, depending on circumstances, to arrange the powder solely or additionally along at least a part of the faces of blocks which are located behind the latter relatively to the mass of the liquid. Indeed, it has been found that the powder advantageously made it poseible to obviate the hydrostatic thrust b achieving tighness to the liquid in the zone located beneath the blocks.

Where the density of the grains of the powder ie less than that of the liquid, joints between blocks containing the powder advantageously comprise at least one high zone and one lower zone, the high zone being farther from the mass of the liquid than the lower zone, the distances being measured along the joints. In this way, if a random cause such as violent currents were to entrain the grains of powder towards the free, surface of the bath, these light grains would be unable to be entrained beyond the high zone towards the bath, since in order to reach it they would first of all have to descend again in the liquid towards the interposed lower zone, which is impossible for grains which are less dense than the liquid. As a result, such entrainment of grains would be prevented beyond the lower zone.

Advantageously, there may be provided along the joints a protuberance which has a form such that it is placed between the surfaces of a contiguous block, equally whether a horizontal direction and a direction perpendicular to the internal face of the wall is considered. This double condition presents a double precaution, since it produces simultaneously the relative inter-locking of the contiguous blocks, and the trapping of the powder in the joints, even if it has a tendency under some conditions to be entrained towards the upper surface of the liquid. This will be more apparent from the description of the drawings.

It is likewise advantageous to provide on the major part of the lower face of the blocks one or more recesses ed ed b a rib, in which projecting parts of the subjacent layer are housed. By such an embodiment, the powder located in the recesses is trapped in similar manner to that stated for the joints between blocks of one and the same layer; for this powder would have to descend beneath the rib in order to be made to float on the liquid.

Preferably, at least a part of the powder is immobilieed by means of a binder, which permits obviating any erosion of the joints even when the latter are plane. On the other hand, the pla cing of the powder is facilitated in this way, particularly in the vertical or thin joints, and good filling of them is ensured.

AB a binder, binders rich in carbon are preferred, so that the binder itself is not wetted by the liquid.

More particularly, solutions containing sugar and heavy hydrocarbons are suitable for use, and when heated leave a residue consisting principally of carbon.

The immobilised powder preferably has an open porosity to ensure easy evacuation of the gases which are formed, if possible not towards the liquid, but towards the exterior of the furnace. These gases include not only those which might be released during the operation of the furnace, but also those which result from the setting of the binder, whether at the temperature of use or during the initial heating up.

It is advantageous to provide suction means for these gases in order to prevent them from escaping towards the liquid. Accor-ding to one embodiment of the invention, an intermediate layer is arranged between the tight layer and the liquid, so that there is no necessity to constitute the internal face bf the wall by the substance or substances which are suitable for the tight layer.

Differential conductivity in longitudinal and transverse direction may be obtained between the blocks of the tight layer, by means of joints between blocks which present a different resistance to heat transmission for one part of the joints from that of another part of the said joints. It is thus possible to limit strongly the heat gradient in one direction whilst providing a strong gradient in the perpendicular direction, or to concentrate a local cooling or heating effect.

The difference in conductivity can be obtained by differentiating the thickness of the joints j this is the simplest method} the joints are filled in operation either by the liquid, if it is be the sealing powder, either alone or immobilised by a binder.

It is also possible to differentiate the conductivity by using materials of different conductivity in the joints - for example, the liquid in some joints and an insulating material in the other joints, Depending upon the materials available, this solution may permit greater flexibility for strong adjustment of th differentiated conductivity.

Thie invention relates in particular but not exclusively to tank furnaces which contain a molten metal or molten glass. In the glass industry, the invention can specially be applied to a furnace for treatment of glass by float process in which at least a part of the tank containing liquid is rendered tight for the latter by the means which are described. In fact, the invention applies particularly wall to the sealing for tin and its alloys or for molten salts of a tank by means more particularly of carbon slabs and powdered carbon. These materials possess to a large degree the properties which have been mentioned either for the blocks, or for the powder, or for the liquid. Also the coating of carbon has the advantage of least braking the convection currents of liquid and of preventing adhesion of the molten glass which may either permanently or accidentally come into contact with the walls of the vessel-that it to say, with the bottom or the sides.

In one embodiment of the invention applied to the said glassworks furnaces, the elements of the floor which are lighter than the bath liquid have no interlocking means; the invention therefore permits a substantial economy of means for the construction of the fluid-tight floor.

The accompanying drawings show embodiments of the invention by way of non-limitati e examples.

Figure 1 shows a wall fragment of a glass float tank in vertical section.

Figures 2 to 7 show variants, likewise in fragmentary vertical sections.

Figures 8 to 10 are fragmentary plan views of other variants. In the furnace according to figure 1, the floor 20 and a lateral wall 22 are formed by means of layers 2k , 26 and 28. The layer 2h is composed of slabs 30 comprising a blank 31, of silico-argillic refractory ceramic, or preferably of silicon carbide.

The said slabs have, on their face 32 oriented towards the interior coating 36 of carbon made compact and adherent by means of a binder of refractory cement. The joints 38 between the said slabs are not filled, but they are fluid-tight. Where the coating 3 of the lateral facee is not well gauged, it is necessary to trim it by planing to ensure that the joints 38 are sufficiently narrow.

However, these joints are tight to the tin bath (not shown) at the service temperatures in float tanks, i.e., up the approximately 1,000°C for example, up to a thickness of the order of 2mm, having regard to the surface and interfacial tensions at the interfaces between the tin, the carbon and the gases present in the joints.

Where opening of the joints 38 beyond the limiting dimension is feared, even locally, it is sometimes to preferred to place the layer 2 k in compression in one direction, or even in both main directions of its plan; the said compression may be obtained by means of adjustable cramps k o exert a thrust through uprights k2 upon cross-members k k braced against the external wall k 6 of the vessel at the level of the layer 2 h . The juprights 1*2 are connected' at their summit, and preferably likewise used for the construction of a known type of the vault (not shown).

Furthermore, the layer 2 k is supported upon and against a layer 26 formed of silico-argillic blocks 50 of current type, which are used particularly for their thermic insulation properties and rest upon the shell 28 of steel plate. The support framework is not shown.

By virtue of this construction, it has been found that no expensive anchorage means was necessary, as the molten tin was unable to raise the slabs 50 since it is unable to pass below their lower face.

The invention may likewise be performed (fig.2) by using a powdered carbon ^ impermeable to molten tin. Its grains preferably have a dimension smaller than ,1mm, or even than 0.1mm. The slabs 5 are of graphite, and their joints 8 are filled with the said powder. They are placed on a thick layer of powdered carbon 60 which contains metallic tubes 62. According to the regions of the furnace floor, the said tubes are used for the heating or the cooling, or even for heating and cooling alternately in places. This thermic effect is obtained by means of water or of cold air, of hot air circulating according to the arrows 6 k or by incorporated resistances, not shown. The heat is readily transmitted from the li- versa by virtue of the good thermic conductivity of the carbon of the powder 5^ and of the graphite of the slabs 56.

The layers 26 and 28 do not differ substantially from the corresponding layers of the embodiment according to figure 1. The same will apply hereinbelow to the parts bearing the same reference numerals* In the case illustrated in figure 3, the joints 61+ between the slabs 66 of silico-argillic ceramic have a sinuous conformation so that an interlocking is effected by the presence of a projection 68 belonging to a face 70 of one block, in a groove 72 belonging to the adjacent face Tk of the contiguous block. The said joints 6 , and also the bottom bed 76, have a mean thickness, for example 2 to 10mm, and they contain powdered carbon.

As a variant (figure ) a refractory insulating concrete 78 has been cast on the shell 28, and its top face bears grooves 80 which intersect at rightangles; rectangular Blabs 82 of graphite have at their bottom face a recess Bk over their total surface except for that which is occupied by the peripheral rib 86. The ribs 86 of two adjacent slabs penetrate together into the grooves 80 The joints 88 between the slabs are open and relatively wide (6mm for example) and the molten tin penetrates into them; it is however stopped at the level of the ribs 86 by the layer 90. The latter may in certain cases be entrained locally through the joint 88, and float upon the tin; but not beyond the horizontal plane which con-tains the bottom faces 92 of the ribe 86. Indeed, the grains located above the said plane cannot be entrained, since they have a tendency to rise. In this way the major part of the slabs 82 is protected against erosion of the subjacent layer, with the result that raising is impossible. It must however be noted that this measure is an additional precaution, since the powder located beneath the joint 88 is already extremely well-protected from erosion by its distance from the liquid mass. Thus the tight layer 90 is separated from the liquid bath by a non-tight layer of blocks 82. In certain case, a series of metallic plates, not welded and not shown, is also used -for example, of tungsten - placed on the fluid tight floor. As a variant, the layer of slabs 82 could be doubled by a second layer of refractory slabs, for instance by superposing on the layer of slabs 82 a layer of slabs of higher density than the molten bath. profiled alonlg their not shown edges in such a way that the joints 96 have a region 98 located higher and farther along the path of the joint than the region 100. As a result, if the grains were accidentally to escape towards the free surface of the bath, the erosion would be arrested immediately after the low region 100. The joint 102 between the slabs 91* of carbon and the blocks 50 of β ilico-argilli c ceramic are without interposed material. In order to facilitate the placing of the powdered carbon in the joint 96, this powder is tempered with the minimum quantity of water neceesa-ry to obtain the consistence of a mortar capable of being retained by adhesion on the lips of the joint 96. The said water is obviously rapidly eliminated by drying, so that in operation the joint 96 is full of unbound powdered carbon.

However, the use of binders which remain after drying has also been tried successfully. It is preferred to use the minimum quantity of binder so as to preserve an open porosity after setting As binders, refractory hydraulic binders, heavy hydrocarbons, bitumens, asphalts, tars, sodium silicates, and sugar solutions hav been used. It is preferred to use a binder rich in carbon, at least for the upper part of the floor joints, which comes into contact with the tin, so that the tin is practically unable to come into contact with materials other than carbon.

The gases formed are , able to escape through the pores of the joints. The disadvantages of bubbles escaping into the tin, parti-cularly beneath the glass ribbon, are advantageously obviated by providing a suction towards the plate 28 which supports the floor. This plate is pierced with an aperture 103 occupied by a pipe lO which is connected to a pump not shown. In order to, channel the gases originating from a wide area, an oblique cut-out 105 of the corners of the blocks 50 has been provided, in which is placed an angle iron 106 welded at a number of points to the plate 28.

Having regard to the small quantities to be exhausted, the gases can easily circulate in the joints 96, 102 and 108 and infiltrate between the angle iron and the plate. The suction through the pipe lOk is set in operation during the starting of the furnace, but after a period of operation the . evacuat ion of the gases can generally be discontinued.

Another variant of embodiment (figure 6) enables the advantages of the jointts according to figures 3 and 5 to be combined. and a high region 98 as in figure 5, but in addition its lower part 111* is inclined to the vertical towards the lefthand slab 112, so that the projecting part 115 of the slab 112 is not only between the regions ll6 and 118 of contiguous slab 113 which are located on the same horizontal, but also between the regions 120 and 122 of the same slab 113 located on the vertical, i.e., on the straight line perpend cular to the surface 12k of the wall in contact with the tin. By this arrangement, a relative interlocking of the slabs is obtained simultaneously with a trapping of the powder in the joint 110, even in the event of accidental erosion. Preferably, the faces 126 and 128 of the projection 115 form an acute angle towards the end of the projection to facilitate the placing; thus the slab 113 need not to be introduced by a movement in the direction perpendicular to figure 6, but may be applied in the direction of the arrow 130; the grip of the tempered powder for laying may thus be ensured during this operation.

A layer of graphite slabs 132 has also been used (figure 7) on one or more beds of divided materials used for their thermic insulation properties, which are definitely superior to those of the usual refractory ceramic blocks 50. Either powders or fibres may be used. In the embodiments of figure 6, there has been placed consecuti ely upon the steel sheet 28, a bed of highly insulating mineral wool 13*+, bed of kaolin fibres 136, for example, with k3% alumina, which is more refractory than mineral wool, then a layer of powdered carbon 138, and lastly the graphite slabs 132. Their joints l o are not filled, and need not be very close. Fluid-tightness is obtained at the upper part of these joint IkO t which is open in the form of a groove 1^2 with oblique face ih'k . In the groove is placed a graphite strip lk6 of trapezoidal shape. The planity, the inclination and the corners of the faces ihk and of the strip lk6 are made accurate *so as to limit the thickness of the joints l 8 obtained. When deformations cause opening of the joints l O, the strips l 6 can descend under the pressure of the tin so as to keep the joints 1^8 thin and fluid-tight.

In certain embodiments of the invention, a differentiated thermic transmission is obtained in the thickness of the layer of carbon slabs. In particular, a layer is created which is relatively insulating in a direction x but has good conductivity in a perpendicular direction y (figures 8 and 9) by executing conductive in the direction y. In the conductive joints 151. the molten metal of the bath is used, or else a filling with conductive powder for example, carbon^ possibly with a binder, preferably conductive! in the insulating joints 153, a ceramic powder is used (for example kaolin, preferably without binder, or the liquid of the bath if it is insulating, for example, glass). Joints filled with wettable powder may be rendered fluid-tight close to the inner surface of th wall by a local thin application or powdered carbon, possibly bound or by a reduced dimension at that point of the joint between the slabs if they are non-wettable . The difference of conductivity may also or alternatively result from a difference in the thickness fro one group of joints 150 to another 152 (figure 8).

Where it is desirable to obtain conduction and insulation along other axes than perpendicular straight lines, the invention likewise makes it possible to obtain this by the design of adequate joints (figure 10). In particular, a hot point 158 can be insulated radially by means of wide circular insulating joints l60, whilst maintaining a circular conduction by narrow joints l62.

The invention may be embodied with many variants, more parti cularly to walls other than the floor, or the combination of various constructions considered separately hereinbefore with other materials, by other liquids, etc... The ambit of the invention is no narrower than the following claims.

Claims (1)

1. 2. WHAT IS CLAIMED IS t Furnace for glass comprising a tank for holding a of molten said tank comprising at least one wall formed at least in part by juxtaposed prefabricated elements and provided with paths along which gas ca extending from the interior of the through at least par of the of the said paths being formed by the Joints between the interior faces of the prefabricated elements while providing in said Joints pulverulent characterised in that the of said Joints is restricted on a pa t of their length arid in that the pulverulent materials provided in part of the due to their surfaoe penetration of the liquid o the bath of molten furnace tank accord ng to Claim characterised the permit passage of the liquid between said elements but have said restricted size at positions behind said A furnace tank according to Claim characterised in that the said paths have said restricted at positions between said A furnace tank acoording to Claim characterised in that said paths also have said restricted sactional size at positions behind said A furnace tank aooo ding to 3. Claim 3 or characterised in that said have restricted size at positions between said elements by virtue of the close relationship of the facing aurfaoea of neighbourin elements A furnaoe tank aooording to any preoeding characterised in t the said elements neither bonded in place nor and are dense than the bath liquid bu said liquid prevented by surface tension effects getting said elements floating ou of place A furnace according to any Claims 1 to 13 characterised tha t the said adjacent elements A furnace tank aooording to Claim characte in that the fa ing sur of neighbourin elements shaped upwardly and downwardly directed inter tongues and grooves A furnace aooording to any preoeding char a in tha t said elemen ts a e os ed holly mainly of carbon at least at their A furn tank according to any precedin characterised in that at least part of the wall of tank at least one layer formed by elements y Joints which in diff rent areas of present different resistances to he A furnace tank co o to any of 1 to characterised in that at least part of a of the tank comprises least one layer formed by elements separated by give the diffe en resistances to heat transfer in two mutually perpendioular directions across A furnaoe tank according to characterised tha t the tank is the treatmen of glass float p A furnace tank according to oharaoteriaed in the said li at least mainly of tin insufficientOCRQuality