EP1007483A1

EP1007483A1 - Melting furnace, in particular for glass, and use thereof

Info

Publication number: EP1007483A1
Application number: EP99920884A
Authority: EP
Inventors: Tanguy Massart; Stéphane Maugendre; Dominica Lizarazu; Didier Jacques; Alain Arnaud
Original assignee: Saint Gobain Isover SA France
Current assignee: Saint Gobain Isover SA France
Priority date: 1998-05-19
Filing date: 1999-05-18
Publication date: 2000-06-14
Also published as: NO20000240L; FR2778910A1; ZA200000145B; AR016039A1; HUP0003124A3; NO20000240D0; CN1272097A; SK492000A3; BR9906464A; WO1999059926A1; KR20010014390A; HUP0003124A2; AU3829499A; PL338081A1; CA2296754A1; JP2002515396A

Abstract

The invention concerns a furnace for melting material with high melting point such as glass, comprising a hearth (2) and side walls (3) defining a bath of molten material (5). At least part of the hearth (2) surface, and optionally the side walls (3), which is in contact with the molten material consists of at least one layer (12, 13, 21, 22, 23) comprising refractory material grit (14, 16), in particular with a mineral binder based on oxides or glassy material. The invention is useful for melting glass, in particular cullet containing metal residues and for separating the metal contained in cullet.

Description

FUSION OVEN, ESPECIALLY A GLASS, AND ITS USE

The present invention relates to techniques for melting thermoplastic materials with a high melting point, such as glass. It relates more particularly to an oven intended for melting such materials, and its use. Such a furnace for melting materials such as glass must be designed so that its walls suitably insulate the molten bath from the outside so as to guarantee good thermal efficiency, avoiding any migration of the molten glass towards the outside.

In this respect, a typical furnace wall construction provides, on the outside a sufficient thickness of insulating material, and on the inside, surfaces of refractory material resistant to corrosion by glass.

These refractory materials are installed in the furnace in the form of slabs or blocks, placed one next to the other, between which it is necessary to make watertight seals to prevent the penetration of glass. At the level of the oven bottom, the slabs of refractory material which have a high thermal conductivity rest on blocks of insulating material by means of an unshaped layer which provides a base having a perfectly horizontal level. It is generally a concrete based on a hydraulic binder. cold deposited on the insulating blocks In principle, the temperature profile in the operating oven is such that the temperature below the refractory is close to the crystallization temperature of the glass, or at least is such that the viscosity of the glass becomes very high, so that if the glass crosses the refractory thickness, it freezes or crystallizes (devitπfication) at the top d e the insulator and its migration is then stopped

Such a passage through glass can happen in particular when a block of refractory cracks under the effect of thermal expansion constraints, or when a joint between two blocks has been poorly closed. This can also occur when the glass introduced into the solid state in the oven contains residue metallic. In fact, the corrosion of refractory materials is accelerated when a drop of molten metal is present at the interface between the refractory and the glass, and veins can form through which the glass quickly penetrates towards the insulating material. Despite all the precautions that can be taken, we still sometimes observe incidents which call into question the tightness of the oven, where it appears that glass may have reached an insulating block with a temperature high enough to not freeze and degrade the insulator In particular, the penetration into the insulating blocks of metal entrained by the glass causes serious degradations because the metal attacks the insulator and creates pockets which the glass comes to dig and / or fill.

It is therefore important to avoid the penetration of glass through the surfaces forming the interior walls of the oven because the risks of glass penetration through the walls of the oven are likely to affect both the production capacity of the oven and the security of its implementation.

The object of the invention is to reduce these risks, and to provide oven walls having improved glass sealing, in particular when metal residues are introduced into the glass bath.

This object, as well as others which will appear subsequently, has been achieved according to the invention by providing at least a portion of the interior surfaces of the furnace, during its construction, with a coating comprising shot of refractory material.

By shot of refractory material is meant in the present application, in the usual way, a refractory material in particulate or granular form which can be obtained in particular by grinding or crushing.

In this regard, the subject of the invention is an oven for melting a material with a high melting point, such as glass, this oven comprising a hearth and side walls delimiting a bath of molten material, and being characterized in that at least part of the surface of the hearth, and possibly of the side walls which is in contact with the molten material is initially constituted by at least one layer comprising shot of refractory material

By "initially" is meant that said surface or part of surface has, from the start of operation of the oven (before or just after soaking), the constitution indicated. The subject of the invention in this respect is a method of manufacturing an oven which will be defined below.

It has surprisingly appeared that a wall surface made from a particulate material such as refractory shot has an improved glass seal compared to a surface made up of the juxtaposition of preformed articles such as slabs.

Subsequently, we will mainly speak of a glass bath to describe the molten mineral material present in the oven, unless otherwise specified, this expression generally designates any fusible mineral material, natural or artificial, in particular glass but also rock.

A problem linked to the conventional production of interior wall surfaces with tiles superimposed on a base layer of a different nature, is cracking under the effect of thermal expansion constraints. Indeed, the layers having different coefficients of thermal expansion, the differential movements of one over the other are made with friction which stresses the slabs in tension, and which can cause cracking or even rupture of the latter. Contrary to this, the use according to the invention of a particulate material makes it possible to constitute a continuous surface layer, without joints, which has excellent resistance to the stresses of thermal expansion of the furnace. Consequently, the risk of cracking is reduced, and the glass seal is improved.

In general, the refractory material may advantageously be of any type resistant to corrosion by glass (the degree of resistance may be higher or lower), in particular of the type based on chromium oxide or based on zirconium oxide. , silicon and / or aluminum (AZS type). The shot usable according to the invention can be derived from refractory recovered material.

The particle size of the shot is variable and may advantageously be less than 50 mm, for example of the order of 1 mm to 50 mm. Particles greater than 50 mm may nevertheless also be useful. To fix the ideas, we will call HERE a "fine" shot with a particle size less than about 5 mm, "medium" a shot with a particle size of the order of 5 to 30 mm, "large" a shot whose particle size is of the order of 30 to 50 mm, and “very large” a shot whose particle size is greater than 50 mm. These particle sizes are understood as the smallest mesh size of a sieve allowing the sieving of the particulate material.

In a particular embodiment, the surface in contact with the glass can consist essentially of shot. The particle size thereof can be advantageously chosen, depending on the nature of the glass present in the bath, in particular its viscosity at the temperature of the wall and its surface tension, so that the shot is not or very little wettable by the glass of the bath and therefore that the progression of the glass in the interstices between the particles of shot is prevented. In general, in this embodiment, a shot is all the more advantageous as it contains particles of fine particle size, since the layer thus formed is all the more compact. The shot may advantageously comprise a mixture of particles of different particle sizes, suitable for obtaining maximum filling or compactness of the layer or optimized for forming a tight layer. In another particular embodiment, which may be preferred in certain aspects, the layer or at least one of the layers of the surface in contact with the glass contains, in addition to the shot, a mineral binder compatible with the molten glass bath, which may be of the chemical or ceramic setting type, in particular a mineral binder formed from molten oxide (s) or vitreous material (s). In this layer embodiment, the interstices between the particles of shot are at least partially filled with said binder, to constitute a composite material. The binder is preferably initially mixed with the shot in particulate form in at least one of said layers.

The composite material based on refractory shot and the binder is a fairly coherent material which does not allow or hardly allow the passage of a molten material such as glass between the particles of shot. It is also a material whose corrosion by glass is slow and which therefore has an improved lifespan.

The grain size of the shot is less critical in this embodiment because the particles are retained by the binder. The use of relatively fine shot nevertheless remains advantageous because it makes it possible to create a compact layer with a high contact surface between the particles and the binder, making the composite layer a very tight barrier against glass and other residues which may be present. in the molten bath. In a particular embodiment, the surface of the sole (or at least a part) and possibly of the walls comprises only a single layer containing refractory shot. The particle size of the latter is preferably less than 50 mm, in particular 30 mm, in particular 20 mm. The shot may advantageously comprise a mixture of particles of different particle sizes, suitable for obtaining maximum filling or compactness of the layer or optimized for forming a tight layer.

In certain applications, however, it is preferable that the shot is not too fine so as to avoid any risk of entrainment of the shot in the molten glass bath as a result of significant stirring on the surface of the hearth and the walls. , a risk which would be detrimental to the quality of the molten glass.

In a particularly preferred embodiment, there is thus placed in contact with the molten bath a first layer, called "contact layer" comprising a first shot and, under said contact layer, at least one other layer called "lower" comprising another shot, the granulometry of the shot of the contact layer being greater than that of the shot or of the mixture of shots of the or each lower layer.

The shot of the contact layer is advantageously such that it cannot be entrained by the stirring of the bath and protects the lower layer from this stirring.

In this case, the layer in contact with the molten bath preferably comprises shot having a particle size greater than 10 mm, in particular of the order of 10 to 50 mm, in particular of the order of 20 to 50 mm, and the or each lower layer preferably comprises grain size shot less than 20 mm or 10 mm as appropriate, in particular of ^the order of 1 to 10 mm, very preferably less than 5 mm, where applicable a mixture of particle sizes.

According to a particular embodiment, the or at least one lower layer contains an inorganic binder as mentioned above, while the contact layer consists essentially of the relatively large shot.

When a layer of the surface coating comprises a binder ensuring cohesion between the particles of shot, this binder can be formed from various mineral materials, in particular from oxides or from vitreous materials such as glass, possibly partially devitrified, or rock such as basalt The glass can be identical to or different from the glass present in the bath. It can in particular be at least partly a recovery glass (cullet) or advantageously a dense glass absorbing radiation in the field. infrared The binder can be advantageously chosen, in particular as a function of its viscosity at the temperature of the wall and of its surface tension, so as to be able to seal (seal) at least partially the interstitial spaces between the particles of shot

In an advantageous alternative embodiment, the binder can be chosen so that its density (in particular at the temperature of the hearth) is greater than the density of the glass present in the furnace. An effective physical separation is thus achieved between the binder glass and the molten glass produced in the oven

Also advantageously, the binder can be chosen such that its viscosity is greater than the viscosity of the glass present in the oven. The binder glass thus has a sufficiently high viscosity at the temperature of the sole to retain the particles of pellets well and the difference in viscosity avoids mixing of the binder with the molten glass produced in the oven.

It may in particular be advantageous to use as a binder a devitπfié glass. Also advantageously, the binder can be chosen so that its thermal conductivity is lower than that of the molten glass produced in the oven, thus ensuring a temperature under the layer. of fairly low shot, the kinetics of corrosion by the glass of the constituent materials of the furnace can be slowed down. Depending in particular on the nature of the refractory shot material that is used, the mineral binder can be more or less chemically inert with respect to shot

Indeed, it may happen that the binder (glass or other binder material) reacts with the refractory material in shot, corroding the latter with a passage of oxide elements from the refractory material to the binder phase This enrichment of the binder in elements refractory oxide generally has the effect of modifying the devitπfication and / or viscosity characteristics of the interstitial mineral binder It would seem that the cohesion of the layer thus formed is linked at least in part to the progressive modification of the chemical composition of the binder, which would lead to an increase in viscosity and / or devitrification of the latter at the temperature of the sole or the wall, preventing the glass of the molten bath from infiltrating between the refractory particles.

This enrichment of the interstitial glass (or other material) is generally all the more pronounced as the surface of exchange with the refractory material is high, that is to say that the granulometry of the shot is fine.

It may be preferable for the so-called “contact” layer, which is directly exposed to the glass of the bath, that the refractory shot material is relatively resistant or insensitive to corrosive attack by the glass. Preferably, the refractory material is resistant to both binder glass and bath glass. The contact layer thus formed then undergoes little or no transformation throughout the operation of the oven, guaranteeing in particular a high and uniform quality level of the glass produced over time.

Advantageously, the refractory shot used for this contact layer contains chromium oxide, preferably at a rate of at least 10%, in particular at least 30% by weight, for example at least 60%.

On the other hand, for the so-called “lower” layer, it is possible to prefer a refractory material at least partially attackable by the interstitial binder, very particularly a material containing alumina. We can then combine two effects: first, glass (or other binder) enriched in refractory oxides is less aggressive towards lower structural levels; secondly, the glass (or other binder) enriched in refractory oxides is more viscous and less subject to convection movements.

The shot used for this layer can be advantageously chosen from AZS type materials. especially recycled, possibly with a limited amount of chromium oxide.

One can also adjust the choice of the binder glass specifically for each layer, in particular according to its oxide composition and its viscosity to interact appropriately with the shot of each of the layers.

We will adjust the choice of particle size and type of binder glass depending on the properties of the material to be melted in the oven. The composite layer can be produced in various ways: in particular, it is possible to spread a mixture of refractory shot and mineral material on the surface and to heat this mixture, for example when the oven is started, to form the composite, or else it is possible to arrange first a layer of shot then a layer of mineral material that is melted to impregnate the shot

In this regard, the invention also relates to a process for manufacturing an oven, such as a glass oven, in which a bottom and side walls are produced intended to delimit a bath of molten material, characterized in that that it includes the steps of ^:

- Apply to at least part of the surface of the sole, and optionally to the side walls, intended to be in contact with the bath, at least one layer comprising shot of refractory material, then

- raise the temperature of the oven and introduce a material of high melting point such as glass, in order to constitute the bath of molten material.

In the first step, a mineral binder can be applied in mixture with the shot of at least one layer, or in a layer surmounting a layer of shot. Advantageously, in this first step, another layer is applied to a layer comprising a binder. essentially comprising shot, with a grain size greater than that of the lower layer or layers

The second step allows the melting and / or thermal activation of the binder so that at least one composite layer is formed

The structure of the sole and / or of the walls can be adapted as required, in particular the layer or layers comprising shot (14, 16) can be applied to a base layer, shaped or not, made in particular of slabs or blocks refractory or insulating material Shaped means a layer made of shaped articles which are installed in the furnace, as opposed to a layer obtained from a shapeless material deposited or spread in the furnace. In particular, one can choose from the following variants - the layer or layers comprising refractory shot can be applied to slabs or blocks of refractory material usually used to produce the contact surface with the molten bath, the layer or layers comprising refractory shot can be applied in place of a traditional block or slab material, either on a layer of leveling concrete, or directly on the insulating blocks.

The layer or layers comprising shot can also be used on the interior walls of the furnace in well-defined zones, chosen in particular as a function of the temperature prevailing in the bath or above the bath in the zones considered, or as a function of the quality of the material in the molten bath in the areas considered.

When it is desired to apply a layer based on refractory shot on a vertical wall of the furnace, it is possible to use means suitable for holding the particulate material in place along a vertical wall element, or else it is possible to deposit the particulate material to make it freely form an embankment, provided that the material has a sufficiently low embankment angle so that the surface layer does not take too great an inclination.

This second embodiment may prove to be particularly advantageous, when the oven has a low bath height (in particular less than 800 mm, in particular 500 mm) because with a reasonable slope angle, the inclined wall does not occupy a very large bath volume. In general, the refractory shot-based composite can be used in all types of ovens, advantageously to constitute the entire surface of the hearth and possibly of the walls of the furnace. Its use can nevertheless vary depending on the type of oven.

Thus, at the level of the sole, the layer comprising shot can be used over the entire surface of the sole in an electric oven, in particular of the plunging electrode type, whereas it may only be used in the area of charging in a burner oven, in which the downstream area can use conventional slabs in contact with the molten material.

It is generally advantageous for the hearth to have a layer comprising refractory shot at least in an area of the furnace where the supply of material to be melted takes place. Thus, when said material contains fusible residues, in particular metallic residues, which tend to deposit at the bottom of the bath in the furnace supply zone, the surface coating according to the invention is perfectly adapted to receive these residues. It can in particular to prevent the progression of these residues to the lower structural levels of the walls, such as insulation blocks.

In particular, the wall surface coating according to the invention has a remarkable advantage when the material to be melted contains metallic residues, in the sense that it withstands corrosion much better than a conventional contact refractory material. melted at a temperature close to its melting point.

In fact, in a glass furnace, the surface of the hearth of which is constituted by a usual refractory slab, the presence of liquid metal on the surface of the hearth causes at the level of the triple point molten glass-liquid-refractory metal very corrosion severe refractory.

We then quickly notice a degradation of the constituent elements of the wall by metal infiltration.

This drawback does not occur or is considerably reduced when a wall surface is produced according to the invention.

In this regard, the invention also relates to the use of an oven as described above for melting recovery glass containing metal residues.

The recovery glass can come from various sources, in particular from mirrors, heated glazing for motor vehicles, in particular rear glasses, or tinned or enamelled glass, in particular for automobile glazing, or also from recycled packaging. The metals present in the form of metallic residues in these recovery glasses can be in particular silver, lead, copper, tin or others. It was surprising to note that, depending on the granulometry of the shot used (for a given mineral binder), the liquid metal resulting from the melting of the recovery glass could or not penetrate into the surface layer (s). The critical size of the particles of shot depends on the nature of the metal in particular on its viscosity in the molten state at the temperature of the bottom, as well as of the interstitial mineral binder and of the molten glass in the bath.

Thus, the surface of an oven wall can be adapted to recover the metal separated from the glass by fusion, this surface being permeable to said metal.

In this regard, the subject of the invention is also a process for the separation of metal present in recovery glass, this process comprising a step consisting in melting the recovery glass in an oven as described above, in which the shot included in the surface layer of the sole which is in contact with the glass has a particle size suitable for making said layer permeable to said metal. In a first embodiment, there can be provided, immediately under said layer, a space for recovering the liquid metal flowing through said layer. Optionally, a perforated element such as a grid can be placed in the upper part of this space, serving as a support for the contact layer. In another embodiment, there can be placed, immediately under said layer, a second so-called “lower” layer comprising shot having a particle size suitable for rendering said lower layer impermeable to liquid metal.

The metal is then trapped at the border between the two shot-based layers and gradually stored during a campaign to use the furnace. After one or more campaigns of use, it suffices to deposit the surface coating of the sole, from which the recovered metal can be easily extracted.

This method allows, in the same device, to recycle the recovery glass while the metal is recovered separately. Other characteristics and advantages of the invention will appear from the detailed description which follows, given with reference to the appended drawings, in which:

- Figure 1 shows a schematic view in partial longitudinal section of an oven according to the invention; - Figure 2 shows an enlarged detail of the silk of the oven of Figure 1;

- Figure 3 shows a schematic view in longitudinal section of another oven according to the invention.

In Figures 1 and 3, only the elements necessary for understanding the invention have been shown, without respecting the scale of the device. In FIG. 2, only the orders of magnitude of the respective elements have been respected.

The oven 1 shown in Figure 1 consists essentially of a hearth 2, side walls 3 and a roof 4, defining a bath 5 of a molten material such as glass. It further comprises supply means 6. such as a conveyor, of material to be melted 7 and a channel 8 for flow of the molten material.

The means for melting the material 7 are not shown. The material may consist of recovery glass (cullet) and / or of a powdery oxide composition The sole 2 consists essentially, from the outside towards the inside, of a wall made of insulating blocks 9 arranged on one or more rows (only one row being shown), an optional layer 10 of refractory concrete on which are optionally placed slabs 11 of refractory material, then a first layer 12 and a second continuous layer 13 based refractory material

The detail of layers 12 and 13 is visible on the enlargement of FIG. 2. The first layer 12, or lower layer, comprises shot 14 of refractory material, in particular of AZS or chromium oxide type, of a relatively granulometry. fine, in particular less than 20 mm, advantageously 10 mm, in particular 5 mm, embedded in or surrounded by a binder 15 formed from oxides or a vitreous material such as glass.

The second layer 13, or contact layer, comprises another shot 16 of refractory material, of composition identical or different from that of shot 14, in particular at least 10 mm, advantageously at least 20 mm, but with a grain size greater than that of said first shot 14, the shot particles 16 being surrounded by an ore binder 17, of composition identical or different from that of the contact layer 12

The production of these layers on the surface of the slabs 11 can take place in various ways. In a first manufacturing method, a lower layer of the shot

14 relatively thin is deposited on the slabs 11, then an upper layer of the relatively large shot 16 is deposited on the lower layer. The whole is then covered with a thickness of fusible cullet of vitreous material, in particular glass, and the furnace is started, the fusion of cullet allows the impregnation of the layers of shot and the progressive coating of the particles of shot 14 and 16 to finally produce the layers 12 and 13 in which the molten cullet acts as a binder and ensures the cohesion of the whole

As it flows between the particles of shot, the glass melted from the cullet interacts with the surface of the shot and becomes charged element (s) of refractory oxide (s), for example Al Zr, Si in the case of AZS shot, or Cr in the case of chrome shot The glass enriched in refractory oxide elements becomes more viscous and possibly may finally devitnfier in the free interstitial spaces, the viscous material devitπfié preventing the passage of glass from the bath 5 to the lower layers

In a variant, a separating element such as a grate or a refractory metal screen could be interposed between the two layers of shot, and possibly a similar element could be placed on the second layer so as to maintain the respective levels of the layers The same technique with a retaining grid could be used to apply one or more similar layers to the side walls 3

In another manufacturing method, layers 14 and 16 are deposited in layers 12 and 13 in intimate mixture with the binder 15 and 17 respectively. When the temperature of oven 1 is increased to start the latter, the binder in fusion coats the particles of shot ensures the cohesion of the whole. The chemical exchange phenomenon described in the previous manufacturing method can of course occur with the same effects

In FIG. 2, the difference in behavior of the two layers 12 and 13 vis-à-vis a metal 18, present in the molten state in the bath 5, has also been illustrated, in particular in the case where the material to be melt 7 is a recovery glass containing metallic residues

The granulometry of the shot 16 and the quality of the bonding glass 17 are such that the layer 13 is permeable to the metal 18

On the contrary, the granulometry of the shot 14 and the quality of the bonding glass 15 are such that the layer 12 is impermeable to the metal 18

Thus, in operation, the metal 18 present in the molten state in the bath 5 flows by gravity to the bottom 2, penetrates through the layer 13 by making a passage between the particles of shot 16, and is blocked at the border between layers 13 and 12, where it accumulates in the form of drops whose size gradually increases

The thickness of the layer 13 is advantageously determined so that it provides a storage capacity for the metal, in the interstitial spaces between the shot, sufficient for a given duration of the campaign of use. Figure 3 shows another embodiment of the invention. When the oven 20 of FIG. 3 comprises elements identical or equivalent to those of the oven 1, these elements are designated by the same reference numeral.

The essential differences with the first embodiment relate to the structure of the sole and the walls.

The sole consists of three layers comprising refractory shot

the lower layer 21 (analogous to the lower layer 12 of the furnace 1) comprises a binder and relatively fine shot, for example having a particle size of the order of 0 to 5 mm, of a type which can be relatively attacked by a binder based on glass, for example of the AZS type which may optionally contain a limited amount of chromium oxide

This layer is impermeable to glass, in particular because the fine shot settles very compactly and saturates the interstitial glass with refractory oxides thanks to the high exchange surface; it is also very resistant to corrosion. It plays in particular the role of a concrete, hence the optional nature of the layer 10 of refractory concrete.

the middle layer 22 comprises a binder and a larger shot than that of the layer 21, for example having a particle size of the order of 10 to 30 mm, and of a type which is relatively attackable by a glass-based binder, identical or different from the type of shot of layer 21. In a particular example, this shot can be of the AZS type which can contain up to 30% chromium oxide.

The role of layer 22 is to enrich the interstitial glass with refractory oxides to make it on the one hand less aggressive when it reaches the lower layer 21, and on the other hand more viscous to limit the convection and the diffusion of aggressive oxides,

the upper layer 23 (which can be brought closer to the contact layer 13 of the oven 1) comprises a relatively large shot, for example at least 50 mm in which the fine particles have been carefully removed, of a type resistant to corrosion by glass, for example single-phase and rich in chromium oxide Its main function is to block convection on the lower layers; it is not carried away by glass currents and does not create defects thanks to its high particle size.

The shot of layers 21, 22 and 23 can be recycling materials.

Each wall is constituted by a lower part made of insulating blocks 9 placed if necessary on the optional layer 10 of refractory concrete. This lower part is surmounted by an upper part made of blocks 3 of refractory material (as used to constitute the walls of the furnace 1). The surface of the walls directed towards the glass bath comprises a coating comprising refractory shot which is in continuity with the upper layer 23.

This coating is inclined relative to the vertical by an angle corresponding to the slope angle of the particulate material used to form the layer 23. It is intended to isolate the blocks 3 and 9 from the glass bath.

As a variant with respect to the first embodiment, the shot-based layers 21, 22 can be produced by first preparing a mixture of the shot concerned and the corresponding glass-based binder in particulate form, in particular cullet, and successively extending: a compact horizontal layer of the mixture for the lower layer 21;

- then a compact horizontal layer of the mixture for the middle layer 22.

The upper layer 23 is produced by depositing a horizontal layer of coarse shot which exceeds the level of separation between refractory block 3 and insulating block 9, and finally by applying the coarse shot along the vertical walls in the form of an embankment.

Finally, one begins to heat the oven to cause the melting of the binder or binders and constitute the layers 21 and 22 respectively. One can then introduce a material with a high melting point such as glass or cullet to start the oven; the shot of the layer 23 is then wetted by the molten material which constitutes a binder.

The chemical exchanges between binder glass and refractory shot can continue for a certain time during the soaking or the starting of the oven before reaching a state ensuring the desired level of tightness. Thanks to the shot-based coating on the interior walls of the furnace, it is possible to reduce the thickness of the refractory blocks 3 and to replace the refractory blocks 3 lower of the furnace 1 with insulating blocks 9 which are less expensive and significantly reduce the cost of the furnace. , without prejudice to thermal insulation or corrosion resistance.

The invention which has just been described in the particular case of a glass furnace, the hearth of which, of given structure, is provided over its entire surface with at least two layers based on shot, is in no way limited to this embodiment. The indications given in the detailed description can be extended to the other embodiments, in particular to the following cases: the sole has another structure (in particular the insulating blocks, the concrete and / or the slabs are absent); only one layer based on shot is used; the layer (s) are only applied to part of the sole.

The other usual arrangements in furnaces of the glass type are also suitable in the present invention.

Claims

1. Oven (1; 20) for melting a material with a high melting point, such as glass, comprising a hearth (2) and side walls (3) delimiting a bath (5) of molten material, characterized in that at least part of the surface of the sole (2), and possibly of the side walls (3), which is in contact with the molten material (5) is initially formed by at least one layer (12,13 ; 21, 22, 23) comprising shot (14, 16) of refractory material.

2. Oven according to claim 1, characterized in that the refractory shot material (14,16) is a material resistant to corrosion by glass, in particular of the type based on chromium oxide or based on zirconium, silicon and / or aluminum.

3. Oven according to claim 1 or 2, characterized in that said layer or at least one of said layers (12,13; 21, 22,23) comprises, in addition to the shot (14,16), a mineral binder ( 15,17) advantageously formed from oxide or a vitreous material such as glass, in particular recovery glass.

4. Oven according to claim 3, characterized in that said layer or at least one of said layers (12, 13; 21, 22) is formed from shot and binder initially mixed in particulate form.

5. Oven according to any one of the preceding claims, characterized in that the or each binder has a density greater than that of the molten material contained in the bath (5).

6. Oven according to any one of the preceding claims, characterized in that the or each binder has a viscosity greater than that of the molten material contained in the bath (5).

7. Oven according to any one of the preceding claims, characterized in that the or each binder has a thermal conductivity lower than that of the molten material contained in the bath (5).

8. Oven according to any one of the preceding claims, characterized in that the said surface or part of the surface comprises a single layer comprising shot, preferably of particle size less than 50 mm, in particular 20 mm.

9. Oven according to any one of claims 1 to 7, characterized in that said surface or surface part comprises a first layer (13; 23) comprising a first shot (16) in contact with the molten material, under which there is at least one lower layer (12, 22,21) comprising lower shot (14), the particle size of the first shot (16) being greater than the grain size of the lower shot (14)

10. Oven according to claim 9, characterized in that the first layer (13; 23) comprises shot (16) having a particle size of at least 10 mm, in particular of the order of 20 to 50 mm, and the lower layer (12; 22,21) comprises shot (14) having a particle size less than 20 mm, in particular of the order of 1 to 10 mm.

11. Oven according to one of claims 9 or 10, characterized in that the shot of the first layer (23) in contact with the molten material is of a type resistant to corrosion by glass, and the shot of the or each lower layer (21, 22) is of a type relatively attackable by glass.

12. Oven according to any one of the preceding claims, characterized in that the layer or layers (12, 13, 21, 22, 23) comprising shot (14, 16) are applied to a base layer, shaped or not , made in particular of slabs (11) or blocks of refractory or insulating material.

13. Oven according to any one of the preceding claims, characterized in that the surface of at least one side wall (3) consists of a coating (23) comprising shot of refractory material and inclined relative to the vertical

14. Oven according to any one of the preceding claims, characterized in that the surface of the hearth comprises a layer comprising refractory shot at least in a portion of the oven where the supply of material to be melted takes place.

15. Method for manufacturing an oven (1), such as a glass oven, in which a hearth (2) and side walls (3) intended to delimit a bath (5) of molten material are produced, characterized in that it includes the steps of:

- apply to at least part of the surface of the silk (2), and optionally to the side walls (3), intended to be in contact with the bath

(5), at least one layer (12,13; 21,22,23) comprising shot (14,16) of refractory material, then

- raise the temperature of the oven (1) and introduce a material of high melting point such as glass, in order to constitute the bath (5) of molten material.

16. A method of manufacturing an oven according to claim 15, characterized in that, in the first step, applying a mineral binder (15,17) in admixture with the shot (14,16) of at least one layer (21, 22), or in a layer surmounting a layer of shot (14,16), and in the second step, the binder (15,17) is melted and / or thermally activated to form at least one layer composite (12,13; 21, 22).

17. A method of manufacturing an oven according to claim 16, characterized in that, in the first step, applied to a layer (22) comprising a binder, another layer comprising essentially (23) of shot, of greater particle size to that of the lower layer (s).

18. Use of an oven according to any one of the preceding claims for melting recovery glass containing metal residues.

19. A method of recovering metal (18) present in recovery glass comprising a step consisting in melting the recovery glass in an oven (1) according to any one of claims 1 to 15 in which the shot (16) included in the layer (13) of the sole (2) which is in contact with the glass has a particle size suitable for making said layer (13) permeable to said metal (18).

20. Recovery process according to claim 19, characterized in that the oven (1) comprises, immediately under said surface layer (13), a lower layer (12) comprising shot (14) whose particle size is suitable for rendering the lower layer (12) impermeable to said metal (18).