GLASS STOVE WITH INSULATED NOSE STONE

Description

technical field

[0001] The invention relates to a glass furnace comprising an insulated nose piece. State of the art

[0002] Many glass products are manufactured by melting and refining a vitrifiable mixture of raw materials, including compounds such as oxides, carbonates, sulfates, and nitrates. These two steps are carried out in furnaces whose main components are refractory materials capable of withstanding the thermal and mechanical stresses encountered in these furnaces, and in particular the high temperatures. Glass furnaces thus generally contain a very large number of refractory materials, arranged in different locations according to their properties. For each part of the furnace, the material chosen is the one that does not cause defects rendering the glass unusable (which would reduce production yields) and that is durable enough to ensure a satisfactory furnace lifespan.

[0003] There figure 1schematically represents half a cross-section of a glass furnace 10. In particular, a tank 12, a metal structure 14 and a superstructure 16 are distinguishable.

[0004] The vat 12, intended to contain the molten glass, has a vertical side wall 22 and a base 24. The side wall 22 is conventionally made up of lateral vat blocks which extend over the entire height of the vat, up to an upper edge 25.

[0005] The superstructure 16 classically comprises, at its base, an intermediate layer 18 by which it rests on the metal structure, a side wall 26 resting on the intermediate layer 18, and a vault 28. Burners, not shown, are arranged in the side wall 26 and operate alternately.

[0006] The metal structure 14, typically made of cast iron, surrounds the side wall 22 of the tank externally. It supports the weight of the superstructure 16.

[0007] The intermediate layer 18 comprises, and preferably consists of, pieces with a base nose 20 ( tuckstones » (in English) which, classically, present the form represented on the figure 2a Typically, each base nose piece 20 has the general shape of an L-shaped cross-section profile. In service, the larger arm of the L, or "superstructure arm" 30, extends horizontally. The smaller arm of the L, or "tank arm" 32, extends vertically, beneath the superstructure arm 30.

[0008] The outer surface of a part with a base nose of 20 consists of: of first and second end surfaces, 201 and 202 respectively, delimiting the length L20 of the base nose piece, i.e., the profile, of a lower surface 203 comprising a horizontal mounting surface 2014 resting, in service, on the metal structure 14, a tank surface 2012, preferably horizontal, extending in service opposite the upper edge 25 of the tank 12, and a lower transition surface 2014-12 connecting the mounting surface 2014 and the tank surface 2012, of an outer lateral surface 204, preferably vertical, of an upper surface 205 comprising a superstructure surface 2026, preferably horizontal, on which, in service, the side wall 26 rests, and an upper transition surface 2026-3 connecting the superstructure surface 20 26 and the lower surface 20 3, and in particular the tank surface 20 12.

[0009] On the figure 2b, the tank surfaces 20 12, the installation surface 20 14 and the superstructure surface 20 26 are delimited by a dashed line.

[0010] The base nose piece 20 must withstand strong thermal stresses since the superstructure branch 30 is partially in an environment at a temperature of around one hundred degrees, generally due to the presence of air blow cooling, while the tank branch 32, partially inside the furnace, is at temperatures of around 1500°C.

[0011] Furthermore, the base nose piece undergoes thermal cycles due to the alternating operation of the burners and maintenance operations, such as operations called "tank plating", which require stopping and then restarting the external cooling of the furnace, or burner or burner block change operations which require stopping and then restarting the burners.

[0012] To withstand these constraints, the basic nosepiece is made of a refractory product, in particular an Alumina-Zircone-Silica (AZS for short) type product generally containing 30 to 45% zirconia by mass, a product with a very high zirconia content (typically more than 85% zirconia by mass), a product with a high alumina content (typically more than 90% alumina by mass), or a zirconia product.

[0013] However, the crack resistance of base nose pieces is sometimes insufficient to meet the evolving needs of glassmakers, who require extended furnace lifespans. Indeed, cracking of a base nose piece can lead to fracturing, causing debris to fall into the molten glass pool and thus generating defects in the glass. Furthermore, the base nose piece then no longer adequately protects the metal structure and the furnace. The rest of the superstructure may also become unbalanced.

[0014] Document JP2017065985 describes a glass melting furnace comprising a nose piece having a body supporting the superstructure. This body includes, in at least part of its lower surface, a concave portion in which a thermally insulating material can be placed.

[0015] Therefore, there is a need to improve the crack resistance of basic nose parts. One aim of the invention is to address this need. Summary of the invention

[0016] The invention relates to a glass furnace according to claim 1, the insulated nose piece comprising as follows: a basic nose piece defining an external surface as described above; an insulating layer having a thermal conductivity of less than 2.0 Wm⁻¹·K⁻¹ between 20°C and 500°C and covering an insulated surface of the basic nose piece, said insulated surface being included in the lower surface 20³ of said basic nose piece, extending into the lower transition surface 20¹⁴-1², and representing more than 20% of the lower transition surface 20¹⁴-1², said insulating layer having a chemical composition, expressed as a mass percentage based on oxides, such that the sum of the Al contents 2 O 3 , SiO 2 , ZrO 2 , CaO, Na 2 O, MgO, K 2 Oh, TiO 2 , Fe 2 O 3 , HfD 2 , P 2 O 5 and Y 2 O 3 , you « Al 2 O 3 + SiO 2 + ZrO 2 + CaO + Na 2 O + MgO + K 2 O + TiO 2 +Fe 2 O 3 + HfO 2 +P 2 O 5 +Y 2 O 3 » > 80%.

[0017] Surprisingly, the inventors found that the presence of such an insulating layer significantly improves the crack resistance of the base nose piece, and consequently its lifespan.

[0018] In the following description, a said nose piece, comprising a basic nose piece and an insulating layer, is referred to as an "insulated nose piece" or a "nose piece of a glass furnace according to the invention".

[0019] The insulating layer has sufficient rigidity to be self-supporting.

[0020] Preferably, the insulating layer has a compressive crush resistance greater than 10 MPa, which improves the stability of the nose piece and its insulation.

[0021] In a particularly advantageous embodiment, the insulating layer is a ceramic matrix composite, or "CMC." A CMC has proven to be particularly resistant to thermal degradation. A CMC also exhibits good resistance to corrosion by sodium vapors. It typically has sufficient rigidity to form a self-supporting insulating layer, as well as a compressive strength greater than 1 MPa and a compressive crush strength greater than 10 MPa.

[0022] A manufacturing process for a furnace comprising a glass melting tank, a superstructure extending above the tank, and a metal structure supporting a side wall of the superstructure is also described, said process comprising the integration of said insulated nose piece into an intermediate layer between the metal structure and said side wall of the superstructure, a side wall of the superstructure resting, directly or not, preferably directly on the superstructure surface of the base nose piece, a mounting surface of the base nose piece resting directly or not, preferably directly on the metal structure, and a tank surface of the base nose piece being opposite an upper edge of the tank.

[0023] The invention also relates to a glass furnace comprising: a tank comprising an upper rim; a metallic structure; and a superstructure comprising an intermediate layer including a nose piece insulated from a glass furnace according to the invention, a side wall of the superstructure resting, directly or not, preferably directly on the superstructure surface of the base nose piece, a mounting surface of the base nose piece resting directly or not, preferably directly on the metal structure, and a tank surface of the base nose piece being opposite an upper edge of the tank.

[0024] Preferably, the intermediate layer consists of so-called isolated nose pieces.

[0025] The said insulated nosepiece may also include one or more of the following optional features: The insulated area extends at least to the installation surface; the insulated area represents more than 60% of the lower transition area; the lower transition area includes a lower junction area connecting said superstructure and tank branches, and the insulated area extends so as to cover at least said lower junction area; the lower junction area connects a horizontal surface of the superstructure branch including the installation area and a horizontal surface of the tank branch including the tank surface; the insulated area extends at least to a part of a horizontal portion of the lower transition area defined by the superstructure branch; the insulated area extends at least to a part of the installation area; the insulated area extends over the entire installation area;The insulated surface extends to a horizontal portion of the lower transition surface defined by the tank branch, without covering said horizontal portion, or the insulated surface extends at least to a part of a horizontal portion of the lower transition surface defined by the tank branch; the insulated surface extends to the tank surface; the insulating layer is fixed to the insulated surface; the insulating layer is selected from felt, insulating panel, ceramic foam, ceramic matrix composite, and mixtures thereof; the insulating layer has a chemical composition, expressed as a mass percentage based on oxides, such as Al₂O₃ + SiO₂ + ZrO₂ + CaO + Na₂O + MgO + K₂O + TiO₂ + Fe₂O₃ + HfO₂ + P₂O₅ + Y₂O₃ > 90%; the insulating layer consists of more than 90% oxides by mass; the insulating layer is made of a sintered material;the insulating layer preferably comprises a ceramic matrix composite made up of fibers bonded together by a ceramic matrix, the fibers preferably representing more than 30%, and / or less than 70% of the volume of the ceramic matrix composite; the fibers are made of an oxide material comprising more than 50% Al 2 O 3 and / or SiO 2 and / or ZrO 2, by mass percentage on the basis of the oxides; the fibers are selected from fibers composed of more than 95% by mass of alumina, fibers composed of more than 95% by mass of silica, fibers composed of more than 95% by mass of mullite, and fibers composed of more than 95% by mass of glass; the matrix comprises Al 2 O 3 and / or SiO 2. the matrix has an Al 2 O 3 content greater than 65% and / or a SiO 2 content greater than 15% and less than 35% and / or a content of oxides other than Al 2 O 3 and SiO 2 less than 3%, as a percentage by mass on the basis of the matrix;The ceramic matrix composite has the following chemical analysis, as a percentage by mass based on oxides and totaling 100%: SiO2: 47% - 67%, Al2O3: 32% - 52%, Oxide species other than Al2O3 and SiO2: < 5%; the insulating layer has a thermal conductivity of less than 0.6 Wm1.K-1 between 20°C and 500°C; the insulating layer has a sandwich structure comprising, in superposition, a first plate of a ceramic matrix composite, a filling material having a thermal conductivity of less than 2.0 Wm1.K-1 between 20°C and 500°C, and a second plate of a ceramic matrix composite. Definitions

[0026] For the sake of clarity, a distinction is made between the "basic" nose piece and the "insulated" nose piece, the insulated nose piece being made up of the basic nose piece and the insulating layer that covers it, that is to say, which is in contact with a part of its lower outer surface.

[0027] A transverse plane is a plane perpendicular to the direction of the length. The median transverse plane is the transverse plane passing through the midpoint of the length.

[0028] "Lower" and "upper," "inner" and "outer," "horizontal" and "vertical," refer to orientations or positions when the insulated nosepiece is in its service position in a glass furnace, as on the figure 1 .

[0029] By "horizontal" and "vertical" we mean an orientation forming with a perfectly horizontal and vertical plane, respectively, an angle of less than 5°, or even less than 2°, or even less than 1°.

[0030] By "molten product", often called "electro-fused", we mean a product obtained by complete solidification of a composition in the liquid state obtained by melting a mixture of suitable raw materials in an electric arc furnace or by any other suitable technique.

[0031] The term "sintered product" means a product obtained by mixing suitable raw materials, then shaping this mixture in its raw state and firing the resulting raw piece at a temperature and for a time sufficient to achieve sintering of this raw piece, said firing being carried out in situ during use.

[0032] By “Ceramic Matrix Composite”, or “CMC”, we classically mean a product composed of fibers rigidly bonded together by a ceramic matrix.

[0033] The term "ceramic" refers to a product that is neither metallic nor organic. For the purposes of this invention, carbon is not considered a ceramic product.

[0034] By "skin" we classically mean the peripheral region of a molten block, made up of the molten material that was less than 5 millimeters (mm) from the mold wall when it solidified.

[0035] A surface exhibits a "skin microstructure" when it has a crystal density greater than 4 times, or even greater than 6 times, or even greater than 7 times, or even greater than 9 times the crystal density measured at a depth of 4 centimeters (cm) below said surface.

[0036] The "crystal density" of a surface is determined by counting the crystals visible on a microscopic image of that surface after polishing it with a diamond grit to a 1-micron grit. Each crystal is delimited by the glassy phase. Only crystals with a surface area greater than 12 square microns are counted. To check if a surface of a basic nosepiece has a skin microstructure, the crystals visible on a polished image of that surface are counted. Then, the basic nosepiece is cut to a depth of 4 cm below this surface, and the crystals visible on a polished image of the exposed surface are counted.

[0037] "Machining" refers to a grinding operation in which the surface of a refractory part is machined to obtain a precise surface geometry. Typically, and in a particular embodiment of the invention, machining involves removing at least the outer skin.

[0038] If one part "supports" or "rests on" another part, these two parts are supported by each other. The two parts may be in contact or separated by an intermediate element, such as an insulating layer.

[0039] The tank surface is the surface that, in the service position, is "opposite" the upper edge of the tank; that is, it extends substantially parallel to, above, and in the immediate vicinity of that edge. The tank surface is thus defined by all the points on the outer surface that are at the minimum distance from the edge of the tank. The tank surface, preferably horizontal, therefore does not extend outwards from the tank, beyond the inner edge 35 which delimits the lower horizontal surface of the tank branch ( figure 2b ). The inner edge 35 can in particular define a right-angled edge.

[0040] For clarity, the chemical formulas of oxides are used to designate the contents of these oxides in a composition. For example, "ZrO2", "SiO2" or "Al2O3" designate the contents of these oxides and "zirconia", "silica" and "alumina" are used to designate phases of these oxides made up of ZrO2, SiO2 and Al2O3, respectively.

[0041] Unless otherwise stated, all oxide contents are mass percentages based on the oxides. A mass content of an oxide of a metallic element refers to the total content of that element expressed in the form of the most stable oxide, according to the usual industry convention.

[0042] HfO₂ is not chemically dissociable from ZrO₂. However, according to the present invention, HfO₂ is not intentionally added. Therefore, HfO₂ refers only to traces of hafnium oxide, this oxide being naturally present in zirconia sources at mass concentrations generally less than 5%, and generally less than 2%. In a basic nosepiece, the mass concentration of HfO₂ is preferably less than 5%, preferably less than 3%, and preferably less than 2%. For clarity, the total zirconium oxide and hafnium oxide content can be referred to interchangeably as "ZrO₂" or "ZrO₂ + HfO₂".

[0043] The sum of oxide contents does not imply the presence of all such oxides. "Contain," "include," or "present" should be interpreted in a non-limiting manner. Brief description of the figures

[0044] Other features and advantages of the invention will become apparent upon reading the detailed description that follows and examining the attached drawing in which: there figure 1 schematically represents half a cross-section of a glass furnace; the figure 2 (2a, 2b, 2c) is a schematic, perspective view of examples of isolated nose pieces from a glass furnace according to the invention, the shape of the basic nose piece shown being the classic shape of conventional nose pieces; the figure 3 is a schematic, perspective view of an example of an isolated nosepiece in a preferred embodiment of the invention; the figure 4 schematically represents the setup used for measuring the pyroscopic resistance of the insulating layer; the figure 5 (5a, 5b, 5c, 5d) illustrates the system implemented to test the examples; the figure 6(6a, 6b) represents, after the second test of the examples, a nose piece of a glass furnace according to the invention and another nose piece, the cracks having been spotted with a marker. Detailed description

[0045] An insulated nose piece of a glass furnace according to the invention comprises a basic nose piece 20 and an insulating layer 40. Basic nose piece

[0046] There figure 1 Having been described in the preamble, we now refer to the figure 2a , partially described in the preamble.

[0047] The shape of the basic nosepiece 20 may be a shape known for conventional nosepieces.

[0048] The length L 20 of the base nose piece 20 is preferably greater than 10 cm and preferably less than 100 cm. Its width l 20 is preferably greater than 30 cm and / or less than 100 cm and its height h 20 is preferably greater than 10 cm and / or less than 50 cm.

[0049] In a cross-sectional plane, that is, perpendicular to the direction of length L 20, the line extending midway between the upper surface 20 5 and the lower surface 20 3 is called the "X-axis". The thickness e 20 of the base nose piece is, at a point on the X-axis contained in the median cross-sectional plane, the smallest dimension measured perpendicular to the X-axis at that point. Preferably, the average thickness of the base nose piece along the X-axis is greater than 10 cm and / or less than 50 cm. Preferably, this thickness is constant along the X-axis.

[0050] Preferably, in any cross-section, the thickness of the basic nose piece is constant.

[0051] The basic nose piece is a profile, so its dimensions in a transverse plane are independent of the transverse cutting plane considered.

[0052] As the method of implementation of the figure 2The upper surface and / or the lower surface may consist of flat panels.

[0053] In a preferred embodiment ( figure 3 ), the upper surface and / or the lower surface have at least one curved surface.

[0054] Preferably, the upper transition surface 20 26-3 of the base nose piece defines, in the junction between the superstructure and tank branches, a curved, i.e., non-planar, edgeless upper junction surface 21, which preferably comprises, or even constitutes, a fraction of a circular base cylinder. Preferably, as shown, this cylindrical fraction extends angularly over 90° (a quarter of a truncated cylinder).

[0055] Preferably, this upper junction surface connects a horizontal surface of the superstructure branch, in particular the horizontal surface that contains the superstructure surface, and a horizontal surface of the tank branch, in particular the tank surface.

[0056] Preferably, the lower transition surface 20 14-12 of the base nose piece defines, in the junction between the superstructure and tank branches, a curved lower junction surface 23 without edges, which preferably comprises, or even constitutes, a portion of a circular base cylinder. Preferably, as shown, this cylindrical portion extends angularly over 90°.

[0057] Preferably, this lower junction surface connects a horizontal surface of the superstructure branch, in particular the horizontal surface that contains the laying surface, and a horizontal surface of the tank branch, in particular the horizontal surface that contains the tank surface.

[0058] In one embodiment, this cylindrical fraction is substantially coaxial with the cylindrical fraction of the upper transition surface.

[0059] When the basic nose part is obtained by casting in a mold, the mold is preferably created by 3D printing, which makes it easier to produce surfaces without edges, and in particular the upper and / or lower transition surfaces, and especially cylindrical portions of these transition surfaces. This improves the mechanical strength of the basic nose part.

[0060] The end surfaces 201 and 202 of the base nose piece are preferably flat, and in particular free from step, preferably substantially parallel to each other, and preferably substantially vertical.

[0061] Furthermore, in one embodiment, the first and second end surfaces of the base nose piece define respectively a tenon and a mortise of complementary shape to said tenon, so that, in the service position, said tenon is housed in a mortise of a first adjacent base nose piece and said mortise receives a tenon of a second adjacent nose piece (male / female interlocking).

[0062] The chemical composition of the basic nosepiece can be a composition known for conventional nosepieces.

[0063] The basic nosepiece is preferably made up of more than 95%, preferably more than 97%, preferably more than 99%, preferably more than 99.5%, preferably more than 99.9% of its mass, of oxides.

[0064] Preferably, the basic nosepiece has a chemical composition, in mass percentage on the basis of oxides, such as Al 2 O 3 + ZrO 2 + SiO 2 > 80.0%.

[0065] In one embodiment, the basic nosepiece, preferably cast, has a chemical composition comprising, as a mass percentage on the basis of oxides, more than 0.5%, or even more than 1.5%, or even more than 3.0%, or even more than 4.0%, or even more than 5.0%, or even more than 6.0%, and / or less than 10.0%, or even less than 9.0%, or even less than 8.0% of a zirconia stabilizer, in particular CaO and / or Y2O3 and / or MgO and / or CeO2, preferably Y2O3 and / or CaO, preferably Y2O3.

[0066] In one embodiment, the basic nose piece, preferably cast, has a chemical composition, expressed as mass percentages based on oxides, such that, for a total of 100%: Al₂O₃ + ZrO₂ + SiO₂: more than 80.0%, preferably more than 84.0%, preferably more than 86.0%, and / or less than 97.0%, or even less than 95.0%, or even less than 94.0%; Y₂O₃: less than 5.0%, or even less than 4.0%, or even less than 3.0%, and preferably more than 0.5%, or even more than 1.5%, or even more than 2.0%; Na₂O: more than 0.1%, or even more than 0.2%, and / or less than 1.5%, preferably less than 1%, preferably less than 0.6%, preferably less than 0.5%, or even less than 0.4%; B₂O₃: more than 0.1%, or even more than 0.2%, and less than 0.6%, preferably less than 0.5%, or even less than 0.4%, oxide species other than Al 2 O 3 , ZrO 2 , SiO 2 , Y 2 O 3 , Na 2 O and B 2 O 3: less than 13.0%, preferably less than 9.0%, preferably less than 8.0%, preferably less than 5.0%, or even less than 3.0%, or even less than 2.0%, or even less than 1.0%, or even less than 0.5%.

[0067] In one embodiment, the basic nose piece, preferably cast, preferably has a chemical composition, expressed as mass percentages based on oxides, such that, for a total of 100%: ZrO₂: more than 12.0%, preferably more than 20.0%, preferably more than 25.0%, preferably more than 30.0%, and / or less than 46.0%, preferably less than 42.0%, and SiO₂: more than 8.0%, preferably more than 10.0%, and / or less than 24.0%, preferably less than 20.0%, preferably less than 17.0%, and Al₂O₃: more than 35.0%, preferably more than 40.0%, and / or less than 60.0%, preferably less than 55.0%, preferably less than 50.0%, and Oxide species other than Al₂O₃, ZrO₂ and SiO₂: less than 10.0%, preferably less than 8.0%, preferably less than 6.0%, or even less than 4.0%, or even less than 3.0%, or such as ZrO2: more than 80.0%, preferably more than 85.0%, and / or less than 97.0%, preferably less than 96.0%, and SiO2: more than 0.5%, preferably more than 1.0%, preferably more than 2.0%, preferably more than 3.0%, and / or less than 15.0%, preferably less than 12.0%, preferably less than 10.0%, and Al2O3: more than 0.2%, and / or less than 3.0%, preferably less than 2.0%,and Oxide species other than Al₂O₃, ZrO₂ and SiO₂: less than 8.0%, preferably less than 6.0%, preferably less than 4.0%, or such that Al₂O₃: more than 90.0%, preferably more than 91.0%, and / or less than 98.0%, preferably less than 97.0%, and SiO₂: more than 0.2%, and / or less than 7.0%, preferably less than 6.0%, or even less than 4.0%, or even less than 3.0%, and Oxide species other than Al₂O₃ and SiO₂: less than 8.0%, preferably less than 6.0%, preferably less than 5.0%, or such that ZrO₂: more than 62.0%, preferably more than 64.0%, and / or less than 71.0%, preferably less than 69.0%, and SiO2: more than 26.0%, preferably more than 28.0%, and / or less than 36.0%, preferably less than 34.0%, and oxide species other than ZrO2 and SiO2: less than 6.0%, preferably less than 4.0%, preferably less than 3.0%, or such as SiO2: more than 90.0%, preferably more than 93.0%, and oxide species other than SiO2: less than 10.0%, preferably less than 7.0%.

[0068] The microstructure of the nosepiece may be a microstructure known for conventional nosepieces.

[0069] Preferably, the nosepiece is a cast product and may further include one or more of the following optional features: at least a portion, preferably the entire lower transition surface of the nose piece, exhibits a skin microstructure; at least a portion, preferably all, of the surfaces of the nose piece intended to be exposed to the environment inside the furnace exhibit a skin microstructure. In particular, preferably at least a portion, preferably the entire surface of the furnace body and / or the upper transition surface exhibit(s) a skin microstructure; at least a portion, preferably the entire mounting surface 20 14 of the base nose piece, preferably the entire lower surface 20 3 and / or all or part of the upper transition surface 20 26-3, preferably at least the non-horizontal portion of the upper transition surface 20 26-3 and / or all or part of the outer lateral surface 20 4 exhibit(s) a skin microstructure. Crack resistance and machining time are thus improved;at least the superstructure surface and the end surfaces of the base nose piece do not exhibit a skin microstructure; the skin microstructure surface has a crystal density less than 30 times, or even less than 25 times, or even less than 20 times the crystal density measured at a depth of 4 cm below said surface; the skin microstructure surface, and in particular at least part of the lower transition surface, has a crystal density greater than 130 crystals per square millimeter (mm²), preferably greater than 150 crystals per mm², preferably greater than 180 crystals per mm², preferably greater than 200 crystals per mm², greater than 230 crystals per mm², or even greater than 250 crystals per mm²;the basic nosepiece has a ZrO2 content, as a mass percentage on the basis of oxides, greater than 80.0%, and the skin microstructure surface, and in particular at least part of the lower transition surface, has a crystal density greater than 600 crystals per mm2, preferably greater than 650 crystals per mm2, preferably greater than 700 crystals per mm2, preferably greater than 800 crystals per mm2, greater than 900 crystals per mm2, greater than 1000 crystals per mm2, or even greater than 1100 crystals per mm2; the nosepiece has a ZrO2 content, as a mass percentage on the basis of oxides, greater than 80.0%, and the average equivalent diameter of said crystals of the skin microstructure surface, and in particular of at least a part of the lower transition surface, is less than 45 µm, preferably less than 40 µm, and / or preferably greater than 20 µm, or greater than 30 µm.

[0070] Obtaining a skin-like microstructure on the surface of a molten nose piece, that is, in a molten product, presents no particular difficulty for those skilled in the art. In particular, those skilled in the art know that a microstructure can be made finer at the surface by increasing the solidification rate of the molten material.

[0071] When the molten material is poured into the mold, the mold properties and temperature can be adjusted to ensure sufficiently rapid cooling to create a skin microstructure. For example, when the mold is initially at room temperature, a skin microstructure forms on the surface in contact with, or near, the mold walls. If, contrary to standard practice, this skin is not removed during machining, a skin microstructure is then formed on the unmachined surfaces of the base nose piece.

[0072] However, limited machining (surfacing) allows a skin microstructure to be preserved.

[0073] In one embodiment, the base nose piece is provided with an anchoring device 42 in the metal casing of the glass furnace. This anchoring device is, for example, a screw, a hook, a metal plate, or a notch. This anchoring device is preferably fixed less than 20 cm, preferably less than 10 cm, preferably less than 5 cm from the superstructure surface, or even fixed to the superstructure surface ( figure 3 ).

[0074] The basic nose piece can be made from a sintered product.

[0075] Of course, the dimensions, shapes and microstructures described above are not limiting. Insulating layer

[0076] Preferably, the insulating layer 40 has a chemical composition, in mass percentage on the basis of oxides, such as Al 2 O 3 + SiO 2 + ZrO 2 + CaO + Na 2 O + MgO + K 2 O + TiO 2 + Fe 2 O 3 + HfO 2 + P 2 O 5 + Y 2 O 3 > 85%, preferably greater than 90%, or even greater than 95%.

[0077] Preferably, the insulating layer 40 has a chemical composition, in mass percentage on the basis of oxides, such as Al 2 O 3 + SiO 2 + ZrO 2 + CaO + Na 2 O + MgO + K 2 O + TiO 2 + Fe 2 O 3 + HfO 2 > 80%, preferably greater than 85%, preferably greater than 90%, or even greater than 95%.

[0078] Preferably, the insulating layer has a chemical composition, in mass percentage on the basis of oxides, such as Al 2 O 3 + SiO 2 + ZrO 2 + CaO + HfO 2 > 80%, preferably greater than 85%, preferably greater than 90%, or even greater than 95%.

[0079] In one embodiment, the insulating layer has a chemical composition, in mass percentage on the basis of oxides, such as Al 2 O 3 + SiO 2 > 80%, preferably greater than 85%, preferably greater than 90%, or even greater than 95%.

[0080] Preferably, the insulating layer is made up of more than 90% of its mass, preferably more than 95% of its mass, preferably more than 98% of its mass, preferably more than 99% of its mass, preferably more than 99.5% of its mass, of oxides.

[0081] Preferably, the insulating layer 40 is chosen from: a felt, preferably a ceramic fibre felt, preferably having an Al 2 O 3 + SiO 2 content greater than 80%, or even greater than 85%, or even greater than 90% by mass, an insulating panel or a rigid fibrous insulating panel, a ceramic foam, preferably having an Al 2 O 3 + SiO 2 content greater than 80%, or even greater than 85%, or even greater than 90% by mass, a ceramic matrix composite (CMC), preferably consisting of more than 90% by mass, more than 95% by mass, more than 98% by mass, more than 99% by mass, more than 99.5% by mass, of oxides, and mixtures thereof.

[0082] The insulating layer 40 has a thermal conductivity of less than 2.0 Wm⁻¹·K⁻¹, preferably less than 1.8 Wm⁻¹·K⁻¹, preferably less than 1.5 Wm⁻¹·K⁻¹, preferably less than 1.3 Wm⁻¹·K⁻¹, preferably less than 1 Wm⁻¹·K⁻¹, preferably less than 0.9 Wm⁻¹·K⁻¹, preferably less than 0.8 Wm⁻¹·K⁻¹, preferably less than 0.7 Wm⁻¹·K⁻¹, preferably less than 0.6 Wm⁻¹·K⁻¹, preferably less than 0.5 Wm⁻¹·K⁻¹ between 20°C and 500°C, preferably between 20°C and 600°C. preferably between 20°C and 700°C, preferably between 20°C and 800°C, preferably between 20°C and 900°C, preferably between 20°C and 1000°C.

[0083] Preferably, the insulating layer 40 covers more than 40%, more than 60%, more than 70%, more than 80%, more than 90%, or even 100% of the lower transition surface 20 14-12.

[0084] The term "insulated surface" refers to the surface of the base nose piece that is included in the lower surface and covered by the insulating layer, i.e., in contact with this layer.

[0085] The insulated surface extends over at least part of the lower transition surface 20 14-12 which connects the mounting surface 20 14 and the tank surface 20 12 of said base nose part, preferably over the entire lower transition surface 20 14-12.

[0086] As depicted on the figure 2c The insulating layer does not necessarily extend to the installation surface in the lower transition area 20 14-12. Preferably, however, it extends to within 30 mm, preferably within 20 mm, preferably within 10 mm of the installation surface. Preferably, the insulated surface extends to the installation surface, i.e., at least to line 44 shown on the figures 2a, 2b And 3 .

[0087] In the embodiments shown, the isolated surface thus extends over at least part of the horizontal portion of the lower transition surface 20 14-12 defined by the superstructure branch, at least until it reaches the laying surface 20 14.

[0088] In one embodiment, the insulated surface does not extend to cover, even partially, the installation surface ( figures 2a and 2b ).

[0089] In one embodiment, the insulated surface extends, in part or even entirely, onto the installation surface, as shown in the figure 3 In the service position ( figure 1), it is therefore pinched between the mounting surface 20 14 and the metal structure 14. When the insulating layer is rigid, pinching the insulating layer between the mounting surface and the metal structure advantageously allows this insulating layer to be held against the insulated surface, without needing to fix it to the base nose piece.

[0090] The insulated area can in particular extend over more than 50%, 60%, 70%, 80%, 90%, or even 100% of the installation area.

[0091] Preferably, the insulated surface extends at least to the lower junction surface 23 which connects the superstructure and tank branches, as shown in the figure 2a .

[0092] Preferably, the insulated surface extends at least to the installation surface and at least to the joint surface. This embodiment is particularly effective in preventing cracking during service.

[0093] In one embodiment, the insulated surface does not extend, on the side of the tank branch, beyond the lower junction surface 23 on the side of the tank branch. Thus, on the figure 2b , the insulated surface does not extend to the lower horizontal surface of the tank branch, i.e. beyond the lower edge 35, which facilitates the implementation of the insulated nose brick.

[0094] In a preferred embodiment, the insulated surface extends over the entire laying surface and up to the lower edge 35.

[0095] In another embodiment, the insulated surface extends, on the side of the tank branch, beyond the lower junction surface 23. In the embodiment shown in the figure 2a , it thus partially covers the lower horizontal surface of the tank branch.

[0096] Preferably, as shown on the figure 2aIt extends to the surface of the tank. However, preferably, it does not extend, on the side of the tank branch, to cover, even partially, the tank surface, that is to say, beyond line 46 shown on the figures 2a, 2b And 3 .

[0097] In a preferred embodiment ( figure 2a ), the isolated surface extends to the entire lower transition surface 20 14-12 of the base nose piece.

[0098] In a preferred embodiment, the insulated surface extends over the entire mounting surface and the entire lower transition surface 20 14-12 of the base nose piece.

[0099] Preferably, the insulated surface is continuous, that is, in one piece.

[0100] The insulating layer can be held in place on the insulated surface by any means known in the prior art.

[0101] Preferably, the insulating layer is rigidly fixed to the base nose piece, forming a monolithic unit with it, which facilitates handling during furnace manufacturing. The insulating layer is preferably glued to the insulated surface, such as on the figure 2a .

[0102] Preferably, the adhesive used to fix the insulating layer to the insulated surface is chosen from mixtures of ceramic powders and binders, preferably applied in liquid form.

[0103] Preferably, the powders are alumina and / or silica and / or mullite powders. Preferably, the binders are chosen from colloidal silica, sodium silicate, organic resins, organic adhesives, and mixtures thereof. The adhesive used may also be a commercial adhesive such as Unifrax's Fixwool FX adhesives.

[0104] In one embodiment, the insulated surface is locally structured to improve the attachment of the insulating layer 40. For example, one or more grooves, for example circular, closed on themselves, may be provided to create one or more attachment zones.

[0105] It can also be fixed by means of fasteners, for example by means of an angle bracket housed in the recess defining the lower transition surface 20 14-12 between the laying surface 20 14 and the inner edge 35 so as to sandwich the insulating layer with said surface.

[0106] Preferably, the insulating layer 40 has an average thickness, preferably constant, of less than 40 mm, preferably less than 32 mm, preferably less than 28 mm, preferably less than 22 mm, or even less than 18 mm or 15 mm, and / or preferably greater than 3 mm, preferably greater than 5 mm, preferably greater than 10 mm.

[0107] Preferably, the insulating layer 40 has sufficient rigidity to be self-supporting, i.e., to retain its shape when handled at room temperature. Preferably, it has a shape complementary to that of the insulated surface.

[0108] The insulating layer 40 preferably comprises ceramic fibers, in particular alumina and / or silica and / or zirconia and / or glass fibers, preferably washed glass.

[0109] Preferably, the insulating layer comprises, preferably is made of, a CMC. Advantageously, the CMC has sufficient mechanical strength to withstand impacts, as well as sufficient rigidity to be easily handled and assembled to the base nose piece without deformation.

[0110] Preferably, the CMC includes one or more of the following optional features: preferably, the CMC is sintered; the CMC has an open porosity, measured by imbibition, according to the principle of Archimedes' buoyancy, greater than 25%, preferably greater than 30% and less than 45%, preferably less than 35%; the CMC is composed of more than 90%, preferably more than 95% by mass, preferably more than 98% by mass, preferably more than 99% by mass, preferably more than 99.5% by mass of oxides; preferably, the CMC comprises more than 30%, preferably more than 40%, preferably more than 50%, preferably more than 60% and / or less than 70% by volume of fibers; the fibers are made of an oxide material preferably comprising more than 50%, preferably more than 60%, or even more than 70%, or even more than 80%, or even more than 90% by mass of Al 2 O 3 and / or SiO 2 and / or ZrO 2;the fibers are fibers selected from fibers composed of more than 95%, preferably more than 98%, preferably more than 99%, preferably approximately 100% by mass of alumina, fibers composed of more than 95%, preferably more than 98%, preferably more than 99%, preferably approximately 100% by mass of silica, preferably composed of more than 95%, preferably more than 98%, preferably more than 99%, preferably approximately 100% by mass of amorphous silica, fibers composed of more than 95%, preferably more than 98%, preferably more than 99%, preferably approximately 100% by mass of mullite, fibers composed of more than 95%, preferably more than 98%, preferably more than 99%, preferably approximately 100% by mass of glass, preferably washed; The fibers are preferably grouped together in the form of threads, a thread typically comprising several hundred to several thousand fibers;The fibers, preferably yarns, are preferably continuous and have a length greater than 50 mm, or even greater than 100 mm. In one embodiment, the fibers, preferably yarns, are arranged in the form of a fabric (having weft and warp yarns) or a web (non-woven). Preferably, the fabrics and / or webs are arranged in the CMC so as to extend substantially parallel to the insulated surface of the base nose piece; the matrix is ​​composed of more than 90%, preferably more than 95%, preferably more than 99% oxides, by mass percentage; preferably the matrix is ​​composed substantially entirely of oxides; the matrix comprises Al₂O₃ and / or SiO₂; preferably, the matrix comprises Al₂O₃ and SiO₂. preferably, the Al 2 O 3 content in the matrix, as a percentage by mass on the basis of the matrix, is greater than 65%, preferably greater than 70%;Preferably, the SiO2 content in the matrix, as a percentage by mass on the basis of the matrix, is greater than 15%, preferably greater than 20% and / or less than 35%, preferably less than 30%; preferably, the content of oxides other than Al2O3 and SiO2 in the matrix, as a percentage by mass on the basis of the matrix, is less than 3%, preferably less than 2%, preferably less than 1%; preferably, the Al2O3 content is greater than 60%, preferably greater than 65%; in one embodiment, the total Al2O3 and SiO2 content is greater than 80%, preferably greater than 85%, preferably greater than 90%, preferably greater than 95%, as a percentage by mass of the matrix on the basis of the oxides; in one embodiment, the silica in the matrix is ​​amorphous;in one embodiment, the CMC presents the following chemical analysis, in mass percentage on the basis of oxides and for a total of 100%: SiO2: 47% - 67%, Al2O3: 32% - 52%, Oxide species other than Al2O3 and SiO2: <5%, preferably <4%, preferably <3%, preferably <2%; CMC has a thermal conductivity of less than 1.3 Wm⁻¹.K⁻¹, preferably less than 1 Wm⁻¹.K⁻¹, preferably less than 0.9 Wm⁻¹.K⁻¹, preferably less than 0.8 Wm⁻¹.K⁻¹, preferably less than 0.7 Wm⁻¹.K⁻¹, preferably less than 0.6 Wm⁻¹.K⁻¹, preferably less than 0.5 Wm⁻¹.K⁻¹, between 20°C and 500°C, preferably between 20°C and 600°C; CMC has an apparent density greater than 1.4 g / cm³, or even greater than 1.50 g / cm³ and / or less than 2 g / cm³, preferably less than 1.9 g / cm³, preferably less than 1.80 g / cm³.

[0111] In one embodiment, the insulating layer has a sandwich structure comprising, in superposition, a first plate, a filling material, and a second plate.

[0112] The first and second plates can be fixed to each other, preferably in such a way as to form a tube open at both ends, a sheath open at one end, or a hermetic shell.

[0113] At least one, preferably each of the first and second plates is made of a CMC.

[0114] At least one, preferably each of the first and second plates has a thickness greater than 2 mm, preferably greater than 3 mm, preferably greater than 5 mm.

[0115] The filling material preferably has a thermal conductivity of less than 2.0 Wm⁻¹·K⁻¹, preferably less than 1.8 Wm⁻¹·K⁻¹, preferably less than 1.5 Wm⁻¹·K⁻¹, preferably less than 1.3 Wm⁻¹·K⁻¹, preferably less than 1 Wm⁻¹·K⁻¹, preferably less than 0.9 Wm⁻¹·K⁻¹, preferably less than 0.8 Wm⁻¹·K⁻¹, preferably less than 0.7 Wm⁻¹·K⁻¹, preferably less than 0.6 Wm⁻¹·K⁻¹, preferably less than 0.5 Wm⁻¹·K⁻¹, between 20°C and 500°C, preferably between 20°C and 600°C. Preferably between 20°C and 700°C, preferably between 20°C and 800°C, preferably between 20°C and 900°C, preferably between 20°C and 1000°C. Preferably, the filling material has a thermal conductivity lower than that of the first and second plates.

[0116] The filling material can be rigid or loose, for example in the form of hollow alumina beads, a fiber wool, for example of alumina.

[0117] Preferably, the insulating layer 40 is configured to exhibit a 3-point flexural strength, measured according to ASTM C1341-13, greater than 3 MPa, preferably greater than 6 MPa, and preferably greater than 10 MPa. Advantageously, the mechanical strength of the insulating layer, particularly its impact resistance, is improved.

[0118] Preferably, and mandatorily when the insulating layer 40 is disposed over at least part of the lower surface of the tank branch of the base nose piece (lower horizontal surface of the tank branch in the figures), the insulating layer is configured to exhibit a pyroscopic resistance greater than 400°C, preferably greater than 600°C, preferably greater than 800°C, preferably greater than 1000°C. Advantageously, this increases the stability of the insulated nose piece.

[0119] The pyroscopic resistance of an insulating layer of thickness e of an insulated nosepiece, at a temperature T, is determined using the following method: a sample of said insulating layer of length a equal to 500 mm, width b equal to 400 mm and of thickness e is placed in an electric kiln, on 48 RI34 bricks of equal thickness 60 mm, according to the assembly shown on the figure 4, the dimension x being equal to 250 mm. In this assembly, one of the RI34 bricks is oriented, relative to the insulating layer, like the metal structure when the insulated nose piece is in the service position.

[0120] The following thermal cycle is then carried out: raising the ambient temperature to temperature T at a rate of 50°C / h, maintaining the temperature at T for 24 hours, then lowering it to ambient temperature at a rate of 50°C / h.

[0121] After complete cooling, the deformation of the plate under its own weight, estimated by the average of the deflections measured along each diagonal, is determined. The insulating layer is considered to have a pyroscopic resistance greater than temperature T if the deformation of the plate under its own weight is less than or equal to 5 mm.

[0122] To measure the compressive strength of an insulating layer of thickness e of an insulated nose part, a sample of dimensions equal to 50 x 50 x 10 mm 3< is extracted from the insulating layer of this part, the thickness of 10 mm being in the direction of the thickness e.

[0123] A load is then applied to the entire 50x50 mm² surface of the sample, at room temperature, along the thickness direction, with a displacement rate of 0.1 mm / min. This load is increased until the sample breaks. The compressive strength is equal to the load expressed in newtons divided by the area over which the load is applied (in this case, 25 cm²).

[0124] Preferably, the insulating layer 40 is configured so as to exhibit a compressive strength, for example measured as described above, greater than 5 MPa, preferably greater than 10 MPa.

[0125] To measure the compressive crush resistance of an insulating layer of thickness e, a sample of dimensions equal to 50 x 50 x 10 mm is extracted, the thickness of 10 mm being along the direction of the thickness e.

[0126] A load is then applied, at room temperature, to the entire 50 x 50 mm² surface of the sample, along the thickness direction, at a rate of 0.1 mm / min. The load is increased until the sample thickness is reduced by half (i.e., by 5 mm). The compressive strength is equal to the load obtained, expressed in newtons, divided by the area over which the load is applied (in this case, 25 cm²).

[0127] Traditionally, to isolate the nose piece from the metal structure, insulating layers made of fiber mats are used. Unlike these layers, the insulating layer 40 preferably has a compressive strength, for example measured as described above, greater than 10 MPa, which improves the stability of the superstructure.

[0128] Preferably, the insulating layer 40 is configured to exhibit a compressive crush resistance, for example measured as described above, greater than 20 MPa, preferably greater than 30 MPa, preferably greater than 50 MPa, which improves the stability of the superstructure.

[0129] The insulating layer 40 thus exhibits a higher resistance to compression crushing than insulating layers made of fibre mats ("insulating mats" in English) classically arranged between the nose piece and the metal structure.

[0130] Preferably, the insulating layer 40 is configured to exhibit high resistance to thermal shock.

[0131] Preferably, the insulating layer 40 is configured to exhibit high resistance to corrosion by sodium vapors. Advantageously, this increases its service life in the glass furnace.

[0132] The use of a CMC, and in particular of the type described above, is particularly well suited to obtain these properties. Manufacturing

[0133] All manufacturing processes for conventional nosepieces can be used.

[0134] All manufacturing processes that allow for the production of a CMC can be implemented.

[0135] The manufacturing process may include the following steps in particular; impregnation of a set of fabrics or sheets, preferably fabrics or sheets of yarn, by means of a slip capable of forming a matrix after drying and / or sintering; stacking of said fabrics and / or sheets, said stacking can be achieved by pressing, or under vacuum.

[0136] The fabrics or layers can be stacked so that the threads of the different fabrics or layers all have essentially the same direction, or different directions, for example at 45°, depending in particular on the desired mechanical properties. The stacking can also be carried out on a rigid support with the profile of the insulated surface of the nosepiece in order to obtain a CMC (Compact Material) with a profile close to that of said insulated surface.

[0137] When the insulating layer is rigid, its shape is preferably adapted to the insulated surface. This shape may result from the manufacturing process of the insulating layer or be obtained subsequently, for example by machining or deformation.

[0138] In one embodiment, the base nose piece and / or the insulating layer are positioned in their raw service position, i.e., before being sintered. The base nose piece is preferably in the form of concrete. The sintering of the base nose piece and / or the insulating layer is then carried out. in situ in the oven. Examples

[0139] To reproduce the stresses experienced in service, basic nose parts in the shape of an L-shaped cross-section profile, with a length L20 equal to 270 mm, a width l20 equal to 625 mm, a height h20 equal to 230 mm and a thickness e20 equal to 170 mm ( figure 2a ), are placed in a furnace in which the operating conditions are recreated, as shown on the figures 5a , 5b , 5c And 5d . THE figure 5a And figure 5brepresent cross-sections of a test setup of a nosepiece that does not characterize a glass furnace according to the invention and of a glass furnace according to the invention, respectively, in a median transverse plane of said nosepiece. The dimensions t, u, w, y and z are equal to 440 mm, 160 mm, 160 mm, 330 mm and 500 mm, respectively. figures 5c And 5d represents a perspective view of the assembly of the nose pieces.

[0140] Intermittently, air at a pressure of 4 bar and at ambient temperature (20°C) is blown onto the lower transition surface of the nose pieces, through an alumina duct with an internal diameter of 25 mm, closed at its end, and having a 4.5 mm wide and 270 mm long opening, allowing the air to escape in the direction symbolized by arrow 56 in the figures 5a And 5b .

[0141] The bearing surface of each nose piece rests on two rows of RI34 bricks (501 and 502), and its bowl surface rests on one row of RI34 bricks (52), each brick being 60 mm thick. The RI34 bricks (541 and 542) rest on two rows of RI30 bricks, each row being 60 mm thick.

[0142] Only the end surfaces of the nose pieces are machined. The other surfaces are as cast and exhibit a skin microstructure. The end surfaces are thermally insulated using a vertical wall consisting of one layer of RI28 bricks and two layers of RI30 bricks (only one of the two walls is shown on the diagram). figure 5c ), each layer of bricks having a thickness of 60 mm.

[0143] On the superstructure surface of each base nose piece, a 55 Insulfrax ®< felt with a thickness of 12 mm marketed by the Unifrax company is laid, followed by a row of 57 RI30 bricks with a thickness of 60 mm.

[0144] RI28, RI30 and RI34 bricks are marketed by the company Saint-Gobain High Performance Refractories.

[0145] The test is performed on two base nose pieces made of the same ER1195 material, marketed by Saint-Gobain SEFPRO, placed side by side. One base nose piece is without an insulating layer and serves as a reference, while the other is coated with an insulating layer. The insulated surface extends across the entire mounting area and the entire lower transition area, thus creating an insulated nose piece. The insulating layer consists of Insulfrax® felt with a constant thickness of 12 mm and a thermal conductivity between 20°C and 1000°C of less than 0.5 Wm⁻¹·K⁻¹, marketed by Unifrax. It is bonded using Fixwool® FX, also marketed by Unifrax.

[0146] A thermocouple T, the location of which is shown in the figure 5c, allows a gas burner to be regulated, so that the temperature can be adjusted on the side of the upper transition surface of the two nose pieces.

[0147] The test performed is as follows, with the temperature regulated using thermocouple T: Raising the ambient temperature to 1400°C at a rate of 25°C / h, without air blowing, Holding for 1 hour at 1400°C, without air blowing, Holding for 6 hours at 1400°C with air blowing, Holding for 6 hours at 1400°C without air blowing, Repeating the 2 immediately preceding phases 5 times consecutively, Lowering to ambient temperature at a rate of 25°C / h.

[0148] Damage to the nose pieces is assessed using a visual inspection. This inspection, carried out before and after the test, helps to highlight the presence of any cracks.

[0149] The analysis and characterization of the microstructures of the products can be performed using a Richert Polyvar 2 optical microscope, preferably at 5x magnification, coupled with ImageJ image analysis software. This software allows for the isolation of independent crystals (i.e., those surrounded by a glassy phase) and the determination of their surface area. In particular, free zirconia crystals and alumina-zirconia eutectic crystals can be distinguished. Only crystals with a surface area greater than 12 square microns are considered.

[0150] The number of crystals (Nc) per mm² of surface area with a skin microstructure (Nc-surface) is evaluated, as well as on an area located 4 cm inside the sample (Nc-internal). The values ​​given are averages over 4 samples. The ratio between Nc-surface and Nc-internal is calculated. A ratio greater than 4 is representative of a skin microstructure.

[0151] The chemical analysis of the products is measured by " Inductively Coupled Plasma "or ICP, after calcining the material to be analyzed at 1000°C for one hour, for elements present in quantities not exceeding 0.5%, as well as for boron and lithium. To determine the content of other elements, a bead of the material to be analyzed is made by melting the material, and then chemical analysis is performed by X-ray fluorescence."

[0152] The thermal conductivity of the insulating layer is classically given by the product of the thermal diffusivity, the apparent density and the specific heat capacity.

[0153] The diffusivity of the insulating layer is measured by the flash method using a halogen lamp with a power of 1000 W.

[0154] The apparent density is determined by weighing a known apparent volume of insulating layer, the apparent density being the ratio of the result of said weighing and said apparent volume.

[0155] Specific heat capacity is measured by differential scanning calorimetry (in English, “differential scanning calorimetry " or "DSC").

[0156] The test performed shows that the reference nose piece exhibits, after testing, two cracks, located on the lower transition surface and on the tank surface, with a length greater than 100 mm and an opening between 0.5 and 1 mm. The isolated nose piece from a glass furnace according to the invention shows no cracks.

[0157] A second test is carried out on two basic nose pieces, made of the same ER1681 material marketed by the company Saint-Gobain SEFPRO, placed side by side.

[0158] The first of the basic nose pieces is without an insulating layer and serves as a reference. The second of the basic nose pieces is coated with an insulating layer, the insulated surface extending over the entire mounting surface and the entire lower transition surface, so as to constitute an insulated nose piece of a glass furnace according to the invention.

[0159] The insulating layer consists of a ceramic matrix composite (CMC) with a constant thickness of 13 mm and a thermal conductivity between 20°C and 500°C of less than 0.6 Wm⁻¹·K⁻¹. This CMC is composed, for 44% of its mass, of woven fabrics made of washed glass fibers (or "leached glass") with a silica content greater than 90% by mass, and an alumina and silica matrix for the remainder. It has an open porosity of 38%, an apparent density of 1.65 g / cm³, an Al₂O₃ content of 42%, a SiO₂ content of 57% and a content of other oxides of 1%, the Al₂O₃, SiO₂ and other oxide contents being expressed as mass percentages on the basis of the oxides of said ceramic matrix composite.

[0160] After testing, the isolated nose piece from a glass furnace according to the invention ( fig. 6a) shows virtually no cracks, whereas the reference nose part ( fig. 6b ) is traversed by cracks, marked with a black marker to be more visible on the figure.

[0161] As is now clearly apparent, the invention improves resistance to cracking and thus increases the lifespan of the furnace.

[0162] Of course, the invention is not limited by the examples provided, which are for illustrative purposes only. It is also understood that the embodiments described are merely examples.

Claims

1. Glass furnace (10) comprising: - a tank (12) comprising an upper edge (25); - a metallic structure (14); and - a superstructure (16) comprising a lateral wall (26) and an intermediate course (18) comprising an insulated tuckstone, said insulated tuckstone comprising: - a cast or sintered basic tuckstone (20), in the form of a profile section of L-shaped cross section comprising a superstructure leg (30) and a tank leg (32), said basic tuckstone defining an exterior surface made up: - of first and second end surfaces (201; 202) delimiting the length (L20) of the basic tuckstone, - of a lower surface (203) comprising a laying surface (2014) resting, directly or indirectly, on the metallic structure (14), a tank surface (2012) extending facing the upper edge (25) of the tank (12), and a lower transition surface (2014-12) connecting the laying surface (2014) and the tank surface (2012), the laying surface being horizontal; - of an exterior lateral surface (204); - of an upper surface (205) comprising a superstructure surface (2026) on which the lateral wall (26) rests, and an upper transition surface (2026-3) connecting the superstructure surface (2026) and the lower surface (203); - an insulating layer (40) exhibiting a thermal conductivity lower than 2.0 W.m-1.K-1 between 20°C and 500°C, exhibiting enough rigidity to be self-supporting, and covering an insulated surface of the basic tuckstone, said insulated surface being included in the lower surface (203) of said basic tuckstone, extending into the lower transition surface (2014-12), and representing more than 20% of the lower transition surface (2014-12), said insulating layer having a chemical composition, as a percentage by mass on the basis of the oxides, such that Al2O3 + SiO2 + ZrO2 + CaO + Na2O + MgO + K2O + TiO2 + Fe2O3 + HfO2 + P2O5 + Y2O3 > 80%, the insulated surface not extending so far as to cover, even partially, the laying surface, or the insulating layer (40) being sandwiched between the laying surface (2014) and the metallic structure (14).

2. Glass furnace according to the immediately preceding claim, wherein the lower transition surface (2014-12) includes a lower junction surface (23) connecting said superstructure leg (30) and tank leg (32), and the insulated surface extends in such a way as to cover at least said lower junction surface (23), the lower junction surface (23) preferably connecting a horizontal surface of the superstructure leg (30) including the laying surface (2014) and a horizontal surface of the tank leg (32) including the tank surface (2012).

3. Glass furnace according to either one of the preceding claims, wherein the insulating layer (40) has a compressive crush strength greater than 10 MPa.

4. Glass furnace according to any one of the preceding claims, wherein the insulating layer (40) comprises, preferably is made up of, a ceramic matrix composite made up of fibres bound together by a ceramic matrix.

15. Glass furnace according to the immediately preceding claim, wherein the fibres are made of an oxide material comprising more than 50% Al2O3 and / or SiO2 and / or ZrO2, as a percentage by mass on the basis of the oxides, and / or wherein the fibres represent more than 30% and preferably less than 70% of the volume of the ceramic matrix composite.

6. Glass furnace according to the immediately preceding claim, wherein the fibres are selected from among - fibres made up, by mass, of more than 95% alumina, - fibres made up, by mass, of more than 95% silica, - fibres made up, by mass, of more than 95% mullite, and - fibres made up, by mass, of more than 95% glass.

7. Glass furnace according to any one of the three immediately preceding claims, wherein the matrix contains Al2O3 and / or SiO2.

8. Glass furnace according to any one of the four immediately preceding claims, wherein the matrix has an Al2O3 content greater than 65% and / or an SiO2 content greater than 15% and less than 35%, and / or a content of oxides other than Al2O3 and SiO2 of less than 3%, as percentages by mass on the basis of the matrix.

9. Glass furnace according to any one of the five immediately preceding claims, wherein the ceramic matrix composite exhibits the following chemical analysis, as percentages by mass on the basis of the oxides and for a total of 100%: - SiO2: 47% - 67%, - Al2O3: 32% - 52%, - oxide species other than Al2O3 et SiO2: < 5%.

10. Glass furnace according to any one of the preceding claims, wherein the insulating layer (40) is attached to the insulated surface.

11. Glass furnace according to any one of the preceding claims, wherein the insulated surface extends at least as far as the laying surface and / or as far as the tank surface (2012).

12. Glass furnace according to any one of the preceding claims, wherein the insulated surface represents more than 60% of the lower transition surface (2014-12) .

13. Glass furnace according to any one of the preceding claims, wherein the insulated surface extends at least to part of a horizontal portion of the lower transition surface (2014-12) defined by the superstructure leg.

14. Glass furnace according to any one of the preceding claims, wherein the insulated surface extends at least to part of the laying surface (2014).

15. Glass furnace according to any one of the preceding claims, wherein the insulated surface extends as far as a horizontal portion of the lower transition surface (2014-12) defined by the tank leg, without covering said horizontal portion.

16. Glass furnace according to any one of Claims 1 to 13, wherein the insulated surface extends at least to part of a horizontal portion of the lower transition surface (2014-12) defined by the tank leg.

17. Glass furnace according to any one of the preceding claims, wherein the insulating layer (40) is made of a sintered material and / or exhibits a thermal conductivity lower than 0.6 W.m-1.K-1 between 20°C and 500°C.

18. Glass furnace according to any one of the preceding claims, wherein the insulating layer (40) exhibits a sandwich structure comprising, in superposition, a first sheet of a ceramic matrix composite, a filling material exhibiting a thermal conductivity lower than 2.0 W.m-1.K-1 between 20°C and 500°C, and a second sheet of a ceramic matrix composite.