TUCKSTONE

Abstract

Fused tuckstone defining lower and upper surfaces. The lower surface includes a support surface to rest on metallic structure of a glass furnace, a tank surface intended to face an upper edge of a tank of the furnace, and a lower transition surface connecting the support and tank surfaces. The upper surface includes a superstructure surface to receive a side wall of a superstructure of the furnace and an upper transition surface connecting the superstructure and lower surfaces. At least a part of the lower transition surface has a crystal density of more than four times the crystal density at a depth of 4 centimeters below the lower transition surface, a crystal density being evaluated by the number of crystals having a surface area of more than 12 m.sup.2 per mm.sup.2 of surface after polishing, the crystal density at the depth being evaluated after cutting of the tuckstone.

Claims

1. Fused tuckstone defining a lower surface comprising: a support surface intended to rest on the metallic structure of a glass furnace, a tank surface intended to face an upper edge of a tank of said glass furnace, a lower transition surface connecting the support surface and the tank surface, an upper surface comprising: a superstructure surface intended to receive a side wall of a superstructure of said glass furnace, an upper transition surface connecting the superstructure surface and the lower surface, characterized in that at least a part of the lower transition surface has a crystal density of more than four times the crystal density at a depth of 4 centimeters below said lower transition surface, such a surface being described as a surface with skin microstructure, a crystal density being evaluated by the number of crystals having a surface area of more than 12 m.sup.2 per mm.sup.2 of surface after polishing, the crystal density at said depth being evaluated over the surface exposed after cutting of the tuckstone to said depth.

2. Tuckstone according to claim 1, wherein at least a part of the upper transition surface is a surface with skin microstructure.

3. Tuckstone according to claim 1, wherein the entire lower surface is a surface with skin microstructure.

4. Tuckstone according to claim 1, wherein at least a part of the superstructure surface has a crystal density of less than four times the density at depth of 4 centimeters below said superstructure surface.

5. Tuckstone according to claim 1, wherein a layer of an interfacing material, which is deformable and/or has a thermal conductivity of less than 1.0 W.Math.m.sup.1.Math.K.sup.1, is arranged on at least a part of a surface with skin microstructure.

6. Tuckstone according to claim 1, having a chemical composition in mass percentage based on oxides such that: Al.sub.2O.sub.3+ZrO.sub.2+SiO.sub.2>80.0%.

7. Tuckstone according to claim 1, comprising, in mass percentage based on oxides, more than 0.5% and less than 10.0% of a zirconia stabilizer.

8. Tuckstone according to claim 1, having a chemical composition in mass percentage based on oxides such that, for a total of 100%: Al.sub.2O.sub.3+ZrO.sub.2+SiO.sub.2: more than 83.8% and less than 97.0%, Y.sub.2O.sub.3: more than 0.5% and less than 5.0%, Na.sub.2O: more than 0.1% and less than 0.6%, B.sub.2O.sub.3: more than 0.1% and less than 0.6%, oxide types other than Al.sub.2O.sub.3, ZrO.sub.2, SiO.sub.2, Y.sub.2O.sub.3, Na.sub.2O and B.sub.2O.sub.3: less than 10.0%.

9. Tuckstone according to claim 1, having a chemical composition in mass percentage based on oxides such that: ZrO.sub.2: more than 12.0% and less than 45.0%, SiO.sub.2: more than 8.0% and less than 24.0%, Al.sub.2O.sub.3: more than 35.0% and less than 60.0%.

10. Tuckstone according to claim 1, having a chemical composition in mass percentage based on oxides such that: ZrO.sub.2: more than 80.0% and less than 97.0%, SiO.sub.2: more than 0.5% and less than 15.0%, Al.sub.2O.sub.3: more than 0.2% and less than 3.0%.

11. Tuckstone according to claim 10, wherein said at least one part of the lower transition surface has a crystal density of more than 650 crystals per mm.sup.2.

12. Tuckstone according to claim 10, wherein the mean equivalent diameter of the crystals of said at least one part of the lower transition surface is less than 45 m.

13. Tuckstone according to claim 1, wherein the support surface defines a single foot or a set of feet, each foot having a terminal face (44) intended to rest during use on the metallic structure, said terminal face having no skin microstructure.

14. Tuckstone according to claim 13, wherein the area of the terminal face of the single foot or the cumulative sum of the areas (S.sub.44) of the terminal faces of the feet represents more than 0.5% and less than 10% of the area of the support surface.

15. Tuckstone according to claim 13, wherein the interfacing material fills the volume which is delimited by the support surface and which extends up to the plane of said terminal face or faces.

16. Tuckstone according to claim 1, wherein the upper transition surface, at the junction between the superstructure and tank arms, comprises a curved upper junction surface with no ridges, which connects a horizontal surface of the superstructure arm and a horizontal surface of the tank arm, and/or the lower transition surface, at the junction between the superstructure and tank arms, comprises a curved lower junction surface with no ridges, which connects a horizontal surface of the superstructure arm and a horizontal surface of the tank arm.

17. Glass furnace comprising: a tank with an upper edge; a metallic structure; a superstructure with an intermediate layer comprising a fused tuckstone according to claim 1, the support surface resting on the metallic structure, the tank surface extending facing the upper edge of the tank, and the superstructure resting on the superstructure surface.

18. Method for production of a tuckstone according to claim 1, the method comprising the following successive steps: a) mixing of raw materials so as to form a starting batch; b) fusion of said starting batch to obtain a bath of molten material; c) casting of said molten material in a mold, and solidification of said molten material by cooling so as to obtain an intermediate piece which has the general form of a tuckstone, and the surface of which in contact with the mold has a skin microstructure; d) removal of said intermediate piece from the mold; e) partial machining of the outer surface of the intermediate piece so as to retain at least part of the surface with a skin microstructure.

19. Method according to claim 18, wherein in step e), the superstructure surface is machined and/or the support surface is not machined, and/or the tank surface is not machined.

20. Method for production of a furnace comprising a glass melting tank, a superstructure extending above the tank, and a metallic structure supporting the superstructure, said method comprising the integration of a tuckstone according to claim 1 in an intermediate layer between the metallic structure and a side wall of the superstructure, the support and superstructure surfaces being in contact with the metallic structure and the side wall of the superstructure respectively, and the tank surface facing an upper edge of the tank.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0100] Further characteristics and advantages of the invention will appear from reading the detailed description below and from examining the appended drawings in which:

[0101] FIG. 1 diagrammatically depicts a half cross-section through a glass furnace;

[0102] FIG. 2 (2a, 2b, 2c and 2d) is a diagrammatic, perspective view of an exemplary tuckstone according to the invention. The form shown is also the usual shape of conventional tuckstones;

[0103] FIG. 3 (3a and 3b) is a diagrammatic, perspective view of an exemplary tuckstone of a glass furnace in a preferred embodiment of the invention.

DETAILED DESCRIPTION

[0104] Since FIG. 1 has been described in the introduction, we will now refer to FIG. 2a, partially described in the introduction.

[0105] The length L.sub.20 of the tuckstone 20 is preferably more than 10 cm and preferably less than 100 cm. Its width I.sub.20 is preferably more than 30 cm and/or less than 100 cm and its height h.sub.20 is preferably more than 10 cm and/or less than 50 cm.

[0106] In a cross-sectional plane, i.e. perpendicular to the direction of the length L.sub.20, the axis X is the line which extends halfway between the upper surface 20.sub.5 and the lower surface 20.sub.3.

[0107] The thickness e.sub.20 of the tuckstone, at a point on axis X contained in the median transverse plane, is the smallest dimension measured perpendicularly to axis X at this point. Preferably, the mean thickness of the tuckstone along axis X is more than 10 cm and/or less than 50 cm. Preferably, this thickness is constant along axis X.

[0108] Preferably, the tuckstone is a profile such that its dimensions in a transverse plane are independent of the cross-sectional plane concerned.

[0109] Preferably, the support surface 20.sub.14 has a skin microstructure. In a preferred embodiment, the entire lower surface 20.sub.3, and/or all or part of the upper transition surface 20.sub.26-3, preferably at least the non-horizontal part of the upper transition surface 20.sub.26-3, and/or the outer side surface 20.sub.4 of the tuckstone has/have a skin microstructure. In this way, the cracking resistance and machining time are improved.

[0110] When the skin microstructure is obtained by rapid cooling resulting from coming into contact with the surface of a mold, the surface of the tuckstone with this microstructure may have geometric variations which are prejudicial to the dry assembly of the tuckstone 20 with the side wall 26 of the superstructure or with a metallic structure.

[0111] In one embodiment, the interfacing material 40 is arranged against at least a part of the surface with skin microstructure. The interfacing material 40 is configured to accommodate two surfaces intended to be in mutual contact, and/or to thermally isolate them from each other.

[0112] The interfacing material may be a deformable material in order to compensate for the geometric variations of the surfaces.

[0113] The interfacing material may be a thermally insulating material with a thermal conductivity of preferably less than 1.0 W.Math.m.sup.1.Math.K.sup.1, less than 0.7 W.Math.m.sup.1.Math.K.sup.1, or less than 0.5 W.Math.m.sup.1.Math.K.sup.1.

[0114] The interfacing material is preferably a felt, preferably a thermally insulating felt, preferably made of ceramic fibers, in particular based on alumina and silica.

[0115] The interfacing material may be arranged over all or part of the surface with a skin microstructure, in particular on contact surfaces which, in the absence of deformable material, would be directly in contact with another piece.

[0116] The thermally insulating and/or deformable interfacing material preferably takes the form of a layer, the thickness of which is preferably less than 40 mm, preferably less than 32 mm, preferably less than 28 mm, preferably less than 22 mm or/or preferably more than 3 mm, or more than 5 mm.

[0117] Further preferably, the interfacing material is fixed to the surface with skin microstructure, preferably by gluing. On FIG. 2a, it is glued onto the support surface which has a skin microstructure. The interfacing material advantageously stabilizes the assembly of the two parts it separates, despite any dimensional variations resulting from the absence of machining.

[0118] In one embodiment, the surface with skin microstructure is locally structured in order to improve the fixing of the interfacing material 40, in particular in the case of a deformable material. For example, one or more circular grooves, closed in themselves, may be provided in order to create one or more attachment zones.

[0119] In one embodiment, the interfacing material extends over the entire lower surface.

[0120] Preferably, the interfacing material does not extend over surfaces which do not have a skin microstructure.

[0121] In a preferred embodiment illustrated on FIG. 2c or 3b: [0122] the entire lower surface 20.sub.3 (support surface 20.sub.14, tank surface 20.sub.12, and lower transition surface 20.sub.14-12 connecting the support surface 20.sub.14 and the tank surface 20.sub.12), [0123] the entire outer side surface 20.sub.4, and [0124] the part of the upper transition surface 20.sub.26-3 which is not horizontal,
have a skin microstructure (hatched area on FIGS. 2c and 3b). The interfacing material extends, preferably exclusively, over the entire support surface 20.sub.14 and over the part of the lower transition surface 20.sub.14-12 which is not horizontal (FIGS. 2c and 3b).

[0125] In an embodiment illustrated on FIG. 2d, the support surface 20.sub.14, i.e. the surface which extends facing the metallic structure in the service position, comprises one or more, preferably two to four feet 42, the end faces 44 of which are flat and coplanar. The height h.sub.42 of the feet is preferably more than 1 mm, preferably more than 2 mm, and/or less than 2 cm, preferably less than 1 cm, preferably less than 8 mm, preferably less than 5 mm.

[0126] The end faces of the feet define surfaces via which the tuckstone rests on the metallic structure. Machining these allows the tuckstone to be installed with perfect accommodation of the surfaces, which allows precise positioning of the tuckstone.

[0127] In a preferred embodiment, the end faces of the feet have no skin microstructure. The rest of the support surface 20.sub.14 and/or the rest of the surface of the feet may however have a skin microstructure.

[0128] Preferably, in the service position, an interfacing material 40 fills the space between the tuckstone and the metallic structure. In other words, the interfacing material 40 extends between the feet. It may take the form of a layer, for example a nonwoven matting pierced by holes 46 adapted to the shape of the feet. Advantageously, the feet thus help hold the interfacing material 40 in position.

[0129] In an embodiment, the support surface 20.sub.14 is not machined, with the exception of the end faces 44. The machining operation is thereby advantageously substantially accelerated.

[0130] The total sum of the areas S.sub.44 of the end faces of the feet, or the area of the end face of the foot when the support surface defines a single foot, preferably represents more than 0.5%, preferably more than 1%, more than 2%, and/or less than 10%, preferably less than 8%, preferably less than 5% of the area of the support surface 20.sub.14. In one embodiment, each end face has a surface area of less than 10 cm.sup.2, less than 5 cm.sup.2, less than 3 cm.sup.2.

[0131] Preferably, the feet are not aligned, which improves the stability of the tuckstone.

[0132] The shape of the feet is not limitative. In particular, they may be cylindrical, preferably with a circular base (as shown), but also conical or parallelepipedic. The feet do not necessarily all have the same shape.

[0133] In one embodiment, at least one or each foot extends along the entire length of the tuckstone.

[0134] Preferably, the shape of the feet has no region with an undercut.

[0135] In one embodiment, a mold is used which has a precisely determined geometry, for example a mold made by three-dimensional printing.

[0136] Preferably, the tuckstone according to the invention comprises, preferably is constituted by an electro-fused material comprising, to more than 80% of its mass, alumina, zirconia, silica and in some cases a zirconia stabilizer, in particular yttrium oxide. The material may be of the AZS type or have a very high zirconia content (typically comprising more than 80% ZrO.sub.2 in mass percentage).

[0137] In one embodiment, the tuckstone according the invention comprises more than 0.5%, more than 1.5%, more than 3.0%, more than 4.0%, more than 5.0%, or more than 6.0%, and/or less than 10.0%, less than 9.0%, or less than 8.0% zirconia stabilizer, in particular CaO and/or Y.sub.2O.sub.3 and/or MgO and/or CeO.sub.2, preferably Y.sub.2O.sub.3 and/or CaO, preferably Y.sub.2O.sub.3.

[0138] Preferably, the tuckstone according to the invention has a chemical composition, in mass percentage based on oxides, such that for a total of 100%, [0139] Al.sub.2O.sub.3+ZrO.sub.2+SiO.sub.2: more than 80.0%, preferably more than 84.0%, preferably more than 86.0%, and/or less than 97.0%, or less than 95.0%, or less than 94.0%, and/or [0140] Y.sub.2O.sub.3: more than 0.5%, more than 1.5%, more than 2.0% and/or less than 5.0%, less than 4.0%, or less than 3.0%, and/or [0141] Na.sub.2O: more than 0.1%, more than 0.2%, and/or less than 0.6%, preferably less than 0.5%, or less than 0.4%, and/or [0142] B.sub.2O.sub.3: more than 0.1%, or more than 0.2%, and/or less than 0.6%, preferably less than 0.5%, or less than 0.4%, and/or [0143] oxide types other than Al.sub.2O.sub.3, ZrO.sub.2, SiO.sub.2, Y.sub.2O.sub.3, Na.sub.2O and B.sub.2O.sub.3: less than 10.0%, preferably less than 9.0%, further preferably less than 8.0%, less than 5.0%, or less than 3.0%, or less than 2.0%, or less than 1.0%, or less than 0.5%.

[0144] According to one embodiment, the tuckstone according to the invention has a chemical composition such that: [0145] ZrO.sub.2: more than 12.0%, preferably more than 15.0%, preferably more than 18.0%, or more than 22.0%, and/or less than 45.0%, or less than 40.0%, or less than 35.0%, or less than 30.0%, or less than 25.0%, and/or [0146] SiO.sub.2: more than 8.0%, preferably more than 10.0%, preferably more than 12.0%, and/or less than 24.0%, or less than 20.0%, less than 17.0%, or less than 14.0%, and/or [0147] Al.sub.2O.sub.3: more than 35.0%, preferably more than 38.0%, or more than 40.0%, and/or less than 60.0%, preferably less than 55.0%, or less than 50.0%, less than 46.0%, or less than 44.0%.

[0148] According to one embodiment, the tuckstone according to the invention has a chemical composition such that: [0149] ZrO.sub.2: more than 80.0%, preferably more than 83.0%, preferably more than 86.0%, and/or less than 97.0%, or less than 95.0%, or less than 94.0%, and/or [0150] SiO.sub.2: more than 0.5%, preferably more than 1.5%, preferably more than 2.5%, preferably more than 4.0%, or more than 6.0%, more than 8.0%, more than 8.5%, and/or less than 15.0%, or less than 12.0%, less than 10.0%, or less than 8.0%, and/or [0151] Al.sub.2O.sub.3: more than 0.2%, preferably more than 1.0%, and/or less than 3.0%, preferably less than 2.0%.

[0152] According to one embodiment, the tuckstone has a device 42 for anchoring in the metallic envelope of the glass furnace. This anchoring device comprises for example a screw, a hook, a metallic plate or notch. This anchoring device is preferably fixed at less than 20 cm, preferably less than 10 cm, preferably less than 5 cm from the superstructure surface (FIG. 2c), or fixed to the superstructure surface (FIG. 3a).

[0153] Naturally, the dimensions and shapes described above are not limitative.

[0154] FIG. 3 shows a diagrammatic, perspective view of a preferred shape of a tuckstone according to the invention.

[0155] In the junction part between the superstructure and tank arms, the upper transition surface 20.sub.26-3 defines an upper junction surface 21 with no ridge, which preferably constitutes a fraction of a circular cylindrical base that preferably (as shown) extends angularly over 90 (quarter of a cylinder body) and preferably connects two respective horizontal surfaces of these arms.

[0156] Preferably, in the junction part between the superstructure and tank arms, the lower transition surface 20.sub.14-12 defines a lower junction surface 23 with no ridge, which preferably comprises or constitutes a fraction of a circular cylindrical base that preferably (as shown) extends angularly over 90, preferably connecting two respective horizontal surfaces of these arms. In one embodiment, this cylinder fraction is substantially coaxial to the cylinder fraction of the upper transition surface.

[0157] The use of three-dimensional printing to produce a mold allows easier production of surfaces without ridges, in particular the upper transition surface and/or the lower transition surface, and in particular cylinder fractions of these transition surfaces. The mechanical strength of the tuckstone is thereby improved.

[0158] In a preferred embodiment, as shown on FIG. 3, the thickness of the tuckstone is constant along axis X.

EXAMPLES

[0159] To reproduce the stresses suffered by tuckstones in service, specimens of dimensions 15010085 mm.sup.3 were arranged in a furnace, a first large face (called the hot face) being close to the heating means, and the opposite, second large surface (called the cold face) being against the door of the furnace when closed.

[0160] The temperature of the heating means was increased at the rate of 30 C. per hour until 1350 C. was reached on the hot face. This temperature was maintained throughout the test.

[0161] The furnace door was then open periodically to cause a variation in the temperature of the cold face between 600 C. and 1000 C. over 3 cycles of 3 hours (door opened for 1.5 hours, door closed for 1.5 hours), then the temperature was maintained at 600 C. for 15 hours. This treatment was repeated for 5 consecutive days.

[0162] The performance of the specimens was evaluated by measuring the dynamic Young's modulus or MOE before and after the test. The MOE was determined by measuring the rate of propagation of ultrasound in the specimen using an Ultrasonic Tester IP8 from the company Ultratest, used in flat mode. The initial MOE, measured at 20 C., is marked MOE ini, the residual MOE after the test is marked MOE res and the loss of MOE (MOE resMOE ini)/MOE initial is marked MOE in table 1.

[0163] The microstructures of the products could be analyzed and characterized using an optical microscope of the type Richert Polyvar 2, preferably using a magnification of 5, coupled with ImageJ image analysis software. The image analysis software allows isolation of independent crystals (i.e. surrounded by the vitreous phase) and determination of their surface area. In particular, it is possible to distinguish crystals of free zirconia or alumina-zirconia eutectic. Only crystals with a surface area of more than 12 square microns were counted.

[0164] The numbers of crystals (Nc) per mm.sup.2 of surface of the cold face (Nc-surface) and on a surface situated 4 cm inside the specimen (Nc-internal) were counted. The given values correspond to the means over 4 readings. The ratio between Nc-surface and Nc-internal was calculated. A ratio of more than 4, or more than 7, is representative of a skin microstructure.

[0165] Specimen no. 1 is a reference specimen machined on all faces and consisting of AZS ER1681 material sold by the company SEFPRO.

[0166] Specimen no. 2 is a reference specimen machined on all faces and consisting of ER1195 material sold by the company SEFPRO.

[0167] Specimen no. 3 is a specimen machined on all faces with the exception of the cold face and consisting of ER1195 material sold by the company SEFPRO.

[0168] Specimen no. 4 is a reference specimen machined on all faces with the exception of the cold face and consisting of ER1681 material sold by the company SEFPRO.

[0169] To measure the corrosion resistance, cylindrical bars of 22 mm diameter and 100 mm height were cut from the specimens and subjected to a test consisting of rotating the bars immersed in a bath of alkali-lime glass. The rotation speed of the specimens was 6 rotations per minute. For examples 2 and 3, the glass was brought to 1550 C. and the test lasted for 72 hours. For example 4, the glass was brought to 1500 C. and the test lasted for 48 hours. At the end of the test, the remaining volume of the corroded specimen for each bar was evaluated. The remaining volume of the reference product (example 1 present in each test) was selected as the comparison basis. The ratio of the remaining volume of any other corroded bar to the remaining volume of the reference corroded bar, multiplied by 100, corresponds to the corrosion index (Ic) and gives an evaluation of the corrosion resistance of the tested specimen relative to that of the reference product. Thus scores of more than 100 represent a smaller corrosion loss than that of the reference product. The products concerned therefore have a better resistance to corrosion by the molten glass than the reference specimen.

[0170] Also, the thermomechanical strength of the specimens at temperature, at 500 C., was evaluated using the MOR/MOE ratio. The force at rupture (MOR) and the MOE were then measured on a specimen of dimensions 1525150 cm.sup.3. The 3-point flexion mounting was produced to ISO NF EN 843 standard using a Shimadzu press with a distance of 125 mm between the two lower supports. Rubbers were placed on the punches to avoid the initiation of cracks. The punch descent speed was constant at 5 mm per minute.

[0171] The results are given in table 1:

TABLE-US-00001 1 2 3 4 Nc-surface 30 77 1135 229 (for 1 mm.sup.2) Nc-internal 29 43 65 29 (for 1 mm.sup.2) Nc-surface/ 1.0 1.8 17.5 7.9 Nc-internal (for 1 mm.sup.2) MOE ini 147 196 182 ND (GPa) MOE res 57 122 148 ND (GPa) MOE (%) 61 38 19 ND Ic 100 158 179 118 MOR/MOE @ 0.48 10.sup.3 0.58 10.sup.3 0.72 10.sup.3 0.77 10.sup.3 500 C.

[0172] The examples show that a skin microstructure (high gradient of crystal density at the periphery of the product) leads to a significant improvement in the product stability, since the MOE can be divided by more than 3.

[0173] The increase in the MOR/MOE ratio indicates the excellent thermomechanical strength of a tuckstone according to the invention.

[0174] It is evident that the embodiments described are merely exemplary and could be modified, in particular by substitution of technical equivalents, without leaving the scope of the invention.