Refractory block and glass-melting furnace

Abstract

A molten refractory product having the following average chemical composition, in wt % on the basis of oxides and for a total of 100%: Al.sub.2O.sub.3: balance to 100%; Fe.sub.2O.sub.3: 0.6%-5.0% and/or TiO.sub.2: 1.5%-10.0%; Fe.sub.2O.sub.3+TiO.sub.210.0%; Na.sub.2O+K.sub.2O: 1.0%-8.0%; SiO.sub.2: 0.2%-2.0%; CaO+BaO+SrO: 0.5%; Other oxide species: 1.5%. Also, a glass-melting furnace and the use of the refractory product in the glass-melting furnace.

Claims

1. A molten refractory product having the following average chemical composition, as weight percentages on the basis of oxides and for a total of 100%: Al.sub.2O.sub.3: balance to 100%; Fe.sub.2O.sub.3: 0.6%-5.0% and/or TiO.sub.2: 1.5%-10.0%; provided that Fe.sub.2O.sub.3+TiO.sub.210.0%; Na.sub.2O+K.sub.2O: 1.0%-8.0%; SiO.sub.2: 0.2%-2.0%; CaO+BaO+SrO: 0.5%; oxide species other than Al.sub.2O.sub.3, Fe.sub.2O.sub.3, TiO.sub.2, Na.sub.2O, K.sub.2O, SiO.sub.2, CaO, BaO and SrO: 1.5%.

2. The product as claimed in claim 1, wherein the content of Fe.sub.2O.sub.3+TiO.sub.2 is less than or equal to 8.0%.

3. The product as claimed in claim 1, wherein the content of Fe.sub.2O.sub.3 is less than or equal to 3.0%.

4. The product as claimed in claim 1, wherein the content of TiO.sub.2 is less than or equal to 6.0%.

5. The product as claimed in claim 1, wherein the content of TiO.sub.2 is between 2.5%-5.0% and the content of Fe.sub.2O.sub.3+TiO.sub.2 is between 2.5%-6.0%.

6. The product as claimed in claim 1, wherein the content of Fe.sub.2O.sub.3 is between 1.0%-3.0% and the content of TiO.sub.2 is between 2.0%-4.0%.

7. The product as claimed in claim 1, wherein the content of SiO.sub.2 is less than or equal to 1.0%.

8. The product as claimed in claim 1, wherein the content of Na.sub.2O+K.sub.2O is less than or equal to 7.0%.

9. The product as claimed in claim 1, which is in the form of a block having a weight of more than 10 kg.

10. A glass-melting furnace, comprising a product as claimed in claim 1.

11. The furnace as claimed in claim 10, wherein said product is arranged in a superstructure.

Description

DETAILED DESCRIPTION

(1) In a molten and cast product according to the invention, the presence of iron, expressed in the Fe.sub.2O.sub.3 form, and/or titanium oxide, expressed in the TiO.sub.2 form, in contents according to the invention, makes it possible, in combination with the other constituents, to obtain a refractory product which is particularly suitable for being used as a glass-melting furnace crown. However, at contents that are too high, the presence of these oxides may be harmful to the hot mechanical properties (in particular the creep) of the products. Their content must thus be limited.

(2) The presence of the alkaline metal oxides Na.sub.2O and K.sub.2O makes it possible to ensure the feasibility, in particular of products in the form of blocks of large dimensions.

(3) In one embodiment, the oxide species other than Al.sub.2O.sub.3, Fe.sub.2O.sub.3, TiO.sub.2, Na.sub.2O, K.sub.2O, SiO.sub.2, CaO, BaO and SrO are limited to species of which the presence is not particularly desired and which are generally present by way of impurities in the raw materials.

(4) The presence of these oxide species other than Al.sub.2O.sub.3, Fe.sub.2O.sub.3, TiO.sub.2, Na.sub.2O, K.sub.2O, SiO.sub.2. CaO, BaO and SrO does not substantially modify the results obtained, provided that their content remains less than 1.5%.

(5) Conventionally, in a molten and cast product, the oxides represent more than 98.5%, more than 99%, or even approximately 100% of the weight of the product. The same is true in a product according to the invention.

(6) Any conventional process for manufacturing alumina-based molten products intended for applications in glass-melting furnaces may be carried out, provided that the composition of the starting feedstock makes it possible to obtain products having a composition in accordance with that of a product according to the invention.

(7) In particular, a product according to the invention may be manufactured according to steps a) to c) described above.

(8) In step a), the raw materials are determined so as to guarantee a composition, in the final product, in accordance with the invention.

(9) In step b), the melting is preferably carried out by means of the combined action of quite a long electric arc, not producing any reduction, and of stirring which promotes reoxidization of the products.

(10) In order to minimize the formation of nodules with a metallic aspect and to avoid the formation of slots or splits in the final product, it is preferable to carry out the melting under oxidizing conditions.

(11) Preferentially, the long arc melting process described in French patent No. 1 208 577 and its additions Nos. 75893 and 82310.

(12) This process consists in using an electric arc furnace of which the arc flies out between the feedstock and at least one electrode which is at a distance from this feedstock and in regulating the length of the arc so that its reductive action is reduced to a minimum, while at the same time maintaining an oxidizing atmosphere above the molten bath and stirring said bath, either by the action of the arc itself, or by bubbling an oxidizing gas (air or oxygen, for example) into the bath or else by adding to the bath oxygen-releasing substances such as peroxides.

(13) In step c), the bath of molten material is preferably cast in a mold that is suitable for the manufacture of a block. The cooling is preferably carried out at a speed of approximately 10 C. per hour.

(14) Any conventional process for manufacturing high-alumina molten products intended for applications in glass-melting furnaces may be carried out, provided that the composition of the starting feedstock makes it possible to obtain products having a composition in accordance with that of a product according to the invention.

(15) A product according to the invention may constitute all or part of a block.

(16) In particular, it may constitute only one region (for example a superficial layer having a thickness of less than 50 mm, less than 40 mm, less than 30 mm, for example of approximately 20 millimeters), in particular a region which is exposed to flame radiation.

(17) The shape of the block is not limiting.

(18) The block may have at least one dimension (thickness, length or width) of at least 150 mm, preferably of at least 200 mm, or even of at least 400 mm, or even of at least 600 mm, or even of at least 800 mm or even of at least 1000 mm, or even more of at least 1600 mm.

(19) In one advantageous embodiment, the thickness, the length and the width of the block are at least 150 mm, or even at least 200 mm, or even at least 300 mm, or even at least 400 mm.

(20) Preferably, the block is part of or constitutes the superstructure (crown) of a furnace, in particular of a glass-melting furnace.

EXAMPLES

(21) The following nonlimiting examples are given for the purpose of illustrating the invention. In these examples, the following raw materials were used: alumina type AC44 sold by the company Pechiney and containing on average 99.4% of Al.sub.2O.sub.3, sodium carbonate containing 58.5% of Na.sub.2O, iron oxide having a purity greater than 99%, titanium oxide (rutile) having a purity greater than 99%.

(22) The products were prepared according to the conventional arc furnace melting process, then cast so as to obtain blocks of 200200200 mm.sup.3 format.

(23) The chemical analysis of the products obtained is given in table 1; it is an average chemical analysis, given as percentage by weight. The impurities constitute the balance to 100%.

(24) Evaluation of Emissivity

(25) The device uses two Fourier transform infrared spectrometers manufactured by Bruker (Vertex 80 v and Vertex 70) which make it possible to carry out measurements of emission in the spectral range of from 1000 to 16 000 cm.sup.1.

(26) The samples have a thickness of approximately 4 mm and the typical diameter of the zone analyzed on the sample is 2 mm. The samples are heated by means of a CO.sub.2 laser (Diamond K500, Coherent Inc.). The beam follows a path which goes through a separator and a set of mirrors making it possible to perform identical heating of the two faces of the sample. Simultaneous measurements were carried out by the two spectrometers of the fluxes emitted by the sample and by the black substance (Pyrox PY8 furnace, having a cylindrical cavity of lanthanum chromite LaCrO.sub.3), pierced with a lateral orifice, the latter having an emissivity equal to 1. The infrared spectrometers are also used as pyrometers for measuring the temperature of the sample. The method used is the Christiansen point method.

(27) Table 1 gives the Em value: mean emissivities measured at 1600 C., between 4000 and 14 000 cm.sup.1. Em is considered to be significantly improved when the value is 2 times higher or more than the value obtained for the reference product (example 1).

(28) The balance to 100% is made up of impurities.

(29) TABLE-US-00001 TABLE 1 No. Al.sub.2O.sub.3 Na.sub.2O SiO.sub.2 Fe.sub.2O.sub.3 TiO.sub.2 Em 1 95.0 3.5 0.7 <0.1 <0.01 0.18 2 95.0 3.4 0.5 0.1 <0.01 0.3 3 94.8 3.4 0.6 0.3 <0.01 0.35 4 95.0 3.5 0.5 0.8 <0.01 0.55 5 94.0 3.4 0.7 1.4 <0.01 0.6 6 92.0 3.3 0.7 2.6 <0.01 0.82 7 91.6 3.8 0.8 2.2 1.6 0.7 8 91.9 3.9 0.7 1.6 1.9 0.68 9 91.0 3.2 0.7 0.9 3.5 0.75 10 88.0 1.7 0.6 0.5 8.9 0.84 11 93.3 3.7 0.6 0.0 1.8 0.45 12 92.4 3.3 0.6 0.1 3.4 0.57 13 88.0 2.1 0.6 0.1 8.4 0.7

(30) The examples of the invention show, in comparison with reference example 1, that the mean emissivity, in the range of wavelengths of between 4000 and 14 000 cm.sup.1, may be improved by virtue of the presence of more than 0.6% of iron oxide and/or of 1.5% of titanium oxide.

(31) Of course, the present invention is not limited to the described embodiments provided by way of illustrative and nonlimiting examples.

(32) In particular, the products according to the invention are not limited to particular forms or dimensions, nor to the application to the glassmaking furnaces.