POROUS REFRACTORY CAST MATERIAL, ITS USE AND PRODUCTION

Abstract

A porous refractory cast material contains a closed refractory aggregate fraction having a minimum particle size and a maximum particle size; the ratio of maximum particle size to minimum particle size is 10:1 or less. This closed refractory aggregate fraction comprises all of the porous refractory cast material having a particle diameter greater than 0.1 mm. The porous refractory cast material also contains a binder phase containing refractory selected from calcium aluminate cement, alumina phosphate, hydratable alumina, colloidal silica and combinations thereof. Also disclosed is a metallurgical vessel with an interior lining incorporating the porous refractory cast material.

Claims

1. A porous refractory cast material comprising: a closed refractory aggregate fraction having a minimum particle size and a maximum particle size, wherein the ratio of maximum particle size to minimum particle size is 10:1 or less; and a binder phase comprising refractory binder selected from the group consisting of calcium aluminate cement, alumina phosphate, alumina formed from hydratable alumina, silica formed from colloidal silica and combinations thereof; wherein the closed refractory aggregate fraction comprises 100 wt % of the material having a particle diameter greater than 0.1 mm and comprises a material selected from the group consisting of alumina, magnesite, zirconia, calcium oxide, silica, spinel, calcium aluminates, mullite, olivine, forsterite, zircon, calcium silicate, alumina zirconia silicate, and combinations of these materials.

2. The porous refractory material of claim 1, wherein the ratio of maximum particle size to minimum particle size is 5:1 or less.

3. The porous refractory material of claim 1, wherein the ratio of maximum particle size to minimum particle size is 2:1 or less.

4. The porous refractory material of claim 1, wherein the weight percentage of the aggregate fraction to the combined weight of the aggregate fraction and the binder phase is within the range from and including 70 weight percent to and including 98 weight percent.

5. The porous refractory material of claim 4, wherein the weight percentage of the aggregate fraction to the combined weight of the aggregate fraction and the binder phase is within the range from and including 75 weight percent to and including 98 weight percent.

6. The porous refractory material of claim 1, wherein 100 wt % of the closed refractory aggregate fraction has a particle size with a diameter of at least 0.2 mm.

7. The porous refractory material of claim 1, wherein the binder phase comprises a material selected from the group consisting of reactive alumina, calcined alumina, tabular alumina, fused alumina, mullite, carbon, silicon carbide, zirconia dioxide, magnesite, aluminum silicates, fume silica, bauxite, chromium oxide and combinations thereof.

8. The porous refractory material of claim 1, wherein the ratio between the size of the smallest particles of refractory aggregate and the largest particles in the binder phase is at least 10:1.

9. The porous refractory material of claim 1, wherein the ratio between the size of the smallest particles of refractory aggregate and the largest particles in the binder phase is at least 2:1.

10. The porous refractory material of claim 1, wherein 100 wt % of the binder phase consists of particles having a size of 100 microns or less.

11. The porous refractory material of claim 1, wherein the porosity is in the range from and including 20 vol % open porosity to and including 60 vol % open porosity.

12. The porous refractory material of claim 1, wherein the porosity is tortuous.

13. A porous refractory cast material structure comprising: a first layer comprising a first porous refractory material according to claim 1, and having a first layer minimum aggregate particle size; and a second layer comprising a second porous refractory material according to claim 1, and having a second layer maximum aggregate particle size wherein the first layer minimum aggregate particle size is greater than the second layer aggregate maximum particle size.

14. A metallurgical vessel having an interior and an exterior, wherein the interior of the metallurgical vessel comprises a lining structure comprising a porous refractory cast material according to claim 1.

15. Process for the minimization of oxidation of a molten metal, comprising a) transferring molten metal to a vessel having a lining structure comprising a porous refractory cast material according to claim 1, and b) transferring the molten metal out of the vessel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Various embodiments of the present invention are illustrated in the attached Figures:

[0044] FIG. 1 is a schematic sectional view of structure containing porous refractory cast material according to the present invention;

[0045] FIG. 2 is a schematic sectional view of a structure containing porous refractory cast material according to the present invention.

[0046] FIG. 3 is a sectional view of structure containing porous refractory cast material according to the present invention; and

[0047] FIG. 4 is a sectional view of a structure containing porous refractory cast material according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0048] It has been found that the presence or combination of certain compositional features produces a porous cast refractory material which is able to withstand the high temperatures and chemical reactivity encountered in the containment of metallurgical processes. The material exhibits the structural strength required in metallurgical applications such as refractory linings. The material contains pores of a width sufficient to admit molten materials, and a tortuosity sufficient to constrain the molten material and to admit impurities.

[0049] Refractory linings are composed of high temperature resistant materials in the form of a wall or panel to contain heat, molten metals and/or slags in furnaces and/or vessels. The refractory materials may include bricks of alumina, bauxite, fireclay, MgO, or graphite-containing pressed bricks or shapes; monolithic refractories such as vibration castable materials, self-flow castable materials, plastic refractories and gunning mixtures; and dry vibration mixtures. Refractory linings may be used in tundishes, ladles, blast furnace troughs, electric arc furnace (EAF) bottoms, and vessels or confinement devices such as troughs, runners, and channels. The porous cast refractory material of the present invention can be used for attracting slag/impurities, insulating vessels, inhibiting the entry of oxygen into molten metals, and reducing erosion or corrosion of a lining.

[0050] The aggregates useful in practicing the present invention are refractory materials, retaining their strength at high temperatures. Refractories are considered to be nonmetallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 538° C. (1000° F.). Refractory aggregates are distinguished from aggregates used in concrete for construction applications, which may consist of crushed rocks such as limestone, slag or granite. Due to the presence of materials such as Na.sub.2O and K.sub.2O, and carbonate decomposition of the aggregates, the concrete strength and modulus of elasticity of these materials gradually decreases with an increase in temperature, and when the temperature exceeds approximately 300° C., the decline in strength becomes more rapid. When the 500° C. threshold is passed, the compressive strength of concrete usually drops by 50% to 60%, and the concrete is considered fully damaged. By drying concrete material, the extent of the phenomenon is significantly reduced, or even eliminated, at up to 400° C. Above this temperature, the mismatch of thermal deformations between the aggregates, which expand, and cement paste, which undergoes shrinkage, prevails and results in the development of cracks. Significant cracking continues, thus altering the material mechanical properties. Refractory aggregates are also distinguished from ceramic frits, which have melting temperatures below 800° C., and may contain sodium silicate and potassium silicate.

[0051] The coarse aggregates useful in practicing the present invention include alumina (Al.sub.2O.sub.3), magnesia (MgO), zirconia (ZrO.sub.2), calcium oxide (CaO), silica (SiO.sub.2) or any combined refractory materials such as spinel (Al.sub.2O.sub.3+MgO), calcium aluminates (CaO+Al.sub.2O.sub.3), mullite (Al.sub.2O.sub.3+SiO.sub.2), olivine and forsterite, (MgO+SiO.sub.2), zircon (ZrO.sub.2+SiO.sub.2), calcium silicate (CaO+SiO.sub.2), and AZS (Al.sub.2O+ZrO.sub.2+SiO.sub.2).

[0052] The coarse aggregates useful in practicing the present invention can have a blocky, rectangular, fibrous, rod, angular or spherical or spherulite shape. Ceramic spherulites may be formed from refractory minerals such as alumina, MgO, silica, or combined materials such as mullite or spinel. Spherulites are available, for example, with diameters in the range of 1 mm to 25 mm. Spherulites may have uniform sizes or have a range of sizes. Spherulites may be dense or lightweight. Spherulites formed by roll-granulation are porous; and have a foliated inner structure resembling the interior of a cabbage. These foliated spherulites have a structure that can retain impurities and slags, and that provides some insulating effects.

[0053] The strength of the porous refractory material is provided by the binder component through cementitious bonding, chemical bonding or ceramic sintering bonding. The corresponding three types of binders are refractory cementitious slurry, chemical solution, and organic polymer. The corresponding three types of resulting binder phases after processing are refractory binder, precipitated solution, and organic polymer.

[0054] Cementitious binder may be made of fine refractory particles (having diameters less than 100 microns (100 micrometers, 0.1 mm), or less than 88 microns (88 micrometers, 0.088 mm), or less than 50 microns (50 micrometers, 0.05 mm), or less than 25 microns (25 micrometers, 0.025 mm) including refractory binder, refractory fine powder and some additives such as a water reducing agent. The fine dry materials are mixed with water to produce a slurry (a suspension) to coat and bond the refractory aggregates together. The cement may be a high temperature refractory binder that is ferrous-capable, and is thus usable at temperatures above 1400° C. The refractory binder may be calcium aluminate cement, alumina phosphate, hydratable alumina, colloidal silica, and combinations of these materials.

[0055] Chemical solution binder may contain phosphate such as monoalumina phosphate (either as a liquid or as a solution produced by mixing powder with water), colloidal silica, hydratable alumina (either as a suspension or as a solution produced by mixing powder with water), or silicone glue.

[0056] Organic polymer binder may contain polymer glue or resin.

[0057] The binder used in the matrix may contain calcium aluminate cement, calcium-magnesium-aluminate cement, alpha bond cement, Portland cement, mono-aluminum phosphate (MALP), clays, reactive alumina, hydratable alumina, colloidal silica and combinations thereof. In certain embodiments, the matrix material according to the present invention does not contain cement.

[0058] Other raw materials used in the matrix may include reactive aluminas, calcined alumina, tabular alumina, fused alumina, mullite, carbon (graphite or carbon black), silicon carbide, zirconium dioxide, magnesium oxide, aluminum silicates (such as kyanite, andalusite, or sillmanite), fume silica, bauxite, chromium oxide and combinations thereof. The portion of the formulation having diameters in the range of 0.01 to 10 microns, or 0.01 to 50 microns, or 0.01 to 100 microns, also known as the fines, may contain reactive aluminas and fume silicas.

[0059] The matrix may also contain dispersing agents, plasticizers, anti-foaming or foaming agents and de-airing components. These agents are well known in the art.

[0060] FIG. 1 is a schematic sectional view of a structure 10 containing porous refractory cast material according to the present invention. Particles of refractory aggregate fraction 14 are bound to each other by binder phase 16, shown as individual particles. Tortuous passages 18 provide open porosity without taking the form of a straight line or arc.

[0061] FIG. 2 is a schematic sectional view of a multilayer structure 30 containing porous refractory cast material according to the present invention. First layer 32 contains porous refractory cast material containing particles of refractory aggregate fraction 34 that are bound to each other by binder phase 36, shown as individual particles. Second layer 42, in communication with first layer 32, contains porous refractory cast material containing particles of refractory aggregate fraction 44 that are bound to each other by binder phase 46. Tortuous passages 18 provide open porosity without taking the form of a straight line or arc.

[0062] Each layer of multilayer structure 30 possesses two major faces. The major faces are a pair of faces, disposed on opposite sides of the layer and having the maximum areas of all faces of the layer. In FIG. 2, first layer 32 has major faces 52 and 54. Second layer 42 has major faces 56 and 58. Major face 54 of first layer 32 is in communication with major face 56 of second layer 42.

[0063] FIG. 3 is a sectional view of a structure 10 containing porous refractory cast material according to the present invention. Particles of refractory aggregate fraction 14 are bound to each other by binder phase 16. Tortuous passages 18 provide open porosity without taking the form of a straight line or arc.

[0064] FIG. 4 is a sectional view of a multilayer structure 30 containing porous refractory cast material according to the present invention. First layer 32 contains porous refractory cast material containing particles of refractory aggregate fraction 34 that are bound to each other by binder phase 36. Second layer 42, in communication with first layer 32, contains porous refractory cast material containing particles of refractory aggregate fraction 44 that are bound to each other by binder phase 46. Tortuous passages 18 provide open porosity without taking the form of a straight line or arc.

Example I

[0065] The composition of the present invention may be prepared from aggregates and binders.

[0066] Binders that may be used in the present invention include particulate suspensions or slurries, liquid solutions, or liquid binders such as glues based on resins or polymers.

[0067] In a cementitious binder, refractory fine particles having diameters or mesh passage sizes of 100 microns or less, composed of materials such as reactive alumina, fume silica, MgO or calcium aluminate cement, may be used. Additives such as dispersants may be added to improve flowability. The solid ingredients may then be mixed in water in a suspension mixer to produce a homogeneous slurry with good fluidity. For some formulations it is advisable to combine the slurry with aggregate within 1 hour of the slurry's production.

[0068] Liquid solution binder may be produced by the mixture of a suitable chemical compound with water. Compounds that may be combined with water to produce a liquid solution binder include aluminum hydrogen phosphate, aluminum dihydrogen phosphate, sodium silicate, potassium silicate, hydratable alumina in the form of an ultra-fine powder or nano alumina, or commercially available liquid solutions such as colloidal silica or colloidal alumina may be used.

[0069] Liquid binders such as resins, polymer glue, silicone glue or polyurethane glue may be used to form the composition of the present invention.

[0070] To form a refractory composition according to the invention, portions of aggregates and binders may be weighted out in the desired weight ratio. Binder is slowly added to the aggregates, and the combination of binder and aggregates is mixed in a mixer such as a cement mixer. After all of the binder is added to the aggregates, mixing may be continued for a period of time, such as 5 minutes, to ensure that all al the aggregates have a uniform binder coating.

[0071] The combination of binder and aggregates may then be used to form a refractory piece. The mixed aggregates and binder may then be placed into a mold, and the surface may be smoothed and settled by tamping or vibration. A subsequent layer or layers may be added to the mold in this manner. The mold is then covered with a plastic film and the mixture is allowed to harden or set. After setting is completed, the piece is demolded from the mold and the film is removed. The formed piece is allowed to undergo curing at temperatures, in the range of 15-30° C., for example. The piece may then be dried in an oven at a temperature of, for example, 110° C. for a period of time of, for example, 24 hours. The resulting piece may be used directly, or may be fired at a temperature of, for example, 1400-1600° C. for a period of time of, for example, 3 hours, which depends on the dimensions of the piece.

[0072] The present invention also relates to the use of the lining structure containing the refractory composition as previously described in a metallurgical vessel, and to a metallurgical vessel having an interior and an exterior, wherein the interior of the metallurgical vessel comprises a lining structure as previously described.

[0073] The present invention also relates to a process for the minimization of oxidation of a molten metal during transfer, comprising (a) transferring molten metal to a vessel having a lining structure as previously described, and (b) transferring the molten metal out of the vessel.

[0074] The present invention also relates to a process for forming a lining of a metallurgical vessel comprising the steps of (a) mixing a closed refractory aggregate fraction having a minimum particle size and a maximum particle size, wherein the ratio of maximum particle size to minimum particle size is 10:1 or less, with a binder phase comprising refractory binder selected from the group consisting of calcium aluminate cement, alumina phosphate, hydratable alumina, colloidal silica and combinations thereof, wherein the closed refractory aggregate fraction comprises 100 wt % of the material having a particle diameter greater than 0.1 mm, to form a castable refractory mixture, and (b) casting the castable refractory mixture in contact with the interior of the metallurgical vessel to form the lining. In embodiments of the invention, the castable refractory mixture is cast into a volume defined between a mould and the interior of the metallurgical vessel.

[0075] Other characteristics and advantages of the invention will become evident from the following detailed description and the implementation examples.

Example II

[0076] Various aggregate to binder ratios may be used in the inventive formulation.

[0077] In particular embodiments of the invention, aggregates used were tabular alumina T64 grains (supplied by Almatis, Inc.) with a closed particle size range between 12 mm and 6 mm. The slurry binder contained reactive alumina, silica fume, and calcium aluminate cement combined with water and additives such as dispersing agents. For a weight ratio of aggregate to slurry of 70/30 or less, excessive slurry binder was found to block the pores (the gaps between individual grains of aggregate) and, in some cases, a pool of slurry formed at the bottom of the piece. If the weight ratio is 85/15 or higher, all the pores are open. But if the weight ratio is 95/5 or higher, the binder strength is insufficient to bind the aggregates together. A weight ratio of 90/10 was found to provide open pores and adequate binder strength.

TABLE-US-00001 TABLE 1 Weight Percentages of Aggregates and Slurry Binders Slurry Formulation # Particle Size Aggregate binder Remark TAB-1 12-6 mm 70% 30% Blocked TAB-2 12-6 mm 80% 20% Partially blocked TAB-3 12-6 mm 85% 15% Open TAB-4 12-6 mm 90% 10% Open TAB-5 12-6 mm 95%  5% Open

Example III

[0078] Comparison of Aggregate Particle Size Ranges in the Formation of Refractories

[0079] Formulations with the same aggregate chemical composition (tabular alumina T64) but with various closed particle size distribution ranges were studies. The largest aggregate particle range used was a 20 mm to 6 mm fraction; the smallest aggregate particle range used was a 1.0 mm to 0.5 mm fraction. It was observed that satisfactory pieces could be contained for aggregate closed particle size distribution ranges if the particles were larger than 100 microns. The ratio of largest to smallest aggregate particles in the closed particle size distribution ranges may be from and including 10 to and including 1. Smaller differences in size between the largest particles and smallest particles in the closed particle size distribution range produce pieces with more gaps and pores. A ratio between 5 and 1, a ratio between 3 and 1, a ratio between 2.5 and 1.5, and a ratio of 2 have been found to produce satisfactory refractory. TAB-7a is an example of a formulation, having an overall particle size distribution range with a 4:1 ratio of largest particle size to lowest particle size, in which a single closed refractory aggregate composition is formed from two refractory aggregate compositions that have adjacent particle size distributions.

TABLE-US-00002 TABLE 2 Comparison of Refractory Material Formed from Aggregates of Various Sizes Slurry Formulation # Particle Size Aggregate binder Remark TAB-6 6-3 mm 90% 10% Open TAB-7 3-1.0 mm 90% 10% Open  TAB-7a 12-6 mm 45% 10% 6-3 mm 45% TAB-8 1.0-0.5 mm 90% 10% Open TAB-9 20-10 mm 90% 10% Open  TAB-10 20-6 mm 90% 10% Open

Example IV

[0080] Comparison of Aggregate Chemical Composition in the Formation of Refractories

[0081] Formulations with the same aggregate to slurry binder ratio, but with different aggregate chemical compositions, were tested. The aggregates included spinel AR 90 or AR 78, dead burned magnesite, fused magnesite, calcium hexaaluminate (CA6, as supplied by Almatis Ltd. under the brand name Bonite), white fused alumina, brown fused alumina, and bauxite. All were found to be capable of forming pieces with open pores.

TABLE-US-00003 TABLE 3 Comparison of Aggregate Chemical Compositions Slurry Formulation # Materials Aggregate binder Remark TAB-11 Spinel 6-3 mm 90% 10% Open TAB-12 Magnesite 6-3 mm 90% 10% Open TAB-13 Bonite 6-3 mm 90% 10% Open TAB-14 Fused alumina 6-3 mm 90% 10% Open TAB-15 Bauxite 6-3 mm 90% 10% Open TAB-16 Magnesite 6-3 mm 45% 10% Open Tabular alumina 6-3 mm 45%

Example V

[0082] Study of Aggregate Shape in the Formation of Refractories

[0083] The aggregates can take the form of spheres or angular grains. Pores in the resulting refractory will be open if an appropriate ratio of aggregate to slurry binder is used and the aggregates have a uniform slurry binder coating.

TABLE-US-00004 TABLE 4 Comparison of Aggregate Sizes and Shapes Slurry Formulation # Materials Aggregate binder Remark TAB-17 Alumina feed balls 20-10 mm 90% 10% Open TAB-18 Mullite balls 8-7 mm 90% 10% Open TAB-19 Mullite balls 3-2 mm 90% 10% Open TAB-20 Angular alumina 90% 10% Open

Example VI

[0084] Cementitious Binder Slurry

[0085] The binder slurry may be hydraulically bonded by refractory binder. The binder slurry can include the calcium aluminate cement Secar-71 (from Kerneos Aluminate Technologies), reactive alumina A-3000FL (from Almatis Ltd USA), silica fume 955U (from ELKEM AS Materials), and/or pulverized sodium polyphosphate glasses in the form of, for example, additive Budit 8H (from BASSTECH). Table 5 shows, with 90% of tabular alumina T64 of size 12 mm-6 mm, the different binder combinations that can be used to bind the aggregates together.

TABLE-US-00005 TABLE 5 Cementitious Binder Slurry Reactive Silica Formulation # Cement Alumina Fume Additives Water TAB-21 10% — — 0.1% 3.5% TAB-22  5% 5% — 0.1% 3.5% TAB-23  5% — 5% 0.1% 3.5% TAB-24  4% 3% 3% 0.1% 3.5% TAB-25  3% 4% 3% 0.1% 3.5% TAB-26  3% 4% 3% — 4.5%

Example VII

[0086] Solution or Polymer Binders

[0087] The binder slurry may also be in the form of chemical solution/liquid or polymer resin. Table 6 shows, with 96% of tabular alumina T64 of size 12 mm-6 mm, the different liquid chemical binder or polymer resins that can be used to bond the aggregates together.

TABLE-US-00006 TABLE 6 Solution or Polymer Binders Colloidal Hydratable Sodium Epoxy Formulation # silica Alumina Phosphate Silicate Resin TAB-27 4% — — — — TAB-28 — 4% — — — TAB 29 — — 4% — — TAB-30 — — — 4% — TAB-31 — — — — 4%

Example VIII

[0088] Complete Formulations

[0089] Table 7 provides some formulations. The first three formulations (TAB 32-TAB 34) use the same aggregates and binders but with different aggregate/binder ratios. The 5 formulations TAB 35 to TAB 39 use different aggregates but with the same slurry binders. The three formulations TAB-40 to TAB-42 use the same aggregates but with different slurry binders.

TABLE-US-00007 TABLE 7 Complete Formulations Formulation # Component TAB-32 TAB-33 TAB-34 TAB-35 TAB-36 TAB-37 Al.sub.2O.sub.3 85%  90%  95%  — — — 12-6 mm Al.sub.2O.sub.3 6-3 mm — — — 90%  — — Al.sub.2O.sub.3 3-1 mm — — — — 90%  — MgO 6-3 mm 85%  Cement 5% 3% 2% 3% 3% 5% Reactive 5% 4% 2% 4% 4% 5% Alumina Silica fume 5% 3% 1% 3% 3% 5% Additives 0.1%.sup.  0.1%.sup.  0.1%.sup.  0.1%.sup.  0.1%.sup.  0.1%.sup.  Water 3% 3% 3% 3% 3% 3% Formulation # Component TAB-38 TAB-39 TAB-40 TAB-41 TAB-42 Al.sub.2O.sub.3 12-6 mm — — 90% 90%  90%  Spinel 6-3 mm 85%  — — — — Bontite 6-3 mm — 85%  — — — Cement 5% 5% 10% 5% 5% Reactive Alumina 5% 5% — 5% — Silica fume 5% 5% — — 5% Additives 0.1%.sup.  0.1%.sup.  0.1%  0.1%.sup.  0.1%.sup.  Water 3.5%.sup.  3.5%.sup.   3% 3% 3%

[0090] Percentages in Table 7 are weight percentages with respect to the total weight of the solid components of the formulation.

[0091] A formulation of the present invention may be installed in the interior of a metallurgical vessel in the form of a precast panel, and fixed in place by cement or mechanical support. On-site installation of the formulation of the present invention may be carried out by placing a mold in a metallurgical vessel so that clearance between the interior wall of the metallurgical vessel and the exterior wall of the mold defines a volume to be occupied by the formulation. The formulation is then placed in this volume and settled. The formulation is allowed to harden or set. It may then be subjected to a curing process and a drying process.

[0092] Devices formed from the materials of the present invention contain a controllable porous structure and exhibit high temperature resistance. Therefore, various uses can be contemplated for them. The materials may be formed into pre-cast panels (pre-fabricated) or directly cast into molds to form specific shapes. Devices formed from these materials may be used as filtration devices, e.g., to remove inclusions from hot metal liquid, or impurities from any solutions or gases. The material may be used to form dams, weirs or baffles for use in refractory devices to filter molten metal. The materials may be used to form linings for high temperature metallurgical or foundry vessels, such as ladles, tundishes and crucibles. Devices formed from these materials may be used as deep bed filters for the liquid purification of aluminum or metal alloys. The materials of the invention may be infiltrated with metal to form brake pads. The materials of the invention may be used as gas or liquid diffusers.

[0093] Numerous modifications and variations of the present invention are possible. It is, therefore, to be understood that within the scope of the following claims, the invention may be practiced otherwise than as specifically described.