LU84121A1 - BASIC REFRACTORY CEMENT MATERIAL, REFRACTORY PARTS OBTAINED BY ITS CAST, AND THEIR MANUFACTURING METHOD - Google Patents

Description

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The present invention relates to a mixture or a basic refractory cement material, and its constituents.

The invention further relates to a process for producing cementitious components exposed to chemical attack} to wear and erosion by molten metals} such as steel.

The refractory components of valves and the refractory nozzles intended for various purposes in the art of metal casting are conventionally produced by compression and Λ curing at high temperatures. Expensively, it has been found that high purity materials, such as zirconium oxide and refractories based on 85-95% A ^ O ^, are necessary due to the extremely harsh service conditions to which the constituents are subject. The energy consumed to produce components by compression and baking is important, since temperatures which normally exceed 1500 ° C must be created and maintained during the baking process. The energy expenditure contributes significantly to the unit cost prices of the constituents made from such cooked refractory materials.

Despite the use of highly baked refractory materials in the art of metal casting, it is common to frequently replace, such as valve plates, at great expense.

Recently, chemically bonded concretes have been proposed, for example for making valve plates with a health-grout door. Like baked refractory plates, it is unlikely that chemically bonded concrete plates will withstand repeated shocks. Also, it is expected that their use in valves for the casting of ingots will be accompanied by unattractive stops with a view to their replacement.

It has just been found that certain basic cementitious materials with hydraulic bonding surprisingly have the power to withstand thermal shocks extremely well, and that the production of constituents or elements from these materials is particularly easy.

According to the present invention, the latter provides a hydraulic refractory cement formulation for manufacturing ti a 2 refractory cast pieces which resist molten metals, the formulation comprising a mixture of three constituents, namely molten or sintered magnesia, alumina and hydraulic cement with a high alumina content, containing at least 45% of A1 "0", at D '5 the magnesia being present in a proportion of at least 607o of the total weight of the three constituents and the alumina being present in a proportion representing at least 17% of the total weight of the three constituents.

The invention also provides cast refractory parts obtained from the formulation, and a method for manufacturing such cast refractory parts.

The formulations according to the invention essentially comprise three constituents, namely magnesia, alumina and aluminous hydraulic cement. Optionally, minor amounts of other components can be added for specific purposes, such as plasticizing compositions, wetting agents and carbon-containing materials, such as tar or pitch. The latter are commonly used in valve plates and nozzles to prevent slag from sticking to it.

The first two components preferably have a high purity, in order to obtain the best results. Thus, magnesia must have an MgO content of at least 94% by weight, and alumina must have an AlgO ^ content of at least 98% by weight. The alumina can be sintered, melted or preferably cal-25 cinée,

The cement can, in principle, be any cement with a high alumina content (Al ^ O ^ content greater than 45% of the weight of the cement). Preferably, however, the aluminous cement has an A ^ O ^ content of not less than 75% by weight of this cement.

Magnesia can be present in a proportion representing 60 to 95% of the total weight of the three constituents. On the same basis, the alumina is present in a proportion of at least 1%, for example between 1 and 36%, and the cement content is between 4 and 15%.

Preferred ranges are 70 to 86% for magnesia, 5 to 15% for alumina and 9 to 12% for cement.

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The formulation should be prepared from classified or screened particulate matter. The cement should preferably have a particle size equal to or less than 75 microns. It can be tolerated that certain cement particles are larger, but preferably at least 90% of the cement has a particle size equal to or less than 75 microns.

It is advisable to choose the formulation taking into account the data appearing in the following table: • Μ-t · è Range of dimensions Range of percentages - aire Preferred Overall Preferred Overall

Magnesia (sintered -5mm + lmm -3mm + lmm 20-40 20-30 or melted)

Magnesia (sintered -lmm + 0.3mm -lmm + 0.3mm 15-35 20-30 or melted) 15 Magnesia (sintered <0.3mm <, 0.3mm 25-40 30-40 or melted)

Alumina (sintered, <0.3 mm <0.3mm 0-20 0-5 melted or calcined)

Alumina (calcined, <45 microns <45 microns 1-20 5-10 20 melted or sintered, but preferably calcined)

Minimum hydraulic cement minimum 4-15 9-12 with 90% to 90% 25 Al ^ O ^ content greater than <75 microns <75 microns greater than 75%

The formulations are mixed with water in an amount sufficient to obtain a workable mixture.

Such a mixture can, for example, contain 7% water, based on the weight of the mixture. The mixture sets on its own at room temperature. The application of heating is not necessary, although moderate heating, intended to accelerate the hardening maturation of the cast elements, is tolerable. However, it is possible to obtain, without heating, in approximately 1 hour, a hardening maturation leading to a state allowing demoulding. Thus, high productivity can be achieved.

The present hydraulic bond formulations have significant advantages over chemically bonded * 4 systems. A problem still present in the case of chemically bonded systems is that, during their setting and drying under the influence of heat, the binder tends to migrate towards the exposed surfaces. Migration of the binder and non-uniformity of the resulting castings does not occur in the case of the formulations of the invention. In addition, a grip is obtained giving a rigid material, so that there is no risk of causing blowing or defects, due to internal stresses, during the handling of the castings. Now, it is not impossible to cause, on chemically bonded castings, harmful effects during handling operations.

The present formulations surprisingly have excellent resistance to thermal shock. They are therefore expected to be used in sliding door valve elements and associated pouring nozzles used in the intermittent casting of molten metals.

A commonly used test for resistance to thermal shock is the torch test developed by the research laboratories of United States Steel Corporation. In this test, the flame of an oxygen-propane torch is slowly passed over the speed of 1.7 mm / s over the refractory material tested, the torch being kept at 6.4 mm from the surface of the refractory piece.

Conventional valve plates of compressed and baked or calcined magnesia usually cannot withstand just one passage of the oxygen-propane flame without suffering irradiating damage at the surface and inside. Known chemically bound magnesia valve plates may be more resistant to flame, but tests have shown moderate degradation following passage.

On the contrary, valve plates made from the present formulations have been found capable of withstanding repeated passages, for example twelve, without undergoing significant surface degradation. This implies their ability to withstand the temperature variations encountered during repeated valve closings, and valve open / close operations will show a marked improvement over calcined or chemically bonded plates.

As indicated above, the present formulations can be used for casting valve plates for sliding door valves, as well as for constituting nozzles such as manifolds and the associated pouring tubes. Ladles and dispensing nozzles can also be produced from the formulations, and other applications will appear to experts.

, 10 Objects obtained by casting from these formulations will usually be supplied in the hydraulically hardened state. However, it may sometimes be desirable to provide the objects cast in the precalcined state, rather than letting them cook and calcine in service. The precooking or precalcination can be applied for example to the case of objects such as replaceable sleeves or liners, which can well resist wear and erosion, for outlet or distribution nozzles.

EXAMPLE

The formulation of this example includes the following pro-portions. The percentages indicated are, once again, by weight relative to the total weight of magnesia, alumina and cement.

Magnesia, dimension between -3 and +1 mm 26¾

Magnesia, dimension between -1 and +0.3 mm 25% 25 Magnesia, dimension less than or equal to 0.3 mm 34%

Calcined alumina, dimension less than or equal to 75 microns 6%

High alumina cement 9%

The cement has an Al ^ O ^ content greater than 75% of the weight of the cement, and at least 90% of the weight of this cement corresponds to a particle size of less than 75 microns. Magnesia and alumina have respective MgO and Al ^ O ^ contents of 94% and 98% by weight of these constituents.

The formulation gives a concrete which can be worked 22 and of adequate fluidity for casting, when it is mixed with a proportion of water representing 7% of its weight. The filling of the mold can be facilitated by a vibration, an example of a vibration frequency 6 being 3000 Hz.

Concrete specimens vibrated and prepared as above have, after setting and drying, the following properties at the temperatures indicated.

5 Properties _Cooking temperature (° C) _110 1000 I 1500 1700. Bulk density (g / cm3) 2.83 2.78 2.85. Apparent porosity (%) 16.0 19.3 17.0

Percentage of permanent linear variation (dry to cooked state) +0.01 -1.24 -3.44 Resistance to cold compression 15 MNm "2 48.3 50.8 85.2 (i.e. kg.cm 2) 492 517,868

Flame test; 1 successful cycle successful

Flame test; 20 12 cycles successful successful

The above properties are considered to be entirely suitable for the production of sliding door valve components which, if desired, can be supplied in the form of parts which have subsequently undergone calcination firing.

Claims (9)

1. Hydraulic refractory cementitious formulation intended for the manufacture of cast refractory parts capable of resisting molten metals, characterized in that it comprises a mixture of three constituents, namely molten or sintered magnesia, alumina and hydraulic cement with high * alumina content, containing at least 45% of Al ^ O ^, magnesia being present in a proportion of at least 60% of the total weight of the three constituents and alumina being present in a proportion 10 of at least 1% of the total weight of the three constituents. 2. Formulation according to claim 1, characterized in that the magnesia is present in a proportion of 60 to 95% and the cement is present in a proportion of 4 to 15%, 3. Formulation according to either of Claims 1 and 2, characterized in that the magnesia has an MgO content of at least 94% by weight of the magnesia, 4. Formulation according to any one of claims 1 to 3, characterized in that the alumina has an A120 ^ content at least equal to 98% of the weight of this alumina. 20 5 - Formulation according to any one of claims 1 to 4, characterized in that 20 to 40% of the total weight of the three constituents are formed by magnesia whose particle size is between -5 mm and -1 mm, 15 at 35%, on the same basis, “are made of magnesia whose particle size is between 25 mm and 40.3 mm, 25 to 40%, on the same basis, are made of magnesia whose particles have a maximum of 0.3 mm. 6. Formulation according to any one of claims 1 to 5, characterized in that 0 to 20% of the total weight of the three constituents correspond to alumina whose particle size-30 is less than or equal to 0.3 mm and 1 to 20%, on the same basis, correspond to alumina whose particle size is equal to or less than 45 microns, 7. Formulation according to any one of claims 1 to 6, characterized in that, on the basis of the weight percentages based on the total weight of the three constituents, it has 8 comprises 26% of magnesia whose particle size is between -3 and +1 mm, 25% of magnesia whose particle size is between -1 and +0.3 mm and 34% of magnesia whose particle size is not less than 0.3 mm; 6% consist of calcined alumina 5 whose particle size is not less than 45 microns and 9% consist of aluminous hydraulic cement of which 90% of the particles are not less than 75 microns. 7. CLAIMS 8. refractory casting, produced from the formulation according to any one of the preceding claims 10 and characterized in that it has resistance to cold crushing, after having been subjected to temperatures of 110 °, 1000 ° and 1500 ° C, 48.3; 50.8 and 85.2 MNm respectively, and an apparent density, after having been subjected to these 3 temperatures, of 2.83; 2.78 and 2.85 g / cm. 15 9 - Process for manufacturing a refractory piece intended to be exposed to wear or erosion caused by molten metal, process characterized in that the piece is vibrated in a mold, from hydraulic concrete prepared by adding water to the formulation according to any one of the claims 20 to 1, the casting is hardened and allowed to dry. Λ