HU186497B - Basic refractory cement preperation for producing refractory casting parts resisting molten metals - Google Patents

Abstract

A cementitious formulation which is self-setting when mixed with water, and which can be cast into monolithic refractory components capable of resisting molten metal and repeated thermal shocks, has three main components: 60-95% of high purity magnesia (at least 94% by weight being MgO); at least 1% of high purity alumina (at least 98% by weight Al2O3) and 4-15% of high alumna cement (preferably 75% Al2O3 by weight, or greater).

Description

(57) Extracts

The present invention relates to a cementitious composition which, after mixing with water, self-cures and can be molded into homogeneous refractory workpieces capable of withstanding the effects of molten metal and repeated heat shock. The preparation has three main components: high purity magnesium oxide (containing at least 94% by weight of MgO); high purity alumina (containing at least 98% by weight of VlaOa; and having a high alumina content (preferably containing 75% or more by weight of AljOj). and at least 1% by weight of the total weight of the three components The castings of the composition are capable of withstanding the flame test, even when exposed to high temperatures.

The present invention relates to the manufacture of basic refractory cement materials and components thereof which are subject to chemical influences, abrasion and erosion by molten metals such as molten steel.

In the metal casting technique, as is known in the art, the refractory parts of the closures and the refractory pipe endings for various purposes are produced by conventional extrusion and firing at high temperatures. It is believed that this requires expensive high purity materials such as high purity zirconia and 85-95% AlaO3 based refractory due to extremely difficult working conditions of the parts. The production of parts by compression and firing requires considerable energy, as the firing temperatures normally exceed 1500 ° C and must be maintained throughout the firing process. The cost of energy contributes significantly to the cost of components of this type made from refractory materials.

Although strong combustible refractory materials are used in metal casting techniques, coatings on some fixtures, such as closures, require frequent replacement and are also costly.

Recently, the use of chemically bonded cements, such as for coating sliding gates, has been proposed. Like burnt refractory coatings, chemically bonded cementitious coatings are unlikely to withstand repeated, shock-induced heat inputs (so-called heat shocks). It is therefore to be expected that movable valves for casting movables will experience breakdowns as they require replacement.

It has now been found that certain hydraulically bonded basic refractory cement materials are surprisingly highly resistant to heat shock, and that these materials are particularly easy to fabricate.

The present invention provides a hydraulic, refractory cement composition for the production of refractory casting parts resistant to molten metals. The composition consists of three components: bulk or tinted magnesium oxide, alumina and alumina-rich hydraulic cement containing at least 45% Al10Aa. The magnesium oxide is present in the mixture in an amount of at least 1% by weight and aluminum oxide at least 1% by weight based on the total weight of the three components.

The invention also relates to refractory casting parts made from the composition and to a method for making such refractory casting parts.

The compositions of the present invention consist essentially of three components: raagne16, alumina, and hydraulic cement containing alumina. Optionally, other materials may be added in small amounts for special purposes, such as plasticizers, wetting agents and carbonaceous materials such as tar or pitch. The latter is commonly used for valve coatings and gate valves, and the tip prevents the formation of molds which adhere to these structural parts.

The first two ingredients should preferably be of high purity for best results. Thus, the MgO content of the Magnesium Magnesium Oxide Component is at least

14 8To be% and the alumina component shall contain at least 98% by weight of Al2O3 +. The alumina may be colored, bulk, preferably halogenated.

In principle, the Cement Component can be any high alumina cement (with an AljOs content greater than 45% by weight of the cement). Preferably, however, the AliCb content of the aluminyl oxide: 3 cement component is not less than 75% by weight of the cement amount.

Magnesium oxide aggregates can represent 60-95% by weight of the three ingredients. On the same percentage basis, the alumina component is present in at least 1%, such as 1-36% in the cement component in 4-15%.

A preferred range for magnesium oxide is 70-86% by weight, for aluminum oxide

5 to 15% by weight and cement to 9 to 12% by weight.

The preparation must be prepared from materials consisting of classified particles. Preferred particle size of the cement component is 75 microns or less. It is permissible for some of the cement particles to be larger in size, but it is preferred that at least 90% of the cement particles have a particle size of 75 microns or less.

It is desirable to formulate the compositions on the basis of the following table:

Material Particle size differences Percent gold complete advantageous tsljee advantageous province province stubble- lurto- inány Statute Magnesium oxide (bulk or in bulk) -5mm +1mm -3mm +1mm 20-40 20-30 Magnesium oxide (almost (bulk or in bulk) -1 mm +0.3 mm -1 mm +0.3 mm 15-35 20-30 Magnesium oxide (almost (bulk or in bulk) <0.3 mm <0.3 mm 25-40 30-40

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Material Differences in particle size Percentage complete province advantageous province complete holder- Statute advantageous holder- Statute Aluminum oxide (sintered, in bulk or calcined) <0.3 mm <0.3 mm 0-20 0-5 Alumina (calcined, bulk or sintered, but preferably calcined) <45 microns <45 microns 1-20 5-10 Hydraulic cement > 75% Al> 0 $ min. 90% min. 90% 4-15 9-12 content <75 microns <75 microns

The formulations are mixed with water, which is added in an amount sufficient to obtain a workable mixture. Such a mixture may contain, for example, 7% water by weight of the mixture. The mixture self-cures at room temperature. Heating is unnecessary, although moderate heating of molds is permitted to accelerate setting. However, even without heating, a bonding state can be achieved within one hour that allows the mold to be removed. Thus, very high productivity can be achieved.

Hydraulic-bonded compositions of the present invention have significant advantages over chemically bonded systems. For chemically bonded systems, the question always arises that, as the curing and drying process occurs, the binder tends to migrate to the exposed surfaces. However, this migration of material and the resulting inhomogeneity that endangers the integrity of castings do not occur with the compositions of the invention. Moreover, solid bonding occurs, so that the treatment of castings does not involve the risk of cracks due to internal stresses. In the case of chemically bonded castings, it is not excluded that adverse effects may occur during treatment.

The compositions of the present invention have surprisingly excellent resistance to heat. As a result, it is expected to be used in the structural parts of sliding gate valves, especially for casting endings used for batch drainage of molten metals.

A commonly used test of resistance to heroes is the welding flame test, which has been recognized at the research sites of the United States Steel Corporation and Research Laboratories. During this test, the oxygen-propane welding flame is slowly passed through the surface of the refractory material at a rate of 1.7 mm / sec, keeping the flame 6.4 mm away from the refractory surface.

Conventionally pressed and burned magnesium oxide valve coatings will undergo only one oxygen-propane flame retardant without significant surface and internal damage. The prior art chemically bonded magnesium oxide valve coatings are more flame-retardant, but tests have shown that after a transition, a slight deterioration occurs.

In contrast, valve coatings made from the compositions of the present invention have been found to be capable of withstanding multiple flame impingement up to 12 times without significant surface degradation. This also means that they are able to withstand temperature fluctuations caused by repeated displacement of the valve; show significant improvements in valve opening and closing operations compared to burnt or chemically bonded coatings.

As mentioned above, the compositions of the present invention can be used for casting valve coatings for sliding gate valves as well as for pipe endings such as those found in, for example, collection tanks and associated spouts. The formulations can be used to make molds and their metering tubes, and other applications can be envisaged.

Molded articles from the compositions of the present invention may be delivered in a hydraulically bound state. In some cases, it may be desirable to burn castings rather than burn them during work. For example, preheating can be applied to articles such as coatings for removable, abrasion and erosion-resistant liners or drainpipes.

Example

The proportions of the composition are shown below. Percentages represent the percentage by weight of the total weight of the magnesium oxide, aluminum oxide and cement components (components, components).

18G497

Magnesium oxide, particle size differences from -3 mm to +1 mm 26%

Magnesium oxide, particle size differences from -1 to +0.3 mm 25%

Magnesium oxide, particle size 0.3 mm or less 34%

Calcined alumina, particle size 75 microns or less 6%

Aluminum oxide-rich cement 9%

The cement has an AlaOa content greater than 1θ of 75% by weight of cement, and a particle size of less than 75 microns in at least 90% by weight of cement. The MgO content of the magnesium oxide is 94% by weight and the AljOs content of the alumina is 98% by weight based on the weight of these components.

When the above composition is mixed with 7% water in a Clogged manner, a workable and sufficiently flowing mixture is obtained for casting. During formatting, loading can be facilitated by vibratory motion, for example, at a frequency of 3000 Hz.

The casting patterns prepared as described above, after setting and drying at the specified temperatures, have the following properties:

Properties t Curing temperature ° C 110 1000 1500 1700 Volumetric weight in g / ml 2.83 2.78 2.85 Apparent Porosity% Permanent linear change from dry state to burn- 16.0 19.3 17.0 to Latvian status,% Cold fracture toughness +0.01 -1.24 -3.44 p.B.l. 7000 7350 12350 MNM ' ³ 48.3 50.8 85.2 Kp.cnr ³ Flame test, 1 cycle Flame test, 12 cycles 492 pass over pass over 517 868 pass over pass over

The properties shown in the table are suitable for making sliding valve parts of the composition, which can be transported in the following state if desired.

Claims (8)

Claims 40 CLAIMS 1. A hydraulic refractory cement composition for the production of refractory castings resistant to molten metals, characterized in that the composition consists of a mixture of three components, which are bulk or colored magnesium oxide, alumina and alumina-rich hydraulic cement containing at least 45% AljOa - and magnesium oxide 50 at least three times the total weight of the three components It is 60% of the total weight, and the alumina component is at least 1% of the total weight of the three components. Composition 55 according to claim 1, characterized in that it contains 60 to 95% by weight of magnesium oxide and 4 to 15% by weight of cement. Composition according to claim 1 or claim 2, characterized in that the magnesium oxide 60 contains at least 94% by weight of pure MgO. 4. A composition according to any one of claims 1 to 4, wherein the alumina contains at least 98% by weight of pure AlaOa. 5. Composition according to any one of claims 1 to 3, characterized in that at least 20-40% by weight of the total weight of the mixture is magnesium oxide having a particle size difference between -5 mm and +1 mm, 15-35% by weight in the same ratio -1 mm and + 0.3 mm and 25-40% by weight of your magnesium having a copper ore content of 0.3 mm or less. 6. I.-5. A composition according to any one of claims 1 to 4, wherein 0 to 20% by weight of the total weight of the blend is alumina having a particle size of 0.3 mm or less and 1 to 20% by weight of alumina having a particle size BOP of 45 microns or less. 7. A composition according to any one of claims 1 to 6, characterized in that 26% by weight, based on the total weight of the mixture, comprises magnesium oxide having a particle size between -3 mm and +1 mm and 25% magnesium oxide having a particle size between -1 mm and +0, It is between 3 mm and 34% of magnesium oxide with a particle size of less than 0.3 mm, 6% of calcined alumina with a particle size of less than 45 microns and 9% of hydraulic alumina cement of which 90% has a particle size of less than 75 microns. 8. Any one of claims -4; 86497