SE457794B - HYDRAULIC, ELFABLE CEMENT MATERIAL FOR MANUFACTURE OF CASTING COMPONENTS, COMPONENTS MANUFACTURED THEREOF, AND WAY TO MANUFACTURE THE COMPONENT - Google Patents

Description

457 794 According to the present invention, this refers to a hydraulic, refractory cement material for the production of cast, refractory components which are resistant to molten metals. The material contains a mixture of three components, namely 70-86% of a magnesium oxide component containing at least 94% Mg0, 5-15% of an alumina component containing at least 98% Al2O3 and 9-12% of a high alumina hydraulic cement containing at least 45% Al2O3, based on the total weight of the three components.

According to the invention, there is also meant cast, refractory components made of the above-mentioned materials and a method of producing such refractory components.

The mixtures according to the invention mainly consist of three components, namely magnesium oxide, alumina and hydraulic aluminate cement. Optionally, smaller amounts of other ingredients may be added for specific purposes, such as plasticizers, wetting agents and carbonaceous materials, such as tar I or pitch. The latter are commonly used in valve blocks and nozzles to prevent slag from adhering to these components.

To obtain the best results, the first two ingredients are of high purity. Thus, the magnesium oxide must have an MgO content of at least 94% by weight and the alumina component must have an Al2O3 content of at least 98% by weight. The alumina may be sintered, molten or preferably calcined.

The cement component should in principle be any cement with a high alumina content (Al2O3 content above 45% by weight based on the cement). Preferably, however, the aluminate cement component has an Al 2 O 3 content of at least 75% by weight based on the cement component. 7- 457 794 The mixture should be made from sorted particulate materials. The cement component should preferably have a particle size of 75 μm or less. Some cement particles may be larger but preferably at least 90% of the cement has a particle size of 75 μm or less.

The mixtures are suitably selected according to the following table: Particle size range Percent range Material Total Preferred Total Preferred range range range range Magnesium oxide (sintered or molten) 1 - 5 mm 1 - 3 mm 20 - 40 20 - 30 Magnesium oxide (sintered or molten) 0.3-1 mm 0.3-1 mm 15 - 35 20 - 30 Magnesium oxide (sintered or molten) <0.3 mm <0.3 mm 25 - 40 30 - 40 Aluminum oxide (sintered, molten or calcined) <0.3 mm <0.3 mm O - 20 0 - 5 Aluminum oxide (calcined, molten or sintered but preferably calcined) <45 μm <45 μm 1 - 20 5 - 10 Hydraulic cement min. 90% min. 90% 4 - 15 9 - 12 with Al 2 O 3 content above 75% <75 μm <75 μm The materials are mixed with water in sufficient quantity to obtain a workable mass. This may, for example, contain 7% water based on the weight of the mixture. The mixture is self-binding at room temperature. Heating is not necessary, but moderate heating may be allowed to accelerate the hardening of the cast components. Without heating, however, the hardening lasts for an hour or so, so that the components can be removed from the molds. This ensures high productivity. The hydraulically binding mixtures according to the invention have significant advantages over chemically bound systems. A constant problem with chemically bonded systems is that the binder tends to migrate to exposed surfaces during heat curing and drying. This migration which causes non-uniformity in the material does not occur in the mixtures according to the present invention. In addition, there is no risk of shrinkage cracking during solidification. It is not impossible with chemically bonded components to adversely affect them during processing.

The mixtures according to the invention have surprisingly good resistance to thermal shock. They can therefore be used as parts of slide hatch valves and associated casting nozzles, which are used in intermittent casting of molten metals.

A commonly applied test for resistance to thermal shock is the burner test developed in the research laboratories of the United States Steel Corporation. In this test, an oxygen-propane flame is passed slowly (1.7 m / second) across the refractory material to be tested. The burner is kept 6.4 mm from the surface of the refractory material.

Conventionally pressed and fired magnesium valve blocks can usually not withstand such a passage of the oxygen-propane flame without significant damage to the surface and inside the material. Known chemically bonded magnesium oxide valve blocks resist the flame better, but samples have shown moderate degradation after a single pass.

In contrast, valve blocks made of the materials according to the invention have been found to be able to withstand repeated passages, for example twelve, without any significant deterioration of the surface. This means that they can bear temperature variations that occur during repeated valve throttling and valve opening and closing show a marked improvement in comparison with burnt or chemically bonded blocks.

As pointed out above, the mixtures according to the invention can be used for casting valve blocks for slide hatch valves and nozzles, such as collectors 40 s 457 794 and associated extended casting tubes. Pouring wells and distribution nozzles can also be made of the materials and other uses are obvious to those skilled in the art.

Components cast from the mixtures according to the invention are normally provided in a hydraulically bonded state. Nevertheless, it may sometimes be desirable to provide the molded articles in a burnt state rather than having them burned during use. Combustion can be applied, for example, to such articles as replaceable wear and erosion-resistant sleeves or lining for discharge nozzles.

Example gel A mixture was prepared from the following ingredients. The percentages are again weight percent calculated on the total weight of magnesium oxide, alumina and cement.

Magnesium oxide, particle size 1 - 3 mm 26% Magnesium oxide, particle size 0.3-1 mm 25% Magnesium oxide, particle size less than or equal to 0.3 mm 34% Calcined alumina, particle size less than or equal to 75 μm 6% Cement with high alumina content 9% The cement had an Al2O3 content greater than 75% by weight of the cement and at least 90% by weight of the cement had a particle size of less than 75 μm.

The magnesium oxide and the alumina had a MgO content of 94 and Al2O3 content of 98% by weight, respectively.

A workable liquid concrete suitable for casting was obtained by mixing the water in an amount of 7% of its weight. The mold filling can be facilitated by vibration, for example with 3000 Hz.

Vibration cast concrete samples prepared according to the above were found after curing and drying to have the following properties at the specified temperatures. ü !! 457 794 40 Property Medium density, g / cma Apparent porosity% Permanent linear change, dry to burnt,% Compressive strength in cold condition psi MN / m2 Kp / cmz Passed the flame test, 1 cycle Passed the flame test, 12 cycles 6 Burning temperature OC 11 1000 1500 1700 2.83 2.78 2.85 16.0 19.3 17.0 +0.01 -1.24 -3.44 7000 7350 12350 48.3 50.8 85.2 492 517 868 yes yes yes yes The above properties are considered to be fully suitable for materials for the manufacture of components in slide shutter valves and they can, if desired, be provided in a burnt state afterwards.

Claims (6)

~, L r 457 794 PATENT REQUIREMENTS Hydraulic, refractory cementitious material for the production of molten, refractory metal components, characterized in that it consists of: 70 to 86% of a magnesium oxide component containing at least 94% of MgO; 5 - 15% of an alumina component containing at least 98% Al O; 2 3 9 - 12% of a hydraulic cement with a high alumina content containing at least 45% Al2O3. Material according to claim 1, characterized in that 20 - 40% by weight of the total weight of the three constituents consists of magnesium oxide with a particle size of 1 - 5 mm, that 15 - 35% by weight of the total weight of the three constituents consists of magnesium oxide with a particle size of 0.3 - 1 mm and that 25 - 40% by weight of the total weight of the three components consists of magnesium oxide with a particle size of 0.3 mm or less. Material according to Claim 1 or 2, characterized in that 0 to 20% by weight of the total weight of the three constituents consists of alumina with one particle; size of 0.3 mm or less and that 1 to 20% by weight of the total weight of the three constituents consists of alumina with a particle size of 45 mm or less. Material according to any one of claims 1 to 3, characterized in that 26% of the total weight of the 45 test components 457 794 consists of magnesium oxide with a particle size of 1-3 mm, 25% of the total of the three components. weight consists of magnesium oxide with a particle size of 0.3 - 1 mm and that 34% of the total weight of the three components consists of magnesium oxide with a particle size of less than 0.3 mm; that 6% of the total weight of the three components is calcined alumina with a particle size of less than 45 μm and that 9% of the total weight of the three components is hydraulic aluminate cement, of which 90% has a particle size of less than 75 μm. 5. Cast, refractory component made from a hydraulic, refractory cement material consisting of: 70 - 86% of a magnesium oxide component containing at least, 94 æ Mgo; 5 - 15% of an alumina component containing at least 98% Al O; 2 3 9 - 12% of a hydraulic cement with a high alumina content containing at least 45% A120 I characterized by a compressive strength in the cold state after firing at 110, 1000 and 1500 C of 492, 517 and 868 kp / cm2 and a average density after being exposed to the effects of said temperatures amounting to 2.83, 2.78 and 2.85 g / cm, respectively. Å 'z 6. A method of producing a refractory component intended to be exposed to abrasion or erosion of molten metal, characterized in that the component of hydraulic concrete produced by adding water to a hydraulic, refractory cement material consisting of: 457 794 f? 70-86% of a magnesium oxide component containing at least 94% MgO; 5 - 15% of an alumina component containing at least 98% Al O; 2 3 9 - 12% of a hydraulic cement with a high alumina content containing at least 45% Al2O3, after which the cast component is hardened and allowed to dry. , a I