FI71718C - HYDRAULIC ELDFAST CEMENTBLANDNING, ELDFAST DEL OCH FOERFARANDE FOER DESS FRAMSTAELLNING. - Google Patents

Description

1 71718

The present invention relates to a hydraulic refractory cement mixture.

The invention further relates to a process for the preparation of cement mixtures which are exposed to chemical action, wear and corrosion by molten metals such as steel.

10 The refractory parts of valves and the refractory nozzles used in metal casting are usually made by pressing and firing at high temperatures. Expensive, high-purity materials such as zirconia and 85-95% Al 2 O 3 -based refractories have been considered necessary given the extremely stringent conditions of use of these parts. When manufacturing parts, pressing and firing consume a lot of energy, as a combustion temperature of more than 1500 ° C must normally be reached throughout the combustion process. Energy consumption significantly increases the unit cost of parts made from such fired refractory materials.

Despite the use of strong, burnt, refractory materials, for example, the valve plate often has to be replaced at great cost.

Recently, chemically bound hetons have been presented, for example, as slide valve plates. Like fired refractory slabs, chemically bonded concrete slabs are unlikely to withstand repeated sudden temperature fluctuations.

Thus, when such plates are used in valves when casting ingots, they have to be changed frequently, which causes inconvenient downtime. It has now been found that certain hydraulically bound basic cementitious materials are surprisingly able to withstand sudden changes in temperature very well and the manufacture of parts from these materials is particularly straightforward.

2,71718 SE 429 959 discloses a dense, refractory concrete mixture consisting of 5-8 parts by weight of at least one aluminate cement, 2.5-4 parts by weight of at least one of clay, kaolin, bentonite and alumina, 0.01 -0.30 parts by weight of alkali metal phosphate or alkali metal polyphosphate and 86-92 parts by weight of base material.

According to the present invention, a hydraulic refractory three-component cement mixture has been developed containing 10 aluminum cements and alumina for the production of cast refractory bodies. The cement mixture according to the invention is characterized in that it consists essentially of 70-86% of a magnesium oxide component containing at least 94% MgO, 5-15% of an alumina component containing at least 98% Al 2 O 3 and 9-15% an aluminum-cement component containing at least 45% Al 2 O 3>

The invention also relates to cast refractory parts made from said mixture and to a method of manufacturing such refractory parts.

The compositions of the invention comprise essentially three components, but small amounts of other components may be added if desired for specific purposes, such as plasticizers, wetting agents and carbonaceous materials such as tar or pitch. The latter are commonly used in valve plates and nozzles to prevent slag from adhering to these parts.

The first two components should be very pure for best results. The alumina can be sintered, melted or preferably calcined.

30 The cement component could in principle be any cement with a high alumina content. That mixture should be made from sorted granular materials. The particle size of the aluminum cement component should preferably not exceed 75 pn. Some of the cement particles may be even larger, but preferably at least 90% of the cement particles have a particle size of less than 75.

3,71718

The components of the mixture should preferably be selected according to the following table:

Substance Size class% class

Size range Best Size range Best 5 Magnesium oxide -5 mm + -3 mm + 20-40 20-30 (sintered or 1 mm 1 mm fused)

Magnesium oxide -1 mm + -1 mm + 15-35 20-30 (sintered or 0.3 mm 0.3 mm fused)

Magnesium oxide <0.3 mm <0.3 mm 25-40 30-40 (sintered or fused)

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

Alumina <45 ^ m <45 pn 1-20 5-10 15 (calcined, fused or sintered, but preferably calcined)

Hydraulic cement- Min. 90% Min. 90% 4-15 9-12 ti with an Al 2 O - <75 ^ <75 „m concentration over 75% '' 20

The mixture material is mixed with water to form a suitably workable mixture. Such a mixture may contain e.g. 7% water by weight of the mixture. The mixture is self-curing at room temperature. Heating is unnecessary, but can be heated to speed to dry the castings. Thus, good productivity can be achieved.

These hydraulically bound materials have significant advantages over chemically bonded systems. The only problem with chemically bonded compounds is the tendency of the binder to migrate to open surfaces when drying and heat-binding are in progress. The compositions of this invention do not undergo binder migration and subsequent deterioration of the integrity of the molded article. Rigid bonding takes place, which has the effect that there is no risk of internal stresses and thus no cracks are formed when handling cast parts.

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It is not impossible to adversely affect chemically bonded castings during processing.

The compositions presented here have surprisingly good resistance to sudden temperature fluctuations. They are therefore expected to have use in spool valve parts and casting orifices used in casting molten metal from a bucket to a die.

A commonly used test to measure the resistance to sudden changes in temperature is the burner test developed by the research laboratories of the United States Steel Corporation. In this test, the oxygen propane flame is passed over the refractory body under test at a speed of 1,7 mm / s and the burner is kept at a distance of 6,4 mm from the surface of the body under test.

15 Conventional compressed and fired magnesia valve plates usually do not withstand even one oxygen-propane flame crossing without significant surface and internal damage. Known chemically bonded magnesia valve plates are more resistant to flame, but tests have shown moderate deterioration after one exceedance.

Valve sheets made from the present cement mix have been found to withstand multiple test runs, e.g., 12, without significant surface shrinkage. This shows that they withstand the temperature fluctuations that occur during repeated valve throttling and valve open / close operations significantly better than burned or chemically bonded sheets.

As discussed above, the present compositions can be used to cast slide valve plates and nozzles, such as manifolds and associated expanded casting tubes. Ladle gutters and manifolds can also be made from the present compositions and other uses will be apparent.

The castings of the present alloys are usually supplied in a hydraulically bound state. Sometimes, however, it is advisable to pre-burn the cast 5,71718 pieces rather than letting them burn in use. Pre-firing can be suitable, for example, for parts such as replaceable, wear- and erosion-resistant sleeves or the inner walls of downcomers.

5 Example This mixture has the following ratios. The percentages given are calculated for the total weight of the magnesium oxide, alumina and Semen component.

Magnesium oxide, particle size -3 to +1 mm 26% 10 Magnesium oxide, particle size -1 to +0.3 mm 25%

Magnesium oxide, particle size 0.33 or less 34%

Calcined alumina, particle size 75 pm or less 6%

Cement with high alumina content 9%

The alumina content of the cement is more than 75% by weight of Semen-15 and at least 90% by weight of the cement had a particle size of less than 75. For magnesium oxide and alumina, the MgO and Al 2 O 2 contents were 94 and 98% by weight of these components, respectively.

The mixture became workable and suitably flowable concrete 20 to be cast when water was added at 7% by weight. Mold filling can be aided by vibration and a good vibration frequency is 3,000 Hz.

After curing and drying, the vibration-cast bodies, as described above, had the following properties at 25 temperatures:

Feature Burning temperature ° C

110 1,000 1,500 1,700

Bulk density g / cm ^ 2.83 2.78 2.85 Apparent porosity% 16.0 19.3 17.0 30 Permanent linear change between dried and calcined space% +0.01 -1.24 -3.44

Cold crushing strength MNm "2 48.3 50.8 85.2 35 Kp / cm" 2 492 517 868 6 71718

Feature Burning temperature ° C

110 1,000 1,500 1,700

Flame test, 1 round passed passed

Flame test, 12 turns passed 5 The above properties are perfectly suitable for the manufacture of slider chamber valve parts which can be subsequently burned if desired.

Claims (5)

71718 A hydraulic, refractory three-component cement mixture containing aluminum cement and alumina for the production of cast refractory bodies resistant to molten metals, characterized in that it consists essentially of 70-86% of a magnesium oxide component containing at least 94 % MgO, 5-15% alumina component containing at least 98% Al 2 O 3 3 9 9% aluminum cement component containing at least 45% Al 2 O.j. Cement mixture according to Claim 1, characterized in that 20-40% of the total weight of the mixture is a magnesium oxide component with a particle size of 1-5 mm, 15-35% of the total weight of the mixture is a magnesium oxide component with a particle size of 0.3-1 mm and 25- 40% of the total weight of the mixture is a magnesium oxide component with a particle size equal to or less than 0.3 mm. Cement mixture according to Claim 1, characterized in that 0-20% of the total weight of the mixture is alumina having a particle size equal to or less than 0.3 mm and 1-20% of the total weight of the mixture is alumina having a particle size of equal to or less than 45 μm. 4. A cast refractory body resistant to molten metals and made of a hydraulic, refractory three-component cement mixture containing aluminum cement and alumina, characterized in that it is made of a cement mixture consisting essentially of 70-86% of a magnesium oxide component, contains at least 94% MgO, 5-15% alumina component containing at least 98% and 9-15% alumina cement component containing at least 45% Al 2 O 2, and that 110 °, 1000 ° and After heating at 1500 ° C, it has a cold crush strength of 492, 517 and 868 kp / cm 3 and a bulk density of 2.83, 2.78 and 2.85 g / cm -1. 5. A method of making a refractory body for withstanding the abrasive and corrosive effects of molten metal, characterized in that a hydraulic, refractory cement mixture is prepared consisting essentially of 70-86% of a magnesium oxide component containing at least 94% MgO, 5- Water is added to a mixture of 15% alumina component containing at least 98% Al 2 O 3 and 9-15% alumina cement component containing at least 45% Al 2 O 3 to obtain hydraulic concrete, the prepared hydraulic concrete is vibrated cast in a mold and the cast body is given harden and dry. 9,71718