NL8201790A - BASIC, FIRE-RESISTANT, CEMENT-CONTAINING MATERIAL AND ITS COMPONENTS. - Google Patents

Description

r: .c. * 1,005

Basic 1 refractory, cementitious material and its components »

The present invention relates to basic, refractory, cementitious material and components thereof.

The invention also relates to a process for the preparation of such cementitious components, which are exposed to chemical attack, wear and erosion by molten metals, such as steel.

Refractory components of valves and refractory nozzles for various purposes in the metal casting technique, are conventionally manufactured by pressing and firing at high temperatures. Expensive, high purity materials such as zirconium oxide and refractories based on 85 to 95% AlgO- (and considered necessary in view of the extremely severe operating conditions to which the components are subjected. The energy consumed for the manufacture of components 15 by pressing and firing is considerable, since fire temperatures, usually exceeding 1500 ° C, must be established and maintained during the firing process. Energy consumption contributes significantly to the unit costs of components produced from such fired refractories are manufactured.

Notwithstanding the use of highly burned refractories in the metal casting technique, parts such as valve plates usually require frequent replacement at great expense.

Recently chemically bonded concrete products have been proposed, for example for valve plates with a sliding port. Like burned refractory plates, chemically bonded concrete slabs are unlikely to withstand repeated thermal shocks. It is therefore expected that their use in ingot casting valves is expected to be complicated by inconvenient interruptions for their replacement.

It has now been found that certain hydraulically bonded basic cementitious materials surprisingly have the ability to withstand thermal shock particularly well and that the production of components from these materials is particularly advanced.

According to the present invention there is provided a hydraulic refractory cementitious formulation for the manufacture of cast refractory parts resistant to molten metals 8201790 2, which formulation contains a mixture of three components, namely molten or sintered magnesium oxide, aluminum oxide and a hydraulic cement with a high aluminum content, containing at least 45%, the magnesium oxide being present in an amount of at least 60% by weight of the total weight of the three components and the alumina component being present in an amount of at least 1% by weight of the total weight of the three components »

The invention also provides cast refractory parts made from the formulation and a method for the manufacture of such cast refractory parts.

Formulations according to the invention mainly comprise three components, namely magnesium oxide, aluminum oxide and aluminum-containing hydraulic cement. If desired, minor amounts of other components for specific purposes can be added, 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 such parts.

The first two components are preferably of high purity for best results. Therefore, the magnesium oxide component should have a MgO content of at least 94 wt% and.

the alumina component must have an Al_0 content of at least ά 98> 25 98% by weight. The alumina can be sintered, melted or preferably calcined *

The cement component can in principle be any cement with a high alumina content (Al 2 O 3 content greater than 45% by weight of the cement). Preferably, the aluminum-containing cement component has an Al 2 O 3 content of not less than 75% by weight of the cement component.

The magnesium oxide components can be present in an amount of 60 to 95% by weight of the total weight of the three components. On the same percentage basis, the alumina component is present in an amount of at least 1 such as 1 to 36% and the cement component in the range of 4 to 15%

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

The formulation should be prepared from graded part-40 materials. Preferably, the cement component should have a particle size of 8 microns of 75 microns or less. It is permissible for some cement particles to be larger, but preferably at least 90% of the cement has a particle size of 75 microns or less.

Formulations will desirably be selected from the data given in the following table: ^

Material_Size range Percentage range total_preference total preference magnesium oxide -5 mm + 1 mm -3 mm + 1 mm 20-40 20-30 (sintered or melted) magnesium oxide -1 mm +0.3 mm -1 mm +0.3 mm 15- 35 20-30 (sintered or melted) magnesium oxide <0.3 mm <0.3 mm 25-40 30-40 (sintered or melted) aluminum oxide ^ 0.3 m <0.3 mm 0-20 0-5 (sintered or calcined) aluminum oxide <45 micro- <45 micro 1-20 5-10 (calcined, meter meters melted or sintered, but preferably calcined) hydraulic cell 90% min 90% ¢ -15 9-12 ment with A ^ O ^ 75 micro- <75 micro stop e greater ^ meter meter than 75 #

The formulations are mixed with water in an appropriate amount to obtain a processable mixture. Such a mixture may contain, for example, 7% by weight of water based on the mixture. The mixture is self-curing at room temperature. * Application of heat is not necessary, although moderate heating to accelerate the hardening of cast molds may be permissible. Without heating, however, curing to a state allowing mold release can be achieved in about 1 hour.

Therefore, a high productivity can be achieved.

The present hydraulically bonded formulations have significant advantages over chemically bonded systems.

A problem, which is always present with chemically bonded systems, is that when they are in the heat curing and drying process, the binder tends to migrate to the exposed surfaces. Binder migration and obtained non-uniformity of the consistency of the castings does not occur with the formulations of the invention. In addition, a rigid curing takes place so that the handling of castings is free from. . . . of risk of introduction / internal stress fractures. With chemically bonded castings it is not impossible to adversely affect them during handling.

The present formulations have a surprisingly good resistance to thermal shock. Therefore, they are expected to find use in parts of sliding gate valves 10 and associated casting nozzles used in intermittent molding of molten metals.

A commonly used thermal shock resistance test is the torch test developed by United States Steel Corporation's Research Laboratories. * In this test, an oxy-propane torch flame is slowly moved transversely across a refractory material to be tested at 1.7 mm per second, the torch is kept 6.2f mm from the refractory surface *.

Traditionally pressed and fired magnesium oxide valve plates can usually withstand only one pass of the oxypropane flame without significant damage to the surface and interior. Known chemically bonded magnesium oxide valve plates are more able to withstand the flame, but tests have shown moderate degradation after one pass.

In contrast, valve plates made from the present formulations have been able to withstand repeated passages, for example twelve, without significant damage to the surface. This implies its ability to cope with the temperature variations encountered during repeated valve chokes and open / close valve treatments. which show a marked improvement over burned or chemically bonded plates.

As indicated above, the subject formulations can be used for casting valve plates for sliding gate valves as well as nozzles, such as collectors and projecting sprues associated therewith. Spoons and delivery nozzles can also be made from the formulations, and other uses will be apparent.

Articles cast from the present formulations *: in-line, will usually be delivered in the hydraulically cured state. Nevertheless, it may sometimes be desirable to provide the molded articles + 0 + in a pre-burned condition instead of burning them in use * Pre-roasting may be applicable, for example, to articles »such as replaceable wear and erosion resistant liners or liners for discharge mouthpieces *

5 EXAMPLE

This formulation had the following proportions; The percentages given are again weight percentages based on the total weight of the magnesium oxide »aluminum oxide and cement components * 10 magnesium oxide, size range -3 to +1 mm 26% magnesium oxide, size range -1 to +0.3 mm 25% magnesium oxide, size smaller than or equal to 0.3 mm 3k% calcined alumina * size less than or equal to 75 μm 6% 15 'cement with high alumina content 9%

The cement had an Al 2 O 2 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 microns. The magnesium oxide and alumina had MgO and Al 2 O 3 contents of 9k 20 and 98% by weight of these components, respectively *

The formulation gave a workable and suitable flow path of cement for pouring when mixed with water in an amount of 7% by weight * The filling of molds can be assisted by vibration * with an example of a vibration frequency being 3000 Hz *

Vibration-cast concrete samples manufactured as before have after curing and drying the following properties at the indicated temperatures.

8201790 6 r vi

Property '' Burning temperature ° C

110 1000 1500 1700 bulk density g / cnr 2.83 2.78 2.85 apparent porosity% 16.0 19 »3 17.0 permanent linear change

dry to roasted% +0.01 -1.24-3, H

cold compressive strength kPa 48 265 50 675 85 150 MNM "2 48.3 50.8 85.2

Kp.cnf2 492 517 868 flame test 1 cycle passed flame test 12 cycles passed

The foregoing properties are considered to be totally suitable for the manufacture of sliding gate valve components, which can be supplied in a subsequently fired state if desired · 8201790

Claims (9)

1. Hydraulic, "refractory", cementitious formulation for the manufacture of cast refractory components ", resistant to molten metals, characterized in that the formulation contains a mixture of three components, namely molten or sintered magnesium oxide, aluminum oxide and a hydraulic cement with a high alumina content that is at least 45. Al-O, wherein the magnesium oxide is present in a C D amount of at least 60 wt.% Of the total weight of the three components and the alumina component is present in an amount of at least 1 wt. var. the total weight of the three components. Formulation according to claim 1, characterized in that the magnesium oxide component is present in an amount of 60 to 95% and the cement component is present in an amount of 4 to 15 % · 3 * Formulation according to claim 1 or 2, characterized in that the magnesium oxide component has a MgO content of at least 94% by weight of the magnesium oxide component. 20 4 * Formulation according to claims 1 to 3 »with the mark». that the aluminum component has an A 1 ^ 0 ^ content of at least 98% by weight of the alumina component » A formulation according to claims 1 to 4, with the value that 20 to 40 wt.% Of the total weight of the three components is magnesium oxide with particle sizes within the range of -5 mm to -1 mm, 15 to 35% on the same-base magnesium oxide is with particle sizes in the range of -1 mm to +0.3 mm and 25 to 40 wt.% on. the same base is magnesium oxide with particle sizes of 0.3 mm or less. 30 Formulation according to one or more of claims 1 to 5, characterized in that 0 to 20% by weight of the total weight of the three components is aluminum oxide with particle sizes of 0.3 mm or less and 1 to 20 % on the same basis is alumina with particle sizes of 45 µm or less »35 Formulation according to one or more of claims 1 to 6, characterized in that, based on weight percentages of the total weight of the three components, 26% magnesium oxide with particle dimensions in the range from -3 to +1 mm, 25 magnesium oxide with particle sizes in the range of 40 -1 to +0.3 mm and 3k% magnesium oxide with particle sizes not 8201790 less than Or3 mm, 6% calcined alumina with particle sizes not smaller than 45 micrometers and 9 ^ hydraulic aluminum oxide cement »of which 90% particle sizes of not less than 75 micrometers are present. 5 Molded refractory part made from the formulation according to any of the preceding claims, characterized by a cold compressive strength after subjecting to temperatures of 110 °, 1000 ° and 1500 ° C of 48265, 50675 and 8515Ο kPa, respectively, and a bulk density. after submission to these temperatures of 2.83, 2.78 and 2.85 g / cra ^ * 9 · A method of manufacturing a refractory part which is subject to wear or erosion by molten metal, characterized in that the part is poured under vibration into a mold of hydraulic concrete prepared by adding water 15 to the formulation according to one or more of claims 1 to 7i the casting hardens and allows to dry. ****** 8201790