CA2075983C

CA2075983C - Material based on refractory oxides for coating a lining of a metallurgical smelting vessel

Info

Publication number: CA2075983C
Application number: CA002075983A
Authority: CA
Inventors: Guenter Moertl; Walter Siegl; Peter Loop
Original assignee: Radex Heraklith Industriebeteiligungs AG
Current assignee: RHI AG
Priority date: 1990-02-16
Filing date: 1991-01-16
Publication date: 1997-11-25
Anticipated expiration: 2011-01-16
Also published as: ITMI910387A0; FR2658503B1; DK0515400T3; ES2047398T3; DE4004870A1; HUT63822A; FR2658503A1; HU214879B; HU912648D0; AU7143891A; BE1004753A5; EP0515400B1; IT1244745B; DE4004870C2; WO1991012217A1; ATE97122T1; CA2075983A1; EP0515400A1; ITMI910387A1

Abstract

The present invention pertains to a composition based on refractory oxides, such as sintered magnesia, chrome magnesia, sintered dolomite, chromium ore, and/or zirconium dioxide, for coating a lining of a metallurgical melting vessel.

Description

MATERIAL BASED ON REFRACTORY OXIDES FOR COATING
A LINING OF A METALLURGICAL SMELTING VESSEL

The present invention pertains to a composition based on refractory oxides, such as sintered magnesia, chrome magnesia, sintered dolomite, chromium ore, and/or zirconium dioxide, for coating a lining of a metallurgical melting vessel.
Such a composition based on sintered magnesite and/or sintered dolomite has been known from West German Patent No. De-PS 37,03,136. The composition additionally contains 0.5 to 5 wt.% bentonite, l to 5 wt.% aluminum sulfate, and 0.5 to 5 wt.%
of an alkaline-earth compound in the form of caustic MgO and/or magnesium hydroxide.
The prior-art composition is said to set rapidly on spraying onto hot surfaces and to possess high refractoriness.
A similar composition has also been known from West German Patent No. DE-PS 37,39,900, in which l0 to 25 wt.% of a zirconium compound with a ZrO2 content of at least 98 wt.% relative to the MgO, are suggested as the refractory oxides, besides sintered or ~Q~5~8~

fused magnesite. Mainly high temperature resistance up to and above temperatures of l,900~C is said to be achieved with this composition as well.
A tlln~;~h composition, which contains 70 to 90 wt,% magnesite clinker (MgO) and 1 to 10 wt.% magnesium carbonate (MgCO3), has been known from World Patent Index, Derwent Publications, Acc~ccion Number 80-91003 (week 8051).
Refractory materials based on MgO, which contain chromium ore and aluminate cement, are described in Chemical Abstracts, Vol.
101 (1984), No. 10 Ref. No. 77725b. The chemical analyses show 8 wt.% CaCO3.
The prior-art compositions of this class have a relatively low CaO content, which is introduced especially when sintered dolomite is used. However, coating compositions rich in calcium oxide are definitely desirable for the purity of steel and the removal of nonmetallic inclusions. However, higher calcium oxide contents can never be used if the composition is prepared with water, because in this case the calcium oxide spontaneously reacts with water to form calcium hydroxide, which impairs processability or makes processing impossible.
Therefore, the basic task of the present invention is to provide a composition of this class, which has the highest possible calcium oxide content and yet can be processed in the wet state.
The present invention is based on the discovery that this goal can be accomplished in a surprisingly simple manner with a composition of this class, which contains 10 to 50 wt.% carbonate-bound calcium and/or magnesium oxide in the form of dolomite (MgCa (C03) 2) or lime (CaCO3) relative to the total composition.
The preferred content is between 10 and 40 wt.% relative to the total composition, and calcium carbonate offers advantages over magnesium carbonate because of its favorable metallurgical effect.
The use of carbonates within the composition is surprising at a first glance, because the carbonate spontaneously decomposes and thus reduces strength during the heat treatment (heating) which E-13~0 usually follows the application of the composition to the lining of a metallurgical melting vessel or during the subsequent heating by the metal melt. One could therefore suspect that the strength of the monolithic composition would markedly decrease and thus jeopardize the stability of the coating due to the decomposition of the carbonate, especially in the case of relatively high contents of carbonate-bound CaO (and MgO).
However, it was surprisingly found that on the fire side (on the side facing the melt), the temperatures of the metal melt are so high that sufficient sintering and consequently consolidation of the monolithic composition, which reduces its refractoriness and stability only insignificantly at best, take place at the same time. In contrast, the decomposition of the carbonate exerts a strength-reducing effect only in the area of the monolithic coating which is turned away from the metal melt and faces the outer lining. This is due to the fact that thé temperatures are inherently lower in this area than on the "fire side," so that sintering does not take place here to the same extent as on the side facing the melt.
Instead, the corresponding part of the composition remains brittle, even if the section facing the metal melt is sintered through completely.
However, this phenomenon is definitely desirable for special applications, where a firm bonding between the coating composition and the outer lining is to be prevented from taking place, because if such bonding is prevented, it is possible to easily detach the monolithic lining, which is used only once, from the outer lining of the metallurgical melting vessel at the time of replacement [of the monolithic lining] and to dump it out with the metal pig without any problem. Another advantage of the decomposition of the carbonate is the fact that the porosity of the composition also increases at the same time, as a result of which thermal insulation is improved.
However, the composition according to the present invention has, above all, the decisive advantage that it is rich in calcium oxide and, as a result, it offers the above-described metallurgical advantages.
-In a preferred embodiment of the present invention, it is suggested that an inorganic binder, e.g., water glass, be added to the composition, preferably in an amount of 1 to 3 wt.% relative to the total composition. However, it is also possible to add an organic binder, such as phenol novolak or dry binderite, advantageously also in an amount of up to 5 wt.% relative to the total composition.
It is also possible to add additives of the following types to the composition; the weights indicated are always related to the total composition:
- inorganic and/or organic fibers (up to 5 wt.%), - inorganic and/or organic plasticizing additives (e.g., clay, polyvinyl alcohol, etc.) (up to 5 wt.%), and - air-entraining and/or liquefying additives (up to 1.0 wt.%).
The composition according to the present invention may be prepared as a dry or wet composition. As a dry composition, it is introduced by vibration behind a corresponding template, and is hardened under the effect of heat at temperatures above 200~C
there.
The composition according to the present invention can also be mixed, in a particularly advantageous manner, with water and, e.g., spread or sprayed on (injected according to the Torkret system). The composition can be mixed with water and made into a slurry rich in air voids, especially if air-entraining or liquefying additives are used, and be applied to the lining of the metallurgical melting vessel according to the pump injection process.
The composition can be used particularly advantageously, among others, as a tundish coating composition.
Further characteristics of the present invention will become apparent from the characteristics of the subclaims.
The following examples will illustrate the properties and advantages described.
Experimental Series I shows a conventional spray composition containing no CaC03 (A) in comparison with two spray compositions according to the present invention, which contain 20 wt.% CaCO3 (B) and 30 wt% CaMg(CO3)3 (C), respectively. The particle size distributions of all compositions are characterized by 98 wt.%
uder 2 mm.
The following table shows specifically the raw material basis, the chemical analysis, the porosity, and the cold compressive strength at different temperatures, as well as the adhesion of the composition to the outer lining after the end of casting.
Experimental Series I (all data in weight percent, unless specified otherwise) Spray composition A B C
Raw material basis Sintered magnesia 96.3 76.3 66.3 CaCO3 -- 20 __ CaMg(CO3) 2 -- -- 30 Water glass (as inorganic binder) 3 3 3 Cellulose fibers 0.5 0.5 0.5 Methyl cellulose 0.2 0.2 0.2 Chemical analysis: MgO 83.2 68.7 67.2 Fe2O3 4.9 4.0 4.0 Al2O3 0.4 0.4 0 3 CaO 5.9 15.5 13.8 SiO2 2.8 2.7 2.8 Loss on ignition 0.9 7.2 10.2 ___ _____________ _____ Porosity (vol.%) at 110~C 35.3 34.7 36.0 1,000~C 39.2 40.1 44.0 1,400~C 34.7 40.6 43.6 1,550~C 32.5 37.8 38.1 Cold compressive strength (N/mm2) at 110~C 4.3 3.9 3.0 1,000~C 2.0 1.6 0.7 1,400~C 13.1 2.2 1.2 1,550~C 31.7 23.4 21.9 Adhesion to outer lining 40 after end of casting ++/+ +/0 0 ++ strong + weak 0 no adhesion 2~5~83 Corresponding to the raw material basis, the CaO content in the spray compositions B and C is considerably higher than in the spray composition A.
It can also clearly be recognized that the porosity in the temperature range of between 1,000~C and 1,400~C (i.e., on the "cold" side of the composition applied) is markedly higher in the batches according to B and C than in composition A, which leads to the above-mentioned improvement of thermal insulation.
The values obtained for the cold compression strength also show that it first decreases markedly with increasing temperature up to ca. l,400~C in the compositions according to the present invention. It follows from this that the compositions according to the present invention have practically no intrinsic strength on their "cold" side, i.e., on the side facing away from the metal melt, and remain "brittle," whereas they again acquire high strength due to sintering on the "fire side," i.e., at temperatures above l,500~C. It can be inferred from this "phenomenon" that the compositions according to the present invention adhere to the outer lining (i.e., on the "cold" side) only weakly or not at all, which leads to the advantage that the composition can easily be detached after use.
In Experimental Series II, a conventional slurry-type spray composition (D) is compared with a slurry-type spray composition according to the present invention (E) containing 25 wt.% CaCO3.
The properties and advantages of the compositions according to the present invention, which were described on the basis of Experimental Series I, are confirmed by the experimental results indicated in this case as well.

207~83 Experimental Series II (all data in weight percent, unless specified otherwise) Slurry-type spray composition D E
Raw material basis Sintered magnesia 96.7 71.7 CaCO3 -- 25 Water glass (as inorganic binder) + 2.5 + 2.5 10 Cellulose fibers + 0.5 + 0.5 Air-entraining additives + 0.3 + 0.3 Chemical analysis: MgO 88.0 68.4 Fe203 1.0 0.9 Al2O3 1.5 1.4 CaO 1.4 14.5 SiO2 5.2 4.6 Loss on ignition l.5 9.0 Porosity (vol.%) at 110~C 52.. 2 51.81,000~C 54.6 55.0 1,400~C 51.7 57.1 1,550~C 48.2 54.6 Cold compressive strength (N/mm2) at 110~C 1.8 1.5 1,000~C 1.6 1.4 1,400~C 6.8 1.1 1,550~C 23 4 18.7 Adhesion to outer lining after the end of casting +/0 0 ++ strong + weak 0 no adhesion

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Composition based on refractory oxides selected from the group consisting of sintered magnesia, chrome magnesia, sintered dolomite, chromium ore, zirconium dioxide and a combination thereof, for coating a lining of a metallurgical melting vessel, characterized in that it contains 3 to 50 wt.%
of a carbonate selected from the group consisting of CaCO3 and a combination of CaCO3 and MgCO3, relative to the total composition.

2. Composition in accordance with claim 1, characterized in that the carbonate is in the form of dolomite.

3. Composition in accordance with claim 1, characterized in that the carbonate is in the form of lime.

4. Composition in accordance with claim 1, 2 or 3, characterized in that the carbonate is present in an amount of between 10 and 40 wt.%.

5. Composition in accordance with claim 1, 2 or 3, characterized in that it is prepared with a particle size of less than 2 mm.

6. Composition in accordance with claim 4, characterized in that it is prepared with a particle size of less than 2 mm.

7. Composition in accordance with claim 1, 2, 3 or 6 characterized in that it contains an inorganic binder in an amount of 1 to 3 wt.% relative to the total composition.

8. Composition in accordance with claim 7, characterized in that the inorganic binder is water glass.

9. Composition in accordance with claim 1, 2, 3 or 6, characterized in that it contains an organic binder in an amount of up to 5 wt.% relative to the total composition.

10. Composition in accordance with claim 9, characterized in that the organic binder is phenol novolak.

11. Composition in accordance with claim 7, characterized in that it contains an organic binder in an amount of up to 5 wt.% relative to the total composition.

12. Composition in accordance with claim 11, characterized in that the organic binder is phenol novolak.

13. Process for applying a refractory composition to a lining of a metallurgical melting vessel, the composition being based on refractory oxides selected from the group consisting of sintered magnesia, chrome magnesia, sintered dolomite, chromium ore, zirconium dioxide and a combination thereof, wherein the composition contains 3 to 50 wt.% of a carbonate selected from the group consisting of CaCO3 and a combination of CaCO3 and MgCO3, relative to the total composition, wherein the composition is introduced in the dry state by vibration behind a corresponding template and a second refractory containing substantially no carbonates is applied thereover.

14. Process in accordance with claim 13, characterized in that the carbonate is in the form of dolomite.

15. Process in accordance with claim 13, characterized in that the carbonate is in the form of lime.

16. Process in accordance with claim 13, 14 or 15, wherein the composition is hardened by the effect of heat at temperatures above 200°C.

17. Process for applying a refractory composition to a lining of a metallurgical melting vessel, the composition being based on refractory oxides selected from the group consisting of sintered magnesia, chrome magnesia, sintered dolomite, chromium ore, zirconium dioxide and a combination thereof, wherein the composition contains 3 to 50 wt.% of a carbonate selected from the group consisting of CaCO3 and a combination of CaCO3 and MgCO3, relative to the total composition, wherein the composition is mixed with water and applied as a first layer to the lining and a second refractory containing substantially no carbonates is applied to the first layer.

18. Process in accordance with claim 17, characterized in that the carbonate is in the form of dolomite.

19. Process in accordance with claim 17, characterized in that the carbonate is in the form of lime.

20. Process in accordance with claim 17, 18 or 19, wherein the composition is hardened by the effect of heat at temperatures above 200°C.