Coating processes – Restoring or repairing – Metal article
Patent
1997-11-18
1999-03-30
Bell, Janyce
Coating processes
Restoring or repairing
Metal article
427140, 427230, 427287, B05D 722
Patent
active
058885862
DESCRIPTION:
BRIEF SUMMARY
The invention concerns the use of a water-containing refractory ceramic casting material on the basis of a metal oxide being susceptible to hydration, such as MgO, particularly in the form of sintered magnesia.
Magnesia carbon bricks (MgO-C-bricks) have been used successfully for a long time as refractory lining in aggregates for the production of steel. These bricks mainly consist of magnesia (MgO), particularly in the form of sintered or fused magnesia and carbon. They are used in their unfired condition at application temperatures of up to 1800.degree. C. Their main characteristics are an excellent temperature change behaviour, an excellent caloric conductibility and particularly a good resistance to aggressive slags. The necessary compact structure of magnesite and carbon is influenced considerably by the used binder.
A method for producing MgO-C-bricks is described in the DE 42 07 249 C1, an aliphatic organic polymer compound being used as a binder. Such a binder is characterized in that the organic part decomposes at higher temperatures without residue and without pollutant emissions. At most, there remain harmless inorganic residues.
Such bricks are used in the slag zone of pouring ladles, as can be gathered from "Veitsch-Radex Rundschau", No. 1-2/1994, 494, among others. While otherwise the ladle lining is realized monolithicly, the said MgO-C-bricks have been used in the region of the slag zone in order to bring the stability of the refractory lining in this region particularly endangered by the aggressive metallurgical slags to about the same level as in the monolithicly lined portions. It is an object of the invention to present a possibility according to which also the wall regions endangered by erosion, especially the slag region, can be lined monolithicly with a refractory casting material.
Here, the use of materials having the recipe disclosed in the DE 42 07 249 C1 is out of the question, because the magnesite component is very susceptible to hydration and would lead to a hydration of the magnesia (MgO) in adding water as is absolutely necessary in a casting material. This is the reason why MgO-C-bricks fabricated under dry conditions are used in the region of the slag zone according to "Veitsch-Radex Rundschau"D (loc cit.).
With the present invention, we succeded in providing a water-containing refractory ceramic casting material on the basis of a metal oxide being susceptible to hydration, as MgO, with a carbon content from 3 to 10% by wt., in which a hydration of the MgO is prevented--in spite of the water content.
The invention is based on the realization that two additional features are necessary for that. Firstly, the carbon component needs to be sufficiently dispersed within the casting material. This is achieved by adding a dispersing agent in an amount of 0.1 to 2.0% by wt, based on the solids content of the material.
By this measure the hydrophilizing treatment of the carbon being absolutely necessary in the prior art according to the DE 43 17 383 A1 is omitted.
Moreover, the casting material comprises a reactive silicic acid in an amount of 1.0 to 10.0% by wt., again based on the solids content of the material. The silicic acid which, as an example, may be added in the form of micro silica is substantially responsible for preventing a hydration of the sintered magnesia.
According to this, the invention in its most general embodiment concerns the use of a water-containing refractory ceramic casting material on the basis of a metal oxide being susceptible to hydration, such as MgO, having a carbon content of 3 to 10% by wt., a dispersing agent in an amount of 0.1 to 2.0% by wt. and a reactive silicic acid in an amount of 1.0 to 10.0% by wt., each on the basis of the solids content of the material, for monolithicly lining or repairing a metallurgical melting vessel, such as a pouring ladle, particularly its zones being endangered by erosion.
The described casting material may be fed behind a corresponding template by charging under vibration--as is described in "Veitsch-Radex Rundsc
REFERENCES:
patent: 5512316 (1996-04-01), Dody et al.
patent: 5646079 (1997-07-01), Eckstein
A. Earley John F.
A. Earley III John F.
Bell Janyce
Veitsch-Radex Aktiengesellschaft fur Feuerfeste Erzeugnisse
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