Compositions: ceramic – Ceramic compositions – Refractory
Patent
1991-08-23
1993-03-09
Group, Karl
Compositions: ceramic
Ceramic compositions
Refractory
501123, 501108, C04B 3506, C04B 3522
Patent
active
051927217
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the field of continuous casting of metals, in particular steel. It relates more particularly to the distributors, or tundishes, and even more particularly to their inner refractory lining.
The refractory lining of a distributor for continuous casting of steel is nowadays frequently applied on a permanent sub-layer, most generally of dense refractory concrete, in aqueous form by means of various techniques such as sputtering, trowelling, casting, vibratory casting or tamping. This lining is then dried before the distributor is used.
Magnesia is the material most commonly used for this application, because, in particular, of its low reactivity towards strong deoxidising elements, such as aluminium or calcium, contained in the liquid steel. However, the magnesia linings which are customarily used still have a silica content which is not negligible (from 5 to 15%). Now, the reduction of silica by strong deoxidising agents leads to the formation of non-metallic inclusions, which pollute the metal. It is therefore necessary that the part of the lining which is in contact with the liquid metal has as low as possible a silica content if a high inclusionary cleanliness is desired for the cast product. The use of magnesia of a higher purity is possible, but substantially increases the cost of the lining.
Another drawback of magnesia is its high apparent mass per unit volume, which has an adverse effect on the thermal insulation properties of the lining. Even in the case where the weight of the lining is reduced by the incorporation of diverse fibres, its mass per unit volume remains of the order of 1600 to 1800 kg/m.sup.3.
In order to lower the content of reducible compounds in the lining, it is known, for example in the European Patent Application 260322, to incorporate in said lining a more or less significant proportion of calcined dolomite. However, this latter material has a high apparent mass per unit volume (more than 3200 kg/m.sup.3). This high density has advantages for the lining of furnaces and casting ladles because it confers on the calcined dolomite a high resistance to wear and to corrosion by the slags. However, these properties are of little importance in the distributors, where the temperature of the liquid metal does not exceed 1600.degree. C., where the time for which the lining is used does not exceed 10 to 20 hours and where only minor quantities of aggressive slags penetrate. On the other hand, the lack of insulating power on the part of the calcined dolomite would be very troublesome with regard to good preservation of the temperature of the metal, which is of prime importance at this stage of casting. For all of these reasons, calcined dolomite is never used on its own to line the distributors for continuous casting.
The aim of the invention is to take advantage of the high chemical inertia of dolomite, and of the carbonates of alkaline earth elements in general, towards strong deoxidising agents in liquid steel while obtaining insulating properties for the distributor lining which are superior to those of magnesia.
To this end, the subject of the invention is a process for lining a distributor for continuous casting of metals, in particular steel, according to which the layer of refractory wear lining is placed in position in aqueous form, characterised in that the said refractory wear lining is composed of raw natural dolomite or of raw natural calcite or of a mixture of these two materials, in that its particle size is between 0 and 5 mm, in that a binder, in proportions of 0.5 to 5% by weight, and an inorganic or organic plasticiser, in proportions of 0.2 to 3% by weight, are incorporated in this lining and in that the decarbonisation of this lining is carried out after it has been placed in position, during the drying and the calcining thereof.
Preferably, the particle size of the raw dolomite and of the raw calcite is between 0 and 1 mm. The density of the lining after drying is less than 1500 kg/m.sup.3 and preferably between 1100 and 1400 kg/m.sup.3.
REFERENCES:
patent: 4789652 (1988-12-01), Ichikawa et al.
Gallo Chris
Group Karl
Sollac
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