LU84609A1 - PROCESS FOR DEPOSITING A PROTECTIVE COATING ON THE INTERIOR WALL OF A CONTINUOUS CASTING DISTRIBUTOR BASKET - Google Patents

Description

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/ Claiming the priority of an application for 3418 / EF / EG

Patent filed in Belgium on February 1, 1982 under No 891.980

Patent of invention.-1--.

C 2166/8202.

METALLURGICAL RESEARCH CENTER -CENTRUM VOOR RESEARCH IN DE METALLURGIE,

Non-profit making association - '

Vereniging zonder winstoo.gmerk in BRUXELLES, (Belgium).

Method for depositing a protective coating on the inner wall of a continuous flow distributor basket.

The present invention relates to a method for depositing a protective coating on the inner wall of a continuous casting distributor basket which is generally formed from the outside towards the inside of a metal carcass covered with a permanent refractory lining.

The continuous casting distribution baskets arranged as is known between a casting ladle and the ingot mold (s) of a continuous casting machine and serving as a buffer tank, must be protected against the stresses which they must undergo from the slag and liquid steel.

These stresses are both chemical and physical: j, they can be due, for example, to the more or less aggressive composition of the slag, at high temperatures, at / 7i \

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- 2 -; the impact of the jet. In addition, two specific functions are required of the refractory layer of the distribution basket in contact with the liquid steel: firstly, to protect the permanent coating which must remain of constant thickness during the life of the basket; this protection must appear not only during casting, but especially after it, when the metal wolf is torn from the basket; in fact, the protective coating must then easily detach from the permanent coating, avoiding as much as possible the removal of bricks or brick fractions; secondly, it must be as insulating as possible, in order to reduce as much as possible, on the one hand, the expenditure of preheating energy and on the other hand, the thermal losses of the bath during casting.

v * - ^ Af: in - to meet these needs in a more or less complete way, various materials have already been proposed to cover the permanent refractory lining of the distributor.

According to a first technique, a layer with a thickness such as for example 2 cm of a basic material known per se, for example MgO, whether or not accompanied by Cr2C> 3, is deposited on the said permanent refractory lining. a usual density of about 3 kg / dm ^, of fairly high thermal conductivity.

Such a method has various drawbacks, among which we can cite: - the need to strongly preheat the distributor basket before it is coated with the said material, - excessive sticking of the protective coating on the permanent refractory, which often causes partial tearing off of this during the removal of the coating after each pouring,

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- the relatively long duration of the basket's use cycle, because it must be waited for it to cool down before it can be refilled with protective material for the next pour.

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According to a second technique, the preheating of the basket can be almost completely avoided by depositing on the permanent refractory, prefabricated plates with high thermal insulation, generally of a silico-aluminous nature.

The use of these plates however requires a drying phase before use. Furthermore, it is not possible to avoid a certain transfer of hydrogen originating from the moisture retained in the plates or in the binder, towards the steel or its pollution by silica. These plates also require a long cycle and have a holding which is sometimes insufficient when faced with the possibility of the installation making long sequences. In addition, their placement is costly in labor.

. . . These two known techniques therefore each have their particular drawbacks which it has been sought to eliminate in the process which is the subject of the present invention.

The process, object of the present invention in which a coating layer is deposited on the permanent refractory, consists in: - making use of a light coating of low density, which eliminates the disadvantage of coating with high density, namely high thermal conductivity, - deposit this light coating on the permanent refractory coating by spraying (hot gunning), which eliminates the disadvantage of having to allow the basket to cool before repairing after casting, - not to pollute the steel, neither by silica, nor by hydrogen, because the deposited material contains neither water, nor non-ceramic binder, nor silica if desired.

The process which is the subject of the present invention is essentially characterized in that, on the wall of the permanent refractory, a refractory pulverulent material, preferably of low density, intended to constitute a light coating and / / therefore of thermal conductivity, is deposited. low.

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According to a first embodiment of the invention, the refractory pulverulent material is deposited, for example by means of a burner, suspended in hot gases originating from combustion by an oxidizing gas which may be pure oxygen, a suitable combustible gas, for example natural gas, the particle size of said pulverulent material being less than 5 mm and advantageously less than 1 mm.

These powdery refractory materials are conveyed by one or more gases such as for example the fuel and / or the oxidant, and preferably by the fuel, according to one of the known methods described above (first technique) or in combination with the use of another method of gunning.

According to a second embodiment of the invention, the heating of the gases is carried out electrically.

According to another embodiment of the invention, the heating of the refractory pulverulent material is carried out by the combustion of a metal (Al, Mg, etc.) transforming into refractory oxide.

The present process, in addition to the advantages already mentioned, makes it possible to appropriate the qualities of the coating deposited to particular desiderata, in particular its thickness, its density, etc., thanks to the fact that during projection, the possibility of acting on several parameters, namely: - the particle size of the material, its chemical composition which influences its refractoriness, its sintered state or not, - the powder / burnt gas proportion, - the distance from the end of the burner to the surface to be covered, - the presence and proportion of accompanying ceramic binder and said material.

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Furthermore, it was found that the removal of this coating after the continuous casting operation did not give rise to tearing off of the permanent refractory and allowed within a very short time, the renewal of the coating and the return to service of the basket.

Another important advantage of this process consists in the fact that, by appropriately varying one or more of the parameters mentioned, the density of the coating deposited can be modified at will; This density increases, for example, if the distance between the burner nose and the wall decreases (to an optimum value), as well as the quantity of powder / burnt gas ratio and vice versa.

It is thus easy, after having uniformly deposited a layer ^ d1 of sufficient thickness djμη low density protective coating, to reinforce the preferential wear zones of the basket, for example the impact zone of the steel jet falling therein, and the area of contact with the light coating of the slag floating on the steel. This is achieved by depositing a thicker local layer over these areas, which is more resistant to erosion and abrasion. These extra thicknesses, which are well attached to the light underlay, can be easily torn off with the latter, when the wolf is torn off. These denser thickenings are produced for example using the same starter gunning equipment as for low density coating and a possible modification of parameters such as the distance between the burner nose and the wall to be protected and the value of the ratio quantity of powder / gas burnt, which has already been mentioned above.

According to the invention, the refractory pulverulent material can advantageously consist of: - MgO with or without C ^ O ^, - <3rd good purity, - silico-aluminous refractories (A ^ O ^ content from 25 to 70%), // - one of the three elements mentioned above containing U in addition to carbon.

Claims (13)

1. Method for depositing a protective coating on the permanent refractory coating constituting the inner wall of a continuous casting distributor basket, characterized in that a refractory pulverulent material, preferably of low density, is deposited on the wall of the permanent refractory intended to constitute a light coating and consequently of low thermal conductivity. 2. Method according to claim 1, characterized in that the refractory pulverulent material is deposited, for example by means of a burner, in suspension in hot gases originating from combustion by an oxidizing gas which may be oxygen pure, of a suitable combustible gas, for example natural gas, the particle size of said pulverulent material being less than 5 mm and advantageously less than 1 mm. 3. Method according to claim 2, characterized in that the pulverulent refractory materials are conveyed by one or more gases such as for example the fuel and / or the oxidant, and preferably by the fuel, according to one of the known methods, or in combination with the use of another gunning process. 4. Method according to either of claims 1 to 3, characterized in that the heating of the gases is carried out electrically. 5. Method according to either of claims 1 to 4, characterized in that the heating of the refractory pulverulent material is carried out by the combustion of a metal (Al, Mg, Si ...) transforming into oxide refractory. 6. Method according to either of claims 1 to 5, λ characterized in that the density of the protective coating U is increased, by reducing the distance between the nose of the ♦ * ji ► · - 7 - · Burner and the wall to be protected and vice versa. 7. Method according to either of claims 1 to 6, characterized in that the density of the protective coating is increased by reducing the value of the quantity of powder / burnt gas ratio and vice versa. 8. Method according to either of claims 1 to 7, characterized in that, after having uniformly deposited a layer of sufficient thickness with a sparse protective coating, the areas of preferential wear are reinforced of the basket, for example the impact zone of the steel jet falling therein, and the zone of contact with the light coating of the slag floating on the steel. 9. Method according to claim 8, characterized in that the areas of preferential wear of the basket are reinforced by depositing on these areas a local excess thickness of a denser layer better resistant to erosion and abrasion. 10. Method according to either of the claims. 1 to 9, characterized in that the refractory pulverulent material consists of MgO with or without 11. Method according to either of claims 1 to 9, characterized in that the refractory pulverulent material consists of Al ^ O ^ of good purity. 12. Method according to either of claims 1 to 9, characterized in that the refractory pulverulent material consists of silico-aluminum refractories (AloO 2 content of * Z 3 to 70%). / m 13. Method according to either of claims 10 to '12, I characterized in that the refractory pulverulent material consists of one of the three elements mentioned above additionally containing carbon. / / '5