EP0703027A1 - Vessel for casting a molten metal and prefabricated sleeve for fixing the casting tube in such a vessel - Google Patents

Abstract

A vessel for containing molten metal has a permanent ceramic lining (3) penetrated in the floor region by at least one frusto-conical opening (6) designed to receive the upper rim (8) of a pouring nozzle (7). An annular sleeve (11) is sandwiched between rim (8) and the wall of opening (6). The sleeve comprises compacted particles which will not significantly sinter together at the molten metal temperature so that the sleeve remains frangible after use, facilitating removal of a clogged nozzle prior to its replacement by a new one. Opening (6) is formed directly in lining (3) or in a brick (5) which forms a continuation thereof. The sleeve wall thickness may be 1-40 mm, and the upper edge of the sleeve may be separated from the molten metal by a refractory cement seal (12). Sleeve (11) may be preformed of particles bonded by an agent which will be decomposed by the heat of molten metal, or the sleeve is formed in situ by pouring material into the gap between rim (8) and opening (9). The sleeve may comprise mineral and organic bonding agents, granular refractory material such as sand or graphite, organic and/or mineral fibres and lubricant. An exemplified mix comprises 68.32% MgO and 19.22% SiO2 with smaller proportions of Cr2O3, Al2O3, CaO, Fe2O3, Na2O, H2O and C, and exhibits a 4.81% weight loss when fired at 1000 degrees C.

Description

The present invention relates to a liquid metal pouring container comprising side walls and a bottom covered by a refractory permanent coating, the bottom comprising at least one pouring orifice in the permanent coating of said bottom, this orifice being constituted by a substantially frustoconical hole. in which is axially engaged a pouring nozzle, an annular space being provided between the hole of the permanent coating and the periphery of the nozzle.

Such a container can be a pouring container of liquid metal such as a ladle or a transfer container such as a tundish.

The permanent coating and especially the pouring nozzle are made of a very hard refractory material.

Conventionally, the pouring nozzle is bonded by a layer of refractory cement to the surface of the frustoconical hole of a seat brick inserted in the permanent covering, or to the surface of a frustoconical hole formed directly in the permanent covering.

At the end of casting, it is necessary to detach the nozzle from the hole in the seat brick or the permanent covering, to replace it with a new nozzle because it is practically blocked by slag adhering to its surface.

To carry out this operation, a cylinder is used which pushes the nozzle towards the interior of the container.

This deteriorates the surface of the frustoconical hole of the seat brick. Therefore the seat brick must be replaced by a new brick after each casting, which represents a long and expensive operation. It is the same in the case where the hole is formed directly in the permanent coating.

Also known from FR-A-2 119 057 is a metallurgical container in which the annular space between the coating hole and the periphery of the nozzle has a small thickness (a few millimeters at most) and is filled with a highly refractory fibrous material which hardly reacts with the materials constituting the surfaces of the joint. This fibrous material is preferably molten kaolin in fibrous form.

This solution requires a delicate and painful manual intervention, in a difficult environment due to the heat, to constitute a joint presenting all the guarantees of safety and tightness with liquid metal required for such a joint.

The object of the present invention is to remedy these drawbacks.

The invention thus relates to a liquid metal pouring container comprising side walls and a bottom covered by a refractory permanent coating, the bottom comprising at least one pouring orifice in the permanent coating of said bottom, this orifice being constituted by a hole substantially frustoconical in which is axially engaged a pouring nozzle, an annular space being formed between the hole of the permanent coating and the periphery of the nozzle.

According to the invention, this container is characterized in that this annular space is filled with a prefabricated sleeve made up of inorganic particles maintained by a binder having a predetermined degradation rate at the temperatures involved during the casting of said liquid metal.

This prefabricated sleeve is easy to install. It is furthermore easy to give it predetermined dimensions, so that it can be adjusted in a precise, safe and reliable manner on the surface of the hole of the container as on the external peripheral surface of the nozzle.

Since the binder has a predetermined degradation rate at the temperatures involved during the casting of the liquid metal, the sleeve loses a predetermined part of its cohesion during said casting, and easily separates from the permanent refractory lining without damaging the peripheral surface of the hole. frustoconical of it after this pouring.

Thus, it is no longer necessary to replace the seat brick or to reconstitute the frustoconical hole of the permanent covering after each casting. On the contrary, this hole does not require any intervention during a very large number of successive flows, so that the flows can succeed one another practically without interruptions.

According to an interesting version of the invention, the particle size and the composition of the inorganic particles constituting the sleeve are chosen so that these particles, at the temperature of the liquid metal contained in the container, do not sinter completely or sinter only weakly so as to create a friable bond with the surfaces with which they are in contact.

The particles of the sleeve therefore do not risk strongly adhering to the surface of the hole of the permanent coating, and can be easily detached from this surface without damage to it.

Furthermore, this partial or weak sintering makes it possible to maintain a certain cohesion of the inorganic particles with one another even if the binder has completely disappeared. Thus, the sleeve provides an absolute seal with respect to the liquid metal.

According to an advantageous version of the invention, the inorganic particles constituting the sleeve are mainly particles of magnesia and / or silica.

The sleeve is thus simple and inexpensive to manufacture.

According to a preferred version of the invention, the thickness of the prefabricated sleeve is between 15 and 35 mm, and the sleeve is thermally insulating.

The sleeve therefore provides a separation and separation function between the pouring nozzle and the permanent refractory lining. It also provides a thermal insulation function between the nozzle and said coating.

The sleeve thus prevents cooling of the nozzle by the permanent coating during casting, which limits the risk of metal freezing on the inner peripheral wall of the nozzle.

The invention also provides a prefabricated sleeve for fixing the nozzle, intended to be used in a liquid metal pouring container according to the first aspect of the invention, this sleeve being characterized in that it is made from particles inorganic bonded together by a binder which has a predetermined degradation rate at the temperatures involved during the casting of said liquid metal.

Other features and advantages of the invention will become apparent in the description which follows.

• la figure 1 est une vue en coupe partielle du fond d'un récipient de coulée comportant le perfectionnement conforme à l'invention, dans deux modes de réalisation représentés respectivement par les demi-vues droite et gauche ;
• la figure 2 est une vue d'un détail de la figure 1 représentant la busette de coulée sur la face périphérique extérieure de laquelle est fixé le manchon préfabriqué selon l'invention ;
• la figure 3 est une vue agrandie d'un détail de la figure 1 selon un autre mode de réalisation de l'invention.

In the accompanying drawings, given solely by way of nonlimiting examples:

• Figure 1 is a partial sectional view of the bottom of a casting container comprising the improvement according to the invention, in two embodiments represented respectively by the right and left half-views;
• Figure 2 is a view of a detail of Figure 1 showing the pouring nozzle on the outer peripheral face of which is fixed the prefabricated sleeve according to the invention;
• Figure 3 is an enlarged view of a detail of Figure 1 according to another embodiment of the invention.

FIG. 1 partially represents a casting container, for example a continuous casting distributor, comprising a side wall 1 and a bottom 2 covered by a permanent coating 3, for example made of refractory concrete. In the right half-view, the bottom 2 comprises a pouring orifice 4 passing through the permanent coating 3 of the bottom 2. This permanent coating 3 has a hole 6 substantially frustoconical, represented for example flared upwards, in which is engaged axially a pouring nozzle 7.

In the left half-view, the bottom 2 comprises a pouring orifice 4 passing through a seat brick 5 inserted into the permanent covering 3 of the bottom 2, the hole 6 passing through the seat brick 5 and receiving the nozzle 7.

An annular space is provided between the hole 6 of the permanent covering 3, or of the seat brick 5, and the periphery 8 of the nozzle 7.

For this purpose, the nozzle 7 has an outer surface 8 preferably of frustoconical shape substantially identical to the frustoconical inner shape of the hole 6.

If necessary, a casting stopper 9 is placed inside the pouring vessel which closes the passage opening 4 of the nozzle 7.

The inner surface of the permanent coating 3 can be covered by a protective layer 10 of consumable material, for example (inorganic particles, fibers and binder) sinterable.

According to the invention, the annular space formed between the hole 6 of the permanent covering 3 or of the seat brick 5 and the periphery 8 of the nozzle 7, is filled by a prefabricated sleeve 11 made up of inorganic particles maintained by a binder or a bond having a predetermined degradation rate at temperatures involved during the pouring of the liquid metal.

This means that after casting, the inorganic particles are only weakly or partially connected to each other. Thus, the sleeve 11 retains a certain sufficient cohesion to ensure a perfect seal against the liquid metal during casting, but has a certain friability which makes it possible to easily release the fragments of the sleeve from the inner peripheral surface of the hole 6.

According to one embodiment, the particle size and the composition of the inorganic particles are chosen so that these particles, at the temperature of the liquid metal contained in the container, do not sinter completely or sinter only weakly so as to create with the surfaces with which they are in contact with a friable bond.

Thus, the sleeve adheres only weakly to the surfaces with which it is in contact, and remains brittle.

The inorganic particles constituting the sleeve can be mainly particles of magnesia and / or silica.

Under these conditions, a conventional mineral and / or organic binder can be used which decomposes at temperatures involved during casting, partial or weak sintering of the particles maintaining the necessary cohesion of the sleeve 11.

Another known type of binder or bond could be used having, after casting, a predetermined degradation rate allowing easy elimination of the sleeve 11 and of the nozzle 7 freeing the hole without damaging the inner peripheral surface of said hole 6.

The composition and the particle size of the inorganic particles can be chosen so that the sleeve has an open porosity greater than 45% and therefore exhibits thermal insulating properties.

The weight composition of the mixture constituting the sleeve 11 can be as follows: mineral binder, for example sodium silicate: 0 to 20% refractory material in grains, for example crushed clay, chamotte, olivine, magnesia and their mixtures: 0 to 98% mineral fibers: 0 to 1% organic fibers: 0 to 2% organic binder, for example dextrin: 0 to 10% rheology agent, for example bentonite: 0 to 5%

A preferred composition by weight of the mixture constituting the sleeve 11 is for example the following: Cr₂O₃ 0.12 to 0.50% for example 0.25% If 18 to 22% 19.22% Al₂O₃ 0.10 to 0.40% 0.28% CaO 1 to 3% 2.00% MgO 60 to 75% 68.32% Fe₂O₃ 1.20 to 4% 2.82% Na₂O 0 to 0.10% 0.01% H₂O 0.50 to 2.50% 1.79% VS 1.7 to 3% 2.43% loss on ignition at 1000 ° C 3 to 5.5% 4.81%

The thickness of the annular space filled by the sleeve 11 can be between 15 and 35 mm approximately.

At the end of casting, the sleeve 11 remains brittle, which means that the sleeve 11 has not completely sintered or has only slightly sintered, due to the high temperature of the liquid metal contained in the casting container.

Thus, the mechanical connection between the nozzle 7 and the surface of the hole 6 remains relatively weak. Thus the nozzle 7 can be easily extracted from the hole 6, by simply inverting the pouring container.

The connection created by the weak sintering or by the partial sintering between the sleeve 11 and the surfaces in contact is however strong enough to prevent any risk of displacement of the nozzle under the effect of the turbulence generated during casting in the liquid metal.

The partial sintering of the sleeve 11 is also favorable to make this sleeve sufficiently tight and to avoid any risk of leakage of liquid metal.

If the sleeve 11 remained in the pulverulent state, the metal could infiltrate, which could have catastrophic consequences.

Furthermore, if the sleeve 11 sintered completely, very strong bonds would be created between the surface of the hole 6 and the external surface of the nozzle and in this case the latter would become difficult to extract, as in the prior art.

Partial sintering is obtained by choosing for the sleeve 11 a mixture of inorganic particles such as silica, alumina, magnesia, the particle size of which is not too fine, since this promotes sintering.

After extraction of the nozzle 7 the surface of the hole 6 is absolutely intact and it is ready to receive a new nozzle for a new pouring of liquid metal.

The sleeve 11 thus ensures, by its thickness, a function of physical separation and distance between the pouring nozzle 7, on the one hand, and the permanent coating 3 or the seat brick 5, on the other hand. It thus eliminates all the consequences of dilation of the nozzle during casting, and of mechanical removal of the nozzle after casting.

The sleeve 11 preferably has an open porosity greater than 45% which gives it thermal insulation properties. This open porosity can come in particular from the decomposition of the mineral binder and / or organic, and that of any organic fibers.

Therefore, and because of its relatively large thickness, the sleeve 11 provides significant thermal insulation between the nozzle and the permanent coating. This avoids any heat loss from the nozzle to the permanent coating, and therefore allows rapid heating of the nozzle before casting, less cooling of the nozzle during casting. The composition of the sleeve 11 must be such that the sleeve does not adhere to the surface of the hole 6 of the permanent coating, at the temperature of this surface. On the other hand, there is no disadvantage in that the sleeve adheres to the nozzle 7, the temperature of which is clearly higher than that of the permanent coating.

The prefabricated sleeve, because of its precise dimensions with small tolerances, allows rapid and precise mounting of the nozzle in hole 6.

In particular, and as shown in FIG. 2, it is advantageous to fix the sleeve 11, by means of a mortar or a refractory glue, on the external peripheral face of the nozzle 7 before the positioning of the latter. ci in hole 6 of the pouring container.

The rapid and precise assembly of the nozzle 7 in the hole 6 is thus facilitated, and does not require any adjustment work, or the use of mortar or glue.

An annular seal 12 made of refractory concrete protecting the sleeve 11 can be placed around the upper part of the nozzle 7, above the sleeve 11.

In the embodiment of FIG. 3, an insulating ring 13, having for example the same composition and the same physical and thermal characteristics as the sleeve 11, is put in place above the sleeve 11, the nozzle 7 and the permanent coating 3 This ring 13 is preferably prefabricated like the sleeve 11.

Of course, the invention is not limited to the example which has just been described and numerous modifications can be made to it without departing from the scope of the invention.

Thus, the external surface of the nozzle 7 could include reliefs or recesses to achieve a certain anchoring of the sleeve 11 on the surface of the nozzle 7, so that during the extraction of the latter, the sleeve 11 is demoulded. same time of hole 6 and thus leaves the surface of this hole intact and smooth.

Claims (10)

Liquid metal pouring vessel, comprising side walls (1) and a bottom (2) covered by a permanent refractory lining (3), the bottom (2) comprising at least one pouring opening (4) in the permanent lining ( 3) of said bottom (2), said orifice being constituted by a hole (6) substantially frustoconical in which is axially engaged a pouring nozzle (7), an annular space being formed between the hole (6) of the permanent coating and the periphery (8) of the nozzle (7), characterized in that this annular space is filled by a prefabricated sleeve (11) made up of inorganic particles maintained by a binder having a predetermined degradation rate at the temperatures involved during the casting of said liquid metal . Container according to Claim 1, characterized in that the particle size and composition of the inorganic particles are chosen so that these particles, at the temperatures involved during the pouring of the liquid metal contained in the container, do not completely sinter or only sinter slightly so as to create a friable bond with the surfaces with which they are in contact. Container according to claim 1 or 2, characterized in that the inorganic particles constituting the sleeve are mainly particles of magnesia and / or silica. Container according to one of Claims 1 to 3, characterized in that the thickness of the prefabricated sleeve is between 15 and 35 mm approximately. Container according to one of Claims 1 to 4, characterized in that the weight composition of the mixture comprising the prefabricated sleeve is as follows: mineral binder: 0 to 20% refractory material in grains: 0 to 98% mineral fibers: 0 to 1% organic fibers: 0 to 2% organic binder: 0 to 10% rheology agent: 0 to 5% Container according to claim 5, characterized in that the weight composition of the mixture making up the prefabricated sleeve is as follows: Cr₂O₃ 0.12 to 0.50% for example 0.25% If 18 to 22% 19.22% Al₂O₃ 0.10 to 0.40% 0.28% CaO 1 to 3% 2.00% MgO 60 to 75% 68.32% Fe₂O₃ 1.20 to 4% 2.82% Na₂O 0 to 0.10% 0.01% H₂O 0.50 to 2.50% 1.79% VS 1.7 to 3% 2.43% loss on ignition at 1000 ° C 3 to 5.5% 4.81% Container according to one of claims 1 to 6, characterized in that a prefabricated insulating ring (13) is placed over the sleeve (11), the nozzle (7) and the permanent refractory lining (3). Prefabricated sleeve for use in a container according to one of claims 1 to 7 for the fixing of the nozzle (7) in said container, characterized in that it is made from inorganic particles linked together by a binder which has a predetermined degradation rate at the temperatures involved during the casting of said liquid metal. Sleeve according to claim 7 or 8, characterized in that it is fixed on the external peripheral face of the nozzle (7), before the positioning of the latter in the hole (6) of the container. Sleeve according to one of claims 7 to 9, characterized in that it is thermally insulating.

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