FR2830472A1 - Manufacture of pouring tube for molten metal involves pouring a refractive sintering compound is into an annular space between an external metallic ferrule and an internal refractive forming tube - Google Patents

Abstract

Manufacture of a pouring or orifice tube in which a cylindrical metallic ferrule (3) is mounted on a support (4) involves coaxially positioning an internal tube (5) with respect to the ferrule, filling the annular space between the tubes with an effectively dry refractory-sintering compound, and heating the assembly to harden the composition and or remove all traces of water. The effectively dry refractory-sintering compound comprises a dry binder that self-hardens or hardens when heated. The internal tube used in manufacture is of refractive material, e.g. self-pouring refractive concrete. An Independent claim is given for the manufactured pouring or orifice tube.

Description

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PROCESS FOR MAKING A CASTING TUBE
The present invention relates to a method for producing a pouring tube. It also relates to a pouring tube produced by the implementation of this method.

 A method is known for producing a pouring tube, this method comprising a step of placing a curable and sinterable refractory mass inside a metal ferrule, and a step of heating the assembly to make it harden. the curable mass.

 We know, for example, from FR-A-2 333 599, a method of the aforementioned type for forming a pouring tube made of thermally insulating material and of low density constituted by a mixture of refractory particles and mineral fibers coated in a binder . This tube is formed around a perforated sleeve from a pasty and aqueous mixture comprising the above constituents. It is reinforced externally by a metal frame, then carried in an oven to evaporate the residual water and harden the binder. When the molten metal is poured, the inorganic particles sinter, which ensures the cohesion of the tube after decomposition or disintegration of the binder.

 Such a process makes it possible to manufacture reliable pouring tubes at a very competitive price. On the other hand, the decomposition of the binder, in particular in the case of an organic binder, causes the evolution of hydrogen which can be captured by the liquid metal.

 However, the users of certain steels are more and more demanding on the nature of the metal they use, and impose levels of the metal cast in

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 increasingly low hydrogen which are difficult to obtain when using a pouring tube of the aforementioned type.

 Also known are refractory casting tubes based on graphite alumina which are, during their manufacture, kept in a baking oven at a temperature high enough to cause a ceramic setting of the particles constituting these tubes. These tubes are very reliable and do not involve any risk of release of hydrogen which could adversely affect the quality of the cast metal. On the other hand, these tubes are produced by implementing a complex process so that these tubes have a high unit price.

 The object of the present invention is to remedy the drawbacks of known methods and to propose a method of the above type making it possible to produce a reliable and economical pouring tube, having a simple structure, and avoiding any risk of evolution of hydrogen at during the casting of molten metal.

 - According to the present invention, the method of the aforementioned type is characterized in that it comprises the following steps: a) a substantially cylindrical metallic ferrule is installed on a support in a substantially vertical position and, inside the metallic ferrule , substantially coaxial thereto, a tube of substantially cylindrical shape made of refractory material baked in the oven; b) a substantially dry sinterable refractory composition comprising a substantially dry heat-curable mineral binder is introduced between the outer surface of the refractory tube and the inner surface of the metal shell;

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 c) the assembly is heated to harden the curable composition.

 The implementation of such a particularly simple method makes it possible to obtain a pouring tube of simple and economical manufacture comprising several substantially coaxial layers. The metallic ferrule and the tube made of refractory material do not generate any gassing at the temperature of the molten metal.

 As for the intermediate layer of sinterable refractory composition, it contains no organic matter and contains practically no more water of constitution. Thus, when it is subjected to the temperatures reached during the casting of the molten metal, this material sintered without practically generating evolution of hydrogen.

 Another version of the present invention relates to a pouring tube produced by the implementation of the above method.

 Other features and advantages of the present invention will appear in the detailed description below.

 In the accompanying drawings, given only by way of nonlimiting examples: - Figure 1 is a schematic view in axial section illustrating the implementation of the main steps of the method according to the present invention; - Figure 2 is an axial sectional view of an embodiment of a pouring tube obtained by the implementation of the method illustrated in Figure 1.

 The process illustrated in FIG. 1 for producing a pouring tube 1 comprises a step of placing a curable and sinterable refractory mass 2 inside a metallic ferrule 3, and

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 a step of heating the assembly to harden the curable mass 2.

 Such a pouring tube 1 is adapted to be put in place, in a known conventional manner which does not need to be described in detail here, under the device for closing the molten metal outlet nozzle d '' a ladle filled with this metal.

 This tube is also placed above a distributor or tundish adapted to receive the molten metal coming from the ladle and to transfer this metal to at least one ingot mold for continuously casting said metal.

 During the casting of the molten metal, the lower part of the pouring tube is immersed in the molten metal and is subjected to the aggression of the molten metal and of the slag which generally covers the upper surface of said metal.

 According to the present invention, the method of the aforementioned type is characterized in that it comprises the following steps: a) installing on a support, shown diagrammatically in 4, in a substantially vertical position, the metallic ferrule '3 substantially cylindrical and, at the inside the metallic ferrule 3, substantially coaxial thereto, a tube 5 of substantially cylindrical shape made of hardened refractory material and baked in the oven; b) is introduced between the outer surface 6 of the refractory tube 5 and the inner surface 7 of the metal shell 3 a sinterable refractory composition 2 substantially dry comprising a substantially dry mineral binder curable with heat; c) the assembly thus obtained is heated in an enclosure of any known type, not shown, in order to harden the curable composition brought to a temperature sufficient to obtain the hardening of the binder.

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 FIG. 1 illustrates a horizontal support 4 comprising an annular shim 8 allowing the metal ferrule 3 to be put in place, and a central stud 9 making it possible to position the refractory tube 5 in a predetermined position substantially coaxial with respect to the ferrule metallic 3.

 The central stud has in its middle a central hole 10 adapted to receive the lower end 11 of a central axis 12 carrying centering devices 13, such as discs or spiders, for centering the axis 12 substantially in the axis of the refractory tube 5.

 It is generally simpler to put the refractory tube 5 first, then the metal ferrule 3.

 The axis 12 is higher than the tube 5 and the ferrule 3 and allows the installation of a device, of any known type, shown diagrammatically at 14, for introducing the curable and sinterable refractory composition 2 into the space free 20 formed between the metal shell 3 and the refractory tube 5.

 The curable and sinterable refractory composition 2 is brought into the device 14 by any means shown diagrammatically by the arrow 15, for example by a chute 16.

 In the example shown, the introduction device 14 is a device comprising an annular hopper making it possible to distribute the refractory composition 2 at the same time over the entire periphery of the space 20 between the shell 3 and the refractory tube 5.

 The distributor 14 can be replaced by any other equivalent means, in particular by means pivoting around the central axis 12.

 In the example shown, the refractory tube 5 has at its lower end in contact with the

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 support 4 a collar 5a projecting radially outward and substantially in contact with the interior surface 7 of the shell 3, so as to retain said refractory composition 2 in the space 20 between the shell 3 and the tube 5 before hardening of said composition.

 Any other known means, not shown, can be used, for example a sheet flange fixed to the lower end of the metal shell 3, to retain the refractory composition 2 before it hardens in space 20.

 The refractory tube 5 may be a one-piece tube, or be made from several substantially coaxial ferrules assembled one on the other, for example by means of a mineral adhesive based on silicate or phosphate.

 The refractory tube 5 can be made of refractory concrete, in particular of self-casting refractory concrete, for example based on tabular alumina. It is known that such self-pouring concrete flows easily and can perfectly fill the molding cavity into which it is poured, which makes it possible, after baking in the oven at an adequate temperature, to obtain the ceramic or hydraulic setting. particles constituting this concrete and the elimination of the preparation and constitution water of this concrete, a refractory tube of relatively precise dimensions.

 The refractory tube 5 has a substantially cylindrical shape. This means that the internal surface 18 and the external surface 6 of said tube 5 can be perfectly cylindrical or that one or the other or each of these two surfaces can be slightly frustoconical by widening slightly upwards or towards the low. Similarly, in the case where the refractory tube 5 consists of several ferrules, these ferrules are of

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 preferably cylindrical but could also have their interior surface and / or their exterior surface slightly frustoconical.

 The inner 18 and outer 6 surfaces of the refractory tube 5 are preferably coaxial, but could if necessary be slightly offset from one another.

 One can make a tube 5 or ferrules having a thickness less than 20 mm.

 The metallic ferrule 3 has any known shape. It is preferably equipped with means to facilitate the attachment of the curable composition 2 once it has hardened on the inner surface 7 of the shell 3.

 The ferrule 3 can thus be of cylindrical shape, and present on its internal surface 7 means, for example protrusions projecting inwardly or outwardly, allowing the attachment of the refractory composition 2 after hardening, and schematized at 17 in Figure 1.

vers le haut. In the example shown in Figure 2, the ferrule 3 'has a slightly frustoconical shape flaring

to the top.

 Thus, when the pouring tube 1 is, in a known conventional manner, supported by means, for example ears, shown diagrammatically in 19 in FIG. 2, projecting outwards with respect to said ferrule 3, the refractory composition 2 hardened is retained in its axial position by the roughness 17 or the shape of the inner surface 7 of the shell 3.

 Thus, and in a conventional manner, the external metal casing 3 allows easy handling of the pouring tube 1 and ensures the air tightness of this tube 1 to avoid any contact between the molten metal poured inside the tube, and oxygen from the air.

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 The sinterable refractory composition 2 is for example based on calcined magnesia, also known as baked to death. Its particle size is chosen so as to obtain a very fluid flow of this composition during its introduction inside the space 20 of the tube 1.

This powder is, for example, formed of grains with a main dimension of less than 1 mm, although larger grains are admissible depending on the thickness of the space 20.

 The substantially dry, heat-curable mineral binder is, for example, a hydrated sodium metasilicate powder, used for example in a proportion of between 0.1 and 5% of the total weight of the composition. It is known that such a binder melts at around 80 ° C. while allowing its water of crystallization to escape and hardening.

 Hardening of the mass 2 is obtained by heating the tube 1 to a temperature of the order of 1800C.

 It is also possible to add to the composition, in particular to compensate for the role of fondant held by the binder, other known constituents such as aluminum powder, at a content of between 0.1 and 5%. It is also possible to add bodies known to make the composition more resistant to aggression by the slag, for example carbon powder or chromium oxide.

 The powder thus introduced inside the pouring tube 1 has, for example, a density before hardening of the order of 1.6 g / cm 3, which gives it a certain porosity and therefore a refractory insulating power.

 It is of course possible to vibrate the support 4 and the tube 1 during the introduction of the refractory composition 2, so as to reduce the porosity and to

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 increase the density of the refractory mass 2 once in place.

 One can also modify the particle size and / or the chemical composition between the powder suitable for filling the lower part of the space 20, on the one hand, and that intended to fill the upper part of this space, to modify one or the other of the characteristics of mass 2 after hardening.

 It is thus possible to reduce the average size of the particles adapted to fill the lower part of the space 20, to increase the compactness and the density of the mass 2 contained in the lower part of the tube 1, and / or increase the percentage of powder d aluminum to increase the resistance of the lower part 21 of the tube 1 to attack by the molten metal.

 We can instead increase the proportion of flux in the powder constituting the mass 2 contained in the upper part of the space 20 to facilitate the sintering of this powder which is not in contact with the molten metal and is therefore brought to a temperature lower than that of the lower part 21 of the tube.

 As already said above, the pouring tube 1 shown diagrammatically in FIG. 2 has an outer metal casing 3 slightly flared upwards. It comprises at least two ears 19 allowing the handling of the pouring tube 1.

 The metal casing 3 also carries on its external surface, in a known manner, means, for example studs shown diagrammatically at 24, allowing the fixing of the pouring tube 1, for example by screwing if these studs are arranged in a helix, under the ladle. It also carries a nozzle such that 25 blows a gas into the porous mass.

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 inert under pressure, for example argon, to prevent the suction of air by the jet of molten metal.

 The lower part 21 of the pouring tube 1, adapted to be immersed in the molten metal is, in this example, covered on the outside by a protective sleeve 23 of any known type, produced for example in a sinterable composition based on powder of magnesia, paper fibers and a binder. The binder used can be an organic binder, for example a phenolic binder, insofar as the evolution of hydrogen caused by the decomposition of the binder in contact with the molten metal occurs outside the pouring tube 1 and has a very low risk of being captured by the molten metal.

 A pouring tube has thus been described in several concentric layers, of simple structure, of easy and rapid manufacture, using only inexpensive materials which are easy to use.

 Such a very competitive price pouring tube can easily be adapted to the particular dimensions of the installations of each user.

 In particular, one can provide at the upper part of the tube 1 any conformation, in particular an upper flange on the refractory tube 5, allowing a substantially sealed fixing under the closure device of a ladle.

 Of course, the present invention is not limited to the embodiments which have just been described, and many changes and modifications can be made to them without departing from the scope of the invention.

Claims (10)

1. Method for producing a pouring tube (1), comprising a step of placing a curable and sinterable refractory mass (2) inside a metal ferrule (3), and a step of heating the assembly for hardening the curable mass, characterized in that it comprises the following stages: a) a metal ferrule (3) is substantially cylindrical and is installed on a support (4), in a substantially vertical position; inside the metal shell (3), substantially coaxial thereto, a tube (5) of substantially cylindrical shape made of hardened refractory material and baked in the oven; b) between the outer surface (6) of the refractory tube (5) and the inner surface (7) of the metal shell (3), a substantially dry sinterable refractory composition comprising a substantially dry heat-curable mineral binder is introduced; c) the assembly is heated to harden the curable composition.  2. Method according to claim 1, characterized in that the refractory tube (5) is made of self-pouring refractory concrete, for example based on tabular alumina.  3. Method according to claim 1 or 2, characterized in that one uses a refractory tube (5) in one piece or made from several coaxial ferrules assembled one on the other.  4. Method according to any one of the preceding claims, characterized in that there is introduced into the space (20) between the refractory tube (5) and the metal shell (3) a powder whose composition varies between the part lower (21) of <Desc / Clms Page number 12>  tube (1), adapted to be immersed in the molten metal, and the upper part (22) of the tube (1).  5. Method according to any one of the preceding claims, characterized in that a powder based on magnesia is used; 6. Method according to any one of the preceding claims, characterized in that a hot-hardening mineral binder of the hydrated sodium metasilicate type is used for the powder; 7. Method according to any one of the preceding claims, characterized in that the tube (1) is vibrated during the introduction of the powder and before hardening; 8. Method according to any one of claims, characterized in that one covers the lower part of the metal shell (3) by means of a protective sleeve (23).  9. pouring tube, characterized in that it is produced by implementing the method according to any one of the preceding claims.  10. pouring tube according to claim 9, characterized in that it comprises, on its external face, projecting means (19) for its handling, and / or projecting means (24) for its fixing under a pocket , and / or a nozzle (25) for injection of an inert gas under pressure.