EP0043160A1 - Casting equipment for fused masses - Google Patents

Abstract

1. A casting nozzle for molten material and more particularly suitable for liquid steel, characterized in that it comprises at least one part of unburned uncompressed concrete consisting of (1) a granulate or aggregate of particules containing more than 99% by weight of alumina which has previously undergone heat treatment up to the temperature of fusion or fritting and (2) a binder consisting of from about 75 to 85% by weight of alumina, the rest of the binder substantially consisting of calcium oxide, this binder having previously undergone heat treatment up to the temperature of fusion, said part being covered with a layer of degradable refractory concrete which is likely to undergo gradual erosion due to contact with the molten materials as they are cast.

Description

The present invention relates to devices for casting molten materials; it advantageously applies to molten materials of mineral origin and is more particularly suitable for liquid steel.

Such devices are already known, notably equipping steelworks pouring ladles, with bottom emptying. These devices allow the complete flow of the steel contained in the pocket.

The pouring equipment for these pockets can take various forms. It can in particular be of the conventional cattail type or of the sliding plate type. In the case of the sliding plate type, for example, the casting equipment for a steelworks ladle consists of at least one internal nozzle, one external nozzle and a system located between the two nozzles. , to adjust or interrupt the flow of molten material.

The internal nozzle, sometimes called the collecting nozzle, is inserted into a seat brick, which is part of the casting equipment, and is itself housed in the refractory lining of the bag.

The external nozzle, which is sometimes called a regulating nozzle, is located under the pocket in the extension of the collecting nozzle; it is used in particular to calibrate and center the casting jet.

Between the two nozzles is disposed a system of flat or cylindrical sliding plates, ensuring the adjustment of the flow rate of the molten material, in particular the speed of casting.

In some cases, the various constituent elements of the casting equipment are provided with a mold, for example a metal casing, which ensures correct shaping of the refractory materials required for their manufacture and which gives them a certain resistance to stresses. mechanical.

Until now, baked refractory materials have been used for the production of the constituent elements of the casting equipment, the cost of which was obviously conditioned by their quality.

However, due to the severe erosion to which these materials are subjected during casting, their service life is extremely short and rarely exceeds a casting operation. The section of the flow channel becomes irregular, the jet is disturbed and the casting is difficult. It is therefore necessary to often replace all of the equipment, which leads to disassembly and reassembly costs, to which is added the price of the equipment itself.

The subject of the present invention is casting equipment which does not have the drawbacks which have just been mentioned.

The casting equipment according to the invention has, compared to previous devices, the double advantage of better resistance to erosion and lower manufacturing cost. Thanks to its increased resistance to erosion which is caused by the molten material, the casting equipment according to the invention has a longer service life and makes it possible to space out the replacements. Furthermore, thanks to the invention, the manufacture of the equipment casting does not require cooking of its various constituent elements, which results in lower energy consumption.

The casting equipment, object of the present invention, is essentially characterized in that at least the surfaces of the parts of the equipment which come into direct contact with the molten material are formed, at least in part, by means of refractory concrete.

According to a first embodiment of the invention, the raw materials necessary for the manufacture of refractory concretes belong to only one of the following three categories of bodies: acids, basic and neutral.

According to another embodiment of the invention, these raw materials comprise a combination of at least two of the three categories of the following bodies: acids, basic or neutral.

According to yet another form of the invention, the refractory concrete is poured directly into a mold, for example a metal casing, which is an integral part of the casting equipment.

According to another embodiment of the invention, the refractory concrete used is reinforced, for example by a metal frame, which makes it possible to avoid the use of the mold forming an integral part of the casting equipment.

In a particularly advantageous embodiment of the invention, the casting equipment consists, at least in part, of a neutral refractory concrete whose alumina content is greater than about 90% by weight.

Preferably, the alumina content of the refractory concrete is between approximately 90 and 99% by weight, this content being more particularly close to 95%.

The refractory concrete used according to the present invention to form at least a portion of the casting equipment, has a silica content less than about 1 _^0/00 and a content of iron of not more than approximately 2 ‰ by weight, for alumina content of about 95% by weight.

The refractory concrete used in the context of the present invention is composed of an aggregate consisting of a very high proportion of alumina and of a refractory binder with hydraulic setting.

The aggregate of refractory concrete whose grains have a dimension of 0 to 6 mm consists essentially of alumina having previously undergone a heat treatment up to the melting or sintering temperature.

The binder of refractory concrete is a refractory cement with hydraulic setting of the superaluminous type, containing approximately 75 to 85% of alumina and calcium oxide. This binder is mixed with the aggregate in a proportion which can vary between approximately 8 and 20% by weight relative to the dry aggregate.

The refractory concrete used to constitute at least part of the casting equipment preferably contains dispersing and stabilizing agents for the binder, advantageously chosen from pyrophosphate. sodium and sodium carbonate, these agents being used in proportions of between approximately 1 ‰ and 4 ‰ of the weight of the binder.

The refractory concrete also preferably contains a plasticizer, for example a cellulose derivative, such as carboxymethylcellulose or sulphite cellulose in a proportion of approximately 1 ‰ by weight relative to the binder.

According to a feature of the invention, the quality of refractory concrete is improved by adding carbon in crystallized or amorphous form in a proportion of up to 7% of the total weight of the concrete.

The parts constituting the casting equipment, in particular the nozzles and the plates, can be obtained by filling a mold having the shape of the desired part by means of a mixture of refractory aggregates and refractory binders previously tempered with a minimum quantity. of water. Before setting the refractory concrete, the above mixture is advantageously subjected to compaction, tamping or vibration to improve the mechanical strength of the concrete.

The invention also relates to casting equipment in which the nozzle or nozzles consist of refractory concrete of the type defined above, but in which the part with which the cast metal comes into contact consists of a degradable refractory concrete, ie that is to say undergoing progressive erosion during the casting, so that it is done at a constant rate. The degradable part of the nozzles advantageously consists of a refractory concrete of the silico-aluminous type having an alumina content of approximately 45 to 65%, preferably approximately 47 to 50% by weight.

It is also possible to use as degradable concrete a refractory concrete containing about 55 to 60% by weight of alumina and titanium dioxide. The content of iron oxide (Fe ₂ 0 ₃ ) in these degradable concretes may not exceed 0.6%.

The aggregate of degradable refractory concrete advantageously has an alumina content of about 45 to 65% by weight, the rest being mainly composed of silica. As for the binder with hydraulic setting of this concrete, it is of the silico-aluminous type containing approximately 25 to 40% by weight of calcium oxide.

The degradable refractory concrete parts can be molded in situ in refractory concrete nozzles with a very high alumina content.

The Applicant has found that the degradable refractory concrete layer adheres perfectly to the part of the nozzle with very high alumina content which surrounds it and that this part undergoes homogeneous wear at its contact surface with the molten metal.

The following examples illustrate the invention.

Example 1

Composition of neutral refractory concrete.

Aggregate: 92%

Binder: 8%

• - plus de 99 % d'alumine (A₂O₃)
• - moins de 1 ‰ de silice
• - moins de 2 ‰ d'oxyde de fer (Fe₂0₃)
• - solde : mélange de magnésie, d'oxyde de potassium et d'oxyde de sodium.

Composition of the aggregate in grains from 0 to 6 mm which have been heat treated beforehand to the melting or sintering temperature:

• - more than 99% of alumina (A ₂ O ₃ )
• - less than 1 ‰ of silica
• - less than 2 ‰ of iron oxide (Fe ₂ 0 ₃ )
• - balance: mixture of magnesia, potassium oxide and sodium oxide.

• - 75 à 85 % d'alumine
• - 20 % d'oxyde de calcium.

Composition of the binder in grains of less than 50 microns heat treated up to the melting temperature:

• - 75 to 85% alumina
• - 20% calcium oxide.

The mixture of aggregate and binder in the above-mentioned proportions is added with a dispersing and stabilizing agent consisting of sodium pyrophosphate or sodium carbonate in an amount of approximately 2 ‰ relative to the binder.

Refractory concrete parts are obtained by spoiling the mixture of aggregate and refractory binder with a minimum amount of water in a mold. Before the hydraulic setting of the binder, the mixture is packed, compacted or vibrated.

Example 2

• Agrégat : 85 %
• Liant : 15 %

Composition of degradable refractory concrete:

• Aggregate: 85%
• Binder: 15%

• - 60 % d'alumine en grains
• - 38 % de silice (Si0₂)
• _{- 1} % de ^Fe ₂ ⁰3
• - 1 % d'un mélange de magnésie, d'oxyde de potassium et d'oxyde de sodium.

Composition of the aggregate (soft chamotte prepared between 800 and 1100 ° C) in grains from 0 to 3 mm:

• - 60% alumina grains
• - 38% silica (Si0 ₂ )
• _{- 1} % ^Fe ₂ ⁰ 3
• - 1% of a mixture of magnesia, potassium oxide and sodium oxide.

• - 50 % d'alumine
• - 10 % de silice
• - 40 % d'oxyde de calcium.

Composition of the binder in grains less than 50 microns heat treated up to the melting temperature:

• - 50% alumina
• - 10% silica
• - 40% calcium oxide.

The mixture of aggregate and binder mixed with a minimum of water is molded in situ in the interior part of a nozzle made of refractory concrete of the type described in Example 1.

The Applicant has used for the casting of steel collecting nozzles made of known cooked refractory materials, having the compositions given in the following table:

With types B and C, it was found, after a single casting of 170 tonnes of steel, with a duration of 35 minutes, a nozzle breakthrough rate of about 10% with type B of refractory material baked and about 15% with type C of baked refractory material.

Furthermore, after a casting of 170 tonnes of steel with a duration of 35 minutes using nozzles of baked refractory material of type A, it has been found that the nozzles have numerous cracks which can lead in 5 to 6 % of cases up to a breakthrough of the molten metal through the wall of the nozzles.

Figure 1 of the accompanying drawings shows schematically a plan view of the head of a nozzle of baked refractory material of type A before a steel casting, while Figure 2 schematically shows a cross section in the body of the same nozzle after a steel casting (170 tonnes in 35 minutes).

In FIG. 1, there is no change in the nozzle, while in FIG. 2, it can be seen that this same nozzle has numerous cracks designated by the reference notation 1.

Using refractory concrete nozzles, according to Example 1, it was possible to make three steel castings (510 tonnes) without any drilling of the nozzles, nor any cracking of the latter, the duration of each casting being included between 35 and 55 minutes. This result is all the more surprising since one should expect erosion of the nozzles faster than the rate of ceramization of the refractory concrete of which they are made up.

Using refractory concrete nozzles, according to Example 1, internally lined with a degradable refractory concrete layer according to Example 2, we found no breakthrough or cracking of the nozzles after several castings, despite the gradual erosion of the internal layer of degradable refractory concrete.

Furthermore, the internal diameter of the nozzle, which was 42 mm before casting, reached a value of 71 mm at the end of this casting. This gradual increase in the internal diameter of the nozzles made it possible to maintain a substantially constant flow rate, despite the decrease in the static pressure of the molten steel contained in the ladle.

The comparative tests described above demonstrate the best reliability manifested by a remarkable erosion resistance of the refractory concrete preferably with a high alumina content used according to the invention, this erosion resistance being surprisingly better than that of the materials. baked refractories commonly used so far, despite the absence of baking during the production of casting equipment.

Since the manufacture of refractory concrete pouring equipment does not require curing, the manufacture and use of these refractory concretes instead of the cooked refractory materials, has significant advantages, since one can use a longer material (refractory concrete) requiring no energy consumption for the manufacture of casting equipment, in particular nozzles.

• 1. une réduction des incidents d'aciérie, par un meilleur centrage et un meilleur calibrage du jet et par une plus grande régularité du débit de coulée;
• 2. une réduction de consommation du nombre d'équipements de coulée, dont la durée de vie est prolongée, ce qui procure une réduction des coûts d'achat et d'entretien;
• 3. un bilan énergétique favorable : les bétons réfractaires ne nécessitent pas de cuisson préalable et acquièrent la résistance désirée par simple séchage à l'air;
• 4. le prix de revient de l'équipement en béton réfractaire suivant l'invention est nettement inférieur à celui d'un équipement en produit réfractaire cuit de type classique du fait que l'équipement suivant l' invention ne nécessite pas de cuisson mais peut être obtenu par simple prise hydraulique.

In short, the casting equipment according to the invention has the following advantages:

• 1. a reduction in steelworks incidents, by better centering and better calibration of the jet and by greater regularity of the flow rate;
• 2. a reduction in consumption of the number of casting equipment, the service life of which is extended, which reduces purchase and maintenance costs;
• 3. a favorable energy balance: refractory concretes do not require prior curing and acquire the desired resistance by simple air drying;
• 4. the cost price of the refractory concrete equipment according to the invention is much lower than that of a cooked refractory product of the conventional type because the equipment according to the invention does not require baking but can be obtained by simple hydraulic plug.

It is obvious that the invention is not limited to the details described above and that numerous modifications can be made without departing from the scope of the invention.

Thus, although the present invention preferably relates to the casting of ladle steel, it is not limited to this unique object; it also relates to the casting of other molten materials in the liquid state, for example non-ferrous materials, glass and other such materials.

Claims (21)

1. Equipment for casting molten materials, more particularly suitable for liquid steel, characterized in that at least the surfaces of the parts of this casting equipment which come into direct contact with the molten material are formed, at least in part, using refractory concrete. 2. casting equipment according to claim 1, characterized in that the raw materials necessary for the manufacture of refractory concretes belong to only one of the following three categories of bodies: acids, basic and neutral. 3. Casting equipment according to claim 1, characterized in that the raw materials necessary for the manufacture of refractory concretes comprise a combination of at least two of the three categories of the following bodies: acids, basic or neutral. 4. casting equipment according to any one of the preceding claims, characterized in that the refractory concrete is poured directly into a mold, for example a metal casing, which is an integral part of the casting equipment. 5. casting equipment according to any one of claims 1 to 3, characterized in that the refractory concrete used is reinforced for example by a metal frame, which avoids the use of the mold forming an integral part of casting equipment. 6. casting equipment according to claim 1, characterized in that it consists, at least in part, of a refractory concrete whose alumina content is greater than about 90% by weight of the dry mixture. 7. Casting equipment as claimed tion 6, characterized in that the alumina content of the refractory concrete is between 90 and 99% by weight of the dry mixture. 8. casting equipment according to either of claims 6 and 7, characterized in that the alumina content of the refractory concrete is about 95% by weight of the dry mixture. 9. casting equipment according to claim 8, characterized in that the silica content of the refractory concrete is less than about 1 ‰ by weight. 10. Casting equipment according to claim 8, characterized in that the iron content is less than about 2 ‰ by weight. 11. casting equipment according to any one of the preceding claims, characterized in that the refractory concrete contains an aggregate formed of more than 99% by weight of alumina having undergone a prior heat treatment up to the melting temperature or sintering. 12. Pouring equipment according to any one of the preceding claims, characterized in that the refractory concrete contains a binder with hydraulic setting with a high alumina content having undergone a heat treatment up to the melting temperature. 13. casting equipment according to claim 12, characterized in that the refractory concrete contains a binder formed from about 75 to 85% by weight of alumina, the rest being essentially calcium oxide. 14. casting equipment according to any one of the preceding claims, characterized in that the refractory concrete consists of about 8% of binder and about 92% of aggregate. 15. Pouring equipment, characterized in that it comprises at least one part of refractory concrete according to any one of the preceding claims, covered with a layer of degradable refractory concrete capable of undergoing progressive erosion due to the contact of molten materials during their casting. 16. casting equipment according to claim 15, characterized in that the degradable refractory concrete contains, as aggregate, a soft chamotte previously treated at a temperature between 800 and 1100 ° C. 17. casting equipment according to any one of claims 15 and 16, characterized in that the degradable refractory concrete is of the silico-aluminous type consisting of about 45 to 65% by weight of alumina. 18. The following casting equipment, claim 17, characterized in that the alumina content of degradable refractory concrete is about 47 to 50% by weight of the dry mixture. 19. casting equipment according to any one of claims 15 to 18, characterized in that the degradable refractory concrete contains an aggregate whose alumina content is approximately 45 to 65% by weight of alumina, the rest being mainly made of silica. 20. casting equipment according to any one of claims 15 to 19, characterized in that the degradable refractory concrete contains a binder with hydraulic setting of the silico-aluminous type containing approximately 25 to 40% by weight of calcium oxide. 21. casting equipment according to any one of claims 17 and 18, characterized in that the degradable refractory concrete contains about 85% by weight of aggregate and about 15% by weight of binder.

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