JPH0711395B2 - Induction furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to an induction furnace having an improved refractory lining structure.

(Prior Art) For example, a crucible induction furnace is generally constructed in a structure as shown in FIG. That is, the outer frame 1 is formed of heat-resistant cement called coil cement.
A water-cooled heating coil 2 is arranged so as to surround the.
An iron container 3 called a former is housed in the outer frame 1, and a fireproof lining 4 is provided between the iron container 3 and the outer frame 1. The ingot 5 to be melted is housed in the iron container 3 as shown in the figure, and is heated and melted together with the iron container 3 by passing a high frequency current through the heating coil 2.

Here, as the above-mentioned refractory lining 4, conventionally, a method of forming it by a wet refractory containing a small amount of water, and a method of forming it by a dry powder refractory that is constructed without water was there.

(Problems to be Solved by the Invention) In this type of induction furnace, since the fireproof lining 4 is heavily consumed, it is common to repeat the furnace construction work for repairing the fireproof lining in about one week. However, in the induction furnace constructed by the former wet refractory, the operation cannot be started unless the water content in the refractory lining 4 is sufficiently removed. Therefore, after the construction, the burner is heated to be sufficiently dried, and then the ingot 5 is removed. Is required to gradually melt the mixture. For this reason, there is a problem that the start-up is slow after the furnace is built, and eventually the casting line is stopped for a long time during the refurbishment / building of the induction furnace and the productivity of the line is reduced.

Moreover, in this type of induction furnace, since the molten metal is repeatedly pumped out and the ingot 5 is replenished, the refractory lining 4 undergoes a large temperature change each time and cracks due to spalling inevitably occur. However,
In the refractory lining 4 made of wet refractory,
Since the whole is in a state of being integrally hardened, the cracks once generated are likely to propagate so as to penetrate the entire refractory lining 4 as shown in FIG. For this reason, there is a problem that the molten metal easily penetrates the refractory lining 4 and reaches the outer frame 1 at an early stage, and there is a high risk of causing a serious accident such as corrosion by the water-cooled heating coil 2 and explosion. .

On the other hand, in the induction furnace constructed with dry powder refractory,
Not only is the furnace construction work easy because the outer frame 1 is filled with powder refractory material, but it is not necessary to remove the water in the refractory lining 4, so the start-up after furnace construction is quick. There is an advantage. Further, since the outer layer of the refractory lining 4 has a sand layer shape that is not integrally solidified, even if the molten metal reaches that portion, the molten metal diffuses into the sand layer and soaks into the sand layer to solidify and heat. Coil 2
The advantage is that the intrusion of molten metal in the direction is blocked and the safety is high.

However, the induction furnace constructed with this powder refractory material has a major drawback that it is apt to cause an electrical failure as described below, and that the refractory lining 4 needs to be frequently repaired and constructed. That is, in this type of induction furnace,
A molten metal leak detector is provided to detect that the molten metal has penetrated the refractory lining 4 to prevent an accident. This is a configuration in which, when the molten metal leaks to the outside through the crack generated in the refractory lining 4, it is detected by utilizing the fact that the electric resistance between the outer peripheral portion of the refractory lining 4 and the molten metal decreases. is there. However, the ingot 5 put into the induction furnace contains a low melting point metal such as zinc due to scrap of the zinc-coated steel sheet, for example. For this reason,
Zinc vapor is generated from the molten metal and gradually penetrates into the refractory lining toward the outside, and finally condenses in the outer periphery of the refractory lining having a low temperature to deposit metallic zinc. Then, due to the metallic zinc, the electrical resistance between the outer peripheral portion of the refractory lining 4 and the molten metal sharply decreases, causing malfunction of the molten metal leak detector. By the way, in this type of induction furnace using a powder refractory, the hot water leak detector malfunctions when the continuous operation is continued for about one day. Moreover, if such a large amount of metallic zinc is deposited, it may cause a short circuit accident of the heating coil 2.

Further, when the crucible induction furnace is in operation, a thin sintered layer of about 1 to 2 cm is formed in the innermost layer of the refractory lining 4 by receiving heat from the molten metal. However, in this operating state, the slag 6 floats on the surface of the molten metal as shown in FIG.
Since the internal molten metal causes thermal convection as shown by the arrow, the portion of the refractory lining 4 that contacts the slag 6 is
The reaction with the slag 6 and oxygen in the air easily occurs, and since the slag 6 rubbed by the convectional molten metal is rubbed, the erosion as shown in the figure proceeds. Once such erosion that scrapes away the sintered layer occurs, the unsintered layer having a lower wear resistance is exposed to the slag 6, so that the erosion progresses at an accelerated rate, and eventually, Fireproof lining 4
Is deteriorated at an early stage, and renovation and construction work is required frequently.

The present invention has been made in view of the above circumstances. Therefore, the purpose is that the repair / construction work is easy and excellent in safety, and yet low melting point metal vapor penetrates the refractory lining to cause an electrical failure, or the refractory lining is slag-induced. (EN) It is an object to provide an induction furnace having a lining structure that can prevent deterioration at an early stage.

[Structure of the Invention] (Means for Solving the Problems) The induction furnace of the present invention has a refractory lining and a water content of 7%.
% Or less of a ramming refractory material or a castable refractory material, which is formed in advance into a predetermined shape, and an outer layer made of a powder refractory material which surrounds the inner layer.

(Function) The inner layer of the refractory lining comes into contact with the high-temperature molten metal during operation and the sintering reaction proceeds, and a sintered layer is formed on the surface. This inner layer is
Since it is formed of a dense ramming refractory or castable refractory having a low porosity, its sintered layer has excellent corrosion resistance as compared with the sintered layer of a powder refractory. Therefore, the corrosion of the refractory lining due to the molten metal can be suppressed for a long period of time, and the life of the induction furnace can be extended.

Moreover, since the sand-layered outer layer made of powder refractory is provided on the outer side of the inner layer, even if a crack occurs in the inner layer and the molten metal enters the crack, the tip of the molten metal is As it diffuses into the interior and soaks into it, it solidifies and prevents further intrusion of the molten metal, providing high safety.

Moreover, since the inner layer is made of a ramming refractory or castable refractory having excellent formability, for example, the inner layer is formed by these refractories on the outer circumference of the iron container, and this is stored in the outer frame of the induction furnace. At the same time, a construction method of filling powder refractory between the outer frame and the inner layer can be adopted. According to this, it is possible to complete the inner layer of the refractory lining with the iron container in the factory production, and bring it to the induction furnace construction site and fill the powder refractory to complete the outer layer, The construction work of the induction furnace is also simpler than the construction in which the entire refractory lining is composed of either wet refractory or dry refractory.

On the other hand, in the case where the refractory lining has a two-layer structure as described above, it is also conceivable that the inner layer is constituted by using another wet refractory such as a plastic refractory, but in the present invention, this is added moisture. Since the amount is 6% or less of ramming refractory or castable refractory, it is possible to reduce the porosity of the refractory lining to prevent penetration of metal vapor and to homogenize the whole. it can. That is, the water added to the wet refractory is removed in the drying step, which causes pores in the refractory. However, since the plastic refractory contains as much as 8% of water for imparting plasticity, the porosity is larger than that of the ramming refractory or the castable refractory, and the penetration of metal vapor is large. On the other hand, in the present invention, since the inner layer is made of a ramming refractory or castable refractory having an added water content of 7% or less, the porosity is small, the penetration of metal vapor is prevented, and the outer peripheral portion of the refractory lining is prevented. Precipitation of metal can be suppressed to a small amount. In addition, ramming refractory or castable refractory need only be filled in the mold space and compacted, so it has better moldability than plastic refractory that is putty-like and needs to be adhered to the mold. It is excellent, and it becomes possible to suppress the generation of defects such as cracks by homogenizing the entire inner layer. The smaller the amount of water added, the more preferable, but the minimum amount of water added is restricted in terms of ensuring workability and formability. Further, the upper limit of the amount of added water, the iron container 16 is arranged concentrically from the viewpoint of suppressing the porosity of the inner layer, the amount of added water in the cylindrical space between the molding frame and the iron container 16 is, for example, 3.5%. Cast castable refractories adjusted to ~ 5.5% range to harden, then
This was done by removing the molding frame. As a result, the solidified inner layer 14 is integrated around the iron container 16, and thus the inner layer 14 is housed in, for example, a drying furnace and dried at about 300 ° C. to sufficiently remove water.

On the other hand, the outer layer 15 is made of, for example, a dry powder refractory made of alumina, magnesia, silica or the like, and is constructed at the site where the induction furnace is installed. That is, the inner layer 14 factory-manufactured as described above is stored in the outer frame 12 in which the powder refractory is put in a predetermined thickness in advance, and the powder refractory is beaten and solidified in the space around the inner layer 14. While filling it closely. This completes the induction furnace construction work shown in FIG. Although not shown in the drawings, since the outer peripheral portion of the outer frame 12 is provided with a molten metal leak detector for detecting the leakage of the molten metal by measuring the electrical resistance between the outer peripheral portion of the refractory lining 11 and the molten metal. It should be 7% or less.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows a completed form of a crucible-type induction furnace. An outer frame 12 made of coil cement is provided outside a container-shaped refractory lining 11.
Is provided, and the heating coil 13 is disposed on the outside thereof. Fireproof lining 11 is inner layer 14 and outer layer
A two-layered structure consisting of 15 is provided inside the fireproof lining 11 with an iron container 16 for loading the ingot 10. The iron container 16 has various diameters depending on the volume of the molten metal required, but here, for example, the inner diameter is about 60 cm, and a large number of them are provided on the peripheral wall thereof in order to enhance the adhesion of the inner layer 14. A through hole 16a is formed.

The inner layer 14 is formed by casting, for example, an alumina castable refractory, and has a thickness of, for example, about 3 to 4 cm. This casting process is in a cylindrical molding frame, for example.

In order to operate the induction furnace constructed in this way, the ingot 10 to be melted is put into the iron container 16 and the heating coil
Apply current to 13. With this, the ingot 10 and the iron container 16
Is heated and melted, and the refractory lining 11 is gradually sintered from the inside. In order to sufficiently advance this sintering reaction, it is preferable to carry out stepwise temperature raising, in which the temperature is maintained at a constant temperature at some temperatures on the way to the final temperature.

In the operating state of the induction furnace, the iron container 16 is melted and the molten metal is in direct contact with the inner layer 14 of the refractory lining 11. In addition, the slag floats on the surface of the molten metal, and this slag continues to rub the surface of the inner layer 14 by riding on the molten metal which causes heat convection. Therefore, the portion of the inner layer 14 that is in contact with the slag always tends to undergo physical and chemical complex erosion. However, in this embodiment, the inner layer of the refractory lining 11 is
Since 14 is made of castable refractory, which has a finer structure than the sintered layer of powder refractory, it has excellent corrosion resistance and can extend the life of the refractory lining 11. The frequency of furnace construction work can be reduced. Since it is necessary to stop the casting line, etc. while the induction furnace is being refurbished and constructed, it is possible to reduce the frequency of induction furnace refurbishment and construction, as in this example, to stop the line. This means that the frequency can be reduced and the productivity can be improved.

Further, while the induction furnace is in operation, the molten metal is repeatedly pumped out and the ingot is replenished, so that the refractory lining 11 is susceptible to thermal shock and spalling.
However, in this embodiment, even if cracks due to spalling occur in the inner layer 14, since the refractory lining 11 has a two-layer structure, the progress thereof stops in the inner layer 14 and does not reach the outer layer 15. Therefore, as shown in FIG. 2, since the crack C generated in the inner layer 14 is relatively large, even if the molten metal immediately penetrates into the inner layer 14, the tip of the molten metal diffuses into the outer layer 15 forming a low temperature sand layer. Soaks and solidifies. With this, the high temperature molten metal can be treated with fireproof lining 11 at a stretch.
It is possible to surely prevent a serious accident such as an explosion by penetrating through and penetrating the water-cooling type heating coil 12 and greatly increasing safety.

Furthermore, according to the crucible-type induction furnace of this embodiment, it becomes possible to easily perform the refurbishment / building work which is regularly performed, and the downtime of the casting line between the refurbishment / building of the induction furnace is shortened. Can increase the productivity of the line. That is,
In order to repair or build an induction furnace, the refractory lining 11 that has been eroded and becomes old must be discarded, and a new refractory lining 11 with the structure shown in Fig. 1 must be built. In this case, As described above, the inner layer 14 with the iron container 16 produced in the factory in advance may be carried into the construction site, housed in the outer frame 12, and filled with the powder refractory to form the outer layer 15. On the other hand, in the conventional structure in which the entire refractory lining is composed of wet refractory, all of the work is on-site construction and requires a large amount of work, and in addition, it takes a long time to dry the large wet refractory. Above, there was a situation that the construction work of the refractory lining is considerably troublesome and takes a long time, but according to the structure of this embodiment, the inner layer 14 pre-manufactured with castable refractory is small, and the factory Since it has been dried sufficiently during production, on-site construction will be significantly easier. Further, in the conventional structure in which the entire refractory lining is composed of a dry powder refractory, it is necessary to fill a large amount of powder refractory, but according to the structure of this embodiment,
Only the outer layer 15 needs to be made of powder refractory,
Construction work is easier than the conventional structure in which the whole is made of powder refractory.

Moreover, in this embodiment, since the inner layer 14 is composed of the castable refractory having the added water content of 7% or less, the entire refractory lining is made of the powder refractory or the plastic refractory having a large amount of the added water. The porosity is smaller than that of the one constituted by the above. Therefore, even if a low melting point metal such as zinc is contained in the molten metal and metal vapor is generated from the molten metal, it is possible to prevent the metal vapor from penetrating into the refractory lining 11. It is possible to suppress the deposition of metal on the outer peripheral portion of 11 to a small amount, and it is possible to prevent the malfunction of the hot water leak detector and the occurrence of a short circuit of the heating coil 2 from occurring. By the way, the apparent porosities of the alumina castable refractory and the plastic refractory used in this example are listed below together with the chemical components and the amount of added water.

In addition, the castable refractory forming the inner layer 14 has excellent workability compared to the plastic refractory, and the entire inner layer 14 can be molded at once, so that the entire inner layer 14 can be homogenized,
Therefore, it is possible to suppress the occurrence of defects such as cracks in the inner layer 14, and it is possible to further extend the life of the refractory lining 11.

Although the inner layer 14 is formed in a cylindrical shape without lowering in the above-described embodiment, the present invention is not limited to this, and may be formed in a container shape with a bottom as shown in FIG. Further, the refractory forming the inner layer is not limited to the alumina castable refractory shown in the above examples, it may be a basic castable refractory containing a large amount of magnesium oxide, also ramming refractory. Is also good. As the ramming refractory material, for example, an alumina-based material having a main component of 83% alumina and a silica content of 10% can be typically used. In this case, the added water content is preferably 5% to 6%. In addition, the present invention is not limited to the embodiments described above and shown in the drawings. For example, the present invention is not limited to a crucible-type induction furnace, but can be applied to a groove-type induction furnace in which only a heated portion of molten metal is independent. However, various modifications can be made without departing from the scope of the invention.

[Effects of the Invention] As described above, in the induction furnace of the present invention, the refractory lining has an inner layer formed in advance into a predetermined shape with a ramming refractory or castable refractory having an added water content of 7% or less, and Since it is composed of an outer layer made of powder refractory that surrounds the inner layer, it is easy to carry out repairs and furnace construction, and has excellent safety, yet the low-melting metal vapor penetrates the refractory lining. It has an excellent effect that it is possible to prevent electrical failure and prevent the fireproof lining from being deteriorated early by slag.

[Brief description of drawings]

1 and 2 show an embodiment of the present invention. FIG. 1 is a vertical cross-sectional view of a crucible induction furnace, and FIG. 2 is an enlarged vertical cross-sectional view showing a state where cracks are generated in an inner layer. FIG. 3 is a view corresponding to FIG. 1 showing a different embodiment of the present invention, FIG. 4 is a view corresponding to FIG. 1 showing a conventional crucible induction furnace, and FIG. 5 is a view corresponding to FIG. [Fig. 3] is a vertical sectional view of the same operating state. In the drawings, 11 is a refractory lining, 13 is a heating coil, 14 is an inner layer, 15 is an outer layer, and 16 is an iron container.

Claims (1)

[Claims] 1. A refractory lining surrounding a molten metal of an induction furnace, wherein the refractory lining is preliminarily formed into a predetermined shape with a ramming refractory or castable refractory having a water content of 7% or less. An induction furnace comprising an inner layer and an outer layer made of powder refractory surrounding the inner layer.