WO2015037408A1

WO2015037408A1 - Crucible for induction heating furnace

Info

Publication number: WO2015037408A1
Application number: PCT/JP2014/071896
Authority: WO
Inventors: 岡田　民雄; 大橋　秀明; 正之奥山; 克行白川
Original assignee: 日本坩堝株式会社
Priority date: 2013-09-13
Filing date: 2014-08-21
Publication date: 2015-03-19
Also published as: JP5745588B2; JP2015055462A

Abstract

Provided is a highly durable crucible for an induction heating furnace with which a high-melting-point metal can be heated and melted efficiently. This induction heating furnace crucible (1), which melts a high-melting-point metal (M) such as cast iron by means of induction heating from an induction coil (11), is equipped with a container-shaped inside layer (2) comprising a refractory holding the high-melting-point metal (M), and an outside layer (3) covering at least the side wall part (20) of the inside layer (2) and comprising a heat-generating body that generates heat by means of induction heating.

Description

Induction furnace crucible

The present invention relates to an induction furnace crucible suitable for melting metals, particularly high melting point metals.

As a container for dissolving and holding a low melting point metal such as aluminum, a crucible (black crucible) mainly composed of graphite or carbon is generally used. On the other hand, when melting and retaining refractory metals such as cast iron, cast steel, special steel, and copper alloys, black crucibles are severely worn away by oxidation when used in a high temperature atmosphere for a long time, and react with molten cast iron. The black crucible cannot be used because of contamination. Therefore, a crucible (white crucible) made of a refractory material, which is mainly composed of alumina, silica, or the like, and is excellent in corrosion resistance against refractory metals, is used.

In order to dissolve the refractory metal using the white crucible, an induction coil 101 is disposed around the white crucible 100 as shown in FIG. Sand (indefinite shape material) 102 is arranged. An insulating material 103 is disposed on the inner surface of the induction coil 101. When the refractory metal M is accommodated in the white crucible 100 and a voltage is applied to the induction coil 101 disposed around the white crucible 100, the refractory metal M in the white crucible 100 is induction-heated by electromagnetic induction. (See, for example, Patent Document 1).

JP 2009-228919 A

However, the white crucible 100 does not generate heat due to electromagnetic induction, and when the refractory metal M is introduced into the white crucible 100 to start melting, the white crucible 100 is in a normal temperature state. Therefore, the white crucible 100 may be deprived of heat from the refractory metal M that is induction-heated until the white crucible 100 is heated. Also, when the melting of the refractory metal M is completed, the molten refractory metal (molten metal) is taken out and the next refractory metal M is melted. Since the white crucible 100 is cooled later, the heat from the refractory metal M may be similarly removed. Therefore, it takes time to heat and dissolve the refractory metal M, and the energy cost increases, and there is a possibility that it cannot be efficiently heated and dissolved. In addition, alumina and silica have lower thermal conductivity than graphite, and insufficient preheating causes a large temperature difference between the inner surface side and the outer surface side of the white crucible 100. When the refractory metal M is melted, there is a risk that cracks are likely to occur due to thermal shock.

The present invention has been made by paying attention to the above-described problems, and an object of the present invention is to provide a highly durable induction furnace crucible that can efficiently heat and melt a high melting point metal.

The object of the present invention is an induction furnace crucible for melting metal by induction heating from an induction coil, wherein a container-shaped inner layer made of a refractory material containing metal and at least a side wall portion of the inner layer are provided. And an outer layer made of a heating element that generates heat by induction heating.

In the induction furnace crucible having the above-described configuration, it is preferable that the refractory mainly contains at least one selected from the group consisting of silicon dioxide, alumina, magnesia, zirconia, silicon carbide, and silicon nitride.

Moreover, it is preferable that the heating element mainly contains at least one selected from the group consisting of carbon and graphite.

In addition, the electrical resistivity value of the outer layer is preferably 100 × 10 ⁻³ Ωcm or less.

Moreover, it is preferable that the thickness of the outer layer is equal to or less than the thickness of the inner layer.

The outer layer is preferably formed in a cylindrical shape that covers only the side wall of the inner layer.

Further, the outer layer is preferably formed by CIP molding, and the inner layer is preferably formed by pouring a casting material into the outer layer in which a mold is disposed. The outer layer may include a slurry mainly including at least one selected from the group consisting of carbon and graphite, or a graphite sheet, carbon fiber paper, or carbon fiber felt attached to the outer peripheral surface of the inner layer. It is preferably formed by applying to the outer peripheral surface of the layer.

According to the crucible for an induction heating furnace of the present invention, since a conductive metal having a high melting point can be efficiently heated and melted, the operation time can be shortened and energy saving can be realized.

It is sectional drawing which shows typically the induction furnace crucible which concerns on one Embodiment of this invention. It is a graph showing the change of the metal surface temperature at the time of heating a refractory metal with the crucible for induction heating furnaces of a present Example. It is a graph showing the change of the metal surface temperature at the time of heating a refractory metal with the crucible for induction heating furnaces of a comparative example. It is a graph showing the change of the power output condition (1st time) at the time of heating a refractory metal with the crucible for induction heating furnaces of a present Example. It is a graph showing the change of the power output condition (2nd time) at the time of heating a refractory metal with the crucible for induction heating furnaces of a present Example. It is a graph showing the change of the power output condition (1st time) at the time of heating a refractory metal with the crucible for induction heating furnaces of a comparative example. It is a graph showing the change of the power output condition (2nd time) at the time of heating a refractory metal with the crucible for induction heating furnaces of a comparative example. It is a graph showing the change of the inner layer outer surface temperature at the time of heating a refractory metal with the crucible for induction heating furnaces of a present Example. It is a graph showing the change of the crucible outer surface temperature at the time of heating a refractory metal with the crucible for induction heating furnaces of a comparative example. It is sectional drawing which shows typically the induction furnace crucible which concerns on other embodiment of this invention. It is sectional drawing which shows typically the crucible for induction heating furnaces of a prior art example.

Hereinafter, the actual state of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a longitudinal sectional view of an induction furnace 10 shown as an example of an induction heating furnace crucible 1 (hereinafter simply referred to as “crucible 1”) according to an embodiment of the present invention. This induction furnace 10 can be particularly suitably used for melting a metal M having a high melting point (eg, 1000 ° C. or higher) such as cast iron, cast steel, special steel, or copper alloy, but melting a low melting point metal such as aluminum or zinc. Can also be used.

In the induction furnace 10, an induction coil 11 is disposed outside the crucible 1, and a back sand (indefinite shape material) 12 such as zirconia, alumina, magnesia, or silica sand is disposed between the crucible 1 and the induction coil 11. Has been. A heat insulating material 13 is disposed on the inner peripheral surface of the induction coil 11. The crucible 1 includes a container-shaped inner layer 2 that contains the refractory metal M, and an outer layer 3 that covers at least the side wall portion 20 of the inner layer 2.

The inner layer 2 is formed in a bottomed cylindrical shape having an opening in the upper portion, and can have an arbitrary shape such as a cylindrical shape or a rectangular tube shape. Since the inner layer 2 contains a refractory metal M such as cast iron, the inner layer 2 is made of a refractory material having excellent heat resistance, high-temperature strength, corrosion resistance against melting refractory metal (molten metal), etc. Silicon (silica, quartz), alumina, magnesia, zirconia, silicon nitride and the like can be preferably exemplified, but other additives and impurities may be included. The inner layer 2 can be formed by various molding methods such as casting, CIP molding, and vibration molding. For example, in the case of forming by casting, a cylindrical outer layer in which a formwork is disposed inside a material obtained by mixing one or more of the above materials at a predetermined mixing ratio and hydromixing them (a casting material) It is formed by pouring between the three molds, curing, solidifying and drying, and then removing the molds.

The inner layer 2 does not necessarily need to be 100% formed of the above-described material, as long as characteristics such as heat resistance and strength can be secured. The thickness of the inner layer 2 varies depending on the size of the inner layer 2, but the side wall portion 20 is, for example, about 10 mm to 70 mm, and the bottom wall portion 21 is, for example, about 10 mm to 100 mm.

Further, in order to improve the heat resistance and corrosion resistance of the molten high-temperature molten metal, silicon nitride-alumina as described in, for example, JP-A-2009-228919 is provided on the inner peripheral surface of the inner layer 2. A protective layer made of a system material may be coated.

In this embodiment, the outer layer 3 is formed in a cylindrical shape that covers only the side wall portion 20 of the inner layer 2. The outer layer 3 is composed of a heating element that generates heat by induction heating from the induction coil 11, and preferably includes a conductive material such as carbon or graphite having conductivity and high thermal conductivity. However, it may contain other additives and impurities. The outer layer 3 has an electrical resistivity value of 100 × 10 ⁻³ Ωcm or less, preferably 50 × 10 ⁻³ Ωcm or less. This is because if the electrical specific resistance value is larger than 100 × 10 ⁻³ Ωcm, the exothermic property is weak.

The thickness of the outer layer 3 is, for example, about 5 mm to 30 mm, and is preferably equal to or less than the thickness of the side wall portion 20 of the inner layer 2. In the induction furnace 10, in order to improve the melting efficiency of the melting metal M, the thickness of the refractory (the crucible 1 and the back sand 12) disposed between the metal M and the induction coil 11 is made as small as possible. There is a need. However, the thickness of the inner layer 2 (side wall portion 20) of the crucible 1 greatly affects the life of the inner layer 2, and it is necessary to make it as thick as possible in order to obtain the required life. Further, the back sand 12 needs to have a thickness (for example, 10 to 50 mm depending on the size) necessary for protecting the induction coil 11 against heat and as a backup material when the crucible 1 is broken. Although the thickness of the outer layer 3 is set in consideration of the above-described circumstances, a larger heat capacity is preferable for the heat retention of the crucible 1 after the molten metal is poured out. In view of this, it is necessary to obtain an optimum thickness, and in this case, the thickness is preferably equal to or less than the thickness of the inner layer 2 (side wall portion 20).

The outer layer 3 can be formed by various molding methods such as CIP molding, casting molding, and vibration molding. For example, in the case of forming by CIP molding, after mixing the above-mentioned conductive material such as graphite and insulating material such as silicon dioxide at a predetermined mixing ratio, adding a slight binder and molding with a hydrostatic pressure molding machine. For example, it can be formed by baking at about 1200 ° C.

The outer layer 3 is made of a slurry prepared by mixing a conductive material such as graphite and an insulating material such as silicon dioxide at a predetermined mixing ratio and adding a binder such as water glass. It can also be formed by applying and spraying the outer peripheral surface of the inner layer 2 formed by casting by spraying or brushing, and then performing heat treatment at about 200 ° C. The outer layer 3 can also be formed by attaching a graphite sheet, carbon fiber paper, carbon fiber felt or the like to the outer peripheral surface of the inner layer 2 formed by CIP molding or casting. Furthermore, the outer layer 3 can also be formed in a container shape having a size capable of completely accommodating the inner layer 2 by a molding method such as CIP molding or casting. In this case, the crucible 1 having a two-layer structure in which the outer layer 3 is integrated with the bottom surface in addition to the outer peripheral surface of the inner layer 2 can be manufactured by fitting the inner layer 2 into the outer layer 3.

Alternatively, after the inner layer 2 is formed by CIP molding or the like, the outer layer 3 may be formed by casting or the like using the same as a part of the mold, and the two layers may be integrated. Alternatively, when CIP molding or casting molding is performed, the material of the inner layer 2 and the outer layer 3 may be divided and filled in the mold, and the inner layer 2 and the outer layer 3 may be molded simultaneously.

The crucible 1 having the above configuration is used as follows. First, refractory metal M (shape is arbitrary shape) such as cast iron, cast steel, special steel, or copper alloy is accommodated in crucible 1. Then, a high frequency current is passed through the induction coil 11. As a result, a magnetic field is formed around the induction coil 11, and as a result of this magnetic field passing through the refractory metal M in the crucible 1, the refractory metal M generates heat due to the electromagnetic induction action and rises in temperature. In addition, when the magnetic field from the induction coil 11 penetrates and penetrates the outer layer 3 of the crucible 1, the heating element constituting the outer layer 3 generates heat and the temperature rises. As a result, the outer layer 3 has a high temperature of 800 ° C. or higher, and the heat is transferred to the inner layer 2 by heat conduction, so that the inner layer 2 becomes high temperature. By both of these actions, the refractory metal M is heated without being cooled from the refractory, and the refractory metal M is melted to become a molten metal and kept in a molten state.

According to the crucible 1 of the present embodiment, the outer layer 3 made of a heating element is heated by the magnetic field from the energized induction coil 11, and the inner layer 2 is heated by heat conduction and is accommodated in the inner layer 2. The refractory metal M is heated. Therefore, the refractory metal M in the inner layer 2 rises in temperature due to heat generation from the refractory metal M itself due to the magnetic field from the energized induction coil 11, and also due to heating due to heat conduction from the inner layer 2. So it quickly reaches the melting point and dissolves. As a result, the high melting point metal M can be efficiently heated and melted, so that the operation time can be shortened and energy saving can be realized.

In addition, since the outer surface of the inner layer 2 is heated by heat conduction from the outer layer 3, there is almost no temperature difference between the inner surface side and the outer surface side in contact with the molten high-temperature molten metal. Therefore, it is possible to prevent the inner layer 2 from being damaged by the thermal shock caused by the temperature difference between the inner surface side and the outer surface side of the inner layer 2, so that the durability of the inner layer 2 can be improved. The life of the crucible 1 can be extended.

Hereinafter, examples of the crucible of the present invention will be shown, but it goes without saying that the present invention is not limited to this example. The crucible of the example is a cylindrical graphite-silicon carbide-based material arranged so as to cover a container-shaped inner layer 2 made of an alumina-silica-based material and a side wall portion 20 of the inner layer 2 as shown in FIG. It has a two-layer structure consisting of an outer layer 3 made of The inner layer 2 has an outer diameter of 150 mm, an inner diameter of 125 mm, and a height of 125 mm. The outer layer 3 has an outer diameter of 170 mm, an inner diameter of 150 mm, and a height of 125 mm. The composition of main materials constituting the inner layer 2 and the outer layer 3 is shown in Table 1 below. In the crucible of the example, first, the cylindrical outer layer 3 was formed by CIP molding and firing at 1200 ° C., and then the inner layer 2 was poured into the outer layer 3 using the outer layer 3 as a mold (120 It was formed by drying). A high frequency induction furnace (3000 Hz × 50 Kw, DC voltage set to 160 V) was used as the induction heating furnace, and a cast iron having a cylindrical shape (diameter: 80 m, height: 100 mm) was used as the refractory metal M to be melted. Around the outer layer 3, a back sand 12 (thickness: about 30 mm) made of silica and an insulating sheet 13 (thickness: about 5 mm) were disposed. The crucible of the comparative example has a one-layer structure made of an alumina-silica-based material as shown in FIG. 11, and has an outer diameter of 170 mm, an inner diameter of 125 mm, and a height of 125 mm. The composition of the material constituting the crucible of the comparative example is shown in Table 1 below.

As an evaluation method, the time until the cast iron melts, the power consumption until the cast iron melts (DC voltage × DC current × time), and the temperature transition in the predetermined part of the crucible of the example and the comparative example (Example and In the comparative examples, the metal surface temperature, the outer surface temperature of the inner layer 2 in the crucible of the example, and the outer surface temperature of the crucible in the crucible of the comparative example were measured. The cast iron melting operation is performed by first melting cast iron, holding the molten cast iron (molten metal) in the crucible for 30 minutes, discharging the molten metal, and allowing the crucible to cool for 30 minutes. The second cast iron was melted. The crucible was cooled by air cooling with the upper opening opened. The measurement results are shown in Table 2, Table 3, and FIGS.

According to FIG. 2, FIG. 3 and Table 2, the time required for the surface temperature of the refractory metal dissolved in the crucible to reach 1000 ° C. in the example and the comparative example is about 10 minutes (the first time) ), About 8 minutes (second time), compared with about 14 minutes (first time) and about 10 minutes (second time) in the comparative example, and there is a large difference in the heating rate of the refractory metal in the crucible. It was confirmed that this occurred. Along with this, the time until the refractory metal in the crucible is completely dissolved is about 17 minutes (first time) and about 12 minutes (second time) in the example, whereas it is about 30 minutes in the comparative example. (First time), about 23 minutes (second time), the refractory metal can be heated more efficiently in the example than in the comparative example, and the melting time (operation time) is greatly reduced (from 40% to 50% shortening) was confirmed. Further, in contrast to the comparative example, the second dissolution time of the example is further shortened than the first dissolution time, but this is favorably heated from inside and outside during the first dissolution of the refractory metal. This is probably because the amount of heat stored in the inner layer 2 is greater than that of the comparative example.

Further, according to FIGS. 6 to 9 and Table 3, in the example and the comparative example, the current value at the time of melting the refractory metal in the crucible is that the outer layer 3 is also energized in the example. In spite of being higher than the comparative example, the power consumption required to completely dissolve the refractory metal is the first and second times because the melting time is greatly shortened in the example. In both cases, it was confirmed that the amount was significantly lower than that of the comparative example. Thereby, it was confirmed that an Example can implement | achieve energy saving and an energy cost can also be reduced rather than a comparative example.

Furthermore, according to FIGS. 4 and 5, in the comparative example, the outer surface temperature of the crucible increased only to about 500 to 600 degrees in both the first and second times, and the temperature of the molten metal in the crucible (from 1100 degrees to And a large temperature difference is generated. On the other hand, in the example, the outer surface temperature of the inner layer 2 of the crucible rises to 1100 to 1200 degrees in both the first and second times, and the temperature of the molten metal in the inner layer 2 (1100 to 1200 degrees) ) Is almost no temperature difference. Therefore, in an Example, it can prevent that the inner layer 2 receives the damage by the thermal shock accompanying the temperature difference between the inner surface side and the outer surface side of the inner layer 2, and can improve the durability of the inner layer 2. Was confirmed.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the present invention. For example, as shown in FIG. 10, a ring-shaped flange portion 22 extending radially outward is formed at the upper end portion of the inner layer 2 of the crucible 1 to prevent the outer layer 3 from being exposed to the outside air. can do. According to this configuration, the outer layer 3 made of carbon, graphite, or the like is completely embedded in the back sand 12 when the refractory metal is dissolved, so that the outer layer 3 can be prevented from being oxidized.

1 Induction furnace crucible 2 Inner layer 3 Outer layer 20 Side wall

Claims

An induction furnace crucible for melting metal by induction heating from an induction coil,
A container-like inner layer made of a refractory containing metal,
A crucible for an induction heating furnace, comprising: an outer layer made of a heating element that covers at least a side wall portion of the inner layer and generates heat by induction heating.
The induction furnace crucible according to claim 1, wherein the refractory mainly contains at least one selected from the group consisting of silicon dioxide, alumina, magnesia, zirconia, silicon carbide and silicon nitride.
The induction heating crucible according to claim 1 or 2, wherein the heating element mainly contains at least one selected from the group consisting of carbon and graphite.
The induction heating furnace crucible according to any one of claims 1 to 3, wherein the electrical resistivity of the outer layer is 100 x 10 -3 Ωcm or less.
The induction furnace crucible according to any one of claims 1 to 4, wherein a thickness of the outer layer is equal to or less than a thickness of the inner layer.
The induction furnace crucible according to any one of claims 1 to 5, wherein the outer layer is formed in a cylindrical shape covering only a side wall portion of the inner layer.
The outer layer is formed by CIP molding,
The induction furnace crucible according to any one of claims 1 to 6, wherein the inner layer is formed by pouring a casting material into the outer layer in which a mold is disposed.
The outer layer is formed by attaching a graphite sheet, carbon fiber paper, or carbon fiber felt to the outer peripheral surface of the inner layer, or a slurry mainly containing at least one selected from the group consisting of carbon and graphite. The induction furnace crucible according to any one of claims 1 to 6, which is formed by coating on an outer peripheral surface.