JPH0667540B2 - Heater device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heater device. This heater device can be used, for example, when it is immersed in a molten metal to heat the molten metal.

[Prior Art] A conventional heater device will be described by taking a continuous casting method as an example. That is, in the continuous casting method, for example, a molten steel of about 1400 to 1600 ° C is temporarily received from a ladle into a tundish, and the molten metal is injected into a cooling mold from a discharge port of the tundish to be cooled and solidified, and then cooled by a cooling spray zone. After that, pulling the cooled and solidified part with a pinch roll,
It is cut into a predetermined length, and slabs and billets are manufactured by this. In the above continuous casting method, the quality of the steel products produced is improved and the yield is also improved as compared with the slabbing method. However, in recent years, steel products have been required to have higher quality. Therefore, continuous casting methods have been earnestly developed to improve the quality of steel products.

In the above continuous casting method, the temperature of the molten steel is apt to be lowered in the tundish because the molten steel is primarily received by the tundish. In particular, in continuous casting, at the end of casting, for example, when 50 to 80 minutes have passed since the start of casting, the temperature of the molten metal is lowered by several to several tens of degrees Celsius depending on the case. Here, since the tundish is the final container just before the molten metal solidifies, the temperature of the molten metal in the tundish has a great influence on the inclusion index under the surface layer of steel products and the center segregation index of carbon. Have a great impact on Therefore, the molten metal in the tundish is several to several tens.
Even if the temperature drops by about 0 ° C, it is not preferable in terms of quality control.

Therefore, in recent years, in order to adjust the temperature of the molten steel in the tundish, the carbon electrode is immersed in the molten metal in the tundish, an electric current is directly applied to the molten metal in the tundish, and the molten metal itself is heated by the Joule heat generated in the molten metal. There is provided a heating device. However, in this case, the electric resistivity of the molten metal is small. Here, the Joule heat generated by the molten metal is the product of the electrical resistance value of the molten metal and the square of the current value flowing through the molten metal. Therefore, if the electrical resistivity of the molten metal is small as described above, the required Joule heat is generated. In order to secure the heat, there is a problem that a considerably large amount of current is required as a current to be passed through the molten metal, and there is a problem that an electric facility becomes large due to a larger current.

As another heater device for heating the molten metal in the tundish, an induction heating type device for inductively heating the molten metal in the tundish has been conventionally provided. Further, there is also provided a plasma heating apparatus in which a plasma torch is installed above the tundish to plasma-heat the molten metal in the tundish.

[Problems to be Solved by the Invention] The present inventor has conducted extensive studies in order to reduce the current flowing through the molten metal, and as a result, has used a heater device including a heating element and an electrode part to reduce the heating element of the heating device. A means for heating the metal melt by immersing it in the metal melt and applying a voltage between the heater device and the metal melt to heat the heating element of the heater device was developed.

The present invention was completed as part of the development of the above-mentioned heater device, and an object thereof is to heat an object to be heated such as molten metal by causing the heating element to generate heat. By forming with the inner layer part,
It is an object of the present invention to provide a heater device that is advantageous in ensuring the degree of freedom in selecting the type of heat generating material that forms the heat generating element and the mixing ratio of the heat generating material.

[Means for Solving the Problems] A heater device according to the present invention is more effective than a cylindrical outer layer portion having a heat-generating material as a base material and an outer peripheral surface serving as a current-carrying surface, and an outer layer portion disposed inside the outer layer portion. It is composed of a heating element formed of a material having a low specific resistance value and at least one inner layer portion whose outer peripheral surface is a current-carrying surface, and an electrode portion electrically contacting the inner layer portion of the heating element. ,
The current-carrying path of the heating element is characterized in that it is arranged in the radial direction of the heating element.

The heating element is composed of an outer layer portion having a heat generating material as a base material and having a required heat generation characteristic, and at least one inner layer portion formed of a material having a specific resistance value lower than that of the outer layer portion.

Here, the term "base material of the heat generating material" means that the heat generating material may be formed of only the heat generating material or may contain a filler other than the heat generating material. The inner layer portion may have one layer or two layers as necessary, and may have more layers in some cases.
The thickness of the outer layer portion can be made substantially uniform in order to ensure the uniformity of heat generation, but there may be a thickness varying portion depending on the heating material. The same applies to the inner layer portion.

The heating element has a tubular shape, and in this embodiment, it can be used as a type that is immersed in a molten metal, and in this case, both the outer layer portion and the inner layer portion can have a tubular shape or a shape similar to a tubular shape. Here, when the heating element has a tubular shape, the outer diameter of the central portion in the length direction of the heating element is substantially the same along the length direction, as shown in Examples described later,
In addition, it is desirable that the thickness of the central portion in the lengthwise direction of the heating element be substantially uniform by making the inner diameter of the central portion substantially the same in the lengthwise direction. The relationship between the outside diameter and the inside diameter of the central part in the length direction can be such that the inside diameter dimension is 30 to 80% of the outside diameter dimension, especially 50 to 70%.
% Is desirable. The reason is that when the ratio of the inner diameter to the outer diameter is small, the amount of heat generated in the inner diameter portion becomes larger than that in the outer diameter portion, and as a result, the inner diameter portion may melt. In addition, when the ratio of the inner diameters becomes large, the thickness of the heat generating layer becomes substantially small, and it is easily affected by the melting loss due to the molten steel.

In the heater device according to the present invention, the exothermic material forming the outer layer portion of the exothermic body and the exothermic material forming the inner layer portion are non-metallic,
Any metal type may be used. In this case, the kind of the heat generating material forming the outer layer portion or the mixing ratio thereof is higher than the kind of the heat generating material forming the inner layer portion or the mixing ratio thereof. By doing so, heat is actively generated in a portion close to an object to be heated (for example, liquid such as molten metal, gas such as air) that comes into contact with the outer layer of the heating element or faces the outer layer. This is advantageous for effectively heating the heated material and increasing the heating efficiency.

Further, since the outer layer portion usually comes into contact with molten metal, air, burner flames during preheating, etc., the type of heat-generating material forming the outer layer portion or the mixing ratio thereof should be in addition to the heat-generating properties, melting resistance and thermal shock resistance. It is necessary to select it in consideration of various factors such as oxidation resistance, corrosion resistance and aging resistance, but since the inner layer does not substantially come in contact with molten metal, air, burner flame, etc. When selecting the type of heat-generating material to be formed or its mixing ratio, such consideration can be reduced or neglected. Therefore, the type of heat-generating material forming the inner layer part or its mixing ratio is The degree of freedom in selection is increased as compared with the type of heat generating material forming the outer layer portion or the mixing ratio thereof.

In the heater device according to the present invention, the metal-based heat generating material forming the heat generating element may be, for example, nickel-chromium alloy, iron-chromium-aluminum alloy, tungsten, molybdenum, tantalum, etc., if necessary. Can be adopted.

Further, as the above-mentioned non-metallic heat generating material forming the heat generating element, oxide-based, nitride-based, boride-based, etc. ceramics having conductivity in the operating temperature range can be adopted. As the electrically conductive ceramics, when the object to be heated is molten steel, it is desirable that the specific resistance is high because the resistance of the molten steel is low and the R of the heating element must be increased. In this case, the specific resistance value at 1500 ° C. is preferably 1 Ωcm or more, particularly preferably 200 Ωcm or more. For example, the specific resistance value is 36
It is possible to use one having a value of about 0 (Ωcm). In addition,
The specific resistance values of the outer layer portion and the inner layer portion forming the heating element can be changed by blending conductive ceramics with non-conductive ceramics or hardly conductive ceramics and adjusting the blending ratio.

In the heater device according to the present invention, as the conductive ceramics forming the outer layer portion, when heating the molten steel, magnesia (MgO), zirconia (ZrO ₂ ),
Alumina (Al ₂ O ₃ ), a mixture of magnesia and zirconia, and a mixture of magnesia, zirconia and alumina can be used. Here, magnesia does not usually have conductivity near room temperature, but has predetermined conductivity near 1500 to 1650 ° C., which is the heating temperature range of molten steel.
When a mixture of magnesia and zirconia is used as a ceramic having conductivity that forms the outer layer portion, the mixing ratio thereof is appropriately selected in consideration of the required resistance value and the like. And magnesia is 60-100
%, Especially 85 to 95% is preferable, zirconia is 0 to 40%,
Especially 5 to 25% is preferable, alumina is 0 to 40%, especially 2.
5 to 15% is preferable.

Further, in the heater device according to the present invention, when the molten metal of steel is heated, zirconium boride, boron nitride, silicon carbide, or the like is used as the conductive ceramics forming the inner layer portion, if necessary. it can. Further, as the conductive ceramics forming the inner layer portion, like the outer layer portion, magnesia (MgO), zirconia (ZrO ₂ ),
Alumina (Al ₂ O ₃ ), a mixture of magnesia and zirconia, and a mixture of magnesia, zirconia and alumina can be used, but the blending ratio can be changed to reduce the heat generation amount than the outer layer part, For example, reducing magnesia, by weight percent, 40-70% magnesia, zirconia,
One or more materials containing alumina, CaO, chromia, beryllia, thoria, and ceria as main components, with a content of 30-
60% or more can be blended. Further, carbon powder, graphite or the like may be contained in a carbon amount of 1 to 5%.

Furthermore, depending on the melting point of the molten metal, conductive ceramics that form the outer and inner layers may be silicon carbide (SiC), lanthanum chromate (LaCrO ₃ ), beryllium oxide (BeO), thorium oxide (ThO). ₂ ), molybdenum silicide (MoSi ₂ ), and those containing titanium nitride (TiN), titanium carbide (TiC), etc. as main components can also be used. For reference, the relationship between operating temperature and specific resistance is shown in FIGS. 8 and 9. In the case of molten iron and steel, as described above, the specific resistance value of the ceramic forming the heating element is preferably 200 Ωcm or more in the operating temperature range, especially when forming the outer layer portion.

However, among the above-mentioned various heat-generating materials, the heating temperature of the object to be heated such as molten metal, the atmosphere of the heater device where it is used, such as acidity and reducibility, the heat resistance of the heat-generating material, and the high temperature resistance of the heat-generating material. It should be appropriately selected in consideration of impact resistance, price, and toxicity.

When the heating element contains zirconia as a main component, calcium oxide (CaO), magnesia (MgO), yttrium oxide (Y ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ ), scandium oxide (Sc ₂ O ₃ ). It is possible to use stabilized zirconia or metastable zirconia that avoids transition by adding ₃ %) to several% to several tens%. This makes it possible to avoid expansion associated with the transition and is advantageous in suppressing distortion of the heating element.

When the heat-generating material is conductive ceramics, the particle size of the conductive ceramics may affect the resistance value, so the maximum particle size is preferably about 1-5 mm,
Especially, it is desirable that the thickness is about 1.5 to 3 mm. The main reason for this is that if the particle size is too large, the current tends to drift. It is also possible to adjust the heat generation characteristics of the outer layer portion and the inner layer portion by changing the particle size between the outer layer portion and the inner layer portion.

The heat-generating materials of the outer layer and the inner layer that form the heating element show the positiveness that the resistance value of the heating element does not change or the resistance value increases even if the operating temperature changes, unless there are other problems. Any thing can be used. In the case of showing the correctness that the resistance value of the heat generating material increases as the temperature rises in this way, when a high temperature portion occurs in the heat generating element, the high temperature portion has a high resistance value. Therefore, an electric current flows through a portion having a temperature lower than that of the high temperature portion, and therefore, it is convenient to uniformly generate heat over the entire heating element. If the heat-generating material has a large negative value that the resistance value greatly decreases as the temperature rises, when a high-temperature portion occurs in the heating element, the high-temperature portion has a low resistance value. Therefore, it becomes difficult for the current to flow in a portion having a lower temperature than the high temperature portion, and the current easily flows in the high temperature portion having a low resistance value. Therefore, the high temperature portion becomes hotter and more likely to contribute to the runaway of the heating element.

The total resistance R (Ω) of the outer layer portion and the inner layer portion forming the heating element is
Specific resistance value ρ (Ωc of heat generating material such as conductive ceramics
m), the wall thickness t (cm) of the heating element, and the area S (cm ² ) of the heating element. At this time, when the outer layer portion and the inner layer portion are formed in a tubular shape, it is necessary to select the resistance value of the heating element in consideration of the following matters. That is, the larger the outer diameter of the heating element,
You can secure a heat dissipation area, but cracks easily occur during molding,
It is easily vulnerable to thermal shock. On the other hand, the smaller the outer diameter of the heating element, the smaller the heat radiation area. Further, the larger the inner diameter of the heating element, the larger the diameter of the electrode portion, and the larger the heat transfer loss from the electrode portion. On the other hand, the smaller the inner diameter of the heating element, the smaller the diameter of the electrode portion and the smaller the loss of heat transfer from the electrode portion, but the uneven heat generation is likely to occur. Further, as the thickness of the heating element is thicker, heat is more likely to be accumulated inside, and the maximum temperature inside the heating element may rise to melt the inside, which is disadvantageous in maintaining the stability of heat generation. On the other hand, as the thickness of the heating element is smaller, heat is less likely to be accumulated inside the heating element, but the required amount of heat generation cannot be obtained, and this easily contributes to runaway heat generation.

In the heater device according to the present invention, the heating element can be manufactured as follows, for example. That is, the raw material ceramic powder for the outer layer portion is sufficiently pulverized and mixed by a ball mill, a vibration mill or the like to adjust to a predetermined composition, and then a slurry obtained by mixing the raw material ceramic powder and water is poured into the mold cavity to form the outer layer portion. Perform a molding process to obtain a molded body by molding into a predetermined shape for
Further, a sintering step is performed in which the molded body for the outer layer portion is heated to a predetermined temperature and sintered. If necessary, a curing step and a drying step are performed prior to the sintering step. In addition, in the molding step, vibration molding can be performed in which the mold is molded while applying vibration. The inner layer portion is also formed through similar steps. Then, the outer layer portion and the inner layer portion are assembled to be integrated.

The heating element can also be manufactured as follows. That is, the raw material ceramic powder for the outer layer portion is sufficiently pulverized and mixed by a ball mill, a vibration mill or the like to prepare the raw material ceramic powder. Then, the raw material ceramic powder is pressure-molded to form a compact for the outer layer portion. Then, if necessary, a drying process is performed, and heating is performed at a high temperature to sinter. For the pressure molding, known means such as a press pressure method, a hydrostatic pressure method, and a hot press method can be adopted. The inner layer portion can be formed by the same process. Then, the outer layer portion and the inner layer portion are assembled to be integrated.

In the heater device according to the present invention, as another manufacturing method for forming the heating element, it is also possible to integrally form the outer layer portion and the inner layer portion and directly fire the outer layer portion and the inner layer portion as they are. In this case, since it is integrated in this case, it is advantageous to secure the degree of electrical contact and the degree of thermal contact between the outer layer portion and the inner layer portion.

In the heater device according to the present invention, it is desirable that the outermost inner layer portion and the outer layer portion have a high degree of contact. Therefore, the granular material, the liquid is charged between the inner layer portion and the outer layer portion, the electrical contact degree between the inner layer portion and the outer layer portion by utilizing the powder grain material, the current diffusion function of the liquid, and the heat diffusion function, The degree of thermal contact can be improved. In this case, even if a gap is likely to be formed at the boundary between the outer layer portion and the inner layer portion, or even if the thermal expansion coefficients of the outer layer portion and the inner layer portion are different, electrical contact and thermal This is advantageous for ensuring contact. The powder or granules have a heat generating property, for example, carbon powder, graphite powder,
Silicon carbide powder can be used, and as the liquid, a liquid having excellent conductivity and a low melting point, for example, a low melting point metal such as tin, lead, bismuth, or sodium, or a copper-based metal in some cases can be used. From the viewpoint of ensuring heat generation, the carbon powder preferably has a fine particle diameter, and the particle diameter range is, for example, 10 μ to 2 mm and 50
It can be in the range of μ to 100μ. Incidentally, if a solid powder or granular material made of a low melting point metal or a copper-based metal is charged between the inner layer portion and the outer layer portion, the solid powder or granular material will be formed if the temperature during use is equal to or higher than its melting point. It melts to form a liquid, which is advantageous for ensuring electrical contact and thermal contact.

Further, in the heater device according to the present invention, the inner layer portion has two or more layers, and when two or more inner layer portions are separately formed and then integrally assembled, one inner layer portion and the adjacent It is also possible to improve the degree of contact between the inner layer portions by interposing the above-mentioned powdery particles and liquid at the boundary portion between the inner layer portion and another inner layer portion.

In the heater device according to the present invention, as illustrated in Examples to be described later, the longitudinal end portions of the inner layer portion and the outer layer portion have a three-dimensional curved surface shape such as a hemispherical shape or a hemispherical shape so that there is no corner portion. It is desirable that the shapes are similar. The reason is that the corners are likely to be nonuniform during molding, and it is difficult to ensure thermal shock resistance. Further, since the electric current is likely to be concentrated in the corners, the temperature of the heat generated in the corners becomes high, which is one of the causes of the runaway of heat generation. When the tip is hemispherical, the radius of the hemispherical tip of the outer layer is, for example, 30 to 10 in the type of immersing in the molten metal in the tundish.
The radius of the hemispherical tip of the inner layer portion can be set to, for example, about 20 to 85 mm.

In the heater device according to the present invention, the electrode portion is for supplying electricity to the heating element, and is usually connected to the inner layer portion. The material of the electrode part is selected in consideration of conductivity, heat transfer coefficient and the like. In this case, the conductivity can be increased and the heat transfer coefficient can be reduced to reduce the heat transfer loss. However, in general, as the conductivity increases, the heat transfer coefficient also tends to increase. Therefore, a material having a higher conductivity and a smaller heat transfer coefficient than the case of forming the electrode part with a single material. It is possible to reduce the apparent degree of heat transfer of the electrode portion while ensuring the required conductivity of the electrode portion by appropriately combining the material.

Alternatively, the electrode portion can be formed of a conductive ceramic having a low electric resistance. In such a case, the electrode part, the outer layer part, and the inner layer part may be integrally molded and baked as they are.

In the heater device according to the present invention, in order to reduce heat transfer loss from the electrode portion, it is desirable that the electrode portion be thin.

Further, it is desirable that the electrical contact between the electrode portion and the heating element is high. Therefore, the heating element and the electrode portion can be integrally molded in order to increase the degree of electrical contact. Further, when the heating element and the electrode part are separately formed and then assembled, the granular material such as carbon powder or graphite powder as described above is provided at the boundary part between the electrode part and the heating element. Or, a liquid having a low melting point having conductivity such as tin, lead or bismuth is charged,
It is also possible to improve the degree of contact between the electrode portion and the heating element by using the liquid. In this case, even when the thermal expansion coefficient of the heating element is different from that of the electrode section, it is advantageous to ensure electrical contact and thermal contact between the two.

In addition, in the heater device according to the present invention, when it is used to heat the molten metal held in the container, a sensor such as a γ-ray level meter for detecting the stored amount of heat generation is provided and the signal of the sensor is used. Accordingly, a control device for controlling the current to the heating element can be provided. With this configuration, the amount of current flowing to the heating element is controlled according to the amount of change in the molten metal held in the container, so that the temperature of the molten metal can be adjusted more accurately.

[Embodiment] A first embodiment of the heater device according to the present invention will be described with reference to FIGS. 1 and 2.

The heater device 1 according to this embodiment is shown in FIGS. 1 and 2. The heater device 1 is of a two-layer type, and is composed of a substantially flask-shaped heating element 2 and a rod-shaped electrode portion 3. The heating element 2 includes an outer layer portion 20 having a substantially flask shape and an inner layer portion 25 having a substantially flask shape. Outer layer 20
Is composed of 90% by weight of magnesia, 5% of zirconia, 5% of alumina, and mixed ceramics containing unavoidable impurities. The inner layer portion 25 is made of mixed ceramics containing 60% of magnesia, 40% of zirconia, and inevitable impurities in weight%.

As shown in FIGS. 1 and 2, the outer layer portion 20 has a large-diameter base end portion 200, a central portion 210 connected to the base end portion 200, and a central portion 210.
And a three-dimensional curved surface shape, that is, a hemispherical tip portion 220 connected to The thickness of the central portion 210 and the thickness of the tip portion 220 are substantially uniform, and the variation in the thickness is about ± 1 mm. Here, in this embodiment, the overall length L1 in the axial direction of the outer layer portion 20 is about 85 cm, the length L2 of the central portion 210 is about 65 cm,
The length L3 of the tip part 220 is about 6 cm, the outer diameter of the center part 210 is 12 cm
The inner diameter of the center part 210 is about 8.4 cm, the diameter of the tip part 220 is R1
Is about 6 cm. The base end portion 200 has a large diameter for mounting on the heater holder.

On the other hand, the inner layer portion 25 includes a base end portion 250, a center portion 260 connected to the base end portion 250, and a three-dimensional curved surface shape, that is, a substantially hemispherical tip portion 270 connected to the center portion 260.
The thickness of the inner layer portion 25 is substantially uniform, and the variation in thickness is about ± 1 mm. Here, in this embodiment, of the inner layer portion 25, the outer diameter of the central portion 260 is about 8 cm, and the inner diameter of the central portion 260 is 4 cm.
The tip end 270 has a diameter R2 of about 4 cm. In the present embodiment, as can be understood from FIG. 4 (showing the molten steel immersion state) described later, the energization path of the heating element 2 is so arranged in the radial direction of the heating element 2. Therefore, the outer peripheral surface 20x of the outer layer portion 20 becomes a current-carrying surface, and the outer peripheral surface 25x of the inner layer portion 25 also becomes a current-carrying surface.
A current flows in the thickness direction of the inner layer portion 25.

The rod-shaped electrode portion 3 is made of carbon and has an outer diameter of 3.
It is about 8 cm and its total length is about 85 mm. The heater device of this example was manufactured as follows. That is, after adjusting the raw material ceramic powder for the outer layer portion 20 at a predetermined mixing ratio, an adjusting step of adding water to form a slurry, a molding step of pouring the slurry into a cavity of a mold for molding, and a molded outer layer portion 20. After removing the molded product for molding from the mold, it is cured at 150 ℃
It was manufactured by sequentially performing a drying step of drying for 15 hours and a drying step of heating the dried molded body for the outer layer portion 20 at 1650 ° C. for 10 hours to sinter. The outer layer 20 used in the adjustment process
The maximum particle size of the raw material ceramic powder is about 3 mm. The inner layer portion 25 was formed using the mold for the inner layer portion 25 in the same procedure. Then, after carbon powder is dispersed as spacers on the inner surface near the bottom of the sintered outer layer portion 20, the inner layer portion 25 is inserted into the outer layer portion 20 and the outer layer portion 20 and the inner layer portion 25 are overlapped with each other. Further, carbon powder is charged into the boundary portion between the outer layer portion 20 and the inner layer portion 25, and the minute gaps between the outer layer portion 20 and the inner layer portion 25 are filled with carbon powder, thereby forming a filling layer 20a having a thickness of about 2 mm. To do. At this time, if necessary, the inner layer portion 25 and the outer layer portion 20 can be rotated while relatively rotating in the circumferential direction. The electrode portion 3 is inserted into the hole defined by the inner peripheral surface of the inner layer portion 25.
Carbon powder is also charged in the boundary portion between the electrode portion 3 and the inner layer portion 25 to form the filling layer 20b having a thickness of about 1 mm.

Using, for example, two heater devices 1 manufactured as described above, a lead wire is fixed to the upper end portion of the rod-shaped electrode portion 3 of each heater device 1 with a band to connect to a power source, and a flame of a burner is applied to the heating element 2. Preheat. And after preheating, the 4th
As shown in the figure, two heater devices 1 were immersed in a molten steel W in a container 4. In this state, the two electrode parts 3 and the molten metal W
A voltage of 0 to 440 V is applied between and, and a current of frequency 60 Hz is applied to about 0 to 800 A. Then, the inner layer portion 25 and the outer layer portion 20 forming the heating element 2 of the one heater device 1 generate heat, and the inner layer portion 25 forming the heating element 2 of the other heater device 1 is generated.
Also, since the outer layer portion 20 generates heat, the molten metal W is heated.

In the present embodiment, since the molten metal is heated by the heat generation amount of the heating element 2 of the heater device 1, when the current is directly applied to the molten metal itself and the Joule heat generated in the molten metal itself causes the molten metal to generate heat. In comparison, the amount of current required is small, and therefore the electrical control thereof is easy to perform, and the electric equipment can be downsized. Yes.

In the present embodiment, since the outer layer portion 20 is formed of the heat-generating material whose main components are magnesia and zirconia and the compounding ratio of which is selected so that the resistance value becomes high, heat is actively generated at the portion in contact with the molten metal W. And the heating efficiency is improved. Moreover, since the inner layer portion 25 does not come into contact with the molten metal, it does not require heat generation characteristics as much as the outer layer portion 20, but rather it is preferable to suppress the heat generation characteristics in order to suppress "heat accumulation" inside the heating element 2. When preheating with the burner, the inner layer 25
Does not come into direct contact with each other, so when selecting the mixing ratio of the heat-generating material forming the inner layer 25, it is not necessary to secure a large amount of heat generation as in the outer layer 20, and great consideration should be given to melting resistance, oxidation resistance, etc. Therefore, the degree of freedom in selecting the type of heat-generating material forming the inner layer portion 25 or the mixing ratio thereof can be increased.

Further, in the present embodiment, when the thickness of the heating element 2 is set to the required thickness in order to secure the required amount of heat generation, the thickness of the outer layer portion 20 itself and the thickness of the inner layer portion 25 themselves can be thinned. Therefore, the outer layer portion 20 and the inner layer portion 25 themselves are less likely to be cracked during molding, sintering, and preheating.

Moreover, in the present embodiment, as shown in FIG. 3, the filling layer 20a made of carbon powder charged in the boundary portion between the outer layer portion 20 and the inner layer portion 25 and the boundary portion between the inner layer portion 25 and the rod-shaped electrode portion 3 are formed. Since the filling layer 20b made of the charged carbon powder has a function as a current diffusion layer and a function as a heat diffusion layer, the outer layer portion 20
Since the degree of electrical contact between the inner layer portion 25 and the inner layer portion 25 is increased and the degree of thermal contact is also increased, local heat generation is suppressed, and therefore, the heat generating element 2 is unlikely to run out of heat, which is advantageous for uniform heat generation.

Further, in the present embodiment, since the filling layers 20a and 20b formed by charging carbon powder also generate heat, the thickness of the outer layer portion 20 and the inner layer portion 25 is varied to secure the required heat generation amount of the heating element 2. It is possible to eliminate thickening.

Further, in this embodiment, since the thickness of the outer layer portion 20 and the inner layer portion 25 forming the heating element 2 are substantially uniform, the uneven flow of the current flowing from the electrode portion 3 through the heating element 2 to the molten metal W. It is effective in preventing aging.

In addition, in this embodiment, the tip 220 of the outer layer 20 and the tip 270 of the inner layer 25 forming the heating element 2 are hemispherical as a three-dimensional curved surface shape, and corners where the current is likely to concentrate are formed. Therefore, it is more advantageous to prevent the current from becoming uneven.

Next, a second embodiment of the heater device according to the present invention will be described with reference to FIGS. 5 and 6. The heater device of the second embodiment has basically the same configuration as that of the first embodiment.
However, the inner layer portion is two layers, and as shown in FIG. 5, the first inner layer portion 27 and the second inner layer portion 28 on the rod-shaped electrode portion 3 side are laminated. The first inner layer portion 27 includes a base end portion 270 and an intermediate portion 271.
And a substantially hemispherical tip 272. The second inner layer portion 28 is formed of a base end portion 280, an intermediate portion 281, and a substantially hemispherical tip portion 282. Then, a carbon powder is charged between the first inner layer portion 27 and the second inner layer portion 28 to form a filling layer 20a, and the first inner layer portion 27 and the second inner layer portion 28 are formed. The degree of electrical contact and the degree of thermal contact with are secured. Of course, the filling layer 20a made of carbon powder is provided at the boundary portion between the outer layer portion 20 and the second inner layer portion 28, and the carbon powder is also provided at the boundary portion between the electrode portion 3 and the sixteenth inner layer portion 27. Is provided with a filling layer 20b.

Also in the heater device of the second embodiment, the same operation and effect as in the case of the first embodiment can be obtained.

Further, in each of the above-described embodiments, the outer peripheral surface of the inner layer portion and the inner peripheral surface of the outer layer portion are smooth as shown in FIGS. 1 and 5, but not shown in a special example. By forming a threaded portion on the outer peripheral surface of the inner layer portion, forming a threaded portion on the inner peripheral surface of the outer layer portion, and by screwing the threaded portion of the outer layer portion and the threaded portion of the inner layer portion to each other, The part and the outer layer part may be integrally assembled, and in this case as well, carbon powder, molten tin or the like can be charged in the boundary part between the both parts.

[Application Example] Next, an example in which the heater device according to the above-described embodiment is applied to the continuous casting method will be described. First, a continuous casting apparatus used in the continuous casting method will be described. As shown in FIG. 7, this continuous casting apparatus includes a tundish 50 as a container for holding molten steel, a water cooling mold 51 arranged below the tundish 50, a cooling spray zone 52,
It is composed of a pinch roll 53 and a straightening roll 54.
The tundish 50 has a capacity for holding the molten metal for about 5 tons.

Next, the case of continuous casting will be described. First, two heater devices 1 shown in FIGS. 1 and 2 are used, and the heating element 2 of each heater device 1 is heated by the flame of the burner to 800 to 1200 ° C.
Preheat to a degree.

In this way, with the heater device 1 preheated, 1400 to 1600 transferred from the ladle 55 and held in the tundish 50.
The two heater devices 1 are immersed in the molten steel at a high temperature of about ℃ from the tip 220. Tundish 5 removed from ladle
The molten metal in 0 flows toward the discharge port 50a shown in FIG.

If the heater device 1 is preheated before the molten metal is immersed as described above, the heating element 2 can be prevented from being rapidly heated and cracks in the heating element 2 can be suppressed as much as possible. Further, by the above-mentioned preheating, since the heating element 2, particularly magnesia as a main component, the conductivity of the outer layer portion 20 which is conductive only in the high temperature region can be secured.

When a crack is generated in the heating element 2, the metal melt that has penetrated into the crack and the electrode portion 3 are directly connected to each other, the heating value of the heating element 2 is reduced, and the heater device 1 cannot be effectively used. Occurs.

In this application example, while the heater device 1 is immersed in the molten metal in the tundish 50 as described above, the terminals of the two electrode parts 3 are connected to an AC power source and a voltage of 100 to 600 V is applied between the terminals. . As a result, a current having a frequency of 60 Hz flows between the heating elements 2 of the heater device 1 through the molten metal held in the tundish 50. The amount of current is about 0 to 800A. At this time, the inner layer portion 25 and the outer layer portion 20 of the heating element 2 generate heat at a high temperature. Therefore, the molten metal held in the tundish 50 is heated to a temperature of about 1 to 30 ° C., and the temperature is adjusted.

In this way, the molten metal whose temperature is adjusted in the tundish 50 is
It is discharged from the discharge port 50a of the tundish 50, and the water-cooled mold 51
It is cooled and solidified by, and further cooled by jetting of cooling water from the cooling spray zone 52 and cooled and solidified is pinch roll 53.
Is pulled downward at. After that, it is cut into a predetermined length by a cutting machine.

In this application example, since the molten metal in the tundish 50 is heated by the heat generation amount of the heating element 2 of the heater device 1, a current is directly applied to the molten metal held in the tundish 50 which has been conventionally provided so that the molten metal itself is supplied. The amount of current required is smaller than that in the case of heating the molten metal with the Joule heat generated in the above, and therefore the electric control thereof is easy to carry out, and the electric equipment can be downsized, so that the existing electric equipment can be effectively used. Can be used.

As described above, in this application example, since the temperature of the molten metal held in the tundish 50 can be adjusted by heating the molten metal held in the tundish 50 by the heater device 1, the temperature of the molten metal held in the tundish 50 can be maintained at an appropriate value, This is advantageous for improving the quality of products such as blooms and billets produced by the continuous casting method.

[Effects of the Invention] According to the heater device of the present invention, it is possible to heat an object to be heated such as molten metal with a heating element, and thus it is possible to adjust the temperature of the object to be heated such as molten metal. Particularly, since the heating element is formed of the outer layer portion and the inner layer portion,
It is possible to increase the degree of freedom in selecting the type of heat-generating material forming the inner layer portion and the mixing ratio thereof, which does not come into contact with molten metal or air.

Further, according to the heater device of the present invention, the inner layer portion is formed of a heat generating material having a smaller heat generating characteristic than the outer layer portion, that is, a smaller specific resistance value.
It is advantageous to suppress.

[Brief description of drawings]

1 to 4 show a first embodiment according to the present invention, FIG. 1 is a sectional view of a heating element, and FIG. 2 is a sectional view of a heater device. FIG. 3 is an enlarged cross-sectional view of the vicinity of the packed bed, and FIG. 4 is a schematic cross-sectional view of a state where electricity is applied between the heater device and the molten metal. 5 and 6 show a second embodiment according to the present invention, FIG. 5 is a sectional view of a heating element, and FIG. 6 is a sectional view of a heater device. FIG. 7 is a schematic sectional view of an apparatus used in the continuous casting method. FIG. 8 and FIG. 9 are graphs showing the relationship between the operating temperature of the conductive material and the specific resistance. In the figure, 1 is a heater device, 2 is a heating element, 3 is a rod-shaped electrode portion,
20 is an outer layer portion, 200 is a base end portion, 210 is a central portion, 220 is a distal end portion, 25 is an inner layer portion, 250 is a proximal end portion, 260 is a central portion, and 270 is a distal end portion.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Tadamasa Yamada 1 Wanowari, Arao-cho, Tokai-shi, Aichi Aichi Steel Co., Ltd. (72) Inventor Kikuo Ariga 51-1 Toki-cho, Mizunami-shi, Gifu (72) Invention Person Yoshitoshi Kato 1113-2 Terakawato-cho, Mizunami-shi, Gifu Prefecture (72) Inventor Eizo Kojima 4-11 Koyawaki, Kagiya-cho, Tokai-shi, Aichi (56) References JP 61-59274 (JP, B2)

Claims (1)

[Claims] 1. A cylindrical outer layer portion having a heat-generating material as a base material and an outer peripheral surface serving as a current-carrying surface, and a material which is disposed inside the outer layer portion and has a specific resistance value lower than that of the outer layer portion. A heating element formed of at least one inner layer portion whose surface is a current-carrying surface; and an electrode portion electrically contacting the inner layer portion of the heating element. A heater device characterized by being so arranged in the radial direction of the body.