JPH074653B2 - Molten metal immersion type 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 primarily received from a ladle in a tundish, and the molten metal is poured into a water-cooled mold from a discharge port of the tundish to be cooled and solidified, and 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 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 also a problem that electric equipment becomes large due to the increase in 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 molten metal by immersing it in the molten metal and applying a voltage between the heater device and the molten metal to heat the heating element of the heater device was developed.

The present invention has been completed as part of the development of the heater device described above, and an object thereof is to heat an object to be heated such as a molten metal by heating the heating element, and further, the heating element and the electrode part. It is an object of the present invention to provide a heater device that is advantageous for ensuring the heat generation property of a heat generating element by interposing a conductive layer between the boundary portion of the heat generating element and the layer forming the heat generating element. Another object of the present invention is to provide a heater device which is more advantageous for ensuring the heat generation of the heating element when the conductive layer has heat generation.

[Means for Solving the Problem] A heater device according to the present invention is immersed in a molten metal, and has a bottomed cylinder which is made of at least one layer and which has a heat-generating material as a base material and which has a central hole and a bottom portion. -Shaped heating element,
An electrode part that is inserted into the central hole of the heating element and conducts electricity in the thickness direction of the heating element between the molten metal and a boundary portion between the inner peripheral portion of the heating element and the outer peripheral portion of the electrode portion, or the heating element A conductive layer made of powder or liquid is interposed between the layers, and the lower end of the conductive layer is covered with the bottom of the heating element to have a non-exposed structure.

The heating element has a heating material as a base material and is formed of at least one layer. The heating element can be composed of an outer layer portion having a required heat generation characteristic and at least one inner layer portion having a heat generation characteristic different from that of the outer layer portion.

Here, the heat-generating material as a base 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. 1 for inner layer if necessary
The number of layers may be two or more, and in some cases, it may be more. The thickness of the heating element is to ensure the uniformity of heat generation,
Although the wall thickness can be made substantially uniform, there may be a wall thickness varying portion depending on the heating material.

The heating element has a tubular shape or a bottomed tubular shape, and in this form, it can be used as a type immersed in molten metal. In this case, when the heating element is formed with the outer layer portion and the inner layer portion, the outer layer portion and the inner layer portion are formed. Both of them can have a cylindrical shape or a shape approximate to a cylindrical shape. Here, when the heating element is formed into a tubular shape, as shown in Examples described later, the outer diameter of the central portion in the longitudinal direction of the heating element is set to be substantially the same in the longitudinal direction, and By making the inner diameter of the portion substantially one dimension in the length direction, it is desirable to make the thickness of the central portion of the heating element in the length direction substantially uniform,
In this case, the relationship between the outer diameter and the inner diameter of the central portion of the heating element in the length direction can be such that the inner diameter dimension is 30 to 80% of the outer diameter dimension, and particularly 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 must be melted.
Further, 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 exothermic body may be either non-metallic or metallic. When the heating element is formed of the outer layer portion and the inner layer portion, the kind of the heat generating material forming the outer layer portion or the mixing ratio thereof is higher than the type of the heat generating material forming the inner layer portion or the mixing ratio thereof in the electric resistance value. It is possible to adopt a high one. 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, in the heater device according to the present invention, 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 is different from the heat-generating characteristics. It is necessary to select in consideration of various factors such as melting resistance, thermal shock resistance, oxidation resistance, corrosion resistance, aging resistance, etc., but the inner layer part is substantially metal melt, air, burner flame etc. When selecting the type of heat-generating material that forms the inner layer or its mixing ratio,
Such consideration can be reduced or neglected. For example, the heat-generating material forming the inner layer portion has a smaller specific resistance value than the heat-generating material forming the outer layer portion, has less heat generation, and has a mixing ratio of can do. Therefore, the degree of freedom in selection of the type of heat-generating material forming the inner layer portion or its mixture ratio is higher than that of the type of heat-generating material forming the outer layer portion or its mixture ratio.

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 value of 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 heating element, 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 it has required conductivity near 1500 to 1650 ° C, which is the heating temperature range of molten steel.
When the heating element is formed of the outer layer portion and the inner layer portion,
A mixture of magnesia and zirconia can be used as the electrically conductive ceramic forming the outer layer portion,
In this case, the blending ratio is appropriately selected in consideration of the required resistance value and the like. For example, in terms of weight%, magnesia is preferably 60 to 100%, particularly 85 to 95%, and zirconia is 0 to 0%. 40%, especially 5 to 25% is preferred, and alumina is 0 to 40
%, Particularly 2.5 to 15% is preferable, and as the electrically conductive ceramics forming the inner layer portion, for example, zirconium boride, boron nitride, silicon carbide or the like can be adopted as necessary. As for the conductive ceramics that form the inner layer, of course, the outer layer is similarly formed of magnesia (Mg
O), 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 amount of heat generation is reduced compared to the outer layer part. In order to reduce the content of magnesia, for example, 40 to 70% by weight of magnesia, zirconia, alumina, CaO, chromia, beryllia, thoria, and ceria can be used as a main component.
One kind or two or more kinds, and the content may be 30 to 60% or more. Further, if necessary, for example, in order to reduce the amount of heat generated compared to the outer layer portion, carbon powder, graphite or the like may be appropriately contained in a carbon amount of 1 to 5%.

Furthermore, depending on the melting point of the metal melt, silicon carbide (Si
C), lanthanum chromate (LaCrO ₃ ), beryllium oxide (BeO), thorium oxide (ThO ₂ ), molybdenum silicide (M
It is also possible to use oSi ₂ ), as well as titanium nitride (TiN), titanium carbide (TiC) and the like as the main components. 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 various heat generating materials mentioned above, the heating temperature of the object to be heated such as molten metal, the acidity of the place where the heater device is used, the reducing atmosphere, the heat resistance of the heat generating material, and the impact resistance of the heat generating material at high temperatures It should be selected appropriately in consideration of sex, 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) It is possible to use stabilized zirconia or meta-stabilized zirconia which avoids the transition by adding about ₃ % to several 10%. 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. When the heating element is formed of the outer layer portion and the inner layer portion, the particle size is changed between the outer layer portion and the inner layer portion to adjust the heat generation characteristics of the outer layer portion and the inner layer portion. In order to suppress the "heat accumulation" inside the body, it is possible to make the heat generation of the inner layer portion smaller than that of the outer layer portion.

In the heater device according to the present invention, the heat-generating material that forms the heat-generating element does not change the resistance value of the heat-generating element even if the operating temperature changes, or has a positive value in which the resistance value increases, as long as there is no problem. 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 exothermic material has a large negative value that the resistance value greatly decreases when the temperature rises, if a high temperature part occurs in the heating element,
The high temperature part 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 heating element is the specific resistance value ρ (Ωcm) of the heating material such as conductive ceramics and the wall thickness t (cm) of the heating element.
And the area S (cm ² ) of the heating element. At this time,
When the heating element has 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, the more the heat radiation area can be secured, but cracks are likely to occur during molding, and are more susceptible 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, the thinner the heating element,
Although heat does not easily accumulate inside the heating element, the required amount of heat generation cannot be obtained, and this tends to cause 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 is sufficiently crushed 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 a mold cavity to be molded into a predetermined shape. A forming step of obtaining a body is performed, and a sintering step of heating the formed body to a predetermined temperature and sintering is performed. 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. Then, the heating element and the electrode portion are assembled to be integrated.

The heating element can also be manufactured as follows. That is, the raw material ceramic powder 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. 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. Then, the heating element and the electrode portion are assembled to be integrated.

Now, the configuration of the main part of the heater device according to the present invention will be described. That is, the conductive layer is interposed between the boundary between the heating element and the electrode portion, or between the layers when the heating element is formed of two or more layers. The conductive layer is formed by interposing a conductive granular material or liquid between the boundary portion between the heating element and the electrode portion, or between layers when the heating element is formed of two or more layers. In this case, by utilizing the current spreading function of the powder or granular material, liquid, etc., the electrical contact degree at the boundary between the heating element and the electrode part,
Alternatively, when the heating element is formed of two or more layers, the degree of electrical contact between the layers can be improved. In this case, even if a gap is likely to occur at the boundary between the heating element and the electrode portion, or if a gap is likely to occur between layers when the heating element is formed of two or more layers. , It is advantageous to secure electrical contact property and thermal contact property between the both. Alternatively, even if the thermal expansion coefficient of the heating element is different from that of the electrode section, or if the thermal expansion coefficient of the layers is different when the heating element is formed of two or more layers, the electrical contact between the two is further improved. It is advantageous to ensure thermal contact. When the conductive layer is formed of a powder or granular material, the powder or granular material is a conductive powder having heat generation property, for example, carbon powder,
Graphite powder can be adopted, or ceramic powder such as silicon carbide powder, metal powder having a high melting point and large specific resistance value can be adopted in some cases, and the above powders can be mixed and used as necessary. You can The relationship between the specific resistance value of carbon powder or graphite powder and the operating temperature range is such that the decrease in the specific resistance value can be reduced even when the operating temperature range is high, and therefore it is advantageous for ensuring heat generation in the high temperature range. When the conductive layer is formed of a liquid, the liquid is
It is possible to employ a material having excellent conductivity and a low melting point, for example, a low melting point metal such as tin, lead, bismuth, or sodium, and in some cases, a copper-based metal or an aluminum-based metal.

When the conductive layer is formed of conductive powder such as carbon powder or graphite powder, a fine particle size is preferable from the viewpoint of ensuring the heat generation property of the conductive layer itself, and the average particle size range is, for example,
It can be set to 50μ to 100μ among 10μ to 2mm. This is because it is considered that the fine particle diameter increases the contact resistance between the powder particles and ensures the heat generation of the conductive layer.

In addition, a solid powder or granular material made of a low melting point metal, a copper-based metal, or the like is used for the boundary portion between the heating element and the electrode portion, or
If it is formed between layers, if it is interposed between layers, if the temperature in use is above its melting point, the solid powdery particles will melt and become a liquid, and the degree of electrical contact and thermal contact It is advantageous to secure the degree.

In the heater device according to the present invention, as illustrated in Examples described later, the end portion in the length direction of the heating element has a three-dimensional curved surface shape, for example, a hemispherical shape or a shape close to a hemispherical shape so that there is no corner portion. Is desirable. 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 heating element is, for example, 30 to 100 mm, especially 40 to 6 in the type of immersing in the molten metal in the tundish.
It can be about 0 mm.

In the heater device according to the present invention, the electrode portion is for allowing electricity to flow in the thickness direction of the heating element between the electrode and the molten metal, and is adjacent to the heating element. 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 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.

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 amount of molten metal stored 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 includes a heating element 2 having a substantially flask shape, that is, a cylindrical shape with a bottom, and a rod-shaped electrode portion 3 inserted into a central hole of the heating element 2. The heating element 2 is of a two-layer type, and is composed of a substantially flask-shaped outer layer portion 20 and a substantially flask-shaped inner layer portion 25. The outer layer portion 20 is
It is made of mixed ceramics containing 90% of magnesia, 5% of zirconia, 5% of alumina, and 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 bottom 220 having a three-dimensional curved surface, that is, a hemisphere. The thickness of the central portion 210 and the thickness of the bottom portion 220 are substantially uniform, and the variation in the thickness is about ± 1 mm. Here, in this embodiment, the overall length L1 of the outer layer portion 20 in the axial direction is about 85 cm, the length L2 of the central portion 210 is about 65 cm, and the bottom portion 2
The length L3 of 20 is about 6 cm, the outer diameter of the central portion 210 is about 12 cm, the inner diameter of the central portion 210 is about 8.4 cm, and the diameter R1 of the bottom portion 220 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 central portion 260 connected to the base end portion 250, and a three-dimensional curved surface shape, that is, a substantially hemispherical bottom portion 270 connected to the central 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 diameter R2 of the bottom portion 270 is about 4 cm.

The rod-shaped electrode part 3 is made of carbon and its outer diameter is 3.8c.
It is about m and its total length is about 85 cm.

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 and further dried for 15 hours at 150 ° C., and a sintering process for heating and drying the dried molded product for the outer layer portion 20 at 1650 ° C. for 10 hours. It manufactured by carrying out in order. The maximum particle size of the raw material ceramic powder used for the outer layer portion 20 used in the adjusting step is about 3 mm. The inner layer portion 25 was formed using the mold for the inner layer portion 25 in the same procedure. The maximum particle size of the raw material ceramic powder for the inner layer portion 25 is about 3 mm. Then, on the inner surface near the bottom of the sintered outer layer portion 20, after dispersing carbon powder having a maximum particle size of about 1.5 mm as a spacer, 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. And put on top of each other.
Further, carbon powder is charged from the upper end 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 the carbon powder, whereby conductive heat generation as a conductive layer is achieved. Form layer 20a. 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. This is because it is easy to load carbon powder. At this time, since the carbon powder is rich in lubricity, the relative rotation operation is smoothly performed. In addition, the electrode portion 3 is formed in the hole defined by the inner peripheral surface of the inner layer portion 25.
Charge. Similarly, carbon powder is similarly charged into the boundary portion between the electrode portion 3 and the inner layer portion 25 to form the conductive heating layer 20b as a conductive layer.

When using the heater device 1 manufactured as described above, for example, two heater devices 1 are used, and a lead wire is fixed to the upper end of the rod-shaped electrode portion 3 of each heater device 1 with a band to connect to a power source and heat is generated. Preheat body 2 with a burner flame. Then, after preheating, as shown in FIG.
The individual heater devices 1 were immersed in the molten steel W in the container 4. In this state, between the two electrode parts 3 and the molten metal W, 0 to 44
A voltage of 0V is applied, and a current of 60Hz is applied at 0 to 800A. 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 and the outer layer portion 20 forming the heating element 2 of the other heater device 1 generate heat, so that 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.

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 proportion of which is selected so that the resistance value becomes high, heat generation is active 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. Rather, the heat generation characteristics of the inner layer portion 25 are controlled so as to suppress “heat accumulation” inside the heating element 2. It is preferable to suppress the inner layer 25 because it does not come into direct contact with the flame of the burner when preheating with the burner.
When selecting the blending ratio of the heat generating material that forms the, it is not necessary to secure a large heat generation amount as the outer layer portion 20, and further, it is not necessary to give great consideration to melting loss resistance, oxidation resistance, etc.
Therefore, it is possible to increase the degree of freedom in selection of the type of heat generating material forming the inner layer portion 25 or the mixing ratio thereof.

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 this embodiment, as shown in FIG. 3, the conductive heating 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 used. Since the conductive heating layer 20b made of carbon powder charged in the above functions as a current diffusion layer and a heat diffusion layer,
Since the degree of electrical contact between the outer layer portion 20 and the inner layer portion 25 is increased and the degree of thermal contact is also increased, local heat generation of the heating element 2 is suppressed,
Therefore, the heat generating element 2 is unlikely to generate heat runaway, and an advantage that uniform heat generation of the heat generating element 2 is obtained can be obtained.

Furthermore, in this embodiment, the conductive heating layer 20a and the conductive heating layer 20b formed by charging carbon powder also generate heat during use. In addition, the specific resistance value of the carbon powder is smaller than that of the conductive ceramics even when the operating temperature range is high, which is advantageous for ensuring heat generation in the high temperature range. Therefore, in order to secure the required heat generation amount of the heating element 2, the outer layer portion
20. It is possible to prevent the thickness of the inner layer portion 25 from being excessively increased. Therefore, the "heat accumulation" or "heat accumulation" inside the heating element 2 due to the thickening of the heating element 2 is caused. It is possible to suppress the "ceramic melting" caused by this. Moreover, since the conductive heating layers 20a and 20b made of carbon powder do not come into contact with the molten metal, the carbon powder does not enter the molten metal and there is no problem in maintaining the amount of carbon in the molten metal.

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.

Further, in the present embodiment, the bottom portion of the outer layer portion 20 forming the heating element 2
The bottom 220 of the inner layer portion 220 and the bottom 270 of the inner layer portion 25 each have a hemispherical shape as a three-dimensional curved surface, and the corner portions where the current easily concentrates are formed, which is more advantageous in preventing 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 bottom portion 272. The second inner layer portion 28 is formed of a base end portion 280, an intermediate portion 281, and a substantially hemispherical bottom portion 282. Then, carbon powder is charged between the first inner layer portion 27 and the second inner layer portion 28 to form a conductive heating layer 20a. Therefore, the first inner layer portion 27 and the second inner layer 28 are formed. The degree of electrical contact and the degree of thermal contact with the portion 28 are secured. Of course, a conductive heating layer 20a made of carbon powder is provided at the boundary between the outer layer portion 20 and the second inner layer portion 28, and further at the boundary portion between the electrode portion 3 and the first inner layer portion 27. Also, a conductive heating layer 20b made of carbon powder is provided.

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 also, a conductive layer can be provided by charging carbon powder, molten tin, or the like at the boundary part between the two 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, the heater device 1 is preheated, and the tundish 50 is moved from the ladle 55 and is held 1400 to 1600.
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 the 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, the conductivity of the heating element 2, particularly the heating element 2 which has conductivity mainly for the first time in the high temperature region since the magnesia is the main part 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 e.g.

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. In particular, since a conductive layer is interposed between the heating element and the electrode portion, or in the case of two or more heating layers, this conductive layer serves as a current spreading layer. Furthermore, since it functions as a heat diffusion layer, it can increase the degree of electrical contact and also the degree of thermal contact, and can suppress local heat generation. An advantageous advantage is obtained in improving the exothermicity.
According to the heater device of the present invention, the outer peripheral portion of the heating element becomes higher in temperature than the inside due to heat transfer when immersed in the molten metal, and the heating element expands in the radial direction. The liquid can be expected to drop or flow downward, so that the replenishment property of the powdery particles or the liquid is improved, which is advantageous for increasing the density of the conductive layer. Furthermore, since the lower end of the conductive layer is covered with the bottom of the heating element and has a non-exposed structure, powder particles or liquid that make up the conductive layer do not mix into the molten metal even if they fall or flow downward. It is advantageous for maintaining the composition of the molten metal.

Furthermore, according to the heater device of the present invention, when the conductive layer has a heat generating property, the conductive layer also generates heat in addition to the heat generated by the heat generating element. It is possible to prevent the thickness of the body from being excessively increased, and thus it is advantageous to suppress "heat accumulation" inside the heating element due to the thickening of the heating element.

Further, according to the heater device of the present invention, when the heating element is formed of two or more layers, the outer layer portion ensures the required heat generating property, and the inner layer has a heat generating characteristic higher than that of the outer layer. It can be formed of a heat-generating material having a small size, which is more advantageous for suppressing "heat accumulation" inside the heat-generating body.

[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 conductive heating layer, 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, 20a is a conductive heating layer (conductive layer), 20b is a conductive heating layer (conductive layer), 200 is a base end portion, 210 is a central portion, 220 is a bottom portion, 25 is an inner layer portion, 250 is a base end portion. , 260 indicates the central portion, and 270 indicates the bottom 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 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-A-61-104581 (JP, A)

Claims (1)

[Claims] 1. A bottomed cylindrical heating element which is immersed in a molten metal and which has at least one layer as a base material and which has a central hole and a bottom, and a central hole of the heating element. And an electrode part that is energized in the thickness direction of the heating element between the molten metal and the metal melt, and a boundary portion between the inner peripheral portion of the heating element and the outer peripheral portion of the electrode portion, or the interlayer of the heating element. A conductive layer made of powder or liquid is interposed in the heater, and the lower end of the conductive layer is covered with the bottom of the heating element so as to have a non-exposed structure. .