Resolution metal heating immersion heater and manufacturing method thereof

Abstract

To provide a resolution metal heating immersion heater capable of realizing a high-output in safety.SOLUTION: In a resolution metal heating immersion heater 20, a conductive part 22 and a heat generation body 23 are vertically integrated, and a molten metal 100 is heated by immersing it into the molten metal 100 used for a resolution or keeping a temperature. In the resolution metal heating immersion heater, at least a first layer 31 and a second layer 32 are provided from an inner side to an outer periphery and a bottom part of one where the conductive part 22 and the heat generation body 23 are vertically integrated so as to be covered from an outside lower part of the heat generation body 23. The first layer 31 is formed by mixing a mixture powder of an alumina 42 and a nitride aluminum 43 to a thermal hardening resin 41, hardening the mixture and sintering the mixture. The second layer 32 is formed by mixing only the alumina 42 to the thermal hardening resin 41, hardening the mixture and sintering the mixture.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an immersion heater for heating molten metal, which heats molten metal used for melting or maintaining the temperature, and a method for manufacturing the immersion heater for heating molten metal. [Background technology]

[0002] Conventionally, as shown in FIG. 8, a known immersion heater 10 for heating molten metal, which heats molten metal used for melting or maintaining the temperature, has been known in which a conductive part 12 and a heating element 13 are provided in a protective tube 11 constituting the heater body, and powder for the purpose of thermal conduction is filled between the protective tube 11 and the heating element 13 (see, for example, Patent Document 1).

[0003] There are various types of filler 14 made of powder with excellent thermal conductivity. Patent Document 1 describes a filler made of magnesium oxide (MgO) or a mixture of magnesium oxide (MgO) and boron nitride (BN), and a second compound such as copper oxide (CuO) or ferric oxide (Fe 2 O 3 ), and triiron tetroxide (Fe 3 O 4 and at least one selected from the group consisting of: [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-139847 A Summary of the Invention [Problem to be solved by the invention]

[0005] Factors that prevent an increase in the output of each molten metal immersion heater 10 include the maximum operating temperature of the heating element 13 and the maximum operating temperature of the filler 14. As shown in Figure 8, if the filler 14 is inside the protective tube 11, the temperature tends to rise when the output is increased, making it difficult to increase the output further. In response to this, in order to increase the maximum operating temperature for higher output, it is conceivable to use silicon carbide (SiC) for heating element 13 and alumina powder for filler 14; however, in this case, it has been difficult to fill protective tube 11 with alumina powder.

[0006] Furthermore, in the molten metal immersion heater 10 in which powder is filled between the protective tube 11 and the heating element 13, the coefficient of friction increases when the surfaces of the conductive part 12 and the heating element 13 oxidize, suppressing thermal expansion and contraction due to temperature changes in the molten metal immersion heater 10 and causing large stresses to act on the conductive part 12 and the heating element 13, which may result in damage to the conductive part 12 and the heating element 13. Furthermore, if the powder has the property of being oxidizable, the oxidation will reduce the insulation resistance, which may cause a risk of electric leakage.

[0007] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide an immersion heater for heating molten metal which is safe and capable of achieving high output, and a method for manufacturing the same. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides an immersion heater for heating molten metal, which is an immersion heater (20) for heating molten metal, in which a conductive part (22) and a heating element (23) are integrally formed on the top and bottom, and which is immersed in molten metal (100) to be used for melting or maintaining the temperature to heat the molten metal (100), At least a first layer (31) is provided so as to cover a lower portion of the conductive portion (22) and the entire heating element (23) integrated therewith from an outer lower portion of the heating element (23), The first layer (31) is characterized in that it is formed by mixing a powder mixture of alumina (42) and aluminum nitride (43) with a thermosetting resin (41) or an ultraviolet curing resin, hardening the mixture, and sintering the mixture.

[0009] The present invention also provides an immersion heater (20) for heating molten metal, in which a conductive portion (22) and a heating element (23) are integrally formed on the top and bottom, and which is immersed in molten metal (100) to be used for melting or maintaining the temperature thereof to heat the molten metal (100), At least a first layer (31) and a second layer (32) are provided from the inside so as to cover the lower part of the conductive portion (22) and the entire heating element (23) integrated therewith from the outer lower part of the heating element (23), The first layer (31) is formed by mixing a powder mixture of alumina (42) and aluminum nitride (43) with a thermosetting resin (41) or an ultraviolet-curing resin, hardening the mixture, and sintering the mixture. The second layer (32) is formed by mixing only alumina (42) with a thermosetting resin (41) or an ultraviolet curing resin, hardening the mixture, and sintering the mixture.

[0010] In the present invention, a third layer (33) is provided between the first layer (31) and the second layer (32), The third layer (33) is formed by mixing a powder mixture of alumina (42) and aluminum nitride (43) with a thermosetting resin (41) or an ultraviolet curing resin, hardening and molding the mixture, and sintering the mixture. The ratio of alumina (42) to aluminum nitride (43) in the third layer (33) is greater than the ratio of alumina (42) to aluminum nitride (43) in the first layer (31).

[0011] The present invention also provides a method for producing an immersion heater for heating molten metal, comprising a conductive portion (22) and a heating element (23) integrally formed on the top and bottom, the immersion heater (20) being immersed in a molten metal (100) to be used for melting or maintaining the temperature thereof to heat the molten metal (100), the method comprising the steps of: At least a first layer (31) and a second layer (32) are provided from the inside so as to cover the lower part of the conductive portion (22) and the entire heating element (23) integrated therewith from the outer lower part of the heating element (23), The first layer (31) is provided on the conductive portion (22) and the heating element (23) by setting a first resin mixed material, which is obtained by mixing a mixture powder of alumina (42) and aluminum nitride (43) with a thermosetting resin (41), in a bottomed hollow cylindrical first frame (51) with a first gap (M1) provided around the outer periphery of the conductive portion (22) and the heating element (23) and at the bottom of the heating element (23), and then filling the first gap (M1) with the first resin mixed material and applying heat from the outside of the first frame (51) to harden the first resin mixed material; The second layer (32) is formed by removing the conductive part (22) and the heating element (23) with the first layer (31) from the first frame (51), and setting a second resin mixed material, which is a mixture of only alumina (42) and thermosetting resin (41), in a bottomed, hollow cylindrical second frame (52) having a larger hollow capacity than the first frame (51), with the conductive part (22) and the heating element (23) with the first layer (31) in a state where a second gap (M2) is provided on the outer periphery and bottom, and then filling the second gap (M2) with the second resin mixed material and applying heat from the outside of the second frame (52) to harden the second resin mixed material, thereby providing the conductive part (22) and the heating element (23).

[0012] In the present invention, a third layer (33) is provided between the first layer (31) and the second layer (32), The third layer (33) is provided before the second layer (32) is provided on the conductive portion (22) and the heating element (23) and after the first layer (31) is provided, and is a third resin mixed material obtained by mixing a mixture powder of alumina (42) and aluminum nitride (43) in a ratio to a thermosetting resin (41) that is greater than the ratio of alumina (42) to aluminum nitride (43) in the first layer (31), and is formed into a bottomed hollow cylinder having a hollower shape than the first frame (51). The conductive part (22) with the first layer (31) and the heating element (23) are set in a third frame (53) having a large capacity and being smaller than the second frame (52) with a third gap (M3) provided on the outer periphery and bottom, and then the third gap (M3) is filled with the third resin mixed material and heat is applied from the outside of the third frame (53) to harden the third resin mixed material, thereby providing the conductive part (22) and the heating element (23).

[0013] The present invention also provides a method for producing an immersion heater for heating molten metal, comprising a conductive portion (22) and a heating element (23) integrally formed on the top and bottom, the immersion heater (20) being immersed in a molten metal (100) to be used for melting or maintaining the temperature thereof to heat the molten metal (100), the method comprising the steps of: At least a first layer (31) and a second layer (32) are provided from the inside so as to cover the lower part of the conductive portion (22) and the entire heating element (23) integrated therewith from the outer lower part of the heating element (23), The first layer (31) is provided on the conductive portion (22) and the heating element (23) by setting a first resin mixed material, which is obtained by mixing a powder mixture of alumina (42) and aluminum nitride (43) with an ultraviolet curing resin, in a bottomed, hollow, cylindrical, ultraviolet-transmitting first frame (51) with the conductive portion (22) and the heating element (23) provided with a first gap (M1) on the outer periphery and bottom thereof, filling the first gap (M1) with the first resin mixed material, and applying ultraviolet light from the outside of the first frame (51) to harden the first resin mixed material, The second layer (32) is formed by removing the conductive part (22) and the heating element (23) with the first layer (31) from the first frame (51), and setting a second resin mixed material, which is an ultraviolet-curable resin mixed with only alumina (42), in a second frame (52) that is hollow and cylindrical with a bottom, is ultraviolet-transmittable, and has a larger hollow capacity than the first frame (51), with the conductive part (22) and the heating element (23) with the first layer (3) set in the second frame (52) with a second gap (M2) on the outer periphery and bottom, and then filling the second gap (M2) with the second resin mixed material and applying ultraviolet light from outside the second frame (52) to harden the second resin mixed material, thereby providing the conductive part (22) and the heating element (23).

[0014] In the present invention, a third layer (33) is provided between the first layer (31) and the second layer (32), The third layer (33) is provided before the second layer (32) is provided on the conductive portion (22) and the heating element (23) and after the first layer (31) is provided, and is a third resin mixed material obtained by mixing alumina (42) and aluminum nitride (43) powder in a ratio of alumina (42) to aluminum nitride (43) that is greater than the ratio of alumina (42) to aluminum nitride (43) in the first layer (31) and is formed into a bottomed hollow cylindrical shape that is ultraviolet ray transmissive and is sandwiched between the first frame (51). The conductive part (22) with the first layer (31) and the heating element (23) are set in a third frame (53) having a larger hollow capacity than the second frame (52) and a third gap (M3) is provided on the outer periphery and bottom thereof, and the third resin mixed material is then filled into the third gap (M3). Ultraviolet light is applied from the outside of the third frame (53) to harden the third resin mixed material, thereby providing the conductive part (22) and the heating element (23).

[0015] The symbols in parentheses above indicate corresponding elements or items shown in the drawings and in the detailed description of the invention described below. Effect of the Invention

[0016] According to the present invention, unlike conventional immersion heaters for heating molten metals which have protective tubes with conductive parts and heating elements built in above and below, the protective tube is not essential; instead, the protective tube itself is not necessary. Instead, a first layer made by sintering a mixture of alumina and aluminum nitride powder and hardening it into a thermosetting resin or ultraviolet-curing resin (thermosetting resins are hardened by applying heat, and ultraviolet-curing resins are hardened by applying ultraviolet light) is provided directly on the conductive parts and heating element, eliminating the hassle of filling the inside of the protective tube with a filler. In addition, since a protective tube is not required, costs can be reduced, and there is no need to worry about the protective tube being damaged due to high heat generation. In other words, the molten metal immersion heater of the present invention is safer and can achieve higher output than conventional examples. In particular, the first layer is made by mixing a mixture of alumina and aluminum nitride powder with thermosetting resin or ultraviolet curing resin, hardening and molding it, and sintering it, so it has high thermal conductivity and is effective for achieving high output.

[0017] Furthermore, according to the present invention, a second layer is provided on the outside of the first layer, which is made by mixing only alumina with thermosetting resin or ultraviolet curing resin, hardening and molding it, and sintering the mixture. Therefore, the inside first side is strongly protected by the second layer, and the overall strength of the integrated conductive part and heating element is greatly improved, thereby increasing safety performance.

[0018] Furthermore, if another layer is provided on the outside of the first layer or the second layer to protect the inner layer (the first layer or the second layer), a more stable immersion heater for heating molten metal can be obtained.

[0019] Furthermore, according to the present invention, a third layer is provided between the first and second layers. The third layer is formed by mixing a powder mixture of alumina and aluminum nitride with thermosetting resin or ultraviolet curing resin, hardening and molding the mixture, and sintering the mixture. The ratio of alumina to aluminum nitride in the third layer is greater than the ratio of alumina to aluminum nitride in the first layer. Therefore, the thermal conductivity increases from the outside to the inside, i.e., from the second layer to the third layer and then to the first layer, and the protective strength increases from the inside to the outside, i.e., from the first layer to the third layer and then to the second layer. This makes it possible to increase the output of the immersion heater for heating molten metal while preventing damage to the conductive parts and the heating element.

[0020] In addition, it is easy to provide a plurality of layers with different performance characteristics around the outer periphery of the integrated conductive portion and heating element.

[0021] Furthermore, according to the present invention, when the first layer is provided on an integrated conductive part and heating element, the integrated conductive part and heating element are set in a bottomed, hollow cylindrical first frame with a first gap provided at the outer periphery and bottom, and the first gap is then filled with a first resin mixed material prepared by mixing a thermosetting resin or ultraviolet curing resin with a mixed powder of alumina and aluminum nitride, and heat or ultraviolet light is applied from the outside of the first frame to harden the first resin mixed material, which is easy and simple to manufacture. Similarly, when the second layer is provided in an integrated conductive part and heating element, the conductive part with the first layer and the heating element are set in a bottomed, hollow cylindrical second frame with a second gap provided on the outer periphery and bottom, and the second gap is then filled with a second resin mixed material made by mixing only alumina with a thermosetting resin or ultraviolet curing resin, and heat or ultraviolet light is applied from the outside of the second frame to harden the second resin mixed material, which is easy and simple to manufacture. Furthermore, when a third layer is provided between the first and second layers, a third frame body that is hollow and cylindrical with a bottom and has a larger hollow volume than the first frame body but smaller than the second frame body is used, and the conductive part and heating element with the first layer are set in the third frame body with a third gap provided on the outer periphery and bottom. The third gap is then filled with a third resin mixed material which is a thermosetting resin or ultraviolet curing resin mixed with a mixed powder of alumina and aluminum nitride in a ratio of alumina to aluminum nitride greater than the ratio of alumina to aluminum nitride in the first layer, and heat or ultraviolet light is applied from the outside of the third frame body to harden the third resin mixed material, making it easy and simple to manufacture. [Brief description of the drawings]

[0022] [Figure 1] 1 is a partial cross-sectional side view showing a state in which an immersion heater for heating molten metal according to an embodiment of the present invention heats molten metal. FIG. [Diagram 2] FIG. 2 is a schematic diagram showing a method for producing materials constituting each layer in a method for producing an immersion heater for heating molten metal according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a partial cross-sectional view showing a molding step of a first layer in a manufacturing method for an immersion heater for heating molten metal according to an embodiment of the present invention. [Figure 4] FIG. 4 is a partial cross-sectional view showing a molding step of a third layer in a manufacturing method for an immersion heater for heating molten metal according to an embodiment of the present invention. [Diagram 5] FIG. 4 is a partial cross-sectional view showing a molding step of a second layer in a manufacturing method of an immersion heater for heating molten metal according to an embodiment of the present invention. [Figure 6] FIG. 2 is a conceptual diagram showing the internal crystal structure of each layer in the immersion heater for heating molten metal according to the embodiment of the present invention. [Figure 7] 1A and 1B show a conductive part and a heating element that constitute an immersion heater for heating molten metal according to an embodiment of the present invention, in which FIG. 1A is a schematic front view, and FIG. 1B is an enlarged cross-sectional view taken along line AA of FIG. [Figure 8] FIG. 1 is a partial cross-sectional view showing a conventional immersion heater for heating molten metal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] 1 to 7, an immersion heater 20 for heating molten metal and a method for manufacturing the same according to an embodiment of the present invention will be described.

[0024] 1, the immersion heater 20 for heating molten metal according to this embodiment is an immersion heater in which a conductive part 22 and a heating element 23 are integrated vertically, and which is immersed in molten metal 100 used for melting or maintaining the temperature to heat the molten metal 100. Here, the immersion heater 20 for heating molten metal is shown attached to the upper wall 201 (top plate or lid) of a melting furnace 200. The lower part of the heating element 23 is immersed in the molten metal 100 to directly heat the molten metal 100.

[0025] A first layer 31, a third layer 33, and a second layer 32 are provided from the inside on the outer periphery and bottom of the integrated conductive part 22 and heating element 23 of molten metal immersion heater 20, covering the outer lower part of heating element 23. Each of these layers 31 to 33 covers the entire heating element 23 (entire periphery) and the lower part of conductive part 22 from the outside, and each of these layers 31 to 33 is fixed to upper wall 201. Here, the innermost layer of the integrated conductive portion 22 and heating element 23 is called the first layer 31, the outermost layer is called the second layer 32, and the layer provided between the first layer 31 and the second layer 32 is called the third layer 33.

[0026] The first layer 31 is made by mixing a powder mixture of alumina 42 and aluminum nitride 43 with a thermosetting resin 41, hardening the mixture, and sintering the mixture, as shown in FIG. The second layer 32 is formed by mixing only alumina 42 with thermosetting resin 41, hardening and molding the mixture, and sintering the mixture. Furthermore, the third layer 33 is formed by mixing a powder mixture of alumina 42 and aluminum nitride 43 with thermosetting resin 41, hardening and molding the mixture, and sintering the mixture. The ratio of alumina 42 to aluminum nitride 43 in the third layer 33 is greater than the ratio of alumina 42 to aluminum nitride 43 in the first layer 31.

[0027] More specifically, the molten metal immersion heater 20 is manufactured as follows. First, as shown in FIG. 2, materials for forming each layer (first layer 31, second layer 32, third layer 33) are prepared. 2(a), the material constituting the first layer 31 is a mixture of a thermosetting resin 41 and a powder mixture of alumina 42 and aluminum nitride 43 (first resin mixture). The thermosetting resin 41 is a resin that undergoes polymerization when heated to form a polymer network structure, hardens by rubbing, and cannot be restored to its original state. Examples of the thermosetting resin 41 include phenolic resin, epoxy resin, melamine resin, alkyd resin, silicone resin, and polyurethane. In this embodiment, phenolic resin is used.

[0028] The material constituting the second layer 32 is, as shown in FIG. 2(c), a mixture of a thermosetting resin 41 and only alumina 42 (second resin mixture material).

[0029] 2(b), the material constituting the third layer 33 is a mixture of a thermosetting resin 41 and a mixed powder of alumina 42 and aluminum nitride 43 (third resin mixture), but the amount of aluminum nitride 43 is less than that of the first resin mixture. That is, the third resin mixture is a mixture of a thermosetting resin 41 and a mixed powder of alumina 42 and aluminum nitride 43, in which the ratio of alumina 42 is greater than the ratio of alumina 42 to aluminum nitride 43 in the first layer 31.

[0030] Next, as shown in Figure 3(a), the integrated conductive part 22 and heating element 23 are set in the center of the inside of a bottomed hollow cylindrical first frame 51, with a first gap M1 provided between the first frame 51 and the integrated conductive part 22 and heating element 23, i.e., at the outer periphery and bottom of the integrated conductive part 22 and heating element 23. Thereafter, as shown in FIG. 3(b), the first gap M1 is filled with a first resin mixture material, and heat is applied from the outside of the first frame 51 to harden the first resin mixture material. As a result, the first layer 31 is provided on the outer periphery of the conductive portion 22 and the heating element 23 that are integrated together.

[0031] Next, the conductive part 22 with the first layer 31 and the heating element 23 are removed from the first frame 51, and then, as shown in Figure 4(a), the conductive part 22 with the first layer 31 and the heating element 23 are set in the center of the interior of a bottomed, hollow cylindrical third frame 53, with a third gap M3 provided between the third frame 53 and the conductive part 22 with the first layer 31 and the heating element 23, i.e., at the outer periphery and bottom of the conductive part 22 with the first layer 31 and the heating element 23. Thereafter, as shown in FIG. 4(b), the third gap M3 is filled with the third resin mixture material, and heat is applied from the outside of the third frame 53 to harden the third resin mixture material. As a result, the third layer 33 is provided on the outer periphery of the conductive portion 22 and the heating element 23 with the first layer 31 attached thereto. The third frame 53 has a larger hollow volume than the first frame 51 .

[0032] Next, the conductive part 22 and the heating element 23 with the first layer 31 and the third layer 33 are removed from the third frame 53, and then, as shown in Figure 5 (a), the conductive part 22 and the heating element 23 with the first layer 31 and the third layer 33 are set in the center of the inside of the bottomed hollow cylindrical second frame 52, with a second gap M2 provided between the second frame 52 and the conductive part 22 and the heating element 23 with the first layer 31 and the third layer 33, i.e., at the outer periphery and bottom of the conductive part 22 and the heating element 23 with the first layer 31 and the third layer 33, as well as at the bottom. Thereafter, as shown in FIG. 5(b), the second gap M2 is filled with the second resin mixed material, and heat is applied from the outside of the second frame 52 to harden the second resin mixed material. As a result, the second layer 32 is provided on the outer periphery of the conductive portion 22 and the heating element 23 with the first layer 31 and the third layer 33 attached thereto. The second frame 52 has a larger hollow volume than the third frame 53 .

[0033] Then, the conductive part 22 and the heating element 23 with the first layer 31, the third layer 33 and the second layer 32 are taken out from the second frame 52, and then stored in an electric furnace with a nitrogen atmosphere (not shown), where they are degreased and fired at about 1500° C. The thermosetting resin 41 disappears completely by the degreasing. Thereafter, the conductive part 22 with the first layer 31, the third layer 33 and the second layer 32 and the heating element 23 are removed from the electric furnace and cooled, completing the immersion heater for heating molten metal 20 according to this embodiment as shown in FIG. 1.

[0034] An image of the internal crystal structure in each layer of the molten metal immersion heater 20 thus manufactured is as shown in FIG. Although the temperature of about 1500°C in the electric furnace is far from the sintering temperature of aluminum nitride 43, in the first layer 31 and the third layer 33, the alumina 42 around the aluminum nitride 43 is sintered to hold the aluminum nitride 43 powder from the surroundings. At this time, the third layer 33 has a smaller amount of aluminum nitride 43 than the first layer 31, so the force of holding by the alumina 42 is greater, and since the second layer 32 does not contain aluminum nitride 43, the second layer 32 has the greatest strength and the first layer 31 has the smallest strength (the strength increases in the order of the first layer 31, the third layer 33, and the second layer 32). Conversely, the thermal conductivity of the first layer 31 is the greatest and the second layer 32 is the smallest (the thermal conductivity increases in the order of the second layer 32, the third layer 33, and the first layer 31).

[0035] The conductive part 22 and heating element 23 that constitute the immersion heater 20 for heating molten metal according to an embodiment of the present invention are generally commercially available SiC (silicon carbide) heaters, and although there is no particular limitation, they may be, for example, as shown in FIG. 7. As shown in FIG. 7(a), the heating element 23 is made of a conductive ceramic material such as SiC or a SiC-Si composite material, generates heat when electricity is applied, and has a double spiral portion at the tip side.

[0036] The conductive part 22 has a pair of long power transmitters 22a, 22b made of a conductive ceramic material such as SiC or a SiC-Si composite material. A slit is formed between the pair of power transmitters 22a, 22b, and a spacer 24 made of an insulating material is inserted into the slit, as shown in Fig. 7(b). A ceramic tightening collar 26 is attached to the upper part of the conductive part 22, and a hose band 27 is wrapped around the outer periphery of the tightening collar 26. This supports the upper parts of the pair of power transmitters 22a, 22b. A pair of terminals 25a, 25b extending from the electrode part 25 are connected to the pair of power transmitters 22a, 22b, respectively, to supply electricity.

[0037] With the immersion heater for heating molten metals 20 manufactured as described above, unlike the conventional immersion heater for heating molten metals 20 having a protective tube 21 with a conductive part 22 and a heating element 23 built in above and below, a filler is not filled inside the protective tube 21. The protective tube 21 itself is not necessary, and a first layer 31 made by mixing a mixed powder of alumina 42 and aluminum nitride 43 with thermosetting resin 41, applying heat to harden and mold it, and sintering the mixture, is provided directly on the conductive part 22 and the heating element 23, so there is no need for the hassle of filling the inside of the protective tube 21 with a filler. In addition, since the protective tube 21 is not required, costs can be reduced, and there is no need to worry about the protective tube 21 being damaged due to high heat generation. In other words, the molten metal immersion heater 20 of this embodiment is safer and can achieve higher output than the conventional example. In particular, the first layer 31 is made by mixing a mixture of powders of alumina 42 and aluminum nitride 43 with thermosetting resin 41, hardening and molding the mixture, and sintering it, so that it has high thermal conductivity and is effective for achieving high output.

[0038] In addition, a second layer 32 is provided on the outside of the first layer 31 and is made by mixing only alumina 42 with thermosetting resin 41, hardening and molding the mixture, and sintering the mixture. This provides strong protection for the inner first side with the second layer, and the overall strength is greatly improved, thereby enhancing safety performance.

[0039] In addition, a third layer 33 is provided between the first layer 31 and the second layer 32. The third layer 33 is formed by mixing a powder mixture of alumina 42 and aluminum nitride 43 with thermosetting resin 41, hardening and molding the mixture, and sintering the mixture. The ratio of alumina 42 to aluminum nitride 43 in the third layer 33 is greater than the ratio of alumina 42 to aluminum nitride 43 in the first layer 31. As a result, the thermal conductivity increases from the outside to the inside, i.e., from the second layer 32 to the third layer 33 and then to the first layer 31, and the protective strength increases from the inside to the outside, i.e., from the first layer 3 to the third layer 33 and then to the second layer 32. This makes it possible to increase the output of the immersion heater 20 for heating the molten metal while preventing damage to the conductive part 22 and the heating element 23.

[0040] Furthermore, when manufacturing the molten metal immersion heater 20, if the first layer 31 is provided on the integrated conductive part 22 and heating element 23, the integrated conductive part 22 and heating element 23 are set in a bottomed, hollow, cylindrical first frame 51 with a first gap M1 provided on the outer periphery and bottom, and then the first gap M1 is filled with a first resin mixed material obtained by mixing a mixture powder of alumina 42 and aluminum nitride 43 with thermosetting resin 41, and heat is applied from the outside of the first frame 51 to harden the first resin mixed material, which makes the manufacture easy and simple. Similarly, when the second layer 32 is provided on the conductive part 22 and the heating element 23 which are integrated, the integrated conductive part 22 and the heating element 23 with the first layer 31 are set in a bottomed hollow cylindrical second frame 52 with a second gap M2 provided on the outer periphery and bottom, and the second gap M2 is then filled with a second resin mixed material obtained by mixing only alumina 42 with thermosetting resin 41, and heat is applied from the outside of the second frame M2 to harden the second resin mixed material, which is easy and simple to manufacture. Furthermore, when providing a third layer 33 between the first layer 31 and the second layer 32, a third frame 53 having a bottomed hollow cylindrical shape with a larger hollow volume than the first frame 51 and smaller than the second frame 52 is used, and the conductive part 22 with the first layer 31 and the heating element 23 integrated together are set in the third frame 53 with a third gap M3 provided on the outer periphery and bottom. The third gap M3 is then filled with a third resin mixed material obtained by mixing a mixed powder of alumina 42 and aluminum nitride 43 in a ratio of thermosetting resin 41 that is greater than the ratio of alumina 42 to aluminum nitride 43 in the first layer 31, and heat is applied from the outside of the third frame 53 to harden the third resin mixed material, which is easy and simple to manufacture.

[0041] In this embodiment, a thermosetting resin is used to prepare the first, second and third resin mixture materials. However, instead of this, an ultraviolet curing resin may be used, and alumina 42 or aluminum nitride 43 may be mixed into the ultraviolet curing resin. UV-curing resins are synthetic resins that react to ultraviolet light and chemically change from liquid to solid, and include acrylic resins and epoxy resins. When using ultraviolet curing resin, the first frame 51, second frame 52, and third frame mentioned above must each be made ultraviolet ray transparent, and the first, second, and third resin mixed materials are cured by applying ultraviolet rays from outside these frames 51 to 53. Furthermore, other methods may be used as long as the first layer 31, the third layer 33, and the second layer 32 are provided on the outer periphery of the conductive portion 22 and the heating element 23 integrated together.

[0042] In addition, in this embodiment, a three-layer structure is formed around the integrated conductive portion 22 and heating element 23, with the first layer 31, the third layer 33, and the second layer 32. However, it is also possible to have a structure with more layers than this, or conversely, to omit the third layer 33 and have a structure with only the first layer 31 and the second layer 32, or even to have only the first layer 31 structure, or to provide one or more protective layers around the outer periphery of the first layer 31 to provide additional protection for the inner first layer 33. [Explanation of symbols]

[0043] 10. Immersion heater for heating molten metal 11 Protection tube 12 Conductive part 13 Heating element 14 Filling material 20 Immersion heater for heating molten metal 22 Conductive part 22a,22b Transmission body 23 Heating element 24 Spacer 25 Electrode part 25a,25b terminal 26 Tightening collar 27 Hose Band 31 1st layer 32 2nd layer 33 3rd layer 41 Thermosetting resin 42 Alumina 43 Aluminum Nitride 51 First frame 52 Second frame 53 Third Frame 100 Molten metal 200 Melting furnace 201 Upper wall M1 First gap M2 Second gap M3 3rd gap

Claims

1. An immersion heater for heating molten metal, which has a conductive part and a heating element integrally formed on the top and bottom, and is immersed in molten metal to be used for melting or maintaining the temperature to heat the molten metal, At least a first layer is provided so as to cover a lower portion of the conductive portion and the entire heating element integrated thereunder from an outer lower portion of the heating element, 1. An immersion heater for heating molten metal, comprising: said first layer being formed by mixing a powder mixture of alumina and aluminum nitride with a thermosetting resin or an ultraviolet curing resin, hardening and molding the mixture, and sintering the mixture.

2. An immersion heater for heating molten metal, which has a conductive part and a heating element integrally formed on the top and bottom, and is immersed in molten metal to be used for melting or maintaining the temperature to heat the molten metal, At least a first layer and a second layer are provided from the inside so as to cover a lower portion of the conductive portion and the entire heating element integrated therebelow from an outer lower portion of the heating element, The first layer is formed by mixing a mixture of alumina and aluminum nitride powder with a thermosetting resin or an ultraviolet curing resin, hardening and molding the mixture, and sintering the mixture.

4. An immersion heater for heating molten metal, comprising: said second layer being formed by mixing only alumina with a thermosetting resin or an ultraviolet curing resin, hardening and molding the mixture, and sintering the mixture.

3. a third layer is provided between the first layer and the second layer; 3. The immersion heater for heating molten metal according to claim 2, characterized in that the third layer is formed by mixing a mixture of alumina and aluminum nitride powder with a thermosetting resin or an ultraviolet curing resin, hardening and molding the mixture, and sintering the mixture, and the ratio of alumina to aluminum nitride in the third layer is greater than the ratio of alumina to aluminum nitride in the first layer.

4. A method for manufacturing an immersion heater for heating molten metal, which has a conductive part and a heating element integrally formed on the top and bottom, and is immersed in molten metal to be used for melting or maintaining the temperature to heat the molten metal, comprising: At least a first layer and a second layer are provided from the inside so as to cover a lower portion of the conductive portion and the entire heating element integrated therebelow from an outer lower portion of the heating element, the first layer is provided on the conductive portion and the heating element by setting a first resin mixed material, which is a thermosetting resin mixed with a mixed powder of alumina and aluminum nitride, in a bottomed hollow cylindrical first frame with a first gap provided around the outer periphery of the conductive portion and the heating element and at the bottom of the heating element, filling the first gap with the first resin mixed material, and applying heat from the outside of the first frame to harden the first resin mixed material; a second resin mixed material having a thickness of about 100 nm to about 150 nm and a thickness of about 100 nm, the second resin mixed material being filled into the second gap and the second gap being formed on the outer periphery and the bottom of the second frame, and heat being applied from the outside of the second frame to harden the second resin mixed material, thereby forming the second layer on the conductive part and the heating element.

5. a third layer is provided between the first layer and the second layer; 5. The method for manufacturing an immersion heater for heating molten metal according to claim 4, wherein the third layer is provided before the second layer is provided on the conductive part and the heating element and after the first layer is provided, and the third layer is provided on the conductive part and the heating element by setting a third resin mixed material, which is a mixed powder of alumina and aluminum nitride, with a ratio of alumina to aluminum nitride being greater than a ratio of alumina to aluminum nitride in the first layer, in a third frame having a bottomed hollow cylinder shape having a larger hollow capacity than the first frame and smaller than the second frame, with a third gap provided on an outer periphery and a bottom, and then filling the third gap with the third resin mixed material and applying heat from outside the third frame to harden the third resin mixed material, so that the third layer is provided on the conductive part and the heating element.

6. A method for manufacturing an immersion heater for heating molten metal, which has a conductive part and a heating element integrally formed on the top and bottom, and is immersed in molten metal to be used for melting or maintaining the temperature to heat the molten metal, comprising: At least a first layer and a second layer are provided from the inside so as to cover a lower portion of the conductive portion and the entire heating element integrated therebelow from an outer lower portion of the heating element, The first layer is provided on the conductive part and the heating element by setting a first resin mixed material, which is a mixture of an ultraviolet curing resin and a mixed powder of alumina and aluminum nitride, in a bottomed, hollow, cylindrical, ultraviolet-transmitting first frame body with a first gap provided at an outer periphery and a bottom, filling the first gap with the first resin mixed material, and applying ultraviolet light from the outside of the first frame body to harden the first resin mixed material; 3. A method for manufacturing an immersion heater for heating molten metal, comprising the steps of: removing the conductive part with the first layer and the heating element from the first frame; setting a second resin mixed material, in which only alumina is mixed with an ultraviolet curing resin, in a second frame, which is hollow and cylindrical with a bottom, ultraviolet light is transmittance, and has a larger hollow volume than the first frame, with the conductive part with the first layer and the heating element being set with a second gap provided on the outer periphery and at the bottom; filling the second gap with the second resin mixed material; and applying ultraviolet light from outside the second frame to harden the second resin mixed material, thereby providing the second layer on the conductive part and the heating element.

7. a third layer is provided between the first layer and the second layer; 7. The method for manufacturing an immersion heater for heating molten metal according to claim 6, wherein the third layer is provided before the second layer is provided on the conductive part and the heating element and after the first layer is provided, and the third layer is provided on the conductive part and the heating element by setting a third resin mixed material, which is a mixed powder of alumina and aluminum nitride, with an ultraviolet-curing resin having a ratio of alumina to aluminum nitride greater than a ratio of alumina to aluminum nitride in the first layer, in a third frame which is hollow and cylindrical with a bottom, capable of transmitting ultraviolet light, has a larger hollow capacity than the first frame and is smaller than the second frame, with a third gap provided on the outer periphery and bottom, and then filling the third gap with the third resin mixed material and applying ultraviolet light from outside the third frame to harden the third resin mixed material.

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