Heater

Abstract

[Problem] To provide a heater in which sealing performance of a tubular part for housing a heating element is improved in a state where cost is suppressed. [Solution] An immersion heater 1 as an example of the heater comprises: a heating element 4; a first lead wire part 6 and a second lead wire part 8 which are connected to the heating element 4; a tubular part 2 for housing the heating element 4; and a sealing part 10 for sealing the tubular part 2 while allowing the first lead wire part 6 and the second lead wire part 8 to pass through. The sealing part 10 is a cured product obtained from a liquid-like, gel-like, paste-like or powdery raw material.

Description

heater

[0001] The present invention relates to heaters, such as immersion heaters, that heat and keep molten metal, which is a liquid metal, warm.

[0002] A known heater is described in Japanese Patent Laid-Open Publication No. 2023-84536 (Patent Document 1). In this heater, a heating element 4 is disposed within the closed tip of a tubular portion 2. A first lead wire portion 6 and a second lead wire portion 8 are connected to the heating element 4. The open base end of the tubular portion 2 is sealed by a sealing portion, allowing the first lead wire portion 6 and the second lead wire portion 8 to pass through. In addition, a filler, which is a powdered, highly thermally conductive filler material, is disposed between the tubular portion 2 and the heating element 4, which prevents the heating element 4 from coming into contact with air containing oxygen gas, thereby preventing embrittlement due to oxidation of the heating element 4 in high-temperature environments.

[0003] JP 2023-84536 A

[0004] The filler's suppression of embrittlement due to oxidation of the heating element 4 may not be sufficient depending on the environment. Oxidation due to contact with air flowing through the sealing portion of the heating element 4 progresses over a long period of time, resulting in embrittlement and wire breakage over long periods of use, which may shorten the lifespan of the heating element 4. Furthermore, as the heat output of the heating element 4 increases and the heating temperature of the heating element 4 increases, oxidation of the heating element 4 progresses more easily. Therefore, there is a need for a simple and low-cost method for suppressing oxidation of the heating element 4 in high-temperature environments. Meanwhile, the details of the sealing portion in the heater described above are unclear, leaving room for improvement in the sealing performance of the tubular portion 2. Improved sealing performance would further suppress oxidation-induced deterioration within the tubular portion 2, including the heating element 4. Furthermore, because the sealing portion passes through a lead wire and is exposed to high heat, it requires insulation and heat resistance in addition to sealing performance. Therefore, there is a need for a sealing portion that possesses these properties while being easily formed at low cost. In particular, improved sealing is required for the heating element 4 made of a material that has weaker resistance to oxidation in high-temperature environments. Furthermore, in harsher environments than conventionally encountered, such as high-temperature environments, there may be limits to the ability of fillers alone to suppress oxidation. A primary object of the present invention is to provide a heater in which the sealing of the tubular portion that houses the heating element is improved. Another primary object of the present invention is to provide a heater in which the sealing of the tubular portion is improved in a simple manner and at reduced cost.

[0005] This specification discloses a heater. The heater may include a heating element. The heater may include a lead wire portion connected to the heating element. The heater may include a tubular portion that houses the heating element. The heater may include a sealing portion that seals the tubular portion while allowing the lead wire portion to pass through. The sealing portion may be a cured product obtained from a liquid, gel, paste, or powder raw material. The cured product may also be formed from a siloxane material. The cured product may also include at least one of quartz and alumina.

[0006] A main advantage of the present invention is that a heater is provided in which the tubular portion housing the heating element has improved sealing performance. This prevents the heating element from becoming brittle and breaking due to oxidation in a high-temperature environment, thereby extending the life of the heating element. Another main advantage of the present invention is that a heater in which the tubular portion has improved sealing performance is provided in a simple and cost-effective manner.

[0007] 5 is a schematic diagram of an immersion heater and its periphery according to the present invention. It is a graph showing the analysis results obtained by a thermogravimetric differential thermal analyzer under condition T1 in Example 2. It is a graph showing the analysis results obtained by a thermogravimetric differential thermal analyzer under condition T2 in Example 2. It is a graph showing the analysis results obtained by a thermogravimetric differential thermal analyzer under condition T3 in Example 2. It is a graph showing the temperature of the sealing portion in FIG. 1 for each air flow rate from the blower in FIG. 1 under conditions R1 to R3. It is a graph showing the difference in temperature of the sealing portion for each air flow rate relative to the temperature of the sealing portion at an air flow rate of 0 L / min in FIG. 5 under conditions R1 to R3.

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments and modifications of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments and modifications.

[0009] FIG. 1 is a schematic diagram of an immersion heater 1 and its surroundings as an example of a heater according to this embodiment. The immersion heater 1 includes a tubular portion 2, a heating element 4, a first lead wire portion 6, a first connection portion 7, a second lead wire portion 8, a second connection portion 9, a sealing portion 10, a heat insulating material 11, a filler (not shown), a support portion 12, a joint portion 14, and a blower portion 16. The immersion heater 1 is intended to heat and insulate molten aluminum W, which is molten aluminum. The immersion heater 1 may also be intended to heat molten aluminum of a non-ferrous metal such as zinc. The immersion heater 1 may also be intended to heat molten aluminum of other metals, including iron. The immersion heater 1 may also be intended to heat other objects. The heater may also be something other than an immersion heater. The molten aluminum W is intended for use in an aluminum die-cast product. The molten aluminum W may also be used for other purposes. When heating the molten aluminum W, the tip of the immersion heater 1 is typically immersed in the molten aluminum W from above, and the immersion heater 1 is positioned so that its longitudinal direction is in the up-down direction and its tip is on the bottom side. The immersion heater 1 is immersed in the molten aluminum W through a hole H opened in the lid T of the molten aluminum tank. The immersion heater 1 may also be used in a position other than the up-down position. Furthermore, the molten aluminum tank does not need to be equipped with a lid T.

[0010] The tubular portion 2 is a cylindrical tube made of ceramics. The tip portion 2P of the tubular portion 2 is closed, forming a closed end, i.e., a sealed end. The shape of the tip portion 2P of the tubular portion 2 is hemispherical. The base end portion 2B of the tubular portion 2 is open, forming an open end. The material of the tubular portion 2 is not limited to ceramics. Furthermore, the shape of the tubular portion 2 is not limited to having a closed end and an open end, and may be, for example, a shape in which both ends are open. Furthermore, the shape of the tip portion 2P of the tubular portion 2 is not limited to being hemispherical.

[0011] The heating element 4 is a single coil overall and generates heat when electricity is applied. The heating element 4 is placed within the tubular portion 2. The heating element 4 is located on the tip end 2P side within the tubular portion 2. The tubular portion 2 is located outside the heating element 4 and covers it. The tubular portion 2 houses the heating element 4. The tubular portion 2 protects the heating element 4. The heating element 4 is made of molybdenum or a molybdenum alloy. Hereinafter, both will be referred to as "molybdenum-made" without distinction. The melting point of molybdenum is approximately 2500°C, which is higher than the melting point of nichrome wire, approximately 1400°C, and the heat-resistant temperature of nichrome wire, 1150°C. Therefore, compared to heating elements made of nichrome wire, a higher heating temperature and greater output can be obtained. The heating element 4 may be a multiple coil or multiple coils. Furthermore, the heating element 4 may be made of a material other than molybdenum.

[0012] The first lead wire portion 6 supplies power to the heating element 4. The first connection portion 7 is made of metal, for example, stainless steel, and connects the heating element 4 and the first lead wire portion 6. The first connection portion 7 is interposed between the heating element 4 and the first lead wire portion 6. The first connection portion 7 is connected to the upper end of the heating element 4. The first lead wire portion 6 is arranged outside the heating element 4. The first lead wire portion 6 and the heating element 4 are aligned in the longitudinal direction.

[0013] The second lead wire portion 8 supplies power to the heating element 4. The second lead wire portion 8 has a single-wire group portion 8G and a stranded wire portion 8B. The single-wire group portion 8G is made up of a plurality of single wires. The stranded wire portion 8B is arranged on the base end side of the single-wire group portion 8G and is connected to the single-wire group portion 8G. The second connection portion 9 is made of metal, such as stainless steel, and connects the heating element 4 to the single-wire group portion 8G of the second lead wire portion 8. The second connection portion 9 is interposed between the heating element 4 and the second lead wire portion 8. The second connection portion 9 is connected to the lower end of the heating element 4. The single-wire group portion 8G on the tip side of the second lead wire portion 8 passes radially inward of the heating element 4. The second lead wire portion 8 passes inside the heating element 4.

[0014] The central portion of the first lead wire portion 6 and the central portion of the second lead wire portion 8 pass through the sealing portion 10 , emerge upward from the upper end of the tubular portion 2 , enter the support portion 12 , and pass through the support portion 12 .

[0015] Of the materials of the first lead wire portion 6 and the second lead wire portion 8, the single-wire group portion 8G in the second lead wire portion 8 is made of molybdenum, and the other portions are made of steel. The single-wire group portion 8G is made of a group of multiple molybdenum single wires. The stranded wire portion 8B of the first lead wire portion 6 and the second lead wire portion 8 is made of a group of multiple steel single wires twisted together. The first lead wire portion 6 and the second lead wire portion 8 may be made entirely of molybdenum, or may be made entirely of a material other than molybdenum. The portion inside the heating element 4 may be made of steel, and the portion outside the heating element 4 may be made of molybdenum, or a combination of three or more materials may be used. Part or all of the first lead wire portion 6 and the second lead wire portion 8 may be covered with an insulating coating. Furthermore, the single-wire group portion 8G may be omitted and the second lead wire portion 8 may be a series of single wires, or the entire second lead wire portion 8 may be a series of single-wire group portion 8G. Also, the first lead wire portion 6 may have a single-wire group portion, or the first lead wire portion 6 may be a series of single wires. At least one of the first lead wire portion 6 and the second lead wire portion 8 may include a rod-shaped portion. Furthermore, the number of lead wire portions may be one, or two or more.

[0016] The sealing portion 10 is disposed at the base end 2B of the tubular portion 2, and closes and seals the base end 2B. The stranded wire portions 8B of the first lead wire portion 6 and the second lead wire portion 8 pass through the sealing portion 10.

[0017] The heat insulating material 11 is disposed adjacent to the sealing portion 10 within the tubular portion 2. The heat insulating material 11 suppresses the transfer of heat from the molten aluminum W and the heated heating element 4 to the sealing portion 10 side and the support portion 12 side. The heat insulating material 11 is, for example, at least one of ceramic fiber and glass fiber wool. The shape of the heat insulating material 11 may be bracket-shaped or fiber-shaped. The heat insulating material 11 may be omitted.

[0018] The filler is filled into the tubular portion 2. The main component of the filler is magnesium oxide (magnesia, MgO). A main component is a component that is the majority by weight or volume. Here, the filler contains 90% or more MgO by volume. MgO is a highly thermally conductive filler with excellent thermal conductivity. The thermal conductivity of MgO is approximately 60 W / m·K (watts per meter per Kelvin). The thermal conductivity of the filler is similar to that of MgO. The filler covers the heating element 4. The filler is in contact with the inner surface of the tip portion 2P of the tubular portion 2. The filler is disposed around the heating element 4 and holds it in place. The filler is disposed between the tubular portion 2 and the heating element 4. The filler is filled in the first connection portion 7 and further forward. The filler also fills between adjacent loop portions of the coil-shaped heating element 4. The filler holds the heating element 4 and enters the gaps between the heating elements 4, preventing adjacent portions of the heating element 4 from coming into contact with each other due to expansion during heat generation, protecting the heating element 4 from electrical leakage. The filler prevents oxygen from coming into contact with the molybdenum heating element 4, preventing oxidation of the heating element 4 in high-temperature environments and preventing embrittlement due to oxidation. The main component of the filler may be something other than magnesium oxide. The filler material may be MgO alone. The filler may also be in a form other than powder, such as a spherical shape. Furthermore, the filler may be filled further forward than the tip of the first lead wire portion 6 and the second lead wire portion 8, or further forward than the sealing portion.

[0019] The support portion 12 is made of metal and is connected to the base end 2B of the tubular portion 2. The support portion 12 has a connection portion 20, a wire guide portion 22, and a plurality of bolts 24. The connection portion 20 has a tubular portion 20T and a flange portion 20F. The tubular portion 20T is tubular and extends vertically. The flange portion 20F is ring-shaped and is fixed to the upper end of the tubular portion 20T and extends laterally. The wire guide portion 22 has a tubular portion 22T and a flange portion 22F. The tubular portion 22T is tubular and extends vertically. The flange portion 22F is ring-shaped and is fixed to the lower end of the tubular portion 22T and extends laterally. The connection portion 20 and the wire guide portion 22 are connected to each other by inserting bolts 24 in the vertical direction into the flange portions 20F, 22F, which are stacked one on top of the other.

[0020] A support SP is interposed between the underside of the flange portion 20F and the upper surface of the lid T. The support SP supports the immersion heater 1. The support SP is extendable and retractable in the vertical direction. By adjusting the vertical length of the support SP, the position of the tubular portion 2 relative to the molten aluminum W can be adjusted. The support SP may be omitted, and the immersion heater 1 may be supported by a hole H in the lid T, for example. The support SP may be a component of the immersion heater 1.

[0021] The base ends of the first lead wire portion 6 and the second lead wire portion 8 are connected to corresponding terminals (not shown) in the wire guide portion 22, and lead wires are connected to each terminal (not shown). Each lead wire is drawn out from the wire guide portion 22 to the outside and connected to a power source (not shown) via a control device (not shown). Note that the wire guide portion 22 does not necessarily have to accommodate each terminal, and the base ends of the first lead wire portion 6 and the second lead wire portion 8 may be drawn out directly from the wire guide portion 22 to the outside. The power source here is single-phase AC. The control device controls the power from the power source to the heating element 4 to control the heat generation in the heating element 4. Note that the power source may be DC, three-phase AC, or other. The voltage of the power source may be selected as appropriate.

[0022] The joint 14 joins the tubular portion 2 and the support portion 12 by brazing. The joint 14 is disposed between a groove formed on the outer surface of the base end 2B of the tubular portion 2 and a step formed on the inner surface of the tubular portion 20T of the connection portion 20 of the support portion 12. The tubular portion 2 and the support portion 12 may be joined by a method other than brazing.

[0023] The sealing portion 10 is disposed within the tubular portion 20T of the connecting portion 20. The connecting portion 20 surrounds the sealing portion 10. The joint portion 14 can maintain the bond between the ceramic tubular portion 2 and the metal connecting portion 20, particularly in a high-temperature environment such as when the molten aluminum W is heated, and in an environment where heated and unheated states are alternately switched, but allows air containing oxygen gas to flow in from the outside.

[0024] If the sealing ability is lost, the heating element 4 will be oxidized and deteriorated by air that flows into the tubular portion 2 and penetrates into the gaps in the filler. In particular, in a heating element 4 made of molybdenum, loss of sealing ability at the sealing portion 10 will cause rapid oxidation in a high-temperature oxygen atmosphere, shortening its lifespan. Additionally, in the immersion heater 1, the first lead wire portion 6 and the second lead wire portion 8 expand when the molten aluminum W is heated or is approaching, and contract when the molten aluminum W is not heated or is not approaching, repeating this cycle of expansion and contraction. Furthermore, the internal pressure of the sealed tubular portion 2 is greater than the external pressure, i.e., positive pressure, when the molten aluminum W is heated or is approaching. On the other hand, the internal pressure of the tubular portion 2 is less than the external pressure, i.e., negative pressure, when the molten aluminum W is not heated or is not approaching, repeating this cycle of change between positive and negative pressures. Due to such repeated expansion and contraction of the first lead wire portion 6 and the second lead wire portion 8 and repeated changes in positive and negative pressure in the tubular portion 2, the sealing portion 10 may deteriorate, or a gap may form between the first lead wire portion 6 and the second lead wire portion 8 (i.e., a lead wire gap), or a gap may form between the sealing portion 10 and the tubular portion 2 (i.e., a tubular portion gap). Furthermore, depending on the material, the sealing portion 10 itself may deteriorate due to repeated temperature increases during heating and temperature decreases during non-heating, causing at least one of a lead wire gap and a tubular portion gap to occur, resulting in a loss of hermeticity. Therefore, it is preferable that the sealing portion 10 be able to withstand the heat from the heated heating element 4 and the molten aluminum W, i.e., the heat during use, while maintaining hermeticity even over a long total usage period.

[0025] Therefore, various materials and physical properties were tested for the sealing portion 10 to withstand the heat during use, to maintain adhesion and sealing to the first lead wire portion 6, the second lead wire portion 8 and the tubular portion 2 even over a long total usage time without losing, to prevent gaps in the lead wires and the tubular portion from forming, and to maintain the sealing property of the tubular portion 2. As a result, it was found that if the sealing portion 10 has at least one of the following materials and physical properties, the sealing property of the tubular portion 2 can be maintained even over a long total usage time.

[0026] That is, first, the sealing portion 10 may be a cured product obtained from a liquid, gel, paste, or powder raw material. An example of the ambient temperature before curing is 25°C. That is, the sealing portion 10 may be a cured product obtained from a liquid, gel, paste, or powder raw material at 25°C. The cured product may be solid or rubber-like. Examples of such materials include at least one of silicone and heat-resistant adhesive. Here, silicone includes silicone resin and silicone rubber. Silicone also includes organopolysiloxanes. In this case, the liquid, gel, paste, or powder raw material is cured at, for example, 25°C while being inserted between the individual strands of the stranded wire portion 8B of the first lead wire portion 6 and the second lead wire portion 8, which are stranded wires, to form the sealing portion 10. Therefore, the sealing portion 10 adheres tightly to the first lead wire portion 6 and the second lead wire portion 8 without any gaps. The sealing portion 10 also adheres sufficiently to the tubular portion 2, particularly to a ceramic tubular portion 2. Therefore, the sealing portion 10 suppresses the formation of gaps between the lead wires and the tubular portion, thereby preventing air from entering the tubular portion 2. Even if the stranded wire portion 8B of the first lead wire portion 6 and the second lead wire portion 8 is a single-wire assembly consisting of a collection of multiple untwisted single wires, the raw material penetrates into the gaps between the individual single wires, as in the case of stranded wires, and provides excellent adhesion. While natural drying may be used for hardening, heat hardening is preferred from the viewpoints of the excellent properties of the resulting sealing portion 10 and the speed of formation. The raw material may be a single substance in a liquid, gel, paste, or powder form (single-component type). The raw material may also be two substances that are originally in a liquid, gel, paste, or powder form (two-component type), in which case the two substances may be mixed to form a liquid, gel, paste, or powder form. The raw material may also be three or more substances that are originally in a liquid, gel, paste, or powder form, and in this case, these three or more substances may be mixed to form a liquid, gel, paste, or powder form.

[0027] Furthermore, even if the first lead wire portion 6 and the second lead wire portion 8 passing through the sealing portion 10 are rod-shaped, oxidation of the heating element 4 due to damage to the sealing portion 10 is suppressed as long as the sealing portion 10 is of the above-described type. That is, the raw material of the sealing portion 10 is distributed over the surfaces of the rod-shaped first lead wire portion 6 and the second lead wire portion 8, and the occurrence of lead wire gaps is suppressed by the hardened sealing portion 10. Therefore, even if the rod-shaped first lead wire portion 6 and the second lead wire portion 8 expand and contract in the longitudinal direction due to repeated heating and non-heating, the occurrence of lead wire gaps is suppressed, and the inflow of air containing oxygen gas into the tubular portion 2 is suppressed, suppressing oxidation of the heating element 4.

[0028] The structure of the sealing portion 10 may be considered to be specified by the manufacturing process, which is the formation by hardening of a raw material that is liquid, gel, paste, or powder before hardening. Even if this is the case, such specification is considered permissible due to the existence of so-called impossible or impractical circumstances. In other words, there are a wide variety of such products, and it is virtually impractical to directly specify the sealing portion 10 by its structure or characteristics by listing specific examples in order to distinguish it from other products. Furthermore, the specific structure of such a cured product is currently unknown, and exploring all types of such structure is considered virtually impossible or impractical, requiring significant equipment and time. Therefore, even if the sealing portion 10 is considered to be specified by the manufacturing process, which is the formation by hardening of the above-mentioned raw material, such specification should be permitted.

[0029] Furthermore, the sealing portion 10 may be made of a heat-resistant insulating material that can withstand temperatures of at least 250°C after hardening. Heat resistance of at least 250°C during heating by the heating element 4, including heating of the molten aluminum W, suppresses damage to the sealing portion 10 during heating, thereby suppressing damage to the immersion heater 1, including oxidation of the heating element 4. Furthermore, if the sealing portion 10 is made of an insulating material, leakage of electricity from at least one of the first lead wire portion 6 and the second lead wire portion 8 to the sealing portion 10 is suppressed, and short circuits between the first lead wire portion 6 and the second lead wire portion 8 are also suppressed. Additionally, if the sealing portion 10 does not expand or expands little, i.e., barely expands at temperatures above 250°C after hardening, cracking due to deterioration caused by expansion or repeated expansion during heating and contraction during non-heating is suppressed. Therefore, oxidation of the heating element 4 due to air inflow through cracks is suppressed. Strictly speaking, no expansion means that the volume remains the same or decreases. However, in the present invention, no expansion includes slight expansion. However, even if slight expansion occurs in the sealing portion 10, the hermeticity of the tubular portion 2 is maintained. Similarly, even if slight contraction occurs in the sealing portion 10, the hermeticity of the tubular portion 2 is maintained. If the hermeticity of the tubular portion 2 is maintained, the inflow of air into the tubular portion 2 is suppressed, and oxidation of the heating element 4 is suppressed.

[0030] The cured sealing portion 10 may be an elastic body, an inelastic solid that does not exhibit elasticity, or a mixture of elastic and inelastic portions. Examples of mixtures of elastic and inelastic portions include silicone containing aluminum oxide (alumina), in which a portion of the elastic body is inelasticated. In the elastic sealing portion 10, heat from the molten aluminum W and the heating element 4 gradually removes the silicone component that provides elasticity from the portion on the tubular portion 2 side, including the heating element 4, leaving alumina, which becomes inelastic. In this case, although the inelasticization often occurs unevenly, the portion of the sealing portion 10 that is primarily on the tubular portion 2 side becomes the inelastic portion, and the upper (outside air) portion of the sealing portion 10 becomes the elastic portion.

[0031] The sealing portion 10 may be formed from a siloxane material. Even in this case, the sealing portion 10 penetrates into gaps in the stranded wire or adheres closely to the surface of the rod-shaped solid wire. This prevents gaps from forming in the lead wire, thereby suppressing oxidation of the heating element 4. The sealing portion 10 in this case also has heat resistance capable of withstanding temperatures of at least 250°C and is insulating. The siloxane material is a material having a siloxane structure and used to form silicone. Examples of the siloxane material include a silicone rubber material, an organohydrogenpolysiloxane material, a reactive cyclic siloxane material, or a combination of two or more of these. While the siloxane material is not particularly limited, a reactive cyclic siloxane material is preferred because it has adhesiveness, heat resistance, insulating properties, and non-expanding properties. The reactive cyclic siloxane material has a cyclic siloxane structure as its main skeleton and multiple reactive functional groups per molecule. The number of -Si-O- groups in the cyclic siloxane structure is not particularly limited, but from the viewpoints of ease of production and handling of the material itself, and good reactivity of the material, it is preferably 3 (trimer) or more and 10 (decamer) or less, more preferably 3 or more and 5 or less. The reactive functional group is not particularly limited, but from the viewpoints of ease of production and handling of the material itself, good reactivity of the material, and good properties when cured to form the sealing portion 10, it is preferably an organic functional group, more preferably an unsaturated hydrocarbon group, and even more preferably a vinyl group. Furthermore, each Si in the cyclic siloxane structure can be bonded to two groups in addition to the bonds to the O on both sides in the main skeleton. Therefore, from the viewpoints of good reactivity of the material and good properties when cured to form the sealing portion 10, it is preferable that all Si in the cyclic siloxane structure have one reactive functional group. An example of a reactive cyclic siloxane material is 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, represented by the following formula (1): The reactive cyclic siloxane material of formula (1) is a tetramer. Each of the four Si atoms in the reactive cyclic siloxane material of formula (1) is a vinyl group, —CH═CH, as a reactive functional group. ２It has one.

[0032]

[0033] The configuration of sealing portion 10 may be considered to be specified by the manufacturing process of forming it using a siloxane material. Even if this is the case, such specification is considered permissible due to the existence of circumstances that make it impossible or impractical. That is, while siloxane materials have a siloxane structure, there are a wide variety of siloxane materials, depending on the number of -Si-O- groups and the type and arrangement of reactive functional groups. Therefore, it is virtually impractical to directly specify sealing portion 10 by its structure or properties by listing specific examples in order to distinguish it from other polymers. Furthermore, the specific structure of the product after the reaction involving such siloxane materials is a polymer structure that varies with each curing step. Searching for every type of structure would require significant equipment and time, making it virtually impossible or impractical. Therefore, even if sealing portion 10 is considered to be specified by the manufacturing process using a siloxane material, such specification should be permitted.

[0034] The sealing portion 10 may be formed solely from a siloxane material. However, from the viewpoint of the excellent properties of the resulting sealing portion 10, it is preferable to add at least one of alumina, quartz, zinc oxide, and carbon black. Alternatively, the sealing portion 10 may be formed from at least one of a siloxane material, alumina, quartz, zinc oxide, and carbon black. The sealing portion 10 has the effect of preventing air from entering the tubular portion 2, which can accelerate oxidation of the heating element 4, even when exposed to high temperatures. Furthermore, the amounts of these materials, in other words, the composition of the composite material, are not particularly limited. However, from the viewpoint of ease of formation and the excellent properties of the resulting sealing portion 10, it is preferable to use a composition related to the following two liquids (Component A and Component B) that are mixed and cured. Here, "x to y" represents x or more and y or less, and the same applies below. At least one of Components A and B may be adjusted so that the total parts by mass is 100 parts by mass. Agent A: 40 to 50 parts by weight of alumina, 30 to 40 parts by weight of quartz, 0.25 to 1 part by weight of zinc oxide, 0.1 to 1 part by weight of carbon black Agent B: 30 to 40 parts by weight of alumina, 30 to 40 parts by weight of quartz, 0.3 to 1.0 part by weight of reactive cyclic siloxane material

[0035] The siloxane material may be cured by any method, including natural drying, but is preferably cured by heat from the viewpoint of good properties when it becomes the sealing portion 10 and speed of formation.

[0036] Furthermore, the sealing portion 10 may be formed from a material containing organohydrogenpolysiloxane. Examples of materials containing organohydrogenpolysiloxane include those described in International Publication No. 2019 / 021824. In this case, as with reactive cyclic siloxane materials, the sealing portion 10 formed has excellent gas inflow prevention properties, heat resistance, insulating properties, and non-expansion properties.

[0037] The air blower 16 sends air N to the sealing unit 10. The air blower 16 is a single fan. The air blower 16 is capable of air-cooling the sealing unit 10. The air blower 16 may be a plurality of fans, a blower duct, or a combination of a fan and a blower duct. The air blower 16 may also be omitted.

[0038] Furthermore, in order to expose the sealing portion 10 to the outside air, one or more openings 20P are provided in the tubular portion 20T, extending from the radially outer side to the inside. Therefore, a portion of the radially outer outer surface of the sealing portion 10 is exposed to the outside air through the openings 20P. The support SP is positioned so as not to block the openings 20P. The openings 20P are positioned above the joint portion 14. The openings 20P allow the sealing portion 10 to come into contact with the outside air, thereby cooling the sealing portion 10. Note that the openings 20P may be provided in common to the tubular portion 2 and the tubular portion 20T, as long as the sealing portion 10 can be exposed. Furthermore, the openings 20P may be omitted.

[0039] An example of a manufacturing method for the immersion heater 1 will now be described. First, the first connection portion 7 is connected to the tip end of the first lead wire portion 6, and the first connection portion 7 is connected to the base end of the heating element 4. Furthermore, the second connection portion 9 is connected to the tip end of the second lead wire portion 8, and the second connection portion 9 is connected to the tip end of the heating element 4. Next, the integrated heating element 4, first lead wire portion 6, first connection portion 7, second lead wire portion 8, and second connection portion 9 are inserted into the tubular portion 2.

[0040] Next, filler and heat insulating material 11 are placed inside the tubular portion 2. Furthermore, support portions 12 are arranged outside the base ends of the first lead wire portion 6 and the second lead wire portion 8. Subsequently, the tubular portion 2 and the support portions 12 are joined by forming joint portions 14. Furthermore, the base ends of the first lead wire portion 6 and the second lead wire portion 8 are connected to terminals.

[0041] Here, the sealing portion 10 is formed by placing a liquid, gel, paste, or powder raw material into the base end of the tubular portion 2 and hardening it by natural drying or heating. In forming the sealing portion 10, the raw material sealing portion 10 before hardening may be subjected to an external force such as compression while it is placed in the base end of the tubular portion 2 and arranged around the first lead wire portion 6 and the second lead wire portion 8. Adding such an external force application step will cause the sealing portion 10 to penetrate further into the gaps between the stranded first lead wire portion 6 and the second lead wire portion 8, or to adhere more closely to the surfaces of the rod-shaped first lead wire portion 6 and the second lead wire portion 8.

[0042] Furthermore, the sealing portion 10 is preferably made from at least one of a reactive cyclic siloxane material and a material containing organohydrogenpolysiloxane. In particular, when the sealing portion 10 is made from the above-mentioned components A and B, a gel-like mixture of components A and B is placed at the proximal end of the tubular portion 2 and placed in an environment at a predetermined temperature, for example, 100° C. or higher, for a predetermined time, for example, 30 minutes, or longer, to be thermally cured.

[0043] An example of the operation of the immersion heater 1 is described below. A user turns on the power and causes the heating element 4 of the immersion heater 1 to generate heat. The heat from the heating element 4 is efficiently transferred to the tubular portion 2 by the filler. Furthermore, the heat transfer to the base end is suppressed by the insulating material 11. The user immerses the tip of the tubular portion 2 from above into the molten aluminum W in the molten metal tank, thereby heating the molten aluminum W by heat transfer from the heating element 4 through the filler and the tubular portion 2. The heat generation amount of the heating element 4 is controlled by a control device. Here, a temperature sensor (not shown) electrically connected to the control device detects the temperature of the molten aluminum W and transmits a temperature signal indicating the detected temperature to the control device. The control device controls the heat generation amount of the heating element 4 in accordance with the temperature associated with the received temperature signal. The heating element 4 may be driven at a constant output without temperature control. The maximum heat generation amount (maximum output) of the heating element 4 can be greater with a molybdenum heating element 4 than with a nichrome heating element 4. The oxidation of molybdenum, which leads to embrittlement of the heating element 4, is suppressed by disposing the filler around the heating element 4.

[0044] Furthermore, the above-described sealing portion 10 prevents the occurrence of gaps in the lead wires and / or gaps in the tubular portion, even if the immersion heater 1 is repeatedly turned on and off and moved close to and away from the molten aluminum W. This prevents air containing oxygen gas from flowing into the tubular portion 2, thereby suppressing oxidation of the heating element 4. Furthermore, if the sealing portion 10 is air-cooled by the air blower 16, deterioration of the sealing portion 10 due to heat is further suppressed, further extending the life of the sealing portion 10.

[0045] The above-described immersion heater 1 has the following advantages. Specifically, the immersion heater 1 comprises a heating element 4, a first lead wire portion 6 and a second lead wire portion 8 connected to the heating element 4, a tubular portion 2 that houses the heating element 4, and a sealing portion 10 that seals the tubular portion 2 while allowing the first lead wire portion 6 and the second lead wire portion 8 to pass through. The sealing portion 10 is a cured product obtained from a liquid, gel, paste, or powder raw material. Thus, an immersion heater 1 is provided that has improved sealing performance for the tubular portion 2 that houses the heating element 4, more simply and at reduced cost.

[0046] Furthermore, the sealing portion 10 is made of a heat-resistant insulator that can withstand temperatures of at least 250°C. Therefore, the sealing and insulating properties of the sealing portion 10 are maintained in high-temperature environments, and oxidation of the heating element 4 is suppressed while insulating the first lead wire portion 6 and the second lead wire portion 8. Furthermore, the sealing portion 10 does not expand in environments of 250°C or higher. Therefore, the occurrence of cracks in the sealing portion 10 in high-temperature environments is suppressed, and oxidation of the heating element 4 due to air inflow through cracks is suppressed. Furthermore, the sealing portion 10 suppresses air inflow into the tubular portion 2. Thus, an immersion heater 1 is provided in which the tubular portion 2 that houses the heating element 4 has improved sealing performance. Furthermore, the sealing portion 10 is formed from at least one of a siloxane material, alumina, quartz, zinc oxide, and carbon black. Thus, an immersion heater 1 is provided in which the tubular portion 2 that houses the heating element 4 has improved sealing performance, more simply and at reduced cost.

[0047] In addition, the immersion heater 1 includes a heating element 4, a first lead wire portion 6 and a second lead wire portion 8 connected to the heating element 4, a tubular portion 2 that houses the heating element 4, and a sealing portion 10 made of a siloxane material that seals the tubular portion 2 while allowing the first lead wire portion 6 and the second lead wire portion 8 to pass through. Thus, an immersion heater 1 is provided that has improved sealing performance for the tubular portion 2 that houses the heating element 4, in a simpler manner and at a reduced cost.

[0048] Furthermore, the siloxane material is a reactive cyclic siloxane material. Therefore, an immersion heater 1 is provided in which the hermetic sealing of the tubular portion 2 housing the heating element 4 is improved, more simply and at reduced cost. Furthermore, the reactive cyclic siloxane material is 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane. Therefore, an immersion heater 1 is provided in which the hermetic sealing of the tubular portion 2 housing the heating element 4 is improved, more simply and at reduced cost. Furthermore, the sealing portion 10 is formed from a siloxane material and at least one of alumina, quartz, zinc oxide, and carbon black. Therefore, an immersion heater 1 is provided in which the hermetic sealing of the tubular portion 2 housing the heating element 4 is improved, more simply and at reduced cost.

[0049] In addition, the immersion heater 1 includes the heating element 4, a first lead wire portion 6 and a second lead wire portion 8 connected to the heating element 4, a tubular portion 2 that houses the heating element 4, and a sealing portion 10 containing at least one of quartz and alumina that seals the tubular portion 2 while allowing the first lead wire portion 6 and the second lead wire portion 8 to pass through. Thus, an immersion heater 1 is provided that has improved sealing performance for the tubular portion 2 that houses the heating element 4, in a simpler manner and at reduced cost.

[0050] Furthermore, the heating element 4 and at least one of the first lead wire portion 6 and the second lead wire portion 8 are made of molybdenum. Therefore, the sealing ability of the tubular portion 2 housing the heating element 4, which is made of molybdenum and is more susceptible to oxidation and embrittlement in high-temperature environments than other materials, is improved more simply and at a reduced cost. Furthermore, the first lead wire portion 6 and the second lead wire portion 8 include a stranded wire portion 8B. Therefore, the sealing portion 10 is formed with a liquid, gel, paste, or powder-like material in the stranded wire portion 8B, thereby improving the sealing ability of the tubular portion 2 housing the heating element 4 more simply and at a reduced cost. Even if the first lead wire portion 6 and the second lead wire portion 8 include a single-wire assembly portion that is an assembly of multiple single wires, the same effect as that of the stranded wire portion 8B can be achieved. Furthermore, even when the first lead wire portion 6 and the second lead wire portion 8 include a rod-shaped portion, the sealing portion 10 is formed with the liquid, gel, paste, or powder raw material in close contact with the surface of the rod-shaped portion. This improves the airtightness of the tubular portion 2 that houses the heating element 4 more simply and at reduced cost.

[0051] Furthermore, the immersion heater 1 is provided with a blower 16 that blows air N to the sealing portion 10. The tubular portion 2 also has an opening 20P for exposing the sealing portion 10 to the outside air. This allows the sealing portion 10 to be cooled, further extending its lifespan.

[0052] Furthermore, the immersion heater 1 includes a heating element 4, a first lead wire portion 6 and a second lead wire portion 8 connected to the heating element 4, a tubular portion 2 that houses the heating element 4, a sealing portion 10 that seals the tubular portion 2 while allowing the first lead wire portion 6 and the second lead wire portion 8 to pass through, and an air blower 16 that blows air toward the sealing portion 10. Thus, the sealing portion 10 is cooled by the air blown, further extending the life of the sealing portion 10.

[0053] The immersion heater 1 also comprises a heating element 4, a first lead wire portion 6 and a second lead wire portion 8 connected to the heating element 4, a tubular portion 2 that houses the heating element 4, a sealing portion 10 that seals the tubular portion 2 while allowing the first lead wire portion 6 and the second lead wire portion 8 to pass through, and a connection portion 20 that surrounds the sealing portion 10. The connection portion 20 has an opening 20P that exposes the sealing portion 10 to the outside air, and therefore the sealing portion 10 is cooled by the outside air through the opening 20P. This further extends the life of the sealing portion 10.

[0054] Hereinafter, more specific examples according to the above-described embodiments of the present invention will be described, but the present invention is not limited to the following examples.

[0055] In Example 1, a one-component heat-resistant silicone was produced in which the sealing portion 10 was formed by hardening one gel-like material. More specifically, the gel-like material was filled into the base end of the tubular portion 2 and heated and hardened by being left in a 100°C environment for 60 minutes. In Example 2, a two-component heat-resistant silicone was produced in which the sealing portion 10 was formed from the above-mentioned components A and B. More specifically, the above-mentioned components A and B were mixed together to form a paste-like material, which was filled into the base end of the tubular portion 2 and heated and hardened by being left in a 100°C environment for 60 minutes.

[0056] The sealing portions 10 according to both Examples 1 and 2 were excellent in gas inflow prevention, heat resistance, insulation, and non-expansion after curing. Comparing these, the sealing portion 10 according to Example 2 was even better in gas inflow prevention than the sealing portion 10 according to Example 1, and also showed better durability in a durability test.

[0057] Composition analysis and hardness measurement were performed under various conditions on samples of the sealing portion 10 of Examples 1 and 2, which were smaller in size than the actual sealing portion 10 but formed similarly to the actual sealing portion 10 and had the same composition. The results of the composition analysis of Example 1 are shown in Table 1 below, and the results of the composition analysis of Example 2 are shown in Table 2 below. Note that the units of values ​​in Tables 1 and 2 are mass %, and if the total is less than 100 mass %, the remainder may be considered to be carbon atoms. Condition A was determined as heating for 41 hours in a temperature environment of 250°C. Condition B was determined as heating for 8 hours in a temperature environment of 400°C. Condition C was determined as heating for 8 hours in a temperature environment of 400°C followed as quickly as possible by heating for 1 hour in a temperature environment of 700°C. Condition D was determined as heating for 4 hours in a temperature environment of 1000°C. Condition E is when 8 hours of heating in a temperature environment of 250°C is one set, and a total of 3 sets are performed for 3 consecutive days, with one set per day. Condition F is when 8 hours of heating in a temperature environment of 600°C is performed. The results of the hardness measurement for Example 1 are shown in Table 3 below, and the results of the hardness measurement for Example 2 are shown in Table 4 below. The higher the hardness value, the harder the material. The letter "A" before the value indicates that the shape of the probe used during measurement was Type A.

[0058]

[0059]

[0060] As shown in Table 1, the major composition of Example 1 before exposure to heat (unheated) was 34 mass% oxygen atoms (O), 61 mass% silicon atoms (Si), and 4 mass% aluminum atoms (Al). After heating under condition A, the major composition of Example 1 was 30 mass% O, 62 mass% Si, and 7 mass% Al. After heating under condition B, the major composition of Example 1 was 42 mass% O, 51 mass% Si, and 6 mass% Al. After heating under condition C, the major composition of Example 1 was 48 mass% O, 40 mass% Si, and 11 mass% Al. After heating under condition D, the major composition of Example 1 was 49 mass% O, 44 mass% Si, and 6 mass% Al. According to such a major composition of Example 1, as the thermal conditions become more severe, the mass proportion of oxygen atoms increases and the mass proportion of silicon atoms decreases relatively. On the other hand, the oxygen atoms are limited to an upper limit of 49 mass% and the silicon atoms to a lower limit of 40 mass%. Therefore, although the sealing portion 10 of Example 1 allows oxidation and partial inelasticity reduction due to heating, the oxidation and partial inelasticity reduction are limited to a predetermined level. Conventionally, the cross-sectional area of ​​a heating element 4 made of a predetermined material has been reduced by approximately 50% in some locations due to oxidation over long periods of use, even when a filler is added. In contrast, in Example 1, the cross-sectional area of ​​the same heating element 4 as in the conventional example is expected to be reduced by a maximum of approximately 10% over the same period of use. Therefore, the sealing portion 10 of Example 1 can maintain a seal that suppresses oxidation of the heating element 4.

[0061] As shown in Table 2, the major composition of Example 2 before heating was 53% by mass of O, 32% by mass of Si, and 15% by mass of Al. After heating under condition E, the major composition of Example 2 was 51% by mass of O, 33% by mass of Si, and 16% by mass of Al. After heating under condition B, the major composition of Example 2 was 58% by mass of O, 24% by mass of Si, and 18% by mass of Al. After heating under condition F, the major composition of Example 2 was 61% by mass of O, 25% by mass of Si, and 14% by mass of Al. After heating under condition D, the major composition of Example 2 was 61% by mass of O, 23% by mass of Si, and 16% by mass of Al. According to such a major composition of Example 2, as the thermal conditions become more severe, the mass proportion of oxygen atoms increases and the mass proportion of silicon atoms decreases relatively. Meanwhile, the upper limit of oxygen atoms is 61% by mass, and the lower limit of silicon atoms is approximately 23% by mass. Therefore, although the sealing portion 10 of Example 2 is subject to oxidation and partial inelasticity reduction due to heating, the oxidation and partial inelasticity reduction are limited to a predetermined level. Furthermore, the sealing portion 10 of Example 2 has a higher mass ratio of aluminum atoms than the sealing portion 10 of Example 1. Conventionally, the cross-sectional area of ​​a heating element 4 made of a predetermined material has been reduced by approximately 50% in some locations due to oxidation over long periods of use, even when a filler is added. In contrast, in Example 2, the cross-sectional area of ​​the same heating element 4 as the conventional heating element is expected to be reduced by only approximately 5% at most over the same period of use. Therefore, the sealing portion 10 of Example 2 is capable of maintaining a seal that suppresses oxidation of the heating element 4.

[0062] Furthermore, as shown in Table 3, the hardness of Example 1 was A35 as the average (average hardness) of five measurements before heating. After heating under condition A, the average hardness of Example 1 was A22. After heating under conditions B, C, and D, the hardness of Example 1 could not be measured because the sample was in powder form. *1 in Tables 3 and 4 indicates that the hardness could not be measured because the sample was in powder form. Based on the hardness of Example 1, the sealing portion 10 of Example 1 becomes softer as the thermal conditions become more severe. Therefore, it can be said that the sealing portion 10 of Example 1 gradually softens and maintains sealing.

[0063] On the other hand, as shown in Table 4, the hardness of Example 2 without heating was A62, the average (average hardness) of five measurements. After heating under condition E, the average hardness of Example 2 was A65. After heating under condition B, the average hardness of Example 2 was A82. However, for Example 2 after heating under condition B, measurement was impossible in two of the five hardness measurements because the durometer indenter penetrated the sample surface. Therefore, the average hardness of Example 2 after heating under condition B is the average value of three measurements. After heating under conditions F and D, the hardness of Example 2 was impossible to measure because the sample was in a powdery state. *2 in Table 4 indicates that measurement was impossible because the durometer indenter penetrated the sample surface. According to the hardness of Example 2, the sealing portion 10 of Example 2 becomes harder as the thermal conditions become more severe. Therefore, it can be said that the sealing portion 10 of Example 2 gradually hardens and maintains the sealing.

[0064] Furthermore, the above-mentioned samples of Example 2, which had not undergone any tests, including the composition analysis and hardness measurement, were heated under the following conditions and then analyzed using a thermogravimetric differential thermal analyzer (TG-GTA). Each sample weighed approximately 10 mg. Each sample was placed in an open alumina container. Condition T1 was defined as heating in air from 40°C to 300°C, followed by holding the sample in a 300°C environment for 8 hours. Condition T2 was defined as heating in air from 40°C to 350°C, followed by holding the sample in a 350°C environment for 8 hours. Condition T3 was defined as heating in air from 40°C to 500°C, followed by holding the sample in a 500°C environment for 8 hours. In all of Conditions T1 to T3, the heating rate was 5°C / min. In addition, under all of the conditions T1 to T3, air was introduced into the heating furnace at a flow rate of 200 mL / min during heating.

[0065] FIG. 2 is a graph showing the results of thermogravimetric differential thermal analysis under condition T1. FIG. 3 is a graph showing the results of thermogravimetric differential thermal analysis under condition T2. ​​FIG. 4 is a graph showing the results of thermogravimetric differential thermal analysis under condition T3. In FIGS. 2 to 4, the horizontal axis represents the elapsed time (min) from the start of heating the sample. The vertical axis represents temperature (°C), TG (%), and DTA (μV). TG is the rate of decrease in thermal mass from the initial value. DTA is differential thermal analysis. In FIGS. 2 to 4, the solid line represents temperature. The dashed-dotted line represents TG. The dashed line represents DTA.

[0066] First, the behavior of the weight change temperature obtained from the thermogravimetric differential thermal analysis results will be explained. Under condition T1, the DTA curve shows a small peak immediately after the start of the analysis, then continues to decrease uniformly until approximately 60 minutes after reaching 300°C. The DTA curve then remains flat until the end of the measurement, with no peak observed. Under condition T2, the DTA curve shows a small peak similar to that under condition T1 immediately after the start of the analysis, then shows one large peak at 70 to 75 minutes, corresponding to a temperature range between just over 300°C and 350°C. The temperature CR at the time indicated by the intersection of the extrapolated line U1 of the DTA curve before the minimum value of the DTA curve immediately before the peak and the extrapolated line U2 of the DTA curve after the minimum value was 329°C. Looking at the TG curve under condition T2, weight loss is observed at approximately the same temperature as the temperature CR. Therefore, it can be said that the weight change temperature in Example 2 is 329°C. Under condition T2, after reaching 350°C, the DTA curve remained flat until the end of the measurement, and no peak was observed. Under condition T3, the DTA curve showed a small exothermic peak immediately after the start of the analysis, as under conditions T1 and T2, followed by a large broad peak on the high-temperature side at 70 to 75 minutes, corresponding to a temperature between just over 300°C and 350°C. This peak is considered to be the same as the peak observed under condition T2, and the temperature CS at the time when the two extrapolated lines V1 and V2 intersect is 329°C, the same as the temperature CR under condition T2. ​​Furthermore, the DTA curve under condition T3 showed multiple peaks from 90 to 100 minutes, corresponding to a temperature between approximately 450°C and 500°C. The temperature CT at the time indicated by the intersection of the extrapolated line W1 of the DTA curve before the immediately preceding minimum value and the extrapolated line W2 of the DTA curve after the minimum value, which is the first peak among the multiple peaks in the DTA curve, was 450°C. Looking at the TG curve under condition T3, weight loss is observed at the time corresponding to the temperature CT. Therefore, it can be said that Example 2 has at least two weight change temperatures, with the first weight change temperature being 329°C, which corresponds to temperature CS, and the second weight change temperature being 450°C, which corresponds to temperature CT. The weight change temperatures under conditions T1 to T3 are summarized in Table 5 below.

[0067]

[0068] According to this behavior of weight change temperature, it can be said that Example 2 undergoes the first major composition change at 329°C, which is higher than 250°C. Therefore, Example 2 can withstand heat of at least 250°C. Furthermore, Example 2 does not expand in an environment of 250°C or higher.

[0069] Next, the behavior of the TG decrease rate obtained from the thermogravimetric differential thermal analysis results will be explained. Under condition T1, the average DTA value during the period beginning 420 minutes after the holding temperature was reached and ending 480 minutes after the holding temperature was reached is determined as the time when the DTA first enters the range from a lower limit corresponding to 99% of the DTA stable average value to an upper limit corresponding to 101% of the DTA stable average value. This is designated as the baseline stabilization start time BS1 for condition T1. Similarly, under condition T2, the point at which the DTA first enters this range is designated as the baseline stabilization start time BS2 for condition T2. ​​Under condition T3, the point at which the DTA first enters this range is designated as the baseline stabilization start time BS3 for condition T3. The TG decrease rates (%) at the following three time points are summarized in Table 6: The three time points for condition T1 are time TA1 when the holding temperature is reached, time BS1 when the baseline stabilization starts, and time 8 hours after the holding temperature is reached. The three time points for condition T2 are time TA2 when the holding temperature is reached, time BS2 when the baseline stabilization starts, and time 8 hours after the holding temperature is reached. The three time points for condition T3 are time TA3 when the holding temperature is reached, time BS3 when the baseline stabilization starts, and time 8 hours after the holding temperature is reached.

[0070]

[0071] According to this behavior of the TG decrease rate, Example 2 has a low decrease rate at 300°C, which is higher than 250°C. Therefore, under condition T1, which involves a holding temperature of 300°C, it can be said that Example 2 does not experience any deterioration, such as general combustion, sublimation, or evaporation. Furthermore, under condition T2, which involves a holding temperature of 350°C, it can be said that Example 2 gradually experiences deterioration, such as general combustion, sublimation, or evaporation, after the holding temperature reaches 350°C. Furthermore, under condition T1, which involves a holding temperature of 500°C, it can be said that Example 2 experiences deterioration due to general combustion, sublimation, or evaporation relatively early after the holding temperature reaches 500°C. Therefore, Example 2 can withstand heat of at least 250°C. Furthermore, Example 2 does not expand in environments above 250°C.

[0072] Meanwhile, the temperature of the sealing portion 10 under specific conditions was measured for an immersion heater 1 in which the sealing portion 10 was actually formed according to Example 2. Such temperature measurements were carried out under four broad conditions, depending on whether or not an opening 20P communicating with the sealing portion 10 was present and whether or not a lid T was present. Furthermore, for each condition, the temperature measurements were carried out under five different output levels for the immersion heater 1: 0 kW (i.e., not lit), 1 kW, 2 kW, 3 kW, and 4 kW. Furthermore, the temperature measurements were carried out one hour after the storage of the molten aluminum W was completed.

[0073] Specifically, the vertical length of the heating element 4, corresponding to arrow LH in FIG. 1, is 200 mm. The vertical length from the bottom surface of the insulating material 11 to the tip 2P of the tubular portion 2, corresponding to arrow LF in FIG. 1, is 550 mm. A filler is filled from the bottom surface of the insulating material 11 to the tip 2P of the tubular portion 2. The vertical length of the sealing portion 10, corresponding to arrow LS in FIG. 1, is 30 mm. The vertical length of the insulating material 11, corresponding to arrow LI in FIG. 1, is 550 mm. The distance from the bottom surface of the lid T to the top surface of the molten aluminum W, corresponding to arrow LP in FIG. 1, is 80 mm. Without the lid T, arrow LP corresponds to the distance from the top surface of the wall of the storage portion for the molten aluminum W to the top surface of the molten aluminum W. The depth from the top surface of the molten aluminum W to the top end of the heating element 4, corresponding to arrow LD in FIG. 1, is 150 mm. Furthermore, the temperature of the molten aluminum W is 680°C. The vertical depth of the stored molten aluminum W is 457 mm. The vertical length of the tubular portion 2 is 600 mm. One circular opening 20P is provided, and its diameter is 5 mm. Furthermore, the temperature of the sealing portion 10 in Example 2 was measured using a thermocouple. The temperature measurement point of the sealing portion 10 in Example 2 was 10 mm below the top surface of the sealing portion 10, inside the sealing portion 10. The temperature measurement results are shown in Table 7 below.

[0074]

[0075] According to Table 7, when the lid T is provided, the temperature of the sealing portion 10 when the opening 20P is provided is lower than when the opening 20P is not provided, at any output, with a difference of approximately 15°C. Furthermore, when the lid T is not provided, the temperature of the sealing portion 10 when the opening 20P is provided is lower than when the opening 20P is not provided, with a difference of approximately 35°C. Thus, when the opening 20P is provided, the temperature rise of the sealing portion 10 is suppressed compared to when the opening 20P is not provided. This temperature suppression effect is more pronounced when the lid T is not provided. Furthermore, this temperature measurement situation is frequently seen when handling molten aluminum W. Furthermore, even at an output of 4 kW, the temperature of the sealing portion 10 when the lid T is provided and the opening 20P is not provided is 179°C, and when the lid T is provided and the opening 20P is not provided, is 177°C. Therefore, if the sealing portion 10 has heat resistance capable of withstanding heat of at least 250° C., that is, if the heat resistance temperature of the sealing portion 10 is 250° C. or higher, the sealing portion 10 will have sufficient durability.

[0076] On the other hand, the relationship between the air volume from the blower 16, i.e., the air flow rate, and the temperature of the sealing portion 10 was measured under the above-mentioned specific conditions. However, in this measurement of the air flow rate, the lid T was provided, but the opening 20P was not. The measurement of the air flow rate was also performed under the following three conditions R1 to R3. That is, first, condition R1 was a condition in which the distance from the lid T to the lower end of the sealing portion 10, corresponding to the arrow LA in FIG. 1, was 80 mm, and the output of the immersion heater 1 was 6 kW. Next, condition R2 was a condition in which the distance from the lid T to the lower end of the sealing portion 10 was 80 mm, and the voltage of the immersion heater 1 was 200 V. Next, condition R3 was a condition in which the distance from the lid T to the lower end of the sealing portion 10 was 5 mm, and the voltage of the immersion heater 1 was 200 V.

[0077] FIG. 5 is a graph showing the temperature of the sealing portion 10 for each air flow rate under these three conditions R1 to R3. FIG. 6 is a graph showing the temperature difference for each air flow rate under these three conditions R1 to R3, relative to the temperature of the sealing portion 10 at an air flow rate of 0 L / min. An air flow rate of 0 L / min corresponds to no air being blown from the air blower 16. According to FIGS. 5 and 6, under all three conditions R1 to R3, the temperature of the sealing portion 10 decreases more significantly as the air flow rate increases. Under conditions R1 and R2, the temperature decreases by 100°C or more at an air flow rate of 50 L / min or more. Furthermore, under condition R3, the temperature decreases by 150°C or more at an air flow rate of 60 L / min. Therefore, the sealing portion 10 is sufficiently cooled by the air from the air blower 16. This further extends the life of the sealing portion 10.

[0078] 1. Immersion heater (heater), 2. Tubular portion, 4. Heating element, 6. First lead wire portion, 7. First connection portion, 8. Second lead wire portion, 9. Second connection portion, 10. Sealing portion, 11. Heat insulating material, 12. Support portion, 14. Joint portion, 16. Air blowing portion, N. Air, 20P. Opening portion.

Claims

1. A heater comprising: a heating element; a lead wire portion connected to said heating element; a tubular portion that houses said heating element; and a sealing portion that seals said tubular portion while allowing said lead wire portion to pass through, wherein said sealing portion is a hardened product obtained from a liquid, gel, paste or powder raw material.

2. The heater according to claim 1, characterized in that the cured material is a heat-resistant insulating material that can withstand heat of at least 250°C.

3. The heater according to claim 1, characterized in that the cured material does not expand in an environment of 250°C or higher.

4. The heater according to claim 1, characterized in that the hardened material prevents air from flowing into the tubular portion.

5. The heater according to claim 1, characterized in that the cured material is made of at least one of a siloxane material, alumina, quartz, zinc oxide, and carbon black.

6. A heater comprising: a heating element; a lead wire portion connected to said heating element; a tubular portion for housing said heating element; and a sealing portion for sealing said tubular portion while allowing said lead wire portion to pass therethrough, said sealing portion being made of a siloxane material.

7. The heater according to claim 6, characterized in that the siloxane material is a reactive cyclic siloxane material.

8. The heater of claim 7, wherein the reactive cyclic siloxane material is 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane.

9. The heater according to claim 6, characterized in that the sealing portion is formed from the siloxane material and at least one of alumina, quartz, zinc oxide, and carbon black.

10. A heater comprising: a heating element; a lead wire portion connected to said heating element; a tubular portion that houses said heating element; and a sealing portion that seals said tubular portion while allowing said lead wire portion to pass through, said sealing portion comprising at least one of quartz and alumina.

11. A heater according to claim 1, claim 6 or claim 10, characterized in that at least one of the heating element and the lead wire portion is made of molybdenum or a molybdenum alloy.

12. A heater as claimed in claim 1, claim 6 or claim 10, characterized in that the lead wire portion includes a stranded wire portion or a single wire assembly portion which is an assembly of a plurality of single wires.

13. A heater according to claim 1, claim 6 or claim 10, characterized in that the lead wire portion includes a rod-shaped portion.

14. A heater as claimed in claim 1, claim 6 or claim 10, further comprising a blower section for blowing air to the sealing section.

15. A heater as described in claim 1, claim 6 or claim 10, further comprising a connection portion surrounding the sealing portion, the connection portion having an opening for exposing the sealing portion to the outside air.

16. A heater comprising: a heating element; a lead wire portion connected to the heating element; a tubular portion that houses the heating element; a sealing portion that seals the tubular portion while allowing the lead wire portion to pass through; and a blower portion that blows air toward the sealing portion.

17. A heater comprising: a heating element; a lead wire portion connected to said heating element; a tubular portion that houses said heating element; a sealing portion that seals said tubular portion while allowing said lead wire portion to pass through; and a connection portion that surrounds said sealing portion, wherein said connection portion has an opening for exposing said sealing portion to the outside air.

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