Immersion heater

Abstract

To provide an immersion heater which is easy to be assembled and produced, can execute stable heating even when the depth of a molten metal is variously changed, and can be applied even to three-phase or wide heating.SOLUTION: A cartridge heater 2 is removably inserted into a protective body 1 made of a high thermal conductivity ceramic stock.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention involves a cartridge heater 2 removably placed within a protective body 1 made of a highly thermally conductive ceramic material such as ceramics primarily made of silicon nitride or silicon carbide. When the protective body 1 is cylindrical, the gap between the two is filled with an insulating material 3 made of a powder or slurry of a highly thermally conductive material. When an insertion hole 4 is provided in the protective body 1, the cartridge heater 2 is removably inserted into the insertion hole 4, and the gap between the two is filled with the insulating material 3. In either case, the invention relates to an improved structure of an immersion heater that increases the overall thermal conductivity. [Background technology]

[0002] The structure of previous immersion heaters consisted of a nichrome wire housed inside a silicon nitride protective tube, with the nichrome wire installed as close as possible to the inner wall of the protective tube, and its heat was transferred to the protective tube to heat and keep the low-melting-point molten metal warm. For example, Figure 1 shows a model sold by our company, which has a single nichrome wire 12 housed in a Si3N4 protective tube 11, so it can only be used in a single phase, and if the heating part is above the surface of the molten metal, the temperature of that part of the heating element will exceed the melting point of the heater material, so there was a limit to the depth from the bottom of the molten metal that it could be used in, which made it difficult to use and shortened its lifespan.

[0003] In the example shown in Figure 1, a thermocouple 15 is inserted in the center, the wound portion of the nichrome wire 12 is the heat generating portion, and the portion of the lead wire 16 connected to the nichrome wire 12 is the non-heat generating portion.

[0004] That is, when this conventional type of immersion heater is used to heat molten aluminum, for example, the melting point of aluminum is 660°C, and because of the properties of the silicon nitride of protective tube 11, protective tube 11 will not crack even if it is directly immersed in molten aluminum from room temperature. Similarly, a silicon carbide protective tube 11 will not crack even if it is immersed because it has a thermal shock resistance of 700°C. However, since the thermal shock resistance of silicon nitride protective tube 11 to rapid cooling is 250°C, if there are areas where nichrome wire 12 is inserted and areas where it is not inserted, the temperature difference at the boundary between the two will be large, causing distortion and the possibility of cracking.

[0005] Figure 2 shows an example of such a heating state, in comparison with the present invention. The immersion heater is placed in a molten metal 20 such as aluminum or zinc contained in a furnace 17 to heat it, with the nichrome wire 12 corresponding to the heat-generating part and the lead wire 16 corresponding to the non-heat-generating part. Therefore, the boundary between them roughly coincides with the molten metal surface. Therefore, the immersion heater must be raised and lowered in accordance with the molten metal surface, with an accuracy of about ±10 mm.

[0006] Therefore, the manufacturer would check the lower limit line of the molten metal surface in 10mm increments to determine the position of the heat generating part before delivery, because if they did not do so, it would be impossible to avoid wire breakage.

[0007] Furthermore, if the heating element of such an immersion heater does not use nichrome wire, the inside is sealed, which causes oxygen deficiency in the heating element, making iron-based high-temperature heating elements prone to breaking even in a short period of time.

[0008] Figure 3 shows a type sold by the French company Lethiger, which has multiple nichrome wires 12 installed inside the Si3N4 protective tube 11, so three phases are possible by inserting a multiple of three nichrome wires, but the shape of the nichrome wires 12 is unstable during assembly, so a special insulating material 18, such as boron nitride (BN) packing and its solidification, must be filled in the gap between the nichrome wires 12 and the protective tube 11, and considerable skill is required to connect the multiple nichrome wires 12, so the reality is that there are no manufacturers in Japan that can reliably supply this product. In the diagram, 15 is a thermocouple.

[0009] [Non-Patent Document 1] https: / / www.ipros.jp / product / detail / 2000517956 (Lethigel's immersion heater website) DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0010] The problem to be solved by the present invention is: (1) It has a structure that does not require skill to manufacture, (2) Three-phase heaters are also applicable. (3) It is resistant to fluctuations in the molten metal surface. (4) The lifespan can be improved by reducing the surface watt density. (5) The heater is easy to maintain (replace). The present invention aims to provide such an immersion heater.

[0011] As shown in Figure 4, this invention consists of a cylindrical protective body 1 made of a highly thermally conductive ceramic material, typically ceramics based on silicon nitride or silicon carbide, and a high-temperature cartridge heater 2 inserted into it, with the gap between the protective body 1 and the cartridge heater 2 filled with insulator 3. This makes it easy to load the cartridge heater 2 into the protective body 1, expands the lower limit of the molten metal surface, and solves the problem of how easy it is to insert an immersion heater into the molten metal. A thermocouple 15 is inserted in the appropriate position.

[0012] Yet another embodiment of the present invention, as shown in Figure 9, aims to solve the same problems as above by providing multiple insertion holes 4 in a protector 1 made of a highly thermally conductive ceramic material, typically ceramics based on silicon nitride or silicon carbide, and removably storing cartridge heaters 2 in the insertion holes 4. The gaps between the insertion holes 4 and the cartridge heaters 2 are filled with an insulator 3 as needed.

[0013] Here are some general features of cartridge heaters 2. Figure 5 shows a standard cartridge heater 2. This heater consists of a core (bobbin) 22 made of insulating material such as MgO, with nichrome wire 23 wound around it (multiple cores (bobbins) 22 may be used for longer lengths). This core (bobbin) 22 is inserted into a heat-resistant metal protective tube 21, the tip of which is sealed off beforehand, and the surrounding area is filled with insulating material 24. The heater is then cold-forged (swaging machine) to reduce its diameter (e.g., from φ14 to φ12), preventing the nichrome wire 23 from moving while also bringing it closer to the protective tube 21, increasing its thermal conductivity. The area around the nichrome wire 23 is the heat-generating portion, while the other area is the non-heat-generating portion. Reference numeral 25 denotes lead wires.

[0014] Therefore, since the nichrome wire 23 generates heat in a location extremely close to the external metal protective tube 21, it is known to have very good heat conduction properties and has been used conventionally for heating molds.

[0015] The conditions for a material that can be used for the insulator 24 of the cartridge heater 2 are high insulation, high heat resistance (above 1000°C), powder form or easy to solidify, etc. Materials that meet these conditions include magnesium oxide (magnesia, MgO), alumina (Al2O3), silica (silicon dioxide, SiCO2), boron nitride (boronite, BN), aluminum nitride (aluminum nitride, AlN), etc., from which the most suitable one can be selected depending on the application, etc.

[0016] Figure 6 shows an outline of a sparsely wound cartridge heater 2. Nichrome wire 23 is wound around a core 22, with the densely wound areas being the heat generating areas, the sparsely wound areas being the low resilience heat generating areas, and the unwound areas being the non-heat generating areas. 24 is a high density insulator, and 25 is a lead wire.

[0017] Figure 7 shows an outline of a cartridge heater 2 with a temperature controller, with a thermocouple 26 attached to the center of the core 22, the part wound with nichrome wire 23 being the heat generating part, and the part with lead wire 25 being the non-heat generating part. 24 is an insulator, and 25 is the lead wire.

[0018] 8 shows a schematic diagram of a three-phase type cartridge heater 2, from which three lead wires 25 are drawn out. Other reference numerals are the same as those described above. [Effects of the Invention]

[0019] In the invention of claim 1, the gap between the cartridge heater 2 and the protector 1 can be filled with an insulator 3 made of a highly insulating, highly thermally conductive material such as alumina, boron nitride, aluminum nitride, or magnesium oxide in the form of powder or slurry using a vibrator, thereby fixing the cartridge heater 2 in place.

[0020] In the invention of claim 2, when inserting the cartridge heater 2 into the insertion hole 4, if the gap is narrow, the insulator 3 is not necessarily required, but if there is a certain amount of width, the insulator 3 similar to that described above can be filled in.

[0021] The materials that can be used for the insulator 3 that surrounds the cartridge heater 2 must be highly heat-resistant (over 1000°C) and be in powder form or easily solidified, but high insulation is not an absolute requirement. It is also desirable that the material be able to be broken down by mechanical pressure even when solidified. Materials that meet these requirements include magnesium oxide, alumina, boron nitride, aluminum nitride, and heat-resistant cement.

[0022] Heat-resistant cement hardens when the water content is increased, but it has very weak mechanical strength and can be easily destroyed with a drill, so by forcibly rotating the cartridge heater 2 in a circumferential direction, a gap is created, allowing the cartridge heater 2 to be easily removed from the protective body 1, and then by drilling it out, the original hole diameter can be restored. This means that even if the cartridge heater 2 is damaged, it can be easily removed from the protective body 1, repaired, and reused.

[0023] Furthermore, if the insulating material 3 is powder, it can be filled into the gap between the protective body 1 and the cartridge heater 2 with a vibrator, allowing stable use in the upright position, and when repairs are required, the powder insulating material 3 can be easily removed by turning the device upside down and vibrating it with a vibrator or the like.

[0024] For these reasons, the cartridge heater 2 is itself straight and has a smooth metal surface on its outer periphery, allowing it to stretch and slide in the vertical direction (lengthwise). Normally it is fixed in place, but it can be removed by applying force. It can also absorb the expansion of the metal when heated, preventing damage to the protective tube 1.

[0025] Furthermore, if the insulating material 3 is a powder or soft slurry, the cartridge heater 2 can be more easily replaced when it breaks down, and the protective body 1 can be reused.

[0026] The thermocouple 15 can be installed at any position between the cartridge heaters 2 inside the protective body 1, allowing for precise temperature control.

[0027] In terms of the molten metal surface, conventionally, the heating element is limited within the protective tube, and even an error of about 10 mm can easily cause cracks. However, in this invention, the internal heating element is a cartridge heater 2 covered in metal, so the temperature is dispersed (it is less sensitive). As shown in Figure 2, even when the heating element is exposed about 50 mm above the liquid surface, no breakage of the heating element was observed. This is because, as mentioned above, the cartridge heater 2 can be said to have a certain slipperiness relative to the protective body 1, making it easy to use. 16 is a lead wire, which, like the conventional example, is a non-heating part.

[0028] Furthermore, the range of uses is expanded by being able to shorten the heating section, wind loosely or tightly, or change the heating capacity in parts, which are features of the cartridge heater 2. Also, in manufacturing, the heating element is not a coiled nichrome wire, but is itself housed in a tube, making it easy to arrange inside the protective tube 1, and even when multiple units are used, it does not require skill and can be easily produced with a high yield. DETAILED DESCRIPTION OF THE INVENTION

[0029] In the embodiment of the present invention shown in Fig. 4, a cartridge heater 2 is inserted into a cylindrical protector 1 made of a highly thermally conductive ceramic material such as a ceramic mainly made of silicon nitride or silicon carbide, and multiple cartridge heaters 2, preferably a multiple of 3, are inserted. As the cartridge heater 2, those shown in Figs. 5 to 8 above are mainly used, but other types may also be used.

[0030] Figure 9 shows a protective body 1 made of a highly thermally conductive ceramic material such as a ceramic mainly made of silicon nitride or silicon carbide, in which insertion holes 4 are formed in advance according to the number of cartridge heaters 2 and cast, or the protective body is cast into an appropriate block such as a pillar and then the insertion holes 4 are drilled, and the cartridge heaters 2 are attached to the insertion holes 4 in a removable manner, and the gap between the insertion holes 4 and the cartridge heaters 2 is filled with an insulator 3 as necessary.

[0031] The insulator 3 is designed to adequately hold the cartridge heater 2 while also providing adequate slip properties. The materials that can be used have been outlined above, but as with the protective body 1, highly thermally conductive ceramic materials such as ceramics based on silicon nitride or silicon carbide, or unshaped refractories and ceramic cements known as castables can be used.

[0032] Here, the protective body 1 or the insulator 3 is selected from silicon nitride-based ceramics, silicon carbide-based ceramics, and SiC-based ceramics known as Drysic. Examples of the ceramics that can be used include those shown in Tables 1, 2, and 3 below.

[0033] Figure 10 shows an example of a wall-type heater, formed by forming multiple insertion holes 4 in a wall-shaped protector 1, inserting cartridge heaters 2 into these insertion holes 4, and filling the gaps with insulator 3. The materials for the protector 1 and insulator 3 are similar to those described above. By using a number of cartridge heaters 2 that is a multiple of three, three-phase operation is possible, and thermocouples 15 can also be placed as needed. As explained above, the cartridge heater 2 is formed by winding nichrome wire 23 around a core 22, with the gap between the two being filled with insulator 24.

[0034] [Table 1]

[0035] [Table 2]

[0036] [Table 3]

[0037] As shown in Tables 1, 2 and 3 above, Protector 1 and Insulator 3 are both suitable for immersion heaters for melting low melting point metals, and inserting Cartridge Heater 2 into Protector 1 solved the problem in one fell swoop. Both Protector 1, which is made of silicon nitride or silicon carbide, and Insulator 3, which is made of SiC ceramics, belong to the category of new ceramics, and it was thanks to the development of these ceramics that they could be combined with cartridge heaters, contributing to energy savings by switching from gas heating to electric heating (good thermal efficiency due to direct heating from the inside of the molten metal), and because no gas is used, it can be said to contribute to CO2 reductions. [Industrial Applicability]

[0038] This heater is suitable for heating molten metals, particularly at relatively low temperatures up to 700°C. Furthermore, by expanding the heater into a plate or wall shape, the surface area of ​​the heating element increases, providing an efficient, high-capacity immersion heater. Figure 11 compares a wall-shaped immersion heater of the present invention with a conventional immersion heater. In this example, assuming a conventional cylindrical heater with a diameter of 40 mm and a heating length of 300 mm, the surface area of ​​the heating element is 377 square centimeters. In contrast, the present invention allows for a wall-shaped immersion heater to be constructed by housing multiple cartridge heaters 2 in a protective body 1 with a thickness of 40 mm and a width of 300 mm. In this case, the surface area of ​​the heating element is 2160 square centimeters. Therefore, when the same 5 W / square centimeter heating element and cartridge heater are applied, the conventional immersion heater requires 1885 W, while the wall-shaped immersion heater of the present invention requires 10800 W, achieving a higher capacity. [Brief explanation of the drawings]

[0039] [Figure 1] A partially omitted schematic side view and end view of a heater currently on sale. [Figure 2] 1 is a schematic cross-sectional view of an immersion heater according to the present invention and the conventional immersion heater according to the present invention in use; FIG. [Figure 3] Schematic and cross-sectional view of Siegel's heater. [Figure 4] 1A and 1B are a schematic perspective view, a cross-sectional view, and a cross-sectional view of a cartridge heater according to an embodiment of the present invention; [Figure 5] 1 is a schematic perspective view of a standard type cartridge heater used in the present invention, with a portion cut away; FIG. [Figure 6] 1 is a schematic perspective view of a partially cutaway state of a loosely wound type cartridge heater used in the present invention. [Figure 7] 1 is a schematic perspective view of a cartridge heater with a T / C used in the present invention, with a portion cut away. [Figure 8]1 is a schematic perspective view of a three-phase cartridge heater used in the present invention, partially cut away; FIG. [Figure 9] 10A and 10B are a schematic perspective view and an enlarged end view of another embodiment of the present invention, with a portion cut away; [Figure 10] 1A and 1B are a schematic perspective view with a portion cut away and a schematic plan view with a portion omitted, showing an embodiment of the present invention in the form of a wall surface; [Figure 11] FIG. 1 is a schematic explanatory diagram comparing the heat generation amount of a conventional cylindrical immersion heater and an immersion heater of an application example of the present invention configured on a wall surface. [Explanation of symbols]

[0040] 1 is the protector, 2 is the cartridge heater, 3 is the insulator, and 4 is the insertion hole.

Claims

1. The immersion heater is constructed by storing a plurality of cartridge heaters 2, 2... in a protective body 1 formed of a highly thermally conductive ceramic material, filling the gap between them with an insulator 3, and making the cartridge heaters 2 removable from the protective body 1.

2. The immersion heater is formed by providing a plurality of insertion holes 4, 4... in a protective body 1 made of a highly heat-conductive ceramic material, storing a cartridge heater 2 in the insertion holes 4, and making the cartridge heater 2 removable from the protective body 1.

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