Ceramic cast-in heater and method of manufacturing the same

Abstract

To provide a ceramic cast-in heater in which a solidified material of a heater 2 is not damaged by heat even at high temperatures, so that the heater 2 can be used stably, and a method of manufacturing the same.SOLUTION: There are provided: a ceramic cast-in heater in which a heater 2 is held in an appropriate position within heat-resistant, electrically insulating and highly thermally conductive ceramics 1 that is cast and solidified; and a method of manufacturing a ceramic cast-in heater, which includes holding a suitable number of heaters 2 within a framework 3, pouring a slurry containing heat-resistant, electrically insulating and highly thermally conductive ceramics 1 into the framework 3, and solidifying the slurry.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cast heater in which a heater 2 for direct electric energization is embedded in a heat-resistant, insulating, and highly heat-conductive ceramic 1, and a method for manufacturing the same.

Background Art

[0002] Generally, a cast heater is known in which a sheathed heater is fixed in a mold, and molten aluminum is cast around it and solidified.

[0003] However, since the melting point of aluminum is 660°C, it results in a high-temperature working environment. Also, the equipment for melting aluminum is large-scale. When the production quantity is small, the yield is poor and the cost is high. Moreover, in small quantities, the connection of multiple processes is not good, there is a lot of waste, the delivery time is long, and there is a drawback of poor yield.

[0004] For example, when a sheathed heater is fixed in a mold and molten aluminum is poured in to hold the heater at a predetermined position, the sheathed heater is arranged at room temperature. However, when 660°C molten aluminum is poured in, the sheathed heater comes into non-uniform contact with the molten aluminum. Therefore, due to non-uniform heating, there is a variation in elongation and deformation occurs, that is, a phenomenon of "running wild" in the mold occurs, and there is a drawback that the arrangement of the heater is not stable, and there is a large variation in the heating accuracy depending on the product. Also, due to the relationship of pouring molten aluminum, it was necessary to ensure a thickness of 20 mm or more.

[0005] The aluminum cast heater obtained in this way was limited to use at 300°C or lower. The reason is that in order for the internal sheathed heater to raise the outer surface of the aluminum cast heater above 300°C, it is necessary to raise the surface temperature of the sheathed heater to at least about 600°C. Therefore, the aluminum around the sheathed heater melts and erodes the surface of the sheathed heater, causing disconnection.

[0006] Therefore, the aluminum cast-in heater is often used by being closely attached to the periphery of the nozzle of an injection molding machine. The object to be heated is mainly metal at 300°C or lower, and it has the drawback that it cannot be used when heating at a higher temperature than that.

[0007] Also, as described in Patent Document 1 below, there is a type in which a heater is cast into ceramics. However, in order for the heater not to be damaged during the firing of the ceramics, it is necessary to previously press-contact an inorganic powder body to the heater, which has the drawback of complicated processes.

[0008]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0009] The present invention is to manufacture a ceramics cast-in heater by pouring a ceramics slurry into a mold in normal temperature air, rather than melting a cast-in metal and enclosing a heater. And it is the development of a ceramics cast-in heater that can withstand use at 300°C or higher. According to the present invention, it is not damaged even in molten metal, and is particularly applicable to heating and melting of molten aluminum and heating of zinc. Also, it is intended to provide a ceramics cast-in heater that can serve as a heat source by emitting hot air at 1000°C and can withstand use inside a furnace type.

Means for Solving the Problems

[0010] The present invention has achieved its object by developing a novel ceramics cast-in heater. Instead of conventional molten aluminum, a heater is fixed with heat-resistant and high heat-conducting ceramics 1 so that it can withstand high heat.

[0011] That is, the present invention, instead of conventional molten aluminum, first solidifies heat-resistant, insulating, and high heat-conducting ceramics 1 to fixedly hold a heater 2.

[0012] In manufacturing, the heater 2 is temporarily fixed in the mold 3, and a slurry obtained by kneading heat-resistant and highly heat-conductive ceramics 1, refractory cement, water, and a solvent is poured therein. This slurry is solidified to enclose and fix the heater 2. After solidification, the mold 3 is removed to obtain a product, and necessary wiring is performed using the protruding terminals so that it can be put into use.

[0013] Also, if the heat-resistant, insulating, and highly heat-conductive ceramics 1 are pre-mixed with a refractory cement component, it is also possible to prepare them by adding water or a solvent thereto.

[0014] Regarding the method of fixing the heater 2 during casting, for example, holes are drilled on both sides of the mold 3, one end of the heater 2 or a temporary fixing wire or the like is passed through, and it can be installed at an arbitrary position, such as the center or an equal number of locations. In the case of a vertical type, the heater 2 can also be suspended and temporarily fixed from above, but the method of temporary fixing and fixing is not limited. Some of them are shown below.

[0015] FIG. 13 shows a heater 2 of the sheathed heater type placed horizontally, which is arranged in the mold 3, and both ends are inserted and held in the guide holes 32 of the fixing plate 31 for temporary fixing made of metal or the like. The fixing plate 31 closes the left and right sides of the mold 3, and a slurry obtained by mixing heat-resistant, insulating, and highly heat-conductive ceramics 1, refractory cement, water, a solution, etc. is poured from the upper casting port. This fixing plate 31 is removed after the solidification of the above slurry or after firing.

[0016] FIG. 14 shows a heater 2 arranged horizontally, which is arranged in the mold 3. The lead wire side of the heater 2 is passed through a horizontal hole in the mold 3 and held, and the lower part of the floating tip is held by a temporary fixing material 33 made of silicon carbide or a material of the same quality as the heat-resistant, insulating, and highly heat-conductive ceramics 1. The above slurry is poured from above. This temporary fixing material 33 may be provided at one location or a plurality of locations with respect to the heater 2, and any shape such as a triangular bar, a square bar, a round bar, etc. can be used. Also, if it is made of a material of the same quality as the heat-resistant, insulating, and highly heat-conductive ceramics 1, it is integrated with the material cast around the heater 2.

[0017] Figure 15 shows that the heater 2 is placed in the mold 3. The lead wire side of the heater 2 is held in the horizontal hole of the mold 3 in the same manner as above. The tip is pulled out of the mold 3 by a thin wire 34 and fixed.

[0018] Figure 16 shows that a coiled heater 2 is wound around a core material 35 made of heat-resistant, insulating, and highly heat-conductive ceramics 1 or a heat-resistant ceramic material such as silicon carbide, and the assembly is placed in the mold 3. The above-mentioned slurry is poured around it. After the slurry solidifies or is fired, the core material 35 is integrated with the heat-resistant, insulating, and highly heat-conductive ceramics 1.

[0019] Figure 17 shows that instead of the coiled type in Figure 16, a sheathed heater type heater 2 is placed. In this case, as shown in Figure 18, the upper end of the pulled-out heater 2 is inserted through the guide hole 32 of the fixing plate 31 for temporary fixing made of metal or the like and temporarily fixed, and then the slurry is poured in.

[0020] The solidification of the heat-resistant, insulating, and highly heat-conductive ceramics 1, that is, drying and firing, takes a long time, but temperature control can be performed as follows by a program controller. In the first stage, a slurry obtained by adding refractory cement, water, solvent, etc. to the heat-resistant, insulating, and highly heat-conductive ceramics 1 and kneading is poured into the mold 3 in which the necessary heater 2 has been temporarily fixed and placed in advance. In the second stage, it is left standing for preliminary drying. In the third stage, it is put into a high-temperature furnace for firing and solidification. The temperature control and the like are detected by temperature detection means such as a temperature detection end, and the temperature change is detected and controlled by a computer as appropriate. This temperature detection means is also used for its function when used as a heating device.

[0021] Here, in the first stage mentioned above, the slurry can be injected into the mold 3 first, and the heater 2 can be placed therein.

[0022] Also, the firing and solidification in the third stage will be set to the required temperature according to the intended use as a heater. That is, if the required temperature for the object to be heated is 300°C, it will be set to at least 300°C; if it is 500°C, it will be set to 500°C; if it is 1000°C, it will be set to 1000°C. However, if firing is performed at the highest temperature, there will be less risk of heat damage during use and it will be possible to stably handle any situation.

[0023] Next, the basic shape of the heater of the present invention is plate-shaped as shown in Fig. 6(a), but it is not limited thereto and can be arbitrarily designed. As shown in Figs. 6(b) to (h), it can be cylindrical, curved plate, triangular prism, donut-shaped, cylindrical, box-shaped, polygonal column, L-shaped, etc. Also, as shown in Fig. 9, if a cold air supply hole 20 and a hot air outlet 21 are made to communicate inside, it can also be used as a hot air generating device. These cold air supply hole 20 and hot air outlet 21 may be formed simultaneously during molding, or may be cut after molding.

[0024] For the heater 2, any type can be used. For example, in addition to the exposed nichrome coil wire as shown in Fig. 7(a) and the sheathed heater as shown in Fig. 7(b), a cartridge heater as shown in Fig. 7(c) and a micro heater similar to it but thinner can be used, but other types are also acceptable. Incidentally, the sheathed heater in Fig. 7(b) is formed by inserting a coiled nichrome wire into an outer cylinder of heat-resistant steel and filling MgO insulator around it. The heat-resistant steel has a heat resistance of 1100°C if its melting point is 1300°C. The micro heater is formed by inserting a linear nichrome wire into a thin tube of heat-resistant steel and filling MgO insulator around it. It is thinner than Fig. 7(b) and is intended for fine objects to be heated. Also, the wiring of the heater 2 is not limited, but by embedding three times the number of wires, a three-phase heater can be manufactured.

[0025] The material of the heat-resistant, insulating, and highly heat-conductive ceramics 1 that holds the heater 2 contains silicon carbide-based ceramics, and in addition, a material blended with refractory cement can be used.

[0026] That is, when preparing a slurry, if the slurry is rich in silicon carbide or silicon nitride, it can be used. Therefore, when adding refractory cement, if, in the blended state, it is rich in silicon carbide or silicon nitride, the refractory cement component will also be rich in them, but the components of the refractory cement itself do not matter.

[0027] As the refractory cement component, for example, commercially available unshaped refractories and those blended with castables can be used. One example is as shown in Table 1 below. Those with silicon carbide as the main component are preferred in the present invention. Although not limited, products with a high content of silicon carbide (SiC) numbered 5 and 5' shown in Table 1 are preferred.

[0028] Also, if there is a product in which the refractory cement component is mixed into the heat-resistant, insulating, and high thermal conductivity ceramic 1 itself, that is also acceptable.

[0029] Also, various types of heat-resistant, insulating, and high thermal conductivity ceramics 1 are known. Examples of those that can be used include, among non-oxides, silicon carbide (SiC), silicon nitride (Si3N4), aluminum nitride (AlN), and among oxides, barium titanate (BaTiO3), lead titanate-zirconate (Pb(Zr,Ti)O3), ferrite (M2+O·Fe2O3), alumina (Al2O3), forsterite (2MgO·SiO2), zirconia (ZrO2), zircon (ZrO2·SiO2), mullite (3Al2O3·2SiO2), steatite (MgO·SiO2), cordierite (2MgO·2Al2O3·5SiO2), etc. One or more of these components can be selected as the main component, and those that meet the performance requirements according to the application can be selected.

[0030] Among these, when extracting in order from the highest strength, it becomes silicon nitride (SN2400) → silicon nitride (SN2410) → sapphire (SA100) → silicon nitride (SN201B) → silicon carbide (SC2110) → silicon carbide (SC1000) → alumina (AO4790). When extracting from the highest insulation, it becomes alumina → sapphire → aluminum nitride → silicon nitride → cordierite → steatite → forsterite → yttria → zirconia → silicon carbide → cermet. Furthermore, the thermal conductivity in descending order is silicon carbide → aluminum nitride → sapphire → alumina → silicon nitride → cermet → yttria → forsterite → cordierite → zirconia → steatite.

[0031] Taking these into comprehensive consideration, as heat-resistant, insulating, and high thermal conductivity ceramics 1, although not limited, it can be said that silicon nitride and silicon carbide have the above three performances, so they are preferable.

[0032] And due to the superiority of thermal conductivity, in addition to the most suitable silicon carbide (SiC, melting point 2730 °C), high melting point ceramics having heat resistance, insulation, and high thermal conductivity, such as magnesium oxide (MgO, melting point 2825 °C), silicon nitride (Si3N4, melting point 1900 °C), alumina (Al2O3, melting point 2054 °C), boron nitride (BN, melting point 2700 °C) can also be used. Appropriately blending refractory castables and castables with these high melting point ceramics is also similarly applicable.

[0033] In addition, this heat-resistant, insulating, and highly thermally conductive ceramic 1 preferably has low thermal shrinkage and low thermal deformability. Since silicon carbide has low values in these aspects, it can be said to be the most preferable. When the thermal deformability is low, as in the present invention, even if the heat-resistant, insulating, and highly thermally conductive ceramic 1 is directly in contact with the heater 2 and fired at a high temperature, the heater 2 is extremely unlikely to be damaged. Also, as shown in Table 2, both silicon nitride and silicon carbide have an appropriate maximum operating temperature (1150 - 1400°C) and thermal shock resistance (rapid heating) of 750°C and 700°C, respectively. However, the thermal shock resistance (rapid cooling) of silicon nitride is 250°C, while that of silicon carbide is 600°C. Therefore, when the process includes rapid cooling, silicon carbide can be said to be preferable. Table 2 also shows the characteristics regarding the thermal shock resistance of silicon nitride, silicon carbide, and alumina against rapid heating and rapid cooling, indicating that silicon nitride and silicon carbide are significantly superior to alumina. Among them, silicon carbide is the most preferable because it has excellent thermal shock resistance for both rapid heating and rapid cooling, and its thermal expansion coefficient is extremely low at 0.2.

[0034] On the other hand, Table 3 is an example of the quality table of silicon carbide-based low cement castables. It contains a large amount of silicon carbide, has high compressive strength, low linear change rate and low thermal expansion rate, and can be said to be suitable.

Table 1

Table 2

Table 3

[0035] For such heat-resistant, insulating, and highly thermally conductive ceramic 1, refractory cement, water, a solvent, etc. are added and kneaded to prepare a slurry. The slurry is uniformly poured around the heater 2 placed in the mold 3 and solidified by firing or the like. The pouring of the slurry is carried out at room temperature.

Advantages of the Invention

[0036] Since the present invention allows the heater to be placed, shaped, and cast in normal temperature and atmosphere, it avoids danger, does not require dangerous and highly skilled work in the manufacturing process, makes the placement of the heater easy, and significantly stabilizes the manufacturing environment and the performance of the product.

[0037] By solidifying the heater 2 with a heat-resistant, insulating, and highly heat-conductive ceramic 1 (preferably a ceramic mainly composed of SiC-based ceramics) that can withstand molten metal, it can also be used for heating high-temperature molten metal.

[0038] That is, although it is a cast-in heater in terms of form, it can be used at 300°C or higher. It can even reach 700°C and can be used, for example, for heating and melting molten metals (aluminum, zinc). Hitherto, gas heating has been relied on, but now electric heating has become easier, enabling energy saving and CO2 reduction.

[0039] Moreover, if an air supply hole and a hot air outlet are provided, hot air of 800°C or higher up to 1000°C can be discharged, so it can be used for devices that require high-temperature heated air.

[0040] Since the heat-resistant temperature of this heat-resistant, insulating, and highly heat-conductive ceramic 1 is 1400°C, for example, if the heat-resistant temperature is 1400°C or lower, even for heating objects of 1000°C or higher, it can be used safely for a long time.

[0041] In addition, the cast-in heater of the present invention can also be embedded in a refractory, so it can also be used as a wall heater. Also, if the mold 3 is made of a heat-resistant metal, for example, stainless steel, it is also possible to use it with the mold 3 attached.

[0042] Here, in the present invention, different from the conventional ceramic cast-in heater, even if the slurry containing the heat-resistant, insulating, and high heat-conducting ceramic 1 is directly cast without any pretreatment on the heater, substantially no damage such as cracks occurs in the heat-resistant, insulating, and high heat-conducting ceramic 1. For example, in the case of a sheathed heater type as shown in Fig. 7(c), since the substantial elongation of the heater 2 when heated is considered to be only in the longitudinal direction, it is considered that no cracks will occur in the heat-resistant, insulating, and high heat-conducting ceramic 1. In fact, even when used for heating at 700 °C, no substantial problems occurred. Also, in the case of the coiled heater or the micro heater shown in Fig. 7(a), even if it tries to deform during heating, there is not enough energy to affect the surrounding heat-resistant, insulating, and high heat-conducting ceramic 1, and it can be inferred that the deformation is absorbed. In fact, in these cases as well, no problems such as wire breakage occurred without pretreatment. Furthermore, to add more explanation, the heat-resistant, insulating, and high heat-conducting ceramic 1 can adjust its hardness by adjusting the moisture content during slurry preparation and the firing temperature and firing time after casting. Therefore, if its hardness is softened, the heater 2 fixed therein can be considered to be able to move slightly in its longitudinal direction at high temperatures, as in the case of Fig. 10. Even if a very small gap of about 0.01 mm is formed, it can be said that the elongation due to heating can be absorbed and no cracks will occur at high temperatures. Also, if a lubricant (such as BN) is coated on the surface of the heater 2 in advance and then the slurry of the heat-resistant, insulating, and high heat-conducting ceramic 1 is cast, the effect can be further enhanced, and this has also been verified. When a gap occurs while using the product according to the present invention and the internal heater 2 is disconnected, the cut portion of the heater 2 is removed from the heat-resistant, insulating, and highly thermally conductive ceramic 1, and a newly manufactured repair heater and a thermal conductive paste (for example, SCP-2 manufactured by Shiohara Seisakusho Co., Ltd.) are inserted into the mark where the paste was removed. In this way, the cut portion can be connected to the remaining heater 2 inside through the thermal conductive paste to energize the new repair heater, and it can be repaired. It can be reused as a ceramic-embedded heater, and maintenance is easy, and it has been demonstrated that the original performance can be ensured. It can be said to be a so-called repairable and renewable ceramic-embedded heater, and this is also a great advantage of this heater.

Embodiments for Carrying Out the Invention

[0043] Figure 3 shows the creation of a product on a vertical flat plate. An appropriate number of heaters 2, 2,... of an appropriate type are inserted into the mold 3 and temporarily fixed as appropriate. Then, as shown in Figure 4, the heat-resistant, insulating, and highly thermally conductive ceramic 1 prepared in a slurry state is poured into the mold 3 from a feeder 10 or the like.

[0044] In this state, it is left standing at room temperature or fired at a low temperature. Usually, a wooden mold is frequently used for the mold 3, but it is not limited to that, and other arbitrary materials, such as a paper material like cardboard, can also be used. If it is a combustible material, it will burn and be removed during the subsequent firing process at a high temperature.

[0045] The slurry mainly composed of the heat-resistant, insulating, and highly thermally conductive ceramic 1 is prepared by adding water and a solvent to a product in which a castable (refractory cement) component is blended as a premixed component in the heat-resistant, insulating, and highly thermally conductive ceramic 1, or by separately blending a castable (refractory cement), water, and a solvent in the heat-resistant, insulating, and highly thermally conductive ceramic 1. In any case, it is desirable that the slurry richly contains heat-resistant, insulating, and highly thermally conductive components such as silicon carbide.

[0046] The following is a specific description of the general outline of the composition, firing temperature, time, etc. through specific examples, as well as a conventional heater using molten aluminum to clarify its performance.

Example

[0047] Figure 10 shows a case where six sheathed heaters are used as heater 2, positioned in a mold 3 of 30 mm × 400 mm × 400 mm. Water is added at a weight ratio of 7% to a material mainly composed of SiC fine ceramics and blended with a refractory cement component (silicon carbide with a content of 83% in product number 5 of Table 1), and kneaded to prepare a slurry. Six heaters 2 are temporarily fixed in the mold 3, and the above slurry is poured from above. Immediately after pouring, if necessary, vibration is applied with a vibrator or the like to make the slurry spread evenly.

[0048] When the slurry has settled, it is pre-dried in a furnace at 100 °C for 1 hour, then taken out of the mold 3 and dried and sintered in a furnace at 400 °C for 12 hours to obtain a product in which heater 2 is held in heat-resistant, insulating, and high thermal conductivity ceramics 1.

[0049] When the temperature of the product obtained in this way is gradually increased from room temperature, an example of its thermal characteristics is as shown in Figure 8. In this example, in the first 4 hours, the surface temperature reaches 200 °C at 50 °C / Hr, held for 5 hours, then for 6 hours, the surface temperature reaches 350 °C at 25 °C / Hr, and after holding for 5 hours, when heated at 50 °C / Hr for 5 hours, the surface temperature reaches 600 °C, but the product can maintain the heating state normally. Incidentally, when the surface temperature of the product is 300 °C, it is 600 °C near heater 2, and when the surface temperature is 350 - 350 °C, it is above 700 °C near heater 2 (see Figure 8). Also, after 25 hours have passed, it was found that the temperature reached 600 °C after 5 more hours of continuous combustion, 700 °C after 7 hours, 800 °C after 9 hours, and 1000 °C after 13 hours.

[0050] The heat source A in which the heater 2 obtained above is cast into the heat-resistant, insulating, and highly heat-conductive ceramic 1 can constitute a plate-shaped heat source A with a thickness of about 30 - 50 mm, a height of 400 - 600 mm, and a width of 300 - 400 mm as shown in FIG. 10, for example, and can be used as the heat source A for dipping in the aluminum and zinc molten metal furnace C as shown in FIG. 11, for example. In this case, the temperature detection terminal B can also be embedded somewhere. In addition, since the temperature detection terminal B includes a thermocouple (measurement range: -200°C to 1600°C), a resistance thermometer (measurement range: -196°C to 600°C), a thermistor (measurement range: -50°C to 500°C), etc., one suitable for the use conditions can be used.

Example

[0051] Using Sample 5' (78% silicon carbide) in Table 1, a slurry was prepared by mixing water at a weight ratio of 5.5%. Otherwise, a product in which the heater 2 was held in the heat-resistant, insulating, and highly heat-conductive ceramic 1 was obtained according to Example 1. This product had substantially the same heat resistance as Example 1. Comparative Example

[0052] Incidentally, FIG. 12 shows a conventional round heat source A' with a silicon nitride protective tube 30. When this is used in the aluminum-zinc molten metal furnace C as described above, it has the drawbacks of a small heat transfer area, inability to obtain a high output, low thermal shock resistance, and being easily cracked (heat-resistant temperature 1000°C). Also, only one temperature detection terminal B can be inserted, and since it is only single-phase, its applications are also limited.

Industrial Applicability

[0053] The present invention significantly improves the usable temperature by holding the heater 2 with heat-resistant, insulating, and high thermal conductivity ceramics 1 instead of molten aluminum. It can be used for heating beyond the conventional range of 300 - 400°C, up to over 700 - 1000°C. For example, in addition to heating furnaces for low-melting metals, it can be used as a heat source with high durability for medium- and high-temperature molten metal furnaces. Also, since the heat-resistant, insulating, and high thermal conductivity ceramics 1 can be perforated after firing, it can also be used as a high-temperature hot air supply device by supplying air. Figure 9 shows an example, where air can be blown from a blower into the air holes 20 to blow out hot air from the outlet 21.

Brief Description of the Drawings

[0054]

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Explanation of symbols

[0055] 1 is heat-resistant, insulating, and highly heat-conductive ceramics, 2 is a heater, and 3 is a mold.

Claims

**Claim 1** A ceramic-encased heater in which a heater 2 is held in place within a cast heat-resistant, insulating, and highly thermally conductive ceramic 1. **Claim 2** The ceramic-encased heater according to claim 1, wherein the heat-resistant, insulating, and highly thermally conductive ceramic 1 contains silicon carbide as a main component. **Claim 3** A method for manufacturing a ceramic-encased heater, characterized by holding an appropriate number of heaters 2 in a mold 3, pouring a slurry containing a heat-resistant, insulating, and highly thermally conductive ceramic 1 into the mold 3, and solidifying it. **Claim 4** The method for manufacturing a ceramic-encased heater according to claim 3, wherein the heat-resistant, insulating, and highly thermally conductive ceramic 1 contains silicon carbide.

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