JP4927433B2 - Electric furnace - Google Patents

Description

  The present invention relates to an electric furnace that uses the inside of a cylindrical resistance heating element mainly composed of lanthanum chromite as a heating chamber.

Mainly composed of lanthanum chromite (LaCrO ₃ ) having a perovskite-type crystal structure. If necessary, part of La is replaced with Sr, Ca, etc., and part of Cr is replaced with Co, Ni, Al, Mg, etc. A heating element having the above composition (hereinafter simply referred to as a lanthanum chromite system) is widely used as a ceramic resistance heating element having excellent stability and long life in a high-temperature oxidizing atmosphere of 1500 ° C. or higher.

  Conventionally, an electric furnace using a resistance heating element generally used has a structure in which a heating chamber is heated using a plurality of rod-shaped heating elements 12 as shown in FIG. Furnace has drawbacks such as complicated and large equipment structure, and low heat efficiency and high power consumption with respect to the volume of the heating chamber. There were limits to the surface. In FIG. 1, 13 is a heat insulating material, and 14 is a core tube.

  Therefore, as shown in FIG. 2, the structure of the heating element is made of a cylindrical heating element 15 and the hollow portion is used as a heating chamber, so that the thermal efficiency of the electric furnace is improved and the operating temperature and temperature rise are increased. It is possible to improve the performance and service life such as the temperature speed, and some silicon carbide (SiC) pipe-type and double-tube type heat generators have been put to practical use. In this case, it is necessary to lengthen the size of the heating element due to characteristics such as oxidation and thermal conductivity, which leads to a problem that the electric furnace becomes large. Also, this method has a problem that the silicon carbide heating element is practically limited to 1600 ° C. and cannot be used at higher temperatures. In FIG. 2, 16 is a heat generating portion, 17 is a terminal portion, 18 is an electrode, 19 is a lead wire, 20 is a heat insulating material, and 21 is a core tube.

  Therefore, lanthanum chromite, which can be used at a high temperature and has a long life, is used as a material for the heating element, and two slits 5 are formed in the cylindrical heating element 1 including the heating part 3 and both ends as shown in FIG. By providing the terminal portion 2 on one side, the length of the heating element is prevented, and as shown in FIG. 4, the electric furnace is integrated by using the inside of the heating element as a heating chamber. Patent Document 1 discloses an electric furnace that solves the above problems by downsizing and setting the shape of the heating element and the characteristics of the material within an appropriate range. In FIG. 3, 4 is a folded end, 6 is an electrode, 7 is a metal lead component, and in FIG. 4, 1 is a heating element, 22 is a heat insulating material, and 23 is a core tube.

  However, since the electric furnace of Patent Document 1 is made of the same material and has the same specific resistance at both ends as the heat generating portion 3 of the heating element 1, the outer diameters of both ends are heated to reduce the resistance value at both ends. It is necessary to prevent the resistance heat generation at both ends by making the cross-sectional area of both ends larger than the cross-sectional area of the heat-generating part by making it larger than the outer diameter of the part. In order to obtain it, since it is necessary to make the outer diameter larger than the inner diameter of the heating element, there is a problem that the electric furnace is not sufficiently compact. In addition, since both ends are thick, they are vulnerable to thermal shock at the boundary between both ends and the heat generating part, and if the shape of the heating element is increased, rapid heating is not possible and the life is shortened. there were.

JP 2003-139472 A

  The present invention solves such conventional problems, the heating element has a large effective heating area, can be used at high temperatures, and has excellent thermal shock resistance, enabling rapid heating, and having a long service life. An object of the present invention is to provide a compact electric furnace comprising a lanthanum chromite heating element.

  In the present invention, the difference in electrical resistance between the heat generating portion and both ends is set to an appropriate ratio by changing the specific resistance itself of the material, not the outer diameter ratio, and heat is generated by reducing the wall thickness at both ends. The above object could be achieved by relatively increasing the inner diameter of the body, thereby increasing the effective heating area, and setting the shape of the heating element within an appropriate range.

  That is, according to the present invention, in a cylindrical lanthanum chromite heating element composed of a heat generating portion and both ends, the specific resistance at 1000 ° C. of the material of the heat generating portion is in the range of 0.1 to 3.5 Ωcm, and The specific resistance at 1000 ° C. is in the range of 0.02 to 0.5 Ωcm, and the ratio of the specific resistance at 1000 ° C. of the material of the heat generating part to the specific resistance of 1000 ° C. of the material at both ends ([specific resistance of the heat generating part] / [Specific resistance of both ends] is in the range of 1.5 to 100, and the ratio of the length of the heat generating portion to the inner diameter ([length of heat generating portion] / [inner diameter]) of the heat generating element is 0.6 to The ratio between the inner diameter and the thickness of the heating element ([inner diameter] / [thickness]) is in the range of 6 to 50, and one end face of the heating element is the base end, and the base By providing two slits in the vertical direction from the position where the end face is divided into two equal parts, the terminal part is concentrated on one side, and A heating element in which the ratio of the length of the lit to the total length of the heating element ([slit length] / [full length]) is in the range of 0.5 to 0.95, and a high-temperature metal electrode film is attached to the terminal portion. An electric furnace comprising: a heat insulating material attached to the outside of the heating element; and a ceramic core tube attached in the hollow portion of the heating element, wherein the hollow portion of the core tube is an effective heating chamber. .

  The electric furnace of the present invention will be described below with reference to the drawings.

  5 and 6 are diagrams showing a heating element of the electric furnace of the present invention. 5 is a view of the heating element of the electric furnace of the present invention as viewed from the front, FIG. 6A is a view of the heating element of the electric furnace of the present invention as viewed from the side, and FIG. 6B is a view of FIG. It is AA 'sectional drawing.

  5 and 6, the heating element 1 is made of a cylindrical lanthanum chromite ceramic composed of a terminal part 2, a heating part 3 and a folded end part 4, and the base end face (terminal part side) of the heating element is divided into two equal parts. Two slits 5 are provided in the vertical direction from the position where the terminal electrode is concentrated, and the terminal portion electrode is concentrated on one side to form the terminal portion 2, and the high temperature electrode 6 and the metal lead component 7 are attached to the terminal portion 2, and heat is generated between both ends. This is part 3. Thus, the current flows from one terminal part → one heat generating part → the folded end part → the other heat generating part → the other terminal part.

  The heating element 1 is provided with a resistance ratio by changing the electrical resistance ratio between the heating part and both ends of the heating element, that is, by changing the specific resistance of the material, not the outer diameter ratio. For this reason, it is not necessary to increase the outer diameter of both ends like the heating element described in JP-A-2003-139472 shown in FIG. Compared to the heating element described in Japanese Patent Application Laid-Open No. 2003-139472, it is possible to make it relatively large, and as a result, it is possible to enlarge the effective heating area in the furnace.

  In the lanthanum chromite ceramic used as the material of the heating element 1, the specific resistance at 1000 ° C. of the material of the heating part is in the range of 0.1 to 3.5 Ωcm, and the specific resistance of 1000 ° C. of the material at both ends is 0. It must be in the range of 0.02 to 0.5 Ωcm. If the specific resistance of the heat generating part is less than 0.1 Ωcm, the resistance value is too low and the heat generating element is driven at a low voltage and a large current, so that the contact between the electrode and the metal terminal is likely to occur, and the lead part is enlarged. Therefore, if it exceeds 3.5 Ωcm, the resistance value of the heating element is too large to generate heat by energization. Although the specific resistance at both ends is theoretically 0, there is no problem. However, in the case of lanthanum chromite ceramics, if the specific resistance is less than 0.015 Ωcm, the heat resistance, strength, and durability of the material are inferior, so there is no practicality. If it exceeds 0.5 Ωcm, the terminal electrode will generate resistance heat, resulting in a short life. For this reason, the specific resistance at 1000 ° C. of the material of the heat generating part is in the range of 0.1 to 3.5 Ωcm, and the specific resistance of 1000 ° C. of the material at both ends is in the range of 0.02 to 0.5 Ωcm. Necessary, the specific resistance at 1000 ° C. of the material of the heat generating part is in the range of 0.15 to 1.0 Ωcm, and the specific resistance of 1000 ° C. of the material at both ends is in the range of 0.025 to 0.2 Ωcm. More preferably, the specific resistance at 1000 ° C. of the heat generating part is in the range of 0.2 to 0.5 Ωcm, and the specific resistance at 1000 ° C. of the material at both ends is in the range of 0.03 to 0.15. More preferred. Further, in the heating element 1, the ratio of the specific resistance at 1000 ° C. of the material of the heat generating portion to the specific resistance at 1000 ° C. of the material at both ends ([specific resistance of the heat generating portion] / [specific resistance of both ends]) is 1. It must be in the range of 5-100. When the ratio of specific resistance is less than 1.5, the resistance ratio between the heat generating part and both end parts is small, and not only the heat generating part but also both end parts and terminal parts generate resistance heat. As a result, both end parts, terminal parts, and terminals The partial electrodes are easily damaged and have a short life. If the ratio of specific resistance is large, there is no particular problem, but if it exceeds 100, the mechanical properties of the material are greatly different, so it is difficult to mold and fire. Therefore, it cannot be used as a heating element. For this reason, it is necessary that the ratio of the specific resistance at 1000 ° C. between the heat generating portion and both ends is in the range of 1.5 to 100, and the ratio of the specific resistance between the heat generating portion and both ends is 1.75 to 50. It is more desirable to be in the range of 2 to 25, and it is more preferable to be in the range of 2 to 25.

  The heating element 1 is made of a material having different specific resistances at the heating part and at both ends. The specific resistance can be controlled by substituting a part of La, which is a constituent element of lanthanum chromite, with Sr, Ca, etc., and a part of Cr with Co, Ni, Al, Mg, etc. Any suitable substitution ratio may be used as long as it has mechanical characteristics, heat resistance and durability that can be sufficiently used as a heating element, and has the ratio of the specific resistance and the specific resistance. Although there are no particular limitations on the type of element to be substituted and the substitution ratio when used as a material, the La is generally substituted by about 0.1 to 20 mol% with Sr or Ca, and the Cr is substituted with about 0 to 40 mol% with Al. In many cases, the above are used (for details, refer to Japanese Patent Laid-Open No. 2005-317210). The heating element 1 can be obtained by integrally forming the heat generating part and both end parts as materials having different characteristics. The method can be performed by a known ceramic forming method. This can be done by filling and molding.

  In the heating element 1, the ratio of the length and the inner diameter of the heat generating portion 3 ([length of the heat generating portion] / [inner diameter]) needs to be in the range of 0.6 to 10. When the ratio between the length of the heat generating portion and the inner diameter is less than 0.6, the length of the heat generating portion is too short with respect to the inner diameter, so that a sufficient furnace temperature distribution cannot be obtained and cannot be used as an electric furnace in practice. . Also, if the length of the heat generating part exceeds 10, the aspect ratio of the effective heating region is too large to be practical, and since the heat generating element becomes longer, not only a compact electric furnace can be obtained, but also due to long time use. Deformation can cause contact between the slits, which can cause a short circuit. For this reason, the ratio of the length and the inner diameter of the heat generating portion 3 ([length of the heat generating portion] / [inner diameter]) needs to be in the range of 0.6 to 10, and should be in the range of 0.8 to 5. Is more desirable and is more preferably in the range of 1.0 to 3.

  In the heating element 1, the ratio of the inner diameter and the thickness of the heating element ([inner diameter] / [thickness]) needs to be in the range of 6-50. When the ratio between the inner diameter and the wall thickness of the heating element exceeds 50, the wall thickness is too small with respect to the inner diameter, and the strength of the heating element cannot be obtained sufficiently, resulting in a short life. When the ratio between the thickness of the heating element and the inner diameter is less than 6, the thickness is too large relative to the inner diameter, and the heat capacity of the heating element increases. When rapid heating is performed, the temperature gradient inside the heating element increases. Damage due to thermal stress may occur. For this reason, the ratio ([inner diameter] / [thickness]) between the inner diameter and the wall thickness of the heating element needs to be in the range of 6 to 50, and more preferably in the range of 10 to 35.

  In the heating element 1, the ratio of the length of the slit 5 provided in the heating element to the total length of the heating element 1 ([slit length] / [full length]) is in the range of 0.5 to 0.95. There is a need. If the ratio of the slit length to the total length of the heating element is less than 0.5, the length of the heating element in the total length of the heating element is too short, and not only a compact electric furnace is required, but also no folded end is required. Therefore, the power consumption per unit heat generating area is increased and the life is shortened. When the ratio between the length of the slit and the total length of the heating element exceeds 0.95, the folded end is too short, and damage due to repeated heating and cooling is likely to occur, resulting in a short life. Therefore, the ratio of the length of the slit 5 to the total length of the heating element 1 ([slit length] / [full length]) needs to be in the range of 0.5 to 0.95. It is more preferable that the ratio ([slit length] / [full length]) to the overall length is in the range of 0.6 to 0.9.

  FIG. 7 is a cross-sectional view showing an example of the electric furnace according to the present invention. A ceramic furnace core tube 8 is mounted in the hollow portion of the heating element 1, and the hollow portion serves as an effective heating chamber. The ceramic furnace core tube 8 can prevent the heated object from being contaminated by the evaporated material from the heating element 1 by placing the heated object therein. The thickness, length, and external dimensions of the ceramic furnace core tube 8 can be determined as appropriate according to the specifications of the electric furnace. Further, the ceramic core tube 8 can be arranged in the length direction according to the specifications of the electric furnace. Depending on the position, the thickness and outer dimensions may be changed. Further, the ceramic core tube 8 may be brought into close contact with the heating element 1, but if the heating part 3 is not in contact, the effect of preventing contamination of the object to be heated is further improved.

  The ceramic furnace tube 8 can use various known ceramics conventionally used as a furnace tube of an electric furnace depending on the temperature range in which the electric furnace is used. It is desirable to use 93% or more of alumina, mullite, spinel, stabilized zirconia (purity including a stabilizer of 95% or more), magnesia or yttria. By using these materials, the ceramic core tube 8 The heat resistance is further improved, the reaction with the heating element 1 is suppressed, and the effect of preventing contamination of the object to be heated is also improved.

  A heat insulating material 9 is attached to the outside of the heating element 1. By mounting the heat insulating material 9 on the outside of the heating element 1, the thermal efficiency of the electric furnace can be increased. As a material of the heat insulating material, various known refractory materials such as refractory bricks, refractory heat insulating bricks, castable refractories and ceramic fiber molded bodies can be used. Further, when the ceramic fiber molded body is used, since the heat insulation is excellent and the heat storage amount is small, the power consumption can be reduced and the life of the heating element 1 can be further extended. When a ceramic fiber molded body is used as the material for the heat insulating material, the heat generating body 1 and the heat insulating material 9 are formed by forming a ceramic layer 10 having a thickness of about 1 to 5 mm between the heat generating body 1 and the heat insulating material 9. Reaction can be further reduced, and the life of the heating element 1 can be further extended.

  In the electric furnace according to the present invention, since the terminal portion is concentrated on one side by providing two slits in the cylindrical lanthanum chromite-based heating element, the heating element can be made shorter than the conventional one. The electrical resistance ratio between the head part and the terminal part is not the outer diameter ratio but the appropriate ratio by changing the specific resistance of the material itself, and the inner diameter of the heating element is relatively reduced by reducing the thickness of the heating element. By enlarging and thereby increasing the effective heating area, and using the inside of the heating element as an effective heating chamber, the electric furnace can be integrated, thereby making the electric furnace compact. In addition, it can be used at high temperatures, has excellent thermal shock resistance, can be rapidly heated, has a long life, and can be controlled in various atmospheres. In addition, the electric furnace can be used in a vertical type as well as in a horizontal type without any problem, and has the merit that a sample can be taken in and out easily.

  Examples of the present invention and comparative examples will be described below, but the present invention is not limited to these examples. Conditions such as dimensions of each heating element are shown in Tables 1 and 2 below.

Example 1
In the electric furnace of FIG. 7, the material forming each of the heat generating portion and both end portions [for example, shown in FIG. 5 and FIG. Using a lanthanum chromite ceramic having a cylindrical shape with an inner diameter of 39 mm, an outer diameter of 45 mm, a wall thickness of 3 mm, a length of the terminal portion 2 of 60 mm, a length of the heat generating portion 3 of 65 mm, a length of the folded end 4 of 30 mm, and a total length of 155 mm The end face of the terminal part is divided into two equal parts from the position where the end face of the terminal part is divided into two in the vertical direction toward the folded end part to form a slit 5 with a groove having a width of 3 mm and a length of 130 mm, and a position 25 mm from the lower end of the terminal part 2 After applying platinum paste to the part (outer peripheral surface and end face) and baking at 1300 ° C. to form the high temperature electrode 6, the metal lead part 7 made of stainless steel SUS304 is attached. . An alumina ceramic core tube 8 (hereinafter referred to as a core tube) (outer diameter 37 mm × inner diameter 30 mm × length 400 mm) having a purity of 99.5% and a relative density of 97% is inserted into the hollow portion of the heating element 1. A cylindrical alumina ceramic 10 (outer diameter 10a is 56mm, outer diameter 10b is 52mm, inner diameter 10 is 48mm, total length 120mm) with 99.5% purity and 97% relative density outside did. Further, as a heat insulating material 9 on the outer side, a molded body (ceramic fiber molded body) made of an α-alumina material having a purity of 95% and having a bulk density of 0.7 g / cm ³ is formed, and an outer diameter 10b of the alumina ceramic 10 is formed at the center. An electric furnace was obtained by arranging and processing into a shape having a through-hole having the same size as in Fig. 1, and surrounding and fixing the outside with a metal can body lined with a refractory material.

Example 2
In the electric furnace of FIG. 7, the lanthanum chromite in which the materials of the heat generating part and both end parts of the heat generating element 1 have the compositions shown in Tables 1 to 3 and the specific resistance at 1000 ° C. is 0.22 Ωcm and 0.11 Ωcm, respectively. The heat generating element 1 is manufactured with a heat generating element having an inner diameter of 64 mm, an outer diameter of 68 mm, and a wall thickness of 2 mm, and an alumina ceramics core tube 8 having a purity of 99.5% and a relative density of 97% in the hollow portion of the heat generating element 1. (Outer diameter 58 mm × inner diameter 50 mm × length 400 mm) is inserted, and outside the heating element 1, a cylindrical alumina ceramic 10 having a purity of 99.5% and a relative density of 97% (the outer diameter 10 a has a size of 88 mm, An electric furnace was obtained in the same manner as in Example 1 except that the outer diameter 10b was 82 mm, the inner diameter 10 was 76 mm, and the total length was 120 mm.

Example 3
In the electric furnace of FIG. 7, the lanthanum chromite having the composition shown in Tables 1 to 3 and the specific resistance at 1000 ° C. of 0.48 Ωcm and 0.18 Ωcm, respectively, in the heating element 1 of the heating element 1. An electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was produced using a ceramic.

Example 4
In the electric furnace of FIG. 7, using the lanthanum chromite ceramics having the compositions and specific resistances shown in Tables 1 to 3, the heating element 1 has an inner diameter of 80 mm, an outer diameter of 88 mm, a thickness of 4 mm, a length of the terminal portion 2 of 100 mm, The heating element 1 is manufactured with a length of the heating part 3 of 150 mm, a length of the folded end part 4 of 50 mm, a total length of 300 mm, a width of the slit 5 of 6 mm, and a length of 265 mm, and a purity of 99.5% in the hollow part of the heating element 1 An alumina ceramic core tube 8 (outer diameter 72 mm × inner diameter 66 mm × length 600 mm) having a relative density of 97% is inserted, and a cylindrical alumina ceramic 10 having a purity of 99.5% and a relative density of 97% is placed outside the heating element 1. (Except that the outer diameter 10a is 108 mm, the outer diameter 10b is 100 mm, the inner diameter 10 is 94 mm, and the total length is 250 mm). An electric furnace was obtained.

Example 5
In the electric furnace of FIG. 7, the lanthanum chromite having the composition shown in Tables 1 to 3 and the specific resistance at 1000 ° C. of 0.4 Ωcm and 0.024 Ωcm, respectively, in the heating element 1 of the heating element 1. The heating element 1 is produced using a ceramic based material with a length of the heat generating part 3 of 60 mm, a length of the folded end 4 of 70 mm, a total length of 190 mm, and a length of the slit 5 of 125 mm. Example except that cylindrical alumina ceramic 10 (outer diameter 10a is 56 mm, outer diameter 10b is 52 mm, inner diameter 10 is 48 mm, total length 150 mm) with 5% and a relative density of 97% is mounted. An electric furnace was obtained in the same manner as in 1.

Example 6
In the electric furnace shown in FIG. 7, using a lanthanum chromite ceramic having the composition and specific resistance shown in Tables 1 to 3, the heating element has an inner diameter of 50 mm, an outer diameter of 55 mm, a thickness of 2.5 mm, and a length of the terminal portion 2 of 110 mm. The heating element 1 is manufactured with a length of the heating part 3 of 150 mm, a length of the folded end 4 of 40 mm, a width of the slit 5 of 5 mm, and a length of 265 mm. The heating part 1 has a purity of 99.5% and a relative density in the hollow part. A 97% alumina ceramic core tube 8 (outer diameter 46 mm × inner diameter 40 mm × length 600 mm) is inserted, and a cylindrical alumina ceramic 10 (outside) having a purity of 99.5% and a relative density of 97% is placed outside the heating element 1. An electric furnace was obtained in the same manner as in Example 1 except that the diameter 10a was 43 mm, the outer diameter 10b was 64 mm, the inner diameter 10 was 59 mm, and the total length was 240 mm.

Comparative Example 1
In the electric furnace of FIG. 7 in Example 1, each of the heat generating part and both ends of the heating element 1 has the composition and physical properties shown in Tables 1 to 3 (particularly, the specific resistance at 1000 ° C. of the heat generating part and both ends is 0 respectively. An electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was produced using lanthanum chromite ceramics (0.09 Ωcm and 0.042 Ωcm).

Comparative Example 2
In the electric furnace of FIG. 7, the heat generating part and both ends of the heat generating element 1 have the compositions and physical properties shown in Tables 1 to 3 (particularly, the specific resistance at 1000 ° C. of each of the heat generating part and both ends is 4.0 Ωcm, 0 An electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was prepared using lanthanum chromite ceramics (.3 Ωcm).

Comparative Example 3
In the electric furnace of FIG. 7, the heat generating portion and both end portions of the heat generating element 1 have the compositions and physical properties shown in Tables 1 to 3 (particularly, the specific resistance at 1000 ° C. of each of the heat generating portion and both end portions is 0.24 Ωcm,. An electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was produced using lanthanum chromite ceramics (017 Ωcm).

Comparative Example 4
In the electric furnace of FIG. 7, the heat generating part and both ends of the heating element 1 have the compositions and physical properties shown in Tables 1 to 3 (particularly, the specific resistance of each of the heat generating part and both ends at 1000 ° C. is 1.2 Ωcm, 0. An electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was produced using lanthanum chromite ceramics (55 Ωcm).

Comparative Example 5
In the electric furnace of FIG. 7, both ends of the heating element 1 have the compositions and physical properties shown in Tables 1 to 3 (particularly, the specific resistance at 1000 ° C. of the heating section and both ends is set to 0.3 Ωcm and 0.23 Ωcm, respectively. ) An electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was produced using lanthanum chromite ceramics.

Comparative Example 6
In the electric furnace of FIG. 7, the heat generating part and both ends of the heating element 1 have the compositions and physical properties shown in Tables 1 to 3 (particularly, the specific resistance of each of the heat generating part and both ends at 1000 ° C. is 2.5 Ωcm, 0. An electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was produced using lanthanum chromite ceramics (which was 024 Ωcm).

Comparative Example 7
In the electric furnace of FIG. 7, the heating element 1 is manufactured with an inner diameter of 54 mm, an outer diameter of 60 mm, a length of the heating part 3 of 30 mm, a total length of 120 mm, and a length of the slit 5 of 95 mm. An alumina ceramic core tube 8 (outer diameter 48 mm × inner diameter 40 mm × length 350 mm) having a purity of 99.5% and a relative density of 97% is inserted, and a purity of 99.5% and a relative density of 97% is placed outside the heating element 1. The electric furnace was installed in the same manner as in Example 1 except that the cylindrical alumina ceramic 10 (the outer diameter 10a was 78 mm, the outer diameter 10b was 72 mm, the inner diameter 10 was 66 mm, and the total length was 90 mm) was mounted. Obtained.

Comparative Example 8
In the electric furnace of FIG. 7, the heating element 1 has an inner diameter of 24 mm, an outer diameter of 30 mm, a heating part 3 of 250 mm length, a folded end 4 length of 50 mm, a total length of 360 mm, a slit 5 width of 2 mm, and a length of 310 mm. 1 is inserted, and an alumina ceramic core tube 8 (outer diameter 20 mm × inner diameter 15 mm × length 800 mm) having a purity of 99.5% and a relative density of 97% is inserted into the hollow portion of the heating element 1, Other than mounting cylindrical alumina ceramic 10 (outer diameter 10a is 43 mm, outer diameter 10b is 39 mm, inner diameter 10 is 35 mm, total length 330 mm) with a purity of 99.5% and a relative density of 97% Obtained an electric furnace in the same manner as in Example 1.

Comparative Example 9
In the electric furnace shown in FIG. 7, the heating element 1 is manufactured with the heating element 1 having an inner diameter of 55 mm, an outer diameter of 57 mm, and a wall thickness of 1 mm, and an alumina ceramic core having a purity of 99.5% and a relative density of 97% in the hollow portion of the heating element 1. A tube 8 (outer diameter 50 mm × inner diameter 46 mm × length 400 mm) is inserted, and a cylindrical alumina ceramic 10 (outer diameter 10a having a purity of 99.5% and a relative density of 97% is placed outside the heating element 1. An electric furnace was obtained in the same manner as in Example 1 except that 75 mm, the outer diameter 10 b was 69 mm, the inner diameter 10 was 63 mm, and the total length was 120 mm.

Comparative Example 10
In the electric furnace shown in FIG. 7, using an lanthanum chromite ceramic having the same composition and specific resistance as in Example 1, the inner diameter is 23 mm, the outer diameter is 32 mm, the wall thickness is 4.5 mm, the heating part 3 is 45 mm long, and the total length is 135 mm. The heating element 1 is manufactured with the slit 5 having a width of 1.5 mm and a length of 110 mm, and an alumina ceramics core tube 8 (outer diameter 20 mm × inner diameter 15 mm) having a purity of 99.5% and a relative density of 97% in the hollow portion of the heating element 1. X length 360 mm) is inserted, and outside of the heating element 1, a cylindrical alumina ceramic 10 having a purity of 99.5% and a relative density of 97% (the outer diameter 10a has a size of 42 mm and the outer diameter 10b has a size). An electric furnace was obtained in the same manner as in Example 1 except that 38 mm, inner diameter 10 was 35 mm, and the total length was 100 mm.

Comparative Example 11
In the electric furnace shown in FIG. 7, the heating element 1 was prepared with the terminal portion 2 having a length of 55 mm, the heating portion 3 having a length of 30 mm, the folded end portion 4 having a length of 105 mm, a total length of 190 mm, and the slit 5 having a length of 90 mm. Outside the body 1, cylindrical alumina ceramic 10 having a purity of 99.5% and a relative density of 97% (the outer diameter 10a is 56 mm, the outer diameter 10b is 52 mm, the inner diameter 10 is 48 mm, and the total length is 150 mm) An electric furnace was obtained in the same manner as in Example 1 except that was attached.

Comparative Example 12
In the electric furnace shown in FIG. 7, the heating element 1 has an inner diameter of 24 mm, an outer diameter of 30 mm, a terminal part 2 length of 240 mm, a folded end part 4 length of 15 mm, a total length of 320 mm, a slit 5 width of 2 mm, and a length of 310 mm. 1 is inserted, and an alumina ceramic core tube 8 (outer diameter 20 mm × inner diameter 15 mm × length 750 mm) having a purity of 99.5% and a relative density of 97% is inserted into the hollow portion of the heating element 1, Other than mounting cylindrical alumina ceramics 10 (outer diameter 10a is 43 mm, outer diameter 10b is 39 mm, inner diameter 10 is 35 mm, total length 270 mm) having a purity of 99.5% and a relative density of 97% Obtained an electric furnace in the same manner as in Example 1.

Comparative Example 13
In the electric furnace having the same structure as the electric furnace of FIG. 7 in the first embodiment, the heating element 1 has the shape shown in FIGS. 3 (A) and 3 (B), the heating part and both ends of the heating element 1. The material of the part has the composition shown in Table 1, and the lanthanum chromite ceramic having a specific resistance at 1000 ° C. of 0.3 Ωcm is used, the inner diameter of the heating element 1 is 32 mm, the outer diameter of the heating part 3 is 36 mm, The heating element 1 is manufactured with the outer diameter of the terminal part 2 being 45 mm, the thickness of the terminal part 2 being 6.5 mm, and the heating part 3 having a thickness of 2 mm. The purity of the heating element 1 is 99.5% and the relative density is 97%. An electric furnace was obtained in the same manner as in Example 1 except that the alumina ceramic core tube 8 (outer diameter 30 mm × inner diameter 24 mm × length 400 mm) was inserted.

Comparative Example 14
In the electric furnace having the same structure as the electric furnace of FIG. 7 in the first embodiment, the heating element 1 has the shape shown in FIGS. 3 (A) and 3 (B), the heating part and both ends of the heating element 1. The material of the part has the composition shown in Table 1, and using lanthanum chromite ceramics with a specific resistance at 1000 ° C. of 0.3 Ωcm, the inner diameter of the heating element 1 is 45 mm, the outer diameter of the heating part 3 is 50 mm, The outer diameter of the terminal part 2 is 55 mm, the thickness of the terminal part 2 is 5 mm, the thickness of the heat generating part 3 is 2.5 mm, the length of the terminal part 2 is 100 mm, the length of the heat generating part 3 is 160 mm, and the length of the folded end part 4 is 40 mm. The heating element 1 is manufactured with a total length of 300 mm, a width of the slit 5 of 5 mm, and a length of 260 mm. The alumina ceramic core tube 8 (outer diameter 40 mm × inner diameter) having a purity of 99.5% and a relative density of 97% in the hollow portion of the heating element 1 34mm x length 600 mm) and a cylindrical alumina ceramic 10 having a purity of 99.5% and a relative density of 97% (the outer diameter 10a is 66 mm, the outer diameter 10b is 60 mm, and the inner diameter is outside the heating element 1). An electric furnace was obtained in the same manner as in Example 1 except that 10 was 55 mm and the total length was 240 mm.

Test example 1
When each of the electric furnaces of Examples 1 to 6 and Comparative Examples 1 to 13 was repeatedly subjected to a cycle energization test at a holding temperature of 1800 ° C., a holding time of 30 minutes, and a temperature raising / lowering speed of 300 ° C./h in the center of the effective furnace. The voltage, current, power consumption, surface load density, and number of cycles until the heating element was damaged were obtained when the temperature reached the maximum temperature. The results are shown in Table 4.

Test example 2
When each of the electric furnaces of Examples 1 and 6 and Comparative Example 14 was subjected to an energization test at a holding temperature of 1800 ° C. in the center of the effective furnace, a holding time of 30 minutes, and a heating / cooling rate of 800 ° C./h, the power consumption was The voltage, current, power consumption, and surface load density when reaching the maximum temperature were determined. The results are shown in Table 5.

  As apparent from Table 4 of Test Example 1, the electric furnaces of Examples 1 to 6 showed high durability. Further, as is apparent from the results of Comparative Examples 1 to 13, an electric furnace using a lanthanum chromite heating element that does not satisfy the requirements of the present invention cannot provide a sufficient effective heating region, and has an excellent durability. Not. Further, as a result of Test Example 2, the electric furnace of the present invention was capable of rapid heating at a heating rate of 800 ° C./h.

FIG. 1A is a longitudinal sectional view of a conventional tubular electric furnace using a plurality of heating elements, and FIG. 1B is a transverse sectional view of a conventional tubular electric furnace. FIG. 2A is a longitudinal sectional view of an integrated tubular electric furnace using a conventional heating element, and FIG. 2B is an integrated tubular electric furnace using a conventional heating element. It is a cross-sectional view of a furnace. 3A is a view of the heating element of the electric furnace of Patent Document 1 as viewed from the front, and FIG. 3B is a view of the heating element as viewed from the side. FIG. 4 is a diagram illustrating an example of an electric furnace disclosed in Patent Document 1. In FIG. FIG. 5 is a front view of the heating element of the electric furnace of the present invention. 6A is a side view of the heating element of the electric furnace of the present invention, and FIG. 6B is a cross-sectional view taken along the line AA ′ of FIG. 6A. FIG. 7 is a longitudinal sectional view showing an example of the electric furnace of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat generating body 2 Terminal part 3 Heat generating part 4 Folding end part 5 Slit 6 Electrode 7 Metal lead part 8 Ceramic furnace core tube 9 Heat insulating material 10 Ceramic layer 10a Ceramic layer 10b Ceramic layer 11 Metal can body 12 Rod-shaped heating element 13 Heat insulating material 14 Core Tube 15 Heating element 16 Heating portion 17 Terminal portion 18 Electrode 19 Lead wire 20 Heat insulating material 21 Core tube 22 Heat insulating material 23 Core tube

Claims (1)

In a cylindrical lanthanum chromite heating element composed of a heating part and both ends, the specific resistance at 1000 ° C. of the material of the heating part is in the range of 0.1 to 3.5 Ωcm, and the specific resistance of 1000 ° C. of the material at both ends Is in the range of 0.02 to 0.5 Ωcm, and the ratio of the specific resistance at 1000 ° C. of the material of the heat generating part to the specific resistance of 1000 ° C. of the material at both end parts ([specific resistance of the heat generating part] / [ratio of both end parts] Resistance]) is in the range of 1.5 to 100, and the ratio of the length of the heat generating portion to the inner diameter ([length of the heat generating portion] / [inner diameter]) of the heating element is in the range of 0.6 to 10 The ratio between the inner diameter and the thickness of the heating element ([inner diameter] / [thickness]) is in the range of 6 to 50, one end face of the heating element is the base end, and the base end face is divided into two equal parts. By providing two slits in the vertical direction from the position where the contact is made, the terminal part is concentrated on one side, the length of the slit and heat generation A heating element having a ratio ([slit length] / [full length]) to a total length of the body in a range of 0.5 to 0.95, and a high-temperature metal electrode film attached to the terminal portion, and the heating element An electric furnace comprising a heat insulating material mounted on the outside of the ceramic core and a ceramic core tube mounted in a hollow portion of the heating element, wherein the hollow portion of the core tube is an effective heating chamber.

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