Heater

Abstract

To provide a technology capable of improving durability of a heater.SOLUTION: A heater includes: a ceramic body; a heat resistor; and a metal case. The ceramic body has a rod-like shape. The heat resistor is embedded at a tip side of the ceramic body. The metal case has a cylindrical shape for surrounding at least a rear end side of the ceramic body and for holding the ceramic body. An outer peripheral surface of a rear end part of the metal case includes: a plurality of side surfaces continuing in the circumferential direction of the metal case; and a ridge line part positioned between the adjacent two side surfaces.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a heater. [Background technology]

[0002] Conventionally, heaters having a heating resistor inside a rod-shaped ceramic body are known. Patent Document 1 discloses a configuration in which a heating resistor is provided at the front end of the ceramic body, and the rear end of the ceramic body is inserted into a cylindrical metal case. The ceramic body is held by the metal case. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-100804 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a technique that can improve the durability of a heater. [Means for solving the problem]

[0005] A heater according to one embodiment of the present disclosure includes a ceramic body, a heating resistor, and a metal case. The ceramic body is rod-shaped. The heating resistor is embedded in the front end side of the ceramic body. The metal case is cylindrical and surrounds at least the rear end side of the ceramic body to hold the ceramic body. The outer peripheral surface of the rear end of the metal case includes a plurality of side surfaces that are continuous in the circumferential direction of the metal case, and a ridge portion located between two adjacent side surfaces. Effect of the Invention

[0006] According to the present disclosure, the durability of the heater can be improved. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view showing a heater according to a first embodiment. [Diagram 2] FIG. 2 is a side view showing an example of a metal case according to the first embodiment. [Diagram 3] FIG. 3 is a perspective view showing an example of a rear end portion of the metal case according to the first embodiment. [Figure 4] FIG. 4 is an explanatory diagram of the metal case according to the first embodiment, viewed from the rear end side. [Diagram 5] FIG. 5 is an example of a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a side view showing another example of the metal case according to the first embodiment. [Figure 7] FIG. 7 is an explanatory diagram of another example of the metal case according to the first embodiment, viewed from the rear end side. [Figure 8] FIG. 8 is an example of a cross-sectional view taken along line IX-IX in FIG. [Figure 9] FIG. 9 is a side view showing an example of the rear end portion shown in FIG. [Figure 10] FIG. 10 is an enlarged side view showing an example of the rear end portion according to the first embodiment. [Figure 11] FIG. 11 is an enlarged side view showing another example of the rear end portion according to the first embodiment. [Figure 12] FIG. 12 is an explanatory diagram of a metal case according to the second embodiment, seen from the rear end side. [Figure 13] FIG. 13 is an example of a cross-sectional view taken along line XIII-XIII in FIG. [Figure 14] FIG. 14 is an explanatory view of another example of a metal case according to the second embodiment, viewed from the rear end side. [Figure 15] FIG. 15 is an example of a cross-sectional view taken along line XV-XV of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, a form for carrying out a heater according to the present disclosure (hereinafter, referred to as an "embodiment") will be described in detail with reference to the drawings. Note that the present disclosure is not limited to this embodiment. In addition, each embodiment can be appropriately combined within a range that does not cause a contradiction in the processing contents. In addition, the same parts in each of the following embodiments are given the same reference numerals, and duplicated explanations will be omitted.

[0009] In addition, in the embodiments described below, expressions such as "constant", "orthogonal", "vertical" and "parallel" may be used, but these expressions do not necessarily mean "constant", "orthogonal", "vertical" and "parallel" strictly. In other words, each of the above expressions allows for deviations due to, for example, manufacturing accuracy and installation accuracy.

[0010] In addition, in the drawings referred to below, for ease of understanding, an orthogonal coordinate system may be shown in which the X-axis, Y-axis, and Z-axis directions are defined as being orthogonal to each other, and the Z-axis positive direction is the vertically upward direction. Also, the direction of rotation about the vertical axis may be referred to as the θ direction.

[0011] In the heater described in Patent Document 1, the front end of the metal case is close to the heat generating part (where the heat generating resistor is provided) in the ceramic body, whereas the rear end is far from the heat generating part. For this reason, a temperature difference is likely to occur between the front end and the rear end of the metal case. That is, the metal case has a large difference in thermal expansion and contraction between the front end and the rear end. In particular, in recent years, there has been a demand for heaters to be used in high-temperature environments. Accordingly, in order to make it difficult for the heat of the heat generating part to affect other parts, the heater is becoming longer in axis than that described in Patent Document 1. As a result, the metal case has a larger difference in thermal expansion and contraction between the front end and the rear end. If this difference causes the metal case to twist, stress is applied to the joint between the metal case and the ceramic body, which may cause microcracks and reduce the durability of the heater.

[0012] Therefore, a technology capable of improving the durability of the heater is desired.

[0013] First Embodiment First, the heater according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view showing the heater 1 according to the first embodiment.

[0014] As shown in FIG. 1, the heater 1 according to the first embodiment includes a heater body 10, a ceramic ring 20, and a metal case 30.

[0015] The heater body 10 has a ceramic body 11, a heating resistor 14, and lead wires 15. The ceramic body 11 is a rod-shaped member. Specifically, the shape of the ceramic body 11 may be a cylindrical shape, an elliptical cylindrical shape, or a rectangular cylindrical shape. The length of the ceramic body 11 may be, for example, about 20 to 150 mm. The diameter of the ceramic body 11 may be, for example, about 3 to 5 mm.

[0016] The material of the ceramic body 11 is, for example, ceramic having insulating properties. This makes it possible to provide a heater 1 that is highly reliable during rapid temperature rise. As the material of the ceramic body 11, for example, oxide ceramics, nitride ceramics, carbide ceramics, etc. can be used. Specifically, alumina ceramics, silicon nitride ceramics, aluminum nitride ceramics, silicon carbide ceramics, etc. can be used. In particular, when silicon nitride ceramics are used, the main component silicon nitride is excellent in terms of strength, toughness, insulation, and heat resistance.

[0017] The ceramic body 11 made of silicon nitride ceramics can be obtained, for example, by mixing silicon nitride as the main component with 3 to 12 mass% of a rare earth oxide such as Y2O3, Yb2O3 or Er2O3 as a sintering aid, 0.5 to 3 mass% Al2O3, and SiO2 so that the SiO2 content in the sintered body is 1.5 to 5 mass%, forming the mixture into a predetermined shape, and then hot-pressing sintering at 1650 to 1780°C.

[0018] When using a silicon nitride ceramic as the ceramic body 11, MoSiO2 or WSi2 may be mixed and dispersed. In this case, the thermal expansion coefficient of the silicon nitride ceramic, which is the base material, can be made close to that of the heating resistor 14, and the durability of the heater 1 can be improved.

[0019] The heating resistor 14 is located inside the ceramic body 11. The heating resistor 14 is embedded in the front end 12 side of the ceramic body 11, and is connected to a third portion 15c and a fourth portion 15d of the lead wire 15 described later. The front end 12 side here may be, for example, one of three regions obtained by dividing the ceramic body 11 into three equal parts in the longitudinal direction of the ceramic body 11, the region including the front end 12. The rear end 13 side may be, for example, one of three regions obtained by dividing the ceramic body 11 into three equal parts in the longitudinal direction of the ceramic body 11, the region including the rear end 13. The total length of the heating resistor 14 may be, for example, about 3 to 15 mm. The cross-sectional area of ​​the heating resistor 14 may be 0.1 to 0.8 mm. 2 It can be about that.

[0020] The heating resistor 14 is a member that generates heat when a current flows through it. The heating resistor 14 may include a high-resistance conductor containing, for example, tungsten, molybdenum, etc. When the ceramic body 11 is made of silicon nitride ceramics, tungsten carbide is an excellent material for the heating resistor 14 because it has a small difference in thermal expansion coefficient with the ceramic body 11 and has high heat resistance.

[0021] When the ceramic body 11 is made of silicon nitride ceramics, the heating resistor 14 may be mainly composed of tungsten carbide, an inorganic conductor, with the content of silicon nitride added to the main component being 20 mass % or more. For example, in the ceramic body 11 made of silicon nitride ceramics, the conductor component that becomes the heating resistor 14 has a higher thermal expansion coefficient than silicon nitride, and is therefore usually under tensile stress. In contrast, by adding silicon nitride to the heating resistor 14, the thermal expansion coefficient can be made closer to that of the ceramic body 11, and the stress caused by the difference in thermal expansion coefficient when the heater 1 is heated and cooled can be alleviated.

[0022] Furthermore, when the content of silicon nitride in the heating resistor 14 is 40 mass % or less, it is possible to reduce the variation in the resistance value of the heating resistor 14. Therefore, the content of silicon nitride in the heating resistor 14 may be 20 to 40 mass %. Alternatively, as a similar additive to the heating resistor 14, 4 to 12 mass % of boron nitride may be added instead of silicon nitride.

[0023] The shape of the heating resistor 14 is not limited to that shown in the figure, and can be changed as appropriate according to the heating characteristics required for the heater 1, for example.

[0024] The lead wire 15 electrically connects the heating resistor 14 to an external power source. Specifically, one end of the lead wire 15 is connected to the heating resistor 14, and the other end is drawn out of the ceramic body 11 and connected to an external power source, and supplies power from the external power source to the heating resistor 14.

[0025] Lead wire 15 has a first portion 15a and a second portion 15b located outside ceramic body 11, and a third portion 15c and a fourth portion 15d located inside ceramic body 11. Lead wire 15 also has a first end 16 connected to first portion 15a and a second end 17 connected to second portion 15b.

[0026] The first portion 15a is located closer to the rear end 13 of the ceramic body 11 than the ceramic ring 20. The first portion 15a includes a coil portion 51 and a terminal portion 52. The coil portion 51 is a portion that is wound around the circumferential surface of the ceramic body 11, and is connected to the first end portion 16. The coil portion 51 that is positioned in a spiral shape along the circumferential surface of the ceramic body 11 may be in contact with the ceramic body 11, or may be located away from the circumferential surface of the ceramic body 11.

[0027] The second portion 15b is located closer to the rear end 13 of the ceramic body 11 than the first portion 15a. The second portion 15b includes a coil portion 61 and a terminal portion 62. The coil portion 61 is a portion wound around the circumferential surface of the ceramic body 11, and is connected to the second end portion 17. The coil portion 61 is positioned in a spiral shape around the circumferential surface of the ceramic body 11, and may be in contact with the ceramic body 11 or may be positioned away from the circumferential surface of the ceramic body 11. The number of turns of the coil portions 51, 61 may be the same as or different from each other.

[0028] The first portion 15a and the second portion 15b are wires containing a metal material such as nickel, iron, or a nickel-based heat-resistant alloy. The cross sections of the first portion 15a and the second portion 15b may be circular, elliptical, or rectangular. The outer diameters of the first portion 15a and the second portion 15b may be, for example, 0.5 to 2.0 mm.

[0029] The terminal portions 52, 62 are located at the ends of the first portion 15a and the second portion 15b, respectively. The direction in which the terminal portions 52, 62 are drawn out is not limited to the shape shown in the drawings and can be changed as appropriate.

[0030] The third portion 15c extends in the longitudinal direction of the ceramic body 11 from the first end portion 16 toward the tip 12 of the ceramic body 11 and is connected to one end of the heating resistor 14. The fourth portion 15d extends in the longitudinal direction of the ceramic body 11 from the second end portion 17 toward the tip 12 of the ceramic body 11 and is connected to the other end of the heating resistor 14.

[0031] The third portion 15c and the fourth portion 15d are formed, for example, using the same material as the heating resistor 14. The third portion 15c and the fourth portion 15d have a larger cross-sectional area than the heating resistor 14, or the content of the material forming the ceramic body 11 is less than that of the heating resistor 14, so that the resistance value per unit length is low. The third portion 15c and the fourth portion 15d may be a tungsten wire, or may be made mainly of tungsten carbide, which is an inorganic conductor, to which silicon nitride is added so that the content is 15 mass% or more. As the content of silicon nitride increases, the thermal expansion coefficient of the third portion 15c and the fourth portion 15d can be made closer to the thermal expansion coefficient of silicon nitride constituting the ceramic body 11. When the content of silicon nitride is 40 mass% or less, the resistance value of the third portion 15c and the fourth portion 15d becomes low and stable. Therefore, the content of silicon nitride may be 15 to 40 mass%.

[0032] The ceramic ring 20 is a member for holding the ceramic body 11. At least the rear end 13 side of the ceramic body 11 is inserted into the ceramic ring 20. In other words, the ceramic ring 20 holds at least the rear end 13 side of the ceramic body 11. The ceramic ring 20 is made of a ceramic material such as alumina or silicon nitride.

[0033] The ceramic ring 20 is a ring-shaped member. Examples of the ring shape include a circular ring shape. Other examples of the ring shape include a polygonal shape including a rectangular shape in the inner circumference and the outer circumference. The shape of the ceramic ring 20 can be set, for example, so that the inner peripheral surface is in close contact with the outer peripheral surface of the ceramic body 11.

[0034] The ceramic ring 20 has a first ceramic ring 21 and a second ceramic ring 22. The first ceramic ring 21 can be shaped so that its inner peripheral surface is in close contact with the outer peripheral surface of the ceramic body 11, and its outer peripheral surface is in close contact with the inner peripheral surface of the metal case 30. An example of the inner peripheral surface of the first ceramic ring 21 being in close contact with the outer peripheral surface of the ceramic body 11 is when the inner peripheral shape of the first ceramic ring 21 and the outer peripheral shape of the ceramic body 11 are the same. For example, when the inner and outer peripheral surfaces of the first ceramic ring 21 are circular, the inner diameter can be designed to be approximately the same as the thickness of the ceramic body 11, and the outer diameter can be designed to be approximately the same as the inner diameter of the metal case 30. Specifically, the outer diameter of the first ceramic ring 21 can be set to about 1 to 100 mm.

[0035] Alternatively, a metallized layer may be provided on the inner peripheral surface of the first ceramic ring 21, and the ceramic body 11 and the first ceramic ring 21 may be joined via the metallized layer by a brazing material such as solder or silver brazing.

[0036] The first ceramic ring 21 and the metal case 30 are joined by a joining material 40. Specifically, the joining material 40 is located between the outer circumferential surface of the first ceramic ring 21 and the inner circumferential surface 32b of the metal case 30. As the joining material 40, for example, a brazing material such as solder or silver brazing can be used.

[0037] The second ceramic ring 22 is located closer to the rear end 13 of the ceramic body 11 than the first ceramic ring 21. Specifically, the main surface of the second ceramic ring 22 located on the front end 12 side of the ceramic body 11 is provided so as to contact the main surface of the first ceramic ring 21 located on the rear end 13 side of the ceramic body 11. The second ceramic ring 22 can be set to a shape in which the inner peripheral surface is in close contact with the outer peripheral surface of the ceramic body 11 and the outer diameter is smaller than the outer diameter of the first ceramic ring 21. An example of the inner peripheral surface of the second ceramic ring 22 in close contact with the outer peripheral surface of the ceramic body 11 is, for example, a case in which the shape of the inner circumference of the second ceramic ring 22 and the shape of the outer circumference of the ceramic body 11 are the same. In this way, by providing the second ceramic ring 22, heat transferred to the first ceramic ring 21 can be released to the second ceramic ring 22, and thermal stress generated in the first ceramic ring 21 can be reduced.

[0038] The metal case 30 is a member for holding the ceramic ring 20 and the ceramic body 11. The metal case 30 is a cylindrical member and is attached so as to surround at least the rear end 13 side of the ceramic body 11 together with the ceramic ring 20. Specifically, the middle part 32 of the metal case 30 has a plurality of (here, two) steps 35 whose inner diameter increases from the front end part 31 side toward the rear end part 33 side, and the first ceramic ring 21 is fixed at the step 35 located on the rear end part 33 side among the plurality of steps 35. Here, the front end part 31 of the metal case 30 is, for example, a part having a portion where the outer diameter decreases toward the front end of the metal case 30. The middle part 32 of the metal case 30 is, for example, a part in which the outer circumferential surface 32a (see FIG. 2) is configured to be parallel to the axial direction (Z-axis direction) of the metal case 30, and is a part of the metal case 30 other than the rear end part 33 and the front end part 31 described later.

[0039] In addition, in FIG. 1, the metal case 30 and the ceramic body 11 are in contact with each other, but a minute gap may exist between the metal case 30 and the ceramic body 11.

[0040] The material of the metal case 30 is, for example, a metal material having heat resistance. For example, an alloy containing Fe and Ni can be used as the material of the metal case 30. Specifically, the metal case 30 can be made of stainless steel, an Fe-Ni-Co alloy, a Ni-based heat-resistant alloy, or the like.

[0041] In the heater 1 configured as described above, the front end 31 of the metal case 30 is close to the heat generating portion of the ceramic body 11 (where the heating resistor 14 is embedded), whereas the rear end 33 is far from the heat generating portion. In addition, the rear end of the metal case 30 may be exposed to the outside air. For this reason, a temperature difference is likely to occur between the front end 31 and the rear end 33 of the metal case 30. That is, the metal case 30 has a large difference in thermal expansion and contraction between the front end 31 and the rear end 33. If this difference causes the metal case 30 to twist, stress is applied to the joint between the metal case 30 and the ceramic body 11, which may cause microcracks and reduce the durability of the heater 1. In particular, stress is applied to the joint between the metal case 30 and the first ceramic ring 21, which may reduce the durability of the heater 1.

[0042] Therefore, the heater 1 according to the first embodiment is configured to have a ridge portion 332 (see FIG. 2) on the outer peripheral surface 33a of the rear end portion 33 of the metal case 30. This makes it less likely that the rear end portion 33 of the metal case 30 will be twisted, compared to a case in which the outer peripheral surface 33a of the rear end portion 33 of the metal case 30 does not have the ridge portion 332, i.e., for example, when the rear end portion 33 is cylindrical. Hereinafter, the details of the configuration of the metal case 30 according to the first embodiment will be described with reference to FIGS. 2 to 11.

[0043] Fig. 2 is a side view showing an example of the metal case 30 according to the first embodiment. Fig. 3 is a perspective view showing an example of the rear end portion 33 of the metal case 30 according to the first embodiment. Fig. 4 is an explanatory diagram of the metal case 30 according to the first embodiment as viewed from the rear end portion 33 side. Fig. 5 is an example of a cross-sectional view taken along line V-V in Fig. 4.

[0044] Moreover, Fig. 6 is a side view showing another example of the metal case 30 according to the first embodiment. Fig. 7 is an explanatory view showing another example of the metal case 30 according to the first embodiment from the rear end portion 33 side. Fig. 8 is an example of a cross-sectional view taken along line IX-IX in Fig. 7. Fig. 9 is a side view showing an example of the rear end portion 33 shown in Fig. 7.

[0045] Moreover, Fig. 10 is an enlarged side view showing an example of the rear end portion 33 according to the first embodiment. Fig. 11 is an enlarged side view showing another example of the rear end portion 33 according to the first embodiment.

[0046] The outer peripheral surface 33a of the rear end 33 of the metal case 30 includes a plurality of (six in FIG. 3) side surfaces 331 that are continuous in the circumferential direction of the metal case 30, and a ridge portion 332 located between two adjacent side surfaces 331. In other words, the shape of the rear end surface 335 of the rear end 33 of the metal case 30 is a shape other than a circle, such as a triangle, a rectangle, or a hexagon. This makes it difficult for the rear end 33 of the metal case 30 to be twisted, compared to when the outer peripheral surface 33a of the rear end 33 of the metal case 30 does not have the ridge portion 332, for example, when the rear end surface 335 is a circle. In addition, as shown in FIG. 4, the portion of the rear end 33 where the ridge portion 332 is located is thick, so that the metal case 30 is unlikely to be deformed in the circumferential direction. When deformation is unlikely to occur in this way, stress is unlikely to be applied to the joint between the metal case 30 and the ceramic body 11, and the durability of the heater 1 can be improved.

[0047] The rear end surface 335 of the metal case 30 may be formed point-symmetrically with respect to the center 335a of the rear end surface 335. In this case, the number of ridges 332 of the metal case 30 is an even number of two or more, and a straight line connecting two corresponding ridges 332 passes through the center 335a of the rear end surface 335. This makes it possible to distribute stress acting on the ridges 332 of the metal case 30, and improve the durability of the heater 1.

[0048] 4, the shape of the rear end surface 335 of the metal case 30 may be a hexagon. In other words, the rear end portion 33 of the metal case 30 has six side surfaces 331 and six ridges 332 located between two adjacent side surfaces 331. This maximizes the inner diameter of the rear end portion 33 of the metal case 30 while dispersing stress acting on the metal case 30 in multiple directions, thereby improving the strength of the heater 1.

[0049] In particular, it is preferable that the shape of rear end surface 335 is a regular hexagon. In this case, six ridge lines 332 are positioned at equal intervals in the circumferential direction of metal case 30. Therefore, the stress acting on metal case 30 can be distributed more evenly.

[0050] However, the shape of the rear end surface 335 is not limited thereto, and may be a hexagon with sides of different lengths. The shape of the rear end surface 335 may be a polygon other than a hexagon. The shape of the rear end surface 335 may have at least one curved side as shown in Fig. 7. Specifically, as shown in Fig. 7, the rear end surface 335 of the metal case 30 may have a racetrack shape in which two straight side surfaces 331 are connected at both ends by two semicircular side surfaces 331.

[0051] 7, as in the case where the rear end face 335 has a polygonal shape, the ridge portion 332 on the outer peripheral surface 33a of the metal case 30 extends linearly in the axial direction of the metal case 30 toward the rear end 33 of the metal case 30, thereby suppressing twisting of the metal case 30 and making it difficult for the metal case 30 to deform in the circumferential direction. When deformation is made difficult in this way, stress is not easily applied to the joint between the metal case 30 and the ceramic body 11, and the durability of the heater 1 can be improved.

[0052] 2, the ridge portion 332 may extend parallel to the axial direction of the metal case 30. This makes it possible to make the stress applied to the ridge portion 332 of the metal case 30 constant in the axial direction of the metal case 30, and to distribute the stress in the axial and circumferential directions of the metal case 30, compared to a case in which the ridge portion 332 is inclined with respect to the axial direction of the metal case 30. This makes it possible to improve the durability of the heater 1.

[0053] 3 and 4, the shape of the middle part 32 of the metal case 30 may be cylindrical. Specifically, as shown in FIG. 4, the metal case 30 may be formed so that a plurality of ridges 332 and the outer peripheral surface 32a of the middle part 32 overlap each other. In this case, the metal case 30 may be provided with an inclined surface 34 connecting the side surface 331 of the rear end part 33 of the metal case 30 and the outer peripheral surface 32a of the middle part 32 of the metal case 30. As shown in FIG. 5, the inclined surface 34 inclines in a direction away from the central axis R0 of the metal case 30 as it moves from the rear end part 33 of the metal case 30 toward the middle part 32. The number of inclined surfaces 34 is the same as the number of side surfaces 331. Here, an example in which there are six inclined surfaces 34 is shown, but the number of inclined surfaces 34 is not limited to six.

[0054] If the inclined surface 34 is not provided, specifically, if the connection portion between the outer circumferential surface 32a of the middle portion 32 of the metal case 30 and the side surface 331 of the rear end portion 33 is stepped, the stress applied to the metal case 30 is likely to concentrate on the step. Therefore, by providing the inclined surface 34 connecting the middle portion 32 and the rear end portion 33 of the metal case 30, the stress applied to the metal case 30 can be dispersed, and the durability of the heater 1 can be improved.

[0055] An example of the inclined surface 34 is shown in Fig. 10. As shown in Fig. 10, the semicircular inclined surface 34b is provided between the side surface 331b of the rear end portion 33 and the middle portion 32, so that the stress applied to the metal case 30 can be dispersed and the durability of the heater 1 can be improved.

[0056] It is not necessary that the side surface 331 of the rear end portion 33 of the metal case 30 and the outer peripheral surface 32a of the middle portion 32 of the metal case 30 are connected by the inclined surface 34. For example, the connection portion between the outer peripheral surface 32a of the middle portion 32 of the metal case 30 and the side surface 331 of the rear end portion 33 may be curved or stepped.

[0057] 2, the boundary line between the side surface 331 of the rear end portion 33 of the metal case 30 and the middle portion 32 of the metal case 30 may be a curved line in a side view. In other words, of the multiple sides constituting the side surface 331 of the rear end portion 33, the side adjacent to the middle portion 32 may be a curved line. Specifically, such a side may be a convex curve that protrudes toward the middle portion 32.

[0058] In this way, by making the boundary between the rear end 33 and the middle part 32 of the metal case 30, which is susceptible to stress, curved, it is possible to distribute the stress applied to the metal case 30 in the longitudinal direction. Also, by not providing corners, stress is less likely to concentrate, and the durability of the heater 1 can be improved.

[0059] In addition, when the inclined surface 34 is provided between the side surface 331 of the rear end portion 33 and the outer circumferential surface 32a of the middle portion 32 as described above, the boundary portion between the rear end portion 33 and the middle portion 32 can be curved by forming the inclined surface 34 in a crescent shape as shown in Fig. 11. By making the center portion of the inclined surface 34 sandwiched between the two ridge portions 332 the center portion of the crescent shape, both ends of the crescent shape can be the intersections of the inclined surface 34 and the ridge portions 332. This makes the area of ​​the inclined surface 34 smaller from the center toward both ends, and further distributes the stress applied to the ridge portions 332 of the metal case 30.

[0060] The boundary line between the side surface 331 of the rear end portion 33 of the metal case 30 and the middle portion 32 of the metal case 30 does not necessarily have to be a curve when the side surface 331 is viewed from the front. For example, as shown in Figures 6 and 9, the boundary line between the side surface 331 or the side surface 331a of the rear end portion 33 of the metal case 30 and the middle portion 32 of the metal case 30 may be a straight line along the X-axis direction when the side surface 331 or the side surface 331a is viewed from the front.

[0061] Furthermore, the shapes of the inner circumferential surface 33b of the rear end portion 33 and the inner circumferential surface 32b of the middle portion 32 may be the same, in other words, the inner circumferential surface 33b of the rear end portion 33 and the inner circumferential surface 32b of the middle portion 32 may be formed flush.

[0062] As described above, the outer peripheral surface 33a of the rear end portion 33 of the metal case 30 according to the first embodiment includes a plurality of side surfaces 331 that are continuous in the circumferential direction of the metal case 30, and a ridge portion 332 that is located between two adjacent side surfaces 331. This makes it difficult for the rear end portion 33 of the metal case 30 to be twisted, compared to a case in which the outer peripheral surface 33a of the rear end portion 33 of the metal case 30 does not have the ridge portion 332. When twisting deformation is thus difficult to occur, stress is less likely to be applied to the joint between the metal case 30 and the ceramic body 11, and the durability of the heater 1 can be improved.

[0063] <Second embodiment> Fig. 12 is an explanatory diagram of a metal case 30 according to the second embodiment, seen from the rear end portion 33 side. Fig. 13 is an example of a cross-sectional view taken along line XIII-XIII in Fig. 12. Fig. 14 is an explanatory diagram of another example of a metal case 30 according to the second embodiment, seen from the rear end portion 33 side. Fig. 15 is an example of a cross-sectional view taken along line XV-XV in Fig. 14.

[0064] The thickness of the rear end portion 33 of the metal case 30 may be thinner than the thickness of the middle portion 32. This can further reduce the stress applied to the rear end portion 33, thereby improving the durability of the heater 1. For example, as shown in Figs. 12 and 13, by forming the rear end portion 33 of the metal case 30 so that the inner diameter thereof is larger than the inner diameter of the middle portion 32, the thickness of the rear end portion 33 can be thinner than the thickness of the middle portion 32.

[0065] Furthermore, for example, as shown in Figures 14 and 15, by forming the outer peripheral surface 33e of the rear end portion 33 of the metal case 30 to be radially inward of the metal case 30 relative to the outer peripheral surface 32a of the middle portion 32, the thickness of the rear end portion 33 can be made thinner than the thickness of the middle portion 32.

[0066] The thickness of the rear end portion 33 may be made thinner than the thickness of the middle portion 32 by combining the above-mentioned two techniques.

[0067] <Other embodiments> In one embodiment, (1) a heater (for example, heater 1) includes a ceramic body (for example, ceramic body 11), a heating resistor (for example, heating resistor 14), and a metal case (for example, metal case 30). The ceramic body is rod-shaped. The heating resistor is embedded in the front end (for example, front end 12) side of the ceramic body. The metal case is cylindrical and surrounds at least the rear end (for example, rear end 13) side of the ceramic body to hold the ceramic body. An outer peripheral surface (for example, outer peripheral surface 33a) of a rear end (for example, rear end 33) of the metal case includes a plurality of side surfaces (for example, side surfaces 331) that are continuous in the circumferential direction of the metal case, and a ridge portion (for example, ridge portion 332) located between two adjacent side surfaces.

[0068] (2) In the heater of (1) above, the rear end surface (335, for example) of the metal case may be formed point-symmetrically with respect to the center of the rear end surface (center 335a, for example).

[0069] (3) In the heater of (2) above, the rear end surface may be hexagonal.

[0070] (4) In the heater according to any one of (1) to (3) above, the ridge portion may extend parallel to the axial direction of the metal case.

[0071] (5) In any one of the heaters (1) to (4) above, the middle portion of the metal case (for example, middle portion 32) may be cylindrical and may further include an inclined surface (for example, inclined surface 34) that connects the side surface of the rear end portion and the outer peripheral surface of the middle portion (for example, outer peripheral surface 32a) and inclines in a direction away from the central axis of the metal case as it goes from the rear end portion to the middle portion.

[0072] (6) In the heater of any one of (1) to (5) above, the middle part of the metal case may be cylindrical, and the boundary between the side surface and the middle part may be a curved line when the side surface is viewed from the front.

[0073] (7) In the heater of any one of (1) to (6) above, the middle part of the metal case may be cylindrical, and the wall thickness of the rear end part may be thinner than the wall thickness of the middle part.

[0074] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. Indeed, the above-described embodiments may be embodied in various forms. In addition, the above-described embodiments may be omitted, substituted, or modified in various forms without departing from the scope and spirit of the appended claims. [Explanation of symbols]

[0075] 1 Heater 10 Heater body 11 Ceramic body 14 Heating resistor 15 Lead Wire 30 Metal Case 31 Tip 32 Middle part 33 Rear end 40 Bonding material 331 Side 332 Ridge 335 Rear end surface

Claims

1. A rod-shaped ceramic body; a heating resistor embedded in the tip side of the ceramic body; a cylindrical metal case that surrounds at least the rear end side of the ceramic body and holds the ceramic body; Equipped with The outer peripheral surface of the rear end of the metal case is A plurality of side surfaces that are continuous in a circumferential direction of the metal case; a ridge portion located between two adjacent side surfaces; A heater comprising:

2. The heater according to claim 1 , wherein the rear end surface of the metal case is formed point-symmetrically with respect to a center of the rear end surface.

3. The heater of claim 2 , wherein the rear end surface is hexagonal.

4. The heater according to claim 1 , wherein the ridge portion extends parallel to an axial direction of the metal case.

5. The intermediate portion of the metal case is cylindrical, 3. The heater according to claim 1, further comprising an inclined surface that connects the side surface of the rear end portion and an outer circumferential surface of the middle portion, and that inclines in a direction away from the central axis of the metal case as it moves from the rear end portion to the middle portion.

6. The intermediate portion of the metal case is cylindrical, The heater according to claim 1 , wherein a boundary line between the side surface and the middle portion is a curve when the side surface is viewed from the front.

7. The intermediate portion of the metal case is cylindrical, 3. The heater according to claim 1, wherein a thickness of the rear end portion is thinner than a thickness of the middle portion.

Images