JP4699816B2 - Manufacturing method of ceramic heater and glow plug - Google Patents

Description

  The present invention relates to a method for manufacturing a ceramic heater and a glow plug. More specifically, the present invention relates to a method for manufacturing a ceramic heater and a glow plug that can more reliably obtain a high bending strength even when fired at a relatively low temperature.

A sintered body containing silicon nitride and a conductive ceramic component such as tungsten carbide is easy to control resistance, has high bending strength, and has excellent durability. It is used as. Among these uses, for example, when used as a heating resistor for a glow plug ceramic heater, a particularly high bending strength is required, but it is not easy to obtain the bending strength stably and reliably.
When manufacturing the heat generating _{resistor, Al 2 O 3 -Y 2 O} 3 system sintering _aid, a relatively low temperature in the liquid phase, such as _{Er 2 O 3 -V 2 O 5} -WO 3 based sintering aid is The type of sintering aid that is formed is used. Further, a technique using a rare earth oxide and silicon oxide as a sintering aid as the operating temperature is increased is also known (see Patent Document 1 below).

JP 2000-327426 A

Of these, it was found that when a sintering aid containing a rare earth oxide and silicon oxide was used, higher bending strength was obtained even at relatively low temperature firing, and the variation could be reduced.
However, with the recent increase in temperature and load on ceramic heaters, there is a need for a method that can be fired at a lower temperature, further suppress variation, and stably obtain a ceramic having sufficient bending strength.
An object of this invention is to provide the manufacturing method of a ceramic heater and a glow plug which can obtain a high bending strength more reliably even when it is fired at a low temperature.

The present invention is as follows.
(1) A method of manufacturing a ceramic heater comprising an insulating substrate and a heating resistor embedded in the insulating substrate,
An unfired heating resistor containing silicon nitride, a conductive ceramic component, and RE ₂ Si ₂ O ₇ as a sintering aid (where “RE” is a rare earth element) and fired to form the heating resistor. Is a method of manufacturing a ceramic heater comprising a firing step of firing in a state where it is fired and embedded in an unfired insulating substrate that becomes the insulating substrate,
The RE is at least one of Er, Yb, and Lu.
(2) the amount of the electrically conductive ceramic component, the sum of the silicon nitride and the above conductive ceramic component the _RE 2 _Si 2 _{O 7} in case of a 100 mol%, a 35～65Mol%,
The amount of the _RE 2 _Si 2 _{O 7} is a sum of the silicon nitride and the above conductive ceramic component the _RE 2 _Si 2 _{O 7} in case of a 100 mol%, is 0.5～5.0Mol% above The manufacturing method of the ceramic heater as described in (1).
( 3 ) The manufacturing method of the ceramic heater as described in said (1) or (2) whose baking temperature in the said baking process is 1730-1830 degreeC.
( 4 ) A metal shell, a fixed cylinder fitted into one end of the metal fitting, and a ceramic heater that is fitted into the fixed cylinder and has a tip projecting from the end surface of the fixed cylinder. A glow plug comprising a ceramic heater obtained by the method for producing a ceramic heater according to any one of (1) to (3) .

According to the method for producing a ceramic heater of the present invention, a ceramic heater having a high bending strength can be obtained more reliably even when fired at a low temperature. Furthermore, this ceramic heater can be obtained by firing in a wide temperature range up to a lower temperature range. Moreover, the obtained ceramic heater can exhibit high durability, and can be rapidly heated with low resistance. In addition, since excellent performance is exhibited even at low temperature firing, the manufacturing cost can be efficiently reduced.
RE is Er, since at least one of Yb and Lu, it is possible to reliably obtain the bending strength higher when fired at a low temperature.
When the firing temperature is 1730 to 1830 ° C., particularly high bending strength can be obtained particularly reliably, and furthermore, low resistance can be obtained more reliably.
According to the glow plug of the present invention, high durability and high reliability can be exhibited.

[1] Ceramic heater An example of the ceramic heater 1 obtained by the production method of the present invention will be described with reference to FIG. FIG. 1 is a longitudinal sectional view of the ceramic heater 1. The ceramic heater 1 has an approximately cylindrical insulating base 11 having a tip 11a formed in a hemispherical shape. A substantially U-shaped heating resistor 12 is embedded in the front end portion 11a of the insulating base 11, and a pair of lead wires 13a and 13b extend from the heating resistor 12 toward the rear end side. Yes. The other ends of the lead wires 13a and 13b are exposed from the insulating substrate 11.

  The insulating substrate 11 is usually made of an insulating ceramic component. Although the kind of this component is not specifically limited, For example, silicon nitride, sialon, aluminum nitride, etc. are mentioned, It is preferable to use silicon nitride among these. These insulating ceramic components may be used alone or in combination of two or more. The content of the insulating ceramic component contained in the insulating substrate 11 is not particularly limited, but is 85% by mass or more (more preferably 90% by mass or more, 100% by mass) when the entire insulating substrate 11 is 100% by mass. It may be preferable.

In addition, the insulating substrate 11 can contain a sintering aid in addition to the insulating ceramic component. For example, RE ₂ Si ₂ O ₇ (this disilicate compound containing a rare earth element is hereinafter also simply referred to as “disilicate”), RE ₂ SiO ₅ , oxide serving as an oxygen supply source, and metals contained therein Examples thereof include a double oxide containing two or more elements. Furthermore, the electroconductive ceramic component which comprises the heating resistor 12 mentioned later is mentioned. Although content of an electroconductive ceramic component is not specifically limited, Usually, when the insulating base | substrate 11 whole is 100 mass%, it is 5 mass% or less. Within this range, the thermal expansion difference with the heating resistor can be reduced. In addition, borides of metal elements such as W, Ta, Nb, Ti, Mo, Zr, Hf, V, and Cr may be contained.

The heating resistor 12 contains silicon nitride, a conductive ceramic component, and RE ₂ Si ₂ O ₇ (where “RE” is a rare earth element).
The amount of silicon nitride contained in the heating resistor 12 is not particularly limited, but silicon nitride is 34.5-60 mol% when the total of silicon nitride, a conductive ceramic component described later, and disilicate is 100 mol%. (More preferably 39 to 57.5 mol%, still more preferably 43.5 to 53 mol%) is preferably contained. This is because, in this range, a silicon nitride conductive ceramic having a particularly low specific resistance and a high bending strength can be obtained.

Examples of the conductive ceramic component include carbides including one or more metal elements such as W, Ta, Nb, Ti, Mo, Zr, Hf, V, and Cr, and one of these metal elements. Alternatively, a silicide containing two or more kinds and a nitride containing one or more of these metal elements can be used. Examples of the carbide include WC, W ₂ C, TaC, Ta ₂ C, NbC, TiC, MoC, Mo ₂ C, ZrC, HfC, VC, V ₂ C, and Cr ₃ C ₂ . Further, as the silicide include _{MoSi 2, W 2 Si 3,} WSi 2, WSi 3, V 2 Si, VSi 2, Cr 3 Si 2, CrSi, Cr 2 Si and CrSi ₂ or the like. Furthermore, examples of the nitride include WN, TaN, NbN, TiN, MoN, ZrN, HfN, VN, and CrN. These conductive ceramic components may be used alone or in combination of two or more.

The conductivity of the conductive ceramic component is not particularly limited, but a material having a specific resistance value of 5000 μΩ · cm or less at room temperature (25 ° C.) is preferable.
In addition, the conductive ceramic component preferably has a small difference in thermal expansion coefficient from silicon nitride. For example, the difference in thermal expansion coefficient from silicon nitride is 5 × 10 ⁻⁶ / ° C. or less (more preferably 3 × 10 ^−6. / ° C. or less) is preferred. Thereby, the exothermic resistor 12 can obtain an excellent temperature rise characteristic capable of raising the temperature to a temperature of 1000 ° C. or higher in a short time (for example, 1 to 8 seconds).
Furthermore, the conductive ceramic component preferably has a high melting point. For example, the melting point is preferably 1850 ° C. or higher (more preferably 2000 ° C. or higher). Accordingly, when used as the heating resistor 12, high temperature durability can be exhibited. And tungsten carbide is mentioned as an optimal electroconductive ceramic component which has these characteristics together.

  The amount of the conductive ceramic component contained in the heating resistor 12 is not particularly limited, but when the total of silicon nitride, the conductive ceramic component, and disilicate is 100 mol%, the conductive ceramic component is 35 to 65 mol%. (More preferably 40 to 60 mol%, still more preferably 45 to 55 mol%) is preferably contained. Within this range, particularly when used as a heating resistor, excellent temperature rise characteristics that can raise the temperature to 1000 ° C. or higher in a short time (eg, 1 to 8 seconds) can be obtained.

The disilicate is a component that becomes a sintering aid for the ceramic raw material containing silicon nitride. At least one of Er, Yb, and Lu is used as the kind of RE that is a rare earth element constituting the disilicate.
Disilicate can be used either as a single ^RE ₁ 2 _Si 2 _{O 7,} including one rare earth element _{^{RE 1, RE 1 2 Si 2}} O 7 and other rare earth elements RE ² comprising one rare earth element RE ¹ Two kinds of disilicates with RE ² ₂ Si ₂ O ₇ containing may be used together, and three or more kinds of disilicates may be used together. Further, RE ¹ RE ² Si ₂ O ₇ containing two kinds of rare earth elements RE ¹ and RE ² at the same time may be used.

  The amount of disilicate contained in the heating resistor 12 is not particularly limited, but when the total of silicon nitride, conductive ceramic component, and disilicate is 100 mol%, the disilicate is 0.5 to 5.0 mol%. (More preferably 1.0 to 2.5 mol%, still more preferably 1.5 to 2.0 mol%) is preferably contained. Within this range, the effect of containing disilicate can be obtained. That is, even when firing at a low temperature, the variation in the bending strength of the product can be kept small.

In addition to the silicon nitride, the conductive ceramic component, and the disilicate, the heating resistor 12 may contain other components. When other components are contained, examples of the other components include oxides that serve as an oxygen supply source during firing. Examples of the oxide serving as the oxygen supply source include oxides of Group 4 elements, Group 5 elements, and Group 6 elements. That is, for example, V ₂ O ₅ , Nb ₂ O ₃ , Ta ₂ O ₃ , Cr ₂ O ₃ , MoO ₃ and WO ₃ . These may use only 1 type and may use 2 or more types together. In addition, borides containing one or more metal elements of W, Ta, Nb, Ti, Mo, Zr, Hf, V, Cr, and the like can be given. When these borides are contained, it is preferable that the thermal expansion coefficient difference with silicon nitride is small as in the case of the conductive ceramic component, and that the melting point is high. Further, for example, other rare earth oxides (such as RE ₂ O ₃ ) excluding the disilicate, silicon oxide, aluminum nitride, alumina and the like may be contained. Only 1 type may contain these and 2 or more types may contain.

  The material constituting the lead wires 13a and 13b is not particularly limited as long as it has conductivity, and examples thereof include W, Re, Ta, Mo, and Nb. These may use only 1 type and may use 2 or more types together. Of these, tungsten is preferably used because of its high heat resistance. In the case of using tungsten, it is preferable to contain 90% by mass or more (more preferably 95% or more, particularly preferably only tungsten) of tungsten when the entire lead wires 13a and 13b are 100% by mass. The wire diameters of the lead wires 13a and 13b are not particularly limited, but may be 0.05 to 0.9 mm (preferably 0.1 to 0.7 mm, more preferably 0.2 to 0.5 mm). .

The connection method between the lead wires 13a and 13b and the heating resistor 12 is not particularly limited, but is normally connected by embedding one end of the lead wires 13a and 13b in the heating resistor 12. Moreover, the electrical connection after baking can also be ensured only by contact between the outer surfaces without being embedded.
On the other hand, the other end portions of the lead wires 13 a and 13 b are exposed from the rear end portion 11 b of the insulating base 11 of the ceramic heater 1.
In addition, the shape of the lead wires 13a and 13b is not particularly limited. For example, the lead wires 13a and 13b may be formed of straight lines having bent portions as shown in FIG.
The lead wires 13a and 13b are usually made of a refractory metal that hardly changes before and after the firing step. Accordingly, the lead wires 13a and 13b are also disposed in the unfired ceramic heater 1 ′. However, for example, a material that does not have conductivity before firing or has different conductive characteristics compared to after firing and can function as the lead wires 13a and 13b by firing may be used.

The ceramic heater 1 obtained by the manufacturing method described later can have a bending strength of 1200 MPa or more and a bending strength variation (3σ) of 300 or less.
This bending strength is based on a method for measuring the bending strength in Examples described later. Usually, the bending strength of the ceramic heater 1 where the highest bending strength is required can be 1200 MPa or more (further 1200 to 1700 MPa, particularly 1250 to 1700 MPa, more particularly 1300 to 1700 MPa). Within this range, excellent durability can be exhibited even when used as a ceramic heater for glow plugs.

Moreover, the variation in the bending strength of the ceramic heater 1 obtained can be suppressed small. That is, for example, the variation (3σ) can be 300 or less.
Moreover, even if the firing temperature is particularly low, these effects can be obtained. That is, for example, when the firing temperature is between 1730 and 1790 ° C., the bending strength is 1250 to 16901 MPa, and the variation (3σ) can be suppressed to 150 to 230. Furthermore, when the firing temperature is between 1730 and 1775 ° C., the bending strength is 1350 to 1690 MPa, and the variation (3σ) can be suppressed to 180 to 230. In particular, when the firing temperature is between 1730 and 1760 ° C., the bending strength is 1390 to 1690 MPa, and the variation (3σ) can be suppressed to 180 to 230.
Therefore, the ceramic heater 1 having excellent performance can be manufactured reliably and stably.

Furthermore, the resistance value of the ceramic heater 1 can be changed depending on the kind and content of the conductive ceramic component contained. For example, the resistance value is 350 to 600 mΩ at a firing temperature of 1730 to 1790 ° C. The variation (3σ) can be suppressed to 30-90. Furthermore, it can be set to a resistance value of 350 to 550 mΩ at a firing temperature of 1730 to 1775 ° C., and the variation (3σ) can be suppressed to 30 to 40. In particular, at a firing temperature of 1730 to 1760 ° C., the resistance value can be 350 to 500 mΩ, and the variation (3σ) can be suppressed to 25 to 30.
Therefore, the ceramic heater 1 having excellent performance can be manufactured reliably and stably.

[2] Manufacturing Method of Ceramic Heater Next, a manufacturing method of the ceramic heater 1 will be described.
The method for manufacturing a ceramic heater according to the present invention is obtained by firing and insulating an unfired heating resistor 12 ′ containing silicon nitride, a conductive ceramic component, and RE ₂ Si ₂ O ₇ and being fired to become a heating resistor 12. And a firing step of firing in a state of being embedded in an unsintered insulating substrate 11 ′ to be a conductive substrate 11.

  The unsintered insulating base 11 ′ is fired to become the insulating base 11. This unsintered insulating base 11 ′ contains the insulating ceramic component that constitutes the insulating base 11 described above. Furthermore, the conductive ceramic component and the like constituting the heating auxiliary component and the heating resistor 12 can be contained. These various components are blended in the unfired insulating substrate 11 ′ so as to have a ratio in the insulating substrate 11.

Further, the unfired heating resistor 12 ′ is fired to become the heating resistor 12. The unsintered heating resistor 12 ′ contains silicon nitride, a conductive ceramic component, and disilicate that constitute the heating resistor 12 described above. In particular, by containing disilicate, variation in the bending strength of the heating resistor 12 obtained even when fired at a low temperature can be suppressed.
Further, the unfired heating resistor 12 ′ includes an oxide that serves as an oxygen supply source at the time of firing, a boride containing various metal elements, the other rare earth oxides excluding disilicate, the silicon oxide, Aluminum nitride, the above alumina and the like can be contained. These various components are blended in the unfired heating resistor 12 ′ so as to have a ratio in the heating resistor 12.

The firing step is a step of firing in a state where the unfired heating resistor 12 ′ is embedded in the unfired insulating base 11 ′. There are no particular limitations on the firing conditions in this firing step, but usually pressure firing is performed in an inert atmosphere.
An inert atmosphere is an atmosphere inert to silicon nitride, conductive ceramic components and disilicate. That is, for example, an atmosphere mainly containing nitrogen and a rare gas (such as argon) (usually 99.9% by volume or more of the whole atmosphere), and oxygen is usually 0.1% or less (preferably 0% of the whole atmosphere). .01% or less).

  Pressure firing is a firing method in which heating is performed while applying pressure. The pressure applied during firing is not particularly limited, but is usually 20 MPa or more (preferably 200 to 500 MPa, more preferably 200 to 300 MPa). Moreover, although baking temperature is not specifically limited, Usually, it is 1700-1850 degreeC (preferably 1720-1830 degreeC, More preferably, 1730-1800 degreeC).

  These pressurizing pressures and firing temperatures can be combined. That is, for example, the pressurizing pressure can be 200 to 500 MPa and the firing temperature can be 1700 to 1850 ° C., preferably 200 to 300 MPa and 1730 to 1800 ° C.

  In the manufacturing method of the ceramic heater of this invention, other processes can be provided besides the said baking process. Other processes include a raw material preparation process (including a powder adjustment process, a granulation process, etc.), a molding process (including an unfired insulating base body forming process, an unfired heating resistor forming process, an integration process, etc.), a preliminary process Examples thereof include a firing step (including an organic vehicle removing step).

  The raw material preparation step is a step of preparing a raw material containing each component. That is, for example, a powder adjustment step in which each component powder has a predetermined particle size, a step of preparing a forming raw material to be an unfired insulating base 11 ′, a silicon nitride powder, a conductive ceramic component powder, a disilicate, and the like Steps of mixing a sintering aid powder and adding an organic component such as a binder to prepare a forming raw material to become an unfired heating resistor 12 ', a granulating step of granulating the forming raw material, etc. It is done.

  In the raw material preparation step, a binder, a solvent, and the like can be used in addition to a powder containing silicon nitride as a raw material for forming the unfired insulating substrate 11 ′. Similarly, a binder, a solvent, and the like can be used as a raw material for forming the unfired heating resistor 12 'in addition to the powder containing silicon nitride, conductive ceramic, and sintering aid.

  The forming step is a step of forming the raw material obtained in the raw material preparation step into a desired shape such as an unfired insulating substrate 11 ′ and an unfired heating resistor 12 ′, an unfired insulating substrate 11 ′, and an unfired material. This is a process including an integration process in which the heating resistor 12 ′ and the lead wires 13a and 13b are integrated to form an unfired ceramic heater 1 ′.

  The unsintered insulating substrate forming step for forming the unsintered insulating substrate 11 ′ may be performed by any method, for example, by a method such as compression molding, injection molding, or print molding. Of these, compression molding is usually used. Further, the unsintered insulating substrate 11 ′ can be formed as a halved mold obtained by compacting a raw material powder for an insulating substrate.

  On the other hand, the unfired heating resistor forming step for forming the unfired heating resistor 12 'may be performed by any method, for example, injection molding, compression molding, printing molding, or the like. Of these, injection molding is usually used. That is, for example, by setting the lead wires 13a and 13b in the molding machine in advance and injecting the raw material for the unfired heating resistor into the molding machine, the lead wires 13a and 13b are not fitted in an optimal manner. A fired heating resistor 12 'can be obtained.

  In the integration step (embedding step of the unfired heating resistor 12 '), the unfired heating resistor in which the lead wires 13a and 13b are already fitted between the two halves of the unfired insulating base 11'. By pressing after sandwiching the body 12 ', a molded product in which the unsintered insulating base 11', the unsintered heating resistor 12 'and the lead wires 13a and 13b are integrated (embedded) can be obtained. Furthermore, after that, the integrated molded product can be pressurized at a pressure of 5 to 12 MPa as necessary.

The pre-baking step is a step of removing the organic components by pre-baking from the molded product obtained in the forming step to obtain the unfired ceramic heater 1 ′. In this preliminary firing step, an inert atmosphere is preferably used as the firing atmosphere.
These other processes may use only 1 type, or may use 2 or more types together.

[3] Glow Plug Next, an example of the glow plug 2 of the present invention will be described with reference to FIG. FIG. 2 is a longitudinal sectional view of the glow plug. This glow plug mainly includes a metal shell 22, a fixed cylinder 21, and a ceramic heater 1. The glow plug 2 is provided with the ceramic heater 1 so that the heating resistor 12 is disposed on the tip side. The ceramic heater 1 is inserted and held in a metal fixed cylinder 21. At the same time, one lead wire 13b exposed on the surface of the insulating substrate 11 is electrically connected to the fixed cylinder 21 by a brazing material. On the other hand, the fixed cylinder 21 is fixed to the front end side of the metal shell 22 by brazing. The other lead wire 13 a of the ceramic heater 1 is electrically connected to the lead coil 24 by brazing, and further connected to the center shaft 25 and connected to the terminal fitting 26. A mounting screw portion 23 for attaching the glow plug to the internal combustion engine is threaded on the outer periphery of the metal shell 22, and a hexagonal tool engaging portion 27 for applying an impact wrench when further mounting is formed. Yes.

Hereinafter, the present invention will be described specifically by way of examples.
[1] Manufacture of ceramic heater 1 (1) Preparation of mixed powder Ratio shown in Table 1 of silicon nitride powder, tungsten carbide powder (purity 99%, average particle size 0.7 μm), and sintering aid powder And mixed for 72 hours to obtain mixed powders of Example 1, Comparative Example 1 and Comparative Example 2.
Silicon nitride powder: purity 99% or more, average particle size 1 μm
Conductive ceramic component powder Tungsten carbide: Purity 99% or more, average particle size 0.7μm
Sintering aid powder Er ₂ Si ₂ O ₇ powder Er ₂ O ₃ powder and mixed powder of the mixed powder Er ₂ O ₃ powder and _V 2 _{O 5} powder and WO ₃ powder and SiO ₂ powder

(2) Production of Unfired Heating Resistor 12 ′ When the obtained mixed powder of Example 1, Comparative Example 1 and Comparative Example 2 and this mixed powder were taken as 100% by mass, 7% by mass of wax (organic Binder), 3% by mass of plasticizer, and 3% by mass of solvent were put into a kneader and kneaded for 4 hours. Thereafter, the obtained kneaded product is cut into pellets, which are put into an injection molding machine in which tungsten lead wires 13a and 13b are set and molded, and the lead wires 13a and 13b are fitted to both ends. In addition, an unfired heating resistor 12 ′ to be a substantially U-shaped heating resistor 12 was produced.

(3) Production of unsintered insulating substrate 11 ′ To 89% by mass of silicon nitride powder, 8% by mass of Er ₂ O ₃ powder, 1% by mass of V ₂ O ₅ powder and 2% by mass of a sintering aid WO ₃ powder, 100% by weight of water as a solvent, wet mixed for 40 hours, granulated by spray dryer method, and unbaked insulation consisting of two halves with this granulated powder A substrate 11 ′ was produced.

(4) Embedding of the unsintered heat generating resistor 12 'in the unsintered insulating substrate 11' A recess (unsintered heat generating resistor 12 'between the two halves of the unfired insulating substrate 11' thus obtained. The unsintered heating resistor 12 ′ including the lead wires 13 a and 13 b obtained in the above (1) was placed in the (recessed part). Thereafter, these were integrally pressed at a pressure of 7 MPa to obtain a molded body to be an unfired ceramic heater.

(5) Pre-baking step and firing step The obtained molded body (molded body in which the unfired heating resistor 12 'is embedded in the unfired insulating base 11') is heated (pre-fired) at 600 ° C. Thus, organic components and the like were removed to obtain an unfired ceramic heater 1 ′.
Next, the obtained unfired ceramic heater 1 ′ was set on a graphite pressing die, and each temperature was 1725 ° C., 1745 ° C., 1765 ° C., 1791 ° C., 1805 ° C., and 1825 ° C. in a nitrogen atmosphere. Firing (main firing) was performed at a pressure of 25 MPa for 1.5 hours to obtain a sintered body.
And the outer surface of each obtained sintered compact was grind | polished, and each end surface of the lead wire 13 (13a and 13b) was exposed to the outer surface of an insulating base | substrate, and the ceramic heater 1 shown in FIG. 1 was manufactured. .

[2] Evaluation of ceramic heater 1 (1) Measurement of flexural strength 6 pieces obtained using the mixed powder of Experimental Example 1, 6 pieces obtained using the mixed powder of Comparative Example 1, and Comparative Example The bending strength of each of the six ceramic heaters 1 obtained using the mixed powder of No. 2 was measured according to the three-point bending strength according to JIS R 1601. The span at this time was 12 mm, and the crosshead speed was 0.5 mm / min. Further, the load point was a point of the heater portion 7.5 mm from the tip. The results are shown in FIGS. Further, the minimum value of the bending strength and 3σ at each firing temperature are shown in Table 2, and Table 2 is graphed and shown in FIG.

(2) Measurement of resistance value 6 obtained using the mixed powder of Experimental Example 1, 6 obtained using the mixed powder of Comparative Example 1, and obtained using the mixed powder of Comparative Example 2 Further, the resistance values of the six ceramic heaters 1 were measured. At the time of measurement, a resistance value was measured by applying a measurement terminal of a milliohm meter to each end face of the lead wires 13a and 13b exposed on the outer surface of the insulating substrate 11. The results are shown in FIGS.
Each ceramic heater 1 is subjected to the measurement of the bending strength after measuring the resistance value.

  From the result of FIGS. 3-5, in the ceramic heater 1 obtained using the mixed powder of the comparative example 2 (refer FIG. 5), dispersion | variation is large and the firing temperature which can obtain the bending strength of 1200 MPa or more reliably is It is very high at 1825 ° C. On the other hand, the ceramic heater 1 obtained using the mixed powder of Comparative Example 1 (see FIG. 4) has a small variation at a firing temperature of 1785 ° C. or higher and can reliably ensure a bending strength of 1200 MPa or higher. I understand. However, this firing temperature is relatively high.

  In comparison with Comparative Examples 1 and 2, the ceramic heater 1 obtained using the mixed powder of Example 1 (see FIG. 3) has a large variation at 1725 ° C., and a ceramic heater 1 of slightly less than 1200 MPa is obtained. However, it can be seen that at a temperature of 1745 ° C. or higher, the bending strength of 1200 MPa or higher can be ensured with little variation. In particular, in Comparative Example 2, a ceramic heater of less than 1200 MPa was obtained. Excellent results were obtained at both temperatures of 1745 ° C. and 1765 ° C. That is, even in firing at these low temperatures, in Example 1, a very high bending strength of 1300 MPa or more can be reliably ensured. In particular, the difference at 1745 ° C. is conspicuous with respect to Comparative Example 2. In Example 1, it can be seen that the bending strength of 1300 MPa or more can be ensured even when firing at a low temperature of 1745 ° C.

Further, from Table 2 and FIG. 9, Comparative Example 1 was excellent in that the minimum value of bending strength (Δ in FIG. 9) was large and the bending strength 3σ (Δ in FIG. 9) was small at a firing temperature of 1785 ° C. Although the performance is exhibited, the minimum bending strength (Δ in FIG. 9) tends to decrease at a firing temperature of 1785 ° C. or lower, and 3σ (Δ in FIG. 9) tends to increase. .
On the other hand, although Example 1 has almost the same performance as Comparative Example 1 at a firing temperature of 1785 ° C., the minimum bending strength (Δ in FIG. 9) is lower at a firing temperature of 1785 ° C. than that of Comparative Example 1. It can be seen that the bending strength 3σ (Δ in FIG. 9) is small.

  That is, Example 1 and Comparative Example 1 were manufactured by blending the same amount of the same elements when the components used as the sintering aid were converted at the element level. However, in Example 1, a large bending strength is stably obtained with a small variation in a wide low temperature range of 1745 to 1785 ° C. as compared with Comparative Example 1 by blending in advance as a predetermined composition. Therefore, it can be seen that the firing temperature can be selected in a wide temperature range in consideration of other factors in the low temperature range. In particular, a remarkable change is observed in low-temperature firing at 1765 ° C. or lower. That is, the bending strength is greatly improved and the variation is greatly reduced. Therefore, it can be seen that by using a sintering aid having a predetermined composition in advance, a product superior in low temperature firing can be obtained more reliably in a wider temperature range (particularly in a low temperature range).

  Moreover, it can be seen from FIGS. 6 to 8 that the resistance value of the ceramic heater 1 varies greatly in Comparative Example 2. On the other hand, in Comparative Example 1, a substantially stable resistance value was obtained except for those fired at 1725 ° C. Similarly, it can be seen that a stable resistance value was obtained in Example 1 except for the one fired at 1725 ° C.

In the present invention, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention depending on the purpose and application. For example, even if the conductive ceramic is not WC but MoSi ₂ or the like, a heating resistor having a small specific resistance and a high bending strength can be formed as in the case of WC. The ceramic heater 1 of the present invention can be used not only for glow plugs but also for various heaters for heating and the like.

Although the application of the ceramic heater obtained by this manufacturing method is not specifically limited, For example, it is widely used as various ignition sources, a heating source, etc. Examples of the ignition source include a glow plug ceramic heater (heating resistor) which is an ignition source of a diesel engine, an ignition ceramic heater of a heating apparatus (such as a stove), and the like. Moreover, the heater for heating various fluids is mentioned as a heating source. That is, for example, a water heater or the like can be mentioned.
Furthermore, the glow plug of the present invention can be used as a glow plug for a diesel engine.

It is sectional drawing which shows typically an example of the ceramic heater 1 of this invention. It is sectional drawing which shows typically an example of the glow plug 2 of this invention. 3 is a graph showing a correlation between a firing temperature and a bending strength of the ceramic heater 1 according to Example 1; 5 is a graph showing a correlation between a firing temperature and a bending strength of a ceramic heater 1 according to Comparative Example 1. 6 is a graph showing a correlation between a firing temperature and a bending strength of a ceramic heater 1 according to Comparative Example 2. 3 is a graph showing a correlation between a firing temperature and a resistance value of the ceramic heater 1 according to Example 1. 5 is a graph showing a correlation between a firing temperature and a resistance value of a ceramic heater 1 according to Comparative Example 1. 6 is a graph showing a correlation between a firing temperature and a resistance value of a ceramic heater 1 according to Comparative Example 2. It is a graph which shows the correlation with the firing temperature of the ceramic heater 1 which concerns on Example 1, and Comparative Examples 1 and 2, the minimum value of bending strength, and 3 (sigma) of bending strength.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1; Ceramic heater, 11; Insulating base | substrate, 12; Heating resistor, 13a, 13b; Lead wire, 2; Glow plug, 21; Main metal fitting, 22; Fixed cylinder, 23; 25; middle shaft, 26; terminal fitting, 27; tool engaging portion

Claims (4)

A ceramic heater manufacturing method comprising: an insulating substrate; and a heating resistor embedded in the insulating substrate,
An unfired heating resistor containing silicon nitride, a conductive ceramic component, and RE ₂ Si ₂ O ₇ as a sintering aid (where “RE” is a rare earth element) and fired to form the heating resistor. Is a method of manufacturing a ceramic heater comprising a firing step of firing in a state where it is fired and embedded in an unfired insulating substrate that becomes the insulating substrate,
The RE is at least one of Er, Yb, and Lu.   The amount of the conductive ceramic component is selected from the group consisting of the silicon nitride, the conductive ceramic component, and the RE. ₂ Si ₂ O ₇ When the total is 100 mol%, it is 35 to 65 mol%,
  Above RE ₂ Si ₂ O ₇ The amount of the silicon nitride, the conductive ceramic component and the RE ₂ Si ₂ O ₇ The method for producing a ceramic heater according to claim 1, wherein the total amount is 100 to 100 mol%. The method for producing a ceramic heater according to claim 1 or 2 , wherein a firing temperature in the firing step is 1730 to 1830 ° C. A glow plug comprising: a metal shell, a fixed cylinder fitted into one end of the metal shell, and a ceramic heater that is fitted into the fixed cylinder and has a tip projecting from an end surface of the fixed cylinder A glow plug, wherein the ceramic heater is a ceramic heater obtained by the method for producing a ceramic heater according to any one of claims 1 to 3 .

Images