JPH10148332A - Heating element made of ceramic, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive to raising the temperature of a heating element made of a ceramic higher, and at the same time, provide a temperature self-control capability, and in addition, prevent the ceramic from cracking, improve the durability, and reduce the cost. SOLUTION: For this heating element, a high melting point metal 11 of which the melting point is 2000 deg.C or higher, is wound on a formed body or a sintered body 31 of a silicon nitride based substance, and these are embedded in a silicone nitride based power 30A of which the material is approx. the same as the formed body or the sintered body of the silicon nitride based substance. Then, by performing a hot press baking at a temperature of 1650 to 1950 deg.C and by a pressure of 20MPa or higher, a heating element 12 made of a ceramic wherein the high melting point metal 11 is embedded in a silicon nitride based substance sintered body 30, for which the relative density for the silicone nitride based substance part becomes 96% or higher, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heating element used for a glow plug for assisting the start of a diesel engine and a method for producing the same, and more particularly to a high-temperature heating element which can be used in a diesel engine complying with exhaust gas regulations. The present invention relates to a ceramic heating element functioning as a heating element and a method for manufacturing a ceramic heating element having self-temperature control performance.

[0002]

2. Description of the Related Art In a glow plug used for assisting starting of a diesel engine, nickel chromium (Ni-Cr), iron chromium (Fe-Cr) is generally used as a heating element.
And the like are known in which a metal heater is embedded in a heat-resistant insulating powder such as magnesia (MgO) and covered with a heat-resistant metal sheath.

[0003] In the heating element of this type of glow plug for a diesel engine, recently, in order to comply with long-term exhaust gas regulations, the time to reach 800 ° C is increased, the peak temperature and the saturation temperature are increased, and the after-glow time after the engine is started. Need to be longer. In order to achieve these requirements, the heater portion of the heating element needs to be made of a high melting point metal, and the sheath forming the outer shell of the heating element has been considered to be made of metal and ceramic which can be used at a high temperature.

[0004] For example, Japanese Patent Publication No. Sho 62-19034 discloses a ceramic heat generator in which a high melting point metal such as tungsten (W) or molybdenum (Mo) is embedded in silicon nitride having excellent oxidation resistance and thermal shock resistance. A structure using a body (a so-called ceramic heater) is disclosed. However, in a conventional glow plug using such a ceramic heating element, the ceramic heating element does not have a self-temperature control function.

For this reason, for example, Japanese Patent Publication No. 3-15094
As disclosed in Japanese Patent Application Publication No. 4-50487, a glow plug is provided with a self-temperature control function by providing a resistor coil separately from a heating element in a housing portion. However, with such a structure in which the resistor coil is provided in the housing, the resistor coil must be embedded in heat-resistant insulating powder such as magnesia (MgO), and the structure is complicated. Assembly is troublesome and costly. Further, the heat generated from the resistor coil is not directly transmitted to the combustion chamber of the diesel engine, resulting in wasteful energy consumption.

In the heating element proposed in, for example, Japanese Patent Publication Nos. 62-19034 and 3-15094, the maximum temperature difference in the circumferential direction at the maximum temperature of the ceramic heating element is 60 ° C. Or more. Further, in such a heating element, it is also difficult to make the highest heat generating portion a tip portion. For this reason, Japanese Unexamined Patent Application Publication No.
In Japanese Patent No. 27, at least two layers of a heat generating resistance layer made of an inorganic conductive material are provided, and in a ceramic heat generating element when the heat generating temperature is saturated, the temperature difference in the circumferential direction of the ceramic heat generating element is reduced. Have solved the problem.

However, the heating resistor layer in the above-mentioned conventional example is a flat surface, the strength of the ceramic portion is required, and when the diameter must be increased, the temperature difference in the circumferential direction increases. Inevitable. In addition, it is necessary to adopt a manufacturing method such as paste printing, and it is technically difficult to produce the printed body. Printing two or more layers on a molded body complicates the process and increases the cost.

In manufacturing the above-mentioned ceramic heating element, generally, a tungsten (W) coil is placed on a preliminarily formed half-split silicon nitride compact, and another half-split silicon nitride compact is placed. And hot press firing is performed. Thereafter, the ceramic heating element can be formed by processing it into a desired shape (for example, in the case of a heating element of a glow plug, the tip is a hemispherical cylindrical shape).

However, in such a manufacturing method, in order to secure a resistance value for obtaining a desired heat generation temperature (1200 ° C. or higher), a tungsten wire (hereinafter, referred to as a W wire) is required to be used.
It must be less than 1 mm. In this case, a reaction may occur between the thin W line and silicon nitride, and a tungsten-silicon (W-Si) compound may be generated around the W line to cause disconnection.

For this reason, for example, Japanese Patent Publication No. 63-3589
As disclosed in Japanese Patent Publication No. 5 (1993), rhenium (Re) is added to tungsten (W) to increase the thickness of the wire. However, in this case, the temperature coefficient of resistance decreases, so that the temperature rises rapidly. It is difficult to achieve a compatible exothermic temperature (1200 ° C. or higher). Further, the cost of processing the W wire into a coil is high, the coil is significantly deformed after firing the ceramic, the need to wind a rush coil (tip heating coil portion) around a lead (connection portion with an electrode outlet), There is a problem such as difficulty in positioning when embedding a high melting point metal such as W and processing into a desired shape.

To solve the above-mentioned problems, Japanese Patent Laid-Open Publication No. Hei 8-135966 has been proposed. In this conventional glow plug, a heating wire made of a high melting point metal is inserted inside a cup-shaped outer shell made of silicon nitride with a difference as a heating portion having a dense winding pitch and a rough control portion. A gas pressure sintering is performed at a temperature of 1400 ° C. and a pressure of 0.93 MPa in a state in which a ceramic containing silicon as a main component is filled in the outer shell and a resin film is provided as a heat shield layer behind the control unit. Is performed to form a ceramic heating element.

[0012]

However, in the above-mentioned ceramic heating element, the heating wire having a different winding pitch is inserted into a cup-shaped outer shell made of silicon nitride, and the ceramic is filled. Requires manufacturing work. Due to the gas pressure sintering at a low temperature in the reaction sintering, the relative density at the insulator portion made of ceramic filled in the outer shell is low. Therefore, the metal wire is easily oxidized and the cost is increased due to the necessity of providing the heat shield layer. Another problem is that the ceramic strength is low.

In particular, in this type of glow plug, there is a limit to the length of a high melting point metal wire that can be embedded in a ceramic heating element. For example, the tip 15 of the heating element
mm, the heating coil portion is set in the above-described JP-A-8-1.
When burying by the method disclosed in Japanese Patent No. 35966, the limit is about 60 mm, and 120
In order to secure a resistance value for obtaining a desired heat generation temperature of 0 ° C. or more, the W line must be 0.1 mm or less.

However, in such a structure, as described above, the thin W line reacts with silicon nitride, and a tungsten-silicon (W-Si) compound is formed around the W line, and the wire breaks. Unavoidable, W has Re
Must be added to increase the wire diameter, so that the temperature coefficient of resistance is reduced.
(0 ° C. or higher)).

The present invention has been made in view of such circumstances, and has been devised in terms of the material of a silicon nitride-based sintered body and a high melting point metal, and has a three-dimensional arrangement of metal heating elements. The temperature difference in the circumferential direction can be reduced, and the self-temperature control performance can be provided by providing a control coil section (brake coil) in a ceramic heating element with a difference in the winding density of the high melting point metal. It is an object to obtain a ceramic heating element that can be used.

Further, the present invention can prevent disconnection and cracking by thickening a high melting point metal, for example, a W line, reduce the processing cost of the high melting point metal coil, suppress deformation of the coil after firing, and reduce the W line. It is an object of the present invention to obtain a method of manufacturing a ceramic heating element that can easily locate a center when a high-melting point metal such as that described above is embedded and processed into a desired shape.

[0017]

In order to meet such an object, a ceramic heating element according to the present invention is a ceramic heating element formed by embedding a high melting point metal in a silicon nitride sintered body. A high melting point metal coil having a melting point of 2,000 ° C. or higher is embedded in a silicon nitride based sintered body having a relative density of the silicon nitride portion of 96% or more. The maximum temperature difference in the circumferential direction of the highest heat generating portion of the body is configured to be small, for example, 30 ° C. or less.

Further, the ceramic heating element according to the present invention is a ceramic heating element formed by embedding a high melting point metal in a silicon nitride sintered body, wherein the relative density of the silicon nitride part is 96. % Of a high melting point metal coil having a melting point of 2,000 ° C. or more is embedded in a silicon nitride sintered body with a difference in winding density between the front end side and the rear end side of the heating element. Sometimes it has a self-temperature control performance. Here, the high-melting-point metal coil is preferably embedded in the silicon nitride-based sintered body in a state where the winding end of the heating element has a higher winding density than the rear end.

Further, in the method of manufacturing a ceramic heating element according to the present invention, a high melting point metal having a melting point of 2000 ° C. or more is wound around a silicon nitride-based compact or sintered body, and these are wrapped with the silicon nitride-based material. It is buried in a silicon nitride powder having substantially the same composition as the compact or sintered body and fired. Here, the firing of the silicon nitride powder in which the high melting point metal coil is embedded may be performed by hot press firing at a temperature between 1650 ° C. and 1950 ° C. and a pressure of 20 MPa or more.

Further, the method of manufacturing a ceramic heating element according to the present invention is characterized in that a high melting point metal having a melting point of 2,000 ° C. or more is added to a silicon nitride compact or sintered body at the front end and rear end of the heating element. The windings are provided with a difference in the winding density between the above, and these are buried in a silicon nitride powder having substantially the same composition as the silicon nitride compact or sintered body, and then fired to obtain a self-temperature control performance. This is for producing a ceramic heating element having:

Here, the firing of the silicon nitride powder in which the high melting point metal coil is embedded is carried out at 1650 ° C. to 1950 ° C.
It is preferable to perform hot press baking at a temperature between 20 MPa and a pressure of 20 MPa or more. Further, it is preferable to wind the high melting point metal on a silicon nitride-based molded body or sintered body in a state in which the heating element has a higher winding density at the front end side than at the rear end side.

According to the present invention, a ceramic heating element in which a silicon nitride-based sintered body in which the relative density of the silicon nitride-based portion is 96% or more and a high melting point metal heating element is embedded therein is added to the ceramic heating element. Embeds a high melting point metal coil having a temperature of 2,000 ° C. or more, so that the maximum temperature difference in the circumferential direction of the highest heating portion of the ceramic heating element can be reduced by 30 when the maximum temperature is reached.
The temperature can be reduced to about ℃ or less.

According to the present invention, the self-temperature control performance can be provided by providing a difference in the winding density of the high melting point metal coil embedded in the silicon nitride sintered body.

According to the present invention, when a heating element made of a high melting point metal is buried in a silicon nitride sintered body, the silicon nitride molded body or sintered body has a melting point of 20%.
A high melting point metal having a temperature of at least 00 ° C. is wound, buried in a silicon nitride powder, and subjected to hot press firing at a temperature of 1650 ° C. to 1950 ° C. and a pressure of 20 MPa or more, thereby obtaining the above-described structure. As described above, a ceramic heating element that functions for high-temperature heating or a ceramic heating element that has self-temperature control performance can be obtained.

[0025]

1 to 5 show one embodiment of a ceramic heating element having a function for self-heating and having a self-temperature control performance according to the present invention and a method for manufacturing the same. In these figures, the configuration of a glow plug 10 for a diesel engine using a ceramic heating element 12 according to the present invention will be described with reference to FIG. 2. The glow plug 10 is a rod-shaped ceramic heater whose tip side functions as a heating section. Ceramic heating element 12
And a substantially tubular metal holder (metal housing) for holding the ceramic heating element 12 at the distal end.
13 is provided. Reference numeral 13a denotes an outer peripheral thread portion of the holder 13. The thread portion 13a is screwed into a screw hole (not shown) on the engine cylinder head side to electrically ground and connect the tip of the heating element 12. It is arranged to protrude into the sub combustion chamber or the combustion chamber.

An external connection terminal 15 is fitted and held concentrically at the rear end of the holder 13 via an insulating sleeve 14. The external connection terminals 15 are connected to lead portions 22 and 2 (described later) constituting the ceramic heating element 12.
3 is connected via a lead wire 16 to one (23). 16a is an insulating tube. Although not shown, the external connection terminal 15 is connected to the anode side of the vehicle-mounted battery.

The heating element 12 made of ceramic which is held at the tip of the holder 13 via an auxiliary pipe 17 is shown in FIGS.
As shown in the figure, the refractory metal heating element 11 is buried in a silicon nitride sintered body. here,
The silicon nitride sintered body forming the ceramic heating element 12 is configured so that the relative density of the silicon nitride portion is 96% or more.

Numeral 11 denotes a coil-like high melting point metal buried in the silicon nitride sintered body, which is made of, for example, a W wire having a melting point of 2000 ° C. or more. According to the present invention, the refractory metal coil 11 is
2 is buried with a difference in the winding density between the front end side and the rear end side. That is, the high-melting-point metal coil 11 is embedded in the silicon nitride-based sintered body in a state in which the front end side of the heating element is the heating coil section 20 and the winding density is higher than that of the resistance coil section 21 on the rear end side. .

The refractory metal coil 11 forming the heating coil section 20 and the resistance coil section 21 is located on the tip side of the heating element 12, and the ends thereof are the lead sections 22 and 23.
The heating element extends to the rear end side. The heating element 12 provided with these refractory metal coils 11 projects outward from the auxiliary pipe 17 or
It is configured to be exposed to the outside through an inner peripheral groove portion 17a provided in and to be capable of dissipating heat. In addition, this high melting point metal coil 1
1, a gap (GAP) is provided between the heating coil unit 20 and the resistance coil unit 21 so that the heat influence on the heating coil unit 20 side is transmitted to the resistance coil unit 21 with a time difference.

Reference numeral 18 denotes a terminal ring fitted on the outer periphery near the rear end of the heating element 12, to which one lead portion 22 is connected, and which is connected to the auxiliary pipe 17 through a connecting piece 18a.
, Or directly to the holder 13. The other lead 23 is connected to the lead 16 via a terminal cap 19 provided to cover the rear end of the heating element 12.

In FIG. 1, reference numeral 30 denotes a heating element main body made of a silicon nitride sintered body 31. The silicon nitride sintered body 31 has a high melting point metal coil 11 as described above, and a heating coil section 20 in a dense state.
This is a portion formed of a silicon nitride-based molded body or a sintered body for coarsely winding the resistance coil portion 21.

Here, the silicon nitride sintered body 30 forming the heating element 12 is a sintered body containing silicon nitride (Si 3 N 4) as a main component, and is a silicon nitride ceramic containing a so-called auxiliary component. That is. As the silicon nitride used for this, those having a high purity are preferable from the viewpoint of sinterability, migration and the like, and the auxiliary agent may be a known auxiliary component system represented by yttria-alumina system. .

The composition of the silicon nitride of the molded body (sintered body) 31 around which the refractory metal 11 embedded inside is wound and the silicon nitride of the outer sintered body 30 is determined by the coefficient of thermal expansion during firing. It is preferable that they have the same composition (the same composition that does not cause cracking in silicon nitride) from the viewpoint of preventing cracking due to the difference between the two.

Further, since the maximum sintering temperature of ceramics such as silicon nitride may be 1950 ° C., the high melting point metal 11 must have a melting point of 2000 ° C. Examples of such a high melting point metal 11 include W, Mo, Nb (niobium), Hf (hafnium), and Ir (iridium). The most preferable one is W (tungsten) which is inexpensive and easy to mold.

In the above configuration, the ceramic heating element 12 can be manufactured as follows. First, a silicon nitride molded body 31 having a shape such as a columnar shape or a cylindrical shape in which a wire is easily wound is prepared. By firing such a molded body 31, a silicon nitride sintered body can be obtained, and any of them may be used. Here, since such a molded body 31 or sintered body 31 is embedded, it is necessary to select a composition such that the thermal expansion coefficient is substantially equal to that of the silicon nitride of the outer cylindrical portion (30A). It is necessary and preferably has the same composition as the silicon nitride of the outer cylinder. In addition, as a manufacturing method, a general manufacturing method such as a uniaxial press, a CIP (isotropic pressure press), an extrusion molding, and an injection molding can be adopted.

When the cylindrical body 31 around which the refractory metal wire 11 is wound is used, the tip 20a of the heating coil portion 20 on the tip side is folded back and guided to the rear end of the heating element 12. Can be performed relatively easily, as shown in FIG. That is, since such a formed body 31 is not so hard, it is easy to pass the metal wire 11 therethrough.

A high melting point metal 11 having a melting point of 2000 ° C. or more is wound around the silicon nitride-based molded body or fired body 31 thus obtained. Here, the fired body 31 includes a degreased body degreased at about 500 ° C. and a calcined body fired at a temperature slightly lower than the sintering temperature. Further, depending on the ease of handling in the manufacturing process, it is possible to select which of the molded body and the fired body is to be wound.

In the case of manufacturing a W coil, a method of winding around a metal such as molybdenum (Mo) and then dissolving Mo or a method of winding up warmly has conventionally been adopted. If this is the case, the winding process can be performed cold, complete automation can be achieved, there is no need to use a metal such as Mo, and the manufacturing method is inexpensive.

First, the high-melting metal 11 wound is buried in a silicon nitride powder 30A to form a ceramic heating element 12. About half of the silicon nitride powder 30A was placed in a mold, and the wire wound with a W wire was placed. The other half of the silicon nitride powder 30A was placed and subjected to uniaxial pressing. Dry CI with a focus on things
Various methods such as a method of performing P can be selected.

Next, the material buried in the silicon nitride powder 30A is heated at a temperature between 1650 ° C. and 1950 ° C. for 2 hours.
By sintering using a hot press method applying a pressure of 0 MPa or more, the heating element 12 in which the high melting point metal 11 (20, 21) and the lead portions 22, 23 are embedded can be obtained. Here, normal pressure sintering, gas pressure sintering and 20 MPa
Hot press sintering at a lower pressure did not sufficiently densify, moving the buried material and creating a gap between the coil and the silicon nitride, but using a hot press method applying a pressure of 20 MPa or more By sintering, the above-mentioned problem can be solved.

When hot pressing is performed at a temperature lower than 1650 ° C., not only the outer silicon nitride material is not sufficiently densified, but also the material obtained by winding the high melting point metal 11 is not integrated. Further, if the temperature is higher than 1950 ° C., a phenomenon occurs in which the silicon nitride is not sufficiently densified due to decomposition thereof and the reaction between the high melting point metal and the silicon nitride becomes intense. 1950 ° C
And hot press firing at a pressure of 20 MPa or more.

With such a configuration, the ceramic heating element 12 in which the heating coil section 20 made of the high melting point metal 11 and the resistance coil section 21 are embedded in the silicon nitride sintered body 30 can be formed. The self-temperature control performance can be obtained only by making the winding density of the high melting point metal coil 11 having a temperature of 2000 ° C. or more different.

[0043]

【Example】

Example 1 As shown in FIG.
mm, inner diameter 0.1 mm, length 25 mm cylindrical silicon nitride molded product (88 wt% Si3 N4 -4 wt% Al2 O
0.2m to 3-4wt% Y2O3-4wt% TaN)
An mW wire (purity: 99%) is passed through the hole, wound 10 times around the distal end of the cylindrical silicon nitride molded product 31 at a pitch of 0.3 mm, and then wound 10 times at a pitch of 1.3 mm.

0.4 g of powder having the same brand and the same composition as the cylindrical silicon nitride molded product 31 was placed in a mold capable of forming a 7 × 40 mm square, and a rectangular parallelepiped was formed by uniaxial pressing under a pressure of 1 t / cm 2. A cylindrical silicon nitride molded product 31 wound with a W wire 11 was placed thereon, and 0.9 g of powder 30A from above was further placed therein and uniaxially pressed at a pressure of 1 t / cm 2, and the W wire 11 was wound. Cylindrical silicon nitride molding 31
A molded body of a rectangular parallelepiped in which is embedded.

Thereafter, the mixture was placed in a graphite mold at 40 MPa, 175
Hot press firing at 0 ° C. × 1 h is performed, and then diameter 3.
Cylindrical grinding was performed so that the two ends of the W wire 11 having a length of 5 mm and a length of 40 mm were exposed from the silicon nitride ceramic (heating element 12), thereby obtaining a heating element 12 made of ceramic. W line 11
Is located at the center of the heating element 12. In this example, re-grinding or the like was not particularly required. Also, W
The wire 11 was removed and the density was measured.
The relative density as a value divided by the theoretical density of 31 is 98.3.
%Met.

A metal auxiliary pipe 17 is brazed to the heating element 12 thus obtained, and the end of the W wire 11 formed in the hole of the molded body is a positive electrode, and the other side is a negative electrode. Was prepared. Then, when the characteristics are evaluated by applying a voltage of 11 V, as shown in FIG. 5, the maximum temperature of 3 mm from the end surface of the ceramic heating element 12 is 13 mm.
The temperature reached at 50 ° C. and 800 ° C. was 3.5 seconds, confirming that it had self-temperature control characteristics.

Example 2 Degreasing after extrusion molding,
Normal pressure sintering at 70 ° C, diameter 2.3mm, inner diameter 0.22
mm, 35 mm long cylindrical sintered body (90 wt% Si3
N4-5 wt% Al2 O3 -5 wt% Y2 O3) is prepared. Then, the relative density becomes 96.8%. afterwards,
A molded body and a sintered body are manufactured under the same conditions as those of the first embodiment, and finally, a glow plug 10 for a diesel engine is manufactured. However, the refractory metal 11 is a Mo wire.

No crack was observed in the sintered body 30 thus manufactured. When the characteristics were evaluated under the same conditions as in Example 1, the temperature reached the maximum at 3 mm from the end face of the ceramic heating element 12. This 3m
Temperature was measured at arbitrary four points at m. They were 1210 ° C, 1208 ° C, 1201 ° C and 1215 ° C, respectively. In addition, the arrival time at 800 ° C. was 3.3 seconds, and it was confirmed that the device had self-temperature control characteristics.

[Embodiment 3] As in Embodiment 1 described above,
A rectangular parallelepiped molded body 30 in which a cylindrical silicon nitride molded article 31 wound with a W wire 11 is embedded is produced. Thereafter, the result of hot press firing under the conditions shown in Table 1 is as follows.

[0050]

[Table 1] In Table 1, “○” is an example corresponding to the region relating to the present invention, and a ceramic heating element 12 having good self-temperature control characteristics without cracks or gaps was obtained. The reason why the relative density of the silicon nitride-based portion forming the sintered body 31 is set to 96% or more is that the metal wire is easily oxidized through an external atmosphere because there is a void at 95% or less. In addition, since the density is insufficient, the ceramic strength is low, and the ceramic cannot be applied to products such as glow plugs.

Example 4 A cylindrical sintered body 31 wound with a Mo wire (degreasing at 600.degree.
Table 2 shows the results of hot-press sintering at 1750 ° C and 35 MPa, respectively, under the conditions of changing the amount and type of silicon nitride-based auxiliary agent at the temperature of 1750 ° C and 1 MPa.

[0052]

[Table 2] Cracks were present in cylindrical ceramics or both,
It was confirmed that if the thermal expansion coefficient was close to a certain extent, it could be manufactured without cracking.

The reason why the refractory metal wire 11 can be made thicker is as follows. Generally, there is a limit to the length of the refractory metal wire 11 that can be embedded in the ceramic heating element 12. For example, if the heating coil portion is buried by the conventional method in the tip portion of about 15 mm, the limit is about 60 mm, and the desired heating temperature (1200 ° C.
In order to secure a resistance value for obtaining the above, the W line must be set to 0.1 mm or less as described above. And, in that case, a thin W line reacts with silicon nitride,
A W-Si-based compound is generated around the W line, causing disconnection. Therefore, Re is added to W to increase the wire diameter.

The resistance value of the metal wire is represented by R = ρl / S. Here, R: resistance (Ω), ρ: resistivity (Ω · c)
m), length 1 (cm), S: surface area (cm 2).
Therefore, assuming that the resistance is constant with the same material, if the wire diameter is increased, the length must be increased. According to the present invention, for example, the cylindrical molded body or sintered body 31
If it has a diameter of mm, if it can be wound 20 times, a length of about 126 mm can be embedded, so that it is possible to obtain the same resistance value with a larger wire diameter than in the past.

Embodiment 5 For example, in a ceramic heating element 12 as shown in FIG. 6, a cylindrical silicon nitride sintered product (88 wt% Si 3 N 4) having a diameter of 2.2 mm, an inner diameter of 0.23 mm and a length of 10 mm was used. -8 wt% Y2 O3 -4
wt% TaN), each of which is provided with 0.2 mm W wires (refractory metal coil 11) at a pitch of 0.5 mm for 15
Wound, embedded in silicon nitride powder of the same composition, 185
Hot press firing was performed at 0 ° C. × 1 hour at a pressure of 30 MPa.

A metal auxiliary pipe (not shown) is brazed to the heating element 12 thus obtained, and a glow plug for a diesel engine (the whole illustration is omitted) is obtained.
This was produced. Note that, in this example, there is a case where only the heating coil portion 20 using the W wire (the high melting point metal coil 11) is provided.

At this time, at the time when the highest temperature of the highest heat generating portion is reached, the temperature at six points in the circumferential direction is measured by a radiation thermometer, and the difference between the highest temperature and the lowest temperature is measured as the temperature difference in the circumferential direction. Table 3 below shows an example.

[Table 3] Here, as a comparative example, a glow plug for a diesel engine composed of a W coil was similarly measured using a conventional heating element as shown in JP-B-63-35895.

[0058]

As described above, according to the ceramic heating element according to the present invention, a ceramic heating element formed by embedding a high melting point metal in a silicon nitride sintered body, A high melting point metal coil having a melting point of 2000 ° C. or higher is embedded in a silicon nitride based sintered body having a relative density of the element portion of 96% or higher. The maximum temperature difference in the circumferential direction of the highest heat generating portion can be reduced to, for example, 30 ° C. or less, so that a ceramic heat generating element can be provided at a low cost. Can be prevented.

Further, according to the present invention, the high-melting-point metal coil is embedded with a difference in the winding density between the front end side and the rear end side of the ceramic heating element. The heating element can be provided at a low cost, and in this regard, a high melting point metal such as a W line can be made thick to prevent disconnection and cracking. Here, the high-melting-point metal coil is preferably embedded in the silicon nitride-based sintered body in a state where the winding end of the heating element has a higher winding density than the rear end.

Further, according to the method for manufacturing a ceramic heating element according to the present invention, a high-melting metal having a melting point of 2000 ° C. or more is wound around a silicon nitride molded body or sintered body, and the silicon nitride-based molded body or sintered body is coated with the silicon nitride. By embedding in a silicon nitride powder having substantially the same composition as the green compact or sintered body and performing hot press firing at a temperature between 1650 ° C. and 1950 ° C. and a pressure of 20 MPa or more, for example, A ceramic heating element capable of reducing the maximum temperature difference in the circumferential direction of the highest heat generating portion of the ceramic heating element to about 30 ° C. or less when the temperature reaches the temperature.

Further, according to the method of manufacturing a ceramic heating element according to the present invention, a high melting point metal having a melting point of 2000 ° C. or more is added to a silicon nitride compact or sintered body at the front end of the heating element. Winding is performed with a difference in winding density between the end side and the winding side (for example, in a state where the winding density is higher at the front end side than at the rear end side), and these are substantially the same composition as the silicon nitride-based compact or sintered body. By embedding in a silicon nitride powder and firing, a ceramic heating element having self-temperature control performance can be obtained.

Further, according to the present invention, a high melting point metal having a melting point of 2000 ° C. or more is wound around a silicon nitride-based molded body or sintered body, and these are combined with the silicon nitride-based molded body or sintered body. By burying in a silicon nitride powder having substantially the same composition and performing hot press firing at a temperature of 1650 ° C. to 1950 ° C. and a pressure of 20 MPa or more, the processing cost of the high melting point metal coil is reduced, A ceramic heating element that suppresses deformation of the coil and allows the brake coil to be manufactured in a ceramic heating element by changing the number of windings, and facilitates centering when embedding a high-melting metal such as W into a desired shape. Can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part showing one embodiment of a ceramic heating element according to the present invention.

FIG. 2 is a sectional view of a glow plug for a diesel engine using a ceramic heating element according to the present invention.

FIG. 3 shows a ceramic heating element according to the present invention.
It is a figure which shows the cylinder-shaped silicon nitride-based molded object or sintered body around which a high melting point metal is wound.

FIG. 4 is a schematic side view for explaining a ceramic heating element and a method for manufacturing the same according to the present invention.

FIG. 5 is a characteristic diagram for explaining an experimental result in FIG. 4;

FIG. 6 is an enlarged sectional view of a main part showing another embodiment of the ceramic heating element according to the present invention.

[Explanation of symbols]

Reference Signs List 10: glow plug for diesel engine, 11: high melting point metal (W wire), 12: ceramic heating element, 13: metal holder, 15: external connection terminal, 17: auxiliary pipe,
Reference numeral 20: heating coil portion, 21: resistance coil portion, 22, 23
... lead part, 30 ... silicon nitride sintered body, 30A ... silicon nitride powder, 31 ... silicon nitride molded or sintered body.

Claims (5)

[Claims] 1. A ceramic heating element formed by embedding a refractory metal in a silicon nitride-based sintered body, wherein the silicon nitride-based sintered body has a relative density of 96% or more. A high melting point metal coil having a melting point of 2000 ° C. or more is embedded therein, and the maximum temperature difference in the circumferential direction of the highest heat generating portion of the ceramic heating element when reaching the maximum temperature is set to, for example, 30 ° C. or less. A ceramic heating element characterized in that it is configured to be small. 2. A ceramic heating element formed by embedding a high melting point metal in a silicon nitride-based sintered body, wherein the silicon nitride-based portion has a relative density of 96% or more. A high melting point metal coil having a melting point of 2,000 ° C. or more is embedded therein with a difference in winding density between the front end side and the rear end side of the heating element so as to have self-temperature control performance during heat generation. A heating element made of ceramic, characterized in that: 3. The method for producing a ceramic heating element according to claim 1, wherein the silicon nitride molded body or the sintered body has a melting point of 2,000.
A high-melting-point metal having a temperature of at least 100 ° C. or more, and burying them in a silicon nitride-based powder having substantially the same composition as the silicon nitride-based compact or sintered body, followed by firing. How to make the body. 4. The method for manufacturing a ceramic heating element having self-temperature control performance according to claim 2, wherein the silicon nitride-based molded or sintered body has a melting point of 2,000.
° C. or higher, and wound with a difference in the winding density between the front end side and the rear end side of the heating element, and these are nitrided having substantially the same composition as the silicon nitride molded body or sintered body. A method for manufacturing a ceramic heating element, wherein the method is embedded in a silicon powder and fired. 5. The ceramic heating element according to claim 3, wherein the firing of the silicon nitride powder in which the high melting point metal coil is embedded is performed at a temperature between 1650 ° C. to 1950 ° C. and 20 MPa.
A method for producing a ceramic heating element, characterized in that the heating is performed by hot press sintering under the above pressure.