JP2001132947A - Ceramic heater and glow plug equipped with it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic heater having superior durability and little varying folding endurance and a glow plug equipped with the heater. SOLUTION: In a ceramic heater which is constituted by burying a conductive component composed of the silicide, carbide, etc. of a metallic element such as W, Ta, Nb, etc., an exothermic resistor formed of an insulating component composed of a sintered silicon nitride material, etc., and lead wires composed of an alloy containing a metal such as W, Re, Ta, etc. or a mixture of these metals as a main component and put on the edge of the exothermic resistor in a substrate composed of a sintered silicon nitride material, etc., the inserting lengths of the lead wires are adjusted to 1-5 mm, particularly, to 2-5 mm, further particularly, to 3-5 mm. The temperature rising rate of the heater can be adjusted to >=300 deg.C/s, particularly, to >=400 deg.C/s, further particular, to >=500 deg.C/s. The heater has such a superior durability that the heater does not cause disconnection, etc., even when the temperature of the heater is raised at such a high rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater and a glow plug having the same. More specifically,
The present invention is provided with a ceramic heater which is excellent in durability evaluated by repetition of energization and stoppage of energization, in particular, excellent in durability when rapidly heated, and which can obtain a sufficient bending strength stably. Regarding glow plug. INDUSTRIAL APPLICABILITY The ceramic heater of the present invention can be used in various applications other than a heating source for a glow plug of a diesel engine.

[0002]

2. Description of the Related Art As a ceramic heater used for a glow plug or the like, there is known a ceramic heater in which a heating resistor containing a conductive component such as WC is embedded in a base made of an insulating ceramic such as a silicon nitride sintered body. I have. An electrode for supplying current to the heating resistor and an edge of the heating resistor are electrically connected to each other by a lead wire made of W or the like. The leading end of the lead wire is fitted and connected to the edge of the heating resistor. Conventionally, however, it has been considered that there is no problem if sufficient conduction is provided. No consideration has been given to the correlation with durability.

[0003] This ceramic heater is useful as a heating source for a glow plug. Normally, in a glow plug used for a diesel engine, the temperature rise rate of a built-in heater is about 200 to 300 ° C./sec.
There is a need for a heater that can rapidly raise the temperature at a rate exceeding two seconds. However, conventionally, depending on the fitting length, the heater may be disconnected early due to thermal shock, which is a problem.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and has a fitting length of a lead wire made of W or the like fitted and connected to an edge of a heating resistor. By specifying the thickness, the durability, especially the durability evaluated by the repetition of rapid temperature rise and fall, is excellent, and the thermal shock resistance near the fitting portion between the heating resistor and the lead wire is improved, It is an object of the present invention to provide a highly reliable ceramic heater having a small variation in bending strength and a glow plug including the same.

[0005]

By changing the fitting length of the lead wire which is fitted to and connected to the edge of the heat generating resistor, a base made of an insulating ceramic and a conductive ceramic can be formed at the time of energization. The temperature at the interface between the heating resistor and the lead wire made of W or the like changes. It has been found that this temperature affects the durability of the heater, and that the lower the temperature, the better the durability. Also, the necessity of a heater having a very high heating rate compared with the conventional one has been increasing. However, the above-described fitting length makes it possible to prevent the heat shock at the periphery of the lead wire, especially near the fitting portion with the heating resistor. The impact resistance is also affected, and when this mating length is within a specific range, the thermal shock resistance is improved,
It has been found that a heater having better durability can be obtained. The present invention has been made based on these findings.

A ceramic heater according to a first aspect of the present invention is a ceramic heater comprising a heating resistor, a lead wire fitted to an edge of the heating resistor, and a base in which the heating resistor and the lead wire are embedded. The fitting length of the lead wire is 1
５5 mm.

Further, in the ceramic heater according to the first aspect of the present invention, it is possible to rapidly raise the temperature of the heater incorporated in the glow plug or the like, exceeding a normal rate of temperature increase. That is, as in the second invention, the temperature can be raised at a rate of 300 ° C./sec or more, and particularly, the temperature can be rapidly raised at a rate of 400 ° C./sec or more, and more preferably 500 ° C./sec or more. . In addition, even when used in applications requiring rapid temperature rise, a ceramic heater having excellent durability, small variation in bending strength, and high reliability can be obtained.

The above-mentioned "heating resistor" is composed of a conductive component and an insulating component. The conductive components are W, Ta, Nb, T
1 selected from i, Mo, Zr, Hf, V, Cr, etc.
At least one of silicides, carbides, nitrides, and the like of at least one metal element is formed by firing. The insulating component is usually made of a silicon nitride sintered body. The conductive component is preferably one having a coefficient of thermal expansion that does not greatly differ from the silicon nitride sintered body constituting the base or the silicon nitride sintered body which is an insulating component. If the conductive component has a small difference in coefficient of thermal expansion, the occurrence of cracks in the base and the heating resistor when the heater is used can be suppressed. Examples of such a conductive component include WC, MoSi ₂ , TiN, and WSi ₂ . Further, it is preferable that the conductive component has a melting point exceeding the operating temperature of the ceramic heater and has high heat resistance. The higher the melting point of the conductive component, the higher the heat resistance of the heater in the operating temperature range.

The amount ratio between the conductive component and the insulating component is not particularly limited. However, when the heating resistor is 100 parts by volume, the conductive component can be 15 to 40 parts by volume, and especially 20 parts by volume.
It can be up to 30 parts by volume.

The above "lead wire" is W, Re, Ta, M
It can be formed of a metal selected from o, Nb, or the like, or an alloy containing these metals as a main component. In particular, W is frequently used.

The above-mentioned "substrate" is usually made of a silicon nitride sintered body. The sintered body may be composed of only silicon nitride, or may be composed of silicon nitride as a main component and a small amount of aluminum nitride, alumina or the like. Further, it may be a sialon. Further, a small amount of a conductive component can be contained in order to reduce the difference in thermal expansion coefficient between the conductive component and the conductive component.

After firing, the lead wire is fitted to the edge of the molded body to be the heating resistor, and is integrally fired and connected.
The “fit length” (the length represented by “d” in FIG. 1) is 1 to 5 mm, particularly 2 to 5 mm.
More preferably, it is 3 to 5 mm. Mating length is 1
mm, when energization at 1400 ° C. and stop of energization are repeated, less than 10,000 cycles,
In particular, disconnection or the like may occur in the vicinity of the end surface of the heating resistor that becomes hot.

On the other hand, when the fitting length exceeds 5 mm,
When a heater molded body is formed by injection molding or the like, a lead wire is not arranged at a target position in a molded body that becomes a heat generating resistor after firing, and is more likely to be inclined. Therefore, mechanical characteristics such as flexural strength vary, and in particular, a heater having low flexural strength may be obtained. 10 seconds in 2 seconds
When the operation of stopping the current supply for 30 seconds is repeated after the temperature is rapidly raised to 00 ° C., the heating resistor made of conductive ceramic and the lead wire, particularly the tip of the lead wire, are obtained in less than 10,000 cycles. Endurance at the interface with the substrate may be reduced, and disconnection or the like may occur.

The ceramic heater according to the first aspect of the invention has excellent durability, small variation in bending strength, and stable quality. That is, energization at 1400 ° C. and stop of energization
An excellent ceramic heater that does not cause disconnection or the like even when it is repeated 10,000 cycles or more, particularly 15,000 cycles or more, and even 20,000 cycles or more can be obtained. In addition, sufficient bending strength is obtained stably,
The minimum value is 700 to 1000 MPa, and the average value is 90
0 to 1100 MPa, and the difference between the maximum value and the minimum value is 400 MPa or less, particularly 300 MPa or less,
A highly reliable ceramic heater having a small variation in strength can be obtained.

Further, the ceramic heater has excellent durability even in applications requiring a rapid temperature rise as in the second invention, and the bending strength and the like are not impaired. In this ceramic heater, as in the third invention, 1 second in 2 seconds
After rapidly raising the temperature to 000 ° C., the operation of stopping the current supply for 30 seconds is performed for 5000 cycles or more, particularly 10,000 cycles.
Even if the cycle is repeated for more than 20,000 cycles, and even for more than 20,000 cycles, a ceramic heater which does not cause disconnection or the like can be obtained.

The ceramic heaters according to the first to third aspects of the present invention are characterized in that the energization at 1400 ° C. and the stop of the energization are repeated, and the temperature is rapidly raised to 1000 ° C. in 2 seconds, and then the energization is performed for 30 seconds. When the stopping operation is repeated, excellent durability is obtained in any case. That is,
The energization at 1400 ° C. and the stop of the energization are performed for 10,000 cycles or more, particularly for 15,000 cycles or more, and moreover for 20 cycles.
No disconnection or the like occurs when repeated over 000 cycles. Furthermore, after rapidly raising the temperature to 1000 ° C. in 2 seconds, the operation of stopping the current supply for 30 seconds is performed for 10,000 cycles or more, particularly for 15,000 cycles or more, and even more for 20 cycles.
No disconnection or the like occurs even when the number of repetitions is 000 or more.

The ceramic heater according to the first to third aspects of the present invention
It can be manufactured as follows. As the raw material powder of the conductive component, a powder made of a silicide, carbide, nitride, or the like of a metal element such as W, Ti, and Mo is used. Further, ceramic raw material powder such as silicon nitride raw material powder and sintering aid powder are used as raw material powder of the insulating component. As the sintering aid powder, rare earth oxide powder is often used,
MgO and Al ₂ O ₃ -Y ₂ O _3, etc., generally a powder of oxide or the like used in a firing of the silicon nitride sintered body can also be used. One kind of these sintering aid powders may be used, but two or more kinds are often used in combination. In addition, E
It is preferable to use a sintering aid powder such as r ₂ O ₃ , in which the grain boundaries upon sintering become a crystal phase, since the heat resistance becomes higher.

The raw material powder for the conductive component, the ceramic raw material powder, and the sintering aid powder are mixed at a predetermined ratio to prepare a mixed powder. This mixing can be performed by an ordinary method such as a wet method. The total amount of the raw material powder for the conductive component, the ceramic raw material powder and the sintering aid powder is 10%.
When the volume is 0 volume parts, the raw material powder for the conductive component is 15 to 4 parts.
0 to 50 parts by volume, particularly 20 to 30 parts by volume, and the remainder of 85 to 60 parts by volume, particularly 80
It can be up to 70 parts by volume.

The mixed powder thus prepared is mixed with an appropriate amount of a binder and the like, kneaded, granulated, and then fired by a method such as injection molding to form a heating resistor. Can be a body. A lead wire made of a metal such as W is attached to a predetermined position of the molded body.

Thereafter, the formed body is embedded in the base material powder. As the method, there is a method of preparing two half molds obtained by compacting the base material powder, placing a compact at a predetermined position between these half molds, and then press molding. Then, these are integrally pressurized to about 50 to 120 atm to obtain a ceramic heater molded body in which a molded body serving as a heating resistor is embedded in a powder molded body having the shape of a base. The ceramic heater molded body is housed in a pressing die made of graphite or the like, housed in a firing furnace, and hot-pressed at a predetermined temperature for a required time to manufacture a ceramic heater. The firing temperature and the firing time are not particularly limited, but the firing temperature can be 1700 to 1850 ° C, particularly 1800 to 1850 ° C, and the firing time can be 30 to 180 minutes, particularly 60 to 120 minutes.

The glow plug according to the fourth aspect of the present invention includes the first to third glow plugs.
It is characterized by comprising the ceramic heater of the invention. In this glow plug, the built-in ceramic heater has excellent durability. In particular, even when the heater is rapidly heated, sufficient durability is not impaired. Therefore, it is also useful as a glow plug for ensuring the same startability as a gasoline engine.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the ceramic heater of the present invention and a glow plug having the same will be described in more detail with reference to examples. (1) Preparation of ceramic heater To 86 wt% of silicon nitride raw material powder, 1
0% by weight of Er ₂ O ₃ powder and 4% by weight of SiO ₂ powder were blended to obtain a raw material for an insulating component. This insulating material 4
0% by weight and 60% by weight of WC powder as a raw material for a conductive component were wet-mixed for 72 hours, and then dried to obtain a mixed powder. Thereafter, the mixed powder and the binder were put into a kneader and kneaded for 4 hours. Next, the obtained kneaded material is cut into pellets, which are then put into an injection molding machine, and tungsten lead wires are fitted to both end edges to form a connected U-shaped heating resistor. I got a body.

On the other hand, 84% by weight of silicon nitride raw material powder
As a sintering aid, 10% by weight of Er ₂ O ₃ powder, 4% by weight of SiO ₂ powder and 2% by weight of MoSi ₂ powder are blended.
The mixture obtained by wet mixing for 0 hour was granulated by a spray drier method, and two half molds obtained by pressing the granulated material were prepared. Thereafter, the molded body to be the heating resistor is placed at a predetermined position between the two half molds, press-molded and embedded, and then pressurized integrally at a pressure of 70 atm. A ceramic heater was obtained. Next, the unfired ceramic heater was calcined at 600 ° C. to remove the binder, and a calcined body was obtained. Thereafter, the calcined body was set in a graphite pressing die and baked under a nitrogen atmosphere at 1800 ° C. for 1.5 hours to produce a ceramic heater.

(2) Structure of Ceramic Heater and Glow Plug Incorporating This Heater FIG. 1 is a longitudinal sectional view showing a fitting portion between an end of a heating resistor of a ceramic heater and a lead wire. Lead wires 13a and 13b made of tungsten are fitted to the edges 121a and 121b of the heating resistor 12 embedded in the base 11. d is the fitting length of the lead wire 13a.

FIG. 2 is a longitudinal sectional view of the ceramic heater. The ceramic heater 1 includes a base 11, a heating resistor 12,
And the lead wires 13a and 13b. The base 11 is made of a silicon nitride sintered body, and the buried heating resistor 12 and the lead wires 13a and 13b are
Protected by The heating resistor 12 is formed of a U-shaped rod and is embedded in the base 11. The heating resistor 12 contains a conductive component and an insulating component. Also, a lead wire 13a made of W,
13b, one end of each of them is located on the surface of the base 11 so that electric power supplied from outside to the ceramic heater 1 can be supplied to the heating resistor 12 embedded in the base 11.
The other end is fitted to both end edges 121a and 121b of the heating resistor 12.

FIG. 3 is a longitudinal sectional view of a glow plug incorporating the ceramic heater. Glow plug 2
A ceramic heater 1 is provided on the tip side, which is a portion that generates heat. The ceramic heater 1 is inserted through a metal fixed cylinder 21, and the fixed cylinder 21 is held at the tip of an outer cylinder 22. The bending strength and durability of this glow plug were evaluated by the following methods.

(3) Evaluation of flexural strength and durability Flexural strength: A three-point bending strength was measured in accordance with JIS R1601. The span was 12 mm and the crosshead speed was 0.5 mm / min. 1400 ° C. cold / heat durability; energizing the heating resistor and setting the temperature of the highest temperature portion on the surface of the ceramic heater to 1
After setting the temperature to 400 ° C. and continuing the energization for 1 minute, the energization was stopped for 1 minute, and this energization and the stop of the energization were repeated. Rapid temperature rise endurance: After energizing the heating resistor and raising the temperature of the highest temperature portion of the surface of the ceramic heater to 1000 ° C. in 2 seconds, energizing is stopped for 30 seconds, and energizing and energizing are stopped. And the stop was repeated. Table 1 shows the results
It is described together.

[0028]

[Table 1]

The exposed length of the heater in Table 1 is D in FIG. 3, and the tip of the ceramic heater 1 exposed from the end face of the metal fixed cylinder 21 in which the ceramic heater 1 of the glow plug 2 is inserted. Side length. The bending strength and durability were evaluated as follows: when the exposed length was 9 mm and the fitting length was 0.5 to 7 mm (Experimental Examples 1 to 5), the exposed length was 12 mm, and the fitting length was 12 mm. Is 0.5 to 7 mm (Experimental Examples 6 to 10) and the exposed length is 2 as an acceleration test.
3 mm and the fitting length was 0.5 to 7 mm (Experimental Examples 11 to 15).

The heat generated in the vicinity of the fitting portion is
Since the light is absorbed by the fixed cylinder 21, in the evaluation of the durability, the shorter the exposed length, the gentler the condition, and the longer the exposed length, the more severe the condition. When the exposed length is 9 mm, the end face of the heating resistor is located at a position slightly entering the inside of the fixed cylinder, and when the exposed length is 12 mm, the end face of the heating resistor is slightly spaced from the end face of the fixed barrel. In a case where the end surface of the heating resistor is located far away from the end surface of the fixed cylinder when the exposed length is 23 mm, the end surface of the heating resistor is located far away from the end surface of the fixed cylinder. Therefore, when the exposed length is 23 mm, the heat is hardly absorbed by the fixed cylinder, which is a very severe test condition. However, practically, there is no such a glow plug, and experimental examples 11 to 1
5 is an accelerated test.

According to the results shown in Table 1, in Examples 2 to 4 and Examples 7 to 9 in which the exposed length of the heater was 9 mm or 12 mm and the fitting length was 1 to 5 mm, the heat resistance was 1400 ° C. The durability is 14820 cycles or more, the rapid temperature rise durability is 12903 cycles or more, and the exposed length is 12
It can be seen that even if the length is as long as mm, it has very excellent durability. Further, the minimum value of the bending strength is 72.
6 to 924 MPa, and the maximum value is 1065 to 1103
MPa, which indicates that the strength is sufficient and the variation is small. On the other hand, in Experimental Examples 1 and 6 in which the fitting length is 0.5 mm, the cooling / heating durability at 1400 ° C. decreases, and in Experimental Examples 5 and 10 in which the fitting length is 7 mm, the rapid temperature rise durability decreases, It can be seen that the bending strength also varies. When the exposed length is 23 mm, the durability, particularly the durability against cold and heat at 1400 ° C., is reduced. However, in Experimental Examples 12 to 14 included in the present invention, the wire is not disconnected until 7568 cycles. Excellent compared to. Also,
In Experimental Example 15, the rapid temperature rise durability was significantly reduced.
There is no disconnection at 0 cycle, and the durability is much higher than that of Experimental Example 15.

It should be noted that the present invention is not limited to the above embodiment, but may be variously modified within the scope of the present invention depending on the purpose and application. That is, the ceramic heater of the present invention can be used not only for a glow plug but also for various heaters for heating and the like.

[0033]

According to the first aspect of the present invention, a highly reliable ceramic heater having excellent durability, small variation in bending strength, and high reliability can be obtained. In particular, according to the second invention, a heater capable of rapidly increasing the temperature can be provided, and even when the temperature is rapidly increased at a specific speed as in the third invention, the ceramic heater has excellent durability. It can be. Further, according to the fourth invention, a glow plug having the ceramic heaters of the first to third inventions and having sufficiently excellent characteristics can be obtained, especially when it is necessary to rapidly raise the temperature.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a fitting portion between an end edge of a heating resistor and a lead wire.

FIG. 2 is a longitudinal sectional view for explaining a ceramic heater.

FIG. 3 is a vertical sectional view of a glow plug incorporating a ceramic heater.

[Explanation of symbols]

1; ceramic heater, 11, base, 12; heating resistor, 121a, 121b; edge of heating resistor, 13a,
13b; lead wire, d; fitting length, D; exposed length, 2;
Glow plug, 21; fixed cylinder, 22; outer cylinder.

Claims (4)

[Claims] 1. A ceramic heater comprising a heating resistor, a lead wire fitted to an edge of the heating resistor, and a base in which the heating resistor and the lead wire are embedded. A ceramic heater having a length of 1 to 5 mm. 2. The ceramic heater according to claim 1, wherein the rate of temperature rise can be 300 ° C./second or more. 3. The heating resistor is energized for 2 seconds, the temperature of the highest temperature portion on the surface of the ceramic heater is set to 1000 ° C., and then the energization is stopped for 30 seconds. 2. The heating resistor according to claim 1, wherein no disconnection occurs when 10,000 cycles are repeated.
Or the ceramic heater according to 2. 4. A glow plug comprising the ceramic heater according to claim 1. Description: