JPH08339882A - Ceramic heater - Google Patents

Abstract

PURPOSE: To provide a ceramic heater which can prevent generating a crack in a ceramic unit of covering a heating unit in the case of press molding. CONSTITUTION: A ceramic heater is constituted such that a non-metal heating unit 9 heated by allowing a current to flow and a pair of head wires 10, 11 connected to an end part of this heating unit 9 are buried to be sintered. In this ceramic heater, each peripheral edge part of one end surface 9a and the other end surface 9b of the heating unit 9, connected to the lead wires 10, 11, is respectively given roughness, to constitute an angular part from the end surfaces 9a, 9b over to a side surface 9c by a smooth curved surface.

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 more particularly to a ceramic heater suitable for ignition of glow plugs and combustors for diesel engines.

[0002]

2. Description of the Related Art Conventionally, for example, a ceramic heater used as a heat source of a glow plug for a diesel engine is known. In this ceramic heater, as shown in FIG. 5, a substantially U-shaped heating element 110 to which the lead wire 100 is connected is formed by injection molding, and the heating element 110 to which the lead wire 100 is connected is made of silicon nitride. After being embedded in powder and press-molded, the press-molded body is hot-press fired to be manufactured.

[0003]

However, in the above-mentioned heating element 110, as shown in FIG. 6, the peripheral edge of the end face 111 of the heating element 110 to which the lead wire 100 is connected has an acute angle (there are corners). Therefore, when press molding is performed in the above manufacturing process, there is a problem that cracks are generated in the ceramic body covering the outside of the heating element 110 starting from the peripheral edge (corner) of the heating element 110, which impairs productivity. there were.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a ceramic heater capable of preventing cracks from being generated in a ceramic body covering a heating element during press molding.

[0004]

The present invention has the following features to attain the object mentioned above. In claim 1,
In a ceramic heater formed by embedding and sintering a non-metallic heating element to which a lead wire is connected in a ceramic powder, the heating element has a curved surface with smooth corners from the end surface to which the lead wire is connected to the side surface. It is characterized by being configured.

According to a second aspect, in the ceramic heater according to the first aspect, the heating element is formed into a U shape having a substantially circular radial cross section, and the lead wires are connected to both ends of the heating element. When the heating element is embedded in the ceramic powder by press molding and the diameter of the heating element is D, the corner has a radius of curvature R = 0.2 to 1 / 2.Dmm.
It is characterized in that it is composed of curved surfaces.

[0006]

In the ceramic heater of the present invention having the above-described structure, since the corners from the end face to the side face of the heating element to which the lead wire is connected are formed by smooth curved surfaces, it is possible to perform the press forming. Moreover, it is possible to prevent the ceramic molded body from being cracked. Particularly, it is effective to prevent the generation of cracks during press molding by forming the corners of the heating element with curved surfaces having a radius of curvature R = 0.2 to 1 / 2.Dmm.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the ceramic heater of the present invention is used as a heat source of a glow plug will be described with reference to the drawings. FIG. 1 is an overall sectional view of a ceramic heater, FIG.
FIG. 3 is an overall sectional view of a glow plug.

As shown in FIG. 3, the glow plug 1 is provided with a mounting screw portion 2a on the outer periphery thereof, and is made of a metal mounting member 2 which constitutes an outer electrode, and the tip of the mounting member 2 (see FIG. 3). (Lower end) Metal support cylinder 3 fitted and joined (brazed) inside, ceramic heater 4 supported at the center by the support cylinder 3 with the tip side protruding from the support cylinder 3, U-shaped cross section A metal cap 5a which is formed integrally, and which is arranged through the shaft center of the mounting member 2 in a state where the metal cap 5a is joined to the rear end surface of the ceramic heater 4, and the rear end of the center shaft 5 And a terminal electrode 8 and the like which is connected to the section and is held by a nut 7 at the rear end of the fitting 2 through an insulator 6.

The ceramic heater 4 has a pair of lead wires 1 made of a non-metal heating element 9 (hereinafter, abbreviated as heating element 9) and tungsten (W) that generate heat by passing an electric current.
0, 11 and a silicon nitride ceramic sintered body 12, the heating element 9 and the lead wires 10, 11 are embedded in the ceramic sintered body 12, and the tip portion protruding from the support cylinder 3 is a diesel engine. Exposed to a pre-combustion chamber (not shown).

The heating element 9 is made of, for example, silicon nitride (Si
₃ N ₄ ) and tungsten carbide (WC) powders are mixed with an organic binder and kneaded to obtain a heating element material, which is obtained by injection molding. As shown in FIG. 1, the entire shape is formed into a substantially U shape. ing. The heating element 9 has a substantially circular cross section in the radial direction. Further, as the material of the heating element 9, in addition to the examples, it is possible to use a slurry-like material obtained by kneading each powder of Si ₃ N ₄ , WC, Re with an organic binder.

One of the lead wires 10 has one end connected to one end surface 9a of the heating element 9 and the other end extending to the end surface of the ceramic sintered body 12 so as to cover the end surface of the ceramic sintered body 12. 5a is connected (brazing).
Therefore, the lead wire 10 is connected to a power source (not shown) through the metal cap 5a, the center pole 5, and the terminal electrode 8. One end of the other lead wire 11 is connected to the other end face 9b of the heating element 9, and the other end is drawn to the side surface of the ceramic sintered body 12 and connected (brazed) to the inner wall surface of the support cylinder 3. There is. Therefore, the lead wire 11 is grounded via the support tube 3 and the mounting fitting 2.

The ceramic sintered body 12 is made of silicon nitride (Si
₃ N ₄ ) powder in heating element 9 and lead wires 10, 11
It is obtained by press-molding in the state of being embedded and then hot-press-sintering, and the whole has a cylindrical shape, and the tip exposed to the pre-combustion chamber of the diesel engine (the lower end in Fig. 1) has a hemispherical shape. It is provided.

Next, a method of manufacturing the ceramic heater 4 will be described. B) First, as shown in FIG. 4, after setting the lead wires 10 and 11 in the injection molding die 13, the above heating element material is injected from the injection port 13a to make a U-shaped space 13b in the die. To fill. By solidifying the filled heating element material, a heating element Assy in which the lead wires 10 and 11 are connected to both ends of the heating element 9 is obtained. In addition, R-roundness is provided at both end corners of the U-shaped space 13b. (B) Subsequently, the molded heating element Assy is embedded in a powder of silicon nitride (Si ₃ N ₄ ) and pressed from above and below in a U-shape to press-mold into a rectangular cross section. C) Subsequently, the press-molded body (prototype of the ceramic heater 4) obtained by press-molding is set in a carbon mold and sintered into a substantially circular shape while applying pressure at high temperature (hot press firing). D) Finally, the outer surface of the sintered ceramic sintered body 12 is polished to a predetermined size.

In the ceramic heater 4 manufactured through the above-mentioned steps, the heating element 9 has an R-shaped end face peripheral portion to which one end of each of the lead wires 10 and 11 is connected, as shown in FIG.
Is given. That is, the heating element 9 has end surfaces (one end surface 9a and the other end surface 9b) of the heating element 9 to which the lead wires 10 and 11 are connected in the injection molding step (a).
The corner from the side surface 9c to the side surface (outer peripheral surface) is formed by a smooth curved surface. In this way, by imparting R (rounding) to the end face corners of the heating element 9, the heating element Assy is replaced with silicon nitride (Si ₃ N ₄ ) in the manufacturing process of the press-formed body of the ceramic heater 4 described above. It is possible to prevent the occurrence of cracks originating from the corners of the end faces of the heat generating element 9 when embedded in the powder and pressed.

Table 1 below shows the experimental results when the end face corners of the heating element 9 were actually rounded and press-molded. However, the diameter D of the heating element 9 = 1.5 mm, and the lead wire 1
W wires having a diameter of 0.3 mm are used as 0 and 11 (see FIG. 2). The number of experimental samples is 100 each.

[Table 1]

According to the results of this experiment, when the roundness imparted to the corners of the end face of the heating element 9 is 0.2R to 1 / 2.D, cracks do not occur even during press molding of the ceramic powder, and in other cases. Cracks occurred during ceramic press molding. Specifically, as shown in Table 1, when roundness was not imparted to the end face corners, 28% (28) defects were generated, and at 0.1R, 15% (15) defects were generated.
At 1.0R, 1% (1 piece) of defects occurred.

As can be seen from the results of this experiment, there is a large step between the end faces 9a, 9b of the heating element 9 and the lead wires 10, 11 and if the corners of the end surface of the heating element 9 are not rounded. Since the corners of the end face have an acute angle, it can be said that when press-molding, cracks are likely to occur in the press-molded product starting from the sharp corner of the end face. Also, the roundness is 1/2
When the temperature is D or more (at 1.0R in Table 1), the connecting surface with the lead wires 10 and 11 is composed of a curved surface, but the heating element 9
Since a ridge line is formed on the side surface 9c (outer peripheral surface) of the above, the occurrence rate is low, but cracks may occur. Therefore, in order to bury the heating element Assy in the ceramic powder and prevent cracks generated during press molding, it is effective to add a roundness of 0.2R to 1/2 · D to the end face corner portion of the heating element 9. It can be said that it is target.

[Brief description of drawings]

FIG. 1 is an overall sectional view of a ceramic heater.

FIG. 2 is a side view showing an end surface shape of a heating element to which a lead wire is connected.

FIG. 3 is an overall sectional view of a glow plug.

FIG. 4 is a plan view of a mold showing a manufacturing process of the heating element Assy.

FIG. 5 is a plan view showing a heating element to which a lead wire is connected (prior art).

FIG. 6 is a side view showing an end face shape of a heating element to which a lead wire is connected (prior art).

[Explanation of symbols]

 4 ceramic heater 9 heating element 9a one end surface 9b other end surface 9c heating element side surface 10 one lead wire 11 the other lead wire 12 ceramic sintered body

Claims (2)

[Claims] 1. A ceramic heater obtained by burying and sintering a non-metallic heating element having a lead wire connected to a ceramic powder, wherein the heating element has a corner portion extending from an end surface to which the lead wire is connected to a side surface. Is a ceramic heater characterized by having a smooth curved surface. 2. The ceramic heater according to claim 1, wherein the heating element is formed in a U shape with a substantially circular radial cross section, and the lead wires are connected to both ends of the heating element. When it is embedded in ceramic powder by press molding, when the diameter of the heating element is D, the corner portion is formed of a curved surface with a radius of curvature R = 0.2 to 1/2 · D mm. Characteristic ceramic heater.