JP3226631B2 - Ceramic heating element - Google Patents

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, and more particularly to a ceramic heating element characterized by a means for attaching a current-carrying electrode.

[0002]

2. Description of the Related Art Ceramic heating elements are mainly used in air heaters for heating, radiant heaters such as cookers, water heaters such as water heaters, and the like. It is roughly classified into a buried type and a type in which a conductive material such as graphite is dispersed in a ceramic matrix and baked, so that the ceramic itself generates heat. Of the above, ceramics that generate heat themselves (hereinafter referred to as self-heating ceramic heating elements)
Is characterized in that the entire heating element can be uniformly heated, and the heating element can have a three-dimensional structure, for example, a honeycomb structure. Therefore, the self-heating type ceramic heating element is an important heating element in a field where a characteristic of uniformly generating heat is important.

As shown in FIG. 16, both ends of a ceramic heating element 1 are cut at right angles to form a surface on which conductive material particles (not shown) are exposed, and an electrode 2 made of a metal film is formed on the surface. Then, as shown in FIG. 17, a lead wire 3 is soldered to the electrode 2 with solder 4 or the like, and a power source (not shown) is formed.
To connect to. Electrode 2 consisting of metal film
Is spraying a metal such as aluminum, brass, nickel, etc. on the surface where the conductive material is exposed, or applying and baking a conductive paste such as platinum, palladium, silver-palladium alloy,
Means such as plating with gold, copper, nickel or the like is used. It is known that among these means, an electrode forming means by plating forms the most stable electrode.

In the self-heating type ceramic heating element, heat generation is inevitable even at an electrode mounting portion. Therefore, there is a problem that the electrode is peeled off from the ceramic or a crack is generated due to a difference in the coefficient of thermal expansion between the electrode and the ceramic.
Therefore, as a means to improve these problems,
Means such that the electrode portion and the heat generating portion have different compositions so that the resistance of the electrode portion is low, and are fired after being integrated by bonding, or a different type of low-resistance body is assembled as an electrode and integrated by firing. Proposed. However, these means complicate the manufacturing process, fail to provide sufficient conductivity of the bonded portion, cause abnormal heat generation, and do not achieve sufficient performance such as peeling or separation of the connection portion.

Therefore, the applicant of the present invention has proposed a material for imparting conductivity in ceramics, glass, or a matrix of glass and ceramics, having a particle diameter of 1 to 100 μm.
m, thickness 1 μm or less, aspect ratio 10 to 5000
We have developed a ceramic heating element made by dispersing and mixing flaky graphite. Next, in order to make the resistance value of the electrode portion lower than that of the heating portion, the amount of flaky graphite added to the electrode portion was larger than that of the heating portion, for example, 0.
We have developed a ceramic heating element that has been increased by 1 part by weight or more and applied for a patent as Japanese Patent Application No. Hei 4-16605.

[0006]

In the self-heating type ceramic heating element, the electrode section and the heating element have an integral structure, and it is necessary to mount the heating element in a limited space. There is a problem that it is difficult to make the temperature sufficiently low. Therefore, for example, when a heat cycle test is performed, there are problems that the tensile strength of the electrode is reduced due to a difference in thermal expansion between the heating element and the brazed portion, peeling and the like are likely to occur, and that the brazing operation is difficult. Improvement was required.

[0007] The present invention has been made in view of the above problems, and a self-heating ceramic heating element is provided.
An object of the present invention is to provide a ceramic heating element which can firmly attach a lead wire to an electrode without being deteriorated for a long period of time and which can easily attach the lead wire.

[0008]

According to a first aspect of the present invention, there is provided a ceramic heating element according to the present invention, in which conductive particles are dispersed and mixed in a matrix for forming ceramics, fired, and integrated. At least one surface is formed as a slope on at least one end of a ceramic molded body having a wide electrode mounting surface, and the electrode mounting surface is plated to form an electrode.

The above-mentioned ceramic molded body can be formed by various manufacturing methods conventionally used. However, it is preferable to use one in which the resistivity of the electrode portion is formed lower than the resistivity of the heat generating portion by means such as the means disclosed in the above-mentioned Japanese Patent Application No. 4-16605 to suppress the heat generation of the electrode portion. . The inclined electrode mounting surface may be flat or round. In addition, the inclination angle is not particularly limited, and may be appropriately determined according to actual conditions.

Further, the ceramic heating element according to the second aspect of the present invention.
The configuration is such that conductive particles are dispersed and mixed in a matrix for forming ceramics, fired to form electrode mounting surfaces at both ends of a ceramic molded body integrated, and the electrode mounting surfaces are plated to form electrodes. Forming and providing at least one through-hole for inserting a lead wire for current supply into the molded body, placing the lead wire by inserting the lead wire into the through-hole and contacting the exposed portion with the electrode, The lead wire was attached to the plated surface by brazing.

There is no particular limitation on the position where the through hole is provided, and the through hole may be provided in the electrode portion or in the heat generating portion. In the case where a plurality of through holes are provided, the interval may be such that a portion where the current density becomes abnormally high does not occur. The attachment of the lead wire is not particularly limited, except that the lead wire is mechanically reinforced and attached when the lead wire is held on the electrode surface of the through hole. For example, the lead wire inserted through the through hole is arranged so as to surround the electrode part, and the lead wire protruding on both sides of the hole is twisted or entangled, or the lead wire is fixed by a clamp member etc. It can be in close contact with the surface. Also, lead wires can be inserted into the plurality of through holes so as to be sewn and closely attached to the mounting electrode surface.

[0012]

The means for forming the electrode surface, that is, the means for forming the electrode area larger by making at least one surface inclined, increases the electrode area with respect to the cross-sectional area of the ceramic heating element. Has the effect of reducing the density of the current flowing into the portion and preventing heat generation at the portion. Further, the means for attaching a lead wire, that is, a means for providing a through hole for inserting a lead wire for supplying electric current into the ceramic molded body, has an effect of reinforcing the attachment strength of the lead wire to the electrode surface and a brazing operation. It has the effect of improving the properties. Therefore, the effect obtained by each of the above means can be synergistically exerted by forming the electrode mounting surface in a slope shape and providing the through hole.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. The ceramic heating element 1 used in Example 1 was prepared by dispersing and mixing a conductor (not shown) made of graphite powder in a ceramic forming matrix, and was about 30 mm in width and about 2 to 4 mm in thickness. As shown in ~ 3,
It is a conductive ceramic in which a heating part 1a having a length of about 70 mm and electrode parts 1b having a lower resistivity than the heating part 1a are formed on both sides to a length of about 10 mm.

The electrode portion 1b is formed by cutting and polishing the both ends of the ceramic heating element 1 to form a tapered slope a.
And the end face b were formed, the conductor dispersed and mixed in the ceramic forming matrix was exposed, and plating was performed thereon to form the electrode 2. That is, the inclined surface a and the end surface b constitute the electrode mounting surface of the present invention. The electrode 2 formed in the inclined shape as described above has a relatively large electrode area with respect to the cross-sectional area of the ceramic heating element 1, reduces the current density on the electrode 2, and reduces the local heat generation of the electrode portion 1b. Can be suppressed.

In order to attach the lead wire 3 to the electrode 2, it is possible to simply braze the lead wire 3 to the electrode 2 as in the prior art. However, in the first embodiment, the lead wire 3 is attached by the following means. It was attached to electrode 2. That is, the electrode portion 1b
In FIG. 1 and FIG. 2, five through-holes 4 having an inner diameter of 0.7 mm are opened, and a lead wire 3 having a diameter of 0.5 mm plated with Ni is inserted into each through-hole 4 one by one. The lead wires 3 protruding from both sides are twisted together as shown in FIGS. 1 and 2, and the lead wires 3 are brought into close contact with each other, and as shown in FIG.
(Sol 84. Nice Co.). Then, the lead wire 3 was cut into a length of about 50 to 70 mm, and a crimp terminal 3a was attached to the end thereof. FIG. 1 shows only one lead wire 3 and omits the other nine lead wires 3.

In each of the lots of the ceramic heating elements 1 formed as described above, a peeling strength of 10 kg / cm ² was obtained in a peel test at a pulling speed of 40 mm / min, and a test result of 5000 Hr or more in a current life test. The defect rate in the production line can be reduced to almost zero,
Reliability could be improved. On the other hand, with the conventional electrode and lead wire mounting means, under the same conditions, the peel test is 1-2 kg / cm ² , and the current life test is several hundred to 5000 Hr. there were.

FIG. 4 shows a modification of the first embodiment, in which five lead wires 3 are bundled and attached to one crimp terminal 3a. 5 and 6 show the ceramic heating element 1 according to the second embodiment in a state before the lead wires are attached, and are formed by the means disclosed in the specification of Japanese Patent Application No. 4-16605. . That is, the heating mixture 1a was mixed with 100 parts by weight of the ceramic powder 6a and the borosilicate glass powder 6b (hereinafter, referred to as a raw material matrix powder), which had been previously pulverized and adjusted in particle size, for 100 parts by weight.
5 to 10 parts by weight of flaky graphite 6c is mixed, and water or other organic vehicle is added as a binder to form a slurry having a predetermined viscosity. The mixture for molding the electrode portion 1b is obtained by adding flaky graphite or other conductive powder to the raw material matrix powder in an amount larger than the above-mentioned amount, and lowering the resistance by 0.5Ωcm or more than the resistivity of the heat generating portion 1a. And a slurry in the same manner. The slurry for the heat generating portion and the slurry for the electrode portion on both sides thereof were arranged and formed into a sheet to form a green sheet 6. A predetermined number of the green sheets 6 (FIG.
), And an insulating layer 6d made of a green sheet composed of only a raw material matrix was stacked on the upper and lower sides of the layers.

As shown in FIG. 6, the conductivity of the ceramic heating element 1 is small in the cross-sectional direction and large in the longitudinal direction in which current flows. Then
As shown in FIG. 5, the electrode portion 1b was cut obliquely to form a slope a exposing the flaky graphite layer, and as shown in FIG. 7, the slope a was plated to form an electrode 2. In addition,
Also in the second embodiment, the through holes (FIGS.
2) 4) can be provided.

FIGS. 8 to 11 are modifications of the second embodiment. In the ceramic heating element 1 shown in FIG. 8, the slopes a of the electrode portions 1b are parallel to each other, and the portions c having sharp tips are formed. The electrode mounting surface was formed by chamfering, and plating was performed to form an electrode 2 (FIG. 9). Further, the slope a of each electrode portion 1b of the ceramic heating element 1 shown in FIG.
An electrode 2 (FIG. 11) was formed by forming an equilateral triangular cross section and plating the slope a.

In the ceramic heating element 1 of Example 3 shown in FIG. 12, an electrode mounting surface is cut at right angles to form an end face b, and as shown in the figure, the end face b is plated to form an electrode 2. The through hole 4 is provided in the same manner as in the first embodiment.
The lead wire 3 was inserted into the ceramic heating element 1, and the lead wire 3 was attached to the ceramic heating element 1. Since this is easy to cut, the performance when the temperature rise in the electrode portion 1b is not so large can be improved as compared with the conventional one.

The ceramic heating element 1 of Example 4 shown in FIG. 13 has a configuration in which the inclined surface a of the electrode portion 1b is not a straight line but a curved surface that is convex outward. This is also described in Examples 1 to 3 above.
Similarly to the above, the mounting strength of the electrode 2 and the lead wire 3 can be improved. An example of means for attaching the ceramic heating element 1 obtained as described above to a heater is shown in FIG.
Explained by 15. The means shown in FIG.
The ceramic heating element 1 is attached via a heat-resistant insulator 7a such as mica, and a pressing member 7b is similarly disposed via the heat-resistant insulator 7a, and is fixed by tightening with a bolt 7c. The means shown in FIG. 15 is one in which the ceramic heating element 1 is supported and attached from both sides by insulators 7d fixed to the casing 7.

[0022]

As described above, since the first structure of the ceramic heating element of the present invention has the inclined surface on which the electrode is formed, the electrode area can be made larger than the sectional area of the heating element. The current density of the portion can be reduced, and uniform voltage application can be performed. Further, a second configuration in which a through hole is provided, and the lead wire of the through hole is inserted and mechanically held by the electrode to attach the lead wire to the electrode surface,
The workability of lead wire attachment, the workability of brazing, the strength of attachment, and the like are improved, the work failure rate is remarkably reduced, and the yield can be improved. Therefore, a highly reliable ceramic heating element can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view of a ceramic heating element according to Embodiment 1 of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a partial perspective view of a ceramic heating element according to a modification of the first embodiment.

FIG. 5 is a sectional view of a ceramic heating element according to Embodiment 2 of the present invention.

6 is a partially enlarged view of a portion A in FIG.

7 is a cross-sectional view showing a state in which electrodes are formed on the ceramic heating element shown in FIG.

FIG. 8 is a sectional view of a ceramic heating element according to a modification of the first embodiment.

9 is a cross-sectional view showing a state in which electrodes are formed on the ceramic heating element shown in FIG.

FIG. 10 is a cross-sectional view of a ceramic heating element according to another modification of the first embodiment.

11 is a cross-sectional view showing a state in which electrodes are formed on the ceramic heating element shown in FIG.

FIG. 12 is a sectional view of a ceramic heating element according to Embodiment 2 of the present invention.

FIG. 13 is a perspective view of a ceramic heating element according to Embodiment 3 of the present invention.

FIG. 14 is a cross-sectional view illustrating a means for holding the ceramic heating element of the present invention in a heating device.

15 is a cross-sectional view illustrating another holding means for the ceramic heating element shown in FIG.

FIG. 16 is a perspective view illustrating a ceramic heating element according to a conventional example.

17 is a side view showing a state where a lead wire is attached to the ceramic heating element shown in FIG. 16;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Ceramic heating element 1a Heating part 1b Electrode part 2 Electrode 3 Lead wire 4 Through hole 5 Solder 6c Flaky graphite (conductive particles) a Slope (electrode mounting surface) b End surface (electrode mounting surface)

Continuing from the front page (72) Inventor Masahiro Ito 1 Kokubu-cho, Tochigi City, Tochigi Prefecture Inside the Mitsui Mining Co., Ltd. Central Research Laboratory (72) Inventor Tsuyoshi Utsugi 1 Kokubu-cho, Tochigi City, Tochigi Prefecture Mitsui Mining Co., Ltd. (72) Inventor Yutaka Yamashita 2-1-1, Nihonbashi-Muromachi, Chuo-ku, Tokyo Mitsui Mining Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) H05B 3/03 C04B 35/495 H05B 3 / 02 H05B 3/14

Claims (2)

(57) [Claims] 1. An electrode mounting surface is formed by dispersing conductive particles in a matrix for forming ceramics, mixing and firing and integrally forming a ceramic molded body with at least one inclined surface at both ends. A ceramic heating element with an electrode formed by plating the electrode mounting surface. 2. An electrode mounting surface is formed on both ends of a ceramic molded body which is obtained by dispersing and mixing conductive particles in a ceramic forming matrix, firing and forming an integrated body, and plating is performed on the electrode mounting surface. And forming at least one through-hole through which a lead wire for current supply is inserted into the molded body, and placing the lead wire by inserting the lead wire into the through-hole and contacting the exposed portion with the electrode. , Ceramic heating element with lead wire brazed to plated surface.