JPH0240886A - Manufacture of ceramic heater - Google Patents

Abstract

PURPOSE:To reduce variation of the resistance value of a ceramic heater by forming conductive ceramic powder into a green sheet, stamping out the sheet into the specific form of a resistor, embedding the resistor into which the sheet is thus stamped out in ceramic powder of silicon nitride and sintering the resistor while pressed in the thickness direction thereof. CONSTITUTION:A green sheet made of conductive ceramic powder is stamped out into U-shape to be a stamped resistor 1. Organic binder for molding powder is applied to the resistor 1, then the binder is processed to adjust ceramic powder of silicon nitride. The ceramic powder is formed into two compacts 2 whose cross section is D-shape by means of a die. The plane portions of the compacts 2 are arranged to face each other and the sheet stamped resistor 1 is disposed therebetween to press them to be integrated. Hot press sintering is then applied to the integrated body with changing pressing direction. Variation of the resistance value of a ceramic heater is thus reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a ceramic heater that constitutes a heater section of a heating element that rapidly raises temperature, such as a ceramic glow plug.

<Prior Art> Ceramic glow plugs have recently been developed and are being used as plugs for diesel engines and the like.

The heater section used here has T i+ as a resistor.
Z r, If f * L a, v, N b+
Ta, Cr.

m such as a nitride of one or more metals selected from Mo and W
In addition to using electrically conductive ceramics, silicon nitride-based porcelain has been proposed as an insulator and has better high-temperature properties. The reason why conductive ceramic is used as a resistor is that unlike conventional coil resistors made of high-melting point metals such as W and Mo embedded in porcelain, the reason why conductive ceramics are used as resistors is that they Its purpose is to reduce the difference in thermal expansion.

<Problems to be Solved by the Invention> However, until now, heater parts using conductive ceramics have been developed by applying a paste containing resistance powder to the surface of an unfired ceramic body, as seen in Japanese Patent Application Laid-open No. 57-106586. A method of manufacturing by coating is known, but it tends to cause variations in coating thickness, and as a result, the resistance value tends to fluctuate. In order to obtain this, it is necessary to repeat coating and drying several times, which is undeniably disadvantageous in terms of man-hours.

Alternatively, if a U-shaped resistor is punched out and buried in a cylindrical ceramic, the ratio of the width of the resistor sheet to the sheet thickness becomes extremely large, resulting in large temperature irregularities in the radial direction of the ceramic heater. There is. Note that this is a drawback also seen in the above-mentioned coating method.

Means for Solving the Problems> The present invention has been made to solve the above problems,
The outline of the process is to form a green sheet from powder mainly made of conductive ceramic, punch it into the shape of a predetermined resistor, and embed the punched resistor in silicon nitride ceramic powder. , is a method for manufacturing a ceramic heater, which comprises a step of firing the monomer antibody while applying pressure from the width direction.

Effects> According to the present invention, ■ any thickness (0, 0,
05 to Kazuryu) are obtained. Moreover, since there is little variation in the thickness dimension, the variation in resistance value of the ceramic heater as a final product is reduced as a result.

■Since it is formed using a die punch press, dimensional accuracy is high and variations in resistance values are reduced.

■Since hot press firing is performed while applying pressure from the width direction of the sheet surface, 50 to 6
Firing shrinkage of 5% occurs.

As a result, the ratio of resistor width/resistor thickness of the resistor in the sintered body is reduced to 50 to 65% of that of the green molded body, and the variation in temperature distribution in the radial direction of the ceramic heater is reduced.

There are effects such as

In the embodiment of the present invention, the step of embedding the punched resistor in silicon nitride ceramic powder is generally carried out by adding a predetermined sintering aid to the silicon nitride ceramic powder, and then adding a sintering agent to the silicon nitride ceramic powder as shown in FIG. Two cross-section shaped molded bodies 2 are created by a mold press, and the flat sides thereof are placed inside to face each other, and the punching resistor 1 is sandwiched between them, and the molded body 2 is molded by mold pressing.

In this case, the shrinkage direction of the product differs depending on the method of firing and pressurization, and if hot pressing is performed while applying pressure from the width direction of the resistor as in the present invention, a ceramic heater with a small temperature distribution and little variation in resistance value can be obtained. .

<Example> Next, examples and comparative examples of the present invention will be described.

To 70% by weight of WC with an average particle size of 0.5 μm and 30% by weight of 5izNa with an average particle size of 1.5 μm, 7% by weight of polyvinyl butyral (organic binder) was added, and further mixed with toluene and ethyl alcohol as a solvent to improve fluidity. A slurry was prepared and poured onto a flat plate using a doctor blade method to volatilize the solvent, thereby creating a green sheet consisting of a resistor with a thickness of 0.4 fins.

Next, the resistor 1 was punched out using a mold into a substantially U-shape as shown in FIG. On the other hand, the average particle size is 0.1 am, Sj+Na 90% by weight, Ah(h 5% by weight, Y!(
h Add ethyl alcohol to 5% by weight and wet mix,
After adding a binder for powder molding, such as ethyl cellulose, 1iJ1.
to prepare ceramic powder.

Next, as shown in FIG. 1, the ceramic powder is molded into a molded body 2 with a cross-sectional shape using a mold, and the flat parts of the two molded bodies are placed facing each other.
Press molding was performed in one piece with the two in between. 3 is an electrode portion of the resistor.

Next, in Figure 3, (la) and (lb
) (present invention), and (3a) and (3b) (comparative examples), hot press firing was performed by changing the pressing direction. This material contracted only in the direction of pressure, but not in the direction of thickness.

Figures 2 (la) and (lb) are punched sheet resistors that were hot-pressed by applying pressure from the width direction, and Figure 2 (2a) and (2h) were simply fired normally without applying pressure. It was the result of a similar situation, and it was a contraction of Tomotsuri.

Furthermore, as shown in FIGS. 2(3a) and 2(3b), it was observed that the thickness of the sheet becomes thinner and thinner when hot pressing is performed while applying pressure in the direction of the thickness of the sheet.

In addition, the shape of the resistor buried inside is transmitted through X-rays.
I watched him on the line.

According to the above, in the case corresponding to the embodiments of the present invention shown in FIGS. 2(1a) and 2(1b), 57% of the firing shrinkage occurred in the plane direction of the sheet, and the width of the sheet contracted at the same rate. Since the sheet thickness hardly changed, the total width of the resistor /I''
7-sa ratio decreased to 57%.

The above sintered body was polished into a cylindrical shape of φ3.5 x l 40 (mm), and the electrode parts exposed by polishing were metallized, and then the metal parts were brazed and electrically heated in order to apply an electric current. As a result, the temperature difference in the radial direction was 550°C, which was good.

On the other hand, in the comparative example, the ratio of the total width/thickness of the resistor does not change when normally fired (Fig. 2 (2)), but when hot press firing is performed by applying pressure from the direction of the thickness of the sheet, the ratio is 1. 7
It expanded to 3 (110, 57) and became smaller.

When electrical heating was carried out in the same manner as in the examples of the present invention, the temperature differences were 150 DEG C. and 300 DEG C., respectively, which were completely unacceptable for practical use.

(When using a comparative example, the shape of the unfired press molded body was changed in consideration of the shrinkage rate during firing.) Furthermore, the 3σ of the ceramic heater according to the example of the present invention was When the variation in resistance was checked, it was found to be extremely stable with -1-=2.7%.

<Effects of the Invention> According to the present invention, it is possible to manufacture a ceramic heater with a narrow range of temperature distribution and less variation in resistance value.

Further, the thickness and shape of the resistor can be set arbitrarily, making it easy to create a heater having the necessary temperature-raising characteristics.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the process of sandwiching and integrating a resistor manufactured by the green sheet punching method between D-type ceramics;
Fig. 2 is a vertical cross-sectional view showing the shape of the resistor in the molded body, Fig. 3 (la) and (lb) are examples of the present invention, Fig. 3 (2a)
), (2b) is an example of normal firing, Figure 3 (3
a) and (3b) show a longitudinal cross-sectional view and a cross-sectional view showing an example of hot pressing while applying pressure in the thickness direction. l...Punching resistor, 2...Silicon nitride ceramics 3...Electrode part

Claims (1)

[Claims] A process of kneading powder mainly made of conductive ceramic and an organic binder for sheet forming into a paste, and forming a green sheet by pouring this into a flat plate; A ceramic heater comprising the steps of punching into the shape of a resistor, embedding the punched resistor in silicon nitride ceramic powder, and firing while applying pressure from the width direction of the resistor. manufacturing method