JP2000306706A - Manufacture of nonlinear resistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve manufacturing efficiency, electrical characteristics and mechanical strength of a nonlinear resistor. SOLUTION: After granulated powder of prescribed compound is molded in a disk type object, a calculated object 3 is obtained by calcinating (calcination serving both as degreasing) the molded body, and the outer peripheral surface of the calcinated body 3 is coated with insulating material. After the calcinated body 3 is put in a sheath composed of alumina or zinc oxide and the outer peripheral surface of the sheath is covered with thermal insulating material 1, the sheath is set in a furnace such as a gyrotron. The calcinated body 3 is irradiated with microwaves of 28 GHz oscillation frequency, and a sintered body is obtained, by baking using the self heat generation of the calcinated body 3. The body 3 may be irradiated with microwaves, in a state where the body 3 is put in a vessel 1 composed of thermal insulating material 1 without using the sheath. After that, both end surfaces of the sintered body are polished flatly, and a nonlinear resistor is completed by spraying electrode material on the polished surfaces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a nonlinear resistor mainly composed of zinc oxide and mainly incorporated in a lightning arrester.

[0002]

2. Description of the Related Art Non-linear resistors (voltage non-linear resistors) include:
Many of them contain zinc oxide (ZnO) as a main component, and as an additive component (additive slurry), a plurality of metals such as bismuth oxide, antimony oxide, cobalt oxide, manganese oxide, chromium oxide, nickel oxide, and silicon oxide. An oxide is added, and the composition is composed of a composition having high non-linearity and low heat loss.

Usually, the additive slurry is wet-pulverized by a ball mill or the like, and then sufficiently mixed with an organic binder (binder) and zinc oxide to obtain a mixture (raw material slurry). The mixture is spray-dried by a spray drier. To obtain granulated powder with good fluidity. The organic binder is an aqueous organic binder such as polyvinyl alcohol.
(PVA) is used.

Next, the granulated powder is formed into, for example, a disk-shaped compact by a die press, and the compact is degreased and calcined to obtain a calcined body. Thereafter, an insulating material is applied to the outer peripheral surface of the calcined body and fired at a temperature of 1000 to 1300 ° C. to obtain a sintered body having a high resistance layer (insulating layer) formed on the outer peripheral surface. And, after polishing both end surfaces of the sintered body smoothly,
Electrode material made of aluminum is sprayed on the polished end faces to complete the non-linear resistor.

[0005]

Generally, an electric furnace or the like is used for firing the calcined body. Electric furnaces, etc.
It is called an externally heated furnace because it uses heat (hereinafter referred to as external heat) of a substance (air or the like) other than the (calcined body) and transmits the external heat to the object to be heated. When calcining the calcined body using the external heating furnace, raise the furnace temperature to a desired temperature, calcinate the calcined body while maintaining a constant temperature for several hours, then reduce the temperature in the furnace. Then, the firing of the calcined body (firing step) is completed.

In the process of firing the calcined body, first, the surface of the calcined body is heated by external heat, and the heat on the heated surface is conducted to the central portion of the calcined body. The central part of the fired body is heated. Therefore, in order to heat the central portion of the calcined body, a time required for the heat conduction (hereinafter, referred to as a heat conduction time) is required.

Since the heat conductivity of the calcined body is low and the heat conduction time is long, and the temperature distribution inside the calcined body is large, the sintering reaction of the calcined body is not uniform. The characteristics of the non-linear resistor may be deteriorated (electrical characteristics and the like may be deteriorated), and in the worst case, a difference in thermal expansion of the calcined body may cause cracking or breakage of the calcined body. Therefore, the rate of temperature rise in firing the calcined body is 5
-10 ° C / min or less.

As a result, it takes tens of hours to sinter the calcined body. In addition, since the molded body is fired by external heat, the first sintered body (densified) is the surface of the calcined body where the temperature tends to be the highest, and the pores existing in the central part inside the calcined body The firing step is completed with the remaining, and a non-linear resistor having low electrical characteristics and low mechanical strength is produced.

Further, it is necessary to heat substances other than the object to be heated not only in terms of time but also in terms of energy, and there is much waste, so that efficient production is impossible. As a method for solving the above-mentioned problem, Japanese Patent Application No. Hei 9-148106
Japanese Patent Application Laid-Open Publication No. Hei 11 (1995) discloses a method for heating a molded body using microwaves.

[0010] The present invention has been made based on the above-mentioned problems, and has been achieved by firing a calcined body using microwaves.
It is an object of the present invention to provide a method for manufacturing a nonlinear resistor that further shortens the heat conduction time and further improves the manufacturing efficiency, electrical characteristics, and mechanical strength of the nonlinear resistor.

[0011]

In order to solve the above problems, the present invention is directed to a first invention in which a plurality of metal oxides are mixed to obtain an additive component, and then mixed with zinc oxide and an organic binder. After drying to obtain granulated powder, the granulated powder is formed into a disk-shaped compact, degreased, calcined to form a calcined body, and an insulating material is applied to the outer peripheral surface of the calcined body. In a method for manufacturing a non-linear resistor comprising applying and firing a sintered body and providing electrodes on both end surfaces of the sintered body, the calcined body is fired by a microwave having an oscillation frequency of 28 GHz. Features. The firing by microwaves is performed by placing the calcined body in a furnace such as a gyrotron and irradiating the calcined body with microwaves.

According to a second aspect of the present invention, in the first aspect, the calcined body is placed in a sheath made of alumina or zinc oxide, the outer peripheral surface of the sheath is covered with a heat insulating material, and the calcined body is calcined. It is characterized by. As the heat insulating material, for example, alumina fiber is used.

According to a third invention, in the first invention, the calcined body is placed in a container made of a heat insulating material, and the calcined body is calcined.

According to the first to third aspects, in firing the calcined body, the rate of temperature rise can be drastically increased, and the time required for firing can be reduced. Further, the occurrence rate of defects such as pinholes in the calcined body can be reduced, and the characteristics (electrical characteristics and the like) of the non-linear resistor can be improved. Further, at a relatively low firing temperature, a more dense nonlinear resistor can be obtained.

Therefore, the manufacturing efficiency, electrical characteristics, and mechanical strength of the non-linear resistor can be further improved.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, the calcined body obtained through a desired process is fired under various conditions (first to third examples) to produce non-linear resistor samples, and the heating time, electric time, The purpose of this study was to investigate the improvement of the production efficiency, electrical characteristics, and mechanical strength of the nonlinear resistor by examining the mechanical characteristics and mechanical strength.

In the present embodiment, first, a predetermined formulation
After molding the granulated powder of (composition composition having high non-linearity and low heat loss) into a disk-shaped molded body with a die press machine, the molded body is calcined (calcining also serving as degreasing) and calcined. Obtain a fired body. Since the compact shrinks (about 20%) when it is sintered, the dimensions of the compact need to be larger than the dimensions of the non-linear resistor that can be produced. For example, φ32-t
When producing a non-linear resistor of 30 (diameter 32 mm, thickness 30 mm), the molded body is molded to about φ40-t38 to about 39.

Next, after applying an insulating material to the outer peripheral surface of the calcined body, the calcined body is placed in a furnace such as a gyrotron capable of oscillating microwaves (hereinafter referred to as a microwave furnace). Is placed. Then, the calcined body is irradiated with microwaves and fired by self-heating of the calcined body to obtain a sintered body. In addition, the microwave has a temperature of 1100 °.
C, Irradiate for 30 minutes holding time. Thereafter, both end surfaces of the sintered body are polished smoothly, and an electrode material is sprayed on the polished surface to complete a non-linear resistor.

(First Embodiment) In the first embodiment, the calcined body is made of alumina sheath (370 mm × 370 mm × (8 mm)).
0 to 90) mm), the sheath is placed in a microwave oven, and the calcined body is irradiated with microwaves to obtain a sintered body, and a sample S1 of a non-linear resistor is obtained. Was prepared. Further, the outer peripheral surface of the sheath made of alumina is covered with a heat insulating material made of alumina fiber, and the sheath is placed in a microwave furnace and sintered by irradiating the calcined body with microwaves. To obtain a non-linear resistor sample S
2 was produced.

(Second Embodiment) In the second embodiment, the calcined body is made of a sheath (370 mm × 370 mm × (8 mm)) made of zinc oxide.
0 to 90) mm, the sheath was placed in a microwave furnace, and the calcined body was irradiated with microwaves to obtain a sintered body, and a non-linear resistor sample S3 was obtained. Was prepared. Further, the outer peripheral surface of the sheath made of zinc oxide is covered with a heat insulating material made of alumina fiber, the sheath is placed in a microwave furnace, and the calcined body is irradiated with microwaves to be fired. After obtaining the union, the sample S of the non-linear resistor
4 was produced.

(Third Embodiment) In the third embodiment, the calcined body is placed in a microwave furnace without using the sheath as in the first and second embodiments, and the calcined body is A sintered body was obtained by irradiating the sample with a microwave, and the sample S of the non-linear resistor was obtained.
5 was produced. Further, the calcined body is put in a container made of a heat insulating material as shown in an explanatory view of FIG. 1 (details will be described later),
The container was placed in a microwave oven, and the calcined body was irradiated with microwaves to obtain a sintered body, thereby producing a non-linear resistor sample S6.

In FIG. 1, reference numeral 1 denotes a container made of, for example, a heat insulating material of alumina fiber.
A floor plate 2 is provided in the container 1. The sole plate 2 is provided with a plurality of calcined bodies 3 to be heated. By placing the container 1 in a microwave furnace and irradiating the calcined body 3 with microwaves, the calcined body 3 is fired to obtain a sintered body.

In the first to third embodiments, a gyrotron was used as a microwave furnace, the firing temperature in the microwave furnace was 1100 ° C., and the holding time was 30 minutes.
It is assumed that a microwave having an oscillation frequency of 28 GHz is irradiated.

Table 1 below shows the firing conditions of the calcined bodies in the samples S1 to S6. In addition, in Table 1 below, for comparison with the samples S1 to S6, the calcined body was placed in a microwave furnace as in the first to third embodiments, and the calcined body was subjected to 2. A sintered body was obtained by irradiating a microwave of 45 GHz, and the results are also shown in Samples S7 to S12 (conventional examples) of non-linear resistors made of the sintered body. further,
The calcined body is placed in a sheath made of alumina, and the sheath is placed in an electric furnace, and the calcined body is calcined at a sintering temperature of 1150 ° C. and a holding time of 13 hours to obtain a sintered body. This is also shown in the non-linear resistor sample S13 (conventional example) manufactured by the above method.

[0025]

[Table 1]

In each of the samples S1 to S13, the time required for raising the temperature during firing (rising to a desired temperature) (hereinafter referred to as the required time), the sintered density (g / cm ³ ), the device
(Non-linear resistor) Operation start voltage per unit thickness (V / m
m), the nonlinear coefficient α value, and the defect occurrence rate (%) were measured, and the results are shown in Table 2 below. In addition, each of the above-mentioned samples S1 to S1
The dimensions of 3 are each φ32-t30.

[0027]

[Table 2]

In the results shown in Table 2 above, samples S1,
In S3 and S5, it can be seen that the required time is longer than those of the samples S2, S4 and S6. The reason for this is that the samples S1, S3, and S5 are manufactured by firing the calcined body without using a heat insulating material, so that the heat of the heated calcined body radiates into the furnace, and the temperature rise time becomes longer. It is possible that it has. That is, in the case of the samples S1, S3, and S5, even if the calcined body is uniformly heated, the heat is released from the outside of the calcined body, and the sintering of the calcined body becomes uneven. As shown in FIG. 2, many defects such as deterioration of electrical characteristics such as the nonlinear coefficient α value and pinholes were observed.

The sheath used for producing the samples S1 and S2 is made of alumina, and the sheath has a low dielectric constant and is not easily heated by microwaves, so that the required time is longer than that of the samples S5 and S6. . The reason for this is considered that if the temperature of the sheath is higher than the temperature of the heated calcined body, the sheath absorbs the heat of the calcined body, causing insufficient heating of the calcined body. For this reason, although the electrical characteristics and the defect occurrence rate of the samples S1 and S2 are lower than those of the samples S5 and S6, they are sufficiently usable.

In samples S3 and S4, these samples S
The material to be heated was used as the material of the sheath used in the production of 3, S4
By using zinc oxide, which is the main component of (calcined body),
Since the temperature of the sheath and the calcined body could be raised in the same manner, more uniform heating could be performed, and good results were obtained in electrical characteristics and mechanical strength.

In samples S5 and S6, sample S1
To S4, S7 to S13, the best electrical characteristics were obtained. It is considered that the reason is that only the calcined body was efficiently irradiated with the microwave, and the temperature was raised in a short time. That is, when the calcined body is usually fired without using the sheath, the electrical characteristics are deteriorated due to evaporation of components such as Bi in the calcined body.
It is considered that the calcined body in was sintered in a short time, and the amount of evaporation of the components such as Bi was suppressed.

On the other hand, in samples S7 to S12 in which the calcined body was fired by the microwave having the oscillation frequency of 2.45 GHz, the required time was shorter and the electric characteristics were better as compared with sample S13 manufactured using an electric furnace. However, samples S1-6
The electrical characteristics were significantly lower than those of. The reason for this is that the microwave having an oscillation frequency of 2.45 GHz has a low frequency and a large microwave penetration depth,
This is probably because the electromagnetic waves generated by the microwaves were not absorbed by the calcined body and the required time was extended.

[0033]

According to the present invention described above, the temperature distribution in the calcined body is made uniform by raising the calcined body by microwave and obtaining a sintered body to produce a non-linear resistor. Since the temperature can be increased, the temperature can be increased at a relatively high speed and the required time can be shortened.

Further, since the inside of the calcined body is heated by the microwave, the internal pores do not remain in the calcined body, so that an element having few defects can be manufactured, and the electrical characteristics of the element can be improved. be able to. Further, the calcined body can be sintered at a relatively low firing temperature.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a calcining step of a calcined body in a third embodiment.

[Explanation of symbols]

 1 ... container (heat insulation material) 2 ... floor plate 3 ... calcined body (heated object)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Naoto Tsuge 2-1-1-17 Osaki, Shinagawa-ku, Tokyo F-term in Meidensha Co., Ltd. 3K090 NB01 PA03 5E034 CA09 CB01 CC02 DA03 DB12 DE07 DE10 EA07

Claims (3)

[Claims] 1. A mixture of a plurality of metal oxides to obtain an additive component, followed by mixing with zinc oxide and an organic binder and drying to obtain granulated powder, and the granulated powder is formed into a disk-shaped compact. After forming into a calcined body by degreasing and calcining to form a calcined body, an insulating material is applied to the outer peripheral surface of the calcined body and calcined to obtain a sintered body, and electrodes are provided on both end faces of the sintered body. The method of manufacturing a nonlinear resistor according to claim 1, wherein the calcined body is fired by a microwave of 28 GHz. 2. The calcined body is placed in a sheath made of alumina or zinc oxide, and the outer peripheral surface of the sheath is covered with a heat insulating material.
The method for manufacturing a non-linear resistor according to claim 1, wherein the calcined body is fired. 3. The method for manufacturing a non-linear resistor according to claim 1, wherein the calcined body is placed in a container made of a heat insulating material, and the calcined body is calcined.