JPH01202801A - Manufacture of nonlinear voltage resistor - Google Patents

Abstract

PURPOSE:To set the voltage (V1mA) of a nonlinear voltage resistor to a desired value without deterioration of various electric characteristics by cooling a blank for a fired nonlinear voltage resistor at a cooling speed determined based on the measured result of a previous test while it is cooled from at least a firing temperature to specific temperature in a cooling step for the blank. CONSTITUTION:A cooling speed determined based on the measured result of a previous test is set to cool a blank for a fired nonlinear voltage resistor while it is cooled from a baking temperature to 850 deg.C in a cooling step for the blank. Thus, a preferable element having less irregularity can be manufactured by controlling the growth of uniform grains during the cooling from the firing temperature to 850 deg.C in which liquid phase is presented. In this manner, the V1mA value of the resistor can be set to a desired value without deterioration of various electric characteristics.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention is concerned with the characteristics of a voltage nonlinear resistor whose main component is zinc oxide, particularly the voltage (Vl, A) required when a current of 1 mA flows through the resistor. ) to a desired value (standard) during the manufacturing process.

(Conventional technology) Conventionally, zinc oxide is the main component and Bizl) 1.5b2
03 It is widely known that elements containing small amounts of additives such as +5iOz, Co=O=, MnO2, etc. exhibit excellent voltage nonlinearity, and are used in lightning arresters etc. by taking advantage of this property. .

Such a voltage nonlinear resistor is usually manufactured through the steps of press-molding a mixed granulated powder made of the above ingredients into a desired shape, firing it, and attaching electrodes to the resulting sintered body. ,
In particular, Vl and A of the resistor were adjusted by appropriately changing the processing temperature or processing time during firing.

(Problem to be Solved by the Invention) By the way, when manufacturing a voltage nonlinear resistor, as mentioned above, in order to set V, , A to desired values, it is necessary to simply change the processing temperature and processing time during firing. However, non-uniform grain growth of zinc oxide that constitutes the voltage non-linear resistor, differences in the diffusion of bismuth, antimony, etc., and the occurrence of voids are unavoidable, resulting in significant variations in electrical characteristics. Ta.

It is an object of the present invention to propose an effective method for setting the V, , A values of a voltage nonlinear resistor to desired values without causing deterioration of other electrical characteristics.

(Means for Solving the Problems) This invention is achieved by press-molding a mixed granulated powder consisting of zinc oxide as a main component and additives containing at least bismuth oxide, antimony oxide, and silicon oxide, and then firing the powder. When manufacturing a voltage nonlinear resistor, the cooling process of the fired voltage nonlinear resistor element from at least the firing temperature to 850°C is determined based on the measurement results of previous tests. This is a method for manufacturing a voltage non-linear resistor, characterized in that cooling is performed at a cooling rate set to a certain temperature.

In order to prevent minute cranks from forming in the element body after firing, the upper limit of the cooling rate in the above method is 300℃/
It is preferable to set it as hr.

(Function) Now, in the production of voltage nonlinear resistors, the cooling rate during the cooling process after firing, at least from the firing temperature to 850°C, is determined in accordance with the data from the previous test described below. The reason why it is possible to set the target Vl- while avoiding variations in the electrical properties of the resistor by cooling the resistor at The presence of a liquid phase ensures uniform grain growth upon cooling from the firing temperature.85
This is thought to be because by controlling the temperature down to 0° C., it is possible to manufacture good elements with less variation.

Note that changing the cooling rate below 850° C. is not preferable because there is a risk that a difference will occur in the crystal phase of bismuth oxide contained in the grain boundary layer and the characteristics will change. For this reason, in the temperature range below 30 to 60 degrees Celsius, which does not affect quality or characteristics.
It is desirable to maintain the cooling rate at about /hr.

Hereinafter, the procedure for setting (1) and (8) in the process of manufacturing a voltage nonlinear resistor will be explained in detail.

First, the main raw material of zinc oxide adjusted to a predetermined particle size, additives such as bismuth oxide, cobalt oxide, manganese oxide, antimony oxide, chromium oxide, silicon oxide, nickel oxide, etc. adjusted to a predetermined particle size, and borosilicate containing preferably silver. Mix a predetermined amount of acid bismuth glass. Next, a predetermined amount of an aqueous polyvinyl alcohol solution and a predetermined amount of an aluminum nitrate solution as an aluminum oxide source are added to these raw material powders. This mixing operation preferably uses an emulsifying machine.

Next, deaeration is performed under reduced pressure, preferably at a vacuum level of 200 mmHg or less, to obtain a mixed slurry. The moisture content of mixed slurry is 30-35
-t%, and the viscosity of the mixed slurry is 100 cp.
It is preferable to set it to ±50.

Next, the obtained mixed slurry is fed to a spray drying device so that the average particle size is 50 to 150 μm, preferably 80 to 120 μm,
Moisture content is 0.5-2. Owt%, more preferably 0.9
-1.5 wt% granulated powder is granulated.

Next, the obtained granulated powder was subjected to a molding process at a molding pressure of 8
00~1000kg/cm'' and molded into a predetermined shape.Then, the molded body is heated at a rising/lowering temperature of 50~70℃/
The binder is scattered and removed by calcining at 800 to 1000° C. for 1 to 5 hours.

Next, an insulating coating layer is formed on the side surface of the calcined body. Specifically, the insulating coating layer contains a predetermined amount of a bismuth compound, preferably bismuth oxide, an antimony compound, preferably antimony oxide, a silicon compound, preferably silicon oxide, a zinc compound, preferably zinc oxide, and ethyl cellulose as an organic binder. It is made of an oxide paste containing butyl calpitol, n-butyl acetate, etc., and is applied to the side surface of the calcined body to a thickness of 100 to 300 μm.

Next, this was heated to 1000 at a heating rate of 30 to 60"C/hrO.
-1300C, preferably 1100-1250C, and main firing is carried out under the conditions of holding in that temperature range for 2 to 7 hours. Next, the cooling rate after the main firing is set according to the data obtained from the preliminary test of the same lot of elements conducted prior to the main firing, and the desired V.
Cool from the firing temperature to 850°C so that the A value is obtained, and further below 850°C, preferably 30 to 6
Cool to room temperature at 0°C/hr.

Here, the cooling from the firing temperature to 850°C is specifically performed in order to promote the growth of crystal grains when the Vl and A of the element determined in the previous test are higher than the target ■ and A. The cooling rate is controlled to be low, and if it is lower than the target value, the cooling rate is controlled to be high in order to promote the growth of crystal grains.

In this invention, in particular, VIm+8 can be easily changed by controlling the cooling rate in the above temperature range. It is disadvantageous from the viewpoint of productivity and energy saving to do so. Therefore, V,,A
It is desirable that the change or adjustment should be within ±10%.

In addition, a glass paste prepared by adding ethyl cellulose, butyl calpitol, n-butyl acetate, etc. as an organic binder to glass powder was applied to the insulating coating layer at a thickness of 100 to 300 μm.
coating to a thickness of 100 to 200℃ in air
It is preferable to form the glass layer by heat-treating the glass layer at 400 to 600°C for 0.5 to 2 hours.

Finally, the electrode-forming surface of the obtained element body is polished smooth, and an electrode made of, for example, aluminum is provided on that surface using a metallcon to obtain a voltage nonlinear resistor.

(Example) Target (7) Diameter 47 with Vl and A value of 4.5 kV
A plurality of voltage nonlinear resistors each having a thickness of 22.5 mm and a thickness of 22.5 mm were manufactured according to the above-mentioned procedure, and each of the obtained elements had ■I-1.
The voltage nonlinearity index α and the breakdown rate of switching surge discharge capacity were measured.

In addition, to obtain a resistor with V and lIA of 4.5 kV,
85 from at least the firing temperature in the cooling process after firing
The cooling rate until the temperature reached 0°C was as follows: a firing temperature of 1220″ C1 holding time of 5 hr as a preliminary test with the same composition;
The value of vlA of the resistor manufactured under the conditions of cooling rate 60°C/hr was 4.7 kV, so that value was compared with the calibration curve and set as 40''C/hr. For the wire, use elements of the same composition in advance, keep the heating rate, firing temperature, and holding time constant under the above conditions, and increase the temperature by 850° from the firing temperature.
The cooling rate to "C" was changed stepwise, the corresponding values of V, and A were measured, and a calibration curve was created using the values.

Table 1 summarizes the processing conditions in the firing and cooling processes together with the conditions when applying the conventional method, and Table 2
The results of the survey are shown below.

Note that the voltage nonlinear index α in Table 2 is I = KVa (I
: current, V: voltage, K: proportionality constant) based on V, , A and V,. . It was determined from μA, and the breakdown rate (%) of the switching surge discharge withstand capacity showed the percentage of breakdown when currents of 100OA, 1100A, and 120OA were repeatedly applied 20 times with a current waveform of 2ms.

Table 1 From Table 2, it is confirmed that the voltage nonlinear resistor manufactured according to the present invention can be set to a value extremely close to the desired V, A, and has small variations and good characteristics. It was done.

In addition, Table 3 shows the V, A, voltage of the voltage nonlinear resistor obtained by variously changing the lower limit value in the temperature range that should be adjusted to the cooling rate determined by the data obtained from the previous test. Table 4 shows the investigation results of the nonlinear index α and the breakdown rate of switching surge discharge capacity, and the V of the voltage nonlinear resistor obtained by variously changing the cooling rate from the firing temperature to 850°C.
, , A shows the investigation results of voltage non-linearity index α and switching surge withstand breakdown rate, respectively.

In Table 3, the cooling rate up to each temperature is all 120"C/hr, and after each temperature is all 60"C/hr.
In Table 4, all cooling rates after 850"C were set to 60"C/hr. The firing details are shown in Table 3.
, 4 were both held at 1225°C for 15 hours.

From Tables 3 and 4, it is clear that unless cooling is done at an appropriate cooling rate from the firing temperature to 850°C, the target V, A cannot be set, and the voltage non-linearity will result in the desired quality. It is clear that no resistor can be obtained.

(Effects of the Invention) According to the present invention, V, A of the voltage nonlinear resistor can be set to desired values without deteriorating electrical characteristics or quality.

Patent applicant: Nippon Insulator Co., Ltd.

Claims (1)

[Claims] 1. When producing a voltage nonlinear resistor by press-molding a mixed granulated powder consisting of zinc oxide as a main component and additives containing at least bismuth oxide, antimony oxide, and silicon oxide, firing is performed. In the cooling process of the applied voltage nonlinear resistor element body, at least from the firing temperature to 850 ° C., the cooling rate is set at a cooling rate determined based on the measurement results of the preceding test. A method for manufacturing a voltage nonlinear resistor.