JPH03250605A - Manufacture of voltage non-linearity resistor - Google Patents

Abstract

PURPOSE:To manufacture a voltage non-linearity resistor capable of improving a discharge withstand current rating, an applied voltage life and a dielectric constant and of reducing a rate of flatness by dispersion-removing a specific percent or more of the added weight of bismuth oxide added to a mixture at the time of baking and by making the percentage content of bismuth oxide in a voltage non-linearity resistor under a specific percent after baking. CONSTITUTION:At the time of baking, 10% or more out of the quantity of bismuth oxide added to a mixture is dispersion-removed. Accordingly, bismuth oxide can be added at first more than the optimum quantity thereof by a portion to be dispersion- removed at the time of baking. That is, bismuth oxide is excessively added in the stage of a first mixture, wetting properties of zinc oxide particle surfaces are improved at the time of baking, and 10% or more out of the added quantity of the bismuth oxide is dispersion-removed also at the time of baking so that the percentage content of zinc oxide in the baked material can be finally made to less 6wt.%. Therefore, it is possible to suppress an adverse effect, which the excessive existence of bismuth oxide in a grain boundary layer has on the characteristics of a zinc oxide element, and to make a rate of flatness, dielectric constant and discharge withstand current rating satisfactory.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a voltage nonlinear resistor containing zinc oxide as a main component.

(Prior Art) Voltage nonlinear resistors containing zinc oxide as a main component are widely used in lightning arresters and surge absorbers for the purpose of voltage stabilization or surge absorption because of their excellent nonlinear voltage-current characteristics. This voltage nonlinear resistor is made by adding small amounts of oxides such as bismuth, antimony, cobalt, manganese, etc. that exhibit voltage nonlinearity to the main component, zinc oxide.
It can be produced by granulating, molding, firing, preferably applying an inorganic substance to form a side surface high resistance layer, firing again, and attaching electrodes to the sintered body.

When manufacturing such a voltage nonlinear resistor, conventionally, a bedding powder or the like was placed inside a sealed casing to actively protect the atmosphere inside the casing. During firing, it is necessary to always add a predetermined amount of additive components, particularly bismuth oxide, to form a liquid phase so that the produced zinc oxide particles are uniformly wetted by the liquid phase.

(Problems to be Solved by the Invention) However, even after firing, bismuth oxide does not form a solid solution in zinc oxide, and grain boundaries are formed between zinc oxide particles. For this reason, when the amount of bismuth oxide added is large, this grain boundary becomes thicker, and as a result, the surge withstand capacity, electrification life, and dielectric constant characteristics of the voltage nonlinear resistor decrease, and the flatness ratio increases.

On the other hand, if the amount of bismuth oxide added is small, the surface of the zinc oxide particles will not be sufficiently wetted during firing, and the sintering of the zinc oxide particles will not proceed.

An object of the present invention is to provide a method for manufacturing a voltage nonlinear resistor that can overcome the above-mentioned problems, improve discharge withstand capacity, energized life, and dielectric constant, and reduce flatness.

(Means for Solving the Problems) The present invention produces a voltage nonlinear resistor by granulating, molding, and firing a mixture containing zinc oxide as a main component and at least bismuth oxide as an additive component. In the method, at least 10% of the added weight of bismuth oxide added to the mixture is scattered and removed during the firing, and the content of bismuth oxide in the voltage nonlinear resistor after firing is reduced to 6.
The present invention relates to a method for manufacturing a voltage nonlinear resistor, characterized in that the amount is less than or equal to % by weight.

(Function) According to the method for manufacturing a voltage nonlinear resistor according to the present invention, the content of bismuth oxide in the voltage nonlinear resistor after firing is 6% by weight or less (preferably 0.5 to 4% by weight). )
Therefore, the adverse effect on the characteristics of the zinc oxide element due to the excessive presence of bismuth oxide in the grain boundary layer can be suppressed, and the flatness, dielectric constant, and discharge durability can be improved. If the content of hismuth oxide exceeds 6% by weight, the flatness will increase and the dielectric constant and discharge withstand capacity will decrease.

In the present invention, it is noteworthy that 10% or more of the amount of bismuth oxide added to the mixture (
Preferably 15 to 25% by weight) is scattered and removed during firing. Therefore, initially, bismuth oxide can be added in excess of its optimum addition amount by the amount to be scattered and removed during firing. That is, at the initial mixture stage, bismuth oxide is added in excess to increase the wettability of the zinc oxide particle surface during firing, and at the time of firing, one of the added amounts of bismuth oxide is
By scattering and removing 0% or more, the final content of zinc oxide in the sintered body can be reduced to 6% by weight or less.

At this time, 10% or more of the added amount of bismuth oxide was scattered and removed during firing because if it was less than 1096, no significant improvement in discharge withstand capacity and dielectric constant was observed.

In order to scatter and remove bismuth oxide during firing in this way, it is preferable to employ, for example, the following method.

That is, conventionally, as described above, the firing casing was sealed,
It was considered essential to protect the atmosphere.

However, in order to realize the configuration of the present invention, contrary to this common sense, for example, a window is provided in the baking casing to make it breathable.
During the main firing, the atmosphere is reduced in pressure to scatter bismuth oxide. At this time, more preferably 1000 to 1300
First, firing is performed in a closed state at a temperature of 1100 to 1250 °C, and then once the temperature is lowered to 900 °C or higher (preferably 900 to 1050 °C), the pressure is reduced to a predetermined temperature. Hold for a certain amount of time to remove bismuth oxide.

When scattering bismuth oxide, the pressure inside the housing is 100-7
It is preferable to set it to 00Torr, and 250 to 550Torr.
It is more preferable to set it to rr. If the temperature is less than 100 Torr, the varistor characteristics will deteriorate, and if it exceeds 700 Torr, the amount of hismuth oxide scattered will decrease. Also, at this time,
Temperature of 900°C or higher, for example 1000°C, for a certain period of time
When the temperature is maintained at a temperature of 4 to 10 hours, it is preferable to maintain the temperature for 4 to 10 hours.

It is preferable to use hismuth trioxide instead of hismuth oxide because a particularly remarkable effect can be obtained.

In addition, when the voltage nonlinear resistor manufactured according to the present invention is applied to a lightning arrester with a gap, the dielectric constant of this resistor becomes high (for example, 600 or more). This is very advantageous in terms of insulation from the horn.

That is, a lightning arrester with a gap is conceptually an arc horn of an insulator device provided with a lightning arresting function, and is composed of a current limiting element portion and a series gap. The current limiting element is made by connecting zinc oxide elements having non-linear voltage resistance characteristics in series and housing them in an insulator (porcelain tube) or molded with an insulator (ethylene, propylene rubber). As a result, when the potential of the steel tower rises due to a lightning strike on a power transmission line, it is discharged in the series gap, and the non-linear resistance characteristics of the current limiting element are used to interrupt the follow-on current in a short period of time, shutting down the substation. The aim is to prevent power outages due to equipment operation.

However, with such a lightning arrester with a gap, the current limiting element must be newly inserted and installed between the existing towers, so there is a problem with insulation coordination with the existing arcing horn, and there is a risk of flashing across the series gap in the event of a lightning strike. It is necessary to prevent flashovers at the arc horn. In this regard, since the voltage nonlinear resistor manufactured according to the present invention has a high dielectric constant,
Since it is possible to reduce the flashover voltage that occurs in the series gap, it is easy to enhance insulation with existing arcing horns.

(Example) To obtain a voltage nonlinear resistor whose main component is zinc oxide,
First, zinc oxide raw material adjusted to a predetermined particle size, bismuth oxide, cobalt oxide, manganese oxide, adjusted to a predetermined particle size,
A predetermined amount of additives such as antimony oxide, chromium oxide, preferably amorphous silicon oxide, nickel oxide, boron oxide, silver oxide, etc. are mixed. In this case, silver nitrate or boric acid may be used instead of silver oxide or boron oxide. Preferably, hismuth borosilicate glass containing silver is used. Alternatively, the additive may be calcined at 800 to 1000°C, then pulverized and adjusted to a predetermined particle size, and the zinc oxide raw material may be mixed with the additive. At this time, a predetermined amount of polyvinyl alcohol aqueous solution or the like is added to these raw material powders.

Next, degassing is preferably carried out under a vacuum degree of 200 mmHg or less, and the water content of the mixed slurry is preferably about 30 to 3 sivt%, and the viscosity of the mixed slurry is preferably 100±50 cp. Next, the obtained mixed slurry is fed to a spray dryer to obtain an average particle size of 50 to 150 μm, preferably 80 to 150 μm.
Granulated powder with a moisture content of 0.5 to 2.0 wt%, more preferably 0.9 to 1.5 wt%, is granulated at 120 μI. Next, the obtained granulated powder was subjected to a molding process at a molding pressure of 80
It is molded into a predetermined shape under 0 to 1000 kg/cm2.

Next, the molded body was heated and cooled at a heating and cooling rate of 50 to 70°C/hr.
Preliminary firing is performed at a temperature of 800 to 900° C. and a holding time of 1 to 5 hours. Note that, before calcining, it is preferable to remove organic components such as the binder by scattering the molded body at a heating/lowering rate of 10 to 100°C/hr and holding time at 400 to 600°C for 1 to 10 hours.

Next, a high resistance layer is formed on the side surface of the calcined body. In this example, B
i2O3,5b203. An insulating coating mixture paste prepared by adding ethyl cellulose, butyl calpitol, n-butyl acetate, etc. as an organic binder to a predetermined amount of ZnO, 5io2, etc. is applied to the side surface of the calcined body to a thickness of 60 to 300 μm.

Next, this is heated at a temperature raising/lowering rate of 20 to 100°C/hr and a maximum holding temperature of 1000 to 1300°C, preferably 1050 to 1000°C.
Main firing is performed at 1250°C. In order to manufacture the voltage nonlinear resistor of the present invention, as described above, - after first firing at a high temperature, the temperature is lowered to 900 to 1050°C, and the pressure inside the housing is reduced at this temperature. , the temperature is held constant for a predetermined period of time to remove bismuth trioxide by scattering.

In addition, a glass paste made by adding ethyl cellulose, butyl calpitol, n-butyl acetate, etc. as an organic binder to glass powder is applied to the high resistance layer on the side surface to a thickness of 100 to 300 μm.
Apply the coating to a thickness of 50-200°C in air
It is preferable to form the glass layer by heat treatment under the conditions of /hr, 400 to 900'C1 holding time of 0.5 to 4 hours.

After that, both end faces of the obtained voltage nonlinear resistor were bonded to SiC,
#400 to #2000 such as Al2O3, diamond, etc.
Polishing is performed with a suitable abrasive using water, preferably oil, as the polishing fluid. Next, after cleaning the polished surface, electrodes made of aluminum or the like are provided on both polished end surfaces by, for example, thermal spraying to obtain a voltage nonlinear resistor.

Hereinafter, the results of actually measuring various characteristics of voltage nonlinear resistors within and outside the scope of the present invention will be described.

Example 1 A predetermined amount of B120a shown in Table 1 was prepared according to the method described above.
, CO2O3 1.0 mol%, Mn0z 0.5 mol%, 5b2031.0 mol 0u, Cr2(L+ 0.5
For the mol O, 0.1 wt% of hismuth borosilicate glass is added to a raw material consisting of 1.0 mol 06 of NiO, 1.0 mol% of SiO□ and the balance ZnO, and this mixture is molded, calcined, and has a high resistance. By forming layers, firing, etc., voltage nonlinear resistors of the present invention examples and comparative examples shown in Table 1 having a diameter of 47 plates and a thickness of 22.5 mm were manufactured. However, the main firing step was performed according to a temperature increase-temperature maintenance-temperature decrease schedule as shown in the drawings. That is, first, the temperature was raised at a rate of 50°C/hr at normal pressure, and 12
Hold at 00°C for 5 hours and 100°C at a rate of 60°C/hr.
The temperature dropped to 0°C. Next, the pressure inside the housing (inside the kiln) was reduced to the pressure shown in Table 1, and the temperature was maintained at 1000°C for the predetermined time shown in Table 1. Next, return the inside of the kiln to normal pressure,
Heat up at a rate of 60°C/hr. The amount of bismuth trioxide scattered was varied by varying the holding time of IQOO'C and the pressure inside the kiln at this time.

For each voltage nonlinear resistor obtained in this way, the dielectric constant (ε) and ΔV, respectively. A (%) and flatness rate V 40 K
A/VI mA was measured. △V1. ．． A (%
) is the rate of change in V ImA after the application of a lightning surge (100 KA), and the flatness ratio vao/■ is the ratio of the limiting voltage at 40 KA and 1 m, 4.

These measurement results are shown in Table 1. Shown below.

As can be seen from the results in Table 1, by following the present invention,
Δv1ffiA, it is possible to decrease the flatness rate and increase the dielectric constant at the same time. It is also clear that the amount of bismuth trioxide scattered can be controlled by changing the holding time at 1000°C and the pressure inside the kiln.

Example 2 In exactly the same manner as in Example 1, voltage nonlinear resistors of the present invention examples and comparative examples shown in Table 2 were manufactured. however,
In this example, the proportion of the amount of bismuth trioxide scattered was 10% or more in all cases, and the amount of bismuth trioxide in the sintered body after firing was varied.

The same measurements as in Example 1 were performed for each of these voltage nonlinear resistors. The results are shown in Table 2.

As can be seen from the results shown in Table 2, it is important to keep the amount of hismuth trierupide remaining in the sintered body to 6.0% by weight or less.

Example 3 A voltage nonlinear resistor was manufactured in the same manner as in Example 1. However, in this example, the amount of bismuth trioxide added was unified to 6.7% by weight, and the holding time for scattering the bismuth trioxide at 1000°C was 5 hours in each case. Each voltage nonlinear resistor shown in Table 3 was manufactured by varying only the pressure as shown in Table 3 and varying the amount of BizO+ scattered during firing. Then, the same measurements as in Example 1 were performed for each of these resistors, and the results are shown in Table 3.

(Effects of the Invention) According to the method for manufacturing a voltage non-linear resistor according to the present invention, the content of bismuth oxide in the voltage non-linear resistor after firing is 6% by weight or less. The adverse effects of the grain boundary layer of bismuth oxide can be suppressed, and the flatness, dielectric constant, and discharge resistance can be improved.

Since more than 10% of the amount of bismuth oxide added to the mixture is removed by scattering during firing, at the time of addition to the mixture, the amount of bismuth oxide to be removed by scattering during firing is less than the optimum amount. Can only be added in excess. That is, in the first stage, excessive bismuth oxide is added to increase the wettability of the zinc oxide particle surface during firing, and at least 10% of the added amount of bismuth oxide is removed by scattering during firing. The bismuth oxide grain boundary layer in the sintered body is reduced to bring the content to 6% by weight or less. Therefore, no problems occur due to insufficient wettability of the zinc oxide particles during firing, and the dielectric constant and discharge resistance do not deteriorate.

[Brief explanation of drawings]

FIG. 1 is a graph showing a temperature schedule for scattering and removing bismuth trioxide in the main firing step. Patent applicant Nippon Insulator stock% formula%

Claims (1)

[Claims] 1. In a method for producing a voltage nonlinear resistor by granulating, molding, and firing a mixture containing zinc oxide as a main component and at least bismuth oxide as an additive component, the addition of bismuth oxide to the mixture. A method for manufacturing a voltage nonlinear resistor, characterized in that 10% or more of the weight of the voltage nonlinear resistor is scattered and removed during the firing, and the content of bismuth oxide in the voltage nonlinear resistor after firing is 6% by weight or less.