JPH0536505A - Manufacture of zinc oxide non-linear resistor - Google Patents

Abstract

PURPOSE:To obtain a zinc oxide non-linear resistor which is excellent in discharge resistance against a lightning surge and a switching surge and which also has high mold intensity and a high mold yield. CONSTITUTION:Granulated powder mainly containing zinc oxide is generated, and after a surface of the granulated powder is subjected to additive treatment of lubricant such as water, molding with pressure is performed. Then after an amount added of the lubricant is made to be 0.1 to 2.7%, molding with pressure or the like is performed to manufacture a zinc oxide non-linear resistor.

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 zinc oxide nonlinear resistor containing zinc oxide as a main component, which is used in lightning arresters, surge absorbers and the like.

[0002]

2. Description of the Related Art In general, a non-linear resistor does not follow Ohm's law and has a non-linear voltage-current characteristic that the resistance decreases and the current increases remarkably when the voltage increases.
It is very effective in applications such as absorption of abnormal voltage such as lightning arresters and surge absorbers.

Si is a typical non-linear resistor.
There are SiC lightning arrester characteristic elements and SiC varistors that apply the voltage sensitivity of the contact resistance of C particles, and these are generally made by adding a porcelain binder composed of SiC particles and clay and sintering at high temperature after molding. The voltage-current characteristic is approximately represented by the following equation.

I = (V / C) ^{k In the} above equation, I is a current, V is a voltage, C is a constant corresponding to a resistance value, and k is a nonlinear index.

The SiC lightning arrester characteristic element has a k value of 3 only in the current range of several hundred amps to 20 kiloamps.
Approximately -7, which is close to the ohmic resistance outside this range, and therefore a lightning arrester using a SiC characteristic element directly connected to the line requires a series gap to maintain the insulation between the line and the ground.

Further, a large number of gaps and characteristic elements are used in a high-voltage / ultra-high voltage lightning arrester, but in this case, capacitors or resistors are required in parallel in order to equalize the voltage sharing of each gap.

As described above, mounting a large number of gaps, capacitors and resistors not only increases the size of the insulator, but also the response to steep waves and the follow-current interruption due to the gap.

Therefore, zinc oxide is used as a main component, and oxides such as bismuth oxide, silicon dioxide, antimony oxide, cobalt oxide, manganese dioxide, chromium oxide, and nickel oxide are mixed as a secondary additive to form a disc shape or a column shape. Alternatively, it is formed into an appropriate shape, and after being sintered at a high temperature, both sides of this sintered semiconductor element body are covered with side insulating material such as epoxy resin,
A zinc oxide voltage nonlinear resistor using an oxide semiconductor having electrodes on the upper and lower surfaces has been proposed.

The above zinc oxide nonlinear resistor has a k value of about 50 in the milliampere current region, and has a conventional S value.
It has much better nonlinearity than the iC resistor and has a considerably large dielectric constant. Usually, this zinc oxide voltage nonlinear resistor is usually manufactured by the following method. That is, the auxiliary additives are preliminarily ground by a ball mill or the like, then mixed with an organic binder and zinc oxide, and dried by a spray dryer to obtain a raw material powder having good fluidity. Next, the raw material powder is molded into a disk shape by a die press, degreased, and then baked at 1000 ° C to 1300 ° C for several hours, and then the side surfaces are subjected to insulating coating, and then both end surfaces are removed. Polish and finish by spraying aluminum electrodes.

The required performance of the zinc oxide non-linear resistor manufactured as described above is the energy withstand capability against lightning surges and switching surges. This withstandability is mainly due to the binding material in the granulated powder, particle size distribution and molding conditions. It is greatly affected by the method.

In the zinc oxide nonlinear resistor, it is important to increase the energy resistance, and as a means therefor, there is a method of increasing the binding material in the granulated powder to increase the molding binding force.

[0012]

However, although the energy resistance is improved by increasing the amount of the binder in the granulated powder as described above, since the binder is usually an organic compound such as polyvinyl alcohol, the addition thereof is not recommended. If the amount exceeds a certain value, the firing induces the generation of voids and, as a result, the energy withstand capability decreases.

Therefore, there is a limit to the improvement of energy resistance by increasing the amount of the binder, and it is not preferable to add more than an appropriate amount.

Regarding the molding conditions, in a generally used dry die press, the better the fluidity of the powder, the more the granulated powder moves during the pressure molding so that the pressure distribution and the density distribution become uniform. This is due to the particle size distribution of the granulated powder.If the particle size distribution spreads to a certain extent or more, the fluidity decreases and voids occur.If the particle size distribution is too narrow, voids occur between the particles, so voids also occur. To do.

Further, when pressure-molding a zinc oxide nonlinear resistor, if the volume and pore size of the molded product are large, the pressure and density are likely to become non-uniform, which causes cracks and lamination to cause molding defects. It is likely to happen.

[0016] In particular, the pressure molding method which is usually performed as described above is a dry die press, but since this molding method applies pressure only to the upper and lower sides, it can be applied to a cold isostatic press (CIP) or the like. In comparison, the pressure distribution tends to be non-uniform, and as the thickness of the molded body becomes thicker, the pressure near the center of the molded body becomes the lowest and lamination, cracks and molding defects are more likely to occur, and the shape after sintering is It becomes easy to transform into a claw shape.

The present invention has been made in view of the above background, and is excellent in discharge withstanding capability against lightning surges and switching surges.
Moreover, it is an object of the present invention to obtain a zinc oxide non-linear resistor having high strength and high molding yield.

[0018]

Means and Actions for Solving the Problems In order to solve the above problems, the present invention comprises a step of producing a granulated powder containing zinc oxide as a main component and press-molding the granulated powder. In the method for manufacturing a zinc nonlinear resistor, pressure molding is performed after the surface of the granulated powder is subjected to a lubricating liquid addition treatment.

By carrying out the lubricating liquid addition treatment as described above, a zinc oxide nonlinear resistor having excellent characteristics by uniformizing the density of the molded body during pressure molding can be obtained. The details will be described below.

Usually, the water content of the spray-dried granulated powder itself is 0% to 0.1 so as not to impair the fluidity of the granulated powder.
It is controlled to 5% or less. Since the strength of the granulated powder itself is high, the granulated powder is not easily crushed during molding.

Therefore, when a molding pressure is applied, the granulated powder moves from the high density portion to the low density portion without being crushed on the spot.
In this way, if the granulated powder itself has a low water content, high fluidity is obtained, and the molding density becomes uniform.

In the present invention, since the granulated powder having a low water content produced by the conventional method is used and the lubricating liquid is adhered only to the surface thereof, the surface of the granulated powder can be maintained without impairing the fluidity of the granulated powder. The lubricity is improved and the molding density is made uniform, and particularly when the addition amount of the lubricating liquid is 1% to 2%, good results are obtained.

When the amount of the lubricating liquid added is less than 0.1%, it is practically difficult to mix uniformly, and the moldability is not improved so much. On the contrary, the amount of lubricant added is 2% to 2.7
If the content exceeds%, the water content in the lubricating liquid permeates the granulated powder and the granulated powder is easily crushed, which reduces the fluidity of the granulated powder and causes problems such as the adherence of the molded product to the mold. .

Therefore, the amount of the lubricating liquid added is 0.1% to 2.
It is desirable to set it to 7%, preferably 1% to 2%.

[0025]

EXAMPLES The present invention will be described below with reference to examples.

In this embodiment, a slurry prepared by adding a binder to a raw material blended with a predetermined composition is spray-dried to obtain a granular powder, and the granular powder is put into a powder mixer having a spray nozzle. Then, the lubricant was added, and pure water as a lubricant was finely sprayed from the spray nozzle, and the powder was mixed while being uniformly sprayed to perform the lubricant addition treatment.

Then, in the same manner as in the conventional manufacturing method, the raw material powder obtained by the above treatment is molded into a disk shape by a die press, degreased, and then fired at 1000 ° C to 1300 ° C for several hours. After applying insulating coating on the side surfaces, polish both end surfaces and spray aluminum electrodes to obtain a diameter of 4
A zinc oxide nonlinear resistor having a thickness of 8 mm and a thickness of 36 mm (φ48-t36) was completed.

In the above manufacturing method, the amount of the lubricating liquid sprayed on the powder is varied in the range of 0 to 3.0% (wet base) to manufacture a zinc oxide nonlinear resistor, and the obtained zinc oxide nonlinear resistor is manufactured. Each of the resistors was subjected to a discharge withstand voltage test against lightning surge and switching surge, and the strength and the molding yield of the molded body were investigated.

From the results of the above-mentioned molded body strength test, a graph was prepared in which the horizontal axis represents the amount of lubricant added and the vertical axis represents the molded body strength.
As shown in FIG. Similarly, a graph in which the abscissa represents the amount of lubricant added and the ordinate represents the molding yield based on the molding yield test results is shown in FIG.

As shown in FIG. 1, the strength of the molded body is less than the addition amount of the lubricating liquid.
If it exceeds about 2%, it will be greatly improved, and the amount of lubricant added will be 3%.
Even when the temperature reaches the above, good strength is maintained, and particularly, high strength of 8 (MPa) is obtained in the range where the amount of lubricating liquid added is about 1 to 2%.

Further, according to FIG. 2, the molding yield is a little over 90% without humidification, whereas it becomes 96% or more when the amount of lubricant added is about 0.1% to 2.7%.
In particular, it can be seen that a high yield of 99% or more is obtained when the amount of lubricating liquid added is in the range of about 0.5% to 2%.

Next, Table 1 shows the results of the discharge withstand voltage test.

[0033]

[Table 1]

In Table 1, the case where the resistor destruction did not occur was represented by O, the case where the resistor destruction occurred was represented by X, and the case where it was clear that the resistor destruction occurred was represented by-.

According to this table, when the amount of lubricating liquid added is 0.1% or more in lightning surge, the lightning surge is improved as compared with that in the non-humidified state, and particularly, the amount of lubricating liquid added is about 1.0% to 2.0%. Then, it can be seen that the resistor is not destroyed and the lightning surge is greatly improved.

Regarding the switching surge, the switching surge is improved in the range of 0.1% or more and less than 3.0% of the addition amount of the lubricating liquid, and particularly when the addition amount of the lubricating liquid is 1.0% to 2.0%. It can be seen that the resistor breakdown did not occur and the switching surge was greatly improved.

Therefore, in this embodiment, the amount of lubricating liquid added is about 0.1% to 2.7%, preferably 1.0% to 2.0%.
It is preferably within the range of about.

Although pure water is used as the lubricating liquid in this embodiment, other organic or inorganic lubricating liquid may be used.

The same effect can be obtained by using general tap water, and the effect is increased by adding a release agent and a lubricant to pure water.

[0040]

INDUSTRIAL APPLICABILITY In the present invention, since the lubricating liquid is adhered to the surface of the granulated powder produced by the conventional method and having a low water content, the granulated powder can be obtained without impairing the fluidity of the granulated powder. The lubricity on the surface is improved and the molding density is uniform.

Therefore, the obtained zinc oxide nonlinear resistor has improved discharge withstanding capability against lightning surges and switching surges, and the molded product strength and molding yield are also greatly improved to obtain a zinc oxide nonlinear resistor having excellent characteristics. To be

[Brief description of drawings]

FIG. 1 is a graph showing the correlation between the amount of lubricant added and the strength of a compact.

FIG. 2 is a graph showing the correlation between the amount of lubricant added and the molding yield.

Claims (2)

[Claims] 1. A method for producing a zinc oxide non-linear resistor, which comprises a step of producing granulated powder containing zinc oxide as a main component and press-molding the granulated powder. A method for producing a zinc oxide nonlinear resistor, which comprises performing pressure forming after performing a lubricating liquid addition treatment. 2. The zinc oxide nonlinear resistor according to claim 1, wherein pure water is used as the lubricating liquid, and the amount of addition is 0.1% to 2.7%. Method.