JPH03155101A - Manufacture of voltage nonlinear resistor - Google Patents

Abstract

PURPOSE:To make viscosity of granulation slurry and grain diameter of a granulated powder uniform and to reduce generation rate of inner defects and loss rate of a raw material by adding mixing a granulated powder of a specified grain diameter or less which is classified by a cyclone classifier in a process of granulation to a new material. CONSTITUTION:Granulation slurry is acquired by mixing a zinc oxide material which becomes a main element, a metallic oxide raw material such as Bi2O3, Sb2O3, etc., which develops voltage nonlinear properties and a binder are mixed in a mixing tank 2. The acquired slurry is supplied to a spray dryer 1 and granulated, a granulated powder of average grain diameter of about 149mum is supplied to a following process, and a granulated powder of grain diameter of 106mum or less, preferably 63mum or less, is classified by a cyclone classifier 3, which is not disposed of and added into a mixing tank 2 to be mixed with a new raw material. A desirable mixing amount of the classified granulated powder of a specified grain size or less, preferably 63mum or less, is about 3 to 20wt.% to the entire of the new raw material since it especially realizes stable viscosity.

Description

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

(Prior art) Conventionally, as a method for manufacturing a voltage nonlinear resistor, zinc oxide powder as the main component and B1zO that exhibits voltage nonlinearity are used.
A method of mixing metal oxide powders such as z+ 5bJ3, granulating the slurry obtained by mixing with a spray dryer, molding the granules into a predetermined shape, and then firing the molded body to obtain a voltage nonlinear resistor. It has been known.

In this manufacturing method, during granulation in the spray dryer 11 of the granulation device shown in FIG. If all granulated powder is used for molding, the particle size distribution of the granulated powder will be wide and lamination will easily occur in the granulated product, and even if the obtained molded product is fired, 0.1 to 1 mm has the drawback that internal defects such as voids and pinholes remain, leading to deterioration of electrical characteristics such as concentration of current due to application of lightning surges, etc. For this reason, after the granulated powder having a predetermined particle size or less is classified and removed by the cyclone classifier 13, the granulated powder having a predetermined particle size or less is discarded.

(Problems to be Solved by the Invention) However, in the conventional manufacturing method described above, the viscosity of the slurry in the mixing tank 12 that is supplied to the spray dryer 11 tends to become unstable. After granulation, the particle size of the granulated powder is not uniform, and the particle size distribution becomes wide, resulting in a problem that the internal defect rate of the voltage nonlinear resistor increases.

Furthermore, the granulated powder of 63 μm or less classified by the cyclone classifier 13 was not reused and was discarded as it was, which caused a problem of loss of raw materials.

An object of the present invention is to solve the above-mentioned problems and provide a method for manufacturing a voltage nonlinear resistor that can obtain a voltage nonlinear resistor with few internal defects, reduce raw material loss, and reduce manufacturing costs as a result. This is what we are trying to provide.

(Means for Solving the Problems) The method for manufacturing a voltage nonlinear resistor of the present invention involves mixing zinc oxide and a metal oxide that exhibits voltage nonlinearity, and granulating the mixed slurry with a spray dryer. , in a method for manufacturing a voltage nonlinear resistor in which the granulated product is molded and then fired, the granulated powder with a particle size of 106 μm or less, which has been classified by a cyclone classifier during the granulation process using a spray dryer, is transferred to the spray dryer. It is characterized by adding a predetermined amount to the supplied slurry.

(Function) In the above-mentioned configuration, the granulated powder with a particle size of 106 μm or less, preferably 63 μm or less, which is classified by a cyclone classifier during the granulation process using a spray dryer, is added to the slurry in the mixing tank, preferably 3 times the total fresh raw material. ~20sL%
By adding and mixing, the viscosity of the slurry supplied to the spray dryer is stabilized, and the particle size of the granulated powder is made uniform.
As a result, a voltage nonlinear resistor with fewer internal defects can be obtained.

In addition, since the powder of 63 μm or less, which was previously discarded, is reused and subjected to granulation again, it is possible to reduce raw material loss, and as a result, it is possible to reduce manufacturing costs.

If granulated powder with a particle size exceeding 106 μm is added to the mixing tank, the dissolution of the granulated powder (secondary particles loosening) in the mixing tank will not proceed sufficiently, and internal defects will occur in the voltage nonlinear resistor. Leads to.

(Example) FIG. 1 is a diagram showing the configuration of an example of an apparatus for carrying out the manufacturing method of the present invention. In Fig. 1, 1 is a spray dryer used for granulation, and 2 is a mixing tank for mixing zinc oxide raw materials, metal oxide raw materials for developing voltage nonlinearity, and binder and storing slurry for granulation. , 3 is a cyclone classifier for classifying powder having a particle size of 106 μm or less, for example 63 μm or less during granulation in the spray dryer 1.

The granulation process of the present invention in the above-mentioned apparatus is as follows. First, a zinc oxide raw material as a main component, a metal oxide raw material such as BizO, 5b203 that exhibits voltage nonlinearity, and a binder are mixed in a mixing tank 2 to obtain a slurry for granulation. Next, the obtained slurry was supplied to the spray dryer 1 and granulated, with an average particle size of 149 μm.
The granulated powder of about m is supplied to the next process, and the granulated powder of less than a predetermined particle size, for example, 63 μl or less, is passed through the cyclone classifier 3.
Classify by. Then, the granulated powder of 63 μm or less after classification is added to the mixing tank 2 without being discarded and mixed with the new raw material. The mixing amount of granulated powder having a predetermined particle size or less, preferably 63 μm or less after classification is 3 to 20 μm based on the entire new raw material.
% is preferable because the viscosity is particularly stabilized.

Actually, 106μm classified by cyclone classification A3
The following powders are added to the mixing tank 2 for the entire new raw material.
When adding each weight ratio shown in the table, the change in viscosity of the slurry, the change in the granulated powder particle size after granulation with a spray dryer, and the internal defect incidence rate of the voltage nonlinear resistor after firing were determined. We were able to obtain the results shown in the table.

Table 1 From the results in Table 1, 106 μm after classification is preferably 63 μm.
When 3 to 20 tm t% of granulated powder of µm or less is mixed with the new raw material, the viscosity becomes more stable, and fluctuations in the average particle diameter of the granulated powder caused by the spray dryer 1 are reduced, resulting in voltage fluctuation. It can be seen that the internal defect occurrence rate of the linear resistor is reduced.

Sample Nα1 shown in Table 1 is a case in which granulated powder granulated in spray dryer 1 is used for molding without being classified in cyclone 3, and sample Nα2 is a case in which granulated powder granulated in spray dryer 1 is used for molding. The case is shown in which molding is performed using granulated powder that has been classified with cyclone 3 and granulated powder of 63 μm or less is removed. The addition rate (wt%) of the recovered material to the new raw material in cyclone 3 is the weight of 1 t (n) of adding the granulated powder classified in cyclone 3 to mixing tank 2 and the weight of the new raw material input to mixing tank 2. ffi (m) *The particle size of the granulated powder produced by the spray dryer is the value of the cumulative particle size distribution of 5% and 95%.The average incidence of internal defects is for a voltage nonlinear resistor after firing with a diameter of 47 mm and a thickness of 20 mm. Ultrasonic flaw detection measurement was performed on the diameter of 0.5
The number of defects larger than mm was investigated and determined based on the incidence rate.

(n = 500) The molding conditions such as molding pressure and the firing conditions after molding were all the same for each sample.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, by mixing the granulated powder after classification with a new raw material, the viscosity of the slurry for granulation and the particle size of the granulated powder are uniform. It is possible to reduce the internal defect occurrence rate of the voltage nonlinear resistor, eliminate raw material loss, and reduce manufacturing costs.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an example of an apparatus for carrying out the manufacturing method of the present invention, and FIG. 2 is a diagram showing the configuration of an example of a conventional granulation apparatus. 1... Spray dryer 2... Mixing tank 3... Cyclone classifier Figure 1

Claims (1)

[Claims] 1. In a method for manufacturing a voltage nonlinear resistor, which involves mixing zinc oxide and a metal oxide that exhibits voltage nonlinearity, granulating the mixed slurry with a spray dryer, molding the granules, and then firing the molded body. A method for producing a voltage nonlinear resistor, which comprises adding a predetermined amount of granulated powder having a particle size of 106 μm or less, which is classified by a cyclone classifier during a granulation process by a spray dryer, to a slurry to be supplied to a spray dryer.