JPH0391203A - Manufacture of voltage nonlinear resistor - Google Patents

Abstract

PURPOSE:To obtain a voltage nonlinear resistor which produces no void in an element after shaping and baking by controlling the moisture content of fine particles in an least one step of manufacturing process within a certain range. CONSTITUTION:A slurried raw material in a slurry tank 1 is sprayed through a slurry nozzle 5 in a drying tower 4, air sent from a blower 2 and heated in an air heater 3 jetted into the drying tower 4, and the sprayed slurry is dried and powdered. The powder is classified with an apparatus 11 such as a cyclone and powder of a specified grain size is selected as raw powder for shaping and baking a lightning arrester. The other powder is returned to the drying tower 4 with a carrier 8' and fine powder remaining in exhausted heat air is recovered with a back filter 6. The moisture content of the powder is restricted to a certain value by controlling the operating conditions such as the air flow rate from the blower 2 to the drying tower 4 and the heating temperature of the air heater 3 to specific conditions based on the experimental data.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the production of a voltage nonlinear resistor obtained by baking zinc oxide as a main component, adding various metal oxides as subcomponents, and firing the resulting material. It is about the method.

[Prior Art] FIG. 10 shows a part of a conventional voltage nonlinear resistor manufacturing apparatus disclosed in, for example, Japanese Unexamined Patent Publication No. 56-153704. This is a schematic diagram of a spray drying device used in the granulation step in the method of manufacturing a voltage nonlinear resistor.

Lightning arresters that protect power systems from lightning damage use lightning arrester elements whose main component is zinc oxide, which is the most common example of voltage nonlinear resistors. Hereinafter, the manufacture of this lightning arrester element will be explained as an example. The slurry-formed raw material in the slurry tank 1 is ejected from the slurry nozzle 5 inside the drying tower 4. At this time, heated hot air is blown into the drying tower 4 from the blower 2 through the air heater 3. This hot air dries the slurry and turns it into granulated powder, which is the raw material for the lightning arrester element before firing. The above-mentioned blown hot air is discharged by the exhaust fan 7, and the fine granulated powder in the discharged hot air is collected by the bag filter 6. The yield of granulated powder obtained from the lower outlet 4a of the drying tower 4 is about 90%, and the remaining granulated powder is collected by the bag filter 6. In order to improve the yield of the raw materials used, the granulated powder collected in the drying tower 4 and the granulated powder recovered from the Bang filter 6 were mixed and used in addition to the raw materials before element firing. .

[Problems to be Solved by the Invention] Conventionally, as described above, since the granulated powder collected in the drying tower 4 and the granulated powder collected from the bag filter 6 are mixed, fluidization occurs during powder molding. sex was declining. For this reason, there is a problem in that many undesirable voids are generated inside the element after molding and firing.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a voltage nonlinear resistor in which no voids are generated inside the element after molding and firing.

[Means for Solving the Problems] The method for manufacturing a voltage nonlinear resistor according to the present invention includes a step of returning the powder obtained in the classification step or the exhaust cleaning step to the granulation step or a step after the granulation step; The present invention is characterized in that at least one step includes a step of controlling the moisture content of the powder in the step within a certain range.

[Function] In the method for manufacturing a voltage nonlinear resistor according to the present invention, the powder obtained in the classification step or the exhaust gas cleaning step is returned to the drying step or a step after the drying step. In at least one step, the moisture content of the powder in the step is controlled within a certain range.

[Example] The method for manufacturing a voltage nonlinear resistor according to the present invention is described in its first embodiment.
This will be explained using FIG. 1, which shows an embodiment of the present invention.

FIG. 1 shows the granulation step, exhaust cleaning step, and classification step in the method for manufacturing a voltage nonlinear resistor. Lightning arresters that protect power systems from lightning damage use lightning arrester elements whose main component is zinc oxide, which is the most common example of voltage nonlinear resistors. Hereinafter, the manufacture of this lightning arrester element will be explained as an example. A raw material containing zinc oxide as a main component and mixed with a metal oxide as a subcomponent that causes voltage nonlinearity shown in Table 1 is stored in a slurry tank 1.

The slurry-formed raw material in the slurry tank 1 in Table 1 is transferred to the drying tower 4.
The slurry is sprayed from the slurry nozzle 5 inside. At this time, hot air heated from the blower 2 through the air heater 3 is blown into the drying tower 4.

The slurry sprayed by this hot air is dried and becomes granulated powder. The above process is the granulation process. This granulated powder is classified by a device 11 such as a cyclone, and particles having a predetermined particle size become granulated powder, which is the raw material for forming and firing the lightning arrester element. The above is the classification process.

The granulated powder classified outside the predetermined particle size in the above classification process is returned to the drying tower 4 by the conveyor 8'.

Further, the above-mentioned blown hot air is discharged by the exhaust fan 7, and the fine granulated powder in the discharged hot air is collected by the bag filter 6. As a result, the hot air discharged outside the device is clean. This process is the exhaust gas cleaning process.

The recovered granulated powder is returned to the drying tower 4 by a conveyor 8.

In this example, the granulated powder obtained as described above has a moisture content of 0.3, 0.5, 1.0, 2.0°5, respectively.
．． Each of the granulated powders whose weight percent was controlled to be 0 and 6.0 was used in the firing described below. In addition, controlling the moisture content of these granulated powders to the above-mentioned constant value is achieved by keeping the operating conditions such as the air flow rate of the blower 2 to the drying tower 4 and the heating temperature of the air heater 3 constant based on empirical data. This is possible through control.

Each of the granulated powders having the above moisture contents was molded into a size of 40 mmφ x 50 mm at a molding pressure of 150.250.500 kg/cm and then fired at 1200° C. to create an element. Next, the number of voids generated in each element thus obtained was counted using an optical microscope. For comparison, the number of voids was divided into three groups: 10 or less, 11 to 19, and 20 or more, and the relationship between the water content of the granulated powder and the molding pressure as the element manufacturing conditions is shown in Figure 2. It was shown to.

The following can be seen from Figure 2.

(1) When the water content of the granulated powder is as low as 0.3% by weight, there are still many voids even if the molding pressure is increased to 500 kg/cm.

(2) When the water content of the granulated powder is 0.5 to 5.0% by weight, the number of voids decreases as the molding pressure increases, and the number of voids decreases when the molding pressure is 500 kg-f/cm.

(3) When the water content of the granulated powder is as high as 6.0% by weight, there are still many voids even if the molding pressure is increased to 500 kg/cm.

The cause of (1) is when the moisture content is less than 0.5% by weight.
This is because the adhesion of the granulated powder to each other decreases, and if the compacting pressure is low, the crushing of the powder particles becomes poor, and a large number of voids are likely to occur.

The reason for (3) is considered to be that when the water content is more than 5.0% by weight, a large amount of water evaporates and vaporizes during firing, causing voids.

Regarding (2), it is well observed from optical micrographs of each element made from granulated powder with a water content of 1.0% by weight. In FIG. 5, which shows a photograph of Experimental Example A obtained at a molding pressure of 150 kg-f/cm, many voids of about 100 μmφ are seen. Figure 6 shows a photograph of an experimental example obtained at a molding pressure of 250 kg-f/cm and a molding pressure of 50
Few voids are seen in FIG. 7, which shows a photograph of Experimental Example C obtained at 0 kg-f/cm.

From the above results, the moisture content of the granulated powder obtained in drying tower 4 was set to 0.
．． If it is in the range of 5 to 5.0% by weight, the molding pressure is 500k.
By forming the film at g−f/cm or more, an element with suppressed generation of voids can be obtained.

In the embodiments described above, the moisture content of the granulated powder is controlled by controlling the operating conditions of the blower 2 and air heater 3 for the drying tower 4. On the other hand, as a second embodiment of the present invention. As shown in FIG. 3, a humidifier 9 may be connected to the lower outlet 4a of the drying tower 4 and the moisture content of the granulated powder may be controlled by the humidifier 9 to obtain the same effect as in the above embodiment.

Further, in the first embodiment, the moisture content of the granulated powder is controlled after the granulated powder collected by the bag filter 6 is returned to the drying tower 4 by the conveyor 8. On the other hand, the granulated powder obtained from the lower outlet 4a of the drying tower 4 and the granulated powder recovered by the bag filter 6 are mixed in a mixer,
Even if the water content is controlled using a humidifier or the like, the same effect as in the above embodiment can be obtained.

Further, as a third embodiment which is a modification of the above-mentioned example using the mixer, an example in which only the granulated powder collected by the bag filter 6 is humidified by the humidifier 9 is shown in FIG. Differences from the embodiment shown in FIG. 1 are particularly explained as follows.

The fine granulated powder (hereinafter referred to as B powder) collected by the back filter 6 is not returned to the drying tower 4, but is sent to the humidifier 9 and humidified. The humidified granulated powder is sent to the dry mixer 10 and mixed with the granulated powder obtained from the lower outlet 4 of the drying tower 4 (hereinafter referred to as powder A).

In this example, the moisture content of powder B was adjusted by the humidifier 9 to 0.2 (non-humidified state) 0.3.0.5°1.0.2.0.3.0.4.0 Humidification was controlled to 5.0 and 6.0% by weight. Next, each B powder and A powder having a moisture content of 1.0% by weight were mixed at a ratio of 1:9, and molded using a molding pressure car of 500 kg-f/am to form 40 mmφX50
mmt and then fired at 1200'C to produce an element. Observation results of internal defects using transmitted X-rays of the element obtained as described above and voids observed using an optical microscope (Table 2 Note 1) Presence or absence of internal defects □ determined by transmitted X-rays 100μm or more) ○...No defects Note 2)
Number of voids observed with an optical microscope: ○...10 or less ×...11-30 In Experimental Example 1 in the table, no internal defects were observed by transmitted X-rays, but as shown in Figure 8, which shows a photograph taken with an optical microscope. As observed, many voids with a diameter of about 100 μm are generated. Furthermore, Comparative Example 1 also gave similar results to Experimental Example 1. The reason for this is thought to be that because the amount of humidification is small, the fluidity of the granulated powder after mixing becomes low, the moldability during pressing for element molding deteriorates, and a large number of voids are generated.

In Experimental Examples 2 to 7, no internal defects were observed using transmitted X-rays, and only a small number of voids were observed using an optical microscope. - As an example, an optical microscope photograph of Experimental Example 5 is shown in FIG.

Accordingly, according to the method of manufacturing a voltage nonlinear resistor of the present invention, voids are generated by mixing powder A and powder B with a water content of 0.5 to 5.0% by weight and molding and firing the mixture. ,
Since the powder obtained in the cyclone or bag filter is returned to the process subsequent to the drying process, the yield of raw materials used is improved. Moreover, since the moisture content of the powder in the process is controlled within a certain range in at least one of the processes including the return process in this manufacturing method, defective products are less likely to occur and the product yield is improved. effective.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an apparatus for manufacturing a voltage nonlinear resistor according to a first embodiment of the present invention, and FIG. 2 is a diagram showing the number of voids as a function of moisture content and molding pressure of granulated powder according to the first embodiment of the present invention. FIG. 3 is a diagram showing a voltage nonlinear resistor manufacturing apparatus according to a second embodiment of the present invention, and FIG. 4 is a diagram showing a voltage nonlinear resistor manufacturing apparatus according to a third embodiment of the present invention. FIG. 5 is an optical microscopic photograph of the particle structure of the device of Example A in FIG. 4, and FIG. 6 is an optical microscopic photograph of the particle structure of the device of Example A in FIG. Figure 7 is Example C in Figure 4.
FIG. 8 is an optical microscope photo of the particle structure of the device of Experimental Example 1 in Table 2, and FIG. 9 is an optical microscope photo of the particle structure of the device of Experimental Example 5 in Table 2. An optical microscope photograph, FIG. 10, is a diagram showing a part of a conventional voltage nonlinear resistor manufacturing apparatus. In the figure, 4 is a drying tower, 6 is a bag filter, 8 is a conveyor,
11 is a cyclone.

Claims (1)

[Claims] (1) A step of returning the powder obtained in the classification process or the exhaust gas cleaning process to the granulation process or a process after the granulation process, and controlling the moisture content of the powder in the process to a certain range in at least one process. A method of manufacturing a voltage nonlinear resistor, comprising the step of controlling.