JPS6329806B2 - - Google Patents

Description

[Detailed description of the invention]

In this invention, when firing a zinc oxide nonlinear resistance element molded body (hereinafter referred to as a molded body) in a continuous furnace, an insulating coating on the side surface of the molded body is formed by a gas-solid reaction between antimony oxide vapor and the molded body. The present invention relates to a method for producing a molded body, which is formed at the same time as the body is fired. Conventionally, molded bodies containing zinc oxide ZnO as a main component have good nonlinearity, so they have become optimal as nonlinear resistors for lightning arresters, that is, as characteristic elements. Since the manufacturing method was not appropriate, there is a drawback that an insulating coating cannot be formed satisfactorily on the side surface of the molded product finally obtained. Generally, the above molded body is made of high purity zinc oxide, for example.
ZnO91mol% Sb ₂ O ₃ , Bi ₂ O ₃ , Co ₂ O ₃ MnO ₂ ,
After adding a total of 9 mol% of SiO ₂ , Cr ₂ O ₃ , etc., mixing, granulating, and compression molding, it is heated at 1000℃ or higher in a special atmosphere.
High temperature below 1400℃ (1100℃~ from electrical characteristics)
It is obtained by firing at a temperature of 1300°C (which is said to be appropriate). In this case, (actual) firing in a special atmosphere is performed at the same time as firing the molded body.
This is necessary to form a high-resistance insulating coating on the side surface. However, in the primary firing ((calcination) process in which the heating temperature is gradually raised for main firing (in this process, the compact shrinks by about 40% in terms of volume) in the temperature range of 800℃ to 1000℃. , the organic binder added during the granulation process is thermally decomposed to produce water H ₂ O, carbon oxide CO ₂ , and hydrogen.
The gas is released to the outside of the molded product in the form of _H2, etc., and this released gas acts on the molded product and has an adverse effect. Specifically, the adverse effects referred to here are problems caused by the reducing gas contained in the emitted gas or the reducing gas newly generated from the high temperature emitted gas reducing the molded product, which is originally an oxide. is pointing to. Additionally, if the thermal decomposition of the organic binder is insufficient during the primary firing process and the release of gas is insufficient, this will have an adverse effect during the main firing process, causing damage between the side surface of the molded body and the molded insulating coating. Problems include poor adhesion, easy peeling, and failure to form a uniform insulating film. Here, the firing method according to the prior art will be explained as follows. That is, FIGS. 1a and 1b show the case where the main firing is performed after the calcination is performed in a substantially closed state. As shown in FIG. crushed powder of calcined compacts, etc.)
Place the molded body 3 through the lid (alumina) 4.
Calcination is performed in a state in which the inside of the firing container 1 is substantially sealed. After calcination, as shown in FIG. 1b, for example, a coating agent for forming an insulating film (at least one of antimony oxides Sb ₂ O ₃ , Sb ₂ O ₄ , and Sb ₂ O ₅ ) is applied to the inner surface of the firing container 1. After the coating agent 2 has dried, the calcined compact 3 is fired with the firing container 1 sealed with the lid 4. This is what I did. Of course, it is also possible to carry out the calcination and main firing simultaneously in the same firing container in the state shown in FIG. 1b. During the main firing, the antimony oxide contained in coating agent 2 sublimates from around 920°C, and at temperatures above 1000°C, the sublimation becomes very active, creating an atmosphere of antimony oxide inside the firing container, which spreads onto the sides of the nonlinear resistor. As a result of this action, spinel (Zn _2,33
Sb ₀ . ₆₇ O ₄ ) is formed. By the way, as mentioned above, it is clear that it is not preferable to calcinate the molded body under a closed condition, and it can be said that it is rather desirable to calcinate the molded body under an open condition. FIG. 2 shows a firing container for this purpose. According to this, the firing container consists of a firing container body (alumina) 7 and a lid (alumina).
However, since the upper edge of the firing container body 7 is provided with a notch 9, even if the inside of the firing container body 7 is tried to be sealed with the lid 8, it will not be possible to keep it in a sealed state. What is possible is different from conventional ones. That is, the compact is not calcined in a sealed state, and the gasified organic binder may be scattered outside the firing container main body 7 through the notch 9 during calcining. Therefore, if the calcination is carried out in the sintering container shown in Fig. 2, and the main sintering is carried out as shown in Fig. 1b, the sides of the molded body will be in good condition and a high-resistance insulating coating will be formed. will be formed. However, not only is it not economical to require separate expensive firing containers for calcination and main firing, but also a new problem arises in that calcination and main firing cannot be performed simultaneously. In addition, if you also perform the main firing using the firing container shown in Figure 2,
Since Bi ₂ O ₃ is scattered, the electrical properties of the final molded product are not good. This invention was made in view of the above circumstances, and it is possible to simultaneously perform calcination and main firing of a molded body in the same firing container without using separate firing containers for each purpose. Moreover, it is an object of the present invention to provide a method for producing a molded body in which a high-resistance insulating coating can be formed on the side surface of the molded body in good condition. An embodiment of the present invention will be described below with reference to the drawings. In FIGS. 3a and 3b, the same parts as in FIGS. 1a and 1b are designated by the same reference numerals. The inside of the firing container 1 is sealed by fitting the lid 17 to the firing container main body 16 from the outside, but the depth of the fitting of the lid 17 to the firing container main body 16 is made shallow. Lower inner surface 21 of lid 17 and firing container body 16
The antimony oxide 22 is interposed in the empty space formed between the outer surface of the substrate and the outer surface of the substrate. Firing container body 16 facing this antimony oxide 22
The reason why the hole 18 is bored in the side surface is to accommodate the antimony oxide 22 in the empty space.
Further, a hole 19 having a certain length is bored in the side surface of the lid 17 upward from a height that corresponds to the upper end surface of the firing container body 16. Furthermore, if necessary, a groove 20 is formed on the inner surface of the lower part of the lid 17, and the antimony oxide 22 is accommodated in this groove 20 through a hole 18 bored in the side surface of the firing container body 16 opposite to the groove 20. be. Therefore, if the firing temperature of the continuous electric furnace, which will be described later, is gradually increased from the illustrated state in which the compact 3 is accommodated, the antimony oxide 22 accommodated in the empty space will be accommodated in the groove 20. The amount of the antimony oxide and other antimony oxide gradually decreases due to sublimation, and as a result, the lid 17 gradually descends due to its own weight and the fitting becomes deeper. Therefore, if the length of the empty space in the vertical direction is set in advance to be larger than that of the hole 19, the gasified organic binder will fit into the hole 1 during calcination.
At the time of main firing, the hole 19 is completely closed by the side surface of the firing container main body 16, and in this sealed state, an atmosphere of sublimated antimony oxide by the antimony oxide 22 is released. The main firing can be carried out inside. Firing container body 1 formed as in the above embodiment
6 are placed at predetermined intervals on a moving table 26 of a continuous electric furnace 25 shown in FIG.
Perform step 6 of firing. The firing pattern at this time is as shown in FIG. That is, in FIG. 5, the furnace length or time is plotted on the horizontal axis, and the temperature is plotted on the vertical axis. As a result, it is gradually heated (calcined). Due to this heating, the organic binder used in the molded body 3 decomposes and evaporates, and the vapor reaches a temperature of 800℃ in the furnace.
As described above, the particles escape to the outside of the firing container main body 16 through the holes 19. Thereafter, when the temperature inside the furnace reaches approximately 850°C, the compact 3 begins to shrink as shown in FIG. 6, and when the temperature reaches 920°C, the antimony oxide 22 begins to sublimate. When the temperature inside the furnace is further increased, the compact 3 is sufficiently shrunk, and the temperature inside the furnace is maintained at a predetermined temperature between 950°C and 1150°C for about 1 to 10 hours. shall be. The antimony oxide 22 that started to sublimate at 920°C becomes activated as the temperature rises.
On the other hand, as described above, the lid 17 gradually descends due to its own weight and the hole 19 is closed by the lid 17, so that the inside of the firing container body 16 is filled with antimony oxide vapor. For this reason, an insulating coating, that is, spinel (Zn ₇ Sb ₃ O ₁₂ ) is formed on the side surface of the molded body 3 through a gas-solid phase reaction between zinc oxide and antimony oxide vapor on the side surface of the molded body 3. . The area A in FIG. 5 is the time period during which the temperature is maintained at a predetermined temperature within the range of 950°C to 1150°C. By forming an insulating coating on the side surface of the molded body 3 as described above, a dense coating can be obtained. After forming the film, the temperature is raised to region B and main firing is performed. The temperature at this time is set at 1160°C to 1300°C. The following table shows the experimental results of the discharge withstand capacity (4 x 10 μs) of molded bodies manufactured by setting the firing temperature to 950° C. to 1150° C. and the firing time to 1 hour to 10 hours. The molded body is 40φ x 38t, and the current is 30KA~
This is the case where 70KA is supplied twice at 1 minute intervals. ○
The mark indicates no abnormality, and the mark x indicates creeping flash.

[Table] As is clear from the above experimental results, the firing temperature at which a dense insulating film is formed on the side surface of the compact 3 and the discharge resistance is practical is 950°C to 1150°C, and the firing time is from 1 hour to 10 It's time. FIG. 7 shows an example in which it is necessary to form a particularly uniform insulating coating on the side surface of the molded body 3. In this FIG. It is arranged inside the firing container body 16 so as to surround the firing container body 18 . By using the plate material 23 in this manner, the sublimated antimony oxide 22 from the hole 18 is appropriately diffused by the plate material 23 and reacts with the side surface of the molded body 3 in a gas-solid state. Note that when Bi ₂ O ₃ is included in the antimony oxide in advance, it is possible to prevent Bi ₂ O ₃ from scattering from the compact during firing. As described above, according to the present invention, antimony oxide is interposed in advance in the firing container in a continuous furnace, and as the oxide becomes vapor, the inside of the container becomes airtight. Since the temperature inside the furnace was maintained at 950°C to 1150°C and the container was fired for an arbitrary period of time from 1 hour to 10 hours, antimony oxidation occurred inside the container after the organic binder was released to the outside of the firing container. A uniform insulating coating is formed on the sides of the molded body because it is filled with vapor. Furthermore, since the coating is formed by a gas-solid phase reaction, a dense coating can be obtained and creeping flash resistance can be improved. Furthermore, compared to the conventional method, the process of making an insulating paint and the process of applying and drying can be omitted, resulting in a dramatic improvement in work efficiency.

[Brief explanation of the drawing]

1a and 1b are diagrams for explaining the firing method according to the prior art, FIG. b is a partially omitted cross-sectional view and side view of a firing container used in an embodiment of the present invention, FIG. 4 is a schematic explanatory diagram when the firing container is fired in a continuous furnace, and FIG. Fig. 6 is a characteristic diagram showing the firing pattern in the continuous furnace shown in Fig. 6; Fig. 6 is a characteristic diagram showing the volumetric shrinkage rate of the compact; Fig. 7 is a partially omitted sectional view of a firing container applied as another embodiment of the present invention. It is. 1... Baking container, 3... Molded body, 16... Baking container body, 17... Lid, 18, 19... Hole, 20
... Groove, 22 ... Antimony oxide, 25 ... Continuous electric furnace, 26 ... Moving table.

Claims (1)

[Claims] 1. In a continuous furnace, when firing a zinc oxide nonlinear resistance element molded body housed in a firing container, antimony oxide is interposed in the firing container in advance, and as the antimony oxide becomes vapor, The inside of the container is gradually closed, and the temperature of the furnace is maintained at 950°C to 1150°C, and the holding time is set to a predetermined time of 1 to 10 hours for firing. A method for manufacturing a zinc oxide nonlinear resistance element molded body, which comprises forming a spinel insulating coating on the side surface of the molded body by gas-solid phase reaction, and then performing main firing by increasing the temperature of the furnace.