JPS62107B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for drying ceramic fabric, and in particular, by intermittently irradiating a molded ceramic fabric with high frequency waves to repeatedly dielectrically heat the fabric and averagely disperse this heat within the fabric.
The present invention relates to a method for drying the fabric within a short time without damaging it by minimizing temperature differences and dryness differences in various parts of the fabric. Traditionally, drying of ceramics involves forming a molded dough containing approximately 20% moisture, and reducing the moisture content to approximately 10%.
The electrode is dried until it becomes about %, and then hot air is dried until it becomes about several %. However,
Such a drying method requires a large amount of time from the start to the end of drying, and also has the disadvantage that cracks may occur in the fabric if the temperature in the atmosphere is increased to shorten this time. Incidentally, drying the insulator fabric using the conventional method takes an average of about 5 to 7 days for electrode drying and about 7 to 10 days for hot air drying, although this varies depending on the size of the insulator. It took a long time, approximately 12 to 17 days. Therefore, the inventor conducted various experiments with a focus on drying ceramic fabrics within a short time using high-frequency dielectric heating. According to this experiment, it was found that continuous high-frequency irradiation causes cracks in the fabric under any conditions. This is because the heat applied to a part of the fabric by continuous irradiation is transferred and dispersed to each part of the fabric before new heat is continuously added and the temperature difference within the fabric expands. This is thought to be due to the fact that there is a large difference in the degree of dryness in each part of the fabric, resulting in an imbalance in the shrinkage rate of the fabric. Therefore, in order to prevent heat from concentrating on one part of the fabric, the inventor aimed to reduce the temperature difference between each part by dispersing the applied heat within the fabric, thereby increasing the dryness and shrinkage rate in each part. It has been found that heating the dough sequentially while keeping the dough balanced is suitable for drying the dough in a short period of time without causing cracks in the dough. An object of the present invention is to dry ceramic fabrics quickly without causing cracks. The invention filed herein involves intermittently irradiating a molded ceramic fabric with high frequency waves to dielectrically heat the fabric through irradiation, and then repeating the process of dispersing the heat within the fabric when the irradiation is stopped. The present invention provides a method for drying ceramic fabric as a specified invention, which is characterized by drying the ceramic fabric, and as a first combined invention, it provides a method for drying ceramic fabric by drying the irradiation and irradiation while ventilating the atmosphere. By intermittent irradiation with high frequency waves at a time ratio of about 1:3 to 1:10, the fabric is heated by dielectric heating by the irradiation, and then when the irradiation is stopped, the heat is dispersed into the fabric, which is repeated. Provides a method for drying ceramic fabric characterized by drying,
Furthermore, as a second combined invention, the molded ceramic fabric is exposed to wind having the same temperature and humidity as the atmosphere, and while the atmosphere is ventilated, the time ratio between the irradiation and the stop of the irradiation is 1. Drying of ceramic fabric characterized by intermittently irradiating the fabric with high frequency waves at a ratio of about 3:3 to about 1:10, dielectrically heating the fabric by the irradiation, and then dispersing the heat into the fabric when the irradiation is stopped. provide a method. The ceramic dough may be formed by extrusion molding, compression molding, or any other molding method. A high frequency wave is irradiated onto the fabric formed into a certain shape by such a forming means, and the fabric is dried by the dielectric heating. High frequencies can be used at frequencies from 300 to 3000MHz. The fabric is irradiated with high frequency waves intermittently. This intermittent irradiation is an important condition of this invention. The irradiation time and irradiation stop time of intermittent irradiation are determined by the ratio of time for the heat given by the irradiation for a certain period of time to be dispersed within the fabric when the irradiation is stopped, and the temperature difference between each part of the fabric is reduced. determined. The entire fabric that has been irradiated with high-frequency waves is not heated uniformly, but a portion of the fabric is heated in a concentrated manner. Therefore, a temperature difference occurs within the fabric, and when this temperature exceeds a certain level, the difference in dryness of the fabric increases in proportion to this, and shrinkage occurs in proportion to the dryness.
As a result, the degree of shrinkage becomes unbalanced throughout, causing cracks. Therefore, the duration of one high-frequency irradiation is set so that the energy of one high-frequency irradiation is kept within the dryness difference and temperature difference that do not cause cracks in the fabric. The irradiation stop time is determined by the time during which the heat applied to a part of the fabric by the irradiation is dispersed throughout the fabric and the temperature difference in each part of the fabric becomes as small as possible. Here, the fact that the temperature difference becomes small does not mean that the temperature difference becomes 0, but it does mean that the temperature difference becomes large enough that no cracks will occur even if more heat is added next time. do. Of course, it is preferable for the temperature difference within the fabric to be close to 0 in order to prevent cracks, but in order to reduce this temperature difference to 0 or close to this, the irradiation stop time is extended to provide sufficient heat. Attempts to disperse the above should be avoided as this would prolong the drying time of the fabric and would defeat the purpose of this invention. The above-mentioned irradiation time and irradiation stop time are different depending on the size, shape, composition, etc. of the fabric, but as a result of the inventor's experiments, the former and the latter are different depending on the time of each irradiation high frequency. It was preferable that the time ratio be about 1:3 to about 1:10 when the frequency and output are the same. Also,
Within this time ratio, it is not necessary to always keep the irradiation time and irradiation stop time the same during a series of intermittent high-frequency irradiations, and either or one of them may be changed as appropriate during the drying process. When the time ratio becomes smaller than about 1:3 (for example, 1:1), the heat applied to a part of the dough is further heated before being dispersed, resulting in large temperature differences between different parts of the dough. This is unsuitable because it will cause cracks in the dough as it ages, and if the ratio is greater than about 1:10 (for example, 1:20), the heat applied to a part of the dough will be dispersed and the next heating process will be difficult. However, the temperature difference between various parts of the dough does not become large, so cracks do not occur, but the time required for drying the dough increases, making it impossible to achieve the object of the present invention. Furthermore, in the early stage of this intermittent high-frequency irradiation, the ratio of the irradiation time to the irradiation stop time is relatively small, about 1:3 to 1:4, which contributes to shortening the drying time. . This is because in the initial stage when the dough is heated from room temperature to around 40-50℃, there is almost no drying progress even after heating, so cracks due to differences in dryness within the dough rarely occur. That's because there isn't. Therefore, relatively rapid heating is possible at this initial stage.
In the initial stage of the intermittent irradiation, the temperature of the fabric increases rapidly. That is, the temperature rises from room temperature to about 40 to 50°C in a short time. After this initial stage, the temperature rise slows down and the temperature remains almost constant. This indicates that the drying of the fabric is proceeding smoothly, and indicates that the balance between heating by high frequency and latent heat is maintained. After this state, the temperature of the dough will slowly rise. This indicates that the heating by the high frequency exceeded the latent heat, and therefore indicates that the progress of drying the fabric was slowed down. This means that the drying of the fabric has entered the finishing stage. Therefore, at this finishing stage, the completion of drying is detected by appropriately determining the color tone of the fabric, measuring humidity, elapsed irradiation time, etc. During the drying process of such fabrics, the atmosphere is ventilated. This is done to remove moisture in the atmosphere caused by drying. This ventilation should be sufficient to prevent sudden changes in the temperature and humidity in the atmosphere. In addition, in order to irradiate the high frequency evenly from the periphery of the fabric, the fabric is turned over using a turntable, etc.
Making a turn is also effective. Furthermore, depending on the shape of the fabric, moisture evaporated from inside may not be diffused and may condense on the surface. When this condensation occurs, the difference in temperature and dryness between different parts of the fabric increases, causing cracks in the areas where condensation has occurred. For example, in the case of fabrics that are difficult to turn over during drying, such as large insulators, and when the brim-like pleats are inclined downward, dew condensation may form on the base of the lower surface of the pleats. Cracks may then occur at the base of the condensed folds, causing one of the folds to detach and fall in its circular shape. To prevent such condensation, expose the fabric to air. This wind has the same temperature and humidity as the atmosphere. When the inventor exposed outside air to the fabric, cracks appeared in the condensed areas. After that,
When various types of wind with different temperatures and humidity were applied to the fabric, it was found that cracks did not occur when the fabric was exposed to air with the same temperature and humidity as the atmosphere. It is effective to generate airflow within the atmosphere that has the same temperature and humidity as the atmosphere. Therefore, in the atmosphere, it is preferable to ventilate the interior and circulate the air inside to blow it out toward the fabric. The direction of this blowout is preferably directed toward the dew condensation area. Note that the above-mentioned intermittent operation of high-frequency irradiation and irradiation stop may be performed either automatically or manually. Intermittent irradiation can also be automatically controlled by detecting the temperature, humidity, etc. in the atmosphere, inside and on the surface of the fabric, and automatically determining the irradiation time, irradiation stop time, and their ratio. FIGS. 1 and 2 show the apparatus directly used in the practice of this invention. A high-frequency oscillator 3 is attached to an oven 2 with a door 1 pivotally attached to the entrance/exit, and a waveguide 5 connects the high-frequency oscillator 3 and a power supply port 4 facing into the oven 2, and an isolator 6 is attached to the waveguide 5. and a high frequency distribution pipe 7 are provided. 8 is a reflector, and 9 is a stirring blade connected to a motor and speed reducer unit 10. A circulation device 11 is installed on the top surface of the oven 2.
is provided, sucks internal air from the suction port 12,
It is circulated from the delivery pipe 13 through the blow-off pipe 14 into the oven 2. The blow-off pipe 14 is made of ceramic fabric 1
It has a structure that blows out air in a direction that matches the shape of 5. Reference numeral 16 denotes a ventilation hole, which exhausts air to an extent that does not cause a sudden change in the atmosphere to prevent condensation inside the oven 2. It is also possible to measure the temperature and humidity of this exhaust gas to detect the degree of dryness and temperature of the fabric 15, thereby automatically controlling the period of intermittent high frequency irradiation and the ratio thereof. 17 is a table on which the dough 15 is placed, and this may be made rotatable. Further, the blowing pipe 14 may be configured to rotate around the dough 15. 18 is a lighting lamp. The high frequency oscillator 3 here uses four magnetrons, each with an output of 1.35 kW and a frequency of 2450 MHz. Next, embodiments of this invention will be described. These examples are examples in which high frequency waves with a frequency of 2450 MHz and an output of 2.3 kW were intermittently irradiated in an oven having the structure shown in FIGS. 1 and 2. The ceramic fabric used was the insulator fabric shown in Figure 3. The fabric was turned over several dozen times from the start to the end of drying to prevent local condensation. In addition, the oven was ventilated to the extent that the temperature and humidity inside the oven did not change rapidly. (Example 1) As shown in Attached Table 1, for the first 10 minutes, high-frequency irradiation was performed for 60 seconds, and intermittent irradiation was performed for 3 minutes after the irradiation was stopped. At this initial stage, the surface temperature of the dough reached 43-54°C. The reason why there is a wide range in surface temperature is because the temperature was measured at multiple locations on the surface of the fabric, with the temperature being lower at the outer periphery of the pleats and higher at the body. After 10 minutes, intermittent irradiation was performed with the irradiation time being 30 seconds and the irradiation stop time being 3 minutes. From 10 minutes after the start of irradiation to around 160 minutes, the surface temperature was approximately 50
The temperature remains at around ℃, and after about 160 minutes, the temperature rises gradually. FIG. 4 is a graph showing the elapsed time and temperature changes in Attached Table 1. According to the graph in Figure 4, the temperature rises in the initial stage (A) for about 10 minutes after the start of drying, followed by the full-fledged drying stage (B) until about 160 minutes, and then the finishing stage (C). It is understandable that When the temperature suddenly rises in the initial stage of high-frequency irradiation, as mentioned above, even though it is heated, there is almost no drying progress, so there is a crack due to the difference in dryness within the fabric.

【table】

[Table] There is no occurrence of slack. The leveling off of the temperature in the drying stage (b) indicates that the balance between heating and latent heat is maintained and drying progresses smoothly. Furthermore, in the finishing stage (c), a temperature rise is observed due to a decrease in latent heat. In this example, the ratio of high frequency irradiation time to irradiation stop time was 1:3 in the initial stage (a), but the ratio was 1:6 in the drying stage (b) and finishing stage (c). The humidity of the dough before drying was approximately 20% and had a bluish tinge, but after 240 minutes, the humidity was approximately 2.8%.
The drying was fairly white and uniform, and no cracks were observed. This drying time is approximately 1/40th of the conventional drying time. The size of the fabric is the same as before, with the length dimension reduced by approximately 5%. (Example 2) As shown in Attached Table 2, on the fabric with a surface temperature of 22℃,
Intermittent irradiation was performed with high frequency irradiation for 30 seconds and 3 minutes of intermittent irradiation. In this embodiment, the intermittent time and the ratio thereof are the same throughout, and are 1:6. The initial stage of temperature rise is seen by the first 37 minutes, and the subsequent drying stage continues until around 300 minutes. In this case, the drying stage remains at around 45°C. After 300 minutes, the temperature gradually rose, indicating that the finishing stage had begun. This attached table 2
FIG. 5 is a graph showing the elapsed time and temperature change. Similarly to FIG. 4, FIG. 5 also shows curves indicating the initial stage (a), drying stage (b), and finishing stage (c). In this example, the dough before drying had a humidity of approximately 20% as in Example 1, but the humidity was 532%.
After a few minutes, it was dried to about 4.9% and no cracks were observed. This drying time is approximately 20% longer than the conventional drying time.
It is 1/1. The size of the fabric has been reduced by about 5% in length, the same as before. In this second example, intermittent irradiation was performed for the same time and at the same time ratio throughout the initial stage, drying stage, and finishing stage (this time and time ratio were the same as in the drying stage and finishing stage of Example 1). ), but the ratio of the high-frequency irradiation time in the initial stage and the irradiation stop time is different from that in the first embodiment, and the total

[Table] The time required to dry the body varies. From these results, it is considered that the ratio of the irradiation time in the initial stage and the irradiation stop time influences the length of the overall drying time. As is clear from the above, according to the present invention, by intermittently irradiating ceramic fabric with high frequency waves to repeat dielectric heating of the fabric and average dispersion of this heat within the fabric, temperature differences in various parts of the fabric can be reduced. It contributes to improving ceramic manufacturing efficiency because it can dry within an extremely short time without damaging the fabric while minimizing the difference in temperature and balancing the overall shrinkage rate.

[Brief explanation of the drawing]

Fig. 1 is a front view showing an example of a device directly used in carrying out this invention, Fig. 2 is a plan view of Fig. 1, Fig. 3 is a sectional view showing the fabric of the insulator used in the embodiment, and Fig. 4 The figure is a graph showing the relationship between time and temperature in one embodiment, and FIG. 5 is a graph showing the relationship between time and temperature in another embodiment. In addition, 15 in the figure is the fabric.

Claims (1)

[Scope of Claims] 1. By intermittently irradiating a molded ceramic fabric with high frequency waves, the fabric is dielectrically heated by the irradiation, and then when the irradiation is stopped, the heat is dispersed within the fabric, which is repeated. A ceramic fabric drying method characterized by drying. 2. By intermittently irradiating the molded ceramic fabric with high frequency waves at a time ratio of about 1:3 to 1:10 between the irradiation and the irradiation while the atmosphere is ventilated, the irradiation causes dielectric A method for drying ceramic fabrics, which comprises heating the fabric and then repeatedly dispersing the heat into the fabric when irradiation is stopped to dry the fabric. 3. Apply wind to the molded ceramic fabric at a temperature and humidity equivalent to that of the atmosphere, and while ventilating the atmosphere, set the time ratio between irradiation and irradiation stop to 1.
Drying of ceramic fabric characterized by intermittently irradiating the fabric with high frequency waves at a ratio of about 3:3 to about 1:10, dielectrically heating the fabric by the irradiation, and then dispersing the heat into the fabric when the irradiation is stopped. Method.