JP4992094B2 - Microwave dryer - Google Patents

Description

  The present invention relates to a microwave drying apparatus for drying an object to be dried such as wood honeycomb, food, medicine, ceramics, and other ceramic honeycombs that are automobile parts.

A honeycomb which is an automobile part is finished as a ceramic product, and the production process includes a drying process of the extruded honeycomb product.
In this drying process, a microwave drying apparatus having a fast drying time and a high drying rate is used.

  FIG. 6 shows the extruded honeycomb product 10, and FIG. 7 is an explanatory view showing a state in which the honeycomb product 10 is dried by a microwave drying apparatus.

The extruded honeycomb product 10 contains about 27% of moisture, but is dehydrated by irradiating with microwave power in the drying chamber 11 and dried to a moisture content of about 5%.
The honeycomb product 10 thus dried is then completed as a ceramic honeycomb through a degreasing process, a sintering process, and the like.

On the other hand, in the microwave drying performed as described above, the external temperature rise is delayed as compared with the internal temperature rise of the honeycomb product 10.
That is, as shown in FIG. 7B, a temperature difference of ΔTL appears between the inside and outside in the cylinder axis direction, and as shown in FIG. 7C, between the inside and outside in the diameter direction. A temperature difference of ΔTR appears.
For this reason, the external drying is delayed with respect to the inside of the honeycomb product 10, and this causes a tensile stress due to the drying shrinkage generated in the honeycomb product 10, thereby generating cracks, wrinkles on the outer wall, deformation and the like.

Figure 8 is a characteristic diagram obtained by experiment the relationship between the temperature and time of the honeycomb product 10 when the micro Namiinui 燥, TC is the central temperature of the honeycomb article 10, TM is an intermediate temperature of the honeycomb article 10, TS Is a characteristic curve showing the outer peripheral temperature of the honeycomb product 10.
FIG. 9 is a characteristic diagram in which the relationship between the remaining moisture and time of the honeycomb product 10 when microwave-dried is experimentally determined. WC is a center moisture, WM is an intermediate moisture, and WS is a characteristic curve showing an outer periphery moisture. is there.
In addition, WD is a characteristic curve indicating a moisture difference (WS-WC).

In this experiment, a honeycomb product 10 having a diameter R = 150 mm, a length L = 220 mm, a mass 920 g, and an initial moisture of about 27% was used as sample conditions.
As drying conditions, a 12 kW batch type microwave drying apparatus was used, with a microwave output of 8 kW (2 kW × 4), exhaust of 9 m / S, steam, and no hot air.
Further, the center temperature TC, the intermediate temperature TM, and the outer peripheral temperature TS are measured using a fiber thermometer, and the center moisture WC, the intermediate moisture WM, and the outer periphery moisture WS are shown in FIGS. 10 (A) and 10 (B). As described above, the moisture of each part 10C, 10M, and 10S of the honeycomb product 10 was measured with a measuring instrument.

As can be seen from the characteristic diagram shown in FIG. 8, the center temperature TC, the intermediate temperature TM, and the outer peripheral temperature TS of the honeycomb product 10 rise to 100 ° C. and become constant.
Further, the time required for the outer periphery to reach 100 ° C. is longer than the center and the middle. That is, the temperature rise is delayed in the outer periphery as compared with the center and the middle.
Further, as can be seen from the characteristic diagram shown in FIG. 9, both the central moisture WC and the outer circumferential moisture WS decrease from a temperature of about 90 ° C. at a constant rate.
That is, the constant rate drying period in which the difference in moisture between the center and the outer periphery is substantially constant.

  Thus, in microwave drying, since the temperature rise of the outer peripheral temperature TS is delayed with respect to the center temperature TC, a certain moisture difference occurs, and as described above, a tensile action due to drying shrinkage occurs, and the honeycomb product 10 will be cracked, wrinkled, deformed, and the like.

Japanese Patent No. 3404345

The problem to be solved is that cracks, wrinkles, deformation and the like occur in the honeycomb product to be microwave dried.
Therefore, an object of the present invention is to provide a microwave drying apparatus that can solve such problems.

To achieve the above object, the present invention has a drying chamber for irradiating microwave power, in a microwave drying apparatus and drying the dehydrated matter to be dried in a drying chamber, the temperature of the inner wall temperature of the drying chamber An inner wall temperature raising means for heating, and an indoor temperature raising means for raising the room temperature by supplying steam or hot air into the drying chamber , irradiating the object to be dried with the microwave power, and the inner wall temperature In addition, a microwave drying apparatus is proposed in which the room temperature is raised to a boiling point temperature or a temperature close to the boiling point temperature, thereby eliminating the heat input and output of the object to be dried and drying the object to be dried. To do.

  Further, as the inner wall temperature raising means provided in the present invention, electric heating means, water vapor means, hot water or hot air means can be used, and it can be configured as a combination means of these means.

The microwave drying apparatus according to the first aspect of the present invention microwaves an object to be dried in a drying chamber whose inner wall is at a boiling point temperature or a temperature close to the boiling point temperature.
For this reason, since the object to be dried has no heat input and output due to radiant heat, the inside and outside of the object to be dried rise in temperature at substantially the same speed by microwave heating.
Therefore, since the temperature of the outside of the object to be dried does not delay with respect to the inside, cracks, wrinkles, deformation and the like hardly occur.

  Heat is released from the object to be dried by heat conduction, convection, and radiation, but heat conduction is negligible and can be neglected. It can be prevented by raising.

Then, the thermal convection, feeding steam or hot air in the drying燥室, the drying chamber can be prevented heat release by heat convection by maintaining a temperature state close to the boiling point temperature or the boiling point temperature.
This either et al, in Rure be added constituting a chamber UchiNoboru raising means can be more uniformly increase in temperature inside and outside of the material to be dried.

  The above inner wall temperature raising means can be constituted by any means such as electric heating means, water vapor means, hot water or hot air means, but may be a combination means of these means.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing a first embodiment implemented as a microwave drying apparatus for drying a honeycomb product.
As shown in the figure, the microwave drying device 20 supplies the microwave power sent from the microwave oscillator 21 into the drying chamber 24 through the microwave three-dimensional circuit 22 and the microwave window 23.
In the microwave drying apparatus 20, a heater 27 is provided between the inner wall 25 and the middle wall 26 of the drying chamber 24, and a heat insulating material 29 is provided between the middle wall 26 and the outer wall 28.

The heater 27 controls the power supply by the control circuit 30 and raises the temperature of the inner wall 25 made of stainless steel.
Specifically, the temperature is raised by heater heating so that the inner wall 25 has a boiling point temperature (100 ° C.).
The temperature of the inner wall 25 is detected by the temperature sensor 31 and the control circuit 30 is controlled so as to maintain the boiling point temperature.

In addition, the microwave drying apparatus 20 is configured to send water vapor from the water vapor supply device 32 into the drying chamber 24 to increase the indoor temperature of the drying chamber 24.
This room temperature is preferably kept at the boiling point temperature (100 ° C.).

In the microwave drying apparatus 20 configured as described above, the inner wall 25 of the drying chamber 24 has a boiling point temperature due to heater heating, and the drying chamber 24 has a boiling point temperature due to water vapor. There is no heat from the heated honeycomb product 10.
That is, since the temperature rise from the inside by the microwave heating is faster than the temperature rise by the heat transmitted from the outside of the honeycomb product 10, the honeycomb product 10 does not generate heat from the outer periphery.

Specifically, if the amount of heat released from the microwave-heated honeycomb product 10 is Q, Q = Qc + Qr = 0.
However, Qc is the amount of heat released as convection, and Qr is the amount of heat released as radiation.
Here, Qc is prevented by the temperature rise in the drying chamber 24 and becomes Qc = 0, and Qr is prevented by the temperature rise of the inner wall 25 and becomes Qr = 0.

As a result, according to this microwave drying apparatus 20, the temperature inside and outside of the honeycomb product 10 rises evenly by microwave heating, so that a tensile action caused by the temperature difference between the inside and outside does not occur.
As a result, the honeycomb product 10 is hardly cracked, wrinkled or deformed.

FIG. 2 is a schematic configuration diagram of the microwave drying apparatus 40 shown as the second embodiment.
In the present embodiment, a heat generating pipe 41 through which water vapor passes is provided between the inner wall 25 and the inner wall 26 of the drying chamber 24, water vapor is sent from the water vapor feeder 42 to the heat generating pipe 41, and the inner wall 25 is heated to the boiling temperature. This is a configuration to be made.
The rest of the configuration is the same as that of the microwave drying apparatus shown in FIG.

FIG. 3 is a schematic configuration diagram of the microwave drying apparatus 50 shown as the third embodiment.
In the present embodiment, a hot water tank 51 is provided between the inner wall 25 and the middle wall 26 of the drying chamber 24, and the inner wall 25 is kept at the boiling point temperature by the hot water sent from the hot water supply device 52 to the hot water tank 51. .
The rest of the configuration is the same as that of the microwave drying apparatus shown in FIG.

In the embodiment shown in FIG. 2, water vapor is used as the inner wall temperature raising means, and in the embodiment shown in FIG. 3, the temperature raising means uses hot water as the inner wall temperature raising means. It can be constituted by a temperature raising means using hot air.
Such an inner wall temperature raising means does not need to keep the inner wall 25 at the boiling temperature accurately, and it is sufficient that the inner wall temperature can be about 100 ° C. ± 10 ° C.

  Further, the room temperature raising means for raising the room temperature of the drying chamber 24 is not limited to the one using steam, but may be a temperature raising means using hot air, and the room temperature is about 100 ° C. ± 10 ° C. Is preferred.

FIG. 4 is a schematic view of a microwave drying apparatus shown as an application example of the present invention , and FIG. 5 is a perspective view of a container used in this application example .
In this application example, a container 61 with a lid that is submerged is provided, and the honeycomb product 10 is microwave-dried in a state of being placed in the container 61.

Specifically, the container 61 (including the lid 61a) is hydrated.
Then, the honeycomb product 10 is put in the container 61 and covered in the drying chamber 62 of the microwave drying device 60 in a state where the lid 61a is covered, and microwave drying is performed.

In this application example , the water-containing container 61 is heated by microwave heating, and accordingly, the container is also heated, so that the temperature inside and outside the honeycomb product 10 rises simultaneously.
As a result, the honeycomb product 10 is hardly cracked, wrinkled or deformed.

In addition, although it is preferable to provide the vent hole 61b in the container 61, when the container 61 is comprised with a breathable material, the vent hole 61b does not necessarily need to be provided.
Furthermore, since the container 61 should just have water immersion, it can also be comprised with a paper material.
Moreover, in this application example using the container 61, a normal microwave drying apparatus can be used.

  In addition to drying honeycomb products performed in the ceramic honeycomb production process, the present invention can also be implemented as a drying device for wood, food, chemicals, ceramics, and the like.

It is a schematic block diagram of the microwave drying apparatus shown as 1st Embodiment. It is a schematic block diagram of the microwave drying apparatus shown as 2nd Embodiment. It is a schematic block diagram of the microwave drying apparatus shown as 3rd Embodiment. It is the schematic of the microwave drying apparatus shown as an application example . It is a perspective view which shows the submerged container used in said application example . It is a perspective view which shows the honeycomb product extruded. FIG. 7A is a schematic view showing a conventional microwave drying apparatus, and FIGS. 7B and 7C are explanatory views showing a temperature difference between the inside and the outside of the honeycomb product. It is the characteristic view which showed the temperature rising state of the inside and the outside of the honeycomb product to be microwave-dried. FIG. 4 is a characteristic diagram showing residual moisture inside and outside the honeycomb product to be microwave-dried. Fig. 10 (A) is a front view of the honeycomb product showing the moisture measuring section, and Fig. 10 (B) is a side view thereof.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Honeycomb product 20 Microwave dryer 24 Drying chamber 25 Inner wall 26 Middle wall 27 Heater 32 Water vapor feeder 40 Microwave dryer 41 Heat generating pipe 42 Water vapor feeder 50 Microwave dryer 51 Hot water tank 52 Hot water feeder 60 Microwave drying Device 61

Claims (2)

In a microwave drying apparatus that has a drying chamber for irradiating microwave power and dehydrates and dries the object to be dried in the drying chamber
The inner wall Atsushi Nobori means for raising the temperature of the inner wall temperature of the drying chamber,
Providing an indoor temperature raising means for raising the room temperature by supplying steam or hot air into the drying chamber ;
Irradiating the object to be dried with the microwave power,
A microwave drying apparatus characterized in that, by raising the inner wall temperature and the room temperature to a boiling point temperature or a temperature close to the boiling point temperature, heat to and from the dried object is eliminated and the dried object is dried. . In the microwave drying device according to claim 1,
The microwave drying apparatus characterized in that the inner wall temperature raising means comprises any means of electric heating means, water vapor means, hot water or hot air means, or a combination means thereof.

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