JPH0816588B2 - Microwave dryer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a microwave dryer.

(B) Conventional Technology Japanese Patent Application No. 2-2230 discloses a microwave drying apparatus for microwave-drying a material to be dried by applying microwaves to the drying chamber. The apparatus is provided with stirring means for stirring the material to be dried in the drying chamber so that the material to be dried can be uniformly dried. The stirring means is connected to a transmission shaft that is inserted from the outside of the drying chamber into the drying chamber, and the stirring force is driven by the stirring force transmitted from the transmission shaft.

By the way, in such a structure, there is a possibility that microwaves may leak to the outside of the drying chamber from the vicinity where the transmission shaft penetrates. Therefore, it is conceivable to provide a microwave choke space around the transmission shaft. However, in this case, if the material to be dried leaks to the outside from the vicinity of the penetration as well and enters the choke space along the transmission shaft, the circuit constant of the choke space deviates from the desired value, and the choke The space will not be able to do enough microwave choke.

Further, if the material to be dried enters and is clogged in the narrow gap between the stirring means and the wall of the drying chamber while the stirring means is being driven, the stirring means will not operate normally.

In order to eliminate the above-mentioned inconvenience, it is conceivable to close the narrow gap between the stirring means and the wall of the drying chamber with a packing having a short length, but it is necessary to move the material to be stirred by the stirring means. Since the force to be applied is applied to the material to be dried, the material to be dried is pushed between the packing and the stirring means depending on how the force is applied, affecting the rotation of the stirring means or drying in the choke space. There is a risk that things will get inside.

(C) Problem to be Solved by the Invention The present invention has a structure in which a microwave choke space is provided around a transmission shaft that gives a transmission force to a stirring means for stirring an object to be dried. An object of the present invention is to provide a microwave drying device that can ensure a state in which wave choking can be performed.

(D) Means for Solving the Problems A microwave drying apparatus of the present invention is a drying chamber to which a granular or powdery material to be dried is supplied, and a microwave for microwave-drying the material to be dried in the drying chamber. A microwave supply means for supplying a wave, a stirring means arranged in the drying chamber for stirring the material to be dried, and a transmission shaft for slidably penetrating the wall of the drying chamber and transmitting a stirring force to the stirring means. The microwave choke space provided around the transmission shaft and outside the wall surface of the drying chamber and the gap between the transmission shaft and the wall of the drying chamber allows the material to be dried to enter the choke space. In order to prevent this, the cylindrical blocking means of low dielectric loss material covers the gap and covers the transmission shaft in the drying chamber from the wall surface of the drying chamber to a position higher than the stirring means.

(E) Action The blocking means made of low dielectric loss material prevents the material to be dried from entering the choke space along the transmission axis,
The circuit constant of the choke space is prevented from deviating from a desired value, and the choke space performs sufficient microwave choke.

Further, the transmission shaft slidably penetrates the wall of the drying chamber, and when an object to be dried enters a narrow gap between the stirring means and the wall of the drying chamber, the transmission shaft should enlarge this gap. The agitation means slides and operates normally without being unable to drive due to clogging of the material to be dried.

(F) Embodiment FIG. 1 shows the structure of a microwave drying apparatus according to an embodiment of the present invention. The apparatus comprises a drying apparatus main body 1 and its peripheral mechanism.

The main body of the drying device main body 1 is an upper lid 2 that can be opened and closed.
There is provided a cylindrical drying chamber 3 having A supply pipe 4 is connected to the upper left portion of the drying chamber, and the tip of the supply pipe reaches a storage tank 6 that stores a granular or powdery material to be dried 5. The storage tank is below the drying chamber 3.
Examples of the material to be dried 5 include resin pellets containing glass, rice, and chemical powder. The resin pellets are molded after being melted, but if the resin pellets are dried prior to such melt molding, the subsequent molding will be well performed. In this example, the glass-containing resin pellets are the dried material.

A suction hopper 7 is connected to the center of the upper lid 2 of the drying chamber 3 via an integrally formed microwave blocking pipe 7a. The suction hopper 7 includes a suction hopper main body 7b and a hopper upper lid 7c that is detachably arranged on the main body. The filter wire mesh 8a and the filter paper 8 are detachably arranged so as to be sandwiched between the suction hopper body 7b and the hopper upper lid 7c. The filter wire netting 8a and the filter paper 8 have a mesh smaller than the material diameter of the material to be dried 5, and the filter paper 8 has a smaller mesh than the filter wire netting 8a.

A poppet valve 9 is provided in an upper lid 7c of the hopper 7 located above the filter wire mesh 8a and the filter paper 8. Then, in the upper part of the poppet valve 9, a suction blower 11 is provided to the suction hopper 7 via an intake pipe 10.
Are connected. In this case, when the suction blower 11 is driven while the poppet valve 9 is driven to open, the suction action of the suction blower 11 reaches the intake pipe 10, the suction hopper 7, the microwave cutoff pipe 4, and the inside of the storage tank 6. The material 5 to be dried is sucked into the drying chamber 3 through the supply pipe 4. When the material to be dried 5 reaches the drying chamber 3, it falls by its own weight and accumulates therein.

Here, there are some things to be dried 5 which do not fall into the drying chamber 3 and are then sucked and reach the inside of the suction hopper 7. However, such a to-be-dried material 5 will be transferred by the filter wire mesh 8a and the filter paper 8 from now on. Therefore, it is impossible to prevent the material to be dried 5 from being sucked toward the suction blower 11 undesirably.

In the drying chamber 3, microwaves are supplied to the inside of the drying chamber 3 from a magnetron 12 serving as a microwave supplying means through a waveguide 13, and the bottom wall portion thereof is as shown in detail in FIGS. 2 and 3. A stirring means for stirring the material to be dried 5, that is, a metal stirring body 15 is provided. Such a stirring body 15 is the above-mentioned drying chamber 3
Is connected and fixed to the upper end of a transmission shaft 15a penetrating the bottom wall 3a via an arm 15b. A gap is provided between the transmission shaft 15a and the bottom wall 3a of the drying chamber 3 so that the transmission shaft 15a can slide and rotate. The transmission shaft 15a is
A linear ball bearing 15d and a needle roller bearing 15 for smoothly rotating the bearing 15d inside a metal housing 15c fixed to the bottom wall 3a of the drying chamber 3 outside the drying chamber 3
It is supported by e so that it can slide up and down. The pin 1 is attached to the lower end of the transmission shaft 15a.
5f is fixed. The lower end of the transmission shaft 15a is loosely fitted to the driving body 14a directly connected to the fixed motor 14 from the upper side, and the pin 15f is loosely fitted in the elongated hole 14b formed beside the driving body 14a. As a result, although the transmission shaft 15a slides up and down, the sliding range is restricted by the vertical dimension of the elongated hole 14b into which the pin 15f is fitted. In such a configuration, the stirring body 15 rotates by the stirring force from the motor 14 being transmitted via the transmission shaft 15a that is vertically slidable and rotates, so that the material to be dried 5 is stirred. It is done.

In this case, the agitator 15 normally agitates the material to be dried 5 in a state where the gap M between the agitator 15 and the bottom wall 3a of the drying chamber is narrow, as shown in FIG. Meanwhile, during such stirring, the stirrer 15 and the bottom wall of the drying chamber
When the material to be dried 5 enters the narrow gap between the agitator 3a and the
15 is pushed by this material to be dried and slides above the transmission shaft 15a, and the gap M between the stirring body 15 and the drying chamber bottom wall 3a is enlarged as shown in FIG. As described above, the article to be dried 5 is normally driven without being clogged and unable to be driven.

Between the drying chamber bottom wall 3a and the housing 15c,
A microwave choke space 15g is formed. The choke space is located around the transmission shaft 15a so as to surround the transmission shaft 15a, and the choke opening directly faces the transmission shaft 15a. The choke space 15a suppresses microwaves from leaking out of the drying chamber from the vicinity of the transmission shaft 15a of the drying chamber bottom wall 3a penetrating therethrough.

In the drying chamber 3, a blocking means, namely a pipe 15b made of ceramics which is a low dielectric loss material, is closely fixed to the drying chamber bottom wall 3a. The transmission shaft 15a passes through the pipe 15h so as to be vertically slidable and rotatable. The upper end of the pipe 15h extends to a position higher than that of the stirring body 15, and preferably has a length such that the upper end protrudes upward from the material to be dried 5. Due to the presence of this pipe 15h, the material to be dried 5 is prevented from leaking to the outside from the vicinity of the transmission shaft 15a of the drying chamber bottom wall 3a which penetrates, that is, the material to be dried 5 is transmitted to the outside. It is ensured that the choke space 15g is prevented from entering the choke space 15g along the axis 15a, so that the circuit constant of the choke space 15g does not deviate from a desired value, and the choke space 15g performs sufficient microwave choke. .

A level sensor 16 and a temperature sensor 17 such as a thermistor are arranged on the side wall of the drying chamber 3. The level sensor 16 detects whether a predetermined amount of the material to be dried 5 has accumulated in the drying chamber 3, and the temperature sensor 17 detects the temperature of the material to be dried 5. A compressor 19 is connected to the left bottom of the drying chamber 3 via an intake valve 18, and the upper lid 2 of the drying chamber 3 is connected.
Is equipped with an exhaust valve 20. The driving of the compressor 19 and the opening of the intake valve 18 and the exhaust valve 20 are performed at the time of drying the material to be dried 5 by microwaves, and the steam generated at the time of drying causes the exhaust valve 20 from the compressor 19 together with the air. It passes through and is discharged to the outside.

Further, a discharge valve 21 is provided on the right bottom portion of the drying chamber 3, and the discharge valve is opened when discharging the dried object 5 to be dried. The material to be dried 5 discharged based on the opening of the discharge valve 21 is discharged through the discharge pipe 22 to the lower preliminary chamber.
It drops to 23 and collects. A warming heater 24 is arranged on the lower inclined wall of the preliminary chamber, and a rotor 25 is provided in the preliminary chamber 23.
Is provided with a level sensor 26. The level sensor 26 normally rotates the rotating body 25, and even if a slight predetermined amount of the material to be dried 5 is accumulated in the preliminary chamber 23 and the rotating body 25 is rotated, the material to be dried 5 is not loaded. Then, when the rotating body 25 cannot be rotated satisfactorily, a predetermined signal is output to detect that the material to be dried 5 has accumulated a slight predetermined amount.

A lower portion of the spare chamber 23 is connected to another suction hopper 27 located at a higher position than the spare chamber 23 through a transfer pipe 28. Like the suction hopper 7, the suction hopper 27 is also provided with a filter wire net 29a and a filter paper 29 having a mesh smaller than the material diameter of the material to be dried 5, and is located above the filter paper and is located on the poppet valve. 30 are provided. Then, in the upper part of the poppet valve 30, the suction blower 11 is also provided to the suction hopper 27 through the intake pipe 31.
Are connected. In this case, when the blower 11 is driven with the poppet valve 30 opened, the intake action of the blower 11 causes the transfer pipe 28 through the intake pipe 31 and the suction hopper 27.
Up to this point, the material to be dried 5 accumulated in the preliminary chamber 23 reaches the suction hopper 27 through the drying pipe 28. When the object to be dried 5 reaches the suction hopper 27, it falls into the hopper by its own weight.

In the suction hopper 27, the warming heater 32 is arranged on the lower inclined wall, the opening / closing valve 33 is provided on the lower end, and the upper and lower limit level sensors 34, 35 are arranged on the upper and lower parts. When the on-off valve 33 is closed, the intake action acts to drop the material 5 to be dried in the suction hopper 27, and the material to be dried 5 is accumulated in the suction hopper 27. On the other hand, when the on-off valve 33 is opened, The material to be dried 5 thus collected drops downward and reaches the next-stage processing section, and the material to be dried 5 that is dried in this processing section, that is, resin pellets, is melt-molded.

FIG. 4 shows a circuit of the microwave dryer, and a microcomputer 36 of Sanyo Denki Co., Ltd., product number LC-65PG23 is provided as a main control unit, and the computer is arranged on the front surface of the dryer main body 1. Based on the operation information from the operating section 37, the temperature information from the temperature sensor 17, the information from the various level sensors 16, 26, 34, 35, etc., the magnetron 12, motor 14, intake valve 18, exhaust valve 20, compressor 19, discharge valve 21, heat insulation heaters 24, 32,
The suction blower 11, the poppet valves 9 and 30, and the opening / closing valve 33 are drive-controlled.

FIG. 5 shows a flow chart of an operation program incorporated in the microcomputer 36, and the operation of the microwave dryer will be described below with reference to the chart.

After turning on the power, go through the S1 step and then use the normal S2, S3, S3a, S
4 and S5 are cyclically executed. In step S1, initial setting operation is performed. That is, a microcomputer
All writable areas in 36 are cleared,
Moreover, the magnetron 12, the motor 14, the compressor 19, the heat insulation heaters 24 and 32, and the suction blower 11 are placed in the drive stopped state, and the intake valve 18, the exhaust valve 20, the discharge valve 21, the poppet valves 9 and 30, the open / close valve 33. Are placed in a closed state. In S2 step, operation information from the operation section 37 is input, and in S3 step, the suction hopper 27 is operated by the lower limit level sensor 35.
It is judged whether or not the material to be dried 5 is accumulated in the room, and in the step S3a, based on the detection by the level sensor 26, the preliminary room is detected.
In 23, it is judged whether or not the material to be dried 5 is accumulated in a slight predetermined amount. In step S4, it is checked whether or not the start flag is set in the microcomputer 36, and in step S5, it is determined whether or not the start key is currently operated by the operation unit 37 based on the input information in step S2.

Thus, when the material to be dried 5 which is a resin pellet is melt-molded, the material to be dried 5 is melted so that such molding can be performed well.
When drying in advance, first set the desired drying time and drying temperature within the range of 20 to 60 minutes and within the range of 70 to 170 ° C by the key operation on the operation unit 37, and turn on the continuous switch 38. Manipulate. These operation information are input in step S2. After that, when the start key is operated on the operation unit 37, such information is similarly input in the step S2, an affirmative judgment is made in the step S5, the start flag is subsequently set in the step S6, and the above in the step S7. Heat insulation heater 24, 32
Drive control is started. That is, the warming heaters 24 and 32 are intermittently driven at a desired ratio so that the insides of the preliminary chamber 23 and the suction hopper 27 are approximately maintained at the set drying temperature. It is kept warm at the above temperature.

Then, steps S8, S9, and S10 are sequentially executed. In step S8, it is checked whether or not the transport flag in the microcomputer 36 is set (in this case, it is checked that it is not set). Drying room 3 at S9 step
The operation of supplying the material to be dried 5 to is performed. That is, the poppet valve 9 is opened and the suction blower 11 is driven, and the object to be dried 5 is supplied from the storage tank 6 into the drying chamber 3 by the suction action of the suction blower 11, and the agitator is driven by driving the motor 14. The upper surface of the article to be dried 5 that is rotated and supplied into the drying chamber 3 is aligned with a smooth horizontal surface. In step S10, it is determined by the detection of the level sensor 16 whether the material to be dried 5 has accumulated in the drying chamber 3 by a predetermined amount (in this case, it is determined that the predetermined amount is not accumulated).

Then, the steps S2, S3, S3a, S4, S11, and S8 to S10 are cyclically executed. At this time, in step S11, it is checked whether or not the supply end flag in the microcomputer 36 is set. Then, a predetermined amount of the material to be dried 5 is accumulated in the drying chamber 3, and if this is determined in step S10, then S12, S1
3 steps are executed. In step S12, the operation of supplying the material to be dried 5 to the drying chamber 3 performed in step S9 is terminated. The supply end flag is set in step S13.

Then, steps S2, S3, S3a, S4, S11, and S14 to S17 are cyclically executed. At this time, in step S14, it is checked whether or not the drying end flag in the microcomputer 36 is set, and in step S15, the drying operation is executed. That is, the magnetron 12 is intermittently driven depending on whether or not the temperature of the article to be dried 5 detected by the temperature sensor 17 has reached the set drying temperature, and the article to be dried 5 is maintained at the drying temperature and microwave-dried. Further, the motor 14 is re-driven to rotate the agitator 15 to agitate the material to be dried 5 so that the material to be dried 5 is evenly dried, and the compressor 19 is driven and the intake valve 18 and the exhaust valve 20 are opened. The water vapor generated from the material to be dried 5 is discharged to the outside. Further, in step S15, the time elapsed for drying is started together with such a drying operation. In step S16, it is determined whether or not the drying time has reached the set drying time, and in step S17, whether or not the transport flag is set is checked as in step S8.

When the elapsed dry time reaches the set dry time,
After the step S16, steps S18 and S19 are executed. S18
In step S15, the measurement of the drying operation and the elapsed drying time, which is executed in step S15, is ended, and the counted time is reset. In step S19, the drying end flag is set.

Then, after steps S17, S2, S, S3a, S4, S11, and S14, steps S20, S21, S22, S23, and S24 are sequentially executed. Microcomputer 36 in S20 step
Whether or not the discharge flag in the inside is set is checked. In step S21, the preliminary room 23 is detected based on the detection of the level sensor 26.
First, it is determined whether or not the material to be dried 5 has already accumulated a slight predetermined amount. In step S22, when the heat retaining operation (described later) in the drying chamber 3 is being performed, this is ended and the discharge flag is set. The step S23 is executed when it is allowed to newly discharge the dried material 5 to the auxiliary chamber 23 from the drying chamber 3 because the material to be dried 5 is not accumulated in the auxiliary chamber 23 in the step S21. What is such S23
In the step, an operation of discharging the dried material 5 to be dried from the drying chamber 3 to the preliminary chamber 23 is executed. That is, the discharge valve 21
Is opened and the motor 14 is continuously driven to rotate the stirring body 15, and as the stirring body 15 rotates, the material to be dried 5 near the stirring body 15 is pushed to the surroundings to be dried. The object 5 is dropped and discharged from the discharge valve 21 through the discharge pipe 22 into the preliminary chamber 23. The material 5 to be dried thus discharged is kept warm in the preliminary chamber 23 from step S7,
There is no natural cooling, and the material to be dried 5 accompanies the natural cooling.
Are prevented from absorbing moisture again. Also, above S2
In step 3, the measurement of the elapsed time of such discharge is started. In the step S24, whether the discharge elapsed time reaches a predetermined discharge time (this is a time sufficient to discharge all the predetermined amount of the material to be dried 5 stored in the drying chamber 3) It is determined whether or not.

Then S2, S3, S3a, S4, S11, S14, S20, S23, S2
4, each step of S17 is cyclically executed, and when a slight predetermined amount of the material to be dried 5 is accumulated in the preliminary chamber 23 due to the discharge,
In such circulation, from S3a step to S25, S26, S27, S28
Each step of is executed sequentially. In step S25, the transport flag is set, and in step S26, when the material to be dried supply operation is being executed in step S9, the operation is stopped. In step S27, an operation of transporting the dried material 5 to be dried from the preliminary chamber 23, which is kept warm, to the suction hopper 27 is executed. That is, the poppet valve 30 is opened to drive the suction blower 11, and the material to be dried 5 is conveyed from the preliminary chamber 23 to the suction hopper 27 by the suction action of the suction blower 11. Since the suction hopper 27 is kept warm from the above step S7, the object to be dried 5 conveyed in this manner is not naturally cooled and is prevented from absorbing moisture again. In step S28, the object to be dried 5 is put into the suction hopper 27 by the detection of the upper limit level sensor 34.
Is determined to have accumulated to the position of such a sensor (in this case, it is determined to be no). Then S4, S11, S14, S2
Each step of 0, S23, S24, S17, S27, and S28 is cyclically executed.During this time, the discharging operation to the preliminary chamber 23 and the conveying operation to the suction hopper 27 are processed in parallel, and the discharged objects discharged to the preliminary chamber 23 are processed. The dried product 5 is immediately conveyed to the suction hopper 27.

Then, when the elapsed discharge time reaches a predetermined discharge time (all the material to be dried 5 is discharged from the drying chamber 3 to the preliminary chamber 23), the steps S29, S30, and S31 are sequentially executed. It In step S29, the discharge operation and discharge elapsed time, which have been executed in step S23, have been timed, and the time measured has been reset. In step S30, all of the above-mentioned supply end flag, drying end flag, and discharge flag are reset. In S31 step 37
At, it is determined whether or not the continuous switch 38 is turned on.

In this case, the continuous switch 38 is in the ON state, then
After step S17, steps S4, S11, S8, S27, and S28 are cyclically executed. Then, the material to be dried 5 in the preparatory chamber 23 is conveyed, and the upper limit level sensor is set in the suction hopper 27.
When the material to be dried 5 is accumulated up to the position of 34, from S28 step to S3
2, S33 step is executed. In S32 step, above S27
The carrying operation executed in step is stopped, and the carrying flag is reset in step S33.

Thus, the material to be dried 5 accumulated in the suction hopper 27 in this way
Is melt-molded in the next-stage processing section.
This is executed when an external command signal P for commanding melt molding is given to the microcomputer 36 in a state where the material to be dried 5 is accumulated in the suction hopper 27 up to the position of the upper limit level sensor 34. That is, at this time, the microcomputer
The on-off valve 33 is opened by 36, and the material to be dried 5 is discharged from the suction hopper 27 to the next stage processing section. The on-off valve 33 is closed again when all the materials to be dried 5 in the suction hopper 27 have been discharged. Then, the discharged material 5 to be dried is melt-molded in the next-stage treatment section. In this case, the resin pellets, that is, the material 5 to be dried is dried in advance, so that the molding is performed well.

Here, when the processing capacity of the next-stage processing unit for the melt molding is slow, the operation of supplying the material to be dried to the operation of carrying the material to be dried are repeatedly performed, so that the material to be dried 5 is stored in the suction hopper 27 and the auxiliary chamber 23. Will remain. And the spare room
If the material 5 to be dried is further discharged from the drying chamber 3 while the material 5 to be dried is accumulated in 23, this is determined in step S21, that is, the material 5 to be dried in the preliminary chamber 23 is a predetermined amount or more. It is judged that the material 5 to be dried is not allowed to be newly discharged from the drying chamber 3 to the preliminary chamber 23. Then, the dried object to be dried 5 is left in the drying chamber 3 as it is after being dried. When such leaving is simply performed, the material to be dried 5 is naturally cooled and absorbs moisture again even if it is dried.
In this embodiment, step S34 is executed at this time to prevent this. That is, in the step S34, the same control as the drying operation in the step S15 is performed, and the material to be dried 5 is kept at the set drying temperature by the microwave, so that the material to be dried 5 absorbs moisture into the drying chamber 3 again. Is prevented.

The above series of operations is ended by turning off the continuous switch 38. That is, when the step S31 is executed at the time of turning off, the step S35 is then executed, the start flag is reset, and the heat insulation heaters
24 and 32 are stopped. Then S2, S3, S3a, S4, S5
The steps are cycled.

(G) Effect of the Invention According to the microwave drying apparatus of the present invention, in the configuration in which the microwave choke space is provided around the transmission shaft that gives the transmission force to the stirring means for stirring the material to be dried, the low dielectric loss material is used. Since the blocking means for blocking the entry of the material to be dried into the choke space along the transmission axis is provided, it is possible to prevent the circuit constant of the choke space from deviating from the desired value due to the material to be dried, and the choke. The space can provide sufficient microwave choke.

Further, the transmission shaft slidably penetrates the wall of the drying chamber, and when an object to be dried enters a narrow gap between the stirring means and the wall of the drying chamber, the transmission shaft should enlarge this gap. Therefore, the stirring means can be driven normally without being unable to drive because the material to be dried is clogged.

Furthermore, since the transmission shaft is slidable, when cleaning the drying chamber, the transmission shaft can be slid to easily clean the gap between the stirring means and the drying chamber wall.

[Brief description of drawings]

The drawings relate to a microwave drying apparatus according to an embodiment of the present invention.
FIG. 4 is a front sectional view, FIGS. 2 and 3 are front sectional views of an essential part, FIG. 4 is a circuit diagram, and FIG. 5 is a flowchart of an operation program of a microcomputer. 3 ... Drying room, 12 ... Magnetron, 15 ... Stirrer, 15
a …… Transmission shaft, 15g …… Microwave choke space, 15h…
…pipe.

Claims (1)

[Claims] 1. A drying chamber to which a granular or powdery material to be dried is supplied, a microwave supplying means for supplying a microwave for microwave-drying the material to be dried to the drying chamber, and the inside of the drying chamber. An agitating means arranged to agitate the material to be dried, a transmission shaft slidably penetrating the wall of the drying chamber to transmit an agitating force to the agitating means, and around the transmission shaft and outside the wall surface of the drying chamber. The microwave choke space provided on one side and the gap between the transmission shaft and the wall of the drying chamber so as to prevent the material to be dried from entering the choke space and cover the gap. A microwave drying device comprising: a cylindrical blocking means of a low dielectric loss material, which covers the transmission shaft in the drying chamber from a wall surface to a position higher than the stirring means.