JPH0432686A - Microwave drier - Google Patents

Abstract

PURPOSE:To prevent material to be dried from clogging to disable driving by a method wherein a transmission shaft pierces a wall of a drying chamber slidably and it slides to expand a gap between a stirring means and the wall of the drying chamber when the object to be dried enters the narrow gap. CONSTITUTION:A blocking means made of ceramics as low dielectric loss material, namely, a pipe 15h is fixed tight on a bottom wall 3a of a drying chamber in the drying chamber 3. A transmission shaft 15a pierces the pipe 15h in such a manner that it can rotate free to slide vertically. The pipe 15 has a length just enough to allow an upper end thereof to stick upward from an object 5 to be dried. With the existence of the pipe 15h, the material 5 to be dried is checked from leaking outside just as a microwave near a part which is pierced by the transmission shaft 15a of the bottom wall of the drying chamber 3a. That is, this checks the object 5 to be dried from entering a choke space 15g along the transmission shaft 15a and eliminates a deviation of a circuit constant of the choke space 15g thereby securing a microwave choking with a sufficient choking space 15g.

Description

[Detailed description of the invention] (b) Industrial application field The present invention relates to a microwave drying device.

(b) Prior art Japanese Patent Application No. 2-2230 discloses a microwave drying apparatus which dries the material to be dried using microwaves by applying microwaves to a drying chamber into which the material is supplied. There is. The apparatus is provided with a stirring means for stirring the material to be dried in the drying chamber so that the material to be dried is evenly dried. The stirring means is connected to a transmission shaft inserted from outside the drying chamber into the drying chamber, and the stirring means is driven by stirring force transmitted from the transmission shaft.

By the way, in such a structure, there is a risk that microwaves may leak outside the drying room from the vicinity where the transmission shaft penetrates, so it may be considered to provide a microwave choke space around the transmission shaft described in 1. . However, in this case, if the material to be dried leaks to the outside from the vicinity of the penetration described above and this material to be dried enters the choke space along the transmission axis, the circuit constant of the choke space will not reach the desired value t. However, the choke space cannot perform sufficient microwave choke.

Furthermore, if the material to be dried enters and clogs 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 properly.

(c) Problems to be Solved by the Invention The present invention provides a structure in which a microwave choke space is provided around a transmission shaft that provides a transmission force to a stirring means for stirring the material to be dried, and the choke space has a sufficient microwave power. It is an object of the present invention to provide a microwave drying apparatus that can ensure a state in which wave choke can be performed and also ensure normal operation of the stirring means.

(d) Means for Solving the Problems The microwave drying apparatus of the present invention includes a drying chamber into 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 waves; a stirring means disposed within the drying chamber for stirring the material to be dried; a transmission shaft slidably penetrating the wall of the drying chamber and transmitting stirring force to the stirring means; , comprising a microwave choke space provided around the transmission shaft, and a blocking means made of a low dielectric loss material to prevent the object to be dried from entering the choke space along the transmission shaft. .

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

In addition, the transmission shaft is slidably penetrating the wall of the drying chamber, and when the material to be dried enters the narrow gap between the stirring means and the wall of the drying chamber, the transmission shaft is designed to enlarge this gap. The agitation means slides and is normally driven without being clogged with the material to be dried and unable to be driven.

(F) Embodiment FIG. 1 shows the structure of a microwave drying apparatus according to an embodiment of the present invention, which consists of a drying apparatus main body 1 and peripheral mechanisms thereof.

The main part of the drying apparatus 1 is provided with a cylindrical drying chamber 3 having an upper lid 2 which can be opened and closed. A supply pipe 4 is connected to the upper left part of the drying chamber, and the tip of the supply pipe is connected to a storage tank 6 that stores the granular or powdery material 5 to be dried.
It has reached within.

The storage tank is located below the drying chamber 3. Such materials to be dried 5 include, for example, glass-containing four-finger pellets, rice, powdered pharmaceutical products, and the like. The resin pellets are molded after being melted, and if the resin pellets are dried prior to such melt molding, the subsequent molding will be better. In this example, a glass-filled resin pellet is the material to be dried.

A suction hopper 7 is connected to the center of the upper lid 2 of the drying chamber 3 via an integrally molded microwave shielding pipe 7a. The μ-reverse hopper 7 is composed of an L-reverse hopper main body 7b and a hopper upper lid 7C that is detachably arranged on the main body. A filter wire mesh 8a and a filter paper 8 are removably arranged so as to be sandwiched between the suction hopper main body 7b and the hopper upper lid 7c. The filter wire mesh 8a and the filter paper 8 have a mesh smaller than the material diameter of the dried fertilizer solution 5, and the filter paper 8 has a mesh smaller than the filter wire mesh 8a.

A poppet valve 9 is provided in the upper lid 7C of the hopper 7 above the filter wire mesh 8a and the filter paper 8. Then, in the upper part of the poppet valve 9,
A suction blower 1 is connected to the suction hopper 7 via an intake via 10. In this case, when the suction blower 1 is driven with the poppet valve 9 being driven open,
The suction action of the suction blower 11 is carried out through the suction pipe] 0, the suction buff, the microwave shielding vibrator 4, and the material to be dried 5 in the storage tank 6 is suctioned and passes through the supply pipe 4 to the drying chamber 3. . When the material to be dried 5 reaches the drying chamber 3, it falls and accumulates inside the drying chamber due to its own weight.

Here, some of the objects 5 to be dried do not fall into the drying chamber 3 and are then sucked into the suction hopper 7, but such objects 5 are transported from this point forward by the filter wire mesh 8a and the filter paper 8. This prevents the drying material 5 from being undesirably sucked towards the suction blower 11.

In the drying chamber 3, there is a magnetron 12 inside.
Microwaves are supplied from the dryer via a waveguide 13, and as shown in detail in FIGS. 2 and 3, a stirring means, that is, a metal stirring body 15 for stirring the material to be dried 5 is provided on the bottom wall. ing. Such a stirrer 5 is connected and fixed to the upper end of a transmission shaft 5a passing through the bottom wall 3a of the drying chamber 3 via an arm 15b. The transmission shaft 15a is provided in a metal housing 15c fixed to the bottom wall 3a of the drying chamber outside the drying chamber 3 by a linear ball bearing 15d and a needle roller bearing 15e that smoothly rotates the bearing. It is supported so that it can slide up and down and rotate. A pin 15f is provided at the lower end of the transmission shaft 15a.
is fixed. The lower end of the transmission shaft 15a is loosely fitted from above into a driving body 14a that is directly connected to the fixed motor 14, and the pin 15f is loosely fitted into a long hole 14b formed on the side of the driving body 14a. As a result, the transmission shaft 15a slides up and down, but its sliding range is limited 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 as the stirring force from the motor 14 is transmitted through the rotating transmission shaft 13a that can freely slide up and down, so that the stirring of the material 5 to be dried is carried out. It will be done.

In this case, as shown in FIG. 2, the stirring body 15 usually stirs the material to be dried 5 with a narrow gap X+ between it and the bottom wall 3a of the drying chamber. On the other hand, if the material to be dried 5 enters the narrow gap between the agitator 15 and the bottom wall 3a of the drying chamber during such stirring, the agitator 15 is pushed by the material to be dried and the transmission shaft 1.5
2 slides upward, and the gap M between the stirring body 15 and the bottom wall 3a of the drying chamber expands as shown in FIG.
5 is driven normally without becoming unable to be driven due to clogging of the dried material 5 as in the conventional case.

A microwave choke space 15g is formed between the drying chamber bottom wall 3a and the housing 15c. The choke space surrounds the transmission shaft 15a.
5a, and the choke opening directly faces the transmission shaft 15a.

The choke space 15g prevents microwaves from leaking out of the drying chamber from the vicinity of the bottom wall 3a of the drying chamber through which the transmission shaft 15a passes.

In the drying chamber 3, on the bottom wall 3a of the drying chamber is a blocking means, ie, a pipe, made of ceramic, which is a low dielectric loss material. 5h is tightly fixed.

The transmission shaft 15a passes through the pipe 13h so as to be vertically slidable and rotatable. Further, the pipe 15h has a length such that its 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 bottom wall 3a of the drying chamber where the transmission shaft 15a passes through, in the same way as microwaves. The axis 15ai: is suppressed from entering the choke space 15g along the axis 15ai, thus ensuring that the circuit constant of 5g does not deviate from the desired value and that the choke space 15g performs sufficient microwave choke. has been done.

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. Further, a compressor/suction valve 9 is connected to the left bottom of the drying chamber 3 via an intake valve 8, and an exhaust valve 20 is provided on the lid 2 of the drying chamber 3. The driving of the compressor 19 and the opening of the intake valve 18 and exhaust valve 20 are performed when the material to be dried 3 is dried by microwaves, and the water vapor generated during drying flows through the exhaust valve 20 together with the air from the compressor 19. through which it is discharged to the outside.

Furthermore, a discharge valve 2 is provided at the bottom right of the drying chamber 3, and the discharge valve is opened when the dried material 5 is discharged. The dried material 5 discharged based on the opening of the discharge fF-21 falls through the discharge pipe 22 into the preliminary chamber 23 below and accumulates therein. A heat-retaining heater 24 is arranged on the F-class slanted wall of the preliminary chamber, and the preliminary chamber 2
3 is provided with a level sensor 26 having a rotating body 25. Such a level sensor 26 normally rotates the rotating body 25, and even if a small predetermined amount of the dried material 5 accumulates in the preliminary chamber 23 and the rotating body 25 is attempted to be rotated, the dried material 5 does not become a load. When the rotating body 25 cannot be rotated satisfactorily, a predetermined signal is output to detect that a small predetermined amount of the material to be dried 5 has accumulated.

The lower part of the preliminary chamber 23 is connected to another suction hopper 27 located higher than the preliminary chamber 23 through a conveying pipe 28. Such a suction hopper 27 also has the above-mentioned suction hopper 7.
Similarly, a filter wire mesh 29a and filter paper 29 having a mesh smaller than the material diameter of the material to be dried 5 are arranged, and a poppet valve 3o is provided above the filter paper. At the top of the poppet valve 30, the suction blower 11 is also connected to the suction hopper 27 via an intake pipe 31.

In this case, with the poppet valve 30 open, the blower
1, the suction action of the blower 11 extends to the conveying pipe 28 via the suction pipe 31 and the suction pumper 27, and the material to be dried 5 accumulated in the preliminary chamber 23 is transferred to the conveying pipe 2.
8 and reaches the suction bow hopper 27. When the material to be dried 5 reaches the suction hopper 27, it falls into the hopper due to its own weight.

In the suction hopper 27, a heat insulating heater 32 is arranged on the lower inclined wall, an on-off valve 33 is provided at the lower end, and upper and lower limit level sensors 34 are provided at the upper and lower ends.
．． 35 are arranged.

When the on-off valve 33 is closed, the suction action is activated and the material to be dried 5 falls into the suction hopper 27, and the material to be dried 5 accumulates inside the suction hopper 27. On the other hand, when the on-off valve 33 is opened, the material to be dried 5 falls into the suction hopper 27. The dried material 5 accumulated in this way falls downward and reaches the next processing section, where the dried material 5, ie, four-finger pellets, is melt-molded.

Fig. 4 shows the circuit of the microwave drying device mentioned above, and the main control section is manufactured by Sanyo Electric Co., Ltd., product number LC-65P G.
23 microcomputers 36 are provided, and these computers receive operation information from an operation section 37 disposed on the front of the drying apparatus main body 1, temperature information from the temperature sensor 7, and various level sensors described above. 6.26.34.
Based on the information of 35, etc., the above magnetron 12
, motor 14, intake valve] 8, exhaust valve 20, compressor 19, discharge valve 21, heat retention heater 24, 32, suction blower 11, pot/to valve 9, 30, and on/off valve 33.

FIG. 5 shows a flowchart of the operation program installed in the microcomputer 36, and the operation of the microwave drying apparatus will be explained below by referring to the same chart.

After turning on the power, after S1 step, normally S2, S3, S
Steps 3a, S4, and S5 are executed cyclically. S1
An initial setting operation is performed in the step. That is, all writable areas in the microcomputer 36 are cleared, and the magnetron 12, motor 14,
The compressor 19, the heat insulating heater 24, 32, and the intake blower 11 are placed in a stopped state, and the intake valve 18
, the exhaust valve 20, the exhaust valve 21, the poppet valve 9, 30, and the on-off valve 33 are each placed in an open state. In the step S2, operation information from the operation unit 37 is input, in the step S3, it is determined by the lower limit level sensor 35 whether or not the material to be dried 5 has accumulated in the suction hopper 27, and in the step S3a, the -F level is determined. Based on the detection by the sensor 26, it is determined whether a small predetermined amount of the material to be dried 5 is accumulated in the preliminary chamber 23. In step S4, the presence or absence of the start flag in the microcomputer 36 is checked, and the
In step 5, it is determined whether or not the start key is currently being operated by the operation unit 37 based on the input information on the S2 steerer.

Therefore, when melt-molding the dried material 5, which is a fat pellet, the dried OI 5 is
When drying in advance, first use the operating section 37 to
The desired drying time and drying temperature are respectively set within the range of 0 minutes and within the range of 70 to 170° C. by key operation, and the continuous switch 38 is turned on. These operating 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 step 82, an affirmative judgment is made in step S5, the start flag is set in step S6, and the above-mentioned information is set in step S7. Driving control of the heat retention heaters 24 and 32 is started.

That is, the heat-retaining heaters 24 and 32 are intermittently driven at a desired ratio so that the interiors of the preliminary chamber 23 and suction hopper 27 are maintained approximately at the set drying temperatures, and therefore the interiors of the preliminary chamber 23 and suction hopper 27 are maintained at approximately the set drying temperature. It is kept warm at the above temperature.

Next, steps S8, S9, and S10 are sequentially executed. In step S8, it is checked whether the transport flag in the microcomputer 36 is set (in this case, it is checked that it is not set). In step S9, the operation of supplying the material to be dried 5 to the drying chamber 3 is executed. That is, the popent valve 9 is opened, the suction blower 11 is driven, the material to be dried 5 is supplied from the storage tank 6 into the drying chamber 3 by the suction action of the suction blower 1, and the motor 14 is driven to supply the agitator. 15 rotates, and the upper surface of the material to be dried 5 supplied into the drying chamber 3 is aligned with a smooth horizontal surface. 51
At step 0, it is determined by the detection by the level sensor 16 whether a predetermined amount of the material to be dried 5 has accumulated in the drying chamber 3 (in this case, it is determined that the predetermined amount has not accumulated).

After that, S2, S3, S3a, S4, Sll, S8~S
Each of the 10 steps is executed cyclically. At this time, in the Sll step, it is checked whether the supply end flag in the microcomputer 36 is set. Then, when a predetermined amount of the material to be dried 5 has accumulated in the drying chamber 3 and this is determined in steps S] and O, steps S12 and S13 are then executed. At step 512, the operation of supplying the material to be dried 5 to the drying chamber 3, which was executed at step S9, is completed. S13
In this step, the supply end flag is set.

After that, S2, S3, S3a, S4.511, S14~
Each step of S17 is executed cyclically.

At this time, in step 514, the microcomputer 36
The presence or absence of the drying end flag in S]5 is checked.
A drying operation is performed in the stamp. That is, depending on whether or not the temperature of the object 5 to be dried detected by the temperature sensor 17 has reached the set drying temperature, the 7-danetron 12 is intermittently driven to maintain the object 5 to be dried at the drying temperature and perform microwave drying. Then, the motor 14 is driven again and the stirring body 1
5 is rotated so that the material to be dried 5 is agitated so as to be dried evenly, and the compressor 19 is driven and the intake valve 1 is
8. The exhaust valve 2o is opened and the water vapor generated from the dried material Th5 is discharged to the outside. Furthermore, in step S15, along with the drying operation as shown in 2, the measurement of the elapsed drying time is started.

In step 516, it is determined whether the elapsed drying time has reached the set drying time, and in step 517, it is checked whether or not the conveyance flag is set, as in step S8.

Therefore, when the elapsed drying time reaches the set drying time, S
] After step S1.8.519 is executed. In step 518, the drying operation performed in step S15 and the measurement of elapsed drying time are terminated, and the measured time is reset. In step S19, the drying end flag is set.

And 517, S2, S3, S3a, S4.511.
After passing through 514 steps, 520. S21, S22, S
Each step of 23.524 is executed sequentially. In step 520, it is checked whether the discharge flag in the microcomputer 36 is set. In step S21, it is determined based on the detection by the level sensor 26 whether or not a predetermined amount of the material to be dried 5 has already accumulated in the preliminary chamber 23.

In S22 Stemp, heat retention operation in drying chamber 3 (described later)
When this is being done, it is finished and the discharge flag is set. Step 523 is executed when the dried material 5 is allowed to be newly discharged from the drying chamber 3 to the preliminary chamber 23 because the material 5 to be dried is not accumulated in the preliminary chamber 23 in step 521. , such S
In step 23, the operation of discharging the dried material 5 from the drying chamber 3 to the preliminary chamber 23 is executed. That is, when the discharge valve 21 is opened, 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 moved around. The material to be dried 5 is discharged from the discharge valve 2 through the discharge pipe 22 into the preliminary chamber 23. The material to be dried 5 discharged in this way is not naturally cooled because the preliminary chamber 23 has been kept warm since step S7.
This prevents the material to be dried 5 from absorbing moisture again due to natural cooling. Furthermore, in step S23, the elapsed time of such discharge is started to be counted. In step S24,
It is determined whether the elapsed discharge time has reached a predetermined discharge time (this is sufficient time to discharge all of the predetermined amount of material to be dried 5 stored in the drying chamber 3). be done.

After that, S2, S3, S3a, S4, S11.514.
Steps 520, S23, S24, and S17 are executed in circulation, and when a small predetermined amount of material 5 to be dried accumulates in the preliminary chamber 23 due to the above-mentioned discharge, steps 53a to S25, 526, and S27 are executed in this circulation. , each step 7 of S28
The steps are executed sequentially. In step S25, a conveyance flag is set, and in step 526, if the drying material supply operation is being executed in step S9, the operation is stopped. In step S27, an operation is carried out to transport the dried material 5 from the preliminary chamber 23, which is kept warm, to the suction hopper 27. That is, poppet valve 3
0 is opened and the suction follower 11 is driven, and the suction action of the suction follower 11 causes the suction hopper 2 to be drawn from the preliminary chamber 23.
The material to be dried 5 is conveyed to 7. The material to be dried 5 transported in this manner is not naturally cooled because the suction hopper 27 is kept warm by the S7 stamp, and the material to be dried is prevented from absorbing moisture again. 528
In step, it is determined by the detection of the upper limit level sensor 34 whether or not the dried material 5 has accumulated in the suction hopper 27 up to the position of the sensor (in this case, it is determined that no).
.

After that, S4, Sol, S14, S20, S23.52
4. Each step of 517, S27, and S28 is executed in circulation, and during this period, the discharge operation to the preliminary chamber 23 and the suction hopper 27
The conveying operation to is performed in parallel, and the dried material 5 discharged to the preliminary chamber 23 is immediately conveyed to the suction hopper 27.

Then, when the elapsed discharge time reaches a predetermined discharge time (all the materials to be dried 5 are discharged from the drying chamber 3 to the preliminary chamber 23), steps S29, S30, and 531 are sequentially executed. Ru.

In step S29, the ejection operation executed in step S23 and the elapsed elapsed time measurement are completed, and the measured time is reset. In step S30, all of the above-mentioned supply end flag, drying end flag, and discharge flag are reset. In step S31, it is determined on the operating section 37 whether the continuous switch 38 is turned on.

In this case, the continuous switch 38 is in the on state, and after passing through 517 stenops, S4, S11, S8, S27
, S28 are executed cyclically. Then, the material to be dried 5 in the preliminary chamber 23 is transported to the suction hopper 2.
When the dried DJ 5 accumulates at the position of the upper limit level sensor 34 at step 7, steps S28 to S32 and S33 are executed. In step S32, the conveyance operation being executed by the steno knob 527 is stopped, and in step 533, the conveyance flag is reset.

Therefore, the dried material 5 accumulated in the suction hopper 27 in this way
is melt-molded in the next processing section, but
Executed when the external command signal P for instructing melt molding is given to the microcomputer 36 in a state where the material to be dried 5 has accumulated in the suction lever 27 up to the position of the -1- limit level sensor 34. be done. That is, at this time, the on-off valve 33 is opened by the microcomputer 36, and the dried material 5 is discharged from the suction hopper 27 to the next stage processing section.

The opening/closing valve 33 is closed again when all of the dried material 5 in the suction hopper 27 is discharged. Then, the discharged material 5 to be dried is melt-molded in the next processing section,
In this case, the resin pellet, that is, the material to be dried 5, has been dried in advance, so that it can be shaped well.

Here, if the processing capacity of the next-stage processing section for the melt-forming is slow, the drying material supply operation to the conveying operation is repeated, so that the drying material is stored in the suction hopper 27 and the preliminary chamber 23. remains accumulated. Therefore, when the drying material 5 is accumulated in the preliminary chamber 23 and the drying material 5 is to be discharged from the drying chamber 3, this is determined in step S21. 5 has accumulated in excess of a predetermined amount, and the to-be-dried material 5 is transferred from the drying chamber 3 to the preliminary chamber 23.
It is determined that the new discharge is not permitted. Then, the dried material 5 is left as it is in the drying chamber 3 even after drying. If the drying material 5 were simply left to stand, it would naturally cool down and absorb moisture again even after being dried, but in this embodiment, step S34 is executed at this time to prevent this. That is, in step S34,
Exactly the same control as the drying operation in step S15 is performed, and the object to be dried 5 is kept warm at the set drying temperature by microwaves, so that the object to be dried 5 is prevented from absorbing moisture again in the drying chamber 3.

The series of operations described above is ended by turning off the continuous switch 38. That is, when step 831 is executed in such an off state, step S35 is executed next, the start flag is reset, and the drive of each of the heat retention heaters 24 and 32 is stopped. After that, S2, S3,
Steps S3a, S4, and S5 are executed cyclically.

(G) Effects of the Invention According to the microwave drying apparatus of the present invention, in the configuration in which a microwave choke space is provided around the transmission shaft that provides transmission force to the stirring means for stirring the material to be dried, it Therefore, although a blocking means is provided to prevent the object 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 due to the object to be dried, and the choke The space is sufficient to carry out the microwave choke.

Furthermore, the transmission shaft is slidably penetrating the wall of the drying chamber, and when the material to be dried enters the narrow gap between the stirring means and the wall of the drying chamber, the transmission shaft is designed to enlarge this gap. Therefore, the stirring means can be driven normally without becoming clogged with the material to be dried and unable to be driven.

Furthermore, since the transmission shaft is slidable, when cleaning the interior of the drying chamber, the gap between the stirring means and the wall of the drying chamber can be easily cleaned by sliding the transmission shaft.

[Brief explanation of the drawing]

The drawings relate to a microwave drying device according to an embodiment of the present invention.
The figure is a front sectional view, FIGS. 2 and 3 are front sectional views of main parts, FIG. 4 is a circuit diagram, and FIG. 5 is a flowchart of the operating program of the microcomputer. 3. Drying chamber, 12... Magnetron, 15... Stirring body, 15a... Transmission shaft, ] 55g... Microwave choke space, ] 5h... Vibrator.

Claims (1)

[Claims] (1) A drying chamber to which a granular or powdery material to be dried is supplied;
a microwave supply means for supplying microwaves for microwave drying the material to be dried to the drying chamber; a stirring means disposed within the drying chamber for stirring the material to be dried; and a sliding means for sliding the wall of the drying chamber. A transmission shaft that freely penetrates and transmits the stirring force to the stirring means, a microwave choke space provided around the transmission shaft, and a microwave choke space made of a low dielectric loss material, and a microwave choke space provided along the transmission shaft and inside the choke space. A microwave drying device comprising a prevention means for preventing the material to be dried from entering.