JP2001347505A - Method and apparatus for drying wood - Google Patents

Abstract

PROBLEM TO BE SOLVED: To safely dry wood by surely preventing its ignition by irradiating each wood with a microwave under optimum conditions to dry it in a short time while a crack is prevented from being generated. SOLUTION: A method for drying wood is a method for drying the wood 1 by irradiating it with the microwave. A weight of the wood 1 to be dried is detected at specified time intervals. Drying is carried out while average output of the microwave is controlled by either or both of the weight of the wood 1 and a weight decrease rate wherein the weight of the wood 1 changes, or drying is ended by stopping the output of the microwave.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for irradiating microwaves to a raw wood or a sawn timber.

[0002]

2. Description of the Related Art When wood is used in an undried state,
Various adverse effects such as a large deformation with time or a contraction to form a gap occur. This evil can be prevented by drying the wood. The most common method of drying wood is to leave the wood to dry naturally, but this method is extremely time-consuming. As a method of drying wood in a short time, a method of heating wood with steam or high frequency has been put to practical use. In the method of heating with steam, the wood is heated to 100 ° C. or more in order to boil and remove moisture contained in the wood in a short time. For this purpose, wood is put into a pressure tank and steam at 100 ° C. or higher is supplied. This method requires a pressure vessel in order to heat the wood to 100 ° C. or higher, and has a drawback that the equipment cost is extremely high.
In addition, since the method of heating wood with steam conducts heat from the surface of the wood and heats it, it takes a considerable time to heat the wood to the inside, and it is difficult to dry the wood efficiently in a short time . In particular, pillars, logs, etc., take a long time to heat the central part and cannot be dried in a short time. In addition, this method also has the disadvantage that the surface shrinks and breaks easily because the wood is dried from the surface.

[0003] As a device for heating wood from the inside, a device for heating and drying wood by sandwiching it between high-frequency electrodes has been put into practical use. This device heats the wood with the high frequency loss of the wood placed between the electrodes. This apparatus can dry a thin wood such as a plate material relatively efficiently. However, there is a drawback that wood having a large surface area such as a pillar or round wood such as a raw wood cannot be efficiently heated. that is,
This is because pillars and the like cannot be sandwiched between wide electrodes, and if a log is sandwiched between planar electrodes, wood cannot efficiently absorb high frequencies. In addition, this device has different ideal electrode shapes and sizes depending on the shape and size of the wood to be dried.
Another drawback is that it is difficult to dry various woods with the same equipment. In addition, there is also a problem that high-frequency waves are radiated to the surroundings between the electrodes as radio waves.

[0004] An apparatus for drying wood by irradiating it with microwaves has excellent features not found in an apparatus sandwiched between electrodes. In particular, since the drying device absorbs microwaves into wood and heats and dries the wood, it has the advantage that wood can be heated from the inside and the whole can be dried in a short time.

[0005]

The apparatus for drying wood with microwaves heats wood from the inside, so that the microwave output can be increased and the drying time can be shortened. This is because the inside can be quickly heated. However, when the output of the microwave is increased, the wood is easily broken. If the wood is broken during the drying process, the commercial value of the wood will be significantly reduced. This disadvantage can be solved by reducing the output of the microwave generator. However, when the output is reduced, the drying time becomes longer, and the feature that the drying can be performed quickly in a short time is lost. For this reason, it is extremely difficult for the method of drying wood using microwaves to optimize the microwave output. The fact that the optimum value of the microwave output varies greatly depending on the type of wood or the size and shape of the wood also makes it difficult to set the optimum value. For this reason, it is extremely difficult to quickly dry various kinds of wood so as not to crack in an optimal state.

[0006] Furthermore, the method of drying the wood by irradiating it with microwaves is a method in which the moisture content of the wood is extremely reduced.
When microwaves are further applied, the wood is overheated and carbonized. Further microwave irradiation may ignite the carbonized parts and cause a fire. This state is
Since it occurs inside wood, it is difficult to accurately detect it from outside. This disadvantage is an adverse effect peculiar to a method of drying wood by microwaves, and does not cause any problem in a conventional drying method, for example, a method of heating wood with steam or hot water to dry the wood. This is because the heating temperature of the wood does not rise to the carbonization temperature with steam or hot water.

The present invention has been developed with the object of solving such disadvantages. An important object of the present invention is to irradiate each piece of wood with microwaves under optimum conditions to prevent cracks. It is an object of the present invention to provide a method and apparatus for drying wood which can be dried in a short time while securely preventing ignition of the wood and drying safely.

[0008]

A method for drying wood according to the present invention is a method for drying wood 1 by irradiating microwaves, wherein the weight of the wood 1 being dried is detected at predetermined time intervals. Then, drying is performed while controlling the average output of the microwave at one or both of the weight of the wood 1 and the weight reduction rate at which the weight of the wood 1 changes, or the drying is terminated by stopping the output of the microwave.

[0009] By the way, in this specification, the "weight reduction rate" of wood means the rate at which the weight of wood decreases per unit time.

In the method for drying wood according to the present invention, for example, the weight of the wood 1 can be measured by lifting both ends of the wood 1. In the drying method of the present invention, drying is preferably performed by controlling the microwave output so that the weight of the wood 1 decreases linearly or the weight reduction rate becomes a substantially constant value.

The output of the microwave can control the average output by controlling the ratio of the irradiation time for irradiating the microwave and the pause time for suspending the irradiation, that is, the duty.

The apparatus for drying wood according to the present invention comprises a shield case 2 for storing wood 1 to be dried,
A plurality of microwave generators 3 for irradiating microwaves to the wood 1 in the inside, a sensor 4 for detecting the weight of the wood 1 in the shield case 2, and the output of the microwave generator 3 is controlled by a signal of the sensor 4 And a control circuit 5 for performing the operation. The control circuit 5 controls the output of the microwave generator 3 to dry the wood 1 at one or both of the weight of the wood 1 and the weight reduction rate at which the weight of the wood 1 decreases.

Each microwave generator 3 includes a magnetron 11, and more preferably, each of the plurality of microwave generators 3 includes a dedicated high-voltage power supply 12 for each magnetron 11. The high-voltage power supply 12 is controlled to control the average output of each microwave generator 3.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. However, the following examples illustrate a wood drying apparatus for embodying the technical idea of the present invention, and the present invention does not specify a drying apparatus as follows.

Further, in this specification, in order to make it easy to understand the claims, the numbers corresponding to the members shown in the embodiments will be referred to as “claims” and “ In the column of “means”. However, the members described in the claims are not limited to the members of the embodiments.

The wood drying apparatus shown in FIG. 1 includes a shield case 2 for carrying wood 1 and a plurality of microwave generators 3 for irradiating the wood 1 in the shield case 2 with microwaves.
And a sensor 4 for detecting the weight of the wood 1 to be dried,
A control circuit 5 for controlling the output of each microwave generator 3 with a signal from the sensor 4 is provided.

The shield case 2 has an elongated hollow cylindrical shape extended in the transport direction of the wood 1 so that the elongated wood 1 such as a pillar or a raw wood can be carried in. The shield case 2 is made of metal such as iron to prevent microwave leakage. Made of shield material. The shield case 2 shown in the figure has a plurality of case units 6 connected in series to form an elongated tubular shape. Case unit 6
Is a rectangular cylindrical shape having both ends open, and is connected so that microwaves do not leak, thereby forming a shield case 2. The shield case 2 having this structure includes a case unit 6
The total length can be easily changed by adjusting the number of connected. The total length of the pillars and logs to be dried is 3-8m. A device for drying short wood reduces the number of connected case units, and a device for drying long wood increases the number of connected case units.

The shield case 2 has a transfer conveyor 7 for loading and unloading the wood 1 at the bottom thereof. Further, a wheel 8 for rotating the log is disposed between the rollers 7A of the transfer conveyor 7. As shown in FIG. 2, a plurality of sets of the wheels 8 are provided with two wheels as a pair. The pair of wheels 8 are separated from each other by an interval at which the wood 1 can be placed and rotated therebetween. The transfer conveyor 7 is disposed in the shield case 2 so that it can be moved up and down by the cylinder 9.

The transfer conveyor 7 is raised above the wheels 8 when loading and unloading the wood 1. Therefore,
The transfer conveyor 7 is moved up and down in a horizontal posture by a vertical mechanism such as a cylinder. The transfer conveyor 7 transfers the wood 1 away from the wheels 8 in the raised position. When the wheel 8 rotates the wood 1, the transport conveyor 7 is lowered,
The wood 1 is put on the wheel 8. Shield case 2 of this structure
Can easily carry the wood 1 in and out, and furthermore, when irradiating the microwave, the wood 1 can be rotated to uniformly irradiate the microwave. Although not shown, the wheels 8 are connected to a motor via a chain or a belt, and are rotated by the motor. The motor preferably rotates the wheels 8 in the opposite direction. This is for uniformly irradiating the microwave to the wood 1.

Further, the transfer conveyor 7 can ascend and move the wood 1 in the vertical direction not only when the wood 1 is loaded or unloaded, but also in the step of irradiating the microwaves. The transfer conveyor 7 ascends, places the wood 1 on the roller 7A, and rotates the roller 7A with a motor or the like (not shown) to move the wood 1 in the vertical direction. After the wood 1 is moved, the wood 1 is lowered and the wood 1 is rotated by the wheels 8.

The cylindrical wood 1 such as a raw wood is rotated by wheels 8, but the wood 1, which is a prism or a plate, cannot be rotated by being placed between the wheels 8. Wood 1 that cannot be rotated with wheels 8
In the step of irradiating microwaves, the wood 1 is placed on the transfer conveyor 7 and reciprocated. This transfer conveyor 7
Roller 7A of transfer conveyor 7 by motor (not shown)
Are rotated in the forward and reverse directions to reciprocate the wood 1 inside the shield case 2. The reciprocating wood 1 is uniformly irradiated with microwaves.

As shown in FIG. 1, the plurality of microwave generators 3 are fixed to the upper part of the shield case 2 so as to be separated in the longitudinal direction. Each of the microwave generators 3 is arranged at an interval capable of uniformly irradiating the microwave to the long wood 1 placed in the shield case 2. The microwave radiated from the microwave generator 3 into the shield case 2 is reflected by the inner surface of the shield case 2 or is reflected and diffused by a diffusion plate (not shown) provided in the shield case 2 or the like. Heat the long wood 1 uniformly. The center distance between the openings of the waveguide 10 from which the microwave generator 3 emits microwaves to the shield case 2 is, for example, 30 to 100 cm.
When the interval between the adjacent waveguides 10 is reduced, the wood 1 can be dried more uniformly. In addition, if the spacing between the waveguides 10 is widened, interference of microwaves radiated from the adjacent microwave generator 3 can be reduced.

As shown in FIG. 3, each of the microwave generators 3 includes a magnetron 11 for generating a microwave, a waveguide 10 for supplying the microwave generated by the magnetron 11 to the shield case 2, and a magnetron 11. A high-voltage power supply 12 for supplying a high-voltage DC to the plate 11 and a heater power supply 13 for heating the heater are provided. Each microwave generator 3 preferably comprises a magnetron 11, a high voltage power supply 12 and a heater power supply 13, but the heater power supply can also be designed to supply heater power to a plurality of magnetrons. . The heater power supply is, for example, common to all microwave generators, and one unit can supply heater power to all magnetrons.

A drying device in which each microwave generator 3 includes a magnetron 11 and a high-voltage power supply 12 includes:
The average output of each microwave generator 3 can be adjusted independently. For this reason, the wood 1 can be dried in a more ideal environment. In particular, as shown in FIG. 1, when a long piece of wood 1 is dried, the wood 1 is dried from both ends first. This is because the water is removed not only from the periphery but also from the end faces of the both ends, so that the surface area from which the water is removed is substantially increased.
The microwave generator 3 that can independently control the output controls, for example, the output of the microwave generators 3 arranged at both ends of the wood 1 to be small or the microwave generators 3 at both ends. Oscillation is stopped first, and the entire wood 1 can be dried uniformly.

The magnetron 11 irradiates the wood 1 in the shield case 2 through the waveguide 10 from above with a microwave having a frequency of, for example, 2 to 4 GHz. The waveguide 10 is opened downward on the upper surface of the shield case 2 and irradiates the wood 1 with microwaves. The high-voltage power supply 12 boosts the input 100 or 200 V commercial power supply with a transformer, and converts the secondary side AC of the transformer to 2000 to 4000 V.
And supply it to the magnetron 11. The heater power supply 13 includes a transformer that reduces the input AC to a heater voltage of the magnetron 11. The magnetron 11 oscillates microwaves and outputs from the waveguide 10 when a high voltage is input from the high-voltage power supply 12 in a state where the heater is heated by electric power supplied from the heater power supply 13.

The microwave generator 3 includes a high-voltage power supply 12
The output of the magnetron 11 can be controlled by the average voltage supplied to the magnetron 11 from. If you lower the average voltage,
The output of the magnetron 11 decreases, and when the average voltage is increased, the output of the magnetron 11 increases. High voltage power supply 12
Can adjust the average voltage of the high-voltage power supply 12 by the capacitance of a capacitor connected to the secondary side of the transformer. When the capacitance of the capacitor is increased, the average voltage increases, and when the capacitance is decreased, the average voltage decreases.

Further, as shown in FIG. 3, the magnetron 11 includes a switch 1 connected to an input side or an output side.
The average output can also be adjusted by the duty for switching 4 on and off. The switch 14 supplies a high voltage to the magnetron 11 in the ON state to cause the magnetron 11 to oscillate. When the switch 14 is turned off, the magnetron 11 stops oscillating and the output becomes zero. Therefore, the average output of the magnetron 11 can be adjusted by the duty at which the switch 14 is turned on and off. If the time for turning on the switch 14 is increased and the time for turning off the switch 14 is shortened, the average output of the magnetron 11 increases. Conversely, if the on time is shortened and the off time is increased, the average output of the magnetron 11 decreases. Become. The switch 14 is turned on and off by the control circuit 5 to control the output of the magnetron 11.

Each microwave generator 3 has a
Is irradiated with microwaves at regular intervals. The microwave radiated from each microwave generator 3 is applied to the waveguide 1
The wood 1 is strongly heated near zero. Therefore, the plurality of microwave generators 3 are fixed to the shield case 2 close to an interval at which the wood 1 can be uniformly heated.

The sensor 4 detects the weight of the wood 1. The sensor 4 measures the weight by lifting both ends of the wood 1 from the wheels 8 and the transfer conveyor 7. Therefore, the sensor 4 includes a support 15 for supporting and lifting the wood 1 from the lower surface, a lifting mechanism 16 for raising the support 15, and a weight sensing unit 17 connecting the lifting mechanism 16. .

The lifting mechanism 16 and the weight sensing unit 17 are disposed outside the shield case 2, and the support 15 penetrates the shield case 2 so that the shield case 2 can slide and microwaves do not leak. ing. The lifting mechanism 16 in the figure is a vertically disposed cylinder, and the lower end is fixed to the weight sensing unit 17. In the sensor 4 having this structure, when the cylinder serving as the lifting mechanism 16 is extended, the support base 15 lifts the wood 1. In this state, the weight of the wood 1 is detected by the two weight sensing units 17. The weight sensing unit 17 detects the weight by adding the weights of the lifting mechanism 16 and the support base 15. Therefore, the weight of the wood 1 is detected by subtracting the weight of the lifting mechanism 16 and the weight of the support 15 from the weight detected by the weight sensing unit 17.

The sensor 4 detects the wood 1 at a predetermined time interval.
Measure the weight of. The time interval at which the sensor 4 detects the weight of the wood 1 is, for example, 1 minute to 2 hours, preferably 3 minutes.
Minutes to 60 minutes, more preferably 5 minutes to 60 minutes. The time interval at which the sensor 4 detects the weight of the wood 1 is constant from the start of drying to the completion thereof, or is changed by weight. The method of changing the detection time interval is, for example, to lengthen the detection time interval when the weight of the wood 1 is heavy,
If the wood is dry and light, it should be shortened. This is because when the dried wood 1 is overheated by microwaves, it becomes easy to ignite.

Reducing the time interval at which the sensor 4 detects the weight has the advantage that the wood 1 can be dried in a more favorable environment. In addition, the method of detecting the weight of the wood 1 raises the wood 1 and irradiates the wood 1 with microwaves at a position different from the transfer conveyor 7 and the wheel 8, so that the wood 1 can be dried more uniformly. is there. However, the method of detecting the weight of the wood 1 can also interrupt the microwave output when detecting the weight.

The weight of the wood 1 detected by the sensor 4 is input to the control circuit 5. The control circuit 5 controls the output of the microwave generator 3 with a signal input from the sensor 4. The control circuit 5 controls the microwave output of the microwave generator 3 using one or both of the weight of the wood 1 and the weight reduction rate at which the weight of the wood 1 decreases.

FIGS. 4 and 5 show characteristics of the control circuit 5 controlling the microwave output of the microwave generator 3 using the weight of the wood 1 as a parameter. FIG. 4 shows that the output of the microwave is linearly controlled when the weight of the wood 1 is within a predetermined range, and the microwave is set to the maximum output when the wood 1 is heavier than the predetermined weight. At a predetermined weight, the microwave output is set to 0, that is, the microwave is not irradiated. FIG. 5 shows that the output of the microwave is controlled in a stepwise manner when the weight of the wood 1 is within a predetermined range, and the microwave is set to the maximum output when the wood 1 is heavier than the predetermined weight. When the predetermined weight is reached, the microwave output is set to 0, that is, the microwave is not irradiated.

When the control circuit 5 dries the wood 1 by controlling the microwave output as shown in FIGS. 4 and 5, as shown in FIG. 6, the weight of the wood 1 decreases with time and the wood 1 is dried. You. At first, the microwave power is large, so the wood weight drops sharply. As the microwave power is reduced linearly or stepwise, the weight loss of the wood becomes progressively smaller. When the wood 1 is dried to a predetermined weight, the microwave output becomes zero and the weight of the wood 1 does not change.
The wood weight at which the microwave output is set to 0 is the weight of the wood dried to a predetermined moisture content.

As shown in FIG. 6, the control circuit 5 controls the weight of the wood so that the weight of the wood decreases first and then gradually decreases.
Alternatively, as shown in FIG. 7, the microwave output can be controlled so that the wood weight decreases linearly.
In the method of reducing the weight of the wood 1 as described above, when the wood 1 is dried to a predetermined weight, the microwave output is set to 0 and the irradiation of the microwave is stopped.

As shown in FIGS. 6 and 7, the control circuit 5 for reducing the weight of the wood 1 increases the microwave output and increases the weight of the wood when the wood weight becomes larger than the value indicated by the function A or B. To the function shown in the figure. Further, when the weight of the wood becomes smaller than the values indicated by the functions A and B, the microwave output is reduced to bring the weight of the wood closer to the functions A and B.

The simplest control circuit 5 controls a plurality of microwave generators 3 so that the microwave outputs are the same. As shown in FIG. 1, a control circuit 5 that detects the weight of both ends of the wood 1 and controls the microwave output of the microwave generator 3 uses the output of the sensor 4 on the right side in FIG. Controlling the microwave output of the wave generator 3,
The output of the sensor 4 on the left side can control the microwave output of the microwave generator 3 on the left half.

[0039]

The method and apparatus for drying wood according to the present invention can be dried in a short time while irradiating microwaves to each piece of wood under optimal conditions to prevent cracking, and to ensure that the wood is ignited. It has the feature that it can be prevented and dried safely. That is, the method and the apparatus for drying wood of the present invention detect the weight of the wood being dried at predetermined time intervals, and determine the weight of the wood or the weight loss rate at which the weight of the wood changes, or both of the weights. Drying while controlling the average power of the waves, or
This is because the microwave output is stopped to end the drying. The drying method and apparatus according to the present invention detects the dry state of the wood based on the weight or weight loss rate of the wood and controls the average output of microwaves or stops the output. Irradiates microwaves to dry in a short time while preventing cracks and ignition. Furthermore, since the drying method and apparatus of the present invention detect the dry state of the wood by detecting the weight of the wood, there is a feature that the irradiation state of the microwave can be ideally controlled with an extremely simple structure.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a wood drying apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the drying device shown in FIG.

FIG. 3 is a schematic configuration diagram of a microwave generator of the drying device shown in FIG.

FIG. 4 is a graph showing an example of controlling microwave output by weight of wood.

FIG. 5 is a graph showing another example of controlling the microwave output by the weight of wood.

FIG. 6 is a graph showing an example of a state in which the weight of wood decreases with time.

FIG. 7 is a graph showing another example of a state in which the weight of wood decreases with time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wood 2 ... Shield case 3 ... Microwave generator 4 ... Sensor 5 ... Control circuit 6 ... Case unit 7 ... Transfer conveyor 7A ... Roller 8 ... Wheel 9 ... Cylinder 10 ... Waveguide 11 ... Magnetron 12 ... High voltage power supply 13 ... heater power supply 14 ... switch 15 ... support base 16 ... lifting mechanism 17 ... weight sensing part

Continued on the front page F term (reference) 2B230 AA15 BA01 EA21 EA30 EB08 EB12 3L113 AA01 AB07 AC12 AC35 AC67 BA05 CA02 CA03 CB07 DA10 DA24

Claims (7)

[Claims] 1. A method for drying wood (1) by irradiating microwaves, wherein the weight of wood (1) is detected at predetermined time intervals, and the weight of wood (1) or the weight of wood (1) is detected. Drying the wood while controlling the average power of the microwave at one or both of the weight loss rates at which the weight decreases. 2. A method of drying wood (1) by irradiating microwaves, wherein the weight of wood (1) is detected at predetermined time intervals, and the weight of wood (1) or the weight of wood (1) is detected. A method for drying wood, comprising stopping the microwave output and terminating the drying at one or both of the weight reduction rates at which the weight decreases. 3. The method for drying wood according to claim 1, wherein the weight of the wood (1) is measured by lifting both ends of the wood (1). 4. The method for drying wood according to claim 1, wherein the microwave output is controlled so that the weight of the wood (1) decreases linearly or the weight reduction rate becomes substantially constant. 5. The method for drying wood according to claim 1, wherein the average power of the microwaves is controlled by changing the duty, which is the ratio of the irradiation time for irradiating the microwaves and the pause time for suspending the radiation. . 6. A shield case (2) for storing wood (1) to be dried, a plurality of microwave generators (3) for irradiating microwaves to the wood (1) in the shield case (2), and a shield. Sensor (4) for detecting the weight of wood (1) in case (2)
And a microwave generator (3) with the signal from this sensor (4)
A control circuit (5) for controlling the output of the microwave generator (5), based on either the weight of the wood (1) or the weight reduction rate at which the weight of the wood (1) decreases. 3) Wood drying equipment to control the output. 7. A plurality of microwave generators (3) each comprising an independent magnetron (11) and a respective magnetron (11).
And a high-voltage power supply (12) for each of the high-voltage power supplies (12).
The wood drying apparatus according to claim 6, wherein the average power of each microwave generator (3) is controlled by controlling the average output of the microwave generator (3).