JPH09133462A - Lumber drying method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lumber drying method and device to dry lumbers in a vacuum chamber by high-frequency heating, which is capable of drying lumbers, especially such lumbers as columns whose distance between the surface and the center is large, in a short period of time without producing shakes and bends. SOLUTION: Lumber heating operation using inside heating by high-frequency heating under a vacuum atmosphere and outside heating by humidified hot-air together is repeated at specified periods. In addition, steam spray into a vacuum chamber that is carried out at the same time of high-frequency heating and evacuation operation to a specified pressure are repeated at specified periods. A desirable device includes a vacuum tank 2 to contain lumbers, a heater 6 to heat air or steam inside the vacuum tank 2, a steam feeder 27 to supply steam into the vacuum tank 2, a high-frequency heater 11 to heat lumbers in the vacuum tank 2, and a vacuum pump 16 to suck and discharge air or steam inside the vacuum tank 2. Thereby, the lumbers can be dried while a balance of differences in outside and inside temperatures and humidities of the lumbers is maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for drying wood, and more particularly to an improvement in a method and a device for heating and drying wood by high frequency heating in a decompression container.

[0002]

2. Description of the Related Art A method and apparatus for heating and drying wood from the inside by high frequency heating in a reduced pressure environment are known.
When high-frequency heating is used, since the wood is heated from the inside, the central part of the wood is dried more quickly than heating from the outside by hot air or the like. Further, in a depressurized environment, the boiling point of water decreases, so that it is possible to dry the wood at a low temperature, and it is possible to quickly suck and remove water vapor from the wood.

However, in the drying of wood, the drying time cannot be shortened by merely increasing the internal temperature of the wood and increasing the vacuum degree of the surroundings. Since water in wood diffuses through cell membranes, it takes some time to dry, and if the drying time is forced to be shortened, the wood will crack or bend.

On the other hand, hot air drying, which has been performed for a long time to heat and dry wood from the outside, is characterized in that the heating cost is lower than that of high frequency heating. However, in the hot air heating, since the wood is heated from the surface side, the temperature of the central part of the wood becomes relatively low, which requires a longer time for drying as compared with the high frequency heating. Particularly, in the case of a pillar having a large cross section and having a large size from the surface of the wood to the central portion, it takes a very long time to dry. 90 for example
It takes about 10 to 14 days to dry a square cedar wood with an initial moisture content of 90% to 20% or less, and even if the surface of the wood is dry, Generally, the water content is high.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a method of drying wood in a shorter time without cracking or bending, and particularly wood having a large size from the wood surface to the central portion such as a pillar material. The first subject is to obtain a method capable of drying the sol in a short time, and the second subject is to obtain a drying device particularly suitable for carrying out such a method.

[0006]

A method for drying wood according to claim 1 of the present application is to store wood in a decompression tank,
In a method of drying wood by heating and drying in a reduced pressure environment, a heating operation of wood using both internal heating by high frequency heating and external heating by humidified hot air is repeated at a predetermined cycle.

A method of drying wood according to a second aspect of the present invention is a method of drying wood in which the wood is stored in a decompression tank and is heated by high-frequency heating in a decompression environment. It is characterized in that the injection of water vapor into and the depressurization operation to a predetermined pressure are repeated in a predetermined cycle.

A wood drying apparatus according to claim 3 of the present application comprises a decompression tank 2 for containing wood to be dried,
Heater 6 for heating air or steam in the decompression tank
A means 27 for supplying steam into the decompression tank, and a high-frequency heating device 11 for heating the wood in the decompression tank with high frequency.
And a vacuum pump 16 for sucking and discharging air or water vapor in the decompression tank.

[0009]

According to the invention of claim 1, the wood is dried while maintaining the balance of the temperature difference between the inside and the outside of the wood during drying and the moisture content so that the wood is not cracked or bent. Moreover, the drying time of the wood can be shortened by the depressurization operation.

According to the second aspect of the invention, the depressurizing operation for promoting the drying of the wood and the operation for adjusting the difference in the water content between the inside and the outside of the wood are alternately performed. The wood can be dried more quickly without cracking or bending.

Further, according to the invention of claim 3, a rational apparatus for carrying out the above-mentioned drying method can be obtained.

[0012]

1 to 3 are views showing an embodiment of a wood drying apparatus of the present invention. The decompression tank 2 for storing the wood 1 to be dried is a horizontal container having a substantially square cross section, and is provided with a door 3 for putting the wood 1 in and out. The timbers 1 are piled up on a cart 4 (by placing thin rails between the piled timbers so that the timbers are stacked with a space between the upper and lower surfaces of the timbers), and both sides of the timber 1 are subjected to high-frequency heating. The electrode plate 5 for the battery is additionally provided and stored in the decompression tank 2 (see FIG. 2).

A heater 6 with heat transfer fins and a fan 7 are arranged in the upper part of the decompression tank 2, and a steaming pipe 8 having ejection holes at several places on the peripheral surface is arranged in the lower part. Has been done. The heater 6 is provided to heat the air or water vapor in the decompression tank 2, and the fan 7 is provided to uniformly circulate the heated air or water vapor in the decompression tank 2. There is something. The steaming pipe 8 is provided for jetting water vapor into the decompression tank 2 at appropriate times to humidify the air in the decompression tank 2.

The above-mentioned electrode plate 5 for high frequency heating is shown in FIG.
As shown in FIG. 5, a large number of through holes 9 are provided so that the circulation of water vapor and air in the decompression tank 2 is not hindered. The electrode plate 5 is connected to the high frequency oscillator 11. As shown in FIG. 2, the wooden piece 1 is placed on two carts 4 and stored in a juxtaposed state. The non-grounded side of the high-frequency oscillator is connected to the electrode plate 5 located inside. The ground side of the high frequency oscillator is connected to the electrode plate 5 located outside. A tuner 12 is connected to the high frequency oscillator 11, and the tuner 12 detects the load in the decompression tank 2 and controls the output of the high frequency oscillator 11.

A condenser 14 is connected to the decompression tank 2 via a valve 13, and a vacuum pump 16 is connected to the condenser 14 via a valve 15. A cooling water pipe is provided in the condenser 14, and the cooling water pipe is connected to a cold water tower 17, and a cooling pump circulates the cooling water in the condenser 14. The drain pipe 19 of the condenser 14 is connected to an automatic drain tank 22 via a valve 21.

Air or water vapor in the decompression tank 2 is sucked by the vacuum pump 16 and guided to the condenser 14.
Most of the sucked water vapor is cooled and condensed by the cooling water in the condenser 14, and flows into the automatic drain tank 22 through the drain pipe 19. Further, the air in the condenser 14 and the water vapor that has not condensed are sucked by the vacuum pump 16 and released to the atmosphere. The automatic drain tank 22 forcibly discharges the water in the tank to the outside of the device when the water level reaches a set value.

A valve 23 is provided in the automatic drain tank 22.
The drain port 24 of the decompression tank 2 is also connected via the, and the water condensed in the decompression tank 2 is also discharged to the outside of the device through the automatic drain tank 22.

A boiler 27 is connected to the steaming pipe 8 at the bottom of the decompression tank via steam valves 25 and 26. Further, the heater 6, the fan 7, the high frequency oscillator 11, the vacuum pump 16 and the like are stopped at a predetermined cycle, and the steam valve 2 is operated at a necessary timing.
A controller 28 for opening and closing 5, 26 and the like is provided.
Further, the decompression tank 2 is provided with an atmosphere release valve 29 for introducing air into the tank.

FIG. 4 is a diagram showing one form of an operation schedule in the apparatus shown in FIGS. 1 to 3. FIG.
The horizontal axis of is the elapsed time, the upper vertical axis is the heating temperature (wood temperature), and the lower vertical axis is the degree of vacuum in the decompression tank. For heating wood, both internal heating by high frequency and external heating by humidified hot air containing steam are used together to raise the internal temperature and external temperature of the wood in a well-balanced manner.

Generally, due to the difference in water content between the outside and the inside of wood during drying, a temperature difference occurs between the inside temperature and the outside temperature of the wood only by high frequency heating. Moreover, the temperature of the surface portion of the wood becomes higher than the temperature of the central portion only by external heating. Therefore, by using both internal heating and external heating, the ratio of internal heating and external heating is controlled so that the temperature of the surface portion and the temperature of the central portion of the wood have the most suitable temperature relationship for drying the wood. This ratio changes depending on the type and size of the wood to be dried, the difference in water content, etc., so the most appropriate conditions should be set based on experimental data.

Further, the water content of the dried wood is inevitably lower than the water content of the central part. If the difference in water content becomes too large, the wood will be cracked or bent, and if drying is performed with the difference in water content between the surface portion and the central portion being made small, the drying time will be long.

Therefore, when the difference in the water content between the surface portion and the central portion of the wood being dried becomes too large, steam is jetted into the decompression tank during external heating to suppress the drying of the wood surface portion. . When there is no risk of cracking or bending due to the difference in water content, the steam jet is stopped to reduce the humidity of the air in the decompression tank 2 and accelerate the drying. Further, as shown in FIG. 4, by periodically repeating heating and depressurization, the drying time is shortened while preventing the water content of the wood surface portion from becoming too low.

In the structure shown in FIG. 4, after the wood 1 to be dried is stored in the decompression tank 2, the internal temperature of the wood and the external temperature of the wood are combined by using the internal heating with high frequency and the external heating with hot air or steam. Is raised to about 90 degrees Celsius, and after reaching a predetermined temperature, vacuuming is performed to reduce the pressure in the decompression tank 2 to about 350 to 300 torr. Then, the heating of the wood at about 90 degrees Celsius and the heating at about 60 degrees Celsius are alternately repeated for a predetermined time, and the pressure in the decompression tank 2 is increased by increasing the degree of vacuum and evacuation to promote drying, By alternately performing pressure recovery for suppressing the water content of the surface of the wood from becoming too low by ejecting steam, the wood is promoted to dry without cracking or bending. By such operation, the drying time can be shortened to 1/2 to 2/3 in comparison with the conventional hot air drying, and it is possible to prevent cracking and bending of the wood during drying as much as possible. can do.

[0024]

According to the method of the present invention described above, it is possible to dry the wood in a shorter time than the conventional method without causing cracking or bending of the wood, and particularly from the surface such as a pillar to the center. It is possible to significantly reduce the drying time of large size wood. Further, with the apparatus of the present invention, it is possible to obtain an apparatus having a rational structure that can perform an optimum drying operation according to the material and cross-sectional area of the wood to be dried.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the entire apparatus.

FIG. 2 is a cross-sectional view of a decompression tank showing a state of containing wood.

FIG. 3 is an explanatory view showing an electrode plate for high frequency heating.

FIG. 4 is a time chart showing an example of an operation schedule of the device.

[Explanation of symbols]

 2 Decompression tank 6 Heater 11 High frequency oscillator 16 Vacuum pump 27 Boiler

Claims (3)

[Claims] 1. A method for drying wood, comprising storing wood in a decompression tank and heating the wood in a decompression environment to dry the wood. The wood heating operation is a combination of internal heating by high frequency heating and external heating by humidified hot air. A method for drying wood, characterized by being repeated in a cycle. 2. A method for drying wood, wherein wood is housed in a tank and heated by high frequency heating in a depressurized environment to dry the wood, and water vapor is injected into the depressurizing tank at the same time as high frequency heating and depressurized to a predetermined pressure. A method for drying wood, characterized by repeating the operation and a predetermined cycle. 3. A decompression tank (2) for containing wood to be dried, a heater (6) for heating air or steam in the decompression tank, means (27) for supplying water vapor into the decompression tank, A wood drying apparatus comprising a high frequency heating device (11) for heating wood in a decompression tank by high frequency and a vacuum pump (16) for sucking and discharging air or water vapor in the decompression tank.