JPH035688A - Method of drying lumber and food - Google Patents

Abstract

PURPOSE:To perform an efficient drying within a short period of time by a method wherein a surface-like heating member is applied to cover a surface of a drying workpiece such as lumber within a pressure reduced container, the drying workpiece is held between the surface-like heating members, an electrical energization is applied to the workpiece and it is dried while the pressure being reduced. CONSTITUTION:Wooden materials 2 are pilled up within a pressure reduced container 1 while being held by planer-like heating members 3 and the lumber is pressed at 4 with a hydraulic pressure got from a hydraulic pump 3 in order to prevent a size error during a drying operation. The planer-like heating material 3 is electrically energized by a power supply 7, vacuum pump 6 is driven to perform a drying operation while an interior of the pressure reduced container 1 being reduced. A temperature of the lumber during a drying operation is detected by a temperature sensor inserted into the lumber 2. An adjuster meter 8 may control an amount of electrical energization and an electrical energization time in response to the detected temperature and then a history of the drying temperature is recorded by a temperature recorder 9. In this way, there is not irregular finished state and moisture content and it is possible to perform a superior finished drying within a short period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for drying wood, foods, etc. under reduced pressure.

[Conventional technology]

In recent years, the importance of drying wood, especially for coniferous wood, has been emphasized, and various dryers, including dehumidifying dryers, have become popular in the lumber industry.

Currently, hot air drying, dehumidification drying, vacuum drying, and solar drying ring drying methods are in practical use as wood drying methods. Although it has advantages such as being able to dry cross-sectional materials in a short time and drying veneers with high quality in a short time while being bundled, it has been pointed out that the disadvantage is that the equipment and running costs are high.

[Problem to be solved by the invention]

A recent trend in the furniture industry is the import of many North American materials, including oak, hirakori, and alder, but these materials are already dried locally. In addition, it is also possible to import not only semi-finished products but also dried materials from NIES' in the future for rubber wood (which is dried locally because it is prone to discoloration bacteria) and other resins.

In order to survive this competition in such a harsh international situation, it is necessary to dry wood in a short time, with high quality, and to survive this competition.
There is a need for the development of a method that is versatile enough to accommodate various tree species and forms, and that can be implemented in an energy-saving manner, in a small space, and at low equipment costs.

[Means to solve the problem]

In order to achieve the above-mentioned object, in the present invention, a planar heating element is placed over the surface of wood, food, or other material to be dried in a reduced pressure or vacuum container, or a sheet of material to be dried is placed between the planar heating elements. A configuration was adopted in which an object was sandwiched between the objects, and the amount of heat necessary for evaporating and drying the moisture was supplied by energizing the planar heating element, and the object was dried while being depressurized.

The reduced pressure or vacuum container may be a pressure-resistant container of about 15 to 20 wmHg. The temperature inside the container is usually 20-50°C
1. In particular, the temperature is 30 to 40° C., and a device equipped with a vacuum suction pump with a displacement that can maintain this temperature and a planar heating element with a calorific value is used.

The planar heating element is made by coating and polymerizing carbon-based conductive paint on a woven fabric woven with copper ITT wires, attaching electrode terminals, laminating it with a polyester film for waterproofing, and then using a PVC sheet. It is preferable to use one with a protective exterior. By applying electricity to the electrode wire, carbon, which is a resistance material, generates heat.

This sheet heating element is different from metal resistance wires such as nichrome,
It is a woven fiber fabric that is flexible, lightweight, difficult to break, and can be folded freely, so it has excellent flexibility, durability, and workability. In addition, since the conductive paint is distributed in a mesh pattern on the woven fiber fabric, it has thermal properties that make the heat generation temperature distribution even, compared to a method in which resistance wires such as nichrome wire are arranged at predetermined intervals. It has a temperature characteristic that the temperature rises quickly afterward.

Of course, a sheet heating element of the type in which metal resistors such as conventional nichrome wires are closely arranged, or a type in which the heating resistor is made of conductive ceramic may be used.

When drying wood, food, and other materials, planar heating elements having the above-mentioned characteristics are waved directly on the surface of the material to be dried, or they are stacked with the material to be dried sandwiched between the surface heating elements. .

When drying plate materials, pillar materials, etc., it is sufficient to simply pile up the materials to be dried, but in order to prevent distortion, it is preferable to equip the pressure container with a press device using a hydraulic cylinder or the like.

According to the drying method of the present invention, for example, beech wood with a moisture content of 140%, a thickness of 5 values, a width of 30 cm, and a length of 188 values is dried under reduced pressure conditions of a surface temperature of a planar heating element of 40° C. and a degree of vacuum of 40 wHH. It is dried to a moisture content of about 10% in 60 to 70 hours. On the other hand, when beech wood of the same size is dried using high frequency heating and reduced pressure drying, it takes 90 to 100 hours, which significantly shortens the drying time.

The drying method of the present invention can be applied not only to wood but also to the rapid drying of products that do not like high temperatures, such as powdered materials such as foods and drugs, and wet ceramics.

[Effect]

The drying method of the present invention involves covering the surface of the object to be dried with a planar heating element or sandwiching the object to be dried between the planar heating elements, bringing the sheet heating element into direct contact with the object to be dried, and drying the object under reduced pressure. Because it dries, it has the following effects:

Since contact heating is used, there is little heat loss, and the temperature distribution of the planar heating element is almost uniform, so the finish and moisture content are uniform, and drying can be done in a short time.

Furthermore, since the temperature of the planar heating element can be easily controlled and complicated electrical system control technology is not required, maintenance and management of the device is also easy.

Furthermore, since there is no need for wooden crosspieces during drying, and the heating element is thin, a large amount of wood can be dried in a small space.

The planar heating element is highly flexible and can be coated freely along the shape of the material, making it easy to handle without causing breakage or curling when using resistance wire such as nichrome wire. be.

〔Example〕

Hereinafter, the effects of the present invention will be specifically explained using examples.

Example 1 (1) Test method As shown in FIG. 1, wood 2 to be dried was stacked in a vacuum can body 1 (inner diameter 75 cm, length 250 cm), sandwiched between planar heating elements 3. In order to prevent distortion during drying, a press 4 was performed from above using a hydraulic cylinder. Planar heating element 3
The test pieces were 2 liters thick, and two types, one for large area (45 x 200 cm+) and one for small area (23 x 100 cm), were placed on the front and back surfaces of wood 2 and heated directly from both sides. The temperature of the material during drying was detected by a temperature sensor (platinum resistor ptloo) inserted into the wood, and was controlled at a predetermined temperature.

In the figure, 5 is a hydraulic pump, 6 is a vacuum pump, 7 is a power supply, 8
is a temperature and time controller, and 9 is a temperature recorder.

The electrical specifications of the planar heating element 3 and the vacuum pump 6 are as follows.

(2) Test material The material used for the test was 3.5 cm thick and 10.30 cm wide.
1. Length 90. It is 188CJl elm wood (produced in Siberia).

(3) Planar heating element The planar heating element used was a woven fabric having a carbon-based conductive paint as a resistor, as described above.

(4) Test results (a) Temperature distribution of the heating element Figure 2 shows the results of measuring the temperature distribution of the heating element, which affects the unevenness of moisture content in the finished wood drying process. In the width direction, the distribution was high at the center and low at the periphery. This is thought to be because heat is trapped in the center, while heat is radiated around the area. This can be seen from the fact that when the moisture content is high at the beginning of drying, the temperature distribution is almost uniform over the entire surface of the test material, but at the end of drying, the surrounding temperature tends to decrease, similar to the distribution described above. .

(b) Drying process The elm material used in this test has good air permeability and is the most suitable material for vacuum drying. Figure 3 shows the results for a width of 10ca+ and a length of 90cm. Initial moisture content 130-140%
It can be seen that the material was dried to 3CI11.5 (thickness) to 10% in a very short time of 50 and 70 hours, respectively. No drying cracks occurred. Next, 4 pieces of 5cffl thick material
FIG. 4 shows the drying results when stacked in layers and heating elements were inserted every two layers. Although the drying time was longer than the results shown in Figure 3, the difference was not significant.

Figures 5a to 5c show the results of the drying process and the moisture content distribution in the thickness and length directions for a 5 cm thick test material when the dimensions of the heating element were increased to dry a large area test material.

Due to good air permeability, the drying time does not increase much as the length increases. It can be seen that the variation in moisture content among the test materials is also small. At the beginning of drying, the change in material temperature remains constant around the boiling point, which corresponds to the surrounding air pressure. After that, the temperature difference between the test materials will be 6 to 7 degrees Celsius in the middle period, and 3 to 4 degrees Celsius in the final period.Also, we expected that there would be a significant difference in the moisture content distribution in the thickness direction due to contact heating. However, it can be seen that the amount of water content is surprisingly small. This is probably because the surface evaporation was moderately adjusted by the cover material of the heating element. There was also little difference in moisture content in the distribution in the length direction. During drying for both materials. Since the material was compacted using a hydraulic press, there were fewer cracks in the material.

〔Effect of the invention〕

As explained above, since the present invention involves contact heating of wood with a planar heating element under reduced pressure, it is possible to obtain a good finish with uniform finish and moisture content and drying in a short time. can.

In addition, the planar heating element allows easy temperature control, easy maintenance and management of the device, low heat loss, energy saving, and space saving, making it possible to dry wood at low cost.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the apparatus used to carry out the present invention, FIG. 2 is a diagram showing an example of the temperature distribution of the planar heating element used to carry out the present invention, and FIGS. 3 and 4. are graphs showing the relationship between drying time and moisture content according to the embodiments of the present invention, FIGS. 5a to 5c, respectively.
also shows an example of the present invention, (5) is a graph showing the relationship between drying time and moisture content, (bl and (C1) are graphs showing the moisture content distribution in the thickness direction and length direction of the wood, respectively. be.

Claims (1)

[Claims] In a reduced pressure or vacuum container, a sheet heating element is placed over the surface of wood, food, or other material to be dried, or the material is sandwiched between sheet heating elements, and moisture is removed by energizing the sheet heating element. A method for drying wood, food, etc., characterized by supplying the amount of heat necessary for evaporative drying and drying while reducing pressure.