Drying and gas or vapor contact with solids – Process – Gas or vapor pressure varies during treatment
Patent
1992-11-04
1995-02-28
Gromada, Denise L.
Drying and gas or vapor contact with solids
Process
Gas or vapor pressure varies during treatment
34411, 34 92, F26B 504
Patent
active
053925300
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of seasoning lumber, and more particularly to a method of seasoning lumber, which eliminates any crack and warp occurring during the whole process from raw wood to seasoned lumber, and also reduces seasoning time in a dryer by using superheated steam, thus raising the turnover ratio of the dryer.
BACKGROUND OF INVENTION
Raw wood must be seasoned to be used as a lumber product and the are three conventional process methods of seasoning lumber as follows; America, wherein hot air is blown on lumber, and dischanged from the both ends of the tunnel. natural seasoning. This method is used in Europe, Japan, and many other countries. uses a pressure vessel and repeats pressurizing and heating with saturated steam and reducing pressure to less than the atmospheric pressure.
According to process (1) described above, enormous loss due to cracks and warps occurs and moisture content doesn't become uniform. Moreover when the moisture content falls and the contained water becomes difficult to evaporate, this method cannot enhance reduction of moisture content, resulting in a disadvantage whereby the tunnel kiln must be greatly lengthened.
On the other hand, method (2) described above, is a common lumber seasoning method used in many areas of the world. The greatest possible care is taken to operate the hot air wood dryer so as to reduce loss due to cracks and warps in the lumbar. However, much loss due to cracks and warps occurs during natural seasoning before artificial seasoning, and such problems are regarded as inevitable and have not yet been solved.
Moreover, method 3 described above is a lumber seasoning method which repeats the cycles, and includes the process of heating and pressurizing with saturated steam, and also the process of reducing the pressure below the atmospheric pressure. Thereby depreciation costs a great deal and moisture content within lumber cannot be reduced below 20%. The reason is, during the process of pressurizing and heating, the water contained within lumber is forced to move into the core portion, thereby low-temperature water lump arises. Since the specific heat of the water is three times as large as that of the lumber, even if the time of pressurizing and heating is extended as long as possible, the temperature within said lumber doesn't become uniform. In the case of reducing pressure while the temperature remains non-uniform, the contained water boils and evaporates only from the surface of the lumber. Therefore taking the quantity of heat into account, even if the time of reducing pressure below the atmospheric pressure is extended, the contained water does not boil, resulting in absorption of the evaporated water from the surface of the material. Therefore, the above-mentioned condition equals to that of reducing the contained water with the hot air wood dryer, and a pressurizing and heating process and a pressure reducing process must be repeated many times with the result that method 3 has fallen into disuse due to the expense of seasoning the lumber.
DISCLOSURE OF THE PRESENT INVENTION
The object of the present invention is to provide a lumber seasoning method, which avoids the occurrence of cracks and warps to the lumber and raises the turnover ratio of the dryer.
Examining the reasons why foregoing seasoning methods 1, 2 and 3 described above, don't meet the above-mentioned object, the following common defects thereof are found.
First, tissues containing water within lumber are roughly divided into vessels, capillary tubes, and cell cavities. Water contained in the vessels is evaporated easily, but the capillary tubes have narrow parts through which only particles as large as water molecules can pass and the cell cavities are bagged. Water contained in the capillary tubes and cell cavities is impossible to evaporate except through a small pit. Therefore, in any of the seasoning methods of methods 1, 2 and 3, the contained water is evaporated in a different manner among every tissues with the result that the moisture content within wh
REFERENCES:
patent: 2548403 (1951-04-01), Smith
patent: 3921309 (1975-11-01), Nakayashiki
patent: 3959529 (1976-05-01), Winn et al.
patent: 4343095 (1982-08-01), Rosen et al.
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