l. Water storage method
The water storage method is a relatively primitive method for reducing the residual growth stress of logs. The logs are stored for a long period of time and become soft, and the residual growth stress is gradually released. However, this method increases the storage period and capital occupation of the logs, and is suitable for occasions with water and water storage conditions.
2. Heat treatment
Tests have shown that logs are heat treated with hot water, steam, furnace gas or flue gas before sawing to soften wood fibers and lignin, which can effectively eliminate residual growth stress. The specific method is:
It can be treated with 70~80 C hot water, or heated by steam or furnace gas to make the internal temperature of the log reach 80 C or above, or use the flue gas above 150 C for treatment. Under different time and water ratio, the surface of the log can be made. The residual growth stress is reduced to less than 50%, or even completely eliminated. After the comparison test, the sawn timber cut by the saw after heat treatment has fewer end cracks, and the flat surface is flat, especially the edge bending (transverse bend) of the diameter cutting board is reduced, and the yield rate is increased by 4% to 6%. However, when the gas is used as a heat source for treatment, the surface water-carrying rate of the log surface is likely to be surface cracking below the fiber saturation point (FSP), so the temperature and humidity during the treatment should be controlled.
3. Other methods
In addition to the above methods, there is also the use of the tree dead leaves method, that is, the trees are removed one year or earlier before the felling, and the growth is terminated to force the growth stress balance in the trunk to reduce the growth stress by 20% to 30%. The same effect as storage in water. In addition, studies to reduce or improve growth stress using genetic selection, forest management techniques, and ring cutting methods during growth are also underway.
The water storage method is a relatively primitive method for reducing the residual growth stress of logs. The logs are stored for a long period of time and become soft, and the residual growth stress is gradually released. However, this method increases the storage period and capital occupation of the logs, and is suitable for occasions with water and water storage conditions.
2. Heat treatment
Tests have shown that logs are heat treated with hot water, steam, furnace gas or flue gas before sawing to soften wood fibers and lignin, which can effectively eliminate residual growth stress. The specific method is:
It can be treated with 70~80 C hot water, or heated by steam or furnace gas to make the internal temperature of the log reach 80 C or above, or use the flue gas above 150 C for treatment. Under different time and water ratio, the surface of the log can be made. The residual growth stress is reduced to less than 50%, or even completely eliminated. After the comparison test, the sawn timber cut by the saw after heat treatment has fewer end cracks, and the flat surface is flat, especially the edge bending (transverse bend) of the diameter cutting board is reduced, and the yield rate is increased by 4% to 6%. However, when the gas is used as a heat source for treatment, the surface water-carrying rate of the log surface is likely to be surface cracking below the fiber saturation point (FSP), so the temperature and humidity during the treatment should be controlled.
3. Other methods
In addition to the above methods, there is also the use of the tree dead leaves method, that is, the trees are removed one year or earlier before the felling, and the growth is terminated to force the growth stress balance in the trunk to reduce the growth stress by 20% to 30%. The same effect as storage in water. In addition, studies to reduce or improve growth stress using genetic selection, forest management techniques, and ring cutting methods during growth are also underway.
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