1. Atmospheric Dryness
That is, the wood pile is hidden on an open field or in a shed, the atmosphere is used as a heat and moisture transfer medium, and the heat of solar radiation is used to remove the moisture in the wood to achieve the purpose of drying. The advantages of atmospheric drying are: simple and easy, energy-saving, relatively economical, and can meet the requirements of air-drying materials. The disadvantage is that it is limited by natural conditions, the drying time is longer, the final moisture content is high, and the space is large. During the air drying, the wood is susceptible to bacteria and insects. At present, the use of simple air drying is gradually decreasing.
2. Chamber Dry
Refers to the method of drying wood by manually controlling the parameters of the drying medium in the drying room. According to the temperature of the drying medium, it can be divided into low-temperature room drying, conventional room drying, and high-temperature room drying. Appropriate room drying methods should be correctly selected according to the tree species, thickness, purpose and other conditions of the wood to be dried. The advantage of room drying is that the drying quality is good, the drying period is shorter than that of atmospheric drying, and the drying conditions can be adjusted flexibly. The disadvantage is that although the time is shorter than atmospheric drying, it also takes several months.
3. Vacuum Drying
That is, the wood is dried in a closed container under negative pressure. According to the operation mode, it can be divided into two types: intermittent vacuum drying and continuous vacuum drying. Intermittent vacuum drying is carried out alternately according to two stages of normal pressure heating and negative pressure drying, heated with steam or hot water. Continuous vacuum drying is continuous heating and vacuum at the same time, heating with a hot plate or high-frequency electrolyte. The advantage is that the drying speed is fast and the drying quality is guaranteed. It is especially suitable for the drying of thick plates and square materials.
4.High Frequency Vacuum Drying
The wet wood is used as a dielectric and placed in a high-frequency electromagnetic field. Under the action of an alternating electromagnetic field, the water molecules in the wood vibrate continuously with the change of the electric field, friction generates heat, and the wood is dried. The application of high-frequency drying tends to be combined drying, such as high-frequency vacuum combined drying. The advantages of high-frequency vacuum drying are that the wood is heated uniformly inside and outside at the same time, the drying speed is very fast, the drying quality is good, and the natural color of the wood can be maintained.
