Basic principles of wood drying equipment :

There are mainly two kinds of water in wood: free water and absorbent water. The moisture present in the large capillary system composed of cell cavities is called free water, and its increase or decrease only affects the weight of the wood, but not the properties of the wood; The moisture present in the microcapillary system composed of cell walls is called sorption water, and its change can not only make wood shrink and expand, but also affect other physical and mechanical properties of wood.

Wood drying is to exclude free water and suction water in the wood to adapt to different uses and quality requirements. Although there are many ways to dry wood, the basic principle is the same, that is, the use of water content gradient along the thickness of wood, as well as the internal large and external small partial pressure difference of water vapor formed after heating, to promote the water in the form of liquid and vapor state from the interior to the outside continuously, and through the wood surface to the outside; The intensity of water movement inside should be coordinated with the intensity of water evaporation on the surface, so that the wood will dry evenly from the surface to the inside.

In the traditional steam drying room, the drying process is: first, wet air with high temperature (below 100 ° C) and high temperature (saturated or close to saturated) is constantly passed through the pile in the circulation flow to preheat the wood. When the wood and its moisture are heated to a certain extent, according to the provisions of the drying standard, reduce the temperature and relative humidity of the medium, forcing the moisture in the wood to evaporate from the surface, which is the beginning of drying. Then in accordance with the procedures specified in the drying standard, gradually increase the temperature of the medium and reduce the relative humidity, so that the evaporation surface of water in the wood gradually moves inward until the end of drying. In the drying process, the internal stress, cracking and deformation should be eliminated or reduced, and the physical and mechanical properties of the wood should not be reduced to ensure the drying quality.