Views:547 Author:Site Editor Publish Time: 2019-08-22 Origin:Site
In the preheating stage, the drying medium is directly in contact with the drying unit, so that the temperature of the material rises rapidly. Generally, no water evaporation occurs during the preheating stage, and the required preheating time varies according to the ambient temperature.
Constant speed drying stage
The constant-speed drying stage is dominated by evaporation of free water, and the evaporation rate is constant. Since the increase or decrease of free water in the wood does not affect the dimensional change of the wood, the evaporation rate of the free water can be increased as much as possible.Artificial board
Deceleration drying stage
The deceleration drying phase can be further divided into two sections: the first section, which mainly evaporates the remaining free water in the second stage and most of the sorbed water; and the second section, evaporates the remaining part to absorb the water. The characteristics of the deceleration and drying stage are: the resistance of moisture movement and evaporation is gradually increased, the drying rate is gradually reduced, and the supplied heat increases the temperature of the drying unit in addition to evaporating water.
In general, it is difficult to strictly divide the apparent boundaries of the three phases from time to time, often with the phenomenon that the previous phase has not yet ended and the latter phase has begun. For example, in the case where the free water has not evaporated, the sorption water of the processing unit has begun to evaporate.
For the drying of veneers, it is very important to choose the proper drying temperature and drying time. Improper handling can cause defects such as warpage, deformation and uneven distribution of water content. Generally speaking, the temperature of the drying medium used should not be too high. . For fiber and shavings, the drying time is relatively short. Usually, the shape of the processing unit is not considered. The temperature of the drying medium is relatively high, and the drying time is relatively short. In the production of medium density fiberboard and particleboard, it is generally used. High temperature rapid drying system.
The drying process of the wood unit essentially contains the sum of the effects of heat transfer and water evaporation.Artificial board