The moisture content of the veneer after peeling is very high, usually %60-%70. If the veneer is directly glued without drying, and then the veneer is hot pressed, when the veneer is glued, it is easy to produce due to too much moisture. Glue infiltration makes the glued surface of the veneer lack glue; during hot pressing, it is easy to produce bubbling, degumming, and glue penetration on the board surface; when the plywood is used, it is easy to produce defects such as degumming, deformation, and surface cracks. In addition, if the moisture content of the slab is too high, the hot pressing time of the hot press will be prolonged and the productivity of the hot press will be affected. Therefore, the veneer after peeling must be dried in a veneer dryer to make the veneer meet the requirements of the plywood production process
The basic principle of veneer drying？
Veneer drying is the process of drying the rotary cut wet veneer to a certain moisture content according to the process requirements.
The relationship between veneer reasons and drying speed？
1. Different tree species have different densities, so the drying speed is also different. In the case of the same thickness, if the same weight of water is evaporated, the value of the moisture content reduction of the veneer of the denser tree species is smaller; on the other hand, from the perspective of the structure, the cell cavity in the wood tissue of the denser tree species is smaller than that of the veneer. Small, the cell wall is thicker, so the resistance of water conduction in the range of low moisture content is large, so the drying speed is reduced. But some tree species are exceptions, for example: Ash veneer with a density of 0.69g/cm³ has a shorter drying time than basswood with a density of 0.63g/cm³, because the ring hole of the ash veneer is large, the material is rough, and it is easy to Evaporate moisture.
2. The moisture content of the veneer increases, and the drying time of the veneer increases with the increase of the initial moisture content of the veneer. The initial moisture content of the veneer depends on the moisture content of the log, the method of transportation and preservation of the log, and whether it is subjected to cooking and heat treatment.In order to ensure that the moisture content of the veneer is uniform at the end point after drying, the veneer should be classified according to the initial moisture content before drying, and the veneer should be dried under the corresponding drying conditions of the veneer. The difference between the wood core and sapwood of some tree species is obvious, the moisture content of the sapwood is relatively high, and the drying time should be increased.
The thickness of the veneer, the greater the thickness of the veneer, the greater the resistance to moisture conduction, so the drying speed is slower; the smaller the thickness of the veneer, the faster the drying speed, and the increase in the thickness of the veneer is not proportional to the slowing down of the drying speed. In order to ensure the uniform final moisture content of the veneer, it should be classified according to the tree species, initial moisture content and the thickness of the veneer before drying. The veneer is dried by different drying processes.
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