| Wood drying modes and their influence on physical properties |
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Wood drying modes are combination of heat and humidity influences of drying component on wood, which provide necessary quality and rate of drying. Depending on requirements, set for the quality of drying, the wood can be dried in different modes and categories of temperature level. When using the modes of high-temperature process the component of drying is superheated vapor by the atmospheric pressure with temperature higher than 100oC. In every specific case the modes of either category are chosen in terms of type of influence on wood properties. Using low-temperature modes of drying, humid air with temperature up to 100o C at the initial stage is used as drying component.Low-temperature modes of drying include soft, normal and forced modes.Soft drying modes provide defectless drying by complete maintenance of physical-mechanical properties, firmness and colors of wood. These modes are recommended for drying to transport humidity of export carving wood, in which the melting of resin, falling out of knots and change of natural color (darkening of softwood or yellowing of beech or birch wood from heating) are not admitted.Low-temperature modes of carving wood drying are divided into 2 groups: 1 – for softwood, 2 – for hardwood. Depending on group low-temperature modes possess several levels (stages). During the process of wood drying the transition from one stage to another is carried out by definite wood humidity.Forced modes of drying produce defectless wood drying by saving the firmness on static bending, tension and pressing but by reducing of firmness on chipping and splitting up to 20 % with wood darkening. Such modes are recommended for drying before the operational humidity of wood and intended for the products processing with large safety efficient. High-temperature modes of drying produce defectless wood drying by insignificant decrease of firmness on static bending, tension and pressing by significant reducing of firmness up to 35 % on chipping and splitting with wood darkening. In these modes the drying is recommended before the operational humidity of wood purposed for products processing with large safety efficient. |
