Do You Understand the Principle of Wood Drying?

Wood drying refers to the process of heat and moisture treatment of wood with appropriate targeted drying process and vacuum timber dryer under the premise of ensuring excellent wood quality, which is the process of continuous removal of moisture from the wood.

First, moisture in wood includes free water, absorbed water, and combined water

1. Free water exists in the large wood capillary system. (This type is easy to remove in wood drying, and the content is the largest, for example, the free water content of Paulownia is up to 250%)

2. Absorbing water exists in the micro-capillary of wood. The content of absorbing water in the wood of different tree species is 23-33%, with an average of 30%. Only by obtaining a certain amount of energy, overcoming the binding force of the micro-capillaries, can water be drawn out of the wood, so this type of water is not easily removed.

3. The compound water exists in the wood chemical composition, and its content is about 1%, which cannot be removed by drying and is generally not considered.

Second, commonly used concepts in wood drying:

1. Moisture content: refers to the moisture content in wood. The ratio of the weight of the moisture contained in the wood to the weight of the absolute dry material is called the absolute moisture content, or moisture content for short, expressed by W.

2. Electrical measurement method: a method for directly determining the moisture content based on the relationship between the electrical characteristics of the wood and the moisture content. Commonly used resistance wood moisture content tester.

3. The fiber saturation point of the wood: the free water of the wet wood in the large capillary is completely evaporated, and the moisture content of the wood when the absorbing water in the capillary system is still saturated. (The intersection of free water and absorbing water) The saturation point of wood fiber is the turning point of wood property variation. The increase or decrease of absorbing water will cause the expansion and contraction of wood and affect the dimensional stability of wood products and other wood physical properties.

4. The equilibrium moisture content of wood: When a piece of wood is in hot and humid air for a period of time, the moisture content in the wood and the moisture in the air will no longer exchange and reach the equilibrium state moisture content is called the equilibrium moisture content in the air state.

3. Moisture movement during wood drying:

Moisture can be removed from both ends of the board along the fiber direction when the wood is dried or can be removed from the surface and side of the board across the fiber direction, because the surface area and side area of the sawn timber are greater than the end area, so the moisture of the sawn timber is dried Mainly move and discharge in the direction of thickness and width. When the water content is higher than the wood fiber saturation point, liquid water moves mainly, and when part of the water content is lower than the wood fiber saturation point, water vapor or steam-water mixing is the main method.

The above information is provided by a wooden angle joining machine manufacturer.