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Why measure the moisture content of wood?

Mar. 30, 21

Wood is a material that is used in modern furniture and all walks of life. The processing of wood products determines. The moisture content is an important parameter of wood. What kind of moisture content is the best for wood?


1. What is the moisture content of wood?

Under normal conditions, wood and its products will have a certain amount of moisture. In China, the percentage of moisture in the wood to the weight of wood after drying is defined as the moisture content of the wood.

The moisture content can be calculated based on the weight of the dry wood. The calculated value is called the absolute moisture content, and is simply referred to as the moisture content (W,%). Calculation formula:

W = (Gs-Ggo) / Ggo × 100% Among them: W—the absolute moisture content of the wood; Gs—the weight of the wet wood; Ggo—the weight of the absolute dry wood.


2. The importance of mastering the moisture content of wood

Why do some wooden products such as wooden doors, wooden floors, wooden furniture, and other wooden products crack and deform after they are sold? How to reduce these problems to the loss of wood enterprises?

After the production of wood products is completed, the shape and material will not change. At this time, the key factors that determine the intrinsic quality of wood products are mainly the moisture content of the wood and the drying stress. Manufacturing enterprises need to correctly grasp the moisture content of wood products. After the wood product reaches the equilibrium moisture content when it is used, the wood at this time is least likely to crack and deform.

Distributors who sell wood products should also test the moisture content of the products they sell to grasp the quality status of the products they sell. Choose a manufacturer with good product quality. Any manufacturer that pays attention to product quality will test the moisture content of its product.

As for the high-quality procurement of wood products, with the continuous growth of professional knowledge, more and more attention has been paid to the moisture content of wood products. In the past, foreign buyers paid much attention to this indicator, and many wood manufacturers that do export products and semi-finished products know this very well.


3. Is the wood dry? How much should it dry?

After the wood is placed in a certain environment, after a long enough time, its moisture content will tend to an equilibrium value, which is called the equilibrium moisture content EMC of the environment. When the moisture content of the wood is higher than the equilibrium moisture content of the environment, the wood will drain moisture and shrink, otherwise, it will absorb moisture and expand. For example, the average annual equilibrium moisture content in Guangzhou is 15.1%, while in Beijing it is 11.4%. Dried 11% of the wood is suitable for Beijing, which can be used in Guangzhou will be hygroscopic expansion and deformation. Therefore, wood should be dried properly, not as dry as possible. Different regions and different users have different requirements for wood moisture content.


4. Wood balance moisture content:

Under a certain air state, the moisture absorption stable moisture content or desorption stability moisture content finally achieved by the wood is called the equilibrium moisture content of the wood (wood moisture stable state).


5. The laboratory measurement method of moisture content:

The methods of measuring the moisture content of wood include drying method, electrical measuring method, dry distillation method, titration method, and humidity method. In the field of wood processing, the drying method is usually used.

Drying method: The drying method is a method of drying the moisture content test piece of wood until it is completely dry to measure its moisture content. First, a representative moisture content test piece with a grain thickness of 10-12 mm was sawn from the tested wood. The so-called representativeness is that the dryness and wetness of this test piece are consistent with the whole piece of wood, and there are no defects such as peeling, knots, decay, and moth. Generally, it should be taken at a distance of 250 ~ 300mm from the end of the sawn timber. Immediately after the burr and sawdust are scraped off from the moisture content test piece, weigh it on a balance with an accuracy of 0.01g and a range of not less than 200g, record the weight as G, and put the test piece in a constant temperature box with a temperature of 103 ± 2 ℃ for about 6 hours, then take out the weight, record it, and then return to the oven to continue drying. Then it was weighed every 2h until the weight of the last two weighings remained unchanged, which was the absolute dry weight, recorded as Go. In this way, the water content W = (G-Go) / Go × 100% can be calculated according to the following formula

Because the moisture of the thin test piece is easy to change when exposed to the air, pay attention to the weight of the test piece immediately after the test piece is taken out or after taking out the oven. If it cannot be weighed immediately, it must be immediately packed in a plastic bag to prevent water evaporation. The drying method is accurate and reliable for measuring the moisture content of wood, and it is not limited by the range of moisture content. However, it is necessary to take a sample during the measurement to damage the wood, and it takes a certain time. The drying method is a basic method for measuring the moisture content of wood, and it is also a commonly used method. The above formula represents the absolute moisture content, which is also commonly referred to as wood moisture content in wood processing.

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