Wood moisture content that should be understood when making furniture
In the production of furniture, it is crucial to know the moisture content of various types of wood. Different wood moisture content is not the same, which explains why some wooden doors, wooden floors, wooden furniture and other wood products will crack and deform after being sold.
First, the wood moisture content
Wood and its products under normal conditions will have a certain amount of water. In China, the weight of the moisture in the wood and the percentage of the weight of the wood after drying are defined as the moisture content of the wood.
The water content can be calculated based on the weight of the whole dry wood, and the calculated value is called the absolute water content, and is simply referred to as the water content (W, %). Calculation formula:
W=(Gs-Ggo)/ Ggo×100%
among them:
W——the absolute moisture content of wood;
Gs - wet wood weight;
Ggoo - the weight of the dry material.
Second, grasp the importance of wood moisture content
After the wood products are finished, the shape and material will not change. At this time, the key factors determining the intrinsic quality of the wood products are the wood moisture content and the dry stress. Manufacturing companies need to correctly grasp the moisture content of wood products. When the wood product reaches an equilibrium moisture content, the wood at this time is the least susceptible to cracking.
Third, the wood is dry, the more dry the better?
When the wood is placed in a certain environment, after a long enough time, the water 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 shrink and contract, and vice versa.
For example, the average annual equilibrium moisture content in Guangzhou is 15.1%, compared with 11.4% in Beijing. Drying to 11% of wood is suitable for Beijing, and it can be used in Guangzhou to absorb moisture and deform. Therefore, wood drying should be appropriate, not as dry as possible. Different areas and different uses have different requirements for wood moisture content.
Fourth, the water content laboratory measurement method:
The method for measuring the moisture content of the wood includes a drying method, an electric measuring method, a dry distillation method, a titration method, and a humidity method. In the field of wood processing, a drying method is usually employed.
Drying method:
The drying method is a method of measuring the moisture content of the wood moisture test piece until it is completely dry.
First, a representative moisture content test piece with a thickness of 10 to 12 mm was sawed in the wood to be tested. The so-called representativeness is that the dry and wet degree of this test piece is consistent with the whole piece of wood, and there are no defects such as skin, thrift, decay, and insects. Generally, it should be taken at a distance of 250~300mm from the end of the sawing material. After scraping the burr and sawdust from the moisture content test piece, immediately weigh the weight on a balance with a precision of 0.01g and a range of not less than 200g, mark the weight as G, and then put the test piece at a temperature of 103± Bake in a 2 ° C incubator for about 6 h, then take out the weighing and record it, then put it back into the oven to continue drying. It is then weighed every 2 hours until the weight of the last two weighings is constant, which is the absolute dry weight, recorded as Go. This allows the water content to be calculated as follows:
W=(G-Go)/ Go×100%
Since the moisture of the thin test piece is easily changed when exposed to the air, it should be measured immediately after the test piece is taken or after the oven is taken out. If it cannot be weighed immediately, it must be packed in a plastic bag to prevent evaporation of water.
Related reading: moisture content of wooden furniture, attention should be paid to the difference between the north and the south
The drying method is used to measure the moisture content of wood accurately and reliably, and is not limited by the water content range. However, it is necessary to intercept the sample and destroy the wood during the measurement, and it takes a certain time.
The drying method is the basic method for measuring the moisture content of wood and is the most common method. The above formula shows the absolute moisture content, which is also the wood moisture content commonly referred to in wood processing.
V. Annual average of wood moisture content in major cities in China:
The balance of water content of wood in different parts of China is different. Therefore, consumers should consider the different environments when purchasing solid wood furniture. They should not buy cross-border land for the sake of cheapness. Otherwise, Nanmu will be easily cracked in the north. The south uses the phenomenon of easy expansion.
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