Wood moisture content you should know when making furniture

In the production of furniture, it is very important to grasp the moisture content of various types of wood. The moisture content of different woods is not the same, which also explains why some wood products such as wooden doors, wooden floors, wooden furniture, etc. will have cracking and deformation problems after they are sold.

1. Wood moisture content
Under normal conditions, wood and its products will have a certain amount of moisture. my country defines the percentage of the weight of the moisture in the wood to the weight of the wood after the absolute dryness as the moisture content of the wood.

The moisture content can be calculated based on the weight of the dry wood, and the calculated value is called the absolute moisture content, and is referred to as the moisture content (W, %) for short. Calculation formula: W=(Gs-Ggo)/ Ggo×100%. Among them: W——absolute moisture content of wood; Gs——wet wood weight; Ggoo——absolute dry wood weight.

2. Master the importance of wood moisture content
After the wood product is finished, the shape and material will not change. At this time, the key factors that determine the internal quality of the wood product are mainly the moisture content and drying stress of the wood. Manufacturing companies need to correctly grasp the moisture content of wood products. When the wood product reaches the equilibrium moisture content when it is used, the wood at this time is not easy to crack and deform.

3. Is the wood dry, the drier the better?
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 absorb moisture and shrink, otherwise it will absorb moisture and expand.

For example, the average annual equilibrium moisture content in Guangzhou is 15.1%, while that in Beijing is 11.4%. Wood dried to 11% is suitable for use in Beijing. It can be used in Guangzhou and will absorb moisture and swell and cause deformation. Therefore, wood drying should be appropriate, not as dry as possible. Different regions and different uses have different requirements for the moisture content of wood.

Fourth, the method of laboratory measurement of moisture content:
The methods of measuring the moisture content of wood include drying method, electrical measurement 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 to dry the wood moisture content test piece to dryness to measure its moisture content.

First, cut a representative moisture content test piece with a thickness of 10-12mm along the grain from the tested wood. The so-called representativeness is that the dryness and wetness of the test piece is consistent with the whole piece of wood, and there are no defects such as peeling, knots, decay, and moth eaten. Generally, it should be cut at a distance of 250~300mm from the end of the sawn timber. After scraping the moisture content test piece to clean the burrs and sawdust, immediately weigh it on a balance with an accuracy of 0.01g and a measuring range of not less than 200g, record the weight as G, and then place the test piece at a temperature of 103± Bake in a constant temperature oven at 2°C for about 6 hours, then take it out for weighing, make a record, and then put it back in the oven to continue drying. Then weigh it every 2h until the last two weighings remain unchanged, which is the absolute dry weight, which is recorded as Go. In this way, the moisture content can be calculated as follows: W=(G-Go)/ Go×100%

Because the moisture of the thin test piece is prone to change when exposed to the air, it should be weighed immediately after the test piece is intercepted or taken out of the oven.

Related reading: Wooden furniture moisture content, pay attention to the difference between north and south

The drying method is accurate and reliable to measure the moisture content of wood, and it is not limited by the range of moisture content. However, it takes a certain amount of time to intercept the sample, destroy the wood, and take a certain amount of time during the measurement.

The drying method is the basic method of measuring the moisture content of wood, and it is also a commonly used method. The above formula expresses the absolute moisture content, which is also commonly referred to as wood moisture content in wood processing.

5. Annual average of wood equilibrium moisture content in major cities in my country:
Annual average of wood equilibrium moisture content in major cities in my country

The equilibrium moisture content of wood in different parts of our country is different, so consumers should consider the different environment when buying solid wood furniture. They must not buy across borders in order to be cheap, otherwise it will happen that the southern wood is easy to crack when used in the north, and the northern wood is in the It is easy to swell when used in the south.