Why do some wooden doors, wooden floors, wooden furniture and other wood products will be sold after the cracking, deformation and other quality problems, how to reduce the loss of these problems to the wood industry?
This is related to the concept of a wood moisture content. A little understanding of the wood of the people will know that the wood moisture content in the appropriate value, the stability of wood products furniture has a great impact. Simply to say that wood floors, wooden doors and so on will crack, deformation. So for the wood enterprises, water control rate of wood is a big issue.
Where is all the water from the wood
Generally, there are three kinds of water in wood, one is the water in the cell gap and the cell gap, which is the water in the capillary, called free water. The second is the water absorbed by the cell wall, called adsorption water. The third is the water that forms the cell tissue, called the chemical water.
When the wet wood water evaporation, the first loss of free water, when the free water evaporation and adsorption of water is still in the saturated state of the water content, known as the fiber saturation point of water content.
The fiber saturation point is a turning point in the properties of wood, wood fiber saturation point, the intensity is constant and does not change with the change of moisture content. At the same time, there was no change in the volume of wood. When the moisture content is below the fiber saturation point, that is, the adsorption of water in the cell wall begins to evaporate, the strength increases with the decrease of the moisture content, and the phenomenon of dry shrinkage is obvious.The moisture content of different wood fiber saturation point is about 22%~33%.
How much moisture content of wood
When the wood products used to achieve the balance of moisture content, this time the wood is not easy to crack deformation.
Sales of wood products dealers, sales of the product should also be on the moisture content of the test, to master the quality of the sales of products. For the high quality of the procurement of wood products, with the continuous growth of professional knowledge, but also more and more attention to the moisture content of wood products. Foreign buyers in the past focused on this indicator, many do export products and semi-finished wood manufacturers have a deep understanding of this.
1、Wood dry, the more the better?
As we all know, not dried wood can not be used for production, because there will be a lot of uncertainty. So, wood enterprises will initially dry health balance of wood, wood is not so doing better?
First to understand a small concept: wood in a certain environment, after a long time, the moisture content will tend to a balance value, known as the environment of the equilibrium moisture content EMC.
Wood moisture content on the impact of the law is what kind of? When the moisture content of wood is higher than the equilibrium moisture content of the environment, the wood will shrink and the moisture will be expanded. For example, the annual average water content of Guangzhou region is 15.1%, but the Beijing area is 11.4%. Drying up to 11% of the wood used for Beijing is suitable and can be used for Guangzhou to swell and produce deformation. Therefore, the wood drying should be appropriate, not the more the better. The most critical is that the moisture content of wood must be in a relative equilibrium with the water content of the surrounding environment, the state of the wood is the most stable.
2、Wood equilibrium moisture content：
Wood in a certain state of air, the last to achieve the moisture absorption or desorption stable moisture content, called the balance of moisture content of wood (wood moisture stable state).
3、Annual average water content of main cities in china:
4、Method for measuring water content in laboratory:
Method for measuring the moisture content of wood drying method, electrometric method, distillation method, titration method and humidity method in the field of wood processing, usually by drying method.
Drying method is to test the moisture content of the wood to the whole dry to measure the moisture content of the method.
First, a typical water cut test piece with a thickness of 10~12mm is obtained from the measured wood. The so-called wetdry representative is the test piece and the whole wood is consistent, and without skin, knurr, rot, insects and other defects. In the general distance end 250~300mm interception of sawn timber. The moisture content of specimen scraped the burr and sawdust, immediately in the accuracy of 0.01g, the range of not less than 200g on the weighing scales of its weight, the weight will be denoted as G, then the test piece into a temperature of 103 + 2 DEG C in baking oven is about 6h, and then remove the weighing, and for the record, and then put it back in the oven to dry. Then once every 2h weighing once, until the last two weighing the weight of the same, is the absolute dry weight, denoted as Go. In this way, the water content can be calculated by the formula: W= (G-Go) / Go * 100%
Because the thin specimen is exposed in the air and the water is easy to change, therefore, should pay attention to when measuring specimen after interception or remove the oven immediately after weighing, if not immediately weighed immediately with plastic bags, to prevent water evaporation.
The moisture content of wood measured by drying method is accurate and reliable, and it is not limited by the range of water cut. But when measuring the need to intercept the specimen, the destruction of wood, and the need for a certain time.
Drying method is the basic method of measuring moisture content of wood, and is the most common method. The absolute water content is the absolute water content of the wood, and it is also known as the moisture content of wood in wood processing.
Schedule: annual average water content in main cities of China
The humidity and temperature of the various regions in the world have relatively stable in different seasons. The wood is in the relative humidity and temperature for a long time, and its moisture content will reach a relatively constant. At this time the moisture content is known as the balance of water content (for example, the annual water content of the Shanghai region of 4.6%).
The equilibrium moisture content of wood varies with the changes of temperature and humidity in the environment. This produces the phenomenon of wet expansion and shrinkage of wood, which is a special physical phenomenon of wood.
Wood is a kind of anisotropic body. In actual use, the moisture content of the wood is below the saturation point of the fiber, so the gain and loss of water is mainly absorbed by the cell wall. Most of the wood cell is longitudinal growth, its expansion and cell wall are perpendicular to the direction, such as a floor, we can find that the longitudinal are generally not what expansion, while the width direction of the inflation rate is generally 3% to 6% (mean moisture content of wood moisture content in the fiber saturation point the following changes).