Solid wood furniture refers to pure solid wood furniture, that is, all materials are unprocessed natural materials, and furniture made of no man-made board is not used. Because there are no two exactly the same trees and two exactly the same materials, each product will have its unique characteristics.
The natural characteristics of wood, such as mineral lines, changes in color and texture, needle knots, resin bags, and other natural marks, all make furniture
more natural and aesthetic. At the same time, the quality of wood is also an important factor to determine the quality of solid wood furniture. What factors will affect the quality of wood?
1.Temperature is the main factor affecting the drying speed of wood. With the increase of temperature, the water pressure in wood increases, and the viscosity of liquid free water decreases, which is conducive to promoting the flow and diffusion of water in wood; At the same time, the moisture solubility of the drying medium is improved and the evaporation rate of water on the wood surface is accelerated. However, it should be noted that if the temperature is too high, it will cause wood cracking and deformation, and reduce mechanical strength and discoloration, which should be propel controlled.
2. Humidity relative humidity is an important factor affecting the drying speed of wood. When the temperature and air velocity are the same, the higher the relative humidity is, the greater the partial pressure of water vapor in the medium is, the less water on the wood surface is easy to evaporate into the medium, and the slower the drying speed.
When the relative humidity is low, the surface moisture evaporates quickly, the surface moisture content decreases, the moisture content gradient increases, the moisture diffusion increases, and the drying speed is fast. However, if the relative humidity is too low, it will cause cracking, honeycomb, and other drying defects, and even aggravate them.
3. Air circulation rate is another factor affecting wood drying rate. High-speed airflow can destroy the saturated vapor boundary layer on the wood surface, so as to improve the heat and mass transfer conditions between the medium and wood and speed up the drying speed.
For difficult to dry wood or when the moisture content of wood is low, the internal moisture movement of wood determines the drying speed; Increasing the flow rate of a large medium to accelerate the evaporation rate of surface water has no practical significance. On the contrary, it will increase the moisture content gradient and increase the risk of drying defects. Therefore, difficult to dry wood and does not need a large medium circulation speed.
The above three factors are external factors that can be artificially controlled. If properly controlled, the drying speed can be accelerated on the premise of ensuring the quality of wood drying.
For example, when drying coniferous wood or soft broad-leaved wood sheet, due to the easy movement of water in the wood, the dry bulb temperature can be appropriately increased, the medium humidity can be reduced, and the air circulation flow rate can be increased to speed up the drying speed;
However, when drying mahogany wood or thick board, lower temperature, higher humidity, and lower air circulation speed should be adopted to avoid drying defects.
4. Wood species and structural characteristics the wood of different species has different structures, and the size and number of pits and the size of micropores on the pit membrane are very different. Therefore, the difficulty of water moving along the above path is different, that is, wood species are the main internal factor affecting the drying speed.
Due to a large amount of filler in the ducts and pits and the small diameter of microscopes on the pit membrane, the drying speed of ring hole hard hardwood (such as acid branch wood) is significantly lower than that of loose hole hardwood; In the same tree species, with the increase of density, the water flow resistance in the large capillary increases, and the water diffusion path in the cell wall is prolonged, which is difficult to dry.
5. The conventional drying process of wood thickness can be approximately regarded as a one-dimensional heat and mass transfer process along the direction of wood thickness. With the increase of thickness, the heat and mass transfer retention distance becomes longer, the resistance increases, and the drying speed decreases significantly
6. Below the fiber saturation point of wood moisture content, with the decrease of moisture content, the transverse diffusion coefficient of absorbed water decreases, while the diffusion coefficient of water vapor in the cell cavity increases. Due to the small proportion of water vapor diffusion in the cell cavity during drying, the lower the moisture content, the longer the water diffusion path, so the lower the moisture content, the more difficult it is to dry.
7. There are more contents in the heartwood cells of hardwood and sapwood, and most of the pits in the heartwood of conifer are blocked, so the heartwood is more difficult to dry than sapwood.
8. The wood ray in the direction of wood texture is conducive to water conduction. The water conduction along the radial direction of wood is about 15% – 20% greater than that along the chord direction. Therefore, the drying speed of chord cut boards is usually faster than that of a radial cut board.
Although the internal causes cannot be controlled, as long as we make good use of drying equipment and technology according to the characteristics of wood, we can also improve the drying speed, reduce unnecessary losses and improve the drying effect on the premise of maintaining the wood properties.
