Passed the ISO9001 quality system certification and the establishment of industrial drying industry alliance standards under the guidance of the Chinese Standardization Research Institute.
- May 06, 2019 -
Microwave drying of wood has two processes. One is the same process as the conventional drying of wood; the other is the unique advantage, that is, by means of the penetration of microwave energy, the moisture inside the wood is rapidly heated and vaporized, forming a strong external diffusion-quot; pressure-quot; so that the moisture inside the wood diffuses to the surface very quickly. It has been proved that in microwave drying, the speed of moisture diffusion from wood interior is much faster than that of water evaporation from wood surface. Therefore, there is no such phenomenon as the hardening of wood surface in natural drying and hot air drying, and its effect on water diffusion outward. Because microwave drying of wood has such a dual process of water displacement, and there are no surface hardening defects, so the drying speed is very fast. In contrast, conventional drying takes 25 days to a month, while microwave drying takes only 10 minutes to dozens of minutes. Because of the special principle of microwave drying, the results of microwave drying are also different. This is: whether the moisture along the cross-section of wood is exactly the same or has a certain gradient, the results of microwave drying show that the moisture near the surface of wood is the largest, while the center is the smallest. This is also advantageous in practical application. The results show that when the microwave power is about 60 kW, and the drying time is only 10 minutes to 26 minutes, the moisture content of the raw material can be dried from 35-40% to 20% from 8 mm thick veneer to 50 mm thick square without causing drying defects. If the microwave power is increased, the appropriate reasonable technology must be adopted. Otherwise, the drying speed will be accelerated, but the cracking will be caused by the sharp rise of temperature, vaporization of water and the sharp increase of air pressure in wood, which exceed the allowable level of wood fiber. Therefore, the increase of output power density of microwave drying wood is limited.p>1) Fast drying speed: Microwave drying is very fast because of its unique advantages.
2) High efficiency: We use & quot; water extraction rate & quot; this index to evaluate drying efficiency. The so-called & quot; water extraction rate & quot; is defined as a kilowatt of microwave power in an hour, so that the number of kilograms of dried matter lost water, in kilograms / kilowatt hours (kg / kwh). The high water extraction rate indicates the high efficiency of the equipment. In this paper, four kinds of tree species were tested under the same specifications. The results showed that the water extraction rate of all kinds of wood species was about 1 kg/kwh or slightly higher. When the thickness and specifications of the same kind of wood are different, the water extraction rate is about 1 kg/kwh. When the length of the same kind of wood along the direction of fiber is different, the drying effect is obviously different. We use oak wood with close fiber structure to test and compare, the water extraction rate is higher when the length is short, and vice versa, the water extraction rate is lower. It is well known that the moisture in the heated wood will evaporate further as the cooling process proceeds. So proper cooling after drying can improve the drying effect.
3) Good quality: The deformation and cracking of wood during conventional drying are due to the uneven shrinkage of wood fibers after water loss. In natural drying, on the one hand, because the evaporation rate on the surface of wood is much faster than the diffusivity of internal moisture, the condition of surface drying and internal wetness is formed. The drying of the surface makes the fibers shrink and produces stress between the surface and the interior. On the one hand, the fibre capillary holes at both ends of wood along the direction of fibers are much larger than other parts, so the shrinkage of fibers is much larger than the other parts, so in fact, there are hardly any non-cracking and deformation at both ends of wood in natural drying. Generally, the length of cracks varies from 10 cm to 30 cm, and serious plate cracking or several pieces of broken board. At the same time, wood is pushed on the drying ground, after repeated erosion and deterioration of wind, sun and rain for a long time, causing many wood mildew. This deformation, cracking, mildew and deterioration have seriously affected the quality of wood and caused a lot of scrap. In microwave drying process, the situation is totally different. Because of the strong permeability and selectivity of microwave drying, the shrinkage of the fibers between the surface and the interior of the board is basically the same, so the cracking and deformation are small. Through practical investigation, it is agreed that the wood quality of microwave drying is better than that of natural drying.
It should be pointed out again that when the microwave power density is too high, wood internal vaporization-quot; pressure-quot; exceeding the allowable limit of wood fiber, wood internal cracking will also occur. This is why microwave drying of wood still requires a certain amount of time.
4) Saving wood: Wood is a kind of national material. Saving wood not only has economic benefits, but also can reduce forest harvesting and has significant environmental benefits. In natural drying, wood scrap caused by deformation, cracking and mildew deterioration is quite serious. Practice has proved that the utilization rate of wood can be increased by at least 5% by microwave drying, which speeds up the use cycle of wood. Because natural drying of wood takes as long as one year or even several years, in order to maintain normal production, a large number of wood must be stored for turnover, not only accounting for 5%. It uses a lot of space and often needs to be exposed to the sun. After microwave drying, wet wood can be dried in time, and the above phenomena can be properly improved.
5) Kill wood borers: Most of the eggs of wood borers live in wood, and when they become adults, they will destroy the appearance and use value of furniture. In the process of microwave, the internal eggs and larvae of wood borers are also killed at the same time. According to the experiment, under the action of 2450 MHz microwave energy, if the temperature of wood is between 70 and 80 degrees, it takes only 3 minutes to kill all the eggs and larvae.microwave wood dryer process advantages summary:
1, short time, fast speed, continuous production;
2, uniform and thorough drying, improve product quality, wood utilization can be increased by about 5%. For example, the surface will not harden, improve toughness, will not crack, deformation, discoloration, correction curvature and so on;3, kill borers; 4, energy saving, high efficiency and environmental protection; 5, easy to control, easy to realize automatic production; 6, save land occupation and improve working conditions.
Label: Wood drying equipment, microwave wood dryer, price of wood microwave drying equipment
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