Microwave wood products drying equipment
Microwave wood products drying equipment several major features:
1) speed: microwave drying Because of its unique advantages, it is extremely fast drying. The actual situation from the dry wood point of view, the results show that: If you increase the microwave power, you must take the appropriate reasonable process. Otherwise, although its drying speed will be accelerated, but due to the sharp rise in temperature inside the wood, moisture vaporization, pressure surge, exceeding the allowable extent of wood fiber, causing cracking. Therefore, microwave drying of wood, the output power density increase is limited.
2) high efficiency: the use of "water rate" to assess the effectiveness of the drying efficiency. The so-called "water rate" is defined as 1 kilowatt of microwave power within 1 hour, to be dried in kilograms of water, in kilograms / kilowatt hour (kg / kwh).
High water rate, indicating the high efficiency of equipment. On the 4 kinds of tree timber, basically the same specifications in its assessment test. The results showed that the water rates of all species of wood were about 1kg / kwh or slightly exceeded. The same kind of wood in the thickness of different specifications, its water rate is also equal to about 1kg / kwh. The same kind of wood along the fiber length of different, the drying effect has obvious differences, with the fiber structure is relatively tight oak test comparison, the length of the short water rate is high, otherwise the water rate is low. It is well-known that heated wood is further evaporated as it gradually cools. So after the appropriate bake cooling, can improve the drying effect.
3) good quality: wood in the conventional drying process becomes deformed, cracking, is due to uneven wood fiber after shrinkage produced. In natural drying, on the one hand, the evaporation speed of the wood surface is far greater than the diffusion rate of the internal moisture, forming a wet condition on the surface. The drying of the surface shrinks the fibers and creates stress between the top and the bottom. On the one hand, the two ends of the wood along the fiber direction have much larger capillary pores than
other parts, so the shrinkage of the fiber greatly exceeds that of the rest, so the ends of the wood are practically not cracked and deformed in natural drying. Generally, the length of the crack In 10 to 30 cm, a serious piece of crack or a few pieces of broken board. At the same time pushing the wood in the drying field, after prolonged wind and rain repeated erosion and deterioration, causing many wood rotten, this deformation, cracking, rotten metamorphism have seriously affected the quality of the wood and caused a lot of scrapped. Dry and uniform, improve product quality, timber utilization can be increased by about 5%. Such as the surface will not compaction, improve toughness, will not crack, deformation, discoloration, correction of curvature, etc .;
4, when the microwave power density is too large, the internal vaporization of wood "pressure" exceeds the allowable limit of wood fiber, there will be the phenomenon of internal wood burst. This is the principle of microwave drying wood still need some time.
a) Saving Timber: Timber is a kind of national material. Saving timber not only has economic benefits, but also reduces deforestation and has significant environmental benefits. In natural drying, due to deformation, cracking, rotten deterioration of wood caused by very serious scrapped, the practice proved that the use of microwave drying, wood utilization increased by at least 5%, speeding up the use of wood cycle: As the natural drying of wood takes up to A year or even a few years, in order to maintain normal production must save a lot of wood for turnover, not only occupy a large venue but also often turn the sun. After the microwave drying, wet wood in time to get dry, the above phenomenon can be properly improved.
b) to kill wood borers: wood borers Most insects hidden habitat in the wood eggs into adults will destroy the appearance and value of furniture, wood in the microwave process, the internal eggs, larvae are also killed . According to the experiment, under the microwave energy of 2450MHz, if the temperature of the wood is 70 to 80 degrees, the eggs and larvae can all be killed in only 3 minutes.
In the microwave drying process, the situation is completely different, due to microwave drying has a strong permeability and selectivity, etc., in the drying process, the wood between the table, the ends and the middle of the fiber contraction is basically the same, so Cracking and deformation small. After the actual inspection, it is agreed that the quality of microwave drying wood is better than natural drying.
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