-The development of drying technology and equipment
Fresh-cut (green) wood contains a lot of moisture. Under natural placement, the moisture will continue to evaporate, resulting in defects such as shrinkage, cracking, bending deformation, mildew, etc., which seriously affect the quality of wood products. Therefore, wood must be dried and processed before being made into various wood products.
Wood drying is a complex process, and the process of treatment has a great impact on the quality of the final wood product. There are different drying methods for different wood species. But it is common sense that the correct technology and equipment can ultimately overcome the defects of wood drying, improve the mechanical strength of wood, and develop the final processing performance. It is an important technical measure to utilize wood resources and increase the value of wood, and it is also an indispensable primary process in the production of wood products.
And when you read this article, I think you have already realized the importance of wood drying, so the next thing I want to explain is how people are drying wood.
Air Drying
A long time ago, actually, it is since people begin to use wood, they begin to dry it by their ways, the drying method used then was called air drying, also called natural air drying. Logs are graded and sorted for the natural process of drying in the open air by stacking them with spacers between each. Logs are left to dry in the open or with cover overhead for a period of time, which can last for 8-16 months depending on the species. As time pass by, the moisture content in the wood adjusts to the environment it is in, which is usually 12%-15% MC.
However, nature is changeable. For example, sunny days and dry winds are beneficial to dryness, while thunderstorms on rainy days are completely the opposite. Some smart people begin to think about how to combine all the beneficial conditions and avoid adverse effects at the same time. The drying kiln appeared. People use different tools to create the best wood drying environment, such as fans to keep the air flowing, dehumidification to keep the air dry, and the boiler to keep the air hot, and this is referred to as kiln drying.
Kiln Drying
Kiln drying is a “human-forced” process, during which people placed wood into a kiln, and heat is applied(by boiler or electricity) by raising the temperature slowly. Because large fans circulate the heated air throughout the kiln， the moisture is forced out from the wood more rapidly, this help maintain a consistent drying rate in the logs. Pumps are used to remove the moisture-laden air from the kiln. This kind of drying can reach a result of 8%-10%MC within 6-8 weeks. The advantage seems to be obvious, but the speed brings more than convenience, it is found that when the wood dries too fast, due to uneven drying (the outside of larger diameter wood dries faster than the center), a large number of cracks appear, and some wood even cannot be reused, at this time some people began to emphasize that the wood can not dry quickly and return to air dry. But luckily, people did not blindly abandon this progress but started to think about the reasons for the problem, and then formed regulations or guidelines for kiln drying, kiln drying had become the common way slowly, in fact now wood drying is still under this process.
Although kiln drying has great advantages, as mentioned before, kiln drying is not simply heating the wood in the drying room. It has high process requirements for stacking and humidity adjustment. It is said that skilled workers are the best guarantee for kiln drying.
Mechanical drying
The update and iterations of the technology are getting faster and faster. When labor costs and land costs rise, people begin to use machinery for more accurate and efficient production, which also affects the wood drying industry. Some forward-looking companies have begun to use the latest technologies like high-frequency Drying, vacuum drying, infrared drying, etc., together with computer control to carry out a new technological revolution, we call this drying way mechanical drying, it is the most cutting edge method.
Mechanical drying covers all the advantages of kiln drying, and at the same time, with the help of computer-aiding-design, it is a step closer to the auto control system. Its requirements for workers are far lower than second-generation kiln drying. The combination of different drying technologies greatly improves the efficiency of energy utilization and ensures the high quality of wood drying. Mechanical drying has different advantages because of the different technologies it adopts. At present, the optimal combination is RVF technology which combines the advantages of high-frequency drying and vacuum drying, and Shuowei dryer is one of the best.
The work process of the Shuowei HF vacuum system
High-frequency waves can penetrate wood deeply and dry wood from core to wood surface wholly and uniformly from the ever beginning. Even thick wood can also be well heated. Meanwhile, under vacuum conditions, wood moisture can be boiled at 50-60 degrees and vaporize rapidly, which can save both time and energy. And low-temperature wood drying can guarantee wood quality to avoid crack problems. The vacuum system will suck wood moisture out due to pressure difference which double increases wood drying speed.
The result of the combination is that more than 50cm thick wood can be dried by shuowei high-frequency vacuum wood dryer machine with uniform moisture content within two weeks. Normally Drying time for one cycle: is 7-12 days
