Veneer drying methods
At present, there are two main methods for the veneer drying process: sun drying and industrial drying process. The Sun drying refers to the veneer sheets under the sand and manually operated by workers, while the industrial drying processes by equipment. The industrial drying is more efficient and productive than sun drying. And the industrial drying include screen dryers and screen dryers.
For the industrial drying, the veneer sheets are transported in different ways, they are transported either between screens or rotating roller. The most advanced drying processes are fully automated from the sheet feeding to grading and stacking. The most important factors in the automatic drying process is strict conditions control according to different parameters based on specific veneer properties.
The veneer drying process can be described by aims of veneer drying, described as following:
1.Removing waters inside the veneer and decreasing moisture content to a suitable level for efficient gluing and pressing process.
2.Preventing over-drying, but still establishing high production volume and high-value yield.
3.Reducing energy consumption which will establish a high-efficiency ration.
Efficient drying process
There are some resources need for the efficient process. Information includes actual conditions of the veneers to be dried, conditions inside the dryer, and drying result. The technology must have numerous control function and automatic adjustment of the process. The workers who operate the veneer dryers must be well trained to understand the full process, he also should be able to adjust parameters in different conditions. The process should follow the parameters for different wood species.And many of these steps are handled optimally by the line itself when using automated drying process.
In order to ensure the right and desired moisture content in the veneers, the key is controlled and optimized industrial drying.
Before fed into the veneer dryers, the veneers should be separated into “Low M.C.” and “High M.C” by different moisture content inside. This can help the veneers reached to the target moisture content with highest efficiency and highest veneer quality.
The green veneer sheets are moisture classified for the efficient drying process to avoid both extensive over-drying of veneer sheets and unnecessary energy consumption, as described in figure 2.
|Feature||No moisture classification||Moisture classification (50/50 % of sheets)|
|Moisture class||Mixed class||Low class||High class|
|Min Moisture content (M.C.)||40%||40%||76%|
|Max Moisture content (M.C.)||120%||76%||120%|
|Average Moisture content (M.C.)||76%||65%||95%|
|Drying time||4 minutes||3 minutes||4 minutes|
|Improved total drying time||3.5 min (-12.5%)|
Table 1. Example calculation of drying efficiency in case of green veneer sheet moisture classification in two classes evenly, both groups 50% of sheets.
It also can save the energy consumption and improve the production efficiency, for the classification of original veneers shortens drying time by 12.5% from 4 minutes to 3.5 minutes.
Conditions inside of the dryers are also a crucial feature for the high-efficiency drying process which leads to high quality veneers with low energy consumption. Practice and wood physiology prove that the highest temperature and humidity inside the dryer establishes lowest energy consumption and the highest quality of veneers, as high humidity transfers heat energy most efficiently.