Drying wood: reasons for defect
In this material, we want to focus on the challenges faced by lumber producers in using classical wood drying technology.
Taking care of the quality of the lumber starts before the drying process.
Unfortunately, classic wood drying technology cannot ensure that a future product is completely defective. Why does a defect occur? Because the drying process is not done properly. Wood is a material with hygroscopic properties that is able to absorb and release the moisture stored in it. And the percentage of moisture contained in the wood is large, and to ensure that the quality of the future woodwork is high, this moisture is removed by drying in drying chambers.
If the technology is not adhered to and the process occurs with violations, it leads to changes in the structure of the lumber its warping and violation of geometric dimensions. Later on, structural irregularities result in deep end fractures and deformations, which are caused by difficulties in removing moisture.
Therefore, it is important to follow one rule during the drying process - to reduce the humidity throughout the stack smoothly and uniformly. Neglecting this will result in financial losses and additional material due to the reduced yield percentage of good quality products.
Any breaches of technology should be considered as inefficient process management.
What types of rejects occur if the wood drying process is not followed?
Reasons for defect
Let's take a closer look at the reasons why a marriage occurs during drying. The wood is very interesting, "living" material and all changes in it are caused by a number of physical processes that cause internal stresses. Imagine that the fibres inside the wood are stretched, creating tension when moisture is carried over the log during drying. All defects are caused by heterogeneous moisture levels on the surface and inside the lumber, the higher the level, the higher the internal stresses.
But there are kinds of defects that appear before the drying process begins. They can be caused by wood-destroying fungi that develop on the surface of felled wood. To prevent the appearance and spread of fungi, you should avoid storing logs for a long time in high humidity. After sawing, lay the material on special pads and place it in an open area for natural drying.
Fungi can also occur in drying chambers. This occurs if errors are made in the design and construction of the drying chambers and if the drying technology is disrupted. In the case of stagnant air circulation zones, moulds appear in the wood. In order to get rid of the problem, the drying chamber design must provide for even circulation of the ventilation system through the stack of lumber. Before starting the drying process, pay attention to heating the loaded lumber, which will prevent its structure from being affected by phytopathogenic organisms. Properly calculate the thermal output of the chamber. It should be calculated at 5-6 kW per 1 cubic meter of lumber to be dried. Even a half-hour exposure of the material to temperatures around 60 degrees will kill most of the pathogenic fungi.
Types and causes of fractures
Materials made of wood are subject to large types of cracks and defects. They can occur both on the surface and inside the material, causing irreversible consequences.
End, surface and internal cracks appear in the lumber due to incorrect drying.
The ends evaporate moisture most intensely, which is why cracks appear on them most quickly. Rigid drying conditions and a rapid reduction in moisture cause internal stresses on the wood fibres to increase. And exceeding the limits of strength causes cracks to appear. First of all, small cracks appear, which continue to penetrate deep into the material if the drying parameters remain unchanged. Surface cracks appear under hard drying conditions that prevent moisture from reaching the top layer of the material and also continue to deepen.
Surface cracks mostly affect those boards that are in the middle of the cell. The number of cracks can be reduced by aligning the moisture level across the material.
Cracks inside the material are mainly formed already at the end of the drying process, at which point the stress inside the material is above its ultimate strength. Such cracks completely break the structure of the lumber and make it completely unusable. The hardwood species (oak or birch) are more susceptible to such cracks.
Long-term exposure to high temperatures and moisture causes the wood material cells to wrinkle and degrade further.
Wood wrinkles are caused by the destruction of wood cells. This defect can occur when drying certain types of wood, such as oak, ash, poplar, eucalyptus, etc., in the wood. Wood cells flattening is formed by prolonged exposure of raw wood to high temperature and humidity air.
The classic wood drying technology depends largely on the human factor. Incorrect laying of material, inattention to the drying process, technological errors in the design of the chamber, failure of the humidification system or incorrect setting of operating modes.
All this leads to the fact that you lose your money and sacrifice your reputation, and the quality of the material raises questions. We offer you an alternative - Agap Tech wood drying technology. With Agap Tech, the reject rate will not exceed 1%. We have created a fully automated wood drying process, which does not require highly qualified personnel to manage.
Drying chambers based on Agap Tech technology operate without a humidification system, and the wood drying process is carried out through rational use of fan modes and an efficient automation system designed specifically for drying chambers.
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