Wood drying is a process of reducing the moisture content from the wood before using it. Moisture content is reduced to be in equilibrium with the air where it’s been used. Normally wood is sawn before drying, but not every time.
Methods in Wood Drying Process
- Natural or air drying
- Artificial drying, which is nothing but kiln drying.
Air Drying
- Air drying is a process of exposing the wood to air to remove the moisture content. This method is the simplest one, and the drying process takes up to 6 to 12 months.
- The humidity and the temperature required for drying wood cannot be controlled.
- Normally, sawn wood are used in this process and the drying speed and quality depends on climatic conditions.
- All the sawn woods are arranged in the form of stack and this stack should be properly taken care to avoid any cracking, decay, splitting, warping of woods.
- The yard layout should be in such a way that the stack of woods gets maximum air.
- Stacking of woods is more important to get satisfactory result.
Two types of wood stacking are followed in air drying process: horizontal stacking, and vertical stacking. Horizontal stacking is the commonly followed method and suitable for all kinds of wood. Some techniques used in horizontal stacking are one in nine methods, close crib method, and open crib method. Vertical stacking is followed for woods that will discolor and mold after sawing.
Kiln Drying:
Kiln drying is a process of keeping wood in a closed chamber under controlled temperature, air circulation and relative humidity, which are conditioned at various stages for effective timber drying.
- The chamber is fitted with equipments to control relative humidity, temperature, and circulation of air through the wood stack.
- The kiln drying is better than air drying because the drying process is much faster, and more precise.
- Kiln drying process helps to dry wood in any desired conditions as one wish irrespective of climatic conditions.
- Time taken for drying wood is normally about 2 to 5 weeks. Industrial kiln are used to dry all commercial lumbers.
- There are numerous kilns that differ in construction, heating procedure, equipment, chamber design, and air circulation.
- In broad classification, there are two kinds of kilns: progressive kiln, and compartment kiln.
- In progressive kilns, the kilns are in the form of long tunnel and the timber moves continuously as it dries.
- In compartment kilns, the timber does not move and it is most commonly used in most of the timber companies.
- There are different types of kiln drying: solar kiln, conventional kiln, vacuum kiln, and dehumidification kiln.
