Drying the wood naturally.

Drying the wood is very important process in the woodworking industry. Every pieces of wood that is used in the woodworking industry should be quite dry and meet certain of standards moisture content. But the fact is, the drying process for the wood is a high energy consuming process.

The fact is every pieces of wet wood will always release its water content when it is placed in the open air. The process of water releasing from the wood will be occurred naturally until a balance between the wood moisture content and the relative humidity of the surrounding air is reached. With this principle then we can dry the wood without any energy consumption. We can maximize the drying speed by arrange the speed of the air convection to the wood pieces.  

Air drying.

 

This method refers to stack to the wood and expose outside and let the water from the timber to release to air. The efficiency of the drying process is controlled by proper arrangement of the stacking and the orientation of the wood stack.

• The proper stacking of the wood planks.

The lumber must be stacked properly to ensure there is good air flow in between the wood pieces. A concrete block can be used as the bottom of the wood pile, the wood planks can be laid as railway tracks orderly to the top. Use the stickers to support and separate each layer of wood. The similar size stickers are needed to get the well ordered wood stacking. The sticker arranged aligned one above the other and placed at a distance 36" or less to avoid the wood warping.  The edge of the wood planks should be based on the sticker. A roof to protect the wood from rain and direct sunlight can be directly placed on the pyre by using big blocks. The roof can be tilted to support water precipitation. Finally, the load is required to hold the roof remains in place.

• The placement and lay out of the wood stack.

The wood stack must be placed on a dry surface such as concrete or asphalt where there is no stagnant water. Stack the wood on the black asphalt can significantly increase the rate of wood drying process compared to the bare soil. The grass or vegetable earth should not be chosen due to the high humidity of the grass that will affect the drying process. The shorter and smaller stack will increase the rate of drying process. The velocity of air flow will determine the drying rate, thus the wood should be stack in the open place, free from buildings, trees or other objects that could block the air flow.

Air circulation through the timber can be run by the natural convection. Hot and dry air would hold water from wood surfaces. As dry air moves over on the wood surface, the water will evaporate from the wood surface. Through the process of evaporation, the air became moist, cooler and thus heavier. The heavier air moves down to the bottom of the pile by the gravitation. If the air can move freely, then the cold air and moist air will soon be replaced with the hotter and drier form its surroundings. Therefore, the height of the base should be reasonably enough to allow enough space at the bottom to keep the drying process running well.

The final moisture content is determined by air temperature, relative humidity of the environment, and drying time. If a long time is used and the equilibrium time is fulfilled, then it will bring the moisture content of wood to a point of equilibrium with the relative humidity of the environment. Usually the wood moisture content from 20% to 30% will easily be achieved with this system.

the wood stacking in air drying 

(picture is from:http://owic.oregonstate.edu)

Drying Sheds.

When lot of wood is needed to be dried, then a drying shed can be built to do better control for the drying process. Drying shed can be made in a very simple construction with the same principle with the air drying. It is a warehouse or a roofed big building with floor of concrete or asphalt. The big room inside must be enough to stack the wood to facilitate the naturally drying as the air drying. The warehouse can be equipped with some fans to blow or suck the air in and out to the room. Warehouses can also be equipped with  portable walls that can be raised or lowered, opened or closed to maximize the air movement. The better adjusting to the air flow rate will make the drying process be more efficient.

Since no heat is added then, the final moisture content is determined by air temperature and relative humidity of the environment. As in the natural air drying, the moisture content of 20% to 30% is easy to be achieved.

The advantages of the naturally drying.

• The low costs of construction and operational.

The naturally of course will need less equipment compare with the machine drying. it utilize natural phenomena to let the wood drying.  The facilities needed are a place and support for laying and arranging wood, which of course is cheaper than a dry kiln machine. This facility does not need energy or heat that is needed in the machine oven. 

•  Less risk of wood damage caused by too quickly drying

The naturally drying means let the wood drying slowly and naturally. There is no too quickly drying that could damage the wood such as : wood crack, wood bending and swelling. 

• The final moisture content is accordance with the environmental conditions in the area.

The naturally drying process will stop when the wood mc is in equilibrium with the humidity of his environment. In this condition wood will stable, no shrinkage and movement will happen. If the wood is going to use the product in the same area, then product will be quite safe from the problem of wood movement because of the fluctuation of the MC.

The disadvantages of the naturally drying.

•  Long time drying process is needed.

The natural drying will take long time, especially when the weather and climate is not good for drying. In the dry air (low humidity), the drying process may run quite fast especially when thin board id used. But when the air is humid or wet, then the process of releasing water from the wood will be disrupted or even stop. It make the drying process will take long time and cannot be scheduled. 

• Increase the risk of fungal

When wood is wet, it is very susceptible to attack by fungi. The uncertainty of the drying process time will put the wood at a high risk of being attacked by fungus. It may create the blue stain on the wood that will reduces wood quality.

• The less control to the drying process.

The natural drying is high dependent to the climate and weather. The result and time process can't be controlled. Thee is no fix schedule when the wood will dry, or how long the process is needed. In the industry this situation is not accepted, then people develop the kiln drying machine. The kiln dry work to manipulate the drying process and control it according to the schedule.