Types of Lumber Drying

Posted by San Group on February 25th, 2021

In the woodworking industry, drying of Canada forest products is carried out both naturally (drying of the material under the influence of the atmosphere), and artificially using various technical means. The most popular methods are natural and chamber drying (for example, in the manufacture of edged boards). Let us analyze what the advantages and disadvantages of the most common methods of drying lumber have.  

Types of Lumber Drying

Natural drying method

The method used from time immemorial has not lost its relevance to this day due to its simplicity and cheapness. Drying takes place by natural evaporation processes under the influence of heat and air movement. The harvested lumber is folded under a canopy on special foundations, in which ventilation gaps are left. The canopy is installed to protect against precipitation and aggressive exposure to the sun, but in fact, drying takes place in the open air. 

Chamber (artificial) drying method

Convective drying chambers

Drying is carried out in chambers by heating the air and intensive circulation. Depending on the design of the chamber, circulation can be either natural or forced, using fans. Air heating is carried out by heaters, through which steam steam (steam-air chambers) or flue gases (gas chambers) are passed.

Vacuum drying chambers

It is carried out in chambers with complete air extraction - i.e. in a vacuum. The drying process is carried out at high pressure and low temperature (700 mm Hg/45C). Under the created conditions, moisture is absorbed by the outer layers of the wood from the deeper ones. Thus, internal stresses in the wood are removed and the likelihood of deformation and cracking is reduced at all levels. 

Contact (conductive) drying chambers

The method is based on the transfer of heat to wood through contact with heated surfaces. It is used in the production of thin and flat lumber, such as veneer, plywood, etc. During the drying process, lumber is clamped between metal plates heated to a temperature of 150 ° C. Removal of moisture is provided by blowing fans, the process is continuously monitored by automation systems. Heating in such installations is carried out by flue gases, steam or high frequency currents. 

Drying in the field of high frequency currents (HFC)

A distinctive feature of this method is that the heat necessary for the evaporation of moisture is not supplied from the outside, but is formed inside the lumber itself. During drying, the wood is located between metal plates, which are connected to the HDTV source. In this case, the most intense heating occurs from the inside, in the wettest layers, providing an intensive movement of moisture from the core to the surface.

Condensing drying chambers

Drying takes place in a chamber completely isolated from the environment. During drying, a stream of warm air is supplied to the lumber, where it is saturated with moisture that evaporates from the wood. Then the moist air enters the condensing unit. When the dew point is reached, the steam turns into water, that is, it condenses, flowing down the walls of the installation, after which it is discharged outside. An important feature of the process is that drying occurs at low temperature conditions (about 40C), which is due to the properties of freon. 

Conclusion

With all the variety of drying methods in woodworking industries, natural and convective methods remain the most popular. Such drying allows you to harvest lumber in large volumes at relatively low cost. Conductive, vacuum, condensation chambers are most efficiently used as an auxiliary option, when more delicate drying is required, or it is required to significantly speed up the process without losing quality.