Timber Humidification & Timber Humidifiers
During its growth, a tree depends on the rapid transfer of water through its internal system to take in nutri-ents from its roots and spread them to the tips of its leaves. Wood is by nature hygroscopic - that is it is affected by the moisture content of the atmosphere surrounding it. If its environment is too wet the timber will swell. If it is too dry it will warp. Although modern preparation techniques reduce this hygroscopic characteristic it is never totally eliminated, even after processing.
The effects of a dry atmosphere on wood include the joints at the corners of frames becoming loose, delicate parts of furniture and internal woodwork beginning to warp, middle layers and edging (venners) showing through and ground surfaces becoming uneven and developing surface cracks.
Maintaining the correct humidity can prevent these problems from occurring after the timber has been processed as well as suppressing dust and maintaining a healthy environment at the saw mill during manufacturing.
Timber Humidity Issues
If wood is not exposed to direct sources of moisture (e.g.rain) its water content corresponds to the humidity of the ambient air, For the purposes of manufacture, the ideal water content of wood is fron 9 to 12%. These values result automatically at a humidity level of between 50 and 60% relative humidity, producing humidity equilibrium between the air and the wood.
Every room in which dried veneers are stored or worked should receive constant artificial humidification, at least in winter, to counteract any fluctuations in humidity level and avoid expensive damage.
The changes a piece of timber undergoes when it is exposed to damp or dry air
are not directionally uniform as wood swells more tangentially than radially. Pine for instance has a ratio of about 2:1 tangentially to radial. The dimensional changes and the more severe warping of the sapwood as compared with the heartwood cause deformation and often cracking when the water content is allowed to change.
This dust suppression application is a major reason why the most popular form of humidifier in the timber industry is a cold water spray system. The other main advantage of using this type of humidifier is that is a low energy unit with a fraction of the running costs of other types of humidifiers that generate and ralease steam into an atmosphere.