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2. BACKGROUND 2.1. KILN DRYING Freshly cut wood always contains large amounts of water (expressed as % moisture content) which is above the fibre saturation point (FSP). The FSP is defined by Simpson (1997) as: "the moisture content at which the cell walls are saturated but no free water remains in the cell cavities" [known as lumens] and it is generally around 30%. Usually, end products should have 15% or less moisture content. The maximum moisture content is 19% for kiln dried dimension lumber. In the living tree, moisture content normally ranges between 50% and 200%. This percentage varies between species and it also depends on the position inside the log (Perre, 2001). This water causes problems in most wood applications if it is not removed (see following paragraph). However, it is important to remove water using proper drying procedures so as to avoid high occurrences of drying defects or excessive costs. In the past, the most common method to remove this water was natural air drying which is time- consuming and requires large areas for storage. Today, most wood is kiln dried (artificial drying) since this provides high quality material without the need for large land requirements and tying up valuable inventory over long periods of time. Kiln drying is an important operation for wood products companies whether they produce commodity lumber or value-added products. Wood is kiln dried in order to (Tsoumis, 1991): • minimize shape deformations and checking i.e., increase stability, • achieve better protection from fungal defects, • decrease shipping costs since water is removed and weight is reduced, • enhance the strength of the material, • improve chemical treatments such as penetration, painting, and finishing, • eliminate fungi and insects that may be present. 3PDF Image | KILN DRYING PROBLEMS AND ISSUES IN CANADA
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