Kiln-dried wood

Kiln-dried wood, without hygroscopic moisture,. 

From Table 3.2-2 it can been seen that the emissions from kiln-dried wood species are small. The critical point for wooden floorings is the surface treatment. From Tables 3.2-3 to 3.2-5 it can be seen that emissions, especially from factory-varnished and oil-treated parquets, are low, but wax treatment may bring an emission problem when solvents are used in applying the product. The solvents are often turpentine- or mineral oil-based. When using heat application the problem should be negligible. 

All the properties of wood depend to some extent on the amount of water it contains. Green wood can contain up to 50% water. Seasoning (for 2 to 10 years) or kiln drying (for a few days) reduces this to around 14%. The wood shrinks, and its modulus and... 

Air-dried wood, with twenty par cent, of hygroscopic moisture, Kiln-dried ten ... 

Kiln-drying does not depend on the weather and, in addition, due to the high temperature used, the wood is essentially sterilized. However, if kiln drying is delayed mould and sapstain fungi may discolor the wood. 

Gerhards (57) reviewed the results of 12 separate studies on strength properties of fire-retardant-treated wood conducted at the FPL and other laboratories. He concluded that modulus of rupture (MOR) is consistently lower and modulus of elasticity (MOE) and work to maximum load are generally lower for fire-retardant-treated wood than for untreated wood if fire-retardant treatment is followed by kiln drying. The effect may be less or negligible if the fire-retardant-treated wood is air dried instead of kiln dried. The most significant loss was in work to maximum load, a measure of shock resistance or brashness, which averaged 34 percent reduction. 

Masson, E., Baumes, R., Moutounet, M., and Puech, J. L. (2000). The effect of kiln drying on the levels of ellagitannins and volatile compounds of European oak (Quercus petraea Liebl.) stave wood. Am. ]. Enol. Vitic. 51, 201-214. 

Swedish Matches are made in Sweden almost exclusively of white poplar wood, it being the cheapest. Blocks of the length of the match are cut by machinery from the round logs and splintered, the splints kiln-dried and ooated with paraffine. The end to be covered with the inflammable compound is dipped in a solution of paraffine in benaine, when they are again dried. They are then dipped into the inflammable compound, which should... 

For barrel manufacturing, in its turn, the wood has to undergo a series of preliminary processing steps. First of all, the wood for the staves used to make the barrels has to be dried to decrease the moisture content of the newly cut wood. Traditionally, drying took place outdoors in the open air for at least three years, but now to save time artificial kiln drying is commonplace, or a combination of the two may be employed. 

The nature of the carbonisation process is such that the charcoal removed from a kiln weighs a lot less than the original wood charge. For kilns of the earthmound type, charcoal yields are around 23% to 27% (based on the original mass of oven-dry wood), or as low as 13% when based on the original air-dried wood mass [7] [8]. These values are well below the theoretically attainable maximum of44-55% [9],... 

The wood component likely to be of greatest interest to charcoal producers is water. Freshly cut wood can have a moisture content in excess of 50% and even air-dried wood has an equilibrium moisture content of 10 to 15%. In kilns, the heat required to drive off this moisture comes from the burning of a fraction of the wood charge. It follows that the greater the wood moisture content, the more wood has to be burnt and the lower is the overall charcoal yield. The longer drying time will also increase the... 

When fresh-cut wood is kiln-dried immediately, the living cells of the sapwood are killed by the heat and the reserve foods are... 

Two mechanisms have been identified. Most of the so-called chemical stains result from oxidation of certain wood extractives by air during air seasoning or kiln drying. Colors observed include shades of brown, blue, green, yellow, and red. Species include both hardwoods (oak, birch, maple, alder, basswood, gum, etc.) and softwoods (eastern and western pines, hemlock). 

Temperature influences the rate of drying in a number of ways. The principal reason for kiln drying at high temperatures is to increase the rate of moisture transfer to the wood surface. Raising the temperature dramatically enhances the rate of diffusion of water molecules across cell walls. The rate of diffusion increases with temperature at approximately the same rate, as does the saturated vapour pressure (Table 8.1 Figure 8.9b). 

Kiln-drying is essential if drying to low moisture contents (<15-18%). Many markets require wood dried to 12% and as low as 6%. 

Case hardening only becomes obvious when wood is recut or when more material is dressed off one face than the other. When case hardened boards are ripped the two halves crook or bow and pinch the saw. The distortion is towards the saw cut because the surface zones of the board are in compression while the centre of the board is under tension. An edge groove, for tongue and grooving, will pinch too. Similarly a board that is machined more heavily on one face will bow towards that face. Kiln-dried lumber ought to be dimensionally stable, and such distortion on processing is undesirable. 

As a rule, wood should be dried to its fiber saturation point or below before preservative treatment. Kiln-drying is eommon for dimension lumber, but the method of drying varies with elimate and eapital resourees. For large timbers and railroad ties air-drying is used, despite the inereased time required. However, in some elimates it is diffieult to air-dry material before it begins to suffer attaek by stain fimgi or even deeay fungi, and alternative approaehes must be eonsidered. 

---