Drying timber conditioning

Case hardening is one condition that the kiln operator prefers to live with and cure rather than prevent. It is not economic to dry timber too slowly. In practice the aim is to dry lumber as fast as one dare without getting excessive checking and to... 

Lead is relatively easily corroded where acetic acid fumes are present and under such conditions it either should not be used or should be efficiently protected. Generally, any contact between lead and organic material containing or developing acids will cause corrosion for instance, unseasoned wood may be detrimental. Trouble from this cause may be prevented by using well-seasoned timber, by maintaining dry conditions, or by separating the lead from the timber by bitumen felt or paint. Lead is also subject to attack by lime and particularly by Portland cement, mortar and concrete, but can be protected by a heavy coat of bitumen. A lead damp-proof course laid without protection in the mortar joint of a brick wall may become severely corroded, especially where the brickwork is in an exposed condition and is excessively damp. 

Zinc in contact with wood Zinc is not generally affected by contact with seasoned wood, but oak and, more particularly, western red cedar can prove corrosive, and waters from these timbers should not drain onto zinc surfaces. Exudations from knots in unseasoned soft woods can also affect zinc while the timber is drying out. Care should be exercised when using zinc or galvanised steel in contact with preservative or fire-retardant-treated timber. Solvent-based preservatives are normally not corrosive to zinc but water-based preservatives, such as salt formulated copper-chrome-arsenic (CCA), can accelerate the rate of corrosion of zinc under moist conditions. Such preservatives are formulated from copper sulphate and sodium dichromate and when the copper chromium and arsenic are absorbed into the timber sodium sulphate remains free and under moist conditions provides an electrolyte for corrosion of the zinc. Flame retardants are frequently based on halogens which are hygroscopic and can be aggressive to zinc (see also Section 18.10). 

Tekmaheat Oy manufacture three kiln systems a compact chamber of 15-25m per batch, having an annual production capability of 1600-3000 m a drive-through chamber having a volume of 40-60 m, with an annual capacity of 5000-10 000 m and a multi-stage production line, in which the timber is pre-heated, dried, heat-treated and conditioned in a continuous throughput process, which has a capacity of 30 000-50 000 m per annum. 

Often the OEM coatings depend on the nature and condition of the substrate to which paint is applied application methods and conditions drying time required and decorative and protective requirements. The substrate most commonly coated with industrial coatings are iron and steel, but also include other metals such as aluminum and its alloys, zinc-coated steel, brass, bronze, copper, and lead. Nonmetalhc substrates include timber and timber products, concrete, cement, glass, ceramics, fabric, paper, leather, and a wide range of different plastic materials. Consequently, industrial coatings are usually formulated for use on either a specific substrate or a group of substrates. 

If wood is conditioned at 20°C and 65% relative humidity the sapwood of most timbers will equilibrate to about 12% moisture content. This corresponds to the typical moisture content of lumber in an unheated building in many temperate regions. There are exceptions. Nothofagus fusca, one of the Southern Beeches, would dry to 9.5% or so under these conditions, so drying to 12% would be inadequate (Harris, 1961). Medium density fibreboard and particleboard also equilibrate at a lower moisture content of about 8-9%. For this reason Hoadley (1979) observed that it is more logical that wood products be dried to a specified relative humidity than to a specified moisture content (Table 4.1). 

Vinden P and Torgnikov G (2002) Microwave conditioning of woodfor combined drying and preservative treatment. Timber Preservation 2002 technology and product opportunities to improve performance. Forest Industry Engineering Association, Rotorua, New Zealand, 7 p... 

Conditions were too dry in Chaco Canyon for trees to grow to any size. Today pine, fir, and spruce grow only at higher elevation in the mountains around the site (Fig. 4.21). Comparison of strontium isotopes in the soils from the mountain area to the south and west of Pueblo Bonito with the timber at the site provided a good match (Fig. 4.22). These areas (Chuska and San Mateo), more than 80 km (50 miles) to the west, were the source of the wood beams at Chaco Canyon (Fig. 4.21). 

Desiccation. The evaporation or drying off of the aqueous portion of solid bodies. Plants and chemical preparations are deprived of their humidity by exposure to the sun, a current of dry air, an atmosphere rendered artificially dry by sulphuric acid, or by the direct application of heat by means of a water-bath, a sand-bath, or a common fire. Planks and timber arc now seasoned, on the large scale, in this way, by which a condition may bo attained in 2 or 3 days, which, on the old system, took as many years to produce. 

A damp condition of the wood is probably the most favorable to decay. Wood can be either so wet or bo dry that the fungi can not live in it. When submerged in water it haB been known to last hundreds of years, and in perfectly dry situations it will often laBt indefinitely. Wood in contact with damp ground usually contains the right amount of moisture for the development of decay. Also, where timber is in contact with wood or other material, water frequently collects in the joints and keeps the wood moist for long periods of time, thus favoring decay at these points. ... 

Moisture Content. In a specific circumstance (a treatment problem of a group of oak timbers), the moisture content and the amount of internal sound wood core were used instead of chemical analyses to assess degradation (6). The wood condition has been classified as follows Class I, the most deteriorated wood, contains over 400% water ([weight of water] / [oven-dry weight of wood] X 100) and virtually no core Class II is 185-400% water, with a core present and Class III is less than 185% water, with only the surface degraded. The analyses included moisture contents and the pin test to determine the extent of sound wood. 

Savory (82) reported that soft-rot attack could occur at quite low moisture contents, as well as under waterlogged conditions. He stated that the mi-croftingi can attack wood which is too wet or too dry for Basidiomycete decay. He also reported severe soft rot in beech strips exposed at a constant relative humidity of 90%, corresponding to an equilibrium moisture content of 20-21%. Apparently it is a misconception that soft rot only occurs in very wet wood. Kirk and Cowling (9) state, for example, that only water-soaked timber is attacked by soft rot. In fact, soft rot may occur over a wide range of moisture conditions, from quite dry to fully waterlogged wood. 

These wooden artifacts, such as digging implements and parts of old pig fences or house timbers, were recovered from the Papua New Guinea Highlands swamps in an excellent condition, with clear surface marks of their means of fabrication by stone axes. The choice of freeze-drying for this material in preference to the indifferent results expected from stewing the artifacts in cauldrons of hot water-soluble wax seemed reasonable at the time. The now-familiar response in wood to attempts at direct vacuum freeze-... 

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