DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 9-10/1955 str. 28 <-- 28 --> PDF |
koja ima manji početni sadržaj vode od točke zasićenosti, dok hrastovina jako puca na površini već kod 110° C. Drvo se suši kod temperature iznad 100° C ili pregrijanom parom ili mješavinom pregrijane pare i uzduha uz reverzibilnu cirkulaciju. Brzina cirkulacije sredstva za sušenje iznosi 1,5 do 2,5 m/s. Smjer cirkulacije se mijenja automatski u kraćim vremenskim intervalima, kod nekih sušionica svakih 15 minuta. Kod sušenja iznad 100° C prirodna boja na površini drveta postaje tamnija. Promjena boje zavisi o stupnju zasićenosti sredstva za sušenje. Ona ne smeta u nekim slučajevima, a tamo gdje smeta može se ukloniti blanjanjem. Sušionice za sušenje kod visoke temperature izrađuju se iz metala i to iz željeza ili aluminiuma i prenosive su. Sušionice se griju električnom strujom, vodenom parom, toplom vodom ili uljem. Postupak se može automatizirati, a to pojednostavljuje sušenje. Potrošnja energije manja je kod sušenja prirodno suhog četinjavog drveta visokom temperaturom za cea 14% nego kod sušenja vlažnim uzduhom. Do danas nije riješeno pitanje sušenja sirovog drveta listača kod visoke temperature, koje imaju veći početni sadržaj vode od točke zasićenosti, a nisu pronađeni ni materijali za gradnju sušionice, koji ne podliježu koroziji kao ni zaštitni premazi, koji bi sigurno štitili od korozije. CONCLUSION In summing up several investigations carried out so far on high-temperature drying of wood, the author draws the following conclusions: Green and air-dry wood of conifers as well as the wood of deciduous species possessing an initial moisture content below the fibre-saturation point (30 per cent) can be seasoned without considerable defects at temperatures above 100° C much faster than by the orthodox method using humid air at temperatures below 100° C. Permissible temperatures for green coniferous wood is 132° C, for air- dry coniferous wood up to 20 mm. thickness 125° C, 20—30 mm. thickness 120° C and 30—40 mm. thickness 115° C. Permissible temperature for air- dry birch wood up to 45 mm. thickness is 127° C, and for teak wood up to 50 mm. theickness 122° C. Beech wood possessing the initial moisture content below saturation point can be seassoned at temperatures from 100 to 130° C, while oak wood shows considerable surface checking already at 110° C. At temperatures over 100° C timber is dried by means of superheated steam or with mixture of superheated steam and Mr under reversible circulation. The circulation speed of drying agent is 1,5—2,5 m/sec. The direction of circulation changes automatically at short intervals, and in several kilns every 15 minutes. When drying at temperatures over 100´- C the natural colour of wood surface becomes darker. The alteration of colour depends upon the saturation degree of the drying medium. This is not troublesome in some cases, but when it is, it can be removed by planing. Kilns for drying at temperatures above 100 ° C are manufactured of metal, i e. of iron or aluminium and are transportable. Kilns are heated by means of electricity, water vapour, hot water or oil. The process of drying can be simplified by the application of automatic control. The consumption of energy at high-temperature of drying of conifers wood is by ca 14 per cent lower than the orthodox humid air method. |