Kinetika sušenja tujerodnih lesnih vrst ; Drying kinetics of alien wood species

Tujerodne drevesne vrste pri nas največkrat najdemo kot parkovna drevesa, večinoma so samostoječa z več gojitvenimi posegi človeka. Les teh dreves se po zgradbi razlikuje, zaradi pogostih poškodovanj pa so močno razširjene diskoloracije. Sušenje je pomemben postopek pred nadaljnjo predelavo lesa, zato smo v nalogi proučevali sušilne karakteristike amerikanskega javorja, divjega kostanja in robinije. Tri debeline (22 mm, 28 mm in 46 mm) vsake vrste smo sušili pri treh temperaturah (20 C, 40 C in 60 C) in z gravimetrično metodo spremljali potek sušenja. Iz posameznih sekcij sušilnih krivulj smo določili hitrost sušenja nad točko nasičenja celičnih sten in pod njo, polovične čase sušenja in difuzijske koeficiente. Izvedli smo še končno kontrolo kakovosti (povprečno vlažnost, vlažnostni gradient, zaskorjenje in vizualno oceno). Hitrosti sušenja so bile v prvi fazi med vrstami zelo variabilne, pomembnejše sušenje pod točko nasičenja celičnih sten pa je potrdilo pričakovanja ; difuzijski koeficienti so se z naraščajočo temperaturo povečevali in so bili pri gostejši robiniji v večini primerov manjši kot pri amerikanskem javorju in divjem kostanju. Podobne zakonitosti smo ugotovili tudi s polovičnimi časi uravnovešanja, kjer smo potrdili tudi daljše čase sušenja debelejših sortimentov. Kakovost osušenega lesa je bila dobra, opozoriti pa moramo na veliko nevarnost kolapsa pri amerikanskem javorju. ; Alien tree species are most often found in our country as park trees, and are mostly independent with several human cultivation interventions. The wood of these trees varies in structure, and discolourations is widespread due to frequent damage. Drying is an important process before further processing of wood, so we studied the drying characteristics of Box elder, Horse chestnut and Black locust. Three thicknesses (22 mm, 28 mm and 46 mm) of each species were dried at three temperatures (20 °C, 40 °C and 60 °C) and the drying process was monitored by the oven drying method. From the individual sections of the drying curves, the drying rate above and below the FSP, the half adjusting times and the diffusion coefficients were determined. We also performed the final quality control (average moisture content, moisture content gradient, case hardening and visual assessment). Drying rates were highly variable between species in the first phase, and more significant drying below the FSP confirmed expectations, as the diffusion coefficients increased with increasing temperature and were in most cases lower in denser Black locust than in Box elder and Horse chestnut. Similar regularities were also found with half adjusting times, where we also confirmed the longer drying times of thicker specimens. The quality of the dried wood was good, but we must point out the great danger of collapse in the Box elder.