Comparison of drying kinetics and quality of beechwood (Fagus sylvatica L.) dried by various techniques

Značilna zgradba bukovine ima velik vpliv tudi na njene sušilne karakteristike, ki pogosto izstopajo kot neugodne napake. Z vidika hitrosti sušenja in doseganja ustrezne kakovosti smo primerjali štiri tehnike sušenja: na prostem, komorsko, vakuumsko in visokofrekvenčno. Bukove elemente debeline 32 mm smo sušili iz svežega stanja (uz = 78 %) do ciljne vlažnosti 10 %. Pred sušenjem, med njim in po njem smo določali hitrost sušenja in ocenjevali kakovost z določanjem vlažnostnega gradienta, zaskorjenja in vidnih napak. Najhitrejše je bilo visokofrekvenčno sušenje, vendar omejeno le na sušenje pod točko nasičenja celičnih sten, nekoliko počasnejše je bilo vakuumsko in nato komorsko sušenje. Najdaljše je bilo sušenje na prostem, vendar s še vedno sprejemljivo hitrostjo v začetnih fazah sušenja. Najvišja kakovost sušenja z vidika vlažnostnega gradienta, zaskorjenja in vidnih napak je bila dosežena z vakuumskim postopkom, ki pa tudi ni bilo najugodnejše pri sušenju svežega lesa, kar kaže, da bi optimalne rezultate dosegli s kombinacijo več različnih postopkov.Specific structure of European beech wood (Fagus sylvatica L.) has great influence on its drying characteristics, which are often negatively expressed as various drying defects. Four drying techniques, i.e. controlled air drying,normal temperature kiln drying, vacuum drying and drying with high frequency (HF) were compared to achieve the best technique. Tangential oriented 32 mm thick, 80 mm wide and 800 mm long beech wood samples were dried from green condition (uz = 78 %) to the final moisture content of 10 %. During drying processes wood quality was evaluated regarding to drying rate, time of drying, moisture content (MC) gradient, casehardening and occurrence of drying defects. Drying with the HF was the fastest, followed by vacuum drying and kiln drying. In air drying wood kept good quality, with the lowest MC gradient, however too high MC of wood was achieved. Good final drying quality, concerning casehardening and visual appearance, was achieved at vacuum drying process. Probably the combination of different drying techniquesw ill give the best results