Abstract
European spruce (Picea abies Karst.) belongs to the most easily dried wood species, but nevertheless cracking and warping often reduce the quality of dried sawnwood. Larger surface and end cracking was noticed at industrial drying practice in cold winter season, especially in using fast drying schedules. For the assessment of factors infl uencing the quality of dried wood some drying runs with varying drying conditions were carried out in an experimental kiln dryer. The quality of sawnwood was evaluated on green material using standard procedures and compared with the quality at the end of drying processes. Drying of spruce sawnwood at sharper drying conditions was more risky, resulting in a larger number of cracks as well as larger fi nal MC distribution, larger MC gradients and casehardening. Additionally, signifi cant correlation was confi rmed between the quality of dried wood and input quality of fresh material. More downgrading after the drying was observed in case of initially low graded material.
Highlights
The slowest drying, taking 56 h, was achieved at drying under mild drying conditions, which is generally ascribed to high equilibrium moisture content (EMC) (Fig. 1)
Sharper drying condition attained with decreasing of EMC significantly increased the drying rate in drying procedure 2
The fastest drying was attained by additional decrease of EMC in the third run, with EMC below 7%, while the average MC was still above fibre saturation
Summary
To be competitive in wooden industry and in the open market, the quality of our products and processes must be well defined. Wood quality depends on many different factors, related to wood material itself and to factors within industrial production. The definition of round and sawn wood quality includes such properties as knots, annual ring width, fibre orientation and resin pockets, together with defects caused by insects and fungi (EN 1310, EN 1311). Wood quality assessment is necessary at several production levels for increasing the utilization rate of material and shortening of processing. For maintaining the wood quality through its processing, it is necessary to apply successful production methods. Several standards for the assessment of drying quality have been recently prepared, defining measuring techniques (EN 13183-1, EN 131832, EN 13183-3), sampling requirements and criteria of drying quality (EN 14298, ENV 14464)
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