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Ovrum A.,Norsk Treteknisk Institutt NTI | Ovrum A.,Norwegian University of Life Sciences | Vestol G.I.,Norwegian University of Life Sciences | Hoibo O.A.,Norwegian University of Life Sciences
Scandinavian Journal of Forest Research | Year: 2011

When the grade is determined by the worst part of a board, the grade yield will decrease with increasing timber length. This length effect varies due to longitudinal variation in the grading features and their appearance on the sawn surface. In this study models identifying the length effect's dependence on site, stand, tree and log-level characteristics have been developed. The study comprised boards from 160 Norway spruce trees (Picea abies (L.) Karst.) sampled from six sites in Norway which were selected based on variation in the occurrence of ramicorn branches, forked trees and sinuosity of stems. The boards were visually graded according to appearance by Nordic Timber and strength was graded by INSTA 142. The negative effect of increasing length on grade yield was strongest at stump level and decreased upwards in the trees. The biggest trees within a stand were most affected by an increase in length. In addition to timber length, position of the board within the tree was the most important factor influencing grade yield. The variation in grade yield within stands was greater than between stands for this material. The models predicting grade probabilities seemed to fit within a 10% margin. © 2011 Taylor & Francis.

Steiner Y.,Norsk Treteknisk Institutt NTI | Vestol G.I.,Norwegian University of Life Sciences | Horn H.,Norsk Treteknisk Institutt NTI | Sandland K.M.,Norsk Treteknisk Institutt NTI
Wood Material Science and Engineering | Year: 2011

The relationship between fan speed and electrical energy consumption, and the price of energy, justify studies on the possibilities for reducing air velocity during the wood-drying process. In this study, effects of air velocity were examined to determine when and how much it can be reduced, without affecting the drying rate of the sawn timber. The first experiments were performed in a laboratory kiln, and 36 samples of 50×100 mm boards (2×log) of Norway spruce [Picea abies (L.) Karst.] were dried at 708C with varying air velocity. Results show that too early or too sharp a reduction in air velocity gives a reduced drying rate and a large variation in moisture content. The next step in the project was a full-scale industrial study in kilns at a Norwegian sawmill. To optimize air velocity conditions, batten spaces were sealed. This had no significant effect on air velocity in the kiln. A reduction in air velocity in the kiln to 60% frequency at 40% moisture content and to 40% frequency at 20% moisture content, without considerable changes in the drying schedule, resulted in an increase in final moisture content. © 2011 Taylor & Francis.

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