Research On Drying Characteristics And Check Within White Birch Disks

The tree disk, which is cross cut from a log, is dried for Food pier, artifacts, LiMu land plate and so on. It has highly effective as well as higher aesthetic value from beautiful grain on its cross. Thus, it has attracted more and more widespread attention. Its high quality’s drying, however, is the key to restraint technological spread.In the study,30mm thick tree disk is considered as object. Under the two drying schedules (constant temperature (T) of40、60℃and stepwise relative humidity (RH) decreasing), drying characteristics (drying curve and rate, heartwood and sapwood drying curve and the moisture content gradient, the distribution of moisture content and strain along with radial) are investigated. The tree disks drying checks’characteristics (such as the position, moisture content of check formation, morphology). On that basis, the effects of geometrical characteristics of tree disk, namely, Growth Eccentricity (GE), Roundness Deviation (RD) and cross-Sectional area (S) on drying checks were investigated. Meanwhile, the transverse shrinkage and basic density are investigated systemically. And the transverse shrinkage for drying checks’effect is explained, qualitatively. Finally, online measuring precision of tree disk moisture content being discussed and investigated is good for actual production.The main study results were as follows:1) Under the two drying schedules, it had200h and160h with moisture content from58%to12%and the drying rate was0.23%/h.0.27%/h, respectively. Although there was difference between heartwood and sapwood in initial moisture content, the moisture content was accordance in20%and18%, respectively, until the end. Due to the existence of difference between heartwood and sapwood and wood rays, the moisture moving along with the radial should be considered. Under the two drying schedules, although the tangential strains were oscillating up and down along radial from pith to bark, all trends were increasing with the passage of drying time. The tangential strains’ sway extent and maxim obviously under60℃drying schedule were higher than that were under40℃drying schedule.2) The early formation of checks within disks with different positions, diameters and Roundness Deviation (RD) had a significant difference. Under40℃and60℃drying conditions, the early formation of checks’ average MC value was43.9%and45.6%, respectively. Under60℃drying condition, the occurrence of checks was earlier than40℃drying condition. Also, the early formation of checks’ position was on the border between heartwood and sapwood. Under60℃drying condition, the position of checks was slightly expansion to inter with heart checks emerging. Although check total length (CTL) and check average width (CAW) under60℃drying condition were greater than40℃drying condition, it was no significant difference under two drying conditions. The number of V-checks under60℃drying condition was more than40℃drying condition, obviously. The Roundness Deviation (RD) and cross-Sectional area (S) were the main factors, which effected check total length and V-check. The disks with larger cross-Sectional area (S) and more irregular shape were prone to triggering drying checks during the drying process.3) The both height and radial position had significant influences on transverse shrinkage and basic density, especially in height’s effect, in White Birch plantation wood. As the height increasing, the coefficient of tangential shrinkage had a decreasing trend, while the coefficient of radial shrinkage decreased firstly and then increased. At the same tree height, the coefficient of tangential shrinkage had a decreasing trend from pith to bark. Except the coefficient of radial shrinkage of stem had a decreasing trend from pith to bark, the coefficient of radial shrinkage had an increasing trend from pith to bark at others.4) Using electrical resistance moisture content apparatus measured white birch tree disk moisture content during drying. The two level empirical model at9-21%moisture content range and the temperature of40℃、60℃were developed.40℃:MCav=1.29MCr-0.95;60℃:MCav=1.31MCr-0.28.