• Journal of the Korean Wood Science and Technology
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• v.21 no.2
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• pp.39-48
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• 1993

End-matched disks of 7.7cm thickness were part-time dried in vacuum press dryer to investigate the drying characteristics by using drying schedules and end treatments. The ginkgo disks could be dried faster with severer end checks and ring failures by C schedule than by S schedule. There were no significant differences in drying rates and amounts of end checks, ring failures and V-shaped checks occurred between ginkgo disks end-taped with Korean traditional paper (KTP) and those untreated. The drying time of walnut disks was slightly reduced by end-taping with KTP. And the length of end checks and V-shaped checks and the frequency of defected disk were decreased more effectively than those untreated. The tangential strains and tangential drying stresses near bark sides of ginkgo and walnut disk untreated were developed in the early stage of drying and incresed slightly curvi-linearly above fiber saturation point (fsp) and more curvi-linearly below fsp. The influence of end-taping with KTP on the drying rate for impermeable walnut disk was stronger than that for permeable ginkgo disk.

• Journal of the Korean Wood Science and Technology
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• v.25 no.4
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• pp.51-60
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• 1997

We investigated the characteristics of air-and vacuum-drying heated by hot plates for 8~14cm-diameter logs or 6~12cm-thick pillars of Pinus koraiensis. And we evaluated the effects of longitudinal kerf and vacuum drying heated by hot plates. The vacuum drying times from green to 10.9~18.6% MC were 15 days, and these times were one-fifth compared to the air-drying times. The longitudinal kerfing had no significant, effect on drying rates during both air-drying and vacuum drying. But drying defects such as surface checks and V-shaped cracks were effectively prevented during air-drying and vacuum drying by longitudinal kerfing. The vacuum drying was more advantageous than air-drying for preventing of surface checks, end checks and V-shaped cracks, and especially, the vacuum dried pillars with longitudinal kerf were almost free from drying defects. In accelerated weathering conditions the resin did not exude for all specimens.

• Journal of the Korean Wood Science and Technology
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• v.35 no.1
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• pp.11-16
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• 2007

This study was carried out to investigate the effect of Vapor-dam treatment on drying drying rates, prevention of checks and V-shaped split during air circulating oven drying bamboo (Phyllostachys pubescens Mazel et Z) tube. It was shown that the drying time from green to around 7~8 % of moisture content was required less as drying schedule was more severe, and distinctly dominated by the drying rate during the initial drying stage. Area shrinkages in cross section and thickness shrinkages measured during air circulating oven drying test were very large. Surface checks and V-shaped splits were occurred in untreated samples just after the beginning of drying, while sixty seven percentages of all the Vapor-dam treated samples could be produced without drying defects. The V-shaped splits occurred in the Vapor-dam treated samples were influenced more by the sealing of the vapor evaporation through the cross section than drying schedule.

• Journal of the Korean Wood Science and Technology
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• v.36 no.6
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• pp.59-68
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• 2008

This study was carried out to investigate the effects of the Inside end-taping (Inside-ET) and Outside end-taping (Outside-ET) treatments on prevention of drying defects during radiofrequency/vacuum (RF/V) drying domestic yellow poplar log cross section with size of 20~75 mm in thickness and 120~470 mm in diameter. The treatments of Inside-ET and Outside-ET were quite effective for producing sound log cross sections with thinner than 33 mm and smaller than 270 mm in diameter. Even the 60 mm- and 75 mm-thick log cross sections, if the diameter was smaller than 30 cm, it might expect preventing formation of border checks by appropriate end-taping treatments. The positions of the observed border checks differed in diameter ranging at a relative radius about 0.50~0.63 diameter, and it was estimated that it was necessary to select the border position of end-taping treatment properly according to the diameter of log cross sections. It was observed that the radius of 0.3 diameter was the critical location for pretreatment for preventing formation of border checks in the log cross section with middle diameter. There were severe border checks and V-shaped cracks in the log cross section with large diameter. This was because of the severe variation of moisture content along radial direction of natural characteristic of domestic yellow poplar.

• Journal of the Korean Wood Science and Technology
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• v.19 no.1
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• pp.31-63
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• 1991

It was proved that in conventional kiln drying of disks piling position in the kiln exerted a great influence on drying rates, and the larger the variation of disk diameter, the more undulating drying rates of disks. While in vacuum drying disks there was no influence on drying rates. By the end-wrapping treatments and the radial direction of disks tangential surface stresses in the core of disks were slightly compressive in three species. In control disks the drying stresses distributed into one step-style that compressive stresses in the pith side of 6cm from pith were larger than those in the bark side, while in the disks end-wrapped with Korean paper the drying stresses distributed uniformly, because flow rates of free water in disks had no difference between heart-and sap-wood by obstruction of evaporating water from surface of disks by end-wrapping with Korean paper. And end-wrapping with Korean paper considerably restrained those. Tangential differential shrinkage stresses developed the maximum tensile stress near the bark and with approaching the pith the stresses gradually reduced and changed into compressive stresses in near the pith. At the end of vacuum drying the maximum tangential tensile stresses of disks end-wrapped with Korean paper were smaller than those of control disks, and critical moisture contents causing the V-shaped crack of disks end-wrapped with Korean paper were lower than those of control disks because of the set by obstruction of evaporating water of end-wrapping with Korean paper. In the experiment of vacuum drying stress distribution the disks end-wrapped with Korean paper or aluminum foil in three species were free from V-shaped cracks and control disks were defected very slightly by V-shaped cracks. And also disks end-wrapped with Korean paper were free from heart checks in Alnus japonica and Juglans sinensis, and heart checks were occurred very slightly in others. Especially, not to speak of disks end-wrapped with Korean paper, vacuum drying of disks end-wrapped with aluminum foil prevented effectively drying defects, moreover drying times could be shortened, that is. Ginkgo biloba, Alnus japonica, and Juglans sinensis disks could be dried from green to in-use moisture content in 110 hours, 272 hours, and 407 hours, respectively.