• Journal of the Korean Wood Science and Technology
• /
• v.25 no.4
• /
• pp.99-107
• /
• 1997

This study was executed to test the possibility of replacement for domestic Japanese larch(Larix leptolepis) for hardwoods and to acquire the information about the effects of drying temperature on internal temperature, moisture content and drying defects. In high-temperature drying, internal temperature increased rapidly to boiling point, immediately after that point the internal temperature rising rate was reduced. In the case of drying at temperature of $125^{\circ}C$, internal temperature could reach at boiling point in a very short time. Moisture content in high-temperature drying showed constant drying rate period and first period of falling rate drying together in 4 hours since experiment begun. There was no strong correlation between initial moisture content and final moisture content. Average drying rate at $115^{\circ}C$, $120^{\circ}C$ and $125^{\circ}C$ was 1.42%/hr, 1.88%/hr and 2.02%/hr, respectively; the case of drying temperature of $125^{\circ}C$ showed most rapid drying rate. Drying rate of $125^{\circ}C$ was so rapid that it showed more severe shrinkage, bow, collapse, end check, and internal check development than in other drying conditions. The result of this study showed the strong possibility of high-temperature drying for Japanese larch, and to dry Japanese larch optimally, dry bulb temperature should not exceed $120^{\circ}C$.

• Journal of the Korean Wood Science and Technology
• /
• v.25 no.4
• /
• pp.51-60
• /
• 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
• /
• v.17 no.1
• /
• pp.22-54
• /
• 1989

Seasonal semi-greenhouse type solar-drying of 2.5cm-and 5.0cm-thick lumber of Quercus aliena Blume and Quercus variailis Blume was carried out to investigate the possibility of solar-drying of wood and to decide the active solar-drying period in Korea. In the active solar-drying period obtained solar-dehumidification, semi-greenhouse type solar-, air- and kiln-drying of 2.5cm -thick lumber of oaks were carried out to analyze drying-rates. -defects, and -yield in each drying-method and to calculate daily total absorbed solar-radiation the solar dryers. The energy balance equations were set up, considering all the energy requirements, to analyze the heat efficiencies of semi-greenhouse type solar and solar-dehumidification-dryer. In a seasonal drying the drying rate of semi-greenhouse type solar-dryer was highest in summer, and greater in fall, spring, and winter in order. Solar-drying time was 45% in summer to 50% in winter of the air-drying rime, and more serious drying-defects occurred in air-drying than in solar-drying. In the active solar-drying period. April, May, and June, the average drying rate in solar-dehumidification-drying was 1.0%/day and greater than 0.8%/day in semi-greenhouse type solar-drying. In solar-dehumidification-drying the time required to dry lumber to 10% moisture content was less than 60 days, and solar-dehumidification-drying showed the highest drying-yield, 65.01%, than the other drying methods. The daily total absorbed solar radiations were 8.51MJ on the roof collector and 6.22 MJ on the south wall collector. In the energy blance 69.48% of total energy input was lost by heat conduction through walls, roof. and floor 11.68% by heat leakage, 0.33% by heating the internal structures of the solar-dryer and 5.38% by air-venting. Therefore the heat efficiency of semi-greenhouse type solar-dryer 13.13%, was lower than that of solar-dehumidification-dryer, 14.04%. Solar-drying of lumber in Korea showed the possibility to reduce the air-drying-time in every season and the efficiency of solar-dehumidification drying was higher than that of semi-greenhouse type solar-drying.

• Journal of Korea Foresty Energy
• /
• v.21 no.3
• /
• pp.10-17
• /
• 2002

This study was carried out to investigate a heat treatment condition and suitable drying schedule of bamboo material(Phyllostachys nigra var. henonis) for a vertical flute with small-notched bamboo. It is very important to prevent drying defects during its drying process. We investigated the effort of heat treatment the most suitable drying schedule for small-notched bamboo vertical flute without drying defects in this research. A direct heat treatment method and drying conditions of 3($20^{\circ}C$ 65%, $40^{\circ}C$ 40%, and dry at air condition) were applied to the Bamboo specimen that felled in several areas for a month. The result suggested that the most suitable drying schedule with the less split and the shortest time was to dry at $40^{\circ}C$, 40% condition and it was useful to direct heat-treatment because of reducing the number and size of split during drying bamboo.

• Journal of the Korean Wood Science and Technology
• /
• v.4 no.1
• /
• pp.48-53
• /
• 1976

This Study was carried out to investigate the course of air-drying and drying defects of red pine (Pinus densiflora S. et Z.) and Italian poplar (Populus eurameriana I-476) boards 1,2 and 3cm thick in the flat pile. The results are as follows. 1. Air-drying curves for red pine and Italian poplar boards were same as figure 1 and 2. These moisture contents were lower in July and August during seasoning periods. 2. Air drying time of red pine board required to dry 15 percent moisture content in one week for 1 cm board, five weeks for 2 cm board and six weeks for 3cm board respectively. In case of Italian poplar boards, in one week for 1 cm board, four weeks for 2 cm and five weeks for 3 cm board. The thickness of board influenced the time for air drying. 3. Drying defects such as checking, warping and staining happened badly in pine than in Italian poplar boards. Especially, checking was severe in thicker board and warping in thinner board.

• Journal of the Korean Wood Science and Technology
• /
• v.22 no.1
• /
• pp.66-71
• /
• 1994

To increase drying rate and reduce drying degradation, pretreatments such as prefreezing and presteaming have been widely used in wood industries. Presteaming lumbers prior to kiln drying is known positively to improve its permeability, to increase diffusion coefficient and to reduce discoloration, but negatively to increase collapse. Prefreezing lumbers prior to kiln drying is also known to reduce significantly its drying defects and its shrinkages. Thus it is no doubt that the pretreated lumbers shrink diversely from the untreated. In this study the shrinkage behaviors of the pretreated specimens are investigated by drying two tropical hardwoods (Apitong and Taun) in three different dying conditions: high temperature and slow drying rate (drying in a closed cylinder), high temperature and rapid drying rate (drying in an oven) and low temperature and slow drying rate(drying at room temperature). The prefrozen specimens show the least volumetric shrinkages in most drying conditions. The specimens dried in cylinders shrink most among all drying conditions. In general the pretreated specimens reached the 30 % moisture content faster than the untreated by about 30 %.

• Journal of the Korean Wood Science and Technology
• /
• v.29 no.3
• /
• pp.21-26
• /
• 2001

Acquisition of precise information on drying characteristics of wood is indispensable for the improvement of drying schedules and wood quality. Recognition of the exact moisture content at which drying defects such as checks occur during drying with given drying conditions may be essential to reduce drying losses. In this study an image-processing system was combined with a laboratory-scale wood dry kiln for experiments and the surface of tree disk of black locust (Robinia pseudoacacia L.) was monitored to investigate the behavior of check formation over all the drying process. This system showed good potential for improving drying schedules and wood product quality.

• Journal of the Korean Wood Science and Technology
• /
• v.51 no.6
• /
• pp.493-508
• /
• 2023

Round timber materials of 600 mm length, cut from large-cross-section round timber of red pine (Pinus densiflora S. et Z.) of 450 mm width and 4.2 m length, were prepared as the target of kiln drying in this study. After treating the target materials through end sealing (ES), end sealing - kerfing (ES-K), lateral sealing - end sealing - boring (LS-ES-B), or lateral sealing - partial end sealing (LS-PES), the effects of the treatment on the incidence of drying defects were determined. The target materials with exposed lateral surface and sealed cross surface were steamed at the initial temperature of 65℃ above the official pest control temperature of 56℃, followed by kiln drying toward the final temperature of 75℃. The target materials with sealed lateral surfaces, on the other hand, were dried at the initial temperature of 90℃ at almost the maximum temperature of conventional kiln drying, as there is no risk of early check formation caused by surface moisture evaporation. The final temperature was set at approximately 100℃. The drying time, taken for the target materials with initial moisture content of 70%-80% to reach the target moisture content of 19%, varied across treatment conditions. The measured drying time was 1,146 hours (approximately 48 days) for the timber with sealed cross surface and 745 hours (approximately 31 days) for the timber with sealed lateral surface, until the moisture content reached the target level. The formation of surface checks could not be prevented in the control and ES groups, but a definite preventive effect was obtained for the LS-ES-B and LS-PES groups.

• Design & Manufacturing
• /
• v.15 no.4
• /
• pp.32-36
• /
• 2021

In this study, the cause of the decrease in transmittance of the outer lens among the causes of the decrease in the amount of light in the automobile headlamp was identified, and the improvement method was selected to determine the effect. The causes of defects that lower the transmittance of the outer lens are divided into a moisture problem and a haze problem. The moisture problem is caused by the temperature difference between the inside and the outside of the head lamp, and the haze problem occurs when the heat inside the head lamp evaporates the haze component contained in the plastic material and attaches it to the outer lens. In order to improve the haze problem that occurs in plastic raw materials, the structures of the bulb light source type headlamp and the LED chip light source type headlamp were analyzed. Among them, the housing material of the LED chip light source type headlamp, which is structurally prone to haze gas, was selected as the test target. In the mass-production injection process of the housing, the drying process was selected as a method to minimize haze gas without adding a separate production process. After extracting a sample every drying time at a constant drying temperature, the sample was put into a haze tester and the residual amount of haze gas was measured. As a result, it was confirmed that the residual amount of Haze gas in the material decreased as the drying time increased.

• Journal of Advanced Marine Engineering and Technology
• /
• v.26 no.2
• /
• pp.226-232
• /
• 2002

In tradition, there have been two kinds of drying methods, which are sun drying and artificial drying. The sun drying method which has been adopted traditionally has been replaced by the hot-air drying method which is one of the most general methods of artificial drying, with its simple drying system, low initial cost of drying plant, and easy operating method. But the hot-air drying method has some defects ; (1)much energy loss happens due to the discharge of hot air during the drying process, (2)control of drying rate is not easy on account of changing relative humidity of inlet air for uniform hot air temperature, (3)high temperature of floods in drying process brings about the production of low-grade drying products. Also, the hot-air drying method is inducing environmental and sanitary problems which are resulting from the emission of high temperature and high humidity air, including stick on the drying progress. Vacuum drying technique, whose drying time and 7uantity of exhausting energy is about 1/3 ~1/4 of hot air drying, is very excellent in the drying efficiency. As the results, it took about 20 hours for material to reach about 18% of the final moisture content in order to store products for a long time, from about 470% of the early moisture content at the beginning of drying, and maximum drying rate comes to about $0.35 kg/m^2hr$ at about 350% of the moisture content.