Research On Drying Characteristics And Drying Technology Of Small Diameter Eucalyptus Logs

Eucalyptus is one of the the fast growing wood species in south of China. It has many characteristics such as fast growth, strong adaptability, large volume, etc. Also it can be deforested in 4-5 years. But it has many difficulties in drying,usually the defects of Eucalyptus timbers are serious.As the result it is rarely used in solid wood furniture.In traditional processing technology of Eucalyptus,logs sawn into timbers and then dried in kilns. Sometimes the utilization rate of timber is less than 35% after the kiln drying. In this paper it studies on the drying characteristics and drying technology of Eucalyptus logs to improve the utilization rate and seriousdrying defects.Combined with the drying characteristics, research and explore dryingschedules for different diameter Eucalyptus logs and optimize the drying processes. The results are shown as follows:（1） The drying time of Eucalyptus logs has a strong correlation with selection height of the specimens, length of the specimens, Specimens with or without bark. The regression equation was as follows Y=50-13X₁-13X₂-5X₃+39.25X₄+5.25X5（X₁: specimen height 4.3meters;X₂: specimen height 3.3meters X₃: specimen height 2.3meters X₄: length of the specimens; X5: with or without bark）. The drying time can be predicted by this equation.The drying defects of Eucalyptus logs has a strong correlation with selection height of specimens, length of specimens,. heartwood proportion of specimens,Specimens with or without bark. The regression equation was as follows : Y=3.855-1.966X₁-1.471X₂-0.633X₃+2.615X₄+0.504X5-0.21X6（X₁: specimen height 4.3meters;X₂: specimen height 3.3meters X₃: specimen height 2.3meters X₄: with or without bark; X5: length of the specimens; X6: heartwood proportion of specimens）. This equation can be used to predict the severity of the drying defects.（2） By usingthecluster analysis method to classifieds the drying defects. Drying defects can be divided into three categories according to its size. Grade1 average size for length x width x depth =20.000 mm x 0.961 mm x 2.955mm; grade 2 average size for length x width x depth = 32.397 to mm x 2.659 mm x 14.479 mm; grade 3 average size for length x width x depth =48.219 mm x 5.688 mm x 39.128 mm.Drying defects classification standard divides drying defects into 4 levels anddrying conditions also divides into 4 levels.（3） For diameter 55 90 mm Eucalyptus logs surface crack is level 2 or level 3, internal crack（honeycomb） is level 1or level 2.The drying process temperature can be set to: Preheat stage: TD=53℃Tw=52℃ 94%RH;Initial stage: TD=50℃Tw=48℃ 90%RH;Terminal stage: TD=66℃Tw=51℃ 46%RH;MC adjustment stage: TD=67℃Tw=65℃ 90%RH. Everage utilization ratio is 90.55%.For diameter 90 125 mm Eucalyptus logs surface crack is level 4, internal crack（honeycomb） is level 3 or level 4.The drying process temperature can be set to: Preheat stage: TD=47℃Tw=46℃ 94%RH;Initial stage: TD=45℃Tw=43℃ 89%RH;Terminal stage: TD=60℃Tw=48℃ 56%RH;MC adjustment stage: TD=60℃Tw=58℃ 90%RH. Everage utilization ratio is 87.6%. For diameter of 85 mm or more Eucalyptus logs when the logs MC of 35%²0% in the drying process it can increase 1 to 2 times intermediate treatment to reduce the drying defects and adjust MC of logs.（4） Temperature gradient mainly occurred in drying stages of MC 45²0%. MC below 20% stage no obvious temperature difference between the surface layer, middle layer and core.