Bogor, 21-22 October 2015
424 A preliminary study with Blackwood has shown that the moisture content, particularly above
FSP, under an intermittent drying regime decreases at more consistent rate than the continuous drying schedule Yuniarti, 2015. According to Viljoen 2012, the moisture
content distribution or gradient profile provides an indication of the internal circumstance that occur in timber during the drying process. Therefore, it is considered that the intermittent
drying has the potential to delay or even prevent the formation of drying defect. Nevertheless, there has not been any work found which provides information about the
moisture gradient or defect development during the intermittent drying of E. saligna. Thus, the study aimed to investigate the moisture distribution and defect development in E. saligna
during intermittent drying.
2. EXPERIMENT METHOD
The Eucalyptus saligna logs from the provenance of Kangaroo Valley were sourced from North East Victoria, near Rutherglen, and further cut at Creswick’s Timber Training Centre. The
final length, width and thickness of each board were approximately 1000 mm, 100 mm and 40 mm respectively. For this study, several boards were further cut into two sample boards of
860 mm long. Two biscuits, measuring 20 mm in thickness, were taken at a distance of 50 mm from both ends of each board. These biscuits were used to determine the initial moisture
content of each board. Only boards with the initial moisture content above 80 were used for this study and those that did not meet this requirement were discarded. Prior to being
dried, all of the sample boards were end sealed with silicone sealant and aluminium foil. The experiment was run from March to May 2013. Two runs were applied for this drying
process with 12 boards used for each run. The intermittent drying schedule used was 12-hour of heating at temperature of 40
o
C and 60 relative humidity and 12-hour of non-heating at ambient condition. The 12-hour for each phase included one hour for ramping-up and
ramping-down times between the heating and non-heating phases. The heating phase was carried out at night and the non-heating period was performed during the day. The
temperature selection was based on the result from a preliminary study Yuniarti, 2015b. The relative humidity of 60 was applied for the heating phase in order to reach the final moisture
content of 10 Waterson, 1997. The moisture distribution and defect external checks and distortion were examined at four
observation levels: above moisture content of 50 carried out at range of 55-65, at moisture content range of 30-50, at moisture content range of 25-30 fiber saturation
point and below moisture content of 25 carried out at moisture range of 14-15. The observation was carried out twice for every moisture range. The 1
st
observation was performed after the heating-phase and the 2
nd
one was executed after the non-heating phase. Of the 12 boards used in every run, eight boards in each run were distributed randomly into
the four moisture ranges and used for observing the moisture distribution. Two samples were allocated randomly into each moisture range. At every moisture range and every phase, two
cylindrical samples with a diameter of 18 mm were cored from the board. One τCenter” cylindrical sample was cored at a distance of 5 cm from the center of the board. The other
τEnd” cylindrical sample was cored at a distance of 10 cm from the end section of the board. In total, there were four cylindrical samples cored from each board at every moisture range.
These cylindrical samples were stored in a freezer. After approximately 24 hours in the freezer, the cored samples were further sliced into eight pieces with each piece having a thickness of 5
+1 mm. The moisture content of each slice was determined with the oven-dried method.
Bogor, 21-22 October 2015
425 On completion, the holes left from the coring in the remaining boards, were filled with
silicone gel. The board was reweighed and returned to the kiln. A multifactor analysis of variance was performed to assess various factors that were assumed
to significantly affect the moisture distribution in the boards. The factors were the core location in the board center, end, observation time heating phase, non-heating phase, the
slice number and the run number run 1 and run 2 for each sample. Interaction between factors was also assessed.
The remaining four boards from each run were randomly used for examining the defects development. The external checks were examined according to the Australian standard about
timber drying quality - ASNZS 4787:2001. The distortion was examined according to the Australian standard- ASNZS 2082:2007. The data collected were the length of surface and
end checks, and the depth of bow, spring, cupping and twist. This data was tabulated and presented in graphs for further descriptive analysis.
3. RESULT AND DISCUSSION 3.1 Moisture distribution: pattern and influential factors
