RESULT AND DISCUSSION 1 Moisture distribution: pattern and influential factors
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
Figure 1 shows the pattern of moisture distribution across the cross section of the centre and end sections of the boards from every moisture range. All charts show higher moisture
content in the mid-zone than that in the surface-zones of the boards from the intermittent regime. This result indicated that the surface zone of the boards dried faster than the mid zone
during all stages of intermittent drying process. For the purpose of the discussion of the moisture distribution, the mid-zone refers to the slice numbers from 3 to 6 of the eight pieces
sliced from the cylindrical-cored samples. The top-surface zone refers to the slice numbers 1-2 and the bottom-surface zone refers to the slice numbers 7-8.
Table 1 shows that the cross sectional location or zones in the boards was the factor significantly affecting the moisture distributionprofile of the boards at all observation levels.
ANOVA tests also showed other, different factors, had significant effect on the moisture content profile of the boards at different observation levels. The kiln factor significantly
affected the moisture distribution in the boards at moisture range above 50. The boards from kiln 2 had higher moisture content 76.8 than that from kiln 1 60.3.
At observation level of 30-50, the sampling time also significantly affected the moisture distribution in the boards. The moisture content in the boards was significantly higher in the
non-heating phase mean value was 53.2 than that in the heating phase mean value was 47.1.
At FSP, the sampling position also significantly affected the moisture distribution in the boards. The end section of the boards retained more moisture 38.83 than the centre
section 34.89. Finally, at observation level below FSP, the moisture distribution in the boards was also affected by the sampling location, observation time, and kilns. The interaction
between: i sample location and time; ii sampling time and slices; and iii sample location, slices and kilns; also showed significant influence. At this observation level, the moisture
content in the end section of the board was significantly higher 17.86 than that in the non- heating phase 14.96. The mean moisture content in the center section of the board during
the heating phase was also significantly lower than that in the end of the boards 15.23- 15.72. The mid-zones of the center and end section of the boards from kiln 2 tended to
contain more moisture than the same zone of the boards from kiln.
Bogor, 21-22 October 2015
426 a. MC 50
b. MC 30-50
c. MC=FSP d. MC FSP
Figure 1: Moisture distribution at different observation levels during intermittent drying 3.2 Defect: checks and distortion
3.2.1 Surface and end check
Figure 2 shows the development of surface and end check in E. saligna boards during the intermittent drying process. Figure 2a shows that surface check affected four of the seven
boards observed. Of all the four boards, one board was from the 1
st
run and the remaining boards were from the 2
nd
run. This result supported the previously held view by Bootle 2005 and Stöhr 1977 regarding the susceptibility of E. saligna to develop surface checks during the
drying process.
20 40
60 80
100 120
1 2 3 4 5 6 7 8 M
o is
tu re
c o
n te
n t
Cross sectional location
Center_Heatin g_Int_50
Center_NonH eating_Int_50
Intermittent 40°C60, 12H12NH
10 20
30 40
50 60
70 80
90
1 2 3 4 5 6 7 8 M
o is
tu re
c o
n te
n t
Cross sectional location
Center_Heating _Int_30-50
Center_NonHeat ing_Int_30-50
End_Heating_Int _30-50
Intermittent 40°C60, 12H
10 20
30 40
50 60
70 80
90
1 2 3 4 5 6 7 8 M
o is
tu re
c o
n te
n t
Cross sectional location
Center_Heating _Int_30-50
Center_NonHeat ing_Int_30-50
End_Heating_Int _30-50
Intermittent 40°C60, 12H12NH
10 20
30 40
50 60
70
1 2 3 4 5 6 7 8 M
o is
tu re
c o
n te
n t
Cross sectional location
Center_Heatin g_Int_FSP
Intermittent 40°C60, 12H12NH
5 10
15 20
25
1 2
3 4
5 6
7 8
M o
is tu
re c
o n
te n
t
Cross sectional location
Center_Heating_ Int_BelowFSP
Center_NonHeat ing_Int_BelowFS
P Intermittent 40°C60, 12H12NH
Bogor, 21-22 October 2015
427 Table 1: Influence of several factors and their interactions on moisture profile of E. saligna at
different observation levels
Main factors\Moisture ranges 50
30-50 FSP
FSP
Location center vs end Sample Time heating vs non-heating
Cross sect.slices 1-8 Runkilns 1-2
1. Interaction between main factors : Location X Sample time
Location X Cross section slices Location X Runkilns
Sample time X Cross section slices Sample time X Runkilns
Cross Section slices X Runkilns Location X Sample time X Cross section
Location X Sample time X RunKilns Location X Cross section slices X Runkilns
Sample time X Cross section slices X Runkilns Location X Sample time X Cross section slices X Runkilns
Remarks: shows significant influence
The result showed that numerous surface checks could develop in a single board, as found for the three boards from run or kiln 2. Some surface checks developed when the moisture of the
boards was still above 50. The maximum initial length of this type of surface checks was 49 cm. When the moisture of the boards decreased to below 50, the length of some of these
surface checks also decreased. One surface check was found to close when the moisture of the affected board reached the moisture range of 30-50.
The other surface checks developed when the moisture of the boards reached 30-50 or FSP. The maximum initial length for this type of checks was that initially developed when the
moisture of the boards was less than 10 cm. These surface checks closed as the moisture of the boards decreased to a lower moisture range.
One fine surface check was observed to develop in one board when the moisture of the affected board already fell to below FSP. The length of this fine surface check remained until
the drying process finished. Surface checks are often formed in the early process of the drying process and close when the moisture of the boards reaches FSP. The fact that a surface check
developed at FSP was not expected. It was possible that this surface check was actually already present from the beginning of the drying process. Possibly due to its fine dimension, its
presence was difficult to be viewed until it became larger.
Bogor, 21-22 October 2015
428 Figure 2b shows that end checks developed in two of the seven boards. The end checks had
two different development patterns. The first development pattern was for the end check that formed when the moisture content of the board was still above 50. They had a maximum
length of 6 cm. This type of end check had similar length throughout the drying process and closed when the board reached moisture content of below 25. Its closure was possibly due
to the stress reversal where the end section of the board was possibly subjected to compression stress. On the other hand, at the same time, the center section of the board was
possibly under tension stress. The second development pattern was for the end checks that developed when the moisture
content of the board was in the range of 30-50. This type of end check was only present for a short time. When the boards reached FSP, the end check closed. This second pattern was
similar to the development pattern of some surface checks previously desribed.
a. Surface checks
b. End checks Figure 2: The development of surface checks a and end checks b during intermittent drying
10 20
30 40
50 60
70 80
50 30-50
25-30 25
Le n
g th
cm
Moisture ranges
SurfaceChecking_Intermittent_Sample1Kiln1 SurfaceChecking_Intermittent_Sample1aKiln2
SurfaceChecking_Intermittent_Sample1bKiln2 SurfaceChecking_Intermittent_Sample1cKiln2
SurfaceChecking_Intermittent_Sample1dKiln2 SurfaceChecking_Intermittent_Sample1eKiln2
SurfaceChecking_Intermittent_Sample2aKiln2 SurfaceChecking_Intermittent_Sample2bKin2
SurfaceChecking_Intermittent_Sample3aKiln2 SurfaceChecking_Intermittent_Sample3bKiln2
Intermittent 40C60 12H12NH
5 10
15 20
25 30
50 30-50
25-30 25
Le n
g th
cm
Moisture ranges
EndCheck_Intermittent_Sample1Kiln2 EndCheck_Intermittent_Sample2Kiln2
Intermittent 40C60 12H12NH
Bogor, 21-22 October 2015
429 3.2.2
Distortion: bow, spring, twist and cupping Figure 3 shows the development of several distortions bow, spring, and twist in E. saligna
during the intermittent drying process. No cupping was observed during the intermittent drying process for E. saligna. This result indicated that E. saligna was possibly less prone to
cupping defect during the drying process. It also indicated the potency of the intermittent process to reduce or eliminate the occurrence of cupping defect in E. saligna.
Figure 3a shows that bow affected six of the seven boards observed. This result indicated the high susceptibility of E. saligna to develop bow defect. All bow defects were observed to
develop when the the moisture of the affected boards was still above 50. The maximum initial depth of bow was 3.28 mm. It was found that the bow increased as the moisture
content decreased.
a. Bow b. Spring
c. Twist Figure 3: The development of bow a, spring b and twist c during intermittent drying
5 10
50 30-
50 25-
30 25
D e
p th
m m
Moisture ranges
Twist_Intermittent_Sample1Kiln1 Twist_Intermittent_Sample2Kin1
Twist_Intermittent_Sample1Kiln2 Intermittent 40C60 12H12NH
5 10
50 30-
50 25-
30 25
D e
p th
m m
Moisture ranges
Bow_Intermittent_Sample1Kiln1 Bow_Intermittent_Sample2Kiln1
Bow_Intermittent_Sample3Kiln1 Intermittent 40C60 12H12NH
2 4
6 8
10
50 30-
50 25-
30 25
D e
p th
m m
Moisture ranges
Spring_Intermittent_Sample1Kiln1 Spring_Intermittent_Sample1Kiln2
Spring_Intermittent_Sample2Kiln2 Intermittent 40C60 12H12NH
Bogor, 21-22 October 2015
430 Figure 3b shows that spring affected three of the the seven boards observed. Different
patterns of spring defect were observed. One board developed spring defect when its moisture content was below 50. The maximum initial depth of this type of spring was 1.89
mm. The depth of this particular spring remained the same during the drying process and slightly decreased as the moisture content of the board fell below 25.
The other samples exhibited spring when the moisture content was above 50. The maximum initial depth of this type of spring was 4.48 mm. The depth of this particular spring
increased to approximatley 5 mm for one board, but remained the same in another board when the moisture content decrease to between 30-50. The depth of spring then decreased
when the moisture content of the boards decreased to below 50. The exact cause of these differences is still unclear. The slight difference in the wood composition or structure and
grain orientation probably contribute to this factor. Figure 3c shows that twist developed in five of the seven boards observed. There were
different patterns observed for the twist development in E.saligna. One board was observed to have twist developing when its moisture content was still above 50. The maximum depth of
this type of twist at its initiation point was 1.49 mm. However, the twist diminished when the moisture content of the board decreased to below 50.
In another board, the twist started to develop when the moisture content of the board was in the range of 30-50. The maximum initial depth of this type of twist was 2.79 mm.This type
of twist remained constant throughout the experiment. For the other three boards, the twist started to develop when the moisture content of the board was already below 25 and
remained during the experiment. This difference is possibly a reaction to the difference in the wood structure or to the stress formed previously.