1
Effect of Component
Properties and Orientation on
Corrugated Container
EnduranceRoman E. Popil, Mike Schaepe
Institute of Paper Science and Technology
Atlanta Georgia
Barry Hojjatie, Valdosta State University, GA. USA
2
Scientific objective: develop an
understanding of effects of physical
properties on box lifetime
• what factors govern the lifetime of stacked boxes
• how can we quantify the effects to predict performance ?
3
• Boxes vertically
stacked
• Experience creep,
i.e. progressive
vertical displacement
• Lifetime of boxes is
shortened by 5X
under cyclic humidity
conditions…
• This is…
“Accelerated creep”
This bottom box
has the classic
panel buckling
structure appears
ready to collapse
in about 30
minutes from this
time of snapshot
This guy won’t be
smiling too much
longer
4
Hygroexpansion of board
components changes how the box
handles load
Outside
(double face)
of the box
absorbs
moisture and
expands
largely in the
vertical
direction
Inside of the box
(single facing
linerboard)
remains the same
dimensions until it
equilibrates to the
same moisture
level
Humid outside Dry inside
5
Hygroexpansion increases the
stress
High
Humidity
outside
Low
humidity
inside
Load from stacked
boxes
Double face linerboard experiences
additional stress from its expansion from
absorbed moisture
Box wall side
view
6
50%
80%
24 hrs
time
doubleface medium
singleface
equilibrium Absorption phase
RH
Desorption phase
As outside humidity
changes, the outside
liner of the box
experiences a different
vertical stress than the
inside of the box which
is at a different moisture
level – so the load is not
evenly distributed
through the cross
section of the box wall
Phenomenon discussed
and modeled
numerically by Coffin
and Habeger JPPS
2001Pictorial representation of a sorption stress
gradient model for accelerated creep
The situation reverses when the
humidity outside decreases
7
Paper fails when combined
stresses exceed paper strength
A buckling pattern forms, the buckles eventually join to form a
crease which leads the board to fold and the box to collapse
ECT creep BCT creep
8
Experimental design
• Hypothesis: if we make the corrugated board
more uniform by having a heavier fluted
medium, stresses are more equalized get
more lifetime !!
• So, at IPST we made a series of corrugated
boards all using the same linerboard facings but
with different weights of medium ranging from
14# to 42#
9
Experimental study to determine effects
of board properties on BCT cyclic
humidity lifetime• Varied the fluted medium
basis weight from 68 to
205 gsm
• Linerboard basis weight
is constant at 205 gsm
• Boards and boxes made
at IPST Pilot Plant
• Box dimensions: 36 x 20
x 20 cm
• Selected flute size “A”
• MD shear rigidity
measured by IPST
torsion pendulum ranged
from 2.9 – 8.6 kN/m
• Static loads set for each
type of box to be at
22.5% of BCT failure load
10
Preparation of various test boxes
RSC boxes were manually
prepared from the IPST made
boards
Medium of various basis weight
were combined with 42#
linerboard using the IPST pilot
corrugator
11
Accelerated creep experiments
• Expose either corrugated board or boxes
to humidity varying from 50 to 80% RH,
keep temperature constant
• For board samples, vary humidity using a
ten hour period
• For boxes, vary the humidity from 50 to
80% RH in a 24 hour period (mimics
weather conditions od southeast US)
12
Basic experimental set-up
Vertical load @
~20% of failure load
Displacement
sensor
Data acquisition
using LabView™
records vertical
displacement with
time up to several
months
Test
specimen
Temperature maintained at 23 deg C, humidity varied from 50 to 80% RH
DAQ
13
Creep measuring equipment at IPST
For Test Boxes, inside a
programmable humidity walk-in
chamber:
BCT creep: 8 stations, 50 – 80%RH
24 hr cycle - used to obtain multiple
regression models for lifetime
prediction.
For board samples :
ECT creep, 12 stations, 50 –
80% RH 5 hour cycle - applied
to the A flute varying medium
basis weight set to compare with
BCT creep – also used for client
contract work
14
ECT creep stationsECT specimens epoxied onto horizontal edge mounts, vertical
load applied via transferring linear rail bearings and lead shot
dead weight , Hall probes measure vertical displacement
Suspended canisters filled with lead shot to 20%
ECT failure load
15
Why a ten hour period for boards ?Corrugated board humidity equilibration time test.
0
0.001
0.002
0.003
0.004
0.005
1000 6000 11000 16000 21000 26000
time (sec)
Co
mp
res
sio
n S
tra
in
26A
33A
18 723D
18A 726E
42A
16A
14A
20A
14A
18A 723D
20A
33A
unloaded corrugated board samples
conditioned at 50% RH, placed in ECT
creep apparatus, RH changed from 50
to 30% then back to 50% RH 23 deg. C.
each point 5 min.
16
BCT creep station detail
Static load transfer
through ball bearing
Combined lead bricks,
steel plates lead shot at
22.5% of BCT load inside
of acrylic box supported
by vertical sliding rails
17Test box
Static load
container
Ultrasonic proximity transducer
measures vertical displacement of load
container
BCT creep station detail (2)
18
-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
1 202 403 604 805 1006 1207 1408 1609 1810 2011 2212 2413 2614 2815 3016 3217 3418 3619 3820 4021 4222
42A
20A
26A
18A 726E
18A723D
16A
14A
33A
creep raw data
Increasing
Compression
strain
Voltage signals
converted to
displacements
through a
calibration
Time
Top of each
cycle
corresponds
to low
humidity
Bottom of each
cycle
corresponds to
high humidity
19
Generalized creep strain curve
x1,y1
x2,y2
x3,y3x4,y4
failure
primary secondary tertiary
time
Compression
strain
20
Secondary creep predicts lifetime
2
43
43
12
12
xx
yy
xx
yy
slope
slope
Alifetime
Calculate slope from the
creep curve:
General relationship between lifetime and the creep slope:
21
ECT (Board) creep summary, 83
observations
Lifetime = 0.0241(strain/sec)-0.98
R2 = 0.92
0.E+00
1.E+05
2.E+05
3.E+05
4.E+05
5.E+05
6.E+05
7.E+05
8.E+05
9.E+05
1.E+06
1.E-08 3.E-08 5.E-08 7.E-08 9.E-08 1.E-07 1.E-07
Creep rate strain/sec
Lif
eti
me
(s
ec
)
33A
26A
20A
18A 1
16A 14A
42A 18A2
Points are averaged by box
types (medium basis
weight)
Error bars are 95%
confidence intervals
22
Lifetime = 1.47E-04x-1.33E+00
R2 = .70
0.00E+00
5.00E+05
1.00E+06
1.50E+06
2.00E+06
2.50E+06
3.00E+06
3.50E+06
4.00E+06
1.00E-08 2.00E-08 3.00E-08 4.00E-08 5.00E-08 6.00E-08 7.00E-08 8.00E-08
Creep (strain/sec)
Life
tim
e (
se
c)
33A
42A18A
723D
14A
20A
18A 726E
16A
26A
Grouping BCT creep data by medium basis weight
Much more scatter evident compared to ECT creep data – same
board set !
This box lasts 37 days on
the average
23
lifetime vs creep rate RSC BCT
Lifetime = 0.1451Creep-0.89
R2 = 0.71
0.00E+00
1.00E+06
2.00E+06
3.00E+06
4.00E+06
5.00E+06
6.00E+06
7.00E+06
0.00E+00 2.00E-08 4.00E-08 6.00E-08 8.00E-08 1.00E-07 1.20E-07 1.40E-07 1.60E-07
creep (strain/sec)
Lif
eti
me
(s
ec
)Same BCT lifetime data plotted by point
68
observations
24
Where does the variability come from ?
• Natural variation in paper properties:» Basis weight ~ 2%
» Strength ~ 5 – 7%
• Preparation of test pieces, boxes» Cutting of edges
» Mounting
» Handling: folding of box flaps, gluing of joints
» Application of load – sudden vs gradual
» Imprecision of applied load
• Systematic error ? » Electrical noise, sensor calibration drifts
» Variations in humidity control
Parallelism, squareness
25
Regression Analyses of creep data
• Attempt to quantify creep, lifetime with measured
properties – single variable:
R2
p R2
p
ect lifetime 0.59 0.03
R55 0.33 0.14 R55 0.71 0.01
ECT 0.31 0.15 ECT 0.69 0.01
BCT 0.19 0.27 SCTm 0.54 0.04
SCTm 0.50 0.05 BWm 0.44 0.07
BWm 0.39 0.1
ECT lifetime BCT lifetime
Note: a) BCT lifetime correlation with ECT lifetime
b) ECT lifetime correlation with shear rigidity R55
26
• Multiple linear regression fits of the data:
Regression Analyses
41017.73.21710.151.917.9 mm BWSCTECTslifetimeECT
51078.23.3231.6729.027.7 BCTBWSCTslifetimeBCT mm
R2 ~ -0.84, SCT of the medium
appears to dominate lifetime in this
data
MEAN ERROR ~ 1 DAY
MEAN ERROR
~ 3 DAYS
27
Another idea: rotate the components
MD of box
components
CD
hygroexpansivity
this way
is larger than in
MD
Paper is directionally oriented - not the best way for strength and
hygroexpansivity
So what if we were to make boxes with one or more of the components rotated
90 degrees ?
MDThis box stretches
and shrinks less
with changes in
humidity, so get a
smaller built-up
stresses
Load = mgF
28
This is not so easy to do:
So we have to turn the paper around 90 degrees, splice it back
into a roll and run that through the corrugator
Lateral corrugator concept (ex Schaepe, 2004 Tappi summit)
MD of
a roll
29
Manual preparation of rotated component test
boxesFull width rolls of linerboard and medium were obtained and CD strips were
spliced together to produce transverse oriented 13” width rolls to run
through the pilot corrugator – 205 gsm linerboard, 127 gsm medium
MD
MD SCT is 1.7X CD SCT
MD hygroexpansivity is 0.4X CD
30
2.7
2.9
3.1
3.3
3.5
3.7
3.9
4.1
Regular Lateral Linear Only double
face rotated
BC
T k
N
BCT increases with component rotation• 36 x 20 x 20 cm test boxes, 205 gsm liners, 127 gsm medium
• BCT increases, 14% for “partial”, 26% for “lateral”, 33% for “linear”
23 %
33 %
14 %
(Medium is
not rotated)
(All components
are rotated)
Obvious
differences here
31
Observation of creep behavior of
rotated component boxes
• 7 boxes data plotted in each case
• lateral corrugated lifetime is somewhat longer,
hygroexpansive strains are smaller as expected
• scatter in BCT lifetime data is typical
strain strain
time time
~ 3.5%
Regular Lateral
32
Effect of rotated components on lifetime
Linear
corrugated
boxes last
about 2
weeks in
cyclic
humidity at
22.5% of
BCT load
Creep and lifetime
2.00E-08
2.50E-08
3.00E-08
3.50E-08
4.00E-08
4.50E-08
5.00E-08
5.50E-08
regular lateral linear
Cre
ep
(str
ain
/sec)
1.00E+05
3.00E+05
5.00E+05
7.00E+05
9.00E+05
1.10E+06
1.30E+06
1.50E+06
1.70E+06
1.90E+06
Lif
eti
me (
sec)
creepratelifetime
!
33
Pilot coating/corrugating trial - sequence
Rod coating of 42#
linerboard at Spectra-kote
Linerboard rolls coated
with polymer or
clay/polymer coatings
Rolls sent through
IPST pilot single facer
combined with WAM
Single facings
manually combined
with double facing
14 x 8 x 8” test
boxes manually
made
Coated test boxes put
through performance tests,
e.g. lifetime in cyclic RH
34
Relationship between hygro strain and creep
• Urbanik 1995 Wood Fibre Sci. hygroexpansion drives
mechanosorptive creep in cyclic humidity
• reduce hygroexpansive strain either through component rotation
of low WVTR coatings, creep rate goes down, lifetime increase
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6 7 8
Creep rate (1/s x 10- 8
)
Hyg
roe
xp
an
sio
n s
tra
in (
mm
/mm
x1
0-
3 )
RSC series II
HSC series III
regular
linear lateral
uncoated
barrier coated linerboards
Lifetime < 1.5 weeks
Lifetime > 3 months
35
Summary
• Lifetime and creep observed for ECT and BCT, ECT creep dependencies are more clear
• Effect of medium properties characterized: fluting SCT and basis weight for BCT lifetime
• Effects of component rotation on lifetime observed, linearly corrugated lifetime is 2x higher,
• Low WVTR coated boxes last months compared to days
• Generally equalization of properties through the board cross section increases lifetime
Top Related