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of 175 C and 162-173 C respectively. P OM is
s em i c ry st al lin e polyme r w i th 75-85 d eg re e o f
crystallinity.
As engineering plas t ics , PolyOxyMethylene
POM has two types, homopolymer and
copo lymerwhich d i ffer s ligh tly in i ts me l ting po in t
INTRODUCTION
ala unc i Analisis retak,Polioksimetilen,Derajat kristalinitas,Termal
ANALISIS RETAKPOLIOKSIMETILEN MENGGUNAKANSCANNING ELECTRON
MICROSCOPE, ANALISIS TERMAL DAN PROSES. Analisis retak dilakukan menggunakan
ScanningElectron Microscope SEM
dan
Differential Scanning Calorimetry DSC .
Perbandingan
karakteristik bahan antara sampel NG dan standar dilakukan.Analisis SEM menunjukkan bahwa
permukaanretakan padasampelNGcenderung lebihmudahpatahdibandingkanretakan pada sampel
standar.Retakan diduga berasal dari vicinity gate location.Derajat kristalinitas patahan NG adalah
59,6 lebihrendah dibandingkandengan sampel standard 65,8 . Tidak adaperbedaan yangjauh
antara suhu leleh 164C) dengan suhu kristalisasi 146 0C).Perubahan danjalur patahan disekitar
gate location berpotensi menyebabkan retakan selama proses. Berdasarkan hasil SEM dan DSC,
retakan diduga berasal dari setting proses yang tidak tepat yang menghasilkan derajat kristalinitas
yang rendah
danJrozen-in stress.
Beban luar yang diterima juga merupakan salah satu penyebab
terjadinya retakan.
ABSTRAK
eywords
Failure, Polyoxymethylene,Crystallinitydegree,Thermal
FAILURE ANALYSISONPOLYOXYMETHYLENE PRODUCT USING SCANNING
ELECTRON MICROSCOPE, THERMAL ANDPROCESSING ANALYSIS.Failure analysisof
PolyOxyMethylene POM) product were carried out using ScanningElectronMicroscope SEM),
DifferentialScanningCalorymetry DSC)and parameterprocess related factors.Comparationof the
failuremode andmaterialpropertiesbetween theNG andProvensampleswere taken. SEManalysis
showed that failure surface tent to have more brittle fracture compared with the proven sample
failure.Theorigin of crackwaspredictedfromthevicinityof gate location.Degreeof crystallinityof
failure part was 59.6 , which was lower than the proven products 65.8 ). Melting Tm) and
CrystallizationTemperature Tc)showedno significantdifferences, 164Cand 146Cformeltingand
crystallizationtemperature respectively. Whiteningand molded streamflowwere shownaround the
gate locationwhich potentiallycausedmolded in stress and crackpropagation during application in
chemicalenvironment.Externalloadalso found inthe vicinityof crack.Basedon the SEM,DSCand
process related factor analysis, the failure of product was supposed due to the combination of
impropersetting process which resulted in lower degree of crystallinity and frozen-in stress around
the gate and external load received have triggered the crack on product.
ABSTRACT
Accepted: 13December2013evised: 13November2013
eceived:
19
July 2013
R
Wijaya, A.Rifathin and
Afrinaldi
Centerfor Polymer Technology STP - BPPT
Kawasan Puspiptek;Serpong
15314,
TangerangSelatan
FAILURE ANALYSISON POLYOXYMETHYLENE
PRODUCT USING SCANNING ELECTRON MICROSCOPE,
THERMAL AND PROCESSING ANALYSIS
Vol.17,No.1, 2014, hal: 16-19
ISSN: 1410-7864
ajalak Polimer Indonesia
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approximately 10mg,placed intoalumina crucible.
The alumina crucible was then placed inThermal
GravimetryAnalysis (TGA) instrumentation. The
test is conducted under temperature program as
follow: Firstly the sample was heated up from
temperature of 50 to 600 under nitrogen gas.
The temperature was held at 600
for 5 minutes
nitrogen gas environtment. The temperature was
then continuing heated up until 900
under
oxygen gas. The rate of heating was 10
per
minute, and the nitrogen/oxygen gas flowratewas
50 mL per minute. After measurement was
completely finished the TGA-thermograms were
analyzed.
DSC821-Mettler Toledo was used to
measure the thermal properties of the samples such
as melting point, glass transition temperature,
thermal history, degree and the growth of
crystallinity. The test was conducted according to
ASTM D 3418-2003. Sample was cut and
weighed approximately 20 mg, placed into Al
crucible. The Al-cruble was then placed in DSC
sample chamber. The test is conducted under
nitrogen gas environment with temperature
program of heating-cooling-heating as follow:
the temperature program was started from 30 to
200 C, then cooled down to -100 C and finally
heated up to 200 C. The rate of heating was
10 c per minute, and the nitrogen gas flow rate
was 50 mL per minute. After the test was
completely finished the DSC-thermograms were
analyzed.
Figure 2. FTIR test results of NG and proven
samples
._
The failure POM product was received as
failured-part applied inmotor cycle.
To identify the main material, possible
degradation and semi quantitatively analysis the
material composition, we used FT-IR-Bruker
Tensor 27, ATR method. Placed the sample on
ATRcrystal. Touched the sample surface perfectly
on the crystall by setting down the stainless steel
tip. Samples analysis were carried out by OPUS
software (Figure 2).
To measure the material composition.
The test was carried out in accordance toASTM
1131-1998. Sample was cut and weighed
EXPERIMENTAL METHOD
Figure 1. Frozen-in orientation (top) and poten
tial shrinkage near to the gate (bottom)
dge p le
\\~I
>:
~I : _____
POM are generally processed in injection
molding with special runner system. Hot runner
types are commonly applied in POM. Wrong
selection of runner type could result in loss of
pressure during process. Toovercome the pressure
reduction, operators usually increase the
temperature. Unfortunately this could severe the
material to degradation.
The melt entering the cavity will form
orientation during fillingphase.Andmelt adjacent
tothemoldwill freeze:firstandleadto highinterfacial
shear stress between the melt and the solid layer.
This frozen-in orientationwill continue to develop
duringholding pressure in order to compensate for
volume shrinkage, particularlynear the gate region
of the part (Figure 1). However, fast cycle time
during production is required. Those process
parameters influentthemicrostructureof partwhich
also affect the properties and performances.
In this paper, we analyzed the effect of
settingprocess to thermalpropertiesas contribution
ofpotential causes of failureby observing the crack
pattern on the failed surface.
Failure Analysis on PolyOxyMethylene Product Using Scanning Electron Microscope, Thermal and Processing
Analysis R. Wijaya)
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Figure
4. DSC test results ofNG (a) and proven
(b) samples oncooling phase after first heating
---; ::; ; ;; j
_ __ _ _ _ _ _ . ._ H ._ _ , _ __ . . . ,_ . __ _ ._ _ _ , _. ._ ..
~: I
to ~,(;~.
....~
,.
.~--....-......----- :;-;.;~=~--=~-- u=~=:=
;~~.:;;::~:.;\.~- ~-::::;i: ~;~~_,.:..
_-6 .'Ii
\ ,)U~.ll:
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REFERENCES
[1]. DuPont, 2008, Problems with Hot Runners.
[2]. DuPont, DuPont Delrin acetal resin
Molding Guide:TechnicalInformation.
[3]. ARCHODOULAKI VM, LUFTL S,
KOCH T, SEIDLER S, Property changes
in polyoxymethylene POM resulting from
processing, ageing andrecycling, Pol Degrad
Stab, 92 2007 2181-2189
[4]. MALLOY RA., Plastic Part Design for
Injection Molding: Introduction, Hanser
Gardner Publications Inc. 1994
The authors are grateful to The Center for
Polymer Technology for supporting this project.
ACKNOWLEDGMENTS
Extemalload onthesurfaceofhighly frozen
in stress part due to improper setting process tend
to form brittle on the surface and layer between
the surface. The inner core part resulted in crack
beginning from the outer surface part and
propagate toward the entire part of thickness
CONCLUSION
Figure 7.Delamination form on the fracture sur
face, supposed due to layer formation between
the skin and the core.
Figure
6. Different pattern surface fracture
Proven sample
N sample
Figure 5. Crack around the gate bottom and
top ofNG sample.
cooling rate. The setting process also tend to
increase the frozen-in stress orientation on the
surface near to the gate see Figure 2 . This
supposed cause two layers formation, surface part
with highly frozen-in stress orientation
smooth
brittle surface-patterncrack ; delamination formed
and ductile fracture mode in the inner core part.
This is in accordance to the information received
about the cycling time reduction duringproduction
Figure 7 .
Frozen-in stress inmicrostructure and the
external load applied from outer surface has
resulted in initial crack and propagate to entire
thickness product.
Failure Analysis on PolyOxyMethylene Product Using Scanning Electron Microscope, Thermal and Processing
Analysis R. Wijaya)