J u rnal Teknologi, Jilid 11, 1997
EXPERIMENTAL STUDY OF PARAFFIN WAX
POTENTIAL AS A PHYSICAL MODELLING
MATERIAL FOR LOCAL ENVIRONMENT
Md. Afendi M. Yusuf
Department of Design
Faculty of Mechanical Engineering
Universiti Teknologi Malaysia
ABSTRACT
An experimental study on paraffin wax was done to investigate its
potential as modelling material and observing the effect of local
environment thermal parameter. Testing and analysis done using
cromatographer,
strength analyzer,
differential
calorimeter
scanner,
instron
durometer and laboratory experimental
equipment have given us the opportunity to clarify certain
elements in understanding the wax characteristics. Wax, through
this experiment, have been proven viable as a modelling material.
The surface finish is found to be better than Industrial Design
(ID) clay and stable for the local environment as long as it is not
exposed to direct heat source such as sunlight.
1.0
INTRODUCTION
Modelling is a part of normal design process. Modelling can be made for
visualisation, 3-dimensional appreciation, design evaluation, aesthetic valuation and
testing.
64
JurnaJ Teknologi, Ji/id II, 1997
Modelling material such as ID clay and wood are frequently used by model
maker. Petroleum by plastic product like polyurethane foam. is found to be very
useful, as the materials can be found in rigid and semi-rigid form as required.
Most of the modelling materials are not recyclable, some are hazardous as it
may cause skin irritation and health deterioration, some contain environmental
unfriendly material and even difficult to dispose and the cost is expensive.
Paraffin wax tum up for an alternative, this is mainly due to the following
factor [1] :
a.
Paraffin wax are inexpensive.
b.
Available in practically unlimited quantities.
c.
The grades do not vary.
But the question is the compatibility and the performance of this material in
our Malaysian weather. Series of testing have been made to overview the material
characteristic and thermal reaction problem.
2.0
EXPERIMENTAL THEORY
Paraffin wax is a hydrocarbon. In all macrocrystalline paraffin waxes with melting
point between 530 C and 610 C, the majority of n-alkane molecules are in the CIS to
C30
range. Generally, the paraffin wax majority components are n-alkanes, branched
alkanes, mono-cyclo-alkanes, polycycloalkanes, monocyc1oaromatics, and aromatic
cycloalkanes groups [2].
2.1
Surface Profile Analysis
The surface profile is one of the important parts to look into, so we could distinguish
the surface roughness. Using Nikon microscope some figures from both material
surfaces finish were taken for the observation purposes.
65
JUri/a! Tekuologi, Jilid fl. 1997
2.2
Shore Hardness Testing
A Shore Hardness Durometer was used to determine both wax and ID clay
indentation hardness. The hardness comparison was made between wax and ID clay.
The hardness range of the materials will give some general ideas of how the
workability condition of the wax.
Generally, ID clay is much softer and stretchable. On the other hand, wax is
more rigid and brittle. This general evaluation is not sufficient to give a definite
comparison. The shore hardness testing method was designed to give some readings
for references and analysis.
Hardness readings were taken on five differences sample from the same wax
and five differences sample from the ID clay. This method is practiced to minimize
error due to uneven distribution of oil content that is naturally present in the wax,
and mixture of sulphur, ash, and wax exists in the ID clay. The average values were
calculated to represent the hardness value for the wax and the ID clay.
2.3
Strength Analysis
The analysis on the strength of paraffin wax could give us the idea about the wax
and the chance to make some comparative studies between wax and ID clay. The
outcome of this test will provide us the data about working condition of both
materials.
Three points bending flexural test was done to overview the strength of both
materials strength as structural member, even though, the use of both materials is
mainly as filler mechanism. This fact will explore new extended application and
evaluation of both materials as strut, beam, pillar, and cantilever.
2.4
Composition Analysis Using Infra Red
Using Fourier Transfer-Infra Red (FTIR) system 2000 we could get a range of infra
red transmitance spectra. Certain carbon compounds has its owns vibration
frequency pattern. When infra red ray is transmitted through the wax sample, some
wavelength will be absorbed and we will get a pattern of wavelength spectra. From
66
JurnaJ Teknologi, Jilid II, 1997
this spectra we could identify certain group in the wax sample that was used in this
research experiment.
The tested sample was required in a form of uniform thin layer below 1 mrn
thickness and rounded dimension about 15 mm in diameter. The sample was then
position in a hollow thin annulus, which act as a holder. The holder will be
positioned in the analyzer to begin the analysis work.
2.5
Chromatography Analysis
Chromatography is another method to identify the components contain in a certain
materia1. Despite IR analysis, which is qualitative, chromatography provides us a
quantitative result. Solvent (Benzene) was used to dissolve the wax. The analyzer
use Ultra 1 Methyl Silicone column type and the capillary dimension is 25 m x 320
urn x 0.17 urn. This technique enable us to separate the alkanes up to C80 carbon
number and provide result in carbon number distribution [3].
2.6
Differential Scanning Calorimeter (DSC)
This machine has been used widely in thermal analysis of wax, petrolatum, oil, gas,
and polymeric materia1. In this testing experimental wax, samples were prepared
using clean cork borer and slice with razor blade into discs of desired thickness.
Samples weight range normally from 5 mg to 12 mg. The waxes were
scanned at the rate 10° C/min during normal heating runs. The first melting scans
were not reported since they are often non-reproducible. This is probably due to a
repositioning of the sample in the sealed pans.
Two types of sample were subjected for testing. First sample is a new
paraffin wax, which is comes directly from supplier. The sample weight is 5.60 mg.
The second sample is a recycled wax, which has been used for several times in the
operation of model making experiment. The recycled wax sample weight is 5.75 mg.
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Jurnal-Teknologi, Jilid II, 1997
Setting parameter of the testing machine healing and cooling rate at 10° C
And the cooling agent used are Sodium Chloride, Methanol and Liquid Nitrogen,
2.7
Cooling Curve Experiment.
In this experiment, a close observation was made on the variation of the wax
volumetric change during cooling time. The purpose of this experiment is to
determine the temperature range in concern of the material volumetric stability. The
volumetric stability is important since it has a significant effect on the dimension of
the mass.
3.0
EXPERIMENTAL SETUP
The analysis on the strength of paraffin wax could gave us the idea about the wax
and the chance to make some comparative studies between wax and ID clay. The
Material hardness of both materials will be tested using Shore Hardness Durometer.
The outcome of this test will provide us the data about working condition of both
materials. Three points bending flexural test was done to overview both materials
strength as structural member, even though, the use of both materials are mainly as
filler mechanism. This fact will explore new extended application of both materials
as strut, beam, pillar, and cantilever,
Temperature has a very distinctive effect on wax characteristic. Thermal
analysis were done to studies and understanding the wax thermal properties. The
local weather provides heat variation from 27° C to 35° C. For this temperature is in
the range of the wax solid-solid transition period, it is expect that, the wax will
undergo some deformation. The behavior of the wax deform under the influence of
the local environmental is essential to predict the performance of the wax as
modelling material in the local environment.
Table I shows the objective of the individual experimental and testing setup
and the equipment and facilities used.
68
?
~
-
Table I Experimental Setup
Experiment
Density Determination
Method
Equipment
Water Displacement
100ml
. Measuring
l:)
~
~
(;)
Objective
Cylinder,
Digital
~
;r.
-
Material Density
~
~
E.::::
Weighing Machine
Density And Volume
Water Displacement
Cylinder, Digital Weighing Machine
Shrinkage
Infra Red
1000mI Cone Beaker, 100ml Measuring Material
Frequency
Density
And
Volume Shrinkage
Pattern Fourier Transfer Infra Red (FTIR System Material Composition' By
(Spectral)
2000)
Quality
1DOOm I Cone Beaker, 100ml Measuring
Volumetric Change Relative
Cylinder, Digital Weighing Machine, Glass
to Temperature Drop.
Identification
Cooling Curve
Water Displacement
tube, Beuret and Insulator.
Vapourise
Column Type Ultra 1 Methyl Silicone
Material
Compound Analysis
HP19091A-012
Percentage Quantity
Shore Hardness
Surface Indentation
Shore Hardness Testing Machine
Material.Hardness
Strength Test
Three Points Bend
Instron Testing Machine
Material Stresses
Gas Chromatography
Q'I
\CI
Composition By
....'0
'0
"l
Jurnal Teknologi, Jilid II, /997
4.0
EXPERIMENTAL RESULT
The experimental results were taken and analyzed. Some of the experiment readings
were compared to the previous testing result and chart to assist the identification of
the material composition.
4.1
Density Determination
A simple test experiment using the method of water displacement was done to
confirm the density of the wax and ID clay. A sample of wax weight 4.27 gram and
ID clay weight 6.36 gram were dipped into a measuring cylinder fill with 50 ml of
water. The displacement reading, obtained from the measuring cylinder was taken as
the sample volume. The density of the individual sample was calculated using mass
over volume equation. Table 2 shows the density of the ID clay aru' the paraffin
wax.
Table 2 Samples Weight, Volume And Density
Sample
Weight g
Volume ml
Volume em:'
Density g/cm"
Wax
4.27
4.50
4.50
0.9488
ID clay
6.36
4.52
4.52
1.4070
4.2
Determination of Paraffin Wax Density and Volume Shrinkage
Another experiments done to observed the volumetric behavior of the wax at liquid
and solid state. Using the same water displacement method, liquefy wax was fill into
1000 ml cone biker at the level of 600 ml and weighed. The wax was let to cool and
solidify under room temperature. All readings and measurements were recorded and
shown in the Table 3.
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Jurnal Teknologi, Jilid II, /997
Table 3 Experimental Readings and Measurements
Temperature "C
Volume ml
Weight g
Density g/crrr'
Biker
27
-
340.00
-
Liquid wax
85
600.00
481.38
0.8023
Water
27
86..20
86.21
1.0001
Solid wax
27
513.79
481.50
0.9372
From the Table 3, an analysis was made on the volumetric change of the wax
from temperature 85°C to 27 "C. The Volumetric analysis shows a negative value
that representing shrinkage (refer to the calculation below)
% Change in volume
1OOx(513.79-600)/600
-14.37 %
The weight at the liquid state, compare to the weight at the solid state also
shows a small difference. The phenomena occur because there was a big different in
temperature. Practically proven that hot air is lighter than the cold air, and the hot air
balloon float. The change in volume also influence the density (refer to the
calculation below)
% Change in density
100x(0.8023-0.9372)10. 9372
-14.39 %
4.3
Thermal Property - DSC Analysis and Cooling Curve Experiment
The results from the DSC (Fig. 1) shows that the are slight changes in melting point
and solid-solid transitions temperature. Table 4 shows the contrast of the changes.
Melting point of used wax is slightly higher than the new one by 1.66° C. On the
71
Jurnal Teknologi, Jilid Il, 1997
other hand, the solid-solid transition temperature of used wax is slightly lower with
the difference of 1.94°C.
Table 4 New And Used Wax Temperature Changes
Paraffin wax
!lO
11.1
Solid-solid transitions °c
Melting point
New
34.47
44.46
Used
32.53
46.12
-c
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Melting point
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.S.37
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Solid-solid
U ••
o
Ii.•
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~.oo
TellPereture leI
iI.DO
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to.oo
Fig. 1: DSC - New Wax Melting And Solid-Solid Transitions Point
As shown in Fig. 2, the cooling curve experiment indicate that at local
temperature variation of 27°C to 35°C the wax has a minimal shrinkage effect of less
then 1%. Above the 35° C line, the wax volume shrinkage was large and very stable
at room temperature.
72
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Jurnal Teknologi, Jilid II, 1997
4.4
Material Composition
Figure 3 shows the IR spectra of a new wax sample and recycled wax sample. The
peaks of the IR spectra represent certain range of carbon compound groups, which
were used to determine the wax composition. The new wax compositions are shown
in Table 5.
Table 5 New Wax Compositions
Spectral Peak
Compound
Description
3607
Aromatics
Cycloalkenes
3367
Aromatics
CH3
CH 3CH2CHCH,OH
3017
Alkenes R2C=CHR
-C-H stretch
3001
Alkanes
C-H stretch
2972
Alkanes
C-H stretch
2956
Alkanes
C-H stretch
2939
Alkanes
C-H stretch
2924
Alkanes
C-H stretch
2888
Alkanes
C-H stretch
2823
Aldehydes
C-H stretch
2735
Aldehydes
C·H stretch
2636
Aldehydes
C-F stretch
2526
Methylphosphine
CH 3PH2
2414
Dimethylsulfonate
(CH3),S02
2336
Alkyl metallic halide
FCH, CH,SiF3
2151
Cycloalkene
C-F stretch
1898
Alkyl metallic halide
FCH 2 CH 2SiF3
1810
Alkenes RCH- CH,
Overtone
1472
Alkanes
CH2 and CH 3 bend
1459
Alkanes
CH, and CH3 bend
1370
Alkanes
CH, and CH) bend
1304
Alkyl halide R-F
C-F stretch
1127
Alkyl halide R-F
C-F stretch
1081
Alkyl halide R-F
C-F stretch
961
Organometalic-amide
889
Alkenes
~C=CH2
NaCNO
C-H out of plane bend
725
Alkanes
CH 2 and CH 3 bend
390
Alkyl halide R-I
C-I
374
Alkyl halide R-I
C-I
74
Jurna/ Teknologi, Jilid II. /997
........-
u....... _
-Fig.3
4.5
- -
--
Infra Red Spectral Analysis Of New And Recycled Wax
Gas Chromatography
The fragments of the wax sample were firstly dissolved with benzene (solvent for
paraffin wax). The mixture concentration was 2.809% wax and 97.191% benzene.
The mixture was manually injected into the heating chamber that slowly heated up
with the rate of 1.50 C/min.
Figure 4 and Table 7 show the quantity and type of alkane contain in the
sample paraffin wax used the form of bar chart. (SC-straight chain, BC-branched
chain, OC-cycloalkanes).
75
Jurna/ Teknologi, Ji/id II, 1997
Table 6 Other Paraffin Waxes Chromatographic Analysis
Type Of Alkanes
% Content In Paraffin Wax
Straight chain
65-95
Branched chain
3-20
Cycloalkanes
3-15
Carbon number range
18-40
By comparing the experimented GC result to the confirm paraffin Waxes
Chromatographic Analysis (Tables 6 and 7), the contents of the sample wax lies in
the paraffin waxes domain. Therefore we could conclude that, the sample wax is a
paraffin wax which major components are straight chain, branched chain, and
cycloalkanes. This result will be used to correct the result generate by IR spectra
which result is mainly qualitative (IR analysis result do not show any quantitative
value besides the material contents) [3].
-- .........
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Fig.4 Gas Chromatography Analysis Of Wax Components
76
Jurnal Teknologi, Jilid fl. 1997
Table 7 Sample Wax Chromatography Analysis
Con1Jonent
Peak
I
Benzene(sol vent)
Ture
SarrpleArea Wax Content %
1.542
SC
0.41
2
Straight chain alkanes
27.108
3
Straight chain alkanes
28.419
lAO
4
Straight chainalkanes
29.691
3.62
5
Straight chain alkanes
30.938
7.99
6
Straight chain alkanes
32145
11.14
7
Branched Alkanes
32.889
8
Straight chain alkanes
33.311
9
Branched Alkanes
34.002
10 Straight chain alkanes
34.425
II
Braoched Alkanes
35.078
12 Straight chain alkanes
35.495
13 Braoched Alkanes
36.115
14
Qhels alkanes
15 Straight chainalkanes
37.121
17 Qhers alkanes
37.243
18 Straight chain alkanes
37.518
19 Braoched Alkanes
38.093
20
alkanes
0.27
0.46
1218
0.48
11.53
0.74
0.26
9.05
0.53
0.38
7.40
0.59
38.212
21 Straight chain alkanes
38.472
22 Braoched Alkanes
39.031
23 Qhers alkanes
39.152
24 Straight chain alkanes
39.399
25 Qhersa1kanes
39.773
26 Braoched Alkanes
39.943
27 Straight chain a1kanes
40.292
28 Qhers alkanes
40.681
29 Branched Alkanes
40.825
0.31
5.41
0.44
0,33
3.92
0.28
0.40
256
0.28
0.30
30 Straight chain alkanes
41.160
1.55
31 Straight chainalkanes
42003
1.06
32 Straight chainalkanes
42.825
0.70
33 Straight chain alkanes
43.692
0.42
34 Straight chain alkanes
44.656
0.31
Content %
OC
13.29
36.2AO
36.524
16 Braoched Alkanes
QOO-s
Be
93.95
4.21
1.84
100.00
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Jurnal Teknologi, Jilid II, 1997
4.6
Material Strength and Hardness
From strength test , wax filled tube was found to have more bigger potential to
withstand bending pressure as shown in Fig. 5. The action in filling the tube also
increase the tube strength compare to the non filled tube.
I .•
•••
I
I
~
Empty aluminum tube
Aluminum tube with ID clay fill
.,.".,..,.,- Aluminum tube with paraffin wax fill
...£J""'"
1.10
I .•
4.11
...
•••
II.'
II.'
14.0
II.'
Fig.5 Instron Testing Machine - Strength Analysis
The average hardness value for the wax sample is 85.8 from the Shore A
readings and the average hardness value of ID clay sample is 23.1 also from the
Shore A readings. Wax is 3.7 time harder than the ID clay as shown in Table 8.
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Jurnal Teknologi, Jilid II, /997
Table 8 Shore Hardness Readings
4.7
Wax
Readings
ID clay
Readings
1
A/30:85.0
1
A/30:23.0
2
A/30:87.5
2
A/30:22.5
3
A/30:86.0
3
A/30:22.5
4
A/30:86.5
4
A/30:23.5
5
A/30:84.0
5
A/30:24.0
Average
A/30:85.8
Average
A/30:23.1
Surface profile
Referring to Figures 6 and 7, Wax surface profile looks like metallic surface profile.
The surface profile seems to be flat all around as we focusing to the higher
magnification level. At only 1000 times, magnification, some areas are out of focus.
Through the microscopic view at 1000 times magnification the wax surface profile
found to be like endless and shallow wavy pattern.
Referring to Figures 6 and 7, ID clay surface profile looks like a sand papers
surface, at higher level of magnification some area were found to be out of focus.
These phenomena show that there are a lot of peak and valley. When focusing were
made on the peak the valley will be out of focussing range and that made the valley
became blur. These became vice-versa as we were focusing the valley.
Using the microscope too, observation also made on the edge cutting profile.
Figure 8 shows both samples wax and ID clay under magnification of 100 times
The effect heat on wax is very critical. Therefore, some picture under series
of magnification has been take to observe the direct sunlight effect. A sample of wax
was expose to direct sunlight for one hour and the surface temperature was 41°C.
Figure 9 shows us the wax surface profile due to heat deformations.
79
Jurnal Teknologi, Jilid II, 1997
Table 8 Shore Hardness Readings
4.7
Wax
Readings
ID clay
Readings
1
N30:85.0
1
N30:23.0
2
N30:87.5
2
N30:22.5
3
N30:86.0
3
N30:22.5
4
N30:86.5
4
N30:23.5
5
N30:84.0
5
N30:24.0
Average
A/30:85.8
Average
A/30:23.1
Surface profile
Referring to Figures 6 and 7, Wax surface profile looks like metallic surface profile.
The surface profile seems to be flat all around as we focusing to the higher
magnification level. At only 1000 times, magnification, some areas are out of focus.
Through the microscopic view at 1000 times magnification the wax surface profile
found to be like endless and shallow wavy pattern.
Referring to Figures 6 and 7, ID clay surface profile looks like a sand papers
surface, at higher level of magnification some area were found to be out of focus.
These phenomena show that there are a lot of peak and valley. When focusing were
made on the peak the valley will be out of focussing range and that made the valley
became blur. These became vice-versa as we were focusing the valley.
Using the microscope too, observation also made on the edge cutting profile.
Figure 8 shows both samples wax and ID clay under magnification of 100 times
The effect heat on wax is very critical. Therefore, some picture under series
of magnification has been take to observe the direct sunlight effect. A sample of wax
was expose to direct sunlight for one hour and the surface temperature was 41°e.
Figure 9 shows us the wax surface profile due to heat deformations.
79
Jurnal Teknologi, Jilid 1/, 1997
Fig. 6
Wax. And ID Clay Surface Under lOX Magnification
Fig.7
Wax. And ill Clay Surface Under lOOX Magnification
Fig.8
Wax. And ill Clay Edge Cutting Profile lOOX Magnification
Fig. 9
Wax Surface Heat Deformation Under lOX and lOOX
Magnification
RO
Jurnal- Teknologi, Ji/id II, 1997
5.0
DISCUSSIONS
During modelling, manual cutting and scraping is normally in practice. Cutting force
used during cutting and scraping is related to the hardness of the material. From the
shore hardness test, it found that the hardness of wax is approximately 4 times the
hardness of the ID clay. Therefore, we can easily estimate how much the force is
required to cut a wax or clay of the same thickness and at the same rate. In case of
wax manual shaping, the model maker will have to adjust the working rate to suit
the job specification and dimension.
Generally, there is not much change in the wax thermal characteristics. The
solid-solid transitions temperature, help us in determine the working condition of the
wax in our local condition. Variation of ambient temperature between 27° C to 35° C
show that facilities to maintain the temperature below 32°C need to be considered.
Comparing the IR spectra between the new and recycled wax, the peaks
presence in both spectra were almost similar. Except for one peak at 1719 represent
Ketone of six membered types was not present in the new wax but occurred in the
spectra of the recycle wax. This indicates that the recycle wax composition has
changed. The source of this changed is not yet define, whether it is an effect of
excessive heat or an additive compound collected through the Modelling
experiment. Despite this difference, the performance of the recycle wax found to be
similar to the new wax in practical.
From the cooling curve experiment, recorded change of volumes at the
respective temperature, levels can be represents by a graph, corresponding to the
cooling period. From Figure 1, the cooling curve graph indicates that between
temperature 38° C and 27° C the volumetric change seems to be stabilized. The level
of shrinkage at this period is 13.7 % to 14 %. Based on the local temperature range
of 27° C and 35° C, the stable period is within the limit.
DSC testing and analysis result shows that, the wax should be used below the
solid-solid transition temperature. Since above the transition temperature the wax is
in the state of viscous.
81
Jurnal Teknologi, Jilid II, '997
In the observations surface profile, wax is much better than the surface of the
ID clay. In the real practice, ID clay always requires Dinoc film for quality measures
for surface finish and material protection. With wax in practice, the Dinoc film is
unnecessary item. The ID clay surface under magnification seems to be very porous
with a lot of holes and uneven height. Wax in comparison shows a very solid and
rigid surface, with minor pinholes and pitting trace problem.
Through this observation, the surface seems to be dramatically change under
the microscopic magnification. Under naked eyes observation, the surface seems to
get a new mat finish surface texture which is initially gloss finish. The condition of
the surface is similar to a surface after undergo sandblast process. One more fact that
learned from this observation is that there is no spot bubble or pinhole and pitting
trace problem. May be from the method of exposing to heat we could find a way to
improve the surface quality. Further studies should be suggests to finds out the
method of controlling the heat exposure for quality measures.
6.0
CONCLUSION
Through this experiment, wax has been proven viable as material in modelling. Its
technical properties give us some clear ideas of how to use wax in the local
environment. Hot and wet climate in Malaysia gives the ambient temperature range
between 27° C to 35° C. This range is lower than the wax softening range between
33° C to 40° C (Estimation figure from sections 5 and 4.3). During the experiment,
the studio environment, is not air-conditioned.
The wax specific gravity (density) is less than clay as describes in Table 2.
The usage of equal volume, given us half of the total weight. This property, allow us
to construct the based structure which required less strength to support the material.
Furthermore, less weight assisted us in handling and transferring the model.
The wax is harder than clay. The average value wax sample readings (table
7) is N30:85.8 and the average readings ofID clay sample is N30:23.1. The wax is
3.7 time harder than the ID clay (Section 4.6). The workability on shaping process
required more energy at the same rate of about 4 times. Even though to work with
82
Jurnal Teknologi, Jilid II, 1997
wax there is more hardship but the surface hardness have given us the assurance that
the wax can withstand applied 4 times applied force. Stability of the surface here is
the right words to describe the wax capability.
Surface finish is one more characterization that came into consideration
when making model. Wax surface finish can be workout to the quality of gloss
finish. Both materials have been observes under microscope. The clay surfaces and
edges found to be rougher than wax. In normal application with additional cost, to
overcome this unevenness, Dinoc film were introduces for improving the quality of
the surface finish and protecting the clay from contaminated by coating and painting
materials. The understanding of the material properties have given us some
assistance in manipulating the material towards the modelling application.
REFERENCES
1. Freund, M. , Paraffin Product, Properties Technologies And Application,
Elsevier Scientific Publishing Co, New York, 1982.
2. Algelt, K. H. And
Gouw, T. H, Chromatography In Petroleum Analysis,
Chevron Research Company Richmond, California, Marcel Dekker Inc, New
York, 1979.
3. Adlard, A. R., Chromatography in The Petroleum Industry, Journal of
Chromatography Library, Vol 56, Elsevier, London, 1995.
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