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Composition, Control and Use of
Investment Casting Wax
Richard Hirst FIMMM
Blayson Olefines Ltd
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Agenda Composition and Structure
Properties Categories
Recycling
Selection
Control and Testing of Wax
Relationship between Wax and InjectionCharacteristics
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Investment Casting Wax
Wax is the oldest thermoplastic material known toman
Beeswax was utilized in the lost wax process bycraftsmen in the ancient civilizations of China & Egypt
Today the name wax applies to any substance
having wax-like properties better described as industrial moulding compounds
If the pattern is wrong, the casting will be wrong
It follows that the choice of wax is critical
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Composition of Investment Casting Wax
Investment casting waxes are complexformulations containing many components : Paraffin wax
Microcrystalline wax
Resins - strong, viscous, brittle
Polymers - ductile Fillers - reduce contraction, improve mechanical
strength
The % addition and control of these additives iscritical in determining the properties of the wax,they make each wax unique
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Structure of Investment Casting Wax
Many variations are formulated to suit differingrequirements
Key properties such as melting point, hardness,viscosity, expansion and contraction, setting rate, etcare all influenced by the structure and composition ofthe wax compound
Understanding the properties of the individualcomponents and how they interact is essential inmeeting foundries individual requirements
The complex composition manifests itself in aphysical behaviour different to that of othersubstances
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Phase Changes of a Typical Wax
Unlike other homogeneous chemicalcompounds, wax does not melt immediatelyon heating but passes through severalintermediate states :
solid plastic semi-plastic semi-liquid liquid
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Expansion & Contraction of Wax
The structure and components used in an investmentcasting wax will influence the expansion andcontraction
Like other materials wax expands on heating andcontracts on cooling
In comparison with a metal the expansion is relativelyhigh
Wax expansion and contraction rates are not uniformbut vary with phase and structure changes duringheating/cooling
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Categories of Investment Casting Wax
Pattern wax
straight (unfilled) emulsified filled
Runner wax Water Soluble wax other Special wax
dipping/patching/adhesive Reclaim & Reconstituted wax
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Wax Recycling
Customers used wax from autoclave returned
to wax manufacturer for reprocessing cleaned & filtered additives to adjust properties to specification
Reclaim wax for runner systems Reconstituted wax for pattern production Environmental and economic benefits
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Wax Selection
Wax selection is determined by the particular applicationand the process criteria are : Injection
state/setting rate/rheology/geometry/equipment/surface finish
Removal,handling,assembly strength/hardness/setting rate/stability/ability to make joins
Dimensional control thermal expansion/contraction/cavitation/distortion
Shelling/mould making strength/wetability/resistance to binders and solvents
Dewax and burnout melting point/viscosity/thermal expansion/thermal diffusivity/ash content Other : cost/availability/recycling/toxicity/environmental
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Process Control of Wax Products
Close control is achieved by :
Automatic temperature control of themelting process
Data monitoring of both temperature of themelt and process equipment
Extensive testing
Statistical Process Control of both rawmaterials and finished products
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Statistical Process Control
O b s e r v a t i o n
IndividualValue
342340338336334332330328326324322320318
0.03
0.02
0.01
0.00
-0.01
_X=0 . 00811
U C L= 0 . 0 2 70 9
LC L=-0.01087
O b s e r v a t i o n
Moving
Range
342340338336334332330328326324322320318
0.03
0.02
0.01
0.00
__M R = 0 . 0 0 7 1 4
U C L= 0 . 0 2 33 2
LC L= 0
1
1
Control chart of incoming ash lev els on f i l ler use d.
Both incoming test results and in-house test results on rawmaterials are fed into a control chart, and use based on the resultsdetermined.
The use of SPC also allows tracking of trends in suppliers
processes, and allowing pre-emptive corrective action.
Out of
Control
(Not used)
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Wax Specification Products are tested to
establish whether they meetspecification
The specification isdetermined during thedevelopment stage
it is a reflection of thecapability of the process
a provisional specification isintroduced which is thenreviewed after 12 batches
The data is used to generatea process capability which isbuilt into the formalisedspecification
74737271706968
LB UB
Process Data
Sample N 13
StDev(Within) 0.679669
StDev(Overall) 0.851196
LB 68
Target *
UB 74
Sample Mean 70
Potential (Within) Capability
Overall Capability
Pp *
PPL *
PPU *
Ppk *
Cpm
Cp
*
*
CPL *
CPU *
Cpk *
Observed Performance
PPM < LB 0.00
PPM > UB 0.00
PPM Total 0.00
Exp. Within Performance
PPM < LB *
PPM > UB *
PPM Total *
Exp. Ov erall Performance
PPM < LB *
PPM > UB *
PPM Total *
Within
Overall
Process Capability of DMP (12 batches)
SPECIFICATION WOULDNEED ADJUSTING INLINE WITH RECORDED
DATA.
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Test Methods
Industry recognised physical tests are :
Congealing Point
Drop Melt Point
Viscosity
Penetration
Ash
Filler content
Mechanical strength
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DSC, Oscillation
DSC analysis gives anindication of the melting
phases of different
compounds.
40 45 50 55 60 65 70 75 80 85
T [C]
0 10
1 10
2 10
3 10
4 10
5 10
6 10
7 10
'[Pas]
0
10
20
30
40
50
60
70
80
90
[]
060085A Osc
' = f (T) = f (T)
060107 (XL21) Osc' = f (T)
= f (T)
Oscillation curves give anindication of the shear properties of
wax at dif ferent temperatures.
Gives a good indication of the
setting properties of a wax.
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Volumetric ExpansionComparison of Microcrystalline w axes and Parr afin waxes (Volum teric Expansion.)
-5.000%
0.000%
5.000%
10.000%
15.000%
20.000%
25.000%
25.1541 30.1761 35.036 40.058 45.242 50.102 55.2859 60.1459 65.1679 70.0279 75.0498 80.0718 85.2558 90.4398 95.1377 100.16
LMP from Korea
MMP FROM KOREA
WAX REX 2460
LMP FROM BLAYSON
Parraff in 56 - 58
Parraff in 62 - 64
Parrafin 68 - 70
C0310
Blayson Japan has developed
a volumetric expansion test to
dewax temperatures.
A unique feature is that data
capture is automatic and not
dependent on operator
measurements.
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Relationship between Wax and
Injection Characteristics
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Wax Fluidity Wax fluidity is key to control of
many problems
flow lines surface finish non fill and air entrapment
A relationship exists betweenwax temperature and fluidity.Important when operating nearthe congealing point
Effect of die temperatureshould not be underestimated
60 65 70 75 80 85
T [C]
0
1
2
3
4
5
6
7
8
9
10
11
[Pa
s]
040178B = f (T)
l0049 = f (T)
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Fluidity Measurement
Wax Fluidity can be measuredusing the Fluidity Spiral
Injected at : fixed wax temperature
fixed die temperature
fixed injection pressure fixed flow rate
Can be used with each newbatch to estimate its flow
characteristics and allowadjustments to be made priorto start of production
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Factors Affecting Fluidity
WAXFLUIDITY
INJECTION
TEMPERATURE
DIE
TEMPERATURE
AIRRESISTANCE/
PRESSURE IN
DIE
SURFACE
TENSION OF
DIE
VISCOSITY
TURBULENCE
AIR
TEMPERATURE
CAVITY
GEOMETRY
INJECTION
PRESSURE
CONGEALING
POINT/ RATE OF
CRYSTALLISATIONDIE THERMAL
CONDUCTIVITY
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Relationships with Injection Pressure
Pressure
Flow
lines
1.00.50.0-0.5-1.0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
S 0.290832R-Sq 95.5%
R-Sq(adj) 94.8%
Fitted Line PlotFlow lines = 2.638 + 1.163 Pressure
Pressure
Surfacefinish
1.00.50.0-0.5-1.0
5
4
3
2
1
S 0.890225
R-Sq 50.3%
R-Sq(adj) 42.0%
Fitted Line PlotSurface finish = 3.150 + 0.7750 Pressure
Recent trials suggest a relationship
between flow l ines and pressure,
higher pressures minimise flow l ines.
Evidence exists for a similarrelationship between pressure and
surface finish (orange peel).
Obviously care must be taken when
using cored parts (core breakage)
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Temperature and Cavitation
Meanof
Sinking
1-1
5
4
3
2
1-1
1-1
5
4
3
2
Flow Pressure
Temperature
Main Effects Plot (data means) for Sinking
Temperature
Sinking
1.00.50.0-0.5-1.0
5
4
3
2
1
S 0.677003
R-Sq 84.6%
R-Sq(adj) 82.1%
Fitted Line PlotSinking = 3.375 - 1.375 Temperature Injection trials suggest a strong link between wax
temperature and cavitation.
Indications are that the cause is the time that the
wax is liquid/semi liquid, increasing thetemperature increases the time.
This explains why sprue size and location affectssinking, and also that sinking is probably relatedto the setting rate of the wax.
Filler reduces liquid by around a third andreduces contraction.
40 45 50 55 60 65 70 75 80 85
T [C]
-1 10
0 10
1 10
2 10
3 10
4 10
5 10
6 10
7 10
'
[Pas]
20
40
60
80
100
[]
L0049 OSC' = f (T) = f (T)
040178B OSC' = f (T) = f (T)
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Summary
Investment casting wax compounds are complex consist of many different components
consequently exhibit a range of properties Wax properties influence pattern behaviour in the
foundry and ultimately the quality of castingsproduced
Correct product choice allied with strict process &quality control procedures is essential
More information available atwww.investmentcasting.com
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