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A R C H I V E S
o f
F O U N D R Y E N G I N E E R I N G
Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences
ISSN (1897-3310) Volume 11
Issue 3/2011
149 – 154
25/3
A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 1 , I s s u e 3 / 2 0 1 1 , 1 4 9 - 1 5 4 149
Effect of pouring temperature
on the Lost Foam Process
T. Pacyniak*, R. Kaczorowski
Department of Materials Engineering and Production Systems, Technical University of Łódź,
1/15 Stefanowskiego Str., 90-924 Łódź, Poland
*Corresponding author. E-mail address: [email protected]
Received 10-05-2011; accepted in revised form 13-05-2011
Abstract
In this study, the analysis of the influence of the pouring temperature on manufacture process of castings by the Lost Foam method was
introduced. In particular, numerical simulation results of effect of silumin and grey cast iron pouring temperature on pouring rate and gas
gap pressure were analyzed. For simulating investigations of the Lost Foam process introduced mathematical model of the process was
used. For calculations, the author's own algorithm was applied. The investigations have proved that with increasing pouring temperature
the pouring rate increases, while pressure in the gas gap are decreasing. The author’s own investigations showed a more significant effect
of the silumin pouring temperature than grey cast iron pouring temperature on the lost foam process.
Keywords: Foundry Engineering, Lost Foam, Foamed Polystyrene Patterns
1. Introduction
The growth of the interest in the process of making castings
by Lost Foam technology became at the close of the eighties of
past century when this technology started being used for mass
production of castings characterized by high accuracy and
repeatability of dimensions, made of light metal alloys and ferrous
alloys both. The great interest in the Lost Foam technology was
mainly due to a definitely lower cost of castings manufacture and
financial outlays very encouraging when compared with the
traditional process [1]. Respective of the traditional casting
process using standard moulding sands, this novel technology
offers a number of undeniable advantages, including also the
following ones:
it is possible to reproduce holes in castings without the
necessity of using cores,
significantly lower costs of the production,
the lack of parting planes and cores reduces the number
of operations necessary for casting fettling and
finishing,
the use of pure sand instead of moulding mixture
eliminates the effect of moisture causing casting
defects, with an extra advantage of cheaper sand
reclamation,
less of foundry tooling and equipment is needed (no
moulding machines, mixers for moulding sand, etc.),
lower labour input in final fettling operations due to the
absence of flashes, burn-on defects, etc.
Many factors have an influence on the quality of casts made
by this technology among other things:
density of foamed polystyrene from which its the
strength depends of the pattern and the quality of its
surface,
the kind of sand, and in the peculiarity its permeability,
refractory coating applied on the pattern which makes
the working surface of the mould. This coating allows
to obtain a necessary quality of cast surface and
prevents metal penetration inside the sand grains,
and pouring rate.
A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 1 , I s s u e 3 / 2 0 1 1 , 1 4 9 - 1 5 4 150
The kind of alloy and pouring temperature are one’s of factors
have influence on pouring rate.
Mould pouring should be as short as possible, without breaks,
to avoid the formation of defects. It is believed that the smaller
the distance (gap) between the model and the metal front, the
lower the risk cracking refractory coating and collapse mold
cavity. Pouring temperature is generally higher than traditional
sand casting, this follows from the fact that the alloy loses some
heat, which is passed to the evaporation of polystyrene pattern.
2. Technological aspects of the pouring
temperature and kind of alloy
Pouring temperature is determined by the type of casting
alloy. In the present study analyzed the effect of temperature of
grey cast iron and silumin AlSi11 on evaporation process of
foamed polystyrene pattern and mould cavity filling process. It
turns out that the process of thermal decomposition of polystyrene
depends on the temperature at which decomposition occurs.
Decomposition in the temperature about 500 C causes that
volatilized products consist primarily of styrene monomer C8H8
[2]. As the temperature is increased further, the monomer
molecule undergoes additional fragmentation to yield light
hydrocarbons such as C7H8, C6H6, C2H4 and C2H2. At
temperatures greater than 1000 C, thermal degradation of
polymer may produce significant quantities of graphitic carbon
and even hydrogen. However, studies have failed to identify over
50% of the compounds [2]. Volume of gas produced per unit mass
of polystyrene, depending on the pouring temperature 750 and
1300 C respectively amount to 250 cm3/g and 800 cm3/g [3].
Thermal degradation of the expanded pattern also depends
on the type of polymer. Table 1 presented physical parameters for
the expanded polystyrene (EPS) and expanded polymethyl
methacrylate (PMMA) patterns.
Table 1.
Physical parameters primary polymers used in the lost foam process [4]
EPS PMMA
Glass transition temperature (°C) 80 do 100 105
Collapse temperature (°C) 110 do 120 140 do 200
Melting temperature (°C) 160 260
Temperature for start of volatilization (°C) 275 do 300 250 do 260
Peak volatilization temperature (°C) 400 do 420 370
End temperature for volatilization (°C) 460 do 500 420 do 430
Heat of polymerization (J/g) 648 578
Heat of degradation (J/g) 912 842
Gas field at. 750°C (cm3/g) 230 273
Gas field at. 1300°C (cm3/g) 760 804
% non-volatile residue at 1400°C 15 3
3. Investigation of an effect of pouring
temperature and kind of alloys on
the mould cavity filling
3.1. System of equations describing the
process of mould filling with molten alloy
The remarks reported [5] concerning kinetics of the evaporation process of foamed polystyrene pattern, on the dynamics of the mould cavity filling process and changes of gas pressure in the gap enabled the process of pattern evaporation and mould filling to be written as a system of differential equations presented below:
220.2.2.2
.2.2.2.21
122
FTTcr
FTTcrcTThyy
d
dy
topmt
partopparcppar
g
c
(1)
1
111
1122
2
11
2
1
12
1
F
y
F
L
F
LF
PyLgFd
L
Fd
LFP
d
d
wd
wd
wg
wg
gwg
wdstwd
wd
wgstwg
wg
Hatm
(2)
11
d
dy (3)
A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 1 , I s s u e 3 / 2 0 1 1 , 1 4 9 - 1 5 4 151
d
yyd
yy
P
PlF
TRsdKPP
Fyy
TRFc
d
dP
g
atm
kpparg
12
12
1
23
22
112
57,1
(4)
For simulation testing of the lost foam process, and specially
of the effect of pouring temperature on mould cavity filling with
casting alloy, the presented mathematical model of the process
was used along with the author’s own algorithm for calculation of
the effect of pattern thickness on, among others, raising of metal
column surface in the mould, gas pressure in the gas gap. Tests
was conducted for the gray cast iron and silumin.
3.2. Simulation tests of the Lost Foam Process
3.2.1. The scope of simulation tests
Tests enclosed analysis of the pouring temperature in the
range of T1=973÷1123 K (for silumin) and T1=1523÷1723 K (for
cast iron). Moreover, in simulation tests the following parameters
were adopted: density of pattern ρ2=20 kg/m3, permeability of
refractory coating Kp=7,7·10-9 m2/Pa·s, pressure in mould Pk=100
kPa, ingate section Fwd=0,5 cm2. The simulation tests of an effect
of pouring temperature on the process of mould cavity filling
were carried out for AlSi11 silumin (ρ1=2700 kg/m3) and for grey
cast iron EN-GJL 200 (ρ1=7200 kg/m3).
3.2.2. Analysis of the results of simulation tests
Simulation tests were carried out on a model mould shown in
Figure 1, and parameters comprised in the range of investigations.
On the basis of the obtained results of calculations, a dependence
was plotted for time-related changes of the main parameters,
characteristic of the process of mould filling with molten metal.
Fig. 1. Schematic representation of the process of mould cavity filling and pressure distribution inside mould
F
F
Ll
q q
y
y
Y
X
F
F
L
S
1
1
2
2
wd
wd
wg
wg
A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 1 , I s s u e 3 / 2 0 1 1 , 1 4 9 - 1 5 4 152
The effect of silumin pouring temperature on pouring rate is
shown in Figure 2. Hence it follows that with increasing pouring
temperature υ1, pouring rate increases, which seems obvious. For
pouring temperatures in the range from 973 K to 1123 K was
obtained the maximum pouring rate from 5 cm/s to about 6.5 cm/s
respectively.
Fig. 2. Changes in pouring rate υ1=f(τ) for different silumin
pouring temperature T1
The change of the cast iron pouring rate for different pouring
temperatures is shown in Figure 3. From the presented results
follows that pouring rate is about two times higher in comparison
with silumin. Furthermore, character of pouring rate changes in
the initial phase of pouring is more dynamic, which is associated
with a significantly higher density of cast iron.
Fig. 3. Changes in pouring rate υ1=f(τ) for different grey cast iron
pouring temperature T1
Comparison of average pouring rate for silumin and cast iron
depending on the pouring temperature is presented in Figure 4.
For the simulation studies concerning silumin, the increase in
temperature of 150 degrees has increased the pouring rate from
υ1=3,8 cm/s to 5,6 cm/s and is almost proportional. However, in
the case of cast iron for a higher range of pouring temperatures
(200 C) were slightly lower an of the pouring rate υ1=9,4 cm/s to
do 10,8 cm/s. The temperature of pouring can be a parameter,
which in a quite simple way to control the pouring rate of mould
depending on the specific casting, on its thickness, shape and
complexity, and even weight.
Fig. 4. Mean pouring rate vs. pouring temperature T1
Effect of pouring temperature on the gas pressure in the gas gap is
shown in Figure 5 (silumin) and Figure 6 (cast iron). This figures
it follows that with increasing the pouring temperature the gas
pressure in the gas gap decreasing. The higher is the pouring
temperature, the higher is the gas temperature in the gas gap, and
hence the viscosity of gases is lower, making them easy filtration
by refractory coating (higher permeability). Thus, the filtration of
gases through the refractory coating and sand with a higher
permeability, may be to filter the same amount of gas at lower
pressure. Gas pressure in the gas gap is significantly higher by
cast iron pouring, because at higher temperatures is formed
considerably higher amount of gaseous decomposition products of
polystyrene.
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8Pouring time, s
0
3
6
9
1
2
4
5
7
8
Po
uri
ng
rate
, c
m/s
Pouring temperature, K
973
998
1023
1073
1123
0 0.4 0.8 1.2 1.6 20.1 0.2 0.3 0.5 0.6 0.7 0.9 1 1.1 1.3 1.4 1.5 1.7 1.8 1.9
Pouring time, s
0
3
6
9
12
15
18
1
2
4
5
7
8
10
11
13
14
16
17
Po
uri
ng
rate
, c
m/s
Pouring temperature, K
1523
1573
1623
1673
1723
1000 1100 1500 1600 1700950 1050 1150 1550 1650 1750
Pouring temperature, K
4
6
8
10
12
3
5
7
9
11
Mean
po
uri
ng
rate
, c
m/s
Cast iron
Silumin
A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 1 , I s s u e 3 / 2 0 1 1 , 1 4 9 - 1 5 4 153
Fig. 5. Changes of pressure in the gas gap Pg=f(τ) for different
silumin pouring temperature T1
Fig. 6. Changes of pressure in the gas gap Pg=f(τ) for different
grey cast iron pouring temperature T1
This nature of the effect of temperature on the quantity the gas
pressure in the gas gap was confirmed in Figure 7 showing the
change of mean pressure in the gas gap depending on the pouring
temperature. For gray cast iron, the increase pouring temperature
about 2000 causes only slightly (0.2 kPa) decrease the average gas
pressure in the gas gap.
Fig. 7. Mean pressure in gas gap vs. pouring temperature T1
4. Summary
Presented simulation studies in this article enable to analyse
of an effect that the pouring temperature to mould filling rate and
pressure in gas gap. The investigations have proved that with
decreasing pouring temperature the pouring rate decreases, while
pressure in the gas gap are increasing. Effect of pouring
temperature on the lost foam process is not as significant as other
parameters: density of polystyrene pattern [6], thickness and
permeability of refractory coating [7], pressure in mould [8].
However, increasing pouring temperature of metal at 150-
200 C can be simple way increase the speed of flooding of about
2 cm/s. An increase of the pouring rate ensures correct making of
castings even of very intricate shapes and small wall thicknesses.
Acknowledgements
The work was made as a part of the research project No. N N508
443536 financed by funds for science in the years 2009-2011
by the Polish Ministry of Science and Higher Education.
References
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100
102
104
106
108
110
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103
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Pre
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102.5
107.5
112.5
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121
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A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e 1 1 , I s s u e 3 / 2 0 1 1 , 1 4 9 - 1 5 4 154
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