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JOURNAL OF IRON AND SfEEL RESEARCH. INTERNATIONAL. 2009. 16(4): 12-17
Application of Numerical Simulation Technique to
Casting Process of Valve Block
MI Guo-fa' , LIU Xiang-yu" , WANG Kuang-fei' , FU Heng-zhi'
(1. School of Materials Science and Engineering. Henan Polytechnic University. Iiaozuo 454000. Henan. China;
2. Department of Mechanical Engineering. Chengde Petroleum College. Chengde 067000. Hebei , China)
Abstract: The numerical simulation technique was applied to the casting process of a valve-type part. The mold-fill-
ing and solidification stages of the casting were numerically analyzed. The filling behavior. solidification sequence.
and thermal stress distribution were reproduced and the possible defects. such as cold shut and shrinkage. were pre-
dicted. Based on the simulation result. the double-gating system was replaced by a single-gating system. Meanwhile.
the chills were used to regulate the solidification sequence of casting. To eliminate the cracks in the casting. the sand
core was converted into a canulate one. By modifying the original process. the defects were eliminated and the casting
with good quality was obtained.
Key words: cast steel; valve-type part; numerical simulation; process modification
Valve-type parts are the nuclear components of
power engineering, the properties of which influence
the operation of assembling unit[l-3]. Comparing
with other types of casting, the valve-type casting
either possesses complex configuration such as flan-
ges, bosses, and ribs, or possesses complex internal
structure and conspicuous wall unevenness. These
characteristics easily cause the defects such as crack.
shrinkage, and dispersed shrinkage. Meanwhile.
the valve-type parts usually service in the caustic
media under high pressure and temperature, and
clearly, stringent demands are placed on them to
prevent leakage accidents[4.5].
The computer-based simulation technique
shows great advantages over the conventional trial-
and-error methodologies for design and optimiza-
tion, and more and more enterprises adopt this pow-
erful tool. Using this method, the shrinkage defects
can be forecast efficiently and its accuracy can reach
a quantitative level. The occurrence of defects dur-
ing the mold-filling stage such as entrapped air, en-
trapped slag, and cold shut can also be predicted. In
the past. several scholars carried out researches in
this field[6-IO]. In the present study, the numerical
simulation system ViewCast was used to simulate the
temperature. velocity and stress fields during the
filling and solidification stages of steel valve-body
casting. The aim of the present study is to predict the
location and volume of the defects, and then the original
process is modified to improve the quality of casting.
An ammonia valve-body with a mass of 180 kg
was cast from 30 steel. The materials of molds and
cores were resign-bonded sand and sodium silicate-
bonded sand, respectively. The pouring temperature
was 1 600 "C. After the castings solidified entirely,
some cracks were found at the root segment of the
flanges and several castings were even damaged by
the through crack, as shown in Fig. 1.
(a) Outside; (b) Inside
Fig. 1 Crack passed through valve body casting
Foundation Item: Item Sponsored by the Innovation Fund for Outstanding Scholar of Henan Province of China (0621000700)
Biegraphy sMl Guo-fat 1966-). Male. Doctor. Professor; E-mail: peter@hpu. edu, en; Revised Date: April 18. 2008

2. Issue 4 Application of Numerical Simulation Technique to Casting Process of Valve Block • 13 •
In the original scheme, the designers adopted
two downsprues , which were placed at the rims of
two large flanges, as shown in Fig. 2. Four flat top
risers were placed at the top of the flanges.
is the pressure; C; is the specific heat of molten
metal; A is the thermal conductivity; T is the tem-
perature; L is the latent heat; and I, is the solid
phase ratio at the solidification stage.
1. 2 Geometric model
The three-dimensional geometric model of steel
valve-body was input into the ViewCast system and
then translated into the FD (finite difference) mod-
el, which consisted of 10 000 000 FD meshes, as
shown in Fig. 3 (b). The step length of mesh gener-
ation was self-adjusting and the thinnest position of
the casting was divided into at least three meshes to
ensure the accuracy of numerical simulation.
Fig. 2 Diagrammatic chart of original scheme
1. 3 Initial parameters of calculation
The material properties of metal and mold are
listed in Table 1 and Table 2, respectively.
1 Experimental 2 Simulation Results and Discussion
Material property Value
Table 1 Material property of 30 steel
(a) Three-dimensional model; ( b) Meshed model
Fig. 3 Models of valve body casting
2. 1 Original scheme
Fig. 4 reveals the simulation result of mold filling.
From Fig. 4 (b), it can be seen that two fluid
streams merge at the bottom of the valve-body.
which is the thinnest region in the casting. Owing to
the heat transmission between the liquid metal and
mold, the temperature of liquid front falls sharply.
0.255
205
80
1 803.0
1 763.0
0.29
7870
6. 2X 10 '
172
50. 7
Density/j kg e rn ,)
Viscosity/r kg > m- I • ,-I)
Specific heat/ (j • kg 1 • K- 1 )
Thermal conductivity/f W s m- I • K I)
Latent heat/(j • kg- I)
Modulus of elasticity/GPa
Shear modulus/GPa
Liquidus temperature/K
Solidus temperature/K
Poisson's ratio
1. 1 Mathematical model
The flow of liquid metal is assumed to be incom-
pressible Newtonian fluid and the governing equa-
tions at the filling and solidification stages are given
below.
Navier-stokes equation
(
au au au au, «»p:.,-- +u -J +v -) +w ::;- - I = - -) +pg +at (X 'y o z: (X
I
,a2u +J2 U +a
2
u I
P,ax2 J y2 JZ2 (1)
[
, av + u Jv + v av + w av l' =_ap+ g +
p at ax ay Jz, Jy P y
I
J2v+az~+azvl (2)
P ax2 ayz az2
"
~w+u dW+ v dU!+w aw:, app =--+pg.+
at ax ay Jz! az
I
, a2w +azw +aZwj (3)
P, axz Jyz azz
Continuity equation
au +Jv +Jw =0 (4)
Jx Jy dz
Heat transfer equation
C IaT+u aT+v JT +w aT]
p P at Jx Jy az
AI' aZT+JzT+a
2T]
+L JI. (5)
axz ay2 azz at
where, p is the density; u , u , and ware the velocity
vectors; t is the time; P is the dynamic viscosity of
the liquid metal; g,r' gy' and g. are the gravitational
acceleration vectors in the directions x , y, and z; P

3. • 14 • Journal of Iron and Steel Research. International
Table 2 Material properties of mold
Vol. 16
Resin-bonded sand
Sodium silicate-bonded sand
Densit y /Lkg > m 3)
Specific heat/(j • kg-- I • K-I)
Thermal conductivity/(W· m- I • K I)
Densit y/Lkg v m t " )
Specific heat/ (J • kg- I • K-I )
Thermal conductivity/ (W • m -I • K - I)
1 600
i. 07
o. 7
2 583
. 202
o. 36
Coefficient of heat transfer between mold and casting/ (W • m - 2 • K- I ) 580
(a) -]. 6551 <b) -3.36 s s (c) -5.6151 <d) -14.845
Fig. 4 Temperature distribution in mold-filling stage of original scheme
Consequently. this may cause the defects such as
cold shut and misrun in the bottom of casting, and
the turbulence of the liquid metal may cause the slag
entrapped in the mold-filling stage.
When the mold cavity was filled entirely. the
solidification simulation followed and the results are
shown in Fig. 5. Fig. 5 indicates the volume and po-
sition of shrinkage defects of the original scheme. It
is seen that the feeding system is not effective and
therefore some isolated liquid regions are created in
the casting. These regions solidify slower than other
positions of casting, and at the final stage of solidifi-
cation, they do not have enough liquid metal to
feed. As a result, the shrinkage defects are formed
at these regions.
The stress analysis was applied to the original
scheme and the results are given in Fig. 6, which are
the thermal stress distribution of the casting at 250 s.
Fig. 7 depicts the temperature distribution at the
same time. The results indicate that at 250 s after
mould filling during solidification stage, the tensile
stress zone is formed at the root segments of flanges
(Fig. 6), at about 1 500 'C (Fig. 7), At this temper-
ature, the metal is in the semi-solid state with poor
strength, and the concentration of stress leads to the
crack of the casting.
2. 2 Process modification
The double-gating system used in the original
scheme caused hidden trouble of cold shut and mis-
run and the feeding system was not effective to feed
the shrinkage of metal during the solidification
stage. Consequently, the process was improved in
three aspects, namely feeding system, gating sys-
tern, and mold.
Fig. 5 Viewer of shrinkage defect distribution
Fig. 6 Stress distribution of the original scheme

4. Issue 4 Application of Numerical Simulation Technique to Casting Process of Valve Block • IS •
Fig. 7 Temperaturedistribution of original scheme
The risers were placed on the crown face of
flanges with pads, as shown in Fig. 2, which were
difficult to cut. In the modified scheme, the risers
were put on the flat surfaces of flange. To enhance
the feeding capacity, the cylindrical risers were used
instead of flat risers, because the former could sup-
ply more liquid metal during the solidification stage,
as shown in Fig. 8 (a). For the purpose of enhan-
cing the cooling capacities of hot spots, some chills
were placed at the relevant positions in the mold.
Fig. 8 (b) explains the positions of chills.
The aim of the pouring system is to lead the liquid
Fig. 8 Diagrammatic chart of riser (a) and chill (b)
metal into the mold cavity rapidly and smoothly.
From the simulation result, it can be seen that the
faulty design of gating system led to underlying de-
fects. Moreover, in the manual operation, the
foundry workers found it difficult to ensure that two
downsprues were filled at the same time using the
double-gating system. Thus, In the modified
scheme, the single-gating system has been adopted,
which consists of pouring cup, downsprue , runners,
and ingates , as shown in Fig. 9.
Fig. 10 reveals the filling behavior of the liquid
metal by use of the modified gating system, Using
the single-gating system, the filling behavior of liq-
uid metal becomes more reliable. The two runners
are of the same size and have symmetrical distribu-
tion; therefore. the two liquid fronts reach the bot-
tom of casting at the same time at a high tempera-
ture, higher than 1 550 ·C. This kind of filling mode
can avoid the defects such as misrun and cold shut.
Fig. 11 indicates the solidification sequence of
casting using the risers and chills. The right color
bars in the figure indicate the time and the unit is
second. The solidified regions have been hidden for
vivid observation.
From Fig. 11, it can be found that the modified
risers and chills can regulate the solidification se-
quence of casting effectively. Owing to the chilling
effect, the bottom of the casting solidified first. By
placing the chills at the root of the flanges. these ar-
eas also solidified faster than other regions. The so-
lidification of the whole casting is from spherical
surface to risers. There is ample hot metal in the
risers, which can feed the shrinkage of liquid metal
in the final stage of solidification.
As a result, the volume of shrinkage defects can
Fig. 9 Diagrammatic chart of modified pouring system

5. • 16 • Journal of Iron and Steel Research. International
(a) -2.69 s; (b) -2.93 s; (c) -3.65 s; (d) -13.3 s
Fig.l0 Temperature distribution in mold-filling stage of modified scheme
Vol. 16
(a) -100 s, (b) -200 s, CC) -300 s, (d) -500 s, (e) -800 s,
Fig. 11 Solidification time of critical regions in casting
CD -1 100 s
be reduced to a certain amount. as shown in Fig. 12.
Fig. 12 indicates that there are only two concentrated
shrinkages in the casting and the rest are placed in
the runners and risers. It can be concluded that the
riser and 'chill are useful to eliminate the shrinkage
defects in the casting.
The structure of casting is complex. In more
detail. there are hot spots at the junctions of flanges
and spherical surface. Meanwhile. the placement of
Fig. 12 Position and volume of defects in
casting with chill and modified riser
top risers on the flanges aggravates the hindering of
the solid shrinkage of casting. According to prac-
tice. the inferior deformability of mold sand at an el-
evated temperature is the immediate cause of the
casting's crack. In such a case. the infarctate sand
core was converted to a canulate core (with a skele-
ton of metal in the sand), as shown in Fig. 13 (a).
Meanwhile, to prevent the collapse of core sand, the
cavity of the sand core was filled with dry sand. as
shown in Fig. 13 (b).
(a) Canulate sand core, (b) Cavity of core filled with dry sand
Fig. 13 Photograph of modified sand core

6. Issue 4 Application of Numerical Simulation Technique to Casting Process of Valve Block • 17 •
2. 3 Practical pouring after processes modification
Fig. 14 shows the valve-body produced by the
modified process. It can be seen that the surface of
the casting has an integrated, smooth, and bright
surface. After observational check, no cracks were
found. The process modification can be considered
to be successful.
(a) Outside; (b) Inside
Fig.14 Valve body cast by modified process
3 Conclusions
The overall process from filling stage to solidifi-
cation stage for the valve block was numerically ana-
lyzed. In addition, various solutions to eliminate or
reduce the casting defects were implemented. The
following conclusions can be drawn from the present
study.
(l) The temperature field, flow pattern, and
stress distribution in the two stages were obtained,
and three kinds of potential defects including cold
shut shrinkage and crack in the casting were predic-
ted.
(2) The modification was applied to the struc-
ture of the pouring system, and temperature distri-
bution during the filling stage was reasonably adjus-
ted. and the defects, namely cold shut and misrun ,
were eliminated.
(3) The combined use of chill and riser was
good for establishing a reasonable temperature gra-
dient, which is beneficial to feeding the shrinkage of
casting.
(4) The infarctate sand core was converted in-
to a canulate core to eliminate the thermal stress
during the solidification stage of casting, and a
sound casting was obtained using the modified
process.
(5) The ViewCast system can be used well to
design and calculate the running and feeding system
of cast steel parts. The example of valve block in
this study indicated that the ViewCast system can be
applied to the cast steel industrial output and can
supply a kind of operative technology for the devel-
opment of view-cast technique.
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