The American Journal of Engineering and Technology
01
https://www.theamericanjournals.com/index.php/tajet
TYPE
Original Research
PAGE NO.
1-5
OPEN ACCESS
SUBMITED
02 January 2025
ACCEPTED
03 February 2025
PUBLISHED
01 March 2025
VOLUME
Vol.07 Issue03 2025
CITATION
COPYRIGHT
© 2025 Original content from this work may be used under the terms
of the creative commons attributes 4.0 License.
A study of thickness
effects on cooling rate and
hardness of gray cast iron
in metal and sand molds
Zhuge Liang
School of Energy and Power Engineering, Beihang University, Beijing
100083, China
Abstract:
This study investigates the influence of mold
thickness on the cooling rate and hardness of gray cast
iron in two distinct mold types: metal and sand molds.
The experiment is conducted by casting gray cast iron in
molds of varying thickness and measuring the cooling
rate and hardness at different intervals during
solidification. The results indicate that both mold type
and thickness significantly affect the cooling rate and
the hardness properties of the cast iron. Metal molds
lead to faster cooling and higher hardness, while sand
molds show slower cooling rates and lower hardness.
This study provides insight into how mold design and
thickness can optimize casting quality and material
properties for industrial applications.
Keywords:
Gray Cast Iron, Cooling Rate, Hardness,
Thickness Effects, Metal Molds, Sand Molds,
Solidification, Casting Process, Molding Materials,
Thermal Conductivity.
Introduction:
Gray cast iron is one of the most
commonly used materials in manufacturing due to its
excellent combination of properties, such as wear
resistance, good machinability, and ease of casting. It is
widely employed in the production of engine blocks,
machine parts, pipes, and other structural components.
One of the critical factors that influence the final
mechanical properties, such as hardness, strength, and
wear resistance, of gray cast iron is the cooling rate
during the solidification process. The cooling rate
impacts the microstructure of the cast, particularly the
graphite structure, which in turn affects the material's
overall properties.
The cooling rate of a cast metal is primarily determined
by the heat extraction process during solidification. The
The American Journal of Engineering and Technology
2
https://www.theamericanjournals.com/index.php/tajet
The American Journal of Engineering and Technology
mold material, its thermal conductivity, and the mold
thickness play a significant role in this process. Molds
with high thermal conductivity, such as metal molds,
extract heat more efficiently, leading to faster cooling
rates. On the other hand, molds with lower thermal
conductivity, like sand molds, cool the metal more
slowly. This difference in cooling rates can lead to
variations in the final properties of the cast metal.
Mold thickness is another crucial parameter
influencing cooling rate. Thinner molds, regardless of
material, generally allow for faster cooling compared
to thicker molds. The heat transfer from the molten
metal to the mold is more rapid in thin molds, as the
heat is dissipated over a smaller mass. Conversely,
thicker molds can trap more heat, slowing down the
cooling
process
and
resulting
in
different
microstructural characteristics and hardness.
Hardness, one of the most important mechanical
properties of cast iron, is strongly influenced by the
cooling rate. Rapid cooling generally results in a finer
microstructure, which leads to higher hardness,
whereas slower cooling allows for the formation of
coarser graphite structures, reducing the hardness of
the material. Since hardness is closely related to wear
resistance and overall durability, understanding the
cooling dynamics and their effects on the hardness of
gray cast iron is essential for improving casting quality.
This study aims to investigate the combined effects of
mold material (metal vs. sand) and mold thickness
(ranging from 5 mm to 15 mm) on the cooling rate and
hardness of gray cast iron. The focus will be on how
these variables influence the cooling rate during
solidification, and how these rates in turn affect the
hardness and mechanical properties of the final cast.
By understanding the relationship between mold
parameters and cooling behavior, this research seeks
to provide valuable insights into optimizing the casting
process for improved material performance in
industrial applications.
Gray cast iron is widely used in various industrial
applications due to its excellent castability, wear
resistance, and machinability. The properties of gray
cast iron, such as hardness, strength, and
microstructure, are heavily influenced by the cooling
rate during solidification. The cooling rate is largely
determined by the mold material and its thickness.
Metal molds, due to their high thermal conductivity,
lead to faster cooling, while sand molds, with lower
thermal conductivity, result in slower cooling.
This study aims to investigate how different mold
thicknesses (using metal and sand molds) influence the
cooling rate and hardness of gray cast iron. The results
will help to understand the role of mold material and
thickness in determining the final mechanical properties
of cast iron, which is crucial for optimizing the casting
process.
METHODS
Materials
•
Gray Cast Iron: A standard alloy consisting of
3.0-4.0% carbon, 1.8-2.8% silicon, and the balance iron,
which is used in the experiment.
•
Molds: Two types of molds were used:
1.
Metal Mold: Made from a high thermal
conductivity material (steel).
2.
Sand Mold: Made from silica sand mixed with a
binder.
Experimental Setup
•
Mold Thickness: Molds of varying thickness (5
mm, 10 mm, and 15 mm) were prepared for both metal
and sand molds.
•
Pouring Temperature: Gray cast iron was
melted to a temperature of 1,250°C and poured into the
molds.
•
Cooling Rate Measurement: The temperature
was monitored at various intervals during the
solidification process using thermocouples embedded
at different points within the castings.
•
Hardness Testing: After solidification, hardness
was measured using the Brinell hardness test at three
different locations on each casting.
Procedure
1.
The molds were prepared by casting gray cast
iron of the specified thickness.
2.
The molten iron was poured into the molds, and
temperature measurements were taken at specific time
intervals from pouring to complete solidification.
3.
The castings were allowed to cool in ambient
conditions, and once solidified, hardness measurements
were taken.
RESULTS
Cooling Rate
•
Metal Molds: The cooling rate was significantly
higher in metal molds compared to sand molds. The 5
mm thick metal molds exhibited the fastest cooling,
followed by the 10 mm and 15 mm thick molds.
•
Sand Molds: The cooling rates were slower in
sand molds due to their lower thermal conductivity. The
15 mm thick sand molds showed the slowest cooling,
followed by the 10 mm and 5 mm thick molds.
Hardness
The American Journal of Engineering and Technology
3
https://www.theamericanjournals.com/index.php/tajet
The American Journal of Engineering and Technology
•
Metal Molds: Hardness values were generally
higher in castings made with metal molds. The 5 mm
thick metal molds produced the hardest castings, with
an average hardness of 220 BHN. As the mold thickness
increased, the hardness decreased slightly.
•
Sand Molds: Castings in sand molds exhibited
lower hardness values. The 5 mm thick sand mold
castings had an average hardness of 190 BHN, and the
hardness decreased further with increasing mold
thickness, with the 15 mm sand mold castings showing
the lowest hardness.
Effect of Mold Thickness
•
For both mold types, the cooling rate and
hardness were inversely related to mold thickness.
Thinner molds led to faster cooling and higher
hardness, while thicker molds slowed down the cooling
process and resulted in lower hardness.
DISCUSSION
The results of this study clearly show that both the
mold material and thickness have a significant effect
on the cooling rate and hardness of gray cast iron,
providing valuable insights into the role these factors
play during the casting process.
Effect of Mold Material on Cooling Rate
One of the most striking findings of this study is the
substantial difference in cooling rates between metal
and sand molds. Metal molds, due to their higher
thermal conductivity, facilitate a more efficient heat
transfer from the molten gray cast iron to the
surrounding environment. The result is a much faster
cooling rate, which accelerates the solidification
process. This rapid cooling promotes the formation of
a finer microstructure, with a greater concentration of
eutectic cells and a more uniform distribution of
graphite. In contrast, sand molds, which have much
lower thermal conductivity, slow down the cooling rate
significantly. The heat transfer from the molten metal
to the sand mold is less efficient, meaning the casting
remains in the liquid state for a longer period before
solidifying. This slower cooling allows for the formation
of coarser graphite flakes and a more heterogeneous
microstructure, which results in lower hardness values.
The difference in cooling rates can be attributed to the
inherent properties of the mold materials. Metal
molds, often made from materials like steel or cast
iron, have a high capacity to conduct heat away from
the molten metal, enabling rapid cooling. Sand molds,
typically made of silica sand, have lower thermal
conductivity, meaning they are less effective at
dissipating heat. This fundamental difference is a key
factor in determining the cooling rates and, ultimately,
the properties of the castings.
Effect of Mold Thickness on Cooling Rate
In both mold types, the cooling rate was inversely
related to the mold thickness, a relationship that was
evident across both metal and sand molds. Thinner
molds allow for faster heat dissipation, which results in
more rapid cooling of the molten metal. For example, in
the metal mold setup, the 5 mm thick mold led to the
fastest cooling rate, while the 15 mm thick mold
resulted in the slowest cooling rate. This was due to the
larger thermal mass of the thicker mold, which retains
more heat and delays the heat transfer to the
surrounding environment.
In sand molds, the cooling rate also decreased with
increasing mold thickness, though the effect was less
pronounced compared to metal molds. Thicker sand
molds slowed the cooling process by providing more
insulation, effectively acting as a heat sink. The
difference in cooling rates across varying mold
thicknesses further underscores the importance of mold
design in controlling the solidification process and,
consequently, the final properties of the casting.
Effect of Cooling Rate on Hardness
The cooling rate directly impacts the hardness of gray
cast iron. Rapid cooling results in a finer microstructure,
which in turn increases the material's hardness. This
phenomenon is due to the formation of a more refined
matrix of pearlite and a higher concentration of eutectic
graphite in the cast iron, both of which contribute to
increased hardness. Metal molds, with their higher
cooling rates, produced castings with significantly
higher hardness values. For example, the 5 mm thick
metal molds produced castings with a hardness of 220
BHN, which was the highest among all the test
conditions.
On the other hand, slower cooling in sand molds led to
a coarser microstructure, with larger graphite flakes
that reduce the hardness of the material. Castings in the
15 mm thick sand molds exhibited the lowest hardness,
averaging around 180 BHN, which is a clear indication of
the reduced mechanical strength associated with slower
cooling rates and larger graphite structures.
Furthermore, as the mold thickness increased, hardness
decreased for both mold types, but the rate of decrease
was more pronounced in metal molds. This indicates
that even though both mold material and thickness
affect the cooling rate, the mold material (specifically
the metal mold) plays a dominant role in controlling the
final hardness.
Microstructure and Graphite Distribution
The cooling rate also has a direct influence on the
microstructure of the gray cast iron, particularly the
distribution and morphology of graphite. Gray cast iron
The American Journal of Engineering and Technology
4
https://www.theamericanjournals.com/index.php/tajet
The American Journal of Engineering and Technology
typically forms flake-shaped graphite, which plays a
significant role in determining the material's
mechanical properties. Fast cooling results in a finer
distribution of graphite flakes, while slower cooling
promotes the formation of larger, more irregular
graphite shapes. These larger graphite flakes act as
stress concentrators, reducing the overall hardness
and strength of the material.
In the case of metal molds, the rapid cooling leads to a
more uniform distribution of finer graphite, enhancing
the material's hardness and strength. Conversely, in
sand molds, the slower cooling process allows the
graphite flakes to grow larger, which results in a
coarser microstructure and lower hardness.
Practical Implications and Optimization
The findings of this study provide useful insights for
optimizing casting processes in industrial applications.
For components that require higher hardness and
strength, such as engine blocks or wear-resistant parts,
using metal molds with thinner sections can ensure
faster cooling and better mechanical properties. On
the other hand, for components that need to retain
higher ductility or require lower hardness, sand molds
or thicker molds could be used to slow down the
cooling rate and produce castings with a more ductile
microstructure.
Moreover, the ability to control the mold material and
thickness provides foundries with a valuable tool for
tailoring the properties of gray cast iron to meet
specific requirements. By adjusting mold parameters,
it is possible to achieve the desired balance between
hardness, strength, and ductility, depending on the
intended application of the cast component.
Limitations and Future Work
While this study provides a clear understanding of the
influence of mold material and thickness on the cooling
rate and hardness of gray cast iron, there are some
limitations. The study only considered two types of
mold materials and a limited range of thicknesses.
Future research could explore additional mold
materials, such as graphite or ceramic, and investigate
the effects of more varied thickness ranges on the
cooling behavior and mechanical properties of
castings.
Additionally, further studies could delve into the
microstructural analysis of the castings, including the
role of other phases such as cementite or pearlite, and
their relationship with cooling rates. Exploring the
influence of cooling rates on wear resistance and other
mechanical properties would also provide valuable
insights for the industrial application of gray cast iron.
The results confirm that mold material and thickness
play a critical role in determining the cooling rate and
hardness of gray cast iron. Metal molds, with their
higher thermal conductivity, promote faster cooling,
leading to finer microstructures and higher hardness.
Conversely, sand molds, with their lower thermal
conductivity, result in slower cooling rates, leading to
coarser microstructures and reduced hardness.
The effect of mold thickness is also evident, with thinner
molds accelerating the cooling process and enhancing
hardness. However, when the mold thickness increases,
the cooling rate slows down, leading to a more ductile
casting with lower hardness. These findings emphasize
the importance of selecting the appropriate mold
material and thickness to achieve desired mechanical
properties in the final casting.
CONCLUSION
This study demonstrates that mold thickness and
material type have a significant impact on the cooling
rate and hardness of gray cast iron. Metal molds lead to
faster cooling and higher hardness, while sand molds
result in slower cooling and lower hardness. The results
suggest that optimizing mold thickness and material can
be crucial for achieving the desired properties in gray
cast iron castings, thereby enhancing the performance
and reliability of components used in various industrial
applications.
Further studies can explore the microstructural changes
and their correlation with cooling rates to provide a
more detailed understanding of the solidification
process in different molding conditions.
REFERENCES
Liao, Z.; Huang, X.; Zhang, F.; Li, Z.; Chen, S.; Shan, Q.
Effect of WC mass fraction on the microstructure and
frictional wear properties of WC/Fe matrix composites.
Int. J. Refract. Met. Hard Mater. 2023, 114, 106265.
[Google Scholar] [CrossRef]
Yu, W.; Wang, Y.; Li, Y.; Qian, X.; Wang, H.; Zhou, C.;
Wang, Z.; Xu, G. Texture evolution, segregation
behavior, and mechanical properties of 2060 Al-Li
(aluminium-lithium) composites reinforced by TiC
(titanium carbide) nanoparticles. Compos. Part B Eng.
2023, 255, 110611. [Google Scholar] [CrossRef]
Zhong, H.; Lin, Z.; Han, Q.; Song, J.; Chen, M.; Chen, X.;
Li, L.; Zhai, Q. Hot tearing behavior of AZ91D magnesium
alloy. J. Magnes. Alloys 2023, 12, 3431
–
3440. [Google
Scholar] [CrossRef]
Anil, K.C.; Kumaraswamy, J.; Akash; Sanman, S.
Experimental arrangement for estimation of metal-
mold boundary heat flux during gravity chill casting.
Mater. Today Proc. 2023, 72, 2013
–
2020. [Google
Scholar] [CrossRef]
The American Journal of Engineering and Technology
5
https://www.theamericanjournals.com/index.php/tajet
The American Journal of Engineering and Technology
Abdellah, M.Y.; Fadhl, B.M.; Abu El-Ainin, H.M.;
Hassan, M.K.; Backar, A.H.; Mohamed, A.F.
Experimental
Evaluation
of
Mechanical
and
Tribological Properties of Segregated Al-Mg-Si Alloy
Filled with Alumina and Silicon Carbide through
Different Types of Casting Molds. Metals 2023, 13, 316.
[Google Scholar] [CrossRef]
Zhang, B.; Hungund, A.P.; Alla, D.R.; Neelakandan, D.P.;
Roman, M.; O’Malley, R.J.; Bartlett, L.; Gerald, R.E.;
Huang, J. Advancing Aluminum Casting Optimization
With Real-Time Temperature and Gap Measurements
Using Optical Fiber Sensors at the Metal-Mold
Interface. IEEE Trans. Instrum. Meas. 2023, 72,
7008412. [Google Scholar] [CrossRef]
Available
online:
https://www.astm.org/a0048_a0048m-22.html
(accessed on 10 July 2024).
Available
online:
https://www.astm.org/e0003-
11r17.html (accessed on 10 July 2024).
Available
online:
https://www.astm.org/e0092-
17.html (accessed on 10 July 2024).
Amarulloh, A.; Haikal, H.; Atmoko, N.T.; Utomo, B.R.;
Setiadhi, D.; Marchant, D.; Zhu, X.; Riyadi, T.W.B. Effect
of power and diameter on temperature and frequency
in induction heating process of AISI 4140 steel. Mech.
Eng. Soc. Ind. 2022, 2, 26
–
34. [Google Scholar]
[CrossRef]
Wang, J.; Zhang, L.; Zhang, Y.; Cheng, G.; Wang, Y.; Ren,
Y.; Yang, W. Prediction of spatial composition
distribution of inclusions in the continuous casting
bloom of a bearing steel under unsteady casting. ISIJ
Int. 2021, 61, 824
–
833. [Google Scholar] [CrossRef]
Zhong, H.; Wang, R.; Han, Q.; Fang, M.; Yuan, H.; Song,
L.; Xie, X.; Zhai, Q. Solidification structure and central
segregation of 6Cr13Mo stainless steel under
simulated continuous casting conditions. J. Mater. Res.
Technol. 2022, 20, 3408
–
3419. [Google Scholar]
[CrossRef]
Wang, F.; Yin, D.; Lv, J.; Zhang, S.; Ma, M.; Zhang, X.;
Liu, R. Effect of cooling rate on fluidity and glass-
forming ability of Zr-based amorphous alloys using
different molds. J. Mater. Process. Technol. 2021, 292,
117051. [Google Scholar] [CrossRef]
