I. KROUPOVÁ et al.: USE OF PRECURSORS FOR THE PRODUCTION OF CAST METALLIC FOAMS
189–191
USE OF PRECURSORS FOR THE PRODUCTION OF CAST
METALLIC FOAMS
UPORABA PREKURZORJEV ZA IZDELAVO LITIH KOVINSKIH
PEN
Ivana Kroupová
1*
, Petr Lichý
1
, Václav Merta
1
, Ivo Lána
2
1
VSB – Technical University of Ostrava, Faculty of Materials Science and Technology, Department of Metallurgy and Foundry Engineering,
17. listopadu 2172/15, 708 00 Ostrava – Poruba, Czech Republic
2
SaM Nové Ransko, s.r.o., Nové Ransko 234, 582 63 @dírec nad Doubravou, Czech Republic
Prejem rokopisa – received: 2018-07-11; sprejem za objavo – accepted for publication: 2018-10-30
doi:10.17222/mit.2018.141
The presented work was devoted to the development of the production processes for metallic foams, which were based on
conventional casting technologies. The use of the standard casting processes and standard materials made it possible to identify
the range of metallic foams amongst affordable materials, thereby making a full use of their application potentials. The
experimental part was focused on the development and subsequent optimization of the casting processes for manufacturing cast
metallic foams with irregular inner-cell structures, and especially on the development of the technology of infiltrating molten
metal into a mold cavity filled with precursors.
Keywords: metallic foam, precursor, casting, irregular structure
Avtorji predstavljajo razvoj procesa izdelave kovinskih pen, ki temelji na konvencionalnih tehnologijah litja. Zaradi uporabe
standardne livarske prakse in materialov spadajo kovinske pene med dostopne materiale, in tako je mogo~ poln izkoristek
njihovega potenciala. Eksperimentalni del {tudije je bil osredoto~en na razvoj in takoj{njo optimizacijo livarskega postopka
izdelave kovinskih pen z nepravilno notranjo celi~no strukturo. Delo je bilo {e posebej osredoto~eno na razvoj tehnologije
infiltracije kovinske taline v votlino orodja, ki je bila pred tem napolnjena s predhodno surovino (prekurzorjem).
Klju~ne besede: kovinske pene, prekurzor, litje, nepravilne strukture
1 INTRODUCTION
Porous metals represent a new type of material with
new physical and mechanical properties. These are
characterized by, e.g., low density, high specific surface
area, acoustic or thermal insulation properties, etc. They
are very suitable for specific applications due to a good
combination of physical and mechanical properties such
as high specific strength and high energy-absorption
capability.
1
As a result, metallic foams can be used in
many fields of human activities. However, the applica-
tion potential of these materials is limited by the
economic demands of their production technologies. In
most cases, these are costly methods based on compli-
cated procedures and the use of non-standard and
expensive input materials.
2–4
For this reason, the appli-
cation of casting processes for the production of such
materials is a suitable solution.
Mastering inexpensive ways of manufacturing me-
tallic foams, not requiring production facilities with
investment-intensive machines and equipment is a pre-
requisite for a full utilization of the application potentials
of these materials. That is why the experimental part of
the presented work was devoted to the casting technol-
ogies for the production of metallic foams based on
conventional foundry processes.
For successful casting, it is necessary to know the
technological and metallurgical parameters of the
production. It is assumed that a thorough knowledge of
the production parameters and conditions will contribute
to the expansion of the foundry assortment, which can
also increase its competitiveness on a global scale.
2 EXPERIMENTAL PART
There are several foundry methods for the production
of porous metals, such as investment casting technology
(using an evaporative pattern), which is considerably
expensive.
5
The experimental part of this paper deals
with an optimization of the procedure for the production
of cast metallic foams, using the infiltration method,
which ensures a rapid and economically feasible pro-
duction of shaped components.
For all experiments, the castings were made of the
Al-Si type alloy (AlSi10MgMn) and the molds were
made from a commonly used molding mixture (green
sand).
Materiali in tehnologije / Materials and technology 53 (2019) 2, 189–191 189
UDK 621.74:532.694-037.53 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 53(2)189(2019)
*Corresponding author e-mail:
ivana.kroupova@vsb.cz

2.1 Infiltration of molten metal into a mold filled with
precursors
The principle of this technology (Figure 1) is to pour
liquid metal into a mold filled with particles (pre-
cursors). The irregular structure of the pores we deal
with can be achieved with the use of various types of
precursors that fill the mold cavity. The precursors must
be made of a material that preserves its shape during the
impact of the molten metal (sufficient strength, low
abrasion, refractoriness) and they must also allow good
disintegration after the casting.
6
In the experiment, we
made castings with irregular cell structures, using par-
ticles based on conventional molding mixtures.
The possibility to control the cellular structure (pore
size, porosity, etc.) is a very important advantage of the
use of a foundry technique to manufacture metallic
foams.
2.2 Precursors – the Croning process
The core particles were manufactured from the mold-
ing mixture (from the rejected cores produced during the
Croning process). The final globular shape of the core
precursors was achieved by splitting them into small
pieces (10–30 mm), followed by tumbling. The mold ca-
vity was filled with these precursors.
2.3 Precursors – a furan molding mixture
To create these precursors a plastic grill was used as
the core box. Using this core box, cubes with a side
length of 25 mm were created. This was followed by
tumbling. The proposed technology provides for a pro-
duction of precursors of the same size, shape and pro-
perties.
2.4 Precursors – a PUR cold box
These precursors were made from rejected special
cores (preforms, used for manufacturing metallic foams
with a regular inner-cell structure), from the materials
commonly used in foundries. This core production
technology is based on a two-component binder system
(benzyletherpolyol and diphenylmethane-4-4-diisocya-
nate) and is a suitable process for producing geome-
trically and formally complex cores. Through this
procedure, we obtained precursors of the same size and
shape.
2.5 Salt precursors
The last tested type of the filler material included
precursors from a salt-based core composition. From the
prepared molding mixture, beams were made, which
were cured and subsequently cut into cubes. These
semi-finished products were then placed on a rotating
screen where they were tumbled. This precursor-manu-
facturing process is similar to that described in section
2.3. The average size of the resulting precursors made
with the above procedure was 20 mm.
3 RESULTS
Four types of materials and technologies for manu-
facturing precursors were investigated. The porosity of
all produced castings amounted to 60 %. The main
advantage of Croning precursors is the possibility of
using waste materials. The disadvantage of these
precursors is their irregular shape, caused by uneven
tumbling of the cullet due to the non-uniform hardening
of the default core mixture. Therefore, a new technology
for precursor manufacturing was proposed – the use of a
molding mixture bonded with a furan resin. This type of
precursor manufacturing should ensure the achievement
of the same size, shape and defined characteristics of the
precursors. In addition, precursors allow good disin-
tegration after the casting. The production of precursors
from preforms (special types of cores) provides for the
possibility of producing particles of the same size and
shape from a waste material. The use of the salt pre-
cursors appears to be very appropriate with respect to
their removal from the casting volume. After the casting,
it is possible to remove them immediately after the soli-
dification of the casting with spillage from all internal
cavities (assuming the precursors touch each other to
form interconnected cavities). The process of mechanical
removal of the filler material, which was a common
disadvantage of all the above-mentioned processes, can
thus be eliminated.
4 DISCUSSION
The use of common molding mixtures for the manu-
facture of precursors was approved. With regard to the
possibility of utilizing waste materials, the use of
rejected cores is optimal. With respect to the possibility
of removing precursors from the complex structure of a
casting, the use of salt precursors or precursors from a
furan molding mixture is particularly advantageous.
I. KROUPOVÁ et al.: USE OF PRECURSORS FOR THE PRODUCTION OF CAST METALLIC FOAMS
190 Materiali in tehnologije / Materials and technology 53 (2019) 2, 189–191
Figure 1: Principle of infiltrating molten metal into a mold filled with
precursors

5 CONCLUSIONS
It was verified that metallic foams can be produced
through a common casting process using the existing
technologies and current materials. With these methods,
foams with irregular internal structures can be prepared
from modified materials that are normally processed in
foundries.
Thanks to the technology of infiltration of molten
metal into a mold filled with precursors, it is possible to
produce shaped castings with open pores that are inter-
connected. The condition for achieving this type of poro-
sity is complete filling of the mold cavity with pre-
cursors. With this technology, we are able to change the
shape, size and location of individual precursors, and
thus the resultant pores in the casting.
This process of manufacturing metallic foams fully
meets the original requirements – it is a low-cost tech-
nology based on commonly used foundry operations. In
addition, when using waste materials, we can partly
address the issue of waste disposal, which is a concern of
every industrial field.
Acknowledgment
The contribution was made with the support of the
Technology Agency of the Czech Republic –
TH02020668 and the support of projects of "Student
Grant Competition" numbers SP2019/148 and
SP2019/43.
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I. KROUPOVÁ et al.: USE OF PRECURSORS FOR THE PRODUCTION OF CAST METALLIC FOAMS
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