V. MERTA, I. LÁNA: MANUFACTURING OF CAST-METAL SPONGES FROM COPPER ALLOYS
117–119
MANUFACTURING OF CAST-METAL SPONGES FROM COPPER
ALLOYS
IZDELA V A LITIH KOVINSKIH GOBIC IZ ZLITIN NA OSNOVI
BAKRA
Václav Merta
1*
, Ivo Lána
2
1
VSB – Technical University of Ostrava, 17. listopadu 2172/15, 708 00 Ostrava – Poruba, Czech Republic
2
Slévárna a modelárna Nové Ransko, s.r.o., Nové Ransko 234, 582 63 @dírec nad Doubravou, Czech Republic
Prejem rokopisa – received: 2019-07-16; sprejem za objavo – accepted for publication: 2019-11-04
doi:10.17222/mit.2019.159
The paper deals with the topic of manufacturing metal sponges from copper alloys using a special foundry technology of “a
two-stage investment-casting process using an evaporative polyurethane (PUR) pattern”. Particular attention is paid to the study
of castability as a technological characteristic, which is a limiting factor for the production of such castings. The castability of
the CuSn12 copper alloy was observed in various production-process conditions (pouring temperature, mould temperature) with
the aim to find dependence trends and set the optimal conditions of the manufacturing process. From the results, it is obvious
that the crucial factor influencing the castability is the mould temperature, although the pouring temperature also has a smallish
influence on it.
Keywords: metal sponge, investment casting, castability
V ~lanku avtorji opisujejo izdelavo kovinskih pen iz bakrovih zlitin z uporabo posebne livarske tehnologije t.i. dvostopenjskega
precizijskega litja, ki uporablja postopek izparevanja poliuretana (PUR). Posebno pozornost so avtorji posvetili {tudiju livnosti,
ki kot tehnolo{ka lastnost omejuje izdelavo tak{nih ulitkov. Livnost bakrove zlitine CuSn12 so opazovali pri razli~nih procesnih
pogojih (temperaturi litja, temperaturi modela oz. forme) z namenom, da bi ugotovili odvisnostne tendence in ugotovili
optimalne pogoje proizvodnega postopka. Iz rezultatov opazovanj oz. preizkusov je o~itno, da je temperatura modela odlo~ilen
faktor, ki vpliva na livnost, ~eprav ima nanjo dolo~en vendar relativno majhen vpliv tudi temperatura litja.
Klju~ne besede: kovinske gobice (pene), precizijsko litje, livnost
1 INTRODUCTION
The paper deals with the possibilities of producing
metal foams using conventional foundry processes and
technologies. Particular attention is paid to the "two-
stage investment-casting process using an evaporative
polyurethane (PUR) pattern". This method produces
a porous metallic material, which is usually called a
"metal sponge". These metal sponges excel the other
types of metal foams due to a high porosity (up to 97 %)
and especially because the pores are open and fully
interconnected. A metal sponge is therefore a material
with a wide range of applications in functional compo-
nents such as filters, heat exchangers or catalyst carriers.
1
One of the most important tasks in the production of
these thin-walled castings with a very complex structure
is to achieve sufficient castability. This is typically
achieved with relatively specific process conditions such
as the use of a reduced or elevated pressure (or a
combination of both) and relatively high pouring tem-
peratures and mould temperatures. Although these
conditions are advantageous in terms of the required
castability, they have a relatively unfavourable effect on
the solidification process. A previous research showed
that it is crucial to set the conditions of the manufactur-
ing process (pouring temperature, mould temperature)
very precisely to achieve the optimal castability. At low
temperatures, misrun defects occur and a number of
defects adversely affecting the mechanical and utility
properties of these castings occur in the case of
overheating. It is therefore necessary to find a suitable
compromise for each cast material to obtain high-quality
castings.
2
2 EXPERIMENTAL PART
The principle of the two-stage investment-casting
manufacturing method is to embed a pattern of polymer
foam into a suitable refractory material, followed by
drying and annealing of the mould. During the anneal-
ing, the foam pattern evaporates. This forms a cavity,
into which molten metal is subsequently cast. After the
removal of the refractory material, a cast metal foam is
obtained, which is an exact copy of the foam pattern.
3
In order to optimize the manufacturing conditions,
the castability of the CuSn12 copper alloy was moni-
tored in the conditions of the cast-metal-sponge
production. The experiment was carried out on a special
Indutherm MC15 casting machine. This allows melting
and casting under a vacuum (20 mbar), while the solidifi-
Materiali in tehnologije / Materials and technology 54 (2020) 1, 117–119 117
UDK 669.1:62-911-026.747:669.35 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(1)117(2020)
*Corresponding author's e-mail:
vaclav.merta@vsb.cz (Václav Merta)

cation is carried out under a super-atmospheric pressure
(2 bar). Reticulated polyurethane foam Bulpren S 32450
(Eurofoam TP, s.r.o., CZ) with a 10-ppi porosity was
used as the pattern and a special plaster composite,
Eurovest (SRS Ltd., GB), was used as the moulding
material. The test casting itself was designed as a pair of
equal pieces made of foam (40 × 30 × 20 mm) and a
ø5-mm sprue in a 1-mm wall
4
(30 × 20 mm). Figure 1
shows the pattern ready for being embedded in plaster.
3 RESULTS
Since the foam samples used for test casting are not
precisely quantifiable (due to their irregular structures),
the experiment could only be evaluated qualitatively. The
evaluation was carried out on the basis of whether the
test mould was fully filled or not. An example of fully
realised test casting obtained after cleaning is presented
in Figure 2. The combinations of the mould temperature
and the lowest appropriate pouring temperature required
to achieve a full filling of the mould were then con-
sidered to be the optimized process conditions sought. It
was observed that the suitable conditions (in terms of cast-
ability) for the production of cast CuSn12 sponges are
pouring temperatures of 1150–1250 °C and mould tem-
peratures of 900–1000 °C. However, the best results
were achieved with pouring temperatures of
1150–1200 °C and mould temperatures of 925–950 °C.
The results of the experiment are graphically illustrated
in Figure 3.
4 DISCUSSION
Based on the results, the influence of the pouring
temperature and the initial mould temperature on the
resulting castability were evaluated in order to determine
the optimized conditions for the casting process. How-
ever, due to the very specific conditions of the process
(the pressure conditions during the casting and solidi-
fication, an irregular structure of the pattern), it is
difficult to evaluate the results of the experiment on the
basis of a full reproducibility. It is also necessary to
realize that the optimized conditions are valid for
achieving a full occupancy for a given sample size. It is
therefore necessary to take the achieved results only as
guidelines for further research.
According to the graph in Figure 3, there can be a
dependence between the two parameters. As the mould
temperature rises, the pouring temperature required for a
full filling of the mould decreases and vice versa. In
addition, it is clear that in the observed area, the
influence of the mould temperature on the castability is
much stronger than that of the pouring temperature.
5 CONCLUSIONS
A series of test castings was realised to monitor the
influence of both the pouring temperature and the mould
temperature on the castability of CuSn12 in laboratory
V. MERTA, I. LÁNA: MANUFACTURING OF CAST-METAL SPONGES FROM COPPER ALLOYS
118 Materiali in tehnologije / Materials and technology 54 (2020) 1, 117–119
Figure 2: Resulting test casting
Figure 3: Results for the castability of CuSn12 according to the
mould and pouring temperature
Figure 1: Test-casting pattern

conditions of an investment-casting metal-sponge pro-
duction. The obtained results show that for the produc-
tion of castings of the required quality, the optimized
values of the monitored parameters are found in the fol-
lowing intervals: a casting temperature of 1150–1200 °C
and a mould temperature of 925–950 °C.
Acknowledgment
The contribution was carried out with the support of
The Ministry of Education, Youth and Sports of the
Czech Republic – CZ.02.1.01/0.0/0.0/17_049/0008399,
the Technology Agency of the Czech Republic –
TH02020668 and projects of "Student Grant Com-
petition", numbers SP2020/39 and SP2020/64.
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V. MERTA, I. LÁNA: MANUFACTURING OF CAST-METAL SPONGES FROM COPPER ALLOYS
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