P. WIŒNIEWSKI et al.: EFFECT OF ADDING WATER-BASED BINDERS ON THE TECHNOLOGICAL PROPERTIES ...
225–227
EFFECT OF ADDING WATER-BASED BINDERS ON THE
TECHNOLOGICAL PROPERTIES OF CERAMIC SLURRIES
BASED ON SILICON CARBIDE
VPLIV DODATKA VODOTOPNEGA VEZIVA NA TEHNOLO[KE
LASTNOSTI SUSPENZIJE SILICIJEVEGA KARBIDA
Pawe³ Wiœniewski, Marcin Ma³ek, Jaros³aw Mizera, Krzysztof Jan Kurzyd³owski
Warsaw University of Technology, Faculty of Materials Science and Engineering, 141 Woloska street, Warszawe, Poland
p.wisniewski@inmat.pw.edu.pl
Prejem rokopisa – received: 2015-07-02; sprejem za objavo – accepted for publication: 2016-03-07
doi:10.17222/mit.2015.194
Presented is research work concerning the possibility of applying new materials for the preparation of ceramic shell moulds.
Most of the methods for the fabrication of ceramic slurries for investment casting are based on alcohol binders. This is one of
the first researches focused on the preparation of ceramic slurries using a new, ecological method based on water-soluble
binders. The work presents the rheological properties of ceramic slurries based on silicon carbide and new binders, i.e.,
polyvinyl alcohol and two polyacrylic binders. The rheological properties of the investigated slurries were modified by the
addition of 15 % of mass fractions of the binders in the solution form. The solid phase content in the ceramic slurries was 62.5
% of mass fractions. Standard industrial parameters such as pH, density, Zhan 4# Cup viscosity and apparent viscosity
determined by a rheometer were studied. The grain size of the silicon carbide powder was determined by SEM observations.
The ceramic slurries were fabricated using a mechanical mixer, and the mixing time was 96 h. The results showed that the
ceramic slurries were stable vs. time and met standard industrial requirements. The ceramic slurries have very promising
properties and they are very promising for future shell moulds fabrication.
Keywords: ceramic shell moulds, silicon carbide, binder, rheological properties, ceramic slurries
Predstavljeno je raziskovalno delo o mo`nostih uporabe novih materialov za pripravo kerami~nih form. Ve~ina metod priprave
kerami~ne suspenzije za precizijsko litje temelji na alkoholnih vezivih. To je ena od prvih raziskav usmerjenih v pripravo
kerami~nih suspenzij, z uporabo nove, ekolo{ke metode na osnovi vodotopnih veziv. Delo predstavlja reolo{ke lastnosti
kerami~nih suspenzij na osnovi silicijevega karbida in novih veziv, kot je polivinil alkohol in dve poliakrilni vezivi. Reolo{ke
lastnosti preiskovanih suspenzij so bile spremenjene z doatkom 15 masnih % veziv v obliki raztopine. Vsebnost trdne faze v
kerami~ni suspenziji je bila 62,5 masnih %. Prou~evani so bili obi~ajni industrijski parametri kot: pH, gostota, viskoznost z
Zhan 4# Cup viskozimetrom in navidezna viskoznost, dolo~ena z reometrom. Velikost zrn silicijevega karbida je bila dolo~ena s
SEM. Kerami~na suspenzija je bila izdelana s pomo~jo mehanskega me{alnika, s ~asom me{anja 96 h. Rezultati so pokazali, da
je suspenzija ~asovno stabilna in ustreza industrijskim zahtevam. Kerami~ne suspenzije imajo obetajo~e lastnosti in so zelo
primerne za bodo~o izdelavo {koljkastih oblik.
Klju~ne besede: kerami~ne {koljkaste forme, silicijev karbid, vezivo, reolo{ke lastnosti, kerami~ne suspenzije
1 INTRODUCTION
Historically, investment-casting technology was
mainly used for the casting of tools, weapons and
ornaments. Nowadays, this technology is employed in
many important manufacturing sectors, both industrial
and artistic.1 Investment castings fabricated by the lost-
wax method are widely used in many fields of industry.
Owing to their merits, including high quality, reliability,
high Weibull modulus this method is the most popular in
aircraft turbine parts manufacturing.2 European environ-
mental regulations press the precision-casting industry
for elimination of to eliminate alcohol binders from the
moulds production process. From the beginning the
process was based on ethyl silicate binders. According to
the European regulations they should be fully replaced
by water-based binders. Water systems need to contain
polymers to improve the "green" state properties. The
application of polymer-modified binders decreases the
strength of moulds after burnout, but increases their
permeability and flexibility.3–4
In comparison with other techniques of casting, in-
vestment casting has many advantages:
• obtaining the highest dimensional accuracy and sur-
face smoothness,
• replacing expensive machining methods to fabrica-
tion precision castings,
• possibility of obtaining castings with very complex
shapes, which cannot be achieved by other methods,
• possibility of casting of any alloy (in mass production
and high volume),
• thin-walled castings can be achieved.
Disadvantages of the process:
• difficult process for mechanization and automation,
• limited casting weight substantially to 1–2 kg, parti-
cularly to 10 kg.5–7
Silicon carbide is widely used in many industrial
areas due to its properties and low cost. New research
Materiali in tehnologije / Materials and technology 51 (2017) 2, 225–227 225
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 622.7.017:66.017:661.665.1 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(2)225(2017)
showed that its application in ceramic shell moulds
improves the technological parameters of the shells, such
as: mechanical strength, thermal conductivity and ther-
mal shock resistance. Shell moulds containing SiC
powder significantly shortened the process of the fabri-
cation of the final cast, reduced grain size of the castings
and improved its mechanical properties.8–11
2 EXPERIMENTAL PART AND
METHODOLOGY
The studies were carried out on silicon carbide
powder (Stanchem, Poland). In addition, three different
water-soluble binders were used i.e., polyvinyl alcohol
(26000 g/mol weight and 88 % hydrolysis content
(PVAL), Moviol, Germany), and two polyacrylic binders
with 20 % of mass fractions (PA) and 40 % of mass frac-
tions (PA2) of vinyl acrylic copolymer (Ransom & Ran-
dolph, USA) as 10 % water solution. The main binder
was a substance with nanoparticles of aluminium oxide
(Evonik, Germany). The SiC powder content in the
slurry was 62.5 % of mass fractions. SEM images of the
SiC powder were taken using a SU70 Hitachi micro-
scope (Japan). Grain size was measured on La-950
Horiba analyser (Japan). The ceramic slurries were fabri-
cated in a reactor with a mechanical mixer. The ceramic
slurries were characterized using a Zahn Cup 4#,
aerometer, plate weight test (adhesion test) and pH
meter. The plate weight test time (120 s) was elaborated
by the authors and determined the stable properties of
the researched ceramic slurries (experience from past
studies). The apparent viscosity was determined using a
DV II+ Brookfield rheometer (USA). The rheological
properties were tested in the speed range 20–200–20
min–1.
3 RESULTS AND DISCUSSION
Figure 1 presents the SEM image of the investigated
silicon carbide power. SiC was characterized by sharp-
edged particles typical for moldings powders. The
average equivalent diameter of the SiC grains was 21.9
μm.
Figures 2 to 4 presents adhesion test results of the
ceramic slurries based on SiC. As seen in all the pre-
sented graphs, the highest weight loss occurred during
the first day of the experiment. The rest of the curves
were similar. A plateau was observed at 80 s for the PA-
(Figure 2) for PA2 the plateau occured at 110 s (Figure
3) and for PVAL was also at 80 s (Figure 4). The time of
the plateau’s appearance depended on the viscosity and
density of the ceramic slurries.
Figure 5 shows the apparent viscosity of the exa-
mined ceramic slurries. The highest viscosity was exhi-
bited by a slurry with 15 % of mass fractions addition of
P. WIŒNIEWSKI et al.: EFFECT OF ADDING WATER-BASED BINDERS ON THE TECHNOLOGICAL PROPERTIES ...
226 Materiali in tehnologije / Materials and technology 51 (2017) 2, 225–227
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 4: Results of plate weight test of slurry with 15 % of mass
fractions of PVAL
Slika 4: Rezultati preizkusa adhezije suspenzije s 15 % masnih
dele`ev PVAL
Figure 1: SEM image of investigated SiC powder
Slika 1: SEM-posnetek preiskovanega SiC prahu
Figure 3: Results of plate weight test of slurry with 15 % of mass
fractions of PA2
Slika 3: Rezultati preizkusa adhezije suspenzije s 15 % masnih
dele`ev PA2
Figure 2: Results of plate weight test of slurry with 15 % of mass
fractions of PA
Slika 2: Rezultati preizkusa adhezije suspenzije s 15 % masnih
dele`ev PA
PA2, while the lowest viscosity had the slurry with 15 %
of mass fractions PVAL.
Figure 6 presents the basic rheological properties of
the ceramic slurries. The addition of 15 % of mass frac-
tions of PA2 and PVAL were inappropriate, because the
viscosity of such slurries was high. A ceramic slurry
with 15 % of mass fractions of PA met the standard indu-
strial requirements. Its viscosity had the optimal value
and slightly decreased with time. The results of the plate
weight test made on daily basis were very comparable
for all types of slurries.
Figure 7 shows the pH and density results of the exa-
mined ceramic slurries. The described properties were
stable over time, and similar for all types of slurries.
4 CONCLUSIONS
According to the work assumption, with connection
to the industrial requirements, these researches were
focused on the rheological and technological properties
of ceramic slurries based on silicon carbide powder. The
main aim of this work was to fabricate ceramic slurries
by using new water-soluble binders. The most desirable
properties from the industry point of view were exhibited
by the slurry with a 15 wt.% addition of PA binder. The
slurries with PA binder were characterized by relatively
low viscosity, the best adhesion and stability confirmed
by the plate weight test. The research conducted in this
work is the first in the world and has a very promising
future in ceramic shell moulds fabrication.
Acknowledgments
Financial support of Structural Funds in the Ope-
rational Programme – Innovative Economy (IE OP)
financed from the European Regional Development Fund
– Project "Modern material technologies in aerospace
industry", No. POIG.01.01.02-00-015/08-00 is gratefully
acknowledged.
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Materiali in tehnologije / Materials and technology 51 (2017) 2, 225–227 227
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 7: Density and pH of the ceramic slurries
Slika 7: Gostota in pH kerami~nih suspenzij
Figure 6: Rheological properties of the ceramic slurries
Slika 6: Reolo{ke lastnosti kerami~nih suspenzij
Figure 5: Apparent viscosity of the ceramic slurries
Slika 5: Navidezna viskoznost kerami~ne suspenzije