Abstract The article concerns a trial of explaining the mechanism of improving the knock-out properties of moulding sands with water glass made in ester technology after using the new additive called Glassex. Within the labour, the variety of technological and basic researches were done, including the researches evaluating the chemical influence of the new additive

K Major-Gabryś

S M Dobosz

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A R C H I V E S  
o f  
F O U N D R Y  E N G I N E E R I N G  
 
 
 
Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences 
ISSN (1897-3310)
Volume 8 
Issue 1/2008 
 
37 – 42 
 
7/1 
 
A R C H I V E S  o f  F O U N D R Y  E N G I N E E R I N G  V o l u m e  8 ,  I s s u e  1 / 2 0 0 8 ,  3 7 - 4 2  37
 
The mechanism of improving 
the knock-out properties 
of moulding sands with water glass 
 
S.M. Dobosz*, K. Major-Gabryś 
Department of Moulding Materials and Environmental Protection, AGH University of Science and Technology, 
Reymonta 23, 30-059 Kraków, Poland 
*Corresponding author. E-mail address: dobosz@agh.edu.pl 
 
Received 16.07.2007; accepted in revised form 24.07.2007 
 
 
Abstract 
 
The article concerns a trial of explaining the mechanism of improving the knock-out properties of moulding sands with water glass made 
in ester technology after using the new additive called Glassex. Within the labour, the variety of technological and basic researches were 
done, including the researches evaluating the chemical influence of the new additive. 
 
Keywords: Moulding sands; Water glass; Knock-out properties; New additive Glassex 
 
 
 
1. Introduction 
 
Loose self-hardened moulding sands with water glass are the 
most widespread moulding sands from the group of moulding 
sands with inorganic binder. According to the pro-ecological 
character of binder, the meaning of these moulding sands 
becomes very crucial for industrial practise. However the 
inorganic binder makes the knock-out properties of these 
moulding sands weaker.  
The authors elaborated a new Glassex for moulding sands 
with water glass. It is an inorganic additive consisting of  SiO2 (65 
– 75%), Al2O3 (10 – 18%), K2O + Na2O (6 – 9%), MgO + CaO (2 
– 6%), Fe2O3 (1 – 5%) and water (2 – 5%). Moulding sands with 
this additive are described with patent no. P-365723. 
Previous publications (1-4) showed the influence of Glassex 
additive on the knock-out properties of moulding sands with 
water glass. Fig 1 shows the influence of the additive on the 
knock-out properties of moulding sand with water glass measured 
according to PN-85/H-11005 and fig. 2 presents the influence of 
the additive on the knock-out properties of moulding sand with 
water glass estimated on the basis of moulding sand’s retained 
strength measurement. 
 
Fig. 1. The influence of Glassex additive on the knock-out 
properties of moulding sands with water glass, described 
according to PN-85/H-1100 
 
0
0.5
1
1.5
2
2.5
re
ta
in
ed
 s
tr
en
gt
h,
 M
Pa
100 200 300 400 500 600 700 800 900 1000 1100 1200
temperature, oC
moulding sand w ithout additive
moulding sand w ith Glassex
 
Fig. 2. The influence of Glassex additive on retained strength of moulding sand with water glass 
 
 
Inserting the Glassex additive to moulding sand with water 
glass leads both to double improvement of its’ knock-out 
properties defined according to PN-85/H-11005 (fig. 1) and to 
lowering the retained strength of moulding sand in measured 
range of temperature (fig. 2)/. Moreover, the change of retained 
strength curve of moulding sand has been noticed after the 
Glassex additive was inserted. On the curve, there is no maximum 
by the temperature of 200oC, which is characteristic for moulding 
sands prepared in ester technology, and the second maximum by 
the temperature of 800oC is moved into direction of higher 
temperatures.  
The article (5) widely explains the influence of Glassex 
additive on the phenomenon of moulding sand’s thermal 
expansion. Presented researches proved that inserting the new 
additive into moulding sand causes the stop of researched 
moulding sand’s thermal expansion, lowers the pressures and 
improves the knock-out properties. The question is: whether the 
influence of this new additive has only the mechanical character, 
so it causes the relaxation of internal stresses or does this 
influence also the chemical character. Within the frames of this 
article, authors present the conclusions of further basic researches, 
tending to explain the mechanism of the additive’s influence. 
 
 
2. Researches  
 
These were researches of moulding sands based on quartz 
sand with water glass R-145 in quantity of 3 part by weight, and 
ester hardener – flodur – in quantity of 0,3 part by weight. The 
Glassex additive was inserted into moulding sand in quantity of 
1,0 part by weight. 
 
 
2.1 Spectroscope researches 
 
The method of spectroscope in infrared was chosen to explain 
the influence of Glassex additive on hardening process of water 
glass. This method gives the possibility of analysis in the whole 
volume of fine-grained material, as the moulding sand.  
These researches were made with Digilab Excalibur FTS 
3000 Mx Spectroscope with DTGS detector, electrically cooled. 
The spectroscope is equipped with ATR unit with ZnSe crystal for 
multiple reflection and transmission unit. The samples for 
transmission measurements were prepared in the form of KBr 
pills pressed in matrix under the thrust of 7Mg. The pill was then 
out into the measuring chamber of FTIR spectrometer. 
Transmission spectrum of samples examined in range of 4000 
– 400 cm-1 were registered. The number of scans was chosen 
depending on the level of received signal within the range of 32-
64 scans. The correction of base line of received spectrums was 
run with MERLIN (FTS 3000) software.  
Structural examination of liquid water glass was run with 
ATR method. Fig 3a shows the spectrum of water glass. The 
spectrum includes absorption bands, standing for stretching 
vibrations of –OH groups in range of 3700 – 2800 cm-1 
By 1643 cm-1 there is an absorption band standing for bending 
vibrations H2O. In the range of wave numbers below 1200 – 900 
cm-1 , there are bands characteristic for silicate lattices complying 
with Si−O−Si and O−Si−O  vibrations.  
Band 1732 cm-1 seen on the spectrum stands most probably 
for asymmetrical stretching vibrations Si=O, and 1376 cm-1 band  
for  symmetric stretching vibrations Si=O.  
ATR technique was used for structural researches of ester 
hardener – flodur.  
Achieved spectrum is presented on Fig. 3b. Very weak and 
blurred band by the 3479 cm-1, standing for ν−OH vibrations, can 
be seen in the spectrum of flodur. As well as weak band by 
2959 cm-1 of stretching vibrations C-H can be noticed. 
Characteristic band by 1736 cm-1 1736 cm-1 complying with 
stretching vibrations C=O in esters (−CO−O−CH2−). Moreover, 
the absorption bands complying with bending vibrations C−H 
(1443 cm-1, 1373 cm-1) and band characteristic for stretching 
vibrations C−O (1215 cm-1).  
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Further examinations were run for water glass hardened with 
flodur. Transmission technique was used for this researches. 
Received spectrum is presented on Fig. 3d.  
In the spectrum of water glass hardened with flodur, there is a 
displacement of band’s maximum from 3341 cm-1 to 3431 cm-1, 
which is connected with creation of influences of physical-
culombus type (hydrogen binder). As a result of hardening the 
water glass with flodur, there is a decay of bands 1732 cm-1 (from 
water glass) and 1736 cm-1 (from flodur). 
However, there is a new band 1568 cm-1 connected with the 
reaction of crosslinking. The displacement of  991 cm-1 band to 
1049 cm-1 is also 1 connected with the reaction of crosslinking.  
Structural examinations of Glassex additive were run using 
the transmission technique. Received spectrum is seen on Graph 
3c. In the spectrum of Glassex additive, bands characteristic for 
symmetrical stretching groups –OH (Si−OH, Al−OH, Fe−OH) 
can be seen. By 1634 cm-1 there is an absorption band complying 
with bending vibrations H2O. In the range of wave numbers 1163 
–789 cm-1, there is a presence of bands characteristic for Si−O−Si, 
Si−O−Al and Si−O−Fe vibrations. 
Structural examinations of water glass with Glassex additive, 
hardened with flodur – were run with transmission technique. 
Received spectrum is shown on Graph 3e. During the hardening 
of water glass with Glassex additive by flodur, there can be seen 
some changes of bands’ location, connected with the reaction of 
water glass with hardener. After hardening, there are some 
noticed changes on the spectrum:  
 
• Displacement of a band → 3447 cm-1 with appearance 
of additional arms in this band: 3285 cm-1, 3161 cm-1, 
• Displacement of a band → 2984 cm-1   
• Appearance of an additional band 1690 cm-1, 
• Appearance of band 1564 cm-1, 
• Displacement of two bands → 1414 cm-1 and 1413 cm-1, 
• Band covered by other bands in ~1200 cm-1, 
• Displacement of band → 1196 cm-1. 
Creation of additional arms in 3285 and 3161 cm-1 can be 
caused by crosslinking of oxides, coming from the Glassex 
additive during the hardening process. These are the bands 
characteristic for systems with crystal structure. There can be few 
parallel reactions resulting in creating new bindings, that have an 
influence on the appearance of new band in 1690 cm-1. Table 1 
presents the compilation of received results. 
Results of structural examinations confirmed the chemical 
influence of Glassex additive on the structure of water glass 
hardened with flodur (Fig. 3d and 3e). Displacements of already 
existing bands on the spectrum of water glass hardened  with 
flodur and the creation of additional bands after insertion of new 
additive, is connected with creation  of additional bindings after 
hardening the water glass. 
 
Fig. 3. Spectrums FT-IR: a) water glass, b) flodur, c) Glassex 
additive, d) water glass hardened with flodur, e) water glass with 
Glassex additive, hardened with flodur 
 
 
2.2. Identification of phase γ-Al2O3 
 
Basing on the literature [6, 7] , it is supposed that the 
interaction of new additive in increased temperatures is caused by 
insertion Al2O3  into moulding sand.  
I.S. Syčev [6] and P. Jelinek [7] have been elaborated the 
topic of Al2O3 additive’s influence on the knock-out properties of 
moulding sands with water glass. They suggest, that after 
insertion of Al2O3 additive, caused by temperature of liquid 
foundry alloy, there is a creation of active γ-Al2O3 phase, which 
makes the displacement of II maximum on the curve of retained 
strength into direction of higher temperatures. 
They proved, that some materials consisting of Al2O3, such as 
ile and boxite displace the II maximum of retained strength in the 
direction of higher temperatures. (above 1000oC).  
Because of the fact, that the creation of molten glass causes 
the presence of II maximum, the displacement in the direction of 
higher temperatures results in transition from the double system 
Na2O – SiO2 into triple system Al2O3 – SiO2 – Na2O with high 
melting point. Such a system is presented on Fig.4 [8].
 .
A R C H I V E S  o f  F O U N D R Y  E N G I N E E R I N G  V o l u m e  8 ,  I s s u e  1 / 2 0 0 8 ,  3 7 - 4 2  39
Table.1 
Characteristic absorption bands in spectrums FT-IR of examined samples and their interpretation 
Water 
glass[cm-1] 
Flodur 
[cm-1] 
Glassex 
[cm-1] 
Glass+Flodur 
[cm-1] 
Glass+Flodur+Glassex 
[cm-1] Element of structure 
3341 3479 3628 3431 
3447 
3285 
3161 
ν-OH 
OH...O-Si-O 
O-H...O-H 
O-H...O=C 
– 2959 – 2959 2984 C-H (stretching) 
– – 2360 2342 2359  
– 1736 – – ~1690 ν-C=O in esters 
1732 – – – – ν -Si=O 
1643 – 1634 1641 1641 Vibrations bending H2O 
– – – 1568 1564 C=O...H 
– 1443 – – 1454 C-H (bending) 
– 1373 – 1414 1414 C-H (bending) 
1376 – – – – ν s-Si=O 
1227 1215 – 1213 ~1200 Si-O in water glass  C-O (stretching, assym.) 
1045 – 1163 1084 1196 Si-O-Me: Si-O-Al 
– 1045 1055 1049 1051 Si-O-Si 
– 961 – 881 866  
991 – 789 787 793 Si-O-Si Si-O-Me: Si-O-Al 
 
 
Fig. 4. Triple system Na2O – Al2O3 – SiO2 [8]
A R C H I V E S  o f  F O U N D R Y  E N G I N E E R I N G  V o l u m e  8 ,  I s s u e  1 / 2 0 0 8 ,  3 7 - 4 2  40
The next beneficial effect of Al2O3 influence on knock-out 
properties, can be α–SiO2 stabilisation in transition direction in 
cristobalite, which is connected with constant expansion growth 
of volume of moulding sand with quartz matrix. Literature data 
show, that γ-Al2O3 phase can be identified while carrying out the 
examination of X-ray diffraction of examined material [9]. Fig.5 
presents typical X-ray diffraction of Al2O3 phase.  
 
 
Fig. 5. Typical curve of X-ray diffraction of γ-Al2O3 phase [9] 
 
 
2.3. X-ray examination 
 
X-ray diffraction examination was carried out using the X-ray 
photograph Krystalloflex 4H from Siemens. 
Fig. 6 presents the curve of X-ray diffraction of Glassex 
additive in the initial state. Peaks characteristic for γ-Al2O3 phase 
couldn’t be found here, which may suggest that this phase may 
not be present in Glassex additive. Curve of X-ray diffraction of 
Glassex additive heated in temperature of 800oC (fig.7) was also 
carried out, just to make sure that the phase didn’t create just after 
heating of additive. Literature sources present that γ-Al2O3 phase 
forms after heating till the temperature of 720oC.  
Diffraction pattern is presented on Fig.7. Also here, the peaks 
characteristic for γ-Al2O3 phase haven’t been noticed. 
 
 
Fig. 6. Diffraction pattern of Glassex additive in initial state 
 
 
Fig. 7. Diffraction pattern of Glassex additive heated in 
temperature of 800oC 
 
It results from the analysis of achieved curves, that there is a 
presence of complicated multicomponent silicates in Glassex 
additive. Definition of kind of silicates would take a precise 
analysis of oxides system, present in Glassex additive and 
creating the data base of diffraction patterns for possibly forming 
silicates. Glassex additive is an amorphous material , so the 
interpretation of X-ray diffraction’s curves is quite difficult. 
However it didn’t show the presence of reactive γ-Al2O3 phase in 
new additive. 
 
 
3. Conclusions 
 
Spectroscope examinations presented in the article, showed 
the chemical influence of applied, new additive on the structure of 
binder (water glass). So, for the improvement of knock-out 
properties of moulding sands with such binder, there can be used 
the additives influencing both on the relaxation of stresses in 
moulding sand after thermal exposure and on chemical properties 
of binder itself. The trial of using the X-ray examination for 
identification the γ-Al2O3 phase - which according to literature 
sources is responsible for the effects of additives’ action - failed. 
It can lead to the fact that this phase doesn’t form in moulding 
sand and that it’s not responsible for the mechanism of improving 
the knock-out properties of moulding sand with water glass. 
Further examinations should lead to the full recognition of 
mechanism of knock-out properties of moulding sands with 
inorganic binders, which will be a basis for elaboration of rules 
and selection’s procedures of composition of these ecological 
moulding sands. 
 
Acknowledgments 
 
Elaborated under research and development study no. 
11.11.170.248 
 
A R C H I V E S  o f  F O U N D R Y  E N G I N E E R I N G  V o l u m e  8 ,  I s s u e  1 / 2 0 0 8 ,  3 7 - 4 2  41
References 
 
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Moulding Sands with Water Glass, DOKSEM 2003, 
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[2] S.M. Dobosz, K. Major-Gabryś: Surface phenomenons 
versus knock-out properties of moulding sands with water 
glass. Archives of Mechanical Technology and Automation, 
Vol. 24, No 1, Poznań, s. 49 – 56 (2004). 
[3] S.M. Dobosz, K. Major-Gabryś: Glassex- a new additive 
improving the knock-out properties of moulding sands with 
water glass. Archives of Foundry, , Vol. 4, No. 13, Katowice, 
s. 63 – 68 (2004). 
[4] K. Major-Gabryś, S.M. Dobosz: The trial of explaining the 
application mechanism of additive upgrading the knock-out 
properties of moulding sands with water glass. XXVIII 
Konferencja Naukowa z Okazji Święta Odlewnika 2004, 
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[5] K. Major-Gabryś, S.M. Dobosz: High-temperature expansion 
and knock-out properties of moulding sands with water 
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1/2007, s. 127 – 130 (2007). 
[6] I.S. Syčev: Elaboration of moulding sands with good knock-
out properties, Litejnoje Proizvodstvo, nr 6 s. 31-37 (1965). 
[7] P. Jelinek: The influence of Al2O3 on knock-out properties of 
moulding sand wit water glass. Sbornik vedeckych praci 
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[8] E.M. Levin, C.R. Robbins, H.F. McMurdie: Phase Diagram 
for Ceramists, Columbus, Ohio, USA (1964). 
[9] G. Paglia: Determination of the Structure of γ-Alumina using 
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[10] K. Major-Gabryś: Moulding sands with water glass binding 
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The mechanism of improving the knock-out properties of moulding sands with water glass

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The mechanism of improving the knock-out properties of moulding sands with water glass

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