ARCHIVES
of
ISSN (1897-3310)
Volume 7
Issue 1/2007
183 – 188
FOUNDRY ENGINEERING
40/1
Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences
Microwaves energy in curing process of
water glass molding sands
a
K. Granata,*, D. Nowaka, M. Pigiela, M. Stachowicza, R. Wikierab
Foundry and Automation Dep. Of Technical University of Wrocław, ul. Łukasiewicza 5, 50-371 Wrocław, Polska
b
Ronal Polska Sp. z o.o., ul. Inżynierska 3, 55-221 Jelcz Laskowice, Polska
*correspondence e-mail: [email protected]
Received 08.02.2007; Approved for print on: 12.03.2007
Abstract
This work presents the results of investigation of microwave heating on hardening process of water glass molding sands. Essential
influence of this heating process on basic properties such as: compression, bending and tensile strength as well as permeability and
abrasion resistance has been found. It has been proved, that all investigated sorts of sodium water glass with a module between 2.0 and 3.3
can be used as a binder of molding sands in microwave curing process. It has been found during analysis of research results of sands with
2.5 % water glass addition that they are practically the same as in case of identical molding sands dried for 120 minutes at the temperature
of 110°C, used for comparative purposes. Application of microwave curing of molding sands with water glass, however, guarantees
reduction of hardening time (from 120 to 4 minutes) as well as significant reduction of energy consumption. Attempts of two stage
hardening of the investigated water glass molding sands have also been carried out, that is after an initial hardening during a classical CO2
process (identical sands have also been tested for comparison after CO2 blowing process) and additional microwave heating. It has been
found that application of this kind of treatment for curing sands with 2.5 % sodium water glass content and module from 2.0 up to 3.3
results in the improvement of properties in comparison to classical CO2 process.
Key words: innovative materials and technologies in foundry, microwaves, molding sand, water glass, mole module
1. Introduction
Microwaves are electromagnetic waves of small length, within
1m to about 1mm range. They are broadly applied in such fields
as telecommunications, meteorology or chemistry. Microwave
energy might also be used, among others, in foundry and curing
process of molding sands, including water glass molding sands [14]. Energy consumption during microwave heating, in comparison
to a conventional process, is even 10 up to 100 times lower, while
microwave heating process time compared to the conventional
heating is 10-200 times shorter [1,2,5].
2. Measuring post
Hardening process investigation (drying, dehydration [6]) of
molding sands conducted in commonly used microwave ovens
does not guarantee parameter repeatability and full process
control. These ovens have a simple power pack which does not
allow for a smooth magnetron power output control. In our
studies we used a microprocessor controlled device allowing for
magnetron power control and regulation of microwave amplitude
(which allows for a smooth power control) as well as possibility
of duration and heating cycle number setting, selected according
to a degree of working chamber filling with stock [2,7]. The
studies have been conducted at the post presented by Figure 1.
2. Preparation of molding sands
It has been determined, basing on literature data as well as results’
analysis of initial studies [2], that introduction of 05.% of water
addition to a mass containing quartz sand and water glass is
beneficial for a microwave hardening process. We used a standard
quartz sand from Nowogród Bobrzański mine of 0.32/0.2/0.16
main fraction and water glass manufactured by Zakłady
Chemiczne „Rudniki” S.A.,whose properties (consistent with
certificate) are presented in table 1, for preparation of molding
sands applied in our studies. The sands have been prepared
ARCHIVES of FOUNDRY ENGINEERING Volume 7, Issue 1/2007, 183-188
183
according to the following formula: a portion of quartz sand (4
kg) have been loaded into a laboratory mixer and 20 ml (0.5%) of
water have been added after its start. Water glass (2.5%) has been
dosed during mixing and mixed for 4 minutes. Samples for
determination of resistance to compression, bending and tensile
strength as well as permeability and abrasion resistance [8-10]
have been formed on a standard rammer from these sands.
sand curing (second stage). The samples of the first series
of second stage were subject only to microwave hardening.
Three samples for compression, bending and tensile
strength measurement were put into a heating chamber.
This number of samples ensured a proper operation of
magnetron and identical curing conditions. Hardening time
and power of 240 seconds and 700 W, respectively, were
assumed basing on literature data [11-17]. The samples
were left to cool down after curing. The second series of
the second stage of our study was conducted on the
samples which were previously hardened in a classical way
during CO2 process for 30 seconds and next by
microwaves, applying the same parameters as in case of the
first series. The samples were also cooled down to ambient
temperature afterwards.
Because compression resistance of the dried samples
hardened by microwaves exceeded measurement range of the
universal laboratory device, determination of this parameter was
conducted using Instron 1126 resistance machine ensuring
identical pressure increase velocity of 0.25 N/cm2.
Fig. 1. Block diagram of the research post
4. Research results
Consolidation degree of the investigated samples has been
determined basing on initial studies, which proved that three-fold
ramming of the investigated sands guarantees consolidation
allowing for taking them out from molds without damage to
profiles and operating them regardless of water glass kind used
for preparation.
A constant, apparent sand density, playing an important role in
our studies has also been determined in this way [3].
3. Sample curing process
The study has been conducted in two stages of two series. In
the first stage the samples were hardened with two classical
methods. The first method consisted in blowing of the samples
with carbon dioxide for 30 seconds. The second method consisted
in drying of the samples in a conventional dryer at the
temperature of 110°C for 120 minutes. After cooling of the
samples down to ambient temperature their resistance to
compression, bending tensile strength and permeability as well as
abrasion resistance have been investigated.
The results of the first stage constitutes comparative
basis for the studies with microwave energy application for
Figures 2 to 5 present a list of study results of sodium water
glass module influence on resistance to compression, bending and
tensile strength of the sands used for both stages. For comparison
purposes the figures present results for both series of the
conducted studies. Measurement points constitute mean value for
three assays.
As appears from analysis of figure 2, resistance to
compression, bending and tensile strength of water glass molding
sands hardened with carbon dioxide is not high and does not
depend on module of the used water glass. The same sands dried
conventionally are characterized by many times higher resistance
depending on the binder module. A significant decrease of all the
determined resistance parameters is observed for water glass kind
with module greater than 2.9.
Figure 3 presents the influence of mole module of water glass
on permeability and abrasion resistance of the investigated
molding sands cured with CO2 process and conventionally.
Permeability of the studied sands is practically constant and
does not depend on water glass module, while higher values are
reached in case of the sands hardened with carbon dioxide. In this
case also an obvious decrease of permeability is observed for the
sands prepared with water glass of 2.9 module characterized by
very high viscosity (table 1).
Table 1.
Physical-chemical properties of sodium water glass
Requirements
Kind
150
149
145
140
137
184
Mole module
SiO2/Na2O
1.9÷2.1
2.8÷3.0
2.4÷2.6
2.9÷3.1
3.2÷3.4
Oxide content
(SiO2+Na2O) %
40.0
42.5
39.0
36
35
Density (20oC) g/cm3
Fe2O3 % max
CaO % max
1.50÷1.53
1.49÷1.51
1.45÷1.48
1.40÷1.43
1.37÷1.40
0.01
0.01
0.01
0.01
0.01
0.1
0.1
0.1
0.1
0.1
Dynamic
viscosity (P)
1
7
1
1
1
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Fig. 2. Influence of water glass mole module on resistance to compression, bending and tensile strength of molding sands hardened in CO2
process and conventionally dried
Fig. 3. Influence of water glass mole module on permeability and abrasion resistance of molding sands hardened in CO2 process and
conventionally dried
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185
Fig. 4. Influence of water glass mole module on resistance to compression, bending and tensile strength of molding sands hardened by
microwaves or in a two-stage process by CO2 and by microwaves
Fig. 5. Influence of water glass mole module on permeability and abrasion resistance of molding sands hardened by microwaves or in a twostage process by CO2 and by microwaves
186
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Abrasion resistance of conventionally dried sands is low
(practically amounting to zero) and does not depend on water glass
module (fig. 3). On the contrary, in case of sands cured with CO2
this parameter strongly depends of water glass module. A very high
sand resistance to abrasion is observed in this case for glass with
module 2.0 as well as quick increase of the sand abrasion resistance
corresponding to water glass module increase. Similarly to
permeability, where this parameter decreased for the water glass
with module of 2.9 (kind 149) and high viscosity, abrasion
resistance of this sand was so high that final determination of this
parameter was impossible.
While analyzing figure 4, we can see that resistance to
compression, bending and tensile strength of water glass molding
sands hardened with microwaves is very high and close to the
values measured for the same sands dried conventionally at the
temperature of 110°C for 120 minutes. A similar resistance
decrease of the investigated sands prepared with water glass with
the highest modules of 3.0 and 3.3 is observed as in case of the
conventionally dried sands. Resistance to compression, bending
and tensile strength of molding sands hardened in two stages, first
in a classical way with CO2 and next by microwaves, is
significantly lower than of those cured with microwaves but much
higher in comparison to the sands hardened in a classical way,
with CO2 process. In this case also sand resistance decreases
visibly with the increase of water glass module, as in case of those
cured with microwaves.
Figure 5 shows influence of water glass mole module on
permeability and abrasion resistance of the investigated molding
sands cured with microwaves and in two stages, with CO2 process
and microwaves.
Permeability of the investigated sands is practically constant
and does not depend on water glass module or curing method.
Only the sands prepared with water glass 149 and 2.9 module and
– when compared to other kinds – very high viscosity, are
characterized by lower permeability.
Abrasion resistance of the sands cured with microwaves is
practically zero, while in case of those dried in two stages (CO2 and
microwaves) it strongly depends on water glass module. In this case
a sudden abrasion resistance increase of the sands with water glass
of module higher than 2.5 is observed; it is higher than in case of
the sands hardened with carbon dioxide.
5. Final conclusions
While analyzing results of the studies of water glass mole
module influence on basic parameters of molding sands hardened
with carbon dioxide and dried conventionally, constituting
comparative basis for microwave curing it has been found that:
•
all used in our studies and offered on the market kinds of
sodium water glass of 2.0 up to 3.3 module (sorts 137,
140, 145, 149 and 150) might be applied as a binder of
molding and core sands used in curing process in the
way of conventional drying as well as with CO2;
•
resistance to compression, bending and tensile strength
of the investigated, conventionally dried sands is very
high and depends on water glass mole module, while
those hardened with CO2 demonstrate lower values of
these parameters; all resistance kinds are reduced with
the increase of module to over 2.9;
•
permeability and abrasion resistance of the sands dried
conventionally and permeability of the sands hardened
with carbon dioxide does not depend on the used binder
module;
•
abrasion resistance of the sand hardened with carbon
dioxide, very low for module 2.0 and increasing fast with
the increase of water glass module, is a parameter
demonstrating dependence on the binder module.
While analyzing the possibility of application of microwave
heating in the process of sodium water glass molding sands of
various mole module it has been found that:
• all used in our studies and offered on the market kinds of
binders (including the most commonly applied in foundry
sorts 145 and 149) after microwave heating guarantee
reaching a very good resistance to compression, bending
and tensile strength as well as permeability and abrasion
resistance, comparable with the ones obtained during the
classical drying process at the temperature of 110°C for 120
minutes;
• decrease of sands’ properties, similar in its course as in
case of conventional drying, occurs with the increase of
water glass module (to over 2.9);
• application of microwave heating in the process of two
stage hardening of the investigated molding sands (CO2
and next microwaves) ensures obtaining of higher strength,
compared only to carbon dioxide curing, and decreasing
with the increase of water glass module;
• mole module influences abrasion resistance of the
investigated molding sands and in case of values higher
than 2.5 it is so high that it eliminates application of these
sands after two-stage curing process;
• no influence of water glass module on permeability of the
investigated sands has been observed;
• molding sands prepared with water glass of module 2.0 –
2.9 (sorts 145, 149 and 150) are characterized with the
best properties during both curing processes;
• application of microwave curing process of water glass
molding sands ensures notable economic benefits
resulting from a significant reduction of curing time as
well as from reduction of energy consumption, while
simultaneously assuring excellent properties of molding
and core sands.
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