TECHNICAL FIELD
[0001] The present invention relates to moulding sand comprising a modified biopolymer and
a method of curing thereof.
BACKGROUND
[0002] Moulding sands are used in the foundry industry for production of moulds and cores,
which are then used to produce castings.
[0003] A typical process of producing a casting comprises filling a mould (prepared from
a moulding sand) with a liquid material (such as metal alloy, gypsum, wax or plastic)
in order to obtain a product having desired structure and properties. After the casting
is solidified, the mould is subject to the process of striking, wherein the material
of the mould is separated from the casting.
[0004] The moulding sand is typically composed of a matrix, usually in the form of an inorganic,
loose material, such as silica sand, and a binder for "connecting" the grains of the
matrix; green sands additionally comprise water.
[0005] The main requirements for the moulding sands are the ability to be moulded while
maintaining appropriate cohesion, as well as the strength of the bonds between sand
grains - i.e. lack of tendency of the mould to be friable, both while waiting for
filling, and during thermal and erosive impact on the mould of liquid material introduced
into the mould.
[0006] The functional properties of moulds and cores made of moulding sand are highly influenced
by the type of the binder applied. One typical binder used for moulding sands is bentonite.
There are also known binders in the form of hydrocarbon resins, wherein bonding process
of the binder is carried out by a chemical reaction. Further, mixtures of synthetic
polymers and biopolymers can be used as binders as well.
[0007] In order to improve the functional properties of casting moulds and cores, various
types of additives can be introduced into moulding sands at the stage of their preparation,
such as pulverised coal or sulphite lye, which are aimed at reducing mould friability
and at reducing the tendency of casting defects to be formed, such as streaks, scars
or dusting.
[0008] In order to reduce the negative impact on the environment, some of the synthetic
additives for moulding sands can be replaced by additives of natural origin, such
as starch, cellulose or modifications thereof, including dextrins, carboxymethyl starch
or carboxymethyl cellulose.
[0009] For example, native starch can be used as an auxiliary substance which improves hardness
and durability of moulding sands with bentonite, and reduces friability. Native starch
can also be introduced in the form of boiled starch, which helps to prevent casting
defects associated with expansion. A side effect of the presence of starch in the
composition of the moulding sand is, however, deterioration in liquidity and in resistance
of the sand to erosion and to penetration of metal into the mould.
[0010] Native starch is composed of glucose mers linked by α-1,4-glycosidic bonds in amylose,
and by α-1,4- and α-1,6-glycosidic bonds in amylopectin. In terms of its chemical
composition, native starch is not homogeneous and is composed of amylose (20-25%,
(C
6H
10O
5)
n with n=5000) and amylopectin (75-80%, (C
6H
10O
5)
n with n=50000). Amylose forms viscous solutions at the temperature of 90°C, and amylopectin
forms hydrogel at the temperature of 70°C. A disadvantage of native starch is its
insolubility in cold water. Native starch begins to partially dissolve and swell at
the temperature of about 70°C. In order to improve solubility of native starch in
water, it is typically modified by introducing polar groups, such as hydroxyl groups.
[0011] The Polish Standard PN-87/A-74820 defines a modified starch as a natural starch in
which one or more of its initial physical or chemical properties are changed by an
appropriate treatment. Modification of starch aims at improving functional properties
of starch or at giving it new characteristics.
[0012] Starch properties can be changed within a wide range by interacting with chemical
agents, physical agents or enzymatically. Products of chemical modification of starch
by esterification, etherification and oxidation are widely used in the industry, including
products with modified molar mass, gelatinisation temperature, solubility, viscosity,
water binding capacity, temperature stability and resistance to acids and enzymes.
[0013] Products of starch modification, such as, for example, etherified starch, i.e. comprising
hydroxyethyl, hydroxypropyl or carboxymethyl groups, for example, carboxymethyl starch,
can be used as binder components of moulding sands in the form of multicomponent mixtures.
[0014] Modified biopolymers, including modified products of starch and cellulose, introduced
into binders due to their natural origin (as renewable raw materials), relatively
low price and biodegradability, do not have a negative impact on the natural environment.
[0015] There are known numerous examples of using starch and its etherified derivatives
in the technology of moulding sands.
[0016] For example, a publication "
Preparation and experiments for a novel kind of foundry core binder made from modified
potato starch" (Wenbin Yu, Hong He, Nanpu Cheng, Bingtai Gan, Xuelian Li, Materials
and Design 30 (2009) pp.210-213), discloses water-soluble modified starch binder (WMSB) is described, which consists
of 28-30% of potato starch, 1% of formaldehyde, 0.1% of phosphoric acid, 2% of polyvinyl
alcohol, 1% of urea and water. The binder is introduced into the sands with bentonite
(2-3%) in the amount of 4-7%. The sand after drying (self-curing under ambient conditions)
has a tensile strength at the level of 0.7-2.5 MPa, depending on the amount of WMSB
in the sand. The sand has a tendency to absorb moisture from the environment and is
a gas generant (14.2 ml/g).
[0018] A publication "
Synthesis and Application of Modified Starch as a Shell-Core Main Adhesive in a Foundry"
(Xia Zhou, Jinzong Yang, Feng Qian,Guohui Qu, Journal of Applied Polymer Science,
116/5 (2010), pp. 2893-2900, DOI 10.1002/app.31781) describes a method for obtaining sand for the preparation
of shell cores with the participation of corn-based binder CMS having DS of 0.25-0.78.
The sand consists of matrix, CMS, bentonite, graphite powder, phosphates, surfactants
and water in the ratio of 100:4.0:0.5:0.3:0.01:0.03:(14-20). The shell cores are prepared
in a core box having the temperature of 100-200°C.
[0019] Publications "
The high-temperature resistant mechanism of α-starch composite binder for foundry"
( Xia Zhou, Jinzong Yang, Depeng Su, Guohui Qu, Journal of Materials Processing Technology
209 (2009) pp. 5394-5398),
"Hygroscopicity-resistant mechanism of an α -starch based composite binder for dry
sand molds and cores" (Xia Zhou , Jiyang Zhou , Guohui QU, China foundry, (2) 2005,
pp. 97-101) and "
Adhesive Bonding and Self-Curing Characteristics of α-Starch Based Composite Binder
for Green Sand Mould/Core" (Xia Zhou ,Jinzong Yang ,Guohui QU., J. Mater. Sci. Technol.,
(20/05)2004,) pp. 617-621) describe a binder consisting of α-starch, kaolin, sodium silicate, dextrin, phosphate
and water in the respective proportions of: 2.5-4.0%, 1.5-3.0%, 0.55%, 0.35%, 0.04%
and 2.5-3.5%. Curing is carried out by annealing at the temperature of 160-200°C for
1 h. This sand is resistant to absorption of moisture from the environment and to
high temperatures, bending strength of the sand at about 1000°C is maintained at the
level of about 0.4 MPa.
[0022] Publications "
Evaluating the Baked Compressive Strength of Produced Sand Cores Using Cassava Starch
as Binder for the Casting of Aluminium Alloy T-Joint Pipe" (Opaluwa A. I and Oyetunji
A., Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (3/1),
pp. 25-32) and "
Littlestudy on the shear strength of foundry sand cores using clay and cassava starch
as binder" (Oyetunji A., Seidu S.O. and Opaluwa A. I., DAFFODIL INTERNATIONAL UNIVERSITY
JOURNAL OF SCIENCE AND TECHNOLOGY, (8/2) 2013, pp. 77- 84) describe a technology for preparing core sands of 4-12% of tapioca starch, 6-12%
of water and 5% of locally occurring clay. Curing of the sand is carried out at the
temperature of 180°C for 2 hours. The maximum compressive strength of the sand (10%
of water, 10% of starch) in wet state is 290 N/mm
2, and that for the dried sand is, respectively, 4122 N/mm
2.
[0023] There are also known compositions of moulding sands which contain biopolymers in
the form of products of chemical modification of starch and cellulose.
[0024] A Japanese patent application JPS5731439 describes a binder for moulding sands which
are obtained by esterification by adding, to the starch, chloroacetic acid and NaOH
solution, and then cold water. However, this publication does not relate to moulding
sands as such and methods for their preparation and curing.
[0025] A Polish patent application
PL285979 describes a moulding sand consisting of a matrix in the form of silica sand, carbon
additive in the amount of 0-6% by weight, starch and cellulose formulations in the
amount of 0.5-3.0% by weight, basaltic loam acting as a binder in the amount of 5-20%
by weight and water.
[0026] A Polish patent application
PL93595 describes an additive for moulding sands, based on silica sand, bentonite and water,
reducing the tendency of the sand to friability. The additive consists of formamyle
in the amount of 40% by weight, flocculant in the amount of 30% by weight, glycol
in the amount of 5% by weight and wood flour or harl flour in the amount of 25% by
weight.
[0027] A Chineese patent application
CN101898226 describes a use of carboxymethyl starch as an additive to the binder in the form
of a multicomponent mixture for binding moulding sands. The moulding sand consists
of sand, modified starch, malt sugar, glycerine, sodium hydroxide, pulverised coal,
iron oxide, starch, carboxymethyl cellulose and water. These components are of natural
origin, which ensures lack of negative impact of the sand on the environment and its
nontoxicity.
[0028] A Dutch patent application
NL6913413 describes a moulding sand consisting of bentonite, water-soluble grafted polymer
of acrylic acid on a base of carboxymethyl cellulose.
[0029] A Chinese patent application
CN103521696 describes a composition of moulding sand, consisting of china clay, pulverised coal,
aluminum powder, carboxymethyl cellulose, sodium hexametaphosphate, stearic acid,
chlorinated paraffin, borax, boron oxide, boric acid and water. The moulding sand
is characterised by good gas permeability and cohesiveness.
[0030] A Polish patent application
PL396105 describes a composition of moulding sand with a biodegradable polymeric binder, consisting
of 100 parts by weight of refractory matrix and of 1-5 parts by weight of organic
binder. The organic binder applied consists of a mixture of aqueous solutions of poly(acrylic
acid) or poly(sodium acrylate) in the amount of 30-70% by weight and of biopolymer
from the group of polysaccharides in the form of modified starch or dextrin in the
amount of 30-70% by weight.
[0031] It follows from the above-mentioned publications, that the known compositions of
moulding sands with biopolymers are characterised by multicomponent nature of the
binder, which is associated with the need to meet specific performance and strength
parameters by the moulding sand. A multicomponent nature of the binder negatively
affects also prolongation of preparation of the sand and its price.
[0032] It would, therefore, be advisable to develop a composition of moulding sand which
would not contain multiple components and would contain primarily substances which
are non-toxic and neutral to the environment. It would also be advisable for such
a composition to exhibit good performance and durability parameters.
SUMMARY
[0033] The object of the invention is a moulding sand comprising water, a binder and a silica
sand matrix, wherein it further comprises sodium salt of carboxymethyl starch (CMS-Na)
having a degree of substitution (DS) in the range of 0.2 to 0.9, in the amount of
0.2 to 2.5 parts by weight per 100 parts by weight of the matrix.
[0034] Preferably, CMS-Na is a binder in the amount of 1.5 to 2.5 parts by weight per 100
parts by weight of the matrix.
[0035] Preferably, the moulding sand is a bentonite-bound sand and CMS-Na is an additive
in the amount of 0.2 to 2.0 parts by weight per 100 parts by weight of matrix.
[0036] Preferably, the moulding sand comprises a binder in the form of activated bentonite
comprising montmorillonite in the amount of 70% to 90% by weight.
[0037] Another object of the present invention is a method of curing a moulding sand as
described above by evaporating water from the sand by subjecting the moulding sand
to electromagnetic waves of microwave frequency in the range of 2 GHz to 3 GHz.
DETAILED DESCRIPTION
[0038] The moulding sand according to the invention comprises a single-component binder,
a matrix and a solvent or it may contain a normally used binding material, such as
an activated bentonite. One of the sand components is a biodegradable sodium salt
of carboxymethyl starch (CMS-Na), wherein depending on the amount of CMS-Na introduced
into the moulding sand, it may serve only as an additive to the sand, improving certain
utility properties, or it may serve as an additive and a binder. As the matrix, silica
sand is used, preferably acidic, and the solvent is constituted by water capable of
solvating CMS-Na, which is generally available, does not influence the environment
negatively, and has a low price.
[0039] CMS-Na for the moulding sand according to the invention can be obtained in any known
manner, for example by etherification of starch, for example potato starch, and then
by neutralization of the etherification product by means of an aqueous solution of
sodium hydroxide (NaOH), preferably having the concentration of: 2-10%, and more preferably
having the concentration of 5%.
[0040] Fig. 1 shows a reaction scheme for obtaining CMS-Na from starch by etherification
of native starch slurry in ethyl alcohol by means of sodium salt of monochloroacetic
acid in the presence of NaOH (Williamson synthesis). Products having different properties
can be obtained, depending on the conditions for conducting modification. Changes
that take place in the starch molecule are determined based on the degree of substitution
(DS) which defines the average number of carboxymethyl groups (-CH
2-COOH) or sodium carboxymethyl groups (-CH
2-COONa) attributable to a single link of starch in each glucopyranose ring. Viscosity,
water solubility and durability of CMS-Na increase proportionally to the degree of
substitution (DS).
[0041] In order to produce the moulding sand according to the invention, CMS-Na is introduced
in a loose form into the matrix, optionally with another loose material, such as for
example activated bentonite, and all the components are stirred. The time of stirring
may be adapted depending on the needs, for example, depending on the efficiency of
the stirrer applied. Preferably, the stirring time is 1 to 2 minutes, and more preferably
the stirring time is 1 minute. After the loose components have been mixed, a polar
solvent (e.g. water) is introduced into the mixture, and the components are stirred
until the mass becomes consistent. Preferably, the stirring time of the loose components
with water is 1 to 2 minutes, and more preferably the stirring time of the loose components
with water is 2 minutes. Addition of the solvent ensures wetting of matrix grains,
which provides appropriate adhesion of the binder-matrix system.
[0042] Research conducted for moulding sands with CMS-Na having various compositions has
shown that CMS-Na introduced into the sand as an additive in minor amounts, i.e. in
the range of 0.2 to 2, and more preferably in the amount of 0.5 parts by weight per
100 parts by weight of the matrix, results in reduction of friability of the moulding
sand. Further, it appeared that CMS-Na serves as a carrier of lustrous carbon in the
moulding sand, and therefore it can be used as a bio-substitute for pulverised coal
and hydrocarbon resins, which allows for achieving a simple composition of the moulding
sand and ensures elimination of components from the sand, which could negatively affect
the natural environment.
[0043] In turn, CMS-Na can also serve as a binder, when introduced into the moulding sand
in the amount of 1.5 to 2.5 parts by weight per 100 parts by weight of the matrix
- it exhibits the ability to bind the moulding sand permanently.
[0044] Research has shown unexpectedly that the binding properties of sodium salt of carboxymethyl
starch (CMS-Na) are better than the binding properties of other known binding biopolymers,
such as carboxymethyl cellulose (CMC) and carboxymethyl starch (CMS), which allows
the use of CMS-Na as the main "binding agent" of the moulding sand - without the need
to introduce auxiliary binding substances or to use binding mixtures having complex
compositions.
[0045] Further research has shown that the degree of substitution (DS) has an impact on
the binding properties of CMS-Na, wherein the best binding properties are achieved
with the degree of substitution (DS) in the range of 0.2 to 0.9, and preferably 0.6
to 0.8. This is caused by the impact of DS on solubility of CMS-Na in polar solvents:
the higher DS (i.e. the greater share of side polar groups within a polymer chain
- starch), the higher the solubility of CMS-Na in polar solvents. Therefore, an increase
in solubility of CMS-Na improves the binding properties of this substance.
[0046] It further appeared that the type of matrix applied has an impact on the increase
in binding properties of CMS-Na. Research results have shown that the best binding
properties of CMS-Na are achieved with acidic matrix materials, including for example
silica sand.
[0047] For example, addition of 1.5-2.5 parts by weight of binder CMS-Na and 3-5 parts by
weight of water to 100 parts by weight of silica sand, very good functional parameters
of sand and very good durability parameters of moulds and cores are achieved.
[0048] In case CMS-Na serves as a binder, the moulding sand can be cured physically - by
evaporating part of the water contained in the sand. The evaporation can be performed
by supplying energy in a thermal way, i.e. by heating the moulding sand until it solidifies.
For example, the moulding sand can be annealed through thermal drying in the temperature
of 80 to 150°C, and preferably in the temperature of 100°C.
[0049] Optionally, with a view to solidification, the sand with CMS-Na binder can be subjected
to electromagnetic radiation having a microwave frequency, preferably in the range
of 2 to 3 GHz, and more preferably 2.45 GHz and with the power of 600 W to 1200 W,
preferably 800 W. Radiation exposure time is selected depending on the amount and/or
the weight of the sand.
[0050] For the composition of the moulding sand which contains CMS-Na as an additive, various
types of typically used binding materials can be used, such as for example activated
bentonite having montmorillonite content of 70 to 90%. For example, the moulding sand
can be composed of 100 parts by weight of mineral matrix, 5-8 parts by weight of bentonite,
0.5-2 parts by weight of CMS-Na and 1.5-4 parts by weight of water.
[0051] One of the advantages of the moulding sand according to the invention is its simple
composition; the sand can be composed of only three components: CMS-Na binder, mineral
matrix and solvent; introduction of CMS-Na as a binder allowed obtaining the effect
of better binding of the matrix, and therefore obtaining moulds and cores having better
functional parameters.
[0052] The simple composition of the moulding sand according to the invention is also related
to the multifunctionality of CMS-Na in the sand. This substance can simultaneously
serve in the moulding sand as a binder and as an additive, providing reduction in
friability of the bentonite-bound sand and allowing elimination from the system of
substances such as pulverised coal or hydrocarbon resins, which significantly simplifies
the composition of the sand.
[0053] The ability to control the properties of CMS-Na binder, such as degree of substitution
(DS) or viscosity, already at the stage of its production (starch modification) provides
additionally the possibility of producing, depending on the needs, the moulding sand
with desired properties, such as bending strength or friability.
[0054] Further, the moulding sand according to the invention does not negatively affect
the environment. CMS-Na is a biodegradable polymer, and products of CMS-Na decomposition
are substances which occur naturally in the environment and are harmless.
[0055] The moulding sand with CMS-Na according to the invention is characterised by allowing
easy striking of the products out of the mould and by a high quality of the castings
produced.
[0056] The moulding sand according to the invention is further characterised by good recoverability.
CMS-Na binder can be retrieved from the sand after a technological process.
[0057] The CMS-Na bound sand is characterised by insignificant harmfulness to the environment
and workers (the used sand can be utilised in the industry).
[0058] An important advantage of the CMS-Na bound sand is the possibility of its preparation
with acidic matrices.
[0059] The CMS-Na bound sand may be an alternative for the sands used in foundry industry
due to the physicochemical characteristics of its components, and technological, ecological
and economic aspects. Further, the starch component of CMS-Na sand can be produced
from cheap raw materials, such as for example potato starch, or from vegetable waste
containing starch (e.g. potato processing waste).
EXAMPLE I
Synthesis of CMS-Na:
[0060] Modification of potato starch with the moisture content of up to 14.0% was conducted
in a glass reactor equipped with a mechanical stirrer, a thermocouple and capillaries
supplying nitrogen to the reaction system. The starch was etherified in a mixture
of isopropanol (IPOH) and water in a single-step process. Monochloroacetic acid (MCA)
was dissolved in IPOH in the reactor, and then was introduced in aqueous solution
of NaOH. The molar ratio of NaOH/(S)MCA was 2.25:1. After stirring for 90 min and
homogenisation of the mixture, a fine fraction of NaOH was introduced into the reactor.
The reaction was conducted for the period of about 150 - 180 min in the temperature
of 50°C. The product obtained was filtered off and neutralised with acetic acid, then
it was washed several times with methanol solution, once with pure methanol, and then
it was left on a heated surface to be dried in the air.
[0061] The above example of the synthesis of CMS-Na should only be considered as illustrative,
while CMS-Na to be used in further examples can be also obtained by other known methods.
EXAMPLE II
Preparation and curing of the sand with starch binder:
[0062] 1.5 parts by weight of non-crosslinked CMS-Na in a loose form having DS=0.87 (properties
for 5% solution: pH=12 and viscosity is 4500 mPa·s) and 100 parts by weight of acidic
silica sand having an average grain size in the range of 0.16-0.32 mm, were introduced
into a roll mixer and the components were stirred for 1 min. Next, 3 parts by weight
of water were added to the mixer and the sand was stirred for another 2 min, and then
the liquidity of the sand was measured. The process of sand preparation was performed
under ambient conditions - humidity of the air: 35% and the temperature of: 23°C.
[0063] From the moulding sand produced, two longitudinal moulded pieces, each weighing 150g,
and four octal moulded pieces, each weighing 75g, were prepared.
[0064] The moulded pieces were subjected to curing under the influence of microwave radiation
with power of 800W and frequency of 2.45 GHz for 120s, an then properties of the cured
sand were examined.
The sand with the following properties was obtained:
Tensile strength
in the cured state after storage time:
- 1 h: 1.4(± 0.1) MPa
- 24 h: 1.4 (± 0.1) MPa
Bending strength
in the cured state after storage time:
- 1 h : 2.4 (± 0.1) MPa
- 24 h : 2.0 (± 0.1) MPa
Sand permeability in the cured state after storage time:
- 1 h: 218 (± 2) 10-8 m2/Pa·s
- 24 h: 268 (± 3) 10-8 m2/Pa·s
Abrasion resistance of sand in the cured state after storage time:
- 1 h: 1.92 (± 0.13) %
- 24 h: 1.63 (± 0.11) %
Dietert liquidity of sand in the uncured state
95 ((± 0.23) %
EXAMPLE III
Preparation and curing of the sand with starch binder:
[0065] 2.5 parts by weight of non-crosslinked CMS-Na in a loose form having DS=0.2 (properties
for 5% solution: pH=11.3 and viscosity = 22000 mPa·s) and 100 parts by weight of acidic
silica sand having an average grain size in the range of 0.16-0.32 mm, were introduced
into a roll mixer and the components were stirred for 1 min. Then, 5 parts by weight
of water were added to the mixer and the sand was stirred for another 2 min, and then
liquidity of the sand was measured. The process of sand preparation was performed
under ambient conditions - humidity of the air: 35% and the temperature of: 23°C.
[0066] From the moulding sand produced, two longitudinal moulded pieces, each weighing 150g,
and four octal moulded pieces, each weighing 75g, were prepared.
[0067] The moulded pieces were subjected to curing under the influence of microwave radiation
with power of 800W and frequency of 2.45 GHz for 120s, an then properties of the cured
sand were examined.
The sand with the following properties was obtained:
Tensile strength
in the cured state after storage time:
- 1 h: 1.3 (± 0.1) MPa
- 24 h: 1.2 (± 0.1) MPa
Bending strength
in the cured state after storage time:
- 1 h: 2.4 (± 0.1) MPa
- 24 h: 2.0 (± 0.1) MPa
Sand permeability in the cured state after storage time:
- 1 h: 210 (± 3) 10-8 m2/Pa·s
- 24 h: 222 (± 2) 10-8 m2/Pa·s
Abrasion resistance of sand in the cured state after storage time:
- 1 h: 1.26 (± 0.15) %
- 24 h: 1.5 (± 0.10) %
Dietert liquidity of sand in the uncured state
89 ((± 0.2) %
EXAMPLE IV
Preparation and curing of the sand with starch binder:
[0068] 2.5 parts by weight of non-crosslinked CMS-Na in a loose form having DS=0.2 (properties
for 5% solution: pH=11.3 and viscosity = 22000 mPa·s) and 100 parts by weight of acidic
silica sand having an average grain size in the range of 0.16-0.32 mm, were introduced
into a roll mixer and the compontents were stirred for 1 min. Then, 5 parts by weight
of water were added to the mixer and the sand was stirred for another 2 min, and then
liquidity of the sand was measured. The process of sand preparation was performed
under ambient conditions - humidity of the air: 42% and the temperature of: 22°C.
[0069] From the moulding sand produced, two longitudinal moulded pieces, each weighing 150g,
and four octal moulded pieces, each weighing 75g, were prepared. The moulded pieces
were cured by thermal annealing in the temperature of 100°C for 30 min, and then their
properties were examined.
The sand with the following properties was obtained:
Tensile strength
in the cured state after storage time:
- 1 h: 1.2 (± 0.06) MPa
- 24 h: 1.2 (± 0.04) MPa
Bending strength
in the cured state after storage time:
- 1 h: 2.6 (± 0.1) MPa
- 24 h: 2.2 (± 0.1) MPa
Sand permeability in the cured state after storage time:
- 1 h: 172 (± 2) 10-8 m2/Pa·s
- 24 h: 192 (± 2) 10-8 m2/Pa·s
Abrasion resistance of sand in the cured state after storage time:
- 1 h: 11.9 (± 0.2) %
- 24 h: 14.9 (± 0.2) %
Dietert liquidity of sand in the uncured state
91.2 (± 0.5) %
EXAMPLE V
Preparation of bentonite-bound green sand moulding with a starch additive:
[0070] 6 parts by weight of activated bentonite containing montmorillonite in the amount
of 70-90%, 100 parts by weight of acidic silica sand having an average grain size
in the range of 0.16-0.32 mm and 0.5 parts by weight of non-crosslinked CMS-Na in
a loose form having DS=0.87 (property of 5% solution having pH of 10.2 and viscosity
of 4500 mPa·s) were introduced into a roll mixer, the entirety was stirred for 1 min,
then water was added to achieve moisture content at the level of 1.5 to 4% (optimal
operating moisture content is 2.54%), and then the entirety was stirred for 2 min.
The process of sand preparation was performed under ambient conditions - humidity
of the air: 54% and the temperature of: 19.7°C. Then, certain parameters of the sand
were measured.
The sand with the following properties was obtained:
Compressive strength of green sand
Shear strength of green sand
Tensile strength of green sand
Permeability Pw= 300 x108 m2/Pa·s
Dietert flowability PD= 72%
Free flowability PS= 25%
Friability S = 10.3%
Compatibility Z = 52.0%
Properties for optimal operating moisture content of the sand being 2.54% determined
on the basis of an indicator of moulding properties Wf = 75%.
EXAMPLE VI
Preparation of bentonite-bound green sand moulding with a starch additive:
[0071] 6 parts by weight of activated bentonite containing montmorillonite in the amount
of 70-90%, 100 parts by weight of acidic silica sand having an average grain size
in the range of 0.16-0.32 mm and 0.5 parts by weight of non-crosslinked CMS-Na in
a loose form having DS=0.2 (property of 5% solution having pH of 11.4 and viscosity
of 22000 mPa·s) were introduced into a roll mixer, the entirety was stirred for 1
min, then water was added to achieve moisture content at the level of 1.5 to 4% (optimal
operating moisture content is 2.10%), and then the entirety was stirred for 2 min.
The process of sand preparation was performed under ambient conditions - humidity
of the air: 47.0% and the temperature of: 26.1°C. Then, certain parameters of the
sand were measured.
The sand with the following properties was obtained:
Compressive strength of green sand
Shear strength of green sand
Tensile strength of green sand
Permeability Pw= 300 x108 m2/Pa·s
Dietert flowability PD= 76.8 %
Free flowability PS= 17.0 %
Friability S = 13.5 %
Compatibility Z = 55.0 %
Properties for optimum operating moisture content of the sand being 2.10% determined
on the basis of an indicator of moulding properties Wf = 75%.