U.S. patent application number 14/706296 was filed with the patent office on 2015-08-20 for coated sand, manufacturing method for same, and manufacturing method for mold.
The applicant listed for this patent is ASAHI ORGANIC CHEMICALS INDUSTRY CO., LTD.. Invention is credited to Yuichiro TANAKA.
Application Number | 20150231691 14/706296 |
Document ID | / |
Family ID | 50978449 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150231691 |
Kind Code |
A1 |
TANAKA; Yuichiro |
August 20, 2015 |
COATED SAND, MANUFACTURING METHOD FOR SAME, AND MANUFACTURING
METHOD FOR MOLD
Abstract
Purposes of the present invention are to provide a dry coated
sand having a high degree of fluidity at the room temperature, a
method of advantageously producing the coated sand, and a method of
producing a casting mold having excellent properties, by using the
coated sand. The dry coated sand is obtained by mixing an aqueous
solution of a water glass used as a binder, with a heated
refractory aggregate, whereby water in the aqueous solution is
evaporated, and a coating layer of the binder is formed on surfaces
of the refractory aggregate. A moisture percentage in the thus
obtained dry coated sand is controlled so as to be not more than
0.5% by mass. The intended casting mold is obtained by filling a
molding cavity of a forming mold, with the dry coated sand, and
passing a steam through the coated sand, to solidify or cure the
coated sand.
Inventors: |
TANAKA; Yuichiro; (Niwa-Gun,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASAHI ORGANIC CHEMICALS INDUSTRY CO., LTD. |
Nobeoka-Shi |
|
JP |
|
|
Family ID: |
50978449 |
Appl. No.: |
14/706296 |
Filed: |
May 7, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2013/083903 |
Dec 18, 2013 |
|
|
|
14706296 |
|
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Current U.S.
Class: |
164/7.1 ;
106/38.3; 106/38.9; 164/24; 164/528; 427/215 |
Current CPC
Class: |
B22C 9/12 20130101; B22C
9/03 20130101; B22C 9/02 20130101; B22C 1/188 20130101; B22C 1/18
20130101 |
International
Class: |
B22C 1/18 20060101
B22C001/18; B22C 9/12 20060101 B22C009/12; B22C 9/03 20060101
B22C009/03 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2012 |
JP |
2012-276478 |
Claims
1. A coated sand which is in a dry state and which has fluidity at
the room temperature, the coated sand being obtained by mixing an
aqueous solution of a water glass used as a binder, with a heated
refractory aggregate, to evaporate water in the aqueous solution of
the water glass, for thereby forming a coating layer of the binder
on surfaces of the refractory aggregate, the coated sand being
characterized in that its moisture percentage is controlled so as
to be not more than 0.5% by mass.
2. The coated sand according to claim 1, characterized in that the
coated sand includes not more than 3% by mass of lumps which do not
pass through a 20-mesh screen.
3. The coated sand according to claim 1, characterized in that the
aqueous solution of the water glass contains an alkali metal
silicate as its major component.
4. The coated sand according to claim 3, characterized in that the
alkali metal silicate has a molar ratio of silicon dioxide to an
alkali metal oxide, which molar ratio is not smaller than 1.0 and
smaller than 3.0.
5. The coated sand according to claim 3, characterized in that the
alkali metal silicate is sodium silicate.
6. The coated sand according to claim 5, characterized in that the
sodium silicate has a molar ratio SiO.sub.2/Na.sub.2O of not
smaller than 1.0 and smaller than 3.0.
7. The coated sand according to claim 1, characterized in that a
nonvolatile content in the aqueous solution of the water glass is
20-45% by mass.
8. The coated sand according to claim 1, characterized in that the
aqueous solution of the water glass is used in an amount of 0.1-2.5
parts by mass, in terms of its solid content, with respect to 100
parts by mass of the refractory aggregate.
9. A method of producing the coated sand according to claim 1,
characterized in that the refractory aggregate and the aqueous
solution of the water glass are mixed together such that the water
in the aqueous solution of the water glass is evaporated within 5
minutes after addition of the aqueous solution of the water glass
to the refractory aggregate, to obtain the coated sand having the
moisture percentage of not more than 0.5% by mass.
10. A method of producing a casting mold, characterized in that the
casting mold is obtained by filling a molding cavity of a forming
mold which gives the casting mold, with the coated sand according
to claim 1, and then passing a steam through the coated sand, to
solidify or cure the coated sand within the forming mold.
11. The method of producing the casting mold according to claim 10,
characterized in that a dry air, a heated dry air, a nitrogen gas
or an argon gas is further passed through a filling phase of the
coated sand filling the molding cavity of the forming mold,
simultaneously with or after passing the steam through the coated
sand.
12. The method of producing the casting mold according to claim 10,
characterized in that at least one of a carbon dioxide gas, an
ester gas and a carbonate gas is passed through a filling phase of
the coated sand filling the molding cavity of the forming mold,
simultaneously with or after passing the steam through the coated
sand.
13. The method of producing the casting mold according to claim 10,
characterized in that a pressure within the molding cavity of the
forming mold is reduced before passing the steam through the coated
sand.
14. The method of producing the casting mold according to claim 10,
characterized in that the coated sand is preheated to a temperature
not lower than 30.degree. C., and then the molding cavity of the
forming mold is filled with the preheated coated sand.
15. The method of producing the casting mold according to claim 10,
characterized in that the forming mold is preheated and kept at an
elevated temperature.
16. A method of producing a casting mold, characterized in that the
casting mold is formed by multilayer molding using the coated sand
according to claim 1.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of the International
Application No. PCT/JP2013/083903, filed on Dec. 18, 2013, which
claims the benefit under 35 U.S.C. .sctn.119(a)-(d) of Japanese
Application No. 2012-276478, filed on Dec. 19, 2012, the entireties
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a coated sand, a method of
producing the same, and a method of producing a casting mold, and
more particularly to a coated sand which is in a dry state and
which has fluidity at the room temperature, a method of producing
the coated sand, and a method of producing a casting mold by using
the coated sand.
[0004] 2. Description of Related Art
[0005] As one type of a casting mold used for casting a molten
metal, a casting mold obtained by forming a coated sand into a
desired shape has been used. The coated sand used for the casting
mold is obtained by coating a molding sand consisting of a
refractory aggregate, with a suitable binder. As examples of the
binder, inorganic binders such as a cement and a water glass, and
organic binders such as a phenolic resin, a furan resin and a
urethane resin are disclosed, together with methods of forming
self-curing molds by using these binders, on pages 78-90 of Chuzou
Kougaku Binran (Handbook of Foundry Engineering) edited by Japan
Foundry Engineering Society.
[0006] JP-A-2009-90334 discloses a method of producing the casting
mold by using a resin-coated sand obtained by coating the molding
sand with a thermosetting resin such as the phenolic resin, which
is one of the above-indicated organic binders. In this method, the
intended casting mold is produced by the following steps: filling a
forming mold with the resin-coated sand; blowing a steam into the
forming mold to raise a temperature of the resin-coated sand; and
then blowing a heated gas into the forming mold to evaporate
condensation water within the forming mold and to heat the binder
of the resin-coated sand to a temperature not lower than a
temperature at which the binder is solidified or cured. However, in
this method, the phenolic resin or other resin is used as the
binder, so that the binder may be decomposed at a high temperature
at the time of formation of the casting mold or casting of the
molten metal, giving rise to a problem of generation of gases due
to decomposition of phenol and aldehyde. Odors and stimulants of
these gases cannot be completely eliminated, so that the
above-described method is not suitable for applications in which
the odors and stimulants should be avoided.
[0007] On the other hand, where the water glass is used as the
inorganic binder, it is necessary to use a curing agent such as a
CO.sub.2 gas to cure the water glass. In the conventional technique
of such a water glass/CO.sub.2 gas process, the molding sand
(refractory aggregate) is kneaded with an aqueous solution of the
water glass used as the binder, to coat surfaces of the molding
sand with the binder, and the casting mold is formed by using the
thus obtained coated sand in a wet state (a moist state) in which
the wet water glass adheres to the surfaces of the molding sand.
Such a coated sand has a low degree of fluidity, so that there
arise inherent problems of difficulty in filling the forming mold
with the coated sand, occurrence of filling defects, and low
productivity of the casting mold.
[0008] Under the above-described circumstances, in order to obtain
a binder-coated refractory (coated sand) having a high degree of
fluidity, JP-A-2012-76115 proposes to use, as the binder, a
water-soluble inorganic compound selected from a group consisting
of the water glass, sodium chloride, sodium phosphate, sodium
carbonate, sodium vanadate, sodium borate, aluminum sodium oxide,
potassium chloride and potassium carbonate. The binder-coated
refractory proposed in this publication is obtained by coating
surfaces of the refractory aggregate with a solid coating layer
containing the water-soluble inorganic compound described above.
This publication further discloses a method of producing the
casting mold, which includes steps of: filling the forming mold
with the binder-coated refractory; blowing a steam into the forming
mold to heat the binder-coated refractory and to moisten the binder
constituting the coating layer; and then solidifying the
binder.
[0009] However, the inventor of the present invention studied the
binder-coated refractory described above, and found that even where
the surfaces of the refractory aggregate are coated with the solid
coating layer of the binder consisting of the water-soluble
inorganic compound such as the water glass and sodium chloride, a
sufficiently high degree of fluidity of the binder-coated
refractory cannot be necessarily secured, and the casting mold
obtained by using the binder-coated refractory does not have a
sufficiently high degree of strength. Further, in order to coat the
refractory aggregate with the water-soluble inorganic compound
(binder), the water-soluble inorganic compound is dissolved in
water, and the thus obtained aqueous solution is used to coat the
refractory aggregate. In this respect, it was found that conditions
of the surfaces of the refractory aggregate coated with the
water-soluble inorganic compound vary depending on a water content
in the aqueous solution, so that physical properties of the
binder-coated refractory vary depending on the water content in the
aqueous solution. Namely, where the water content is excessively
small, the refractory aggregate cannot be uniformly coated with the
water-soluble inorganic compound. On the other hand, where the
water content is excessively large, the binder-coated refractory
cannot be sufficiently dried. Therefore, the use of the
binder-coated refractory gives rise to problems that formability
and the physical properties of the binder-coated refractory are not
satisfactory or have undesirable variations. Further, the
properties of the binder-coated refractory considerably vary
depending on the kind of the water-soluble inorganic compound, so
that where the binder-coated refractory is produced by using
different kinds of the water-soluble inorganic compounds, under the
same conditions, the physical properties of the binder-coated
refractory have undesirable variations, giving rise to an inherent
problem of difficulty in optimizing the conditions of its
production.
SUMMARY OF THE INVENTION
[0010] The present invention was made based on the background art
described above. Therefore, objects of the present invention are to
provide: a coated sand which is in a dry state and which has
fluidity at the room temperature; a method of advantageously
producing the coated sand; and a method of producing a casting mold
having excellent properties by using the coated sand. Other objects
of the present invention are to provide: a coated sand which
permits a considerable improvement in ease of filling of a molding
cavity of a forming mold used for producing a casting mold, with
the coated sand, and a further improvement of a strength of the
obtained casting mold; a method of producing the coated sand; and a
method of producing the casting mold by using the coated sand.
[0011] In order to achieve the above-described objects, the present
invention can be preferably embodied in various modes which will be
described below. The various modes of the invention described below
may be practiced in any combination. It is to be understood that
the modes and technical features of the present invention are not
limited to those described below, and can be recognized based on
the inventive concept disclosed in the specification taken as a
whole.
[0012] (1) A coated sand which is in a dry state and which has
fluidity at the room temperature, the coated sand being obtained by
mixing an aqueous solution of a water glass used as a binder, with
a heated refractory aggregate, to evaporate water in the aqueous
solution of the water glass, for thereby forming a coating layer of
the binder on surfaces of the refractory aggregate, the coated sand
being characterized in that its moisture percentage is controlled
so as to be not more than 0.5% by mass.
[0013] (2) The coated sand according to the above-described mode
(1), characterized in that the coated sand includes not more than
3% by mass of lumps which do not pass through a 20-mesh screen.
[0014] (3) The coated sand according to the above-described mode
(1) or (2), characterized in that the aqueous solution of the water
glass is an aqueous solution of an alkali metal silicate.
[0015] (4) The coated sand according to the above-described mode
(3), characterized in that the alkali metal silicate has a molar
ratio of silicon dioxide to an alkali metal oxide, which molar
ratio is not smaller than 1.0 and smaller than 3.0.
[0016] (5) The coated sand according to the above-described mode
(3) or (4), characterized in that the alkali metal silicate is
sodium silicate.
[0017] (6) The coated sand according to the above-described mode
(5), characterized in that the sodium silicate has a molar ratio
SiO.sub.2/Na.sub.2O of not smaller than 1.0 and smaller than
3.0.
[0018] (7) The coated sand according to any one of the
above-described modes (1) to (6), characterized in that a
nonvolatile content in the aqueous solution of the water glass is
20-45% by mass.
[0019] (8) The coated sand according to any one of the
above-described modes (1) to (7), characterized in that the aqueous
solution of the water glass is used in an amount of 0.1-2.5 parts
by mass, in terms of its solid content, with respect to 100 parts
by mass of the refractory aggregate.
[0020] (9) A method of producing the coated sand according to any
one of the above-described modes (1) to (8), characterized in that
the refractory aggregate and the aqueous solution of the water
glass are mixed together such that the water in the aqueous
solution of the water glass is evaporated within 5 minutes after
addition of the aqueous solution of the water glass to the
refractory aggregate, to obtain the coated sand having the moisture
percentage of not more than 0.5% by mass.
[0021] (10) A method of producing a casting mold, characterized in
that the casting mold is obtained by filling a molding cavity of a
forming mold which gives the casting mold, with the coated sand
according to any one of the above-described modes (1) to (8), and
then passing a steam through the coated sand, to solidify or cure
the coated sand within the forming mold.
[0022] (11) The method of producing the casting mold according to
the above-described mode (10), characterized in that a dry air, a
heated dry air, a nitrogen gas or an argon gas is further passed
through a filling phase of the coated sand filling the molding
cavity of the forming mold, simultaneously with passing the steam
through the coated sand.
[0023] (12) The method of producing the casting mold according to
the above-described mode (10) or (11), characterized in that a dry
air, a heated dry air, a nitrogen gas or an argon gas is further
passed through a filling phase of the coated sand filling the
molding cavity of the forming mold, after passing the steam through
the coated sand.
[0024] (13) The method of producing the casting mold according to
any one of the above-described modes (10) to (12), characterized in
that at least one of a carbon dioxide gas, an ester gas and a
carbonate gas is passed through a filling phase of the coated sand
filling the molding cavity of the forming mold, simultaneously with
or after passing the steam through the coated sand.
[0025] (14) The method of producing the casting mold according to
any one of the above-described modes (10) to (13), characterized in
that a pressure within the molding cavity of the forming mold is
reduced before passing the steam through the coated sand.
[0026] (15) The method of producing the casting mold according to
any one of the above-described modes (10) to (14), characterized in
that the coated sand is preheated to a temperature not lower than
30.degree. C., and then the molding cavity of the forming mold is
filled with the preheated coated sand.
[0027] (16) The method of producing the casting mold according to
any one of the above-described modes (10) to (15), characterized in
that the forming mold is preheated and kept at an elevated
temperature.
[0028] (17) A method of producing a casting mold, characterized in
that the casting mold is formed by multilayer molding using the
coated sand according to any one of the above-described modes (1)
to (8).
[0029] In the present invention, the water glass is used as the
binder, and the aqueous solution of the water glass is used to coat
the refractory aggregate. By evaporating the water in the thus
formed coating layer of the binder on the surfaces of the
refractory aggregate, the coated sand is obtained in the dry state,
such that the entirety of the coated sand has the moisture
percentage of not more than 0.5% by mass. Thus, it is possible to
further improve the fluidity of the coated sand, and considerably
improve the ease of filling of the molding cavity of the forming
mold used for producing the casting mold, with the coated sand, to
advantageously produce the sound casting mold having a high degree
of strength.
[0030] The strength of the casting mold obtained by using the
coated sand can be further improved by reducing the amount of the
lumps included in the coated sand, according to the preferable mode
of the present invention. Further, by controlling the nonvolatile
content in the aqueous solution of the water glass so as to be a
low value, the water glass having a high concentration can be
diluted with the water, and the thus obtained aqueous solution of
the water glass can be used to efficiently and uniformly coat the
refractory aggregate with the water glass. Thus, it is possible to
advantageously obtain the coated sand including only a small amount
of the lumps, and more advantageously improve the strength of the
casting mold obtained by using the coated sand.
[0031] The coated sand according to the present invention is
obtained by using the water glass as the binder. Accordingly,
unlike the conventional resin coated sand obtained by using the
organic binders such as the phenolic resin and the furan resin, the
coated sand of the present invention can reduce or prevent
generation of a gas component which has a low molecular weight and
emits an odor, at the time of formation of the casting mold and
casting of the molten metal. Therefore, the coated sand of the
present invention has an advantage that its use does not result in
generation of a gas, tar, odor and the like, and does not give rise
to a problem of deterioration of production environment.
DETAILED DESCRIPTION OF THE INVENTION
[0032] A coated sand according to the present invention is obtained
by mixing an aqueous solution of a water glass used as a binder,
with a heated refractory aggregate, and evaporating water in the
thus obtained mixture, in other words, evaporating the water
contained in the aqueous solution of the water glass, for thereby
forming a dry coating layer consisting of the water glass which
serves as the binder, on surfaces of the refractory aggregate. The
coated sand is in a dry state and has a sufficiently high degree of
fluidity at the room temperature. In the present invention, a
moisture percentage of the coated sand is controlled so as to be
not more than 0.5% by mass, and advantageously not more than 0.3%
by mass. It is recognized that the moisture percentage is
preferably close to zero as far as possible. The coated sand which
is provided with the coating layer of the water glass and which has
the extremely low moisture percentage is used in the dry state in
the absence of water, so that the coated sand flows smoothly and
has excellent properties such as the sufficiently high degree of
fluidity at the room temperature. Accordingly, it is possible to
effectively improve ease of filling of a molding cavity of a
forming mold used for producing a casting mold, with the coated
sand, to advantageously obtain a sound casting mold and effectively
improve a strength of the casting mold.
[0033] The coated sand according to the present invention
preferably includes only a small amount of composite particles
so-called lumps, each of which is formed of a plurality of
particles combined with each other, and which are generated during
a production process of the coated sand. Generally, it is
recommended that where the coated sand obtained by the production
process is sieved with a 20-mesh screen, an amount of the coated
sand which does not pass through the 20-mesh screen, namely, an
amount of the lumps left on the 20-mesh screen is not more than 3%
by mass, and more preferably not more than 1% by mass, with respect
to a whole amount of the coated sand. An excessively large amount
of the lumps deteriorates the ease of filling of the molding cavity
of the forming mold used for producing the casting mold, with the
coated sand, giving rise to problems that the produced casting mold
is likely to have defects, and the strength of the casting mold is
difficult to be improved.
[0034] The refractory aggregate of the coated sand is a refractory
material which serves as a base material of the casting mold. Any
one of various refractory particulate materials conventionally used
for the casting mold may be used as the refractory aggregate.
Specific examples of the refractory aggregate include: a silica
sand; a regenerated silica sand; special sands such as an alumina
sand, an olivine sand, a zircon sand and a chromite sand; slag
particles such as a ferrochromium slag, a ferronickel slag and a
converter slag; artificial particles such as alumina particles and
mullite particles, and regenerated particles thereof; an alumina
ball; and a magnesia clinker. The above-indicated refractory
aggregates may be: a new or fresh sand; a regenerated or reclaimed
sand which has been used once or a plurality of times as a molding
sand to form the casting mold; or a mixture of the regenerated or
reclaimed sand and the new or fresh sand. The refractory aggregate
used in the present invention generally has a grain size of about
AFS 40-80, and preferably not larger than about AFS 60 in order to
make it easy to pass a steam through the coated sand and dry the
coated sand in formation of the casting mold.
[0035] The water glass used as the binder of the coated sand
according to the present invention is a soluble silicate compound,
and preferably an aqueous solution of an alkali metal silicate,
such as sodium silicate, potassium silicate, sodium metasilicate,
potassium metasilicate, lithium silicate, ammonium silicate,
colloidal silica and alkyl silicate. It is possible to use a
mixture of a plurality of kinds of the alkali metal silicates.
Among various kinds of the alkali metal silicates, those having a
molar ratio of silicon dioxide to an alkali metal oxide, which
molar ratio is not smaller than 1.0 and smaller than 3.0, are
preferably used. In the present invention, sodium silicate
(silicate of soda) is advantageously used, since the coated sand
obtained by using sodium silicate is not likely to suffer from
blocking and has a high degree of formability. Commercially
available sodium silicates are generally classified into No. 1 to
No. 5 based on their SiO.sub.2/Na.sub.2O molar ratios. Specifically
described, the sodium silicate No. 1 has the molar ratio
SiO.sub.2/Na.sub.2O within a range between 2.0 and 2.3, the sodium
silicate No. 2 has the molar ratio SiO.sub.2/Na.sub.2O within a
range between 2.4 and 2.5, the sodium silicate No. 3 has the molar
ratio SiO.sub.2/Na.sub.2O within a range between 3.1 and 3.3, the
sodium silicate No. 4 has the molar ratio SiO.sub.2/Na.sub.2O
within a range between 3.3 and 3.5, and the sodium silicate No. 5
has the molar ratio SiO.sub.2/Na.sub.2O within a range between 3.6
and 3.8. Among these, the sodium silicates No. 1 to No. 3 are also
specified in JIS K1408. Any one or a mixture of the above-indicated
sodium silicates may be used in the present invention. It is
possible to control the molar ratio SiO.sub.2/Na.sub.2O by mixing a
plurality of kinds of the above-indicated sodium silicates.
[0036] In the present invention, the sodium silicate used as the
binder preferably has the molar ratio SiO.sub.2/Na.sub.2O not
smaller than 1.0 and smaller than 3.0, and more preferably not
smaller than 2.0 and smaller than 3.0, in order to obtain the
coated sand which can fill the molding cavity with a particularly
high filling density and which can give the casting mold having a
high degree of the strength. Although the sodium silicate having
the molar ratio SiO.sub.2/Na.sub.2O smaller than 2.0 is not
commercially available, such a sodium silicate may be formed and
used in the present invention. The sodium silicates having the
molar ratio SiO.sub.2/Na.sub.2O not smaller than 2.0 and smaller
than 3.0 are preferably used, since they are easily available and
they give the coated sand having high degrees of fluidity and
formability. Among the sodium silicates classified as described
above, the sodium silicates Nos. 1 and 2 are advantageously used.
The sodium silicates Nos. 1 and 2 give the coated sand having
satisfactory filling properties and strength properties, with a
high degree of stability, within a wide range of concentration of
these sodium silicates in the aqueous solution of the water glass.
The coated sand obtained by using, as the binder, the sodium
silicate having the molar ratio SiO.sub.2/Na.sub.2O not smaller
than 2.0 and smaller than 3.0 has the high degrees of fluidity and
formability, but absorbs a larger amount of water than the coated
sands obtained by using the other kinds of the sodium silicates.
Therefore, the coated sand using the sodium silicate having the
molar ratio SiO.sub.2/Na.sub.2O not smaller than 2.0 and smaller
than 3.0 is preferably used for applications where the coated sand
is used right after its production, and suitably used in dry
environments such as in dry regions and cold regions. Further, it
is recommended to store the coated sand in the absence of
water.
[0037] The aqueous solution of the water glass used in the present
invention is obtained by dissolving the water glass in water. A
commercially available aqueous solution of the water glass is used
as an undiluted solution, as purchased, or as a diluted solution
obtained by adding water to the undiluted solution. A solid content
in the aqueous solution, which is obtained by subtracting amounts
of volatile substances such as the water and a solvent contained in
the aqueous solution from an amount of the aqueous solution, is
called a nonvolatile content and corresponds to an amount of the
soluble silicate compound such as the sodium silicate described
above. A higher ratio of the nonvolatile content (solid content) in
the aqueous solution indicates a higher concentration of the water
glass in the aqueous solution. Where the aqueous solution of the
water glass consists solely of the undiluted solution, the
nonvolatile content in the aqueous solution corresponds to an
amount of a portion of the undiluted solution other than the water
contained therein. On the other hand, where the diluted solution
obtained by diluting the undiluted solution with the water is used
as the aqueous solution of the water glass, the nonvolatile content
in the aqueous solution corresponds to an amount of a portion of
the aqueous solution other than the water contained in the
undiluted solution and the water used to dilute the undiluted
solution.
[0038] The nonvolatile content in the aqueous solution of the water
glass is adequately selected depending on the kind of the water
glass, for example, but preferably held within a range of 20-45% by
mass. Where an adequate amount of a water glass component
corresponding to the nonvolatile content is contained in the
aqueous solution, the surfaces of the refractory aggregate can be
evenly and uniformly coated with the water glass component, when
the refractory aggregate and the aqueous solution of the water
glass are mixed (kneaded) together. As a result, the casting mold
having high degrees of flexural strength and hardness or resistance
to scratching of its surface can be advantageously produced. Where
an excessively small amount of the water glass component is
contained in the aqueous solution of the water glass such that a
total amount of the nonvolatile content is less than 20% by mass,
it is necessary to dry the coated sand at a higher temperature for
a longer period of time, so that there arises a problem of energy
loss, for example. On the other hand, where the ratio of the
nonvolatile content in the aqueous solution of the water glass is
excessively high, it is difficult to uniformly coat the surfaces of
the refractory aggregate with the water glass component, and a
larger amount of the lumps are generated, giving rise to problems
in improving properties of the casting mold. Therefore, the aqueous
solution of the water glass is preferably prepared such that the
nonvolatile content in the aqueous solution is not more than 45% by
mass, and accordingly, a water content is not less than 55% by
mass.
[0039] The coating layer of the water glass is formed on the
surfaces of the refractory aggregate by using the aqueous solution
of the water glass preferably in an amount of 0.1-2.5 parts by
mass, and particularly advantageously in an amount of 0.2-2.0 parts
by mass, in terms of the solid content or the nonvolatile content
in the aqueous solution, per 100 parts by mass of the refractory
aggregate. Here, the solid content in the aqueous solution of the
water glass is measured in a manner described below: 10 g of a
sample of the aqueous solution is weighed and put in a sample dish
(a length: 90 mm; a width: 90 mm; a depth of 15 mm) formed of an
aluminum foil; the sample dish is held on a heating plate whose
temperature is held at 180.+-.1.degree. C., for 20 minutes; the
sample dish is reversed upside down and held on the heating plate
for 20 minutes; the sample dish is removed from the heating plate
and cooled within a desiccator; then the sample is weighed. The
solid content is calculated according to the following formula:
Solid content (%)=[Amount (g) of the sample after drying/Amount (g)
of the sample before drying].times.100
Where the aqueous solution of the water glass is used in an
excessively small amount, it is difficult to effectively form the
coating layer of the water glass on the surfaces of the refractory
aggregate, so that it is difficult to sufficiently solidify or cure
the obtained coated sand. On the other hand, where the aqueous
solution of the water glass is used in an excessively large amount,
an extra amount of the aqueous solution adherers to the surfaces of
the refractory aggregate, so that it is difficult to uniformly form
the coating layer, and there arises a risk of an increase of the
amount of the lumps, an adverse influence on physical properties of
the casting mold, and difficulty in removing the molding sand from
a core after casting of a metal.
[0040] In the coated sand according to the present invention, the
coating layer is formed on the surfaces of the refractory aggregate
by using the aqueous solution of the water glass described above.
However, the coating layer may contain suitable additives as
necessary. The coating layer containing the additives is formed by:
a method of initially mixing the suitable additives into the
aqueous solution of the water glass, and then kneading or mixing
the thus obtained mixture with the refractory aggregate; or a
method of adding to the refractory aggregate, the suitable
additives and the aqueous solution of the water glass separately
from each other, and then uniformly kneading or mixing the thus
obtained mixture.
[0041] Solid oxides and salts are advantageously used as the
additives. The solid oxides and salts contained in the coating
layer permit an advantageous improvement of a moisture resistance
of the coated sand. It is effective to use the solid oxides such as
oxides of silicon, zinc, magnesium, aluminum, calcium, lead and
boron. Among these, silicon dioxide, zinc oxide, aluminum oxide and
boron oxide are particularly preferably used. The silicon dioxide
is preferably a precipitated silica or a pyrogenic silica. On the
other hand, examples of the salts include silicofluoride salts,
silicates, phosphates, borates, tetraborates and carbonates. Among
these, zinc carbonate, potassium metaborate, sodium tetraborate and
potassium tetraborate are preferably used. The above-indicated
solid oxides and salts are used in an amount of not more than 100%
by mass, and preferably about 0.5-5% by mass, with respect to the
nonvolatile content in the aqueous solution of the water glass.
[0042] Further, it is effective to use, as other additives,
coupling agents which strengthen a bond between the refractory
aggregate and the water glass (binder). Examples of the coupling
agents include silane coupling agents, zirconate coupling agents
and titanate coupling agents. Also, it is effective to use
lubricants which serve to improve the fluidity of the coated sand.
Examples of the lubricants include: waxes such as paraffin wax,
synthetic polyethylene wax and montanic acid wax; fatty acid amides
such as stearic acid amide, oleic acid amide, and erucic acid
amide; alkylene fatty acid amides such as methylenebis stearic acid
amide and ethylenebis stearic acid amide; stearic acid; stearyl
alcohol; metal stearate; lead stearate; zinc stearate; calcium
stearate; magnesium stearate; monoglyceride stearate; stearyl
stearate; and hydrogenated oils. Further, it is possible to use
mold releasing agents such as paraffins, waxes, light oils, machine
oils, spindle oils, insulating oils, waste oils, plant oils, fatty
acid esters, organic acids, graphite particulates, mica,
vermiculite, fluorine-based mold releasing agents, and
silicone-based mold releasing agents. Each of the above-indicated
additives other than the above-described solid oxides and salts is
generally used in an amount of not more than 5% by mass, and
preferably not more than 3% by mass, with respect to the
nonvolatile content in the aqueous solution of the water glass.
[0043] The coated sand according to the present invention is
produced by a method of uniformly kneading or mixing the aqueous
solution of the water glass used as the binder and the additives
used as necessary, with the heated refractory aggregate, such that
the surfaces of the refractory aggregate are coated with the
aqueous solution of the water glass and the water in the aqueous
solution is evaporated, whereby the coated sand in the form of dry
granules having fluidity at the room temperature is obtained. The
water in the aqueous solution of the water glass (the coating
layer) should be rapidly evaporated before solidification or curing
of the water glass proceeds. Accordingly, in the present invention,
the water in the aqueous solution of the water glass is evaporated
within five minutes, and preferably within three minutes, after the
aqueous solution is added to (mixed with) the refractory aggregate,
to obtain the coated sand in the form of the dry granules. Where
evaporation of the water takes an excessively long time,
productivity of the coated sand is lowered due to an increase of a
time required for the mixing (kneading) operation, and a risk of
deactivation of the aqueous solution of the water glass is
increased since the aqueous solution is exposed to CO.sub.2 in the
air for a longer period of time.
[0044] As effective means for rapidly evaporating the water in the
aqueous solution of the water glass, the above-described method of
producing the coated sand according to the present invention
includes the steps of: preheating the refractory aggregate; and
kneading or mixing the preheated refractory aggregate with the
aqueous solution of the water glass. By kneading or mixing the
aqueous solution of the water glass with the preheated refractory
aggregate, the water in the aqueous solution can be extremely
rapidly evaporated by the heat of the refractory aggregate, whereby
the moisture percentage of the obtained coated sand is effectively
reduced, so that the dry granules having fluidity at the room
temperature are advantageously obtained. A temperature to which the
refractory aggregate is preheated is adequately selected depending
on the water content in the aqueous solution of the water glass and
the amount of use of the aqueous solution, for example. It is
desirable to preheat the refractory aggregate to a temperature of
generally about 100-150.degree. C., and preferably about
100-120.degree. C. Where the preheating temperature of the
refractory aggregate is excessively low, the water cannot be
effectively evaporated, so that a time required for drying the
coated sand is undesirably increased. Therefore, it is desirable to
preheat the refractory aggregate to a temperature not lower than
100.degree. C. On the other hand, where the refractory aggregate is
preheated to an excessively high temperature, curing of the water
glass proceeds while the obtained coated sand is cooled, and the
composite particles are formed, so that the coated sand has
problems in terms of its function, particularly in its strength or
other physical properties.
[0045] In the coated sand obtained by the method described above,
the amount of the lumps in the form of the composite particles is
effectively reduced. Thus, it is possible to advantageously obtain
the coated sand including not more than 3% by mass of the lumps
whose particle diameter is larger than 20-mesh and which would be
left on the 20-mesh screen when the coated sand was sieved with the
screen.
[0046] The coated sand according to the present invention is
produced as described above, such that the moisture percentage of
the coated sand is controlled so as to be not more than 0.5% by
mass, and preferably not more than 0.3% by mass, whereby the coated
sand can more easily fill the molding cavity of the forming mold
used for producing the casting mold, and the casting mold formed by
using the coated sand is given excellent properties.
[0047] By using the thus obtained coated sand according to the
present invention, the casting mold is produced by a method
including the steps of: filling the molding cavity of the forming
mold which gives the intended casting mold, with the coated sand;
blowing a steam into the molding cavity such that the steam is
passed through a filling phase of the coated sand; and holding the
coated sand within the forming mold until the coated sand is dried
and solidified or cured.
[0048] The forming mold such as a metallic forming mold or a wooden
forming mold to be filled with the dry coated sand is preferably
preheated and kept at an elevated temperature, to advantageously
dry the coated sand moistened with the steam. The forming mold is
generally preheated to and kept at a temperature of about
60-140.degree. C., preferably about 80-130.degree. C., and
particularly preferably about 100-120.degree. C. Where the forming
mold is kept at an excessively high temperature, the steam does not
sufficiently reach a surface of the filling phase of the coated
sand filling the forming mold. On the other hand, where the forming
mold is kept at an excessively low temperature, an undesirably long
time is required for drying the formed casting mold. After the
steam has been passed through the filling phase of the coated sand,
the coated sand is preferably held within the forming mold for a
predetermined period of time, before the obtained casting mold is
removed from the forming mold. The coated sand is preferably held
within the forming mold for 30-300 seconds, and more preferably for
30-180 seconds, after passing of the steam through the coated sand,
such that the coated sand is dried while being held within the
forming mold. The coated sand moistened with the steam has a high
degree of thermal conductivity, so that by holding the coated sand
within the preheated forming mold, the coated sand can be uniformly
heated and solidified or cured. Additionally, the dry coated sand
used to fill the forming mold is preferably preheated. Generally,
where the forming mold is filled with the coated sand heated to a
temperature not lower than 30.degree. C., a flexural strength of
the obtained casting mold can be advantageously improved. The
coated sand is preferably heated to a temperature of about
30-100.degree. C., and advantageously about 40-80.degree. C.
[0049] After the preheated forming mold, specifically, its molding
cavity has been filled with the dry coated sand, a pressurized
steam is blown into the molding cavity through inlets provided in
the forming mold, such that the steam is passed through the filling
phase of the coated sand formed within the molding cavity, to
moisten the filling phase and bond together particles of the coated
sand, whereby a mass of the coated sand (a mass of the bonded
particles of the coated sand) in the form of an integral casting
mold is obtained. In the case where no additives are used, the
water glass is generally solidified by evaporation of the water to
dryness. On the other hand, where the oxides and the salts are used
as a curing agent, the water glass is cured. In practical
applications of the present invention, the curing agent is added,
so that the filling phase of the coated sand is cured. However, the
filling phase of the coated sand may be merely solidified. The
steam may be a saturated steam or a superheated steam. The
superheated steam is used in the state of a wet steam containing
water drops. In the present invention, the superheated steam in the
state of a dry steam which does not contain the water drops is not
used to moisten the coated sand, but may be used to dry the coated
sand.
[0050] A temperature of the steam blown into the molding cavity
through the inlets in the forming mold and passed through the
filling phase of the coated sand is generally held within a range
of about 80-150.degree. C., and preferably about 95-120.degree. C.
Particularly, the steam having a temperature around 100.degree. C.
is advantageously used, since the steam having an excessively high
temperature requires a large amount of energy for its production.
In the present invention, the steam is passed through the filling
phase of the coated sand at a gauge pressure of about 0.01-0.3 MPa,
and preferably about 0.01-0.1 MPa. In the case where the coated
sand allows the steam to easily pass therethrough, the gauge
pressure within the above-described ranges makes it possible to
pass the steam through the entirety of the casting mold formed
within the forming mold, and to reduce times required for passing
of the steam and drying of the casting mold, and accordingly reduce
a time required for formation of the casting mold. Further, the
gauge pressure within the above-described ranges permits formation
of the casting mold even in the case where the coated sand does not
allow the steam to easily pass therethrough. An excessively high
gauge pressure causes occurrence of staining around the inlets,
while an excessively low gauge pressure gives rise to a risk that
the steam cannot be passed through the entirety of the filling
phase of the coated sand, so that the coated sand cannot be
sufficiently moistened.
[0051] The steam is blown into the molding cavity through the
inlets provided in the forming mold, and passed through the coated
sand (filling phase) filling the molding cavity, as described
above. A period for blowing the steam is adequately selected
depending on the size of the forming mold and the number of the
inlets, for example, so as to sufficiently moisten the water glass
which covers the surfaces of the coated sand and serves as the
binder, by blowing the steam to the surfaces of the coated sand,
and accordingly to bond (bind) together the particles of the coated
sand. The steam is generally blown into the molding cavity for a
period of about 2-60 seconds. Where the period for blowing the
steam is excessively short, it is difficult to sufficiently moisten
the surfaces of the coated sand. On the other hand, where the
period for blowing the steam is excessively long, there arises a
risk of dissolution and discharge flow of the binder covering the
surfaces of the coated sand. Passage of the steam through the
coated sand filling the forming mold may be further improved by
blowing the steam into the forming mold while sucking out an
atmosphere within the forming mold through an exhaust vent provided
in the forming mold. In the present invention, the method of
moistening the coated sand is not particularly limited, but the
above-described method of passing the steam through the coated sand
is advantageously employed, from standpoints of the time required
for forming the casting mold and simplicity of the process for
forming the casting mold.
[0052] In the present invention, the steam may be blown into the
molding cavity while a dry air, a heated dry air, a nitrogen gas or
an argon gas is simultaneously blown into the molding cavity and
passed through the filling phase of the coated sand, in order to
actively dry the filling phase of the coated sand moistened with
the steam. By blowing the steam into the molding cavity with the
simultaneous blowing of the dry air or the like, the steam is
easily blown throughout the molding cavity owing to the dry air or
the like, so that uneven curing of the obtained casting mold can be
avoided.
[0053] Further, in the present invention, the dry air, the heated
dry air, the nitrogen gas or the argon gas is preferably blown into
the molding cavity and passed through the filling phase of the
casting mold, after the blowing of the steam into the molding
cavity, in order to actively dry the filling phase of the coated
sand moistened with the steam. By blowing the dry air, the heated
dry air, the nitrogen gas or the argon gas into the molding cavity
as described above, the filling phase of the coated sand is rapidly
dried even in its central part, whereby curing or solidification of
the filling phase is more advantageously accelerated to
advantageously increase a curing rate of the filling phase.
Further, the flexural strength or other properties of the obtained
casting mold can be advantageously improved, and the time required
for formation of the casting mold can be advantageously reduced.
Blowing of the dry air or the like into the molding cavity is
desirably carried out simultaneously with the blowing of the steam,
and continued after termination of the blowing of the steam.
[0054] In the present invention, at least one of a carbon dioxide
gas (a CO.sub.2 gas), an ester gas, and a carbonate gas may be
blown into the molding cavity, between a moment of initiation of
the blowing of the steam and a moment of termination of the blowing
of the dry air or the like. Solidification of the binder can be
further accelerated by neutralizing the binder with the carbon
dioxide gas, the ester gas, or the carbonate gas. Blowing of the
carbon dioxide gas, the ester gas, or the carbonate gas may be
carried out simultaneously with the blowing of the steam, or after
termination of the blowing of the steam. Also, the blowing of the
carbon dioxide gas, the ester gas, or the carbonate gas may be
carried out simultaneously with the blowing of the dry air or the
like, or with a time lag with respect to the blowing of the dry air
or the like.
[0055] Further, before the steam is blown into the molding cavity,
a pressure within the molding cavity may be reduced to a pressure
preferably lower than the atmospheric pressure. For this purpose, a
production machine of the casting mold may be provided with an
apparatus for sucking the air from the molding cavity. By reducing
the pressure within the molding cavity before the blowing of the
steam, the steam can be more rapidly dispersed within the molding
cavity, owing to the reduced pressure within the molding
cavity.
[0056] The casting mold formed as described above may be heated
with a micro wave to selectively evaporate the water only. If the
water exists within the casting mold, the binder may be redissolved
in the water, giving rise to a risk of deterioration of the
flexural strength of the casting mold. Further, the water within
the casting mold may be decomposed by the heat at the time of
pouring of a molten metal, with a result of generation of a
hydrogen gas, giving rise to an inherent problem of occurrence of a
gas defect in the obtained cast product. Therefore, heating the
formed casting mold with the micro wave to remove the water within
the casting mold is an effective means for storage of the casting
mold and an improvement of the quality of the cast product.
[0057] As the method of forming the casting mold by using the
coated sand according to the present invention, it is possible to
employ various known methods other than the above-described method
of filling the forming mold with the coated sand. For example, it
is possible to employ a multilayer molding method, specifically, a
method of directly forming a three-dimensional casting mold by
stacking layers of the coated sand, and curing a part of a stack of
the layers of the coated sand, which part corresponds to the
intended casting mold, as disclosed in JP-T-7-507508 and
JP-A-9-141386, for example.
EXAMPLES
[0058] To clarify the present invention more specifically, some
examples of the present invention will be described. However, it is
to be understood that the present invention is by no means limited
by the details of the illustrated examples. In the examples and
comparative examples described below, "part" and "%" respectively
indicate "part by mass" and "% by mass", unless otherwise
specified. Coated sands (CS) obtained in the examples and
comparative examples were measured of their moisture percentage,
amount of lumps, filling percentage and state of the sand, and
casting molds obtained by using the respective coated sands were
measured of their flexural strength and scratch hardness, while
adhesion of sands to a surface of a kneading pot was observed, as
described below.
[0059] --Measurement of the Moisture Percentage (%)--
[0060] 2.0 g of each of the obtained coated sands (CS) was thrown
into a flask of Karl Fischer Moisture Titrator (AQV-7 HIRANUMA
AQUACOUNTER; available from Hiranuma Sanygo Co., Ltd., JAPAN)
containing 100 ml of a dehydration solvent: AQUAMICRON ML
(available from Mitsubishi Chemical Corporation, JAPAN) [Karl
Fischer reagent (HYDRANAL Composite 5; available from Sigma-Aldrich
Laborchemikalien Gmbh) was dropped into the flask in advance, to
reduce the moisture amount to zero]. After stirring the mixture in
the flask for several minutes with a magnetic stirrer, the HYDRANAL
Composite 5 was dropped into the flask to determine a moisture
amount and to calculate the moisture percentage from the determined
value of the moisture amount.
[0061] --Measurement of the Amount (%) of the Lumps--
[0062] The CS obtained in each example was sieved with a 20-mesh
screen to obtain composite particles (lumps) whose diameter is not
smaller than 20-mesh and which were left on the screen. The amount
of the lumps was obtained as a percentage value of the mass of the
lumps with respect to the mass of the kneaded sand.
Amount (%) of the lumps=Mass of the lumps/[(Mass of the
lumps)+(Mass of the sand not larger than 20-mesh)].times.100
[0063] --Measurement of the Flexural Strength (kgf/cm.sup.2)--
[0064] By using each CS, a test piece having a width of 25.4 mm, a
thickness of 25.4 mm and a length of 200 mm was formed, and
measured of its breaking load by using a measuring device (a
digital molding sand strength tester available from TAKACHIHO SEIKI
CO., LTD., JAPAN). The flexural strength was calculated from the
measured breaking load according to the following formula.
Flexural strength=1.5.times.LW/ab.sup.2
[L: length (cm) of a support span, W: breaking load (kgf), a: width
(cm) of the test piece, b: thickness (cm) of the test piece]
[0065] --Measurement of the Scratch Hardness (mm)--
[0066] The test piece formed by using each CS and having the width
of 25.4 mm, the thickness of 25.4 mm and the length of 200 mm was
measured of its scratch hardness by using a scratch hardness tester
(GF type). Initially, a tooth provided at a distal end of the
scratch hardness tester was pressed against a surface of the test
piece. Then, a black lever provided in an upper portion of the
tester was revolved one turn in the clockwise direction, and then
revolved one turn in the counterclockwise direction. This set of
operations of revolving the lever was repeated five more times, so
that the tooth was gradually embedded into the test piece. A depth
(mm) by which the tooth was embedded into the test piece was read
on a scale provided on a side surface of the tester. A smaller
depth indicates a higher degree of the scratch hardness of the test
piece, while a larger depth indicates a lower degree of the scratch
hardness.
[0067] --Measurement of the Filling Percentage (%)--
[0068] The filling percentage was calculated as a percentage value
of a specific gravity (calculated by dividing a mass of the test
piece by its volume) of the above-described test piece with respect
to an absolute specific gravity of an aggregate.
Filling percentage (%)=[Mass (g) of the test piece/Volume
(cm.sup.3) of the test piece]/Absolute specific gravity
(g/cm.sup.3) of the aggregate.times.100
[0069] --Observation of Adhesion of the Sand to the Surface of the
Kneading Pot--
[0070] After a kneading operation, conditions of adhesion of the
sand to the surface of the kneading pot were examined by visually
observing and rubbing the surface of the kneading pot. The
conditions of adhesion were evaluated as "Good" where the sand does
not adhere to the surface of the kneading pot, "Average" where the
sand adheres to the surface of the kneading pot, but can be easily
removed by rubbing, and "Poor" where the sand adheres to the
surface of the kneading pot, and cannot be easily removed by
rubbing.
Production Example 1 (Example 1) of the CS
[0071] A commercially available artificial molding sand LUNAMOS #50
(Trade Name; available from Kao Corporation, JAPAN) was provided as
a refractory aggregate. An aqueous solution of a water glass was
prepared by diluting commercially available sodium silicate No. 1
(Trade Name; available from Fuji Kagaku Corp., JAPAN) used as a
binder, with water, such that the aqueous solution of the water
glass has a nonvolatile content (an amount of a portion of the
aqueous solution except the water contained therein) of 46.1%.
[0072] A Shinagawa-shiki universal stirrer (5DM-r type;
manufactured by DALTON CO., LTD., JAPAN) was charged with the
LUNAMOS #50 heated to a temperature of about 120.degree. C., and
the above-described aqueous solution of the water glass was
introduced into the stirrer in an amount of 0.5 part, in terms of
its nonvolatile content, with respect to 100 parts of the LUNAMOS
#50. The contents in the stirrer were kneaded for three minutes to
evaporate the water. After the contents were stirred and mixed
until an aggregate structure of the sand particles collapsed, the
contents were taken out of the stirrer, whereby a dry coated sand
(CS) No. 1 having free flowing characteristics at the room
temperature was obtained. The amount of the lumps included in the
thus obtained CS and the moisture amount in the CS were measured.
Further, the conditions of adhesion of the sand to the surface of
the kneading pot were observed. Results of the measurements and
observation are shown in a table given below.
Production Examples 2 to 9 (Examples 2 to 9) of the CS
[0073] CS Nos. 2 to 9 were obtained by the same procedure as in the
Production Example 1, except that aqueous solutions of the water
glass were prepared by diluting the commercially available sodium
silicate No. 1 (Trade Name; available from Fuji Kagaku Corp.) used
as the binder, with the water, such that the aqueous solutions have
the respective different nonvolatile contents of 44.0%, 41.6%,
39.7%, 37.5%, 33.5%, 30.0%, 25.0% and 20.0%.
Production Examples 10 to 15 (Examples 10 to 15) of the CS
[0074] CS Nos. 10 to 15 were obtained by the same procedure as in
the Production Example 1, except that aqueous solutions of the
water glass were prepared by diluting commercially available sodium
silicate No. 2 (Trade Name; available from Fuji Kagaku Corp.) used
as the binder, with the water, such that the aqueous solutions have
the respective different nonvolatile contents of 46.3%, 44.1%,
41.3%, 38.3%, 26.9% and 20.0%.
Production Examples 16 to 18 (Examples 16 to 18) of the CS
[0075] CS Nos. 16 to 18 were obtained by the same procedure as in
the Production Example 1, except that aqueous solutions of the
water glass were prepared by diluting commercially available sodium
silicate No. 3 (Trade Name; available from Fuji Kagaku Corp.) used
as the binder, with the water, such that the aqueous solutions have
the respective different nonvolatile contents of 37.5%, 25.6% and
12.8%.
Production Examples 19 to 21 (Examples 19 to 21) of the CS
[0076] CS Nos. 19 to 21 were obtained by the same procedure as in
the Production Example 1, except that aqueous solutions of the
water glass were prepared by diluting commercially available sodium
silicate No. 5 (Trade Name; available from Fuji Kagaku Corp.) used
as the binder, with the water, such that the aqueous solutions have
the respective different nonvolatile contents of 33.2%, 27.3% and
20.0%.
Production Example 22 (Example 22) of the CS
[0077] CS No. 22 was obtained by the same procedure as in the
Production Example 1, except that a commercially available
alumina-based spherical aggregate ESPEARL #60 (Trade Name;
available from Yamakawa Sangyo Co., Ltd., JAPAN) was used as the
refractory aggregate, and that the nonvolatile content in the
aqueous solution of the water glass was 33.5%.
Production Example 23 (Example 23) of the CS
[0078] CS No. 23 was obtained by the same procedure as in the
Production Example 1, except that MIKAWA KEISA No. 7 (Trade Name;
available from Mikawa Keisa K.K., JAPAN) was used as the refractory
aggregate, and that the water glass was used in an amount of 1.0
part, in terms of its nonvolatile content, with respect to 100
parts of the MIKAWA KEISA No. 7, while the nonvolatile content in
the aqueous solution of the water glass was 33.5%.
Production Example 24 (Comparative Example 1) of the CS
[0079] CS No. 24 was obtained by the same procedure as in the
Production Example 1, except that an aqueous solution of the water
glass was prepared by diluting the commercially available sodium
silicate No. 1 (Trade Name; available from Fuji Kagaku Corp.) used
as the binder, with the water, such that the aqueous solution has
the nonvolatile content (the amount of the portion of the aqueous
solution except the water contained therein) of 15.0%.
Production Example 25 (Comparative Example 2) of the CS
[0080] CS No. 25 was obtained by the same procedure as in the
Production Example 1, except that an aqueous solution of the water
glass was prepared by diluting the commercially available sodium
silicate No. 2 (Trade Name; available from Fuji Kagaku Corp.) used
as the binder, with the water, such that the aqueous solution has
the nonvolatile content (the amount of the portion of the aqueous
solution except the water contained therein) of 13.3%.
Production Example 26 (Comparative Example 3) of the CS
[0081] CS No. 26 was obtained by the same procedure as in the
Production Example 1, except that an aqueous solution of the water
glass was prepared by diluting the commercially available sodium
silicate No. 3 (Trade Name; available from Fuji Kagaku Corp.) used
as the binder, with the water, such that the aqueous solution has
the nonvolatile content (the amount of the portion of the aqueous
solution except the water contained therein) of 9.6%.
Production Example 27 (Comparative Example 4) of the CS
[0082] CS No. 27 was obtained by the same procedure as in the
Production Example 1, except that the commercially available sodium
silicate No. 5 (Trade Name; available from Fuji Kagaku Corp.) used
as the binder was diluted with the water, such that the thus
prepared aqueous solution has the nonvolatile content (the amount
of the portion of the aqueous solution except the water contained
therein) of 15.0%.
[0083] --Production Example of the Casting Mold--
[0084] Each of the CS Nos. 1 to 27 obtained in the above-described
Production Examples and having a temperature of 20.degree. C. was
blown into a forming mold heated to 110.degree. C., at a gauge
pressure of 0.3 MPa, such that the forming mold was filled with the
CS. Then, a steam having a temperature of 99.degree. C. was blown
into the forming mold, at a gauge pressure of 0.05 MPa for five
seconds, such that the steam was passed through a filling phase of
the coated sand filling the forming mold. After blowing of the
steam was terminated, a hot air having a temperature of 150.degree.
C. was blown into the forming mold, at a gauge pressure of 0.03 MPa
for two minutes, to cure the CS filling the forming mold. The thus
produced casting mold was used as a test piece (25.4 mm.times.25.4
mm.times.200 mm).
[0085] --Measurement of the Casting Mold--
[0086] The thus obtained test pieces produced by using the
respective CS Nos. 1 to 27 were measured of their filling
percentage, flexural strength and scratch hardness, according to
the methods described above. Results of the measurements are shown
in Tables 1 to 3 given below.
TABLE-US-00001 TABLE 1 Example Example Example Example Example
Example Example Example Example 1 2 3 4 5 6 7 8 9 Refractory
LUNAMOS #50 100 100 100 100 100 100 100 100 100 Aggregate Aqueous
Sodium Silicate 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Solution of No.
1 Water Glass Nonvolatile Content (%) of Water Glass 46.1 44.0 41.6
39.7 37.5 33.5 30.0 25.0 20.0 Conditions of Adhesion of Sand to
Good Good Good Good Good Good Good Good Average Kneading Pot
Properties Moisture Percentage (%) <0.1 <0.1 <0.1 <0.1
<0.1 <0.1 <0.1 <0.1 0.2 of Sand Amount (%) of Lumps
1.37 0.40 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1
Filling Percentage (%) 52.4 53.5 56.1 57.0 56.5 56.2 56.1 56.7 57.2
State of Sand Dry Dry Dry Dry Dry Dry Dry Dry Dry Properties of
Flexural Strength (kgf/cm.sup.2) 27.0 35.7 58.4 56.7 63.3 62.7 57.5
56.8 57.8 Casing Mold Scratch Hardness (mm) 6.5 6.0 5.6 4.5 3.7 3.3
3.3 3.3 3.0
TABLE-US-00002 TABLE 2 Example Example Example Example Example
Example Example Example Example 10 11 12 13 14 15 16 17 18
Refractory LUNAMOS #50 100 100 100 100 100 100 100 100 100
Aggregate Aqueous Sodium Silicate 0.5 0.5 0.5 0.5 0.5 0.5 -- -- --
Solution of No. 2 Water Glass Sodium Silicate -- -- -- -- -- -- 0.5
0.5 0.5 No.3 Nonvolatile Content (%) of Water Glass 46.3 44.1 41.3
38.3 26.9 20.0 37.5 25.6 12.8 Conditions of Adhesion of Sand to
Good Good Good Good Good Average Good Good Average Kneading Pot
Properties Moisture Percentage (%) <0.1 <0.1 <0.1 <0.1
<0.1 0.2 <0.1 <0.1 0.33 of Sand Amount (%) of Lumps 3.62
1.50 1.02 0.13 0.24 <0.1 3.50 0.30 0.14 Filling Percentage (%)
52.9 53.5 54.7 54.5 56.7 57.3 48.7 56.8 57.6 State of Sand Dry Dry
Dry Dry Dry Dry Dry Dry Dry Properties of Flexural Strength
(kgf/cm.sup.2) 15.1 21.6 38.4 40.2 59.3 50.3 15.7 54.5 53.1 Casting
Mold Scratch Hardness (mm) 6.2 6.0 5.8 4.9 3.5 3.1 5.1 1.7 0.9
TABLE-US-00003 TABLE 3 Comparative Comparative Comparative
Comparative Example Example Example Example Example Example Example
Example Example 19 20 21 22 23 1 2 3 4 Refractory LUNAMOS #50 100
100 100 -- -- 100 100 100 100 Aggregate ESPEARL #60 -- -- -- 100 --
-- -- -- -- MIKAWA KEISA No. 7 -- -- -- -- 100 -- -- -- -- Aqueous
Sodium Silicate No. 1 -- -- -- 0.5 1.0 0.5 -- -- -- Solution of
Sodium Silicate No. 2 -- -- -- -- -- -- 0.5 -- -- Water Glass
Sodium Silicate No. 3 -- -- -- -- -- -- -- 0.5 -- Sodium Silicate
No. 5 0.5 0.5 0.5 -- -- -- -- -- 0.5 Nonvolatile Content (%) of
Water Glass 33.2 27.3 20.0 33.5 33.5 15.0 13.3 9.6 15.0 Conditions
of Adhesion of Sand to Good Good Average Good Good Poor Poor Poor
Poor Kneading Pot Properties Moisture Percentage (%) <0.1
<0.1 0.35 <0.1 <0.1 0.85 0.74 1.39 1.31 of Sand Amount (%)
of Lumps 1.9 0.1 0.21 <0.1 <0.1 Could not be Could not be
Could not be Could not be measured measured measured measured
Filling Percentage (%) 54.4 55.5 56.7 54.2 48.1 Could not be Could
not be Could not be Could not be measured measured measured
measured State of Sand Dry Dry Dry Dry Dry Wet Wet Wet Wet
Properties of Flexural Strength (kgf/cm.sup.2) 15.2 19.5 16.2 68.9
15.8 Could not be Could not be Could not be Could not be Casting
Mold measured measured measured measured Scratch Hardness (mm)
>7.0 5.9 4.5 2.4 5.7 Could not be Could not be Could not be
Could not be measured measured measured measured
[0087] As is apparent from the results shown in Tables 1 to 3, it
is recognized that the CS Nos. 24 to 27 which were obtained in the
Comparative Examples 1 to 4 in the wet state and whose moisture
percentages are not less than 0.5% could not satisfactorily fill
the forming mold, whereas the CS Nos. 1 to 23 obtained in the
Examples 1 to 23 and having the moisture percentages of not more
than 0.5% have sufficiently high degrees of fluidity. Also, it is
recognized that the use of the sodium silicate Nos. 1 and 2 having
SiO.sub.2/Na.sub.2O molar ratios not smaller than 2.0 and smaller
than 3.0 results in high degrees of the filling percentage and the
flexural strength, within a wide range of the nonvolatile content
in the aqueous solution of the water glass. Accordingly, by using
the sodium silicate Nos. 1 and 2, the coated sand can be produced
with a high degree of freedom of choice of its composition, and the
obtained coated sand has a high degree of formability. On the other
hand, where the sodium silicate Nos. 3 to 5 having the
SiO.sub.2/Na.sub.2O molar ratios within a range between 3.0 and 4.0
are used, as in the Examples 16 to 21, sufficiently high degrees of
the physical properties and formability are achieved only within a
narrow range of the nonvolatile content in the aqueous solution of
the water glass. Accordingly, it is understood that the use of the
sodium silicate Nos. 3 to 5 results in reduction of the freedom of
choice of the composition of the coated sand. Further, it is
recognized that particularly higher degrees of the filling
percentage, flexural strength and scratch hardness can be achieved
in the case where the coated sands were produced by using the
aqueous solutions of the water glass prepared by using the sodium
silicate Nos. 1 and 2 such that the aqueous solutions have 20-45%
by mass of the nonvolatile content. In this respect, it is noted
that undiluted solutions of the sodium silicate Nos. 3 to 5 have
not less than about 30% and less than about 40% of the nonvolatile
content, so that no experiment was conducted on aqueous solutions
of the sodium silicate Nos. 3 to 5 having the nonvolatile content
more than the above-indicated range.
* * * * *