U.S. patent application number 10/783740 was filed with the patent office on 2004-12-02 for water-soluble casting mold and method for manufacturing the same.
This patent application is currently assigned to Mazda Motor Corporation. Invention is credited to Hori, Yuji, Kambayashi, Hitoshi, Kurokawa, Yutaka, Miura, Naohiro.
Application Number | 20040238157 10/783740 |
Document ID | / |
Family ID | 32732979 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040238157 |
Kind Code |
A1 |
Hori, Yuji ; et al. |
December 2, 2004 |
Water-soluble casting mold and method for manufacturing the
same
Abstract
In a water-soluble casting mold according to the present
invention, after casting sand is obtained by adding a water-soluble
binder containing an inorganic sulfate compound such as magnesium
sulfate or the like easily solved in water and water to a
refractory granular material for casting sand, the casting sand is
dried by microwave radiation or the like in such a manner that the
inorganic sulfate compound in the binder is kept retaining at least
a portion of crystal water and accordingly, since the inorganic
sulfate compound exists in hydrate state in the mold, the mold
after drying is provided with good water-solubility and a
sufficiently high strength as well, thereby it is possible to
recover easily and use repeatedly the binder.
Inventors: |
Hori, Yuji; (Hiroshima,
JP) ; Miura, Naohiro; (Hiroshima, JP) ;
Kurokawa, Yutaka; (Hiroshima, JP) ; Kambayashi,
Hitoshi; (Hiroshima, JP) |
Correspondence
Address: |
BROOKS KUSHMAN P.C.
1000 TOWN CENTER
TWENTY-SECOND FLOOR
SOUTHFIELD
MI
48075
US
|
Assignee: |
Mazda Motor Corporation
Aki-gun
JP
Tsuchiyoshi Industry Co., Ltd.
Hiroshima-shi
JP
|
Family ID: |
32732979 |
Appl. No.: |
10/783740 |
Filed: |
February 20, 2004 |
Current U.S.
Class: |
164/528 ;
164/522 |
Current CPC
Class: |
B22C 9/10 20130101; B22C
15/24 20130101; B22C 9/12 20130101 |
Class at
Publication: |
164/528 ;
164/522 |
International
Class: |
B22C 001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2003 |
JP |
2003-043692 |
Claims
What is claimed is:
1. A water-soluble casting mold comprising a refractory granular
material for casting sand and a water-soluble binder containing at
least one inorganic sulfate compound selected from magnesium
sulfate, aluminum sulfate, sodium sulfate, nickel sulfate,
manganese sulfate, wherein the inorganic sulfate compound has
crystal water in dry state.
2. A water-soluble casting mold comprising 100 parts by weight of a
refractory granular material for casting sand and a binder
containing 0.5 to 10.0 parts by weight of magnesium sulfate
heptahydrate, wherein the magnesium sulfate has crystal water in
dry state.
3. The water-soluble casting mold according to claim 2, wherein the
magnesium sulfate has crystal water equivalent to mono- to
penta-hydrate in dry state.
4. The water-soluble casting mold according to claim 1, wherein the
binder contains the inorganic sulfate compound and not more than
75% by weight of at least one of sodium dihydrogen phosphate and
potassium dihydrogen phosphate.
5. The water-soluble casting mold according to claim 1, wherein the
binder contains the inorganic sulfate compound and not more than
50% by weight of at least one of tricalcium phosphate, aluminum
phosphate, trisodium phosphate, sodium diphosphate, and disodium
hydrogen phosphate dodecahydrate.
6. The water-soluble casting mold according to claim 1, wherein the
binder is a mixture of the inorganic sulfate compound and not more
than 75% by weight of magnesium chloride.
7. A method for manufacturing a water-soluble casting mold
including a first step of obtaining casing sand by mixing a
refractory granular material for casting sand with a water-soluble
binder containing at least one inorganic sulfate compound selected
from magnesium sulfate, aluminum sulfate, sodium sulfate, nickel
sulfate, and manganese sulfate and water; a second step of forming
the resulting casting sand; and a third step of obtaining a mold by
drying the casting sand in such a manner that the inorganic sulfate
compound in the casting sand is kept retaining at least a portion
of the crystal water.
8. A method for manufacturing a water-soluble casting mold
including a first step of obtaining casing sand by mixing 100 parts
by weight of a refractory granular material for casting sand with a
binder containing 0.5 to 10.0 parts by weight on the basis of
magnesium sulfate heptahydrate and water in an amount sufficient to
completely dissolve the magnesium sulfate in the binder; a second
step of forming the resulting casting sand; and a third step of
obtaining a mold by drying the casting sand in such a manner that
the magnesium sulfate in the casting sand is kept retaining at
least a portion of the crystal water.
9. The method for manufacturing a water-soluble casting mold
according to claim 7, wherein the binder contains the inorganic
sulfate compound and not more than 75% by weight of at least one of
sodium dihydrogen phosphate and potassium dihydrogen phosphate.
10. The method for manufacturing a water-soluble casting mold
according to claim 7, the binder contains the inorganic sulfate
compound and not more than 50% by weight of at least one of
tricalcium phosphate, aluminum phosphate, trisodium phosphate,
sodium diphosphate, and disodium hydrogen phosphate
dodecahydrate.
11. The method for manufacturing a water-soluble casting mold
according to claim 7, wherein the binder is a mixture of the
inorganic sulfate compound and not more than 75% by weight of
magnesium chloride.
12. The method for manufacturing a water-soluble casting mold
according to claim 7, wherein the third step is carried out by
drying the casting sand with microwave or hot air heating.
13. The method for manufacturing a water-soluble casting mold
according to claim 7, wherein forming in the second step is carried
out by filling a cavity of a ventilative ceramic mold with the
casting sand.
14. The method for manufacturing a water-soluble casting mold
according to claim 8, wherein the third step is carried out by
drying the casting sand with microwave or hot air heating.
15. The method for manufacturing a water-soluble casting mold
according to claim 8, wherein forming in the second step is carried
out by filling a cavity of a ventilative ceramic mold with the
casting sand.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a water-soluble casting mold and a
method for manufacturing the mold, more particularly to a technique
wherein a binder is water-soluble and repeatedly usable but the
strength of a mold can be sufficiently maintained
[0003] 2. Description of the Related Art
[0004] In the case of manufacturing a casting mold, techniques for
coating refractory granular materials for casting sand such as
siliceous sand with binders have widely been employed. The binders
to be used in such cases can broadly be divided into organic
binders and inorganic binders. Organic binders, in general, start
decomposing at about 400.degree. C., so that it is impossible to
repeatedly recover the binders and use them. Therefore, in the case
that it is required to recover binders and use them repeatedly,
inorganic binders have often been used in many cases. Among the
inorganic binders, specifically, if sulfate compounds such as
magnesium sulfate that are easy to be dissolved in water are used,
a mold can easily be collapsed only by immersing the mold in water
after pouring a molten metal into the mold, and the binders can be
easily recovered.
[0005] In casting process of an aluminum alloy cast such as a
cylinder head or the like of an engine for automobiles, the molten
metal pouring temperature reaches about 770.degree. C. Accordingly,
when the melting point of an inorganic sulfate compound in a binder
to be used for a mold for an aluminum alloy cast is lower than
770.degree. C., the inorganic sulfate compound is melted and
vitrified and it becomes impossible to recover the binder after
pouring the molten metal. Accordingly, an inorganic sulfate
compound having a melting point of 770.degree. C. or higher should
be used. Here, as such inorganic compound, magnesium sulfate or the
like can be exemplified and conventionally, a variety of techniques
for using the magnesium sulfate for casting molds have already been
proposed.
[0006] For example, Japanese Patent Publication No. 46-4818 (Prior
art 1) discloses, in pages 1 and 2 thereof, for example, a
technique of forming magnesium sulfate itself as aggregate and
using it as a water-soluble core for a high pressure die-casting.
Also, Japanese Patent Laid-Open Publication No. 53-119724 (Prior
art 2) discloses, in pages 1 and 2 thereof, for example, a
technique of using magnesium sulfate as a binder for a refractory
granular material for casting sand and mixing the refractory
granular material with magnesium sulfate and water, thereafter
forcibly drying the obtained mixture at a temperature of 200 to
300.degree. C., thereby obtaining a mold. Further, Japanese Patent
Laid-Open Publication No. 11-285777 (Prior art 3) discloses, in
pages 3, 4 and FIG. 3 thereof, for example, a technique of
obtaining a mold by using calcium sulfate and magnesium sulfate as
binders and mixing a refractory granular material such as siliceous
sand with the binders and drying the mixture at 350.degree. C. for
4 hours.
[0007] However, with respect to the mold described in the
above-mentioned Prior art 1, since the magnesium sulfate itself is
formed and used as aggregate for molding and the obtained mold is
not provided with a sufficient ventilation property, a gas evolved
from a metal to be cast at the time of pouring the molten metal
cannot be discharged sufficiently. Therefore, obtained cast tends
to have defects. With respect to the mold described in the
above-mentioned Prior art 2, after the refractory granular material
is mixed with magnesium sulfate and water, the mixture is dried
forcibly at a temperature of 200 to 300.degree. C., and since
magnesium sulfate hydrate is dehydrated at a temperature of
200.degree. C. or higher, the magnesium sulfate in the obtained
mold is supposed to be an anhydride. However, magnesium sulfate in
the anhydride state has a rather decreased strength as compared
with that in hydrate state containing crystal water. Therefore, in
order to retain a sufficient strength of the mold, the addition
amount of magnesium sulfate has to be increased and that is
significantly disadvantageous in terms of moldability of the mold,
easiness of drying, or recovery of the binder and results in
decrease of working efficiency.
[0008] Further, with respect to the mold described in Prior art 3,
drying is carried out in a temperature condition as high as
350.degree. C. and the bending strength of a test piece is found as
extremely low as 0.04 kg/mm.sup.2 in the case where magnesium
sulfate is used alone as a binder for the pest piece. Therefore,
similarly to that of the foregoing Prior art 2, magnesium sulfate
in the mold is supposed to be an anhydride. Accordingly, the
addition amount of magnesium sulfate has to be considerably
increased in order to maintain sufficient strength of the mold.
Further, the solubility of calcium sulfate in water is at highest
0.210 g/100 g at 42.degree. C., which is a rather low value, and
therefore it cannot be suitable for practical use for the
water-soluble mold.
SUMMARY OF THE INVENTION
[0009] The basic objects of the present invention are to make
recovery of a binder easy and allow repeat use of the binder
efficiently by using a binder containing water-soluble sulfate
compounds as a main ingredient, and to assure sufficient strength
of a mold by using an appropriate amount of the binder.
[0010] In accordance with a first aspect of the invention, there is
provided a water-soluble casting mold comprising a refractory
granular material for casting sand and a water-soluble binder
containing at least one inorganic sulfate compound selected from
magnesium sulfate, aluminum sulfate, sodium sulfate, nickel
sulfate, manganese sulfate and wherein the inorganic sulfate
compound contains crystal water in dry state.
[0011] The magnesium sulfate, aluminum sulfate, sodium sulfate,
nickel sulfate, and manganese sulfate to be used as the inorganic
sulfate compound contained in the binder for the mold respectively
have good solubility in water. Accordingly, a mold obtained using
the binder can easily be collapsed only by being submerged and it
is possible to recover the binder, thereby it is possible to use
the binder repeatedly, even if the mold is used as a core for a
casting with a complicated shape. Further, these inorganic sulfate
compounds respectively have a melting point of 770.degree. C. or
higher. Accordingly, even if the mold is used to cast an aluminum
alloy casting product such as an automotive part, since the pouring
temperature of the molten metal for the aluminum alloy casting is
generally at about 770.degree. C., the sulfate compounds are
prevented from melting and their vitrification can be avoided, and
thus the binder can easily be recovered.
[0012] In general, an inorganic sulfate compound has a high
strength in the hydrated state having crystal water as compared
with that in the anhydride state having no crystal water. With
respect to the water-soluble casting mold according to the present
invention, since the inorganic sulfate compound of the binder
contains crystal water in dry state, the strength of the mold is
extremely high. It is to be noted that the binder is not limited to
those containing only one inorganic sulfate compounds among a
plurality of kinds of such sulfate compounds. The respective
inorganic sulfate compounds show the maximum strength in prescribed
hydrated states, and when the quantity of the contained crystal
water is fluctuated owing to humidification deterioration or the
like, the strength of the respective inorganic sulfate compounds is
decreased. Also, at the time of drying the casting sand, it may be
possible that the crystal water of the inorganic sulfate compounds
is not evenly evaporated in the casting sand. Therefore, a
plurality of the inorganic sulfate compounds are mixed at
prescribed ratios and at the time of drying the casting sand, they
are made to be a mixed crystal to make the peak of the strength
moderate in relation to the quantity of the crystal water contained
in the binder and consequently, the strength of the entire body of
the mold can sufficiently be assured even if the quantity of the
crystal water is fluctuated or the content of the crystal water in
the mold is uneven.
[0013] In accordance with a second aspect of the invention, there
is provided a water-soluble casting mold comprising 100 parts by
weight of a refractory granular material for casting sand and a
binder containing 0.5 to 10.0 parts by weight on the basis of
magnesium sulfate equivalent to hepta-hydrate and wherein the
magnesium sulfate contains crystal water in dry state. Since
magnesium sulfate has good solubility in water, it is easy to
recover a binder by collapsing the mold only by adding water after
pouring molten metal. Further, the melting point of magnesium
sulfate is 1,185.degree. C. and even if the mold is used to cast an
aluminum alloy casting product such as an automotive part, since
the pouring temperature of the molten metal of the aluminum alloy
casting is generally about 770.degree. C., magnesium sulfate is
prevented from melting and its vitrification can be avoided, and
thus the binder can easily be recovered.
[0014] Further, since the binder contains 0.5 to 10.0 parts by
weight of magnesium sulfate, a sufficient strength of the mold can
be assured with an appropriate amount of magnesium sulfate. That
is, if the amount of magnesium sulfate is less than 0.5 parts by
weight, the mold cannot be provided with a sufficient strength. On
the other hand, if the amount of magnesium sulfate is more than
10.0 parts by weight, in the case of mixing the binder with the
refractory granular material for casting sand, a large quantity of
water for dissolving magnesium sulfate has to be added. This
results in deterioration of the filling property of the casting
sand in a die for molding the casting sand, and void formation of
the mold because of evaporation of the large quantity of water
contained in the casting sand when the casting sand is dried after
the molding; and consequent strength decrease of the mold.
[0015] In one embodiment of the present invention, preferably, the
magnesium sulfate contains crystal water equivalent to mono- to
penta-hydrate in dry state. Since magnesium sulfate shows higher
strength in the hydrate state than that in anhydride state, a
sufficient strength of the mold can be assured by making magnesium
sulfate have crystal water equivalent to mono- to penta-hydrate in
dry state. Further, since magnesium sulfate exhibits the maximum
strength in a form of tri- to tetra-hydrate, it is further
preferable that magnesium sulfate in the mold has crystal water
equivalent to tri to tetra-hydrate in dry state.
[0016] In one embodiment of the present invention, preferably, the
binder contains the inorganic sulfate compounds and not more than
75% by weight of at least one of sodium dihydrogen phosphate and
potassium dihydrogen phosphate. At the time of pouring molten
metal, a portion of the mold becomes locally a high temperature and
crystal water of the inorganic sulfate compounds is isolated,
evaporated, and dehydrated. Thereby, the inorganic sulfate
compounds become anhydrides to result in decrease of the strength.
Consequently, at least one of sodium dihydrogen phosphate and
potassium dihydrogen phosphate in an amount of 75% or less by
weight is added to the inorganic sulfate compounds so as to retain
the water-solubility of the mold and improve the heat resistance
property.
[0017] In one embodiment of the present invention, preferably, the
binder contains the inorganic sulfate compounds and not more than
50% by weight of at least one of tricalcium phosphate, aluminum
phosphate, trisodium phosphate, sodium diphosphate, and disodium
hydrogen phosphate dodecahydrate. At the time of pouring molten
metal, a portion of the mold becomes locally a high temperature and
crystal water of the inorganic sulfate compounds is isolated,
evaporated, and dehydrated. Thereby, the inorganic sulfate
compounds become anhydrides to result in decrease of the strength.
Consequently, at least one of tricalcium phosphate, aluminum
phosphate, trisodium phosphate, sodium diphosphate, and disodium
hydrogen phosphate dodecahydrate in an amount of 50% or less by
weight is added to the inorganic sulfate compounds so as to retain
the water-solubility of the mold and improve the heat
resistance.
[0018] In one embodiment of the present invention, preferably, the
binder contains the inorganic sulfate compounds and not more than
75% by weight of magnesium chloride. At the time of pouring molten
metal, a portion of the mold becomes locally a high temperature and
crystal water of the inorganic sulfate compounds is isolated,
evaporated, and dehydrated. Thereby, the inorganic sulfate
compounds become anhydrides to result in decrease of the strength.
Consequently, magnesium chloride in an amount of 75% or less by
weight is added to the inorganic sulfate compounds so as to retain
the water-solubility of the mold and improve the heat
resistance.
[0019] In accordance with a third aspect of the invention, there is
provided a method for manufacturing a water-soluble casting mold
including a first step of obtaining casting sand by mixing a
refractory granular material for casting sand with a water-soluble
binder containing at least one inorganic sulfate compound selected
from magnesium sulfate, aluminum sulfate, sodium sulfate, nickel
sulfate, and manganese sulfate and water; a second step of forming
a mold with the resulting casting sand; and a third step of
obtaining a casting mold by drying the casting sand in such a
manner that the inorganic sulfate compound in the casting sand is
kept retaining at least a portion of the crystal water.
[0020] In the case of producing the mold, first of all, in the
first step, a water-soluble binder containing at least one
inorganic sulfate compound selected from magnesium sulfate,
aluminum sulfate, sodium sulfate, nickel sulfate, and manganese
sulfate and water by which the binder is dissolved are added to and
mixed with a refractory granular material such as siliceous sand or
the like to obtain casting sand. In the second step, the obtained
casting sand is formed into a prescribed mold. Further, in the
third step, the molded casting sand is dried by heating or the like
to remove water from the casting sand, and at that time, since the
casting sand is dried in the state that the inorganic sulfate
compound therein is kept retaining at least a portion of crystal
water, the inorganic sulfate compound exists in hydrate state in
the mold after the drying and consequently, the strength of the
mold can be obtained.
[0021] Incidentally, in the third step, a method for drying the
casting sand is preferably a method of evaporating water in the
casting sand with a higher dielectric constant than that of the
crystal water by irradiating microwave to the casting sand since
water has to be removed while at least a portion of the crystal
water being kept in the inorganic sulfate compound. However, unless
the inorganic sulfate compound becomes an anhydride, any method
other than such a method using microwave can be employed.
Practically, a method for evaporating water with heat by supplying
hot air to the mold, a method for hardening the casting sand by
filling a heated die with the sand, a method for evaporating water
by decreasing pressure after a mold is filled with the casting
sand, and the like can be exemplified. Further, these methods can
be employed in combination.
[0022] In accordance with a fourth aspect of the invention, there
is provided a method for manufacturing a water-soluble casting mold
including a first step of obtaining casting sand by mixing 100
parts by weight of a refractory granular material for casting sand
with a binder containing 0.5 to 10.0 parts by weight of magnesium
sulfate equivalent to hepta-hydrate and water in an amount
sufficient to completely dissolve the magnesium sulfate in the
binder; a second step of forming the resulting casting sand; and a
third step of obtaining a mold by drying the casting sand in such a
manner that the magnesium sulfate in the casting sand is kept
retaining at least a portion of the crystal water.
[0023] In the case of manufacturing the mold, first of all, in the
first step, a water-soluble binder containing magnesium sulfate
heptahydrate in an amount of 0.5 to 10.0 parts by weight and water
in an amount sufficient to completely dissolve the magnesium
sulfate in the binder are added to and mixed with 100 parts by
weight of a refractory granular material for casting sand such as
siliceous sand or the like to obtain casting sand. In the second
step, the obtained casting sand is formed into a prescribed mold.
Further, in the third step, the molded casting sand is dried by
heating or the like to remove water from the casting sand and at
that time, since the casting sand is dried in the state that the
magnesium sulfate therein is kept retaining at least a portion of
crystal water, the magnesium sulfate exists in hydrate state in the
mold after the drying and consequently, the strength of the mold
can be obtained.
[0024] Further, in this case, since a proper quantity of water is
added to completely dissolve magnesium sulfate, the binder is
sufficiently mixed with the refractory granular material for
casting sand and the refractory granular material for casting sand
is reliably coated with the binder.
[0025] In addition, as explained above, a variety of methods
employing microwave, hot air and the like can be applicable as a
method for drying the casting sand.
[0026] In one embodiment of the present invention, preferably, the
binder contains the inorganic sulfate compound and not more than
75% by weight of at least one of sodium dihydrogen phosphate and
potassium dihydrogen phosphate. The water-solubility of the mold
can be retained and the heat resistance is improved, by adding at
least one of sodium dihydrogen phosphate and potassium dihydrogen
phosphate in an amount of 75% or less by weight to the inorganic
sulfate compound.
[0027] In one embodiment of the present invention, preferably, the
binder contains the inorganic sulfate compound and not more than
50% by weight of at least one of tricalcium phosphate, aluminum
phosphate, trisodium phosphate, sodium diphosphate, and disodium
hydrogen phosphate dodecahydrate. The water-solubility of the mold
can be retained and the heat resistance is improved, by adding at
least one of tricalcium phosphate, aluminum phosphate, trisodium
phosphate, sodium diphosphate, and disodium hydrogen phosphate
dodecahydrate in an amount of 50% or less by weight to the
inorganic sulfate compound.
[0028] In one embodiment of the present invention, preferably, the
binder contains the inorganic sulfate compound and not more than
75% by weight of magnesium chloride. The water-solubility of the
mold can be retained and the heat resistance is improved by adding
magnesium chloride in an amount of 75% or less by weight to the
inorganic sulfate compound.
[0029] In one embodiment of the present invention, preferably, the
casting sand is dried by microwave or heating with hot air in the
third step. When microwave is radiated to the casting sand, since
water in the casting sand has a higher dielectric constant than
that of the crystal water of the inorganic sulfate compound, the
water in the casting sand is easily evaporated than that of the
crystal water. Accordingly, the water can be removed while the
inorganic sulfate compound is kept retaining at least a portion of
the crystal water.
[0030] In the case where the casting sand is heated by blowing hot
air to the casting sand, if the temperature of the hot air is set
to be a prescribed temperature (e.g. 200.degree. C.) or lower at
which the crystal water contained in the inorganic sulfate compound
is not completely dehydrated, the water in the casting sand is
evaporated prior at 100.degree. C. under a normal pressure
condition and therefore, similarly to the above-mentioned drying by
using microwave, the water can be removed while the inorganic
sulfate compound is kept retaining at least a portion of the
crystal water.
[0031] In one embodiment of the present invention, preferably, the
second step of forming the casting sand is carried out by filling a
cavity of a ventilative ceramic mold with the casting sand.
Accordingly, at the time of drying the casting sand in the third
step, the evaporated water can be released evenly to the outside
from the ceramic mold, so that the strength of the manufactured
mold can be made uniform.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a graph showing a correlation between a magnesium
sulfate hydrate according to an embodiment of the invention and the
compressive strength;
[0033] FIG. 2 is a graph showing a solubility of magnesium sulfate
heptahydrate in water;
[0034] FIG. 3 is an explanatory drawing showing the filling work of
casting sand into a die in the second step;
[0035] FIG. 4 is an explanatory drawing showing the drying work by
microwave in the third step;
[0036] FIG. 5 is an explanatory drawing showing the filling work by
hot air blow in the third step.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] Hereinafter, the embodiments of the invention will be
described. The embodiments are examples of the inventions applied
to a casting mold of an aluminum alloy casting product and its
manufacturing method. At first, a water-soluble casting mold
according to the invention will be explained.
[0038] Firstly, a water-soluble casting mold containing a binder
that contains magnesium sulfate hydrate which is to be mixed with a
refractory granular material for casting sand such as flatterry
siliceous sand or the like (hereinafter, referred to as a
refractory granular material) will be described. In the case of
manufacturing such a casting mold, magnesium sulfate heptahydrate
and water sufficient to completely dissolve the magnesium sulfate
heptahydrate are added to and mixed with the refractory granular
material to coat the refractory granular material with the binder
and obtain the casting sand. After the casting sand is formed into
a prescribed shape by filling a mold with the sand, water in the
casting sand is evaporated to obtain a mold.
[0039] In magnesium sulfate, the strength considerably fluctuates
depending on the quantity of the crystal water contained therein.
FIG. 1 shows the correlation between the hydration quantity of
magnesium sulfate and the strength of the casting mold. It was
obtained by the following experiments. That is, 100 parts by weight
of flatterry siliceous sand is used as the refractory granular
material and 3 parts by weight of magnesium sulfate heptahydrate
and water are added thereto to obtain casting sand. Each specimen
of the casting sand with a diameter of 30 mm and a height of 50 mm
is formed by using a specimen beating and hardening apparatus
standardized according to JIS Z 2601. Each specimen is formed by
beating and hardening three times using the apparatus. The specimen
is then dried by irradiating microwave of 700 W output. At that
time, the drying duration (microwave radiation duration) is
adjusted so as to alter the quantity of the crystal water contained
in the magnesium sulfate in the specimen and the compressive
strength of each specimen is measured. The quantity of the crystal
water contained in magnesium sulfate of each specimen is determined
by drying further magnesium sulfate at 300.degree. C. after drying
with microwave until it becomes completely anhydride, assuming
decrease of the weight of the specimen before and after the drying
to be the crystal water contained in magnesium sulfate in the
specimen, and carrying out calculation by mole ratio from the
amount of magnesium sulfate added.
[0040] Hydrates of magnesium sulfates include mono, tetra, hepta,
and dodeca hydrates and as shown in FIG. 1, about mono- to
hexa-hydrates are applicable for a casting mold. Further, mono to
penta-hydrates are preferable to provide strength. Accordingly, it
is desirable for magnesium sulfate in the mold in dry state to have
crystal water equivalent to mono to penta hydrates. Further, it is
more desirable for magnesium sulfate to have crystal water
equivalent to tri to tetra hydrates.
[0041] Next, the correlations of the addition amount of magnesium
sulfate heptahydrate with compressive strength of the mold and the
quantity of crystal water of magnesium sulfate will be described.
Here, water is evaporated from each specimen, which is formed in
the same manner as mentioned above, by a method of irradiating
microwave of 700 W output for a prescribed duration and also by a
method of blowing hot air at 200.degree. C. for 1 hour and then the
strength of the specimen and the crystal water in magnesium sulfate
are measured. Since the dielectric constant of water in the
specimen is higher than that of the crystal water of magnesium
sulfate, m the case of radiating microwave to the specimen, water
is easily evaporated prior to the crystal water. Accordingly, the
quantity of the crystal water contained in magnesium sulfate can be
changed by adjusting the duration of microwave radiation. The
results are shown in Table 1.
1TABLE 1 Crystal Conversion Compressive water into Drying method
strength kg/cm.sup.2 % hydrate Remarks magnesium sulfate 0.5 parts
by weight Microwave drying for 1 minute 0.6 0.23 3.09 In the case
of using molten heptahydrate Microwave drying for 3 minutes 0.2 0.1
1.34 ceramic sand, water 0.4 parts by weight Drying at 200.degree.
C. for 1 hour 0.0 0.01 0.13 1.7 kg/cm.sup.2 (microwave drying for 1
minute) magnesium sulfate 1.0 parts by weight Microwave drying for
1 minute 2.5 0.44 2.97 heptahydrate Microwave drying for 3 minutes
0.2 0.19 1.28 water 0.8 parts by weight Drying at 200.degree. C.
for 1 hour 0.0 0.02 0.14 magnesium sulfate 3.0 parts by weight
Microwave drying for 1 minute 25.8 0.76 1.75 heptahydrate Microwave
drying for 3 minutes 13.8 0.57 1.31 water 2.4 parts by weight
Drying at 200.degree. C. for 1 hour 0.0 0.1 0.23 magnesium sulfate
5.0 parts by weight Microwave drying for 1 minute 30.7 1.06 1.49
heptahydrate Microwave drying for 3 minutes 26.6 0.65 0.91 water
4.0 parts by weight Drying at 200.degree. C. for 1 hour 0.6 0.14
0.20 magnesium sulfate 10 parts by weight Microwave drying for 1
minute 57.0 2.12 1.56 heptahydrate Microwave drying for 3 minutes
28.9 1.09 0.80 water 8.0 parts by weight Drying at 200.degree. C.
for 1 hour 1.0 0.32 0.24 magnesium sulfate 12.5 parts by weight
Microwave drying for 1 minute 24.1 -- -- No normal specimen
heptahydrate Microwave drying for 3 minutes 27.0 -- -- obtained at
the time of water 10 parts by weight Drying at 200.degree. C. for 1
hour 0.0 -- -- drying. Voids existing in the inside magnesium
sulfate 15 parts by weight Microwave drying for 1 minute 1.3 -- --
No normal specimen heptahydrate Microwave drying for 3 minutes 15.9
-- -- obtained at the time of water 12 parts by weight Drying at
200.degree. C. for 1 hour 8.0 -- -- drying. Voids existing in the
inside magnesium sulfate 20 parts by weight Microwave drying for 1
minute forming impossible -- -- heptahydrate Microwave drying for 3
minutes forming impossible -- -- water 16 parts by weight Drying at
200.degree. C. for 1 hour forming impossible -- --
[0042] As shown in Table 1, high compressive strength is obtained
in the case of microwave drying for 1 minute and the quantity of
crystal water in such a case is found equivalent to mono to
trihydrate on the basis of hydrate. Specimens subjected to drying
at 200.degree. C. for 1 hour are scarcely provided with compressive
strength and the quantity of crystal water is less than
monohydrate. The crystal water is supposed to be water absorbed
from atmospheric air. In the case where the addition amount of
magnesium sulfate heptahydrate is 0.5 parts by weight, the strength
approximately same as that of a green sand mold is obtained. In the
case where the addition amount of magnesium sulfate heptahydrate is
12.5 parts by weight or more, voids are formed in the inside of the
specimens owing to evaporation of a large quantity of free water
existing in the specimens at the time of drying of the specimens
and consequently the strength is decreased.
[0043] On the other hand, in the case where the addition amount of
magnesium sulfate heptahydrate is increased, the amount of water to
be added so as to dissolve the magnesium sulfate heptahydrate is
inevitably increased. Consequently, in the case of forming the
casting sand, the filling property of the casting sand into a mold
is significantly deteriorated. Especially, when a core with a
complicated shape just like a core for a water jacket in an
automotive engine is manufactured, the filling property is a
particularly important matter. The strength needed for a casting
mold and excellent filling property into a mold can be obtained in
the case where the addition amount of the magnesium sulfate
heptahydrate is in a range of 0.5 parts by weight to 10 parts by
weight.
[0044] If magnesium sulfate heptahydrate is added alone, as shown
in FIG. 1, the compressive strength becomes the maximum when the
content of crystal water is a prescribed amount (crystal water
equivalent to tri to tetrahydrate) and the crystal water in the
casting mold is not necessarily evaporated uniformly at the time of
drying. Further, magnesium sulfate has a problem that the amount of
crystal water is fluctuated owing to moisture absorption to result
in decrease of the strength. Therefore, investigations have been
made so as to find whether it is possible or not that an inorganic
sulfate compound is used in combination with magnesium sulfate to
form a mixed crystal at the time of drying and the strength can be
obtained with different mole ratios in relation to the crystal
water and whether it is possible that the strength is hardly
decreased at the time of moisture absorption. Table 2 shows the
strength of each specimen after microwave drying, the compressive
strength after moisture absorption, and results of a
water-solubility test at 600.degree. C.
2 TABLE 2 Compressive strength kg/cm.sup.2 immediately after water
after drying moisture absorption 600.degree. C. .times. 15 min
firing, parts by Microwave (700 W) Microwave (700 W)
water-solubility test, weight 1 minute 3 minutes 1 minute 3 minutes
dissolution state magnesium sulfate heptahydrate 3 parts by weight
2.4 28.7 16.3 15.8 14.2 collapsed in 4.1 seconds magnesium sulfate
heptahydrate 2.7 parts by weight 2.4 26.9 26.7 18.4 22.1 collapsed
in 8.5 seconds aluminum sulfate dodecahydrate 0.3 parts by weight
magnesium sulfate heptahydrate 2.7 parts by weight 2.4 25.2 23.1
22.3 20.5 collapsed in 8.3 seconds aluminum sulfate 0.3 parts by
weight magnesium sulfate heptahydrate 2.7 parts by weight 2.4 17.2
25.2 10.1 11.1 collapsed in 4.9 seconds sodium sulfate decahydrate
0.3 parts by weight magnesium sulfate heptahydrate 2.7 parts by
weight 2.4 26.3 24.2 20.9 20.2 collapsed in 14.0 seconds nickel
sulfate hexahydrate 0.3 parts by weight magnesium sulfate
heptahydrate 2.7 parts by weight 2.4 17.3 22.9 19.9 18.2 collapsed
in 4.3 seconds manganese sulfate pentahydrate 0.3 parts by
weight
[0045] Here, as another inorganic sulfate compound, aluminum
sulfate dodecahydrate, aluminum sulfate, sodium sulfate
decahydrate, nickel sulfate hexahydrate, and manganese sulfate
pentahydrate are used. As the refractory granular material,
flatterry siliceous sand is used. As a binder, magnesium sulfate
heptahydrate 2.7 parts by weight and another inorganic sulfate
compound 0.3 parts by weight are added to the refractory granular
material and further water 2.4 parts by weight is added to obtain
casting sand. The forming is carried out in the same manner as
described above to obtain each specimen with a diameter of 30 mm
and a height of 50 mm. Microwave radiation duration is set to be 1
minute and 3 minutes and the compressive strength is measured
immediately after drying. Further, in order to absorb moisture in
each specimen, the specimen after microwave drying is left for 24
hours in a desiccator containing water and after moisture
absorption of the specimen in such a manner, the compressive
strength is again measured.
[0046] The compressive strength is deteriorated after 3-minute
microwave radiation in the case of using magnesium sulfate
heptahydrate alone, meanwhile the strength decrease is prevented by
using another inorganic sulfate compound in combination. Further,
the strength after moisture absorption is more increased by adding
aluminum sulfate dodecahydrate, aluminum sulfate, nickel sulfate
hexahydrate, or manganese sulfate pentahydrate than adding solely
magnesium sulfate heptahydrate and thus it is confirmed that the
strength is improved after moisture absorption.
[0047] As another inorganic compound to be combined with magnesium
sulfate, the following inorganic sulfates shown in Table 3 are
preferable. They have a melting point of 770.degree. C. or higher,
an average molten metal pouring temperature of an aluminum alloy
casting product, and are thus not melted at the time of the pouring
molten metal and are easy to be dissolved in water and to form a
mixed crystal with magnesium sulfate.
3 TABLE 3 solubility in 100 g of water melting point Magnesium
sulfate 26.9 g/100 g (0.degree. C.) 1185.degree. C. Aluminum
sulfate dodecahydrate 36.2 g/100 g (20.degree. C.) 770.degree. C.
Aluminum sulfate 36.2 g/100 g (20.degree. C.) 770.degree. C. sodium
sulfate decahydrate 19.4 g/100 g (20.degree. C.) 884.degree. C.
nickel sulfate hexahydrate 39.7 g/100 g (20.degree. C.) 840.degree.
C. Manganese sulfate pentahydrate 75.3 g/100 g (25.degree. C.)
850.degree. C.
[0048] Specimens of casting molds containing binders containing
these inorganic sulfate compounds, as shown in Table 2, are easily
collapsed in water in a 600.degree. C. water-solubility test. The
600.degree. C. water-solubility test is carried out by firing each
specimen subjected to 1-minute microwave radiation at 600.degree.
C. for 15 minutes and immersing the specimen in water after cooling
to find whether the specimen is collapsed or not. Incidentally, any
inorganic compound may be used if it has a melting point of
770.degree. C. or higher and, similarly to the inorganic sulfate
compounds shown in Table 3, has a high water-solubility at lowest
19.4 g (at 20.degree. C.), the minimum value of the solubility in
100 g water.
[0049] Further, Table 4 to Table 7 show the compressive strength
and the result of the 600.degree. C. water-solubility test of each
specimen in the case where other inorganic sulfate compounds are
added at different mixing ratios to magnesium sulfate
heptahydrate.
4 TABLE 4 compressive strength kg/cm.sup.2 mixing ratio of binder
(%) 1-hour magnesium sulfate aluminum sulfate microwave drying
drying at 600.degree. C. .times. 15 min firing, heptahydrate
dodecahydrate 1 minute 3 minutes 200.degree. C. water-solubility
test, dissolution state 0 100 24.5 27.2 0.0 collapsed by stirring
for 60 seconds or longer 50 50 32.7 37.6 0.0 collapsed by stirring
for 60 seconds or longer 75 25 42 47.1 0.0 collapsed by stirring
for 60 seconds or longer 100 0 25.8 13.8 0.0 collapsed in 4.1
seconds
[0050]
5 TABLE 5 compressive strength kg/cm.sup.2 mixing ratio of binder
(%) 1-hour 600.degree. C. .times. 15 min firing, magnesium sulfate
sodium sulfate microwave drying drying at water-solubility test,
heptahydrate decahydrate 1 minute 3 minutes 200.degree. C.
dissolution state 0 100 1.41 1.77 0.0 collapsed in 1.8 seconds 50
50 21.7 28.1 0.0 collapsed in 3.4 seconds 75 25 35.1 35.2 0.0
collapsed in 5.5 seconds 100 0 25.8 13.8 0.0 collapsed in 4.1
seconds
[0051]
6 TABLE 6 compressive strength kg/cm.sup.2 mixing ratio of binder
(%) 1-hour 600.degree. C. .times. 15 min firing, magnesium sulfate
nickel sulfate microwave drying drying at water-solubility test,
heptahydrate hexahydrate 1 minute 3 minutes 200.degree. C.
dissolution state 0 100 28.3 35.3 0.0 collapsed by stirring for 60
seconds or longer 50 50 26.5 32.3 0.0 collapsed by stirring for 60
seconds or longer 75 25 25.4 30.3 0.0 collapsed by stirring for 60
seconds or longer 100 0 25.8 13.8 0.0 collapsed in 4.1 seconds
[0052]
7TABLE 7 mixing ratio of binder (%) compressive strength
kg/cm.sup.2 manganese 1-hour 600.degree. C. .times. 15 min firing,
magnesium sulfate sulfate microwave drying drying at
water-solubility test, heptahydrate pentahydrate 1 minute 3 minutes
200.degree. C. dissolution state 0 100 0.4 1.5 1.5 collapsed in 2.3
seconds 50 50 22.5 14.4 0.2 collapsed in 3.6 seconds 75 25 19.4
23.6 0.0 collapsed in 5.1 seconds 100 0 25.8 13.8 0.0 collapsed in
4.1 seconds
[0053] As the refractory granular material, flatterry siliceous
sand is used and a binder 3 parts by weight in total and water 2.4
parts by weight are added to produce specimens. And a compressive
test is carried out after the specimens are dried by microwave
radiation and 1-hour drying at 200.degree. C. for reference data to
find compressive strength. Even in the case where aluminum sulfate
dodecahydrate, sodium sulfate decahydrate, nickel sulfate
hexahydrate, and manganese sulfate pentahydrate are used alone as a
binder, the strength is provided by drying with microwave radiation
and also in the case where they are added to magnesium sulfate
heptahydrate, the strength can be obtained. In any combination, the
results of the 600.degree. C. water-solubility test are excellent
and molds containing binders using those inorganic compounds in
combination can easily be collapsed while being submerged. As being
made clear from Table 4 to Table 7, especially in the case of
mixing magnesium sulfate and aluminum sulfate, a high compressive
strength can be obtained.
[0054] From the fact that no strength is exhibited in all of the
combinations in the case of 1-hour drying at 200.degree. C., it can
be understood that crystal water is important to be left in the
inorganic sulfate compound since no strength is obtained in the
anhydride state. Also, it is no need to say that even if an
anhydride of an inorganic sulfate compound is used for a binder,
since a hydrate can be obtained at the time of water addition and
therefore the same effect can be obtained.
[0055] Next, the case another inorganic compound is added to
magnesium sulfate heptahydrate will be described. The average
molten metal pouring temperature of an aluminum alloy cast is about
770.degree. C. and a portion of a mold locally becomes high
temperature at the time of pouring molten metal, however crystal
water of magnesium sulfate is isolated, evaporated, and dehydrated
at 200.degree. C. or higher, and magnesium sulfate becomes an
anhydride, so that the strength is decreased locally. For that,
together with magnesium sulfate heptahydrate, another inorganic
compound as described below is added to the refractory granular
material so as to improve the heat resistance.
[0056] Table 8 and Table 9 show the compressive strength and the
results of the 600.degree. C. water-solubility test given in the
case of casting molds using sodium dihydrogen phosphate or
potassium dihydrogen phosphate in combination with magnesium
sulfate heptahydrate.
8TABLE 8 mixing ratio of binder (%) compressive strength
kg/cm.sup.2 sodium 1-hour 600.degree. C. .times. 15 min firing,
magnesium sulfate dihydrogen microwave drying drying at
water-solubility test, heptahydrate phosphate 1 minute 3 minutes
200.degree. C. dissolution state 0 100 7.5 11.1 4.8 Insoluble 10 90
11.3 12.0 7.2 Insoluble 25 75 29.9 31.9 32.2 collapsed by
pressurizing for 60 seconds or longer 50 50 34.6 44.9 47.8
collapsed by pressurizing for 60 seconds or longer 66.7 33.3 32.3
40.4 31.1 collapsed by pressurizing for 60 seconds or longer 75 25
36.8 41.7 19.3 collapsed by pressurizing for 60 seconds or longer
90 10 25.2 31.8 13.2 collapsed by pressurizing for 60 seconds or
longer 100 0 25.8 13.8 0.0 collapsed in 4.1 seconds
[0057]
9TABLE 9 mixing ratio of binder (%) compressive strength
kg/cm.sup.2 potassium 1-hour 600.degree. C. .times. 15 min firing,
magnesium sulfate dihydrogen microwave drying drying at
water-solubility test, heptahydrate phosphate 1 minute 3 minutes
200.degree. C. dissolution state 0 100 10.5 14.2 12.2 Insoluble 10
90 12.2 16.1 10.9 Insoluble 25 75 18.8 32.2 24.4 collapsed by
pressurizing for 60 seconds or longer 50 50 24.9 30.0 21.3
collapsed by pressurizing for 60 seconds or longer 66.7 33.3 31.5
27.7 10.3 collapsed by pressurizing for 60 seconds or longer 75 25
30.4 25.1 10.6 collapsed by pressurizing for 60 seconds or longer
90 10 31.7 23.1 2.6 collapsed by pressurizing for 60 seconds or
longer 100 0 25.8 13.8 0.0 collapsed in 4.1 seconds
[0058] As the refractory granular material, flatterry siliceous
sand is used and a binder 3 parts by weight in total and water 2.4
parts by weight are added to produce specimens and a compressive
test is carried out after the specimens are dried by microwave
radiation and 1-hour drying at 200.degree. C. for reference data to
find compressive strength. Both of sodium dihydrogen phosphate and
potassium dihydrogen phosphate are effective to give the strength
even in the case of using them alone and therefore they are usable
as a binder, however specimens become water-insoluble in the
600.degree. C. water-solubility test. If they are added in an
amount of 75% or less by weight to magnesium sulfate heptahydrate,
the specimens are collapsed into sand particles by stirring the
specimens in water under pressurizing condition (described as
collapsed by pressurizing for 60 seconds or longer) and show
water-solubility. Further, since strength is exhibited even after
1-hour drying at 200.degree. C., the heat resistance is excellent
and various problems such as washing, deformation, cracking and the
like of molds at the time of pouring molten metal can be solved. In
addition, since both of sodium dihydrogen phosphate and potassium
dihydrogen phosphate contribute to heat resistance improvement as
described above, they can be mixed and in such a case, both are
preferable to be added in an amount of 75% less by weight to
magnesium sulfate heptahydrate.
[0059] Next, Table 10 to Table 14 show the compressive strength and
the results of the 600.degree. C. water-solubility test given in
the case where molds are produced by using other inorganic
phosphate compounds in combination with magnesium sulfate
heptahydrate.
10 TABLE 10 compressive strength kg/cm.sup.2 mixing ratio of binder
(%) 1-hour 600.degree. C. .times. 15 min firing, magnesium sulfate
tricalcium microwave drying drying at water-solubility test,
heptahydrate phosphate 1 minute 3 minutes 200.degree. C.
dissolution state 0 100 0.0 0.0 0.0 -- 50 50 6.2 4.3 0.5 collapsed
by pressurizing for 60 seconds or longer 66.7 33.3 9.4 7.1 5.8
collapsed by pressurizing for 60 seconds or longer 75 25 12.6 15.2
4.2 collapsed by pressurizing for 60 seconds or longer 90 10 22.6
12.4 1.2 collapsed by pressurizing for 60 seconds or longer 100 0
25.8 13.8 0.0 collapsed in 4.1 seconds
[0060]
11 TABLE 11 compressive strength kg/cm.sup.2 mixing ratio of binder
(%) 1-hour 600.degree. C. .times. 15 min firing, magnesium sulfate
aluminum microwave drying drying at water-solubility test,
heptahydrate phosphate 1 minute 3 minutes 200.degree. C.
dissolution state 0 100 0.0 0.0 0.0 -- 50 50 5.9 4.0 0.9 collapsed
by pressurizing for 60 seconds or longer 66.7 33.3 7.3 6.4 0.9
collapsed by pressurizing for 60 seconds or longer 75 25 12.9 9.7
0.7 collapsed by pressurizing for 60 seconds or longer 90 10 15.1
13.7 0.5 collapsed by pressurizing for 60 seconds or longer 100 0
25.8 13.8 0.0 collapsed in 4.1 seconds
[0061]
12TABLE 12 mixing ratio of binder (%) compressive strength
kg/cm.sup.2 trisodium 1-hour magnesium sulfate phosphate microwave
drying drying at 600.degree. C. .times. 15 min firing, heptahydrate
dodecahydrate 1 minute 3 minutes 200.degree. C. water-solubility
test, dissolution state 0 100 0.0 0.0 0.0 -- 50 50 0.7 0.6 0.3
collapsed by pressurizing for 60 seconds or longer 66.7 33.3 0.9
1.0 0.4 collapsed by pressurizing for 60 seconds or longer 75 25
5.4 3.2 0.3 collapsed by pressurizing for 60 seconds or longer 90
10 15.6 11.1 0.3 collapsed by pressurizing for 60 seconds or longer
100 0 25.8 13.8 0.0 collapsed in 4.1 seconds
[0062]
13 TABLE 13 compressive strength kg/cm.sup.2 mixing ratio of binder
(%) 1-hour magnesium sulfate sodium microwave drying drying at
600.degree. C. .times. 15 min firing, heptahydrate diphosphate 1
minute 3 minutes 200.degree. C. water-solubility test, dissolution
state 0 100 0.0 0.0 0.0 -- 50 50 6.2 6.4 2.1 collapsed by
pressurizing for 60 seconds or longer 66.7 33.3 17.7 23.3 4.2
collapsed by pressurizing for 60 seconds or longer 75 25 16.5 17.1
3.0 collapsed by pressurizing for 60 seconds or longer 90 10 19.8
15.0 1.4 collapsed by pressurizing for 60 seconds or longer 100 0
25.8 13.8 0.0 collapsed in 4.1 seconds
[0063]
14TABLE 14 mixing ratio of binder (%) disodium compressive strength
kg/cm.sup.2 hydrogen 1-hour magnesium sulfate phosphate microwave
drying drying at 600.degree. C. .times. 15 min firing, heptahydrate
dodecahydrate 1 minute 3 minutes 200.degree. C. water-solubility
test, dissolution state 0 100 0.2 0.1 0.1 -- 50 50 3.2 2.9 0.9
collapsed by pressurizing for 60 seconds or longer 66.7 33.3 4.1
0.5 1.2 collapsed by pressurizing for 60 seconds or longer 75 25
7.2 3.2 2.3 collapsed by pressurizing for 60 seconds or longer 90
10 15.8 16.0 3.4 collapsed by pressurizing for 60 seconds or longer
100 0 25.8 13.8 0.0 collapsed in 4.1 seconds
[0064] As other inorganic phosphate compounds, tricalcium
phosphate, aluminum phosphate, trisodium phosphate dodecahydrate,
sodium diphosphate, and disodium hydrogen phosphate dodecahydrate
are used. These phosphate compounds cannot give the strength if
they are used alone and therefore, they cannot solely be used as a
binder. However, in the case of mixing them in an amount of 50% or
less by weight to magnesium sulfate, they give the compressive
strength and assure the water-solubility in both cases; microwave
drying and 1-hour drying at 200.degree. C. and therefore, they can
be used as a binder.
[0065] Further, Table 15 shows the compressive strength test and
the results of the 0.600.degree. C. water-solubility test given in
the case where molds are produced by using magnesium chloride in
combination with magnesium sulfate heptahydrate.
15TABLE 15 mixing ratio of binder (%) compressive strength
kg/cm.sup.2 magnesium 1-hour 600.degree. C. .times. 15 min firing,
sulfate magnesium microwave drying drying at water-solubility test,
dissolution heptahydrate chloride 30 seconds 1 minute 3 minutes
200.degree. C. state 0 100 25.0 19.7 12.6 3.5 Insoluble 10 90 26.5
21.7 13.3 3.2 Insoluble 25 75 18.3 17.6 10.4 3.2 collapsed by
pressurizing for 60 seconds or longer 50 50 19.0 12.6 6.0 2.9
collapsed by pressurizing for 60 seconds or longer 66.7 33.3 14.9
12.1 9.2 1.6 collapsed by pressurizing for 60 seconds or longer 75
25 10.5 9.9 7.2 0.6 collapsed by pressurizing for 60 seconds or
longer 90 10 10.7 18.4 9.4 0.6 collapsed by pressurizing for 60
seconds or longer 100 0 3.7 25.8 13.8 0.0 collapsed in 4.1
seconds
[0066] Also, in the case of using magnesium chloride alone, the
strength can be given and therefore magnesium chloride can be used
alone as a binder, however the specimen becomes water-insoluble in
the 600.degree. C. water-solubility test. On the other hand, in the
case of using magnesium chloride in an amount of 75% or less by
weight in combination with magnesium sulfate heptahydrate, water
solubility is assured. Further, the strength is given even after
1-hour drying at 200.degree. C. and the heat resistance is thus
improved and various problems such as washing, deformation,
cracking and the like of casting molds at the time of pouring
molten metal can be solved. In addition, in the case of drying with
microwave radiation, high strength can be given by radiation for a
duration as short as 30 seconds, the productivity of forming the
molds can be improved.
[0067] With respect to the water-soluble casting molds described
above, Table 16 shows the compressive strength in the case of
producing molds by using magnesium sulfate heptahydrate alone for a
variety of refractory granular materials, which are used commonly,
or adding other inorganic sulfate compounds having a melting point
of 770.degree. C. or higher and showing water-solubility at various
mixing ratios to magnesium sulfate heptahydrate and drying in
various drying manners. As reference example, Table 17 shows the
results of a confirmation test for the molds described in the
foregoing Prior art 2.
16 TABLE 16 refractory granular binder compressive material for
casting parts by water parts strength sand type of binder weight by
weight drying method kg/cm.sup.2 Example-1 melted ceramic sand
magnesium sulfate heptahydrate 1.5 1.2 1-minute 17.6 100 parts by
weight 100% microwave drying Example-2 flatterry siliceous sand
magnesium sulfate heptahydrate 5.0 -- after vapor 44.4 100 parts by
weight 100% ventilation, 1-minute microwave drying Example-3
flatterry siliceous sand magnesium sulfate heptahydrate 3.0 1.0
1-minute 15.4 100 parts by weight 100% microwave drying after
addition of a solution containing a binder and water after heating
to 100.degree. C. Example-4 flatterry siliceous sand magnesium
sulfate heptahydrate 3.0 2.0 1-minute 15.0 100 parts by weight 100%
microwave drying after addition of a binder and water to casting
sand heated at 100.degree. C. Example-5 flatterry siliceous sand
magnesium sulfate heptahydrate 3.0 1.0 adding a binder and 12.2 100
parts by weight 100% water at 100.degree. C. to casting sand at
100.degree. C. and then purging heated air. Example-6 flatterry
siliceous sand magnesium sulfate heptahydrate 3.0 1.8 3-minute
heating of 9.9 100 parts by weight 100% casting sand at 100.degree.
C. in a mold at 120.degree. C. and then purging heated air.
Example-7 flatterry siliceous sand magnesium sulfate heptahydrate
3.0 1.0 adding a binder and 11.3 100 parts by weight 100% water at
100.degree. C. to casting sand at 100.degree. C. and then purging
heated air. Example-8 flatterry siliceous sand magnesium sulfate
heptahydrate 3.0 1.0 adding a binder and 9.0 100 parts by weight
100% water at 100.degree. C. to casting sand at 100.degree. C. and
then dehydrating by reducing pressure. Example-9 melted ceramic
sand magnesium sulfate heptahydrate 1.5 1.2 1-minute 20.9 100 parts
by weight 75% microwave drying aluminum sulfate dodecahydrate 25%
Example-10 melted ceramic sand magnesium sulfate heptahydrate 1.5
1.2 1-minute 24.7 100 parts by weight 50% microwave drying aluminum
sulfate dodecahydrate 25% sodium sulfate decahydrate 25% Example-11
melted ceramic sand magnesium sulfate heptahydrate 1.5 1.2 1-minute
28.9 100 parts by weight 75% microwave drying sodium dihydrogen
phosphate 25% Example-12 melted ceramic sand magnesium sulfate
heptahydrate 1.5 1.2 1-minute 27.3 100 parts by weight 50%
microwave drying aluminum sulfate dodecahydrate 25% sodium
dihydrogen phosphate 25%
[0068]
17 TABLE 17 water binder parts compressive refractory granular
parts by by strength material for casting sand type of binder
weight weight drying method kg/cm.sup.2 Comparative Albany
siliceous sand magnesium sulfate 10.0 3.0 drying at 200.degree. C.
0.0 Example-1 100 parts by weight heptahydrate 100% Comparative
Albany siliceous sand magnesium sulfate 20.0 5.0 drying at
300.degree. C. 0.8 Example-2 100 parts by weight heptahydrate 100%
after addition of a solution containing a binder and water to
casting sand heated at 80.degree. C.
[0069] From the results shown in Table 16 and Table 17, it is
confirmed that molds in the scope of the invention are produced
with a small amount of a binder and are provided with sufficiently
high compressive strength as compared with molds described in Prior
art 2. As mixing examples of the binder in the invention, based on
the data of the compressive strength and the collapsing property of
molds of the respective tables, the mixture of magnesium sulfate
and aluminum sulfate, the mixtures of magnesium sulfate with sodium
dihydrogen phosphate and potassium dihydrogen phosphate, the
mixtures of magnesium sulfate with aluminum sulfate, sodium
dihydrogen phosphate and potassium dihydrogen phosphate are
preferable examples.
[0070] Incidentally, as the refractory granular material, any type
can be used if it can be used as casting sand and has a particle
size satisfying an average particle diameter in a range from about
0.05 mm (280 mesh) to 1 mm (16 mesh). The following are examples of
a variety of refractory granular materials for casting sand such as
domestically produced siliceous sand, imported siliceous sand,
zircon sand, chromite sand, olivine sand, slag sand, carbon sand,
mullite sand, alumina sand, chamotte sand, ceramic sand, porous
ceramic sand, melted ceramic sand, various glass sand, hollow glass
spherical sand, crushed materials of various refractory materials,
metal granular materials such as shot beads, and their reproduced
sand.
[0071] The casting sand or the binder may also contain a prescribed
amount of a rouge, an iron powder, a coal powder, a graphite
powder, a wood powder, a talc, a starch powder, a grain powder, a
silica flour, a zircon flour, an olivine flour and the like, which
are commonly added to casting sand for preventing casting
defects.
[0072] Further, the casting sand or the binder may contain a
prescribed amount of tungsten disulfide and molybdenum disulfide as
an inorganic lubricant and a hydrocarbon-based lubricant,
polyalkylene glycol, a silicone-based lubricant, a fluoro type
lubricant, phenyl ether, and a phosphoric acid ester type lubricant
as an organic lubricant for improving the filling property into a
mold.
[0073] Further, materials generally applied to the surface of a
casting mold such as an alcohol-based mold wash, a water-based mold
wash, a powder-based mold wash, a surface stabilizer, a tellurium
powder for preventing shrinkage can be used.
[0074] Next, a method for manufacturing a casting mold by using a
water-soluble binder containing the above-mentioned various
inorganic sulfate compounds will be described. The mold
manufacturing method is an example in which the invention is
applied as a core for aluminum alloy casting.
[0075] The mold manufacturing method include a first step of
obtaining casing sand by mixing a refractory casting sand with the
above-mentioned water-soluble binder containing inorganic sulfate
compounds and water; a second step of forming the resulting casting
sand; and a third step of obtaining a mold by drying the casting
sand in such a manner that the inorganic sulfate compounds in the
casting sand are kept retaining at least a portion of the crystal
water.
[0076] At first, in the first step, the binder to be added to the
refractory casting sand includes inorganic sulfate compounds having
a melting point equal to or higher than the average molten metal
pouring temperature (770.degree. C.) of aluminum alloy casting.
Practically, as described above, the binder includes magnesium
sulfate heptahydrate alone; mixtures of magnesium sulfate
heptahydrate with other inorganic sulfate compounds such as
aluminum sulfate or the like; or solely another inorganic sulfate
compound. Further, mixtures containing a variety of the foregoing
phosphate compounds such as sodium dihydrogen phosphate or the like
and magnesium chloride in a prescribed amount with which the
water-solubility can be assured may be used in order to improve the
heat resistance of the binder.
[0077] The addition amount of water is desirable to be satisfactory
to dissolve the binder. That is because the binder can be applied
evenly to the refractory granular material and gives high strength
only in the case where the binder is dissolved. However, the
solubility differs depending on the temperature. For example, in
the case where the refractory granular material is previously
heated at 200.degree. C. (the temperature at which crystal water in
the inorganic sulfate compounds is dehydrated) or lower or in the
case where the mold is dried by heating at 200.degree. C. or lower,
the solubility of the binder is increased because water is heated.
Accordingly, the minimum amount of water to be added in the first
step is an amount sufficient to completely dissolve the binder at
200.degree. C. and the maximum amount is the amount sufficient to
completely dissolve the binder at around a normal temperature.
[0078] The boiling point of water in atmospheric air is 100.degree.
C., however the boiling point is increased by pressurization. FIG.
2 shows the solubility of magnesium sulfate heptahydrate in water
at different water temperatures. As being understood, the
solubility of magnesium sulfate is also increased as the
temperature of water is increased. For example, the solubility at
0.degree. C. is 53.9% and in such a case, the ratio of water to be
added is 46.1 to a binder 53.9. On the other hand, the solubility
at 200.degree. C. is 95.5% and the ratio of water is 4.5 to a
binder 95.5 to make it possible to considerably decrease the water
addition amount. However, since it is rather industrially difficult
to assemble an apparatus for pressurizing water and increasing the
boiling point of water to 200.degree. C. in a molding machine,
around 100C is supposed to be the maximum limit. The concentration
at 100.degree. C. is 74.7% and in such a case, the water content is
15.3 to a binder 74.7.
[0079] Next, as shown in FIG. 3, in the second step, the casting
sand S obtained in the first step is blown to a cavity 2 of a
ventilative ceramic die 1 for forming a core. The ceramic die 1 is
composed of an upper and a lower separate die parts 1a and 1b. The
ceramic die is covered with a case member 3 made of an aluminum.
When the casting sand S is packed in the cavity 2, pressurized air
is supplied to a blow head 4 installed on the top part of the
ceramic die 1 and the casting sand S is blown into the cavity 2 of
the ceramic die 1 for forming a core through the blow nozzle 5 and
thus the casting sand S is compressed and filled into the cavity 2
to form the casting sand S in a prescribed shape.
[0080] Further, as shown in FIG. 4, in the third step, while a
stirrer 6 being rotated so as to evenly radiate microwave to the
ceramic die 1 filled with the casting sand S, microwave is radiated
for a prescribed period from a magnetron 7. Being transmitted
through the ceramic die 1, the microwave works on the casting sand
S in the cavity 2. At that time, although water exists in two
states; free water and crystal water of inorganic sulfate
compounds; since free water has a higher dielectric constant than
that of the crystal water, free water is easily evaporated prior to
crystal water and accordingly, free water in the casting sand S can
be evaporated in such a state that the inorganic sulfate compounds
in the casting sand are kept retaining at least a portion of
crystal water. The moisture generated by evaporation is discharged
to the outside of the ceramic die by a suction pump 8 through a
suction hood 9 and a suction hose 10. Since the inorganic sulfate
compounds in the binder contain crystal water even in dry state by
drying the casting sand in such a manner to result in exhibition of
strength, the resulting mold obtained by such drying can surely be
provided with a sufficient strength.
[0081] Since the ceramic die 1 has the ventilation property, the
evaporated moisture can be released uniformly to the outside from
the ventilative ceramic die 1. Therefore, unevenness in the
quantity of crystal water contained in the inorganic sulfate
compounds can be restrained as small as possible and the strength
of the obtained mold can be made uniform.
[0082] A die forming the cavity 2 is not necessarily limited to the
ceramic die 1 and may be any die made of another material such as a
die made of a synthetic resin if it can transmit microwave.
[0083] In the third step, the casting sand S may be dried by
supplying hot air to the die filled with the casting sand S and
heating the casting sand S by the hot air. That is, as shown in
FIG. 5, hot air is supplied through an air hose 12 to an air hood
11 formed in the upper part of the die 1 and hot air is supplied to
the die 1 from the air hood 11 to heat the casting sand S packed in
the cavity 2 of the die 1. In that case, it is required to supply
the hot air at a proper temperature (for example, 200.degree. C. or
lower) for a sufficient supply time to avoid dehydration of the
inorganic sulfate compounds in the casting sand S.
[0084] The following methods are also applicable: a method for
filling the casting sand into a die heated to 200.degree. C. or
lower, thereby hardening the casting sand; a method for packing the
casting sand heated at 200.degree. C. or lower in a die so as to
evaporate water and thereby hardening the casting sand; a method
for packing the casting sand in a die and then evaporating water by
decreasing the pressure; and the like. Any method can be employed
if the method is capable of drying the casting sand in such a
manner that the inorganic sulfate compounds contained in the binder
are kept retaining crystal water.
[0085] The following effects can be provided by a water-soluble
casting mold of the invention and a method for manufacturing the
casting mold.
[0086] 1) Since a water-soluble casting mold is constituted by
using a binder containing inorganic sulfate compounds having high
solubility in water, the mold can easily be collapsed by being
submerged into water, and it is possible to recover easily the
binder and make the binder repeatedly usable at a high efficiency.
Further, since the melting point of the inorganic sulfate compounds
is 770.degree. C. or higher, when the mold is used for molding an
aluminum alloy castings, the inorganic sulfate compounds are
prevented from melting and vitrification. Therefore, the binder can
easily be recovered. Further, the gas generated at the time of
casting is only steam and therefore, the casting work can be
carried out in safe environmental conditions.
[0087] The inorganic sulfate compounds have higher strength in the
hydrate state containing crystal water than that in the anhydride
state, and in the dry state of the water-soluble casting mold of
the invention, since the inorganic sulfate compounds of the binder
contain crystal water, sufficiently high strength of the mold can
be assured. Further, a plurality of types of inorganic sulfate
compounds are mixed at prescribed ratios to form a mixed crystal at
the time of drying the casting sand, so that the peak for
exhibiting the strength in the entire binder can be moderated and
the strength can be obtained in a wide range of mole ratios and
accordingly, even if the quantity of the crystal water fluctuates
or the content of the crystal water in the mold is rather variable,
the strength of the entire body of the mold can sufficiently be
retained.
[0088] 2) Since the binder contains 0.5 to 10.0 parts by weight of
magnesium sulfate, the mold is provided with sufficient strength
with a proper amount of magnesium sulfate and the amount of water
to be added to dissolve magnesium sulfate can be suppressed and
therefore, the filling property of the casting sand is kept
excellent. Further, since magnesium sulfate can bring strength more
in hydrate state, particularly in form of tri to tetrahydrate
state, than in dehydrated state, proper strength of the mold can be
assured by setting magnesium sulfate in the mold to contain crystal
water equivalent to mono- to pentahydrate in dry state.
[0089] 3) Use of a binder obtained by mixing at prescribed ratios
of phosphate compounds and magnesium chloride with the inorganic
sulfate compounds makes it possible to assure the water-solubility
of the mold and improve the heat resistance at the time of pouring
molten metal.
[0090] 4) At the time of manufacturing a water-soluble casting
mold, casting sand obtained by adding a water-soluble binder
containing inorganic sulfate compounds and water in a proper amount
to solve the inorganic sulfate compounds to the refractory granular
material is dried by radiating microwave, so that free water in the
casting sand which has a higher dielectric constant than crystal
water contained in the inorganic sulfate compounds can easily be
evaporated prior and the casting sand can be dried in such a manner
that the inorganic sulfate compounds are kept retaining at least a
portion of crystal water. The same effects can be obtained by
supplying hot air to the casting sand at a prescribed temperature
or lower at which the inorganic sulfate compounds are
dehydrated.
[0091] 5) At the time of manufacturing a water-soluble casting
mold, the casting sand is formed by filling a cavity of a
ventilative ceramic die with the casting sand and in the case of
drying the casting sand after formation, the evaporated moisture
can be released evenly to the outside from the ventilative ceramic
die. Accordingly, unevenness in the content of crystal water in the
inorganic sulfate compounds can be restrained as small as possible
and consequently, the strength of the mold can be made uniform.
* * * * *