METHOD OF MANUFACTURING EXPENDABLE SALT CORE FOR CASTING AND EXPENDABLE SALT CORE FOR CASTING
A die casting method for forming an expandable salt core includes, first, a salt mixture containing at least a potassium salt and a sodium salt is melted by heating to obtain a melt. Subsequently, the temperature of the melt is decreased to set the melt in a semi-solidified (solid-liquid coexisting) state. The melt in the semi-solidified state is injected into a metal mold under a high pressure and solidified. After solidification, the obtained expendable salt core is taken out of the metal mold.
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1. Field of the Invention
The present invention relates to a method of manufacturing a water soluble expendable salt core, and an expendable salt core.
2. Description of the Related Art
As is well known, casting methods such as aluminum high pressure die casting (HPDC) is a technique that injects a molten aluminum alloy into a metal mold at high speed under a high pressure in order to cast a near-net-shaped structure. In this casting, when molding a cast product having a hollow structure, e.g., a water cooling water jacket in a closed-deck type cylinder block of an internal combustion engine, an expendable core is used. The expendable core used in these instances must have a strength that can withstand a high pressure and high temperature because it may be subject to a large impact or impulse force fluctuation upon collision of a molten metal injected from the gate at high speed mold filling and because a high static compressive casting pressure is applied until solidification completion. After casting, the expendable core is removed from the cast product. When the cast product has a complicated internal structure, if a commonly used phenol resin bonded sand core is used as the expendable core, it is not easy to remove. In contrast to this, a water soluble expendable salt core is available as the expendable core that can be removed by dissolution with, e.g., high-temperature water (see Japanese Patent Laid-Open No. 48-039696, Japanese Patent Laid-Open No. 50-136225, and Japanese Patent Laid-Open No. 52-010803).
The expendable salt core described above is formed by using a salt mixture of, e.g., sodium carbonate (Na2CO3), potassium chloride (KCl), and sodium chloride (NaCl), melting these components, and molding. Hence, a high static compressive casting pressure resistance is obtained, and workability and stability of dimension accuracy in casting are improved.
However, when an expendable fused salt core is formed by melting a salt and casting the formation of a shrinkage cavity, micro-porosity, small heat cracks, and the like are caused in the salt core due to a change in volume such as solidification shrinkage occurring in the solidification process. It is therefore not easy to mold the expendable fused salt core so that it will precisely conform to the mold. Also, depending on the composition of the respective components, the resultant melting point is 700° C. or more, which is not suitable for molding by melting. In this manner, with the prior art, an expendable fused salt core cannot be manufactured easily by casting using a molten salt.
SUMMARY OF THE INVENTIONThe preferred embodiments of the present invention have been made to solve the above problems, and are able to facilitate a manufacture of a water soluble expendable salt core which is formed of a salt cast product obtained by molding after melting salts such as sodium and potassium.
A method of manufacturing an expendable salt core according to a preferred embodiment of the present invention comprises at least a first step of heating a salt mixture containing at least a potassium salt and a sodium salt to form a melt in a solid-liquid coexisting state in which a solid phase and a liquid phase coexist, a second step of charging the melt in the solid-liquid coexisting state into a core mold, and a third step of solidifying the melt in the mold to mold an expendable salt core for casting. Therefore, at the point when the mold is charged with the melt, the melt is partly solidified.
An expendable salt core according to the present invention is molded by heating a salt mixture containing at least a potassium salt and a sodium salt to provide a melt in a solid-liquid coexisting state in which a solid phase and a liquid phase coexist, charging the melt in the solid-liquid coexisting state into a core mold, and solidifying the melt in the mold. This expendable salt core for casting includes, e.g., a core to mold a water jacket for water cooling a closed-deck type cylinder block of engine.
According to preferred embodiments of the present invention, an expendable salt core is cast using a melt in a solid-liquid coexisting state. Therefore, a water soluble expendable salt core is made of a salt cast product, which is molded by melting salts such as sodium and potassium, and can be easily manufactured.
Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.
Preferred embodiments of the present invention will be described hereinafter with reference to the drawings. First, how an expendable salt core for casting according to a preferred embodiment of the present invention is used will be described with reference to
The cylinder block 1 shown in
The cylinder body 4 is a so-called closed-deck-type cylinder body, and has a water jacket 6 which is provided in it using the expendable salt core 2. The water jacket 6 is arranged to include a cooling water passage forming portion 7, cooling water inlet port 8, main cooling water passage 9, and communication passage 10. The cooling water passage forming portion 7 projects on one side of the cylinder body 4 and extends in the direction in which the cylinder bores 3 line up with one another. The cooling water inlet port 8 is provided in the cooling water passage forming portion 7. The main cooling water passage 9 is provided to communicate with a cooling water distribution passage (not shown) provided in the cooling water passage forming portion 7 and cover all the cylinder bores 3. The communication passage 10 extends upward in
The water jacket 6 described above supplies cooling water flowing in from the cooling water inlet port 8 to the main cooling water passage 9 around the cylinder bores through the cooling water distribution passage, and guides the cooling water from the main cooling water passage 9 to a cooling water passage in the cylinder head (not shown) through the communication passage 10. Since the water jacket 6 is provided in this manner, the cylinder body 4 is covered with the ceiling wall (the wall that provides the mating surface 4a) of the cylinder body 4 except that the communication passage 10 of the water jacket 6 opens to the mating surface 4a at the upper end to which the cylinder head is connected. Hence, a closed-deck-type arrangement is provided.
The expendable salt core 2 has a shape identical to that obtained by integrally connecting the respective portions of the water jacket 6. In
The expendable salt core 2 according to this preferred embodiment is formed using a plurality of types of salts such as sodium carbonate, sodium chloride, and potassium chloride by, e.g., die casting in a solid-liquid coexisting state such as a semi-solidified state into the shape of the water jacket 6. The expendable salt core 2 may be formed by heating a salt mixture containing at least a potassium salt and a sodium salt to form a melt in a solid-liquid coexisting state in which a solid phase and liquid phase coexist, charging the melt into a core mold, and solidifying the melt in the mold. A method for manufacturing the expendable salt core 2 will be described later in detail.
Note that the expendable salt core 2 can be formed by a casting method other than die casting, e.g., gravity casting. In forming the expendable salt core 2 which employs die casting, first, a mixture consisting of a plurality of salts (to be described later) is melted by heating to obtain a melt. Then, the temperature of the melt is decreased to set the melt in a semi-solidified (solid-liquid coexisting) state. The melt in the semi-solidified state is injected into an expendable salt core forming metal mold under a high pressure and solidified. After solidification, the obtained expendable salt core 2 is taken out from the mold.
As shown in
To remove the expendable salt core 2 after casting, the cylinder block 1 may be dipped in a dissolution tank (not shown) which contains dissolving liquid consisting of hydrochloric acid and hot water. When dipping the cylinder block 1 in the dissolving liquid, the passage forming portion 2a and the projections 2c exposed to the mating surface 4a, of the expendable salt core 2 come into contact with the dissolving liquid and dissolve. Dissolving portions expand gradually until all of the portions completely dissolve. In this core removing process hot water or vapor may be sprayed under a pressure from a hole to promote dissolution of the expendable salt core 2 left in the water jacket 6. In the expendable salt core 2, in place of the projections 2c, a core print may be inserted in portions where the projections 2c are to be provided.
If hydrochloric acid is used in the process of removing the expendable salt core 2 from the cylinder block 1 as a cast product, carbon dioxide gas will foam. The foam provides a stirring function and promotes effective dissolution. Because the expendable salt core 2 contains potassium carbonate and sodium carbonate, when it is dissolved in water, the resultant water will exhibit alkaline. This alkali state poses problems such as corrosion of the cylinder block 1 which is an aluminum cast product. Regarding this problem, corrosion of the cylinder block can be prevented by adding hydrochloric acid to maintain pH to near 7.
A method of manufacturing the expendable salt core 2 will now be described in detail. First, a case will be described in which the melt is not injected (pressure-injected) under a high pressure as in die casting, but flowed (poured) into the metal mold to manufacture the expendable salt core 2 (gravity casting). To form the expendable salt core 2 of this preferred embodiment, first, sodium carbonate, potassium carbonate, sodium chloride, and potassium chloride are mixed and heated until they are melted, thus preparing a melt of a salt mixture. For example, when the salts are mixed such that a molar ratio XK+ (=[K+]/([Na+]+[K+])×100) of potassium ions in the entire cations is 33 mol % and that a molar ratio YCO32− (=[CO32−]/([CO32−]+[Cl−])×100) of carbonate ions in the entire anions is 67 mol %, the salt mixture dissolves at 647° C. For example, the salt mixture described above may be put in an alumina crucible and dissolved in an electric furnace.
Subsequently, when the temperature of the salt mixture accommodated in the crucible reached about 647° C., which is a liquidus temperature or more, the crucible was taken out from the electric furnace and air-cooled. The cooling speed was about 0.3° C. to about 1.2° C. per sec. At this time, the salt mixture in the crucible was stirred with an alumina stirrer with a rotation speed of about 3 rps, and was poured into the metal mold when the temperature of the melt of the salt mixture was about 638° C. When the melt of the salt mixture is about 638° C., the melt is in a semi-solidified state in which the solid phase and liquid phase coexist. The melt in this state is charged into a metal mold for an expendable salt core and solidified, and is taken out from the metal mold after solidification. In the above description, after the salt mixture was heated to set it in a liquid-phase-only state, it was cooled, thus obtaining a melt in a solid-liquid coexisting state. However, the present invention is not limited to this. A melt in the semi-solidified state may also be obtained by heating the salt mixture to a semi-solidification temperature.
The thus obtained expendable salt core 2 had a strength (bending strength) as high as about 21.4 MPa to about 24.6 MPa. The solidification structure of the expendable salt core 2 comprised fine crystal particles as is seen from the photograph shown in
As described above, in the process of cooling the dissolved melt, when the melt temperature reaches the liquidus temperature (melting point) or less, a plurality of solid phase particles are formed and dispersed in the remaining liquid phase. At this time, when stirring the melt in the semi-solidified state, a state can be obtained in which the solid phase is dispersed more evenly in the liquid phase. Note that stirring is not always necessary.
As an example,
As described above, stirring may be performed, although it is not necessary. Stirring can decrease the temperature distribution in the salt mixture in the solid-liquid coexisting state so that a salt mixture with an even solid phase ratio can be obtained more easily. Also, because stirring can miniaturize and spheroidize solid phase particles in the salt mixture in the solid-liquid coexisting state, it improves moldability. When molding a core with a high solid phase ratio, stirring is preferred. When mechanical stirring is to be performed, a ceramic stirrer which is resistant to corrosion by a molten salt may be employed.
When core molding is initiated in the semi-solidified state having the characteristic features as described above, the amount of solidification shrinkage occurring in the solidification process can be suppressed. Thus, a shrinkage cavity, micro-porosity, small heat crack, or the like which is formed in the expendable salt core can be suppressed. As the amount of solidification shrinkage can be suppressed, the expendable salt core can be more precisely molded to be true to the mold. When casting is initiated in the completely molten state as in the conventional case, the amount of solidification shrinkage is large, so that a shrinkage cavity, micro-porosity, small heat crack, or the like is formed often. The semi-solidification method can suppress these defects, thus improving the strength.
According to the melting molding method, the amount of solidification shrinkage of the core to be molded is larger than the amount of shrinkage of the metal mold. When molding a cylindrical annular core such a water jacket in a cylinder, a shrinkage cavity, micro-porosity, small heat crack, or the like may be formed in the expendable salt core. Depending on the case, the expendable salt core may be broken in the mold. In contrast to this, as described above, use of a melt in the semi-solidified state can reduce the ratio of solidification shrinkage. As a result, a cylindrical annular core such as a water jacket can be formed.
In injection molding using a melt, if the melt is injected with an injection force larger than the machine clamp force of the mold, the melt is scattered from the parting surface, i.e., so-called flushing occurs. In contras to this, in injection molding using a melt in a solid-liquid coexisting state, the leading end of the melt solidifies immediately. Even if the melt is injected with an injection force larger than the mold cavity projected area, flushing does not occur. Therefore, during solidification shrinkage of the melt, a large injection pressure can be applied to replenish the melt, so that the shrinkage cavity can be eliminated. When the melt in the solid-liquid coexisting state is employed, casting can be performed at a temperature lower than that required by the completely molten state. This can improve the workability and decrease the heat load to the casting mold.
As opposed to metals, salt will not oxidize. Even when stirring described above is performed in the atmosphere, no oxide is caught in the melt. Thus, the melt can be stirred easily for a long period of time. Even when molding an annular shape from a semi-solidified state, no oxide skin is formed on a confluence-junction portion on the opposite side of the melt which separates from the gate into two groups in the circumferential direction. Hence, cold shut does not occur, and separation at the bonding portion does not occur after molding.
In order to obtain the solid-liquid coexisting state, the melt is cooled from the molten state to a semi-solidified range, thus achieving the solid-liquid coexisting state. However, the present invention is not limited to this. For example, a salt mixture in the solid phase may be heated to a semi-molten range so that a solid-liquid coexisting state is obtained. A solid powder salt (salt mixture) may be added to a molten salt so that a solid-liquid coexisting state is obtained. Alternatively, a molten salt may be added to a preheated solid salt (salt mixture) so that a solid-liquid coexisting state is obtained.
In the above description, a case in which sodium carbonate, potassium carbonate, sodium chloride, and potassium chloride are mixed such that the molar ratio XK+ (=[K+]/([Na+]+[K+])×100) of potassium ions in the entire cations is 33 mol % and that the molar ratio YCO32− (=[CO32−]/([CO32−]+[Cl−])×100) of carbonate ions in the entire anions is 67 mol % is described. However, the present invention is not limited to this. For example, when the salt mixture has any one of the compositions shown in the following Tables 1 and 2, casting using a melt in a semi-solidified state is possible. In any case, the salt mixture is formed of only potassium ions, sodium ions, chloride ions, and carbonate ions.
Table 1 also shows the measurement results (maximum bending loads) of the bending strengths of the fabricated test pieces, and Table 2 also shows the measurement results (maximum bending strengths) of the bending strengths of the fabricated test pieces. Tables 1 and 2 are identical except that representations of the measurement results are different. The state of the bending load and that of the bending strength are shown in
As is apparent from Tables 1 and 2,
Measurement of the bending strength will now be described. To measure the bending strength, a prismatic test piece with a predetermined size is fabricated. A load is applied to the test piece, and the bending load is obtained from the maximum load needed to break the test piece. Fabrication of the test piece will be described first. A rod-like test piece 901 as shown in
To measure the bending strength of the rod-like test piece 901 fabricated in the above manner, first, as shown in
A bending strength σ (MPa) can be obtained from a bending load P in accordance with an equation σ=3LP/BH2 where H is the length of the load direction in the section of the test piece, B is a length perpendicular to the load direction in the section of the test piece, and L is the distance from the support portions 1001 serving as fulcrums to the load portions 1002 where the load acts. Although the test piece 901 is formed by pouring the melt in the solid-liquid coexisting state into the metal mold, it is difficult to form a test piece completely free from flow marks or shrinkage cavity and having a shape completely coinciding with the size true to the mold. Therefore, the bending strength is calculated based on an approximation that the test piece has a rectangular section and that H≈20 mm, B≈18 mm, and L=20 mm. Due to this approximation, the estimated strength is lower than the actual strength by approximately 0% to approximately 20%. For example, it can be assumed that a test piece which is broken by a bending load of 1200N is stronger than an ideal test piece having a bending strength of 10 MPa.
A method of manufacturing another expendable salt core according to another preferred embodiment of the present invention will be described. The following description exemplifies a case in which a mold (metal mold) is charged with a melt under a pressure to manufacture an expendable salt core 2 (die casting). A close-packed alumina crucible made of the same material as that of a Tamman tube is employed as the crucible. A predetermined amount of salt mixture consisting of sodium carbonate, potassium carbonate, sodium chloride, and potassium chloride is put in the crucible, the crucible is placed in a heating furnace, and the temperature is raised. For the purpose of protection of the crucible, the temperature is raised gradually to reach the target temperature in about 14 hours.
The target temperature is set at a value higher than the liquidus temperature corresponding to the molar ratio of the salt mixture by about 10 to about 30° C. Once the temperature reaches the target temperature, it is held at the target temperature. The temperatures of the metal mold and injection sleeve are set to approximately 180 to approximately 220° C. As the metal mold, one that can be heated to a mold temperature of about 250° C. is preferable. Also, a metal mold is preferred the casting cavity of which can be eliminated by applying a casting injection pressure of as high as about 120 MPa at maximum.
Subsequently, the melt of the salt mixture which is molten in the crucible is dipped up with a dipper. Prior to dipping up, the dipper must be heated to about 500° C. to about 600° C. by a heating device such as a burner. As soon as the melt in the crucible is dipped up with the dipper, it is started to be gradually deprived of heat by the dipper. Thus, the temperature of the melt decreases to be lower than the liquidus temperature, thus providing the solid-liquid coexisting state. During dipping up, the melt is stirred as it is shaken in the moving dipper, and primary crystals are deposited to form particles. In this manner, during the process of transporting the melt from the crucible and pouring it into the injection sleeve, the melt of the salt mixture in the dipper is set in the solid-liquid coexisting state.
When pouring the melt of the salt mixture in the semi-solidified state into the injection sleeve in this manner, the semi-solidified state progresses in the sleeve as well. Subsequently, the melt is injected into the cavity under high pressure. After charging with the melt, the casting pressure is continuously applied into the mold. For example, a pressure of about 120 MPa in the pressure ratio of a hydraulic cylinder which advances the plunger is applied into the mold. In this process, the plunger is advanced to replenish solidification shrinkage that takes place during solidification, thus continuously applying the pressure of about 120 MPa. The solidification time is about 65 to about 75 sec. In the solidification process, the plunger is continuously moved forward as long as solidification shrinkage can be replenished, thus continuously applying the pressure of about 120 MPa.
After charging the mold with the melt under the pressure and solidifying the melt in the above manner, the solidified expendable salt core is taken out from the mold. A push pin and return pin may be placed in the stationary mold so that when the mold is opened, the obtained salt core is released from the stationary mold well. The taken-out expendable salt core may be gradually cooled, and the cooled expendable salt core may be put in a dried container.
An example will be described regarding the manufacturing conditions and strength measurement result of the expendable salt core which is manufactured by injecting into a metal mold under a high pressure a melt of a salt mixture in a semi-solidified state in which the solid phase and liquid phase coexist.
The conditions are as follows:
(1) The test piece subjected to strength measurement had an almost rectangular solid shape in the same manner as in
(2) The melt was fabricated by mixing sodium carbonate, potassium carbonate, sodium chloride, and potassium chloride and melting them. The resultant melt was adjusted such that the molar ratio XK+ (=[K+]/([Na+]+[K+])×100) of potassium ions in the entire cations was 30 mol % and that a molar ratio YCO32− (=[CO32−]/([CO32−]+[Cl−])×100) of carbonate ions in the entire anions was 54 mol %.
(3) The liquidus temperature of the salt mixture is 630° C.
(4) The salt mixture contained in the crucible was dissolved by gradually raising the temperature to exceed the liquidus temperature of 630° C. in 14 hours. Then, the dissolved melt was held at 640 to 660° C. The temperature was controlled automatically.
(5) The dipper was heated to about 500° C. to about 600° C.
(6) The melt was dipped up with the dipper and cooled in the dipper to about 630° C. or less, so that the melt was set in the semi-solidified state.
(7) The sleeve temperature and metal mold temperature were about 180° C. to about 220° C.
(8) When the temperature of the melt of the salt mixture was 620° C. in the injection sleeve, the melt was injected into the metal mold under a high pressure as indicated by an injection curve to be described later. When the temperature of the melt of the mixture salt is 620° C., the melt is in the semi-solidified state in which the solid and liquid coexist.
To measure the pressure in the cavity, the pressures acting on the push pins provided to two portions, i.e., a gate portion 1101 shown in
In die casting of a metal, such as aluminum, the melt has high thermal conductivity and requires a short solidification time. Hence, that portion of the melt which is located at the intermediate portion of the mold often solidifies before that portion of the melt which is located at the distal end of the mold. Then, the distal end of the mold may not be sufficiently replenished with the melt. In contrast to this, a molten salt has low thermal conductivity and requires a solidification time about three times that of aluminum. Accordingly, as shown in
Test pieces manufactured as described above were subjected to bending strength measurement in the same manner as described above. A high strength exceeding about 40 MPa was obtained as shown in the following Tables 3 and 4. In general, a bending strength of about 20 MPa to about 37 MPa is obtained by a widely employed expendable salt core which is manufactured by sintering after press molding (see, for example: U.S. Pat. No. 3,963,818). According to this preferred embodiment, a higher bending strength is obtained. With an expendable salt core which is manufactured by sintering after press molding, a complicated shape such as a water jacket cannot be formed. According to this preferred embodiment, however, an expendable salt core with a complicated shape can be manufactured easily. As the expendable salt core of this preferred embodiment is formed by solidifying a molten salt, the surface state of the expendable salt core reflects the surface state of the metal mold, so that a smooth surface can be obtained. Therefore, in a cast product using the expendable salt core according to this preferred embodiment, a portion which is in contact with the expendable salt core is formed to be highly smooth.
Although a salt mixture of sodium carbonate, potassium carbonate, sodium chloride, and potassium chloride is used in the above description, the present invention is not limited to this. For example, potassium carbonate, sodium chloride, and potassium chloride may be mixed, or sodium carbonate, sodium chloride, and potassium chloride may be mixed. Alternatively, other salts such as sodium bromide, potassium bromide, sodium iodide, potassium iodide, calcium chloride, potassium nitrate, sodium nitrate, potassium sulfate, lithium sulfate, magnesium sulfate, sodium sulfate, barium carbonate, and calcium carbonate may be mixed. A reinforcing ceramic material or any other reinforcing agent may be contained in the mixture.
Another example of how an expendable salt core according to a preferred embodiment of the present invention is used will be described with reference to
The cylinder block 1301 shown in
The cylinder body 1304 is a so-called closed-deck-type cylinder body, and has a water jacket 1306 which is provided in the cylinder body 1304 using the expendable salt core 1302. The water jacket 1306 is arranged to include a cooling water passage forming portion (not shown), a cooling water inlet port (not shown), a main cooling water passage 1309, and a communication passage 1310. The cooling water passage forming portion projects on one side of the cylinder body 1304. The cooling water inlet port is provided in the cooling water passage portion. The main cooling water passage 1309 is arranged to communicate with a cooling water supply passage (not shown) provided in the cooling water passage forming portion and cover the cylinder bore 1303. The communication passage 1310 extends upward in
The water jacket 1306 described above supplies cooling water flowing in from the cooling water inlet port (not shown) to the main cooling water passage 1309 around the cylinder bore through the cooling water supply passage, and guides the cooling water from the main cooling water passage 1309 to a cooling water passage in the cylinder head (not shown) through the communication passage 1310. Since the water jacket 1306 is provided in this manner, the cylinder body 1304 is covered with the ceiling wall (the wall that forms the mating surface 1304a) of the cylinder body 1304 except that the communication passage 1310 of the water jacket 1306 opens to the mating surface 1304a at the upper end to which the cylinder head is connected. Hence, a closed-deck-type arrangement is provided.
The expendable salt core 1302 to form the water jacket 1306 has a shape identical to that obtained by integrally connecting the respective portions of the water jacket 1306, as shown in the photograph of
The expendable salt core 1302 shown in
As shown in
To remove the expendable salt core 1302 after casting, the cylinder block 1301 may be dipped in a dissolution tank (not shown) which contains dissolving liquid including of hydrochloric acid, hot water, or the like. When dipping the cylinder block 1301 in the dissolving liquid, the cooling water inlet port of the cooling water passage portion (not shown) and the projections 1302a exposed to the mating surface 1304a, of the expendable salt core 1302 come into contact with the dissolving liquid and dissolve. The dissolved portions expand gradually until all the portions dissolve finally. In this core removing process, to promote dissolution of the expendable salt core 1302 left in the water jacket 1306, hot water or vapor may be sprayed from a hole under pressure. In the expendable salt core 1302, in place of the projections 1302a, a core print may be inserted in portions where the projections 1302a are to be provided.
As described above, according to the present invention, the annular expendable salt core 1302 can be formed easily. Note that the region of the core print shown in the photograph of
Preferred embodiments of the present invention can be suitably used as a core for a casting such as aluminum die casting.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
Claims
1-13. (canceled)
14: A method of manufacturing an expendable salt core comprising:
- a first step of heating a salt mixture containing at least a potassium salt and a sodium salt to form a melt in a solid-liquid coexisting state in which a solid phase and a liquid phase coexist;
- a second step of charging said melt in the solid-liquid coexisting state into a core mold; and
- a third step of solidifying the melt in the mold to mold an expendable salt core for casting.
15: A method of manufacturing an expendable salt core according to claim 14, wherein:
- in the first step, the salt mixture is heated to be set in a liquid-phase-only state, and thereafter the salt mixture is cooled, thus forming the melt in the solid-liquid coexisting state.
16: A method of manufacturing an expendable salt core according to claim 14, wherein:
- in the second step and the third step, the mold is charged with the melt under pressure and the melt is solidified.
17: A method of manufacturing an expendable salt core according to claim 16, wherein:
- the pressure is applied evenly until the mold is opened.
18: A method of manufacturing an expendable salt core according to claim 14, wherein:
- the salt mixture is formed of only potassium ions, sodium ions, chloride ions, and carbonate ions; and
- a molar ratio of the potassium ions in all the cations is about 50 mol % at maximum and a molar ratio of carbonate ions in all the anions is about 30 mol % to about 80 mol %.
19: A method of manufacturing an expendable salt core according to claim 18, wherein:
- in said salt mixture, the molar ratio of the potassium ions in all the cations is 40 mol % at maximum and the molar ratio of carbonate ions in all the anions is 50 to 70 mol %.
20: A method of manufacturing an expendable salt core, the method comprising:
- molding an expendable salt core by heating a salt mixture containing at least a potassium salt and a sodium salt to form a melt in a solid-liquid coexisting state in which a solid phase and a liquid phase coexist;
- charging the melt in the solid-liquid coexisting state into a core mold; and
- solidifying the melt in the mold.
21: The method of manufacturing an expendable salt core according to claim 20, wherein:
- the melt in the solid-liquid coexisting state is formed by heating the salt mixture to be set in a liquid-phase-only state, and thereafter cooling the salt mixture.
22: The method of manufacturing an expendable salt core according to claim 20, wherein:
- the expendable salt core is formed by charging the mold with the melt under a pressure and then solidifying the melt.
23: The method of manufacturing an expendable salt core according to claim 22, wherein:
- the pressure is applied evenly until the mold is opened.
24: The method of manufacturing an expendable salt core according to claim 20, wherein:
- the salt mixture is formed of only potassium ions, sodium ions, chloride ions, and carbonate ions; and
- a molar ratio of the potassium ions in all cations is about 50 mol % at maximum and a molar ratio of carbonate ions in all the anions is about 30 mol % to about 80 mol %.
25: The method of manufacturing an expendable salt core according to claim 24, wherein:
- the molar ratio of the potassium ions in all the anions is about 40 mol % at maximum and the molar ratio of carbonate ions in all the cations is about 50 mol % to about 70 mol % in the salt mixture.
26: The method of manufacturing an expendable salt core according to claim 20, wherein:
- the expendable salt core includes a core to mold a water jacket arranged to water cool a closed-deck type cylinder block of engine.
Type: Application
Filed: May 18, 2007
Publication Date: Aug 20, 2009
Applicant: YAMAHA HATSUDOKI KABUSHIKI KAISHA (Iwata-shi, Shizuoka)
Inventors: Jun Yaokawa (Miyagi), Koichi Anzai (Miyagi), Youji Yamada (Shizuoka)
Application Number: 12/301,073
International Classification: B22C 9/10 (20060101); B22C 1/00 (20060101);