Method for producing light-alloy casting

Abstract

A light-alloy casting producing method is provided in which a T6 treatment can be given to a light-alloy casting without any heat treatment furnace (or aging furnace), so that its mechanical properties such as tensile strength can be adequately heightened. This method includes: a mold preparing process of preparing a mold which includes a sand mold part which is provided with a riser section, and a metal mold part which is disposed apart from the riser section, the sand mold part and the metal mold part forming a cavity section; a casting process of pouring a molten light-alloy into the cavity section of the mold; a metal mold part removing process of separating the metal mold part from a casting which is formed by pouring; a quenching process of bringing a cooling medium into contact with the surface of the casting from which the metal mold part is removed, and thereby, cooling the casting rapidly; an aging process of covering the metal mold part-removed section of the casting with a heat keeper, and keeping the whole casting which is surrounded with the sand mold part and the heat keeper at an aging temperature for a predetermined period of time, using the heat which is kept by a riser portion.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for producing a light-alloy casting in which a casting made of a light alloy, such as an aluminum alloy and a magnesium alloy, is cast using a mold.

2. Description of the Related Art

In general, an aluminum-alloy casting or a magnesium-alloy casting undergoes a heat treatment in order to enhance its mechanical properties such as the strength.

As such heat treatment, the so-called T6 treatment is effective. The T6 treatment is a heat treatment where an artificial age-hardening treatment follows a solution treatment. In the case where an aluminum-alloy casting is subjected to the T6 treatment, a solution treatment is given, for example, for 8 to 10 hours at a temperature of approximately 500° C., and then the age hardening treatment is conducted for 5 to 10 hours at a temperature of about 180° C. This age hardening treatment is given to the aluminum-alloy casting which is placed in a heating furnace (i.e., an aging furnace). This presents a disadvantage in that as a matter of course, the heating furnace is needed for the heat treatment. In addition, disadvantageously, the efficiency of production becomes lower, and more energy is consumed.

As a method of producing an aluminum-alloy casting using a mold, the following method is disclosed in Japanese Patent No. 3068185 which corresponds to U.S. Pat. Nos. 5,297,611 and No. 5,477,906.

Specifically, in the case where a cylinder block for a V-type engine is made by casting an aluminum-alloy in a mold comprising a sand mold part and a metal mold part. The portion of the cylinder block that defines a combustion chamber is formed with the metal mold, and the other portion is formed with the sand mold part. The mold has a cavity section, a riser section, and a runner. A sealing mechanism is provided to the runner. A molten aluminum-alloy is upwardly poured into the cavity section through the runner, the opened sealing mechanism and the riser section. Next, the sealing mechanism is closed, and the whole mold is turned over. The metal mold part is first removed after the molten alloy is solidified. The mold-removed surface of the casting is cooled using a liquid cooling medium to cause directional solidification.

However, in the conventional method disclosed in the above-mentioned Japanese Patent, the whole mold is required to be turned over, which results in the disadvantage that the casting apparatus has a complicated construction. Further, this patent does not refer to the solution treatment (or quenching treatment) and the aging treatment after casting that serve to increase the mechanical properties such as strength of the aluminum-alloy casting.

Another conventional method is disclosed in Japanese Patent Laid-Open No. 8-225903. In this conventional method, a molten aluminum-alloy is filled into a metal mold part with pressurized at a pouring pressure of 49 MPa or more, and it is solidified. After being solidified, it is taken out, and it is immersed in water to be quenched. After being quenched, it undergoes an artificial aging treatment.

This conventional method is a method in which casting is conducted using only metal mold parts. Besides, the above-described heat treatment, i.e., quenching treatment and age hardening treatment, are conducted after the casted product is taken out from the metal mold part. In such respects, an aging furnace is inevitably required for the artificial aging treatment, and thus, energy consumption is presumed to rise.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a light-alloy casting production method which is free from the problems residing in the prior art.

According to an aspect of the present invention, a light-alloy casting is produced by: preparing a casting mold including a sand mold part provided with a riser section, and a metal mold part disposed apart from the riser section, the sand mold part and the metal mold part forming a cavity section; pouring a molten light-alloy into the cavity section of the casting mold; removing the metal mold part from a casting of the light-alloy; allowing a mold-removed surface of the casting to come into contact with a cooling medium to thereby quench the mold-removed surface; and aging the casting by heat retained by a solidified light-alloy in the riser section for a predetermined period of time.

This production method enables a heat treatment without any heat treatment furnace, and can produce a light-alloy casting having increased mechanical properties such as tensile strength.

These and other objects, features and advantages of the present invention will become more apparent upon reading of the following detailed description along with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a mold according to an embodiment of the present invention, showing the mold constructed by a sand mold part and a metal mold part.

FIG. 2 is a flowchart showing a first production flow according to the embodiment.

FIG. 3 is a sectional view of the mold in which a molten light-alloy is poured.

FIG. 4 is a sectional view of the mold in which the light-alloy is solidified.

FIG. 5 is a sectional view of the mold, the metal mold part being removed.

FIG. 6 is a sectional view, showing that an exposed surface of the casting is rapidly cooled with the sand mold part kept attached thereto.

FIG. 7 is a sectional view, showing that the casting is covered with the sand mold part and a heat keeper for aging process.

FIG. 8 is a graph showing a change in temperature at different portions of the casting after the metal mold part is removed.

FIG. 9 is a graph showing a difference between a tensile strength of a casting produced according to the embodiment and a tensile strength of a casting according to the prior art.

FIG. 10 is a graph showing a difference between 0.2% proof strength of a casting produced according to the embodiment and 0.2% proof strength of a casting according to the prior art.

FIG. 11 is a graph showing a difference between a rupture elongation of a casting produced according to the embodiment and a rupture elongation of a casting according to the prior art.

FIG. 12 is a flowchart showing a second production flow according to the embodiment.

FIG. 13 is a sectional view, showing that a casting is rapidly cooled with the sand mold part kept attached thereto.

FIG. 14 is a sectional view, showing that the rapidly cooled casting is slowly cooled with the sand mold part kept attached thereto.

FIG. 15 is a sectional view, showing that the casting is covered with the sand mold part and a heat keeper for aging process.

FIG. 16 is a graph showing a change in temperature at different portions of the casting after the metal mold part is removed.

FIG. 17 is a flowchart showing a third production flow according to the embodiment.

FIG. 18 is a sectional view, showing that a casting is rapidly cooled with the sand mold part kept attached thereto.

FIG. 19 is a sectional view, showing that a casting with the sand mold part kept attached thereto is rapidly cooled after a cooling guide plate is attached thereto.

FIG. 20 is a sectional view, showing that a casting is immersed in water and the sand mold part is broken up.

FIG. 21 is a sectional view, showing that the casting is covered with a heat keeper for aging process.

FIG. 22 is a graph showing a change in temperature at different portions of the casting after the metal mold part is removed.

FIG. 23 is a flowchart showing a fourth production flow according to the embodiment.

FIG. 24 is a sectional view, a casting with the sand mold part attached thereto being placed on a lifting apparatus.

FIG. 25 is a sectional view, showing that the casting with sand mold parts attached thereto is immersed in water for quenching.

FIG. 26 is a graph showing a change in temperature at different portions of the casting after the metal mold part is removed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

A preferred embodiment of the present invention will be described with reference to production of a cylinder head made of an aluminum alloy, e.g., an aluminum alloy defined as Japanese Industrial Standard (JIS) AC4B. However, this production method may be applicable for production of a cylinder head made of a magnesium alloy, or other light alloy.

With reference to FIG. 1 showing a sectional view of a mold for producing a cylinder head, a mold is configured by a plurality of sand mold parts 1 to 5 and cores 6, and a metal mold part 7. Among the plurality of sand mold parts 1 to 5, the sand mold parts 1, 2 and 3 form a riser section 8. At the end of this riser section 8 in the direction (i.e., the longitudinal direction) of a line of cylinders of the cylinder head, a pouring gate 9 is formed through which a molten aluminum alloy or a molten magnesium alloy is poured in as a molten light alloy.

Among the plurality of sand mold parts 1 to 5, the sand mold parts 3, 4, 5 and the metal mold part 7 which is placed apart from the riser section 8 form a cavity section 10. Inside of this cavity section 10, the cores 6 are placed which are each molded using a sand mold part. In addition, a plurality of runners 11 (herein, for the sake of convenience, only one runner is shown in the figure) which are formed in the sand mold part 3 lead to the riser section 8 on the upside and the cavity section 10 on the downside.

Herein, the surface of a light-alloy casting that is to be formed with the metal mold part 7 corresponds to the surface of the cylinder head on the side of a combustion chamber.

Next, with reference to FIGS. 2 to 7, a light-alloy casting producing flow according to the embodiment will be described in detail, using the above-described mold (see FIG. 1).

As shown in FIG. 2, a light-alloy casting is produced in a mold preparing process S1, a casting process S2, a metal mold part removing process S3, a quenching process S4, and an aging process S5, in this order.

First, in the mold preparing process S1, the sand mold parts 1 to 5 are molded by combining casting sand and binder. Then, they are combined with the metal mold part 7, so that a mold is created which has such a configuration as shown in FIG. 1.

Next, in the casting process S2, as shown in FIG. 3, a molten light-alloy (i.e., aluminum alloy) 12 is poured from the pouring gate 9 into the cavity section 10 through the riser section 8 and the runners 11. Then, the molten light-alloy 12 is solidified. Consequently, as shown in FIG. 4, a casting is formed which has a cylinder head portion 13 and a riser portion 14.

Thereafter, in the metal mold part removing process S3, as shown in FIG. 5, only the metal mold part 7 is removed with the sand mold parts 1 to 5 and the cores 6 kept remaining.

In the quenching process S4, as shown in FIG. 6, cooling water 15 as a cooling medium is sprayed to the surface of the casting that the metal mold part 7 is removed from and is exposed, that is, to the surface of the cylinder head that is to face a combustion chamber. Thereby, the casting is rapidly cooled, so that the cylinder head portion 13 is quenched.

Herein, the quenching temperature is set between 480° C. and 530° C. (in the case of an aluminum-alloy casting). The cooling water 15 from several nozzles 16 is sprayed to the surface of the cylinder head portion 13 from which the metal mold part 7 is removed and exposed. The cooling water is sprayed for approximately 1 minute to cool the surface until 300° C. or lower for a short time.

The water 15 as the cooling medium continues to be sprayed for a predetermined period of time, and thereafter, the water spraying is stopped.

The water 15 sprayed from the nozzles 16 onto the cylinder head portion 13 flows down. Thus, in a cooling station ST1, a tank 17 is provided to receive the water 15.

The water spraying is stopped at such a timing that in the following aging treatment, the respective temperatures of an exposed-surface-near zone and a riser-near zone of the cylinder head portion 13 can return to an aging temperature (e.g., between 160° C. and 240° C. in the case of an aluminum-alloy casting), owing to the heat to be transmitted from the riser portion 14 of the casting. The exposed-surface-near zone is indicated at A in FIG. 6 and the riser-near zone is indicated at B.

Next, in the aging process S5, as shown in FIG. 7, in the state where both the cylinder head portion 13 and the riser portion 14 are covered with the sand mold parts 1 to 5, a heat insulating member 18 made of glass-wool is attached to the sand mold part 5 to close the exposed surface of the casting. The heat insulating member 18 serves as a heat keeper. An aging treatment is performed by keeping the whole casting at the aging temperature, e.g., within the range of 160 and 240° C. in the case of an aluminum-alloy casting, for a predetermined period of time, e.g., for 1 to 2 hours, owing to the heat retained in the riser portion 14.

As shown in FIG. 7, with the sand mold parts 1 to 5 kept left around the casting, the cylinder head portion 13, the riser portion 14 and the sand mold parts 1 to 5 are placed on the heat insulating member 18 so that the casting is thermally insulated from the outside. The zones A and B receive the heat from the riser portion 14 to thereby rise to the temperature effective for aging treatment. They are aged by being kept for the predetermined period of time in a thermally uniform state. Particularly, the exposed-surface-near zone A undergoes both of the quenching treatment in the quenching process S3 and the aging treatment in the aging process S5, that is, the so-called T6 treatment.

FIG. 8 shows a change in temperature at different portions of the aluminum-alloy (AC4B) casting in the above-described production flow. As shown in this figure, in the quenching process S4, the water spraying period of time during which the cooling water 15 is sprayed is set at about 20 minutes. Thereby, the temperature Ta of the exposed-surface-near zone A falls below 100° C., the temperature Tb of the riser-near zone B drops to lower than 150° C., and the temperature Tc of the riser portion 14 lowers to nearly 300° C. In the aging process S5, the temperature of each portion can be kept within a temperature range of 160 and 240° C.

Next, such mechanical properties as tensile strength, 0.2% proof strength, and rupture elongation of an aluminum-alloy (AC4B) casting produced according to the above-described flow are compared with those of aluminum-alloy (AC4B) castings produced according to a first conventional method in which the aluminum alloy is poured in the same mold as that in FIG. 1, and is left without removing any mold part; and a second conventional method in which the aluminum alloy is poured in the same mold as that in FIG. 1, and the mold is entirely removed, and is cooled by water.

In FIG. 9 showing a tensile strength comparison, FIG. 10 showing a 0.2% proof strength comparison, FIG. 11 showing a rupture elongation comparison, indicated at X is the casting according to the first conventional method, indicated at Y is the casting according to the second conventional method, and indicated at Z is the casting according to this embodiment of the present invention.

In FIGS. 9 to 11, each mechanical property value required for a cylinder head is shown. Specifically, the required tensile strength is 206 MPa, the required 0.2% proof strength is 190 MPa, and the required rupture elongation is 0.25%.

As seen from FIGS. 9 and 10, the tensile strength and 0.2% proof strength of each zone A (B) of the casting produced according to the above-mentioned embodiment (hereinafter, referred to as the first production flow) are both satisfied with the above-described required values and are both superior to those of the castings produced according to the conventional methods.

In addition, as is obvious from FIG. 11, the rupture elongation of each zone A (B) of the casting produced according to the above-mentioned embodiment is lower than those of the casting produced according to the conventional methods. However, this satisfies the required value for the cylinder head.

The light-alloy casting production according to the first production flow includes: the mold preparing process S1 of preparing the mold which includes the sand mold parts 1 to 5 which form the riser section 8, and the metal mold part 7 which is disposed apart from the riser section 8, the sand mold parts 1 to 5 and the metal mold part 7 forming the cavity section 10; the casting process S2 of pouring the molten light-alloy 12 into the cavity section 10; the metal mold part removing process S3 of removing the metal mold part 7 after the pouring; the quenching process S4 of applying a cooling medium (i.e., the water 15) for rapid cooling onto the mold-removed surface of the casting to thereby quench (or giving a solution treatment to) the casting, continuing to cool it for a predetermined period of time, and thereafter, stopping applying the cooling medium; and the aging process S5 of, following the quenching, covering the casting with the sand mold parts 1 to 5 and the heat insulating member 18, and keeping the whole casting at an aging temperature for a predetermined period of time utilizing the heat retained in the riser portion 14.

Accordingly, in the mold preparing process S1, the mold is prepared which has the cavity section 10 by using the sand mold parts 1 to 5 and the metal mold part 7. In the casting process S2, the molten light-alloy 12 is poured into the cavity section 10. In the following metal mold part removing process S3, after the pouring, only the metal mold part 7 is removed (or parted) with the sand mold parts 1 to 5 kept remaining. In the following quenching process S4, the cooling medium (i.e., the water 15) is sprayed onto the surface of the casting from which the metal mold part 7 is removed, and thereby, the casting is quenched. Sequentially, it continues to be sprayed for the predetermined period of time, and then, the water applying is stopped. In the following aging process S5, the portion of the casting from which the metal mold part 7 is removed is covered with the heat insulating member 18. Thereby, the whole casting can be kept at the aging temperature for a predetermined period of time utilizing the heat which is kept in the riser portion 14.

Hence, after the metal mold part 7 is removed, the casting is rapidly cooled using the cooling medium (i.e., the water 15), so that it is quenched. In addition, the casting is covered with the sand mold parts 1 to 5 and the heat insulating member 18. This makes an age-hardening treatment easier. Besides, the aging treatment is conducted effectively utilizing the heat retained by the riser portion 14. Therefore, the T6 treatment can be conducted without any heat treatment furnace (or aging furnace), which remarkably suppresses the energy consumption. This helps adequately enhance the mechanical properties of the casting such as tensile strength.

Herein, since the riser section 8 is provided, as a matter of course, any hollows, such as shrinkage cavities, cavities are not formed inside of the casting, and the sand mold parts 1 to 5 and the cores 6 can be reused after they are broken up.

According to the first production flow, the heat insulating member 18 is used as the heat keeper. Specifically, if the heat insulating member 18 is used as the heat keeper, there is no need for power consumption, thus helping save energy.

According to the embodiment, as the heat keeper, a low-temperature heater may be used in place of the heat insulating member.

Furthermore, according to the first production flow, in the quenching treatment of an aluminum-alloy casting, its quenching temperature is set between 480° C. to 530° C. In the aging treatment, the casting is set to be kept for one to two hours within a temperature range of 160 to 240° C. This allows the main portion (e.g., the cylinder head portion 13) of the produced casting to have an adequate tensile strength and proof stress.

Moreover, in the cylinder head (i.e., the cylinder head portion 13) produced by the aluminum-alloy casting, the surface of the casting that is formed with the metal mold part 7 is to define a combustion chamber. Thus, in the surface layer of the cylinder head on the combustion-chamber side that is in contact with the metal mold part 7, the molten alloy solidifies more rapidly than the other portions at the sand mold parts 1 to 5. This makes its metallographic structure finer and also heightens the dimensional accuracy. Besides, the casting has a fine metallographic structure and undergoes the T6 treatment, so that its mechanical properties can be improved. Thus, it also has a strong resistance to a thermal-fatigue crack, which is useful when the surface layer of the cylinder head on the combustion-chamber side is repeatedly heated and cooled while an engine is in operation.

Next, with reference to FIG. 12 to FIG. 16, a second light-alloy casting production flow will be described in detail, using the above-described mold shown in FIG. 1.

According to the second production flow, as shown in FIG. 12, a light-alloy casting is produced in a mold preparing process S11, a casting process S12, a metal mold part removing process S13, a quenching process S14, a slowly-cooling process S15, and an aging process S16, in this order.

The mold preparing process S11, the casting process S12 and the metal mold part removing process S13, have the same procedures as those according to the above described first production flow.

Next, in the quenching process S14, as shown in FIG. 13, when the metal mold part 7 is removed, cooling water 15 as the cooling medium for rapid cooling is sprayed on the surface of the cylinder head portion 13, that is, the surface of a cylinder head that is to define a combustion chamber. Thereby, the required portion of the casting (i.e., the surface portion of the casting which the metal mold part 7 is removed from) is rapidly cooled, so that it is locally quenched.

Herein, the quenching temperature is set between 480° C. and 530° C. (in the case of an aluminum-alloy casting). The cooling water 15 from several nozzles 16 is sprayed on the surface of the cylinder head portion 13 on the combustion-chamber side from which the metal mold part 7 is removed so that the casting's surface is exposed. The cylinder head portion 13 is rapidly cooled to 300° C. or lower, so that it is quenched.

Herein, the water 15 that has been sprayed from the nozzles 16 on the cylinder head portion 13 flows down. Thus, in a quenching station ST2, a tank 17 is provided which receives the water 15.

Next, in the slowly-cooling process S15, as shown in FIG. 14, a spray of water or atomized water 19 as a cooling medium for slow cooling is applied to the surface of the casting. Then, it continues to be sprayed for a predetermined period of time, and thereafter, the spraying is stopped.

The timing in which the spraying of the atomized water 19 is stopped is set so that in the following aging treatment, the temperature of the zone A near a combustion chamber of the cylinder head portion 13 and the temperature of the zone B near the riser portion 14 return to an aging temperature (i.e., between 160° C. and 240° C. in the case of an aluminum-alloy casting), utilizing the heat which is transmitted from the riser portion 14.

In this second production flow, in the quenching process S14, the period of time during which the water 15 is sprayed is set at approximately 5 minutes. In the slowly-cooling process S15, the period of time during which the atomized water 19 is sprayed is set at about 30 minutes. Thus, a temperature Ta of the zone A falls below 100° C. while a temperature Tb of the zone B drops below 150° C. In addition, a temperature Tc of the riser portion 14 lowers to nearly 300° C.

Next, in the aging process S16, as shown in FIG. 15, the cylinder head portion 13 and the riser portion 14 of the casting are covered with the sand mold parts 1 to 5 and a heat insulating member 18 made of a glass-wool molding as the heat keeper. Then, an aging treatment is given by keeping the whole casting at the above-described aging temperature (i.e., within the range of 160° C. and 240° C. in the case of an aluminum-alloy casting) for a predetermined period of time (i.e., 1 to 2 hours), by utilizing the heat which is retained in the riser portion 14.

As shown in FIG. 15, with the sand mold parts 1 to 5 kept left around the casting, the cylinder head portion 13, the riser portion 14 and the sand mold parts 1 to 5 are placed on the heat insulating member 18, so that the casting can be thermally insulated from the outside. The zones A and B receive the heat transmitted from the riser portion 14, and thereby, they are recuperated to the range of temperature that is effective in the aging treatment. Then, they are aged by being kept for a predetermined period of time in a thermally-uniform state. Particularly, the zone A undergoes both of the quenching treatment in the quenching process S14 and the aging treatment in the aging process S16, so that it can come under the above-described T6 treatment.

FIG. 16 shows a change in temperature at different portions of the aluminum-alloy casting which is produced according to this second production flow. As shown in this figure, the period of time when the water 15 is sprayed in the quenching process S14, and the period of time when the atomized water 19 is sprayed in the slowly-cooling process S15, are set at about 35 minutes in total. Thereby, when the slowly-cooling process S15 is completed, the temperature Ta of the zone A falls below 150° C., the temperature Tb of the zone B drops to lower than 180° C., and the temperature Tc of the riser portion 14 lowers to nearly 300° C. Then, in the aging process S16, the temperature of each portion within can be kept within a temperature range of 160 and 240° C.

Hence, the light-alloy casting producing method according to the second production flow includes: the mold preparing process S11 of preparing the mold which includes the sand mold parts 1 to 5 which form the riser section 8, and the metal mold part 7 which is disposed apart from the riser section 8, the sand mold parts 1 to 5 and the metal mold part 7 forming the cavity section 10; the casting process S12 of pouring the molten light-alloy 12 into the cavity section 10; the metal mold part removing process S13 of removing the metal mold part 7 after the pouring; the quenching process S14 of applying the cooling medium (i.e., the water 15) for rapid cooling on the surface of the casting from which the metal mold part 7 is removed and thereby quenching the casting; the slowly-cooling process S15 of, following the quenching, applying the cooling medium (i.e., the atomized water 19) for slow cooling on the surface of the casting, continuing to cool it for a predetermined period of time, and thereafter, stopping the cooling; and the aging process S16 of covering the casting with the sand mold parts 1 to 5 and the heat keeper (i.e., the heat insulating member 18), and keeping the whole casting at an aging temperature for a predetermined period of time, utilizing the heat which is kept by the riser portion 14.

The cooling medium for rapid cooling and the cooling medium for slow cooling which are sprayed on the surface of the casting are both set to be water. In the quenching process S14, the cooling water 15 is sprayed, while in the slowly-cooling process S15, the atomized water 19 is sprayed. In addition, the cooling is shifted from the cooling water 15 to the atomized water 19, so that the temperature of each portion of the casting can be controlled within a temperature range (refer to Td in FIG. 16) where it is effectively aged.

According to this configuration of the second production flow, in the mold preparing process S11, using the sand mold parts 1 to 5 and the metal mold part 7, the mold is prepared which has the cavity section 10. In the casting process S12, the molten light-alloy 12 is poured into the cavity section 10. In the following metal mold part removing process S13, only the metal mold part 7 is removed (or parted) with the sand mold parts 1 to 5 kept remaining. In the following quenching process S14, the cooling medium for rapid cooling (i.e., the water 15) is sprayed on the surface of the casting from which the metal mold part 7 has been removed, and thereby, the casting is quenched. In the following slowly-cooling process S15, following the quenching, the cooling medium (i.e., the atomized water 19) for slow cooling is sprayed on the surface of the casting, the cooling lasts for a predetermined period of time, and thereafter, the cooling is stopped. In the following aging process S16, the casting (e.g., the cylinder head portion 13) is covered with the heat keeper (i.e., the heat insulating member 18). Thereby, the whole casting which is surrounded with the sand mold parts 1 to 5 and the heat insulating member 18 can be kept at an aging temperature for a predetermined period of time, by utilizing the heat which is kept by the riser portion 14.

Hence, after the metal mold part 7 is removed, the casting is rapidly cooled using the cooling medium (i.e., the water 15), so that the surface part of the casting from which the metal mold part 7 has been removed is quenched. In addition, the casting is covered with the sand mold parts 1 to 5 and the heat keeper (i.e., the heat insulating member 18). This makes an aging treatment easier. Furthermore, the aging treatment is conducted, effectively using the heat which is kept by the riser portion 14. Therefore, the T6 treatment can be conducted without any heat treatment furnace (i.e., aging furnace) and without energy consumption. This helps adequately enhance the casting's mechanical properties such as tensile strength.

Besides, in the slowly-cooling process S15, atomized water or a blow of air can be used as this cooling medium. However, in the example shown in the second production flow, the atomized water 19 is sprayed. In this case, the atomized water 19 vaporizes after it is sprayed on the surface of a casting. As a result, there is no need for a fixed cooling station, and the casting can be slowly cooled while being conveyed. This is advantageous in reducing the installation space and raising the production efficiency.

In the respects other than the ones described above, this second production flow has almost the same operation and advantages as those according to the first production flow described earlier. Hence, in FIG. 12 to FIG. 16, the identical parts in their corresponding figures are given the same reference characters and numerals, and thus, their detailed description is omitted.

Next, with reference to FIG. 17 to FIG. 22, a third light-alloy casting production flow will be described in detail, using the above-described mold shown in FIG. 1.

According to the third production flow, as shown in FIG. 17, a light-alloy casting is produced in accordance with a mold preparing process S21, a casting process S22, a metal mold part removing process S23, a quenching process S24, a casting immersing process S25, and an aging process S27, in this order. An air blowing process S26 may also be added between the casting immersing process S25 and the aging process S27.

The mold preparing process S21, the casting process S22 and the metal mold part removing process S23 have the same procedures as those according to the above described first production flow.

Next, in the quenching process S24, as shown in FIG. 18, the cooling water 15 as the cooling medium is sprayed on the surface of the cylinder head portion 13 which the metal mold part 7 is removed from, in other words, the surface of a cylinder head that is to define a combustion chamber. Thereby, the required part of the casting is locally cooled so that it is quenched.

Herein, the quenching temperature is set between 480° C. and 530° C. (in the case of an aluminum-alloy casting). Cooling water 15 from several nozzles 16 is sprayed on the surface of the cylinder head portion 13 on the combustion-chamber side from which the metal mold part 7 is removed so that the casting's surface is exposed. The cylinder head portion 13 is rapidly cooled to 300° C. or lower, so that it is quenched.

In addition, as shown in FIG. 19, a guide plate 20 may also be provided between the above-described nozzle 16, and the sand mold parts 1 to 5 and the cylinder head portion 13. It is used to guide the water 15 only to the surface of the cylinder head portion 13 on the combustion-chamber side, and prevent the water 15 from being sprayed on the sand mold part 5.

Herein, the water 15 that is sprayed from the nozzles 16 on the cylinder head portion 13 flows down. Thus, in a quenching station ST2, a tank 17 is provided which receives the water 15.

Next, in the casting immersing process S25, as shown in FIG. 20, the sand mold parts 1 to 5, the cores 6 and the whole casting are immersed in water 22 which is stored in advance in a tank 21. Thereby, the cylinder head portion 13 and the riser portion 14 of the casting are cooled, and in addition, the sand mold parts 1 to 5 and the cores 6 are broken up in the water.

In this case, in order to avoid steam explosion, the immersion is started after the point of time when the riser portion 14 is solidified. The period of time when they are kept immersed is set at several seconds.

In this third production flow, the period of time during which the quenching process S24 is conducted, and the period of time during which the casting immersing process S25 is conducted, are set at approximately 5 minutes in total.

Besides, the riser portion 14 and zones A and B are immersed in a state where a predetermined difference in temperature between them is kept. Herein, the zone A is the part of the cylinder head portion 13 which is located on the side of a combustion chamber, and the zone B is the part of the cylinder head portion 13 which is located on the side close to the riser portion 14.

Preferably, the sand mold parts 1 to 5 are molded using a water soluble binder, so that the sand mold parts 1 to 5 and the cores 6 can be broken up satisfactorily when the casting is immersed. In this third production flow, a magnesium sulfate hydrate is used as the water soluble binder.

After it is immersed for several seconds, the cylinder head portion 13 and the riser portion 14 of the casting are moved out of the water 22 in the tank 21. Thereby, the heat of the riser portion 14 is gradually transmitted to the zones A, B of the cylinder head portion 13.

Then, in the air blowing process S26, air is allowed to blow to the cylinder head portion 13 and the riser portion 14 which is pulled up from the water. Thereby, the water 22 that adheres to them is removed. Herein, it is also possible for the heat of the riser portion 14 to gradually raise the temperature of the zones A and B so that the adhering water 22 can be naturally dried. In that case, the air blowing process S26 may also be omitted.

Next, in the aging process S27, as shown in FIG. 21, the cylinder head portion 13 and the riser portion 14 subjected to the air blowing are fully covered with heat insulating members 18 and 23 made of glass-wool molding as the heat keeper. Then, an age hardening treatment is given by keeping the whole casting (i.e., the cylinder head portion 13 and the riser portion 14) at an aging temperature for a predetermined period of time, utilizing the heat that is kept by the riser portion 14.

This aging treatment is set, so that an aluminum-alloy casting is kept for 1 to 2 hours within a temperature range of 160 and 240° C. (in the case of an aluminum-alloy casting). To conduct those settings, the timing (i.e., the temperature of the casting) is adjusted in which the casting is taken out from the water 22.

As shown in FIG. 21, the entire casting is surrounded with the heat insulating members 18 and 23 so that the casting can be thermally insulated from the outside. The zones A and B receive the heat that is conducted from the riser portion 14, and thereby, they are recuperated to the range of temperature that is effective in the aging treatment. Then, they are aged by being kept for a predetermined period of time in a thermally uniform state. Particularly, the zone A undergoes both of the quenching treatment in the quenching process S24 and the aging treatment in the aging process S27 so that it can come under the above-described T6 treatment.

FIG. 22 shows a change in temperature at different portions of an aluminum-alloy casting which is produced according to the third production flow of the embodiment. As shown in this figure, in the quenching process S24, the period of time for the cooling is set at about 5 minutes, and then, the casting is immersed in the water. Thereby, the temperature Ta of the zone A falls below 240° C., the temperature Tb of the zone B drops to lower than 150° C., and the temperature Tc of the riser portion 14 lowers to nearly 300° C. Then, in the aging process S27, the temperature of each portion can be kept within a temperature range of 160 and 240° C.

Hence, the third light-alloy casting production flow includes: the mold preparing process S21 of preparing the mold having the sand mold parts 1 to 5 unified by the water-soluble binder and form the riser section 8 (see FIG. 1), and the metal mold part 7 which is disposed apart from the riser section 8, the sand mold parts 1 to 5 and the metal mold part 7 forming the cavity section 10; the casting process S22 of pouring the molten light-alloy 12 into the cavity section 10; the metal mold part removing process S23 of removing the metal mold part 7 after the pouring; the quenching process S24 of applying a cooling medium (i.e., the water 15) on the surface of the casting from which the metal mold part 7 is removed and thereby quenching the casting; the casting immersing process S25 of immersing the sand mold parts 1 to 5 and the casting (i.e., the cylinder head portion 13 and the riser portion 14) in the water 22 and thereby cooling the casting, and breaking up the sand mold parts 1 to 5 and the cores 6; and the aging process S27 of taking out the casting from the water 22, thereafter covering the casting with the heat keeper (i.e., the heat insulating members 18, 23), and keeping the whole casting at an aging temperature for a predetermined period of time, utilizing the heat which is kept by the riser portion 14.

According to this configuration of the third production flow, in the mold preparing process S21, using the sand mold parts 1 to 5 which has a water-soluble binder and the metal mold part 7, the mold is prepared which has the cavity section 10. In the casting process S22, the molten light-alloy 12 is poured into the cavity section 10. In the following metal mold part removing process S23, after the pouring, only the metal mold part 7 is removed (or parted) with the sand mold parts 1 to 5 kept remaining. In the following quenching process S24, the cooling medium (i.e., the water 15) is sprayed on the surface of the casting from which the metal mold part 7 is removed, and thereby, the casting is quenched. In the following casting immersing process S25, the sand mold parts 1 to 5 and the casting are immersed in the water 22 and thereby the casting is cooled, and the sand mold parts 1 to 5 and the cores 6 which are molded out of the water-soluble binder are broken up. In the following aging process S27, the casting is taken out from the water 22, and thereafter, the casting is covered with the heat keeper (i.e., the heat insulating members 18, 23). Thereby, the whole casting can be kept at an aging temperature for a predetermined period of time, utilizing the heat which is kept by the riser portion 14.

Hence, after the metal mold part 7 is removed, the casting is rapidly cooled by the cooling medium (i.e., the water 15), so that the mold-removed surface part of the casting from which the metal mold part 7 is removed is quenched. In addition, after the casting is immersed in the water 22 and is taken out from the water 22, the casting is covered with the heat keeper (i.e., the heat insulating members 18, 23), so that an age-hardening treatment can be easily conducted. Furthermore, the mold-removed surface part of the casting from which the metal mold part 7 is removed is cooled more rapidly, and thereby, its metallographic structure becomes finer. In addition, the aging treatment is conducted, effectively utilizing the heat that is kept by the riser portion 14. Therefore, the T6 treatment can be conducted without any heat treatment furnace (i.e., aging furnace) and without energy consumption. This helps adequately enhance the casting's mechanical properties such as tensile strength.

Besides, in the casting immersing process S25, the sand mold parts 1 to 5 and the casting (i.e., the cylinder head portion 13 and the riser portion 14) are immersed in the water. Therefore, the sand mold parts 1 to 5 and the cores 6 which are molded with the water-soluble binder are broken up. In addition, the immersion eliminates the excess heat of the riser portion 14, the period of time when the casting is cooled from the quenching process S24 to the aging process S27 can be efficiently shortened.

In the respects other than the ones described above, the third production flow has almost the same operation and advantages as those according to the production flows described earlier. Hence, in FIG. 17 to FIG. 22, the identical parts in their corresponding figures are given the same reference characters and numerals, and thus, their detailed description is omitted.

Next, with reference to FIG. 23 to FIG. 26, a fourth light-alloy casting production flow will be described in detail, using the above-described mold shown in FIG. 1.

According to the fourth production flow, as shown in FIG. 23, a light-alloy casting is produced in accordance with a mold preparing process S31, a casting process S32, a metal mold part removing process S33, a quenching process S34, and an aging process S35, in this order.

The mold preparing process S31, the casting process S32 and the metal mold part removing process S33, have the same procedures as those according to the above described first production flow.

Next, in the quenching process S34, as shown in FIG. 25, the sand mold parts 1 to 5, the cores 6 and the whole casting are immersed in high temperature water 25 which is stored beforehand in the tank 24, by using a lifting apparatus 26 as shown in FIG. 24. Thereby, the cylinder head portion 13 and the riser portion 14 of the casting are cooled, without breaking up the sand mold parts 1 to 5 and the cores 6. Especially, the surface of the cylinder head portion on the combustion-chamber side from which the metal mold part 7 is removed so that the casting's surface is exposed is rapidly cooled using the high temperature water 25, and thereby, it is quenched.

Herein, the quenching temperature is set between 480° C. and 530° C. (in the case of an aluminum-alloy casting). The high temperature water 25 in the tank 24 comes into contact with the surface of the cylinder head portion 13 on the combustion chamber side from which the metal mold part 7 is removed to expose it. The cylinder head portion 13 is rapidly cooled to 300° C. or lower so that it is quenched.

The lifting apparatus 26 shown in FIG. 24 includes: a plurality of guide rods 27 fixed to a side wall of the tank 24 and extending up and down; a drive cylinder 28 which is disposed along the guide rod 27 and includes a hydraulic cylinder or the like; a support frame 30 which is disposed at the upper end of a piston rod 29 of this drive cylinder 28 and moves up and down along the plurality of guide rods 27; a support member 31 which is disposed on the side of the support frame 30 that corresponds to the tank 24; a stand 32 which is horizontally attached to the lower part of the support member 31; and a pair of stoppers 33, 33 which is fixedly attached to the stand 32. Between the pair of stoppers 33, 33 on the stand 32, as shown in FIG. 24, the sand mold parts 1 to 5, the cores 6 and the whole casting are grasped by a robot. Thereby, they are placed and fixed there so that their position cannot be shifted. Then, the stand 32 that is guided by the piston rod 29 of the drive cylinder 28 and the guide rods 27 is moved down. This, as shown in FIG. 25, the sand mold parts 1 to 5, the cores 6 and the whole casting are immersed in the high-temperature water 25.

In the quenching process S34, the high temperature water 25 (which is 100° C. or lower) is used as the cooling medium, and in addition, the immersion is started after the point of time when the riser portion 14 is solidified. The period of time during which they are kept immersed is set within approximately 15 minutes. Besides, they are immersed so that the high temperature water 25 cannot go into the casting through the sand mold parts 1 to 5. It is preferable that the temperature of the high temperature water 25 be within a temperature range of 90 to 99° C. If such high-temperature water is used, the cylinder head portion 13 can be prevented from having a large difference in temperature when being quenched. This keeps it from having a great residuary stress.

The sand mold parts 1 to 5 and the cores 6 have a water insoluble hardening binder and are molded in a cold box molding process. Herein, this hardening binder is made of phenol resin as its main material and polyisocyanate as the hardener and is hardened by an amine gas, and thereby, a sand mold part which is molded using this cannot be broken up, even if it comes into contact with water.

Herein, as the water insoluble hardening binder, a thermosetting binder, which contains phenol resin as its main material and hexamethylenetetramine as the hardener, can also be used. However, preferably, the above-described gas-hardening binder should be used. This is because it is hardened at a normal temperature using an amine gas, so that a sand mold part's dimensional accuracy becomes higher and its molding time becomes shorter.

Sequentially, after a predetermined period of time (e.g., approximately 15 minutes) has passed since the sand mold parts 1 to 5, the cores 6 and the casting were immersed, the drive cylinder 28 operates to move up the stand 32. Thus, the sand mold parts 1 to 5, the cores 6 and the casting are pulled out of the tank 24. Then, using a robot, they are transferred to the following aging process. Herein, while the sand mold parts 1 to 5, the cores 6 and the casting are being immersed in the high temperature water 25, the water can be almost prevented from going into the sand mold parts 1 to 5 to cool the casting. After the immersion, the cylinder head portion 13 and the riser portion 14 of the casting with the sand mold parts 1 to 5 kept attached thereto are taken out from the high-temperature water 25 in the tank 24. Thereby, the heat of the riser portion 14 is gradually transmitted to the zones A and B of the cylinder head portion 13.

Next, in the aging process S35, as shown in FIG. 7 in the first production flow, the cylinder head portion 13 and the riser portion 14, which are taken out from the water 25, are covered with the sand mold parts 1 to 5 and the heat insulating member 18 (i.e., the glass wool molding). Then, an age hardening treatment is given by keeping the whole casting (i.e., the cylinder head portion 13 and the riser portion 14) at an aging temperature for a predetermined period of time, utilizing the heat that is kept by the riser portion 14.

The aging treatment is set, so that an aluminum-alloy casting is kept for 1 to 2 hours within a temperature range of 160 and 240° C. (in the case of an aluminum-alloy casting). To conduct those settings, the timing (i.e., the temperature of the casting) is adjusted in which the casting is taken out from the high temperature water 25.

Then, the whole casting is surrounded with the sand mold parts 1 to 5 and the heat insulating members 18 so that the casting can be thermally insulated from the outside The zones A and B receive the heat that is transmitted from the riser portion 14, and thereby, they are recuperated to the range of temperature that is effective in the aging treatment. Then, they are aged by being kept for a predetermined period of time in a thermally uniform state. Particularly, the zone A undergoes both of the quenching treatment in the quenching process S34 and the aging hardening treatment in the aging process S35 so that it can come under the above-described T6 treatment.

FIG. 26 shows a change in temperature at different portions of the aluminum-alloy casting which is produced according to the fourth production flow. As shown in this figure, in the quenching process S34, the immersion time is set at about 15 minutes. Thereby, the temperature Ta of the zone A and the temperature Tb of the zone B fall to about 100° C. and some 150° C., respectively. The temperature Tc of the riser portion 14 lowers to approximately 400° C. Then, in the following aging process S35, the temperature of each portion can be converged and kept within a temperature range of 160 and 240° C.

Hence, the fourth light-alloy casting production flow includes: the mold preparing process S31 of preparing the mold having the sand mold parts 1 to 5 unified by the water insoluble hardening binder and form the riser section 8, and the metal mold part 7 which is disposed apart from the riser section 8, the sand mold parts 1 to 5 and the metal mold part 7 forming the cavity section 10; the casting process S32 of pouring the molten light-alloy 12 into the cavity section 10; the metal mold part removing process S33 of removing the metal mold part 7 after the pouring; the quenching process S34 of immersing the sand mold parts 1 to 5 and the casting (i.e., the cylinder head portion 13 and the riser portion 14) in the high temperature water 25, and thereby cooling the surface of the casting from which the metal mold part 7 is removed; and the aging process S35 of taking out the sand mold parts 1 to 5 and the casting from the high temperature water 25, thereafter covering the casting with the sand mold parts 1 to 5 and the heat keeper (i.e., the heat insulating members 18), and keeping the whole casting at an aging temperature for a predetermined period of time, utilizing the heat which is retained by the riser portion 14.

According to this configuration of the fourth production flow, in the mold preparing process S31, using the sand mold parts 1 to 5 unified by the water insoluble hardening binder and the metal mold part 7, the mold is prepared which has the cavity section 10. In the casting process S32, the molten light-alloy 12 is poured into the cavity section 10. In the following metal mold part removing process S33, only the metal mold part 7 is removed (or parted) with the sand mold parts 1 to 5 kept remaining. In the following quenching process S34, the sand mold parts 1 to 5 and the whole casting are cooled in the high-temperature water 25, and in addition, the surface of the casting from which the metal mold part 7 is removed is rapidly cooled and is quenched. In the following aging process S35, the casting is taken out from the high-temperature water 25, and thereafter, the mold-removed section of the casting from which the metal mold part 7 is removed is covered with the heat keeper (i.e., the heat insulating member 18). Thereby, the whole casting can be kept at an aging temperature for a predetermined period of time, utilizing the heat which is kept by the riser portion 14.

Hence, after the metal mold part 7 is removed, the casting is immersed in the high-temperature water, so that the mold-removed surface section of the casting from which the metal mold part 7 is removed is quenched. In addition, the casting taken out from the water is covered with the sand mold parts 1 to 5 and the heat keeper (i.e., the heat insulating member 18) so that an age hardening treatment can be easily realized. Furthermore, the mold-removed surface section of the casting from which the metal mold part 7 is removed is cooled more rapidly, and thereby, its metallographic structure becomes finer. In addition, the aging treatment is conducted, by effectively utilizing the heat kept in the riser portion 14. Therefore, the T6 treatment can be conducted without any heat treatment furnace (i.e., aging furnace) and without energy consumption. This helps adequately enhance the casting's mechanical properties such as tensile strength.

Besides, in the quenching process S34, the excess heat of the riser portion 14 can be eliminated by immersing the sand mold parts 1 to 5 and the casting in the high temperature water 25, so the period of time during which the casting is cooled from the quenching process S34 to the aging process S35 can be efficiently shortened.

In the respects other than the ones described above, this fourth production flow has almost the same operation and advantages as those according to the production flows described earlier. Hence, in FIG. 23 to FIG. 26, the identical parts in their corresponding figures are given the same reference characters and numerals, and thus, their detailed description is omitted.

In the foregoing embodiment, the aluminum alloy which is specified in Japanese Industrial Standard as AC4B is used as the light alloy. However, instead of the aluminum alloy, another aluminum alloy or a magnesium alloy (e.g., JIS MC1) may also be used.

If the light-alloy casting is made of a magnesium alloy, it is preferable that the quenching temperature of the casting in the quenching treatment be within a range of 380 to 390° C. While being aged, preferably, the casting should be kept for 1 to 2 hours within a temperature range of 220 to 260° C.

In the foregoing embodiment, further, a cylinder head is illustrated as a target casting. However, the present invention is not limited to this product. The method according to the present invention can be applied to production of various light-alloy castings, so long as the quenching treatment and the age hardening treatment which are shown in the above-described embodiment are conducted, so that the casting's mechanical properties at its main parts can be enhanced, thus improving the product's usage performance.

Besides, the configuration according to the present invention corresponds to those according to the above-described embodiment, as shown below. Specifically, the cooling medium corresponds to the water 15; the cooling medium for rapid cooling, the water 15; the cooling medium for slow cooling, the atomized water 19; the heat keeper, the heat insulating members 18, 23; and the water soluble binder, the magnesium sulfate hydrate. However, it is natural that the present invention should not be limited only to such configurations.

According to the embodiment of the present invention, a sand mold part, which is provided with a riser section, and a metal mold part, forms a cavity section. Only the metal mold part is removed after pouring, and then, the surface of a casting from which the metal mold part is removed is locally cooled, using a cooling medium, so that it undergoes a quenching treatment (including a solution treatment). Thereafter, it undergoes an aging treatment effectively utilizing the heat that is retained in a solidified alloy in the riser section. Therefore, the light-alloy casting undergoes a T6 treatment without any heat treatment furnace (i.e., aging furnace), so that its mechanical properties such as tensile strength and the 0.2% proof strength can be adequately enhanced.

As described above, an inventive light-alloy casting is produced by: preparing a casting mold including a sand mold part provided with a riser section, and a metal mold part disposed apart from the riser section, the sand mold part and the metal mold part forming a cavity section; pouring a molten light-alloy into the cavity section of the casting mold; removing the metal mold part from a casting of the light-alloy; allowing a mold-removed surface of the casting to come into contact with a cooling medium to thereby quench the mold-removed surface; and aging the casting by heat retained by a solidified light-alloy in the riser section for a predetermined period of time.

More specifically, an inventive light-alloy casting producing method comprising: a mold preparing process of preparing a mold including a sand mold part which is provided with a riser section, and a metal mold part which is disposed apart from the riser section, the sand mold part and the metal mold part forming a cavity section; a casting process of pouring a molten light-alloy into the cavity section of the mold; a metal mold part removing process of removing the metal mold part from a casting which is formed by pouring; a quenching process of bringing a cooling medium into contact with the surface of the casting from which the metal mold part is removed, and thereby, cooling the casting rapidly; and an aging process of covering the metal mold part-removed section of the casting with a heat keeper, and keeping the whole casting which is surrounded with the sand mold part and the heat keeper at an aging temperature for a predetermined period of time utilizing the heat which is retained by a solidified alloy in the riser portion.

Another inventive light-alloy casting producing method comprising: a mold preparing process of preparing a mold including a sand mold part which is provided with a riser section, and a metal mold part which is disposed apart from the riser section, the sand mold part and the metal mold part forming a cavity section; a casting process of pouring a molten light-alloy into the cavity section; a metal mold part removing process of removing the metal mold part from a casting which is formed by pouring; a quenching process of applying a cooling medium on the surface of the casting from which the metal mold part is removed and thereby cooling the casting rapidly, continuing to apply the cooling medium for a predetermined period of time, and thereafter, stopping blowing the cooling medium; and an aging process of covering the metal mold part-removed section of the casting with a heat keeper, and keeping the whole casting which is surrounded with the sand mold part and the heat keeper at an aging temperature for a predetermined period of time utilizing the heat which is retained by a solidified alloy in the riser portion.

Still another inventive light-alloy casting producing method comprising: a mold preparing process of preparing a mold including a sand mold part which is provided with a riser section, and a metal mold part which is disposed apart from the riser section, the sand mold part and the metal mold part forming a cavity section; a casting process of pouring a molten light-alloy into the cavity section; a metal mold part removing process of removing the metal mold part from a casting which is formed by pouring; a quenching process of applying a cooling medium for rapid cooling on the surface of the casting from which the metal mold part is removed, and thereby, cooling the casting rapidly; a slowly-cooling process of, following the rapid cooling, applying the cooling medium for slow cooling on the surface of the casting, continuing to cool the casting for a predetermined period of time, and thereafter, stopping blowing the cooling medium for slow cooling; and an aging process of covering the metal mold part-removed section of the casting with a heat keeper, and keeping the whole casting which is surrounded with the sand mold part and the heat keeper at an aging temperature for a predetermined period of time utilizing the heat retained in a solidified alloy in the riser portion.

Yet another inventive light-alloy casting producing method comprising: a mold preparing process of preparing a mold including a sand mold part which has a water soluble binder and is provided with a riser section, and a metal mold part which is disposed apart from the riser section, the sand mold part and the metal mold part forming a cavity section; a casting process of pouring a molten light-alloy into the cavity section of the mold; a metal mold part removing process of removing the metal mold part from a casting which is formed by pouring; a quenching process of applying a cooling medium on the surface of the casting from which the metal mold part is removed, and thereby, cooling the casting rapidly; a casting immersing process of immersing the casting in water with the sand mold part attached thereto and thereby cooling the casting, and breaking up the sand mold part; and an aging process of taking out the casting from the water, thereafter, covering the casting with a heat keeper, and keeping the whole casting which is surrounded with the heat keeper at an aging temperature for a predetermined period of time utilizing the heat retained in a solidified alloy in the riser portion.

Still yet another inventive light-alloy casting producing method comprising: a mold preparing process of preparing a mold including a sand mold part which has a water insoluble hardening binder and is provided with a riser section, and a metal mold part which is disposed apart from the riser section, the sand mold part and the metal mold part forming a cavity section; a casting process of pouring a molten light-alloy into the cavity section; a metal mold part removing process of removing the metal mold part from a casting which is formed by pouring; a quenching process of immersing the casting in water with the sand mold part attached thereto, and thereby, rapidly cooling the surface of the casting; and an aging process of taking out the casting from the water, thereafter, covering the metal mold part-removed section of the casting with a heat keeper, and keeping the whole casting which is surrounded with the sand mold part and the heat keeper at an aging temperature for a predetermined period of time utilizing the heat retained in a solidified alloy in the riser portion.

With the production method, only the metal mold part is removed after pouring, the surface of the casting from which the metal mold part has been removed is rapidly cooled locally by applying a cooling medium so that it undergoes a quenching treatment (including a solution treatment). Thereafter, it undergoes an age-hardening treatment effectively utilizing the heat that is retained in a solidified alloy in the riser section. Therefore, a T6 treatment is conducted without any heat treatment furnace (i.e., aging furnace), so that a light-alloy casting that has superior mechanical properties such as tensile strength can be obtained.

Furthermore, in the process of conducting slow cooling, atomized water or a blow of cooling air can also be used as a cooling medium for slow cooling. In this case, atomized water vaporizes after it is sprayed on the surface of the casting. Thus, there is no need for a fixed cooling station, and the casting can be slowly cooled while being conveyed. This is advantageous in reduction of the installation space and increasing of the production efficiency.

The light-alloy casting producing method is especially useful for producing a cylinder head that is made of an aluminum alloy or a magnesium alloy. In the case where a cylinder head is produced using the inventive method, the surface of the casting that comes into contact with the metal mold part corresponds to the surface of the cylinder head that is to define a combustion chamber.

In the case of a cylinder head being produced by the inventive method, the combustion chamber defining surface of the cylinder head is in contact with the metal mold part, the molten alloy solidifies more rapidly than its part at the sand mold parts. This makes its metallographic structure finer and also heightens the casting's dimensional accuracy. Besides, the casting has a fine metallographic structure and undergoes the T6 treatment, so that its mechanical properties can be improved. Thus, it also has a strong resistance to thermal-fatigue crack. This is advantageous in the case where the combustion chamber defining surface of the cylinder head is repeatedly heated and cooled during the operation of the engine.

In the case where an aluminum alloy is used for a cylinder head, it is preferable to use an aluminum alloy specified in Japanese Industrial Standard (JIS H5202) AC4B. This aluminum alloy AC4B contains Cu: 2.0 to 4.0%, Si: 7.0 to 10.0%, Mg: 0.6% or less, Zn: 1.0% or less, Fe: 1.2% or less, Mn: 0.8% or less, Ni: 0.5% or less, Ti: 0.2% or less and Al: the remaining.

In the case where a magnesium alloy is used for a cylinder head, it is preferable to use a magnesium alloy specified in Japanese Industrial Standard (JIS H5203) MC1. This magnesium alloy contains Al: 5.3 to 6.7%, Zn: 2.5 to 3.5%, Mn: 0.15 to 0.6%, Si: 0.30% or less, Cu: 0.10% or less, Ni: 0.01% or less and Mg: the remaining. This alloy corresponds to a magnesium-alloy casting Type-1.

An aging temperature is determined according to the alloy type and its chemical composition of a light-alloy casting. It is set by choosing the timing in which the casting goes out of contact with a cooling medium or it stops being sprayed with the cooling medium after having been quenched (or after having been slowly cooled in the case where it is sequentially cooled slowly). Alternatively, it is set by choosing the timing in which the casting is taken out from the water after having been immersed. This timing is affected by the type, shape, size or structure of a casting, the size (i.e., the heat which is kept by) of a riser portion, the type, contact area or applying quantity of a cooling medium, or the like. In addition, the aging time when a casting is kept aged is set so that its mechanical properties such as tensile strength becomes most suitable at the aging temperature.

In the case where a light-alloy casting is made of an aluminum alloy, it is preferable that the quenching temperature of the casting in the quenching treatment be within a range of 480 to 530° C. While being aged, preferably, the casting should be kept for 1 to 2 hours within a temperature range of 160 to 240° C. If the temperature of the casting when it is quenched is below 480° C., a solution treatment becomes inadequate. On the other hand, if it is above 530° C., the casting softens and cannot easily retain its shape. In addition, if the temperature of the casting when it is aged is below 160° C., the aging takes a long time. On the other hand, if it is above 240° C., the casting is overly aged, and thus, becomes less strong. Furthermore, the period of time when it is aged should be at least 1 hour within the above-described temperature range. If the casting is kept for 2 hours, it can be aged sufficiently (i.e., nearly to the saturation point of its aging).

After having been quenched (or after having been slowly cooled in the case where it is sequentially cooled slowly), the timing when the casting goes out of contact with a cooling medium or it stops being sprayed with the cooling medium is set, so that in the following aging treatment, using a recuperated heat from the heat which is kept by a solidified alloy in the riser portion, the temperature of the whole casting excluding the riser portion becomes within the range of the above-described aging temperature. The same is also applied to the timing when the casting is taken out from the water after having been immersed. Hence, it is set so that using a recuperated heat from the heat which is kept by a riser portion, the temperature of the whole casting excluding the riser portion becomes within the range of the aging temperature.

As the binder that is used for the sand mold parts and the cores, a water soluble binder and a gas hardening binder or a heat hardening binder as a water insoluble binder may be used.

In addition, in order to break up the sand mold part in the casting immersing process, the sand mold part needs to be molded using a water soluble binder. As this water soluble binder, at least one inorganic sulfate compound can be used among a magnesium sulfate hydrate, an aluminum sulfate hydrate, a sodium sulfate hydrate, a nickel sulfate hydrate and a manganese sulfate hydrate. It is especially preferable that the binder that mainly includes a magnesium sulfate hydrate be used, so that the casting mold can be stably strengthened.

In order not to break up the sand mold part when the casting is immersed for quenching, the sand mold part needs to be molded using a water insoluble hardening binder. As this water insoluble binder, preferably, a gas hardening binder which is hardened by an amine gas should be used, which is made of phenol resin as its main material and polyisocyanate as the hardener.

As the heat keeper, a heat insulating member or a low temperature heater can be used. As the heat insulating member, a glass-wool molding or a gypsum plasterboard can be used.

It should be noted that the term “the solidified alloy in the riser section” in this specification includes a partially solidified alloy portion. Therefore, the heat retained in the solidified alloy in the riser section includes the latent heat from the liquid state in the process of transforming to the solid state.

This application is based on Japanese Patent application No. 2003-388889, filed in Japan Patent Office on Nov. 19, 2003 and Japanese Patent application No. 2004-267768, filed in Japan Patent Office on Sep. 15, 2004, the contents of which are hereby incorporated by reference.

Although the present invention has been fully described by way of example with reference to the accompanied drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein.

Claims

1. A method for producing a light-alloy casting, comprising steps of:

preparing a casting mold including a sand mold part provided with a riser section, and a metal mold part disposed apart from the riser section, the sand mold part and the metal mold part forming a cavity section;

pouring a molten light-alloy into the cavity section of the casting mold;

removing the metal mold part from a casting made of the light-alloy;

allowing a mold-removed surface of the casting to come into contact with a cooling medium to thereby quench the mold-removed surface; and

aging the casting by heat retained by a solidified light-alloy in the riser section for a predetermined period of time.

2. A method according to claim 1, wherein in the step of aging the casting, the mold-removed surface of the casting is covered with a heat keeper to hold the casting subjected to aging by the retained heat of the solidified light-alloy in the riser section.

3. A method according to claim 2, wherein the cooling medium is blown to the mold-removed surface.

4. A method according to claim 3, wherein the cooling medium is a medium for rapid cooling, further comprising, after the step of blowing the medium for rapid cooling, a step of blowing another cooling medium for slow cooling to the mold-removed surface of the casting for a predetermined period of time.

5. A method according to claim 4, wherein:

the cooling medium for rapid cooling is water; and

the cooling medium for slow cooling is atomized water or air.

6. A method according to claim 3, wherein the sand mold part includes a water soluble binder, further comprising, after the step of blowing the cooling medium to the mold-removed surface, a step of immersing the casting in water with the sand mold part attached thereto to thereby cool the casting and break up the sand mold part.

7. A method according to claim 6, wherein in the step of aging the casting, the casting is placed outside the water, and is entirely covered with an insulator to hold the casting subjected to aging by the retained heat of the solidified light-alloy in the riser section.

8. A method according to claim 1, wherein the sand mold part includes a water insoluble binder, and in the step of quenching the mold-removed surface, the casting attached with the sand mold part is immersed in water to allow the mold-removed surface of the casting to come into contact with the water to thereby quench the mold-removed surface, and in the step of aging the casting, the mold-removed surface of the casting is covered with a heat keeper to hold the casting subjected to aging by the retained heat of the solidified light-alloy in the riser section.

9. A method according to claim 8, wherein the water insoluble binder includes a gas-hardening binder having phenol resin as a main material and polyisocyanate as a hardener material.

10. A method according to claim 9, wherein the sand mold part is hardened by an amine gas.

11. A method according to claim 2, wherein the heat keeper is a heat insulating member.

12. A method according to claim 1, wherein the light-alloy casting is made of an aluminum alloy.

13. A method according to claim 12, wherein the quenching temperature is from 480° C. to 530° C.

14. A method according to claim 12, wherein in the step of aging, the casting is kept for 1 to 2 hours within a temperature of 160 to 240° C.

15. A method according to claim 1, wherein the casting is a cylinder head of an engine, the surface of the casting that comes into contact with the metal mold part defines a combustion chamber of the engine.

16. A method according to claim 1, wherein the cooling medium is water.