METHOD OF MANUFACTURING ROTOR SUCH AS IMPELLER OR TURBINE WHEEL

Abstract

Disclosed is a method of manufacturing an impeller or a turbine wheel having a disk hub and an air foil. The method includes forming a mold for casting including a cavity of a shape corresponding to the rotor, arranging a core at a location corresponding to an inside of the rotor in the cavity of the mold for casting, injecting molten metal into the mold for casting where the core has been arranged, and removing the core from a casting which has been cast in the mold for casting.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority from Korean Patent Application No. 10-2012-0084990, filed on Aug. 2, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

1. Field

Methods consistent with exemplary embodiments relate to manufacturing a rotor such as an impeller or a turbine wheel, and more particularly, to manufacturing an impeller or a turbine wheel that may be used to various machines such as a compressor and a turbine.

2. Description of the Related Art

A rotor such as an impeller or a turbine wheel is used for a machine, such as a compressor and a turbine.

FIG. 1A schematically illustrates a cross-sectional shape of an impeller or a turbine wheel 1 of a compressor. Referring to FIG. 1A, the impeller or the turbine wheel 1 includes a disk hub 12 and a plurality of wings (air foil 14) that are arranged along the outer circumference of the disk hub 12. A fillet 18 is formed at a portion where the disk hub 12 is connected to the air foil 14. A penetration hole 11 is processed for combination with a shaft (not shown) in the integrally manufactured impeller or turbine wheel 1.

The impeller or turbine wheel 1 is a part that is rapidly rotated which generates a very large centrifugal load during operation, thereby also generating a high stress state due to the centrifugal load. In order to ensure an appropriate lifespan and structural stability in such an operation environment, the impeller or turbine wheel 1 should use materials of a high strength. However, there is a limit in selecting materials of the impeller or turbine wheel 1.

Furthermore, there is a large difference in a volume between the air foil 14 and the disk hub 12 when precisely casting. Thus, the thin air foil part is first solidified in molten metal, and the disk hub of a large volume is solidified later. Since, however, contraction occurs as the disk hub is solidified, tensile stress occurs within the disk hub.

FIG. 1B schematically illustrates a casting process of the impeller or the turbine wheel 1. As illustrated in FIG. 1B, in the molten metal injected into a mold 20, as solidification progresses in a direction from the air foil 14 to a central part 15 of the disk hub 12, the disk hub 12 contracts and tensile stress occurs. In some cases, a cavity may be formed within the disk hub 12.

Such tensile stress may generate remaining stress at the fillet 18, which is a connection part between the air foil 14 and the disk hub 12, or may cause a defect such as a hot tear or a crack. Furthermore, the shape of the air foil 14 may be distorted or the outer shape of the disk hub 12 may be changed by internal stress generated when the disk hub 12 is solidified.

The problem at the time of precision casting worsens as the size of the impeller or the turbine wheel increases. Since, however, casting materials usually have a low mechanical strength, the casting method may not be suitable for manufacturing a large-scale impeller or turbine. Hence, in the case of a large impeller or turbine wheel, a manufacturing method that mechanically processes an expensive forged bar should be used, which significantly increases manufacturing costs.

SUMMARY

One or more exemplary embodiments provide a method of manufacturing a rotor such as an impeller or a turbine wheel for effectively restricting casting defects such as a hot crack and a dimensional defect that may be generated during a precision casting process.

According to an aspect of an exemplary embodiment, there is provided a method of manufacturing a rotor, the method including: forming a mold for casting including a cavity of a shape corresponding to the rotor; arranging a core at a location corresponding to an inside of the rotor in the cavity of the mold for casting; injecting molten metal into the mold for casting where the core has been arranged; and removing the core from a casting which has been cast in the mold for casting.

The forming the mold for casting may include slurry-coating a wax model of the shape corresponding to the rotor, and the core may have been injected into the wax model in advance when arranging the core in the cavity of the mold for casting.

The method may further include: preparing a mold for wax having a cavity of the shape corresponding to the rotor; arranging the core in an inside of the cavity of the mold for wax; injecting wax into the inside of the cavity of the mold for wax where the core has been arranged, and solidifying the wax; and extracting the wax model solidified in the mold for wax so that the core is injected into the wax model in advance.

The core may be arranged to revolve around a rotation axis of the rotor in the inside of the rotor.

The core may include ceramic, and the core may be removed by a ceramic leaching process when removing the core from the casting.

The removing the mold for casting and the removing the core from the casing may be performed simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects will become more apparent by describing in detail exemplary embodiments with reference to the attached drawings, in which:

FIG. 1A a diagram schematically illustrating a cross-section of a related art impeller or turbine wheel;

FIG. 1B is a diagram schematically illustrating a part of a casting process of the related art impeller or turbine wheel;

FIG. 2 is a flowchart schematically illustrating a method of manufacturing an impeller, according to an exemplary embodiment;

FIG. 3 is a cross-section schematically illustrating a first mold for casting a wax model, according to an exemplary embodiment;

FIG. 4 is a perspective diagram schematically illustrating a core inserted into a wax model, according to an exemplary embodiment;

FIG. 5 is a cross-sectional diagram schematically illustrating insertion of a core into a cavity of a first mold, according to an exemplary embodiment;

FIG. 6 is a cross-sectional diagram schematically illustrating insertion of a wax into a first mold into which the core has been inserted, according to an exemplary embodiment;

FIG. 7 is a cross-sectional diagram schematically illustrating a wax model into which a core has been inserted, according to an exemplary embodiment;

FIG. 8 is a cross-sectional diagram schematically illustrating a second mold that has been manufactured by slurry-coating a core model, according to an exemplary embodiment;

FIG. 9 is a cross-sectional diagram schematically illustrating the second mold from which a wax model has been removed, according to an exemplary embodiment;

FIG. 10 is a cross-sectional diagram schematically illustrating the second mold into which molten metal has been injected, according to an exemplary embodiment; and

FIG. 11 is a cross-sectional diagram schematically illustrating an impeller manufactured by removing a second mold and a core, according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

A method of manufacturing a rotor such as an impeller or a turbine wheel, according to an embodiment, will be described with reference to the attached drawings. However, shapes of the impeller and the turbine wheel are similar in that both the impeller and the turbine wheel include a disk hub and an air foil, and they may be manufactured in the same manufacturing method, and thus, only a method of manufacturing an impeller is described for the convenience of description.

FIG. 2 is a flowchart schematically illustrating a method of manufacturing an impeller, according to an exemplary embodiment. Referring to FIG. 2, the method of manufacturing an impeller of the present embodiment includes an operation of preparing a mold for wax (S10), an operation of arranging a core in a cavity of the mold for wax (S20), an operation of injecting wax into the mold for wax (S30), an operation of extracting a wax model (S40), an operation of forming a mold for casting by using the wax model (S50), an operation of removing the wax model (S60), an operation of injecting molten metal into the mold for casting (S70), an operation of forming a cavity in a casting by removing the core (S80), and an operation of extracting the casting (S90).

The operation of preparing the mold for wax (S10) prepares a mold for casting a wax model having a shape of an impeller. FIG. 3 schematically illustrates a mold for wax 100. Referring to FIG. 3, the mold for wax 100 includes a cavity 102 of a shape corresponding to an impeller. The mold for wax 100 also includes a wax injection hole 104 through which wax is injected thereto. Furthermore, the mold for wax 100 may include a core guide 110 so that a core to be described later may be placed at an accurate location. The mold for wax 100 may be manufactured in a manner that is the same as a mold for wax used in a general lost wax process, and thus, the detailed description thereof is omitted here.

The operation of arranging a core in the cavity 102 of the mold for wax 100 (S20) includes placing the core in the cavity 102 of the mold for wax so that the core may be placed at a corresponding location inside a disk hub of the impeller. FIG. 4 is a perspective view schematically illustrating a core 200, and FIG. 5 is a cross-sectional diagram schematically illustrating the core 200 of FIG. 4 that is arranged within the mold for wax 100 of FIG. 3. Referring to FIG. 4, the core 200 is hollow so that a rotation axis of the impeller may pass, the core 200 is formed to revolve on a basis of the rotation axis of the impeller, and occupy an internal space of the disk hub of the impeller. Furthermore, the core 200 includes a connection part 210 so that the core 200 may be put in the core guide 110 of the mold for wax 100. As illustrated in FIG. 5, the core 200 is placed in the cavity 102 of the mold for wax 100, and thus, the core 200 may be stably placed at a right location. The core 200 may be formed of ceramic materials having a strong resistance.

The operation of injecting wax into the mold for wax 100 (S30) includes casting a wax model by injecting wax into the cavity 102 of the mold for wax 100 through the wax injection hole 104. FIG. 6 schematically illustrates a state where wax has been injected into the mold for wax 100 into which the core 200 has been inserted. As illustrated in FIG. 6, after the liquid wax is injected into the mold for wax 100, the wax solidifies as the wax is cooled, a wax model 30 of the same shape as that of the cavity 102 of the mold for wax 100 is formed. That is, the wax model 30 is formed in the same shape as that of the impeller. The wax model 30 includes a portion 300 corresponding to the disk hub of the impeller and a portion 310 corresponding to the air foil of the impeller. Furthermore, the core 200 is arranged in advance at the mold for wax 100, and occupies the internal space 300 of the disk hub of the impeller.

The operation of extracting the wax model 30 (S40) is an operation of releasing the mold for wax 100 and extracting the wax model 30 within the mold for wax 100. The core 200 was inserted into the disk hub part 300 of the extracted wax model 30. At this time, the connection part 210 of the core 200 protrudes from the wax model 30. FIG. 7 illustrates the wax model 30 released from the mold for wax 100.

The operation of forming a mold for casting process by using the wax model (S50) is an operation of manufacturing a mold for casting of an impeller by slurry-coating an external surface of the wax model 30. The slurry coating forms a mold for casting of ceramic materials by repeating a process of applying and solidifying a ceramic slurry on the external surface of the wax model 30, and is widely used in the Lost wax method. FIG. 8 schematically illustrates a cross-section of a mold for casting 400 that covers the wax model 30, and as illustrated in FIG. 8, the mold for casting 400 is formed by the slurry coating, and thus, the mold for casting 400 includes a cavity of the same shape as that of the wax model 30. The mold for casting 400 may include a molten metal injection hole 406 and a wax discharge hole 404 for discharging melted wax.

The operation of removing the wax model 30 (S60) includes removing the wax model 30 within the mold for casting 400 by melting the wax model 30, thereby leaving the mold for casting 400. If the entire mold for casting 400 is heated in a state where the wax model 30 is arranged within the mold for casting 400, the wax model 30 is melted into liquid. If the liquid wax is discharged through the wax discharge hole 404 of the mold for casting 400, the mold for casting 400 remains. FIG. 9 is a cross-sectional diagram schematically illustrating a state where the wax model 30 has been removed from the mold for casting 400. As illustrated in FIG. 9, if the wax model 30 within the mold for casting 400 is removed, the mold for casting 400 includes a cavity 402 of an impeller shape, and the core 200, which has been inserted within the wax model 30, remains at a location corresponding to the disk hub of the impeller at the inside of the mold for casting 400.

In the present embodiment, the core 200 forms the mold for casting 400 by slurry-coating the already inserted wax model 30. Thus the operation of forming the mold for casting 400 and the operation of inserting the core 200 into the mold for casting 400 are simultaneously performed.

The operation of injecting molten metal into the mold for casting 400 (S70) is an operation of forming a casting 50 by injecting the molten metal for casting the impeller into the mold for casting 400 and solidifying the molten metal. FIG. 10 is a cross-sectional diagram schematically illustrating a state where the molten metal is injected into the mold for casting 400 and solidifies. As illustrated in FIG. 10, the core 200 is arranged within the mold for casting 400, and thus, the molten metal may not occupy by as much as the space occupied by the core 200.

The core 200 is arranged at a disk hub part 500 of the casting 50, and thus, the mass and volume of the molten metal that forms the disk hub part 500 are low compared to a case in the related art impeller casting method, as illustrated in FIG. 1B. Hence, the amount of latent heat of the disk hub part 500 may be significantly reduced, and thus, various casting defects such as a hot crack by heat contraction and deformation of the impeller shape may be prevented.

Furthermore, in the case of the related art impeller casting method, as illustrated in FIG. 1B, the molten metal solidifies only in a disk hub direction at an air foil portion of the impeller, and thus, the stress may concentrate on the disk hub part or a cavity may be formed. However, in the present embodiment, the molten metal is cooled even in an area around the core 200, and thus, internal thermal stress may be effectively distributed as the molten metal solidifies overall. Hence, the casting 50 formed in the present operation is manufactured such that internal stress is significantly released compared to the related art impeller casting method.

The operation of forming a cavity in the casting 50 by removing the core 200 (S80) is an operation of removing the core 200 having been inserted in the disk hub part 500 of the casting 50 in a ceramic leaching process. The ceramic leaching process is a process of melting to remove ceramic through a special solution and heating process. This process is generally used as a method of removing ceramic, and thus, a detailed description thereof is omitted here. If the core 200 is removed in the casting through the leaching process, a cavity 502 is formed at a part corresponding to the core 200 in a disk hub portion 500 of the casting.

The operation of extracting the casting (S90) is an operation of extracting the casting 50 by removing the mold for casting 400. The operation of extracting the casting (S90) may be independently performed before or after the operation of forming a cavity at the casting 50 by removing the core from the casting 50 (S80). However, when the slurry coat that forms the mold 400 for casting is ceramic material that may be removed by the leaching process, the operation of removing the core 200 (S90) may also be simultaneously performed.

FIG. 11 is a cross-sectional diagram schematically illustrating an impeller 2 completed by extracting the casting 50. As illustrated in FIG. 11, the cavity 502 of a shape corresponding to the core is formed in the disk hub portion 500 of the impeller 2. In the impeller 2 manufactured in the manufacturing method of the present embodiment, the disk hub portion 500 is hollow, and thus, the weight is reduced, and the centrifugal load that may be generated at the time of operation of the impeller may be significantly reduced. Hence, the impeller 2 has a superior structural stability and lifespan compared to the related art impeller 1.

A penetration hole 520 may be formed in the impeller 2 formed by the above-described method for later combination of a shaft (not shown).

Above, the method of manufacturing an impeller used in a compressor has been described, but the inventive concept may also be applied to a method of manufacturing a turbine wheel.

Although the Lost wax method is used for the above embodiments, but a separate mold may be formed without preparing a wax model. That is, a mold for casting may be manufactured without slurry-coating, and then a core is arranged within the mold for casting and molten metal may be injected. If the molten metal coagulates, the casting is extracted and the core having been inserted in the casting is removed through the leaching process, etc., so as to manufacture an impeller or a turbine. When a mold for casting is manufactured without using the Lost wax method, the operation of forming the mold for casting and the operation of arranging the core in the inside of the mold for casting are temporally separated.

Each operation described above is not necessarily performed in the order described above, and the order may be changed or may be simultaneously performed.

It was described above that the core 200 revolves around the circumference of the rotation axis of the impeller in a consecutive form like a donut. However, the core 200 may be intermittently arranged along the circumference of the rotation axis of the impeller. In this case, the core 200 may be arranged at regular intervals in terms of the distance and the angle from the rotation axis so that mass does not become eccentric in the impeller.

In the above embodiments, the cavity 502 having a shape of the core 200 was formed inside the disk hub portion 500. However, the shape and/or location of the cavity 502 and the core 200 are not limited thereto according to the inventive concept. Also, wax is used to form the mold for wax 100 and the wax model 30 in the above embodiments. However, a different material may be used to form a corresponding mold and a corresponding model. The above embodiments also describe slurry-coating to form the mold for casting 400. However, the inventive concept is not limited to this coating, and any corresponding coating method may be used to form the mold for casting 400.

According to a method of manufacturing an impeller or a turbine wheel of the above embodiments, casting defects such as a hot crack and a dimensional defect may be effectively restricted by relieving internal stress of the impeller or the turbine wheel, which may be generated at the time of precision casting.

Furthermore, the above method may be applied to a large impeller or turbine wheel. Hence, the manufacturing costs of a large impeller or turbine wheel may be significantly reduced.

Furthermore, in an impeller or turbine wheel manufactured by the above method, mass of the disk hub is reduced and the size of the centrifugal load is reduced, thereby significantly enhancing durability and mechanical stability.

While the inventive concept has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the inventive concept as defined by the following claims.

Claims

1. A method of manufacturing a rotor, the method comprising:

forming a mold for casting including a cavity of a shape corresponding to the rotor; arranging a core at a location corresponding to an inside of the rotor in the cavity of the mold for casting; injecting molten metal into the mold for casting where the core has been arranged; and removing the core from a casting which has been cast in the mold for casting.

2. The method of claim 1, wherein the core is arranged to revolve around a rotation axis of the impeller or the turbine wheel in the inside of the rotor.

3. The method of claim 1, wherein the core is a material comprising ceramic, and

wherein the core is removed by a ceramic leaching process when removing the core from the casting.

4. The method of claim 1, wherein the forming the mold for casting comprises coating a model of the shape corresponding to the rotor, and

wherein the core has been injected into the model in advance when arranging the core in the cavity of the mold for casting.

5. The method of claim 4, wherein the model comprises wax.

6. The method of claim 4, wherein the coating comprises slurry-coating.

7. The method of claim 4, wherein the core is arranged to revolve around a rotation axis of the rotor in the inside of the rotor.

8. The method of claim 4, wherein the core is a material comprising ceramic, and

wherein the core is removed by a ceramic leaching process when removing the core from the casting.

9. The method of claim 4, further comprising:

preparing a modeling mold having a cavity of the shape corresponding to the rotor;

arranging the core in an inside of the cavity of the modeling mold;

injecting a model material into the inside of the cavity of the modeling mold where the core has been arranged, and solidifying the model material; and

extracting the model solidified in the modeling mold so that the core is injected into the model in advance.

10. The method of claim 9, wherein the core is arranged to revolve around a rotation axis of the rotor in the inside of the rotor.

11. The method of claim 10, wherein the core comprises ceramic, and

wherein the core is removed by a ceramic leaching process when removing the core from the casting.

12. The method of claim 9, wherein the core is a material comprising ceramic, and

wherein the core is removed by a ceramic leaching process when removing the core from the casting.

13. The method of claim 9, wherein the model material comprises wax.

14. The method of claim 1 further comprising extracting the casting by removing the mold for casting.

15. The method of claim 14, wherein the removing the mold for casting and the removing the core from the casing are performed simultaneously.

16. The method of claim 14, wherein the removing the mold for casting is performed before the removing the core from the casting.

17. The method of claim 14, wherein the removing the mold for casting is performed after the removing the core from the casting.

18. The method of claim 1, further comprising forming a cavity inside the casting by the removing the core from the casting.

19. The method of claim 1, wherein the rotor is an impeller or a turbine wheel.