KR20140039734A - Vacuum casting device for impeller, casting method of impeller, and impeller - Google Patents

Abstract

Provided are an impeller vacuum casting apparatus with an improved cooling structure of an impeller mold, an impeller casting method, and a casted impeller. The impeller vacuum casting apparatus comprises: i) an airtight chamber connected with an intake pump for maintaining the vacuum state inside thereof; ii) a crucible which is located inside the airtight chamber and is surrounded by high-frequency induction heating coils; iii) a mold support which is located under the crucible inside the airtight chamber and which supports the impeller mold connected with a riser; and iv) a cooling device which cools the impeller mold. The cooling device has a gas cooling unit cooling the impeller mold by spraying an inert gas under the center of the impeller mold in an axial direction of the impeller mold.

Description

Impeller vacuum casting device and impeller casting method and casting impeller {VACUUM CASTING DEVICE FOR IMPELLER, CASTING METHOD OF IMPELLER, AND IMPELLER}

The present invention relates to an impeller, and more particularly, to an impeller vacuum casting device, an impeller casting method, and a casting impeller, which improve the cooling structure of the impeller mold to increase the rigidity by miniaturizing the structure of the impeller.

An investment casting method, also known as a lost-wax method, is known among casting methods for manufacturing mechanical parts. This method includes the steps of fabricating a model by processing wax, coating a fireproofing material on the surface of the model, applying a molding sand, and drying the mold to produce a mold, removing the model by heating, and then firing the mold at a high temperature. And solidifying the molten metal after injecting the molten metal into the mold, and removing the product by removing the mold.

The investment casting method enables the precise production of special alloy steel products and mechanical parts with complex shapes, and provides excellent dimensional accuracy and surface condition. Therefore, a technique for producing an impeller mounted on a turbocharger, a turbine wheel, a turbo blower, or the like by an investment casting method, in particular, an impeller vacuum casting technique for injecting molten metal into a mold in a vacuum state has been applied.

When the molten metal is injected in a vacuum atmosphere, oxidation of the molten metal can be prevented, and a problem of inflow of air into the mold through the micro gaps or pores present in the mold can be prevented. A conventional impeller vacuum casting apparatus includes a hermetic chamber, a crucible installed inside the hermetic chamber, a high frequency induction heating apparatus for melting a metal material inside the crucible, a mold pedestal for supporting the impeller mold to which the hot water is connected, and a mold pedestal for cooling the mold pedestal. It includes a cooling device.

The impeller has a size and a direction of the tissue depending on the direction of cooling and the cooling rate during the solidification after the injection of the molten metal. Since the size and direction of the tissue is an important factor in determining the rigidity of the impeller, there is a demand for an optimal cooling technique capable of increasing the rigidity by miniaturizing the structure of the impeller.

The present invention is to provide an impeller vacuum casting apparatus in which the cooling structure is improved so that the structure of the impeller can be finely grown to increase the rigidity of the impeller.

The present invention is to provide a casting impeller by improving the heat resistance and mechanical properties at the same time by finely controlling the central crystal structure of the impeller by the investment method using a vacuum casting device.

The present invention is to provide an impeller casting method capable of finely controlling the central crystal structure of the impeller by an investment method using a vacuum casting device.

An impeller vacuum casting apparatus according to an embodiment of the present invention includes: (i) a hermetic chamber connected to a suction pump to keep the interior vacuum; ii) a crucible located inside the hermetic chamber and surrounded by a high frequency induction heating coil; Located inside the crucible, the mold support for supporting the impeller mold connected to the hot water, and iii) a cooling device for cooling the impeller mold. The cooling apparatus includes a gas cooling unit that cools the impeller mold by injecting an inert gas along the axial direction of the impeller mold at the center lower portion of the impeller mold.

The impeller mold may form a wing surface, an edge surface, and a base surface on an inner wall, and may be disposed such that the base surface faces the crucible and the wing surface faces the mold support.

The mold support may form an opening. The gas cooling unit may include a gas supply pipe positioned over the inside and the outside of the hermetic chamber, and an injection nozzle connected to the gas supply pipe and penetrating through the opening of the mold support to protrude to the top of the mold support.

The impeller mold may form a recess corresponding to the drive shaft accommodating portion of the impeller under the wing surface, and a part of the injection nozzle may be located inside the recess.

The cooling apparatus includes: (i) a coolant accommodating portion located below the mold support and forming a coolant accommodating space to cool the mold support, and ii) providing coolant to the coolant accommodating space, and discharging the coolant used for cooling to circulate the coolant. It may further comprise a cooling water circulation to.

The coolant accommodating part includes: iii) a first plate which is located inside the hermetic chamber and is in surface contact with the mold support, and ii) a second which is fixed to the lower part of the first plate while forming a cooling water accommodating space therebetween. It may include a plate.

The cooling water circulation unit may include a supply pipe and a discharge pipe that are positioned over the inside and outside of the hermetic chamber and penetrate the second plate to be connected to the cooling water accommodation space. The coolant accommodating part may further include a nozzle protector positioned at the center of the first plate and penetrating through the opening of the mold support to protrude upwardly of the mold support.

The nozzle protector may have a through hole formed at an upper end thereof, and one end of the spray nozzle may be fitted into and fixed to the through hole of the nozzle protector. The inner wall of the nozzle protector below the through hole may have a diameter larger than the outer diameter of the spray nozzle. The cooling water circulation unit may further include an injection pipe that is connected to the supply pipe, receives the cooling water, and injects the cooling water into the space between the injection nozzle and the nozzle protector.

The impeller vacuum casting device may further include a lifting device connected to the cooling device outside the hermetic chamber to adjust the height of the cooling water receiver and the mold support. The cooling apparatus may further include a support shaft for supporting the coolant accommodating portion, and a plurality of movement guides for smoothly moving when descending. The support shaft and the plurality of movement guides may be located inside and outside the hermetic chamber.

The movement guide may be formed in a hollow cylindrical shape. The gas supply pipe and the supply pipe may be located inside one of the moving guides, and the discharge pipe may be located inside the other moving guide.

Casting impeller according to an embodiment of the present invention is cast by the investment casting method, using a metal raw material of any one of the super heat-resistant alloy and nickel alloy, and cast in a vacuum casting apparatus. The solidified casting structure was visually observed so that the surface portion of the impeller was dendritic, and the center of the impeller contained the casting structure consisting of fine grains having an average grain size of 5 mm or less.

The cast structure may be observed under an optical microscope to have a diameter of the average grains of the central portion of 250 μm or less. In the cast structure, the elements forming carbides can be evenly dispersed in the grains without diffusing to the grain boundaries.

The impeller may have a tensile strength (T.S) at room temperature of 790 MPa to 874 MPa and a yield strength of 721 MPa to 819 MPa. The metal raw material may be Inconel 713LC.

Impeller casting method according to an embodiment of the present invention, i) charging a metal raw material of any one of the super heat-resistant alloy, nickel alloy, and Inconel 713LC in the crucible installed inside the impeller vacuum casting apparatus, ii) the investment method Supporting the impeller mold manufactured and attached to the upper part of the support, iii) maintaining the vacuum casting apparatus in a vacuum state and operating a high frequency induction heating coil to melt the metal raw material, iv) rotating the crucible to impeller the molten metal V) cooling the coolant accommodating part using the cooling device of the vacuum casting apparatus, and operating the gas cooling part to rapidly cool the impeller mold by injecting an inert gas through the injection nozzle into the recess of the impeller mold. It includes.

According to the present invention, an impeller vacuum casting device for rapidly cooling a lower part of an impeller mold in a vacuum state can finely control the structure of the impeller. In addition, fine control of the central crystal structure of the impeller can simultaneously improve the heat resistance and mechanical properties of the impeller. In addition, it is possible to effectively control the central crystal structure of the impeller.

1 is a block diagram of an impeller vacuum casting apparatus according to an embodiment of the present invention.
FIG. 2 is a partially enlarged view of the impeller vacuum casting device shown in FIG. 1.
FIG. 3 is a cross-sectional view illustrating a pressure bath and an impeller mold in the impeller vacuum casting apparatus illustrated in FIG. 1.
4 is a cross-sectional view of an impeller manufactured using the impeller mold shown in FIG. 3.
5 is an enlarged view of a cooling device of the impeller vacuum casting device shown in FIG. 1.
FIG. 6 is an enlarged view of a portion C of the cooling device illustrated in FIG. 5.
7A and 7B are longitudinal cross-sectional crystallographic images of impellers cast according to Examples 1 and 2, respectively.
8A and 8B are micrographs observing the cross-sectional center portion of the impeller cast according to Example 1. FIG.
9A and 9B are micrographs observing the cross-sectional center portion of the impeller cast according to Example 2. FIG.
FIG. 10 is a photograph showing a portion of a sample taken to measure mechanical properties of an impeller cast according to Example 2. FIG.
11A and 11B are graphs showing the mechanical properties of the impeller cast according to Example 1 and Example 2, respectively.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

1 is a configuration diagram of an impeller vacuum casting apparatus according to an embodiment of the present invention, Figure 2 is a partially enlarged view of the impeller vacuum casting apparatus shown in FIG.

1 and 2, the impeller vacuum casting apparatus 100 of the present embodiment includes an airtight chamber 11, a vacuum forming unit 12, a crucible 13, a high frequency induction heating coil 14, and a rotating device 15. ), Mold support 16, and cooling device 200. The mold support 16 supports the impeller mold 30 to which the hot water 17 is connected, and the cooling device 200 cools the mold support 16 and the impeller mold 30.

The hermetic chamber 11 maintains the interior in a vacuum state by the action of the vacuum forming unit 12. The vacuum forming unit 12 includes an air discharge pipe 121 positioned at one side of the airtight chamber 11 and a suction pump 122 connected to the air discharge pipe 121. The inside of the hermetic chamber 11 can be exhausted by the powerful intake action of the suction pump 122 to form a certain degree of vacuum. Vacuum formation may remove impurities and offgases generated during melting of the metal in the crucible 13 to produce a high purity molten metal.

The crucible 13 has an open top shape and is surrounded by a high frequency induction heating coil 14. A door 18 is installed at the upper portion of the airtight chamber 11 to allow the metal raw material to be introduced into the crucible 13 when the door 18 is opened. The high frequency induction heating coil 14 has its end drawn out of the hermetic chamber 11 to receive a high frequency current for dissolving the metal raw material. The crucible 13 and the high frequency induction heating coil 14 are surrounded by a heat insulating container 19.

The rotating device 15 is fixed to the outer wall of the heat insulation container 19. The rotating device 15 operates after melting the metal raw materials introduced into the crucible 13 to form a molten metal, and tilts the crucible 13 to pour the molten metal downward. To this end, the rotating device 15 includes a pair of support beams 151 fixed to the left and right sides of the heat insulation container 19, and an extension beam 152 fixed to the heat insulation container 19 at a lower portion of the support beam 151. And a rotation driver 153 installed on one of the support beams 151 to rotate the support beams 151.

In FIG. 1, reference numeral 20 denotes a pressure regulating valve, reference numeral 21 denotes a see-through window, and reference numeral 22 denotes a temperature sensor for detecting a temperature of a molten metal.

The impeller mold 30 to which the hot water 17 is connected is located under the crucible 13, and the mold support 16 supports the impeller mold 30. The mold support 16 is formed in a box shape with an open upper portion to surround the whole or part of the impeller mold 30. The molten metal 17 receives the molten metal from the crucible 13, and the molten metal poured into the molten metal 17 is sucked into the inlet of the impeller mold 30 by gravity to fill the internal space of the impeller mold 30.

3 is a cross-sectional view showing a hot water and an impeller mold of the impeller vacuum casting apparatus shown in FIG. 1, and FIG. 4 is a cross-sectional view of an impeller manufactured using the impeller mold shown in FIG.

Referring to FIGS. 3 and 4, the impeller mold 30 forms an internal space 31 having the same shape as the impeller 40 to be manufactured, and is directly connected to the hot water 17 to the upper portion of the internal space 31. To remove the hot water 17 after casting.

The impeller 40 includes a base portion 41 parallel to the central axis (see A-A line) and a plurality of blades 42 formed on the outer circumferential surface of the base portion 41. The blade 42 includes a wing surface 43, an edge surface 44, and a base surface 45. During the action of the impeller 40, the gas is introduced into the space between the blades 42, compressed by the rotating blade 42, and then discharged out of the edge surface 44. The base portion 41 may form a drive shaft accommodating portion 46 for inserting the drive shaft, and the longitudinal direction of the drive shaft accommodating portion 46 coincides with the central axis (see line A-A).

The impeller mold 30 forms an internal space having the same shape as the base portion 41 and the plurality of blades 42 described above. Accordingly, the wing surface 33, the edge surface 34, and the base surface 35 corresponding to the blade 42 are also formed on the inner wall of the impeller mold 30. In addition, the impeller mold 30 forms a recess 36 corresponding to the drive shaft accommodating portion 46 of the impeller 40.

The impeller mold 30 is disposed above the mold support 16 with the base surface 35 facing the crucible and the recess 36 facing the bottom 161 (see FIG. 2) of the mold support 16. The central axis of the impeller mold 30 (see line B-B) is perpendicular to the ground and coincides with the central axis of the impeller 40 (see line A-A). End portions of the nozzle protector 54 and the spray nozzle 72 described below may be located inside the recess 36 of the impeller mold 30.

Referring to FIG. 2, the cooling device 200 is basically located under the mold support 16, and a part of the cooling device 200 penetrates the mold support 16 and protrudes above the mold support 16. do. To this end, an opening 162 is formed in the bottom portion 161 of the mold support 16.

The cooling device 200 indirectly cools the impeller mold 30 disposed on the mold support 16 by circulating cooling water to cool the mold support 16. At the same time, the cooling device 200 increases the cooling rate of the impeller mold 30 by injecting an inert gas directly toward the impeller mold 30 in the hermetic chamber 11.

FIG. 5 is an enlarged view of a cooling device of the impeller vacuum casting device shown in FIG. 1, and FIG. 6 is an enlarged view of a C circular portion of the cooling device shown in FIG. 5.

2, 5, and 6, the cooling device 200 includes a coolant accommodating part 50, a coolant circulating part 60, and a gas cooling part 70. The coolant accommodating part 50 is located inside the hermetic chamber 11, and the coolant circulation part 60 and the gas cooling part 70 are located outside and inside the hermetic chamber 11.

The coolant accommodating part 50 is positioned below the mold support 16 and forms a coolant accommodating space 51 filled with the coolant. The coolant accommodating part 50 is formed by forming a coolant accommodating space 51 between the first plate 52, which is in surface contact with the bottom part 161 of the mold support 16, and the first plate 52. The second plate 53 is fixed to the lower portion of the first plate (52).

At the center of the first plate 52 is a nozzle protector 54 which penetrates through the opening 162 of the mold support 16 and protrudes above the bottom 161 of the mold support 16. The through hole 55 is formed at the upper end of the nozzle protector 54.

The coolant circulation part 60 includes a supply pipe 61, an injection pipe 62, and a discharge pipe 63. One end of the supply pipe 61 is located outside the hermetic chamber 11 and is connected to a cooling water supply pump (not shown) to receive the cooling water. One end of the opposite side of the supply pipe 61 penetrates through the second plate 53 inside the hermetic chamber 11 and is located in the coolant accommodating space 51.

The injection pipe 62 is located at the center of the coolant accommodating space 51 and is connected to the supply pipe 61 to receive the coolant therefrom. The injection pipe 62 injects the coolant to the uppermost end of the coolant accommodating part 50 that is closest to the impeller mold 30, that is, to the inner wall of the nozzle protector 54. For this purpose, the injection pipe 62 may include an annular circulation pipe 621 and an extension pipe 622 extending from the circulation pipe 621 toward the inner wall of the nozzle protector 54.

The coolant discharged from the extension pipe 622 fills the entire coolant accommodating space 51 and cools the nozzle protector 54, the first plate 52, and the mold support 16 in contact with the first plate 52. Let's do it. The shape of the injection pipe 62 is not limited to the illustrated example and can be variously modified. In addition, the injection pipe 62 may be omitted as needed.

One end of the discharge pipe 63 penetrates through the second plate 53 and is connected to the coolant accommodation space 51, and the other end of the discharge pipe 63 is connected to the cooling water suction pump not shown outside of the hermetic chamber 11. Connected with. As a result, the cooling water used for cooling the mold support 16 is discharged to the outside of the airtight chamber 11 via the discharge pipe 63.

The gas cooling unit 70 includes a gas supply pipe 71 and an injection nozzle 72.

The injection nozzle 72 is a pipe shape having a predetermined inner diameter and an outer diameter, one end of which is fitted into the through hole 55 of the nozzle protector 54 and the other end of which is supported by the second plate 53. The outer diameter of the spray nozzle 72 is smaller than the inner wall diameter of the nozzle protector 54 positioned below the through-hole 55 to maintain the distance between the spray nozzle 72 and the inner wall of the nozzle protector 54. Therefore, since the coolant circulates outside the injection nozzle 72, the temperature of the inert gas flowing in the injection nozzle 72 can be lowered.

End portions of the nozzle protector 54 and the injection nozzle 72 may be located inside the recess 36 formed in the impeller mold 30. In this case, the distance between the end of the injection nozzle 72 and the impeller mold 30 may be minimized to increase the cooling speed and the cooling efficiency of the impeller 40.

One end of the gas supply pipe 71 is located outside the hermetic chamber 11 and is connected to an inert gas injection pump (not shown) to receive an inert gas. One end of the opposite side of the gas supply pipe 71 is connected to a support shaft 23 supporting the central lower portion of the second plate 53 in the hermetic chamber 11. A gas flow passage 24 connecting the injection nozzle 72 and the gas supply pipe 71 is formed in the support shaft 23 and the second plate 53. It may be an inert gas argon gas or helium gas.

According to the above-described configuration of the cooling device 200, the coolant circulation part 60 cools the mold support 16 to indirectly cool the impeller mold 30, and the gas cooler 70 of the impeller mold 30. The impeller mold 30 is directly cooled by directly injecting an inert gas along the direction of the central axis of the impeller mold 30 at the center lower portion.

Therefore, the cooling speed of the impeller 40 may be increased to refine the structure of the impeller 40, and as a result, the impeller 40 may be manufactured with excellent rigidity. At this time, the cooling direction of the impeller mold 30 is a direction from the lower side of the impeller mold 30 to the upper side, which is the direction from the wing surface 33 of the impeller mold 30 toward the base surface 35. Coincides with the direction of the central axis.

The cooling device 200 is connected to the lifting device 80 (see Fig. 1) and the height thereof is adjusted. The elevating device 80 includes a motor and a gear box (not shown) connected to the support shaft 23, and the cooling device 200 includes at least two moving guides 25 so as to smoothly move during elevating. The support shaft 23 and the movement guide 25 are fixed to the lower part of the second plate 53 and are positioned over the inside and outside of the hermetic chamber 11. A bearing block 26 for supporting the support shaft 23 and the movement guide 25 is installed on the inner bottom surface of the hermetic chamber 11.

The movement guide 25 has a hollow cylindrical shape and is formed of a solid metal material. The supply pipe 61 and the gas supply pipe 71 may be located inside one of the moving guides 25, and the discharge pipe 63 may be located inside the other moving guide 25. Therefore, it is possible to surround and protect the supply pipe 61, the gas supply pipe 71, and the discharge pipe 63 using the movement guide 25. The elevating device 80 serves to adjust the relative height of the impeller mold 30 relative to the crucible 13 by elevating the impeller mold 30.

Next, the casting method of the impeller 40 using the impeller vacuum casting apparatus 100 mentioned above is demonstrated.

Impeller castings are cast by investment casting (or lost wax process).

In order to cast the impeller casting, an impeller mold 30 is first manufactured using an impeller model made of wax. The impeller mold 30 is manufactured according to a conventional investment casting method. Here, the hot water 17 attached to the impeller mold 30 is directly attached to the hot water type, and the hot water 17 can be appropriately soaked even in a thin thickness, such as the impeller wing surface 33 or the edge surface 34. ) Volume is at least larger than the volume of the impeller.

And the outside of the impeller mold 30 may be coated with a heat insulating material to maintain a constant heat retention, in which case the molten metal can be evenly penetrated to the corner of the impeller mold (30).

The manufactured impeller mold 30 is mounted in the vacuum casting apparatus 100, and a metal raw material is charged into the crucible 13. The metal raw material used for manufacturing the impeller uses a super heat-resistant alloy or a nickel alloy, preferably Inconel 714LC.

The composition of Inconel 713L as an example of the used metal raw material is shown in Table 1 below.

A metal raw material is charged into the crucible 13 and the suction pump 122 is operated while the impeller mold 30 is supported on the mold support 16 to maintain the inside of the airtight chamber 11 in a vacuum. In this state, an inert gas such as nitrogen gas or argon gas may be selectively injected to keep the inside of the hermetic chamber 11 inactive.

Then, a current is applied to the high frequency induction heating coil 14 to melt the metal raw material inside the crucible 13. At this time, the melting temperature of the metal raw material is 1600 ℃ to 1680 ℃, the temperature of the impeller mold 30 is maintained at 1000 ℃ to 1100 ℃.

The molten metal of the molten metal raw material is injected into the upper part (inlet) of the impeller mold 30 by the rotation of the crucible 13 by the operation of the rotating device 15. The impeller mold 30 into which the molten metal is injected begins to cool under the influence of the mold support 16 having a relatively low temperature. The impeller mold 30 solidifies rapidly from the thin blade 42 and solidifies in a dendrite shape.

In addition, the gas cooling unit 70 of the cooling device 200 is operated so that the inert gas is ejected from the injection nozzle 72 to rapidly cool the recess 36 of the impeller mold 30. As a result, the central volume portion which is not solidified in the impeller mold 30 is rapidly cooled to finely solidify the cast structure.

The inert gas used at this time may be nitrogen, argon, or helium gas. In addition, the cooling rate of the impeller mold 30 due to the injection of inert gas may be 100 ℃ / min to 150 ℃ / min.

The impeller 40 solidified by the above process is used after cutting the pressure bath 17 and subjecting it to surface processing if necessary.

[Example]

An impeller mold 30 manufactured according to a conventional investment casting method was mounted on the mold support 16 located inside the vacuum casting apparatus 100. In addition, a metal raw material having an Inconel 713LC composition was charged into the crucible 13.

In the state prepared as described above, a current was applied to the high frequency induction heating coil 14 to melt the metal raw material inside the crucible 13. At this time, the melting temperature of the metal raw material was 1600 ℃ to 1680 ℃.

Next, the crucible 13 was rotated into the impeller mold 30 maintained at 1000 ° C to 1100 ° C to inject molten metal. Then, only the coolant circulation part 60 of the cooling device 200 was operated to cool the impeller mold 30 while cooling the mold support 16. The impeller 40 cooled and cast under such conditions is referred to as a first embodiment.

Then, the molten metal is injected into the impeller mold 30 using the same materials and conditions as those of the first embodiment, and then the coolant circulation unit 60 and the gas cooling unit 70 of the cooling apparatus 200 are operated at the same time to impeller mold 30. Argon gas was injected into the concave portion 36 through the injection nozzle 72 to rapidly cool the impeller mold 30. The impeller 40 cooled and cast under such conditions is referred to as a second embodiment.

Impellers 40 were manufactured by removing the impeller mold 30 and the hot water 17 from the castings cast according to Examples 1 and 2 above.

The prepared impellers 40 were cut along the A-A plane of FIG. 4 and then polished and corroded to observe the casting structure with the naked eye and an optical microscope. In addition, the manufactured impellers 40 measured mechanical properties such as tensile strength, yield strength, and elongation according to ASTM E8.

7A and 7B are longitudinal cross-sectional micrographs of the impeller cast according to Example 1 and Example 2, respectively.

As can be seen in Figure 7a, the impeller cast by Example 1 has a dendrite developed in a direction substantially perpendicular to the wall of the impeller mold, so that coarse crystal grains are formed in the center of the impeller.

In contrast, as shown in FIG. 7B, the impeller casted according to Example 2 has a dendrite formed at a portion (ie, a surface portion) close to the wall of the impeller mold, but a fine grain is formed at the inner center of the impeller due to forced cooling. It turns out that this is formed. At this time, when viewed with the naked eye, the average grain size at the center was 5 mm or less, and the grain size was uniform and the grain boundaries were dense.

8A and 8B are micrographs observing a cross-section center of an impeller casted according to Example 1, and FIGS. 9A and 9B are micrographs observing a cross-section center of an impeller casted according to Example 2. FIG.

As can be seen in Figure 8a (scale bar is 250㎛), the microstructure of the impeller cast according to Example 1 is a coarse grain with a large diameter of the grains, the grain boundaries are thick and black spots appeared. It can be seen that black spots are concentrated at the grain boundaries in FIG. 8B (the scale bar is 50 µm), which is further enlarged in FIG. These black spots are carbides and are concentrated at grain boundaries.

However, as can be seen in Figure 9a (scale bar is 250㎛), the microstructure of the impeller cast according to Example 2 is very fine grains, the grain boundaries are narrow and the average grain size observed by the optical microscope after corrosion The diameter was found to be 250 μm or less. 9b (the scale bar is 50 µm), which is further enlarged, it can be seen that no foreign matter such as carbide is deposited at the grain boundaries. This is because the element which forms carbide by rapid solidification does not diffuse to a grain boundary, but is disperse | distributed evenly in a grain.

Next, in order to investigate the mechanical properties of the impeller cast according to Example 1 and Example 2, the cast impeller was cut along the line A-A of FIG. 4, and then the test piece was cut as shown in the rectangle in FIG. (FIG. 10 is an impeller cast in accordance with Example 2.)

Specimens cut out for the tensile test of the three specimens approximately parallel to the line A-A of Figure 10 to Figure 4, the left side of Example 1 and Example 2. 21 specimens, the center of which is No. 1 of Example 1 and Example 2. 22 specimens, the right side of which is No. 1 and Example 2 Nos. 23 The location of the specimen.

The specimens thus cut were subjected to HIP treatment and heat treatment, followed by a tensile test, and the results for Example 1 and Example 2 are shown in Table 2 and Table 3, respectively.

As can be seen from Table 2 and Table 3 it can be seen that the impeller according to Example 2 exhibits not only mechanical properties at room temperature but also mechanical properties at high temperature from 10% to 20% better than the impeller according to Example 1 . This difference in mechanical properties is due to the difference in the microstructure of the impeller according to Example 1 and Example 2.

Thus, the tensile test results in Table 2 and Table 3 are shown in FIG.

11A and 11B are graphs showing the mechanical properties of the impeller cast according to Example 1 and Example 2, respectively. 11A and 11B, T.S represents tensile strength, Y.S represents yield strength, and EL represents elongation.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Of course.

100: impeller vacuum casting device 11: hermetic chamber
12: vacuum forming unit 13: crucible
14: high frequency induction heating coil 15: rotating device
16: mold support 200: cooling device
30: impeller mold 40: impeller
50: cooling water accommodating part 60: cooling water circulation part
70: gas cooling unit 72: injection nozzle

Claims (19)

An airtight chamber connected to the suction pump to keep the interior vacuum;
A crucible located inside the hermetic chamber and surrounded by a high frequency induction heating coil;
A mold support positioned below the crucible in the hermetic chamber and supporting an impeller mold to which a hot water is connected; And
Cooling device for cooling the impeller mold
Including;
The cooling apparatus includes an impeller vacuum casting apparatus for cooling the impeller mold by injecting an inert gas along the axial direction of the impeller mold in the lower center of the impeller mold. The method of claim 1,
The impeller mold forms a wing surface, an edge surface and a base surface on an inner wall, and the base surface faces the crucible and the wing surface faces the mold support. 3. The method of claim 2,
The mold support forms an opening,
The gas cooling unit includes a gas supply pipe positioned over the inside and outside of the hermetic chamber, and an injection nozzle connected to the gas supply pipe and penetrating through an opening of the mold support to protrude upwardly of the mold support. . The method of claim 3,
The impeller mold is formed under the wing surface to form a recess corresponding to the drive shaft receiving portion of the impeller, a part of the injection nozzle is an impeller vacuum casting apparatus located in the recess. The method of claim 3,
The cooling device,
A coolant accommodating part positioned below the mold support to form a coolant accommodating space to cool the mold support; And
Cooling water circulation unit for providing a cooling water to the cooling water receiving space, circulating the cooling water by discharging the cooling water used for cooling
Impeller vacuum casting device further comprising. 6. The method of claim 5,
The cooling water receiving portion,
A first plate positioned in the hermetic chamber and in surface contact with the mold support; And
A second plate fixed to the lower portion of the first plate while forming the cooling water accommodating space therebetween;
Impeller vacuum casting device comprising a. The method according to claim 6,
The cooling water circulation unit, the impeller vacuum casting apparatus including a supply pipe and a discharge pipe which is located over the inside and outside of the hermetic chamber and penetrates through the second plate and connected to the cooling water receiving space. 8. The method of claim 7,
The cooling water receiving unit, the impeller vacuum casting apparatus further comprises a nozzle protector which is located in the center of the first plate and penetrates through the opening of the mold support to the upper portion of the mold support. 9. The method of claim 8,
The nozzle protector has a through hole formed at an upper end thereof, and one end of the spray nozzle is fixed to the through hole of the nozzle protector. An inner wall of the nozzle protector under the through hole has a diameter larger than an outer diameter of the spray nozzle. Impeller vacuum casting device. 10. The method of claim 9,
The cooling water circulation unit, the impeller vacuum casting apparatus further comprises a spray pipe connected to the supply pipe receives the cooling water and sprays the cooling water into the space between the spray nozzle and the nozzle protector. 11. The method according to any one of claims 5 to 10,
And an elevating device connected to the cooling device outside the hermetic chamber to adjust the height of the cooling water receiver and the mold support. 12. The method of claim 11,
The cooling device further includes a support shaft for supporting the cooling water accommodating portion, and a plurality of movement guides to smoothly move during ascending and descending.
The support shaft and the plurality of movement guides are located on the inside and outside of the hermetic chamber. 13. The method of claim 12,
The moving guide is formed in a hollow cylindrical shape, the gas supply pipe and the supply pipe is located in any one of the moving guide, the discharge pipe is an impeller vacuum casting device located in the other moving guide. In the impeller cast by the investment casting method,
Using the metal raw material of any one of the super heat-resistant alloy and nickel alloy,
Is cast in a vacuum casting device,
Visually observing the solidified cast structure, the surface portion of the impeller is dendrite, and the center of the impeller is a casting impeller comprising a cast structure consisting of fine grains having an average grain diameter of 5mm or less. 15. The method of claim 14,
The cast structure is observed by an optical microscope, the casting impeller of the average grain size of the central portion is 250㎛ or less. 16. The method of claim 15,
The casting structure is a casting impeller in which carbide forming elements are uniformly dispersed in grains without diffusion to grain boundaries. 17. The method of claim 16,
The impeller is a cast impeller having a tensile strength (TS) at room temperature of 790 MPa to 874 MPa and a yield strength of 721 MPa to 819 MPa. 18. The method according to any one of claims 14 to 17,
The metal raw material is Inconel 713LC casting impeller. In the impeller casting by the investment casting method,
Charging a metal raw material of any one of a super heat-resistant alloy, a nickel alloy, and Inconel 713LC into a crucible installed inside an impeller vacuum casting apparatus;
Supporting an impeller mold manufactured by an investment method and attached with a hot water on an upper portion of the support;
Maintaining the vacuum casting apparatus in vacuum and operating a high frequency induction heating coil to melt the metal raw material;
Rotating the crucible to inject molten metal into the impeller mold; And
Cooling the coolant accommodating part by using the cooling device of the vacuum casting device, and operating the gas cooling unit to rapidly cool the impeller mold by injecting an inert gas through the injection nozzle in the recess of the impeller mold
Impeller casting method comprising a.

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