JPH1058119A - Method for casting aluminum alloy-made impeller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an impeller without developing cast defect caused by misrun, etc., by inserting a heated ceramic-made vessel at the center part of the casting of the impeller and pouring molten Al alloy having different compositions from the inner part of the vessel and from the outer part of the vessel. SOLUTION: At the position of the center upper part of the impeller 20 in a mold assembled with metallic molds 5, 6 and a core 7, the heated ceramic- made vessel 8 and a stopper 9 are arranged. The molten Al alloy 2 applying degassing treatment in a ladle 1 is poured from a pouring hole 11 and reached to a prescribed molten metal surface level 23. Together with this, the molten Al alloy 4 applying the degassing treatment in a ladle 3 and having higher strength and higher ductility than these of the molten Al alloy 2 in the ladle 1, is poured to a prescribed molten metal surface level 24 in the vessel 8. The stopper 9 in the vessel is pulled up and a nozzle 10 is opened and the molten metal pressures in the outer part and the inner part of the vessel 8 are balanced. Successively, the vessel 8 is gradually risen and the molten Al alloy in the vessel 8 is shifted into the casting (the impeller product) through the nozzle 10 with the static pressure difference between the molten metals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method and a casting apparatus for an aluminum alloy impeller of a rotary machine, such as an impeller of a compressor for a turbo refrigerator, an impeller of a centrifugal blower, and a compressor of an exhaust turbocharger. .

[0002]

2. Description of the Related Art A high-speed rotating impeller such as an impeller of a turbo refrigerator compressor requires high strength and ductility.
An aluminum alloy casting (JIS standard AC4CH, AC4D, etc.) manufactured by a sand method or a plaster mold, or a casting method using a combination of these molds and a mold is used.

[0003] Such aluminum alloys are usually subjected to a heat treatment in which a solution treatment and an aging treatment are combined after casting, since mechanical properties such as tensile strength and elongation are greatly changed by heat treatment.

FIG. 4 shows an example of a casting apparatus for an aluminum alloy impeller for a turbo refrigerator. In FIG.
20 is an impeller (product part), 5 is an upper mold, 6 is a lower mold, and 7 is a silica sand or gypsum core. Also, 1
Reference numeral 8 denotes a feeder provided above the central boss, and reference numeral 19 denotes a feeder provided above the outer periphery of the blade. This relatively large feeder is liable to be generated in an aluminum alloy casting. Prevents shrinkage nests.

[0005] 11 is a casting hole for molten metal, 12 is a pouring gate, 13
Is a runner, and is communicated from the end of the runner 13 into the product section 20 via a weir 14. 1 is a ladle and 2 is a molten aluminum alloy.

At the time of casting such an impeller, a ladle 1 is used to add a molten metal of an aluminum alloy having a predetermined composition to a mold composed of a mold 5, a mold 6, and a core 7 made of silica sand or gypsum. 2 is a casting port 11, a gate 12, a runner 13
And pouring through the weir 14. The outer surfaces of the molds 5 and 6 are water-cooled as necessary.

FIG. 5 shows a schematic shape cut at the center (rotary axis) of the impeller casting cast as described above. Feeders 18 and 19 are cut and removed from the shape shown in FIG. FIG. 6 shows the shapes after the processing.

As shown in FIG. 6, the impeller is provided with a mounting portion 26 for mounting on a rotating shaft (not shown) and a mounting bolt hole 25 immediately below the center feeder portion 18. However, since this portion 17 is a portion where the cooling rate at the time of solidification immediately below the feeder portion 18 is slowed down and the mechanical properties are slightly reduced, the amount of the feeder and the amount of the feeder during casting are reduced. Particular attention is paid to the shape, composition of the components, and the like.

[0009]

The JIS-AC4CH, AC4D or aluminum alloy castings corresponding to them used in the impeller are relatively small casting products having a high cooling rate during solidification, and are not suitable for crystal grains and crystals. Microstructures such as deposits and precipitates become fine, and have high strength and elongation,
Large castings have the problem that the cooling rate at the time of solidification is low, which results in a coarse structure and low strength and ductility.

[0010] Such a problem is that the strength (yield strength and tensile strength) can be adjusted to some extent by solution treatment and aging heat treatment, but when the aging temperature is increased to increase the aging time,
Increases, but the ductility (elongation and drawing) decreases. Conversely, if the aging temperature is lowered to shorten the aging time, the opposite result will be obtained. Therefore, in such an aluminum alloy casting, it is difficult to simultaneously increase strength and elongation only by heat treatment.

However, as an aluminum alloy casting having relatively high strength and ductility, which solves the above problems to some extent, there is known a JIS-AC1B material which does not contain silicon and secures strength by copper and magnesium. Have been. However, since this AC1B material does not contain silicon, it has the following technical problems when it is used for castings having a large shape, such as an impeller, having a complicated shape and also having a thin portion. . (1) The fluidity of the molten metal is poor, and poor running of the molten metal into the thin portion (poor filling) occurs. (2) Shrinkage cavities are likely to occur due to a large amount of shrinkage during coagulation. As a result, the roughness of the casting surface becomes poor. (3) Since the amount of shrinkage during solidification is large, large deformation occurs, which causes cracking.

The present invention has been made in view of the problems of the prior art, and
Excellent mechanical properties (both sufficient strength and ductility)
It is an object of the present invention to provide a casting method and a casting apparatus for an impeller, which does not have a casting defect such as poor running water and poor surface roughness of shrinkage cavities.

[0013]

According to the present invention, there is provided an aluminum alloy impeller comprising a center boss connected to a rotating shaft and a blade formed on an outer peripheral side of the boss. In casting, a ceramic container heated to a solidification temperature or higher of the aluminum alloy is inserted into a central portion of the casting of the impeller, including a portion serving as the central boss portion, and a mold outside the container is inserted. Into the product part formed, an aluminum alloy having a predetermined composition is poured, and simultaneously or after the pouring, an aluminum alloy having a composition different from that of the aluminum alloy is poured into the container. At the same time or after the pouring, an aluminum alloy having a composition different from that of the aluminum alloy is poured into the container, and then the bottom of the ceramic container is placed in the product section. The aluminum alloy in the container is poured into the mold through the opening by casting the aluminum alloy impeller through the opening. Suggest a method.

[0014] In the above method, the product section includes:
Contains silicon such as JIS-AC4D material and AC4CH material,
Pouring a first aluminum alloy having good castability and pouring a second aluminum alloy having higher strength and higher ductility than the first aluminum alloy such as JIS-AC1B material into the container. It is preferable to do so.

Further, according to the present invention, as an apparatus for carrying out the casting method, there is provided an aluminum alloy impeller comprising a center boss portion connected to a rotating shaft and a blade portion formed on an outer peripheral side of the boss portion. A casting device for casting, wherein a runner and a casting hole for pouring the first aluminum alloy as the material for the impeller are communicated with a product portion formed in a mold, and a center of the impeller is provided. A second portion having a composition different from that of the first aluminum alloy is provided at a central portion including a portion serving as a boss portion.
And a bottomed hollow container having an opening at the bottom which can be opened and closed with respect to the product part is disposed, and the container is moved up and down in the product part. A casting device for an aluminum alloy impeller, characterized by connecting a lifting device, is proposed.

According to the invention, the JIS-AC is used for a portion which is liable to cause casting defects such as a thin wall, a complicated shape, poor running of the molten metal and a crack in the surface roughness of the shrinkage cavity, as in the blade portion of the impeller.
A first aluminum alloy containing silicon such as 4D material or AC4CH material and having excellent castability is poured, and the casting defect does not become a problem, and high strength and high ductility mechanical properties are required. In the center boss portion, a high strength and high ductility second material such as JIS-AC1B material, which is slightly inferior in castability but excellent in mechanical properties, is used.
Is poured using a ceramic container having an openable / closable opening at the bottom so as not to mix with the molten metal of the first aluminum alloy.

Thus, the vicinity of the center boss portion of the impeller can be made of an aluminum alloy having high strength and high ductility without requiring casting difficulties and without occurrence of casting defects. The thin and complex outer blades can be made of aluminum alloy of the required composition without seeing the occurrence of casting defects.
A product having both high ductility and avoiding the occurrence of casting defects and having high quality and high reliability can be obtained.

[0018]

Embodiments of the present invention will be described with reference to the following drawings.

FIG. 1 is a sectional view of an aluminum alloy casting impeller for a centrifugal chiller according to an embodiment of the present invention, and FIG. 2 is a sectional view of a casting of the impeller. In FIG. 1, 20 is an impeller (product part), 5 is an upper mold, 6
Is a lower mold, and 7 is a core of silica sand or gypsum.

1 is a ladle and 2 is JIS-A with good castability.
A molten metal of an aluminum alloy such as C4D material;
Is a pouring gate, 12 is a gate, and 13 is a runner.
The tip of 3 is communicated with the inside of the product section 20 via the weir 14.

Reference numeral 8 denotes a bottomed cylindrical ceramic container provided in the center of the impeller 20 in a vertical direction, and has a high strength, high ductility molten aluminum alloy such as JIS-AC1B material therein. 4 is accommodated, and a nozzle 10 is opened in the bottom plate of the container. Reference numeral 9 denotes a stopper which is inserted into the center of the container 8 and opens and closes the nozzle 10.

Numeral 15 denotes an elevating device for the ceramic container 8, which comprises a screw rod 31, a moving element 35 screwed to the screw rod 31 and moving up and down by the rotation of the screw rod 31, and a moving element 35. The movable member 35 is connected to the container 8 via an arm 32.

On the other hand, the screw rod 31 of the lifting device 15
Is connected to the electric motor 16 via a pulley mechanism 34, and the screw rod 3 is connected via the pulley mechanism 34 by the rotation of the electric motor 16.
1 can be rotated.

As described above, according to the present invention, the center of the impeller 20, which requires high strength and high ductility mechanical properties, is made of aluminum such as AC1B material, which has poor castability but has the above mechanical properties. An aluminum alloy such as JIS-AC4D material having a slightly inferior mechanical property but good castability is used for the outer peripheral blade portion, so that mixing during casting does not occur between both materials. A boundary is formed by the container 8.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a casting process of an aluminum alloy impeller using the impeller casting apparatus constructed as described above will be described below. In this embodiment, a molten metal made of JIS-AC4D material is poured from a normal runner 13 and a molten metal made of JIS-AC1B material having higher strength and higher ductility than the material is poured from the ceramic container 8. .

In FIG. 1, the mold 5 and the mold 6 preheated to about 250.degree. C. and the core 7 made of gypsum preheated to about 170.degree. , About 800 ° C
As shown in FIG. 1, a ceramic container 8 and a graphite stopper 9 having, for example, an inner diameter of 180 mm and a thickness of 6 mm (the thickness of the bottom plate is about 10 mm) are installed at an upper central position of the impeller 20 as shown in FIG. The nozzle 10 provided on the bottom plate of the container 8 is closed by the stopper 9.

Then, the molten metal 2 of the AC4D alloy (aluminum alloy) which has been degassed immediately in the ladle 1 is poured at about 700 ° C. from the casting port 11. An AC1B alloy (high-strength, high-ductility aluminum alloy) of about 700 ° C. degassed in the ladle 3 after reaching a predetermined molten metal level 23 by this pouring or almost simultaneously with this pouring. 4 is poured to a predetermined molten metal level 24 in the container 8. Thereafter, the stopper 9 in the ceramic container 8 is immediately removed, the nozzle 10 is opened, and the pressure of the molten metal inside and outside the ceramic container 8 is balanced. Thereafter, the electric motor 16 is operated to gradually raise the container 8 via the lifting device 15 and the arm 32. Then, due to the molten metal static pressure difference, the molten metal of the AC1B alloy in the container 8 passes through the nozzle 10 and moves from the container 8 to the casting (the product part 20).

The rising speed of the ceramic container 8 is as follows:
If this is excessive, the molten metal in the casting portion is agitated and the molten aluminum alloy inside and outside the container 8 is mixed, but on the other hand, if the temperature rise is too low and it takes time to raise the container 8, the alloy solidifies. Progresses, making it difficult or impossible to raise the container 8.

In this embodiment, in the impeller having a diameter of 1380 mm, the suitable rising speed of the ceramic container 8 is 75 mm / min. However, this depends on the size of the casting, the diameter of the nozzle 10, etc.
In the present invention, the rising speed is not particularly limited. In this case, the rise of the container 8 lowers the melt levels 23 and 24 of the two alloys by the volume of the container 8 itself. Therefore, it is necessary to supply the AC1B melt 4 or the AC4D melt 2 as necessary. desirable.

In this embodiment, the JIS-AC4D material is used as the aluminum alloy poured from the ladle 1. However, in addition to the AC4D material, JIS-AC4C material, AC4CH material, or a composition similar to these materials is used. An aluminum alloy may be used.

When the raising of the ceramic container 8 is completed, the molten metal is solidified and cooled in the same manner as in ordinary casting. Through the above steps, a casting of the impeller 20 as shown in FIG. 2 is completed.

Next, in the casting of the impeller 20 shown in FIG. 2, the center A part 21 which is located in the vicinity of the ceramic container 8 and the B part 22 which is closer to the outer periphery than the A part 21.
Tensile test pieces were collected from the locations, and a tensile test was performed at room temperature.

That is, the A portion 21 mainly composed of the AC1B material in the center portion and the B portion 22 mainly composed of the AC4D material in a portion closer to the outer periphery than the A portion 21 have different compositions.
A test piece was collected from the location and a tensile test was performed at room temperature. The result is shown in FIG.

As shown in FIG. 3, the mechanical properties of the portion of the shaft portion of the impeller 20 where high stress is generated, that is, the portion A, are as shown in FIGS. Both the ductility shown in (4) and the properties superior to the part (B). The surface roughness of the blade portion 20a in the vicinity of the outer periphery and the run of the molten metal (filled in the molten metal) were good, and it was confirmed that cracking due to casting did not occur. AC1B material and AC4D
There is no crack at the boundary of the composition with the material, no hot water, etc.
A product with good performance as an impeller material and good quality as a cast product was obtained.

[0035]

As described above, according to the present invention, even a large-sized aluminum alloy impeller having a low cooling rate at the time of solidification has high strength, high ductility, and is free from casting defects. The production of high quality castings is possible. This makes it possible to provide a product having high fatigue strength and high quality even in an impeller in which a large stress is generated.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a casting apparatus for an aluminum alloy casting impeller for a turbo refrigerator according to an embodiment of the present invention.

FIG. 2 is a structural diagram of an impeller casting in the embodiment.

FIG. 3 is a graph showing measurement results of strength and ductility of the impeller casting.

FIG. 4 is an equivalent view of FIG. 1 showing a conventional impeller casting apparatus.

FIG. 5 is a structural view showing a shape after casting of a conventional impeller.

FIG. 6 is an equivalent view of FIG. 2 showing a conventional impeller casting.

[Explanation of symbols]

 2 AC4D molten metal 4 AC1B molten metal 5 Mold (upper mold) 6 Mold (lower mold) 7 Core 8 Ceramic container 9 Stopper 10 Nozzle 11 Casting port 12 Faucet 13 Runway 14 Weir 15 Lifting device 16 Motor 20 Impeller (Product Department)

Claims (3)

[Claims] In casting an aluminum alloy impeller comprising a center boss connected to a rotating shaft and a blade formed on the outer periphery of the boss, the center boss of the casting of the impeller is used. A ceramic container heated above the solidification temperature of the aluminum alloy is inserted into the central portion including the portion to be formed, and an aluminum alloy having a predetermined composition is poured into a product portion formed in a mold outside the container. Simultaneously with or after the pouring, an aluminum alloy having a composition different from that of the aluminum alloy is poured into the container, and then the bottom of the ceramic container is opened into the product section, Casting an aluminum alloy impeller wherein the container is raised at a predetermined speed and the aluminum alloy in the container is poured into the mold through the opening. Law. 2. The product part includes a JIS-AC4D material,
A first aluminum alloy containing silicon such as AC4CH material and having good castability is poured, and JIS-
2. The casting method for an aluminum alloy impeller according to claim 1, wherein a second aluminum alloy having a higher strength and a higher ductility than the first aluminum alloy such as an AC1B material is poured. 3. A casting apparatus for casting an aluminum alloy impeller comprising a center boss portion connected to a rotating shaft and a blade portion formed on the outer peripheral side of the center boss portion, wherein the casting device is formed in a mold. A runner and a casting port for pouring the first aluminum alloy as the impeller material are communicated with the product portion, and the first portion is provided at a central portion including a portion serving as a central boss portion of the impeller. A second aluminum alloy having a composition different from that of the aluminum alloy is accommodated, and a bottomed hollow container having an opening at the bottom that can be opened and closed with respect to the product portion is disposed, and the container has A casting device for an aluminum alloy impeller, wherein a lifting device for lifting a container up and down in the product section is connected.