JP2018168761A - Impeller, impeller manufacturing method, and rotary machine - Google Patents

Abstract

To provide an impeller which achieves excellent fatigue strength.SOLUTION: An impeller 1 of the invention includes: a disk part 30 fixed to a rotary shaft 101 which rotates around an axis O; a cover part 50 which is disposed facing the disk part 30; and multiple blade parts 40 provided between the disk part 30 and the cover part 50. A compressive residual stress layer CRS is provided on a surface layer of a border part with the disk part 30 and a surface layer of a border part with the cover part 50 which are located at tips of the respective blade parts 40.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an impeller used in a rotating machine.

  Rotating machines such as industrial compressors, turbo refrigerators, and small gas turbines include an impeller in which a plurality of blades are attached to a disk fixed to a rotating shaft. This rotating machine gives pressure energy and velocity energy to gas by rotating an impeller.

The impeller is subjected to tensile stress due to centrifugal force generated during rotation, and the impeller is damaged when the tensile stress exceeds the material strength. In order to face this tensile stress, for example, as described in Patent Document 1 and Patent Document 2, it has been proposed to apply a compressive stress to the impeller.
In Patent Document 1 and Patent Document 2, a compressive residual stress is applied to an impeller by pressing the impeller radially outward from the inside of the fitting hole by a jig inserted into the fitting hole into which the rotating shaft is fitted. Give. In Cited Document 1 and Cited Document 2, since the root of the maximum outer diameter portion is most susceptible to tensile stress during rotation, compressive residual stress is applied to the root.

JP 2012-017713 A JP 2013-104306 A

Even if the impeller is not subjected to tensile stress exceeding the material strength, the impeller may be damaged due to fatigue.
Then, an object of this invention is to provide the impeller excellent in fatigue strength, and its manufacturing method.

  The impeller of the present invention includes a disk portion fixed to a rotating shaft that rotates about an axis, a cover portion that is disposed to face the disk portion, and a plurality of blade portions that are provided between the disk portion and the cover portion, And a compressive residual stress layer is provided on the surface layer of the boundary portion with the disk portion and the surface layer of the boundary portion with the cover portion at the tip of each blade portion.

  In the impeller of the present invention, the blade part and the disk part can be formed integrally or joined to the boundary part with the disk part. Joining is based on the premise that the disk portion and the blade portion are manufactured separately. The same applies to the boundary portion with the cover portion, and the blade portion and the cover portion can be formed integrally or can be joined. Joining is based on the premise that the blade part and the cover part are produced separately.

  The present invention includes a disk portion fixed to a rotating shaft that rotates around an axis, a cover portion that is disposed to face the disk portion, and a plurality of blade portions that are provided between the disk portion and the cover portion. A method of manufacturing an impeller, characterized in that compressive residual stress is applied by shot peening to a surface layer at a boundary portion with a disk portion and a surface layer at a boundary portion with a cover portion at a blade tip of a blade portion. To do.

  The application of compressive residual stress by shot peening in the present invention includes a first step of shot peening using a first shot having a first particle size, and a shot having a second particle size smaller than the first particle size. It is preferable that the second step of using and shot peening is performed in at least two stages.

  Moreover, according to this invention, a rotary machine provided with the impeller demonstrated above is provided.

According to the impeller of the present invention, the residual compressive stress layer is provided at the tip of the blade, which is likely to be damaged by fatigue, so that the fatigue strength against continuous operation of the impeller can be improved.
Further, according to the impeller manufacturing method of the present invention, the compressive residual stress is applied by shot peening, so that even if it is a closed impeller, the compressive residual stress can be easily applied only to the tip.

It is sectional drawing of the centrifugal compressor in embodiment of this invention. It is a perspective view which shows the impeller in this embodiment. It is sectional drawing which shows the impeller in this embodiment. It is a figure which shows the manufacturing method of the impeller in this embodiment. It is a graph which shows the relationship between the compression residual stress provided to the impeller in this embodiment, and the depth from a surface layer, (a) shows the case where one step shot peening is performed, (a) shows two steps shot peening It shows the case of doing.

Hereinafter, a rotary machine according to an embodiment of the present invention will be described using a centrifugal compressor 100 as an example with reference to the accompanying drawings.
[Configuration of Centrifugal Compressor 100]
As shown in FIG. 1, the centrifugal compressor 100 according to the first embodiment includes a casing 102 and a rotating shaft 101 that is pivotally supported on the casing 102 via a journal bearing 103 and a thrust bearing 104. The rotating shaft 101 is supported so as to be rotatable around the axis O, and a plurality of impellers 1 are attached to the rotating shaft 101 side by side in the direction of the axis O.

As shown in FIG. 2, each impeller 1 has a substantially disk shape. The impeller 1 discharges the fluid sucked from the introduction port 3 opened on one side in the direction of the axis O from the discharge port 4 on the outer side in the radial direction through the flow path 105 formed inside the impeller 1. Is configured to do.
Each impeller 1 compresses the gas G supplied from the upstream flow path 105 formed in the casing 102 into the downstream flow path 105 in a stepwise manner using centrifugal force generated by the rotation of the rotary shaft 101. Shed.

  As shown in FIG. 1, the casing 102 is formed with a suction port 106 for allowing the gas G to flow in from the outside on the front side (F) in the direction of the axis O of the rotating shaft 101. Further, the casing 102 is formed with a discharge port 107 for allowing the gas G to flow out to the outside on the rear side (B) in the direction of the axis O.

  According to the centrifugal compressor 100, when the rotary shaft 101 rotates, the gas G flows into the flow path 105 from the suction port 106, and the gas G is compressed stepwise by the impeller 1 and discharged from the discharge port 107. . Although FIG. 1 shows an example in which six impellers 1 are provided in series on the rotating shaft 101, it is sufficient that at least one impeller 1 is provided on the rotating shaft 101. In the following description, in order to simplify the description, a case where only one impeller 1 is provided on the rotating shaft 101 will be described.

[Configuration of Impeller 1]
As shown in FIGS. 2 and 3, the impeller 1 includes a disk unit 30, a blade unit 40, and a cover unit 50.
The disk part 30 is attached to the rotating shaft 101 by being fitted from the outside in the radial direction. As shown in FIG. 3, the disk unit 30 includes a first disk unit 31 and a second disk unit 35 that are divided into two in the direction of the axis O by a bonding layer CL orthogonal to the axis O. The first disk part 31 and the second disk part 35 are joined by a joining layer CL. The bonding layer CL is preferably constituted by an adhesive and friction welding.

The first disk portion 31 has a substantially cylindrical shape with the axis O as the center. The first disk portion 31 includes a grip portion A that is fitted to the rotating shaft 101 with a tightening margin on the front end portion 33 side on the front side (F) of the axis O. Here, in order to fit the first disk portion 31 to the rotating shaft 101 with the allowance in the grip portion A, cold fitting or shrink fitting can be applied. The impeller 1 in this embodiment is fixed to the rotating shaft 101 only by the grip portion A.
The first disk portion 31 includes an outer peripheral surface 34 that gradually increases in diameter toward the rear side (B) of the axis O. This outer peripheral surface 34 is a concave curved surface toward the outside in a cross section including the axis O.
In the first disk portion 31, the rear end surface 32 of the rear side (B) of the axis O is bonded to the second disk portion 35 via a bonding layer CL formed by friction welding.

The second disk portion 35 is formed in a disc shape extending from the rear end portion 36 side opposite to the front end portion 33 side in the direction of the axis O toward the radially outer side.
In the second disk portion 35, the inner diameter side region 38 of the front end surface 37 is bonded to the rear end surface 32 of the first disk portion 31 via the bonding layer CL. The rear end face 32 and the inner diameter side region 38 of the front end face 37 constitute a bonding layer CL orthogonal to the axis O.

As shown in FIG. 2, a plurality of blade parts 40 are arranged at predetermined intervals in the circumferential direction of the disk part 30.
As shown in FIG. 3, the blade portion 40 is formed with a substantially constant plate thickness and protrudes from the front end surface 37 of the disk portion 30 toward the front side (F) in the direction of the axis O. As shown in FIG. 3, the blade portion 40 has a slightly tapered shape toward the outside in the radial direction in a side view.

  As shown in FIG. 2, each blade portion 40 is formed so as to go to the rear side in the rotation direction R of the impeller 1 as it goes to the outer side in the radial direction of the disk portion 30 when viewed from the direction of the axis O. Each blade portion 40 is formed to be concavely curved toward the rear side in the rotational direction R when viewed from the direction of the axis O. Here, an example in which the blade portion 40 is formed to be curved as viewed from the direction of the axis O has been described. However, the blade portion 40 only needs to extend to the rear side in the rotational direction R toward the outer side in the radial direction. . For example, the blade portion 40 may be formed linearly when viewed from the direction of the axis O.

As shown in FIG. 3, the cover portion 50 covers the blade portion 40 from the front end portion 33 side in the direction of the axis O.
The cover portion 50 has a rear end surface 52 in the direction of the axis O formed integrally with the front edge 41 of the blade portion 40. The cover part 50 is formed in a plate shape having a slightly thinner outer thickness in the radial direction, like the disk parts 30 arranged to face each other. The cover part 50 has a bent part 51 bent toward the front side in the direction of the axis O at the position of the inner end 42 of the blade part 40.

  In the impeller 1 configured as described above, the bonding layer CL is arranged inside the blade portion 40 in the radial direction. Further, the front end portion 33 of the first disk portion 31 is disposed so as to protrude forward (F) in the direction of the axis O from the front end edge 53 of the bent portion 51. Further, the impeller 1 has a flow path 105 through which the gas G flows by the outer peripheral surface 34 of the first disk portion 31, the front end surface 37 of the second disk portion 35, the side surface 43 of the blade portion 40, and the rear end surface 52 of the cover portion 50. Is formed.

  The impeller 1 described above is on the discharge port 107 side of the flow path 105, that is, on the surface layer of the boundary portion with the disk portion 30 (second disk portion 35) at the tip E of the blade portion 40, and at the tip of the blade portion 40. A compressive residual stress layer is provided on the surface layer at the boundary with the cover 50. The region where the compressive residual stress layer is provided is shown as CRS in FIGS.

[Compressive residual stress]
According to the study by the present inventors, when the impeller 1 is continuously operated, as shown in FIG. FIG. 2 shows an example in which a crack C has occurred at the boundary between the blade portion 40 and the disk portion 30. As a result of observing the cross section of the portion where the crack C was generated, it was found that the crack C was caused by fatigue due to repeated application of tensile stress to the tip E as the impeller 1 was operated. Therefore, in order to prevent or reduce the occurrence of the crack C, a compressive residual stress CRS is applied to the portion of the impeller 1.

Fracture failure is broadly divided into crack initiation and propagation processes. Residual stress mainly affects the crack growth process. The mechanism of crack growth due to fatigue is due to repeated crack opening due to plastic slip at the crack edge (blunting), re-sharpening of the crack edge due to reverse stress, and new plastic slip due to the next cyclic stress. If a new plastic slip occurs at the crack edge, the crack does not progress.
The compressive residual stress improves the fatigue strength by closing the crack, thereby suppressing the progress of the crack.

As shown in FIG. 5 (a), the compressive residual stress shows a peak at a certain depth from the surface layer, but the value of the compressive residual stress decreases when the depth becomes deeper than the position where the peak is shown, and when the depth exceeds a certain depth, the tensile residual stress becomes tensile. It turns into residual stress. Thus, since the compressive stress remains in the boundary part of the blade part 40 and the disk part 30, and the boundary part part of the blade part 40 and the cover part 50, the impeller 1 prevents or suppresses the generation | occurrence | production of the crack C by fatigue. Is done.
In FIG. 4A, a positive value of residual stress indicates tension, and a negative value indicates compression.

[Method of applying compressive residual stress]
In the present embodiment, compressive residual stress is applied by shot peening. In order to apply the compressive residual stress, means other than shot peening, for example, surface treatment such as quenching or nitriding can be adopted. However, in order to apply the compressive residual stress only in the vicinity of the tip of the blade portion 40, shot peening is applied. Is effective.

  Shot peening is a kind of machining in which a large number of minute spherical particles, typically metal spheres collide with a metal surface at a high speed, and these metal spheres are called shots. Since shots are generally harder than the workpiece, when the shot collides with the surface of the workpiece at a high speed, the surface of the workpiece is dented and a round recess remains. Therefore, the surface subjected to shot peening has a pear-like pattern, but in addition to the compressive residual stress being applied to the surface, the hardness of the surface is increased more than before shot peening. In the present embodiment, by providing the compressive residual stress layer at the tip of the blade portion 40, it is possible to prevent the occurrence or development of cracks in the portion.

Shot peening includes an impeller method and a compressed air nozzle method based on a means for projecting a shot, but a compressed air nozzle method is suitable for obtaining a high compressive residual stress.
FIG. 4 shows how shot peening is performed on the impeller 1 by the compressed air nozzle method. As shown in FIG. 4, the air nozzle 110 is disposed toward the impeller 1, and a shot S is projected from the air nozzle 110. Specifically, in shot peening, the air nozzle 110 is projected toward the boundary portion of the disk portion 30 at the tip E of the blade portion 40, and the air nozzle 110 is projected to the cover portion 50 at the tip E of the blade portion 40. A shot S is projected toward the boundary.

  The shot S used for shot peening is generally one having a particle size (diameter) in the range of 0.2 mm to 1.2 mm, but a shot having a finer particle size of 0.04 to 0.2 mm. There is also Fine Particle Peening. One or both of shot peening and fine particle peening with a general particle size can be applied to the present embodiment.

  The main difference between general shot peening and fine particle peening appears in the depth at which the peak of compressive residual stress occurs. That is, the position where the peak of compressive residual stress is closer to the surface in fine particle peening than in shot peening having a general particle size. Specifically, in the case of fine particle peening, the peak depth is about 0.01 mm, for example, whereas in the case of shot peening with the general particle size described above, the peak depth is about 0.05 mm, for example. It is. That is, the compressive residual stress due to fine particle peening is given to a relatively shallow range from the surface layer, and the compressive residual stress due to shot peening due to a general particle size is applied to a relatively deep range from the surface layer.

  Therefore, in this embodiment, it is possible to apply two-stage shot peening in which shots having different particle diameters are projected in two stages. By performing the two-stage shot peening, as shown in FIG. 5B as a two-stage, a compression residual in which the compression residual stress by shot peening by a shot having a general particle diameter and the compression residual stress by fine particle shot peening are superimposed. Stress is applied. That is, since the peak due to the compressive residual stress occurs at two different locations in the depth direction, the compressive residual stress can be applied to a wider range in the depth direction.

When performing two-stage shot peening, perform shot peening with a general particle size (first particle size) as the first step, and then perform fine particle (second particle size) shot peening as the second step. Is preferred.
Note that three or more stages of shot peening can be performed using shots having different particle sizes.

[Effect]
The effects obtained by the impeller 1 described above and the manufacturing method thereof will be described.
The impeller 1 of the present embodiment is provided with a compressive residual stress layer at the tip E of the blade part 40 and at the boundary part with the first disk part 31 and the boundary part with the cover part 50. Therefore, according to the impeller 1, since the fatigue strength of the boundary portion where cracks are likely to occur due to fatigue is improved and the occurrence and development of cracks can be prevented, the impeller 1 can have a longer life. Moreover, since the compressive residual stress is given to the said boundary part, the corresponding force corrosion cracking property of the said boundary part can be improved.
In particular, since the impeller 1 applies compressive residual stress only to the tip portion where cracks are likely to occur, the generation and progress of cracks can be prevented efficiently.

  Further, according to the present embodiment, since shot peening is used, the shot S is projected from the air nozzle 110 toward the tip E of the blade portion 40, so that even a closed impeller is easily limited to the tip. Residual stress can be applied.

In addition to the above, as long as the gist of the present invention is not deviated, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.
For example, the impeller 1 in the present embodiment has the disk part 30 divided into a first disk part 31 and a second disk part 35, and the second disk part 35, the blade part 40, and the cover part 50 are integrally formed. Although having a structure, the impeller of the present invention is not limited to this. For example, the present invention can also be applied to an impeller that joins a disk portion and a blade portion that are formed integrally with a cover portion that is formed separately from these.

DESCRIPTION OF SYMBOLS 1 Impeller 3 Inlet 4 Outlet 30 Disc part 31 First disk part 32 Rear end surface 33 Front end part 34 Outer peripheral surface 35 Second disk part 36 Rear end part 37 Front end surface 38 Inner diameter side area 40 Blade part 41 Front edge 42 Inner end 43 Side surface 50 Cover portion 51 Bending portion 52 Rear end surface 53 Front end edge 100 Centrifugal compressor 101 Rotating shaft 102 Casing 103 Journal bearing 104 Thrust bearing 105 Channel 106 Suction port 107 Outlet port 110 Air nozzle A Grip portion C Crack CL Bonding layer CRS Compression Residual stress E Tip G Gas S Shot

Claims (5)

A disk portion fixed to a rotating shaft that rotates about an axis;
A cover portion disposed opposite to the disk portion;
A plurality of blade portions provided between the disk portion and the cover portion,
A compressive residual stress layer is provided on the surface layer of the boundary part with the disk part and the surface layer of the boundary part with the cover part at the tip of each blade part,
Impeller characterized by that. The boundary part between the disk part and the blade part and the disk part are integrally formed or joined,
In the boundary portion with the cover portion, the blade portion and the cover portion are integrally formed or joined,
The impeller according to claim 1. A disk portion fixed to a rotating shaft that rotates about an axis;
A cover portion disposed opposite to the disk portion;
A plurality of blade portions provided between the disk portion and the cover portion, and an impeller manufacturing method comprising:
Applying compressive residual stress by shot peening to the surface layer of the boundary part with the disk part and the surface layer of the boundary part with the cover part at the tip of the blade part,
An impeller manufacturing method characterized by the above. Giving compressive residual stress by shot peening
A first step of peening the shot with a first shot having a first particle size;
A second step of peening the shot with the shot having a second particle size smaller than the first particle size, and is performed in at least two stages.
The manufacturing method of the impeller of Claim 3.   A rotating machine comprising the impeller according to claim 1 or 2.

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