FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patents Rules  2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

1. METHOD FOR MANUFACTURING IMPELLER

2.

1. (A) MITSUBISHI HEAVY INDUSTRIES  LTD.
(B) Japan
(C) 16-5  Konan 2-chome  Minato-ku  Tokyo 1088215 Japan

The following specification particularly describes the invention and the manner in which it is to be performed.

Technical Field
The present invention relates to a method for manufacturing an impeller that is used for a centrifugal rotating machine such as a centrifugal compressor.

Background Art
Conventionally  as an impeller used for a centrifugal rotating machine such as a centrifugal compressor  there has been known a covered impeller (closed impeller) including a disc attached to a rotating shaft  a cover installed with a space being provided with respect to the disc  and a plurality of blades for connecting the cover to the disc. For this impeller  a portion surrounded by the side surfaces of blades  the cover  and the disc constitutes a passage for compressing air.
As a method for manufacturing this impeller  there has been known a method in which the disc and the cover  which are produced separately  are joined to each other. In this method  the blades are often formed integrally with either of the disc and the cover. As a method for joining the disc and the cover to each other  welding or brazing is selected. In the joining by welding  a welding torch must be inserted into the passage  and it has been pointed out that if the passage is narrow  it is difficult to insert the welding torch into the passage  and therefore welding defects are liable to occur. In contrast  in the joining by brazing  for example  when the cover with blade is joined to the disc  a brazing filler metal is placed on the joint surface  and the cover and the disc are inserted into a heating furnace in a lapped state to join them  so that even if the passage is narrow  the joining work can be performed easily.
Patent Document 1 proposes a method for joining the disc to the cover by brazing. In this method  the cover is placed so that the blade mounting surface faces up  and brazing is performed in the state in which the blade and disc are placed on the cover. According to the method proposed by Patent Document 1  insufficient supply of brazing filler metal to a portion that is a joint portion of the blade to the cover and the disc  on the inner periphery side in the radial direction of impeller  on which portion the rotational stresses at the impeller operation time concentrate  is prevented.

Citation List
Patent Document
Patent Document 1: Japanese Patent Laid-Open No. 2010-174652

Summary of Invention
Technical Problem
In Patent Document 1  although insufficient supply of a blazing filler metal to the inner periphery side in the radial direction of impeller is prevented  a problem described below is presented concerning the method for manufacturing an impeller by brazing. When brazing is performed in the state in which the blade and disc are placed on the cover  the weights of the disc and further the blade are applied to the molten brazing filler metal. Therefore  the brazing filler metal melted during the brazing operation flows out of the joint surface  and the thickness of the brazing layer after the brazing filler metal has solidified (brazing operation has been finished) becomes smaller than the assumed thickness. Thereby  the toughness value of the joint portion (joint toughness value) is made insufficient. For example  when brazing is performed by placing a brazing filler metal having a thickness of 100 ?m  the thickness of brazing layer becomes 50 ?m. Even if a thick brazing filler metal is used  the amount of brazing filler metal flowing out of the joint surface simply increases  and the brazing filler metal is consumed wastefully.
The present invention has been devised to solve the above problem  and accordingly an object thereof is to provide a method for manufacturing an impeller  in which a brazing layer having a necessary thickness can be secured easily while the waste of a brazing filler metal is eliminated.

Solution to Problem
To achieve the above object  the present invention provides a novel method for manufacturing an impeller.
An impeller relating to the present invention includes a disc  a cover arranged facing to the disc  and a plurality of blades provided between the disc and the cover. This impeller is formed with a passage between the disc and the cover.
The method of the present invention includes a step X of separately producing the disc and the cover. Either one of the disc and the cover is formed integrally with the blades.
As the next step  the method of the present invention includes a step Y of joining the disc and the cover to each other by brazing in the state in which a first brazing filler metal is interposed between a first joint surface provided on the blade and a second joint surface provided on either one of the disc and the cover.
The present invention is characterized in that in the step Y  brazing operation is performed by providing a spacer  which is used to maintain a space between the first joint surface and the second joint surface  on the outer periphery side of the impeller. The thickness of the spacer is preferably smaller than that of the brazing filler metal before melting.
In the present invention  as a mode for providing the spacer  either of the two modes described below can be selected.
A first mode is to produce the spacer separately from the disc and the cover. In this case  the spacer is placed between the first joint surface and the second joint surface.
A second mode is to form the spacer integrally with the blade or to form the spacer integrally with either one of the disc and the cover. For example  in the case where the blade is produced integrally with the disc  the spacer is formed integrally with the blade or integrally with the cover.
In the second mode  if the spacer is formed integrally when the disc or the cover is produced  the subsequent work for placing the spacer between the first joint surface and the second joint surface can be omitted. Therefore  the second mode has an advantage that the manufacturing process can be simplified as compared with the first mode.
In the present invention  after the brazing operation has been ended  a portion in a predetermined range on the outer periphery side of the impeller can be removed. The impeller is subjected to heat treatment including brazing  and distortion occurs on account of the heat treatment. This distortion increases toward the outer periphery side of impeller. Therefore  to secure the dimensional accuracy of impeller  too  it is preferable to remove  by cutting or the like  the portion in a predetermined range on the outer periphery side of the impeller.
The brazing operation is performed without providing the brazing filler metal between the spacer and the first or second joint surface. Therefore  the joint between the spacer and the first or second joint surface is insufficient. Accordingly  in the present invention  from the viewpoint of ensuring the strength of the impeller  it is preferable that after the brazing operation has been completed  the spacer be removed by cutting or the like by removing the portion in a predetermined range on the outer periphery side of the impeller.
In the present invention  before the brazing operation  the first brazing filler metal is interposed between the first joint surface and the second joint surface. It is preferable that the brazing filler metal be divided into plural numbers in the lengthwise direction to form brazing filler metal segments  and the brazing filler metal segments be interposed between the first joint surface and the second joint surface. Since the first joint surface (or the second joint surface) is sloped  it is not easy to gaplessly place the rigid integral first brazing filler metal along the first joint surface (or the second joint surface). For this reason  the first brazing filler metal is divided in the lengthwise direction. Since the divided individual brazing filler metal segment is short  it can easily be placed gaplessly along the first joint surface (or the second joint surface). In this case  a second brazing filler metal is preferably provided in a location corresponding to the joint of the adjacent brazing filler metal segments. The reason for this is that the brazing operation in the joint portion is performed more reliably. Also  it is preferable that the brazing operation be performed by providing a third brazing filler metal to form a fillet in the joint portion after brazing.
In the step Y of the present invention  the brazing operation can be performed in a state in which a pressure is applied in the axial direction to the disc and the cover by using a jig  whereby the degree of close adhesion of the brazing filler metal to the joint surface can be increased. It is preferable that this jig coaxially include a first restraint part which is in contact with the inside diameter of the cover to restrain the radial movement of the cover  and a second restraint part which is in contact with the inside diameter of the disc to restrain the radial movement of the disc. With such a jig  at the brazing time  the disc and the cover can be prevented from positionally shifting in the radial direction. Also  even if the outside diameters of the disc and cover change  the inside diameter thereof fitted onto a rotating shaft often has the same dimension. Therefore  this jig has an advantage that the kinds of jigs prepared to manufacture an impeller (disc  cover) having different outside diameters can be decreased.

Advantageous Effect of Invention
In the present invention  brazing operation for joining is performed by providing a spacer  which is used to maintain a space between the first joint surface and the second joint surface  on the outer periphery side of the impeller. Therefore  the brazing filler metal can be prevented from flowing excessively out of the joint surface on account of the own weights of the disc and the cover during the brazing operation  so that after solidification  a brazing layer having an assumed thickness can be obtained.

Brief Description of Drawings
[FIG. 1] FIG. 1 a sectional view along a blade of an impeller manufactured by a method in accordance with an embodiment of the present invention.
[FIGS. 2A and 2B] FIGS. 2A and 2B are sectional views showing a brazing method in accordance with an embodiment of the present invention  FIG. 2A showing a state in which a disc and a cover are separated  and FIG. 2B showing a state in which the disc and the cover are lapped on each other.
[FIGS. 3A and 3B] FIGS. 3A and 3B are sectional views showing a situation in which a brazing filler metal is placed onto the tip end surface of blade (a first joint surface)  FIG. 3A being a partial sectional view  and FIG. 3B being a sectional view taken along the line 3b-3b of FIG. 3A.
[FIGS. 4A and 4B] FIG. 4A is a sectional view showing a state in which a cover is fixed to a disc by using a jig in accordance with an embodiment of the present invention  and FIG. 4B is a plan view of a first fixing member.
[FIGS. 5A and 5B] FIGS. 5A and 5B are sectional views of an impeller in accordance with an embodiment of the present invention  FIG. 5A showing a state before an outer peripheral part is removed by cutting  and FIG. 5B showing a state after the outer peripheral part has been removed by cutting.
[FIG. 6] FIG. 6 is a graph showing the relationship between the thickness of a brazing layer after brazing and the absorbed energy of a joint portion.

Description of Embodiment
The present invention will now be described in detail based on an embodiment shown in the accompanying drawings.
An impeller 10 manufactured by a method in accordance with this embodiment is mounted in a rotating machine such as a centrifugal compressor as a rotating body assembled to a rotating shaft.
As shown in FIG. 1  the impeller 10 includes a disc 11  a cover 12  and a plurality of blade-shaped blades 13 as principal constituent elements.
The disc 11 is a substantially disc-shaped member attached coaxially to the rotating shaft  not shown.
The plurality of blades 13 are arranged radially with the rotation axis line C of the rotating shaft being the center so that one end (the lower side in FIG. 1) of each of the blades is in contact with the disc 11. In this embodiment  the blades 13 are formed integrally with the disc 11 by machining a raw material for the disc 11. However  the blades 13 can be formed integrally with the cover 12.
The cover 12 is arranged so as to face to the disc 11. Also  the cover 12 is in contact with the other end (the upper side in FIG. 1) of each of the blades 13. A space formed by the side surfaces of the blade 13 and the opposing surfaces with which the disc 11 and the cover 12 face to each other functions as a passage R for gas compressed by the compressor mounted with this impeller.
In this embodiment  the side close to the rotation axis line C is the inner periphery side of the impeller 10  and the side far from the rotation axis line C is the outer periphery side thereof. Also  in FIG. 1  the compressed gas flows in the passage R in the direction indicated by the arrow mark E. Further  the direction of the rotation axis line C of the impeller 10 is taken as Y-direction  and the radial direction of the impeller 10 as X-direction.
The disc 11 is made of a high-strength and heat-resistant alloy such as a stainless steel  and includes a shaft hole 111 through which the rotating shaft  not shown  is inserted  and a body part 112 extending from the shaft hole 111 toward the outer periphery side. The disc 11 includes a top surface 11a on the upper side (the gas passage R side) facing to the cover 12  and a back surface 11b on the opposite lower side. The top surface 11a has a shape curved so as to project to the tip end 112a side of the body part 112 from the outer periphery side toward the inner periphery side. That is  on the inner periphery side of the top surface 11a of the disc 11  a curved surface 112d having a shape extending along a curved part Ra of the passage R is formed.
Each of the blades 13 provided between the disc 11 and the cover 12 is formed so as to be curved smoothly so as to project to the tip end side in the rotating shaft direction Y and toward the inner periphery side in the radial direction X along the top surface 11a of the disc 11  and be also curved in the circumferential direction of the disc 11. This curved portion (a curved surface 13d) takes a shape extending along the curved part Ra of the passage R.
In the blade 13  an edge portion located on the disc 11 side is taken as a disc-side blade edge part 13a  and an edge portion located on the cover 12 side is taken as a cover-side blade edge part 13b. In this embodiment  in the blade 13  the disc-side blade edge part 13a and the top surface 11a of the disc 11 are formed integrally  and the cover-side blade edge part 13b is joined to a blade mounting surface 12a of the cover 12 via a brazing filler metal 14. In the case where the blade mounting surface 12a of the cover 12 and the cover-side blade edge part 13b are formed integrally  the disc-side blade edge part 13a is joined to the top surface 11a of the disc 11 via the brazing filler metal 14.
The lower surface (the blade mounting surface 12a) of the cover 12 is joined to the cover-side blade edge part 13b of the blade 13 via the brazing filler metal 14  and is curved so as to project to the tip end side in the rotating shaft direction Y from the outer periphery side toward the inner periphery side. That is  on the inner periphery side of the blade mounting surface 12a of the cover 12  a curved surface 12d having a shape extending along the curved part Ra of the passage R is formed.
As described above  between the adjacent blades 13  the passage R is formed to generate compressed air with the rotation of the impeller 10. The passage R has a shape curved in the radial direction X and the rotating shaft direction Y along with the shapes of the disc 11  the blade 13  and the cover 12.
When the impeller 10 for a compressor configured as described above is rotationally driven around the rotation axis line C by a driving part  not shown  an air flow indicated by the arrow mark E  which is directed from the inner periphery side toward the outer periphery side  is generated in the passage R  and the air is accelerated by a centrifugal force created by the rotation. Thereby  the air sucked through an inlet R1 of the passage R is compressed in the passage R and is discharged through an outlet R2. Thereafter  the compressed air is sent to an external equipment  not shown  on the downstream side.
Next  a method for manufacturing the above-described impeller 10 is explained with reference to FIGS. 2 to 5.
First  as shown in FIG. 2A  the disc 11 and the plurality of blades 13 are integrally formed by machining a raw material. At the time of integral forming  a spacer 13c is formed in the cover-side blade edge part 13b. The spacer 13c projects from the cover-side blade edge part 13b toward the cover 12. Also  the spacer 13c is provided on the outer periphery side of the blade 13. The projection height of the spacer 13c is determined according to the thickness of the brazing filler metal as described below.
The spacer 13c may be provided on all of the blades 13. However  when the disc 11 is viewed from the top  the spacer 13c may be provided on at least three blades 13 so as to correspond to the vertexes of a triangle  or provided on every other blade 13. This is favorable in terms of the reduction in man-hour for forming the spacers 13c. FIGS. 2A and 2B show the disc 11 and the cover 12 that are turned over from the state shown in FIG. 1. Brazing is performed in the state shown in FIGS. 2A and 2B like Patent Document 1.
Prior to brazing operation  the brazing filler metal 14 is placed on the cover-side blade edge part 13b. Since the cover-side blade edge part 13b is curved  it is not easy to gaplessly place the sheet-shaped brazing filler metal 14 having a thickness of 100 ?m or larger on the cover-side blade edge part 13b. In this embodiment  therefore  as shown in FIGS. 3A and 3B  brazing filler metal segments 14a to 14c formed by dividing the brazing filler metal into plural numbers in the lengthwise direction are used. Even if the cover-side blade edge part 13b is curved  the brazing filler metal segments 14a to 14c divided as described above can be placed gaplessly on the cover-side blade edge part 13b. The thicknesses of the brazing filler metal segments 14a to 14c are preferably a little larger than the projection heights (thicknesses) of the spacers 13c. Thereby  a pressure is applied to the brazing filler metal segments 14a to 14c at the brazing time  so that the brazing filler metal can be spread thoroughly.
In this embodiment  in addition to the brazing filler metal segments 14a to 14c (a first brazing filler metal) placed between the cover-side blade edge part (a first joint surface) 13b and the blade mounting surface (a second joint surface) 12a  auxiliary brazing filler metals (a second brazing filler metal) 15 are placed in locations corresponding to the joint between the adjacent brazing filler metal segment 14a and brazing filler metal segment 14b and the joint between the brazing filler metal segment 14b and the brazing filler metal segment 14c. This is because when the brazing filler metal runs short in the joint portion  the shortage is compensated  and the brazing operation is performed more reliably. Also  in this embodiment  to form a fillet in the joint portion after brazing  brazing is performed by providing a brazing filler metal (a third brazing filler metal) 16. The brazing filler metal 16 is placed on both side surfaces of the blade 13 in the vicinity of the cover-side blade edge part 13b. The brazing filler metal segments 14a to 14c and the brazing filler metals 15 and 16 are fixed to predetermined positions of the blade 13 by a means such as spot welding. The fillet means a brazing portion protruding from the brazing joint surface.
As shown in FIG. 2B  the disc 11 on which the brazing filler metal segment 14a and the like are placed is lapped on the cover 12 produced separately. The disc 11 is placed so that the cover-side blade edge part (the first joint surface) 13b is directed downward  and the cover 12 is placed so that the blade mounting surface (the second joint surface) 12a is directed upward. The disc 11 and the cover 12 thus lapped on each other are transferred into a heating furnace  and thereafter brazing operation is performed in which heating is performed at a temperature corresponding to the melting temperature of the brazing filler metals for a necessary time period  and further cooling is performed  whereby the disc 11 and the cover 12 are joined to each other.
When brazing is performed  the brazing filler metal segments 14a to 14c are preferably brought into close contact with the joint surfaces (the cover-side blade edge part 13b and the blade mounting surface 12a)  and a fixing jig 20 shown in FIGS. 4A and 4B is preferably used to prevent a relative positional shift between the disc 11 and the cover 12.
The fixing jig 20 includes a first fixing member 21 for positioning the disc 11 and the cover 12  a second fixing member 26 arranged on the back surface 11b side of the disc 11 so as to face to the first fixing member 21  and a fastening shaft 28 for fastening the first fixing member 21 and the second fixing member 26 to each other.
The first fixing member 21 includes a disc-shaped body 22  a first restraint part 23  and a second restraint part 24.
In the central portion of the body 22  a hole 22a through which the fastening shaft 28 passes is formed. The first restraint part 23 is a ring-shaped protrusion extending in the circumferential direction of the body 22  and is provided on one surface side of the body 22. The second restraint part 24 is provided on the inside of the first restraint part 23. The second restraint part 24 is a hollow cylindrical shaped protrusion in which a portion in which the hole 22a of the body 22 extends is a space. The first restraint part 23 and the second restraint part 24 are arranged coaxially.
The second fixing member 26 is a disc-shaped member  and is formed with a hole 26a through which the fastening shaft 28 passes.
The first fixing member 21 is arranged so as to be in contact with the surface of the tip end 112a of the disc 11. In this state  the first restraint part 23 is fitted onto the inner periphery of the cover 12. Therefore  the diameter of an outer peripheral face 23O of the first restraint part 23 is set considering the diameter of an inner peripheral surface 12I of the cover 12. Also  for the first fixing member 21  the second restraint part 24 is fitted into the shaft hole 111 of the disc 11. Therefore  the diameter of an outer peripheral face 24O of the second restraint part 24 is set considering the diameter of the shaft hole 111.
On the other hand  the second fixing member 26 is arranged so as to be in contact with the surface of the back surface 11b of the disc 11. The fastening shaft 28 is arranged so as to pass through the hole 22a in the first fixing member 21 and the hole 26a in the second fixing member 26. For the fastening shaft 28  a portion projecting from the first fixing member 21 and a portion projecting from the second fixing member 26 are threaded (illustration is omitted)  and bolts B are screwed in the threaded portions. By adjusting the threading amount  the disc 11 and the cover 12  which are held between the first fixing member 21 and the second fixing member 26  are pushed against each other with a necessary force. At this time  the first restraint part 23 provided on the body 22 is fitted onto the inner periphery of the cover 12  and the second restraint part 24 provided on the body 22 is fitted into the shaft hole 111 of the disc 11  whereby the positioning in the radial direction of the disc 11 and the cover 12 is performed.
After the brazing operation has been ended  and the joining of the disc 11 and the cover 12 has been completed  the fixing jig 20 is removed  and a finish machining operation is performed.
As one finish machining operation  a work is cited in which the impeller 10 having been brazed as shown in FIG. 5A is machined so as to turn the flat outer surface of the cover 12 into a curved surface as shown in FIG. 5B. Also  as another finish machining operation  a work is cited in which a portion in a predetermined range is removed from the outer periphery of the impeller 10 (disc 11  cover 12) as shown in FIG. 5B. This machining operation is performed to remove the distorted portion of the impeller 10 to secure the dimensional accuracy thereof  as described above. By this operation  the spacer 13c is preferably removed. Since no brazing filler metal is interposed between the spacer 13c and the blade mounting surface 12a of the cover 12  the joining in this portion is insufficient. Also  the spacer 13c itself is not a necessary component of the impeller 10. Therefore  from the viewpoint of ensuring the strength of the impeller 10  it is preferable that after the brazing operation has been ended  the spacer 13c be removed along with the finish machining operation for cutting out the outer periphery of the impeller 10.

Experiment example
Hereunder  an example of experiment conducted to confirm the effect of the present invention is explained.
Two steel pieces consisting of SUS630 were butted against each other and brazed with a gold brazing filler metal to produce a test specimen for Charpy impact test (in conformity to JIS Z2242). The chemical composition of the used steel pieces and the composition of the brazing filler metal are described below. As the brazing filler metal  a sheet-shaped metal having the thickness described below was used  and a spacer is provided between the two steel pieces to maintain the initial thickness  thus performing heat treatment of brazing. However  for the brazing filler metal having a thickness of 100 ?m  brazing operation was performed without providing the spacer.
Chemical composition of steel pieces (in conformity to JIS SUS630):
Cr: 15.5%  Ni: 4.3%  Cu: 3.5%  Nb+Ta: 0.35%
C: 0.05%  Si: 0.25%  Mn: 0.8%  P: 0.0035%  S: 0.007%
Balance: Fe and unavoidable impurities
Composition of brazing filler metal: 18%Ni-82%Au
Thickness of brazing filler metal: 100 ?m  200 ?m  300 ?m
A joint portion of a specimen obtained by brazing performed under the above-described conditions is subjected to a Charpy impact test  and absorbed energy was determined. The result is shown in FIG. 6.
In FIG. 6  the abscissas represent the brazing layer thickness and the ordinates the absorbed energy. The example in which the brazing layer thickness is 50 ?m indicates the case where the thickness of the brazing filler metal is 100 ?m. In this case  since the brazing filler metal flowed out of the joint surface in the process of brazing  the brazing layer thickness decreased to a half of the thickness of brazing filler metal.
The relationship between the brazing layer thickness and the Charpy absorbed energy reveals that when the thickness is 50 ?m  only Charpy absorbed energy of 5J or less is obtained  whereas when the thickness is 200 ?m  Charpy absorbed energy of about 15J is obtained  and when the thickness is 300 ?m  Charpy absorbed energy of 20J or more is obtained.
As described above  in this embodiment  by providing the spacer 13c  the space between the cover-side blade edge part 13b (the first joint surface) and the blade mounting surface 12a (the second joint surface) can be maintained during the brazing operation. Therefore  the brazing filler metal can be prevented from excessively flowing out from between the cover-side blade edge part 13b and the blade mounting surface 12a  so that a necessary thickness of brazing layer can be ensured while the waste of the brazing filler metal is eliminated.
Especially in this embodiment  since the spacer 13c is provided on the outer peripheral side that is to be removed after brazing  a process for removing the spacer 13c need not be added newly.
The above is an explanation of an embodiment of a method for manufacturing an impeller. The present invention is not limited to the above-described embodiment  and changes can be made as appropriate.
In particular  concerning the spacer 13c  an example in which the spacer 13c is provided integrally with the blade 13 formed integrally with the disc 11 has been explained. However  the present invention is not limited to this configuration. The spacer can be produced separately from the constituent elements of the impeller 10 such as the disc 11 and the cover 12. Also  in the case where the blade 13 is formed integrally with the disc 11  the spacer can be provided integrally on the cover 12 side. Further  in the case where the blade 13 is formed integrally with the cover 12  the spacer can be formed integrally with the blade 13  or can be formed integrally on the disc 11 side.
Also  the shape  size  or the like of the disc 11  the cover 12  and the blade 13 shown in this embodiment is one example  and other shapes and the like can be employed.

Reference Signs List
10 ... impeller
11 ... disc
12 ... cover  12a ... blade mounting surface (second joint surface)
13 ... blade  13a ... disc-side blade edge part (first joint surface)  13c ... spacer
14  15  16 ... brazing filler metal  14a  14b  14c ... brazing filler metal segment
20 ... fixing jig  21 ... first fixing member  23 ... first restraint part  24 ... second restraint part
R ... passage

We claim: -

[Claim 1]
A method for manufacturing an impeller comprising a disc  a cover arranged facing to the disc  and a plurality of blades provided between the disc and the cover  wherein a passage is formed between the disc and the cover  the method comprising:
a step X of separately producing the disc and the cover only either one of which is formed integrally with the blades; and
a step Y of joining the disc and the cover to each other by brazing in a state in which a first brazing filler metal is interposed between a first joint surface provided on the blade and a second joint surface provided on either one of the disc and the cover  wherein:
in the step Y  brazing operation is performed by providing a spacer  which is used to maintain a space between the first joint surface and the second joint surface  on the outer periphery side of the impeller; and
the thickness of the spacer is smaller than that of the first brazing filler metal before melting.
[Claim 2]
The method for manufacturing an impeller according to claim 1  wherein
the spacer is formed integrally with the blade  or is formed integrally with either one of the disc and the cover.
[Claim 3]
The method for manufacturing an impeller according to claim 1 or 2  wherein
after the brazing operation is completed  a portion in a predetermined range on the outer periphery side of the impeller is removed.
[Claim 4]
The method for manufacturing an impeller according to claim 3  wherein
a portion in a predetermined range on the outer periphery side of the impeller is removed so as to remove the spacer.
[Claim 5]
The method for manufacturing an impeller according to claim 1  wherein
in the step Y  prior to the brazing operation  the first brazing filler metal is divided into plural numbers in the lengthwise direction to form brazing filler metal segments  and the brazing filler metal segments are interposed between the first joint surface and the second joint surface.
[Claim 6]
The method for manufacturing an impeller according to claim 5  wherein
in the step Y  a second brazing filler metal is provided in a location corresponding to the joint of the adjacent brazing filler metal segments.

[Claim 7]
The method for manufacturing an impeller according to claim 1  wherein
in the step Y  the brazing operation is performed in a state in which a pressure is applied in the axial direction to the disc and the cover by using a jig; and
the jig coaxially comprises a first restraint part which is in contact with the inside diameter of the cover to restrain the radial movement of the cover  and a second restraint part which is in contact with the inside diameter of the disc to restrain the radial movement of the disc.
Dated this 20th day of December 2011