Abstract:
A method of deburring channel inlet edges inside a cavity of a gas diffuser case is disclosed. The diffuser case has a plurality of channels each having an inner surface and an inlet edge defining an inlet of the channel. The surfaces of adjacent channels co-operate to provide said inlet edge therebetween. The inlet edges of the channels are provided in an inwardly facing circular array around a central axis of the gas diffuser case. The method comprises: inserting a tool head having at least one nozzle in the cavity of the gas diffuser case; and then ejecting abrasive particles from at least one nozzle towards at least one of the channel inlet edges of the gas diffuser case to at least one of decrease a radius of at least one said edge and improve a smoothness of at least one said surface.

Description:
TECHNICAL FIELD 
       [0001]    The technical field generally relates to centrifugal compressor diffusers, and in particular, to the manufacturing of gas diffuser cases therefor. 
       BACKGROUND 
       [0002]    A gas diffuser case for use in collecting compressed gas ejected from a centrifugal compressor generally comprises a plurality of internal channels known as diffuser passages. Each channel has an inlet axis which is somewhat tangential to the compressor&#39;s rotational axis, and is thus oriented in a direction to receive the compressed gas ejected from the compressor. 
         [0003]    In many applications, the acute angle which forms the edge between adjacent channel inlets requires a very small radius at its tip and a very smooth surface to provide optimal efficiency for the compressor-diffuser assembly. Providing such radius and surface, however, can be challenging and room for improvement exists. 
       SUMMARY 
       [0004]    In one aspect, the present concept provides a method of deburring channel inlet edges inside a cavity of a gas diffuser case, the diffuser case having a plurality of channels each having an inner surface and an inlet edge defining an inlet of the channel, the surfaces of adjacent channels co-operating to provide said inlet edge therebetween, the inlet edges of the channels being provided in an inwardly facing circular array around a central axis of the gas diffuser case, the method comprising: inserting a tool head having at least one nozzle in the cavity of the gas diffuser case; and then ejecting abrasive particles from the at least one nozzle towards at least one of the channel inlet edges of the gas diffuser case to at least one of decrease a radius of at least one said edge and improve a smoothness of at least one said surface. 
         [0005]    In another aspect, the present concept provides a system for deburring channel inlet edges circumferentially disposed inside a circular cavity of a gas diffuser case, the system comprising: a tool head having at least one nozzle at an outer periphery of the tool head, the tool head configured for insertion inside the gas diffuser case, the at least one nozzle of the tool head configured to be directed substantially coaxially with an inlet channel of the gas diffuser case; a source of abrasive particles, the source in fluid communication with the at least one nozzle of the tool head; and an apparatus for forcing the particles out of the at least one nozzle of the tool head. 
         [0006]    In another aspect, the present concept provides a method of providing a diffuser case, the diffuser case having a plurality of channels each having an inner surface and an inlet edge defining an inlet of the channel, the surfaces of adjacent channels co-operating to provide one said edge therebetween, the inlet edges of the channels being provided in an inwardly facing circular array around a central axis of the diffuser case, the method comprising the steps of: providing a plurality of said channels in the diffuser case, the step of providing causing machining burrs to form on said edges; and then directing a flow of abrasive particles radially outwardly towards the channel inlet edges of the diffuser case to remove the burrs and thereby deburr the inlets. 
         [0007]    Further details of these and other aspects will be apparent from the following detailed description and appended figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0008]      FIG. 1  schematically shows a generic gas turbine engine to illustrate one among numerous examples of environments in which a gas diffuser case can be used; 
           [0009]      FIG. 2  is an isometric view showing an example of a gas diffuser case, the example including diffuser pipes connected around the gas diffuser case; 
           [0010]      FIG. 3  is a schematic radial cross-section view, taken generally along line  3 - 3  in  FIG. 2 , showing the channels inside the gas diffuser case and the channel inlet edges before deburring; 
           [0011]      FIG. 4  is an enlarged view showing two of the channel inlet edges in  FIG. 3 ; 
           [0012]      FIG. 5  is a schematic view showing a portion of one of the channel inlet edges, as viewed from a radial direction depicted by arrow  5  in  FIG. 3 ; 
           [0013]      FIG. 6  is a view similar to  FIG. 4 , showing the channel inlet edges after a rough deburring; 
           [0014]      FIG. 7  is an enlarged view of one of the channel inlet edges shown in  FIG. 6 ; 
           [0015]      FIG. 8  is a view similar to  FIG. 5 , showing the channel inlet edge after the rough deburring; 
           [0016]      FIG. 9  is a schematic axial cross-section view of an example of a system for performing deburring; 
           [0017]      FIG. 10  is a schematic radial cross-section view, taken along line  10 - 10  in  FIG. 9 , showing schematically the deburring of one of the channel inlet edges; 
           [0018]      FIGS. 11 and 12  show another example of a tool head of a system for performing the deburring, in which  FIG. 11  is a schematic axial cross-section view, taken along line  11 - 11  in  FIG. 12 , and  FIG. 12  is a schematic radial cross-section view, taken along line  12 - 12  in  FIG. 11 ; 
           [0019]      FIG. 13  is a view similar to  FIG. 4 , showing the channel inlet edges after the deburring; 
           [0020]      FIG. 14  is an enlarged view of one of the channel inlet edges shown in  FIG. 13 ; 
           [0021]      FIGS. 15 and 16  show another example of a tool head of a system for performing the deburring, in which  FIG. 15  is a schematic axial cross-section view, taken along line  15 - 15  in  FIG. 16 , and  FIG. 16  is a schematic radial cross-section view taken along line  16 - 16  in  FIG. 15 ; and 
           [0022]      FIGS. 17 and 18  show another example of a tool head of a system for performing the deburring, in which  FIG. 17  is a schematic axial cross-section view, taken along line  17 - 17  in  FIG. 18 , and  FIG. 18  is a schematic radial cross-section view taken along line  18 - 18  in  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  illustrates an example of a gas turbine engine  10  generally comprising in serial flow communication a fan  12  through which ambient air is propelled, a multistage compressor section  14  for pressurizing the air, a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  18  for extracting energy from the combustion gases. The compressor section  14  includes a centrifugal compressor  20  from which air exits in a substantially tangential direction at the outer periphery thereof when the engine  10  is operated. Air coming out of the centrifugal compressor  20  immediately enters channels inside a gas diffuser case  22  surrounding its outer periphery, which gas diffuser case  22  is schematically illustrated in  FIG. 1 . The illustrated example also shows diffuser pipes  24  receiving the air from channel outlets around the gas diffuser case  22 . 
         [0024]    It should be noted that a gas turbine engine is only one example among numerous possible environments in which a gas diffuser case can be used. Therefore, the techniques presented herein are not limited to gas diffuser cases for gas turbine engines. 
         [0025]      FIG. 2  is an isometric view showing an example of a gas diffuser case  22 . The illustrated example is for use in a gas turbine engine. The gas diffuser case  22  is shown with an example of a diffuser pipe model. A plurality of these gas diffuser pipes  24  are bolted or otherwise fastened at the outer periphery of the gas diffuser case  22 . Each diffuser pipe  24  has an inlet in registry with an outlet of a corresponding one among a plurality of channels  26  inside the gas diffuser case  22 . The channels  26  have inlets which are defined by peripheral edges  28 . It should be noted, however, that other arrangements are possible. For instance, it is possible to provide a plenum chamber surrounding the gas diffuser case  22  instead of using diffuser pipes. 
         [0026]      FIG. 2  also shows the generally circular cavity  30  inside which the rotating device, for instance the centrifugal compressor  20  depicted in  FIG. 1 , is located once the gas diffuser case  22  is set in a machine. The rotation axis of the rotating device is then coincident with the central axis  32  of the cavity  30  of the gas diffuser case  22 . The outer periphery of the rotating device is also very close to the channel inlet edges  28  inside the cavity  30  of the gas diffuser case  22 . These edges  28  are located in an annular section  34  inside the cavity  30  of the gas diffuser case  22 .  FIG. 3  is a schematic radial cross-section view of the annular section  34  of the gas diffuser case  22  before deburring. As can be seen, each channel  26  has a corresponding inlet  26   a . In the illustrated example, the channel inlet edges  28  form a circular array around the annular section  34 . They are also farther from the center of the cavity  30  than the inner edge  36  of the spaced-apart walls  38  (only one of which is shown in  FIG. 3 ) delimiting the annular section  34 . Each of the edges  28  may have, during manufacturing, burrs  40  resulting from a previous manufacturing stage of the gas diffuser case  22  and which are generally desirable to remove. 
         [0027]    Furthermore, the smoothness of the inners surfaces of adjacent channels  26  which defining the edges  28  may need to be improved so as to lower the drag, thereby maximizing the efficiency of the centrifugal compressor. 
         [0028]      FIG. 4  is an enlarged view showing an example of burrs  40 . 
         [0029]      FIG. 5  is a schematic view showing one of the channel inlets  28 , as viewed from the radial direction depicted by arrow  5  in  FIG. 3 . This figure shows that each edge  28  may have a plurality of irregular burrs  40  of various sizes and shapes. The spaced-apart walls  38  and their inner edge  36  are shown in  FIG. 5 . It also shows that the edges  28  may have a non-linear profile, such a parabolic profile. Other kinds of profiles are possible as well. The stippled line  35  shows the target dimensions of the edge  28  after deburring. Moreover, the width of diffuser case material between the surfaces  42  on either side of the edge  28 , may progressively increase immediately downstream the tip of the edge  28 . 
         [0030]    The deburring may first include a rough deburring stage where pieces of larger burrs  40  on at least some of the channel inlet edges  28  are removed, for instance by using a hand tool or another machine (schematically depicted as  46  in  FIG. 5 ) in preparation of a deburring stage described hereafter. This may result in something as shown in  FIG. 6 . Tools can include, for instance, files, plies, etc. 
         [0031]    Generally, large burrs  40  are very thin and are easy to remove. They are also very sharp. They thus have a radius of curvature at their tip that is relatively small. However, the removal of large burr pieces in the rough deburring often substantially flattens the tip  28   a  of the edges  28  and therefore, they may loose their sharpness, as shown for instance in  FIG. 7 , where the tip  28   a  of the edge  28  is almost flat. The rough deburring, however, brings the dimensions of the edges  28  close or on the target, as shown in  FIG. 8 , where the dimensions of the edge  28  corresponds approximately to the target depicted by the stippled line  35  in  FIG. 5 . However, as aforesaid, the edge  28  in  FIG. 8  is dull and the smoothness of the surfaces surrounding the edge  28 , for instance the surfaces  42  on each side, may need to be improved. 
         [0032]      FIGS. 9 and 10  are schematic views depicting an example of the deburring for the channel inlet edges  28 . The deburring is done by impinging particles on the edges  28 , the particles being ejected from one or more nozzles  50  (only one being shown in  FIGS. 9 and 10 ) in a direction that is substantially parallel to an inlet axis of the channel—i.e. in substantially the same direction that, in use, gases exiting at the centrifugal compressor would enter the inlets of channels  26  of the gas diffuser case  22 . Typically, this direction will be more or less in a tangential direction relative to the diffuser case circumference, since the air exit in compressor will be generally tangentially oriented. 
         [0033]    Particles used in the particle stream may be abrasive for removing some of the material on the edges  28 . Abrasive particles can be dry or wet. Water and/or any other liquid may be used to wet the abrasive particles, for instance to improve the surface finish or to control the dust being generated by the particles. 
         [0034]    There are different ways of imparting energy to the particles for the deburring. One is to use a compressed gas, for instance compressed air, as a substrate to carry the particles out of the nozzle or nozzles  50 . Any suitable approach may be used. In  FIG. 9 , the compressed gas is supplied by a channel  45 .  FIG. 9  also shows a liquid  47  being supplied to the nozzle  50  by means of a tube  49 . Wet particles then exit the nozzle  50  and will hit the edge  28 , which edge  28  is as close as possible to the nozzle  50  (distance “I” being minimal). It should be noted that the distance “I” in  FIG. 9  is not necessarily to scale. 
         [0035]      FIG. 11  shows an example of a system  48  having a tool head  52  carrying four nozzles  50 .  FIG. 12  is a schematic radial cross section view of the tool head  52 . The tool head  52  comprises a central plenum  54  in fluid communication with internal conduits  56  leading to the nozzles  50  located at the outer periphery of the tool head  52 . The plenum  54  is itself in fluid communication with a compressed gas source  58  and a particle source  60 , as shown in  FIG. 11 . The plenum  54  can also be in fluid communication with a liquid source  62  for wetting the particles, if desired. 
         [0036]      FIG. 12  shows that the system  48  has curved conduits  56  in the tool head  52  that are decreasing in height towards the periphery (from H 1  to H 2 ) so as to accelerate the stream of particles. The nozzle  50  of each conduit  56 , as shown in  FIG. 11 , has a height H 2  approximately equal to the width of the edge  28 . Also, the gap G between the outer periphery of nozzles  50  and the innermost portion of the edges  28  is as small as possible. The nozzles  50  may be configured and disposed to enter the annular section  34 , the outer periphery of the nozzles  50  having a radial distance from the center of the cavity  30  that is greater than that of the inner edge  36 , as shown in  FIG. 11 . This, along with the curvature of the conduits  56 , impart to the stream of particles a direction that is as close as possible to the path of the gases as they leave the rotating device to be used with the gas diffuser case  22 . 
         [0037]    The time required for processing each edge  28  during the deburring will depend on many factors, for instance the hardness of the metal used for the channel inlet edges  28 , the kind of particles, the velocity and density of the particles, the extent of the rough deburring, etc. The desired smoothness of the surfaces around the edges  28  and the target radius of curvature of the tip  28   a  of the edges  28  are other factors that may dictate the processing time. Thus, the deburring is completed only once the desired surface finish is obtained and the radius of curvature of the edges  28  is equal or smaller than the target value. 
         [0038]      FIG. 13  shows two adjacent edges  28  after the deburring and  FIG. 14  is an enlarged view of the tip  28   a  of one of these edges  28 , which tip  28   a  has a radius R. 
         [0039]    During the machining process, the tool head  52  of the system  48  can remain in a fixed position with reference to the edges  28  of the gas diffuser case  22  being deburred. The tool head  52  will then need to be repositioned if the number of nozzles  50  is lower than the number of edges  28  of the gas diffuser case  22 . The gas diffuser case  22 , which would then be held in a corresponding support or arrangement (not shown), can otherwise be pivoted until the corresponding edges  28  are in the right position with reference to the corresponding nozzle or nozzles  50  of the fixed tool head  52 . 
         [0040]    Another possibility is to allow the tool head  52  to rotate at high speeds within the cavity  30  of the gas diffuser case  22  during the deburring. The rotation can give the stream of particles a direction that is even closer to the direction of the gases during the operation of the gas diffuser case  22 . This will also render unnecessary any angular repositioning between the tool head  52  and the edges  28  of the gas diffuser case  22 . Referring back to  FIGS. 11 and 12 , the tool head  52  can be allowed to rotate freely around the central axis  32  using a supporting arrangement (not shown). The tool head  52  is driven by the jet effect created by the changes in direction of the compressed gas and the particle streams inside the tool head  52 . The rotation direction is shown by arrow  53 . 
         [0041]      FIGS. 15 and 16  show another example of the system  48  for deburring. In this example, the tool head  52  is rotated at high speeds by a motor  64  in direction  53  and the stream of particles is ejected out through the nozzles  50  by the centrifugal effect. The direction  53  is opposite that of  FIGS. 11 and 12 . 
         [0042]    If desired, the system  48  of  FIGS. 15 and 16  can also be used with a compressed gas, for instance to eject the particles with more force and to prevent particles from accumulating somewhere in the gas diffuser case  22 . Still,  FIGS. 15 and 16  show that the conduits  56  in the tool head  52  can have a decreasing width in the radial plane ( FIG. 16 ) and a constant height in the axial plane ( FIG. 15 ). The tool head  52  illustrated in the example of  FIGS. 15 and 16  has a gap G′ that is larger than the gap G in the example of  FIGS. 11 and 12 . As best shown in  FIG. 16 , the nozzles  50  are not beyond the inner edge  36  of the walls  38 . 
         [0043]      FIGS. 17 and 18  show a variant of the example shown in  FIGS. 15 and 16 . The configuration of the conduits  56  is similar to what is shown in the example of  FIGS. 11 and 12 . 
         [0044]    Furthermore, it is possible to configure the system  48  with both a decrease in width and a decrease in height of the conduits  56 , thereby combining the features of the conduits  56  in  FIGS. 15 and 16  with those in  FIGS. 17 and 18  to decrease the cross section of the conduits  56  along at least some of their length. 
         [0045]    Overall, the above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to what is described while still remaining within the same concept. The gas diffuser case can be different from the one shown and described herein. The tool head of the system can have more or less nozzles than what is shown and described herein. It is possible to omit the rough deburring in some instances, for example if the previous manufacturing process only leaves relatively small burrs or if large burrs can be easily removed by the stream of particles during the deburring. The method can include a plurality of sub-steps for the deburring. For instance, more than one kind of particles can be used successively. Still other modifications will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the scope of the appended claims.