Patent Publication Number: US-6984108-B2

Title: Compressor stator vane

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/358,931 filed Feb. 22, 2002, the contents of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Compressor stator vanes in an industrial gas turbine are loaded and unloaded during start-stop cycles. In addition, the vanes are subject to small pressure fluctuations during operation. These result in relative motion between the vane base and the casing in which the vanes are assembled. The relative motion results in wear of both the vane base and casing, which, in turn, results in loose vanes. An example of the wear pattern on the base of a vane unit and in particular on a projection on the contact surface is shown in  FIGS. 17A and 17B . The loose vanes become more susceptible to relative motion and begin to chatter. Expensive repair or replacement of the vanes and case does not solve the wear and chatter problem; it simply begins the process anew. Repair and/or replacement of the vanes and casing is expensive. 
     SUMMARY OF THE INVENTION 
     This invention relates generally to a compressor having a casing having at least one slot. The slot has a pair of side edges wherein each side edge has a groove. A plurality of vane units each have base and airfoil vane projecting from the base. The base has a pair of holes. A pin extends between the holes in adjacent bases of the vane units for forming a ring from a plurality of vane units. 
     In one embodiment, at least one shim is interposed between a pair of adjacent vane units, the shim having a hole through which the pin between the adjacent vane units extends. 
     In one embodiment, the pin is a slotted spring pin having a hollow cylindrical tube having a longitudinal slot. The cylindrical tube has chamfered ends. 
     A compressor has a rotor having a plurality of blades and a casing for encircling the rotor. The casing has at least one slot for retaining a plurality of vanes. Each vane unit has a base and at least one airfoil vane projecting from the base. A coupling device extends between adjacent bases for forming a ring unit from a plurality of vane units to stiffen the airfoil vanes. 
     In one embodiment, the coupling device is at least one pin extending between holes in adjacent bases. The pin is a slotted spring pin having a hollow cylindrical tube having a longitudinal slot. In another embodiment, the coupling device is a projection on one base received by a hole on the adjacent base. In alternative embodiment, the coupling device is a groove on one vane unit for receiving a tongue on an adjacent vane unit. 
     A repair kit for repairing a compressor includes a device for placing a hole in a base of a vane unit, a device for inserting a pin into the hole of the base, and a blade assembly tool for positioning and connecting adjacent vane units. 
     The blade assembly tool has a main portion having a pair of face edges and a pair of side edges. The main portion has a curvature and a width for receipt of the pair of side edges by a slot in a casing. The tool has a pair of contact blocks. Each contact block is secured to one of the face edges. 
     In one embodiment, the contact blocks have a width for fitting between a pair of side walls of the slot, The main portion has a pair of holes and a series of scribe lines. 
     A method of repairing at least one loose stator vane includes the step of securing at least one vane unit to another vane unit for stiffening the vane units. 
     In an embodiment, the method includes securing at least one vane unit to another vane unit by connecting the plurality of vane units to each other by a plurality of pins. 
     In an embodiment, the base of the vane unit has a base having a pair of mounting surfaces and a pair of engaging surfaces. A hole is drilled in at least one of the engaging surfaces for receiving one of the pins for connecting to another engaging surface of another vane unit. 
     A method of repairing of a compressor further includes the step of removing the existing the vane units from the casing of the compressor. The holes drilled into the base of the vane unit are drilled into the base of the vane units while they are removed from the casing. 
     A method of repairing of a compressor includes the step of positioning a vane unit at the dead center of the casing. At least one assembly tool is slid in the slot by placing the edges of the assembly tool in the grooves in the slot. The tool engages the vane unit with the contact block for maintaining the second vane unit with a pin projecting from the engaging side of the base is slid into the slot with the projection of the mounting edge received by the groove in the slot. The pin is driven into the hole on the engaging edge of the base of the first vane unit by sliding at least one assembly tool in the slot by placing the edges of the assembly tool in the grooves in the slot and engaging the vane unit with the contact block and driving the second vane unit towards the first vane unit. 
     The method of repairing of a compressor further includes removing of the assembly tool in engagement with the second vane unit. Another vane unit with a pin projecting from the engaging side of the base is slid into the slot with the projection of the mounting edge received by the groove in the slot. The pin is driven into the hole on the engaging edge of the base of the previous vane unit by sliding at least one assembly tool in the slot by placing the edges of the assembly tool in the grooves in the slot and engaging the vane unit with the contact block and driving the another vane unit towards the previous vane unit. The process is repeated until the vane units fill the slot in the casing. 
     The method of repairing a compressor also includes the step in one embodiment of interposing at least one shim between adjacent vane units for positioning one of the engaging edges of a vane unit flush with the edge of the casing. 
     A compressor has a rotor having a plurality of blades and a casing for encircling the rotor. A plurality of vane units each having a base and at least one airfoil vane projecting from the base. The casing has at least one slot for retaining the vanes and an air extraction slot. The air extraction slot underlies the slot and defines a casing hook. A coupling device extends between adjacent bases for forming a ring unit from a plurality of vane units to stiffen the airfoil vanes. At least one bracket is carried by one vane unit engaging the casing hook. 
     In one embodiment, the coupling device is at least one pin extending between holes in adjacent bases. The pin is a slotted spring pin having a hollow cylindrical tube having a longitudinal slot. The cylindrical tube has chamfered ends. 
     In an embodiment, the bracket is secured by a fastener extending through the casing and to the base of the vane unit. 
     A stator vane system has a casing having a curved inner surface and a pair of joint surfaces for mounting with at least another casing for encircling a rotor of compressor. The casing has at least one slot. The slot extends from one joint surface edge to the other joint surface. The slot has a bottom and a pair of side edges. Each side edge has a groove extending from one joint surface to the other joint surface and can include an air extraction slot. The air extraction slot underlies the slot and defines casing hook joint surface. 
     A plurality of vane units each having a base and airfoil vane projecting from the base. The base has a pair of mountings sides opposite each other and each having a projection receivable by the groove in the slot for retaining the vane unit, and a pair of engaging edges opposite each other for engaging adjacent vane units. Each vane unit has a hole in each engaging edge. A pin extends between the holes in adjacent bases of the units for damping the movement of the vane. In a preferred embodiment, a bracket is carried by one of the vane units. 
     The invention is a means for modifying a set of compressor stator vanes for an industrial gas turbine so as to avoid wear of the vane base and reduce chatter. The vanes are joined by a simple mechanical means such that the discrete vanes form a rigid ring of vanes and are less susceptible to individual vane motion caused by pressure fluctuations. 
     The vanes, according to the invention, result in changing the reaction points on the vane base. The relative motion between the vane base and the supporting case is greatly reduced. 
     The vane units in a preferred embodiment can be installed into existing gas turbines using prior art vanes during the gas turbine overhaul cycle. The vane units according to the invention require less repair and/or replacement of the vanes and/or the casing than the prior art vanes. 
     The objective of the invention is to change the load distribution on the vane base without altering the fit or function of the vane. The vanes are connected (coupled) by use of a slotted spring pin so that the tangential pressure load on the vane is opposed by the spring pin and does not cause tangential displacement of the vane base. The vanes are connected such that they form a rigid ring of vanes and do not move relative to one another when acted upon by pressure fluctuations. The frictional force produced by the spring pin acts in opposition to the axial gas load and prevents, or at least reduces, axial motion of the vane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1A  is a schematic of a gas turbine; 
         FIG. 1B  is a exploded perspective view of a compressor section of the gas turbine; 
         FIG. 2  is a front view of a plurality of compressor stator vanes assembled in the casing; 
         FIG. 3  is a side view of the casing; 
         FIG. 4A  is a perspective view of a vane unit, according to this invention; 
         FIG. 4B  is a plan view of a spring pin; 
         FIG. 5A  is an enlarged view of the edge of the casing showing the fifth stage; 
         FIG. 5B  is an enlarged view of the edge of the casing showing the seventh stage; 
         FIG. 5C  is an enlarged view of the fourth stage; 
         FIG. 6  is an exploded view of a pair of vane units and an interposed spring pin; 
         FIG. 7  is side front perspective view of a pair of vane units assembled together; 
         FIG. 8  is a sectional view of a plurality of vane units in the casing; 
         FIG. 9  is a side view of a shim; 
         FIG. 10A  is a side view of the casing with shims protruding; 
         FIG. 10B  is a front view of the fifth stage in the casing with a missing shim; 
         FIG. 11  is a sectional view of the casing with vane assembly and shims; 
         FIG. 12  is a side perspective view of a shim carried by a pin adjacent to a pair of vane units; 
         FIG. 13  is a side perspective view of a drill fixture; 
         FIG. 14A  is a front view of an assembly tool; 
         FIG. 14B  is a side view of the assembly tool; 
         FIGS. 15A-15C  are top, front, and side views of a prior art vane unit showing the reaction forces; 
         FIGS. 16A-16C  are top, front, and side views of a vane unit according to the invention showing the reaction forces; 
         FIGS. 17A and 17B  are front views and bottom views of a prior art vane unit. 
         FIG. 18  is a side view of an alternative compressor; 
         FIG. 19  is a side view of a portion of a casing with an alternative vane system; 
         FIG. 20  is a top view of vane unit with holes shown in hidden line; and 
         FIG. 21  is an exploded view of a pair of vane units with a tongue and groove. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings in detail, where like numerals indicate like elements, there is illustrated a vane system including a vane unit in accordance with the present invention designated generally as  20 . 
     Gas turbines are used in various locations such as aircraft, ships, and in power plants. Referring to  FIG. 1A  a schematic of a gas turbine  24  is shown. The turbine  24  has a compressor section  26  that compresses atmospheric air prior to the air being mixed and combusted with a fuel, i.e., gas, in a combustion chamber  28 . 
     The turbine  24  has a turbine section  30  that converts the energy of the compressed heated air to rotation energy. The turbine section  30  is tailored differently depending on the purpose of the turbine. In a power plant scenario, the turbine section  30  of the gas turbine  24  has two portions. One portion  32  drives a shaft  34  to the compressor section  26  and the second portion is a power turbine  36  for driving a generator  38 . 
     Referring to  FIG. 1B , the compressor section  26  of the turbine  24  has a rotor  42  that is driven, rotated, by the shaft  34  that is typically driven by the turbine section  30  of the gas turbine  24 , as seen in FIG.  1 A. The rotor  42  has a plurality of blades or vanes  44 . Interposed between the rotating blades  44  are stator blades or vanes  46  which are retained by a casing or housing  48  of the compressor section  26  of the gas turbine  24 . In keeping with the convention of the industry, the air foils on the rotor  42  are referred to as rotating blades  44  or blades  44  and the air foils on the casing  48  are referred to as stator vanes  46  or vanes  46 . 
     As the shaft  34  rotates, the air is compressed as it moves through various stages of the compressor  26  with the blades  44  and the vanes directing the air. The movement of the air places resulting forces on the rotor blades  44  and vanes  46 . These forces cause relative motion between the blades  44  and the casing  48  that retains the vanes  46 . 
     In that the blades  44  on the rotor  42  in the embodiment described are rotating in a range of 3000 to 6000 rotations per minute (RPM), the rotation of the rotor  42  creates a centrifugal force on the blades therein preventing movement. Therefore, the vane system  22  is not necessary with the rotor  42 . It is recognized that other rotors rotate at other ranges including at higher ranges. 
     Referring to  FIG. 2 , a view of a portion of the casing  48  of the compressor section  26  is shown. The casing  48  is formed of at least two semi-circular portions that are fitted together to encircle the rotor  42  shown in FIG.  1 B. In the embodiment shown, the casing  48  is semi-circular or 180.degree. in curvature. Two units encircle the rotor  42 . Referring back to  FIG. 2 , the casing  48  has a plurality of stages  50  or rows of stator vanes  46 . The vane unit  20  has vane or airfoil  46  that projects from the inner surface  52  of the casing  48 . 
     Still referring to  FIG. 2 , the fourth through eighth stage,  50   d - 50   h , of the stator vanes are shown. In conventional compressors, there is a different method of attaching stage  1 - 4 ,  50   a - 50   d , to the housing  48  than that of stage  5 ,  50   e , and higher stages, as discussed below. It is recognized that the style of the stages varies from gas turbine  24  to gas turbine  24 . 
     As seen in  FIG. 2  located in proximity to each of the fifth stage  50   e  stator vanes  46  is a hole  54  to allow air to be drawn from the compressor section  26  through an air extraction cavity  56  to bearing seals. The stages  50  are referred to both as ordinal number stage or stage cardinal number (i.e., fifth stage or stage five). 
     The casing  48  has a mounting edge  58 , also referred to as a joint surface, that is secured to a mounting edge  58  on another section of casing with fasteners extending through a plurality of holes  60  found on the edge  58 . The spacing of holes  60  are based on various features and may result in unevenly spaced holes. 
       FIG. 3  shows the mounting edge  58  of the upper half casing  48  and a portion of the inner surface  52  of the casing  48 . The third through the seventh stages  50   c - 50   g , stator vanes  46  are shown. A locking bar  62 , which is received in a groove  63  as shown in  FIGS. 3 and 5B , is used to secure the stator vanes  46  in stages  5 - 7 . The air extraction cavity  56  Is shown below the stage  5  stator vanes  46 . As seen in  FIG. 2 , holes  54  are located near the fifth stage stator vanes  46  for drawing air into the air extraction cavity  56 . The fourth stage  50   d , which is shown to the right of the fifth stage  50   e  in  FIG. 3 , is secured by using a ring and locking method as described below with respect to FIG.  5 C. 
     In the embodiment shown, the vanes  46  for the fifth stage and higher stages in the compressor section  26  are secured to the casing  48  by each vane  46  being part of the section compressor vane unit  20 . The compressor vane unit  20 , as seen in  FIG. 4A , has a base  64  from which the airfoil or the vane  46  projects. The base  64  has a pair of mounting edges  65  that are opposite each other and a pair of engaging edges  68  for engaging adjacent bases of vane units  20 . 
     The base  64  of the vane unit  20  has a pair of projections  66  for securing to the casing  48  as discussed below. The projection  66  extends from each of the mounting edges  65 . For those vane units  20  that are for the fifth stage  50   e , the base  64  has the hole  54  for drawing air into the air extraction cavity  58 . It is recognized that while each stage is similarly constructed, the individual compressor vane units  20  are sized for the respective stage and for factors such as curvature, clearance length, and width. 
       FIG. 5A  illustrates an enlarged side view of the casing  48  showing the fifth stage  50   e . A plurality of the compressor vane units  20  are assembled in the casing  48  to form the stator vane stage, as seen in FIG.  3 . The casing  48  has a plurality of slots  70  for receiving the vane units  20 . The slot  70  has a pair of side edges  74  which have a groove or a pair of dovetails  76 . The square base dovetall  76  holds the vane units  20  in place. Each vane unit  20  is allowed to slide into place with the base  64  received in the slot  70  and the projections  66  received in the grooves  76 . The casing  48  in the embodiment shown has the air extraction cavity  56  that underlies the fifth stage  50   e  and is formed by the slot  70  and the vane units  20 . The air extraction cavity  56  draws air through the hole  54  in a base  64  of the vane unit  20  as seen in FIG.  4 A. 
     The vanes in the prior art located above the air extraction cavity  56  were more susceptible to relative motion to the casing as discussed above. 
       FIG. 5B  shows the view of the mounting edge  58 , also referred to as a joint surface, of the casing with the slot  70  for the seventh stage  50   g . The vane units  20  for the seventh stage  50   g  have a base  64  with a pair of projections  66  for securing to the casing  48 . The base  64  has a relief space  77  between it and the bottom of the slot  70 ; the relief space  77  aids in the installation and removal. The base  64  does not have a hole through which air passes. A groove  63  for the locking bar  62  as shown. 
     As indicated above, the first four stages  50   a - 50   d  of stator vanes are attached using a ring and blade assembly.  FIG. 5C  shows a ring segment  78  that is slid out and away from the casing  48 . The ring segment  78  receives a plurality of blades  80 . (As indicated above, blades that are stationary are typically referred to as stator vanes.) One of the problems with the existing first stage through fourth stage installation is the method about replacement of a blade  80  when it is damaged in that the ring segments  78  need to be hammered out of the slot  70  since it is typical that the ring segment  78  gets bound in the slot  70 . In addition to destroying the ring segment  78 , there is a risk of damaging other components of the turbine. One of the reasons why the first four stages are assembled using this blade and ring assembly is that these blades are larger and have more forces placed on them and therefore need a stiffer base mount. The invention as described below allows the vane units  20  as improved to be used in the first four stages. 
     The first four stages use the blade  80  and ring segment  78  method, in conventional compressor as described above, because these vanes which are longer than those of other stages have more force placed on them. With the vane system  22  as described in further detail below, the ring  78  and blades  80  can be replaced by a square base vane unit  20  as shown in FIG.  4 A. The use of individual vane units, such as represented by reference numeral  86  as a separation of the ring into multiple vane units allows for reduce cost from that of the ring segment and blade. The use of multiple vane units provides for the pinning together of the vane units  20  provides for a stiffer mount. 
     Referring back to  FIG. 4A , each vane unit  20  has the airfoil vane  46  that extends upwards radially inward towards the shaft  34  of the rotor section  42  when in the compressor section  26  from the base  64 . The airfoil vanes  46 , stator vanes, are interposed between the rotor blades  44 . The base  64  has a projection  66  on each of the two opposing mounting edge  65  to be received by the groove  76  in the side edge  74  of the slot  74  of the casing  48  to retain the vane unit  20  in place, as described above. In addition, the base  64  of each of the vane units  20  has a pair of blind holes  94  machined into the base  64 . The blind holes  94  are each located on one of the engaging sides  68  of the base  64 , the sides not having the projections  66 . A spring pin  96  is inserted into the blind hole  94  in one square base  64  and into the corresponding hole  94  in the base  64  of the adjacent vane unit  20 . 
     While a square base  64  for the vane unit  20  is shown, it is recognized that other shapes may be desired dependent on the number, size and shape of the airfoil. For example, the base  64  can have a rectangular shape or a parallelogram shape. 
       FIG. 4B  shows a plan view of the spring pin  96 . The spring pin  96  is a slotted spring pin  142  that is a headless hollow cylindrical tube  144  having a longitudinal slot  146  down the entire length. The ends  148  are chamfered to aid installation. The spring pin  96  is selected to a controlled outside diameter slightly greater than the blind hole  94  in which it will be installed. Compressed as it is installed, the pin  96  applies continuous pressure towards the sides of the hole wall. The pressure provides tension in a radial manner to prevent loosening created by vibration or shock. 
     In a preferred embodiment, the spring pin  96  is made of Nickel Stainless Steel. The pin has a length of 1 inch, an outer diameter of in a range of 0.385 to 0.395 inches in an uncompressed state, and a wall thickness of 0.077 inches. The chamfer length is a range of 0.016 to 0.095 inches. A spring pin  96  such as described above is sold by Spirol Precision Engineered Products of Danielson, Conn. as 1 inch length ⅜ Corrosion Resistant Steel AISI420. 
       FIG. 6  shows an exploded view of a pair of vane units  20  with the interposed spring pin  96 . In one embodiment, the spring pin  96  has a stiffness to provide enough frictional force to resist motion; or damp vibration (reducing wear) if static friction is overcome. The process of joining vane units  20  by the spring pin  96  is continued until a vane ring  88 , as seen in  FIG. 2  extends from one edge  58  of the casing  48  as shown in  FIG. 2  to the other edge  58  of the casing  48 , for example, 180° in a preferred embodiment. The size of the vane ring  88  is dependent on several factors including the curvature of the casing and therefore alternative arc sizes are also possible, depending on the requirements of the particular compressor design. While it is possible to link a vane unit  20  of the lower casing  48  to the adjoining vane unit  20  of the upper casing  48 , with the spring pin  96  it is not necessary. 
       FIG. 7  illustrates two vane units  20  for the fifth stage  50   e  that are attached. The bases  64  are attached by the spring pin  96 . While the pinned vane units  20  are shown removed from the casing  48 , the vane units  20  are connected in the slot in the casing  48 . In that the vane units  20  are for the fifth stage, the base  64  of each unit  20  has a hole  54  through which air is drawn. 
     A gap  98  is created between the bases  64  of the vane units  20 . The gap  98  is created because of the square base  64  of the vane unit  20  in combination with the curvature of the slot  70 . While the bases can be tapered, the taper would increase the cost of each vane unit  20  because of machining. Furthermore, it is not desired to have a tight fit because of thermal expansion. 
     In installing the vane units  20  with the airfoil blades  46 , the first vane unit  20  is positioned halfway between the edges  58  of the casing  48 . The first vane unit  20  has the two blind holes  94 . The second vane unit  20  has a spring pin  96  that is to be received by one of the blade holes  94  on the first vane unit.  FIG. 8  shows a sectional view of a pair of vane units  20  in the slot  70  of the casing  48 . The slot  70  has the side edge  74  with the groove  76 . The slot  70  includes the air extraction cavity  56  that underlies the vane units  20 . 
     The casing  48  shown is the upper portion and includes an air extraction hole  100  at top dead center (TDC). The vane units  20  are placed in the slot  70  in the casing  48  and are built up from the center of the casing  48 . As the vane units  20  are placed into the slot  70 , the vane system  22  has a plurality of shims  102 , which are interposed between vane units  20 , to space the vane units  20  such that the last vane unit&#39;s engaging edge  68  is within an allowable clearance with the edge  58  of the casing  48 . In the prior art, the shims  102  as seen in  FIG. 9  have a pair of tabs  104  which are received in the groove  76  on the side edge  74  of the slot  70  to retain the shim in position. 
     In the prior art, with the vane units and the shims moving because of aerodynamic forces on the airfoils, the tabs  104  wear away and the shims  102  can protrude into the flow path as seen in  FIGS. 10A and 11 . The example shown of the protruding shim  110  does not exist in the vane system  22  of the invention which the remainder of  FIG. 11  shows. The protruding shims  110  can cause rotating blade stimulation and flow blockage. In addition, the shims can work their way totally out of the slot  70  in the casing  48  and enter into the air stream and cause blade foreign object damage (FOD) on downstream blades and vanes.  FIG. 10B  shows a gap  108  between two airfoil blades  46  because of loss of shims and movement of vane units. 
     Referring to  FIG. 11 , a sectional view of the casing  48  with the vane system  22  in proximity to the edge  58  of the casing  48  is shown. Interposed between the last three vane units  20  are shims  102  secured by the pin  96  between the adjacent vane units  22 . The shims  102  space the bases  64  of the vane units  20  so that the last vane unit&#39;s  20  engaging edge  68  is within an allowable clearance with the edge  58  of the casing  48 . 
       FIG. 12  shows a side perspective view of a shim  102  carried by the pin  96  adjacent to a pair of vane units  20 . The shim  102  has a hole  106  through which the spring pin  96  extends from the blind hole  94  of one of the bases to the blind hole  94  of the adjacent base. The spring pin  96  prevents the shim  102  from moving out of position and possibly entering the air stream and hitting a blade or vane down stream. 
     It is recognized that while a pin, a spring pin  96 , is shown and described above, between every adjacent vane unit  20 , that the lack of a spring pin  96  at sporadic locations will not substantially reduce the performance. For example, in a preferred embodiment there is no spring pin spanning between the two casing portions  48 . 
     In addition, while the above has shown vane units  20  each having a single airfoil or blade, it is recognized that a unit may have a plurality of airfoils. The number of airfoils in a unit is dependent on the size and the shape of the airfoil and the curvature of the casing  48 . While not limited to this number, generally 5 to 7 airfoils to a single base is the maximum. It is also recognized that increasing the number of airfoils on a single base increases the overall cost of the unit for various reasons including machining, forging, investment casting, or welding the unit. Furthermore, the multiple airfoils increase the difficulty of accessing all sides of the airfoils on one unit. In addition, the curvature of the base adds to the cost. 
     The vane system  22  is described with respect to the compressor section  26  of the gas turbine  24 . The compressor section  26  operates in a temperature range of ambient temperature to approximately 600° F. 
     The turbine section  30 , also referred to as the hot section, operates and can operate at temperatures in excess of 800° F. and higher. Spring pins will soften and will not function at the high temperature of the turbine section. In addition, there needs to be some movement to allow for thermal expansion. However, slip pins can be used to link several vane units together to allow movement between adjacent pinned units. 
     In order to install the vane system  22  with the vane units  20  and the spring pin  96 , existing vane units need to have a hole  94  located on either side, the engaging edge  68 , of the base  64 , that is the edge that does not have the projection  66 .  FIG. 13  shows a fixture  112  for drilling pin holes  94  in the base  64  of the vane unit  20 . The channel  114  has a pair of grooves  115  similar to the grooves  76  of the side edges  74  and the slot  70  as seen in FIG.  5 A. The groove  115  receives the projection  66  of the base  64 . The groove  115  is set at an angle such that when the fixture  112  is placed on a machining device, the hole placed in the base  64  of the vane unit  20  is of the proper angle for the curvature of the slot  70  in the casing  48 . For example, in one embodiment, the casing receives eighty two ( 82 ) vane units  20  between the two halves. Each hole is drilled at 2.195° incline relative to being parallel to the top and bottom base  64  in this preferred embodiment. The fixture  112  has a channel  114  that receives the base  64  of the vane unit  20 . 
     A pin  116  projects from the base  118  of the channel  114  to position the base  64  of the stator vane unit  20  relative to the top  120  of the fixture  112 . The positioning of the hole on the base is done by alignment on a milling machine of the drill bit with the hole  122  in the fixture  112 . The head of the milling machine is translated a specific distance such as an inch from that alignment hole  122  to position the drill bit for drilling the hole in the base  64 . 
     The installation of the vane units  20  in the casing  48  can be done with the rotor section  42  in place in the compressor section  26 . In order to do this, the installer needs to reach the vane units  20 . 
       FIG. 14A  shows the front view of an assembly tool  130  and  FIG. 14B  shows a side view of the tool  130  that can be used in the installation of the vane unit  20 . The vane units  20  are placed into the slot  70  in the casing  48  by sliding the first vane unit  20  down so that the first vane unit  20  is located at the bottom dead center in the casing  48  such that the unit is equally distant from the edges  68  of the casing. A plurality of the assembly tools  130  are slid in such that the lowest one engages the vane unit  20  from one side. 
     The assembly tool  130  has a main portion  132  that has a curvature similar to the slot  70  in the casing  48 . The main portion  132  of the assembly tool  130  has a width and thickness such that it extends between the two grooves  76  in the side edges  74  of the slot  70 . Located at each end of the main portion  132  is a contact block  134  which has a greater thickness. The contact block  134  has a width that when received by the slot  70  in the casing  48  extends approximately to the side edges  74  of the slot  70 , that is of a width approximate to the base  64  of the vane unit  20 . The assembly tools  130  can be linked together using a cabling that extends between a hole  136  located in the main portion  132  of the assembly tool  130 . 
     A second vane unit  20  is slid into the slot  70  in the casing  48  on the side not having the assembly tools  130 . Additional assembly tools  130  are used to move the second vane unit  20  into engagement with the first vane unit  20 . The assembly tool  130  has a series of lines or scribe lines  138  such that the assembly tool  130  that extends from the slot  70  above the edge  58  of the casing  48  can be used to determine if the second vane unit  20  is in full engagement with the first vane unit  20 . When the second vane unit  20  is initially slid in, the spring pin  96  rests against the base  64  of the first vane unit  20 , but does not enter the blind hole  94 . The installer can look at the scribe lines  138  on the assembly tool  130  and determine to what line  138  on the assembly tool  130  the edge  58  of the casing  48  must be aligned to by driving the assembly tool  130  in order to install the second vane unit  20  properly. 
     The assembly tools  130  are then removed from the slot  70  and the next vane unit  20  is slid into the slot  70 . The assembly tools  130  are then reinstalled to position the vane unit  20 . 
     When the vane unit  20  approaches the edge  58  of the casing  48 , the last several vane units  20  are slid into the slot  70  in the casing  48  without spring pins  96  interposed between the vane units  20 . It is determined how many shims  102  are required to result in the engaging edge  68  of the base  64  of the last vane unit  20  being within an allowable clearance with the edge  58  of the casing  48 . After the proper number of shims  102  are determined by a “dry fitting,” the vane units  20  are removed from the slot  70  in the casing  48  and are installed using spring pins  96  that in addition to holding the vane units  20  secure, retain the interposed shims  102  such as shown in FIG.  11 . The shims  102  have a hole  106  through which the spring pin  96  passes. The tabs  104  of the shims  102  are received in the groove  76  on the side edge  74  of the slot  70  in the casing  48 . 
     When the first side is completed by building up the vane units  20  to the edge  58  of the casing  48 , the plurality of assembly tools  130  that were slid into the other side are removed and the vane units  20  are built up towards the other edge  58  of the casing  48 . 
     In a preferred embodiment, the assembly tool  130  has a length of 12 inches and a width of 2.6 inches excluding the contact blocks  134 . The main portion  130  has a thickness of an eighth (⅛) of an inch and a radius of curvature of 32 inches. The contact blocks  134 , which are welded onto the main portion  132  of the tool  130 , each have a length of 2 inches and a height and depth of a quarter (¼) of an inch. 
     The two holes  136  in the main portion  132  of the assembly tool  130  have a diameter of ⅝ of an inch. The center of each of the holes  136  is spaced from the main portion  132  and contact block  134  interface by 2 inches. The holes  136  are for securing assembly tools  130  together with cable or assisting for retrieving the assembly tools. It is recognized that the size of the tool  130  is dependent on various factors such as the size of the slot  70  and the curvature of the casing  48 . 
     It is recognized that the assembly tool  130  is designed to fit the respective casing and slot that would be receiving the respective vane unit  20  during installation. For example, the assembly tool dimensions given above are for a GE  7 EA gas turbine engine. 
       FIGS. 15A-15C  show the reaction forces on the vane unit of the prior art with the forces including the aerodynamic loading and the interaction between the vane unit and casing.  FIGS. 16A-16C  show the reaction forces on the vane unit  20  of the invention with the forces including the air loading, the interaction between the vane unit  20  and the casing  48 , and the spring pin  96  interaction. 
     The vane unit according to the invention can be used to retrofit existing gas turbines that have square base compressor vanes. The retrofit will solve the wear problem in the existing gas turbines 
     The spring pin  96  is used for ease of modification and low cost. It is recognized that other mechanisms such as bolting, welding, brazing, can be used to fasten the vane units  20  together. 
     By use of the vane system with the vane units  20  and the spring pin  96 , axial and circumferential tip movement of the vane  46 , which possibly could result in interference with a blade  44  on the rotor section  42 , is reduced. The measurement of movement of the free edge of the airfoil went from 0.063 inches to approximately zero (0). There is no free movement of the vane unit  20 . 
     By use of the spring pin  96  between the bases  64  of the vane unit  20 , the vane unit  20  forms a rigid unit of plurality of vane units wherein the edges of the projection  66  are not the engaging surface that get worn away. But rather, the centered portion of the projection  66  is the portion that is in firm contact within the groove  76  in the side edge  74  of the slot  70 . Therefore there is no movement between the bases  64  of the vane unit  20  and the casing. 
     In addition, with the use of this spring pin  96  extending through the shim  102 , the migration of the shim  102  into the flow stream is prevented. As indicated above, the existing gas turbine  24  embodiments use the vane units  20  with projections  66  from the base  64  received in grooves  76  in the side edges  74  of the slot  70 . Therefore, the vane unit system  22  with the vane unit  20  and spring pin  96  does not require new vane units unit stator blades  46 . The vane units are removed and modified with the blind hole  94  to receive the pin  96 . The task of determining if the set of blades are good operationally or have the proper tip clearance has already been done when the blades were initially produced for this compressor section  26  of the gas turbine  24 . 
     By pinning the vane unit  20  with the spring pin  96  and the vane system  22  together, the vane units are held simply so that any previous wear prior to use of the invention on the forward edge and aft edge of the projection  66  is not of a concern. Therefore, the owner of the gas turbine  24  is not required to machine out the slot  70  in the casing  48  wherein the operator needs to take the gas turbine out of commission while the slot is machined out and a patch ring is installed having the slot  76  within it. 
     The use of the vane system  22  allows the overhaul of the current gas turbines  24  to be within the normal time constraints and not affect others&#39; work. 
     While the above disclosure describes the retrofitting of an existing gas turbine  24 , it is recognized that the main system may be used on new gas turbine designs. For example,  FIG. 5C  shows the configuration with the ring and blade used for the first four stages  50   a - 50   d  of current gas turbine designs. The reason for this different design for the first four stages is because the first four stages have larger airfoils or vanes and therefore more aerodynamic force and thus require more stability. With the vane system  22 , the individual vane units  20  are linked together and the reason for having a different design for stages  1 - 4  is not required. Therefore, the vane system  22  as described above may be used in the first four stages. This will result in lower cost. The vane unit  20  can have an airfoil  46  secured to the base  64  or a separate blade unit  80  attached to the ring segment unit or vane base. 
     As indicated above, the vane system  22  can be formed by pinning together vane units  20  with a pin  96  using a prior art vane unit  20  with the addition of a pair of blind holes  94 . It is recognized that other methods of coupling vane units  20  to each other can be done. For example, the vane unit can have a projection on one engaging edge that is receivable in a hole in an adjacent engaging edge. Another alternative is an adhesive pad that mounts between and to the two adjacent engaging edges. Other components and apparatus are a tongue and groove arrangement. 
     The above discusses the issues of where the stator vane units  20  become loose or shims  102  work their way loose and into the air flow stream. The vane unit system according to the invention in addition can solve additional problems on the compressor section  26  of the gas turbine  24 . As seen in  FIG. 18 , certain compressors  156  have an air extraction slot  158  that has a 360.degree. opening onto the inner surface  52  of the casing  48 . This results in a cantilever portion of the casing retaining a stage of stator vanes such as the tenth stage in a GE Frame 5 Gas Turbine. The cantilever portion has a tendency to crack away from the remainder of the casing and has a potential to enter the air stream and destroy downstream blades and vanes. 
     The tenth stage of the compressor with the air extraction slot is shown in  FIGS. 18 and 19 . The vane system according to the invention has a plurality of vane units  162 , spring pins  96  and at least one hook-capturing bracket  164 . The hook-capturing bracket  164  captures the cracked casing hook  166  at the edges and prevents further crack propagation. 
     The conventional method was to remove the rotor  42  from the casing  48  and machine out a casing hook  166 . A new ring is installed and machined to have the slot  70  with groove  76 . 
       FIG. 19  shows a casing  48  with a horizontal joint or edge  58 . The vane unit  162  that is adjacent to the edge  58  in addition has a blind hole  174  for a spring pin  96  for connecting to the remaining vane units  162 . The base  172  of the vane unit  162  has a threaded hole  168  through its bottom. The bracket  164  is used to secure the casing hook portion  166  of the casing  48 . A bolt  170  extends through the bracket  164 , the casing  48  and into the threaded hole  168  of the vane unit  162 . 
       FIG. 20  is a top view of the vane unit  162 . The base  64  of the vane unit  162  shows the pair of blind holes  174  in hidden line and the threaded hole  168  for the retaining bolt  170  is shown. in this embodiment, the blind holes  174  are shifted from the centerline. It is recognized that the location of the blind holes  174  can be shifted. While the embodiment above describes use of two brackets  164 , it is recognized that additional brackets  164  can be included. The upper casing  48  which is separated from the rotor  42 , allows placement of multiple brackets. With respect to the lower casing  48 , if the rotor  42  is removed, additional brackets can be installed. The bracket  164  is bent to secure the bolt  170 . 
       FIG. 21  shows an exploded view of a pair of vane units  180  of an alternative embodiment. Each vane unit  180  has a groove  182  on one engaging edge  68  and a tongue  184  on the other engaging edge  68 . The tongue  184  of one vane unit is received by the groove  182  of the adjacent vane unit  180  to form the vane units  180  together in a ring unit. This provides enough frictional force to resist motion; or damp vibration (reducing wear) if static friction is overcome. The process of joining vane units  180  continues until a vane ring extends from one edge  58  of the casing  48  to the other edge  58  of the casing  48 . 
     In addition to spring pins, other types of pins can be used. Other potential pins include a coiled spring pin, an interference fit pin, such as a groove pin. With an interference fit pin such as a grooved pin, however, the vanes could not be used again with the same sized pin because the hole in the base would have been distorted and gouged from removing the pin. Likewise, a coiled compression spring could be placed in the base holes and compressed as the bases are slid together. This would provide vibration damping and limited movement of the base in the casing groove. All these devices could work to varying degrees of success relative to the slotted spring pin. 
     The claims should not be read as limited to the described order or elements unless stated to that effect. Therefore, all embodiments that come within the scope and spirit of the following claims and equivalents thereto are claimed as the invention.