Patent Publication Number: US-9427839-B2

Title: Lapping tool

Description:
FIELD OF THE INVENTION 
     This invention relates to devices for lapping a surface, and more particularly, to a lapping tool having removable lapping inserts for lapping sealing surfaces of fittings used in a gas turbine. 
     BACKGROUND OF THE INVENTION 
     Fuel supply lines are attached to fuel system components of a gas turbine by fittings. The fittings each include a sealing arrangement that utilizes metal to metal contact in order to inhibit the leakage of fuel from the fitting. Referring to  FIG. 1 , a type of fitting that is frequently used includes a projecting cone portion  10  having a clearance surface  12  located between first  14  and second  16  cone sealing surfaces. The first  14  and second  16  sealing surfaces each taper toward a connection end  18  of the cone portion  10 . The taper of the first sealing surface  14  is substantially identical to the taper of the second sealing surface  16 . 
     In use, the cone portion  10  is received by a receptacle portion of the fitting. The receptacle portion includes a cavity having a tapered receptacle sealing surface which corresponds to the taper of the first  14  and second  16  sealing surfaces. When a fuel supply line is attached to a fuel system component, the first  14  and second  16  sealing surfaces come in contact with the receptacle sealing surface and form a seal. It is noted that the clearance surface  12  is located beneath the plane of first  14  and second  16  sealing surfaces. Thus, the clearance surface  12  does not contact the receptacle sealing surface and does not provide any sealing functionality. 
     Sections of the first  14  and/or second  16  sealing surfaces and/or clearance surface  12  may become damaged as a result of accidental contact with another component or equipment. For example, this may occur if the fuel line is accidentally dropped by an operator during assembly operations. In particular,  FIG. 1  depicts damage in the form of an exemplary first  20  and second  21  gouges formed on the first sealing surface  14  and the clearance surface  12 , respectively. 
     Referring to  FIG. 2 , a cross sectional view of the first sealing surface  14 , a receptacle sealing surface  22  and gouge  20  is shown. Formation of the gouge  20  typically results in material from the first sealing surface  14  being displaced and reshaped into raised bulges  24 . The bulges  24  cause misalignment between the first sealing surface  14  and the receptacle sealing surface  22  in the area of the bulges  24 , thus resulting in a compromised seal and the possibility of fuel leaks. 
     A damaged portion of a fitting, such as cone portion  10 , is replaced by cutting the cone portion  10  from the fuel line and welding a new cone portion  10  in its place. The weld then undergoes an x-ray inspection procedure to verify that welding requirements are met. However, welding requires a qualified welder and a hot work permit. In addition, performing an x-ray inspection requires a certified technician and the clearance of personnel from the work area in order to prevent exposure to x-rays. Further, there is a long wait time in obtaining replacement fittings. As such, the current process for replacing a damaged fitting is expensive and time consuming. 
     SUMMARY OF THE INVENTION 
     A lapping tool for lapping sealing surfaces of a fitting used in a gas turbine is disclosed. The tool includes a shaft having first and second ends and a longitudinal axis. A removable handle is attached to the first end and is oriented in a direction transverse to the axis. The tool also includes a removable lapping insert having an outwardly extending attachment portion that is attached to the second end of the shaft. The lapping insert includes a lapping surface which corresponds to the shape of a sealing surface of the fitting. In one embodiment, the lapping insert includes a cavity for receiving a cone portion of a fitting. Alternatively, the lapping insert includes a projection for insertion into a receptacle portion of a fitting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: 
         FIG. 1  depicts a cone portion of a fitting used in conjunction with a fuel line of a gas turbine. 
         FIG. 2  is a cross sectional view of a receptacle sealing surface and a gouge formed on a first sealing surface. 
         FIG. 3  is a perspective view of a lapping tool in accordance with the present invention. 
         FIG. 4  is a cross sectional view of a lapping tool in accordance with the present invention. 
         FIG. 5  is a cross sectional view of a second lapping insert. 
         FIG. 6  is a view of the cone portion of  FIG. 1  after bulges formed on a first sealing surface have been removed. 
         FIG. 7  is a cross sectional view of a bluing tool. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
     Referring to  FIGS. 3 and 4 , perspective and cross sectional views, respectively, are shown of a lapping tool  26  in accordance with the present invention. The tool  26  includes an elongated shaft  28  located between a handle  30  and a first lapping insert  32 . The first insert  32  includes a housing  34  having an internal cavity wall  35  to define an internal cavity  36  for receiving a component or other item to be lapped. In one embodiment, a diameter of the cavity  36  decreases from an entry end  37  of the cavity  36  to an end wall  38  in accordance with a taper angle θ to form a tapered cavity. The cavity  36  is shaped to correspond with the shape of an item to be lapped such that the internal cavity wall  35  serves as a lapping surface. For example, the cavity  36  may be shaped to correspond to the shape of the cone portion  10  of a fuel line fitting. Further, the cavity  36  may have a taper angle of approximately 24 degrees, for example. In a preferred embodiment, the shaft  28 , handle  30  and first lapping insert  32  are fabricated from aluminum. Alternatively, copper may be used. 
     A first end  40  of the shaft  28  includes a first hole  42  oriented along a longitudinal axis  44  of the shaft  28 . The first insert  32  includes an outwardly extending attachment portion  46  which is received by the first hole  42 . A fastener  48  extends through the shaft  28  in a direction transverse to the axis  44  and abuts against the attachment portion  46  to removably attach the first insert  32  to the shaft  28 . This enables removal of the first insert  32  and replacement with a first insert  32  having a cavity  36  that has a different size, shape or taper angle or combinations thereof. 
     The handle  30  extends through a through hole  50  located on a second end  41  of the shaft and is oriented in a direction transverse to the axis  44 . A fastener  52  extends through the shaft  28  and abuts against the handle  30  to removably attach the handle  30  to the shaft  28 . The handle  30  may be grasped by an operator to enable clockwise and counterclockwise rotation of the shaft  28  and thus the housing  34  about the axis  44 . In addition, the handle  30  may be replaced by a longer handle in order to provide additional leverage for rotating the shaft  28  or by a shorter handle due to space limitations. Further, the shaft  28  may be knurled in order to assist in holding and stabilizing the shaft  28  while the shaft  28  is being rotated. 
     Referring to  FIG. 5 , a cross sectional view of a second lapping insert  54  is shown. The second insert  54  includes a head portion  56  and the previously described attachment portion  46 . A diameter of the head portion  56  increases from a lead end  58  to a base end  60  in accordance with a taper angle to form a tapered projection  62  having a tapered outer wall  64 . The projection  62  is shaped to correspond with the shape of a receptacle sealing surface to be lapped such that the outer wall  64  serves as a lapping surface. For example, the projection  62  may be shaped to correspond to a tapered receptacle sealing surface  22  of a receptacle portion of a fuel line fitting. In use, the lead end  58  is inserted into the cavity of the receptacle portion in order to lap receptacle sealing surface  22 . The second insert  54  is removably attached to the shaft  28  by the attachment portion  46  and the fastener  48  as previously described. This enables removal of the second insert  54  and replacement with a second insert  54  having a projection  62  that has a different size, shape or taper angle or combinations thereof. 
     The tool  26  is used in conjunction with a paste impregnated with abrasive particles, i.e. a lapping compound, to remove raised material from a surface in order to provide a smooth surface finish. The lapping compound is applied between a surface to be lapped and the internal cavity wall  35  of the first insert  32  or the outer wall  64  of the second insert  54 . The tool  26  is then rotated by hand using the handle  30  in partial clockwise and counterclockwise directions in an oscillating motion to remove raised material on the surface in order to provide a relatively smooth surface. The surface may also be lapped in a plurality of sequential stages, at first using relatively course abrasive particles and subsequently using progressively finer abrasive particles until a desired smooth surface finish is achieved. 
     In one embodiment, the tool  26  is used to lap a cone portion of a fitting used in a gas turbine such as cone portion  10  previously described in relation to  FIGS. 1 and 2 . For example, the first sealing surface  14  may become damaged as a result of accidental contact with another component or equipment resulting in the first gouge  20  and associated raised bulges  24 . In order to remove bulges  24  from the first sealing surface  14 , the first insert  32  is attached to the first end  40  of the shaft  28 . A medium grade lapping compound is then applied to the first  14  and second  16  sealing surfaces and the internal cavity wall  35 . Next, the cone portion  10  is inserted into the entry end  37  of the cavity  36 . The tool  26  is then rotated in partial clockwise and counterclockwise directions in an oscillating motion as previously described while the cone portion  10  is firmly held. It is noted that only slight pressure along the axis is necessary. It is important that sufficient lapping compound is used such that no metal to metal contact occurs between the first  14  and second  16  sealing surfaces and the internal cavity wall  35 . The rotations of the tool  26  are continued until a rough surface finish is achieved. The medium grade polish is then completely removed from the first  14  and second  16  sealing surfaces and the internal cavity wall  35  of the first insert  32 . Next, the first  14  and second  16  sealing surfaces are lapped using a fine grade lapping compound in order to provide a desired smooth surface finish. When this is complete, the lapping compound is completely cleaned from the cone portion  10 . 
     Referring to  FIG. 6 , a view of the cone portion  10  is shown after the raised material from the bulges  24  adjacent to the first gouge  20  have been removed to provide a smooth surface finish on the first  14  sealing surface. It is noted that the current invention may also be used to remove bulges from the second sealing surface  16  or both the first  14  and second  16  sealing surfaces simultaneously. Further, although the clearance surface  12  is located beneath the plane of first  14  and second  16  sealing surfaces, portions of any raised material or bulges formed on the clearance surface  12  which extend beyond the plane of the first  14  and second  16  sealing surfaces are also smoothed by the first insert  32 . 
     Referring to  FIG. 7 , a cross sectional view of a bluing tool  66  is shown. The bluing tool  66  serves as a reference tool for checking the smoothness of a surface, such as the receptacle sealing surface  22 . The bluing tool  66  includes a reference portion  68  and the previously described attachment portion  46 . A diameter of the reference portion  68  increases from a lead end  70  to a base end  72  in accordance with a taper angle to form a tapered reference head  74  having a tapered outer wall  76 . The bluing tool  66  is removably attached to the shaft  28  by the attachment portion  46  and the fastener  48  as previously described. This enables removal of the bluing tool  66  and replacement with a bluing tool  66  having a reference portion  68  that has a different size, shape or taper angle or combinations thereof. 
     The bluing tool  66  is used in conjunction with a paste known as engineer&#39;s blue to determine whether a high spot exists on a surface. In use, the paste is applied to the bluing tool  66 . The lead end  70  of the bluing tool  66  is then inserted into the cavity of the receptacle portion of a fitting. Any high spots on the receptacle sealing surface  22  contacts the bluing tool  66 . This causes a portion of the engineer&#39;s blue that is contacted by a high spot to transfer to the high spot, thus indicated the location of the high spot. A lapping procedure may then be used to reduce the high spot. In one embodiment, the bluing tool  66  is fabricated from tool steel in order to avoid galling or other damage to the receptacle sealing surface  22 . 
     Thus, the first  32  and second  54  inserts and the bluing tool  66  may each be removably attached to the shaft  28 . This enables lapping of the first  14  and second  16  sealing surfaces of cone portion  10  and the receptacle sealing surface  22  of a receptacle portion, in addition to checking for high spots in a sealing surface, through the use of a single tool. Further, the tool  26  enables repair of a fitting of a gas turbine thereby eliminating the need to remove the fitting and welding a new fitting in its place, thus avoiding associated costs and time delays. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.