Patent Publication Number: US-2005120558-A1

Title: Method Of Producing A Bearing Housing From A Worn Housing, And Fixture Implementing Such A Method

Description:
BACKGROUND  
      The present invention relates to a method of producing a bearing housing from a worn housing, and in particular a housing normally used in aircraft turbines and of the type comprising a casing, and a shield fitted integrally inside the casing as a heat shield.  
      The in-service stress to which the housing is subjected results in the formation of cracks in the shield and, above all, in the weld areas between the shield and casing.  
      To prevent damage caused by such cracks, the worn housing is replaced by a housing comprising practically all new component parts, and which involves considerable time and cost to produce and substitute.  
     SUMMARY  
      It is an object of the present invention to provide a method of producing a bearing housing from a worn housing, and which provides a straightforward, low-cost solution to the aforementioned problems.  
      According to the present invention, there is provided a method of producing a bearing housing from a worn housing extending along an axis and comprising a used intermediate portion; a first and a second used front portions aligned with said used intermediate portion; a first and a second used rear portions also aligned with said used intermediate portion; and a used shield inside said used intermediate, front and rear portions, and the ends of which are integral with said used intermediate portion and said first used front portion respectively; characterized by comprising the steps of detaching said used shield from said first used front portion and from said used intermediate portion; detaching said used intermediate portion from said first used rear portion and from said second used front portion; and connecting a new shield integrally to a new intermediate portion and to said first used front portion.  
      The present invention also relates to a fixture for producing a bearing housing from a worn housing, and which provides for achieving parallelism, squareness, flatness, roundness, and flat surface and diameter dimensions within tolerances of a hundredth of a millimeter. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      A non-limiting embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which:  
      FIGS.  1  to  8  show a number of steps in a preferred embodiment of the method for producing a bearing housing from a worn housing according to the present invention;  
       FIG. 9  shows a plan view of a fixture for producing a bearing housing in accordance with the method shown in FIGS.  1  to  8 ;  
       FIG. 10  shows a larger-scale section of the  FIG. 9  fixture along line X-X in  FIG. 9 . 
    
    
     DETAILED DESCRIPTION  
      Number  1  in  FIG. 1  indicates a bearing housing fitted, in use, to a turbine  2  of an aircraft engine (shown partly and schematically) and commonly referred to as “nÂ°4 bearing housing”.  
      Housing  1  is bolted (in a manner not shown in detail) to a diffuser  15  of the aircraft engine, and houses a double ball bearing  3  (shown schematically) supporting for rotation a hollow shaft  4  of the aircraft engine compressor rear hub. Housing  1  is fitted with three oil drain fittings or pipes  4   a  (only two shown), and with a two-stage oil recovery pump (not shown), which is bolted (in a manner not shown) to the front of housing  1  and driven by the compressor to recover oil from housing  1  and the so-called “nÂ°5 bearing housing”, and expel the recovered oil from the engine.  
      The terms “front” and “rear” used here and hereinafter refer to the gas flow direction of the turbine, and indicate the parts on the left and right respectively in FIGS.  1  to  8 .  
      Housing  1  extends along an axis  5 , is coaxial with shaft  4  in use, and comprises a tubular casing  6  terminating axially with a front connecting flange  13  and a rear connecting flange  14 .  
      Still with reference to  FIG. 1 , casing  6  comprises an intermediate axial portion  7  fitted on the outside with a locating ring  8  having a free C-section appendix  9 , and a tab  10  welded to the outer surface of portion  7 .  
      Casing  6  also comprises two portions  11 ,  12  located at opposite axial ends of portion  7 . Portion  12  is substantially cylindrical, and is interposed between and connected to portion  7  and flange  14  by welds  12   a  shown schematically; while portion  11  is actually defined by two portions  16 ,  17  welded to each other and to portion  7  by electron beam welds (EBW)  11   a  shown schematically.  
      Portion  17  is substantially cylindrical, defines an axial extension of portions  7  and  12 , is welded at the rear to portion  7 , and has an outer flange  19  connected, in use, to the engine structure.  
      Portion  17  terminates at the front with a substantially truncated-cone-shaped portion  18 , from which portion  16  extends axially.  
      Portion  16  terminates with flange  13 , and is fitted inside with a projecting cylindrical sleeve  20 , which houses and supports bearing  3  and is made integral with portion  16  by an intermediate radial ring  21 .  
      Housing  1  also comprises a wall or shield  22 , which acts as a heat shield, is housed inside casing  6 , facing portions  17 ,  18 , and is connected at the ends  23 ,  24  to portion  18  and portion  7  respectively.  
      Housing  1  is subject, in use, to the formation of cracks, particularly at the joins between shield  22  and portion  7 , so a process is implemented to salvage part of housing  1  with which to produce a reusable housing  31  ( FIG. 8 ). With reference to  FIG. 1 , according to said process, portion  7  is detached from portions  12  and  17  by two cutting operations along parallel ideal surfaces  32 ,  33 . The cut along surface  32  also removes end  24  of shield  22  and the end of ring  8 , which remain welded to portion  7 ; and the rest of shield  22  is then detached from portion  18  by a further cutting operation at end  23 .  
      With reference to  FIGS. 2 and 3 , after sandblasting the inner surface of portion  17  and cleaning portion  18  with hydrochloric acid and pressurized water, portion  7  is replaced with a new portion  35 , which is aligned with portion  17  and then connected to portion  17  by a “TIG” weld  36  (shown schematically).  
      Two fastening appendixes  37 ,  38  are then formed on portion  11  by TIG welding and from weld metal. Appendixes  37 ,  38  are L-shaped, are welded to and project from respective portions  18  and  17 , and are located facing each other adjacent to portion  35 .  
      As shown in  FIG. 4 , after stress relieving, appendixes  37 ,  38  are machined to form bevels and/or fillets (not dimensioned or described in detail) on surfaces  39 ,  40 , which is followed by shotblasting the inner surface of portions  17 ,  18 .  
      As shown in  FIG. 5 , a new shield  42  is welded to appendixes  37 ,  38 , is located closer to axis  5  than former shield  22 , and in which three relief holes (not shown) are formed.  
      With reference to  FIG. 6 , after further stress relieving, appendix  9  is changed and resistance welded integrally to the outer surface of portion  35 .  
      As shown in  FIG. 7 , portion  12  is recovered, and end surfaces  43  and  44  of respective portions  35  and  12  are machined to obtain the required total axial length of housing  31  measured between flanges  13  and  14 .  
      As shown in  FIG. 8 , after aligning and mating surfaces  43  and  44 , portions  12  and  35  are connected integrally to each other by a weld  46  (shown schematically).  
      At the end of the process, a full dimensional check of housing  31  is made; and, at the end of each welding operation, visual inspection is made of the relative positions of the welded components, and fluorescent penetrant testing is conducted to reveal any cracks or porosity.  
      As stated, portions  35 ,  11 ,  12  are only welded after aligning portions  35 ,  11 ,  12 , flanges  13 ,  14 , and sleeve  20  with one another along axis  5  using a fixture  51  shown in  FIGS. 9, 10 .  
      Fixture  51  comprises a base  52 , which is connected to flange  14  and centred with respect to axis  5 ; a head  53 , which is connected to flange  13 ; and a disk  54  connected integrally to head  53  and base  52  by respective pairs of columns  55 ,  56 .  
      Head  53  comprises a top cover  58 ; and a locating and supporting disk  59 , which is interposed axially between cover  58  and disk  54 , is connected integrally to columns  55 , and centres sleeve  20  with respect to axis  5 .  
      Disk  54  is fitted with four sectors  60 , which face disk  59 , are angularly spaced about axis  5 , are arranged about a central truncated-cone-shaped wedge  61 , and have respective conical surfaces  62  converging towards base  52  and mating in sliding manner with the lateral surface of wedge  61 .  
      Sectors  60  are connected to disk  54  by respective guide-and-slide connecting devices  63  enabling sectors  60  to slide radially outwards to align portions  12  and  17  when wedge  61  moves down axially towards disk  54 . The downward movement of wedge  61  is controlled by a screw-nut screw device  65  in opposition to the elastic action of a spring  66  interposed axially between wedge  61  and disk  54 .  
      With reference to  FIG. 10 , in actual use, portions  12 ,  35  and  17  (shown schematically and partly with respect to FIGS.  1  to  8 ) are positioned on fixture  51  by fitting portions  12 ,  35  and  17  about sectors  60 , fixing flange  14  to base  52  by means of bolts, and resting the end flange  20   a  of sleeve  20  on disk  59 .  
      Cover  58  is then connected to flange  13  by means of further bolts, and is locked to columns  55  by means of two knobs  67  screwed to the ends of columns  55 . Working device  65  through an axial hole in cover  58  and disk  59 , wedge  61  is then pushed downwards to part sectors  60  radially by equal amounts, so that the inner surfaces of portions  17 ,  35  and  12  are forced radially outwards to mate the surfaces for welding perfectly.  
      Fixture  51  therefore provides for controlling weld distortion and shrinkage to obtain the required flatness, roundness, parallelism, squareness and dimensions of housing  31 .  
      Moreover, the method described and illustrated obviously provides for producing a housing  31  from a worn housing  1  using several salvaged parts of housing  1  itself, thus eliminating the need for new spare parts, and so saving time and money.  
      In fact, only portion  7 , shield  22  and ring  8  are replaced, whereas the known art involves replacing at least components  18 ,  8 ,  7 ,  12 ,  22 , electron beam welding (EBW), highly complex turning, milling and reaming operations, profile reconstructions, and numerous drilling operations and adjustments.  
      In the method according to the present invention, on the other hand, all the components, with the exception of  7 ,  22  and  8 , are used again, after being cleaned, for example, and are welded to the new components, with appropriate checks and stress relieving to ensure maximum weld quality.  
      The method is relatively straightforward, by involving only one cutting operation to detach portion  7  from portion  11 , appendix  9  and shield  22 . Moreover, appendixes  37 ,  38  enable shield  42  to be connected easily to, and at a distance from the inner surface of, portion  11 .  
      Clearly, changes may be made to the method as described herein without, however, departing from the scope of the present invention.  
      In particular, the sequence of some of the steps described may be other than as indicated by way of example, and/or portion  12  need not be salvaged entirely.