Abstract:
A rotary milling head for boiler tube stub removal with cylindrical cutting pieces removably secured to the milling head by forces exerted by the material being cut and by friction, without any separate securing element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of provisional patent application Ser. No. 60/958,017 filed Jul. 2, 2007, which is incorporated herein by reference, and is a continuation-in-part of patent application Ser. No. 11/901,529 filed Sep. 18, 2007, which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a system for removing boiler tube stubs. More specifically, it relates to the use of a rotary milling head to remove the boiler tube stubs quickly and economically without damaging the boiler drum. 
       BACKGROUND OF THE INVENTION 
       [0003]    Commercial boilers generally have multiple drums or heads (collectively, “drums”) interconnected with numerous steel boiler tubes in the range of 1-5 inches in diameter. As shown in  FIG. 1 , an end  8  of a boiler tube  9  is inserted through an opening  10  in a boiler drum  11  (represented here by a section of boiler drum) so that the end  8  extends into the boiler drum  11 . The boiler tube  9  is expanded against the circumference  12  of the opening, and the end  8  is flared  14  against the drum  11  on the inner periphery of the opening  10 . 
         [0004]    Boiler tubes are routinely replaced for repair or maintenance. Boiler tube removal has been achieved in the prior art by cutting the tube close to the exterior periphery of the drum opening and then notching the remaining boiler tube stub with a torch and mechanically forcing the stub out of the opening in the drum into the drum. This often leads to damage to the opening in the drum. 
         [0005]    Other techniques in the prior art for removing boiler tube stubs include using a special tool to slit the stub through its entire length, as described in U.S. Pat. No. 5,974,642. This technique requires expensive special purpose cutting tools. 
         [0006]    Still another technique, as described in U.S. Pat. No. 7,093,360, involves a piloted rotary cutting tool that is inserted in the stub and used to remove all but a thin shell of the stub. The remaining thin shell of the stub is then manually pushed away from the periphery of the opening in the drum. This technique involves a cutting tool that is expensive to replace and to sharpen. Moreover, it does not provide for removal of the flared portion of the stub. 
       SUMMARY 
       [0007]    The present invention is a milling head to remove boiler tube stubs. It includes cutting pieces with circular cutting faces that are inserted in holes in the milling head and are removably secured therein by forces exerted on the cutting pieces by the material being cut and by friction without any separate means for securing the cutting pieces to the milling head. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein: 
           [0009]      FIG. 1  is a diagram of a boiler tube stub in an opening in a section of boiler drum; 
           [0010]      FIG. 2  is a diagram of a preferred embodiment of the rotary milling head of the present invention; 
           [0011]      FIG. 3  is a diagram of a cutting piece for the preferred embodiment of the rotary milling head of the present invention shown in  FIG. 2 ; 
           [0012]      FIG. 4  is a side view diagram of a preferred embodiment of the rotary milling head of the present invention; 
           [0013]      FIG. 5  is a top view diagram of the preferred embodiment of the rotary milling head of the present invention shown in  FIG. 4 ; 
           [0014]      FIG. 6  is a schematic diagram of a preferred embodiment of the rotary milling head of the present invention; and 
           [0015]      FIG. 7  is a side view diagram of a preferred embodiment of the rotary milling head of the present invention that includes a mandrel. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]    A preferred embodiment of the rotary milling head of the present invention is shown in  FIG. 2 . The rotary milling head  16  has a cutting diameter slightly smaller than the diameter of a boiler drum opening. The rotary milling head  16  has cutting pieces  17  comprising cylindrical cutting blades  18  with concave faces  19 . Other embodiments (not shown) have other cutting blades of other shapes known to those skilled in the art. The rotary milling head  16  also has chip gullets  20  for removal of material cut from the inner diameter of a boiler tube stub. 
         [0017]    Referring to  FIG. 3 , another preferred embodiment has a cutting piece  21  that comprises a cutting blade in the shape of a truncated conical section  22  with a concave circular face  24 . The other end of the cutting blade  23  is attached to the larger end  27  of a truncated conical section comprising a cutting piece body  28  with a truncated end  29 . The cutting piece  21  is made of tungsten carbide or high-speed steel. The cutting piece  21  is commercially available and is marketed for mounting in a stationary position as opposed to the position on the rotating milling head of the present invention. 
         [0018]    Also,  FIGS. 4 and 5  show yet another preferred embodiment of the rotary milling head  30  of the present invention. The rotary milling head  30  has a plurality of axially extending radial cutting piece supports  36  at one end  41  and a tool mounting portion  38  at the other end with body  34  between them. The mounting portion  38  has a cylindrical bore  42  for removably receiving rotary gearing of a rotary milling tool. Various means for mounting the milling head  30  known to the art can be utilized. 
         [0019]    The rotary milling head  30  has a plurality of axially extending radial cutting piece supports  36 . Each of the cutting piece supports has a face, sides and a back with a hole  50  in its face  51  with walls. The hole is approximately the same size and shape as the truncated conical section  28  of the cutting piece  21 . The hole  50  is extended through the back  52  (or through the side depending on the precise configuration) of the cutting piece support  36 , the extension of the hole being preferably in the shape of a cylinder of a diameter of approximately the same size as, or slightly smaller than, the diameter of the truncated end  29  of the cutting piece  21 . 
         [0020]    The truncated conical section  28  of a cutting piece  21  is inserted in a hole  50 . The cutting piece  21  is removably secured to the cutting piece support  36  by the force exerted by the material being removed from the boiler tube stub against the cutting piece  21  and by friction between the truncated conical section  28  of the cutting piece  21  and the walls of the hole  50  in the cutting blade support  36 . If a cutting blade  22  breaks off a cutting piece  21 , the portion of the cutting piece remaining in the hole  50  in the cutting piece support  36  can be removed by inserting a tool (not shown) into the extension of the hole through the back  52  of the cutting support  36  and simply pushing the remaining portion of the cutting piece  21  out of the hole. Moreover, if one or more of cutting blades  22  becomes dull, they can easily and economically be replaced rather than sharpening the entire rotary milling head. 
         [0021]    Another preferred embodiment of the rotary milling head  62  of the present invention is shown in  FIG. 6 . This embodiment has a chip gullet  63  for removal of material cut from the inner diameter of a boiler tube stub. The chip gullet  63  is one of three gullets placed 120° apart and rotating 90° from the first and  64  of the rotary milling head  62  to the second end  65 . The gullet  63  starts 30° ahead of the cutting face  67  of a cutting piece  68 . 
         [0022]    Another preferred embodiment of the rotary milling head of the present invention also includes flare cutting heads  71  as shown in  FIG. 7 . The flare cutting heads  71  are mounted on the rotary milling head  30  between the end  41  with the cutting piece supports  36  and end with the tool mounting portion  38 . The flare cutting heads  71 , which may be cutting pieces  21  as used for the boiler tube stub removal, as described above, or other shape known to those skilled in the art. The flare cutting pieces  71  shown in  FIG. 7  are generally rectangular shaped and have one cutting edge  72  generally perpendicular to the rotational axis of the rotary milling head  30  and one cutting edge  73  generally parallel to the rotational axis of the rotary milling head  30 . The flare cutting heads  71  remove the boiler tube stub flare at the same time the cutting pieces  21  are removing material from the inner diameter of the boiler tube stub. In addition, this preferred embodiment uses a mandrel  80  for insertion into the boiler tube stub to locate the rotary milling head on the correct longitudinal axis in the boiler tube stub end and to provide a mechanism to advance both the cutting pieces  21  and the flare cutting heads  71 . 
         [0023]    Referring to the drawings, in use the rotary milling head  30  of the present invention is centered on the longitudinal axis of a boiler tube stub (preferably at the flared end  14 ). The mandrel  80  is inserted into the boiler tube stub to locate the rotary milling head  30  on the correct longitudinal axis and to provide a means for advancing the cutting pieces  21  into the boiler tube stub. As the rotary milling head advances, the cutting pieces  21  remove material from the inner diameter of the tube stub, leaving only a thin shell of material. The flare cutting heads  71  also remove material from the flared tube end  14 . When the tube cutting pieces  21  have advanced sufficiently through the boiler tube stub and the flare cutting heads  71  have removed enough of the flared tube end  14 , the mandrel  80  is released and the rotary milling head  30  is withdrawn from the boiler tube stub. The remaining thin shell of the tube stub can then be manually pulled away from the drum opening  10  and removed. 
         [0024]    The system of this invention is simple and inexpensive and allows quick and easy removal of boiler tube stubs without damaging or distorting the openings in the boiler drum. 
         [0025]    While the principles of the invention have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the invention. Other embodiments are contemplated within the scope of the present invention in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention.