Abstract:
A system is disclosed to use a rotary milling head to break or cut the bond of a heat transfer fin base to a boiler tube, thereby removing the heat transfer fins from the boiler tube to facilitate the more efficient repair of the boiler tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of provisional patent application Ser. No. 60/662,448 filed Mar. 16, 2005, which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     This invention relates to the repair of boiler tubes. More specifically, it relates to a system for removing heat transfer fins from a section of boiler tube to facilitate the repair of the boiler tube.  
       BACKGROUND OF THE INVENTION  
       [0003]     Steam-generating boilers are generally large structures containing numerous boiler tubes, usually made of steel, that are in thermal contact with a burning fuel, such as coal. The burning fuel heats water circulating through the boiler tubes. The heated water, or more usually the resulting steam, is used to drive turbines for generation of electricity or other purposes. In order to facilitate thermal transfer to the water in a boiler tube, heat transfer fins are placed around the boiler tube. They are typically brazed or welded to the boiler tube by high frequency welding.  
         [0004]     Because of deterioration due to corrosion and the like, boiler tubes may require replacement. Ordinarily repair of a damaged boiler tube involves cutting and removal of the damaged section of the tube and replacement with a new section. The section of boiler tube to be replaced is generally cut out using a power saw or cutting torch. However, heat transfer fins on the boiler tube must first be removed to gain access to the boiler tube. Removal of the heat transfer fins from the boiler tube has, before the present invention, been done with portable power tools such as a grinding tool having a rotary abrasive wheel or with air chisels. These techniques are at best time consuming. It is, therefor, an object of the present invention to remove heat transfer fins from boiler tubes more quickly and efficiently.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention is a system for breaking or cutting the bonds holding a heat transfer fin base to a boiler tube. It includes a rotary milling head that has a cutting tip that traverses a circular path slightly larger than the outer diameter of the boiler tube. The cutting tip extends between adjacent windings of the heat transfer fin base. As the rotary milling head is rotated, the cutting tip cuts or breaks the bonds of the heat transfer fin base by exerting forces both in the direction of rotation of the rotary milling head and in the direction toward the rotary milling head. The rotary milling head is also guided and stabilized by a mandrel that fits on the inside of the boiler tube. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     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:  
         [0007]      FIG. 1  is a schematic diagram of a heat transfer base as it is wound around a boiler tube.  
         [0008]      FIG. 2  is a schematic diagram of a preferred embodiment of the present invention.  
         [0009]      FIG. 3  is a diagram of another preferred embodiment of the present invention.  
         [0010]      FIG. 4  is a diagram of an embodiment of the present invention with a pneumatic means of rotation.  
         [0011]      FIG. 5  is a diagram of an embodiment of the present invention with a manual means of rotation.  
         [0012]      FIG. 6  is a schematic diagram of another preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]      FIG. 1  shows a boiler tube  2  with inner diameter  3 , an outer diameter  4  and a circumference  5 . Heat transfer fins  6  are attached to a heat transfer fin base  7  that is wound around the tube  2  in a corkscrew fashion. The base  7  is then bonded to the boiler tube, typically by brazing or welding. Thus, one winding  8  of the base  7  is adjacent to another winding  9  of the base  7 .  
         [0014]     The present invention is a system for removing the heat transfer fins from the boiler tube  2  by cutting or breaking the bonds holding the heat transfer fin base  7  to the boiler tube  2 . As shown in  FIGS. 2 and 3 , a preferred embodiment of the rotary milling head  30  of the present invention includes a milling head base  32  rotatable around a center of rotation  33  extending through a first side  34  and a second side  35  with the first side  34  adapted to be connected to a means of rotation. This embodiment has three holes  37  extending through the first side  34  to allow it to be attached to a power tool or other means of rotation.  
         [0015]     A cutting tool  40  has a cutting end  41  and a mounting end  42  with the mounting end  42  attached to the second side  35  of the milling head base  32 . The cutting end  41  of the cutting tool  40  is attached to a cutting tip  43  that comprises an upper cutting surface  44  and a lower cutting surface  45  that intersect at a cutting angle  46 . The cutting tip  43  is oriented to move in the direction of rotation of the milling head base  32 .  
         [0016]     The mounting end  42  of the cutting tool  40  is attached to the second side  35  of the milling head base  32  a distance from the center of rotation  33  of the milling head base  32  such that the cutting tip  43  traverse a circular path whose diameter  47  is slightly larger than the outside diameter  4  of a boiler tube  2  when the milling head base  32  is rotated. It is to be understood that both the means for attaching mounting end  42  of the cutting tool  40  to the second side  35  of the milling head base  32  and the means for attaching the cutting end  41  of the cutting tool  40  to the cutting tip  43  include manufacturing cutting tip  43 , the cutting tool  40 , and the milling head base  32  out of one piece of metal, as well as other means known to those skilled in the art.  
         [0017]     Also, as shown in  FIGS. 2, 3  and  5 , in operation, another preferred embodiment of the present invention, has a cutting tip  43  that extends between adjacent windings  8 ,  9  of the heat transfer fin base  7 . The bond of the base  7  to the boiler tube  2  in one of the windings  8 ,  9  is cut or broken by forces exerted by the cutting tip  43  both in the direction of rotation of the milling head base  32  and in the direction toward the milling head base  32  as the cutting tool  40  is rotated around the boiler tube  2 . In this preferred embodiment, the cutting angle  46  formed by the upper cutting surface  44  and the lower cutting surface  45  of the cutting tip  43  is chosen based on the spacing of the rows  8 ,  9  of the heat transfer fin base  7 . The cutting tip  43  may be constructed of S7 steel or other steels known to those skilled in the art.  
         [0018]     Further, as shown in  FIG. 5 , in operation, the cutting tool  40  is rotated around the boiler tube  2  and the cutting tip  43  breaks or cuts the bond of the heat transfer fin base  7  to the boiler tube  2 . The cutting tool  40  can be rotated manually as shown in  FIG. 5  or through the use of other means of rotation, including an electric or pneumatic power tool. In another preferred embodiment of the present invention, the cutting angle  46  is such that it causes the cutting tip  43  to advance or self-feed as the cutting tool  40  is rotated around the boiler tube  2 . In another embodiment, gravity may be utilized to cause such an advance.  
         [0019]     In another embodiment of the present invention, as shown in  FIG. 4 , a power tool  10  is used to rotate the rotary milling head  30 . The power tool  10  also has a means to guide and stabilize the rotary milling head  30 , which in this embodiment is a mandrel  14 , but which may be other means known to those skilled in the art. The mandrel  14  fits on the inside of the boiler tube  2  to guide and stabilize the rotary milling head  30  during operation. The mandrel  14  has three clamp fingers  16  to lock against the inner diameter  3  of the boiler tube. The clamp fingers  16  are extended by turning the nut  18  on an extension of the mandrel  20  extending out of the back of the power tool  10 . In yet another embodiment of the present invention, the cutting tip  43  can be advanced by a feed mechanism, not here shown but known to those skilled in the art, on the extension of the mandrel  20 .  
         [0020]     Yet another preferred embodiment of the rotary milling head of the present invention is shown in  FIG. 6 . This embodiment includes a bevel cutting blade  60  that is capable of forming a frustoconical bevel  61  on the end of the boiler tube  2 , as shown in  FIG. 1 . The second side  35  of the milling head base  32  has one or more recesses  62 . The bevel cutting blade  60  has a blade securing portion  63  that fits into the recess  62  and is secured therein by a securing means, not here shown, such as a set screw or other securing means known to those skilled in the art. In operation, this embodiment removes the heat transfer fins from a boiler tube and forms a frustoconical bevel on the end of the boiler tube to facilitate welding, or otherwise connecting, the end of the boiler tube to the beveled end of another boiler tube.  
         [0021]     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, which is not to be limited except by the following claims.