Abstract:
A system is disclosed to use a first 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, and a second rotary milling head to bevel the exposed end of the boiler tube, thereby facilitating 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. 60/736,895 filed Nov. 16, 2005, which is incorporated herein by reference and is a continuation in part of patent application Ser. No. 11/377,839 filed Mar. 16, 2006. 
     
    
     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 and for preparing the tube end 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. 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.  
         [0004]     In addition, after removal of the damaged section of boiler tube, it may be necessary to remove heat transfer fins at or near the end of the remaining tube ends and to prepare the tube ends for welding to a new section of boiler tube. Proper preparation of the exposed tube ends requires beveling of the exposed tube ends for a good weld. More specifically, the exposed tube ends should have a frustoconical bevel to facilitate a good weld. It is highly desirable that this be done as quickly as possible.  
         [0005]     It is, therefor, an object of the present invention to remove heat transfer fins from boiler tubes, more quickly and efficiently, and at the same time to bevel the exposed tube ends.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is a system for breaking or cutting the bonds holding a heat transfer fin base to a boiler tube and for concurrently beveling the exposed end of the boiler tube. It includes a first 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 first 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 first rotary milling head and in the direction toward the first rotary milling head. It also includes a second rotary milling head that bevel the exposed end of the boiler tube. The rotary milling heads are guided and stabilized by a mandrel that fits on the inside of the boiler tube. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     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 preferred embodiments as shown as follows:  
         [0008]      FIG. 1  is a schematic diagram of a heat transfer base as it is wound around a boiler tube.  
         [0009]      FIG. 2  is a schematic diagram of the first rotary milling head of the present invention.  
         [0010]      FIG. 3  is a diagram of another view of the first rotary milling head of the present invention.  
         [0011]      FIG. 4  is a diagram of the first rotary milling head of the present invention with a pneumatic means of rotation.  
         [0012]      FIG. 5  is a diagram of the first rotary milling head of the present invention with a manual means of rotation.  
         [0013]      FIG. 6  is a schematic diagram of the second rotary milling head of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]      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 .  
         [0015]     The present invention includes 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  FIG. 2  and  3 , a preferred embodiment of the first rotary milling head  30  of the present invention includes a first 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 second rotary milling head described below. This embodiment has three holes  37  extending through the first side  34  and the second side  35  to allow it to be attached to the second rotary milling head.  
         [0016]     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 first 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 first milling head base  32 .  
         [0017]     The mounting end  42  of the cutting tool  40  is attached to the second side  35  of the first milling head base  32  a distance from the center of rotation  33  of the first 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 first milling head base  32  is rotated. The first milling head base  32  also has a hole  49  of diameter  47 , which is slightly larger than the outside diameter  4  of a boiler tube  2 , extending through the first milling head base  32  from the first side  34  through the second side  35 . 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 first 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 first milling head base  32  out of one piece of metal, as well as other means known to those skilled in the art.  
         [0018]     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 first milling head base  32  and in the direction toward the first 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 S 7  steel or other steels known to those skilled in the art.  
         [0019]     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.  
         [0020]     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 first 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 first 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 .  
         [0021]     A second rotary milling head  100  of one embodiment of the present invention is shown in  FIG. 6 . The second rotary milling head has a first side  110  and a second side  111  and is used to form a frustoconical bevel on the end of the tube  2 . The second rotary milling head  100  has a plurality of openings  101  on the second side  111  to receive cutting blades  102 . Each cutting blade  102  has a securing portion  103  that fits into opening  101  and is secured therein by securing element  104 . The first side  110  of the second rotary milling head  100  is mounted coaxially with the mandrel  14  to the output shaft of the power tool  10 . There are a number of different methods known to those skilled in the art for mounting the first side  110  of the second rotary milling head to  100  to the output shaft of the power tool  10 , including tool chucks.  
         [0022]     In this embodiment, the first side  34  of the first rotary milling head  12  is then attached to the second side  111  of the second rotary milling head  100  by any one of a number of means known to those skilled in the art including using bolts from the second rotary milling head extending through the holes  37  in the first rotary milling head  12  so that the tube  2  extends through the hole  49  in the first milling head base  32 . While the first rotary milling head  12  is removing the heat transfer fin  6 , the second rotary milling head  100  is concurrently beveling the end of tube  2 . The desired length of fin removal is determined by the length of the first cutting head  12 .  
         [0023]     The cutting blades  102  in the second rotary milling head  100  have cutting edges  105  that are angled at an approximate angle for producing the desired frustoconical bevel on the end of tube  2 . The first rotary milling head  12  and second rotary milling head  100  are advanced or retracted by the feed mechanism of the present invention.  
         [0024]     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.