Abstract:
A method of forming a finned tube in which the fins are planar, paralleled and extend radially to the tube longitudinal axis, including the steps of positioning at least one rotating forming roll against the tube exterior surface, the forming roll being spaced from the tube and rotatable about an axis that is parallel to said tube longitudinal axis, the forming roll having on the surface thereof an elongated helically arranged fin forming protrusion, the helical protrusion having a pitch of “x” and linearly advancing the tube past the forming tool a distance of “x” for each revolution of the forming roll.

Description:
REFERENCE TO PENDING APPLICATIONS 
   This application is not related to any pending domestic or international patent applications. 
   REFERENCE TO MICROFICHE APPENDIX 
   This application is not referenced in any microfiche appendix. 
   FIELD OF THE INVENTION 
   The invention relates to a method and the machine for carrying out the method for forming parallel fins on the surface of an elongated tubular member. 
   BACKGROUND OF THE INVENTION 
   The basic method for providing fins on a tube is by a forming roll rotating against the surface of the tube. A tubular work piece on the tube external surfaces is caused to flow by plastic deformation to form upstanding spiral fins. Machines for accomplishing this method are well-known in the industry and commonly commercially available—that is, each finned tube has a continuous spiral fin formed on its exterior surface. Tubes having spirally formed fins are commonly used in the construction of heat exchangers. 
   A prior issued patent that illustrates methods of forming spiral fins on a tube is U.S. Pat. No.5,003,690 issued on Apr. 2,1991 entitled FINNING AND THREAD ROLLING MACHINE. Other patents showing the construction of spirally wound fins on tubular members include the following: 
   
     
       
             
             
             
           
         
             
                 
             
             
               PATENT 
                 
                 
             
             
               NUMBER 
               INVENTOR(S) 
               TITLE 
             
             
                 
             
           
           
             
               4,612,791 
               Przbyla, et al. 
               Method and Apparatus for Rolling 
             
             
                 
                 
               Transversely Ribbed Bimetallic Pipes 
             
             
               5,146,979 
               Zohler 
               Enhanced Heat Transfer Surface and 
             
             
                 
                 
               Apparatus and Method of Manufacture 
             
             
               5,222,299 
               Zohler 
               Enhanced Heat Transfer Surface and 
             
             
                 
                 
               Apparatus and Method of Manufacture 
             
             
               5,803,164 
               Schuez, et al. 
               Multiple Finned Tube and a Method for its 
             
             
                 
                 
               Manufacture 
             
             
               5,916,318 
               Anderson 
               Machine for Simultaneously Forming 
             
             
                 
                 
               Threads or Fins on Multiple 
             
             
                 
                 
               Cylindrical Work pieces 
             
             
                 
             
           
        
       
     
   
   By and large each of these references teach a method and/or machine for producing an integral fin tube in which the fin is spiraled. Typically, a spiraled fin is formed on an elongated tubular member by rotating the tubular member against one or more forming rolls that are supported by arbors capably of being adjustably positioned inwardly and outwardly radially from the work piece. Rotary motion is applied to one or more forming rolls to cause the work piece to also rotate as fins are formed by metal displacement on the exterior of the work piece. 
   In each case, the formed fin is an elongated spiral. The invention herein is, in contrast with these prior art references, concerned not with the production of a spiral fin, but with the production of radial fins. By “radial fins” it is meant a sequence of closely spaced, paralleled fins where each fin is a complete, uninterrupted circular portion extending in a radial plane of the axis of a tubular member. 
   Air flowing through a heat exchanger having tubes with parallel fins undergoes reduced pressure drop compared to a heat exchanger of the same size and capacity wherein the fins are spiraled. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is a method and machine for forming planer, paralleled and spaced apart fins on the exterior of a tube. A machine for practicing the method includes a plurality of at least three arbor blocks arranged in a common plane around the work piece and spaced an equal distance from the work piece axis of rotation. A forming roll is supported by each of the arbor blocks. Each forming roll has a surface with an elongated helically arranged fin forming protrusion that bears against the exterior surface of the tubular work piece. Each forming roll is rotatable about an axis that is parallel to the work piece axis of rotation. 
   Rotary energy is coupled to the forming rolls so that the rolls are rotated simultaneously. Further, the forming rolls are rotationally in interlocked relationship with respect to each other. When three forming rolls are used, each forming roll is rotationally displaced 120° from each of the adjacent forming rolls. The forming rolls cause the tubular work piece to rotate. 
   The work piece advances axially due to the helically or spirally wound fin forming protrusion on each of the forming rolls. 
   In a preferred arrangement, the protrusions formed on each of the forming rolls is arranged to have an outer work piece engaging a peripheral edge that increases in diameter from one end towards the opposite end of forming roll. Stated another way, the fin forming protrusion of each of forming roll progresses in depth with respect to the forming roll rotational axis. 
   A better understanding of the invention will be obtained from the following description of the preferred embodiment of the invention taken in conjunction with the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a fragmentary elevational view illustrating a system for forming parallel fins on the external surface of a tubular member. In the arrangement of  FIG. 1  the tubular member has a concentric outer shell, referred to as a “muff,” that is cold flowed by forming rolls to form radially extending parallel circumferential fins. 
       FIG. 2  is an external cross-sectional view taken along the line  2 — 2  of  FIG. 1  showing the use of three forming rolls for forming spaced apart parallel radial fins in an alloy muff positioned on the exterior of a base tube. In the arrangement of  FIG. 2 , three forming rolls equally spaced about the base tube are employed. 
       FIG. 3  is an elevational view of a portion of a completed fin tube having parallel radial fins. 
       FIG. 4  is an end view of a forming roll. 
       FIG. 5  is an elevational external view of a forming roll. 
       FIG. 6  is an enlarged cross-sectional view of the forming roll as taken along the line  6 — 6  of FIG.  4 . 
       FIG. 7  is an enlarged view of a portion of the length of a base tube having a flow deformable tubular muff thereon and showing a portion of a forming roll that is used for cold flowing the muff into radial, paralleled fins. 
       FIG. 8  shows the arrangement such as in  FIG. 2  but showing the use of four spaced apart forming rolls. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a fragmentary external view showing diagrammatically the principles of the invention. In this figure, a base tube  10  that may typically be made of a heat conductive metal such as steel has formed on the exterior surface thereof low height integral fins  12 . These low height fins  12  cause an external concentric tubular muff  14  securely adhered to the base tube. Muff  14  is formed of a material that is easily cold flowable—that is, of a material that can be deformed relatively easily at ambient temperatures. Aluminum or alloys of aluminum are ideal metals for this purpose. The muff  14  has an internal diameter closely fitting the external diameter of base tube  10 . 
   The objective of the system of this invention is to cold flow the muff  14  to form paralleled radial fins for purposes of heat exchange. In order to form muff  14  into such radial fins a plurality of forming rolls is employed. In  FIG. 1  two such forming rolls seen, each generally indicated by the numeral  16 , that is, specifically a first forming roll  16 A and a second forming roll  16 B. Forming roll  16 A is supported by a shaft  18 A and in like manner forming roll  16 B is rotatably supported by shaft  18 B. 
   Each of forming rolls  16 A and  16 B is provided with spirally formed helical grooves, the helical grooves on forming roll  16 A being indicated by the numeral  20 A and those on forming roll  16 B by the numeral  20 B. The helical grooves contact and deform the deformable muff  14  to generate radial fins  22 . Each of the fins  22  is radial—that is, each fin is in a plane perpendicular to the longitudinal axis of base tube  10  and correspondingly, the longitudinal axis of the muff  14 . Fins  22  are coplanar with each other and, that is parallel to each other; as contrasted with the typical heat exchanger finned tube in which fins are helically arranged. Further, fins  22  are not helical—that is, the fins are not continuations of adjacent fins but instead they extend individually and radially from the muff of which they are formed and therefore extend individually and radially in parallel planes from base tube  10 . 
     FIG. 2  is an elevational view as taken along the line  2 — 2  of FIG.  1 . This view shows a bearing block  24  that supports shaft  18 A and  18 B. In this arrangement, three such shafts are employed there being a third shaft  18 C that is not seen in  FIG. 1  since it is directly behind second shaft  18 B. The three shafts  18 A,  18 B and  18 C are supported at equal distances about the longitudinal axis  25  of base tube  10  and are radially spaced 120° apart. Shaft  18 C supports a forming roll generally indicated by the numeral  16 C that has thereon helical groove  20 C. The three forming rolls,  16 A,  16 B and  16 C, are, as previously indicated, spaced equal angular distances about the radius  25  of base pipe  10  and therefore the forming roll firmly secure the base pipe  10  and tubular muff  14  so that the rotation of the forming rolls causes the base tube and muff to concurrently rotate. 
     FIG. 5  is an external view of formal roll  16 A. Note that the outer circumferential periphery of the forming roll  16 A is tapered relative to the forming roll longitudinal axis  26 . 
     FIG. 6  is an enlarged cross-sectional view of the forming roll of  FIGS. 4 and 5 . The forming roll  16 A has a cylindrical opening  28  therethrough that receives shaft  18 A, the shaft not being shown in  FIG. 4 ,  5  or  6 . The cylindrical opening  28  is provided with a longitudinal keyway  30  by which it is keyed to shaft  18 A that supports it when in use. Keyway  30  is indicative of the fact that the system of the invention requires the forming rolls to be rotationally interlocked with respect to each other. Each of the forming rolls  16 A,  16 B and  16 C are manufactured to be identical. The forming rolls must be rotationally interlocked to each other since each groove in each forming roll must receive a radial fin being formed on the muff tube as the muff tube linearly advances during the manufacturing process. For this purpose, each of the forming rolls  16 A,  16 B and  16 C have, as illustrated in  FIG. 6 , grooves  32  therein that are spirally formed as a part of the forming rolls. These grooves  32  receive the cold flow of metal from the muff tube so that the fins  22  as seen in  FIG. 1 , are cold flowed into the grooves  32 . Therefore, it is imperative that the position of each of the three forming rolls,  16 A,  16 B and  16 C be precisely aligned relative to each other not only in their longitudinal position but also in their radial relationship. Therefore, the rotational axis of each of the forming rolls  16 A,  16 B and  16 C is longitudinally positioned exactly parallel to each other and to the longitudinal axis of the base tube. Further, the forming rolls are rotationally positioned 120° apart  FIG. 2  shows a keyway  30  in forming roll  16 A. Keyway  30  is in like manner provided in forming roll  16 B and  16 C and the keyways are rotationally positioned 1200° apart as illustrated. 
   As previously stated, the helical groove  32  in each of the forming rolls  16 A,  16 B and  16 C is spirally formed. 
     FIG. 7  shows a fragmentary portion of forming roll  16 A and shows the grooves  32  of increasing depth in the external surface  34 . As the forming roll presses against the deformable muff portion  14 , the metal of the muff portion cold flows into grooves  32  to form the radial fins  22 . In this process the resulting base thickness of the deformable tubular muff  14  is reduced from the full thickness of the right side of  FIG. 7  to a substantially reduced thickness at the left side, the metal resulting from the reduction in thickness forming fins  22 . 
   The invention herein employs forming rolls to cold flow the external surface of a tube or, as illustrated in this case, a deformable tubular muff affixed to the external surface of a base tube to generate fins. The difference in this invention is that the grooves in the forming rolls are helically arranged and the plurality of forming rolls are rotationally interlocked so that the fins formed on the tubular muff passing between the spaced apart forming rolls are in radial planes compared to the formation of a continuous helical wound fin as has been customary with previously produced fin tube machines. 
   An illustration of a machine that could be used for practicing this invention is shown in U.S. Pat. No. 5,003,690 entitled FINNING AND THREAD ROLLING MACHINE that issued on Apr. 2, 1991. This machine can be employed to practice this invention with the significant difference being that the forming rolls are rotationally interlocked with respect to each other to ensure that the fins formed are in radial planes and are not the result of a continuous spirally wound fin as in this patent. 
     FIG. 8  shows the principals of this invention wherein four shafts are employed—that is, shafts  36 A through  36 D that are equally spaced about base tube  10  and tubular muff  14 . Forming rolls  38 A through  38 D are rotationally interlocked to each other 90° apart as shown by the placement of keys  40 A through  40 D. The base tube and muff axially advance, so that resulting fins  20  will be in parallel spaced apart planes and will not be an elongated helical spiral as with previous fin tube manufacturing machines. 
   It is understood that the invention is not limited in its application to the details of construction and arrangement of components illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. Phraseology and terminology employed herein are for the purpose of description and not limitation. 
   While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. The invention is not limited to the embodiments set forth herein for purposes of exemplification, but is to be limited only by the scope of the attached claims, including the full range of equivalency to which each element thereof is entitled.