Abstract:
A die assembly for machines used to bend lengths of pipe for pipeline applications. The die assembly includes three major components, an exterior housing, a flexible die, and an eggcrate assembly. The exterior housing encompasses the flexible die and eggcrate assembly and pins into conventional bending machines. The flexible die includes a plurality of narrow plate segments positioned along a pair of tie rods. The plate segments are free floating and spaced so as to converge or diverge with respect to the direction of flex of the tie rods. The eggcrate assembly provides support for a plurality of spring plates. Each spring plate has a radius of curvature consistent with the amount of desired bend in the length of pipe.

Description:
This application claim Benefit of Provisional application No. 60/178,112 filed Jan. 26, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to bending machines and equipment for bending lengths of pipe used in oil, gas, water, and other types of transmission pipelines and specifically to bending dies used in pipe bending machines. 
     2. Background of the Invention 
     Conventional dies used in pipe bending machines include half-cylindrical geometries machined so as to have a curve along their length. The radius of curvature of these dies depends upon the diameter of the pipe and have been determined over time. Such radii of curvature as well as known information relating to the recommended degrees of bend are known in the art and can be found on various tables. 
     A substantial defect inherent in conventional dies is the fact that in practice, the bending force applied is concentrated at one point along the rigid die thereby creating the effect of bending the pipe over a transverse cylinder as opposed to a radius of curvature. The result being the creation of a hot spot on the pipe where the bend occurs. At this spot the pipe weakens from being stretched and also tends to oval in cross-section. 
     If the bending machine operator is not careful and attentive and pulls too much of a bend, the pipe is known to wrinkle at this hot spot rendering it unusable. The wrinkled section must then be cut out creating waste of very expensive pipe material. As a matter of caution, recommended degrees of bend are small using only a small stroke of the hydraulic cylinders of the bending apparatus. Substantial bends over shorter lengths of pipe result. A need, therefore, exists for a die assembly which includes a flexible die portion to distribute the bending force over a longer length of the pipe thereby creating a uniform bend without hot spots and their attendant ovalization or weakening of the pipe wall. A further need exists for such a die which will further allow greater degrees of bend over longer segments of pipe. 
     SUMMARY OF THE INVENTION 
     The die assembly of the present invention includes three major components, an exterior housing, a flexible die, and an eggcrate assembly. The exterior housing encompasses the flexible die and eggcrate assembly and pins into conventional bending machines. 
     The flexible die includes a plurality of plate segments positioned along a pair of tie rods. Each plate segment is narrow in width and is hung on the tie rods so as to be free floating thereon. The plate segments are arranged so as to provide a space between adjacent plate segments such that flex of the tie rods causes the plate segments to converge on the end in the direction of the flex and diverge (accordian) in the direction opposite the flex. 
     The eggcrate assembly provides a support for a plurality of spring plates. Each spring plate has a radius of curvature consistent with the amount of bend desired in the pipe. During the bending process, a force is applied by the stiffback of the bending machine against the pipe. The pipe in turn forces the flexible die in contact with the spring plates of the eggcrate assembly. Since each plate segment is independent and free floating on the tie rods, the bending force exerted by the die to the pipe is distributed among the plate segments thereby creating a uniform bend. A plurality of liner bars may be positioned between the plate segments and the pipe to further distribute the force evenly over a greater length of pipe than the conventional die. 
     An object of the present invention is therefore to provide a die assembly with a flexible die that distributes the bending force over the entire bend. 
     A further object of the present invention is to provide such a die assembly which may be retrofit into conventional pipe bending machines. 
     Further objects and advantages of the present invention will become apparent from the specification and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view detail of the die of the present invention shown on a length of pipe with the die outer housing removed and prior to bending. 
     FIG. 2 is a view taken along line A—A of FIG. 1 illustrating one of the interior plates in position prior to bending. 
     FIG. 3 is an end view cross-sectional of the die of FIG.  1 . 
     FIG. 4 is an end elevation of the die of FIG.  1 . 
     FIG. 5 is a bottom view of the die of the present invention wherein the liner bars are not shown. 
     FIG. 6 is a top plan view detail of the eggcrate assembly of the die of FIG.  1 . 
     FIG. 7 is a side view of the eggcrate assembly of FIG.  7 . 
     FIG. 8 is an elevational cross-section of the die of FIG.  1 . 
     FIG. 9 is a section of the die of FIG. 1 illustration placement of the liner bars without a coating thereon and without the retaining bands on each end. 
     FIG. 10 is a schematic illustrating the die of FIG. 1 in a flex position with only one flex bar in place. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The die assembly described with respect to the drawings and specification is designed for use in bending pipe in a pipe bending machine which includes a main frame having connected thereto, directly or indirectly, a stiffback, and stiffback clamp, a pin-up shoe and pin-up clamp and associated power actuating means which are well known and have been described in U.S. Pat. No. 3,834,210, incorporated herein by reference. Therefore, they will not be shown in detail herein. 
     Attention is first directed to FIG. 1 which is an elevational view of the die assembly of the present invention shown apart from the pipe bending machine with its external housing removed. Die assembly  10  is shown in a relaxed position resting upon a section of pipe  12  prior to bending. Shown therein, die assembly  10  includes a plurality of essentially identical plate segments  14 - 14 N retained between first end plate  16  and second end plate  18 . These plate segments include an arcuate internal shape as will be described in greater detail below with regard to FIG.  2  and are arranged along the length of die assembly  10 . Die assembly  10  further includes an eggcrate assembly  20 . Eggcrate assembly  20  (described further below) includes a spring plate  22  which is the member which determines the curvature of the bend of pipe  12 . 
     Referencing FIG. 2, a view taken along line A—A of FIG. 1, external housing  11  enshrouds die plates  14 - 14 N and eggcrate assembly  20 . External housing  11  is shaped and notched so as to fit into and replace the conventional die in the known pipe bending apparatus such as disclosed in U.S. Pat. No. 3,834, 210. The shape of external housing  11  takes into consideration the supporting structure within the conventional pipe bending apparatus. It is understood that without the limitations imposed by the conventional bender design, external housing  11  and plate segments  14  could be shaped and configured differently without departing from the spirit and scope of this invention. 
     FIG. 1, when taken in combination with FIG. 2, shows the orientation and geometry of plate segments  14  which shall next be described. Each individual plate segment  14  is shaped so as to include an arcuate cut out  26  therein. Arcuate cut out  26  is sized and shaped to conform to the external circumference of pipe  12  and is dependent upon the size of pipe selected. Each segment plate  14  includes a planer top surface  28  which abuts eggcrate assembly  20 . 
     The die assembly  10  of FIG. 2 is depicted in a relaxed state where no force is applied to pipe  12  against die assembly  10  as when in the bending process. A space  46  and  48  exists between each plate segment  14  and the inside of the external housing  11 . The purpose for this is to allow plate segments  14  to move in response to flex of tie rods  30  and  32  and to ensure that plate segments abut against spring plates  22  at top surface  28  and not against exterior housing  11 . 
     The plurality of plate segments  14  through  14 N are aligned within die assembly  10  supported from and resting upon a pair of tie rods  30  and  32 . Tie rods  30  and  32  extend the length of die assembly  10  through first end plate  16 , each individual segment plate  14 - 14 N and out from second end plate  18 . Each individual segment plate  14 - 14 N is placed on tie rods  30  and  32  such that a space exists between each individual segment plate  14 - 14 N. In the preferred embodiment, these spaces are maintained through the use of a series of small metal shims or spacers inserted between each individual segment plate. As a result, plate segments  14 - 14 N are substantially free floating on tie rods  30  and  32  and not connected to one another. When assembled, flexible die  8  is not rigid but rather highly flexible. 
     Tie rods  30  and  32  are capable of substantial flex along their respective longitudinal axes. In the preferred embodiment, tie rods  30  and  32  are constructed of 5160 spring steel, commercially available. However, it is understood that other suitable known flexible materials could be substituted. 
     A spacer  34  is inserted on each tie rod  30  and  32  between end plate  16  and plate segment  14 . Similarly, three washers  36  or other suitable bushing materials are positioned on each tie rod  30  and  32  between segment plate  14 N and second end plate  18 . Accordingly, plate segments  14 - 14 N are “sandwiched” between spacer  34  and bushing  36  along tie rods  30  and  32  and maintained in free floating alignment thereon. Gaps  17  and  19  are created by spacers  34  and  36  along the lengths of tie rods  30  and  32 . Gaps  17  and  19  are contemplated to allow die assembly  10  to be retrofit into the conventional pipe bender apparatus which typically includes two arcuate supports which bound and secure the conventional die. Since in the preferred embodiment, die assembly  10  is longer than the conventional die, the assembly must allow for, and integrate, these supports without the necessity of extensive machining or modification for retrofit of the bender apparatus. 
     The number and position of plate segments of  14 - 14 N corresponds to the length of eggcrate assembly  20  and is determined by the diameter of pipe selected. The radius of curvature of spring plate  22  will vary according to the diameter of pipe selected. 
     The ends of tie rods  30  and  32  are threaded to receive nuts  38  and  40  thereon. A spring  42  is inserted between nut  38  and end plate  16 . Likewise, a spring  44  is inserted between nut  40  and end plate  18 . It is understood that although only tie rod  30  is illustrated in FIG. 1, tie rods  30  and  32  are assembled in identical manner. Springs  42  and  44  apply pressure to end plate  16  and  18  toward plate segments  14 - 14 N but allow plate segments  14 - 14 N to move along the length of tie rods  30  and  32  when tie rods  30  and  32  flex. 
     Accordingly, an assembly is described wherein plate segments  14 - 14 N are sandwiched between end plates  16  and  18  with spaces between each individual plate segment  14 - 14 N wherein each plate segment floats, or moves freely with regard to its adjacent plate segment in response to flex of tie rods  30  and  32 . The free floating plate assembly allows the pressure point (hotspot) applied to the pipe during the bend to move and be distributed along the length of the die from one plate segment to another. 
     Die assembly  10  is pinned into the bending machine by shaft  24  in a conventional manner. A shaft  24  pins die assembly  10  within the bending machine. Shaft  24  extends through first end plate  16 , eggcrate assembly  20  and out of second end plate  18 . The die assembly hangs inside the bender from shaft  24  while the eggcrate assembly is bolted to the exterior housing. 
     Referring to FIG. 3, a section taken just inboard of first end plate  16  which depicts external housing  11  and includes a housing face  13  thereon. Housing face  13  is secured to external housing  11  such as by welding or other suitable means and is an integral part thereof. Flexible die  8  including plate segments  14 - 14 N are within external housing  11 . A housing face is likewise secured to external housing  11  on the opposite end (FIG.  4 ). 
     FIG. 4 is an assembled end elevation of die assembly  10  surrounding a pipeline pipe  12 . Die assembly  10  includes external housing  11  with housing face  13  thereon wherein the flexible die  8  (of FIG. 3) is retained within external housing  11 . FIG. 4 shows first end plate  16  adjacent housing face  13 . Tie rods  30  and  32  are shown extending through first end plate  16  but not through housing face  13 . This is so that flexible die  8  as well as tie rods  30  and  32  are able to flex freely within external housing  11  and not retained thereby. 
     Shaft  24  is shown extending through first end plate  16  and housing face  13  and into eggcrate assembly  20  (as depicted in FIG.  1 ). As stated previously, shaft  24  secures and suspends die assembly  10  within the bending apparatus. Shaft  24  extends through an oval channel  50  in first end plate  16 . Oval channel  50  allows first end plate  16  to move vertically in response to flex of tie rods  30  and  32  so that shaft  24  does not hinder the flex- of tie rods  30  and  32  in the entirety of flexible die  8  within external housing  11 . 
     FIG. 5 is a bottom view of die assembly  10  which depicts external housing  11  including housing face  13  and housing back  52 . Flexible die  8  is shown positioned within external housing  11  in an assembled fashion with the exception that FIG. 5 does not show the liner bars (discussed below). Plate segments  14 - 14 N are shown positioned within housing  11  aligned along tie rods  30  and  32  with spaces therebetween so that each individual liner plate segment is capable of independent movement with respect to its adjacent plate segments in response to flex of liner bars  30  and/or  32 . FIG. 5 shows the manner in which plate segments  14 - 14 N are free floating along tie rods  30  and  32  while being retained or sandwiched between first end plate  16  and second end plate  18  of flexible die  8 . 
     With reference to FIG. 6, eggcrate assembly  20  shall now be discussed. FIG. 6 is a top plan view of eggcrate assembly  20  which includes a substantially rectangular welded frame  54  with a plurality of support ribs  55  and  56  welded longitudinally therein. Ribs  55  and  56  provide structural support to eggcrate assembly  20  and also provide structural support for the spring plates secured onto eggcrate assembly  20 . The number of ribs  56  is dependent upon the size of the eggcrate which varies according the diameter of pipe which is to be bent. A series of cross-supports  58  are welded within frame  54  between ribs  56  to provide additional support. A pair of middle cross-supports  60  are welded between middle ribs  56  but are recessed within frame  54  so as to allow shaft  24  (of FIG. 2) to extend along the length of eggcrate assembly  20  when the die is assembled. A mounting plate  62  is welded on each corner of eggcrate assembly  20  within frame  54 . Mounting plate  62  includes a hole  64  drilled and tapped therein. Holes  64  on mounting plate  62  align with holes drilled in the exterior housing of the die assembly so that eggcrate assembly  20  is bolted within the exterior housing upon assembly of the die. 
     A plurality of spring plate mounting plates  68  are welded within the framework of eggcrate assembly  20 . Spring plates  66  are screwed onto spring plate mounting plates  68  by screws  70  countersunk into the surface of spring plates  66 . 
     FIG. 7 is a view taken along line  7 — 7  of FIG.  6  and depicts the manner in which the spring plates  66  are secured to eggcrate assembly  20 . Spring plates  66  are a series of spring steel plates machined to a predetermined external radius and bolted to eggcrate assembly  20 . In a preferred embodiment, three or more such spring plates  66  are bolted to eggcrate assembly  20  to substantially cover its width. Spring plates  66  form the structure against which flexible die  8  is pressed against during the bending process. The radius of curvature of spring plates  66  determines the radius of curvature of the resulting bend in the pipe. 
     The fulcrum point  72  of spring plate  66  is positioned toward the pin-up end  74  of eggcrate assembly  20 . It is at this fulcrum point  72  that the radius of curvature of spring plate  66  is determined. Since the fulcrum point  72  is positioned closer to pin-up end  74  then stiffback end  76  of eggcrate assembly  20 , the radius of curvature intersection with pin-up end  74  means that eggcrate assembly  20  will be thicker at pin-up end  74  than stiffback end  76  since spring plate  66  follows the radius of curvature as set from fulcrum point  72 . It is known in the art that a certain amount of bend can be achieved by the pin-up clamp on pin-up end  74 . 
     FIG. 8 is an elevational cross-section of the die assembly  10  of the present invention in a relaxed state prior to bending. Flexible die  8  of die assembly  10  may also include a plurality of liner bars positioned within the arcuate cut-out portion of the plate segments  14 - 14 N. Referring to FIG. 8 with combination of FIG. 2, a plurality of liner bars  80 - 80 N. Liner bars  80 - 80 N are in the preferred embodiment ½″×½″4140 heat treated spring steel which extends the length of flexible die  8  between first end plate  16  and second end plate  18 . Liner bars  80 - 80 N contact pipe  12  between the individual plate segments  14 - 14 N and pipe  12 . Liner bars  80 - 80 N are flexible so as to be able to flex in accordance with the flex of tie rods  30  and  32 . Liner bars  80 - 80 N are preferably coated with a material such as urethane in order to minimize the potential of scratching or scarring to the exterior of pipe  12  which may otherwise be caused by metal- to- metal contact between the flexible die  8  and the pipe  12 . 
     Liner bars  80 - 80 N are positioned within arcuate cut-out  26  of plate segments  14 - 14 N so as to include a space therebetween. The urethane  82  is applied to the liner bars so that it fills the space between adjacent liner bars within arcuate cut-out  26 . Liner bars  80 - 80 N are preferably coated with urethane in pairs such that two adjacent liner bars are fused together. Urethane on one edge of the formed pair bridges the space between adjacent pairs of liner bars. It is understood, however, that liner bars  80 - 80 N could be coated individually or in groups greater than two depending upon the application. 
     Liner bars  80 - 80 N serve to distribute the pressure applied against the pipe by plate segments  14 - 14 N in order to avoid transverse scratching or scarring of the exterior of pipe  12  which could occur by direct contact between plate segments  14 - 14 N and the exterior of pipe  12 . 
     Each individual liner bar  80  is of a length sufficient to span the distance between first end plate  16  and second end plate  18 . Each liner bar  80  includes a tab on each end wherein the liner bar is bent beyond the last plate segment on the end of flexible die  8 . 
     FIG. 3 depicts liner bars  80 - 80 N encoated with urethane  82  in contact with the exterior surface of pipe  12  such as in the process of bending. 
     Taking FIG. 4 in combination with FIG. 9, wherein FIG. 9 is a cross-section showing liner bars  80 - 80 N in place. FIG. 4 illustrates the manner in which liner bars  80 - 80 N are retained within die assembly  10 . The crimp segments of each liner bar  80 - 80 N extends beyond first end plate  16  on the pin-up end and beyond second end plate  18  on the stiffback end. First end plate  16  and second end plate  18  include a pair of tabs  84  positioned on its face with one on the side of tie rod  30  and one on the side of tie rod  32 . Tabs  84  extend outwardly from first end plate  16  and second end plate  18  in the pin-up and stiffback directions, respectively. A retaining ring  86  is positioned adjacent liner bars  80 - 80 N and secured to tabs  84  such as by bolting. Retainer ring  86  thereby clamps the crimp segments of liner bars  80 - 80 N between itself and arcuate cut-out  26  of first end plate  16 . In likewise fashion, a retaining ring is secured to the crimp segmentss of second end plate  18  thereby clamping the crimp segments on the opposite ends of liner bars  80 - 80 N between itself and the arcuate cut-out of second end plate  18 . Liner bars  80 - 80 N are thereby clamped on each end of die assembly  10 . In the preferred embodiment, the crimp segments crimp segments of liner bars  80 - 80 N are not coated with urethane. Although liner bars  80 - 80 N are clamped to first end segment  16  and second end segment  18 , they are capable of movement within the circumference of arcuate cut-out  26 . 
     FIG. 10 is schematic view of the die assembly  10  of the present invention to illustrate the manner in which the flexible die  8  acts against pipe  12  and spring plates  66  in order to produce a uniform bend in pipe  12 . The die apparatus  10  is shown in FIG. 10 in a full flex position. In the position of FIG. 10, the pin-up applies a force in the direction identified as A and B upon pipe  12 . In response, pipe  12  begins to bend and transfers the force against plate segments  14  to  14 (N−x) (wherein x equals the number of plate segments between fulcrum point  72  and plate segment  14 N). Tie rod  32  then flexes in response to forces A and B applied to plate segments  14  through  14 (N−x) against radius plate  66  of eggcrate assembly  20 . Eggcrate assembly  20  applies resistive forces A′ and B′ back upon plate segments  14 - 14 (N−x). Since plate segments  14 - 14 (N−x) are free floating and spaced along tie rod  32 , the ends of plate segments  14 - 14 (N−x) adjacent to pipe  12  fan apart and distribute the resistive forces A′ and B′ substantially equally among plate segments  14 - 14 (N−x). This force is further distributed through liner bars  80  which are placed transverse to the plate segments  14 . As a result, the forces causing pipe  12  to bend are distributed evenly along the bend corresponding to the number of plate segments. The result is the bend in pipe  12  conforms to the radius of curvature of spring plate  66  between fulcrum  72  and pin-up end  74 . 
     In like manner, the stiffback of the bending apparatus applies a bending force to pipe  12  represented as C, D, E, and F in FIG.  10 . This force is transferred from pipe  12  to plate segments  14 (N−x) through  14 N. This force is then transferred to spring plate  66  of eggcrate assembly  20 . Eggcrate assembly  20  applies a resistive force represented as C′, D′, E′, F′ against plate segments  14 (N−x) through  14 N. Plate segments  14 (N−x) through  14 N being free floating on tie rod  32  and spaced from one another assume the radius of curvature of spring plate  66  between fulcrum  72  and stiffback end  76 . In response to the flex of tie rod  32 , the portions of the plate segment adjacent the pipe fan out such that the resistive force transferred through plate segments  14 (N−x) through  14 N are distributed substantially equally among plate segments  14 (N−x) through  14 N. Liner bars  80  further distribute the bending force along the length of pipe  12  where the bend is achieved. A smooth, uniform bend in pipe  12  substantially equal to the radius of curvature of spring plate  66  between fulcrum  72  and stiffback end  76  is obtained in pipe  12 . 
     The optimal radius of curvature for the spring plate  22  on the eggcrate assembly  20  is dependent upon the diameter of the pipe. The amount of bend per arc foot is dependent upon factors such as the wall thickness of the pipe, the yield point of the pipe material and the use of a pipe mandrel. However, for the purpose of exemplification, it has been found that where all factors are equal, and the die of the present invention is used, the recommended die radius was determined to be 1.33 times that of the conventional die. For example, for 12″ X-52 pipe having a wall thickness of ⅜″ (12 ⅜″ O.D.), the recommended conventional die radius is 12′9″. However, using the die of the present invention for the same pipe, a die radius of 17′0″ has been found to be acceptable. As a result, where the recommended bend per arc foot is 2.3° using a conventional static die, the bend per arc foot using the die of the present invention was determined to be 5.5°. 
     For the purpose of exemplification, a die assembly such as die assembly  10  intended to bend 12 inch x-52 pipe (12 ⅜″ D) may have the following suitable configuration: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Number of ½ wide plate segments 
                 64 
               
               
                   
                 Spaced apart 
                 ⅛″ 
               
               
                   
                 with a 7″ radius on arcuate cut-out 
               
               
                   
                 Number of liner bars 
                 30 
               
               
                   
                 Spaced apart 
                 ⅛″ 
               
               
                   
                 coated with 90 durometer urethane 
               
               
                   
                 formed in pairs 
               
               
                   
                 Number of 32″ spring plates 
                  4 
               
               
                   
                 formed of 5160 spring steel having a 
               
               
                   
                 Radius of curvature of 
                 17′ 0″ 
               
               
                   
                 with fulcrum point 12″ from pin-up end 
               
               
                   
                   
               
             
          
         
       
     
     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 without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiment set forth herein for purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.