Abstract:
A fusion machine which can be top-loaded on very large polyolefin pipes and pipelines has jaws which consist of an upper half jaw and lower left and right complemental jaws which pivot on the half jaw. Left and right actuators connected between the complemental jaws and the half jaw operate in one direction to cause the complemental jaws to rotate to an opened condition in which the upper half jaw can be lowered onto and lifted from the pipes to be fused and in the other direction to cause the complemental jaws to rotate to a closed condition in which the pipes to be fused are gripped so substantially around their circumferences as to resist their deformation from round during manipulation by the machine. The top-loading machine minimizes the need for heavy equipment to load and unload pipe to and from the fusion machine.

Description:
BACKGROUND OF INVENTION 
       [0001]    This invention relates generally to fusion of polyolefin pipes and more particularly concerns the machines used to perform the pipe fusion process. 
         [0002]    Fusion of small diameter pipe may usually be accomplished by hand-held, stand-mounted or cart-carried fusion devices. Little, if any, heavy equipment is necessary in the performance of the fusion process. Sticks of small diameter pipe are typically manually loaded through the top or end of the device for fusion. The fusion device can often be manually disconnected and removed from the pipeline or, at worst, the pipeline is manually released and pulled from the device manually or using a relatively small motorized vehicle. 
         [0003]    Fusion of large diameter pipe typically requires fusion machines mounted on wheeled carts or motorized vehicles and the pipe sticks and pipelines are loaded and unloaded using various types of heavy equipment. A first pipe stick is loaded onto the top of lower fixed half jaws and upper half jaws pivoted on the lower half jaws, usually manually, to clamp the first pipe stick to the fixed jaws. A second pipe stick is loaded onto the top of lower sliding half jaws and upper half jaws are pivoted on the lower jaws, usually manually, to clamp the second pipe stick to the sliding jaws. Once the fusion process is completed and the fixed and sliding jaws are opened, the fused pipeline is pulled to position the free end of second stick in the fixed jaws and a third stick is loaded onto the sliding jaws for fusion into the pipeline. The equipment for loading the pipe sticks onto the sliding jaws and pulling the pipeline from the fixed jaws is likely very heavy and expensive and requires additional operators. 
         [0004]    It is, therefore, an object of this invention to provide a pipe fusion machine which reduces the need for use of additional heavy pipe-handling equipment in performance of the pipe fusion process. And it is an object of this invention to provide a pipe fusion machine which simplifies the pipe-handling steps of the pipe fusion process. 
       SUMMARY OF INVENTION 
       [0005]    In accordance with the invention, a machine for fusing polyolefin pipes has an upper half jaw, lower left and right complemental jaws, left and right pivots and at least one, and preferably left and right, actuators. The upper half jaw has an inside radius that is substantially equal to the selected outside radius of the pipes being fused. The lower left and right complemental jaws each have an inside radius that is substantially equal to the inside radius of the upper half jaw. The left and right pivots connect the lower left and right complemental jaws to their respective left and right portions of the half jaw. The left and right actuators are connected between the lower left and right complemental jaws and their respective left and right portions of the half jaw. Operation of the actuators in one direction causes the lower left and right complemental jaws to rotate to an opened condition in which the upper half jaw can be lowered onto and lifted from the pipes to be fused. Operation of the actuators in its other direction causes the lower left and right complemental jaws to rotate to a closed condition in which the pipes to be fused are gripped so substantially around their circumferences as to resist their deformation from round during manipulation by the machine and resist axial slippage during fusion. 
         [0006]    The machine may also include at least one replacement set of lower left and right complemental jaws. Each of the replacement sets is interchangeable with the lower left and right complemental jaws and with each other. Each replacement set has a different inside radius and their inside radii are each different than the inside radius of the upper half jaw. For each replacement set of complemental jaws, at least one insert is provided that can be mounted on the inside radius of the upper half jaw. The inside radius of the insert or inserts associated with a set of complemental jaws is substantially equal to the inside radius of that set of complemental jaws. Thus, each replacement set of complemental jaws and its corresponding half jaw inserts enables use of the same machine to handle pipes and/or pipelines of a different outside radius. 
         [0007]    The free ends of the lower left and right complemental jaws and their replacement sets, if any, are tapered toward their respective inside radii to facilitate their closure beneath the pipe or pipeline lying on the ground during pick-up. 
         [0008]    Each actuator preferably includes a piston cylinder and a linkage that are serially connected between the lower left and right complemental jaws and the left and right portions of the half jaw, respectively. Each linkage preferably includes a toggle and a link. The toggle is pivoted at a first axis on the upper half jaw. It is also pivotally connected at a second axis to a piston of its respective cylinder and at a third axis to one end of a link. The other end of the link is pivotally connected at a fourth axis to a complemental jaw hub which is pivoted on the lower portion of the upper half jaw. The complemental jaw is attached to and moves in unison with the complemental jaw hub. The axes are parallel and the linkage provides such a mechanical advantage between its respective cylinder and complemental jaw as to assure that sufficient resistance to deviation of the pipeline or pipe stick from round during manipulation by the machine is maintained as long as the grip is closed on the pipeline or pipe stick and to resist axial slippage. 
         [0009]    The machine preferably includes a gantry, a pair of spaced apart tracks and telescoping legs mounted at the front and rear of each track and supporting the gantry above the tracks. A carriage mounted on the gantry has spaced parallel guide rods. One upper half jaw is mounted for reciprocal sliding on the guide rods toward and away from another upper half jaw which is fixed on the guide rods. Another set of lower left and right complemental jaws, each having an inner radius substantially equal to the inner radius of said upper half jaw, is connected by another set of left and right pivots to their corresponding other left and right portions of the other half jaw. Another actuator, and preferably another set of left and right actuators, are each connected between their corresponding other lower left and right complemental jaws and left and right portions of the other half jaw, respectively. One direction of operation of the other left and right actuators causes the other lower left and right complemental jaws to simultaneously rotate to an opened condition in which the other upper half jaw can be lowered onto and lifted from the pipes to be fused. The other direction of operation of the other left and right actuators causes the other lower left and right complemental jaws to rotate to a closed condition in which the pipes to be fused are gripped so substantially around their circumferences as to resist deformation thereof from round during manipulation by the machine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
           [0011]      FIG. 1  is a front elevation view of a fusion machine according to the invention; 
           [0012]      FIG. 2  is a perspective view of the machine of  FIG. 1 ; 
           [0013]      FIG. 3  is a top plan view of the carriage of the machine of  FIG. 1 ; 
           [0014]      FIG. 4  is a perspective view of the machine of  FIG. 1  gripping a pipe stick/pipeline; 
           [0015]      FIG. 5A  is a front elevation view of a fully opened jaw of the machine of  FIG. 1  positioned over a pipe/pipeline; 
           [0016]      FIG. 5B  is a front elevation view of the jaw of  FIG. 5A  lowered and partially closed at ground level on the pipe/pipeline; 
           [0017]      FIG. 5C  is a front elevation view of the jaw of  FIG. 5A  fully closed on the pipe/pipeline; 
           [0018]      FIG. 6A  is a perspective assembly view of a complemental jaw and a complemental jaw adapter hub of the machine of  FIG. 1 ; 
           [0019]      FIG. 6B  is a perspective view of the complemental jaw and complemental jaw adapter hub of  FIG. 6A  assembled; 
           [0020]      FIG. 7A  is a front elevation view of a fully opened jaw of the machine of  FIG. 1  modified by replacement complemental jaws and half jaw inserts and positioned over a pipe/pipeline; 
           [0021]      FIG. 7B  is a front elevation view of the jaw of  FIG. 7A  lowered and partially closed at ground level on the pipe/pipeline; 
           [0022]      FIG. 7C  is a front elevation view of the jaw of  FIG. 7A  fully closed on the pipe/pipeline; 
           [0023]      FIG. 8A  is a front elevation assembly view of the jaw of  FIG. 7A ; 
           [0024]      FIG. 8B  is an enlarged front elevation view of the area BB of  FIG. 8E ; 
           [0025]      FIG. 8C  is an enlarged front elevation view of the area CC of  FIG. 8E ; 
           [0026]      FIG. 8D  is an enlarged perspective assembly view of the upper half jaw and inserts of  FIG. 8A ; 
           [0027]      FIG. 8E  is a front elevation view of the jaw of  FIG. 8A  assembled; 
           [0028]      FIG. 9A  is a front elevation view illustrating the operation of the cylinders/pistons and linkages of the jaw of  FIG. 7A  to open the jaw; 
           [0029]      FIG. 9B  is a front elevation view illustrating the operation of the cylinders/pistons and linkages of the jaw of  FIG. 7A  to close the jaw; 
           [0030]      FIG. 9C  is a front elevation view illustrating the operation of the cylinders/pistons and linkages of the jaw of  FIG. 7A  to tightly grip the pipe/pipeline; and 
           [0031]      FIG. 10  is a schematic diagram of the hydraulic system of the machine of  FIG. 1 . 
       
    
    
       [0032]    While the invention will be described in connection with a preferred embodiment thereof, it will be understood that it is not intended to limit the invention to that embodiment or to the details of the construction or arrangement of parts illustrated in the accompanying drawings. 
       DETAILED DESCRIPTION 
     The Machine 
       [0033]    Looking first at  FIGS. 1 and 2 , a track-driven pipe fusion machine  10  is configured to be top-loaded onto a pipe stick S and onto a pipeline L to which the stick is to be fused. 
         [0034]    The machine  10  has a gantry  20  which is transported on a pair of parallel tracks  21  to travel along the pipeline path terrain. Telescoping cylinder legs  23 ,  25 ,  27  and  29  connected to the gantry  20  at each of its corners are operable to vary the gantry&#39;s elevation and level in relation to the terrain. A carriage assembly  30  including jaws  60  for grabbing the pipeline L and pipe stick S during the fusion process is suspended from and changes elevation and level with the gantry  20 . 
         [0035]    The machine  10  performs the fusion process while stopped in a position in which the tracks  21  straddle and the gantry  20  spans across the pipeline L and the pipe stick S. The jaws  60  are used to pick up, manipulate and release the pipeline L and a pipe stick S during the fusion process. 
         [0036]    The jaws  60  are opened and closed in response to actuators  110  which assure that sufficient resistance to deviation of the pipeline L and/or pipe stick S from round during manipulation by the machine  10  is maintained as long as the grip is closed on the pipeline L and/or pipe stick S and prevent axial slippage. 
         [0037]    The machine  10  also includes an operator&#39;s platform  11  and control center  13 , a facer assembly  15  and a heater assembly  17  for performance of the fusion process steps. 
       The Carriage Assembly 
       [0038]    Turning to  FIGS. 3 and 4 , at least one fixed jaw  31  is mounted on the rear end of the carriage assembly  30  for handling the pipeline L. Two sliding jaws  32  and  33  are mounted on the carriage assembly  30  for handling the pipe stick S. A fourth jaw  34  can be selectively connected for operation either as a second fixed or as a third sliding jaw. The carriage assembly  30  as shown in an exemplary 2×2 configuration in which the first  31  and fourth  34  jaws are fixed and the second  32  and third  33  jaws are sliding in unison. As best seen in  FIG. 4 , in this configuration the fixed jaws  31  and  34  will usually be used to grip the pipeline L and the sliding jaws  32  and  33  will usually be used to grip the pipe stick S. In a 3×1 configuration (not shown), the first jaw  31  is fixed and the second, third and fourth jaws  32 ,  33  and  34  are sliding in unison. In the 3×1 configuration the single fixed jaw  31  will usually be used to grip the pipeline L and the three sliding jaws  32 ,  33  and  34  will usually be used to grip the pipe stick S. This is especially useful if the pipe stick S is to be connected to a T-junction in a pipeline, in which case the length of the T may be too short for a multiple jaw grip. The principles herein disclosed are applicable to both the 2×2 and the 3×1 configurations of the carriage assembly  30 . 
         [0039]    In the 2×2 configuration shown, the carriage  30  has a guide rod support plate  35  at its forward end and the outboard fixed jaw  31  at its aft end. Guide rods  37  extend in parallel and are fixed between the plate  35  and the outboard fixed jaw  31 . The support plate  35  has a central aperture  39  for connection to a mounting link  41  on the forward end of the gantry  20 . The fixed jaw  31  has lugs  43  symmetrically positioned and engagable on the aft end of the gantry  20 . The sliding jaws  32  and  33  are mounted on the forward portion of the guide rods  37  and are fixed against the opposite ends of the carriage cylinders  45  so that the sliding jaws  32  and  33  and the cylinders  45  move in unison on the guide rods  37 . The fourth jaw  34  is mounted between the outboard fixed jaw  31  and the inboard sliding jaw  32  but is fixed in relation to the outboard fixed jaw  31  by jaw conversion links  47 . The piston rods  49  of the carriage cylinders  45  extend through the inboard sliding jaw  32  and are fixed by rod extensions  51  to the first jaw  31 . Thus, when the pistons  49  are retracted in the cylinders  45 , the sliding jaws  32  and  33  move toward the fixed jaws  31  and  34  and, when the piston rods  49  are extended from the cylinders  45 , the sliding jaws  32  and  33  move away from the fixed jaws  31  and  34 . 
         [0040]    In the 3×1 configuration, the jaw conversion links  47  connect the fourth jaw  34  to the inboard sliding jaw  32  and the rod extensions  51  extend through the fourth jaw  34  and are fixed to the fixed jaw  31 . 
       The Jaws 
       [0041]    Turning to  FIGS. 5A ,  5 B and  5 C, each carriage assembly jaw  60 , whether fixed or sliding, includes an upper half jaw  61 , lower left  63  and right  65  complemental jaws and left  67  and right  69  pivots. In this disclosure, the upper half jaw  61  is so-called because, as shown, it substantially affords 180° of the grip. The lower jaws  63  and  65  as shown are quarter or 90° grips, but need not necessarily be quarter or 90° jaws. They are referred to as complemental because, as shown, they substantially afford the remaining 180° to complete the circular grip. In the quarter jaw embodiment shown, the complemental jaws are symmetric with respect to the center plane  73 , but in non-quarter jaw embodiments the complemental jaws will not by symmetric. The upper half jaw  61  has a generally trapezoidal outer perimeter  71  and is symmetric in relation to a vertical plane  73  through the center longitudinal axis  75  of the pipeline L and pipe stick S to be grasped. As best seen in  FIG. 5C , it has an inside radius  77  that is substantially equal to the selected outside radius of the pipeline L and pipe stick S being fused. 
         [0042]    For the purposes of this description, assume that the pipeline L or pipe stick S of  FIGS. 5A ,  5 B and  5 C have a two meter outside diameter and the upper half jaw  61 , therefore, has a one meter inside radius. As best seen in  FIG. 5C , the complemental jaws  61  and  63  each have an inside radius  79  that is substantially equal to the inside radius of the upper half jaw  61 , in this example also one meter. 
         [0043]    As best seen in  FIG. 5B , the outer perimeters of the complemental jaws  63  and  65  are tapered toward their free ends to facilitate their insertion between the lower half of the pipe stick S or pipeline L and the ground G to pick up the pipe stick S or pipeline L. As shown, the tapers increase incrementally toward the tips of the complemental jaws  63  and  65  so as to converge toward their respective inside radii  79 . 
         [0044]    Continuing to look at  FIGS. 5A ,  5 B and  5 C, the complemental jaws  63  and  65  have adapter hubs  81  at their upper ends. As best seen in  FIGS. 6A and 6B , the left hub  81  has a hook  83  on its inside portion and a clevis  85  on its outside portion with lands  87  on the bottom of the clevis  85 . The left complemental jaw  63  has a retaining pin  89  on its upper inside portion and a stop plate  91  on its upper outside portion. The left complemental jaw  63  is attached to the left hub  81  by seating the retaining pin  89  in the hook  83  and securing the stop plate  91  in abutment with the lands  87  on the clevis  85  using screws  93  extending through the stop plate  91  and into the clevis  85 . The left hub  81  is pivoted for rotation on the lower portion of the left upper half jaw  61  about a shaft  95  on the left upper half jaw  61  and the left complemental jaw  63  pivots in unison with the left hub  81  to which it is attached. The right hub  81  and complemental jaw pivot  69  configuration mirrors the left hub  81  and complemental jaw pivot  69  configuration of  FIGS. 6A and 6B . 
         [0045]    As seen in  FIGS. 7A ,  7 B and  7 C, the machine may also include at least one replacement set  160  of lower left  163  and right  165  complemental jaws. Each replacement set  160  of complemental jaws  163  and  165  has a different inside radius  179  than the two meter diameter set  60  discussed above and the other replacement sets  160 . Assume that the pipeline L or pipe stick S of  FIGS. 7A ,  7 B and  7 C have a 54″ outside diameter and the upper half jaw  61 , therefore, has a 27″ inside radius  77 . As best seen in  FIG. 7C , the lower left and right complemental jaws  163  and  165  each have an inside radius  179  that is substantially equal to the inside radius of the upper half jaw inserts  180 , in this example also 27″. For this replacement set  160  of complemental jaws  163  and  165 , at least one, and as shown two, inserts  180  are provided that are mountable on the inside radius  77  of the upper half jaw  61 . The lower complemental jaw  FIGS. 6A and 6B  for replacements  160  are installed as explained above in relation to the complemental jaws  63  and  65  of the two meter outside diameter pipeline L and pipe sticks S. 
         [0046]    Installation of the inserts  180  for the upper half jaw  61  is illustrated in  FIGS. 8A ,  8 B,  8 C,  8 D and  8 E in relation to the 27″ outside radius pipeline L and pipe sticks S. As seen in  FIG. 8A , two inserts  180  are used to change the inside radius  77  of the upper half jaw  61 . Looking at  FIG. 8B , an L-shaped retainer  181  extends outward from the insert  180  for engagement against a bar  183  on the half jaw  61 . Turning to  FIG. 8C , once the insert retainer  181  is engaged against the half jaw bar  183 , a latch  185  on the insert  180  slides into and out of engagement with a catch  187  on the half jaw  61  to secure or release the insert  180  to or from the half jaw  61 , respectively. As seen in  FIG. 8E , the inside radius  189  of the inserts  180  associated with a set of complemental jaws  160  is substantially equal to the inside radius  79  of that set of complemental jaws  160 . Thus, each set of corresponding complemental jaws  160  and half jaw inserts  180  enables use of the same machine  10  to handle pipe sticks S and pipelines L of a different outside radius. 
         [0047]    In this exemplary application, the pipeline L or pipe sticks S of  FIGS. 7A ,  7 B and  7 C have 54″ outside diameters. The upper half jaw  61  and its associated replacement lower complemental jaws  163  and  165  will, therefore, have one or more, and as shown, two inserts  180  defining a 27″ inside radius. 
         [0048]    As seen in  FIGS. 7A ,  7 B and  7 C, the free ends of the replacement sets  160  of lower left and right complemental jaws  163  and  165  are, similar to the two meter diameter complemental jaws  63  and  65 , tapered toward their respective inside radii  179  to facilitate their closure beneath the pipe sticks S or pipeline L during pick-up. 
         [0049]    The two meter (78.7″) and 54″ pipe diameters have been chosen for  FIGS. 5A-C  and  7 A-C, respectively, because it is presently anticipated that the same fusion machine  10  will be useful for fusing pipes of any diameter within that range. However, fusion machines applying the principles herein taught can be made in many different sizes to accommodate different ranges of pipe diameters. 
       The Actuators 
       [0050]    Turning to  FIGS. 9A ,  9 B and  9 C, the left and right actuators  110  are connected between the replacement lower left and right complemental jaws  163  and  165  and their respective left and right portions of the half jaw  61 . As shown, the left and right actuators  110  are mirrored in relation to the plane  73 . Each actuator  110  includes a cylinder  111  and piston  113  and a linkage  120  serially connected between their respective lower replacement left and right complemental jaws  163  and  165  and left and right portions of the half jaw  61 . Each linkage  120  preferably includes a toggle  121  and a link  123 . The toggle  121  is pivoted at a first axis  125  on the upper half jaw  61 . It is also pivotally connected at a second axis  127  to the piston  113  of its respective cylinder  111  and at a third axis  129  to one end of the link  123 . The link  123  is also pivotally connected at a fourth axis  131  at its other end to the complemental jaw adapter hub  81  which is pivotally mounted at a fifth axis  133  on the lower portion of the upper half jaw  61 . The replacement complemental jaw  163  or  165  is secured to and moves in unison with its respective complemental jaw hub  81  as explained in relation to  FIGS. 6A and 6B  and the complemental jaws  63  and  65 . The axes  125 ,  127 ,  129 ,  131  and  133  are parallel. 
         [0051]    When an actuator piston  113  is retracted into its cylinder  111 , its toggle  121  is pivoted on the first axis  125  toward the cylinder  111 . The toggle  121  pulls the link  123  in tension, causing its complemental jaw hub  81  to rotate about its pivot axis  97 . The replacement complemental jaw  163  or  165  moves in unison with its hub  81 , opening the complemental jaw  163  or  165 . When an actuator piston  113  is extended from its cylinder  111 , its toggle  121  is pivoted on the first axis  125  away from the cylinder  111 . The toggle  125  pushes the link  123  in compression, causing its complemental jaw hub  81  to rotate about its pivot axis  133 . The complemental jaw  163  or  165  moves in unison with its hub  81 , closing the complemental jaw  163  or  165 . The linkage  120  provides such a mechanical advantage between its respective cylinder  111  and complemental jaw  163  or  165  as to assure that sufficient resistance to deviation of the pipeline L and/or pipe stick S from round during manipulation by the machine  10  is maintained as long as the grip is closed on the pipeline L and/or pipe stick S and that it resists axial slippage. 
       Hydraulic System 
       [0052]    Turning to  FIG. 10 , the machine hydraulic system  140  includes an engine  141 , preferably an industrial liquid cooled diesel engine, closed loop track drive pumps  143 , an auxiliary open loop pump  145  and a hydraulic fluid reservoir  147 . The system  140  powers right and left track motors  149  to drive and steer the machine  10  from one fusion location to another and into operating positions in which the machine  10  can pick up, manipulate and/or fuse pipeline L and pipe sticks S. The elevation and level of the gantry  20  is varied by simultaneous operation of the two front gantry telescoping cylinders  23  and  25  and independent operation of the two rear gantry telescoping cylinders  27  and  29  to raise and lower the corners of the gantry  20  as necessary. The spacing of the fixed and sliding jaws  60  is controlled by operation of the carriage cylinders  45  to reciprocate the sliding jaws on the guide rods  37 . The fusion machine jaws  60  are opened and closed by operation of their respective actuator cylinders  31   a  and  31   b ,  34   a  and  34   b ,  32   a  and  32   b  and  33   a  and  33   c . As seen in  FIGS. 9A ,  9 B and  9 C, operation of the actuator cylinders  111  in one direction causes the lower left and right complemental jaws  63  and  65  or replacements  163  and  165  to rotate to an opened condition in which the upper half jaw  61  can be lowered onto and lifted from the pipe sticks S and/or pipeline L to be fused. Operation of the cylinders  111  in the opposite direction causes the lower left and right complemental jaws  63  and  65  or replacements  163  and  165  to rotate to a closed condition in which the pipe sticks S and/or pipeline L to be fused are gripped so substantially around their circumferences as to resist their deviation from round during manipulation by the machine  10  and to prevent slippage. The machine may also include a number of stripper cylinders  151  for use in removal of the heater during separation of the jaws after heating. 
       Operation 
       [0053]    Assume for the exemplary application herein described that several sticks S of pipe to be fused into a pipeline L are in end-to-end alignment with the pipeline L, that the jaws  60  of the fusion machine  10  have been equipped with complemental jaws  63  and  65  or replacements  163  and  165  and half jaw inserts  180  corresponding to the pipe outer diameter and that the fourth jaw  34 , if any, has been secured for operation in the 2×2 configuration. Assume further that it is desirable that the pipeline L be manipulated by the fixed jaws  31  and  34  and the pipe stick S be manipulated by the sliding jaws  32  and  33 . 
         [0054]    In performing the fusion process, the operator opens the complemental jaws  63  and  65  or replacements  163  and  165  to a fully opened configuration and adjusts the gantry  20  to a level suitable for the pipe stick S to be received in the carriage assembly  30 . The operator then drives the machine  10  into a position in which the tracks  21  straddle, the gantry  20  spans across and the carriage assembly  30  is aligned with the pipe stick S to be fused with the sliding jaws  32  and  33  proximate the end of the pipe stick S to be fused. 
         [0055]    In this position, the operator lowers the gantry  20  and begins closing the sliding complemental jaws  63  and  65  or  163  and  165  as the tips drop below the midpoint of the pipe stick circumference. Lowering of the gantry  20  can, but need not necessarily, continue until the tips of the complemental jaw  63  and  65  or  163  and  165  contact the ground G. Closing of the complemental jaws  63  and  65  or  163  and  165  continues until they are in the fully closed condition. At this point, the complemental jaws  63  and  65  or  163  and  165  and half jaw  61 , or half jaw inserts  180 , if necessary, tightly grip the pipe stick S. 
         [0056]    Once the pipe stick S is gripped, the gantry  20  can be raised, if necessary, to lift the gripped end of the pipe stick S above ground G. The operator can then drive the machine  10  and further change the elevation of the gantry  20  to a condition in which the gripped end of the pipe stick S is proximate, higher than and in longitudinal alignment with the end of the pipeline L to which the pipe stick S will be fused and the fixed jaws  31  and  34  are aligned above the end of the pipeline L to which the pipe stick S will be fused. 
         [0057]    In this position, the operator again lowers the gantry  20  and begins closing the fixed complemental jaws  63  and  65  or  163  and  165  as the tips of the fixed complemental jaws  63  and  65  or  163  and  165  drop below the midpoint of the pipeline circumference. Lowering of the gantry  20  can, but need not necessarily, continue until the tips of the complemental jaw  63  and  65  or  163  and  165  contact the ground G. Closing of the complemental jaws  63  and  65  or  163  and  165  continues until they are in the fully closed condition. At this point, the complemental jaws  63  and  65  or  163  and  165  and half jaw  61 , or half jaw inserts  180 , if necessary, tightly grip the pipeline L. 
         [0058]    Once the pipeline L is gripped, the gantry  20  can be raised to lift the gripped ends of the pipe stick S and pipeline L above ground G to fusion level. With the center axes  75  of the pipeline L and pipe stick S longitudinally aligned at fusion level, the operator adjusts the spacing between the fixed  32  and  33  and sliding jaws  32  and  33 , if necessary, inserts the facer assembly  15  into a suitable facing position between the fixed  31  and  34  and sliding jaws  32  and  33  and closes the spacing to bring the pipeline L and pipe stick S into abutment with opposite sides of the facer. 
         [0059]    After facing, the operator spreads the spacing between the fixed  31  and  34  and sliding jaws  32  and  33 , removes the facer assembly  15  from the space, prepares a heater assembly  17  for insertion between the ends of the pipeline L and pipe stick S to be fused, adjusts the spacing if necessary to receive the heater assembly  17 , inserts the heater assembly  17  into a suitable heating position between the fixed  31  and  34  and sliding  32  and  33  jaws and closes the spacing to bring the pipeline L and pipe stick S into abutment with opposite sides of the heater. 
         [0060]    After heating, the operator spreads the spacing between the fixed  31  and  34  and sliding  32  and  33  jaws, removes the heater assembly  17  and closes the spacing to bring the molten ends of the pipeline L and pipe stick S together. This condition is maintained under force until the joint has cooled sufficiently. 
         [0061]    Once the joint has cooled, the operator lowers the gantry  20  and opens all of the jaws  60  simultaneously to release the fused pipeline L to the ground G. This completes this exemplary fusion process for one pipe stick S. The operator can then raise the gantry  20  sufficiently to allow the machine  10  to be driven forward from the fused pipe stick S to another pipe stick S for repetition of the process. 
         [0062]    In some applications, rather than the exemplary process as above described, it may be desirable to use the fusion machine  10  to bring the pipe sticks S into their end-to-end alignment with the pipeline L at the beginning of the process, and/or to secure the fourth jaw  34  to the sliding jaw  32  rather than to the fixed jaw  31  and/or to apply the fixed jaws  31  and  34  to the pipe stick S and sliding jaws  32  and  33  to the pipeline L. 
         [0063]    The fusion process can be performed using known facer and heater assemblies  15  and  17  and methods for control of the relative axial movement of the sliding jaw or jaws with respect to the fixed jaws, examples of which are disclosed in U.S. Pat. No. 5,814,182, No. 6,021,832, No. 6,212,747 and No. 6,212,748. 
         [0064]    Thus, it is apparent that there has been provided, in accordance with the invention, a straddle-mounted pipe fusion machine that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art and in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit of the appended claims.