Abstract:
A method, apparatus, and design of a fusion welded pipe wherein the effects of an inner bead of the fusion weld are minimized. The internal shape of the pipe prior to welding may be configured in several different shapes so that the beads or lips produced by the fusion welding process are unobtrusive and do not interfere with the function of the pipe. In a likewise manner, the outer shape of the pipe prior to welding may be configured so that the lips are unobtrusive on the external surface of the pipe.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is based upon and claims the benefit of U.S. Utility patent application Ser. No. 10/384,916, filed Mar. 6, 2003, which claims priority of U.S. Provisional Patent Application Ser. No. 60/363,126 filed Mar. 8, 2002, the entire contents of all of which is hereby specifically incorporated by reference for all they disclose and teach. 
    
    
     BACKGROUND OF THE INVENTION 
     a. Field of the Invention 
     The present invention pertains generally to the fusion of plastic pipe and specifically to the fusion of plastic pipe wherein seams created by the fusion process are minimized. 
     b. Description of the Background 
     Polyethylene pipe is used commercially for the construction of pipelines for various applications such as natural gas, water, sewer, and other materials. In addition, polyethylene pipe may be used as conduit to protect transmission cables such as high voltage electricity, fiber optic telecommunication, telephone, cable television, and other signal cables. 
     Polyethylene pipe is typically joined through a process called fusion welding, the most common joint being a butt joint. A butt joint is formed by holding the two sections of pipe rigidly, performing a facing operation to square the ends of the pipes and prepare the pipes for welding, then heating the prepared faces of the pipes on a hot plate to the melting point, removing the heating element, and forcing the two melted faces together. The resulting joint may be cooled before being subjected to any handling forces. The result is a fused joint that is as strong or stronger than the parent material and is very reliable. 
     U.S. Pat. No. 4,990,209 issued to George Rakes entitled “Self Propelled Fusion Machine” (Rakes) is a machine adapted to perform butt joints on polyethylene pipe as described above. Rakes is specifically incorporated herein by reference for all that it discloses and teaches. The Rakes machine performs the sequence of butt fusing in a semi automated fashion, with provisions for easily loading and unloading the pipe as it is welded. Additionally, the Rakes device performs the butt fusion process in an enclosed environment, adding to the consistency and throughput of the machine in all types of weather. 
       FIG. 1  illustrates cross section of a butt joint made on the Rakes machine or any similar machine common in the industry. A first pipe  102  and a second pipe  104  are joined at the weld line  106 . During the fusion process, the material in the zone  108  is melted and then forced together. When the pipes  102  and  104  are forced together, excess melted material forms outer lips  110  and  112  and inner lips  114  and  116 . The material along the weld line  106  solidly and rigidly joins together, forming a very strong and reliable joint. 
     The inner lips  114  and  116  can create problems in certain applications. For example, when a pipeline is used as a conduit, the maximum amount of wires or transmission cables that may be installed in the conduit are limited by the innermost diameter of the lips  114  and  116 . In such cases, the pipeline constructor may be forced to use a larger diameter pipe to compensate for the effects of the lips  114  and  116 . 
     The inner lips  114  and  116  may create problems when the pipe is used as a conduit. The lips  114  and  116  may catch or impede the cables or transmission lines when the lines are installed into the conduit after it is buried. In such cases, it would be advantageous to remove or minimize the lips  114  and  116 . 
     The inner lips  114  and  116  may be cut away by inserting a cutter inside the pipe. Such an operation is time consuming and costly. Not only is it difficult to insert a cutter deep into the pipe, but the chips from the cutting operation may be difficult to remove completely. 
     In some cases, the inner lips  114  and  116  may impede the function of the pipe. For example, in the case of a sewer pipe wherein semi solid and other wastes in a water stream flow by gravity, the lips  114  and  116  may cause some of the wastes to collect and be prevented from flowing to their intended destination. 
     In some cases, the outer lips  110  and  112  may impede the function of the pipe. For example, when the assembled pipe is installed using a feeder system that moves and guides the pipe into position, the lips  110  and  112  around the outside of the pipe may catch on the feeder apparatus. In such cases, the lips  110  and  112  may be removed manually or with a machine as a secondary operation. 
     It would therefore be advantageous to provide a method of fusing pipe wherein the effects of lips commonly formed during the fusion process are minimized or eliminated. It would be further advantageous for the process of eliminating the effects of the lips to be simple, easy to implement, and consistent from weld to weld. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages and limitations of the prior art by providing a simple method for eliminating the effects of the lips of a butt welded fusion joint. Prior to welding and during the facing operation normally performed as part of the welding process, a profile is cut into the inner diameter of the weld. When the weld is performed, the lips do not protrude into the inner diameter of the pipe. Alternatively, the profile may be designed so as to minimize the external protrusion of the lips. 
     The present invention may therefore comprise a method for joining a first plastic pipe to a second plastic pipe with at least a partially recessed internal bead comprising: placing the first plastic pipe in a holder; cutting the first plastic pipe substantially perpendicular to the axis of the first pipe with a profile that reduces the wall thickness of the first pipe with an undercut region on the internal side of the first pipe; cutting the second plastic pipe substantially perpendicular to the axis of the second pipe with a profile that reduces the wall thickness of the second pipe with an undercut region on the internal side of the second pipe; heating the ends of the first pipe and second pipe substantially simultaneously; and forcing the first pipe and second pipe together to form a weld, the weld having a bead that is substantially recessed within the undercut region of the first pipe and the undercut region of the second pipe. 
     The present invention may further comprise a fused butt joint with at least a partially recessed internal bead for plastic pipe comprising: a first pipe having an undercut region near the butt joint substantially axially symmetric and having a profile that is formed by cutting the first plastic pipe substantially perpendicular to the axis of the first pipe with a profile that reduces the wall thickness of the first pipe with an undercut region on the internal side of the first pipe; a second pipe having an undercut region near the butt joint substantially axially symmetric and having a profile that is formed by cutting the second plastic pipe substantially perpendicular to the axis of the second pipe with a profile that reduces the wall thickness of the second pipe with an undercut region on the internal side of the second pipe; and a bead formed by the heat fusing of the first pipe to the second pipe. 
     The present invention may further comprise a machine for butt welding a first plastic pipe to a second plastic pipe with at least a partially recessed internal bead comprising: a holder for receiving the first plastic pipe; a cutter adapted to cutting the first plastic pipe substantially perpendicular to the axis of the first pipe with a profile that reduces the wall thickness of the first pipe with an undercut region on the internal side of the first pipe; a holder for receiving the second plastic pipe; a cutter adapted to cutting the second plastic pipe substantially perpendicular to the axis of the second pipe with a profile that reduces the wall thickness of the second pipe with an undercut region on the internal side of the second pipe; a heater for heating the ends of the first pipe and second pipe substantially simultaneously; and a clamping mechanism for forcing the first pipe and second pipe together to form a weld, the weld having a bead that is substantially recessed within the undercut region of the first pipe and the undercut region of the second pipe. 
     The present invention may further comprise a machine for butt welding a first plastic pipe to a second plastic pipe with at least a partially recessed external bead comprising: a holder for receiving the first plastic pipe; a cutter adapted to cutting the first plastic pipe substantially perpendicular to the axis of the first pipe with a profile that reduces the wall thickness of the first pipe with an undercut region on the external side of the first pipe; a holder for receiving the second plastic pipe; a cutter adapted to cutting the second plastic pipe substantially perpendicular to the axis of the second pipe with a profile that reduces the wall thickness of the second pipe with an undercut region on the external side of the second pipe; a heater for heating the ends of the first pipe and second pipe substantially simultaneously; and a clamping mechanism for forcing the first pipe and second pipe together to form a weld, the weld having a bead that is substantially recessed within the undercut region of the first pipe and the undercut region of the second pipe. 
     The advantages of the present invention are that fused butt joints may be produced to minimize the mechanical interference of the lips produced by the butt joint process. The butt joints may be manufactured without adding any production time or cost to the manufacturing process. The apparatus for making the joints may be adjustable or rigidly mounted, depending on the application and needs of the production process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, 
         FIG. 1  is an illustration of a cross section of a butt joint common in the industry. 
         FIG. 2A  is an illustration of a cross section of embodiment of the present invention wherein a first pipe is joined to a second pipe with an undercut region in the inner diameter. 
         FIG. 2B  is an illustration of a cross section of the pipe of  FIG. 2A  prior to welding. 
         FIG. 3A  is an illustration of a cross section of embodiment of the present invention wherein a first pipe is joined to a second pipe with a beveled region in the inner diameter. 
         FIG. 3B  is an illustration of a cross section of the pipe of  FIG. 3A  prior to welding. 
         FIG. 4A  is an illustration of a cross section of two sections of pipe prior to welding. 
         FIG. 4B  is an illustration of the cross section of  FIG. 4A  wherein shaped cutters are used to cut a profile into the inner diameter of the pipes. 
         FIG. 4C  is an illustration of the cross section of  FIG. 4B  wherein the pipes are pressed against a hot plate. 
         FIG. 4D  is an illustration of the cross section of  FIG. 4C  wherein the pipes are pressed against each other to form a weld. 
         FIG. 5  is an illustration of a perspective view of an embodiment of the present invention of a facing cutter configured with specialized cutting blades. 
         FIG. 6  is an illustration of a perspective view of an embodiment of the present invention of a facing cutter configured with specialized cutting blades wherein the blades are adjustable. 
         FIG. 7A  is an illustration of a cross section of embodiment of the present invention wherein a first pipe is joined to a second pipe with a beveled region in the outer diameter. 
         FIG. 7B  is an illustration of a cross section of the pipe of  FIG. 7A  prior to welding. 
         FIG. 8A  is an illustration of a cross section of embodiment of the present invention wherein a first pipe is joined to a second pipe with a beveled region on both the inner and outer diameter. 
         FIG. 8B  is an illustration of a cross section of the pipe of  FIG. 8A  prior to welding. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2A  illustrates a cross section of embodiment  200  of the present invention wherein a first pipe  202  is joined to a second pipe  204  along the fusion weld line  206 . Pipe  202  has an undercut area  208  that allows the inner lip  210  to be recessed below the normal inner diameter  212 . 
     The recessed area  208  in the present invention is formed during the normal facing operation as explained hereinafter. The shape of the recessed area  208  is selected so that the inner lip  210  may be partially or fully recessed below the inner diameter  212  of the pipe. The recessed lip allows fluids to flow through past the joint with a minimum of obstruction to collect solids and other items such as in sewer applications. In other applications, the recessed lip allows a bundle of wires, fiber optic cables, or other conductors to use the full inner diameter of the pipe. When the pipe is used as a protective conduit, the recessed lips may make it easier to install the cables or transmission lines, as the lips may not catch or impede the installation of the cables. 
     In applications such as conduits and sewers, the pipe is generally not pressurized. The strength of the joint is typically only stressed when the pipe is handled as it is being placed underground for burial. Once the pipe is in place and buried, very little forces are acting on the joint. This is in contrast to pressurized situations such as natural gas where the pipe may undergo more stress in normal service than during installation. 
     The applications where the inner lips pose a problem also tend to be those applications where the strength of the joint is not paramount. Hence, the present invention provides improved functionality while still meeting the minimum strength requirements. 
       FIG. 2B  illustrates a cross section of embodiment  200  of the present invention showing pipe  202  prior to welding. Recessed area  208  is shown in this view. 
       FIG. 3A  illustrates a cross section of embodiment  300  of the present invention wherein a first pipe  302  is joined to a second pipe  304  along the fusion weld line  306 . Pipe  302  has a beveled area  308  that allows the inner lip  310  to be recessed below the normal inner diameter  312 . 
       FIG. 3B  illustrates a cross section of embodiment  300  of the present invention showing pipe  302  prior to welding. Beveled area  308  is shown in this view. 
     Embodiment  300  is similar to embodiment  200  in all aspects except that the shape of the recessed area is varied. Various shapes for the recessed area may be developed by those skilled in the art while maintaining within the scope and intent of the present invention. For example, bevels of various angles and depths may be used. Curved, straight, angled, or other shaped sections may also be used. 
       FIG. 4A  illustrates a cross section of a first section of pipe  402  and a second section of pipe  404  prior to welding. The sections of pipe  402  and  404  are typically clamped into a fixture during the process described herein. 
       FIG. 4B  illustrates a cross section of pipes  402  and  404  wherein shaped cutters  406  and  408  are used to cut a profile into the center of the respective pipes. The shaped cutters  406  and  408  may be simultaneously applied to the two pipes  402  and  404  during the cutting process. The cutting process removes any abnormalities, burrs, dirt, or other items that may effect the quality of the weld. Since the pipes  402  and  404  are rigidly held in a fixture during the welding process, the cutting process of  FIG. 4B  ensures that the pipes  402  and  404  will be perpendicular and square for the welding process. 
     In some embodiments, the cutting process may continue until an operator inspects the pipe to determine that the full face of the pipe has been cut properly. The operator may need to adjust the position of the pipe and recut the pipe if one or more of the pipes were severely gashed or some other abnormality. In other embodiments, the cutting may continue until the holding mechanism is pressed up against a hard stop, a sensor is tripped, or otherwise the cut ends of the pipe were brought to a known location. 
       FIG. 4C  illustrates a cross section of pipes  402  and  404  wherein the pipes are pressed against a hot plate  410 . As the pipe  402  heats up against the hot plate  410 , lips  412  and  414  begin to form. 
     In some embodiments, the pipes  402  and  404  are pressed against the hot plate  410  for a specified time and held against the hot plate at a specified force. As the plastic pipes  402  and  404  melt, the pressure against the plate forms the lips  412  and  414 . In other embodiments, the pipes  402  and  404  may be held against the hot plate  410  for a specified time, but the pipes  402  and  404  may allowed to squeeze against the hot plate  410  until a hard stop is reached. Such an embodiment may limit the size of the lips  412  and  414  before the fusion process occurs. 
       FIG. 4D  illustrates a cross section of pipes  402  and  404  wherein the pipes are pressed against each other to form a weld along the weld line  416 . As the pipes  402  and  404  are pressed together, the lips  418  and  420  grow larger as the fusion occurs. 
     In some embodiments, the pipes  402  and  404  may be pressed against each other at a specified pressure and held for a specified time. As the pipes  402  and  404  are pressed together, the plastic of each pipe fuses against the other pipe, forming a weld. At the same time, the joint cools rapidly and sets up. In some embodiments, when the pipes  402  and  404  are pressed together, the pipes  402  and  404  may be pressed towards each other until a stop is reached. Such an embodiment may be result in more consistent sized lips  418  and  420  from joint to joint. 
     The joint  416  may be cooled passively or actively. The passive cooling may amount to holding the fused pipe in the machine for a certain period of time to allow the pipe to be handled. In embodiments with active cooling, a cool air supply, water mist, or other active cooling method may be applied to the joint  416   
       FIG. 5  illustrates a perspective view of a facing cutter  502  typically used in industry, configured with an embodiment of specialized cutting blades  504 ,  506 , and  508 . The blade  504  has a profile area  510  that is adapted to cut a bevel on the inner diameter of a pipe to be welded. The blades  506  and  508  have similar profile areas  512  and  514 , respectively. 
     In the present embodiment, the blades are fixed and cannot be moved. Because the profile is fixed, the profile that is made in each pipe will be consistent from cut to cut. Further, since the blades may be located with a pin to the faceplate  516 , the profile will be consistent even when the blades are changed for service. 
     Various blade configurations may be created for various applications. For example, the blade configurations may be adapted to cut a profile on the outer diameter of the pipe, the inner diameter of the pipe, or both the outer and inner diameter. Various shapes are also possible, including chamfers, rounded profiles, straight undercut profiles, and various combinations of geometries. In some embodiments, a first blade may cut an internal profile and a second blade may cut an external profile. In other embodiments, the blade profile may include both the internal and external profile. 
       FIG. 6  illustrates a perspective view of a facing cutter  602  typically used in industry, configured with a movable embodiment of specialized cutting blades  604 ,  606 , and  608 . The standard cutting blades  610 ,  612 , and  614  machine the perpendicular surface of the pipe. The specialized cutting blades  604 ,  606 , and  608  machine a profile into the inner diameter of the pipe being cut. 
     The cutting blade  604  is shown exploded from the facing cutter  602 . A T-slot  616  in the faceplate  618  engages the T-shaped feature  620 . A set screw  622  locks the cutting blade  604  into position. 
     Various blade shapes may be created for various applications. For example, the blade configurations may be adapted to cut a profile on the outer diameter of the pipe, the inner diameter of the pipe, or both the outer and inner diameter. Various shapes are also possible, including chamfers, rounded profiles, straight undercut profiles, and various combinations of geometries. In some embodiments, a first blade may cut an internal profile and a second blade may cut an external profile. In other embodiments, the blade profile may include both the internal and external profile. 
     The movable cutting blades have the advantage that any size pipe may be cut on the inventive device. However, the disadvantage is that the cutting blades  604  may need to be accurately positioned so that they produce a uniform cut. 
     In some embodiments, special locating features in the faceplate  618  may be engaged by locating features of the movable cutting blades to that the cutting blades may be accurately and repeatably positioned. Those skilled in the arts may use various designs of positioning and locating mechanisms to achieve the equivalent results without violating the spirit or intent of the present invention. 
       FIG. 7A  illustrates a cross section of embodiment  700  of the present invention wherein a first pipe  702  is joined to a second pipe  704  along the fusion weld line  706 . Pipe  702  has a beveled area  708  that allows the outer lip  710  to be recessed below the normal outer diameter  712 . 
       FIG. 7B  illustrates a cross section of embodiment  700  of the present invention showing pipe  702  prior to welding. Beveled area  708  is shown in this view. 
     The embodiment  700  is applicable to applications where the lips on the exterior side of the pipe are problematic, such as when the assembled pipe is handled through a conveyor mechanism, feeding mechanisms, transportation devices, or other apparatus where a circumferential lip may catch or impede the movement of the pipe. It is common practice to manually cut off the lips after the welding process if the lips are problematic. The present embodiment eliminates the secondary process and hence cost of removing the lips. 
       FIG. 8A  illustrates a cross section of embodiment  800  of the present invention wherein a first pipe  802  is joined to a second pipe  804  along the fusion weld line  806 . Pipe  802  has an external beveled area  808  that allows the outer lip  810  to be recessed below the normal outer diameter  812 . Pipe  802  has an internal beveled area  814  that allows the inner lip  816  to be recessed below the normal inner diameter  818 . 
       FIG. 8B  illustrates a cross section of embodiment  800  of the present invention showing pipe  802  prior to welding. Beveled areas  808  and  814  are shown in this view. 
     Embodiment  800  is suited to applications where both the internal and external lips pose problems to the functionality of the welded pipe. Such applications may be for a telecommunications conduit that is installed using an installation apparatus that may be adversely caught by a lip on the outside. 
     The various embodiments exemplify how at least a portion of the bead formed by a butt joint may be recessed. An internally recessed bead may avoid problems with feeding material through the pipe while an externally recessed bead may avoid problems with handling the pipe from the outside. The embodiments allow at least part of the bead to be recessed. In some embodiments, only a slight portion of the bead will be recessed while in other embodiments the whole bead will be recessed significantly. 
     The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.