Debeading tool for butt-welded plastic pipe

A debeading tool capable of internally debeading butt-welded pipe made of PVC and similarly hard plastics has a work head that can be coupled to a distal end of a torque tube. The work head includes a motor carrying a cutter which is oriented at an angle, e.g., 12 degrees, to the interior pipe wall for cutting the weld bead as the tool is rotated inside the pipe. The work head cutter can be moved between an insertion/removal position away from the side wall and a cutting position against the bead on the side wall. A locator assembly that contacts the bead during insertion of the work head aids in positioning the cutter to straddle the weld bead. A pipe cleaner can be prepositioned in the pipe before butt-welding to be engaged upon removal of the work head to pull weld bead chips and fines from the pipe.

BACKGROUND OF THE INVENTION

This invention relates to debeading or trimming of weld flash inside a butt-welded plastic pipe and more particularly to a tool that can be used with hard plastics such as PVC, PVDF, polypropylene and the like. Plastic pipes and pipe liners typically are made in standard lengths, such as 20 feet or 40 feet, and are interconnected end-to-end to make a long pipe string.

Butt welding of plastic pipe produces a weld bead or flash that is preferably removed before the pipe is placed in service for conveying liquids to reduce flow restriction and reduction, turbulence wear, biofilm/bacteria entrapment and potential for blockages forming at the joints. Plastic pipes are also used as conduit for cable, and, again, it is desirable to remove the weld flash before attempting to pull cable into the butt-welded pipe string.

In the past, such pipes have been made of polyethylene, which is a relatively soft thermoplastic that can be readily butt-welded and easily debeaded. A tool known as the Bead Trimmer II™ has been made and sold by R & L Manufacturing Inc. of Camas, Wash. The tool includes a bead trimmer head assembly that mounts on one end of a series of interconnected torque tubes and is pushed into the butt-welded pipe until the internal bead or weld flash is contacted. The head assembly has a central shaft that couples to the torque tube end and has a centering disk sized to the pipe for retaining the head assembly centered in the pipe as it is inserted. A gauge mounted on the periphery of the centering disk contacts the bead when the tool reaches the bead. When contact is made, the operator manually rotates a T-shaped bar mounted at the opposite end of the torque tube string to rotate a cutter around a full circle inside of the pipe. The cutter includes a fixed blade that extends lengthwise along the sidewall of the pipe, aligned with the gauge so that, when the gauge contacts the weld flash or bead, the blade straddles the bead. The blade has an edge that is beveled to cut into the bead when rotated until locating registers at each end of the blade holder contact the inner wall of the pipe, at which point the blade holder maintains a constant cutting depth of the blade edge. Continued rotation of the head assembly cuts the bead away from the pipe wall. When this action is completed, the head assembly is withdrawn from the pipe. Several hooks distributed radially around the downstream end of the head assembly engage the cut-away bead and drag it from the pipe.

Recent formulations of PVC, such as C-900 and C-905 fusible PVC, have enabled butt-welding PVC pipes. The fusion methods developed for this material likewise produces a weld flash or bead, which it is also desirable to remove. PVC is much harder than polyethylene; so hard, in fact, that the Bead Trimmer II™ is incapable of cutting the weld flash or bead. Other plastics that are similarly hard include PVDF and polypropylene.

Accordingly, a need remains for a way to debead butt-welded pipe made of PVC, PVDF, polypropylene and other similarly hard plastics.

SUMMARY OF THE INVENTION

One aspect of the invention is a tool capable of internally debeading butt-welded pipe made of PVC and similarly hard plastics. The tool has rotary cutter that can be positioned in alignment with and pressed against the weld bead for cutting the bead. The cutter is preferably positioned at an angle to the pipe side wall.

Another aspect of the invention is a method for internally debeading butt-welded pipe made of PVC and similarly hard plastics. The rotary cutter is operated while the tool is rotated around the inside of the pipe.

DETAILED DESCRIPTION

FIGS. 1-6are various views of one embodiment of the work head10of a debeading tool for debeading a joint in butt-welded plastic pipe according to the invention. The debeading tool comprises generally the work head10, a torque tube12for insertion into a length of cylindrical pipe14, and a handle structure16for rotating the torque tube about an axis that is substantially coaxial with the pipe. The handle structure can be a simple T-bar, or a pair of torque arms18as shown inFIGS. 4A and 4B, or a steering wheel mounted on the operator or proximal end of the torque tube12. The torque tube can be a continuous length of pipe with coupler at each end to connect to the handle structure16and to the cutting head10, or can be a known structure consisting of a series of shorter tube lengths, e.g., 8-foot lengths, each interconnected by couplers (not shown) that link the tube lengths together and to the cutting head and handle structure. A control box20, further described below, is mounted on the handle structure16over the operator end of the torque tube.

The debeading tool10includes a clamp22positioned along the torque tube to fix the tool in a debeading position lengthwise in the pipe. In the embodiment shown inFIGS. 1-6, the clamp is integrated into the work head10to fit inside the PVD pipe, as further described below.

The work head10of the debeading tool includes including a frame sized to fit within the pipe, coupled to a distal end of the torque tube12. In the illustrated embodiment, this frame includes a pair of parallel spaced side frame members24coupled to the torque tube and extending approximately parallel to the torque tube axis. Three transverse web members26,28,30interconnect the side members. Web members28,30support a rotary cutter motor32and web member26supports a locating gauge34for contacting the interior weld flash or bead36in the butt-welded pipe when the tool is pushed longitudinally into the pipe, as described below.

The frame members24are coupled to a transverse track structure mounted on a distal end of the torque tube. This track structure can be formed by a rectangular metal bar37affixed perpendicularly to the end of a coupler received in the end of the torque tube. The metal bar has parallel ridges38on opposite sides which are slidable in grooves40in the interior sidewalls of the side frame members. The side frame members also have eight bearing rollers42, four each mounted on each side of the metal bar37. The ridges38, mating grooves40and rollers42rigidly support the frame structure in parallel relationship to the torque tube while allowing translational movement as indicated by arrows44.

A pneumatic actuator46having a cylinder coupled to one end of the track structure by a mounting arm48(not shown inFIG. 2) and a ram coupled to a transverse pivot50between the side frame members. The actuator could alternatively be hydraulic or an electric solenoid. This actuator moves the frame structure transversely toward and away from the axis of the torque tube, thereby moving the rotary cutting motor32between the insertion/removal position shown inFIG. 5and a cutting position shown inFIG. 6. The rotary cutter motor32in this embodiment is mounted on the frame at an angle to the torque tube such that the motor's output shaft and chuck33are oriented in the cutting position at a predetermined angle, such as 12 degrees, relative to the torque tube axis.

A rotary multifluted cutter50is mounted in the motor's chuck33on the output shaft and the motor is mounted longitudinally relative to the frame side members so that the cutter50is positioned in longitudinal alignment with the locating gauge34. The cutter50has a central shaft52and a plurality of carbide cutting flutes52oriented at an angle54to the motor output shaft, e.g., 12 degrees, as shown inFIG. 7, such that the cutting flutes are substantially parallel to an interior wall56of the pipe14when the tool is in the cutting position for cutting the weld bead36. When the locating gauge contacts the weld bead, the cutting flutes52span the weld bead; that is, the length of the flutes is approximately bisected by the weld bead. The cutting flutes52are curved outwardly then inwardly from end-to-end about an arc of a predetermined radius, e.g., of about 3.5 inches (8.9 cm). A bearing roller58is mounted on the distal end of the cutter50, in axial alignment with the central shaft52. The bearing roller serves as a depth gauge which contacts the pipe side wall56to maintain the cutting flutes at an elevation that cuts the weld bead without cutting too deeply into the pipe sidewall.

The rotary motor32in this embodiment is a pneumatic rotary motor, preferably capable of high speed operation, e.g., 20,000 rpm, but a hydraulic or electric motor could be used instead. The control panel20positioned adjacent the handle structure16contains valves and handles for the operator manually independently to operate clamp22to fix the work head10longitudinally in the pipe once the locating gauge34contacts the weld bead36, to operate the actuator46for moving the frame, cutter motor and cutter from the insertion/removal position to the cutting position and back, and to turn the cutter motor32on and off. If hydraulic or electric actuators and/or motors are used instead of pneumatic, those skilled in the art can readily substitute the appropriate types of controls in panel20.

The clamp22in the illustrated embodiment is mounted between the distal end of the torque tube and the work head, but need not be. For example, the clamp can be positioned around the operator end of the torque tube and can be an annular fitting adjacent the control box that can move with the torque tube during insertion into the PVC pipe and, when the work head contacts the internal bead at the butt-welded joint in two pipes, can be coupled to the operator end of the pipe to fix the torque tube axially in position. In the illustrated embodiment ofFIGS. 1-6, the clamp22is journaled on a cylindrical sleeve58to rotate freely over a central shaft extending axially between the distal end of the torque tube and the work head. The clamp structure includes three radial vanes60,62,64arranged substantially parallel and equi-angularly around the axis of the torque tube on two longitudinally-spaced disks mounted around sleeve58. Two of the vanes62,64can be fixed to the disks. The third vane64is movable radially in slots in the disks. Two longitudinally-spaced actuators66each have a cylinder mounted on the sleeve58and a ram coupled to an inner edge of the vane64to push the vane outward to compress radially against the interior side wall of the pipe when actuated.

The control panel20includes a coupling70in the proximal end of the handle structure through which pressurized air is supplied to a manifold inside the handle structure having three output conduits72,74,76. Conduit72connects to a valve82and conduits74,76to valves84,86, respectively, which can be actuated from the upper side of the control panel. These valves are coupled to hoses83,85,87that extend along the length of the torque tube, respectively, to the motor32, the motor positioning actuator46, and clamp actuators66. The line to the motor positioning actuator46includes a relief line90and flow control valve92to dampen the actuation of movement of the motor toward the cutting position, to avoid damage to the cutter. Sufficient length for the hoses is provided at the control panel and also at the work head to permit the handle structure, control panel, torque tube and work head to rotate through a full circle relative to the clamp22without stressing or crimping the hoses.

The locating gauge34in this embodiment comprises a pair of bearing rollers94mounted in transversely-spaced position on a cross-member96supported on web member26by a pair of laterally spaced studs98. The studs connect to cross member96through oblong holes97so that the cross member has some lateral play to accommodate variations in alignment between the axis of the debeading tool and that of the pipe. The bearing rollers94are spaced to fit loosely within the pipe, for example, providing about one-quarter inch of play. This structure is arranged to position the forward end of the bearing rollers axially in alignment with approximately the lengthwise center of the cutter. When the bearing rollers are in contact with the weld bead36, the cutter straddles the weld bead.

Referring toFIG. 8, another embodiment of the debeading tool has a frame that is fixed relative to the axis of the torque tube, rather than on a transversely movable track. The rotary cutting motor32is pivotably mounted on the side members by pivot pin99and the actuator46is connected to the rearward end of the motor for movement of the cutter50between a retracted position and the cutting position at the predetermined angle relative to the torque tube axis. As mentioned above, the cutter50includes a rotatable gauge58at its distal end having a diameter sized relative to the cutter such that the gauge supports the cutter on a side wall of the pipe at the predetermined angle54, e.g., 12 degrees. In this embodiment, the gauge58again supports the cutter at that angle against the pressure toward the pipe exerted on the motor by actuator46.

Referring toFIG. 9, a pipe cleaner100sized to fit the diameter of pipe is inserted into one section of pipe before a next section is butt-welded to it. The pipe cleaner is made of circular disks of a flexible material, such as neoprene, rubber, flexible PVC and the like, mounted coaxially on a shaft. In one embodiment, shown inFIG. 9, the pipe cleaner is formed as three spaced rubber disks102,104,106mounted on a shaft. The middle disk104is neoprene foam and the two end disks are 60-70 durometer neoprene. The disks are held in spaced position between pairs of large metal or rigid plastic washers108, mounted on the shaft concentrically with the disks, leaving only a peripheral ¾ inch or so of the rubber or neoprene exposed. Other arrangements can be used to effectively drag and wipe chips and chaff from cutting the PVC pipe bead from inside the pipe. An engagement structure110is provided at one end of the disk and shaft assembly, in position to be engaged by a hook or harpoon112on the end of the locator assembly, for pulling the pipe cleaner through the pipe as the debeading tool is withdrawn after cutting away the internal bead. The engagement structure is shown as a wire mesh with a spacing of the wires close enough for the harpoon to fit into the openings in the mesh and then engage the adjacent wires when retracted. Alternatively, the engagement structure can be formed by looped structure at the end of the shaft that is simply a series of loops of small gauge twisted wire cable arranged in a donut-shaped nest or cup around the center shaft so the harpoon112on the bead locator assembly grabs a few strands of the twisted wire cable to pull the pipe cleaner through the pipe as the debeading tool is being retracted.

In operation, the pipe cleaner100is inserted into an end of a first pipe segment before butt-welding a second pipe segment to it. Then the two pipe segments are butt-welded together. Then, the debeading tool work head10and torque tube12are inserted into the distal or upstream end of the second pipe segment until the locating gauge34contacts the weld bead36. At this time, the handle structure16is close to the end of the second pipe. The operator then actuates the actuators66to operate the clamp assembly and thereby fix the work head in place in the pipe with the locator assembly34and cutter50aligned longitudinally with the weld bead36. Then the actuator48is operated to move the cutter50against the weld bead36. The bearing roller58contacts the interior wall of the pipe to maintain the predetermined angle, (e.g., 12 degrees). Then, the motor32is turned on to rotate the cutter50while actuator48maintains pressure of the cutter against the weld bead. The operator then rotates handle structure16to rotate the work head around the inside of the pipe as the cutter cuts the weld bead. When finished, the motor is turned off, the cutter is moved away from the side wall and the clamp22is unclamped; then the debeading tool is pushed further into the pipe so that the harpoon112is protruding into the mesh or nest of wires110in the pipe cleaner100. Then, the tools are retracted from the pipe. The engagement structure110is engaged by a hook or harpoon112and pulls the pipe cleaner100through the pipe, cleaning the pipe. This procedure is then repeated for each successive segment of pipe.

Having described and illustrated the principles of the invention in various embodiments thereof, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications and variations coming within the spirit and scope of the following claims.