Abstract:
A tube remover for extracting a tube from an opening in which the tube is mounted in a wall. The remover includes a nipper roll and an anvil roll, each of which is provided with a plurality of teeth formed in a radially outward facing surface of each respective roll. The teeth, which can be oriented helically in the respective surfaces, mesh and draw the tube into a nip between the two rolls. At least one of the rolls is provided with an anvil block formed in its radially outwardly facing surface. Such an anvil block cooperates with the teeth of the opposite roll to effect distressing of the tube and severing of a segment of the tube from the rest of the tube.

Description:
This application claims the benefit of Provisional Application No. 60/022,106 filed Jul. 17, 1996 
    
    
     TECHNICAL FIELD 
     The present invention relates to devices for removing metal tubes from heat exchangers and surface condensers. More specifically, the invention relates to a device capable of both pulling a tube out of a heat exchanger, flattening the tube, and chopping the tube into smaller lengths for disposal. 
     BACKGROUND OF THE INVENTION 
     Many heat exchangers utilize tubes for carrying a heat transfer fluid. A large number of tubes are commonly mounted in parallel between two tube sheets. The tube ends are tightly mounted in openings in the tube sheets, forming a tight seal. The tight fit is often effected using a press fit. A high temperature fluid such as combustion gas or hot water is passed between the tube sheets and around the outside of the tubes. A lower temperature heat transfer fluid such as water is passed through the interior of the tubes. Heat is transferred from the higher temperature tube exterior to the lower temperature tube interior. 
     Tubes often have to be removed from the heat exchanger. Tubes often become corroded, lined with scale or even plugged. Tubes also develop leaks, requiring tube removal. Heat exchanger downtime is often unexpected, and speed is critical in removing one or more tubes, replacing them with others, and returning the heat exchanger to service. 
     Heat exchanger preventative maintenance is often planned, with several or all tubes in an array being removed and replaced before leaks and severe scaling are likely to occur. In large power generation systems there may be thousands of tubes to replace during the same downtime interval, significantly reducing the power generating capacity while the preventative maintenance is being performed. The downtime in such situations is expensive, the expense depending on how quickly the tubes can be replaced. 
     Removing tubes from a heat exchanger is accomplished by first relieving the interference fit between the tube and tube sheet. The tubes are axially pulled out a few centimeters to expose a grippable tube end projecting from the tube sheet. Such pulling is accomplished with an internal gripping device called a tube puller. Suitable tube pullers are disclosed in commonly owned U.S. Pat. No. 3,835,520 or U.S. Pat. No. 3,628,246. 
     After the tube has been loosened and has an end projecting from the tube sheet, a pulling device is used to pull the tube totally out of the tube sheet. A typical pulling device comprises a pair of rotating serrated traveller rolls having parallel axes and rotating in opposite directions. The projecting tube end is introduced into the nip between the rollers. The puller rapidly removes the tube from the tube sheet. Prior art devices for removing long tubes from tube sheets axially at high rates of speed are disclosed in U.S. Pat. Nos. 3,149,021 (Curfman), U.S. Pat. No. 3,785,026 (Ohmstede), U.S. Pat. No. 4,044,444 (Harris) and U.S. Pat. No. 4,815,201 (Harris), the later two invented by the applicant. 
     The tube can be 10 to 20 meters long in large power installations. This rapidly moving tube typically requires two people to handle the tube as it is being pulled out of the tube sheet. After removal, the tube is feed to a chopper, to cut the tube into pieces to be hauled away as scrap. The use of typical tube pullers thus requires people to handle the withdrawn tube, a separate chopper, and people to feed the withdrawn tube to the chopper. Each additional step requires additional time as well as additional workers. 
     What remains to be provided is a tube puller which eliminates the need for a separate chopper. A tube puller which does not require additional workers to handle the long tubes being extracted would be desirable. It would also be advantageous to eliminate the safety considerations of maneuvering long tubes into nippers in power houses. 
     SUMMARY OF THE INVENTION 
     The present invention is a tube remover for extracting a tube from an opening in a wall in which the tube is mounted. The remover includes a nipper roll and an anvil roll. Each roll has, formed on a radially outward facing surface thereof, a plurality of teeth. Further, each roll is disposed for rotation about an axis. The axes of rotation are spaced from one another so that the rolls, together, define a nip within which the tube to be removed can be fed. The rolls are rotated in opposite directions and draw the tube into the nip and between the rolls. A cutting surface is provided on one of the rolls, and, as the cutting surface and teeth on the opposing roll cooperate to distress the pinched tube as it passes between the rolls, the tube is cut at a desired length. 
     In a preferred embodiment, the teeth formed on both the nipper roll and the anvil roll are helically oriented. The angle of helical disposition is such that, when the rolls rotate with respect to one another, the teeth mesh. 
     In the preferred embodiment also, teeth provided on the outwardly facing surface of the anvil roll are inclined at a designated angle. This enables more secure retention of the tube and more efficient drawing of the tube between the rolls. 
     Further, the preferred embodiment employs a nipper roll and an anvil roll which have different diameters. In consequence, the teeth on the nipper roll, as the nipper roll is rotated, engage different teeth on the anvil roll on subsequent rotations. 
    
    
     The present invention is thus an improved tube remover apparatus which addresses problems and dictates of the prior art. More specific features and advantages obtained in view of those features will become apparent with reference to the DETAILED DESCRIPTION OF THE INVENTION, appended claims and accompanying drawing figures. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a tube remover; 
     FIG. 2 is a fragmentary perspective view of a tube end prior to removal; 
     FIG. 3 is a perspective view of a tube remover pulling and flattening a tube; 
     FIG. 4 is a perspective view of a tubing piece flattened and cut by a tube remover; 
     FIG. 5 is an elevation view of a tube remover pulling and cutting a tube; 
     FIG. 6 is an enlarged elevation view of the tube remover depicted in FIG. 3 taken along line  6 — 6 , pulling, flattening and cutting a tube; 
     FIG. 7 is a more enlarged elevation view of the tube remover detail area of FIG. 6; 
     FIG. 8 is an elevation view of the tube remover depicted in FIG. 5, showing a cut tubing piece separating from the main tubing piece; and 
     FIG. 9 is an enlarged elevation view of the tube remover depicted in FIG. 8, showing the teeth engaging, flattening and crimping a tube. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an embodiment of a tube remover  20  having a nipper roll  22  and an anvil roll  24 . Nipper roll  22  has nipper teeth  26  having a tooth ridge  28 , with nipper teeth  26  having a helical orientation on nipper roll  22 . Anvil roll  24  has teeth  34  having a helical orientation, a tooth ridge  46 , and anvil block inserts  30  each having a cutting surface  32 . In a preferred embodiment, both rolls  22  and  24  are mounted on driven shafts (not shown) using keys  58 . As illustrated, rolls  22  and  24  have chamfer  56  on the outside edge of the inner radial opening. In a preferred embodiment, both rolls  22  and  24  are driven by hydraulic motors hydraulically connected either in series or in parallel using a flow divider. 
     FIG. 2 illustrates a typical tube  46  before engagement with the tube remover. The Tube  46  illustrated has a partially flattened profile. The present invention works equally well with tubes having circular profiles (not shown). 
     FIG. 3 illustrates the tube remover embodiment depicted in FIG. 1 pulling, flattening and cutting tube  36 . Nipper roll  22  and anvil roll  24  rotate in opposite directions, nipper roll  22  shown rotating counter-clockwise and anvil roll  24  clockwise, acting to pull tube  38  into nip  42 . Tube  36  includes an un-flattened portion  38  and flattened portion  40 . Flattened portion  40  is shown having crimp marks  44  made by nipper teeth  26  and anvil roll teeth  34 . 
     FIG. 4 illustrates tube detached flattened portion  48  after cutting, having crimp marks  44 . Flattened portion  48  results from tube flattened portion  40  being cut between cutting surface  32  and nipper teeth  26 . 
     FIG. 5 illustrates tube remover  20  removing tube  36 . A preferred embodiment is shown, having two anvil blocks  30  on anvil roll  24 . Embodiments having one or more anvil blocks are within the scope of the invention. A preferred embodiment utilizes anvil block inserts  30  each having a cutting surface  32  to support the flattened tube during nipping. Rolls having integral cutting are also within the scope of the invention. The cutting surface embodiment shown in FIG. 5 has a surface geometry approximating that of a cylinder having the radius of the anvil roll. Another embodiment has a flat cutting surface. A preferred embodiment anvil insert  30  is formed of hardened tool steel for long life. Another preferred anvil insert is made of carbide steel. A most preferred embodiment cutting surface  32  has a width equal to about 1 and ¼ times the distance between nipper teeth  26  to insure a tube cut upon cutting surface  32  by at least one tooth. 
     FIG. 6 illustrates the embodiment of FIG. 5, showing tube cutting in detail. The embodiment shown has nipper teeth  26  being normal to the circumference of nipper roll  22  and anvil roll teeth  34  having an incline angle θ relative to normal. Specifically, a line drawn from an anvil roll tooth base midpoint  50  through tooth apex  52  forms an angle θ with respect to a line drawn through both the same tooth base midpoint  50  and the anvil roll axis of rotation. Teeth having an incline angle provide increased gripping by teeth  34  of tube  36 . As illustrated in FIG. 6, when nipper tooth  26  severs tube  36 , freeing flattened portion  40 , the nipper tooth no longer has the ability to pull the tube at the point where the tube was cut. Nipper teeth past the point of severance have the ability to pull the severed piece  40 , but not the ability to pull tube piece  38 . The presence of anvil block  30  in place of teeth  34  on the anvil roll also diminishes the ability of the anvil roll to pull tube  36 . The advantage of the incline angle is illustrated by the tooth at  54 , having increased purchase of tube  36 , giving some additional grip to compensate for the diminished anvil roll grip at cutting surface  32 . A preferred embodiment has a significant positive incline angle θ for anvil roll teeth  34 . 
     FIG. 7 illustrates in detail the cutting action of tube  36  between a nipper tooth  26  and cutting surface  32 . In a preferred embodiment, nipper tooth  26  does not touch cutting surface  32 . Rather, nipper tooth  26  distresses tube  36  by a wedging action, forcing the tube material apart and away from the cutting surface. The distress and movement of material in severed tube top  70 , severed tube bottom  72 , still attached tube top  74 , and still attached tube bottom  76  is illustrated by the respective arrows in FIG.  7 . The tube material is distressed to the point where the tube separates into flattened portion  40  and un-flattened portion  38 . Tube remover embodiments in which nipper tooth  26  touches cutting surface  32  increases wear on both tooth  26  and cutting surface  32 . 
     FIG. 8 illustrates a severed piece  56  falling away from tube remover  20 . In use, the rotation of rolls  22  and  24  impart an axial velocity to tube  36  and severed portion  56  such that the piece is ejected down and away from the tube remover. In preferred use, the severed piece falls directly into a scrap bin. FIG. 8 shows severed piece  56 , having been cut on anvil block  30 , given forward momentum, resulting in the trajectory shown. 
     FIG. 9 further illustrates the flattening and crimping action in an area away from cutting surface  32 . Tube  36  is shown being pulled axially between anvil roll teeth  34  and nipper roll teeth  26 . 
     Referring to FIG. 1, the helical orientation of both cutting surface  32  and teeth  26  and  34  is illustrated. The helical angle φ is denoted in FIG.  1 . In a preferred embodiment, teeth  26  and  34  are oriented helically across the roll surface as in a helical gear, rather than straight across as in a spur gear. In a preferred embodiment, cutting surface  32  is also oriented helically. The helical tooth arrangement provides increased pulling ability while the tube is being cut, relative to a spur arrangement. If cutting surface  32  and teeth  26  were both oriented straight across, the entire tube would be line cut at the same instant in time. Prior to this instant, tube  36  would be pulled mainly by teeth  34  past cutting surface  32  and some by teeth at  64 , before cutting surface  32 . After this cutting instant, as shown in FIG. 6, only the relatively weak grip of the teeth before cutting surface  32  would remain. 
     As illustrated in FIG. 1, when the cutting surface at  60  is under the tube portion being cut, teeth at  62  are gripping a soon to be cut, but still attached, portion of the tube. When the cutting surface at  66  is under the tube portion being cut, teeth at  64  are gripping a newly formed end of the tube. In this way, grip is increased and the chance of jamming or loss of grip is decreased. A less desirable embodiment, having cutting surface and teeth in straight across orientation, has decreased grip and increased chance of jamming or loss of grip. The helical orientation has the added advantage of providing a point cut of tube  36  over a time interval rather than a line cut across the tube at the same instant. This progressing cut causes less shock to the tube remover, decreasing both maintenance and the chance of jamming or loss of the pulling grip. 
     In a preferred embodiment, rolls  22  and  24  have a width of about 2 inches and a diameter of about 4 inches. Such an embodiment has 48 teeth in each roll. This embodiment has a tooth and cutting surface helical angle φ of about 30 degrees relative to the straight across spur arrangement. 
     The preferred embodiment has one roll slightly smaller than the other. In the preferred embodiment, the size difference is provided by the non-zero incline angle of the anvil roll teeth alone, resulting in a smaller diameter than, if the teeth had an orientation normal to the roll. When the rolls are driven by hydraulic motors connected either in series or through a flow divider and the rolls rotating at about the same speed, this slight size difference causes the anvil roll cutting surface to be presented to a different nipper tooth on successive rotations. This succession results in an even distribution of wear over all nipper teeth rather than the concentrated wear that would result from perfectly synchronized, matched rolls. The even wear distribution allows for decreased maintenance. 
     It will be understood that this disclosure, in many respects, is only illustrative. Changes may be made in details, particularly in matters of shape, size, material, and arrangement of parts without exceeding the scope of the invention. Accordingly, the scope of the invention is as defined in the language of the appended claims.