Abstract:
Apparatus for forming tapered spiral tubes from strips, is disclosed. The apparatus comprises a spiral tube forming system for forming a strip into a spiral tube; a strip infeed system adapted for feeding a strip to the pipe forming system; and computer-controlled means for continuously varying the angular orientation of the tube forming system relative to the strip infeed system to selectively vary the diameter of the forming tube. The selective variation of the diameter includes linearly tapered and curved profiles, as well as constant (unchanging) diameter profiles and combinations thereof.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to spiral tubes and pipes formed by spiralled, joined strips.  
           [0003]    2. Definitions and Applicability  
           [0004]    The present invention is applicable to spiral tubular products generally, including both tubes and pipes. Frequently here for brevity, we use one word or the other, but it is understood the invention is applicable to both. Also, although the exemplary system forms smooth wall tubular products, it will be readily apparent to those familiar with the technology that the invention is applicable, in addition to smooth wall tubular products, to profiled (including sinusoidal or corrugated) tubular products.  
           [0005]    3. Current State of the Relevant Field  
           [0006]    Typically, spiral tubes and pipes are formed to a constant diameter. The relevant factors (1) strip width, (2) angle of strip entry into the rolls, and (3) the position of the pressure roll relative to the other rolls, are held constant to maintain the desired diameter. Several approaches are available in the technology to prevent diameter deviations and thus maintain diameter control in such a system. For example, commonly assigned U.S. Pat. Nos. 3,650,015 and 3,940,962 describe equipment and methods for forming spiral tubular products. The &#39;015 patent describes a unique free-forming approach for forming parallel wall corrugated tubes. The &#39;962 patent discloses methods and apparatus for controlling the diameter of spiral tubing made with a three-roll mill by displacing the joined edges of the helical convolutions radially relative to the longitudinal axis of the tubing to correct for diameter deviations. The &#39;015 and &#39;962 patent are incorporated by reference.  
         SUMMARY OF THE INVENTION  
         [0007]    In one aspect, the present invention is embodied in apparatus for forming tapered spiral tubes from strips, which comprises a tube forming system which forms a strip of material such as metal into a spiral tube; and a strip infeed system which is adapted for feeding a strip to the spiral tube forming system. The tube forming system and the strip infeed system are adapted for pivotal movement relative to one another to vary the helix angle between these components and thus vary the diameter of the resulting spiral tube. The apparatus further includes a drive system for effecting the desired pivotal movement between the strip infeed system and the tube forming system; and a computer system which is operatively connected to the motor drive system for operating the motor drive system to vary the helix angle as required.  
           [0008]    In another embodiment, the strip infeed system itself is adapted for pivotal movement relative to the tube forming system to vary the helix angle. In yet another embodiment, the strip infeed system is mounted on wheels for pivotal movement relative to the tube forming system to effect the desired variation of the helix angle. In a preferred embodiment, the tube forming system is a three roll system comprising cooperating lead roll, buttress roll and mandrel sets.  
           [0009]    Other aspects and embodiments of the present invention are described in the specification, drawings and claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The above and other aspects of the invention are described below in conjunction with the following drawings.  
         [0011]    [0011]FIG. 1 is a simplified, schematic representation of one embodiment of a taper tube spiral mill apparatus or system in accordance with the present invention.  
         [0012]    [0012]FIG. 2 is a simplified top plan view of a taper tube spiral mill system in accordance with the present invention.  
         [0013]    [0013]FIG. 3 is a side elevation view of the taper tube spiral mill system of FIG. 2.  
         [0014]    [0014]FIG. 4 is an end elevation view of the taper tube spiral mill system of FIG. 2.  
         [0015]    [0015]FIG. 5 is a chart showing the variation of tube diameter as a function of the helix angle Θ as Θ is varied linearly.  
         [0016]    [0016]FIG. 6 is a chart showing the variation of tube diameter as a function of the helix angle Θ as Θ is varied sinusoidally.  
         [0017]    [0017]FIG. 7 depicts an example of a tapered spiral tube or pipe formed by the apparatus of FIGS.  1 - 4 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    [0018]FIG. 1 is a simplified, schematic representation of one embodiment  10  of a taper tube spiral mill system or apparatus in accordance with the present invention. The mill apparatus  10  comprises (1) an infeed section or system  11  for continuously unwinding a strip  16 , FIG. 3, of material such metal, typically carbon steel; (2) an exemplary three roll spiral tube-forming machine system  12 , for forming the strip into a spiral tube of controlled, preferably constant slope, varying diameter; and (3) a discharge section or system  13 . The strip infeed section  11  feeds the strip  16  (hereafter steel strip) into the three roll spiral tube-forming machine system  12 , where the strip is spirally wound into a tube such as the illustrated tube  17 , FIG. 7. The illustrated apparatus  10  uses a smooth wall pipe mill. However, the apparatus is applicable to form the various types of spiral pipes or tubes, including smooth wall welded seam, smooth wall lockseamed, corrugated lockseamed and corrugated welded seam pipes or tubes.  
         [0019]    The relationship between the width of a steel strip such as the exemplary strip  16  and the diameter, d, of the resulting tube such as  17  is given by the formula:  
       d   =     FSW     π                 sin                 θ                             
 
         [0020]    where: d= pipe diameter (see FIGS. 4 and 7),  
         [0021]    FSW= finished strip width, and  
         [0022]    Θ=the angle between the infeed section  11  and a line  14  perpendicular  
         [0023]    to the spiral pipe discharge table (the helix angle).  
         [0024]    If the helix angle Θ and the finished strip width, FSW, of the strip  16  being fed into the machine stay constant, the pipe diameter will also remain constant. However, if the helix angle Θ is varied while the finished strip width remains constant, the diameter of the tube produced will vary according to the above formula. If Θ is varied while the mill is running, that is, while strip  16  is continuously fed into the mill and formed, a tapered tube of changing diameter will result. More specifically, if the helix angle Θ of the mill is increased as the mill is running, the diameter of the tube will decrease. Conversely, if the helix angle Θ is decreased, the diameter of the tube will increase.  
         [0025]    Referring now to FIGS.  2 - 4 , in one embodiment according to the present invention, the taper tube spiral mill system  10  comprises an elongated mill base  18  on which is mounted the components of the strip infeed system  11 . Wheels  19 - 19 , FIG. 3, are mounted on the bottom side of the mill base  18  and permit the base to be rolled along the shop floor. A motor-driven screw jack  21  is connected to the mill base for moving the base bidirectionally to pivot the infeed system  11  as indicated by arrow  15 , FIGS. 1 and 2, and vary the helix angle Θ. The infeed system  11  includes a conventional uncoiler  22  which is mounted on the mill base  18 . A coil of the steel strip  16  is wrapped around the uncoiler and plays out along the infeed section  11  to the spiral tube-forming machine  12 . (Strip  16  is omitted in FIG. 2 to facilitate viewing the components of the system.) The strip exiting the uncoiler  22  is fed to a conventional coil end joiner  23 , which squares the trailing and leading ends of consecutive strips and welds the ends to form the continuous strip  16 .. From there the strip  16  is driven through the main mill drive system  24 , which comprises a plurality of stands or pairs of rolls, each having an upper roll and a lower roll. The pairs of rolls receive the strip  16  and drive it into the spiral machine system  12 . Preferably, the spiral machine system  12  comprises three sets of rolls, a lead roll set  25 , FIG. 4, a mandrel set  26 , and a buttress roll set  27 . As discussed below, preferably the lead roll set and the buttress roll set are articulated. The three roll apparatus bends the strip  16  into spiral tube  17 . In the illustrated up curve system  10 , the inner roll of the inner and outer rolls (upper and lower rolls) which comprise the mandrel roll set  26  serves as a fulcrum. As the strip  16  is driven forward by the drive roll system  24 , the opposing lead roll set and buttress roll set curl the continuously advancing strip  16  around the mandrel set  26 , upwardly in the direction of arrow  36 , in an arc which describes the selected diameter relative to the center axis  35  of the tube.  
         [0026]    The desired pipe diameter, d, and specifically, the desired varied diameter profile is effected by a computer or programmable logic controller system  29 , FIG. 2, which is connected to an electrical motor that drives the screw jack mechanism. The computer is programmed to control the winding and unwinding of the screw jack and thus bidirectionally move the infeed section  11  and alter (increase and decrease) the helix angle Θ as required as the strip  16  is fed to the spiral machine  12 . Thus, the computer-controlled drive system can continuously control (increase, decrease and/or maintain constant) the helix angle Θ.  
         [0027]    As indicated in the above formula, the diameter of the tube is inversely proportional to the sine of the helix angle Θ. Referring to FIG. 5, when the helix angle Θ is varied linearly, as indicated by curve  42 , the sides of the tube are not straight or linear; rather they have a sinusoidal curvature and the tube diameter varies sinusoidally, as indicated by curve  43 . FIG. 6 illustrates that by varying the helix angle Θ according to a sinusoidal profile, curve  44 , during the tube formation process, the tube can have straight sides and the diameter varies linearly, curve  45 . Thus, to obtain a linearly varying, or curved, or constant diameter profile, the computer  29  is programmed to drive the screw jack so that the helix angle Θ varies sinusoidally, or linearly, or is maintained constant. In addition, the computer system  29  can control the helix angle Θ to provide combinations of these profiles along a given tube, that is to provide different profiles, including positive and negative linear and curved slopes, along different sections of a tube. In short, preferably the tube walls are linearly tapered, forming concentric circles of increasing or decreasing diameter centered about and perpendicular to axis  35 , see FIG. 7. However, the illustrated apparatus can be used to form constant radius parallel wall tubular products, or irregularly tapered tubular products, or curved wall products, or combination products in which different sections have different wall profiles selected from parallel and/or linearly tapered and/or curved and/or irregularly tapered.  
         [0028]    Illustratively, at least two methods can be used to vary the mill helix angle (Θ). First, and preferably, as described above, the helix angle (Θ) of the mill can be varied using the electrically driven screw jack mechanism  21 , which is driven by a motor whose output speed is controlled by the programmable motor controller. The programmable motor controller can be programmed to vary the motor speed continuously according to any required profile. Alternatively, the helix angle (Θ) of the mill can be varied using a rack and pinion drive (or a traction wheel drive) whose driving speed is varied using by the programmable motor controller. The driving unit will be mounted to the infeed section mill base with the rack mounted to the floor.  
         [0029]    The prior art approach described previously uses apparatus which is referenced to the center line or axis of the constant diameter tube. In contrast, and referring to FIGS. 4 and 7, to facilitate manufacturing of varied diameter tubular products, the present invention preferably uses a common pass line  31 , which is defined by the upper (inner) mandrel roll, FIG. 4, and corresponds approximately to the bottom center line  32  of the tube  17 , FIG. 7. In a presently preferred arrangement, to maintain the required location and orientation as the diameter changes, the lead and buttress roll sets are articulated.  
         [0030]    Instead of the illustrated up curve machine, a down curve machine may be preferred for forming large diameter spiral tubes. In the down curve arrangement, the three forming rolls and common pass line  33  are located at the top of the machine and the advancing strip  16  curls downward from the top center line  34  of the tube, FIG. 7, in the direction opposite to that of arrow  36 .  
         [0031]    Presently, the system  10  can be used for tubular products having diameters as small as about 5 inches and to form tubular products which taper as much as approximately 0.25 inches per foot of tube length.  
         [0032]    Various types of spiral edge joining and fastening approaches and materials can be used, including lockseam, submerged arc welding and high speed welding. Lockseam joining is similar to that used for spiral corrugated rib pipe product, but with the lockseam on inside of tube to provide a smooth exterior. It may be advantageous to use a precoating on steel strip materials to protect from corrosion. Precoating materials include zinc and/or aluminum and/or polymers and/or combinations thereof. The submerged arc welding is the same as for spiral constant diameter pipes. This involves welding inside and out. Uncoated, mild steel can be used. Finally, but not exhaustively, high speed weld uses high frequency contact resistance welding developing a mash lap type of weld wherein the two strip edges are heated to a plastic state and pressed one into the other from a top and bottom position. This system could utilize both precoated zinc strips and uncoated metals.  
         [0033]    Please note, using the common pass line manufacturing approach, before separation into individual tubes, the profile of the continuously formed tube looks somewhat like a saw. One side of the tube structure is flat and the other side has tapered “saw teeth” corresponding to the different tapered tubes or tube sections included in the continuous tube structure. For the illustrated up curve machine and its bottom common pass line, the bottom of the continuous tube is flat and the top has the saw tooth appearance. Referring to FIG. 7 (which depicts one tapered section or tube), the tube axes  35  of the individual tapered tubes or tapered tube sections and the associated diameters of the tubes are oriented at complementary, non-perpendicular acute angles to the horizontal common pass line  31  ( 32 ). This orientation is taken into account during separation into the individual tubes. For example, to make each end cut of a tube perpendicular to the pipe axis  35 , one approach is to use a double cut-off process with plasma torches or with a mechanical cut-off such as friction saws or rotary cutting tools.  
         [0034]    Regardless of the method used to vary the helix angle (Θ) of the mill, the result will be a tapered tube such as  17 , FIG. 7, the final shape of which is controlled by varying the helix angle (Θ) of the mill according to a schedule derived from the above formula.  
         [0035]    The present invention has been described in terms of a preferred and other embodiments. The invention, however, is not limited to the embodiments described and depicted. One familiar with the art to which the present invention pertains will appreciate from the embodiments disclosed here, that the present invention is applicable in general to spiral tubular products, including corrugated, ribbed and smooth wall spiral tubular products. The invention is defined by the claims appended hereto.