Abstract:
A method and apparatus for continuously producing preselected lengths of coiled tubing are disclosed. According to the method, plastic tubing is continuously wound onto a rotating main tube shaft ( 24 ). Downstream from the point where the tubing begins to wind about the shaft, a heat source ( 46 ) is directed toward the coiled tubing, softening it as it traverses thereby. Further downstream, a cool-air source ( 48 ) directed at the softened tubing sets the tubing into its coiled form. Subsequently, the coiled tubing is cut into preselected lengths by a cutter ( 50 ) downstream from the cool-air source.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/US2004/032322, filed Oct. 1, 2004, which includes a claim for Convention priority based on U.S. patent application Ser. No. 60/508,024, filed Oct. 1, 2003. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to plastic tubing and, more particularly, to a method for forming plastic tubing into coils and to a coiling system for practicing the method. 
     2. Description of the Prior Art 
     In the prior art, plastic tubing, such as tubing made from polyvinyl chloride (PVC), has been placed into coiled form by wrapping or coiling the tubing onto a mandrel, which may either be made of ultra-high molecular weight (UHMW) polyethylene, or have a sleeve or covering of that material, and by placing the mandrel into an oven for a suitable length of time to heat-form the tubing into a coil. Not only is this prior-art method inefficient, but it is also very labor-intensive and prohibitively expensive. 
     As a consequence, there has long been sought a more economical and straightforward method for producing a coil from a length of plastic tubing. Such a method is made possible with the use of the coiling system of the present invention. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is a coiling system for continuously forming coiled plastic tubing in desired lengths. The present invention also encompasses a method for forming lengths of coiled plastic tubing. The method may be practiced using the coiling system described below. 
     The coiling system comprises a main tube shaft which is rotated at a desired rate by a main drive shaft driven by a variable-speed motor. The plastic tubing is supplied either directly from an extruder or from a reel of previously extruded tubing, and is fed toward the main tube shaft through a gap in a tube guide. The gap is an opening cut at an oblique angle through the tube guide to direct the plastic tubing at an angle suitable for winding it continuously onto the main tube shaft in the form of a helix. 
     The coiled tubing traverses along the main tube shaft as it is wound thereabout. At one point downstream from the tube guide, a heat source is directed toward the coiled tubing, softening it as it traverses thereby. Further downstream from the heat source is a cool-air source, which is directed toward the coiled tubing and sets it into its coiled form. Subsequently, the coiled tubing is cut into desired lengths by a cutter downstream from the cool-air source. 
     The present invention will now be described in more complete detail with frequent reference being made to the figures identified below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view of a first embodiment of the coiling system of the present invention; 
         FIGS. 2A ,  2 B and  2 C illustrate the construction of the main tube shaft used on the first embodiment of the coiling system; 
         FIGS. 3A and 3B  are plan and edge views, respectively, of the tube guide used on the first embodiment of the coiling system; 
         FIGS. 4A and 4B  are top and side plan views, respectively, of a second embodiment of the coiling system of the present invention; 
         FIG. 5  is a plan view of the cutter and carousel components of the coiling system of  FIGS. 4A and 4B ; 
         FIG. 6  is a cross-sectional view taken as indicated in  FIG. 5 ; 
         FIG. 7A  is also a cross-sectional view taken as indicated in  FIG. 5 ; and 
         FIG. 7B  is a cross-sectional view taken in the same manner as  FIG. 7A  when the cutter is activated. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to  FIG. 1 , a schematic plan view of the coiling system  10  of the present invention, the coiling system  10  comprises a motor  12  and a speed controller  14  therefor. Motor  12  may be set, using speed controller  14 , to rotate at speeds in a range from 1 RPM (rotation per minute) to 1000 RPM. 
     Motor  12  is connected to a main drive shaft  16  by means of coupling  18 . Main drive shaft  16  is turned by motor  12  within bearings  20 , and passes through a support block  22 . A main tube shaft  24  is threadingly connected to main drive shaft  16  beyond support block  22  from motor  12  and bearings  20 , and is the component of coiling system  10  on which the tubing is actually coiled. 
     A more detailed view of main tube shaft  24  is provided in  FIGS. 2A through 2C . Main tube shaft  24  may be seen to have four sections, as identified in  FIG. 2C , and has a male threaded member  26  by which it is connected to main drive shaft  16  in  FIG. 1 . In a first section  28 , main tube shaft  24  has a first diameter which includes a first sleeve  30  of UHMW polyethylene, shown sectioned in  FIG. 2C , the purpose of which will be described below. First sleeve  30  may be readily removed by sliding from main tube shaft  24  and replaced when necessary. 
     In a second section  32 , main tube shaft  24 , which, for example, is made of aluminum or steel, tapers from the first diameter to a smaller second diameter. In a third section  34 , main tube shaft  24  is of the second diameter which includes a second sleeve  36  of UHMW polyethylene, also shown sectional in  FIG. 2C . The purpose of the second sleeve  36  will also be described below. 
     Finally, in a fourth section  38 , which is threadingly connected to the rest of main tube shaft  24  at the end of the third section  34  by male threaded member  56  and female threaded hole  58 , shown in phantom in  FIG. 2B , to enable second sleeve  36  to be removed and replaced, main tube shaft  24  is of the second diameter. As in the second section  32 , the main tube shaft  24  has a metal surface in the fourth section  38 . 
     Turning now, back to  FIG. 1 , main tube shaft  24  passes through tube guide  40  beyond motor  12  and bearings  20 . Tube guide  40  is shown in  FIGS. 3A and 3B , the former being a plan view and the latter being a view looking down on the top edge in  FIG. 3A . 
     In  FIG. 3A , tube guide  40  has a circular hole  42 . Extending more or less radially upward from hole  42  is a gap  44 . In  FIG. 3B , gap  44  may be seen to provide an opening at an oblique angle θ relative to the plane of the tube guide  40 . The gap  44  may, for example, make an angle of 158° with the plane of tube guide  40 , an angle found empirically to provide the best results for forming coils of tubing having an outside diameter of 0.125 inch and a wall thickness of 30 mil, typical dimensions of the tubing that may be coiled with the present invention. 
     Turning, again, back to  FIG. 1 , gap  44  in tube guide  40  is directly above main tube shaft  24 , which passes through hole  42  in tube guide  40 . Typically, hole  42  has a diameter that is 0.25 inch larger than first diameter of first section  28  of main tube shaft  24 , providing a clearance of 0.125 inch between the tube guide  40  and the main tube shaft  24  at the hole  42 . 
     Coiling system  10  may be used either downstream from an extruder used to produce plastic tubing or off-line. In the latter situation, the plastic tubing has been previously extruded and wound onto a spool or reel, from which it may be fed to the coiling system  10 . In either case, various pulleys and tensioners would be used to feed the tubing to the coiling system  10 , as would be readily clear to those of ordinary skill in the art. 
     Referring again to  FIG. 1 , in either case plastic tubing, not shown in the figure, is fed between support block  22  and tube guide  40  and through gap  44 . The tubing may additionally be passed through a hole in optional guide block  60  before entering the space between support block  22  and the tube guide  40 . Motor  12  rotates main drive shaft  16  and main tube shaft  24  in the direction indicated by the arrows therearound, pulling the tubing through the gap  44  at the oblique angle the gap  44  makes with the plane of the tube guide  40 , so that it is continually wound onto the main tube shaft  24  in the form of a helix. In this regard, first sleeve  30  of UHMW polyethylene assists in the winding of the tubing by virtue of the frictional forces acting therebetween. These frictional forces are greater than those that would act between the tubing and the bare metallic surface of the second portion  32  of the main tube shaft  24 . 
     A heat source  46 , which may be a precise heat gun, such as a Steinel 3002 LCD electronic hot air gun, or an oven, heats the coiled tubing to a temperature typically in a range from 400° F. to 700° F., the exact temperature used depending on the composition of the tubing being coiled. As the main tube shaft  24  rotates, the coiled plastic tubing traverses therealong past the heat source  46  and beyond. 
     Downstream from the heat source  46 , that is, to its left in  FIG. 1 , is a cool-air source  48 , such as one having a vortex cooling tube. The cool-air source  48  sets the previously heated tubing into coiled form. It will be recalled that second portion  32  of main tube shaft  24  tapers gradually from a first diameter to a second diameter which is slightly smaller. This ensures that the coiled tube will be readily removable from the main tube shaft  24  downstream from the cool-air source  48  as the coil will have a slightly larger diameter than the shaft  24  at that point. 
     Further downstream along main tube shaft  24 , additional sources of compressed air may be directed at the coiled tubing to further cool and set it in its coiled form. 
     It will be further recalled that third section  34  of main tube shaft  24  has a second sleeve  36  of UHMW polyethylene. Adjacent to the second sleeve  36  is a cutter  50  having a blade  52 . The cutter  50 , when signaled by cutter controller  62 , cuts the coiled tubing at intervals to produce desired lengths thereof. Blade  52  cuts the coiled tubing against second sleeve  36 , which is much softer than a metal surface and prevents the blade  52  from wearing out too quickly. 
     Finally, downstream beyond the cutter  50  is an air ejector  54 , or similar device, to remove the cut lengths of coiled tubing from the main tube shaft  24  when signaled to do so by air ejector controller  64 . 
     In general, the main tube shaft  24  may have an outer diameter in a range from 0.1 inch to 20.0 inches and larger, although outer diameters in a range from 0.5 inch to 1.0 inch are more commonly used. 
     The plastic tubing itself may be extruded from any of the materials commonly used by those of ordinary skill in the art for that purpose. For example, the plastic tubing may be of polymers and copolymers of vinyls, olefins urethanes, such as polyvinyl chloride (PVC), polyethylene (PE), polyurethane (PU), TPE, COPE, ethylene-vinyl acetate (EVA), or may be of multi-layer coextrusions. The tubing may have an inner diameter in a range from 0.005 inch to 1.0 inch and a wall thickness in a range from 0.003 inch to 0.2 inch or more. 
     The plastic tubing may be coated with a heat-activated adhesive or sprayed with a solvent prior to coiling, so that the coiled tubing produced on the coiling system  10  may have individual coiled turns which are adhered to those adjacent to it. 
     The main tube shaft  24  and tube guide  40  together give the tubing the proper orientation to achieve a continuously coiling system. In this regard, gap  44 , shown in  FIG. 3B , is oriented at an oblique angle which may vary depending upon the diameter of the shaft and the outer diameter of the plastic tubing being coiled. As stated above, the oblique angle may be 158° in some situations. In any event, the gap  44  is at least 0.015 inch (15 mil) wider than the outer diameter of the plastic tubing being coiled to allow the tubing to pass freely therethrough. 
       FIGS. 4A and 4B  are top and side plan views, respectively, of a second embodiment of the coiling system  70 . As above, coiling system  70  has a motor  72 , which may be a stepper motor. Motor  72  may be set to rotate at speeds in a range from 1 RPM (rotation per minute) to 1000 RPM. 
     Motor  72  is connected to a main drive shaft  74 , which rotates within bearings  76  and passes through a support block  78 . A main tube shaft  80  is connected, such as by a threaded connection, to main drive shaft  74  beyond the support block  78  from motor  72  and bearings  74 , and, again, is the component of the coiling system  70  on which the tubing is actually coiled. 
     Like main tube shaft  24  described above, main tube shaft  80  has a sleeve of UHMW polyethylene, not shown in  FIGS. 4A and 4B , adjacent to main drive shaft  74  and extending a distance therefrom to facilitate the winding of tubing thereabout. Thereafter, the main tube shaft  80  tapers gradually along its length from a first diameter to a smaller second diameter to permit tubing coiled about it to be removed easily at the downstream end. Except for the UHMW polyethylene, main tube shaft  80  is made of aluminum or steel. 
     As before, main tube shaft  80  passes through a tube guide  82  beyond main drive shaft  74 , bearings  76  and support block  78 . Tube guide  82  is the same as tube guide  40  previously described, and has a gap  84  through which tubing is fed to be wound around main tube shaft  80 . 
     Coiling system  70  also includes a tube tension controller  86  having individual pulleys and tensioners, not shown, but well known to those of ordinary skill in the art, to facilitate the feeding of the tubing to the coiling system  70 . 
     In any event, plastic tubing, not shown in  FIGS. 4A and 4B , is fed between support block  78  and tube guide  82  and through gap  84 . Motor  72  rotates main drive shaft  74  and main tube shaft  80  in the direction indicated by the arrows therearound, pulling the tubing through the gap  84  so that the tubing is continually wound onto the main tube shaft  80  in the form of a helix. 
     A heat source  88 , namely, a heat gun, heats the coiled tubing to a temperature typically in a range from 400° F. to 700° F., the exact temperature used depending on the composition of the tubing being coiled. As the main tube shaft  80  rotates, the coiled plastic tubing traverses therealong past the heat source  88  and beyond. 
     Downstream from the heat source  88 , that is, to its left in  FIG. 4A , is a cool-air source  90 , such as a vortex cool-air gun. The cool-air source  90  sets the previously heated tubing into coiled form. It will be recalled that main tube shaft  80  tapers gradually from a first diameter to a second slightly smaller diameter. This ensures that the coiled tube will be readily removable from the main tube shaft  80  downstream from the cool-air source  90  as the coil will have a slightly larger diameter than the shaft  80  at that point. 
     Further downstream along main tube shaft  80 , additional sources of compressed air may be directed at the coiled tubing to farther cool and set it into its coiled form. 
     Eventually, the coiled tubing takes up the entire length of main tube shaft  80 , reaching the cutter  92  and carousel  94 , which work together to provide coiled tubing of desired lengths. Turning first to the carousel  94 , it comprises a stepper motor  96 , which operates to rotate the carousel  94  by quarter turns (90°) at desired intervals. Carousel  94  also includes a plate  98  of generally circular shape. Evenly spaced about the circumference thereof are four shafts  100  having a diameter substantially equal to the second diameter of the main tube shaft  80 . As the carousel  94  is rotated in quarter turns, each of the shafts  100  aligns, in turn, with the main tube shaft  80  for a desired interval of time. While so aligned, a length of coiled tubing proceeds from main tube shaft  80  onto individual shafts  100 . At the end of the desired time interval, in which a desired length of coiled tubing is disposed on a shaft  100 , the carousel rotates by a quarter turn in the direction indicated by the arrows in  FIGS. 4A and 4B  to bring the next shaft  100  into position. During this rotation of one quarter turn, the tubing is cut in a manner to be described below by cutter  92  to leave the desired length on shaft  100 . 
     As the carousel  94  turns in steps by 90°, the lengths of coiled tubing may be removed from shafts  100 , preferably after having rotated about the carousel  94  by three quarters of a turn, by any means available and known to those of ordinary skill in the art, such as by compressed air, so that the shaft  100  is able to accommodate a new length of coiled tubing as it moves into position in line with main tube shaft  80  when the carousel makes an additional quarter turn. 
       FIG. 5  is a somewhat enlarged plan view of the cutter  92  and carousel  94 , and  FIG. 6  is a view of the plate  98  taken as indicated in  FIG. 5 . Stepper motor  96 , as discussed above, rotates the carousel  94  in quarter-turn increments. Adjacent to each hole  102  for mounting a shaft  100  is a notch  104 . Mounted on the carousel  94  is an electric solenoid  106  having a wheel  108  which partially engages notch  104 . When stepper motor  96  begins a quarter rotation, wheel  108  is forced out of notch  104 , engaging for a time with the circumferential edge  110  of the plate  98 . This outward motion of the wheel  108  activates the solenoid  106 , causing the cutter  92  to operate during the interval when the carousel  94  is making the quarter turn. 
       FIG. 7A  is a view of the cutter  92  taken as indicated in  FIG. 5 , and  FIG. 7B  is an analogous view taken when the cutter  92  has just completed a cutting stroke. The cutter  92  includes an air piston  112 , which is activated when signaled by solenoid  106  to cut the coiled tubing. 
     Referring first to  FIG. 7A , main tube shaft  80  extends through cutter  92  and is disposed in the center thereof. Coiled tubing  114  is wrapped around the main tube shaft  80 . The cutter  92  itself is mounted on a stationary plate  116  through which the main tube shaft  80  also extends. The cutter  92  itself comprises a stationary inner element  118  having a cutting edge  122 , and a rotatable outer element  120  having a cutting edge  124  which rotates the stationary inner element  118  by about 45° when the air piston  112  is activated, as shown in  FIG. 7B . The cross-hatched portions of the inner element  118  and the outer element  120  are recessed relative to the other portions as viewed in  FIGS. 7A and 7B . Accordingly, when the carousel  94  begins to make a quarter turn, a length of tubing extends from main tube shaft  80  to a shaft  100  through the area represented by the cross-hatched portions. Then, when the air piston is activated, the tubing is cut in a scissor-like manner when the cutting edge  124  of the outer element meets the cutting edge  122  of the inner element at point  126 . 
     Modifications to the above would be obvious to those of ordinary skill in the art without bringing the invention so modified beyond the scope of the appended claims.