Abstract:
A system and method of winding a length of tubing into a coil. The system uses a mandrel to wind a length of tubing into the form of a coil. The length of tubing is both internally pressurized and placed under tension prior to being wound around the mandrel. The tension experienced by the length of tubing causes the tubing to conform to the shape of the mandrel as the mandrel rotates. The internal pressurization of the tubing keeps the diameter of the tubing round as it is deformed around the mandrel. As such, the tubing is prevented from crushing or buckling as it winds around the mandrel.

Description:
REFERENCE TO DOCUMENT DISCLOSURE 
     The matter of this application corresponds to the matter contained in Disclosure Document 454,147, filed Apr. 1, 1999, wherein this application assumes the priority date of that document. 
     RELATED APPLICATIONS 
     This application is related to co-pending patent application Ser. No. 09/702,636, entitled HYDROGEN DIFFUSION CELL ASSEMBLY AND ITS METHOD OF MANUFACTURE. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to systems and methods of winding metal tubing into coils. 
     2. Description of the Prior Art 
     There are many different devices that contain coils made from hollow tubing. Such coils are commonplace in refrigerators, air conditioners, dehumidifiers and the like. When manufacturing such coils, a straight piece of metal tubing is connected at one end to a mandrel. The mandrel is then rotated, thereby cause the metal tubing to wind around the mandrel and create the desired coil. Such prior art coil production techniques work well for metal tubing that has thick walls. With such a thick walled tubing, the strength of the tubing itself prevents the tubing from crushing or buckling as it is wound around the mandrel. However, metal tube coils are made of many different materials and with many different wall thicknesses. In many applications, the strength of the tubing itself is insufficient to withstand a traditional winding procedure. 
     One application of a metal tube coil is described in co-pending patent application Ser. No. 09/702,636, entitled Hydrogen Diffusion Cell Assembly And Its Method Of Manufacture. In such an application, a coil is produced from palladium or a palladium alloy. Furthermore, the tubing is extremely thin walled, having an average wall thickness of between 0.001 inches and 0.005 inches. Such a thin walled tubing cannot be wound into a coil using prior art coil winding techniques. If such a thin walled tube were to be connected to a mandrel and wound in a traditional manner, the forces applied during the winding procedure would crush the tubing flat and/or cause the tubing to buckle. 
     A need therefore exists for a method and system that can be used to wind very thin walled tubing into coils. The need is met by the present invention as it is described and claimed below. 
     SUMMARY OF THE INVENTION 
     The present invention is a system and method of winding a length of tubing into a coil. The system uses a mandrel to wind a length of tubing into the form of a coil. However, prior to winding, the length of tubing is both internally pressurized and placed under tension prior to being wound around the mandrel. The tension experienced by the length of tubing causes the tubing to conform to the shape of the mandrel as the mandrel rotates. The internal pressurization of the tubing keeps the diameter of the tubing round as it is wound around the mandrel. As such, the tubing is prevented from crushing or bulking as it is wound around the mandrel. 
     The tension force applied to the length of tubing can be either constant or variable, depending upon the winding technique used. A constant tension force is used when the elongation of the length of tubing is left to chance. A variable tension force is used when the elongation of the length of tubing is monitored and controlled. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to the following description of an exemplary embodiment thereof, considered in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a tubing coil made utilizing the present invention system and method; and 
     FIG. 2 is a schematic illustrating the present invention system and its method of use. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the present invention system and method can be used to produce coils from most any type of metal tubing, such as copper tubing, stainless steel tubing or the like, the present invention is especially well suited for winding thin walled, special metal tubing into coils. Consequently, by way of example, the present invention will be described in an application where it is used to wind palladium tubing having a wall thickness of only between 0.001 inches and 0.005 inches. 
     Referring to FIG. 1, there is shown a coil  10  that has been fabricated using the present invention system and method. The coil  10  is made of metal tubing  12  that has been wound. In the shown embodiment, the metal tubing  12  being used is made of palladium or a palladium alloy. The tubing  12  has a diameter D 1  of between 0.1 inches and 0.5 inches. The thickness of the wall of the tubing  12  can be as thin as 0.001 inches. The tubing  12  is wound into a coil having a coil diameter D 2  and a winding pitch spacing P 1  of at least as long as the diameter D 1  of the tubing  12 . 
     Referring to FIG. 2, a winding system  20  is shown for use in fabricating the wound coil  12  shown previously in FIG.  1 . The winding system  20  contains a winding mandrel  22 . The winding mandrel has an outer diameter D 3  that corresponds to the coil diameter D 2  (FIG. 1) of the coil to be produced. The mandrel  22  has a helical groove  24  formed on its exterior surface. The helical groove  24  has a radius of curvature that corresponds to that of the tubing  12  being wound. The helical groove  24  in the mandrel  22  also has a winding pitch spacing P 2  that corresponds to the winding pitch spacing P 1  (FIG. 1) of the coil being produced. 
     The mandrel  22  is turned by a motor  26 . An optional transmission  23  may be placed between the motor  26  and the mandrel  22  if the rotational speed of the motor  26  is different from what is practical for the winding procedure. A transmission  23  can also be used if the torque produced by the motor  26  is insufficient to directly wind the tubing  12 . 
     Prior to attaching the tubing  12  to the mandrel  22 , the first end of the tubing  12  is soldered closed to create a gas tight seal at the first end of the tubing  12 . The first end of the tubing  12  is then connected to the mandrel  22  at the beginning of the helical groove  24 . When the tubing  12  is first attached to the mandrel  22 , the tubing  12  is straight. The length of the straight section of tubing  12  is made to correspond to the length of tubing needed to complete the coil  10  (FIG.  1 ). 
     The second end of the tubing  12  is connected to a wheeled cart assembly  30 . The wheeled cart assembly  30  has a front end and a rear end. At the front end of the wheeled cart  30  is a connection nipple  32 . The second end of the tubing  12  is soldered or otherwise interconnected to the connection nipple  32 . The connection nipple  32  is connected to a flexible hose  34  that leads to a gas supply manifold  36 . A gas flow restrictor  38  is positioned between the gas supply manifold  36  and the connection nipple  32  for a purpose which will later be explained. 
     The gas supply manifold  36  is connected to a supply hose  40  that connects the manifold  36  to a source of compressed gas  42 . Although many different types of gas can be used, the preferred gas is compressed nitrogen. A supply valve  44  is disposed between the manifold  36  and the supply hose  40  to selectively control the flow of compressed gas into the manifold  36  from the source of compressed gas  42 . 
     A vent port  46  is also connected to the gas supply manifold  36 . A venting valve  48  is disposed between the manifold  36  and the vent port  46  to selectively control the venting of gas from the gas supply manifold  36 . A pressure gauge  50  is also connected to the gas supply manifold  36  on the wheeled cart assembly  30 . The pressure gauge  50  measures the pressure in the gas supply manifold  36 . 
     When the second end of the tubing  12  is soldered to the connection nipple  32 , the interior of the tubing  12  becomes interconnected with the gas supply manifold  36 . Accordingly, as the source of compressed gas  42  pressurizes the gas supply manifold  36 , the interior of the tubing  12  also becomes pressurized. Consequently, the pressure gauge  50  that measures the pressure within the gas supply manifold  36  also measures the gas pressure that exists inside the tubing  12 . The flow restrictor  38  is used as a safety feature to prevent the tubing  12  from whipping around should the tubing  12  ever break or become severed while under pressure. 
     The pressure supplied to the tubing  12  depends upon the material and wall thickness of the tubing  12 . Preferably, the tubing  12  is pressurized to a pressure between one tenth and one half its designed rupture pressure. 
     The wheels  54  at the front end of the cart assembly  30  are attached to a front axle assembly  56  that is free to pivot. As a result, as the tubing  12  is wound along the length of the mandrel  22 , the wheeled cart assembly  30  can turn laterally and track along the length of the mandrel  22  with the advancing tubing  12 . Although not required, the tracking of the wheeled cart assembly  30  can be improved by providing a set of tracks  31  on which the wheeled cart assembly  30  rides. The tracks  31  guide the wheeled cart assembly  30  so that the wheeled cart assembly  30  is always at the proper position with respect to the mandrel  22  as the tubing  12  is wound. 
     The wheeled cart assembly  30  is free rolling and supplies only limited resistance to the rotating mandrel  22 . To keep the tubing  12  taut during winding, a tether  58  is attached to the rear end of the wheeled cart assembly  30 . The tether  58  supplies the wheeled cart assembly  30  with an resistance force F that opposes the rotational pull of the mandrel  22 . The resistance force F supplied through the tether  58  is created by a tension force mechanism  59 . The tension force mechanism  59  be a series of weights and pulleys, a clutched motor, a variable inclined plane or any other mechanism capable of providing a resistance to a tether under tension. The magnitude of the resistance force is dependent upon the characteristics of the tubing  12  being wound. 
     To operate the present invention system  20 , a segment of straight tubing  12  is supplied. The first end of the tubing  12  is sealed and is attached to the mandrel  22 . The opposite end of the tubing  12  is soldered to the connection nipple  32  on the wheeled cart assembly  30 . An appropriate resistance force F is applied to the tether  58  at the end of the wheeled cart assembly  30 . The resistance force F is thus experienced by the tubing  12 . The tension in the tubing  12  keeps the tubing  12  straight and causes the tubing  12  to conform to the helical groove  24  in the mandrel  22  as the mandrel  22  is wound. 
     Prior to winding the tubing  12  around the mandrel  22 , the supply valve  44  is opened on the wheeled cart assembly  30 . The supply valve  44  connects the pressurized gas source  42  to the connection nipple  32  through the supply manifold  36 . The pressurized gas in the supply manifold  36  fills the inside of the tubing  12 . The pressure of the gas is brought to a predetermined level as measured by the pressure gauge  50  on the wheeled cart assembly  30 . 
     Once the tubing  12  is pressurized and is under tension, the mandrel  22  is rotated. The tension experienced by the tubing  12  causes the tubing  12  to conform to the helical groove  24  on the mandrel  22 . The pressure within the tubing  12  causes the tubing  12  to maintain its round cross-section while it is deformed around the mandrel  22 . As such, the tubing  12  does not crush or buckle as it is deformed into a coil. 
     Once the tubing  12  is fully wound around the mandrel  22 , the supply valve  44  on the wheeled cart assembly  30  is closed and the tension of the tether  58  is released. The pressurized gas within the wound tubing  12  is then released by opening the venting valve  48  on the wheeled cart assembly  30 . The two ends of the wound tubing  12  are then freed and the wound tubing  12  is removed from the mandrel  22 . 
     The described method of operation can be varied in two ways. In a first technique, the resistance force F applied to the tether  58  by the tension force mechanism  59  can be kept constant. In a second technique, the resistance force F applied to the tether  58  by the tension force mechanism  59  is varied. 
     As the tubing  12  is placed in tension between the mandrel  22  and the wheeled cart assembly  30 , the tubing elongates. Using the first technique of constant tension, the resistance force F supplied by the tension force mechanism  59  is calibrated to be just slightly greater than what is needed to cause the tubing  12  to conform to the helical groove  24  in the mandrel  22 . Under these conditions the degree to which the tubing  12  stretches is dependent upon the wall thickness of the tubing  12  and the annealing of the tubing  12 . The wall thickness and annealing of the tubing  12  vary along the length of the tubing  12 . As such, the tube does not stretch evenly. The result is that different sections of tubing  12  may increase in length by between one percent and six percent. The variability in elongation also corresponds to variability of wall thickness causes by the elongation. The result is a wound coil hat has thin spots at different points in the tubing  12 . 
     A second technique used when winding the tubing  12  is to vary the tension force F as a function of tube elongation. To utilize this technique, a rotation sensor  60  is attached to the mandrel  22 , the mandrel motor  26  or the transmission  23  between the motor  26  and the mandrel  22 . The rotation sensor  60  detects the number of degrees the mandrel  22  has turned in a given period of time. Furthermore, a distance sensor  61  is coupled either to the wheeled cart assembly  30  or the tether  58  extending to the wheeled cart assembly  30 . The distance sensor  61  detects how far the wheeled cart assembly  30  has moved in a given period of time. 
     The rotation sensor  60  and the distance sensor  61  are both coupled to a controller  62 . The controller  62  controls the tension force mechanism  59 . The controller  62  varies the tension force mechanism so that the amount of tubing  12  wound on the mandrel  22  in a predetermined period of time corresponds to a predetermined degree of movement of the wheeled cart assembly  30  in that same predetermined period of time. The result is that the degree of elongation experienced by the tubing  12  is kept relatively constant along its entire length. 
     There are many variations to the present invention system and method that can made. For instance, the wheeled cart assembly  30  can be substituted with a sled, a tracked vehicle or any other assembly capable of linear movement. Furthermore, there are many different types of gas supply manifolds that can be used and there are many different connectors that can be used to connect the tubing  12  to the supply manifold  36 . It will therefore be understood that a person skilled in the art can make numerous alterations and modifications to the shown embodiment utilizing functionally equivalent components to those shown and described. All such modifications are intended to be included within the scope of the present invention as defined by the appended claims.