Abstract:
A one piece composite tube having a hollow wall structure. The outside and inside of the tube have a standard surface and shape for bonding or fastening. The hollow wall reduces vibration and allows consistent flexure and torsion. The shape of the hollow wall may be tuned to maintain light weight and optimize strength for a given application.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is a continuation-in-part application of U.S. provisional patent application, Ser. No. 61/606,186, filed Mar. 2, 2012, by Robert Burch Fraidenburgh, Woodside, Calif., included by reference herein and for which benefit of the priority date is hereby claimed. 
         [0002]    The present application is a continuation-in-part application of U.S. provisional patent application, Ser. No. 61/656,010, filed Jun. 6, 2012, by Robert Burch Fraidenburgh, Woodside, Calif., included by reference herein and for which benefit of the priority date is hereby claimed. 
         [0003]    The present application is a continuation-in-part application of U..S provisional patent application, Ser. No. 61/671,700, filed Jul. 14, 2012, by Robert Burch Fraidenburgh, Woodside, Calif., included by reference herein and for which benefit of the priority date is hereby claimed. 
     
    
     FIELD OF THE INVENTION 
       [0004]    The present invention relates to products made from composite tubing and, more particularly, to tubular items in which strength and weight are at a premium. Golf club shafts, tennis rackets, ski poles, hockey sticks, fishing rods, and arrows are some examples. The invention also relates to lightweight structural members used in aerospace, sailboats, automobiles, and bicycles. 
       BACKGROUND OF THE INVENTION 
       [0005]    Composite tubing is used because of its high strength-to-weight ratio. When more strength is desired in a composite tube, options are limited. Material can be upgraded, and wall thickness can be increased. When less weight is desired, wall thickness can be decreased, or holes can be added through the wall. Also a standard composite tube is configured exactly like a tubular bell. Having a single, solid wall like a bell creates maximum vibration after striking an object or flexural release. It also transmits vibration most efficiently to the human hand and adjacent bone structure, or in the case of an assembly, to the connecting components. 
         [0006]    Other solutions have involved substituting higher modulus fiber (generally carbon fiber), wrapping with filament or fabric at varying angles to create biased plies, using higher stiffness epoxy to increase strength, and decreasing wall thickness to decrease weight. 
         [0007]    Decreasing wall thickness to reduce weight can have catastrophic results. A single unsupported wall is subject to distortion, vibration, buckling, even cracking and splitting. Increasing strength by thickening the wall adds weight. 
         [0008]    Changing material can increase strength, but within narrow limits. Changing material can increase cost. 
       SUMMARY OF THE INVENTION 
       [0009]    In accordance with the present invention, there is provided a one piece composite tube having a hollow wall. The outside and inside diameters, and ends of the tube may have standard surfaces and shapes suitable for bonding or fastening. 
         [0010]    It would be advantageous to provide a composite tube having a hollow wall for light weight and strength. 
         [0011]    It would also be advantageous to provide a composite tube resistant to vibration, while maintaining light weight. 
         [0012]    It would also be advantageous to provide a composite tube resistant to distortion when flexed, loaded, or subjected to torque. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent, detailed description, in which: 
           [0014]      FIG. 1  is a section view of a hollow wall composite tube; 
           [0015]      FIG. 2  is a perspective view of a flexible, shaped core, spiral wrapped with fiber or fabric, then spiral wrapped around a removable mandrel; and 
           [0016]      FIG. 3  is a perspective view of a finished hollow wall composite tube with the hollow wall on one end exposed in detail. 
       
    
    
       [0017]    For purposes of clarity and brevity, like elements and components will bear the same designations and numbering throughout the Figures. 
       DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]      FIG. 1  is a section view of a hollow wall composite tube in accordance with the invention. The section view in  FIG. 1  is cut parallel to the axis of the tube. The hollow  4  shown is arched for strength, like an architectural arch. The shape of the hollow  4  can be tuned to optimize performance in a given application. For example, if the tube is to be used as a golf club shaft, subject to severe side loads, the arch shaped hollow  4  strengthens the wall against collapse. 
         [0019]      FIG. 2  is a perspective view showing constituent tube  7  being wound onto a removable mandrel  5 . Also shown is constituent tube  7  being produced by spiral wrapping core  6  with tow (filaments) or fabric  8  prior to being wound on mandrel  5 . Tuning of the hollow  4  shape can be accomplished by changing the shape of core  6 . An elongated oval core  6  will produce an elongated oval hollow  4  after curing in a manner well known to those skilled in the art, and core  6  is removed by dissolving or melting. Likewise a round or rectangular cross section core  6  (wrapped with fabric or filaments to form constituent tube  7 ) can produce a round or rectangular shaped hollow  4 . Material used for making the core  6  may be wax, styrofoam, or otherwise meltable or soluble materials. After curing, the core can be melted or dissolved, with the helically traversing hollow providing a path for the core to drain out, leaving hollow  4  empty. 
         [0020]    If core  6  is tubing, it can be pressurized and the mold and mandrel  5  can hold the constituent tube  7  supported by the core  6 , in a restrained position during epoxy cure, and the finish cured hollow  4  will have a shape corresponding to the mold and mandrel  5 . 
         [0021]    Mandrels are commonly used for the “layup” of composite fiber fabric, or filament winding of composite fiber in the manufacture of composite tubes. Typically carbon fiber filaments (called “tow”) or carbon fiber fabric is used, though other fibers and fabrics are also used. In a common method of producing composite tubing, tow or fabric is wrapped on the mandrel already “wetted out” (called a “prepreg”) or encapsulated later, by injecting epoxy into the mold used to encapsulate the fibers and/or fabric. In the manufacture of golf shafts these mandrels are tapered and coated with mold release or wax to facilitate easy removal. The mandrel forms the internal diameter of the tube, and typically a mold forms the outer diameter of the tube. Mandrels can be made from hardened steel or other metal and re-used. The present invention may have a ribbed interior on its inner diameter, in the form of a shallow helical groove if constituent tube  7  is crowned. This is due to the helical track formed by constituent tube  7  having been spirally wound on mandrel  5 . If the hollow  4  is crowned or arched as shown in  FIG. 1 , there will be a small valley where the crowned winds of constituent tube  7  are tangent to each other. If the small valley on the internal diameter of the finished tube is “unfilled” and thus the internal diameter has ribs, then mandrel  5  extraction can be facilitated by rotating it, unscrewing it from the finished product. Leaving the internal surface unfilled and thus helically ribbed creates a slightly lighter structure without affecting aerodynamics if the shaft is to be swung through the air as with a golf shaft. 
         [0022]    Or the ribbed inner diameter of the tube to be produced may be filled between the crowned tops of the winds with fill, or just epoxy. This would produce a smooth inner diameter in the finished tube. In this case the mandrel  5  can be extracted by pulling it straight out axially after curing in a manner well known to those skilled in the art. 
         [0023]    To strengthen and fill between the crowned areas of the constituent tube  7 , a narrow strip or strips of fiber or fabric can be wound on mandrel  5  before the constituent tube is wound onto mandrel  5 . This can produce a smoother inside diameter. Constituent tube  7  would necessarily be wound such that the crowned portion (if the preferred shape of hollow  4  is crowned) lies between the fill. So fill, consisting of stitching or fiber or fabric or any combination thereof, bridges the valley between the winds, and strengthens the area that would be prone to stress concentration. If core  6  is not pressurized with fluid or air, the winds of constituent tube  7  can be stitched together with carbon fiber thread, aramid fiber thread, or other suitable thread. This stitching can be done while constituent tube  7  is wound on the mandrel  5  or in combination with a strip or strip of tow or fabric  8  to fill the small unfilled area between the ribs, in accordance with provisional patent applications 61/656,010 and 61/671,700, referenced herein under “Related Applications”. 
         [0024]    If the unfilled area on the outer diameter is filled by strips of fabric or stitching, or both, the fiber content of the finished composite tube will be greater, resulting in higher strength. Likewise fill can be added in the helically traversing valley on the outer diameter of the pre-molded tube that would be formed by using a crowned core  6  inside constituent tube  7 . 
         [0025]    Further strengthening of the outer diameter can be accomplished by wrapping, in a manner well known to those skilled in the art, with carbon fiber fabric or filament winding or any combination, forming an outer sleeve. Likewise strengthening of the inner diameter can be accomplished by wrapping the mandrel  5  with fabric or fiber before the constituent tube  7  is deposited on it, forming an inner sleeve. 
         [0026]    In  FIG. 2 , an end portion of constituent tube  7  is shown extended into the foreground, containing core  6 . In the finished product, this extended portion would not be present. Both ends would be cut perpendicular to the tube axis like a standard tube cut to length. The present invention&#39;s wound construction is in accordance with provisional patent applications 61/656,010 , 61/606,186, and 61/671,700, referenced herein under “Related Applications”, specifically FIG. 1 of each of the three listed provisional applications. 
         [0027]    Both  FIG. 1  and  FIG. 2  show a random length of the invention. 
         [0028]      FIG. 3  shows the invention configured as a golf shaft, mandrel  5  having been removed and core  6  melted or dissolved out or bonded in. In the case of many golf shafts, the tube would be about 46 inches long. The gripped end would be approximately ⅝″ diameter for an adult golf club, tapering smaller toward the clubhead end in the foreground. 
         [0029]    Thus having suitable epoxy, tow and/or fabric, core material, a mandrel and a mold, those skilled in the art can wind the tow or fabric on a shaped core, wind that wrapped core around a mandrel, and clamp the assembly in a mold, the fiber having been pre-impregnated or to be encapsulated by epoxy injection while in the mold. 
         [0030]    After epoxy cure, the mandrel can be removed and the core liquified and drained out (or in the opposite order), or in the case of a bonded in core, pressure is turned off to the core. Then the mold is opened, and the finished tube removed from the mold. The mold may be opened anytime after full cure, but for dimensional stability, it is usually preferable to open it as the last operation. 
         [0031]    Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention. 
         [0032]    Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims.