Patent Document

CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority to and the benefit of U.S. provisional patent application serial No. 60/417,315, filed Oct. 9, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to archery bows. More particularly, the invention relates to an archery bow having spars formed from a preform including a plurality of fiber tows braided to each other.  
           [0004]    2. Description of the Related Art  
           [0005]    An archery bow generally includes spars or limbs extending between a riser and a rotating member, such as a cam or wheel. The spars store energy as the bow is drawn, and then release this energy to an arrow when a string is let go.  
           [0006]    One method for manufacturing bow spars involves molding a resin to a plurality of fibers. This manufacturing method has, however, certain drawbacks. First, since the plurality of fibers are not held into place in any way, the resin has a tendency to wash out the plurality of fibers. As a result, the molded spar includes resin rich areas that are completely devoid of the plurality of fibers. Second, there is the possibility that the resin will only flow to portions of the plurality of fibers, thereby leaving a number of the plurality of fibers completely dry. The presence of either the resin rich areas or the dry fibers results in a spar that is weak and susceptible to cracking upon use of the bow.  
           [0007]    Thus, there is a need for a molded bow spar or limb in which a polymeric material is distributed throughout a preform.  
         SUMMARY OF THE INVENTION  
         [0008]    According to one aspect of the invention, there is provided an archery bow component including a preform having a plurality of fiber tows braided to each other. A polymeric material is applied to the preform. The polymeric material coats the plurality of fiber tows during molding of the preform. The dispersal of the polymeric material throughout the preform is effected by the braiding of the plurality of fiber tows to each other. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0010]    [0010]FIG. 1 is a side view of an archery bow;  
         [0011]    [0011]FIG. 2 is a perspective view of a preform for forming a spar of the archery bow;  
         [0012]    [0012]FIG. 3 is a perspective view of the preform and a scrim cloth;  
         [0013]    [0013]FIG. 4 is a fragmentary, perspective view of the preform including a reinforcement strip secured thereto;  
         [0014]    [0014]FIG. 5 is a fragmentary, perspective view of the preform including a molding pin; and  
         [0015]    [0015]FIG. 6 is a perspective view of a molded spar. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Referring to FIG. 1, an archery bow, generally shown at  10 , includes a handle or riser  12  and a pair of limb pockets  14 ,  16  coupled to the riser  12 . Although a compound bow is shown in FIG. 1, it is contemplated that the following description is equally applicable to other bows including, but not limited to, cross bows and recurve bows. A pair of limbs or spars  20  extends between each of the limb pockets  14 ,  16  and a rotating member  22 . As the bow  10  is drawn, the spars  20  store energy that is eventually released to an arrow (not shown).  
         [0017]    Referring to FIG. 2, a preform, generally indicated at  24 , for one of the spars  20  includes a plurality of fiber tows  26  continuously braided to each other. The braided plurality of fiber tows  26  encompasses the braiding and intertwining of one bundle of fibers with one or more other bundles of fibers. The braided and intertwined plurality of fiber tows  26  also encompasses the braiding and intertwining of an individual fiber with one or more individual fibers. It is further contemplated that the preform  24  can be formed by securing two or more of the preforms  24  together as a single preform.  
         [0018]    The fibers selected to form the preform  24  include, but are not limited to, fiberglass, carbon fibers, and various fiber composites. Each of the plurality of fiber tows  26  may be made up of many different fiber materials. In addition, each of the plurality of fiber tows  26  may include fibers of varying diameters.  
         [0019]    The preform  24  is an elongated structure that approximates the configuration of the spar  20 . To form the preform  24 , the plurality of fiber tows  26  is positioned side-by-side so that the plurality of fiber tows  26  are parallel to one another. The braiding of the plurality of fiber tows  26  produces a stable preform  24  that is resistant to deformation. The fiber content and volume of the preform  24  is precisely controlled by a computer. One example of a computer utilized to form the preform is a computer numerical control (CNC) machine.  
         [0020]    The preform  24  includes a base portion  28  extending between first  30  and second  32  ends. A pocket hole  34  is formed at the first end  30  for receiving one of the limb pockets  14 ,  16 . An axle hole  36  is formed at the second end  32  for receiving an axle  38  (shown in FIG. 1). In a preferred embodiment, at least one of the pocket  34  and axle  36  holes is a counterbore. A spacer or dowel  40  is placed within the holes  34 ,  36  in order to prevent the plurality of fiber tows  26  from filling the holes  34 ,  36 . The spacer  40  is removed from each hole  34 ,  36  before molding the preform  24  into the spar  20 .  
         [0021]    The plurality of fiber tows  26  is arranged in a predetermined, uniform pattern all along the base portion  28  of the preform  24 . As a result, a cross section taken at one part of the base portion  28  will appear the same as a cross section taken at any other part of the base portion  28 . The plurality of fiber tows  26  is also arranged in a predetermined pattern at the first  30  and second  32  ends of the preform  24  around the holes  34 ,  36  thereof. The arrangement of the plurality of fiber tows  26  in these predetermined patterns results in a stable preform structure. In addition, the braiding of the plurality of fiber tows  26  to one another ensures that all of the individual fibers are wet-out during the molding process.  
         [0022]    Referring to FIG. 3, a scrim cloth  42  is wrapped around the preform  24 . The scrim cloth  42  covers the entire preform  24  between the first  30  and second  32  ends thereof. An adhesive material may be applied along an inner surface  44  of the scrim cloth  42  in order to secure the scrim cloth  42  to the preform  24 . The scrim cloth  42  is a dense fabric material that allows for passage of a molding material therethrough to the underlying preform  24  during the molding process. The scrim cloth  42  acts as a runner for spreading the molding material along the preform  24 . In addition, the scrim cloth  42  provides structural support for the preform  24 .  
         [0023]    Referring to FIG. 4, a reinforcement strip  46  is applied over the scrim cloth  42  adjacent to at least one of the first  30  and second  32  ends of the preform  24 . In a preferred embodiment, the reinforcement strip  46  is a woven fiberglass strip. The reinforcement strip  46  defines an aperture  48  that aligns with one of the holes  34 ,  36  of the preform  24 . The reinforcement strip  46  strengthens the preform  24  at the first  30  and second  32  ends thereof around the respective pocket  34  and axle  36  holes.  
         [0024]    Referring to FIG. 5, a molding pin  50  is inserted into the pocket hole  34  at the first end  30  of the preform  24 . Although not shown, the molding pin  50  is also inserted into the axle hole  38 . The molding pin  50  maintains the shape of each hole  34 ,  36  during molding of the preform  24 . After the molding process is complete, the molding pin  50  is removed from each hole  34 ,  36 . The molding pin  50  is coated with a releasing agent to effect such removal.  
         [0025]    Referring to FIG. 6, to manufacture the spar  20 , the preform  24 , along with the scrim cloth  42  and the reinforcement strip  46 , is first placed in a mold  52 . A polymeric material  54  is injected into the mold  52  through an injection runner  56  at a first end  58 . The polymeric material  54  is pulled by a vacuum to a second end  60  of the mold  52 . The polymeric material  54  passes through the scrim cloth  42  to contact the plurality of fiber tows  26 . The braided plurality of fiber tows  26  distribute the polymeric material  54  throughout the entire preform  24 . At the same time, the scrim cloth  42  expands to further distribute the polymeric material  54  throughout the preform  24 . As a result, all of the individual fibers are coated with the polymeric material  54 . It is also appreciated that the plurality of fiber tows  26  may be pre-soaked with the polymeric material  54  prior to initiation of the molding process to further ensure complete wet-out of the fibers.  
         [0026]    The spar  20  may be molded by resin transfer molding, compression molding, hydroforming, or similar molding processes. The polymeric material used in the molding process may be a thermoplastic polymer, a thermoset polymer, or a like material.  
         [0027]    The preform  24  is molded into the exact shape of the spar  20 , as shown in FIG. 7, during the molding process. Alternatively, the preform  24  is molded first and then machined to the exact shape of the spar  20  in a later step. The braiding of the plurality of fiber tows  26  guarantees that the plurality of fiber tows  26  remains in place relative to each other as the polymeric material  54  is introduced thereto. Thus, the fibers are distributed evenly throughout the molded spar  20 . The spar  20  is, therefore, devoid of any areas that are rich in polymeric material  54 , which can contribute to spar failure. In addition, the braiding of the plurality of fiber tows  26  ensures complete wet-out thereof.  
         [0028]    It is hereby appreciated that although the preform  24  has been described with regard to the manufacture of the spar  20 , the preform  24  including the braided plurality of fiber tows  26  may also be utilized in the manufacture of other archery bow components. Further, the plurality of fiber tows  26  may be braided to each other in such a way as to form a preform in various shapes and configurations.  
         [0029]    The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.

Technology Category: 2