Abstract:
The method of the present invention comprises inserting a moldable slug having a plurality of longitudinally oriented resin impregnated predominantly glass fiber filaments into a bow limb profiling mold. The mold consists of two halves, the first half containing a female cavity and a second half having a matching fitted male section. The cavity receives a pre-determined volume and weight of continuous longitudinal fibrous reinforcement material and plastic resin matrix material. Heat and pressure are applied during initial curing and the uncured end is removed. The slug is then finally cured and the slug is severed to form a right limb portion and a left limb portion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to archery bows and more particularly pertains to an improved compression molded archery bow limb for use in a compound bow and method for manufacturing the same. 
     2. Description of the Prior Art 
     Archery bow limbs perform the important function of storing energy when the archer draws the bowstring. When the bowstring is drawn, the pre-stressed bow limbs, which are typically made of resilient material, are further flexed to store additional energy. When the bowstring is released, the stored energy propels the arrow. 
     In conventional compound bows, the limb is typically formed of a single element of rectangular cross section, wherein one end is attached to the bow handle and the other end has a limb tip slot formed therein, in which an eccentric wheel is mounted. 
     Reinforced glass fiber materials have been utilized in archery bow limbs for a number of years. In some instances, the limb profile is machined from extruded solid glass fiber billets, and in other instances the limb profile is machined from pre-formed compression molded billets, which in some cases may be pre-formed to such near net shape that only secondary machining operations are required to remove excess material from the limb tip area and from the butt slot area, where the limb is joined to the handle. In all such cases, the secondary machining operations are costly and time consuming. Further, the machining operations result in the severing of load bearing fibers which reduces the maximum limb operating stress level and the fatigue life of the limbs. 
     To lessen the problems associated with machining the reinforcing glass fiber material, several processes have been developed, such as those disclosed in U.S. Pat. Nos. 4,649,889; 4,660,537; and 4,735,667. More recently, there is disclosed in U.S. Pat. No. 5,141,689, issued to G. Simonds, a method of forming a partial limb tip slot in a molded limb profile, and then severing the remaining glass fibers in the limb tip slot area to form the limb tip. This method reduces the number of glass fibers that are severed so that the fatigue life of the resultant limb tip is substantially improved, and the necessity of providing reinforcement washers to the limb tip slot is avoided. It is not believed, however, that a glass fiber limb for a compound bow has been produced which completely avoided having to sever glass fiber filaments when the limb tip slot was formed. 
     Further, it was popularly believed (see, for example, U.S. Pat. No. 4,735,667, issued to R. Johnson) that glass fiber limbs should be of a substantially constant cross sectional area in order to maintain a constant glass fiber to resin ratio in the limb. 
     Thus far the discussion has been concerned with conventional compound bows formed with single element glass fiber limbs of rectangular cross section. A different approach is disclosed in U.S. Pat. No. 4,350,138, issued to J. Caldwell. The limb portions-disclosed therein are formed of left and right limb portions. Significantly, the limb portions disclosed therein are not compression molded, and it is not believed that any such split limb portions have been formed by compression molding despite the fact that the compression molding of limbs has been widely known for many years. More contemporaneous versions of such split limbs are, for example, being sold by Hoyt U.S.A. under the Alpha Tec mark and by High country under the Split Force mark. 
     SUMMARY OF THE INVENTION 
     The present invention is concerned with a method for manufacturing discrete compression molded archery bow limb portions and the archery bow limbs produced thereby. The limb portions comprise compression molded upper left and right limb portions and compression molded lower left and right limb portions. In this manner, the respective left and right limb portions form the limb tip slots and the costly and time-consuming limb tip slot machining process is avoided, together with the attendant disadvantages associated with such machining, namely, the reduction in the maximum limb operating stress level and the reduction in the limb fatigue life. Further, and contrary to the teaching of the prior art, the upper and lower left and right limb portions may be provided with a varying cross sectional lengthwise profile so that the glass fiber to resin ratio may be made higher in the limb portion area which experiences high stress and lower in the limb portion area in which perhaps more stiffness is desired. Still further, it is desirable that the complementary left and right limb portions have identical glass fiber to resin ratios throughout the length of the limbs and identical mirror image physical configurations and that is achieved through the present invention. 
     The method of the present invention comprises inserting a moldable slug having a plurality of longitudinally oriented resin impregnated predominantly glass fiber filaments into a limb portion profiling mold. The limb portions comprise a right limb portion and a left limb portion. The mold consists of two halves, the first half containing a female cavity profiled to provide the configuration of the right limb portion in axial alignment with the configuration of the left limb portion, and a second half having a mating male section. The first cavity is profiled to provide the configuration of the right limb portion and the second cavity is profiled to provide the configuration of the left limb portion. The cavities are in parallel relationship with each other and are connected along their longitudinal axis. Each cavity receives a predetermined volume and weight of continuous longitudinal fibrous reinforcement material and plastic resin matrix material. Heat and pressure are applied during initial curing and the uncured end is removed. The slug is then finally cured, either in its entire length or after being severed into a left limb portion and a right limb portion. 
     Accordingly, it is an object of this invention to provide a method of manufacturing compression molded discrete left and right archery bow limb portions, and the archery bow having limb portions produced thereby. 
     It is a further object of this invention to provide a method of manufacturing compression molded archery bow limb portions having varying cross sectional lengthwise profiles, and the archery bow having limb portions produced thereby. 
     Other objects and attendant advantages of this invention will be readily appreciated as the same become more clearly understood by references to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects and advantages of the present invention will become apparent as the following description of an illustrative embodiment takes place, taken in conjunction with the accompanying drawing, in which: 
     FIG. 1 is a perspective view of a compound archery bow illustrating the various components thereof and including the bow limb portions of the present invention. 
     FIG. 2 is a plan elevation view of a slug frame with impregnated filaments wrapped thereon. 
     FIG. 3 is a perspective side elevation view of the mold assembly used in producing the bow limb portions of the present invention. 
     FIG. 4 is a perspective side elevation view of the mold assembly during curing with the filament tail extending from the mold assembly. 
     FIG. 5 is a sectional elevation view taken approximately along line  5 — 5  of FIG. 3 viewed in the direction of the arrows. 
     FIG. 6 is a sectional elevation view taken approximately along line  6 — 6  of FIG. 3 viewed in the direction of the arrows. 
     FIG. 7 is a plan elevation view of the cured limb slug as it is when removed from the mold assembly and after the filament tail is severed. 
     FIG. 8 is a plan elevation enlarged view of a left and right limb portions produced according to the present invention. 
     FIG. 9 is a side elevation view of the left and right limb portions shown in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the illustrated embodiment of FIG. 1, a compound archery bow generally designated as  10  includes, when viewed from the perspective of an archer holding the bow  10 , an upper right limb portion  12 A, an upper left limb portion  12 B, a lower right limb portion  14 A and a lower left limb portion  14 B. Centrally disposed variable leverage units such as eccentric pulleys  16  and  18  are supported for rotary movement about axles  20  and  22 . The axle  20  is carried in the outer limb tip portions between upper right limb portion  12 A and upper left limb portion  12 B, which form limb slot  24 . The axle  22  is carried in the outer limb tip portions between lower right limb portion  14 A and lower left limb portion  14 B, which form limb slot  26 . 
     One end of bowstring  34  extends to the upper end of the bow where it wraps around at least a portion of the eccentric pulley  16  and is connected thereto, and the other end of bowstring  34  extends to the lower end of the bow where it is trained around a portion of eccentric pulley  18  and is connected thereto. Anchor cable  32 A extends from eccentric pulley  16  to the extremities of axle  22 . The other anchor cable  32 B extends from eccentric pulley  18  to upper axle  20 . The opposed pairs of upper bow limb portions  12 A and  12 B and lower bow limb portions  14 A and  14 B are relatively short and will characteristically have high spring rates. When the bowstring  34  is drawn, it causes eccentric pulleys  16  and  18  at each end of the bow to rotate, which shortens the length of the anchor cables  32 A and  32 B to bend the limb portions  12 A,  12 B,  14 A and  14 B causing additional energy to be stored therein. When the bowstring  34  is released with an arrow attached to the bowstring, the limb portions  12 A,  12 B,  14 A and  14 B return to their rest position, causing the eccentric pulleys  16  and  18  to rotate in the opposite direction to take up the bowstring  34  and launch the arrow with an amount of energy proportional to the energy initially stored in the bow limbs. 
     Referring to FIG. 2, there is illustrated the glass fiber slug  36  from which the bow limb portions  12 A,  12 B,  14 A and  14 B of the instant invention are fabricated. Glass fiber filaments  40 , which form the glass fiber slug  36 , are initially drawn through a wet out tank containing a suitable resin. After absorbing the desirable amount of resin, the glass fiber filaments  40  are wrapped around frame  42 . Each wrap consists of one complete turn or loop around a frame  42 . A plurality of wraps are necessary to form each limb set and therefore each slug  36  consists of a number of individual wraps. 
     Both the glass fiber and the resins used in this process are well known in the art. Suitable materials include glass fiber filaments packaged in spools and sold by Pittsburgh Plate Glass Corp. under the designation No. 712-218 to be employed with Shell 826 epoxy resin and a suitable heat activated catalyst such as Lindride 6K manufactured by Lindow Chemical Company. It has been found that the range of suitable glass fiber to resin ratios by weight is from 60% to 75% which is the equivalent of a glass fiber to resin ratio by volume in the range of 42% to 59%. 
     The slug  36  is in suitable condition to be molded by inserting it into the mold assembly  44  illustrated in FIG.  3 . The frame  42  is positioned so that the slug  36  extends longitudinally within the lower mold  46  and the glass fiber filaments  40  extend out of the assembly  44  in the form of a tail  41  (see FIG.  4 ). The cavity  48  of the lower mold  46  in conjunction with the mating member  50  of upper mold  52  is shaped to form the slug  36  into the partially completed right limb portion  12 A and left limb portion  12 B, illustrated in FIG.  8 . Cavity  48  contains a first cavity  51  which is profiled to provide the configuration of the right limb portion  12 A and a second cavity  53  which is profiled to provide the configuration of the left limb portion  12 B. First cavity  51  is in axial alignment with second cavity  53  and is connected therewith. As upper limb portions  12 A and  12 B are identical to lower limb portions  14 A and  14 B, only upper limb portions  12 A and  12 B are further described. The face  56  of the lower mold  46  is provided with stops  58  which limit the depth of penetration of member  50  into the cavity  48 . Openings  60  of upper mold  52  receive alignment pins  62  of lower mold  46  when the mold is closed. 
     Two different cross sections of the glass fiber slug  36  in the upper mold  52  and lower mold  46  are shown in FIGS. 5 and 6. It will be noted that the cross section of slug  36  shown in FIG. 5 is of greater thickness, T 1 , than the cross section of slug  36 , T 2 , shown in FIG.  6 . Therefore, the glass fiber to resin ratio of the slug  36  cross section shown in FIG. 5 may be less than the glass fiber to resin ratio of the slug  36  cross section shown in FIG.  6 . It is reasonable to have a lower glass fiber to resin ratio in the slug  36  cross section shown in FIG. 5 because the limb is subject to less stress in this area. Further, the increased thickness T 1  increases the desired limb stiffness in this area. On the other hand, it is desirable to have a higher glass fiber to resin ratio in the slug  36  cross section shown in FIG. 6 because the limb is subject to increased bending stress in this area. As shown in FIGS. 5 and 6, the differences in the greater thickness T 1  of slug  36  in FIG. 5 is achieved by increasing the depth of cavity  48  of lower mold  46 . 
     As seen in FIGS. 5 and 6, the lower corner edges  64  of the formed slug  36  are molded with a radius along their length. This is provided to avoid having to machine out stress-inducing sharp corners and also by molding in this radius the fiber filaments are uncut, continuous and protectively sealed in this highly stressed area. 
     The initial curing of the slug  36  occurs when slug  36  is inserted into the mold assembly  44  which has been heated to an operating temperature of approximately 300° to 350° F. Slug  36  is maintained in the closed mold assembly  44  at this temperature for a period of 5 to 10 minutes, whereby slug  36  is set to assume the profile determined by the mold assembly  44 . Slug  36  is then removed from the mold assembly  44  and the uncured glass fiber filaments forming the tail  38  (only one of which is shown) are severed (see FIG. 7) The slug  36  can be finally cured in its full length as shown in FIG. 7, or it can be severed into limb portions  12 A and  12 B shown in FIGS. 8 and 9, and then cured in an oven. Openings  66  are then machined in right limb portion  12 A and left limb portion  12 B for the purposes of receiving axle  20 . 
     Having thus described the invention, it will be apparent to those skilled in the art that various modifications can be made within the scope of the invention.