Patent Application
20160025444
Bowstrings serve an important role in the shooting of a bow. Sometimes, bowstrings break before their life expectancy. Other times, bowstrings lose elasticity, resulting in a slack that hinders shooting performance. Fibers for use in strands of bowstrings of bows and crossbows experience challenges that are not experienced by fibers in other fields. For example, a bowstring may be formed through a manufacturing tensioning process. In the manufacturing tensioning process, the manufacturer tensions a plurality of individual strands, each strand including a plurality of fibers, to a predetermined manufacturing tension (e.g. 600 lbs of force). While under the predetermined manufacturing tension, the plurality of individual strands may then be twisted at a predetermined pitch (e.g. one twist for every 1.25 inches of length). Servings, such as wax and/or dye, may be applied while under the predetermined manufacturing tension. As a result of tensioning the strands at the pre-determined manufacturing tension during the twisting process, the individual strands settle or set into a twisted state. This setting or settling helps to prevent the bowstring from creeping and elongating after the manufacturing tensioning process, such as during use of the bowstring in a bow.
A number of materials are used in the formation of bowstrings, such asultra high molecular weight polyolefins. Ultra high molecular weight polyolefins are polyolefins that have a molecular weight greater than about one million and often between three million and six million. Examples of ultra high molecular weight polyolefin fibers include the fibers sold under the tradenames SPECTRA® and DYNEEMA®. Bowstrings formed from SPECTRA® 1000 experience undesirable creep (the tendency to stretch under tension without return when the tension is removed, resulting in slack) when tensioned in a bow or crossbow. Undesirable creep can occur during use of the bowstring. For example, the bowstring may have an initial length when under an initial installation tension as installed on a bow. When the archer draws back the bowstring, applying a drawback tension, the bowstring stretches to a drawback length that is much greater than the initial length. When the archer releases the bowstring and the drawback tension, the bowstring shortens to a return length. Due to creep, the return length can be substantially greater than the initial length, resulting in undesirable slack in the bowstring. This slack can hinder shooting performance and accuracy.
Bowstrings formed from DYNEEMA® experience high elasticity (the tendency to stretch under tension and then return when the tension is removed), but the return action can be counterproductive to the manufacturing tensioning and setting process described above. Bowstrings with high elasticity have been found to be unsuitable with the manufacturing tensioning and setting process described above—the bowstrings return to their original states too readily, and the setting process fails during or upon completion of the manufacturing tensioning process. Issues such as elasticity and elongation are particularly pertinent to bowstrings that have servings applied while the bowstring was under the predetermined tension. In these bowstrings, servings tend to separate or deteriorate when the bowstrings elongate after returning to their original states. For example, lower grade DYNEEMA® will elongate through the pre-stretching manufacturing process, but may also be subject to future elongation and does not have the same feel and stability of the material with the higher grade DYNEEMA®. When higher grade DYNEEMA® is used, the elasticity levels are greater (creating stability and superior feel) but, due to this elasticity, the pre-stretching manufacturing process causes the bowstring to take a temporary set, resulting in a finite amount of “return.” For example, a bowstring may be pre-tensioned to have a finished length of fifty-eight inches after finishing (hot length). This is a standard measurement used in the archery industry where the measurement is taken at 100 lbs of tension measure on one-quarter dowel pins. Once this bowstring has sat for several hours, the finished length may decrease and return anywhere from one-quarter to one-eighth inch due to the elasticity. Combining DYNEEMA® with VECTRAN® can still result in an undesirable decrease and return of one-sixteenth to one-eighth inch of change.
Materials used in the formation of bowstrings also include liquid crystal polymer fibers. Examples of liquid crystal polymer fibers include the fibers sold under the tradename VECTRAN®. Bowstrings formed from VECTRAN® are prone to break during use. Such bowstrings are also unsuitable with the manufacturing tensioning and setting process described above. The servings of such bowstrings tend to separate or deteriorate after the bowstrings return to their original states.
Some bowstrings have been formed from a blend of ultra high molecular weight polyolefin fibers and liquid crystal polymer fibers (e.g. 10-30% liquid crystal polymer fibers and 70-90% ultra high molecular weight polyolefin fibers). While bowstrings formed from such a blend experience improved creep and reduced tendency to break, they have still been found to be unsuitable for use with the manufacturing tensioning and setting process described above. The servings of such bowstrings tend to separate or deteriorate after the bowstrings return to their original states.
Materials used in the formation of bowstrings also include blends of ultra high molecular weight polyolefin fibers and stretched polytetrafluoroethylene fibers. Examples of stretched polytetrafluoroethylene fibers include the fibers sold under the tradename GORE-TEX®. While bowstrings formed from such a blend experience improved creep and reduced tendency to break, they have still been found to be unsuitable for use with the manufacturing tensioning and setting process described above. The servings of such bowstrings tend to separate or deteriorate after the bowstrings return to their original states.
The foregoing background describes some, but not necessarily all, of the problems, disadvantages and shortcomings related to compositions, structures, and manufacture of bowstrings.
The bowstring and method disclosed herein combine two grades of High Molecular Weight Polyethylene (HMWPE), one with higher elasticity and one with lower elasticity to reduce the shooting return or creep to zero or substantially zero, while maintaining a suitable level of overall elasticity during the manufacturing setting process. In an embodiment, the bowstring includes first and second ultra high molecular weight polyolefin fibers. The first and second ultra high molecular weight polyolefin fibers have different compositions such that the first ultra high molecular weight polyolefin fibers have a greater elasticity than the second ultra high molecular weight polyolefin fibers.
A gigapascal (GPa) is a decimal multiple of the pascal, which is the unit of pressure derived from the International System of Units (SI), a measurement of stress, Young's modulus and tensile strength. The GPa can measure or indicate the tensile strength of the bowstring, a strand of the bowstring, or a fiber of a strand of the bowstring. Therefore, there is a relationship or association between the GPa of each fiber and the elasticity of each fiber.
Within a unit, such as a strand, of the bowstring, the different types of fibers can have different mass percentages. For example, a strand can include fiber types A and B, where fiber type A has GPa A and elasticity A, and fiber type B has GPa B and elasticity B. In such strand, fiber type A may have a mass percentage or mass per mass (m/m) of 40%, and fiber type B may have a mass percentage or mass per mass (m/m) of 60%.
In an embodiment, a bowstring includes a first ultra high molecular weight polyolefin fiber having a first elasticity and a second ultra high molecular weight polyolefin fiber in contact with the first ultra high molecular weight polyolefin. The second ultra high molecular weight polyolefin has a second elasticity that is greater than the first elasticity. A serving material is applied to the first and second ultra high molecular weight polyolefin fibers when the first and second ultra high molecular weight polyolefin fibers are under a manufacturing tension so as to set the bowstring. The first and second high molecular weight polyolefin fibers cooperate to reduce a loss in bowstring elasticity so as to reduce bowstring creep during use of the bowstring. The first and second ultra high molecular weight polyolefin fibers are chemically configured or structured to facilitate the setting of the bowstring.
In another embodiment, a bowstring includes a plurality of strands twisted together to form the bowstring. Each one of the strands includes a plurality of first ultra high molecular weight polyethylene fibers and a plurality of second ultra high molecular weight polyethylene fibers. Each of the plurality of first ultra high molecular weight polyethylene fibers has a first elasticity that is greater than a second elasticity of each of the plurality of second ultra high molecular weight polyethylene fibers.
In yet another embodiment, a bowstring produced through a method is described. The method includes forming a plurality of first ultra high molecular weight polyolefin fibers and forming a plurality of second ultra high molecular weight polyolefin fibers. Each one of the plurality of first ultra high molecular weight polyolefin fibers has a first elasticity that is greater than a second elasticity of each one of the plurality of second ultra high molecular weight polyolefin fibers. The method further includes combining a plurality of the first ultra high molecular weight polyolefin fibers with a plurality of the second ultra high molecular weight polyolefm fibers to form a first strand and combining a plurality of the first ultra high molecular weight polyolefin fibers with a plurality of the second ultra high molecular weight polyolefin fibers to form a second strand. Further, the method includes tensioning the first and second strands to a predetermined tension to produce pre-tensioned strands and twisting the pre-tensioned strands together at a predetermined pitch to produce a pre-tensioned, twisted strand assembly. In addition, the method includes applying one or more servings to the twisted strand assembly and releasing the predetermined tension.
Additional features and advantages of the present disclosure are described in, and will be apparent from, the following Brief Description of the Drawings and Detailed Description.
The first and second ultra high molecular weight polyolefin fibers have different chemical structures or compositions such that the first ultra high molecular weight polyolefin fibers have a greater elasticity than the second ultra high molecular weight polyolefin fibers. Ultra high molecular weight polyolefin fibers with different elasticity values are commercial available. For example, DYNEEMA® is commercially available in different grades (e.g. DYNEEMA® SK75, DYNEEMA® SK90, etc.) each of which has a different modulus of elasticity.
In an embodiment, the bowstring 2 is produced or manufactured according to the manufacturing steps of: (a) placing the bowstring under a designated amount of manufacturing tension for a designated period of time; and (b) during the period, applying one or more serving materials to the bowstring to set or cure the bowstring. In another embodiment, the bowstring 2 is produced or manufactured according to the manufacturing steps of: (a) applying one or more serving materials to the bowstring to set or cure the bowstring; and (b) then placing the bowstring under a designated amount of manufacturing tension for a designated period of time. The tensioning step converts the bowstring (including its strands and fibers) to a manufacturing stretched state. At the end of the tensioning step, when the manufacturing tension is released and the bowstring is in a tension-free state, the bowstring has an initial length. Afterwards, the bow manufacturer installs the bowstring in a bow under a designated installation tension associated with an initial or installation length. During use of the bow, the archer draws the bowstring backward under a draw-back tension, stretching the bowstring to a drawback length. When the archer releases the bowstring, the bowstring elastically compresses to a return length. The initial or installation length and the final or return length are each less than the drawback length. The fiber structure or composition described above reduces or eliminates undesirable creep or elongation of the bowstring following application and release of a tension, such as a draw-back tension. As a result, the final or return length is the same as, or substantially the same as, the initial or installation length. Depending upon the embodiment, the curing or serving material can include, in liquid or solid form, a wax, adhesive, resin, dye, paint, polymer or other solution configured to enhance the integrity and lifespan of the bowstring. The end-loop serving materials tightly grip the underlying string strands to prevent separations, loosening, and fraying. The center serving material provides for a smooth and consistent release from the shooting tab surface, and the center serving material also resists separation and loosening of the strands, and it also resists wear from brushing against the archer's armguard after the shot. Also, the center serving material maintains or retains the constant diameter of the bowstring over a relatively long period of time.
In one embodiment, the chemically blended structure of the bowstring further comprises a stretched polytetrafluoroethylene fiber, that is, a polytetrafluoroethylene fiber which has been stretched through the manufacturing tension process. One such bowstring blend is shown in Table 1, wherein a 1545 denier bowstring is provided that consists essentially of DYNEEMA® SK90, SPECTRA® 1000 and GORE-TEX®.
In another embodiment, a bowstring has a structure based on a chemically blended composition of first, second and third ultra high molecular weight polyolefin fibers. The first and second ultra high molecular weight polyolefin fibers have different compositions such that the first ultra high molecular weight polyolefin fibers have a greater elasticity than the second ultra high molecular weight polyolefin fibers. The third ultra high molecular weight polyolefin fibers are different from the first and second ultra high molecular weight polyolefin fibers in that they have an elasticity that is less than the elasticity of both the first and the second ultra high molecular weight polyolefin fibers. One such bowstring blend is shown in Table 2, wherein a 1345 denier bowstring is provided that consists essentially of DYNEEMA® SK90, DYNEEMA® SK75 and SPECTRA® 1000. In one embodiment, the bowstring further comprises a stretched polytetrafluoroethylene fiber.
In another embodiment, a bowstring has a structure based on a chemically blended composition comprising first, second and third ultra high molecular weight polyolefin fibers in combination with liquid crystal polymer fibers and stretched polytetrafluoroethylene fibers. The first and second ultra high molecular weight polyolefin fibers have different compositions such that the first ultra high molecular weight polyolefin fibers have a greater elasticity than the second ultra high molecular weight polyolefin fibers. The third ultra high molecular weight polyolefin fibers are different from the first and second ultra high molecular weight polyolefin fibers in that they have an elasticity that is less than the elasticity of both the first and the second ultra high molecular weight polyolefin fibers. One such bowstring blend is shown in Table 7, wherein a 1300 denier bowstring is provided that consists essentially of DYNEEMA® SK90, DYNEEMA® SK75, SPECTRA® 1000, VECTRAN® and GORE-TEX®. In the embodiment of Table 3, the ultra high molecular weight polyolefin fibers and the liquid crystal polymer fibers of a unit of the bowstring are present in equal proportions. The unit has a total weight. The stretched polytetrafluoroethylene fibers provide the balance of the total weight less the weight of the ultra high molecular weight polyolefin fibers and the liquid crystal polymer fibers.
In another embodiment, a bowstring has a structure based on a chemically blended composition comprising first and second ultra high molecular weight polyolefin fibers in combination with a liquid crystal polymer fiber is provided. The first and second ultra high molecular weight polyolefin fibers have different compositions such that the first ultra high molecular weight polyolefin fibers have a greater elasticity than the second ultra high molecular weight polyolefin fibers. One such bowstring blend is shown in Table 4, wherein a 1345 denier bowstring is provided that consists essentially of DYNEEMA® SK90, DYNEEMA® SK75 and VECTRAN®. Another such bowstring blend is shown in Table 5, wherein a 1345 denier bowstring is provided that consists essentially of DYNEEMA® SK90, SPECTRA® 1000 and VECTRAN®.
In another embodiment, a bowstring has a structure based on a chemically blended composition comprising first and second ultra high molecular weight polyolefin fibers in combination with a liquid crystal polymer fiber and stretched polytetrafluoroethylene fibers is provided. The first and second ultra high molecular weight polyolefin fibers have different compositions such that the first ultra high molecular weight polyolefin fibers have a greater elasticity than the second ultra high molecular weight polyolefin fibers. One such bowstring blend is shown in Table 6, wherein a 1300 denier bowstring is provided that consists essentially of DYNEEMA® SK90, SPECTRA® 1000, VECTRAN® and GORE-TEX®. A similar bowstring blend is shown in Table 7 wherein a 1200 denier bowstring is provided.
In some embodiments, the first ultra high molecular weight polyethylene fiber is structured or configured to have an elasticity that is at least 5 GPa greater than the elasticity of the second ultra high molecular weight polyethylene fiber. In some embodiments the difference is at least 10 GPa. The first ultra high molecular weight polyethylene fiber may be selected to have an elasticity that is greater than 135 GPa (e.g. between about 135 GPa and 145 GPa). The second ultra high molecular weight polyethylene fiber may be selected to have an elasticity that is less than 135 GPa (e.g. between about 100 GPa and about 135 GPa). In another embodiment, the second ultra high molecular weight polyethylene fiber may be selected to have an elasticity that is less than 120 GPa (e.g. between about 100 GPa and about 120 GPa). In those embodiments where a third ultra high molecular weight polyethylene fiber is present, the elasticity of the third ultra high molecular weight polyethylene fiber is, in some embodiments, at least 5 GPa different than the elasticity of both the first and second ultra high molecular weight polyethylene fibers. The liquid crystal polymer fiber may be selected to have an elasticity between 50 GPa and 90 GPa. In one embodiment, the bowstring is twisted (e.g. unbraided).
Additional embodiments include any one of the embodiments described above, where one or more of its components, functionalities or structures is interchanged with, replaced by or augmented by one or more of the components, functionalities or structures of a different embodiment described above.
It should be understood that various changes and modifications to the embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present disclosure and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.
Although several embodiments of the disclosure have been disclosed in the foregoing specification, it is understood by those skilled in the art that many modifications and other embodiments of the disclosure will come to mind to which the disclosure pertains, having the benefit of the teaching presented in the foregoing description and associated drawings. It is thus understood that the disclosure is not limited to the specific embodiments disclosed herein above, and that many modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although specific terms are employed herein, as well as in the claims which follow, they are used only in a generic and descriptive sense, and not for the purposes of limiting the present disclosure, nor the claims which follow.
This application is a non-provisional of, and claims the benefit and priority of, U.S. Provisional Patent Application No. 62/028,885, filed on Jul. 25, 2014. The entire contents of such application are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62028885 | Jul 2014 | US |
