KR20020050693A - Metal and composite golf club shaft - Google Patents

Abstract

PURPOSE: A golf club shaft is provided to combine the separate advantages of metal and composite shafts into a single, hybrid design. CONSTITUTION: The golf club shaft includes a metal tip section(18) and a composite butt section(20). The butt section(20) includes a reduced diameter portion(32) telescopically received within an axial bore of the tip section(18). An adhesive(31) is disposed between the tip section(18) and the butt section(20) to secure the two together. An insulating layer may be disposed between the tip section(18) and the butt section(20) to prevent galvanic corrosion. Therefore, it is retained the advantages of both materials while eliminating their disadvantages.

Description

Metal and Composite Golf Club Shafts {METAL AND COMPOSITE GOLF CLUB SHAFT}

The present invention relates to a golf club shaft with improved performance characteristics, and more particularly, to a two piece golf club shaft that combines a metal part and a composite part that eliminate the disadvantages while retaining the advantages of both materials.

Adjustment and accuracy in golf play are influenced by the torsional rigidity of the shaft. The torsional stiffness of the shaft resists torsion of the club head during swings, especially when there is no complete contact between the golf ball and the club head. Metal golf club shafts made of steel, the most common metal, are used by many golfers. Known in the art as "low torque" shafts, the advantage of steel shafts is their high torsional stiffness.

Many golf shaft manufacturers provide composite shafts, commonly called graphite shafts, which are generally made of a composite of graphite or carbon fiber and an epoxy resin. Composite shafts can be significantly lighter than metal shafts, but the torsional stiffness of conventional graphite shafts is less than that of steel shafts. Thus, graphite shafts are known in the art as "high torque" than steel shafts.

In an attempt to torsionally resistant composite shafts, manufacturers used other fiber types such as high modulus carbon, aramid and boron fibers. They also changed the structure by wrapping the fibers at different angles in an attempt to improve torsional stiffness. Most of these changes increased costs and sometimes had a bad effect on shaft performance.

Recent studies show that only the tip section of the shaft provides torsional resistance to prevent club head torsion due to insufficient contact of the ball / head. The contact of the club head with the construction is a very short dynamic event, only the tip section of the shaft being loaded during this contact time. The event ends effectively before the entire length of the shaft is loaded. Therefore, it is preferable that the tip section of the shaft is made of a metal having a large torsional rigidity such as steel, while the butt section can be made of a composite such as graphite having a low torsional rigidity. In this way, the effective torque characteristics of the shaft can be enhanced while maintaining light weight.

Attempts to combine the advantages of metal and composite shafts are disclosed in US Pat. No. 4,836,545 to Pompa. However, the Pompa patent did not explain the effect of the physical characteristics of both shaft sections on shaft performance. The length and weight of the two sections of the shaft of the Pompa patent were chosen arbitrarily. The test also indicates that the weight of the metal tip section is very heavy compared to the weight of the composite butt section. Having a too heavy tip section, the center of gravity (CG) of the shaft is towards the tip end, which is undesirable for the club swing. To increase weight.

Swing weight is a measure of the static moment of the assembled club, typically about 14 ″ from the grip end. The absolute weight and balance point (CG position) of the head, shaft and grip all affect the club swing weight. It is common for most club manufacturers to specify the head weight to achieve the desired club swing weight as known in the shaft and grip specifications, but this approach is not always possible. Component suppliers typically provide club head weights that match industry acceptable weight ranges. As such, it is highly desirable to provide a shaft that can be used with such a head that constitutes a typical club swing weight.

Moreover, it is not desirable for the head to receive additional weight to achieve the desired club swing weight. Secondary weight is generally introduced at the tip end of the shaft into which the shaft is inserted into the hosel of the head. This position is not optimal away from the center of gravity of the head, thus reducing the momentum transfer to the ball for a given swing speed. Less momentum transfer to the ball reduces the distance the ball will travel.

The Pompa patent also failed to detect the difficulty of joining metal and composite sections of the shaft. The joints must be decoratively acceptable and strong enough to prevent breakage.

In view of the foregoing, it would be desirable to provide an improved golf club shaft that exhibits the advantages of both metal and composite shafts while eliminating each of the disadvantages.

It is a primary object and essential goal of the present invention to provide a golf club shaft that combines the individual advantages of metal and composite shafts into a single, hybrid design.

Another goal of the present invention is to eliminate the individual disadvantages of metal and composite shafts in a single, hybrid design.

Another object of the present invention is to provide a method of manufacturing a golf club shaft having a tip section of metal material and a butt section of composite material.

Yet another object of the present invention is to provide a method and apparatus for achieving the goal while consistent with golf rules defined by the American Golf Association.

1 is a schematic side view of a golf club shaft embodying the spirit of the present invention;

2 is a graph showing the relationship between torsional resistance and metal tip length;

3 is a graph showing the relationship between torsional resistance and metal and composite tip lengths;

4 is a graph showing the relationship between shaft weight and tip length and its impact on club swing weight;

FIG. 5 is a detailed perspective cross-sectional view of the metal / composite joint of the golf club shaft of FIG. 1; FIG.

6 is a graph showing the relationship between tip bending stiffness of a shaft of the present invention and tip bending stiffness of a conventional steel shaft;

7 is a graph showing the relationship between the tip wall thickness of the shaft of the present invention and the tip wall thickness of a conventional steel shaft;

8 is a graph showing the relationship between the butt wall thickness of the shaft of the present invention and the butt wall thickness of a conventional graphite shaft;

9 is a detailed perspective cross-sectional view of the metal / composite joint of the golf club shaft of FIG. 1 in accordance with a second embodiment of the present invention;

10 is a detailed perspective cross-sectional view of the metal / composite joint of the golf club shaft of FIG. 1 in accordance with a third embodiment of the present invention; And

11A and 11B are detailed perspective cross-sectional views of the metal / composite joint of the golf club shaft of FIG. 1 in accordance with a fourth embodiment of the present invention.

According to one embodiment of the invention, a golf club shaft is provided comprising a metal tip section and a composite butt section. The cylindrical tip section is formed of a metal material such as steel. The cylindrical butt section is formed of a composite material such as graphite and includes a plug or diameter reducing portion formed at the end thereof. The plug of the butt section is nested and received at the end of the tip section, so that the tip of the tip section surrounds the diameter reducing portion of the butt section. Adhesives such as epoxy are provided between the tip and butt sections to secure the two sections to each other.

In another embodiment of the present invention, a separation layer is disposed between the tip and the butt section to prevent the metal from contacting the composite in the metal / composite joint. By preventing the metal from contacting the composite, the separation layer reduces or eliminates the potential for galvanic corrosion in the joint. The separation layer may be formed of a plurality of separation spacers, such as glass beads or glass layers made in the butt section within the joint.

The present invention will be better understood upon reading the detailed description taken in conjunction with the drawings, and other objects and advantages will become more apparent.

Detailed Description of the Examples

Referring to FIG. 1, a golf club 10 with a grip 12, a head 14, and a tubular shaft 16 is shown. Although club 10 is illustrated in wood, it may be an iron or putter. The shaft 16 includes a tip section 18 and a butt section 20. Tip section 18 is preferably formed of a metallic material, such as high tensile steel, while butt section 20 is preferably formed of a composite material, such as graphite. Although illustrated as a shaft 16 with smooth, tapered sidewalls 22, it can be appreciated that parallel or stepped sidewalls can be substituted.

Tip section 18 is secured to head 14 by being sized to fit a standard club head hosel socket at lower end 24. The upper end 26 of the tip section 18 can be overlaid and slip fit over the lower end 28 of the butt section 20. The physical characteristics of the tip section 18 from the head 14 to the joint 30 in contact with the butt section 20 are characterized by torsional stiffness, bending stiffness (flexibility), and strength to achieve the best performance when combined with the composite butt section Is designed to provide the desired balance of weight and weight.

The relationship between the physical characteristics of the tip 18 and the playing power of the shaft 16 is complex and many factors must be considered.

1) As the metal tip section 18 is shortened, the torsional stiffness becomes less important. As the tip section 18 is lengthened, the weight of the tip section 18 becomes more important.

2) An industry standard diameter of either .335 or .350 inches is preferably maintained at the lower end 24 of the tip section 18 to be recognized as an accessory of the industry standard club head. However, the diameter can be increased towards the upper end 26 of the tip section 18 to increase both torsional and bending stiffness.

3) For tip sections 18 of equal weight, an increase in diameter at the upper end 26 reduces wall thickness and reduces durability.

4) In order to minimize the weight of the tip section 18, the wall of the tip section 18 can be made thinner. However, as the wall thickness decreases, the strength and stiffness of the tip section 18 decreases.

5) As the diameter and wall thickness of the tip section 18 change, the bending stiffness (flexibility) also changes. If the bending stiffness (flexibility) is too high or too low, the performance and feel of the shaft will be unsatisfactory.

Extensive performance and endurance testing has taken into account an acceptable contour range and a limited preferred contour for the tip section 18 of a 46 inch wood shaft weighing between 65g and 90g.

If the tip section 18 is less than 6 inches in length, it does not provide satisfactory torsional stiffness to improve shot accuracy. Figure 2 shows how the torque of the club measured using the torque test decreases as the length of the tip section increases. 3 shows the lower torque characteristics of the steel tip compared to the graphite tip.

When the tip section 18 is larger than 12 inches, the weight of the shaft increases undesirably and the center of gravity position of the shaft 16 is moved too far towards the tip end 24. 4 shows how shaft weight increases with tip length. FIG. 4 also shows shaft weights suitable for tip lengths between 6 and 12 inches, which can achieve club swing weights from D1 to D5 using industry acceptable head weights.

If the diameter of the upper end 26 of the tip section 18 is increased to greater than .415 inches, the bending stiffness becomes undesirably large, adversely affecting tip flexibility and providing low ball trajectory and roughness to the club. Likewise, if the diameter of the upper end 26 of the tip section 18 decreases to less than or equal to .385 inches, the bending stiffness is undesirably small, providing high ball trajectory and too soft sensation to the club.

Durability tests conducted with air cannons have a diameter of at least .415 inches for the upper end 26 of the tip section 18 with a length in the range of 6 to 12 inches and the overall diameter of the shaft 16 less than 65 g. The weight shows that the tip section 18 does not provide sufficient durability.

In a preferred embodiment, the 46-inch wood shaft weighs 75 grams, has a tip section 18 of 8 inches in length and a diameter of .4 inches at the lower end 24 and a diameter at the upper end 26 of .4 inches. It has a diameter of .350 inches. This preferred tip section 18, when measured using a torque test, has less than 0.6 degree of torque over an eight inch length. This compares with a torque greater than 1.5 degrees for the tip section of a typical graphite shaft measured using the same test method.

Referring now to FIG. 5, the joint 30 of FIG. 1 is illustrated in more detail. One important aspect that affects the durability of the shaft 16 is the strength of the joint 30 between the metal tip section 18 and the composite butt section 20. As shown, the tip section 18 is in the shape of a hollow metal cylinder, and the butt section 20 is formed in a hollow composite cylinder. Butt section 20 includes a diameter reducing cylindrical portion or plug 32 for insertion into tip section 18. The diameter reducing portion 32 may be formed during the lay-up of the composite butt section 20 or may be formed by shaving a preselected annular material after initial formation. The diameter reducing portion 32 is dimensioned to ensure a durable connection and a sufficient overlap with the tip section 18.

The metal tip section 18 and the composite butt section 20 are bonded to each other with an adhesive such as epoxy bond 31. The thickness of the adhesive 31 is carefully controlled and the surface area of the tip section 18 and the butt section 20 along the adhesive 31 is sufficient to ensure sufficient strength. Bond strength is selected so that the joint 30 will not break into shear deformation from the torsional loads applied to the generally accepted level of abuse during a golf game. The limitation of the highest thickness of the adhesive 31 and the increase in the surface area of the joint 30 also maintain the highest straightness standard in the assembled shaft 16.

Static and dynamic durability tests show the bond thickness to be adjusted between .003 ″ and .006 ″. The test showed that for the metal tip section 18 having a diameter between the upper end 26 between 0.385 ″ and 0.415 ″, the composite butt section 20 was between about 0.75 ″ and about 1.5 ″ to provide a suitable bond area. It also shows that it should be inserted into the metal tip section 18. In a preferred embodiment, the 46 inch shaft driver has a bond thickness of .0045 ″ and the composite butt section 20 is inserted 1.25 ″ into the metal chip section 18. This contour has been demonstrated to provide adequate strength and straightness to the assembled shaft 16.

The total bending stiffness of the shaft 16 forming shaft flexibility is influenced by the design of the tip section 18, butt section 20 and joint contour 30. Partial stiffness in the joint can be large and the length of the joint 30 should provide sufficient durability without excessively hardening.

A range of flexibility suitable for various classes of players with different swing characteristics is generally accepted throughout the industry provided by True Temper Dynamic ™ shafts, which are commonly used as criteria. Using the above mentioned contour range and total shaft weight, FIG. 6 shows the bending stiffness of the shaft 16 through the joint in comparison to the bending stiffness of the dynamic shaft, which ensures good feel and desirable ball flight. In Figure 6 the stiffness of the shaft is measured by tip deflection in a simple cantilever load test.

7 and 8 show wall thicknesses along the length of the metal tip section 18 and the composite butt section 20 in a preferred embodiment of the shaft 16, a typical True Temper Dynamic steel shaft, and a typical Grafalloy Prolite trademark. ) The wall thicknesses identified in the graphite shaft are compared. It is evident that the wall thickness at the shaft 16 is very different from the wall thickness at the available True Temper steel and Grafalloy graphite shafts. This illustrates that the shaft 16 cannot be made by connecting the tip and butt sections cut out from commercially available steel and graphite shafts to one another.

Referring again to FIG. 5, the formation of the diameter reducing portion 32 also forms an edge in the form of the radial wall 34 in the butt section 20. Although radial wall 34 is illustrated extending at right angles to diameter reducing portion 32, radial wall 34 may also be formed at an acute or obtuse angle. The radial wall 34 is preferably made to a dimension which is preferably equal to or slightly larger than the sum of the thickness of the tip 38 of the tip section 18 and the thickness of the adhesive 31, such that the shaft adjacent the joint 30. Along the perimeter of 16 a smooth wall and concentric transitions are obtained between the tip section 18 and the butt section 20.

9, a second embodiment of the present invention is illustrated. In this embodiment, the same components as in the previous embodiment are the same with the same reference numbers, but 200 is added. The second embodiment differs from the previous embodiment by the insertion of a separation layer 252 in the form of a plurality of spacers between the tip section 218 and the butt section 220. Separation spacer 252 is preferably bead shaped and is preferably formed of a separation material such as ceramic or glass. In order to reduce or eliminate Galvesny corrosion within the joint 230, the separating beads 252 prevent the metal of the tip section 218 from contacting the graphite of the butt section 220.

Bead 252 also helps to control the alignment and detachment of tip section 218 relative to butt section 220. In this regard, the diameter of the beads 252 is chosen according to the gap 242 to provide sufficient space for the adhesive 231 between the beads, while smoothing along the shaft 216 adjacent to the joint 230. The tip section 218 is also aligned coaxially with the butt section 220 to ensure a peripheral surface. Preferably, the beads 252 are premixed with the adhesive 246 before being applied in the joint 230.

10, a third embodiment of the present invention is illustrated. In this embodiment, the same components as in the previous embodiment are the same with the same reference numbers, but added 300. The third embodiment differs from the previous embodiments by the inclusion of an isolation layer 352 in the form of an overlay between the tip section 318 and the butt section 320. Overlayer 352 is preferably in the form of a separation layer integrally formed along the outer surface of diameter reducing portion 332, and in order to reduce or eliminate galvanic corrosion in joint 320. It is preferably formed of a separating material such as to prevent the metal of the tip section 318 from contacting the graphite portion of the butt section 320. Layer 352 also helps to control the alignment and detachment of tip section 318 relative to butt section 320.

Layer 352 is preferably formed by forming a butt section 320 with a relatively thick glass layer at one end prior to formation of diameter reducing portion 332. Thus, the diameter reducing portion 332 is formed by grinding the annular portion of the preselected glass to make a layer 352 such as the outer surface of the diameter reducing portion 332. In this way, the fabric 352 separates the remaining composite of the butt section 320 from the metal material of the tip section 318.

11A and 11B, in the shaft, a plastic ferrule 500 is coupled to the joint 430 between the metal tip 418 and the graphite butt section 420. Ferrule 500 was made of a suitably extruded or injection molded plastic and was used to accommodate any slight outward alignment between graphite section 420 and steel section 418. The outer diameter of the ferrule 500 is made to be slightly larger than the diameter of the graphite section 410 or the steel section 418. After assembly, excess material may be removed from the plastic ferrule 500 by buffing the thin adhesive belt or wiping with a solvent such as acetone. In this way removal of material from ferrule 500 can provide a smooth transition on the outer surface between steel and graphite sections 418 and 420.

The cross section of the ferrule 500 can be changed from the rectangle in FIG. 11A to the inwardly inclined surface as shown in FIG. 11B. This contour of ferrule may be used to accommodate a small radius at the corners of the machined graphite butt section 420, which may facilitate the manufacture of the shaft 416.

Referring again to FIGS. 1 and 2, the steps for manufacturing the shaft 16 are described. The hollow cylindrical butt section 20 is formed to a predetermined length by aligning a plurality of layers of a composite fibrous tissue, such as graphite, preselected at different angles with respect to each other, and by combining with synthetic resin. The butt section 20 may be formed with parallel, tapered or stepped sidewalls as desired. The diameter reducing portion 32 is formed at one end of the butt section 20 during lay-up or by grinding the annular portion of the preselected material at one end.

The hollow cylindrical tip section 18 is formed to a predetermined length by drawing a void of a metallic material such as high tensile steel or aluminum through the mandrel. Tip section 18 may be formed as parallel, tapered or stepped sidewalls as desired. The length and weight of the tip section 18 is selected as described above.

The adhesive is placed in at least one of the diameter reducing portion 32 and the interior of the tip section 18. Thus, the reduced diameter portion 32 can be nested and inserted into the tip section 18. As illustrated in FIGS. 9 and 10, a separation layer 52 may be inserted between the tip section 18 and the butt section 20 to prevent galvanic corrosion in the joint 30.

The foregoing relates to preferred exemplary embodiments of the invention, and it is understood that other implementations and changes are possible within the scope of the invention and are defined in the appended claims.

According to the present invention, a golf club shaft is formed that combines the individual advantages of the metal and composite shafts in a single, hybrid design.

It also has the effect of eliminating individual disadvantages of metal and composite shafts in single, hybrid designs.

Claims (20)

A tip section formed of a metallic material and having a length between about 6 and about 12 inches and a diameter between about .385 and about .415 inches at the top end; And And a butt section formed of a composite material associated with the tip section. The shaft of claim 1, wherein the tip section has a lower end, and the diameter of the lower end is about .335 inches or .350 inches. The shaft of claim 1, wherein the tip section has a wall thickness between about .0125 and about .0175 inches. The shaft of claim 1 wherein the butt section has a wall thickness between about .025 and about .125 inches. The shaft of claim 1 further comprising an adhesive disposed between the tip section and the butt section. 6. The shaft of claim 5, wherein the adhesive has a thickness between about .003 and about .006 inches. The shaft of claim 1 wherein said butt section has a plug nested within said tip section. The shaft of claim 1 wherein said tip section wraps said plug over a length of about .75 to about 1.5 inches. The shaft of claim 1 further comprising a plastic ferrule disposed between the tip section and the butt section. 2. The shaft of claim 1, further comprising a separation layer disposed between the tip section and the butt section. 11. The separator of claim 10 wherein the separation layer comprises one of a plurality of separation spacers disposed between the tip section and the butt section, and a glass layer formed outside of the tip section to be positioned adjacent to the butt section. The shaft further comprises. A tip section formed of a metallic material; And A butt section formed of a composite material and having a plug extending from one end received and nested within the tip section, the tip section surrounding the plug by a length between about .75 to 1.5 inches. Shaft. 13. The shaft of claim 12 wherein the tip section has a length between about 6 and about 12 inches. 13. The shaft of claim 12 wherein the butt section has a wall thickness between about .025 and .125 inches. 13. The shaft of claim 12, wherein the tip section has a wall thickness between about 0.015 to about 0.175 inches. 13. The shaft of claim 12, wherein the tip section has an upper end and a lower end, and the diameter of the lower end is about .335 inches or .350 inches. 13. The shaft of claim 12, wherein the tip section has an upper end and a lower end, and the diameter of the upper end is between about .385 inches and .415 inches. 13. The shaft of claim 12 further comprising an adhesive disposed between the tip section and the butt section. 19. The shaft of claim 18, wherein the adhesive has a thickness between about .003 and about .006 inches. 13. The shaft of claim 12 further comprising a plastic ferrule disposed between the tip section and the butt section.