This invention relates generally to golf equipment and, in particular, to golf clubs.
Golf clubs such as drivers, irons and putters have club heads that are conventionally manufactured by investment casting, forging or machining from a solid bar. Use of materials with a high strength-to-density ratio such as titanium has been suggested to enable greater flexibility in designing golf clubs. Polymer foams have been utilized as cores in club heads of hollow metal drivers to prevent weld slag and other debris inside the club head from making the club head rattle; however, polymer foams provide negligible structural support for the face and crown of the club head. Conversely, a metallic or ceramic foam core would provide structural support for the face and other surfaces of the club head with an unprecedented strength to density ratio, which in turn, would enable unprecedented improvements in golf club performance.
With reference to
Club head pre-form 12 may be manufactured in a closed-cell foam structure by injecting gas into the molten material and/or by mixing a foaming agent such as powdered titanium hydride into the alloy composition prior to melting. In the illustrative embodiment, however, club head pre-form 12 comprises an open-cell reticulated structure with interconnected voids which is formed by metalization of a polymer template such as polyurethane foam. In one aspect of the invention, metal such as nickel alloy is deposited onto a sponge-like non-metallic material such as polymer having a shape approximating at least a portion of a club head body such as a face insert. This forms a metallic foam member which is then covered with a coating that is preferably non-metallic material. In another aspect of the invention, metal is deposited onto a sponge-like non-metallic material in the shape of club head perform 12. Then, the club head perform 12 is formed into the shape of at least a portion of a club head body and, if desired, covered with a coating. The polymer template mentioned above is removed from the club head perform 12 by pyrolyzing to leave a reticulated rigid foam structure 14 composed of the pure metallic or ceramic material consisting of from 80% to 98% voids and therefore from 2% to 20% of the bulk density of an equivalent volume of solid material.
With reference to
With reference to
Once core 20 has been properly shaped, a coating 22 is applied to the outer surface of core 20. In the illustrative embodiment of
As shown in
Once coating 22 or 24 has been applied to rigid foam composite core 20, second material 16 is pyrolized by subjecting club head 28 to heat below the melting point of reticulated structure 14 and also below the decomposition temperature of coating 22 or 24 but above the decomposition or melting point of second material 16. Once second material 16 has been decomposed, it is drained through an aperture in coating 22 or 24 (not shown). In the case of a club head pre-form 12 having a closed-cell structure, only the surface pores are intercalated with second material 16. Consequently, if the pore size is controlled, typically to cell sizes of 1 mm to 8 mm preferably 1 mm to 4 mm, and most preferably about 1 mm pore size, the volume fraction of second material 16 is sufficiently small to make the pyrolization step unnecessary. Moreover, if coating 24 is applied in a molding process such as with a composite coating 24, second material 16 and coating 24 can be made of the same material applied at the same time.
As noted hereinbefore, because the metallic foam material from which club head pre-form 12 is fabricated has a bulk density of from 2% to 20% of the density of an equivalent volume of solid material, a club head incorporating features of the present invention can be fabricated with a core having a bulk density of from 0.05 grams per cubic centimeter to 0.5 grams per cubic centimeter if an aluminum reticulated structure is used, while maintaining substantially the same rigidity as a solid aluminum core structure. Corresponding benefits can be gained relative to other materials such as titanium, silicon carbide and carbon. This translates into a golf club head having substantially improved rigidity, with commensurate ability to redistribute weight to the side and sole walls as necessary to improve moment of inertia, center of gravity location and other properties of the golf club.
Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations in modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. For example, although the illustrative embodiment of