This invention relates to a handheld striking implement which includes a vibration-damping element isolating the portion which is held from the portion used for striking.
Various attempts have been made to manufacture sports implements e.g. tennis rackets or cricket bats which incorporate some form of vibration-damping mechanism to minimise the risk of injury to the player. Problems in making such articles are that intricate multi-component manufacturing steps are often necessary whereas relatively unskilled labour is required to keep costs down. Also, any feature which adds weight to the final product is undesirable.
In British Patent Application No. 2149311A (Tarr) a novel racket is described in which the handle is discontinuous and the two parts are adjustably held together by a tensioning means (e.g. a spring, rod and screw assembly) and between the said two parts is a damping means.
The present invention provides a striking implement such as a tennis racket which has a discontinuity between the part gripped in use and the part used to strike. It incorporates features in which elements extending from each of the separate parts of the implement overlap in a unique manner and are bonded where they overlap by a vibration-damping material such that the parts are strongly joined together and yet are mechanically isolated one from another so that shock waves and vibration passing from the striking part to the gripping part are substantially absorbed. The product is strong but light and is easy to manufacture.
Although the present invention will be described with particular reference to a games racket or a cricket bat it is not to be construed as limited thereto as it is applicable equally to other striking implements such as sports equipment e.g. hockey sticks, golf clubs, baseball bats, hurley sticks, polo sticks, croquet mallets, and also batons, truncheons and shillelaghs.
The present invention provides a striking implement which comprises a hollow handle portion and a striking portion, in which the striking implement is discontinuous in that it comprises two parts one part including the striking portion and the other part including at least a part of the hollow handle portion, the said two parts having complementary formations which are assembled to overlap axially with a vibration-damping material interposed therebetween characterised in that the vibration-damping material is bonded to said formations and is in substantially mutually perpendicular planes parallel to the longitudinal axis of the handle portion, whereby said formations are inseparably connected together but mechanically isolated one from another by the vibration-damping material.
Preferably the complementary formations assemble so as to constitute a substantially identical cross-section to that of the remainder of the handle portion. Examples of complementary formations are:
The axial overlap of the complementary formations means that the confronting faces extend in planes angled to each other and in a preferred embodiment these planes are substantially perpendicular to each other. Where the complementary formations are substantially identical but merely rotated through 90° in the final assembly it is possible and convenient to mould in one piece hollow handle portions with formations, cut through the formations, rotate one of the handle portions 90° and then assemble the complementary formations. The assembly must be suitably jigged to align the components prior to the vibration-damping material being injected to fill the gap between the said complementary formations.
The vibration-damping material may suitably be a thermosetting or a thermoplastics material and especially an injectable material, for example a polyurethane resin. A suitable material may be based upon an elastomeric material compounded to produce the properties of a vibration-damping material.
A preferred polyurethane resin comprises an injectable thermosetting elastomeric material particularly in the form of a two-part, curable polyurethane which is mixed in liquid form and can therefore be readily injected and subsequently cures in situ. Such a material is available from Compounding Ingredients Limited as CILCAST 101 (which is cured by the addition of CILCURE B). The words CILCAST and CILCURE are Registered Trade Marks. (The hardness and resilience of the vibration-damping materials are measured according to British Standards (B.S.) tests which are internationally available and familiar to the skilled artisan). Such a material has the properties desirable for the vibration-damping material of the present invention being of a hardness greater than 60° SHORE A measured according to BS 2782 Part 3 "Indentation Hardness by Durometer (Shore A)" and resilience below 20% when measured according to BS 903 Part A8 Method B "Method for Rebound Resilience". More preferably the vibration-damping material has a hardness in the range 70 to 95° SHORE A measured according to BS 2782 Part 3 "Indentation Hardness by Durometer (Shore A)", the preferable resilience for the vibration-damping material being in the range 5 to 15% measured according to BS 903 Part A8 Method B "Method for Rebound Resilience".
Preferably the vibration-damping material is self-bonding to the complementary formations of the two parts of the striking implement i.e. no separate adhesive is required. The aforementioned two-part curable polyurethanes have this desirable property.
Preferably the handle portion includes only one discontinuity according to the present invention but the handle portion itself may be joined to the striking portion rather than being integral therewith.
The present invention is particularly applicable for use in a cricket bat where it is important for the handle to be light, strong and able to absorb at least some of the shock received when the striking portion (i.e. the blade) strikes a cricket ball. Preferably the part which includes the handle portion is designed so that the formations are substantially in a plane perpendicular to the face of the striking portion (blade) and thus the formations of the part which includes the blade are in a plane substantially parallel to the face of the blade. This arrangement will improve shock absorbency of the final product.
Particularly where the formation of one part consists of 2 or more fingers which interdigitate with the corresponding 2 or more fingers of the other part it may be preferable to provide a web between the fingers of one said part to reduce bending of the formations when the implement is used for striking and thus to reduce the strain imposed on the bond between the complementary formations. To take advantage of this potential improvement the web should be provided between the formations, the free ends of which will be nearer to the striking portion when the striking implement is in use.
Preferred materials for the handle portion are of fibres e.g. of carbon or glass impregnated with a thermosetting or thermoplastics resin. Such compositions can be moulded to give hollow, and thus light, strong handle portions. Particularly for striking implements where there is a high degree of shock in use, e.g. a cricket bat or hockey stick, the fibres may be of material with increased shock absorbency properties e.g. aramid or polyethylene fibres.
The present invention will be illustrated merely by way of examples in the following description and with reference to the accompanying drawings in which:-
Referring to Figures 1, 2, 3 and 4 a part handle portion 1 has formations (fingers) 2 and 3. The part handle portion 1 is hollow and made by wrapping layers of resin impregnated fibre in fabric or 'warp sheet' form around an inflation tube and then moulding under heat and internal pressure, as is well known to those skilled in the art of making hollow articles from polymer composite materials. Alternatively the inflation tube may be replaced by a plastic material capable of expanding under the action of heat to produce the necessary internal consolidating pressure. Fibre alignment of the wrapping layers is chosen to produce the desirable directional strength in the handle portion, and the fibre type may be chosen to produce desirable properties of enhanced shock absorbency over and above that provided by the vibration-damping material interposed between the complementary formations. Such fibres with good shock absorbency are glass fibres, aramid fibres and polyethylene fibres, and such fibres may be used in combination with each other or with carbon fibres to achieve the desirable properties. A part handle portion 4 is made in the same way and has formations 5 and 6 (which lies behind formation 3 in Figure 3). The complementary formations (fingers) of these two part handle portions are assembled so as to interdigitate and vibration-damping material 7 is injected between the said formations. When the vibration-damping material 7 sets it bonds to the formations. Thus the part handle portions are mechanically isolated but strongly bonded by the vibration-damping material. Such an assembly may be used e.g. as part of a games racket.
Referring to Figures 5 to 8, the construction is of a very similar principle to that shown in Figures 1 to 4 but uses instead complementary formations of three fingers each.
Referring to Figures 9 and 10, a cricket bat which incorporates a further embodiment of the present invention consists of a part handle portion 8 with formations 9, 10 assembled with and bonded via a vibration-damping material 11 to complementary formations 12, 13 of part handle portion 14. The handle assembly is hollow and of consolidated resin impregnated fibre composite and is bonded to a wooden blade 15.
The main direction in which a cricket ball will strike is shown by the arrow F in Figure 10. In this arrangement the formations 9, 10 of the part handle portion 8 are in a plane perpendicular to the face of the bat and thus there will be improved shock absorbency compared to an arrangement where the formations 9, 10 are in a plane parallel to the face of the bat.
Referring to Figure 11, the part handle portion 16 has hollow fingers 17 and 18 joined along part of their length by an integral web 19. Referring to Figure 12, the part handle portion 20 has hollow fingers 21 and 22 (22 lies behind 21). The complementary formations (fingers) of the two part handle portions shown in Figures 11 and 12 are assembled so as to interdigitate as shown in Figure 13. Vibration-damping material 23 is injected between the said formations including transversely 24 of the longitudinal axis of the striking implement and then set to bond to the formations as shown in Figure 14. The arrow F indicates the direction of the force which will be experienced by the striking implement, whether it be a cricket bat or tennis racket, during use. Thus the web 19 resists the opening of the fingers 17 and 18 which would otherwise occur during use of the striking implement.