Abstract
The invention relates to a method of manufacturing an elongated article having a shaft and a functional head section. The method includes the steps of providing a dimensionally stable core mandrel; overlaying first reinforcing fibers onto the core mandrel to form one or more first wall parts; providing at least one shaping element to the overlaid core mandrel; overlaying second reinforcing fibers onto the core mandrel and the at least one shaping element to form one or more second wall parts; and providing a matrix material and consolidating the matrix material. The core mandrel is provided to form an elongated article having a well defined inner cavity. Overlaying fibers is preferably performed by in-situ braiding. The cross-section of the elongated article includes fiber reinforced wall parts that impart stiffness to the article. The inner cavity may be filled with weight distributing element(s).
Claims
1.-30. (canceled)
31. A method of manufacturing an elongated curved article having a shaft and a functional head section, the method comprising the steps of: a) providing a dimensionally stable core mandrel, wherein the core mandrel substantially extends from a grip end of the shaft to an outer end of the functional head section; b) overlaying first reinforcing fibers onto the core mandrel to form one or more first wall parts; c) providing at least one shaping element to the overlaid core mandrel; d) overlaying second reinforcing fibers onto the core mandrel and the at least one shaping element to form one or more second wall parts; e) providing a matrix material and consolidating the matrix material; wherein the core mandrel is provided to form an elongated curved article having a well defined inner cavity, wherein the method further comprises f) removing the core mandrel or a part of the core mandrel after step e) to form the inner cavity, wherein the inner cavity substantially extends from a grip end of the shaft to an outer end of the functional head section, and g) providing the inner cavity with at least one weight distributing element of which a cross-sectional dimension is about equal to a cross-sectional dimension of the inner cavity, wherein the at least one weight distributing element has a relatively low stiffness to be able to accommodate a curvature in the elongated article.
32. The method according to claim 31, wherein the core mandrel is provided with at least one shaping element before overlaying the first reinforcing fibers.
33. The method according to claim 31, wherein the core mandrel is provided with an internal part that when removed forms a well defined inner cavity.
34. The method according to claim 31, wherein overlaying with the first and/or second reinforcing fibers is performed by in situ braiding the reinforcing fibers onto the core mandrel or overlaid core mandrel.
35. The method according to claim 34, wherein the in-situ braiding is performed from a grip end of the shaft to an outer end of the functional head section and/or vice versa.
36. The method according to claim 31, wherein the core mandrel has a constant cross-section along the elongated article.
37. The method according to claim 36, wherein the cross-section of the core mandrel is rectangular.
38. The method according to claim 31, wherein the functional head section of the elongated article comprises a contacting surface, and a first wall part extends perpendicular to said contacting surface.
39. The method according to claim 31, wherein weight distributing elements are interconnected to form a string of interconnected weight distributing elements.
40. The method according to claim 31, wherein a cross-sectional dimension of the at least one weight distributing element is about equal to a cross-sectional dimension of the inner cavity.
41. The method according to claim 40, wherein the cross-section of the at least one weight distributing element is about equal to the cross-section of the inner cavity.
42. The method according to claim 31, wherein the weight distributing elements in the string are interconnected through a hook-like connection.
43. The method according to claim 42, wherein the hook-like connection is obtained by interlocking cantilevered end sections of adjacent weight distributing elements.
44. The method according to claim 31, wherein a part of the at least one weight distributing element is slightly oversized with respect to the cross-section of the inner cavity.
45. The method according to claim 31, wherein the at least one weight distributing element extends from a grip end of the shaft to an outer end of the functional head section.
46. The method according to claim 31, wherein weight distributing elements with a different density and/or shape are provided in the inner cavity.
47. The method according to claim 31, wherein the at least one weight distributing element comprises a stack of lamellae.
48. The method according to claim 31, wherein the matrix material comprises a thermosetting resin that is consolidated by curing.
49. The method according to claim 31, wherein the matrix material comprises a thermoplastic polymer that is consolidated by cooling.
50. The method according to claim 31, wherein the elongated article comprises a field hockey stick, an ice hockey stick or a cricket stick, preferably a field hockey stick.
51. An elongated curved article, obtainable by a method according to claim 31, comprising a shaft and a functional head section, and a well defined inner cavity, wherein the inner cavity substantially extends from a grip end of the shaft to an outer end of the functional head section, and wherein the inner cavity is provided with at least one weight distributing element of which a cross-sectional dimension is about equal to a cross-sectional dimension of the inner cavity, wherein the at least one weight distributing element has a relatively low stiffness to be able to accommodate a curvature in the elongated article, and wherein dimensions of the inner cavity do not deviate between cross-sections of the elongated article by more than 10%, more preferably by more than 5%, and most preferably by more than 2%.
52. The elongated curved article according to claim 51, wherein the elongated article comprises a field hockey stick, an ice hockey stick or a cricket stick.
53. The elongated curved article according to claim 52, wherein the elongated article comprises a field hockey stick.
Description
BRIEF DESCRIPTION OF THE FIGURES
[0043] The invention will now be described in more detail by reference to the accompanying figures and a description of specific embodiments, without however being limited thereto. In the figures:
[0044] FIGS. 1A-1F schematically show a number of steps of the method of manufacturing a hockey article in accordance with an embodiment of the invention;
[0045] FIG. 2 schematically shows a perspective view of a braiding device to be used in an embodiment of the present invention;
[0046] FIGS. 3A-3E schematically show a number of steps of the method of manufacturing a hockey article in accordance with another embodiment of the invention;
[0047] FIGS. 4A-4D schematically show a number of steps of a method to obtain a reinforced shaping element in accordance with the invention;
[0048] FIGS. 5A-5D schematically show a perspective view of weight distributing elements in accordance with embodiments of the invention;
[0049] FIG. 6 schematically shows a perspective view of a weight distributing system in accordance with an embodiment of the invention; and
[0050] FIG. 7 schematically shows a perspective view of the weight distributing system of FIG. 6 in a shape that conforms to the shape of a core mandrel 1, or inner cavity in which the string is received.
DETAILED DESCRIPTION OF EMBODIMENTS
[0051] With reference to FIGS. 1A-1F an embodiment of the method according to the invention is shown, in particular for manufacturing a field hockey stick 10. The field hockey stick 10 shown in FIG. 1F comprises a shaft 20 and a curled head section 30. The head section 30 is configured to hit a hockey ball, for which purpose the head section 30 is provided at one side with a relatively flat hitting surface 30a, as shown in FIG. 1F. The opposite (or backhand side) side usually comprises a curved surface 30b. The hockey stick 10 is at a non-hitting end of the shaft 20 provided with a grip section 20a, which is for comfort provided with a wrapped tape and optionally a foamed grip.
[0052] In a first step of the manufacturing method, shown in FIG. 1A, a dimensionally stable core mandrel 1 is provided in the form of a high density polyethylene (HDPE) or POM polymer rod with a constant cross-section along the length direction 40 of the field hockey stick 10. Although the core mandrel 1 may be provided with a well defined inner cavity, the embodiment shown employs a solid core mandrel 1. The cross-section of the core mandrel 1 is rectangular and defines an upper surface 11, a lower surface 12, and two side surfaces (13a, 13b). The core mandrel 1 substantially extends from the grip end 20a of the shaft 20 to an outer end 31 of the head section 30, and is therefore provided with a curled section 14 that corresponds to the curled head section 30 of the hockey stick 10. In order to define a well defined inner cavity of the field hockey stick 10, the core mandrel 1 has well defined outer surfaces (11, 12,13a, 13b). The cross-dimensions of the core mandrel 1 thereto do not deviate between cross-sections of the mandrel 1 by more than 10%, more preferably by more than 5%, and most preferably by more than 2%.
[0053] In a next step of the method, the core mandrel 1 is provided with two shaping elements (2a, 2b), as shown in FIG. 1A in exploded view and in FIG. 1B in assembled view, to form an intermediate product 16. Shaping element 2a is provided in contact with upper surface 11 and extends in the length direction 40 of the field hockey stick 10 along substantially its complete length, i.e. from the grip section 20a to about the outer end 31 of the head section 30. Shaping element 2b is provided in contact with lower surface 12, extends in the length direction 40 of the field hockey stick 10 along a part of the length only, and is tapered down in the direction of the head section 30. As shown in FIG. 1C, the shaping element 2a forms a capped end portion 2a-1 of the core mandrel 1. The shaping elements (2a, 2b) in the embodiment shown comprise polyurethane foam elements that have been foamed in-situ. They may also be foamed prior to molding and milled or cut into the desired shape.
[0054] FIG. 1D shows another step of the method in which the assembly of core mandrel 1 and shaping elements (2a, 2b) is overlaid with first reinforcing fibers to form an intermediate product 15 having first wall parts (31, 32, 33a, 33b). Overlaying is conveniently performed by in-situ braiding, as will be described further below. The first wall parts comprise an upper wall part 31, a lower wall part 32, and two side wall parts (33a, 33b), but form a continuous structure around core mandrel 1 and shaping parts (2a, 2b).
[0055] FIG. 1E shows yet another step of the method in which the overlaid structure 15 of FIG. 1D is provided with additional shaping elements (4a, 4b), as shown in FIG. 1E in exploded view. Shaping element 4a is provided in contact with the left hand first wall part 33a and extends in the length direction 40 of the field hockey stick 10 along substantially its complete length, i.e. from the grip section 20a to about the outer end 31 of the head section 30. Shaping element 4b is provided in contact with the right hand side first wall part 33b, and also extends in the length direction 40 of the field hockey stick 10 along substantially its complete length. As shown in the cross-sections of FIG. 1F, the shaping elements (4a, 4b) are applied at both sides of the overlaid structure 15 in contact with side wall parts (33a, 33b), and leave the upper and lower first wall parts (31, 32) uncovered. The shaping elements (4a, 4b) may also comprise polyurethane foam elements for instance.
[0056] FIG. 1F shows yet another step of the method in which the assembly of core mandrel 1 and shaping elements (2a, 2b, 4a, 4b) is overlaid with second reinforcing fibers to form a product 10, having second continuous wall part 41, again conveniently formed by in-situ braiding of reinforcing fibers, such as carbon or graphite fibers for instance. The second wall part 41 comprises a relatively flat lower wall part 41-1 that is in immediate contact with lower first wall part 32 to form a stiff and elastic hitting surface 30a. The wording elastic here means that only a minor amount of energy, or nil, is dissipated. The stiffness of the hitting surface 30a is also provided by first wall parts (33a, 33b) that extend perpendicular to said hitting surface 30a.
[0057] In a further step of the method, a matrix material such as an epoxy resin is provided to the assembly and cured at a pressure and temperature level in accordance with the suppliers instructions. Typical pressures may range from 1 bar to more than 7 bar, whereas typical temperatures may range from room temperature up to 175 C. and more. The material of the core mandrel 1 is selected such that its dimensions do not substantially change at the pressure and temperature levels used in the method.
[0058] In another step of the method the core mandrel 1 is finally removed from the formed hockey stick 10. Removal can be performed by sliding the core mandrel 1 out of the hockey stick 10 through an opening at the grip end section 20 for instance. A hockey stick 10 is now formed having a well defined inner cavity with internal dimensions that conform to the outer dimensions of the removed core mandrel 1. In the embodiment shown in FIGS. 1A to 1F, the shaping elements (2a, 2b, 4a, 4b) remain in the manufactured field hockey stick 10. In other embodiments, some of the shaping elements (2a, 2b, 4a, 4b) may be removed from the hockey stick 10, for instance shaping element 2b, in order to save additional weight.
[0059] In useful embodiments of the method according to the invention, overlaying with the first and/or second reinforcing fibers is performed by in situ braiding the reinforcing fibers onto the core mandrel 1, optionally supplemented with shaping elements (2a, 2b, 4a, 4b).
[0060] With reference to FIG. 2, a useful device 5 for braiding the first and/or second reinforcing fibers (not shown) onto core mandrels 1 (or intermediate products 15-17, or product 10) to obtain a braided field hockey stick 20 is shown. Other devices may also be used. Device 5 comprises a braiding machine 51 with a track plate 53 that carries a number of fiber bobbin carriers 54, provided with reinforcing fibers, and a forming ring 52, attached to the track plate 53. The braiding machine 51 encloses a looped braiding mandrel, comprising a number of core mandrels 1, intermediate products (15-17) or products 10, positioned in series, and is adapted to braid layers of reinforcing fibers around the braided mandrel. A fully overlaid core mandrel 1 corresponds to a hockey stick 10. Positioning means in the form of a robot 55 effectuate relative movement of the mandrel and the braiding machine 51 during braiding. The robot 55 essentially consists of a turntable 56 around which a pivoting arm 57 can be rotated. Pivoting arm 57 is at an end thereof provided with gripping means 58 that act upon the braiding machine 51. The robot 55 is connected to a computer (not shown), which contains the data to steer the robot 55, in particular pivoting arm 57 and gripping means 58 along any desirable path. The looped mandrel formed by mandrels (1, 15-17, or 10) positioned in series is held in a stationary position by support poles 59 provided with gripping means. The braiding machine 51 is manipulated by the robot 55 about the mandrel along a path, determined by the computer, while simultaneously rotating the bobbins 54 around a central axis of the track plate 53 and forming ring 52. In this way a plurality of reinforcing fibers is positioned onto the mandrel to produce several fiber layers that form a continuous looped braided structure. In order for the braiding machine 51 to pass a support pole 59, support poles 59 may be temporarily placed in a tilted position, as shown in FIG. 2 by pole 59a.
[0061] In an exemplary embodiment, the mandrel formed by the series of mandrels (1, 15-17 or 10) is braided with high strength carbon fibers. The multilayered fibrous braided structures thus created form the first (31, 32, 33a, 33b) and second (41, 41-1) wall parts of the hockey stick 10. The braided structures extend from a grip end of the shaft of each mandrel (1, 15-17 or 10) to an outer end of the head section of each mandrel (1, 15-17 or 10) and form a continuous looped structure. The braided structures are then divided to form separate hockey sticks 10 and impregnated with a matrix material and consolidated.
[0062] With reference to FIGS. 3A-3E another embodiment of the method for manufacturing a field hockey stick 10 according to the invention is shown.
[0063] In a first step of the manufacturing method, shown in FIGS. 3A and 3B, a dimensionally stable solid core mandrel 1 is provided. The high density polyethylene (HDPE) or POM polymer rod has a constant cross-section along the length direction 40 of the field hockey stick 10. The cross-section of the core mandrel 1 is rectangular and defines an upper surface 11, a lower surface 12, and two side surfaces (13a, 13b). The core mandrel 1 substantially extends from the grip end 20a of the shaft 20 to an outer end 31 of the head section 30, and is provided with a curled section 14 that corresponds to the curled head section 30 of the hockey stick 10. In order to define a well defined inner cavity of the field hockey stick 10, the core mandrel 1 has well defined outer surfaces (11, 12,13a, 13b). The cross-dimensions of the core mandrel 1 thereto do not deviate between cross-sections of the mandrel 1 by more than 10%, more preferably by more than 5% and most preferably by more than 2%.
[0064] FIG. 3C shows a next step of the present embodiment in which the core mandrel 1 of FIGS. (3A, 3B) is overlaid with first reinforcing fibers to form first wall parts (61, 62, 63a, 63b), which is conveniently performed by in-situ braiding, as was described above. The first wall parts comprise an upper wall part 61, a lower wall part 62, and two side wall parts (63a, 63b), but form a continuous structure around the core mandrel 1.
[0065] FIG. 3D shows yet another step of the present embodiment in which the overlaid structure 15 of FIG. 3C is provided with a shaping element 6, as shown in FIG. 3D in exploded view to form an intermediate product 17. Shaping element 6 is at the grip end section 20a provided around the overlaid structure 15 in contact with the left hand first wall part 63a, the right hand first wall part 63b, the upper first wall part 61 and the lower first wall part 62, and extends in the length direction 40 of the field hockey stick 10 along substantially its complete length, i.e. from the grip section 20a to about the outer end 31 of the head section 30. Shaping element 6 at the outer end 31 is provided in contact with the side wall parts (63a, 63b) and the upper wall part 61 only. The shaping element 6 may comprise a polyurethane foam for instance.
[0066] FIG. 3E shows yet another step of this embodiment in which the intermediate product 17 (the assembly of core mandrel 1 and shaping element 6) is overlaid with second reinforcing fibers to form a second continuous wall part 71, again conveniently formed by in-situ braiding of reinforcing fibers, such as carbon or graphite fibers for instance. The second wall part 71 comprises a relatively flat lower wall part 71-1 that is in immediate contact with lower first wall part 62 to form a stiff and elastic hitting surface 30a.
[0067] As already described above, further steps of the method comprise providing and consolidating a matrix material and removal of the core mandrel 1 from the formed hockey stick 10. A hockey stick 10 is again formed having a well defined inner cavity with internal dimensions that conform to the outer dimensions of the removed core mandrel 1. In the embodiment shown in FIGS. 3A to 3E, the shaping element 6 remains in the manufactured field hockey stick 10, but it may also be removed from the hockey stick 10 to save additional weight.
[0068] FIGS. 4A-4D shows the possibility of adding local reinforcements to a shaping element 8 and/or to a shaping element provided on a (partly overlaid) core mandrel. FIG. 4A shows a shaping element 8, a section 81 of which is reduced in dimensions, for instance by rejuvenating. The cross-section of the shaping element 8 changes along the length of the hockey stick 10, as appears from cross-sections A-A and B-B of FIG. 4C.
[0069] As shown in FIG. 4C, the reduced dimension part 81 of the shaping element 8 is overlaid with reinforcing fibers to form a wall part 82 around the reduced dimension part 81 of the shaping element 8. As shown in FIG. 4D, the thickness of the wall part 82 is built up to conform with those parts of the shaping element 8 that were not reduced in dimension. The resulting, locally reinforced shaping element 8 of FIG. 4D may then be used in the method according to the invention, as described above in the context of the embodiments shown in FIGS. 1A-1F and 3A-3E. In the present example, the reinforced shaping element 8 of FIG. 4D may for instance be used as shaping element 4a of FIG. 1E and/or shaping element 6 of FIG. 3D.
[0070] With reference to FIGS. 5A-5D and FIGS. 6 and 7, a weight distributing system 9 in accordance with another aspect of the invention is shown. The weight distributing system 9 comprises a string of interconnected weight distributing elements 90, of which several embodiments are shown in FIGS. 5A-5D. The weight distributing system 9 is adapted to be provided in the well defined inner cavity of the hockey stick 10, which inner cavity corresponds dimensionally with the removed core mandrel 1, as shown in FIG. 7, or with an inner cavity of a hollow core mandrel 1. The string 9 of weight distributing elements 90 in the embodiment shown in FIGS. 6 and 7 extends from the grip end 20a of the shaft 20 to an outer end 31 of the head section 30.
[0071] The weight distributing elements 90 in the string 9 are interconnected through a hook-like connection, which, in the embodiments shown in FIGS. 5A-5D comprise first cantilevered end sections (91a, 91b) provided at one end side of a weight distributing element 90 and second cantilevered end sections (92a, 92b) provided at another end side of said weight distributing element 90. The cantilevered end sections (91b, 92b) are each provided with an upstanding end ridge of lip 93 by which two end sections (91b, 92b) may be interlocked to form a string 9, as shown in FIG. 7 for instance. The interlock allows the string 9 to be provided in the inner cavity of the hockey stick 10, but also to pull the string out of the inner cavity without the need for a separate carrier for the weight distributing elements 90.
[0072] The cross-sectional dimensions of the weight distributing elements 90 is about equal to a cross-sectional dimension of the inner cavity (or of the core mandrel 1) to avoid any noise generation and/or vibrations when handling the stick 10. As shown in FIGS. 5A-5D, a part 94 of the weight distributing element 90, in particular a part 94 of the cantilevered end sections (91a, 92b), is slightly oversized with respect to the cross-section of the inner cavity. The cantilevered end sections (91a, 92b) in this embodiment act as resilient pressurizing elements that keep the elements 90 in position within the inner cavity.
[0073] As shown in the embodiments of FIGS. 5C and 5D, weight distributing elements 90 may be provided comprising a stack of lamellae 95. Such elements 90 are provided at an end of the string 9 (see FIG. 6) and readily conform to the rather large curvature, encountered in the curl-shaped head section 31 of a field hockey stick 10 by mutual shearing of the lamellae 95 in the inner cavity. The embodiment shown in FIG. 5D uses a weight distributing element 90 in which the lamellae 95 originate from a common solid part 96 of the element 90. This effectively holds the lamellae 95 together.
[0074] Weight distributing elements 90 with a different density and/or shape may also be provided in the string 9, for instance by providing the elements 90 with holes 97, as shown in FIG. 5B.
[0075] The method according to the invention allows to produce a sport stick or other elongated article having a well defined inner cavity that, in a preferred embodiment, substantially extends from the grip end of the shaft to the outer end of the head section of the sport stick, and allows to accept the string 9 of weight distributing elements 90.
[0076] The sport stick thereto preferably has dimensions of the inner cavity thereof that do not deviate between cross-sections of the sport stick by more than 10%, more preferably by more than 5%, and most preferably by more than 2%.
[0077] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
