FIBER REINFORCED BRAIDED SKI CORE AND METHOD AND APPARATUS FOR MAKING SAME

Abstract: A wrapped core for a ski has a longitudinal core (24) and a first set of continuous strands of fiber (18) braided directly thereon. The first set of strands (18) is helically wrapped about the core (24) and biased at angles with respect to the longitudinal dimension of the core (24). A second set of longitudinally extending strands of fiber reinforcement (46) may be intertwined with the first set of braided stands (18) and a further third set of strands of fiberglass (52), or other suitable material, may be fed onto either or both the top and bottom surfaces of the core (24), prior to braiding, such that the longitudinal strands (52) are captured and held by the overlying braid. This provides a wrapped core for a ski which makes efficient use of the high tensile strength characteristics of fiberglass and produces a uniform, lightweight ski having pre-selected torsional and longitudinal flex characteristics.

Description: The present invention relates to a wrapped ski core and a method and apparatus for manufacture thereof. More particularly, the present invention relates to a wrapped ski core of the kind having a longitudinal core and a plurality of continuous strands of a first set of fibres helically surrounding said core and braided thereon to conform to the surface of the core, the braided strands of the first set of fibres being biased at an angle with respect to the longitudinal dimension of the core, and an example of such a ski core is seen in published abstract JP-A-51 135725. In the past, "wet wrap" or "torsion box" skis have typically been formed by impregnating a sheet of unidirectional fiberglass with epoxy resin. The core and any other internal components of the ski, such as fiberglass mat or a bias-ply precured fiberglass strip, are placed in the center of the unidirectional glass, again with resin applied. The unidirectinal glass is then wrapped tightly around the core on all four sides. This unit is then placed in a mold, the base assembly set on top, and the mold closed. The unit is "cooked" under fairly high pressure for a period of time and, after the cure cycle, is removed from the mold. At this point, the ski is basically complete structurally and the rest of the production process is devoted to sanding, topping, finishing and other cosmetic operations. Ski cores have typically been wrapped or "laid up" by hand and this is a labor intensive and time-consuming process. It is known that unidirectional fiberglass is a material of great longitudinal tensile strength but little lateral strength. Thus, the torsional rigidity of skis was typically increased through the addition of randomly oriented fiberglass mat or angularly biased, precured fiberglass strips to the "sock" unit prior to wrapping. The longitudinally oriented unidirectional fiberglass imparted longitudinal rigidity to the ski. It is known that the orientation of fiberglass at a 45 degree angle to the longitudinal dimension of the ski core imparts the highest torsional rigidity to the ski. Of necessity, the use of a randomly oriented mat to increase torsional rigidity also resulted in unnecessarily increasing ski weight and expense since only a small percentage of the mat fibers were oriented at angles which enhanced torsional stiffness. The placement of 45 degree biased, precured fiberglass strips in the "sock" was an improvement in that it represented a more effective use of the strength characteristics of fiberglass in controlling torsional rigidity, but was undesirable in that it required additional lay-up and curing steps for the strips themselves. Further, the biased fiberglass was not wrapped around the core and thus did not obtain the benefits of strength and durability provided thereby. Another problem of the prior construction technique was that variations in lay-up from ski-to-ski created differences in torsional and longitudinal rigidity, thus making it difficult to produce a truly matched pair of skis. Further the known wrap process involves wrapping a rectangular sheet of fiberglass around the ski core which has a varying cross section along its length. This creates a large overlap of the sheet at the narrow waist of the ski and a small overlap at the wide tip. This adversely affects molded tolerances in the ski. The problems of hand lay-up have been attempted to be overcome in the past through the use of prebraided bias fiberglass socks which were slipped over a ski core prior to resin impregnation. Such socks were formed of multiple strands of fiberglass oriented at angles with respect to each other such that when the finished sock was slipped over the ski core, the strands were also oriented at angles, preferably 45 degree angles, to the ski core. Such prebraided fiberglass socks were difficult to use in that the braid tended to become loosened and unbraided while being slipped onto the ski core. In addition, the sock invariably fit loosely upon the ski core, thus creating difficulties in manufacture as well as quality control. The technique was also labor intensive and inflexible in design and still required premade contoured strips of longitudinal fiberglass. Prebraided fiberglass socks including longitudinally extending strands of fiberglass, as well as the angularly biased strands, were successful in overcoming the tendency of the solely angularly biased strand prebraided socks to become unbraided. Such three strand socks, however, had such little ability to expand that it was extremely difficult to slip them onto a ski core and they could not be effectively used in a production process. The present invention aims to provide a ski core which is an improvement over known ski cores of the kind defined and the invention is characterised in that a second set of strands of fibre aligned with the longitudinal dimension of the core are interwoven with said strands of the first set of fibres. The invention also provides a method of wrapping a ski core comprising steps of: causing relative longitudinal movement along a path through a braiding machine between a core and the machine, braiding continuous strands of a first set of reinforcing fibres about the core from the leading end of the core to the trailing end such that said strands are angularly oriented with respect to the length of the core, and maintaining tension on said strands during braiding, characterised by the further step of positioning a second set of strands of reinforcing fibre longitudinally along at least one of the top and bottom surfaces of the core and intertwining said strands of the second set of fibres with said strands of the first set of fibres. The invention further provides apparatus for wrapping a core for a ski, comprising translating means for causing relative longitudinal movement along a path through a braiding machine between a core and the machine, means for wrapping a first set of continuous strands of reinforcing fibre about the core as there is relative movement between the core and the machine along said path, and first guide means for forming said first set of fibres into a braided pattern on the core with the fibres arranged at biaxial directions to the length of the core, characterised in that said apparatus comprises second guide means operable in conjunction with said first guide means for positioning a second set of strands of reinforcing fibre longitudinally along at least one of the top and bottom sides of the core and intertwining the strands of the second set of fibres with the strands of the first set of fibres. The present invention makes possible a lighter and yet stronger ski in that the use of randomly oriented fiberglass is eliminated and all strands which are used are either oriented longitudinally or at preselected angles such that the best use can be made of their tensile strength characteristics. The amount of fiberglass braided onto the ski core, as well as the angle of the braided fiberglass strands with respect to the ski core, can be varied by increasing or decreasing the speed of movement of the ski core through the braiding machine or the speed of the braiding machine itself. The equipment may be operated to allow the angle of the braided fiberglass strands with respect to the longitudinal dimension of the ski core to be varied along the ski core to separately control the torsional rigidity characteristics of the shovel or tail of a ski as desired. Braiding of the fiberglass onto the ski core under slight tension prevents unbraiding and holds the orientation of the fiberglass with respect to the ski after it is removed from the braiding machine and prior to its impregnation with epoxy and placement into a mold. The details of a typical embodiment of the present invention will be described in connection with the accompanying drawings in which: Figure 1 is a side elevation view of one embodiment of an apparatus for producing a wrapped core of the present invention; Figure 2 is a partial perspective view of the apparatus of Figure 1; Figure 3 is an enlarged partial perspective view of the braiding nip portion of the apparatus of Figure 1; Figure 4 is a side elevation view of the braiding nip portion of the apparatus of Figure 1; Figure 5 is a sectional view taken along lines 5-5 of Figure 4; Figure 6 is a top, plan view of the apparatus of Figure 4; Figure 7 is a plan view of a portion of a ski core showing angularly biased braid positioned thereon; Figure 8 is a top, plan view of a portion of a ski core showing angularly biased braid including longitudinally extending fibers intertwined therewith; Figure 9 is a plan view of a portion of a ski core showing angularly biased braid overlying longitudinally extending fibers positioned on the top surface of a ski core; and FIGURE 10 is a plan view of a portion of a ski core showing angularly biased braid including intertwined longitudinally extending fibers overlying longitudinally extending fibers positioned on the top surface of a ski core. FIGURE 1 illustrates an apparatus 10 made according to the present invention for producing a wrapped ski core. The apparatus includes a conventional braiding machine indicated generally at 12 for producing tubular braid. Such machines are commonly known as "maypole" braiders, and one source for such a machine is Mossberg Industries, Inc., 160 Bear Hill Road, Cumberland, Rhode Island 02864. As is best seen in FIGURE 2, the braiding machine includes a plurality of spools 14 positioned on a circular peripheral track 16. The spools carry strands of fiberglass and are adapted to move over and under each other as they travel around the periphery of the track 16. The strands of fiberglass 18 extending from the spools are directed through a guide ring 20 to a braiding nip area 22 where the movement of the spools causes the strands of yarn to be wrapped in opposing helixes to produce a braid about a ski core 24 passing longitudinally through guide 20. As illustrated, the strands of yarn initially pass over a larger outer guide ring 26, whose purpose, like that of guide ring 20, is to guide and direct the strands of fiberglass such that they are directed to the braiding nip at similar angles to allow braiding to easily occur. Referring again to FIGURE 1, it will be seen that horizontal and vertical guide rollers 28 and 30 are positioned immediately adjacent the braiding nip area to guide the braid covered ski core from the braiding knit to the haul-off apparatus 32. Haul-off apparatus 32 comprises a pair of endless belts 34 running around the pairs of rollers 36 and 38. Rollers 38 are rotatably driven. At least one pair of rollers 36 and 38 are also mounted on pneumatic cylinders or the like to allow the pairs of cylinders and overlying belts 34 to be moved toward each other to press against and grip the braid covered ski core to haul it through the braiding machine. A conventional cutting mechanism 40 is positioned outwardly of haul-off 32 to separate braid covered cores from each other. The location of the cut-off mechanism outward of the haul-off apparatus 32 and rollers 28 and 30 allow the braiding machine to braid on a continual basis by maintaining tension in the strands running from the bobbins on the braiding machine. The tension at which the strands are removed from the spools for braiding is about 5N (about .25 pounds) but may be any reasonably larger or smaller number so long as the machine braids effectively and the orientation of the strands on the core is maintained. Operation of the braiding machine 12 to braid angularly biased strands of fiberglass about ski core 24 produces a ski core covered in angularly biased braid, such as that shown in FIGURE 7. The fiberglass strands may be oriented at a variety of angles with respect to the longitudinal direction of the ski core with it being understood that maximum torsional stiffness occurs when the braid fibers are oriented at a 45 degree angle to the ski core. It will be understood that the thickness or thinness of the foamed plastic or wooden core over which the braid is laid grossly controls both the longitudinal and torsional flex of a ski at any point along its length. The thinner a ski core at any point, the less stiff it is. The ability to control the angle at which the braided fibers are placed on the ski by the apparatus of the present invention allows, for the first time, separate control of the longitudinal and torsional flex characteristics of a ski. For example, as the speed of movement of a ski core through the braiding machine 12 is increased, the angle at which the knitted fibers are laid on the ski core with respect to the longitudinal dimension of the ski core is lowered, i.e., the braided strands move toward longitudinal alignment with the ski core and, thus, the longitudinal stiffness of the ski increases while the torsional rigidity is reduced. Such independent control of these two flex characteristics was not possible by simply making the ski core thinner or thicker. Referring again to FIGURE 1, it will be seen that rack 42 holding a plurality of spools 44 of fiberglass roving is also disclosed. Fiberglass strands 46, which are drawn from each of the spools 44, are directed over guide ring 48 through openings 51 in circular track 16 of the braiding machine 12 (FIGURE 2), over circular guide ring 26, through circular guide ring 20 and into the braiding nip area 22. It will be understood that the openings 51 on track 16 of the braiding machine do not move and, thus, strands 46 are not truly braided in braiding nip 22, but rather are merely intertwined with braided strands 18. Fiberglass strands 46, while intertwined with strands 18, maintain their longitudinal direction along the ski core 24 and, thus, add to the longitudinal stiffness of the completed ski. Referring to FIGURE 8, the longitudinal strands 46 are shown intertwined with the angularly biased braided strands 18. This three-strand fiberglass sock is tightly woven onto the ski core and conforms closely to its outer dimensions. It will be understood that the braided strands 18 of the three-strand braided sock of FIGURE 8 may still be varied in angular orientation by speeding or slowing the movement of the ski core through the braiding machine, or the speeding or slowing of the braiding machine itself. Referring again to FIGURE 1, it will be noted that racks 42 hold other spools 50 of fiberglass material, the strands 52 of which are led to fiber guide 54 which is best shown in FIGURES 3 and 4. Fiber guide 54 includes a strand receiving screen 56 comprising a metal plate having a plurality of holes 57 positioned above and below opening 58 through which ski core 24 passes. Holes 57 direct strands 52 toward springs 60 positioned above and below the ski core near the opposite end of fiber guide 54. As best shown in FIGURE 5, springs 60 are end mounted in vertically oriented posts 66 and spiral about pins 62, which may be conventional bolts and nuts which are, in turn, mounted in openings 64 in posts 66. Fiberglass strands 52 are locked in springs 60 by removing pins 62 therefrom, pulling the fiberglass upwardly or downwardly through springs 60 and then reinserting locking pins 62. As shown in FIGURE 5, fiber strands 52 are then locked between springs 60 and pins 62. Strands 52 then extend through guide ring 20 and onto the top and bottom surfaces of the ski core in nip area 22 where they are covered and held by braided strands 18 and intertwined longitudinal strands 46. It will be understood that strands 52 may be formed of fiberglass similar to longitudinal strands 46, or may be fiberglass roving, or any other material having a characteristic useful in ski manufacture such as carbon, kevlar, polyester, metal wire or the like. It will also be understood that unequal amounts of fiber material may be deposited on the top or bottom surface of the ski core as desired by varying the number of spools of material feeding fiber strands to the upper or lower guide holes 57 of plate 56. While only a pair of spools have been shown feeding strands of material to the fiber guide in FIGURE 1, it will be understood that many more spools will actually be used during ski production. Referring additionally to FIGURE 6, it will be seen that vertical posts 66 are mounted on pivoting arms 68. The distal ends of arms 68 are mounted upon pivotal vertical shafts 70 which extend downwardly through fiber guide support plate 72. Meshing toothed gears 74 are fixedly mounted to the bottom of each shaft 70 such that the angular rotation of one shaft 70 caused by the inward or outward movement of the distal end of arms 68 as a ski core 24 moves therebetween is equally imparted to the other shaft 70 through gears 74. A conventional cylinder and piston arrangement 76 is mounted to the periphery of one of the toothed gears 74 to angularly bias the gear, interconnected arms 68 and posts 66 against the lateral side of ski core 24. In this way, as the width of the ski core narrows or widens as it passes between posts 66, arms 68 are continuously biased against the sides of the ski core and move inwardly and outwardly therewith. Since, as best shown in FIGURE 5, the ends of springs 60 are fixedly mounted in posts 66, the lateral movement of posts 66 as a ski core of varying width passes therebetween causes springs 60 to flex inwardly and outwardly. Since fiberglass strands 52 are captured beneath the turns of springs 60, the strands are also moved inwardly and outwardly as springs 60 flex and, in this way, fiberglass strands 52 are variably spaced or contoured with respect to the upper and lower surfaces of ski core 24 on which they are deposited as the width of the ski core varies. As is best shown in FIGURE 4, upper and lower guide rollers 78 are also mounted on the arms 68 of fiber guide 54 and at least the upper roller is biased downwardly against the top of ski core 24 by means of a conventional spring 80 mounted on the side of arm 68. Referring to FIGURE 9, strands of longitudinal material positioned on the top surface of ski core 24 and captured by angularly biased braid 18 are disclosed. Referring to FIGURE 10, longitudinally extending strands 52 extending beneath and captured by angularly biased strands 18 and intertwined longitudinally extending strands 46 are disclosed. It will be understood that any of the braided fiberglass covered ski core constructions shown in FIGURES 7-10 are considered to be novel products of the present invention. These fibers are braided and placed directly on a moving ski core in a continuous fashion to produce structures having improved characteristics not heretofore available in the art. The above-described apparatus and the method of manufacturing these and other unique braided ski cores are also considered to be novel features of this invention. It is contemplated that varying the speed of movement of a ski core through the braiding machine, or varying the speed of the braiding machine as a ski core moves therethrough, will allow the impartation of differing flex patterns along the length of a single ski core. It is also contemplated that the speed of travel of the ski core or the speed of the braiding machine may be automatically controlled in a known manner to allow ski cores of a preselected flex pattern to be repeatedly and uniformly produced.

Claims: A wrapped ski core of the kind having a longitudinal core (24) and a plurality of continuous strands of a first set (18) of fibres helically surrounding said core and braided thereon to conform to the surface of the core, the braided strands of the first set of fibres being biased at an angle with respect to the longitudinal dimension of the core, characterised in that a second set (46) of strands of fibre aligned with the longitudinal dimension of the core (24) are interwoven with said strands of the first set (18) of fibres. A wrapped ski core as claimed in Claim 1 further including a plurality of longitudinally extending strands of a third set (52) of fibres positioned on at least one of the top and bottom surfaces of the core (24) beneath said strands of the first (18) and second (46) sets of fibres. A wrapped ski core as claimed in Claim 2, wherein the number of strands of the third set (52) of fibres is varied to alter the flexibility or stiffness of the ski. A wrapped ski core as claimed in Claim 2 or Claim 3, wherein the strands of the third set (52) of fibres are formed from material selected from the group consisting of fiberglass, carbon, Kevlar and polyester. A wrapped ski core as claimed in Claim 3 or Claim 4, wherein the strands of the third set (52) of fibres are laterally spaced from each other at greater or smaller distances corresponding to the width of the core (24). A wrapped ski core as claimed in any preceding Claim, wherein the strands of the first (18) and second (46) sets of fibres are disposed in a triaxial pattern on the core (24) along two axial directions extending diagonally to the length of the core, and the third axial direction extending along the length of the core. A wrapped ski core as claimed in any preceding Claim, wherein the strands of the second set (46) of fibres are positioned on at least one of the top and bottom surfaces of the core (24). A wrapped ski core as claimed in any preceding Claim, wherein the number of the strands of the second set (46) of fibres is altered to vary the flexiblity or stiffness of the ski. A wrapped ski core as claimed in any preceding Claim, wherein the strands of the second set (46) of fibres are formed of material selected from the group consisting of fibreglass, carbon, Kevlar and polyester. A wrapped ski core as claimed in any preceding Claim, wherein the angle of said strands of the first set (18) of fibres with said longitudinal dimension of the core (24) is changed along the length of the core to vary the torsional and longitudinal stiffness of the ski along its length. A method of wrapping a ski core comprising steps of: causing relative longitudinal movement along a path through a braiding machine (12) between a core (24) and the machine, braiding continuous strands of a first set (18) of reinforcing fibres about the core from the leading end of the core to the trailing end such that said strands are angularly oriented with respect to the length of the core, and maintaining tension on said strands during braiding, characterised by the further step of positioning a second set (46) of strands of reinforcing fibre longitudinally along at least one of the top and bottom surfaces of the core (24) and intertwining said strands of the second set of fibres with said strands of the first set (18) of fibres. A method as claimed in Claim 11, wherein the strands of the first (18) and second (46) sets of fibres are disposed in a triaxial pattern on the core (24) along two axial directions extending diagonally to the length of the core, and a third axial direction extending along the length of the core. A method as claimed in Claim 11 or Claim 12, further including the step of feeding a third set (52) of strands of reinforcing fibre along at least one of the top and bottom surfaces of the core (24) as the strands of the first (18) and second (46) sets of fibres are braided and intertwined thereon to capture and hold the strands of the third set of fibres beneath the strands of the first and second sets of fibres. A method as claimed in Claim 13, further including the step of contouring the strands of the third set (52) of fibres to the width of the core (24) so that the strands of the third set of fibres are spaced further apart from each other where the width of the core is enlarged, and closer to each other where the width of the core is narrowed. A method as claimed in Claim 13 or 14, further including the step of varying the number of the strands of the third set (52) of fibres to alter the flexibility or stiffness of the ski. A method as claimed in Claim 13, Claim 14 or Claim 15, including the step of selecting the strands of the first (18), second (46) and third (52) sets of fibres from the group of materials consisting of fibreglass, carbon, Kevlar and polyester. A method of wrapping a ski core as claimed in any of Claims 11 to 16 and comprising the further step of varying the angle of orientation of the strands of the first set (18) of fibres with respect to the core (24) along the length of the core to change the torsional and longitudinal stiffness of a ski incorporating said core along its length. A ski characterised in that it comprises a wrapped ski core as claimed in any one of claims 1 to 10. Apparatus for wrapping a core for a ski, comprising translating means for causing relative longitudinal movement along a path through a braiding machine (12) between a core (24) and the machine, means for wrapping a first set (18) of continuous strands of reinforcing fibre about the core as there is relative movement between the core and the machine along said path, and first guide means for forming said first set of fibres into a braided pattern on the core with the fibres arranged at biaxial directions to the length of the core, characterised in that said apparatus comprises second guide means operable in conjunction with said first guide means for positioning a second set of strands of reinforcing fibre (46) longitudinally along at least one of the top and bottom sides of the core (24) and intertwining the strands of the second set (46) of fibres with the strands of the first set (18) of fibres. Apparatus as claimed in Claim 19 and further comprising means for positioning a third set (52) of strands of reinforcing fibre on at least one of the top and bottom surfaces of the core (24) beneath said strands of the first set (18) of fibres. Apparatus as claimed in Claim 20 wherein said third guide means is operable to vary the spacing of the strands of the third set (52) of fibres laterally relative to the core (24) to correspond to changes in the width of the core. Apparatus as claimed in any of Claims 19 to 21 and including means for varying the angle of the strands of the first set (18) of fibres relative to the length of the core (24). Apparatus as claimed in Claim 22 wherein said angle varying means comprises means for adjusting the speed of relative movement between the core (24) and the machine (12) along said path while the strands of the first set (18) of fibres are being braided thereon.

Inventors: FEZIO, LOUIS J.
Applicants: K-2 CORPORATION
Application year: 1987
Main classification: A63C5
IPC codes: B32B37, B32B5, B29B11, B29C53, A63C5, B29C70, D04C3, D04C1