EP3251730A1 - Ski with lightweight core - Google Patents

Abstract

Ski (1), comprising: A core (10) including longitudinal beams (13, 14, 15) made from corrugated board, € ¢ side edges (20, 21) bordering the core (10), characterized in that it includes at least one stiffening longitudinal member (16, 17) extending over the entire height of the core (10), separating two longitudinal corrugated board-based beams (13, 14, 15), wherein the width 1 of the longitudinal stiffening element (16,17) measured transversely to the mid-point of the shoe is less than that of the longitudinal beams made of corrugated cardboard.

Description

Technical area

The invention relates to the field of snow sliding sports, and more specifically to that of cross-country skiing, or ski touring. It is more particularly a new internal structure of cross-country skiing whose core is constituted so that it has interesting combined performance in terms of weight, strength, and ease and cost of manufacture.

Background of the invention

Conventionally, a cross-country ski has an internal structure that combines upper and lower reinforcement layers, which are separated by a spacer core. This core has the function of maintaining the distance between the reinforcing layers, to impart a certain stiffness in longitudinal bending of the ski. The core also has the function of avoiding crushing the ski and must therefore have some resistance to crushing for forces exerted vertically.

Various structures and materials have already been proposed to ensure these mechanical functions, while limiting the impact of the weight of the core in the overall weight of the ski. Thus, an improved solution is to use a so-called "honeycomb" material having cells whose main axis is oriented vertically, and which are generally filled with the lightest foam possible. By its cellular structure, this material provides crush resistance, and if necessary, the filling foam is chosen a minimum density, to avoid increasing the weight of the ski too much.

This material has the advantage of being quite easily machinable to the shape of the core, which has side faces that are not strictly flat due to the coast line of the ski, which can be more or less hollow, and which has moreover, a thickness that varies considerably over the length of the ski.

The honeycomb material is therefore chosen to provide the strength properties at the level where the mechanical stresses are highest. Insofar as this material is difficult to handle at low thickness, the ski is generally designed so that the core portion of this material extends only a fraction of the length of the ski. In addition, the end portions of the core, finer, are thus made of another material, usually wood, which has lower performance in terms of weight, but is also less expensive.

The construction of this core combining different parts of different nature is a meticulous operation, which requires the assembly of separate parts.

Among the structures employing this type of material, the one described in document FR 2,248,860 , which comprises a ski core combining corrugated cardboard type elements based on cellular structure, embedded in a polymeric foam injected during molding.

Presentation of the invention

One of the objectives of the invention is to obtain a ski that is as light as possible, from a simple manufacturing process, while reducing the cost of the materials used. Another object of the invention is to preserve the mechanical properties of crush resistance in particular. An additional objective is also to allow the easy manufacture of skis whose dimensions can be very variable, and which can in particular have different types of length, but also have more or less hollow coastlines.

To do this, the invention therefore relates to a ski, which comprises a core including longitudinal beams made from corrugated cardboard, and side edges bordering the core. The beams are designed such that the corrugations of the cardboard are parallel, and have ridges oriented perpendicularly to the underside of the core. In this way, the forces exerted vertically are supported by generators of corrugated sheet of cardboard, with good resistance to crushing.

According to the invention, this ski is characterized in that it includes at least one longitudinal stiffening element extending over the entire height of the core, and separating two longitudinal beams based corrugated cardboard. The width of this longitudinal stiffening element measured transversely to the mid-point of the shoe is less than that of the longitudinal beams made of corrugated cardboard.

In other words, the invention consists in using, in order to manufacture the core, a light and inexpensive material that is corrugated cardboard, and combining these portions with more rigid, preferably solid, elements extending over the entire height. of the core, advantageously where the maximum stresses are greatest, and where the material has a higher crush strength. In other words, the invention makes it possible to combine the lightness and the low cost of the corrugated board with more rigid specific portions, but by segmenting the core in width so that the overall strength is satisfactory.

A compromise is thus found between the width of these more rigid elements, which must be sufficiently narrow to avoid increasing too much the weight of the ski, while being sufficient to ensure good mechanical strength. Good results have been obtained when the ratio between the height of the stiffening element and its width measured transversely to the mid-point of the shoe is greater than 8.

Advantageously in practice, the lateral elements which form the songs of the core may have a variable width along the length of the ski. In other words, these elements have a compact structure that allows them to be machined to adapt to the variable width of the core, and therefore the ski.

On the other hand, advantageously, the longitudinal beams based on corrugated cardboard, and the longitudinal stiffening elements inserted between these beams are of constant width over the entire length of the ski. Thus, the core can be made by stacking layers of constant thickness, and produced in large volume parts then allowing the individual machining of the cores.

Advantageously in practice, the ski may comprise an upper protective layer which covers the upper reinforcement (s) of the ski and which extends laterally to cover the side edges to the sole, so as to form a waterproof box protecting the core structure. and in particular corrugated cardboard, any external moisture.

Advantageously in practice, the longitudinal beams made of corrugated board extend over a length greater than 80% of the load-bearing length of the ski, it being understood that the load-bearing length is defined as the distance between the front and rear contact lines when the ski is not loaded, or in other words the total length of the ski, to which we subtract the length of spatula and heel readings measured when the ski has its intrinsic camber. In other words, the characteristic core, which has a reduced cost can thus be implanted on almost all of the ski, without requiring or limiting, as in the prior art, the use of lower cost parts arranged in the front ends and back of the kernel.

In practice, in a preferred form, at the mid-point of the shoe, the ratio between the cumulative width of the corrugated board-based longitudinal beams and the width of the core is greater than 80%. In other words, the core is mainly made from corrugated board beams, and therefore has a reduced weight and cost.

In a particular form of manufacture, the core may be constituted by the assembly of three corrugated board-based beams separated by two stiffening elements between which are thus found the central corrugated beam.

In practice, the corrugated cardboard beams can be made by assembling several corrugated cardboard plies, and typically based on two associated plies for the beam or beams located at the central level of the core, and four plies for the beams arranged in lateral part of the nucleus.

The invention also relates to a method of manufacturing a ski core including longitudinal beams made from corrugated cardboard. This method is characterized in that it includes a step of producing a stack of assemblies comprising at least one corrugated cardboard layer, alternating with one or more layers of a homogeneous material, typically based on wood, having a thickness less than that of said sets comprising at least one layer of corrugated cardboard, and then a step of cutting said stack to the shape of the future core.

Advantageously in practice, it can be provided that the stack is made by including external layers of a homogeneous material, intended to form the lateral edges bordering the core of the ski, and which can be machined to the outer shape of the ski.

Brief description of the figures

• La figure 1 est une vue de côté d'un ski de fond conforme à l'invention.
• La figure 2 est une vue de dessus du ski de la figure 1.
• Les figures 3 et 4 sont des vues partielles en perspective sommaire du ski de la figure 1, dont les plans de coupe transversale correspondent respectivement aux plans de coupe III-III' et IV-IV'.
• La figure 5 est une vue illustrant l'assemblage des différentes couches composant du noyau, en vue de la réalisation d'un ou plusieurs noyaux de ski tel que celui de la figure 1,
• La figure 6 est une vue en perspective sommaire de l'assemblage de la figure 5, montré assemblé.
• La figure 7 est une vue partielle en perspective d'une bande découpée destinée à former le noyau muni des chants latéraux.

The manner of carrying out the invention, as well as the advantages which result therefrom, will emerge from the description of the embodiment which follows, in support of the appended figures in which:

• The figure 1 is a side view of a cross-country ski according to the invention.
• The figure 2 is a top view of the ski from the figure 1 .
• The Figures 3 and 4 are partial views in summary perspective of the ski of the figure 1 , whose cross-sectional planes respectively correspond to sectional planes III-III 'and IV-IV'.
• The figure 5 is a view illustrating the assembly of the various component layers of the core, with a view to producing one or more ski cores such as that of the figure 1 ,
• The figure 6 is a brief perspective view of the assembly of the figure 5 , shown assembled.
• The figure 7 is a partial perspective view of a cut strip intended to form the core provided with side edges.

Of course, the dimensions as they appear in the figures may differ from reality, and have been shown to facilitate understanding of the invention without limiting it. In particular, the thicknesses of the different layers may have been exaggerated with respect to the layer thicknesses actually employed.

Way of realizing the invention

As illustrated in figure 1 , the ski 1 has a skid zone 2 or central area on which will be installed the attachment for attachment of the shoe of the skier. This ski is shown with a camber, which will be canceled by the weight of the skier. This central zone 2 is extended at the front by a raised portion forming the spatula 3, and at the rear by an end portion forming the heel 4.

In general, cross-country skis are known to have a thickness that is quite variable along their length, and that has a maximum at the level of the foot support zone, corresponding substantially to the middle of the shoe.

Typically, this thickness can adopt minimum values, of the order of 1 to 4 millimeters at the spatula and heel ends, and a maximum value of the order of 25 to 30 millimeters at the midpoint of the shoe.

The same ski 1 shown in the figure 2 reveals by transparency the core 10 of the board which extends over most of the length of the ski, with the exception of a few centimeters corresponding to the heel survey, and one or several tens of centimeters corresponding to the record of spatula. This core 10 extends over the load-bearing length of the ski and consists essentially of the characteristic structure, combining layers of corrugated cardboard and stiffening elements, as well as additional elements 11, 12 located at the front and rear ends of this characteristic structure. . These additional elements 11, 12 are typically based on wood or polymeric foam, or more generally a more compact material, to allow their machining to the small thickness corresponding to that of the ski in the extreme areas. Beyond the core 10 , and more precisely additional elements 11, 12 , the board has in its thickness only the sole, a generally textile reinforcing layer, for example based on glass or carbon fibers, and the layer superior protection.

In practice, the characteristic structure 10 based on corrugated board extends over a length of the order of 75% or even preferably 85% of the total length of the ski, this to obtain a sufficiently light ski.

As illustrated in figure 3 , the ski 1 comprises mainly a sole 5 on which rests a reinforcement 6 , itself covered by the core 10 flanked by side edges 20, 21 , and whose upper face receives a reinforcing layer 7 . This reinforcing layer 7 is covered by the upper protective layer 8 , which extends laterally on the sidewalls 9 covering the lateral faces of the edges 20, 21 to the vicinity of the soleplate 5 , so as to ensure the tightness vis-à-vis the outside, and avoid any penetration of moisture.

More specifically, the core 10 is composed by the assembly of three longitudinal beams 13, 14, 15 , made from corrugated cardboard. More specifically, the two beams 13, 14 located on the lateral faces of the core 10 are composed by the assembly of two layers of corrugated cardboard each having two plies, overall thickness of 6 millimeters, while the central beam 13 consists of a single layer of corrugated cardboard also double folds. The corrugated board is arranged to exert the greatest resistance in the vertical direction, and thus has the peaks of its vertically oriented corrugations. Of course, depending on the dimensions of the beams, as well as those of the elementary layers of corrugated cardboard, these numbers can be adapted accordingly. The central beam 15 is separated from the lateral beams 13, 14 by means of two stiffening elements 16, 17 , of small width, formed of a continuous material, chosen for its resistance to crushing and lightened mass. The width, measured in the transverse direction of these stiffening elements, is calculated to ensure overall resistance of the core to crushing efforts observed in the context of the usual practice of skiing. In the exemplary embodiment the width of these stiffening elements is about 2 millimeters, while the width of the corrugated beams is either 6 or 12 millimeters, for a core of overall width of 32 mm. Thus, the width of the stiffening elements is significantly lower than that of the corrugated beams, to optimize the overall weight of the ski.

As we observe at figure 3 , the overall width of the core 10 is mainly occupied by the corrugated beams 13, 14, 15 , which represent of the order of 90% of the overall width of the core 10 .

As illustrated figure 3 , the core 10 is laterally bordered by edge-forming elements 20, 21 , made of a compact material, and typically based on light wood, and in particular poplar. These elements 20, 21 forming the edges have a substantially trapezoidal shape, with their substantially vertical internal face, and an outer surface slightly inclined to give the ski a trapezoidal overall section, with an upper base slightly narrower than the sole.

In comparison with the figure 4 , which corresponds to a section made further on the ski, the core 10 is less thick, but it is bordered by two edge elements 20,21 , which have a slightly greater width, corresponding to the widening of the line of ribs , or the adoption of a variable inclination of the lateral faces of the ski along the length of the latter. Thus, the ski having a variable rib line, the elements forming the songs 20,21 have a variable width along the entire length of the ski, to adapt to this line of dimensions.

The assembly formed of the core 10 and the side edges 20,21 of such a board can be produced as illustrated in FIG. figure 5 by the manufacture of a plate 30 consisting of an assembly by stacking on one another these different constituents. It is thus observed that the core 10 is composed of the stack of different layers of cardboard 25 , of the order of 6 millimeters thick, and a density of the order of 0.15, in the dry state. the ridges of its corrugations being then oriented horizontally, with layers 26 of finer wood, of the order of 1.5 to 2 millimeters in thickness, with a density of about 0.4. Above and below the outermost cardboard layers 25 are positioned additional thicker wood layers 27 for forming side edges 20,21 . These different layers are glued together and then pressed, to give the assembly 29 illustrated in the figure 6 which has an overall density of 0.22. This plate 30 is then cut into strips 31 of width corresponding to the maximum thickness of the ski core to form several ski cores, according to the dotted lines of the figure 6 . Each band is then rotated 90 degrees to position the wood layers in the vertical direction as shown in the illustration. figure 7 . The strip 31 is then machined to the desired geometry, that is to say to the thickness curve of the core with respect to the upper surface of the strip as illustrated by the dotted line 40 at the figure 7 , and to the curves of the ski hill line with respect to both lateral sides of the strip, as illustrated by the dotted lines 41,42 of the figure 7 to form the core 10 equipped with side edges 30, 31 . Note that the corrugated layers 25 are all stacked so oriented that the corrugations of the cardboard are parallel, and have ridges 28 oriented perpendicularly to the underside of the core, so as to give the mechanical strength to the strongest crushing. Thus, the core is obtained by a method combining a stack of alternating elementary layers, which are glued together, then cut to the final shape of the core.

In the above description, the invention is described more particularly in its application to cross-country skiing, but it can of course be applied to other types of snow board, with the necessary adaptations in terms of number of layers and their relative thicknesses. For example, for a ski touring, the core may comprise corrugated beams which are formed of more than two folds, and which are alternated between three longitudinal stiffening elements or more.

It follows from the above that the invention allows the realization of low-weight skis, comparable to that of skis obtained with honeycomb structures, but with a lower overall cost. Indeed, not only is the cost density of the corrugated board lower than the honeycomb type structures, but in addition, this type of structure is more easily machinable at low thicknesses, which allows for a larger fraction of the core. from this structure.

Claims (11)

Ski (1), comprising: A core (10) including longitudinal beams (13, 14, 15) made of corrugated board, in which the corrugations of the board are parallel, and have ridges oriented perpendicularly to the lower face of the core; Lateral edges (20, 21) bordering the core (10), characterized in that it includes at least one stiffening longitudinal member (16, 17) extending over the entire height of the core (10), separating two corrugated board-based longitudinal beams (13, 14, 15), wherein the width 1 of the longitudinal stiffening element (16,17) measured transversely to the mid-point of the shoe is less than that of the longitudinal beams made of corrugated cardboard. Ski according to claim 1, characterized in that the ratio between the height (h) of the stiffening element (16, 17) and its width (1) measured transversely to the mid-point of the boot is greater than 8. Ski according to claim 1, characterized in that the side elements (20, 21) forming the edges have a variable width along the length of the ski. Ski according to claim 1, characterized in that the longitudinal beams (13, 14, 15) made from corrugated board and the longitudinal stiffening elements are of constant width along the length of the ski. Ski according to claim 1, characterized in that it comprises an upper protective layer (8) which covers the upper reinforcing layers of the ski and extends laterally to cover the side edges (20,21). Ski according to claim 1, characterized in that the longitudinal beams (13, 14, 15) based on corrugated cardboard extend over a length greater than 80% of the load-bearing length of the ski. Ski according to claim 1, characterized in that the ratio between the cumulative width of the corrugated board longitudinal beams (13, 14, 15) and the core width is greater than 80% at the mid-shoe point. Ski according to claim 1, characterized: • in that the core may be constituted by the assembly of three corrugated board-based beams separated by two stiffening elements between which are thus found the central corrugated beam; And in that the corrugated cardboard beams can be made by assembling several corrugated cardboard folds, and typically based on two associated plies for the beam or beams located at the central level of the core, and four plies for the beams. arranged in the lateral part of the core. Ski according to claim 1, characterized in that all or part of the corrugated beams are formed of the assembly of two or four plies of corrugated cardboard. A method of manufacturing a ski core (10) including longitudinal beams (13, 14, 15) made of corrugated board,
characterized in that it includes a step of producing a stack of assemblies comprising at least one corrugated cardboard layers, alternating with one or more layers of a homogeneous material having a thickness less than that of said sets comprising at least one layers of corrugated cardboard, then a step of cutting said stack to the shape of the future core. The method of claim 10, wherein the stack is made by including outer layers of a homogeneous material for forming the side edges (20, 21) bordering the core (10) of the ski.

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