EP2450086B1 - Snowboard comprising a lightened core - Google Patents

Description

Technical area

The invention relates to the field of gliding boards, especially boards sliding on snow. It relates more particularly to a new core structure, making it possible to confer good mechanical properties on the board, particularly in terms of compressive and flexural strength, and this, for a significantly reduced core density compared to the prior art. .

Previous techniques

In general, a gliding board comprises a core extending over almost the entire length of the board, and whose role is essentially to give the ski a thickness by separating mechanical reinforcements and keeping them at a distance from the neutral fiber.

These mechanical reinforcements may be of various constitutions, but a marked tendency is to favor fibrous reinforcements impregnated with thermosetting resin, which have the advantage of being easily configurable to the shape of the board, and in particular to three-dimensional configurations of the upper side.

The cores may consist either of a foam formed by the reaction of two components injected into the mold of the ski, during its molding, or by a cut and / or machined before it is molded. The invention relates more specifically to this family of nuclei.

These cores can thus be of various materials, such as wood or a foam based on polymeric materials.

This core is therefore made in a pre-molding operation, and it is cut so that its outer contour corresponds to the desired volume, so as to separate sufficiently the fibrous reinforcements that come to its contact.

Efforts have been made to limit the weight of the planks, by reducing the weight of the core, particularly by using materials having a relatively low density.

However, by reducing the density of the core, there is a risk of degradation of the latter when the board undergoes bending forces. Indeed, under these conditions, the reinforcements present on the two faces of the core work in opposite ways, and induce shear stresses within the core.

Various proposals have already been made to ensure resistance to these shear stresses.

So, we described in the document EP 0 846 479 a gliding board core which has longitudinal recesses extending over most of its length. These recesses receive a textile element consisting of a nonwoven which is compressed to enter the recesses. This nonwoven is impregnated with a thermosetting resin, so that it forms rigid spacers, and more rigid than the material of the core itself, between the two fibrous reinforcements resting on the upper and lower faces of the core.

This solution prevents crushing of the core, concentrating the stresses exerted on the board at these recesses. However, because of their large size, these recesses form stress concentrations and constitute zones of fragility of the core, especially since these recesses are rectilinear and parallel. Thus, if the flexural strength can be improved by these arrangements, the fact remains that the torsional behavior is not homogeneous.

Another solution has been described in the document EP 2,204,276 . It consists in producing inside the core recesses oriented substantially vertically and serving as sheaths to the passage of fibrous wicks. The ends of the fibrous strands protrude substantially from these recesses, and are folded over the upper and lower surfaces of the core, where they are then covered with fibrous reinforcements.

By adhering to the two fibrous reinforcements located on either side of the core, the pillars formed by these fibrous strands ensure a resistance to tearing, preventing fibrous reinforcements from delaminating in case of intense flexion of the core.

However, the realization of these recesses is also weak points since their dimension inevitably ensures a degradation of the homogeneity of the core.

In addition, during the manufacture of the core, it is necessary to drill the recesses, then the establishment of fibrous locks with spreading and distribution of their ends, which are all delicate operations, complex and which increase the manufacture of the core.

The objective of the invention is to provide a solution which ensures a strengthening of the core in compression, traction and shear, which is as homogeneous as possible to avoid the risk of crushing the core material, and this, by seeking maximum lightening.

Presentation of the invention

The invention therefore relates to a gliding board having a core covered on both sides by fibrous reinforcing layers. This core has rectilinear fibrous elements which pass right through it by being in contact with the two fibrous reinforcing layers.

According to one characteristic of the invention, these fibrous elements are rectilinear segments of threads which are stuck inside the material of the core and pass through holes formed during their insertion into the core, these threads being present in a proportion of at least one hole per square centimeter, and this on more than 50 cm ² on the surface of the nucleus.

Complementarily, the core, including the characteristic son, has an overall density of less than 120 kg / m ³ , preferably less than 100, and very preferably less than 70 kg / m ³ .

In other words, the invention consists in ensuring a bridging between the two faces of the core, and more specifically the two impregnated fibrous reinforcements, via a plurality of fibrous bridges, which are impregnated with thermosetting resin advantageously the same as that fibrous reinforcements, which are distributed homogeneously over a large part of the core surface.

Due to the homogeneous distribution of these bridges, by a regular distribution on the surface of the core, one does not create a zone of concentration of constraints, while obtaining an effective reinforcement, and this by employing a light material.

These son being stiffened by the thermosetting resin, they provide both a reinforcement in compression and also in tension, so that they maintain the integrity of the rest of the core material when it is stressed in bending but also in torsion .

The fact that the wires pass through small diameter holes greatly limits the risk of rupture of the core since no resin accumulation zone is formed. In practice, the holes are formed during the insertion of the threads and the material of the core is separated by the passage of the wire, so that there is almost no gap between the wire and the material of the core. Anyway, during the impregnation with the resin, any gaps that may appear between the wire and the material of the core during the insertion of the son, are completely filled.

In addition, the overall volume of the holes remains particularly low so that the impact of mechanical reinforcement by the characteristic son remains weakly sensitive to the overall weight of the core.

Finally, thanks to this very global distribution of the points of reinforcement, the mechanical properties of the core remain very homogeneous, and thus allow the use of very low density materials, of the order of a few tens of kilos per m ³ only, this which leads to particularly light gliding boards.

Thus, for example, as a material for the core it is possible to use expanded foams, and in particular polyurethane-based foams, but also very sparse woods, such as balsa or the like. .

In the absence of the characteristic yarns, this material of the core may have a density of less than 100 kg / m ³ , preferably less than 80 kg / m ³ , and very preferentially less than 50 kg / m ³ , and in a preferred form, of the order of 35 kg / m ³ .

According to various embodiments, all or part of the holes formed by the passage of the characteristic son may have an inclination either substantially perpendicular to the main core plane, or still with an inclination substantially non-perpendicular to the core plane.

This inclination can be chosen according to the main deformation that will be experienced by the gliding board, so as to orient the fiber bridges optimally. Thus an angle of 45 ° is advantageous for countering shear forces of the core.

It is also possible that the core material undergo deformations during molding, in particular when it is a compressible material, or even thermoformable, in which case the initial inclination of the fibrous bridges can be modified after molding. In this case, the fibrous bridges can then be found after molding in an optimal configuration to fulfill their mechanical function in a preferred manner.

In practice, the characteristic threads may protrude through holes that receive them in the core so as to come into contact with the impregnated fibrous layer.

In this case, and very preferably, the fibrous reinforcing layers are impregnated with a thermosetting resin which can thus migrate in the characteristic son by capillarity during molding, since it is in sufficient excess on these fibrous reinforcements. In another embodiment, a complementary layer, such as a layer of a nonwoven impregnated with the same resin, can be interposed between the fibrous reinforcements and the core, so as to serve as resin reserve during molding. .

The invention also covers other variants for which the threads themselves are previously impregnated with a resin, this resin hardening during the molding operation.

In a particular embodiment of the invention, the core may comprise one or more continuous son sewn through the core.

The manufacture of the core can thus be greatly simplified, since the establishment of future fibrous bridges can be done on the low density material, before its machining and cutting to the shape of the core. These operations thus greatly limit the time and cost of manufacture.

In an alternative embodiment, it is possible that the placement of the son occurs while the fibrous reinforcements have been arranged on the upper and / or lower faces of the core, so that the characteristic son also ensure the joining of the reinforcements to the intermediate layer of the core.

In practice, the characteristic yarns may be based on a material selected from the group consisting of glass fibers, carbon fibers, aramid fibers, basalt fibers and natural fibers.

Advantageously, the number of holes receiving a wire and opening on one of the faces of the core, is between 0.3 and 5 holes per cm ² , preferably between 0.5 and 3 holes per cm ² , or very preferentially between 0, 7 and 2 holes per cm ² .

Of course, the distribution of the holes may be constant but also variable on the surface of the core. The densities mentioned above correspond to a representative surface of the core, which is at least 50 cm ² , and preferably 500 cm ² , corresponding to a substantial fraction of the surface of the board. In other words, the invention covers variants in which this fibrous bridge density is present in a particular area only, while the rest of the core may not need this reinforcement, in which case the fibrous bridges are absent, or present to a lesser extent.

Similarly, the diameter of the hole may advantageously be between 0.3 and 2 mm, corresponding substantially to the diameter of the needles which serve to insert the characteristic threads into the core.

• dépôt sur une face de la couche d'un ensemble de segments de fils présentant une longueur supérieure à l'épaisseur de la couche,
• aiguilletage de la couche où reposent les segments de fils afin de les entrainer dans ladite couche et les faire apparaître sur la face opposée.
• découpe de la couche à la forme du noyau.

The invention also relates to a method of manufacturing a gliding board core from a layer of foam material or the like. This process comprises the following steps:

• deposition on one side of the layer of a set of wire segments having a length greater than the thickness of the layer,
• needling the layer where the segments of son rest to cause them in said layer and make them appear on the opposite side.
• cutting the layer to the shape of the core.

In other words, are spread on the core layer of the cut son which are then inserted inside the core by needles which have a geometry provided for this purpose, so as to exceed them on the other side, and thus form the fibrous part of the future bridges.

In practice, the needles used during the needling may have various inclinations, and in particular a non-perpendicular inclination to the face of the layer where the son segments lie. It is also possible to implement yarns in several orientations, by a succession of needling operations with differently oriented needles.

In a particular embodiment, it is possible to carry out a conformation operation of the layer, after needling, to give a three-dimensional shape to one of the faces of the core. Thus, it is possible to make light and strong cores, which can incorporate bending breaks for the production of shaped skis.

Brief description of the figures

• La figure 1 est une vue en coupe transversale d'une planche de glisse, montrant le noyau, les renforts et les autres éléments constitutifs d'une planche réalisée conformément à l'invention.
• Les figures 2, 4 et 5 sont des vues en coupe transversales d'un noyau et des renforts fibreux d'une planche de glisse, montrés selon trois variantes de réalisation.
• La figure 3 est une vue en coupe longitudinale d'une partie d'un noyau et des renforts fibreux d'une planche de glisse, montrés selon une variante de réalisation
• La figure 6 est une vue en perspective sommaire d'une partie d'un noyau réalisé conformément à l'invention.

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

• The figure 1 is a cross-sectional view of a gliding board, showing the core, the reinforcements and the other components of a board made according to the invention.
• The Figures 2, 4 and 5 are cross-sectional views of a core and fibrous reinforcements of a gliding board, shown according to three alternative embodiments.
• The figure 3 is a longitudinal sectional view of a portion of a core and fibrous reinforcements of a gliding board, shown according to an alternative embodiment
• The figure 6 is a brief perspective view of a portion of a core made in accordance with the invention.

Of course, the figures have been made for the sole purpose of making the invention clearly understood and the shapes and dimensions of the various elements shown are only illustrative. Thus, certain elements could be represented with dimensions much larger than those encountered in reality, and only for the purpose of understanding the interest of the invention.

Way of realizing the invention

As already mentioned, the invention relates to a new core structure for gliding board, an example of which is illustrated in FIG. figure 1 .

Thus, a gliding board 1 comprises in a traditional manner a flange 2 edged with edges 3, and surmounted by one or more reinforcements in particular fibrous 4. The gliding board also comprises an upper protective assembly 5 which directly or indirectly covers a or several reinforcements 6, in particular fibrous.

The two fibrous reinforcements 4, 6 are separated by a core 10 which, in the context of the invention, is made of a low density material, which may be for example a polyurethane foam or else any other material having a low density.

In accordance with the invention, this core 10 is traversed by wires 20 which connect the upper 11 and lower 12 faces of the core while coming into contact with the fibrous reinforcements 6, 4.

Multiple variants can be implemented to ensure the distribution of the forces exerted on the core 10, and this by implanting the characteristic son 20 in orientations and distributions adapted to applications.

Thus, as illustrated in figure 2 , the material of the core may be traversed by wire portions 21. These wires 21 have zones 22 internal to the cores which are formed by driving the wire from the upper face 11 to the lower face 12, to form a or a plurality of rectilinear segments 23, 24 substantially perpendicular to the main plane of the core 10.

Some of these segments 23, 24 are connected by a portion 25 forming a flush loop on the lower face 12 of the core, and coming into contact with the lower fibrous reinforcement 4. On the opposite face, the son 21 have free ends 26 which come in contact with the upper fibrous reinforcement 6.

These segments 23, 24 of the wire thus pass through the core 10 through a hole 15 created during the insertion of the wire, and which has a diameter of the order of that of the wire 21.

The realization of the core is illustrated in figure 6 , in which are observed on the side of the foam block, passages within which are present the segments 23,24 of son, and on both sides, the apparent areas 25, 26 of the wire 21, which will come into contact fibrous reinforcements 4,6. This configuration corresponds to the case where during manufacture, the son which rest on the upper face are driven by needles whose end straddles the central part of the wire. In some cases, the forked end of the needle catches the wire rather close to one end, and the trained length is too short for a loop to form on the opposite side. Thus, only one segment passes through the core material.

In practice, the fibrous reinforcements 4, 6 are impregnated with a resin that comes into contact with the wire 21. More specifically, the portions 26 of the wire 21, present on the upper face 11 of the core come into contact with the underside of the reinforcement fibrous In the same way, the looping portions 25 present on the lower face 12 of the core 10 come into contact with the upper face of the lower fibrous reinforcement 4.

By capillary phenomena, the resin present in the fibrous reinforcements 4, 6 migrates to completely impregnate the segments 23, 24 of the characteristic wire 21.

When this resin is advantageously of thermosetting nature, the heat provided during the molding operation causes the polymerization of this resin. It is also possible to use a wire previously coated with a thermosetting resin, in a state that allows it to be manipulated and inserted into the core material.

By way of example, fiber-based yarns having a high tenacity such as glass yarns, carbon or aramid yarns or the like can be used. The resins employed may be of the thermosetting type and in particular of the epoxy type.

Once the molded board, we see in a section that composite bridges (wire / resin) connecting the upper and lower faces. The portions of the threads that protruded from the faces of the core merge with the fibrous reinforcement layers also impregnated with polymerized resin.

It is possible, as illustrated in figure 3 to give a particular inclination to the son 31 through the core 10. This inclination is chosen so that the fibers can best cope shear forces. Indeed, in the case of bending by pressing on the pad area, the portion of the son near the lower reinforcement is biased in tension, while the portion near the upper zone of the core is biased in compression. By the judicious choice of this inclination, one can limit the influence of the shear resulting from this difference of behavior within the nucleus. For example, two inclinations at + 45 ° and -45 °, measured in planes parallel to the longitudinal axis of the ski, and perpendicular to the underside of the core, give good results in terms of shear strength when bending the board.

Of course, it is possible to vary this inclination within the same core, giving the optimal values depending on the configuration of the core and in particular its thickness, and the localized mechanical stresses. It is also possible to use within the same area several different inclinations, so as to optimize the mechanical strength.

Likewise, the optimization of this mechanical resistance can be achieved by the choice of the density of wires present inside the core. Thus, a satisfactory mechanical strength is obtained when the distribution of the son is of the order of a few son per square decimeter. Of course, the density of these wires can be modulated on the surface of the core, with higher concentrations in the areas mechanically stressed, such as in particular the proximity of the implantation of fasteners in the case of a surfboard or a ski.

As illustrated in figure 4 it is also possible to use for the core 40 a material which has a deformation capacity, by compression so that during molding, it follows the three-dimensional shape that is desired to give the board, without the need for preform it by a machining operation.

In this case, the core is made from a block of constant thickness, which has son 41 present over the entire height of the core. During molding, the thickness of the core 40 tends to decrease in certain areas 43, so that the characteristic son 42 rearrange, for example by settling inside the hole that accommodates them, or by seeing their inclination change, or by adopting a wavy form.

It is also possible that the core is shaped three-dimensionally before the molding operation, during a specific intervention through the use of a thermoformable material, or a machining operation. In practice, it is possible to implement the characteristic son after this formatting, so that son crossings are done directly, and are not modified by a subsequent compression.

In a variant illustrated in figure 5 , the core 50 can be made with prior integration of the fibrous reinforcement layers 54, 56. In this case, the insertion operation of the characteristic son 51 is through the fibrous reinforcement layers 54, 56 and the core 50 , so as to form a sandwich structure.

In this case, the fibrous reinforcement layers 54, 56 are associated with the core, which allows easier handling. The impregnation can thus take place directly on the complex previously made.

In practice, good results have been obtained using the polyurethane type foam which has a density of the order of 50 kg / m ³ . The son used are glass son. These yarns are present with a surface density such as the number of segments per cm ² and of the order of 0.5 to 3.

These threads are coated with an epoxy resin which, when it impregnates the threads by capillarity, gives an overall density of the core, integrating the impregnated threads of less than 120 kg / m ³ , preferably between 40 and 100 kg / m. ³ .

In alternative embodiments, it is possible to make the core by impregnating the son specifically, even before the establishment of the core in the mold. It is possible to impregnate the threads, for example with a nonwoven layer forming a resin reservoir, so as to allow the resin to propagate in the threads by capillarity, before they come into contact with the fibrous reinforcements. We can also use pre-impregnated son of a resin, which is polymerized after inserting the wires into the core. Impregnation can also be ensured by the addition of all or part of the layers of impregnated fibrous reinforcements, in a specific operation, prior to molding. A core is thus obtained integrating the polymerized bridges, and thus stiffened before molding. This core is more resistant to the high pressure exerted during molding.

The structure of the core according to the invention thus provides boards particularly lighter, and having mechanical strengths particularly improved compared to existing boards. These boards can be used in various applications such as downhill skiing, Nordic skiing, or even snowboarding.

Claims (11)

1. A snow gliding board (1), comprising a core (10) covered on at least one of its two surfaces with one or several fibrous reinforcement layers (4, 6), said core (10) having rectilinear fibrous elements crossing it thoroughly while being in contact with the at least one fibrous reinforcement layer, characterized in that the fibrous elements are yarn segments (23, 24) inserted in the core material and present by a proportion of at least 0.3 yarn segments per square centimeter, over more than 50 cm², the core, including the fibrous elements, having a density lower than 120 kg/m³.
2. The gliding board of claim 1, characterized in that the yarn segments are inserted in holes having a diameter smaller than 2 millimeters.
3. The gliding board of claim 1, characterized in that the core material is selected from the group comprising expanded foams, in particular polyurethane-based foams, and wood.
4. The gliding board of claim 1, characterized in that all or part of the holes formed by the passing of the yarns (23, 24) have an inclination substantially perpendicular to the main plane of the core.
5. The gliding board of claim 1, characterized in that all or part of the holes formed by the passing of the yarns (31) have an inclination substantially non-perpendicular to the main plane of the core.
6. The gliding board of claim 1, characterized in that the yarns (21) protrude from the holes and come into contact with the impregnated fibrous reinforcement layer(s).
7. The gliding board of claim 1, characterized in that the yarns are impregnated with the thermosetting resin impregnating the fibrous reinforcement layers.
8. The gliding board of claim 1, characterized in that the core material has a density lower than 100 kg/m³, preferably lower than 80 kg/m³, most preferably lower than 50 kg/m³.
9. The gliding board of claim 1, characterized in that the core, including the fibrous elements, has a general density lower than 100 kg/m³, preferably lower than 70 kg/m³.
10. The gliding board of claim 1, characterized in that the number of holes receiving a yarn emerging on a surface of the core ranges between 0.3 and 5 holes per square centimeter, preferably between 0.5 and 3 holes per cm², and most preferably between 0.7 and 2 holes per cm².
11. The gliding board of claim 1, characterized in that the yarns are based on a material selected from the group comprising glass fibers, carbon fibers, aramid fibers, natural fibers, basalt fibers.

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