FR2967080A1 - SLIDING BOARD COMPRISING AN ALLEGE CORE - Google Patents

Abstract

Gliding board (1) comprising a core (10) covered on at least one of its two faces by one or more reinforcing fibrous layers (4, 6), said core (10) having rectilinear fibrous elements passing therethrough in part by being in contact with the two fibrous reinforcing layers, characterized in that the fibrous elements are segments of threads (23, 24) stuck in the material of the core, and present in a proportion of at least one hole per centimeter square, more than 50 cm, the core including fibrous elements with a density of less than 120 kg / m.

Description

-1- SLIDING BOARD COMPRISING AN ALLEGE CORE

TECHNICAL FIELD The invention relates to the field of gliding boards, in particular 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. .

PRIOR ART 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 bay. 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 boards by reducing the weight of the core, particularly by using relatively low density materials.

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 provide resistance to these shear stresses.

Thus, EP 0 846 479 discloses a board core which has longitudinal recesses extending over most of its length. These recesses receive a textile element consisting of a nonwoven 20 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 by 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, while 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 document EP 2 204 276. It consists in producing inside the core recesses oriented substantially vertically and serving as sleeves for the passage of fibrous strands. The ends of the fibrous strands extend well beyond 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 locks provide a resistance to tearing, 10 preventing the 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. SUMMARY OF THE INVENTION The invention therefore relates to a gliding board comprising 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 layers of reinforcement. According to a characteristic of the invention, these fibrous elements are straight segments of threads which are stuck inside the core material 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 core.

Complementarily, the core, including the characteristic yarns, has an overall density of less than 120 kg / m3, preferably less than 100, and very preferably less than 70 kg / m3. In other words, the invention consists in 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 of the fibrous reinforcements, and which are distributed homogeneously over a large part of the surface of the core.

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 core failure 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 thread, so that there is almost no gap between the wire and the core material . 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 the mechanical reinforcement by the characteristic threads remains weakly sensitive to the overall weight of the core. Finally, thanks to this very global distribution of reinforcement points, 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 kilograms per cubic meter only. 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 particularly sparse woods, such as balsa or similar.

In the absence of the characteristic threads, 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 20 kg / m3.

According to various embodiments, all or part of the holes formed by the passage of the characteristic threads 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 or even thermoformable material, 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 optimum 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 excess sufficient 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 form of the invention, the core may comprise one or more continuous yarns 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 make it possible to 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 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 preferably between 0.7. and 2 holes per cm2.

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 density of fibrous bridges 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.

The invention also relates to a method of manufacturing a gliding board core from a layer of foam material or the like. This method comprises the following steps: deposition on one side of the layer of a set of segments of threads having a length greater than the thickness of the layer, needling of the layer on which the son 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, cut wires are spread over the core layer, which are then inserted inside the core by needles which have a geometry provided for this purpose, so as to make them pass on the other side. , and thus form the fibrous part of 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 rest. 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 perform a conformation operation of the layer, after needling, to give a three-dimensional shape to one of the faces of the core. Thus, lightweight and strong cores can be made, which can incorporate curvature breaks for the production of shaped skis.

Brief Description of the Figures 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:

Figure 1 is a cross-sectional view of a gliding board, showing the core, the reinforcements and other components of a board made according to the invention. Figures 2, 4 and 5 are cross-sectional views of a core and fibrous reinforcements of a gliding board, shown in three alternative embodiments. FIG. 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. FIG. 6 is a brief perspective view of a part of a core made according to 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 illustrative only. Thus, certain elements have been able to be represented with dimensions much greater than those encountered in reality, and only in order to make it possible to understand the interest of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As already mentioned, the invention relates to a new core structure 15 for gliding boards, an example of which is illustrated in FIG.

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 one or more 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 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. 2967080 -10- 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 FIG. 2, the core material 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 core. at the lower face 12, to form one or more 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 into 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 embodiment of the core is illustrated in FIG. 6, in which are observed on the side of the foam block, passages inside which are present the segments 23,24 son, and on both sides, the apparent areas. 25, 26 of the wire 21, which will come into contact with the 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 which 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 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 preferably thermosetting in 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, high-tenacity fiber-based yarns 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 board has been molded, only composite (wire / resin) bridges connecting the upper and lower faces are seen in a section. 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 FIG. 3, to give a particular inclination to the wires 31 passing through the core 10. This inclination is chosen so that the fibers make it possible to best counter the shearing 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 °, 2967080 -12- 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 flexing the board.

Of course, it is possible to vary this inclination within the same core, giving the optimum 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 strength 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 that are mechanically stressed, such as, in particular, the proximity of the fastener implantation in the case of a board. surf or ski.

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

In this case, the core is made from a block of constant thickness, which has threads 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 modify, or again 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 shaping, so that the son 5 crossings are done directly, and are not modified by a subsequent compression.

In a variant illustrated in FIG. 5, the core 50 can be made with a prior integration of the fibrous reinforcement layers 54, 56. In this case, the operation of insertion of the characteristic threads 51 is done through the layers of fibrous reinforcement 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 wires used are glass wires. These yarns are present with a surface density such that 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. The yarns may be impregnated, for example with a non-woven layer forming a resin reservoir, so as to allow the resin to propagate in the yarns by capillarity, prior to their contact with the fibrous reinforcements. It is also possible to use pre-impregnated threads of a resin, which are polymerized after insertion of the threads 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. This gives a core incorporating 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 makes it possible to obtain boards which are particularly lighter and which have particularly improved mechanical strengths compared with existing boards. These boards can be used in various applications such as downhill skiing, Nordic skiing, or even snowboarding.

Claims (1)

CLAIMS1 / Gliding board (1) having a core (10) covered on at least one of its two faces by one or more reinforcing fibrous layers (4, 6), said core (10) having rectilinear fibrous elements which cross it completely in contact with the at least one reinforcing fibrous layer, characterized in that the fibrous elements are thread segments (23, 24) stuck in the core material and present in a proportion of at least 0 , 3 segments of yarn per square centimeter, over 50 cm 2, the core, including fibrous elements having a density of less than 120 kg / m 3. 2 / gliding board according to claim 1, characterized in that the son segments are stuck in holes whose diameter is less than 2 millimeters. 3 / gliding board according to claim 1, characterized in that the core material is selected from the group comprising expanded foams, especially polyurethane foams, and wood. 4 / gliding board according to claim 1, characterized in that all or part of the holes formed by the passage of the son (23, 24) have an inclination substantially perpendicular to the main plane of the core. 5 / gliding board according to claim 1, characterized in that all or part of the holes 25 formed by the passage of the son (31) have an inclination substantially non-perpendicular to the main plane of the core. 6 / Gliding board according to claim 1, characterized in that the son (21) protrude from the holes and come into contact with the impregnated fibrous reinforcing layer or layers. 2967080 -16- 7 / Gliding board according to claim 1, characterized in that the son are impregnated with the thermosetting resin impregnating the fibrous reinforcing layers. 5 / Gliding board according to claim 1, characterized in that the core material has a density of less than 100 kg / m3, preferably less than 80 kg / m3, very preferably less than 50 kg / m3. 9 / gliding board according to claim 1, characterized in that the core, including the fibrous elements, has an overall density of less than 100 kg / m3, preferably less than 70 kg / m3 10 / gliding board according to claim 1 , characterized in that the number of holes receiving a wire opening on one face of the core is between 0.3 and 5 holes per square centimeter, preferably between 0.5 and 3 holes per cm 2, and very preferably between 0 , 7 and 2 holes per cm '. 11 / gliding board according to claim 1, characterized in that the son are based on a material selected from the group consisting of glass fibers, carbon fibers, aramid fibers, natural fibers, basalt. 12 / A method of manufacturing a gliding board core, from a layer of a foam-type material, characterized in that it comprises the following steps: - depositing on one side of the layer of a set of wire segments having a length greater than the thickness of the layer, - needling of the layer in which the wire segments rest, in order to drive them into said layer and make them appear on the opposite face. - Cutting the layer to the shape of the core. The method of claim 12, wherein the needles used during needling have a non-perpendicular inclination to the face of the layer where the thread segments are resting. 14 / A method according to claim 12, wherein one carries out a conformation operation of the layer after needling to give a three-dimensional shape to one of the faces of the core. 15 / A method according to claim 12, wherein there is carried out a step 10 of impregnation and polymerization of a resin impregnating the segments of wire.