FR2738495A1 - Method for fabrication of ski - Google Patents

Abstract

The method includes the step during which part of a preform of the wooden core, in the form of an elongated beam having an initial set of dimensions different from the final dimensions, is submitted to densification by thermocompression of the structure during which one augments the pressure and temperature in order to obtain a core in the preferred form or the preferred dimensions. The preform is submitted to a pressure directed essentially along a direction perpendicular to the top and bottom surfaces in order to confer on it the final thickness. The thermo-compression is done in a mould (30,31) with layer of film (6) to ensure separation after moulding.

Description

 Method for the manufacture of a ski or ski component comprising a step of thermocompression of a blank of wooden core.

 The invention relates to a new method for manufacturing a ski or a ski component. The 1ski1 terminology must be understood broadly and includes alpine skiing, cross-country skiing, monoskiing and snowboarding.

 Today's skis, including the simplest, combine a number of essential elements, each having its own function and together forming a complex composite structure.

 The ski is a reinforced beam which optimizes the characteristics of resistance to mechanical stresses (compression, bending, torsion ...).

 Among the constituent elements of the ski, there is in particular the core, the role of which is essentially to maintain the ideal distance between the reinforcing elements and to resist compressive and shear stresses.

 The materials currently used for the manufacture of cores can be varied. The most common are woods, injected or pre-molded foams, acrylic foams and honeycombs. These materials have all the qualities of resistance necessary for their role; their choice can be dictated by the more specific qualities linked to each of them (lightness, cost, implementation ...).

In some skis, you can also find a combination of different materials to form the core.

 Even today, wooden cores are certainly the most economical.

We also recognize wooden cores, qualities of nervousness that make them incomparable products. They are also ecological products, the waste of which can be removed without costly treatment, unlike certain foams, for example.

 Among the wooden cores, one generally uses the laminated wooden cores which are formed by association of vertical strips of different species.

Their structure combines hard, resistant and heavy woods like beech, ash ... and softer, less resistant and lower density woods like birch, poplar, exotic wood of the okoume type or others ...

 In the manufacture of current wooden core skis, we start from an elongated beam, generally parallelepiped, which is machined on a numerically controlled machine to obtain the core in its desired shape and final dimensions.

 Generally, the machines used are equipped with tool holders of the 'revolver' type which allow machining of the upper surface of the beam to give the distribution of thickness to the core during a first pass, and the machining of the flanks of the beam to give the distribution of width or side line of the core. Usually only one core is machined at a time. The operation of machining a core is therefore a rather long operation.

 The machining parameters must be changed as often as the size or model of the ski varies. The design of the machining programs is therefore quite complex and generates significant costs. This is all the more so, as we increasingly seek to produce cores with complex shapes which are found externally on the ski, such as inclined songs in the shape of a propeller, bosses or hollows. in different places on the surface ... etc. The realization of the forms can have an objective of response to a functional need or on the contrary be purely aesthetic; in order to increase the attractiveness of the product towards the consumer for example.

 The machining of the cores also generates the formation of large volumes of chips and sawdust which require the installation of fairly heavy and sometimes noisy evacuation devices.

 Finally, the machining causes a removal of material and therefore a decrease in mechanical characteristics which are difficult to control, in particular in the areas of the ends where the remaining final thicknesses are very small.

 Usually, the weakened ends of laminated wood crumble making the core completely unusable. One solution is to plan to make cores of shorter length and to add plastic inserts at the ends which extend the core of the desired length. However, this solution is not satisfactory because it requires the separate production of inserts which must adapt perfectly to the cores to which they are attached. In addition, the structure of the ski is no longer homogeneous; which can be generally harmful.

 Machined wooden cores are also relatively porous and therefore have a tendency to warp and twist during hot assembly operations.

 Mechanically, these cores have stiffness characteristics in flexion and torsion certainly, superior to those of foam cores but which remain insufficient to reinforce the ski. It is therefore necessary to insert into the structure many reinforcing layers based on fibers and resin or metal in order to obtain satisfactory final characteristics.

 Finally, the machining operation, given the large variations in thickness and width carried out, produces a very high rate of waste; which economically is not a satisfactory solution.

 The object of the present invention is to provide a new solution to the methods of manufacturing skis; more particularly wood core skis, avoiding as far as possible the complete operations of machining the core in its final determined configuration.

 Another object of the invention is to be able to produce a ski whose core has overall mechanical characteristics superior to those of the conventionally used wood cores. It is also able to vary the mechanical characteristics according to specific needs, such as increasing the resistance of certain parts such as the ends.

 Another object of the invention is to be able to guarantee the homogeneity of the final structure of the ski produced.

 Another object is to save the use of reinforcing layers by achieving a simplified ski structure thanks to the increase in the mechanical characteristics of the core.

 Another object of the invention is to be able to more easily impart to the core, and consequently to the ski itself, a complex geometry, such as for example the production of bosses or hollows on the upper surface of the ski, or also of edges with curvature or inclination continuously or sequentially along the ski.

 Another object of the invention is to produce a ski more economically without prejudice to the quality of the final product obtained.

 For this, the invention relates to a method of manufacturing a ski or a ski component formed from an assembly of several elements including an internal wooden core having a determined shape and final dimensions. It comprises a step during which at least part of a core blank is subjected in the form of an elongated beam having a shape and / or initial dimensions different from the shape and / or final dimensions, to a densification phase. by thermocompression of its structure during which the pressure and temperature are combined to obtain the core in its predetermined shape and / or final dimensions.

 This step also has the effect of very clearly improving the mechanical characteristics of the core thus formed; in particular, its surface hardness and its modulus of elasticity. Overall, the increase in density obtained by thermocompression gives the core the same mechanical resistance as a core chosen from wood which has this density naturally, but at a lower cost.

 According to another characteristic of the invention, the core blank is subjected to a pressure directed essentially in a direction perpendicular to the lower and upper surfaces of the blank in order to give the core its distribution of final thickness. Thus, the completion of a final machining step is no longer necessary. The core is obtained at its own thickness distribution and therefore stiffness.

 According to another characteristic, the blank is subjected to a pressure directed essentially perpendicular to the surfaces of the blank in order to give the core its final width distribution. This characteristic preferably complements the previous one so that the core is obtained during a single and same step in its final configuration without a resumption of machining operation.

According to an additional characteristic of the invention, the following is implemented in the first part of a compression mold:
- the metal edges spaced laterally from one another in the desired final configuration; then
- at least one solid bonding film, which covers the edges; then
- The core blank which rests on the metal edges covered with the bonding film.

 Then, the mold is preheated to a temperature greater than or equal to the softening temperature of the bonding film, and the pressure is applied over the entire length of the blank by bringing together, at least a second part of the mold, serving as punch, towards said first part, or vice versa so as to simultaneously carry out the shaping by densification of the core, the anchoring and the bonding of the metal edges in the structure of the core, then it is removed from the mold.

 The manner in which the invention can be implemented in more detail and the advantages which ensue therefrom will emerge more clearly from the exemplary embodiments which follow and which are given by way of nonlimiting indication in support of the appended figures.

- Figure 1 is a perspective view of a core blank;
- Figure 2 schematically shows the densification phase of the blank of Figure 1;
- Figure 3 shows the core in its final configuration;
- Figure 4 is a side view of the core;
- Figure 5 is an elevational view of the core;
- Figures 6 to 10 show a variant of the method according to the invention;
- Figure 6 shows the placement of the elements, including the core blank, in the thermocompression mold;
- Figure 7 illustrates the closing of the mold;
- Figure 8 shows the actual densification phase;
- Figure 9 shows the sub-assembly after leaving the mold;
- Figure 10 shows a finished ski from a subset of Figure 9;
- Figure 1 1 shows a blank core before the densification phase;
- Figure 12 shows the nucleus obtained after the densification phase;
- Figure 13 is a view similar to that of Figure 1 1 according to a variant;
- Figure 14 is a view similar to that of Figure 12 according to a variant;
- Figure 15 is a view similar to that of Figure 1 1 according to another variant;
- Figure 16 is a view similar to that of Figure 12 according to another variant;
FIG. 17 illustrates the curve of variation of the force or load as a function of the elongation for a bending test carried out on a spruce board without treatment by thermocompression;
- Figure 18 illustrates the variation curve for a bending test carried out on a spruce board after thermocompression treatment;
- Figure 19 illustrates the variation curve for a bending test on a Carolina pine board without thermocompression treatment;
- Figure 20 illustrates the variation curve for a bending test on a Carolina pine board after thermocompression treatment;
- Figure 21 illustrates the variation curve on an untreated okoumé board and the variation curve on a board treated by thermocompression.

 The holding times are of course a function of the pressure and temperature parameters.

 Satisfactory results could be obtained by maintaining a pressure of 20 bars at 1600 for three minutes for different species.

 As shown in Figure 1, we choose a blank core 1 in solid wood, having the general shape of an elongated beam to the shape and to the initial dimensions determined. In the example illustrated, the beam has a thickness in the center which decreases progressively towards each of its ends. The width of the beam is, in turn, substantially constant.

 Of course, the desired final characteristics of the core condition the shape and the initial dimensions of the blank which are not limited.

 FIG. 2 illustrates the densification phase by thermocompression in a press 2. The blank is deposited on a flat support 20 traversed by heating cables 200 from the press to bring the blank by thermal conduction to the desired temperature. An upper cover 23 having a surface 231 lower than the final shape of the top of the core and moved by hydraulic cylinder, subjects the blank to a pressure directed essentially in a direction perpendicular to the upper surface of the blank. The pressure is exerted until the desired final thickness distribution is obtained. The cover can also be crossed by heating cables 230.

 Likewise, two lateral plates 21, 22, the internal faces 210, 220 of which have the shape of the final faces of the core to be produced, subject the blank to a pressure directed essentially perpendicularly to the lateral surfaces of the blank.

Each plate is also moved by hydraulic cylinders. The pressure is exerted until the final width distribution of the core is obtained.

 Preferably, the blank is formed by concomitant displacement of the cover 23 and the side plates 21, 22.

 The pressure exerted on the blank is at least 10 bars, preferably between 20 and 30 bars for a temperature between 70 and 170 "C.

 Of course, these conditions are also dependent on various parameters including, among others, the mechanical characteristics of the wood used, the shape and dimensions of the blanks and of the cores to be produced, the final mechanical characteristics of the sought-after core, etc.

 The holding times are of course a function of the pressure and temperature parameters.

 Satisfactory results could be obtained by maintaining a pressure of 20 bars at 1600 for three minutes for different species.

 Figures 3 to 5 show the core in its shape and final dimensions in width Lf and thickness ef. By comparison, in FIGS. 4 and 5, the shape of the initial blank of initial thickness ei and width Li has been shown in dotted lines.

 Figures 6 to 10 illustrate a variant of the method of the invention in which one takes advantage of the core thermocompression operation to carry out the assembly of different mechanical elements entering into the composition of the ski and constituting a component of the ski.

 Firstly, in the first part 30 of a compression mold 3, the metal edges 4 are spaced laterally apart from one another in the desired final configuration. Then there is between the metal edges 4 a lower rigid reinforcement element 5, preferably an openwork plate. Then, at least one bonding film 6 is put in place which covers the edges 4 and the bottom reinforcing element 5. Then, the core blank 1 is deposited which rests on the metal edges covered with the bonding film .

 The mold is then preheated to a temperature greater than or equal to the softening temperature of the bonding film and the pressure is applied over the entire length of the blank while bringing together, at least a second part of the mold 31 serving as a punch towards the first mold part 30. The shaping of the core is thus carried out simultaneously by densification, anchoring and bonding of the metal edges of the core. Finally, the subassembly thus formed is demolded and assembled.

 Of course, it is advantageous to take advantage of this operation to anchor the lower reinforcing element. However, the same operation can be envisaged without interposing a lower reinforcing element; this being assembled during a subsequent operation.

 Conversely, it is possible to provide for the addition of an upper reinforcing element deposited on the upper surface of the blank of the core before thermocompression. In this case, the element is similar in nature to the lower element 5.

 Figures 8 and 9 show that it is possible to easily achieve particular raised or hollow shapes such as ribs 10 or grooves 1 1 in the core by providing suitable shapes in the impression of the compression mold. It is also possible to obtain edges 12 with particular inclinations and possibly variable continuously or not over the entire length of the core.

 FIG. 10 illustrates a section of a finished ski after assembly on the subassembly of FIG. 9 of a sliding sole 7, generally made of polyethylene, of an upper reinforcement element 8, made of fiberglass or the like, and d 'a decorative and protective top 9 consisting of one or more layers of thermoplastic material resistant to abrasion and predecorated. There are many and varied methods of assembling these elements on the subset. It is not the object of this request to detail the possibilities offered to those skilled in the art to achieve this.

 On the other hand, one of the objects of the invention is to be able to confer on the core various mechanical characteristics according to needs and from a blank with shapes and dimensions determined in advance. By way of illustration, reference may be made to the examples of FIGS. 11 to 16 which show different possibilities among others.

 Figures 1 1 and 12 show that it is possible to improve the mechanical characteristics of the ends of the core, in particular the modulus of elasticity, density and surface hardness; from a substantially parallelepipedic blank. Starting from a large initial thickness at the ends 1a, 1b, a core is obtained which has at these locations mechanical characteristics much superior to those of a machined core of identical final shape.

The mass distribution of such a core is also different from that of a machined core. In this example in particular, the density of the ends la, lb is greater than that of the intermediate zone lc; so that the flexural stiffness characteristics and the moments of inertia at the ends are increased. A ski equipped with such a core will be more rigid at the ends and will be relatively stable, damping and little pivoting for example.

 On the contrary, in the mode of FIGS. 13 and 14, one starts from a blank which has a very thick central or intermediate zone lc and ends 1a, 1b, comparatively thinner. After the densification phase by thermocompression, the core has a shape identical to that of FIG. 12 but with completely different mechanical characteristics.

 In particular, the intermediate zone lc is much denser and has a higher modulus of elasticity than the ends la, lb. With an equal structure, moreover, the ski which will use such a core will be more flexible at the ends and will have greater pivoting qualities.

 Of course, the possibilities of varying the mechanical characteristics of the core as required by the process of the invention know no limits. Figures 15 and 16 illustrate a final example where the blank has a front part 1 d of significant thickness and a posteriorly thinner part comparatively. In the end, the core will therefore have a denser and stiffer front part 1 d than the rear part 1c for a shape identical to that of FIGS. 12 and 14.

 It is possible thanks to the process of the invention and by increasing the mechanical properties of the core to achieve a substantial saving in expensive materials forming the reinforcements, generally based on glass fibers, carbon or the like while retaining a resistant structure. .

 Of course, it is possible to provide for making a composite core comprising only a part only of wood, the rest being able to be made of foam, honeycomb or other light synthetic material resistant to compression.

 In this case, only the wooden part is subjected to the densification phase according to the invention, then connected by any means to the rest of the core of different material.

 Preferably, the part at least, subjected to the densification phase is chosen from solid wood of low density less than or equal to 0.45.

 The wood is chosen from the group consisting of spruce, pine, Okoume and poplar. The best results have however been obtained using spruce which will be preferred for a better implementation of the invention.

 The following test makes it possible to verify that the thermocompression treatment favorably affects the stiffness in bending.

 The tests consist in determining by the implementation of three-point bending, the bending stiffness on a wooden board. The board which constitutes the test piece placed flat on two supports of determined shape is subjected to a bending force applied in the middle. The arrows are measured as a function of the forces applied.

 The equipment used is detailed in standard NF T-54606. The distance between supports is 250 mm.

 A test is carried out on a board of equal size of 400x60x15 mm which has not undergone a thermocompression treatment. Then a second test is carried out on a test piece having undergone a thermocompression treatment.

The thermocompression treatment, to prepare this test piece, consists in subjecting a board of dimension 400x60x15 mm to a press treatment, the conditions of which are as follows:
Pressure: 20 bars - Temperature: 160 OC - Time: three minutes.

The tests are carried out in turn on the following species: Spruce, Pine
Caroline, Okoumé.

 FIG. 17 shows the reference curve of variation (A) of the applied force or load (in MPa) as a function of the deflection (expressed in elongation in%) for a reference board of Spruce which has not been subjected to treatment by thermocompression.

 FIG. 18 shows the curve (B) for a Epicea board having undergone the treatment by thermocompression.

Figure 19 shows the reference curve (C) for a Pine plank of
Caroline.

 Figure 20 shows the curve (D) for a Carolina Pine board treated by thermocompression.

 Figure 21 shows the reference curve (E) and the curve (F) of an Okoume board treated by thermocompression.

The results are presented in the following table:
Young module F max All F max F mpt. All rupt.

(MPa) (MPa) (%) (MPa) (%)
(A) 9682 78.18 1.1 21.11 1.2
(B) 14,965 121.26 1.2 24.90 1.2
(C) 9033 81.34 1.2 4.25 1.3
(D) 12023 96.90 0.9 18.65 1.0
(E) 7933 69.37 1.1 26.60 1.2
(F) 9488 79.15 1.1 51.17 1.1
Of course, the invention is not limited to these few examples of application but covers other possibilities and variants which may be understood within the scope of the claims which follow.

Claims (6)

 1- Method of manufacturing a ski or a ski component formed from an assembly of several elements including an internal wooden core having a determined shape and final dimensions, characterized in that it comprises a step during from which at least part of a core blank is subjected in the form of an elongated beam having a shape and / or initial dimensions different from the shape and / or final dimensions, to a densification phase by thermocompression of its structure during which the pressure and the temperature are combined to obtain the core in its predetermined shape and / or final dimensions.  2- The manufacturing method according to claim 1, characterized in that the core blank is subjected to a pressure directed essentially in a direction perpendicular to the lower and upper surfaces of the blank in order to give the core its distribution of final thickness.  3- The manufacturing method according to claim 1 or 2, characterized in that the blank is subjected to a pressure directed essentially perpendicular to the surfaces of the blank in order to give the core its final width distribution.  4- Manufacturing method according to any one of the preceding claims, characterized in that one places in the first part (30) of a compression mold (3):  - the metal edges (4) spaced laterally from one another in the desired final configuration; then  - at least one solid bonding film (6), which covers the edges (4); then  - The core blank (1) which rests on the metal edges (4) covered with the bonding film (6).  Then, the mold is preheated to a temperature greater than or equal to the softening temperature of the bonding film, and the pressure is applied over the entire length of the blank while bringing at least a second part (31) of the mold. , serving as a punch, towards said first part, or vice versa so as to simultaneously carry out the shaping by densification of the core, the anchoring and the bonding of the metal edges in the structure of the core, then it is removed from the mold.  5- Manufacturing method according to claim 4, characterized in that before the establishment of the solid bonding film (6), there is, between the metal edges (4), a lower reinforcing element (5) rigid, preferably an openwork metal plate.  6- The manufacturing method according to any one of the preceding claims, characterized in that the wood is chosen from the group consisting of pine, spruce, okoume and poplar.