WO1987005525A1

WO1987005525A1 - Method of making a ski and a ski

Info

Publication number: WO1987005525A1
Application number: PCT/FI1987/000037
Authority: WO
Inventors: Toivo Liljemark
Original assignee: Karhu-Titan Oy
Priority date: 1986-03-20
Filing date: 1987-03-17
Publication date: 1987-09-24
Also published as: EP0260310A1; FI861171A; FI861171A0

Abstract

A method of producing a ski comprises the following steps: A) manufacturing at least one body (Rm) or at least one series (OR1...ORn) of bodies (R1...Rm), the length of each body matching the total length of a corresponding ski, which are provided with a glide surface and which have a certain bending stiffness B) manufacturing at least one series of inserts (L1,1...Li,j) which are shorter than the total length of a ski and each of which has a different bending stiffness, C) selecting according to the qualities and requirements of a skier a body (Rm) and at least one insert (Li,j) and D) joining body (Rm) and at least one insert (Li,j) together for producing a ski suitable for a skier as for its total bending stiffness and camber profile, so that the insert/inserts are fixedly mounted on the midsection of the top body surface over their entire length. The invention relates also to the ski manufactured in accordance with the method.

Description

Method of making a ski and a ski

The present invention relates to a method of making a ski, as set forth in the preamble of claim 1.

The manufacturing process of so-called sandwich- structure skis, which are overwhelmingly most popular today, is an entity involving versatile problems, e- specially in view of the entire manufacturing process including all ski manufacturing stages, skiing cσn- ditions for which the ski is intended, and the in¬ dividual qualities and requirements of a ski user. In principle, a ski manufacturer must resolve a function of the final characteristics of a ski, whose effect¬ ive variables include several, if not dozens of different qualities required of a ski. The present- day methods of manufacturing sandwich-structure skis and the skis manufactured thereby are based on the idea that, after clearing the values of variable.s necessary for obtaining the required operating cha¬ racteristics of a ski, e.g. a ski intended for ski races in skating style, whose bending stiffness agrees with the tested height/weight distribution curve of a skier, the ski will be completed and finished. In other words, the final characteristics of a ski are "decided on" before the manufacturing process is started.

This presently used manufacturing method is disad¬ vantageous in many respects in view of ski manu¬ facturing as a whole. The way of thinking and manu¬ facturing applied today leads to drawbacks for both ski manufacturers and ski users. First of all, it is obviously difficult to control in the manufacturing process a plurality of variables required for the final characteristics of a ski when making a sand¬ wich-structure ski. In manufacturing and production there is of course the inevitable fact that the simple and large-scale manufacturing of identical products is cheaper and involves less possibilities of mistakes and errors than a complicated production process, in which the final characteristics of a product to be made are revised several times which is the case in present-day ski manufacturing technology. Another drawback is a market situation which affects production and capitals tied in production and in¬ fluences also the consumers. Especially, the mass production of seasonally used articles, such as skis, in a manner that the individual demands of users and the availability of skis can be quaranteed means, considering the accuracy of the information based on present market researches and statistical height/ weight distributions, that the manufacturer is forced to tie up considerable capitals in the supply of ready-to-use skis. If demand does not match predict¬ ions, the skis manufactured for storage may become more or less non-current goods. This drawback originates from the very fact that skis are manu¬ factured in a manner that the final characteristics of skis are "decided on" before the ski manufacturing process is started even though demand, and especially its distribution, is always based on unreliable probability calculations and predictions. A third drawback in present-day manufacturing is the fact that skis fulfilling the individual requirements of a user are not available for the very reasons stated above.

US Patent 4 300 786 discloses a ski structure, whose bending stiffness is adjustable by fixing replaceable inserts in the voids made on either side of a ski body in the lateral faces thereof. Thus, this solut¬ ion does not even aim at providing a ski with pre¬ determined final characteristics but, instead, the inserts are replaceable according to the properties of a user and the skiing conditions. The solution disclosed in the cited specification is also technically disadvantageous, since the inserts are placed on the neutral axis of ski deflection. Hence, the inserts must have considerable bending stiffness and the void in a ski body must possess considerable strength in order to achieve changes in the charac¬ teristics of a ski necessary for a user. In other words, the position of inserts is not desirable.

An object of this invention is to eliminate the above drawbacks. The invention is based on the basic idea that ski manufacturing is simplified, the amount of capital tied up by a manufacturer in production and storages is reduced and, at the same time, a user can be quaranteed availability of a ski suitable for his or her individual qualities and requirements if the ski manufacturing process is decentralized in a manner that the final characteristics of a ski are not brought about until the manufacturer and/or wholesale or retail people have knowledge about the distribution of demand.

In order to achieve this object of the invention, the method is mainly characterized in that the insert/in¬ serts are fixedly mounted on the midsection of the top body surface over their entire length.

First of all, the above-described method offers the advantage that production is simplified in the sense that the number of variables to be considered at each stage of production will be reduced. In the product¬ ion of a body or bodies of a given series, it is not necessary to change the bending stiffness charac¬ teristics of a body in the middle of a production process but all bodies or certain bodies in a certain series are identical as to their bending stiffness. This bending stiffness is selected in a manner that the characteristics of an end product, i.e. a ski, will be optimal in view of the purpose of a ski, skiing style and the type and temperature of snow. The inserts, in turn, are manufactured in a manner that certain inserts in certain series have always the same bending stiffness, but different inserts in the same series have a different bending stiffness.

Thus, the number of variables to be controlled in the production of inserts will be small. Referring to what has been stated above, after producing series of bodies and series of inserts, a manufacturer will be comparatively free to combine at least one, given insert with a given body for providing a ski fulfill¬ ing the requirements of a user. These possibilities of free selection render it possible to reduce the capitals tied up in production.

Other features characteristic of a method of the invention appear in the accompanying subclaims directed to a method.

The invention relates also to a ski manufactured by applying the method. A ski of the invention is mainly characterized in that an insert is fixedly mounted on a body over the midsection of its top surface over its entire length by using fastening means provided on the top surface of body and on the bottom surface of insert. As fastening means it is possible to use the top surface of a body and the bottom surface of an insert which, as to their configurations, are substantially flat and are joined together by gluing. The body and the insert may also be provided with projection-groove combinations of various shapes, which serve as fastening means and which can be used in the assembly of a ski in addition to or instead of gluing. It is also possible to employ extra fasten- ers, such as screws.

This type of ski offers a possibility of providing a ski fulfilling the individual demands of a user, as the insert can be selected in view of the qualities and demands of a user.

Other features characteristic of a ski of the invention appear in the accompanying subclaims.

A method and a ski of the invention will now be described in more detail with reference made to the accompanying drawings, in which

fig. 1 shows a set of bending stiffness curves for a ski as a function of the length of a ski when using various inserts of a given series of inserts together with a given body of a given series of bodies,

fig. 2 is a schematic view of a system applicable in a method of the invention,

fig. 3 is a perspective view of one embodiment of a ski of the invention as well as a longitudinal partial section thereof. fig. 4 is a layerwise shown perspective view of one embodiment of an insert of the invention,

fig. 5 is a similar layerwise shown perspective view of one embodiment of a body, and

figs. 6-10 are sectional views of various embodiments of the cross-section of a ski, showing various types of embodiments of inserts.

Referring to figs. 1 and 2 and to the enclosed table, it is first of all possible to illustrate the problems encountered by a ski manufacturer. The table discloses by way of example some of the requirements that a ski manufacturer should observe. In the manu¬ facture of a body portion, it is necessary to con¬ sider the purpose of a ski, e.g. whether a ski is intended for racing, exercise or special use. As for this purpose-based classification, there exists a so-called SAL I-classification, used by ski manu¬ facturers. Another aspect that should be considered is a skiing style since, in addition to the old, traditionl, so-called diagonal style, there is today a so-called skating style. A skier can also apply a combination of both styles or modes. Another aspect to be observed in the structure are the charac¬ teristics of snow, as exemplified in the table. In general, it can be noted that the best possible operation of a ski in all skiing conditions requires the consideration of several variable factors. These factors include temperature of snow, moisture of snow, composition of snow (fresh, snowing snow, driving snow, fine-grained snow and old, coarse¬ grained snow) . In order to provide an optimal ski structure, the following aspects must be observed in the structure of a body portion:

A glide surface material to conform with skiing conditions, e.g. smooth UHM PE in intensely cold conditions, heat-conducting PE in mild conditions and grooved UHMWPE in wet conditions.

A correct surface pressure distribution that can be provided by a common bending stiffness of both the body and the insert. In order to obtain a proper total bending stiffness, this factor must be observed in the bending stiffness of a body. Also the camber configuration has an effect on the surface pressure distribution acting between the glide surface of a ski and snow.

Optimal absorption properties, achieved by the joint structure of a body and insert but must also be observed in the body structure. In principle, a ski structure can be absorbing or vibrating and resilient. On a hard, icy track, for instance, the action is achieved by an ab¬ sorbing structure and a short camber configurat¬ ion with the ski sliding on the short pressure areas provided by the front and rear portions. On a soft track of frosty snow, however, the best action is achieved by a vibrating, resilient ski having a long camber configuration, with the ski sliding on an extensive area provided by the front and rear portions.

- The characteristics, heigth and weight of a skier should also be observed and, as a special charac¬ teristic, the kicking force of a skier. The following can. be presented, as. an example of a presently used, ski manufacturing method, wherein the components of each combination in question are separ¬ ately worked into finished skis over a single working step, in so-called compression, in which partial com¬ ponents are joined together. The lengths of adults' skis are 8 in number, at intervals of 5 cm from 180 cm up to 215 cm. In each length category, it is pos¬ sible to use e.g. three different degrees of rigidity or stiffness for alternate skiing mode. In addition, there will be a fourth category of stiffness for a so- called ski skating mode. Skating skis include e.g. three different lengths. Furthermore, it is possible to take into consideration a glide surface material selected according to skiing conditions (see above) , comprising three different materials. These can be worked out into the following number of combinations: alternate mode skis 72 in number (8 x 3 3) and skat¬ ing mode skis 9 in number (3 x 1 x 3) or totalling 81 different combinations of skis.

If, on the other hand, a system of the invention is studied by way of an example in a manner that the total number of inserts is 9 (see table) classified in three different categories of bending stiffness A, B, C and also in three length categories determined by the total length of a ski. The number of bodies needed in a given series (OR., fig. 2) 8 and the num¬ ber of series needed is 3 (OR., OR- and O , in which the variable factor is a bottom material selected on the basis of the applicability of a ski to skiing con¬ ditions. Thus, the necessary number of alternatives total 24 bodies (8 x 3, diagonal mode), 3 bodies (3 x 1, skating mode) and 9 inserts (3 x 3) , the total number being 36. Even if inserts were made in lengths suitable for each body length, the -number of necessary components would only be 51 .

This comparative example reveals clearly the super¬ iority of a method of the invention and a ski manu¬ factured thereby over the traditional manufacturing technology.

Fig. 1 illustrates the basic way of thinking behind a method of the invention. The bending stiffness curve of a body R belonging in a given series (set of characteristics) ORn as a function of the leng³th of a ski is similar to the one shown in fig. 1 e.g. for achieving certain characteristics. When a body

ORn/Rm is fitted with one of the inserts, selected in consideration of the length of body OR /R (index j), the total bending stiffness of a ski will be as de- sired since the bending stiffness of inserts is dif¬ ferent (index i) . The curves indicated by arrows il¬ lustrate the total bending stiffness of a ski when an insert L. . is mounted on the body. The camber con-

^~~ r 3 figuration of a ski is also made final at the time the insert is attached. The body naturally possess a basic camber imparted during the manufacturing pro¬ cess and, at the time of attachment, the body is bent in a desired degree for giving the ski a total degree of camber. The bending is effected by applying to the upper surface of a body more or less tensile stress

Fig. 2, in turn, depicts the system as a whole, where¬ by the number of body series (sets of characteristics OR) is n and the total number of alternative inserts is i x j . It is obvious that j, i.e. an index accord¬ ing to the length of inserts, is at its greatest equal to m or the number of bodies in a given series ORn.

The minimum value of index j. is naturally 1. Index i refers to various alternative degrees of bending stiff- ness. The fluctuation range of index i can be e.g. 2-6.

The bending stiffness El of a body is, as well known, the product of the module of elasticity based on mater- ial characteristics and the moment of inertia based on the dimensional characteristics and size of the cross-sectional area of a body. In other words, the bending stiffness of a body can be adjusted either by changing the module of elasticity (material character- istics) or the shape and/or size of the cross-sectional area of a body. In view of a ski, it is preferable in a method of the invention that, at least in a cer¬ tain length category (index j), the shape of the cross- sectional area of an insert be substantially the same, whereby the attachment of bindings and other access¬ ories of a ski is done the same way on all skis. In other words, it preferable to change the module of elasticity of an insert for the adjustment of El-value.

Fig. 3 is a perspective view showing by way of an example one embodiment of a ski manufactured accord¬ ing to the invention. The ski comprises a entity con¬ sisting of a body portion 1 and an insert 2. Insert 2 is mounted on the midsection of body 1 upon its upper surface 3 e.g. by one of the methods shown in figs. 6-10.

Fig. 4 shows in a layerwise view the structure of an insert. In this embodiment, insert 2 comprises a core 4 in the shape of a trapezoid having an equal-sided cross-section, whose longer parallel side faces to- wards the lower surface of said insert. The upper surface of core 5 is designed to curve slightly in the longitudinal direction of said insert. A suitable core material is e.g. polyurethane cellular plastics 3 (density e.g. 120 kg/m ) . On top of core 4 is applied a first strip 6, whose side skirts 7 are flush with the lower surface of said core on either side thereof. On top of the first, strip 6, in alignment with the core upper surface 5, there is mounted a reinforcement lamella 8. On top of said reinforcement lamella 8 is further applied a second strip 9, also provided with side skirts 10 extending on either side of the core.

Strips 6 and 9 surround reinforcement lamella 8. As a material for strips 6 and 9 it is possible to use

2 fiberglass fabric (circa 200-250 g/m ) . On top of said second strip 9 there are further applied strips

11 and 12, also provided with side skirts. Strip 11 can be e.g. a glass fabric (circa 35 g/m ) . Its pur- pose is to provide a surface quality for an insert together with strip 12, which can be e.g. a poly¬ propylene film whose surface coming against strip 11 is painted e.g. with an acrylic-based paint. The lower surface of an insert is possibly further pro- vided with a protective strip 13, e.g. a glass fabric serving as a gluing substrate for the above components. It can also be roughened for improving the attachment of an insert. Protective strip 13 also protects core 4 when grinding the bottom of an insert.

Thus, the total width of insert 2 is determined by the length of the lower side of the cross-sectional area of core 4 and the total width of the skirts associated therewith. It is naturally preferable that in an in¬ sert, core 4 is positioned centrally in the cross- section of an insert, the joining skirts forming fringe portions 14 on the lower edges of an insert, said fringe portions being, of equal width on either side of the core and the lamellae covering it. However, a reinforcement lamella 8 is critical in view of the stiffness characteristics of an insert. The material of a. reinforcement lamella 8, which is sub¬ stantially of the same length as. the upper surface of core 4, is selected so as to produce a desired bending stiffness. Examples of materials that can be used alone or in combinations as a material for reinforce¬ ment lamella 8 include carbon fiber and fiberglass. The module of elasticity of carbon fiber is circa 3-4 fold as compared to that of fiberglass (figures from literature: fluctuation range of the module of elastic¬ ity of carbon fiber is circa 235-370 GPa and fluctuat¬ ion range of the module of elasticity of fiberglass is circa 72-86 GPa) . It is conceivable to build a re- inforcement lamella 8 either exclusively of fiberglass, combinations of fiberglass and carbon fiber, in which case said reinforcement lamella 8 consists of a port¬ ion of fiberglass and a portion of carbon fiber whereby, by varying their relative thickness ratio it is possible to obtain different bending stiffness characteristics, or exclusively of carbon fiber. It is obvious that this is a way of producing a considerable number of inserts having different bending stiffnesses but still retaining a substantially identical shape. The bend- ing stiffness curve of an insert, whose maximum will be located roughly on the mid-portion of an insert in the longitudinal direction thereof, is produced by changing the cross-sectional area of a core so as to reduce it towards the ends of an insert (see the cross- sectional view in fig. 3) . The shape of the upper surface 5 of core 4, in a side view, may be a gentle parabolic curve, which opens towards the lower surface of an insert and whose culmination is in alignment with the mid-portion of an insert. At the ends of an insert, the upper surface 5 merges into the core lower surface 15 which is flat.

Fig. 6 depicts one embodiment of body 1. The body comprises a glide bottom 16, a reinforcement laminate 17 on top of it, whose material may be kevlar fiber. On top of the laminate there is placed a beehive struc¬ ture 18 serving as a core layer. On the sides of said beehive structure there are layers 19, 20 and 21. Of such lateral layers, layer 19 may be a strip made of cross-bonded plywood for increasing the torsional rigidity of a body, layer 20 may be a composite la¬ minateof.fiberglass and kevlar material and layer 21 may be a coating material, e.g. Duroplast. Mounted on top of core layer 18 is a laminate structure 22, serving as the upper surface of body 1 and comprising e.g. a composite laminate of fiberglass and carbon fiber. In principle, the body structure may be quite similar to present-day skis as for its sandwich struc¬ ture. The design of a body and selections of material are effected so that the bodies of a given series al- ways acquire a desired bending stiffness curve and a certain camber profile. This can be realized by means of presently available technology by designing a core member 18 so as to affect the moment of inertia and by suitably selecting the material of laminate structure 22 so as to affect the module of elasticity for chang¬ ing the bending stiffness of a body portion.

Figs. 6-10 depict different alternatives for embodying an insert.

Fig. 6 illustrates the embodiment shown in figs. 3 and 4 in which an insert 2 is provided with a core 4 that is narrower than the width of body 1. Thus, the upper surface of a ski is provided with, a ridge 23 with shoulders 14 on either side thereof. This embodiment offers the advantage that a skiing boot can be pro¬ vided with a groove of a matching shape for producing a directionally very stable system consisting of a boot, a binding and a ski. The joint for attaching insert 2 to body 1 is in this case a gluing, whereby the lower surface (fabric 13) serving as an insert fastening means is adfixed to the upper surface (la¬ minate structure 22) serving as a body fastening means. The surface of said laminate structure can be roughen¬ ed, ground or treated prior to gluing for improving the adhesion of glue. The attachment is effected in this case only by means of a gluing between the flat sections of the upper body surface and lower insert surface.

Fig. 7 shows a cross-sectional ski structure joined the same way as in fig. 6. In this case, however, the outer insert surface is provided with a groove 24, formed in the mid-portion of an insert and extend- ing in the longitudinal direction of an insert. When applying this type of system, a skiing boot may be provided with a matching ridge for producing a direct¬ ionally stable system as shown in fig. 6.

Fig. 8 depicts an attachment between insert 1 and a body, which attachment can be used instead of or to¬ gether with gluing. The shoulders of an insert are provided, at least over a portion of the length of an insert, with projections 25, resembling a dove tail in cross-section. The body, in turn, is pro- vided at matching locations with grooves 26, whose shapes correspond to said projections. In this em¬ bodiment, the upper insert surface is flat.

Fig. 9 shows an insert with a flat upper surface, comprising a. ridge or an array of ridges or dowels 27 on the lower insert surface. The similarly shaped grooves, recesses or holes 28 are provided at matching locations on body 1.

Fig. 10, in turn, shows the use of a. screw attachment for joining an insert and a body together, either as an exclusive attachment or in addition to gluing. A screw 29 is fixed through a hole 30 in the upper in¬ sert surface into a hole 30 in the upper surface of body 1. The flat-headed screw lies below the plane of the upper insert surface or flush therewith. A necessary number of screws can be used for fastening.

It should be noted that the embodiments shown in figs. 6-10 can be combined so the embodiments of the invent- ion include, in addition to the above figures, all variations obtained by combining the details set out in figs. 6-10. The snadwich structure shown in fig. 4 can also be realized in the insert structures shown in figs. 7-10, as obvious for a person skilled in the art.

A B E

a) race d) skating g) old snow length b) exercise e) diagonal h) fres snow c) special f) combination i) -25°...-8

(SALWI-classif ication ) j) -8' k) -I' + 1°

Claims

1. A method of producing a ski, comprising the follow¬ ing steps:

- manufacturing at least one body (R ) or at least one series (OR....OR ) of bodies (R._j...R_m),

- the length of each body matching the total length of a corresponding ski,

- which are provided with a glide surface and

- which have a certain bending stiffness,

- manufacturing at least one series of inserts (L.

'1,1

'1,3'

- which are shorter than the total length of a ski and

- each of which has a different bending stiffness,

- selecting according to the qualities and requirements of a skier a body (Rm) and at least one insert (L1. ,j.) and

- joining body (R ) and at least one insert (L. .) to- gether for producing a ski suitable for a skier as for its total bending stiffness and camber profile, c h a r a c t e r i z e d in that the insert/inserts are fixedly mounted on the midsection of the top body surface over their entire length.

2. A method as set forth in claim 1, c h a r a c t e r ¬ i z e d in that the bending stiffness of a given series of inserts (L....L. .) is adjusted by changing the module of elasticity of the inserts.

3. A method as set forth in claim 1, c h a r a c t e r ¬ i z e d in that at least some of the inserts (L ) are made for series of bodies (R, 1...R ) in seve

series, whose categorization is based, on one hand, on variation of the length of bodies (R ...R ) (index j) and, on the other hand, on variation of bending stiff¬ ness (index i) .

4. A ski, comprising a body (1) whose length matches the total length of said ski and whose lower surface is designed as a glide surface (^~6) of the ski, and at least one insert (2) which is shorter than the total length of said ski, c h a r a c t e r i z e d in that an insert (2) is fixedly mounted on a body (1) over the midsection of its top surface over its entire length by using fastening means provided on the top surface (22) of body (1) and on the bottom surface (13) of insert (2) .

5. A ski as set forth in claim 4, c h a r a c t e r ¬ i z e d in that said fastening comprise, on one hand, the upper surface (22) of body (1) and, on the other hand, the lower surface (13) of insert (2), which are both substantially flat and joined together by gluing.

6. A ski as set forth in claims 4 and 5, c h a r - a c t e r i z e d in that said body (1) and insert (2) are provided with at least one projection/groove combination (25, 26, 27, 28).

7. A ski as set forth in claims 4-6, c h a r a c - t e r i z e d in that the attachement between body

(1) and insert (2) is effected by using separate fast- ening means, such as screws (29) .

8. A ski as set forth in claim 4, c h a r a c t e r ¬ i z e d in that body (1) and insert (2) are of substant¬ ially equal width.

9. A ski as set forth in claim 4, c h a r a c t e r ¬ i z e d in that the insert is provided with a ridge (23) which extends lengthwise of the insert and is narrower than the total width of the ski.

10. A ski as set forth in claim 4, c h a r a c t e r ¬ i z e d in that the insert is provided with a groove (24) , which extends lengthwise of the insert and is narrower than the total width of the ski.

11. A ski as set forth in claim 4, c h a r a c t e r ¬ i z e d in that the upper insert surface is flat.

12. A ski as set forth in claim 4, c h a r a c t e r - i z e d in that said insert (2) comprises a sandwich structure with an innermost core member (4), whose cross-sectional area decreases from the mid-portion of said core towards the ends of said insert, a re¬ inforcement lamella (8) or the like connected with the core and a protective and coating structure (6, 9, 11, 12, 13) surrounding the core and the reinforcement lamella.

13. A ski as set forth in claims 4 and 12, c h a r - a c t e r i z e d in that said reinforcement lamella (8) is made of carbon fiber and/or fiberglass and that the module of elasticity of insert (2) is adapted to be adjusted by the selection of a carbon fiber/ fiberglass ratio.

14. A ski as set forth in claims 4, 12 and 13, c h a r a c t e r i z e d in that the cross-sectional profile of said core is an equal-sided trapezium, whose lower parallel side is facing the lower insert surface, the length of this side being less than the total width of the insert, whereby said protective and coating structure (6, 9, 11, 12, 13) forms on the sides of said core a shoulder portion (14) and that re¬ inforcement lamella (8) is positioned in alignment with the shorter parallel side of said core.