WO1994019175A1

WO1994019175A1 - Process for making a hollow ski and hollow ski made thereby

Info

Publication number: WO1994019175A1
Application number: PCT/DE1994/000185
Authority: WO
Inventors: Thomas Brenn; Wolfgang Danz; Michael H. Von Schweinichen
Original assignee: Germina Sport-Equipment Gmbh
Priority date: 1993-02-23
Filing date: 1994-02-17
Publication date: 1994-09-01
Also published as: FI953950A; NO953296L; NO953296D0; AU6106294A; EP0686083A1; SI9400092A; FI953950A0

Abstract

In prior art hollow skis the raw material is arranged in a mould in such a way that it surrounds an elastic air chamber which is pressurised, whereafter the material is cured. The process of the invention is intended to provide a hollow ski of low weight and high rigidity. To this end the air chamber takes the form of two sections of a double hose (6, 7) side-by-side in the longitudinal direction of the ski. In each section of the double chamber a fibre-fabric outer hose (7) is pushed over an airtight, thin-walled and expandable plastic inner chamber (6) and, after impregnation with a synthetic resin, it is inflated through the inner hose and pressed against the running surface and against the fibre-fabric material forming the outer layer of the hollow body which is also impregnated with synthetic resin so that a vertical ridge (8) is formed along the hollow ski. The components are firmly bonded together by curing and form the ridig bond of the hollow ski.

Description

Process for the production of a hollow ski and hollow ski produced thereafter

The invention relates to the production of a hollow ski, in particular a cross-country ski, from fiber-reinforced plastic, the starting materials of which, which comprise a tread part and a material forming the outer layer of the hollow body, are inserted into a mold and thereby enclose an air chamber, wherein the mold is then closed and the air chamber is inflated under pressure, as a result of which the starting materials attach themselves to the inside of the mold and a hollow body is formed, and then the hollow ski is hardened and a hollow ski produced thereafter.

Patent DE 12 04 983 already discloses a method for producing a hollow ski, in which the starting material of the hollow ski is arranged in a press mold in such a way that it surrounds an elastic air chamber which is pressurized, after which the material is hardened leaves, as a starting material in a manner known per se, a mixture of plastic and glass fibers is arranged in the press mold in such a way that at least some of the glass fibers run longitudinally and that the longitudinal glass fibers are aerated by means of the air chamber before the mixture hardens there is known bias.

The air chamber used to pretension the longitudinal glass fibers is somewhat shorter than the press mold and very elastic. For example, it is made of rubber.

To manufacture the hollow ski, a glass fiber fabric in the form of bands is placed in a two-part form and the air chamber is arranged under the bands, whereupon the edge parts are wrapped around the air chamber. A valve is inserted from above in the air chamber through which the air is pressed into the air chamber.

After the ski has been manufactured, either the valve must be cut off. ten and the air chamber remains in the ski or the air chamber is pulled up out of the hollow ski. To do this, a larger hole must be cut in the top chord. The air chamber can also remain in the ski with the valve. In all cases, the hollow ski is weakened in terms of strength in the area of the upper flange.

The firmness of the hollow ski consists of the hollow body formed by the bands and the sliding sole molded into the press mold. The air chamber itself serves only for the production of the ski with the production of a pretension for longitudinal glass fibers.

It is known from patent AT 241 311 that in the manufacture of hollow skis from preferably thermosetting and glass fiber reinforced plastic, which is pressed against the walls of the mold by inflating tubes arranged in the mold, the latter having a lower molded part of at least has an approximated U-shaped cross section, so that a flexible plate is provided as the upper molded part, which deforms in the transverse plane when the tubes are inflated. The aim here is to give the top flange of the hollow ski a different curvature and thus to change its flexibility. At least three inflatable tubes are used. These tubes are also used exclusively to form the shape of the hollow ski.

With these solutions it was not possible to produce hollow skis with sufficient strength. Therefore, prefabricated profiles are used for the ski bodies in newer solutions.

A ski with a tread part and a hollow ski body is known from WO 90/03205, the height of which, measured normal to the tread part, differs over the length of the ski. The ski body is designed as a hollow body with parallel side edges that run in the longitudinal direction of the ski. Det, wherein the width of the ski body is measured less than or equal to the smallest width of the waisted tread part transverse to the longitudinal direction of the ski. The hollow body is designed as a shell body and closed on the side facing away from the tread part with an upper belt component. Such a shell body consists of extruded profiles, which are endlessly manufactured and cut to length. The thickness contour can be milled onto the upper and / or lower shell.

This configuration ensures that the strength, elasticity and torsion properties can be defined more precisely over the length of the ski.

However, a ski made in this way has a relatively high weight and is therefore particularly unsuitable for cross-country skiing. In addition, the production costs are quite high despite the possible use of extruded profiles.

A method for producing a ski from a strand-shaped hollow body is also known from PCT application WO 91/6350. Here, the strand-like hollow body is first brought into an approximately oval shape by extrusion, extrusion or the like. Then sections of the length of the ski to be produced are separated from this hollow body. These sections are then subjected to a pressure treatment, such as rolling, pressing, pressing or the like, the middle region of the ski, which later carries the binding, not being exposed to the pressure treatment, or only to a small extent, while the pressure treatment with the distance from the middle Area increases. Finally - as is known per se - steel profiles are placed on the edges of the lower surface, the sliding surface of the ski. The strand-shaped hollow body forming the ski is expediently brought into the form of a flat lens.

The hollow body of such a ski also consists of an extruded profile. Such a strand-like hollow body should, however, expediently be produced by extrusion from a light metal profile. Because of the pressure treatment provided, this disclosed solution is certainly not at all or hardly suitable for extruded plastic profiles. A ski made in this way also has a relatively high weight.

Due to its specific material properties, a metal ski, particularly in cross-country skiing, has hardly been able to establish itself.

From DE 32 36 016 AI a hollow body ski is known which has a hollow body running in the longitudinal axis of the ski, which can also be subdivided by webs in the longitudinal and / or transverse axis. The shape of the ski is given an upwardly directed, semicircular curvature by the hollow body in the transverse axis. According to the requirements, the hollow body can form a vacuum, be filled with air, gas or other solid and liquid substances.

The ski body itself is disclosed as a one-piece body on which further parts, such as the ski sole, are arranged. Such a body provided with webs can practically only be produced as an extruded profile, so that this hollow ski also has a high weight.

The invention is based on the object of a method for producing a hollow ski, in particular a cross-country ski, from fiber-reinforced plastic, the starting materials of which, which comprise a tread part and a material forming the outer layer of the hollow body, are inserted into a mold and thereby enclose an air chamber , the mold then being closed and the air chamber being inflated under pressure, as a result of which the starting materials attach themselves to the inside of the mold and a hollow body is formed and attached finally, the hollow ski is cured, and to create a hollow ski produced thereafter, which has a low weight and high strength.

According to the invention, the object is achieved in that the air chamber is formed from two sections of a double hose lying next to one another in the longitudinal direction of the hollow ski, with an outer hose consisting of a fiber fabric being placed on an airtight, thin-walled and stretchable inner hose made of plastic in each section of the double hose is pushed open and this outer tube is inflated after the impregnation with a synthetic resin through the inner tube and on the tread part and on the outer layer of the hollow body which is also impregnated with synthetic resin and consists of a fiber fabric and in the central area of the hollow body is pressed against the outer tube of the second section of the double tube, thereby forming a vertical web which extends in the longitudinal direction of the hollow ski, all parts being firmly connected to one another by the hardening and the firmness of the hollow ski form.

The solution according to the invention ensures that a very light hollow ski with high strength is produced in a press mold by inflating an air chamber. The air chamber consists of a component in the form of the double tube, the outer tube of which is itself a functional component of the strength structure of the hollow ski. The inner tube has only a low weight and, as explained below, can also form a functional component. This avoids that these parts have to be removed, which means an additional manufacturing effort and can always lead to damage to the hollow ski produced.

It is advantageous if the adjacent sections of the double hoses forming the air chamber consist of one piece which is approximately twice the length of the hollow ski. is seated and inserted from the rear end of the hollow ski on one side into the form into the area of the ski tip, bent there by 180 "and inserted parallel to the first position on the other side of the form up to the rear end of the hollow ski A further reduction in the production outlay is thereby achieved.

The two open ends of the inner tube of the one-piece double tube located in the region of the rear end of the hollow ski are expediently connected to a common compressed air source and inflated at the same time and with the same pressure, as a result of which the hollow body is formed.

This ensures that the production time is reduced with a uniform design of the hollow body. The strength build-up of the ski is not impaired by connecting the compressed air source at the rear end of the ski. The upper and lower belt are not interrupted, and the sensitive area of the ski tip is not used. The rear ends can be easily closed in terms of production technology after inflation and curing.

A preferred production is that from the rear end of the hollow ski to the area of the ski tip, by inflating the double hoses forming the air chamber, the cross section of the hollow body is formed as an arc segment with the tread part as a chord.

The arc segment can be designed as a circle segment, the cross-section of the circle segment being formed in different dimensions along the length of the hollow body.

The solution according to the invention makes it possible to optimally use the method for inflating the ski and, with a low weight, the strength of the hollow ski produced further increase. This shape also makes it possible to create smooth transitions, although curved and circular segments can also be used with a hollow ski. It will always be advisable to provide the largest cross-sections in the central area of the ski, with a flatter design towards the rear and the front being preferred.

In order to achieve high strength also in the area of the ski tip, the hollow ski is made flat there and the ski tip is used in the form of a plastic part. It has been found in tests that in this way a manufacturing-related breaking of the ski tip can be avoided. It is possible to finally produce the shape of the ski tip, for example by milling.

A further improvement in the strength of the hollow ski can be achieved by placing reinforcement elements on the material forming the outer layer of the hollow body when it is inserted into the mold, which reinforcement elements exist in the finished hollow ski between the inside of the material and the outside of the outer hose.

Carbon and / or glass fibers extending in the longitudinal direction of the hollow ski can be placed as reinforcing elements.

However, it is also possible for the reinforcing elements to be placed on points of the hollow body which are subject to strength, such as in the region of the binding.

In order to achieve good properties of a hollow ski, a preferred selection of materials is that

the tread part made of an outsole made of polyethylene and a lower flange made of a carbon laminate firmly connected to it, the material forming the outer layer of the hollow body from a carbon and / or glass fiber fabric impregnated with synthetic resin or a corresponding prepreg,

the outer tube of the double tube through a carbon fiber fabric or glass fiber fabric or aramid fabric impregnated with synthetic resin or a carbon fiber / glass fiber mixed fabric or a corresponding prepreg,

- The inner tube made of a polyamide film

is formed.

The inner tube can be used as a functional component in the manufacture of the hollow ski, in that the inside of the hollow body is sealed by the inner tube which is firmly connected to the outer tube during curing.

In a further embodiment of the hollow ski, the hollow body can be filled with a gas or a gas / air mixture, for example by blowing in helium.

It is also possible for the hollow body to be filled with a sliding wax and to be connected to the surface of the outsole of the tread part via exits for the sliding wax.

In a further embodiment of the invention, this also comprises a hollow ski, in particular a cross-country ski, made of fiber-reinforced plastic with a material which forms a tread part and a material which forms the outer layer of a hollow body, produced by the method described above, two in the hollow body enclosed by the tread part and the material In the longitudinal direction of the hollow ski, adjacent sections of a double tube are arranged, in which an outer tube consisting of a fiber fabric is placed on an airtight, thin-walled and stretchable inner tube made of plastic is pushed on and this outer tube after the formation of the hollow body and the hardening of the hollow ski on the tread part and on which form the outer layer of the hollow body, likewise impregnated with a synthetic resin and consisting of a fiber fabric and in the central region of the hollow body on the Outer hose of the second double hose abuts and is firmly connected to these parts, the abutting sections of the outer hoses being designed as a vertical web extending in the longitudinal direction of the hollow ski. The sections of the double tube are preferably formed as a coherent piece which has approximately twice the length of the hollow ski, these being arranged in the hollow body from the rear end of the hollow ski parallel to one another and into the area of the ski tip and around this front area Are bent 180 ° to each other.

A preferred embodiment of the hollow ski is that the hollow body is designed in its cross section as an arc segment with the tread part as a chord.

The arc segment is expediently designed as a circular segment, which has different dimensions along the length of the hollow body. This makes it possible to use a hollow ski in the desired shape in accordance with the intended use, such as a cross-country ski for sporting competitions, but also as a tourist ski. It is even possible to train downhill or slalom skis in this way. The tread part can also be provided with steel edges.

In order to be able to attach the ski binding to a hollow ski designed in this way, it is expedient that a binding part receiving the ski binding is detachably arranged on the hollow body, the underside of which is adapted to the shape of the hollow body. To further increase the strength of the hollow ski, reinforcing elements can be arranged locally in the hollow body between the inside of the material forming the outer layer and the outside of the outer tube. These reinforcing elements can consist of carbon and / or glass fibers which extend in the longitudinal direction of the hollow ski and are arranged in particular in the region of the upper flange. However, they can also be designed as surface elements. In a preferred manner, the hollow ski can be constructed such that

the tread part made of an outsole made of polyethylene and a lower flange made of a carbon laminate firmly connected to it,

the material forming the outer layer of the hollow body from a carbon and / or glass fiber fabric impregnated with synthetic resin or a corresponding prepreg,

the outer tube of the double tube made of a carbon fiber fabric or glass fiber fabric or aramid fabric impregnated with synthetic resin or a carbon fiber / glass fiber mixed fabric or a corresponding prepreg,

- The inner tube made of a polyamide film

consists.

Furthermore, it is expedient if the interior of the hollow body is sealed by the inner hose which is firmly connected to the outer hose. As a result, the hollow body can be filled with a gas or a gas / air mixture, both of which have a lower specific gravity than air.

A sliding wax can also be located in the hollow body, this region then being connected to the outsole of the tread part. The invention is explained in more detail using an exemplary embodiment. In the accompanying drawing:

Fig. 1 is a plan view of a tread part

2 shows a plan view of a material blank for the production of a hollow ski

3 shows a cross section through a mold with inserted components and a non-inflated double hose

4 shows a cross section through a mold according to FIG. 3 with an inflated double hose

Fig. 5 is a plan view of a hollow ski, connected to the compressed air source

6 shows a cross section through a hollow ski in the middle region.

A ski manufactured according to the method according to the invention has as base components a tread part 1 shown in FIG. 1, a material 5, which is shown as a blank in FIG. 2, and a double hose 6; 7 on.

The tread part 1 consists of an outsole 2 and a lower flange 3 connected thereto. The outsole 2 is preferably made of polyethylene. Your bottom can already be profiled. However, it is also possible to edit them later, for example by milling climbing aids. The lower flange consists of a carbon laminate.

The outsole 2 and the lower flange 3 can be cut off from a band according to the ski length and inserted into a mold 14.

The material 5 forms the outer layer of the hollow body 4 of the hollow ski. It consists of a carbon and / or glass fiber fabric impregnated with synthetic resin or a corresponding prepreg. The fibers can be arranged differently in the material 5. It is possible to use both mats and fabrics clog. An increase in strength is achieved if carbon fibers or also glass fibers are arranged in the longitudinal direction, particularly in the region of the upper flange. This is particularly advantageous for cross-country skis.

The material 5 receives a cut according to the intended shape of the hollow ski before it is inserted into the mold 14. In this way it is possible to produce hollow skis with very different hollow bodies 4. The individual cross sections of the ski can also have a very different design. This is achieved without a large number of different parts having to be used for the hollow body 4, as when using extruded profiles.

A possible cutting of the material 5 is shown schematically in FIG. 2. The material 5 generally has its greatest width in the central region, since the hollow body 4 also has its greatest circumference in this section. It is of course also possible for the material 5 to consist of several parts which are put together in the mold 14.

Another basic component is a double hose 6; 7. This is formed in that an outer tube 7 is pushed onto an inner tube 6. The inner tube 7 forms an inflatable air chamber and consists of a thin, very extensible material, such as a polyamide film. The outer tube 7, which forms part of the strength connection of the hollow ski, consists of a carbon fiber fabric or glass fiber fabric or aramide fabric impregnated with synthetic resin or a carbon fiber / glass fiber mixed fabric or a corresponding prepreg.

3 and 4 show how the components of the hollow ski are placed in a mold 14 and how the hollow ski is manufactured. The tread part 1 is placed with the outsole 2 downward in a lower part 14a of the mold 14. The cut material 5, which forms the outer layer of the hollow body 4, is placed in an upper part 14b of the mold 14. This basically consists of several individual fabric webs, for example four webs. These are inserted one after the other and soaked with a synthetic resin, such as an epoxy resin. Preferably, contact is already made with the inner wall of the mold so that wrinkling leading to rejects is avoided. The prepared double tube 6; 7 inserted. Here, as can be seen from FIG. 5, it consists of one piece. The double hose 6; 7 is inserted from the rear end 11 of the hollow ski on one side of the mold 14. It is led into the area of the ski tip 9. There it is bent by 180 ° and returned parallel to the first layer on the other side of the mold 14 to the rear end 11 of the hollow ski.

The ski tip 9 itself is in the front part of the material 5 before the double hose 6; 7 inserted (Fig. 5). It consists of a plastic part, which is only finished after the hollow ski has been pressed. Experiments have shown that breakage of the ski tip 9 can be largely avoided in this way. At the rear end 11 of the hollow ski, the two adjacent ends of the inner tube 6, which forms the air chamber, are connected to a compressed air source 13, as shown in FIG. 5. This ensures an even inflation.

It is of course also possible to use two double tubes 6; 7 to insert. Inserting a double hose 6; 7 and a kink in the front area of the hollow ski has proven to be more expedient.

After this preparation, mold 14 is closed. The position of the components in the mold 14 is shown schematically in FIG. 3. After the mold 14 has been closed, the inner tube 6 is inflated evenly from both sides. This is basically done by blowing in air, which is released again after the end of production. By inflating the inner tube 6, the outer tube 7, as described above, consisting of a fiber fabric, is attached to the tread part 1, specifically to the lower flange 2, and to the inside of the material 5 of the hollow ski that forms the outer layer of the hollow body 4 pressed. In the central region of the hollow body 4 that forms, the two adjacent sides of the outer tube 7 are pressed against one another and thus form a vertical web 8, as shown in FIG. 4.

After the shaping is finished, the hollow ski hardens. It is expedient to cure the hollow ski at a temperature between 70 ° C. and 150 ° C. within 20 minutes to 30 minutes. All parts, including the outer tube 7, form the strength bond of the hollow ski. This has a low inherent weight of the hollow ski and its high strength.

After the pressing process, the hollow ski is removed from the mold 14 and the connections to the compressed air source 13 are removed. The rear end 11 of the same is then closed in a manner known per se and the hollow ski is finished. It is no longer necessary to remove components from the interior of the hollow ski, as a result of which the processing times are reduced and possible damage to the hollow ski is avoided.

The inner tube 6, which consists of a stretchable film, is firmly connected to the outer tube 7 and seals the hollow body 4 to the outside.

7 shows a cross section through the hollow ski according to the invention in the central region. The tread part 1 forms the lower part thereof. sole 2 and the lower flange 3, both parts being firmly connected. The hollow body 4 of the hollow ski is enclosed by a material 5 forming the outer layer.

This material 5 consists of several fabric sheets impregnated with synthetic resin and lies against the tread part 1. In the hollow body 4, the double hose 6; 7 arranged, which has adjacent sections in the longitudinal direction of the hollow ski. These parts are firmly pressed together during the production by the inflation process and are permanently connected by the curing. The outer tubes 7 simultaneously form a vertical web 8 in the central region of the cross-section of the hollow ski, which extends along the hollow body 4.

A preferred embodiment consists in that the hollow body 4 is designed in its cross-section as an arc segment with the tread part 1 as a chord. The arc segment can be a circular segment which has 4 different dimensions along the length of the hollow body. This results in a particularly torsionally rigid design and, in conjunction with the web 8, a rigid design.

In the area of the ski tip 9, the hollow ski is flat, the ski tip 9 being inserted in the form of a plastic part.

To further increase the strength, locally reinforcing elements are arranged between the inside of the outer layer of the material 5 and the outside of the outer tube 7. These can consist of carbon and glass fibers which extend in the longitudinal direction of the hollow ski and which are arranged in particular in the region of the upper chord.

It is also possible to use surface elements in particularly stressed areas, in the area of the binding or in the area of the tere end 11 or in the region of the ski tip 9 of the hollow ski to be arranged. These reinforcing elements 11 can be easily inserted into the mold during manufacture.

In order to be able to properly attach the binding to the hollow ski even when the surface of the hollow body 4 is in the form of an arc segment, a binding plate 10 can be arranged. This has the same shape as its surface on the side facing the hollow body 4, whereby it is flat on the side of the binding.

In a preferred embodiment, the binding plate 10 is releasably attached to the hollow ski. But it is also possible to firmly connect them to the material 5.

As already explained, the hollow body is sealed by the inner tube 6. The interior can thus be filled with a gas or a gas / air mixture, such as helium. However, it is also possible to incorporate a sliding wax that exits in the direction of the outsole and improves the sliding properties of the hollow ski.

The hollow ski can of course also be designed in a different shape, for example rectangular. However, its manufacture makes it easy to implement the same with arc-shaped or circular-segment-shaped cross-sections and flowing transition shapes, so that this shape, which has already been proposed, can now actually be manufactured inexpensively.

The hollow ski according to the invention has a high strength with a low weight. This solution is therefore particularly suitable for cross-country skis in sporting and tourist use.

Claims

1. A method for producing a hollow ski, in particular a cross-country ski, made of fiber-reinforced plastic, the starting materials, which comprise a tread part and a material forming the outer layer of the hollow body, are inserted into a mold and thereby enclose an air chamber, the mold subsequently is closed and the air chamber is inflated under pressure, as a result of which the starting materials attach themselves to the inside of the mold and a hollow body is formed and the hollow ski is then cured, characterized in that the air chamber consists of two sections lying next to one another in the longitudinal direction of the hollow ski of a double hose (6; 7) are formed, with each section of the double hose (6; 7) being pushed onto an airtight, thin-walled and expandable inner hose (6) made of plastic, an outer hose (7) consisting of a fiber fabric and this outer hose (7) n After impregnation with a synthetic resin, it is inflated through the inner tube (6) and onto the tread part (1) as well as the material (5), which is also impregnated with synthetic resin and which is also impregnated with synthetic resin in the central area of the hollow body (4) to the outer tube (7) of the second section of the double tube (6; 7) is pressed and a vertical web (8) extending in the longitudinal direction of the hollow ski is formed, all parts being firmly connected to one another by the hardening and forming the strength bond of the hollow ski.

2. The method according to claim 1, characterized in that the juxtaposed, the air chamber forming sections of the double hoses (6; 7) consist of one piece, which have approximately twice the length of the hollow ski and of the rear end (11) of the hollow ski from one side into the mold (14) into the area of the ski tip (9), where it is bent by 180 ° and parallel to the first layer on the other side of the mold (14) to the rear end (11) of the Hollow skis are inserted.

3. The method according to claim 1 and 2, characterized in that the two lying in the region of the rear end (11) of the Hohl¬ skis open ends of the inner tube (6) of the one-piece double tube (6; 7) to a common compressed air source (13) are connected and at the same time the air chamber is inflated with the same pressure and the hollow body (4) is formed.

4. The method according to claims 1 to 4, characterized gekennzeich¬ net that from the rear end (11) of the hollow ski to the area of the ski tip (9) by inflating the double hoses forming the Luft¬ chamber (6; 7) Hollow body (4) is designed in its cross section as an arc segment with the tread part (1) as a chord.

5. The method according to claim 4, characterized in that the arc segment is formed as a circle segment, the circle segment being formed in cross section in different dimensions along the length of the hollow body (4).

6. The method according to one or more of claims 1 to 5, characterized in that in the region of the ski tip (9) the hollow ski is flat and the ski tip (9) is used in the form of a plastic part.

7. The method according to claims 1 to 6, characterized gekennzeich¬ net that on the outer layer of the hollow body (4) forming material (5) when inserted into the mold (14) reinforcing elements are placed, which in the finished hollow ski between the Inside of the material (5) and the outside of the outer tube (7).

8. The method according to claim 7, characterized in that carbon and / or glass fibers extending as reinforcing elements in the longitudinal direction of the hollow ski are placed.

9. The method according to claim 7, characterized in that the reinforcing elements at Stel¬ len strengthened parts of the hollow body (4), such as in the region of the bond, are placed on.

10. The method according to claims 1 to 9, characterized gekennzeich¬ net that

- The tread part (1) made of an outsole (2) made of polyethylene and a lower flange (3) firmly connected to it made of a carbon laminate,

the material (5) forming the outer layer of the hollow body (4) from a carbon and / or glass fiber fabric impregnated with synthetic resin or a corresponding prepreg,

the outer tube (7) of the double tube (6; 7) through a carbon fiber fabric or glass fiber fabric or aramid fabric or a carbon fiber / glass fiber mixed fabric or a corresponding prepreg soaked with synthetic resin,

- The inner tube (6) made of a polyamide film

is formed.

11. The method according to one or more of claims 1 to 10, characterized in that the inside of the hollow body (4) is sealed by the inner tube (6) which is fixedly connected to the outer tube (7) during curing.

12. The method according to one or more of claims 1 to 11, characterized in that the hollow body (4) is filled with a gas or a gas / air mixture.

13. The method according to claim 12, characterized in that helium is blown in as the gas in the hollow body (4).

14. The method according to one or more of claims 1 to 11, characterized in that the hollow body (4) is filled with a liquid sliding wax and is connected to the surface of the outsole (2) of the tread part (1) via exits for the sliding wax.

15. Hollow skis, in particular cross-country skis, made of fiber-reinforced plastic with a material with a tread part and an outer layer of a hollow body, produced by the method according to claims 1 to 14, characterized in that in the through the tread part (1) and Material (5) enclosed hollow body (4) two sections of a double tube (6; 7) lying next to each other in the longitudinal direction of the hollow ski are arranged, in which an outer tube consisting of a fiber fabric is placed on an airtight, thin-walled and stretchable inner tube (6) made of plastic (7) is pushed on and this outer tube (7) after the formation of the hollow body (4) and the hardening of the hollow ski on the tread part (1) as well as on the outer layer of the hollow body (4), also with a synthetic resin impregnated material (5) consisting of a fiber fabric and in the central region of the hollow body (4) on the outer surface outer hose (7) of the second double hose (6; 7) and is firmly connected to these parts, the abutting sections of the outer tubes (7) being designed as a vertical web (8) extending in the longitudinal direction of the hollow ski.

16. Hollow ski according to claim 15, characterized in that the sections of the double tube (6; 7) are formed as a contiguous piece which has approximately the double length of the hollow ski, these in the hollow body (4) from the rear end (11) of the hollow ski to the area of the ski tip (9) are arranged parallel next to each other and are bent 180 ° to each other in this front area.

17. Hollow ski according to claim 15 and 16, characterized in that the hollow body (4) is designed in its cross section as a Bogen¬ segment with the tread part (1) as a chord.

18. Hollow ski according to claim 17, characterized in that the arc segment is designed as a circle segment which has different dimensions along the length of the hollow body (4).

19. Hollow ski according to claim 16 and 17, characterized in that on the hollow body (4) a binding plate receiving the ski binding (10) is detachably arranged, the underside of which is adapted to the shape of the hollow body (4).

20. Hollow ski according to one or more of claims 15 to 19, characterized in that in the region of the ski tip (9) the hollow ski is flat and the ski tip is inserted in the form of a plastic part.

21. Hollow ski according to one or more of claims 15 to 20, characterized in that locally reinforcing elements are arranged in the hollow body (4) between the inside of the material forming the outer layer (5) and the outside of the outer tube (7).

22. Hollow ski according to claim 21, characterized in that the reinforcing elements consist of carbon and / or glass fibers which extend in the longitudinal direction of the hollow ski and which are arranged in particular in the region of the upper flange.

23. Hollow ski according to claim 21, characterized in that the reinforcing elements are designed as surface elements.

24. Hollow ski according to claims 15 to 23, characterized gekennzeich¬ net that

- The tread part (1) consists of an outsole (2) made of polyethylene and a lower flange (3) made of a carbon laminate, which is firmly connected to it.

- the outer tube (7) of the double tube (6; 7) made of a carbon fiber fabric or glass fiber fabric or aramid fabric impregnated with synthetic resin or a carbon fiber / glass fiber mixed fabric or a corresponding prepreg,

- The inner tube (6) made of a polyamide film

consists.

25. Hollow ski according to one or more of claims 15 to 24, characterized in that the interior of the hollow body (4) is sealed by the inner hose (6) which is firmly connected to the outer hose (7).

26. Hollow ski according to one or more of claims 15 to 25, characterized in that the hollow body (4) is filled with a gas or a gas / air mixture, both having a lower specific gravity than air.

27. Hollow ski according to one or more of claims 15 to 25, characterized in that there is a sliding wax in the hollow body (4) and this area is connected to the outsole (2) of the tread part (1).