The present invention relates to a sliding element for the summer use of slopes, for example, ski-jumping slopes, which sliding element includes a sliding surface formed of one or several yarn layers attached together, in which sliding element each yarn layer is formed of individual yarns.

Finnish published patent application FI 71065 is known from the prior art, in which application a sliding element for slopes is disclosed, in which the yarns are attached to each other at one end, and then attached in turn at the same end to a bottom sheet. For example, on ski-jumping slopes the sliding properties of the sliding element are improved by pouring irrigation water on top of the sliding elements. However, the water easily flows off the top of the yarns and, in addition, in sunny weather the water evaporates rapidly from the surface of the yarns. Irrigation must be repeated frequently, which considerably increases the consumption of water and through it the operating costs of the slope.

The yarns of sliding elements according to the prior art generally have a cross-section with an oval shape, because it is difficult to manufacture yarns with a circular cross-section. A problem with such yarns is also the large friction surface that they create. This weakens the sliding properties of the slope. In addition, the manufacture of a single sliding element requires a considerable amount of yarn manufacturing material. The invention is intended to create a sliding element for the summer use of slopes, which is better than the prior art, and with the aid of which it is possible to achieve material savings and improve the sliding properties of the slope. The characteristic features of the invention appear in the accompa- nying Claim 1. This intention can be achieved by means of the sliding element according to the invention for the summer use of slopes, for example ski-jumping slopes, in which at least some of the yarns include at least one groove in the longitudinal direction of the yarn, for binding water to the yarns. The sliding element includes a sliding surface formed from one or several yarn layers attached together, in which sliding layer each yarn layer is formed of individual yarns. With the aid of the groove or grooves, the amount of material required for manufacturing the yarns can be reduced by as much as 30 %. At the same time, the need for irrigation water on the slope decreases, as the groove or grooves bind water considerably better than a solid yarn . The sliding element preferably includes a bottom sheet attached under the sliding surface. The bottom sheet prevents the ground vegetation from penetrating through the sliding element.

The cross-section of the yarn is preferably shaped like a multi-leaved clover. In such a yarn, there will then be at least two grooves for binding irrigation water to the yarn. In this connection, the term a multi-leaved clover refers to the shape of a clover with a least two leaves, i.e. a cross-sectional shape in the yarn., in which there are at least two grooves.

Each yarn preferably includes at least four longitudinal grooves. By increasing the number of grooves, a greater material saving is achieved, as well as a lower surface pressure at the points of contact with the bottom of the skier's ski or board. At lower pressure at the points of contact will, for its part, improve wear resistance.

Each groove can have a depth of 5 - 35 ¾, preferably 15 - 25 % of the diameter of the cross-section of the yarn. The depth of the groove affects the groove's ability to bind water to the yarn, i.e. in other words the said groove is a free space in the yarn for binding water.

Each groove can have a width of 3 - 20 %, preferably 5 - 10 % of the circumference of the cross-section. The width of the groove affects the magnitude of the contact surface between the yarn and the skier.

According to one embodiment, each yarn includes grooves with differing depths and widths. In such a solution, the yarn can have different properties on different sides of the yarn.

According to one embodiment, the groove has a cross-section with a semi-circular shape. According to a second embodiment, the groove has a cross-section with a square shape. The shape of the groove affects its property of holding water inside it. A yarn with a cross-section shaped like a four-leaved clover is particularly advantageous, because the grooves in it are wide, in which case the material savings are considerable.

The yarn is preferably manufactured using an extruder nozzle with the shape of the cross-section of the yarn. The cross- section of each yarn is preferably shaped like a four-leaved clover. With the aid of an extruded nozzle, it is easy to manufacture yarns equipped with different cross-sections.

At least some of the grooves are preferably continuous and in the direction of the longitudinal axis of the yarn over the entire length of the yarn. The greatest savings in material will be achieved in this way.

According to one embodiment, at least some of the grooves are continuous over the entire length of the yarn and are arranged helically on the outer surface of the yarn. According to a second embodiment, at least some of the grooves can be arranged over at least 50 % of the total length of the yarn . According to one embodiment, the bottom sheet includes ribs set in the longitudinal direction of the sliding element, which rise towards the sliding surface, and the sliding element further includes a sheet part forming the upper part of the suspension element, arranged on top of the ribs and partly on top of the sliding surface. With the aid of the suspension element made from the bottom sheet, the attachment point of the sliding surface is made more even than the prior art, so that the slope will feel smoother to one descending it. The bottom sheet and sheet part are preferably formed by folding a bottom-sheet blank double. Thus, the bottom sheet and the suspension element can be formed from a single uniform part, so that the totality has excellent strength. According to one embodiment, the bottom sheet includes ribs in the longitudinal direction of the bottom sheet, for holding the sliding surface in place. The ribs prevent the yarns from moving to the side under the weight of the person descending. According to one embodiment, the sheet part includes a first fold for folding the sheet part from a base-sheet blank, a second fold for folding the sheet part on top of the rising ribs, as well as a third fold for folding the sheet part partly on top of the sliding surface. With the aid of the folds, the suspension element can be formed without having to attach separate pieces to each other.

The rising ribs are preferably at the end of the sliding sur ^¬ face. Thus, the sheet part takes up a gently sloping angle, which helps to make a slope even to descend. By means of the sliding element according to the invention, the use of raw material, the weight of the surfacing, and the storage and transport space can be minimized. The sliding element according to the invention reduces considerably the amount of irrigation water required. In the present application, the term groove refers to a recess in the surface of the yarn in the longitudinal direction of the yarn, deviating from a circular or corresponding shape in the cross-section of the yarn towards the centre-point of the yarn. The groove forms a space in the surface of the yarn for irrigation water.

In the following, the invention is described in detail reference to the accompanying drawings, showing some embodiments of the invention, in which

Figure 1 shows an axonometric view of the bottom sheet of a sliding element according to one embodiment of to the invention, depicted without the sliding surface,

Figure 2 shows an axonometric view of the suspension element of a sliding element according to one embodiment of the invention,

Figure 3 shows a more detailed axonometric view of the yarns used in the sliding element according to one embodiment of the invention.

Figures 1 - 3 show a sliding element according to one embodiment, in which the sliding surface is attached to the bottom sheet with the aid of a suspension element folded from the bottom sheet. The sliding element according to the invention can also be according to the prior art in terms of the attachment of the sliding surface.

Figure 1 shows the bottom-sheet blank 16' of the sliding element according to the invention, prior to the attachment of the sliding surface and the folding of the sheet part 20 of the bottom-sheet blank 16'. The bottom-sheet blank 16' preferably includes longitudinal ribs 22, rising ribs 24, a sheet 34, and two folding flat surfaces 26 and a second flat surface 28 of the sheet part 20. In the figure, the sheet part 20 is open in a position, in which the transverse folding grooves 36 of the sheet part 20 are clearly visible.

The purpose of the longitudinal ribs 22 is to hold the yarn layer of the sliding surface in place in the lateral direction of the bottom sheet 16. Thanks to the longitudinal ribs 22, the yarn layer 14 of Figure 2 will remain in place laterally, without the individual yarns 32 of the yarn layer 14 moving to the side under the weight of someone descending. This means that a slope can be descended without ^' the skis of the skier making contact with the bottom sheet. The ribs are preferably lower than the thickness of the sliding surface, so that the ribs will not be able to touch the bottom of a ski. The width of the ribs is only in the order of a few millimetres, so that openings will not appear in the yarn layer at the location of the ribs. Instead of longitudinal ribs, there can also be pimples set in line in the bottom sheet of the sliding element. Stiffening ribs can also be manufactured in the undersurface of the bottom sheet, which lies against the ground. Despite the ribs, even when packed the sliding element does not require extra storage or transport space, unlike existing safety sheets or wide-bottomed sliding elements.

When the sheet part 20 is folded into the locking position of the sliding surface, the sheet part 20 is folded along the folding groove 36 closest to the rising ribs 24, on top of the rising ribs 24. The folding grooves can be made in the bottom- sheet blank, for example, by milling, or during moulding, if the bottom-sheet blank is plastic. The folding flat surface 26 closest to the rising ribs 24 settles onto the surface of the sheet 34 between the folding groove 36 and the rising ribs 24, the middle folding groove 36 settles onto the position of the lower edge 38 of the rising ribs 24, and the second flat sur- face 28 settles on top of the rising ribs 24. In the position according to Figure 1, the folding groove 36 farthest from the rising ribs 24 settles into the position of the upper edge 40 of the rising ribs 24 and the second folding surface 26 folds 5 on top of the surface of the sheet 34 between the rising ribs 24 and the longitudinal ribs 22.

The sheet part 20 forms the upper part of the suspension element 18 according to Figure 2, which holds the sliding surface

10 12 formed of yarn layers 14 in place on top of the bottom sheet 16. The sheet part 20 is formed into the upper part of the bottom sheet in the operating position, so that it secures the sliding surface in place. In other words, the suspension element 18 is formed of the sheet part 20 and the bottom sheet 16

15 belonging to one end 30 of the bottom-sheet blank 16'. By means of such a construction, the yarn layers can be attached without a separate base part, which forms an unevenness in the sliding element. It also reduces the number of components used, which in turn reduces the cost of manufacture of sliding elements

20 compared to that of sliding elements according to the prior art .

According to Figure 2, the end 41 of the sliding surface 12 remains under the folding flat surface 26 of the suspension

25 element 18. The sliding surface can be finally attached to the suspension element by, for example, running a thin layer of moulding compound between the folding flat surface and the sliding surface, as well as the sliding surface and the bottom sheet, with the aid of which the folding flat surface and the

30 sliding surface, as well as the sliding surface and the bottom sheet are welded together.

The sliding element 10 as a totality includes a sliding surface 12 formed from one or several yarn layers 14 attached together, 35 a bottom sheet 16, of a surface-area size essentially that of* the sliding element 10, attached under the sliding surface 12, and a suspension element 18 for attaching the sliding surface 12 to the bottom sheet 16. The term a surface-area size essentially that of the sliding element 10 refers to the fact that the surface area of the bottom sheet 16 is at least the size of the surface area of the entire sliding surface 12. The bottom sheet is preferably manufactured as a unified sheet, which extends from under the sliding surface as far as the suspension element . Figure 2 also shows the attachment holes 42 of the sliding element 10, with the aid of which the sliding element 10 is attached to the slope. The sliding element 10 shown in Figure 2 has been cut off short, but in reality the sliding element 10 can have a length of 1 - 2 m. The width of the sliding element can 0.4 - 1.0 m and its thickness 0.3 - 10 cm. The thickness of the sliding surface 12 can be, for example, 12 mm and the thickness of the bottom-sheet blank 1 - 10 mm. The size of the sliding element can vary according to where it is used. Thanks to the rising ribs 24 belonging essentially near to the sheet part 20, the second flat surface 28 is given a gentle angle, so that a skier can descend the slope without bumps caused by the suspension element 18. In this connection, the word essentially refers to the fact that the rising ribs 24 are at a distance of the folding flat surface 26 from the folding groove 36 closest to the rising ribs 24. The rising ribs 24 can be longer than the rising ribs according to one embodiment according to Figures 1 and 2, in which case their rising angle will be made even smaller, which will even the sliding element even further. The rising ribs 24 are at least the height of the thickness of the sliding surface 12, so that the folding flat surface 26 of the sheet part 20 will be brought on top of the sliding surface 12. The second flat surface 28 can be at least the size of the rising ribs 24, so that the folding flat sur- face 26 can be folded on top of the sliding surface 12. The sliding element can be manufactured, for example, from an extrusion-moulded base blank, or from a bottom sheet equipped with longitudinal ribs manufactured directly in its shape, which is combined with the sliding surface. The sliding surface can be manufactured from extrusion-moulded yarns, which are cut to a suitable length and melted together at one end to form a yarn layer. Immediately before attachment to the bottom-sheet blank, a thin layer of molten moulding compound is extruded on top of the melted end of the sliding surface. The bottom-sheet blank is heated to a welding temperature, after which it is folded at the sheet part to form a hollow-core structure. In this connection, the term hollow-core structure refers to the fact that an empty space for the sliding surface remains in the structure of the suspension element, so that the suspension element is not solid, as it is in sliding elements according to the prior art. The molten end of the sliding surface is pushed inside the hollow-core-structure sheet part and the sheet part is pressed by cooled rollers, so that the bottom sheet and the sliding surface are welded to each other, thus forming a fin- ished sliding element. Despite the hollow-core structure, the suspension element is durable, as it is supported by the rising ribs .

Sliding elements can be manufactured as a continuous band, in which case a cutter is used to cut the sliding elements into suitable lengths. The sliding elements can be manufactured more quickly than sliding elements according to the prior art, as, thanks to the sheet part, the sliding element does not contain large masses of plastic to be cooled, unlike the solid-bottomed sliding elements according to the prior art.

Figure 3 shows the structure of the grooved yarns 32 preferably used in the sliding element. The yarns can preferably be manufactured to be hollow like the yarns 32, because in practice the surfaces of the yarns 32 only wear at the highest points of the crimped yarns. The first yarn 44 shows a non-grooved and solid yarn according to the prior art. Grooves according to the invention, essentially in the longitudinal direction of the yarn, are made in the yarns to be used in the sliding elements, in the manner of the second yarn 46, or two thin yarns like the first yarn 44 can be combined to form a third yarn 48. The term a groove essentially in the longitudinal direction of the yarn refers to the fact that the groove progress from one end of the yarn towards its other end. The fourth yarn 50 show an alternative, in which there are grooves 62 in many different direc- tions in the yarn. In the yarns, there can be one or several grooves and the yarns can be solid in structure or equipped with one or several holes, i.e. hollow. The fifth yarn 52 is an example of a yarn model crimped in two directions. The yarns can preferably be crimped in two directions, instead of the waving made in one direction according to the prior art, so that the yarns will support _. each other better, to form a more unified yarn layer. It is also preferable to give the cross-sections of the yarns a shape, for example, like that of a four-leaved clover, in which the point of contact between a ski and a yarn will be distributed over several points in the yarn, and thus the surface pressure at the points of contact will remain small. Due to the shaping, grooves are formed in the surface of the yarn, by means of which the irrigation water used periodically on a slope will remain longer on the surface of the yarn. Water flows rapidly off a traditional yarn. Minimum dimensions for the width/strength of yarns are set in the regulations governing the use of plastic on slopes. By shaping the cross-section of the yarns and by making the yarns hollow it is possible, within the scope of the regulations for plastic slopes, to reduce the weight of the sliding element by as much as 30 %.

According to one embodiment, the yarn layers of the sliding surface can be manufactured from two different layers, in which case only the yarns of the outer yarn layer are coloured and UV protected. According to a second embodiment, each individual plastic yarn is surfaced with a second layer, which is, for example, a UV-protected layer or a coloured layer. The properties of the sliding element can be affected by selecting a raw- material grade suitable for the purpose at the time for the outer layer of the yarn. For example, in the acceleration section of a ski-jumping slope, plastic grades that reduce friction between the bottom of the ski and the yarns of the sliding element, and which also better withstand the increase in temperature caused by the friction, can be used in the surface of the yarns.

The yarns used are preferably plastic yarns, the plastic of which can be, for example, recycled plastic. The bottom-sheet blank of the sliding element according to the invention can be manufactured from, for example, plastic or a similar material.

The sliding element according to the invention can be used advantageously for surfacing a ski-jumping slope for the summer season. The sliding element can also be used for other purposes, for example, surfacing slopes for slalom skiing or snow- boarding, or for surfacing ski trails. The sliding element can also be used for surfacing sledge and toboggan slopes for summer use.