Patent Application
20160001152
Curling is a winter sport played on ice, which is similar to Boules games and Bocce. Two teams of four players each try to slide their curling stones closer to the center of a target circle than the opposing team. Curling is very popular in particular in Canada, Scotland, Scandinavia and Switzerland. Curling is played worldwide by about two million athletes and is represented in the Olympic games. Due to the attractiveness of the sport, curling enjoys a very large media presence. Curling is one of the precision sports.
Curling stones have a round, polished form; they normally consist of granite and have a handle.
The bottom side of a curling stone is concave, so that the actual sliding, or running, surface of the curling stone is fored as an annular surface having a width of approximately 6 to 12 mm.
When the curling stone slides over the ice, it collects a thin layer of water on the annular surface. This water layer is greater in the front due to the rotation of the stone around its vertical axis and the higher pressure on the front side thereof caused by the braking of the curling stone. Thereby, the friction is reduced in front, resulting in a curvature of the runway.
The curling stone is shifted in its delivery targeted in a slow, rotational movement, so that it does run straight, but describes a parabolic trajectory. This makes it possible to play around an opposing stone. The curvature of the trajectory can be influenced by wiping the runway in front of the curling stone with a curling broom. If the path in front of a curling stone is wiped, while it moves forward, the curve radius is enlarged and the curling stone runs straighter. In addition to the curvature, the wiping also influences the runtime of a curling stone. A wiped curling stone loses speed less quickly and thus covers a larger track.
In particular, the Scots are convinced that curling stones with the best quality are made from a certain type of granite named “Ailsite.” This granite is mined on Ailsa Craig, a small island off the coast of Ayrshire in Scotland. Due to the scarceness of ailsite, such curling stones cost up to 1,300 Euro. Many curling clubs use curling stones of lower quality, which are available from about 500 Euro and are made from a granite of lesser value.
The main requirement for a running surface of a curling stone having a concave running surface is that the water absorption of the granite is as small as possible, since otherwise the sliding properties on ice are changed. Furthermore, the wear on the running surface should be as low as possible, since the costs and logistical effort for regrinding are very high. The grinding costs can amount to about 500 /set of curling stones. Curling stones in playing operation must be reground at least once per season.
Modern high performance curling stones comprise two separate parts, namely a stone main base and an insert part connected thereto, which determines the running surface of the curling stone. The insert part consists of a higher value material in comparison to the material of the stone main base. The insert part of the known high performance curling stones is usually made from granite, and can be reground only a few times. If too much material is worn off, then the curling stone is no longer usable or the insert part is detached from the stone and replaced with a new insert part.
The principal components of granite are feldspar, quartz and mica minerals. Due to this composition of several minerals of varying hardness, a minor but undesirable absorption of water is unavoidable or always present. The Vicker's hardness HV is approximately 850 GPa (Mohs hardness 6-7). Due to the composition of several minerals with different and also relatively low hardnesses, curling stones “in operation” have a certain level of wear, so that a defined grinding—as explained above—must be restored regularly.
The specifications stated below are set down in Chapter R2 of the bylaws of the World Curling Federation (WCU Rules of Curling):
The WCF Rules do not, however, stipulate the material from which the curling stone must be made or the “construction design” thereof.
Curling stones in use up to now have deficiencies due to material properties resulting from the use of natural products and production methods, which are problematic for use. Essential to good properties of the curling stone is a high homogeneity of the raw material used in combination with low wear and constant wear behavior. With a natural substance such as granite, this is not ensured with different mining batches of the granite. The different sliding properties within a curling stone series make a fair competition impossible. Extremely critical is the situation of the availability of the only granite currently used in the world, which—as mentioned above—is mined on the island Ailsa Craig off the Ayrshire coast in Scotland. The deposits are largely exhausted, and equivalent material from other sites is not yet known. For this reason, the price for this coveted raw material is very high and will rise further. A consequence of this factor is that the price of the curling stones will rise further due to the scarcity of raw material. It is of critical importance to require a set of eight stones with identical properties per sports team, to have consistent conditions. If a curling stone is damaged, then it must be replaced by an equivalent curling stone. But this is very difficult with a natural product, so that it cannot be ruled out that the entire set of eight curling stones cannot be used. In the foreseeable future a shortage of suitable curling stones is therefore to be expected.
Attempts to use other materials such as metals or plastics have not been successful to date, since the property potential deviates too much from the granite previously used.
In view of these circumstances the object of the invention is to create a curling stone, with which the sport of curling can be operated as before, whereby the deficiencies of the known suggested solutions are eliminated by simple means.
This object is achieved according to the invention in that at least the sliding, i.e. running, surface of the curling stone is composed of a hard-wearing technical ceramic.
Preferred refinements and improvements of the invention of the curling stone according to the invention are characterized in the dependent claims.
Surprisingly, it was discovered that technical ceramics can solve the problems of known is curling stones by preferably forming the running surface of the curling stone from an insert part (referred to hereinafter as insert) made of technical ceramics.
The property potential of the technical ceramics is predestined for this application, because thereby a curling stone is created, which is both hard-wearing and also has good sliding properties. Aluminum oxide for the insert part has proven to be particularly advantageous with regard to the sliding properties. For this, the good tribological properties of aluminum oxide have been found to be particularly advantageous, because the optimal friction and good wear behavior of aluminum oxide are of vital importance.
In addition, technical ceramics possess the following good mechanical and physical properties:
It has been shown that these material properties of aluminium oxide are predestined for use as an insert for curling stones, to replace the granite used up until now. Due to the greater hardness and good wear behavior, wear and tear of the sliding surface is extremely low, whereby the associated problems are solved. Furthermore, the problem of water absorption is advantageously eliminated by the aluminum oxide material.
A significant further advantage of technical ceramics for the insert part is the problem-free permanent availability thereof.
It follows from the above that technical ceramics provide an optimal substitute for the previously used granite, whereby with technical ceramics existing problems, as mentioned above, can be solved.
In addition to the use of technical ceramics for the insert part of curling stones, the installation of the insert part has vital importance. The know-how of a ceramics-oriented construction in conjunction with the use of suitable high-performance adhesives is a basic prerequisite for such a functioning composite system.
The ceramic insert part can be produced in a first process step by isostatic pressing, uniaxial pressing, slip casting, injection molding or another known ceramic shaping technology. In a subsequent second process step the green parts are processed by green machining to the specified size. However, the processing may also take place hard-ceramic after the sintering.
This is followed by a sintering process adjusted to the particular ceramic material employed, to which a hard-ceramic finishing process can be applied next by grinding, lapping or polishing. This is not necessary the case with Near-Net-Forming.
Different variants are possible when installing the ceramic insert part into the stone base, for example a granite blank. Thereby the insert part may be joined to the granite stone base by a form-fitting, force-fitting, chemical or adhesive bonding.
The invention will be further explained hereafter by means of several examples, it being understood that the invention is not limited to these examples.
In a first process step a ceramic body with dimensions 250×250×25 mm is produced from ALOTEC 92 uniaxial with a pressing force of 2,850 kN and a pressing pressure >40 MPa on a axial-press. The green density achieved is >2.00 g/cm3. The green body is further treated in a second process step in a processing center, to prepare a disk having a diameter of 200 mm and a thickness of 35 mm. The disk is then tapered in the center area to 10 mm by means of a jigger to obtain the required annular sliding surface. In addition, a 12 mm bore hole is introduced into the disk center. The sintering is performed at 1,600° C. in the gas furnace under standard sintering conditions (50 h, HZ=1 h). The ceramic body has the following ceramic properties:
Sliding tests on ice with a curling stone thus prepared gave very good results.
In a first process step a ceramic body with dimensions 220×220×50 mm is isostatically pressed from ALOTEC 99 with a pressing force of 1,000 bar.
The green density obtained is 2.37 g/cm3. In a subsequent second working step, a biscuit firing is carried out at 1,100° C., to stabilize the green body for further processing steps. The green body is then further treated on the jigger to produce a disk having a diameter of 200 mm and a thickness of 35 mm. The disk is then tapered in the center is area to 10 mm by means of a jigger, to obtain the required annular sliding surface. The sintering is performed at 1,620° C. in the gas furnace under standard sintering conditions (48 h, HZ=3 h). The ceramic body has the following ceramic properties:
Sliding tests on ice with a curling stone having an insert part thus prepared gave very good results.
Grinding tests were performed on this production example. After grinding, the following roughness values were:
The sliding properties are still very good. However, the sliding tests on ice demonstrate that the disks are “too smooth” for use. When sliding over the ice, a thin water layer accumulates particularly on the annular gliding surface. This thin water layer is greater in the front due to the rotation of the stone around its vertical axis and the higher pressure on the front side thereof caused by the braking of the curling stone.
Due to the smooth surface of the ceramic insert part, the desired and necessary so-called Curl-Effect, i.e. the parabolic curved path, is not adequately achieved.
3.1) The insert part is glued exactly into the base of the granite curling stone. For this, an elastic adhesive is used, which must have a low resistance to high temperature. Thereby, by thermal treatment of the curling stone a damaged or worn insert part can be removed from the curling stone base and replaced.
3.2) The insert part is glued exactly into the base of the granite curling stone. For this, an elastic adhesive is used, which has a low resistance to high temperature in order to prevent the insert part from falling out unintentionally, or
3.3) The insert part is combined with a screw, by means of which the handle is fixed on the top side of the curling stone. With such a design of the latter type, a simpler, easier and time-saving replacement of the insert part is possible.
In addition to the significantly improved properties of the sliding or running surface, these three assembly methods provide an essential advantage of the curling stone according to the invention.
Previously, worn, defective curling stones had to be milled again at high cost, and then were provided with a new insert part made of granite and thus reconditioned.
According to the invention, rings or disks made from ceramics, hollow ceramic bodies, ceramic tubes, ceramic blanks, or one-piece ceramic curling stones may be used.
The dimensions of the components can naturally be adapted to the particular requests and/or requirements in a simple manner.
The curling stones can also be manufactured from alternative materials, since the granite supply is increasingly scarce and thus the price for curling stones made from granite is always higher. According to the invention, at least the sliding, i.e. running surface, of the curling stone is composed of technical ceramics as wear-resistant materials having the desired sliding properties.
If alternative materials are applied, then the insert part can be selected from ceramics so that the stipulated weight of the curling stone is obtained. For this purpose it is possible that the curling stones made from the particular material according to the invention may comprise, for example, a recess or a pocket for an additional weight to achieve the required total weight of the curling stone. Likewise, it is possible to provide a recess for an electronic circuit in the curling stone and/or in the base body thereof.
If the discussion above is always of a curling stone, this does not mean that it concerns a stone material or granite for the base body, but rather to achieve the desired and/or required properties such as wear resistance and sliding behavior, it can be sufficient if at least the sliding, i.e. running surface, of the curling stone according to the invention consists of a suitable material.
Further details, characteristics and advantages will be apparent in the following description of exemplary embodiments of the curling stone according to the invention depicted in sectional views.
In the drawings:
The base body 12 can consist of natural stone. The natural stone can be granite, for example. However, the base body 12 can also comprise metal, glass or wood. Likewise it is possible that the base body 12 may comprise a plastic material and that in the production of the curling stone 10 the insert part 14 is directly and immediately overmolded and permanently joined with the plastic material of the base body.
Identical details are denoted in
With the embodiment according to
The same details are each designated with the same reference numerals in each of
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 002 869.8 | Feb 2013 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/053169 | 2/19/2014 | WO | 00 |
