24th International Colloquium Tribology - January 2024 23 Sustainability in Winter Sports - The Tribological Perspective Matthias Scherge 1 1 Fraunhofer/ KIT MikroTribologie Centrum, Rintheimer Querallee 2b, 76131 Karlsruhe 1. Introduction This contribution highlights the topic of sustainability in winter sports with a focus on tribology, i.e. processes related to friction, lubrication and wear. It will be shown what measures have been taken in skiing and skating to conserve energy and resources. Since snow and ice have unique properties related to gliding, it is assessed how these properties are changed by substitute products. Furthermore, it is explained how the tribological mechanisms change, for example, when switching from the runner - ice system to a runner - polymer system. 2. Example I: Ski Jumping Ski jumps are operated in winter as well as in summer. Therefore, there are various friction partners with which the skis make contact, such as e.g. snow, ice, porcelain, various plastic mats and grass. All the above-mentioned materials result in a wide range of friction coefficients. In the inrun of a ski jump as well as in the landing hill, the friction in the direction of travel must be significantly lower than perpendicular to it. Inside the inrun, this is taken into account in that movement perpendicular to the direction of travel is not possible due to side restraints. In the landing hill, this requirement is implemented by the structure of the mats, which provide a certain degree of resistance when the skis are edging. Naturally, different inrun tracks exist for winter and summer operation. In winter one finds tracks made of snow or ice, while in the rest of the year tracks made of metal or metal with sliding bodies are used. To reduce friction, these tracks are rinsed with water. To further reduce friction, the tracks are given hemispherical, partially flattened knobs. Plastic (POM), ceramic or porcelain are used as material. In some cases, embossing is also used to structure the metal track in such a way that nubs are formed, see Fig. 1. While in the inrun the lowest friction is required, in the landing hill there is the demand for a safe landing, which requires a certain friction value for lateral guidance. Since the 70’s, mainly green mats consisting of a multitude of individual threads have proven their worth, see Fig. 1a. Like the inrun, the mats must also be watered to reduce friction. When magnified it can be shown, how the mats retain water. The used plastic is hydrophilic and wets very well. If this were not the case, the water would run through the mat into the ground and the water demand of the hill would be very high. Friction measurements with a portable tribometer proved the clear difference between dry and lubricated friction. Fig. 1: Different kinds of inruns of a ski jump. The type of mat presented in Fig. 2 was installed on a small hill at Steinbach-Hallenberg in 2018. Due to the combination of plastic fiber and loop shape, smaller friction was achieved with these mats than on their green predecessor. Due to the fiber bundles, the mats hold significantly more water. This reduces the water consumption of the system. Fig. 2: A modern type of mats. As with the inrun, the tribological mechanism can be found in the hydrodynamics. The water stored in the fiber composite of the mats serves as a lubricant. Since contact between the ski and the mat is very rapid during landing, there is not enough time for the water to be forced out of contact and a lubricating effect is created, see Fig. 3. 24 24th International Colloquium Tribology - January 2024 Sustainability in Winter Sports - The Tribological Perspective Fig. 3: Mats and watering system for lubrication. 3. Example II: Ice-Skating and Bobsledding Skating on artificial ice usually refers to activities such as ice skating and ice hockey. Artificial ice in the form of polymer sheets is often used in ice halls, ice rinks or ice parks to provide year-round ice activities. Artificial ice offers the advantage of being less sensitive to temperature fluctuations and does not require any energy for cooling. The ice substitute, like most ski bases, is made of ultrahigh molecular weight polyethylene filled to the limit with oils. The oil diffuses to the surface, where it forms a very thin lubricating film that is imperceptible by hand but efficiently separates the friction partners. A few nanometers are sufficient for this. With additional contact pressure, the oil is pressed out of the sintered granules and improves lubrication. As a result, freshly ground runners glide better because the contact pressure is higher. However, the fact that the coefficient of friction is higher than against ice, can also be read indirectly from the wear. According to users, the skates become dull about twice as fast as against ice. If you compare the friction mechanisms, you will notice that when the skate and ice come into contact, the friction power causes the ice to melt near the surface and forms the lubricating water film. This water cannot be formed by pressure alone. In the case of skate-polymer contact, however, the contact pressure plays the decisive role, because it conveys the lubricant from the interior of the polymer to the surface. For the sport of bobsleigh, it was shown that with polymer sliding surfaces, that do not need to be cooled or watered, training and competition are possible as well. Fig. 4: Bobsled track. As an example, a completely new and innovative push-off training track was developed and already put into use, see Fig. 4. This training track can be set up at any location and does not require a specially cooled building. This achieves several advantages at once. Besides saving cooling power, there is no need for ammonia as the chemical basis of cooling. Since the track can be set up anywhere, realistic training is possible even for smaller clubs that cannot afford to train in a “cold store” and the transportation costs. If the track is used in a social environment, e.g. at city festivals, many new possibilities for recruiting new talent open up. The sliding mechanism is the same as described for skating. Since the bobsleigh runners have considerably more contact surface with the polymer, a higher mass is required to build up the necessary pressure. The total mass of the mono bobsleigh shown above is 248 kg. Thus, the necessary pressure can be built up and low friction can be ensured. 4. Summary Sustainability in winter sports is of great importance to protect the environment in which we enjoy these activities. By conserving resources, protecting nature and promoting responsible behavior among winter sports enthusiasts, we can ensure that future generations will be able to experience the same fascination and enjoyment of winter sports. In addition, mobile facilities can ensure that more people find their way to this sport. By promoting sustainable tourism, we can also support local communities while maintaining the economic benefits of winter sports. Combining fun and responsibility is the key to a sustainable future in winter sports.