Varför svänger stenen?
En studie i curlingens komplexa tribosystem
The tribo system ice-curling stone was investigated in order to understand the mechanisms behind the stones' behavior on the ice sheet. The problem with non-identical stones should also be addressed.The stone curls, that is, its sliding path deviates from a straight line to the right for a clock-wise rotation and to the left for a anti-clock-wise rotation. Several mechanisms to explain this behavior have been proposed over the years but none has been successful.By carrying out experiments at the local curling rink and studying silicon castings of ice- and stone-surfaces with scanning electron microscopy and vertical scanning interferometry, it has been decided that the curl is not due to dry friction, ice-debris or the difference in friction on the left and right side of the stone. The side force comes from the fact that the friction is higher at the back of the stone than at the front.The contact between stone and ice is never completely dry, nor in the hydrodynamic lubrication regime. It is probably a combination of hydrodynamic lubrication and a contribution from mechanical scratching of the ice. The coefficient of friction depends upon the velocity, from 0.01 for velocities around 1 m/s to higher values for lower velocities. It is not possible to make identical stones, that is identical glide band structures out of Blue Hone granite, since its composition is too inhomogeneous and its grain size is too course. It is recommended to use an amorphous or very fine grained material, at least in the surface of the glideband.