Given Canada’s bountiful lakes and rivers, it's no surprise that Creighton and his friends took advantage of the natural freeze to enjoy winter sports. In a modern stadium, though, skilled technicians combine under-ice refrigeration systems, environmental controls, cutting-edge refrigerants, and ponderous resurfacing vehicles to produce and manage the ice.
In its liquid state, water molecules jostle around as the bonds between them constantly break and re-form. As water cools, these molecules slow and the bonds stabilize. Around 0 °C, they become rigid, initiating the change from liquid to solid.
In nature, frozen water takes on an array of irregular structures, including snow, icebergs, hail, and icicles, depending on conditions. That variability won’t do for a rink, which must have a level, low-friction surface perfect for a fast puck and efficient skating. Making that takes more than just cooling down a pool of water. Rinks use a sophisticated system that sprays ultrathin layers of water on a bed of sand or concrete embedded with cooling pipes filled with refrigerant. The layers are frozen, one-by-one, stacking up to a smooth playing surface measuring between one inch and one-and-a-half inches thick.
An ice hockey player's ability to skate relies on a key feature of ice: its slipperiness. This comes from a quasi-liquid layer on the ice surface that reduces friction with the skate.
Credit: Davide Donadio/University of California, Davis
Water molecules in ice crystals form three hydrogen-bonding interactions with their neighbors, which hold them securely together. However, at temperatures close to the melting point, these interactions weaken in the top two layers of water molecules.
Credit: J. Phys. Chem. Lett. 2018, DOI: 10.1021/acs.jpclett.8b01188
The water molecules in the top layers become mobile and are able to tumble and roll across the surface of the ice. The layers of mobile water molecules provide a smooth and lubricated surface over which ice skates slide easily. Recently, teams in the Netherlands and Germany found
that the optimal temperature for sliding on ice is about −7 °C. Indeed, that's the temperature at which most skating rinks are kept to provide the fastest skating.
Even the water itself is engineered. “Some arenas, including the NHL buildings, process their water in special ways,” says Kelly McMillen, an engineer at Zamboni Co. The rinks want to control the amounts of total dissolved solids in the water, such as minerals and salts, and use processes such as deionization and filtration to achieve the desired levels. Harvested rainwater, used at rinks such as the Abbotsford Entertainment and Sports Centre in Canada, has a low mineral content, whereas the mineral content of water from lakes or the ground varies widely. The higher the number of mineral particles in the ice, the greater the friction between surface and blade; more friction equals less speed.
“The most common water treatment method in the ice rink industry is reverse osmosis to control water hardness,” explains Jeff Theiler, chief operating officer at the U.S. Ice Rink Association. “The main impurities that we want to minimize are calcium and magnesium.” He adds that the harder water lowers water’s freezing temperature and creates a less dense ice, which lead to higher costs.
No matter how good the water and resulting ice is, it won't stay smooth for long. “Over the course of play, the skates are cutting into the ice,” explains Noce, who has been fascinated by the ice-making process since he was a kid. “You're scarring it.”
Rutted ice slows play and needs to be resurfaced. Originally, to clear the shavings left by passing skates, workers resurfaced the ice with shovels, then covered it with fresh water from a hose. This filled in the grooves and marks left by the charging skaters, making the top layer of ice smooth again. That whole process, then lasting over an hour, is now repeated four times per NHL game and is carried out by modern machines that repair the ice in minutes.
Frank Zamboni gets the thanks for that. An engineer, Zamboni, patented his eponymous vehicle in 1949. The Zamboni® machine creates a smooth surface in three steps that all happen as the machine glides over the ice. First, it shaves the ice and collects the shavings. Next, it washes the top layer of the ice and vacuums up the dirty water. Finally, it lays down a fresh layer of warm water and smooths it out. (Warm water contains fewer impurities—which produce distorted ice with greater friction—than cold water.)
The much-loved Zamboni® machine has taken on the role of mascot in many arenas, McMillen says, adding that the contrast between the machine's slow movements and the speed of hockey appeals to spectators. “It's amazing to see people mesmerized by the resurfacing process,” he says.