Frozen Pucks

Over the last couple of years, I’ve turned into a bit of a local ice hockey fan; the speed, music and terrible interval hot-dog combine to make a great Saturday night out. However, I only recently learned that some teams travel with a portable freezer; not for a mid-game snack but instead to freeze the ice hockey pucks!

A standard ice hockey puck is about an inch thick, three inches in diameter and made from vulcanized rubber. Named after the Roman god of fire Vulcan, sulphur is added to natural rubber to create the more durable vulcanized rubber. Inside the material is made of polymer chains and it’s these which are affected by temperature.

At warmer temperatures the polymer chains contract. If the puck is dropped onto a hard ice surface the polymer chains may be stretched on impact but will quickly return to their previous positions, this makes the rubber elastic and it gives the puck the ability to bounce (only a small amount of energy is lost to heat and sound). If the puck is frozen, the polymer chains are already stretched out, making the material less elastic and therefore the puck less likely to be able to bounce up. A colder puck can also slide faster as there is less friction between the rubber and ice rink. Though caution is required, if the rubber is too cold the material can become brittle and shatter. Thankfully for the ice hockey players, an ice-cream freezer won’t get that cold – you would need to dip the puck in liquid nitrogen to risk it shattering.

To give a consistent game, the National Hockey League states the puck must be exchanged after two minutes of actual play; time taken up with player disagreements doesn’t count! Usually there are freezers near the penalty box and the linesmen have a well-rehearsed routine to allow the warm pucks to be swapped with cold. A bit like a magic trick, I’ve never spotted this happening. So next week at the game I’ll be watching out for the frozen puck swap as well as the goals….