Getting Technical
Modern rinks have a specific procedure for preparing the
surface. With the refrigeration plant running so that the pipes
are cold, a thin layer of water is sprayed on the concrete to seal
and level it. This thin layer is painted white or pale blue for better
contrast so that markings necessary for sports, along with
logos or other decorations put onto this surface show up clearly
through further subsequent upper layers.
The ice sheet is built
progressively in 1–2mm thick
layers up to a total thickness of
between 20 – 35mm.
The ice sheet is built progressively in 1–2mm thick layers up
to a total thickness of between 20–35mm. Total volumes of
water used usually amount to between 40 000 and 50 000 litres,
thereby making 40–50 metric tons of ice. Ice temperatures
required are only a few degrees below freezing. The general
temperature level for recreational skating is -3°C which is also
widely used by figure skaters and hockey players for training.
For competitive displays and hockey matches, however, a
“faster” ice surface is created by reducing ice temperature to
between -5 to -6°C.
WATER QUALITY REQUIRED FOR ICE MAKING
Quality ice can only be made from water that is pure — but
not too pure. Demineralisation and filtration of the water used
to build ice sheets is now generally done for the removal of
impurities such as suspended solids and gases. Ice will always
try to freeze as pure as it is able to. Impurities in the ice may
result in a friable surface on top, which is the frozen equivalent
Figure 2: A modern “Zamboni” type ice surface treatment
machine.
52
RACA Journal I June 2019
of foam or froth forming an impure surface layer which, from a
skating point of view, is known as “really poor ice”. This impure
layer also puts more loading on the refrigeration system than
purer, denser ice does. Purer, denser ice has greater structural
integrity and thus can withstand the rigours of skating
manoeuvres and ice hockey as a thinner sheet. Also, it is much
less difficult (and less costly) to keep pure ice frozen.
One of the most common contaminants in water inhibiting
the formation of quality ice is trapped air bubbles. University
of California, Berkeley chemistry professor Gabor Somorjai,
author of Introduction to Surface Chemistry and Catalysis, has
demonstrated that there is always a layer of water on the
surface of ice regardless of its temperature.
For a number of years before Somorjai’s research, there was
debate as to whether pressure or friction created the water
lubricant that was believed to be required for skating. Most
scientists seemed to think that it was pressure. According to
Somorjai’s findings this is not the case. So what does a skate
slide on? Somorjai proposes that it slides on vibrating molecules.
Professor Somorjai and his team used the most up-to-date
methods to examine the surface structure and composition
of the atoms and molecules that make up ice, and what they
found was surprising. Initially, they found that the structure
was an almost impossible one, indicating that every second
water molecule on the surface was missing. Since that was
not realistically possible, the team expanded their research
programme which determined that the “missing” water [or
ice] molecules were in fact there, but vibrating so rapidly that
they were not visible to the technique currently being used.
Finally, after further study, the team found that these
molecules behave like a liquid, but they only move up and
down and not from side to side on the surface of the ice. This
was an important distinction. If the atoms moved side to side,
the “liquid-like” layer would literally become liquid, which is
what happens when the temperature rises above 0°C.
This “liquid-like” layer is now thought to be what makes
ice slippery and provides skaters with a lubricant on which to
glide, not the “melt water” many have long believed results
from skate blade pressure. The layer becomes even thinner at
extremely cold temperatures and thickens as ice approaches
the melting point – each extreme reducing “skate-glide”
accordingly. Air bubbles amplify this water/ice interface effect,
resulting in slow ice at both normal and colder temperatures.
The method used to reduce trapped air bubbles sufficiently
to avoid their adverse effects on ice is the same as for
obtaining clear shiny ice cubes in domestic or commercial
refrigerators. Start with good quality water and heat it up to
around 60°C before beginning the refrigerating process. Ice
rink operators try to reduce costs by heating the water up to
a few degrees less and normally find that about 55°C works
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