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Friction in Ice Hockey: Comparison of different models of skate blades

by A. Manolova | 9 February 2018

ice hockey, skate blade, ice, blades, performance, friction, resistance, speed, sliding, science, sport
Graphical representation of the main forces involved in skating with: P, athlete's weight, R, ground reaction force, RA, aerodynamic drag resistance and RF, friction resistance between skate blade and ice

Figure 1. Graphical representation of the main forces... (Cliquez sur l'image pour l'agrandir)

In ice hockey, and in skating in general, the speed of movement is limited by two main resistances: the aerodynamic drag resistance (RA, in N) and friction resistance (RF, in N) between the ice and the skate blade (Fig. 1). At speeds equal to or greater than about 10 m/s, aerodynamic drag and friction resistance account for 75% and 25%, respectively, of the power produced by the athlete.

For lower speeds, it is RF that is predominant. It represents the friction that exists between two materials in contact that move on one another. It depends on two variables, the coefficient of kinetic friction (μ, without units) and the force (R, in N). R represents the ground reaction of the athlete's weight where m (in kg) is the mass of the athlete and g (in m/s), the gravitational acceleration :

formule1

The coefficient of kinetic friction allows to characterize the friction resistance between two defined surfaces and under precise conditions. For example, the kinetic friction between steel and ice will be different from that between wood and ice, etc.

As you may have guessed, ice hockey performance does not depend solely on the physical and technical skills of the hockey players. Equipment plays an important role, and the skate blade is a key element. For many skating maneuvers, such as sudden acceleration or directional changes, the blade must provide good ice resistance while minimizing friction with the ice to maintain a high speed during the "no skating" phases. Although the design and shape of the skate blades have not changed much, new types of blades have emerged in recent years with the aim of improving the performance of hockey players.

Figure 2. Section of the different skate blades... (Cliquez sur l'image pour l'agrandir)

The Study

In 2008, researchers from the University of Calgary, Canada compared the friction characteristics of a new type of skate blade (CT Edge Skate Design Inc) with a standard one. The patent for this new type of skate blade was filed in 2004 and has the specificity to flare outward on both sides at an angle varying from 4 to 8 degrees (Fig. 2).

In order to compare the 4 slides, the authors used the deceleration method using an aluminum sledge (36 kg) under which were fixed 3 identical skate blades, and on which rested a constant load (53 kg × 3) (Fig. 3). Each blade type was mounted on the sledge and tested several times: 33 times for the standard blade, 28 times for the 4° blade, 7 times for the 6° blade and 26 times for the 8° blade.

Illustration of the experimental protocol.

Figure 3. Illustration of the experimental protocol.

The sled was mechanically propelled and still at the same starting speed, equal to about 1.8 m/s. At this low speed, they assumed negligible aerodynamic resistance. The sledge passed between 0, 2, 12 and 14 m photocells to record the passage times. From Newton's second law (F = m × a), where a is the sled deceleration, the coefficient of kinetic friction is expressed:

formule2

To determine μ, the researchers assumed the deceleration of the constant sled. Then from the equations of the movement, they determined according to the time and the displacement of the sled, its deceleration and thus obtained μ.

Results & Analyzes

The main results of this study show that the mean coefficients of kinetic friction measured for the different types of blades were :

  • Standard blade : μ = 0.0071
  • Blade at 4°: μ = 0.0061
  • Blade at 6°: μ = 0.0061
  • Blade at 8°: μ = 0.0056

Nevertheless, the authors found that these mean values fluctuated significantly between the different days of testing. These variations were probably due to the different temperature and surface conditions of the ice. To avoid this problem, the authors compared the coefficients of kinetic friction as a percentage of the coefficient of kinetic friction of the standard blade for the same day (Fig. 4). They found a decrease of μ from 13 to 22% on average compared to that of the standard blade.

Mean coefficients of kinetic friction expressed as a percentage of the coefficient of kinetic friction of the standard blade.

Figure 4. Mean coefficients of kinetic friction expressed as a percentage of the coefficient of kinetic friction of the standard blade.

These results seem to suggest that the shape of the blade has an influence on the coefficient of kinetic of friction. Increasing the base of the blade, which is in contact with the ice, would improve the sliding of the ice skate by decreasing the friction resistance. Nevertheless, these results remain to be confirmed because the observed variations were large and the coefficient of friction depends on many factors: the geometric characteristics of the blade, the temperature of the ice, the temperature of the air, the temperature of the blade and the humidity.

In addition, the blade test conditions are not representative of the actual sliding conditions during a hockey game:

  1. Speed : The initial speed used during the tests was very low compared to the speeds achieved in ice hockey.
  2. Thermal insulation : The aluminum sledge was not thermally insulated from the skate blades. On the ice skate, the blades are mounted on plastic plates, which inhibits heat transfer.

Practical Applications

In ice hockey, the phases of sliding in a straight line are rare. As the authors admit, improving the friction of the blades will not necessarily have an impact on the performance of the players, because it is mainly related to acceleration, abrupt change of direction, etc. In addition, in sprints of 5 m, the frictional resistance intervenes only a few thousandths of a meter-1. The characteristics of the skate blades should be studied from different angles to best meet the requirements of the activity.

The result of this study is however applicable to other ice sports such as speed skating, bobsleigh or sled / skeleton. Indeed, in these speed sports, the minimization of aerodynamic and friction resistances is strongly correlated with the performance. And it would be interesting to study the influence of the width of the blade on the speed, especially as the blades of the speed skating are very thin (~ 1.1 - 1.4 mm).

Références

  1. Federolf PA, Mills R and Nigg B. Ice friction of flared ice hockey skate blades. J Sports Sci 26 (11): 1201-1208, 2008.

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