The rapid growth in material and processing technology makes it essential
for plastics manufacturers, mouldmakers, and designers to keep in close
touch. In the development of plastics components, the properties of the
material and its processing behaviour should be taken into account right
at the draft
Figure 1. A dynamic biomorphic
design stage. In this example, material and technological studies of
frogdesign, a design agency in Altensteig, Germany, and of WST, a manufacturer
of sports articles in Villingen-Schwenningen, Germany, led to the selection
of a suitable plastic and to a creative design for an ice skate blade (Figure
The blade of an ice hockey skate produces frictional heat through pressure
and movement, causing the ice to melt and a film of water to form between
the blade surface and the ice. It is only this film of water that makes
skating on ice possible. The better the process of water film formation,
the faster the ice hockey player can go. Therefore, the aim is for the
blade to reach a high temperature quickly and for the
temperature to remain constant, if possible.
The good thermal conductivity of metals, shared by the solid steel blades
used in conventional systems, has the effect of rapidly dissipating the
frictional heat generated. The requirements of the material selected for
development of the new skate blade were specified to combat this effect.
The quest for a suitable plastic began with a definition of the way
the system would function and thus ran parallel to design and engineering
development (Figure 2).
CAD design, the designer allows no compromises.
The first draft sketch
The preliminary model,
After design release
The CAD design data make it possible to construct a stereolithographic
The extreme physical requirements the plastic is exposed to and the
conditions imposed by production processes made this search the most time-consuming
stage in this entire development project (Figure 3).
Figure 3. The detail modifications
Particular problems were posed by the connection between the blade surface
of the skate system ? a metal profile ? and the plastic.
When a suitable plastic had been found to withstand the physical stresses,
different expansion and shrinkage coefficients of the plastic and metal
profile both in moulding and demoulding caused a defective connection between
the plastic and metal. On the other hand, when this connection succeeded,
then other properties such as the notched impact strength, inherent rigidity,
and chemical resistance of the materials proved inadequate (Figure 4).
After numerous injection moulding trials, testing of prototype moulds,
and skating trials, close cooperation between the plastic manufacturer,
designer, and mouldmaker led to the selection of a material that met the
Figure 4. In a test at -41°C,
An injection mouldable, high-impact polyamide with 35 percent glass-fiber
reinforcement stood up to the extreme stresses that occur in an ice hockey
match. This plastic serves as the base material for the entire skate system
and also for the blade itself.
The blade, i.e., the actual runner surface of the system, consists of
a .7-mm-thick, high-strength metal profile. This metal profile, consisting
of a spring-hard metal alloy, is laser-welded in a fully automated process
to a second metal band provided with apertures, and is then permanently
joined to the plastic during the injection moulding process.
The result is a blade which, because of the insulating effect of the
plastic, does not dissipate the generated frictional heat so rapidly. The
resulting heat buildup increases the temperature of the blade surface by
about 3°C compared with conventional blades. As a consequence of this
and the highly polished blade surface, the sliding action of the skate
blade is improved by 40 percent. This, in turn, increases skating speed
as compared with conventional skate blades.
The practical implementation of the design for the basic skate and
provision of laterally integrated stabilizers for the skate blade proved
a further challenge. The physical demands made on these components were
virtually identical to those made on the blade. However, this time it was
not necessary to account for expansion and shrinkage coefficients as was
the case with the plastic/metal composite forming the blade. One design
objective was to reduce the weight of the skate system and yet still meet
the high requirements of competitive sport. The skate blade developed from
the polyamide/metal composite is 140g lighter than traditional skate blades
and at present the lightest blade system.
This weight minimization was only made possible by the use of plastics
in conjunction with a carefully thought-out design. The reduction in wall
thickness required for weight minimization called for a design capable
of withstanding the very different force effects. Lightweight structures
found in nature and the laws of force distribution used in architecture
served as the basis for the design. Thus, it was possible to reduce the
wall thickness of the largest part of the basic skate to only 1.5 mm. The
inherent rigidity of the system is retained, even if the player is a heavyweight.
The skate blade resists compressive forces of up to 3,000N, such as act
on the system when the skate is braked, for example, and also the impact
forces exerted by the puck traveling at speeds of up to 150 km/hour, even
at extremely low temperatures down to ?35°C.
Figure 5. The initial mouldings
To find the correct material, numerous injection moulding trials in
prototype moulds and tests under practical conditions were required. This
enabled resolution of problems relating to the flow behaviour of the plastics,
such as sink marks in areas of high material accumulation and difficulties
with fit in the individual component groups. By reducing the fiber content,
it was possible to adapt notched impact strength at minus temperatures
to the required torsional rigidity of the basic skate.
Time-consuming blade grinding, required with traditional steel blades,
is unnecessary with the skate blade in the plastic/metal system. The service
life of this blade is three times longer than that of conventional systems
because of the special metal alloy and the high surface hardening. Postgrinding
of the blades costs more than purchasing a new blade and replacing the
old one, which is taken back in the worn condition by the manufacturer
The skate blade can be changed by the player in a few seconds without
taking off the skate. The stabilizers at the sides can be removed by undoing
special screws and the blade changed. It is also possible to use different
blades for varying player requirements. For this purpose, the injection
mould has interchangeable inserts that make it possible to provide different
radial curves on the blade surface in order to meet different player requirements.
The close tolerances between the individual component groups (blade,
stabilizers, and base ? Figure 5) favour the force line paths within
the system. The inherent rigidity achieved is greater than with any other
skate blade. Colour variations in the system are possible by changing the
pigment, as is surface decoration with special-effect paints.
33 D-72213 Altensteig Germany Phone: (49) 7453-2740 Fax: (49) 7453-27436
frogdesign inc. 1327 Chesapeake Terrace Sunnyvale, CA 94089, USA Phone:
(1) 408-734-5800 Fax: (1) 408-734-5801