Note: Descriptions are shown in the official language in which they were submitted.
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1 The present invention relates to a ski, in particular
a cross-country or excursion ski.
The use of plastics material for ski bottoms was
introduced in skis for downhill running, but today almost
exclusively plastics bottoms are also used for cross-country
skis. A serious drawback of plastics bottoms in such skis is
that the plastics yive poor hold. Attempts have been made to
solve this problem along two main lines.
One of the main lines consists of making the bottom
1~ of the ski relatively coarsely grooved~ whereby a grooving
has been concerned that is readily visible to the eye.
These skis have not been successful in practice, obviously owing
to unsatisfactory glide. ~ closely related solution is that
a fluffy fabric is used with a sli~ht inclination resis~ance
in a certain direction. Such a ski bottom is~ however, expensive
-to manufacture, besides which the wear resistance of the
fabric has proved insufficient. Nor is it possible to replace
the ~abric ~y means of reasonable operations.
The other main line has consisted of attempts~ in
different ways, to make the bottom of the ski porous in ordex
that the wax should adhere to the ski better. An example of
solutions in this direction is disclosed in the Finnish Announce-
ment Publication No. 48,676. In this way, true enough, sat~
isfactory results have been obtained in respect of the hold, but
a requirement is, however, careful application of wax, which
involves a relatively great trouble for the layman, especially
because the wax is in any case worn and must be renewed.
The object of the present invention is to provide a
new cross-country s]ci that has both good glide and good hold
without the use of the ski wax.
B
~L~Z(~65
1 The ski in accordance with the present invention is
characterized in that its bottom, at least at the middle por-
tion of the ski, i.e. at the portion loaded by the foot, is
made of a hard and elastic, massive plastics material, whose
surface is shaped as fluffy with sharp edges, the fluff length
being approximately 0.0l to 0.l mm.
The plastics material is pre~erably polyacetal plastics
or an elastomer with corresponding propertiesD
The term "fluffy" is in ~his connection not to be
misunderstood as meaning a fluff similar to that described,
e.gO, in the Finnish Patent 43,401. In the present case, viz.,
the bottom face of the ski feels completely smooth when it is
stroked with the hand, but light passing parallel to the ski
bottom discloses the nature of the bottom, which has ~ screen~
like a~pearance by the effect of the light shadows~. T~e ~lu~
moves easily and changes direction even when touched l:ightly
by the finger, which is in appropriate illumination seen as
the place concerned becoming darker or lighter.
When the ski glides forwards on crystals of ice, the
~ fluff is bent and its friction is low. The layer of water that
is formed between the ski and the crystals of ice likewise
improves the glide in the same way as in the case of skis
provided with wax, because the short fluff does not break the
layer of water. When the glide has stopped, the fluf again
assumes its original shape, when the foot is pressed down, and
by means of its hard and sharp edges bites into the ice and gives
a surprisingly good hold.
The desired fluff can be produced advantageously by
means of so-called vibration grinding, which takes place in a
totally haphazard way as regards the direction, so that the fluff
6~i
1 does not receive an advance inclination in any direction. It
has been noticed that if the fluff is, e,g.~ given ~n advance
inclination b~ckwards, the hold is decreased remarkably, because
the fluff is not able to raise itself sufficiently~ The same
phonomenon tends to occur if -the fluff is too long in relation
to its thickness; this begins to be noticed when the ratio of
length to thickness exceeds 2:l. This drawback is avoided most
reliably if the length of fluff is maintained within the range
of O.Ol to 0.05 ~m. A manufacturing-technical advantage due to
the fact that the fluff is complelely irregular is that during
installation of the bottom layer that ski bottom has no "front
end" or "rear end 71 .
In order to obtain su-fficient hold, it is not necessary
to manufacture more than the so-called foot-loaded portion of
the ski bottom in the described way, whereas the front and rear
parts of the bottom may be untreated or, as in skis so far,
e~g., made of polyethylene, which is considerably less expensive
than, e.g., polyacetal. In this way the glide of the ski also
becomes better. In view of so-called week-end skiers it would,
~ however, also be acceptable to make the entire bottom of the
ski fluffy in the described way.
When skiing on tracks with lively traffic of skis with
ski wax, detached ski wax present on the track tends to adhere to
the fluff and to impair its functioning. This can be counter-
acted by mixing into the plastics material an agent that rejects
ski wax. Such an agent is, e.g., polytetrafluoroethylene
~PTFE), which can be mixed into the plastics material in the form
of grains. The quantity of polytetrafluoroethylene may be
appropriately approximately 20 per cent.
The invention will be described below with reference
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1 to the exemplifying embodiment shown in the attached drawing.
Figure l shows a bottom of a ski in accordance with
the inventi:on,
Figures 2 and 3 show a schematical enlarged view of
the portion of the ski bottom that provides the hold, during
gliding and during hold, respectively, and
Figure 4 is a schematical view of the way in which an
agent rejec-ting ski wax may be mixed into the ski bottom.
The ski bottom of a ski in accordance with the invention
is denoted with numeral l, the foot-loaded portion, which is
mainly responsible for the hold of the ski, with numeral 2, the
front part of the bottom with 3, and the rear part with 4. The
front part and the rear part are made of, e.g., polyethylene,
as in known skis. The middle, foot-loaded, part 2 is made of
hard and elastic, massive polyacetal plastics or of an elastomer
of similar properties, and its surrace is ground in order to
produce elastic fluff 5 with sharp edges, as is shown schematic-
ally in Figures 2 to 4. The hardness of the material gives the
individual ~luff hairs 5 good resistance to wear, and the
elasticity provides the desired glide-hold effect. The length
h of the individual fluff hairs may vary within the range
of O.Ol to O.l mm, but in order to obtain good so-called form
memory, the ratio of length h to the width or thickness b of
the hair 5 at the root should preferably not exceed about 2:l.
The fluff is appropriately produced by means of a
manually operated vibra-tion device making use of grinding paper
of appropriate coarseness in order to produce, as regards the
direction, a haphazardly random grinding, which has proved
give the best results. It is also possible to use totally
mechanical grinding, in which case the configuration of the
fluff becomes regular, e.g., in the form of transverse or
--4--
longitudinal "grooyes", but the final result is then somewhat
nferlor .
It has been noticed that if the fluEf is, in the way
indicated above, ground to a length closer to the gi~en upper
limit of 0.1 mm, a relatively high proportion of the fluff
hairs become so narrow that they do not straighten up sufficiently
after the gliding stage of the ski, and therefore it is preferred
that the fluff length be limited to about 0.01 to 0.05 mm.
In order to avoid adhesion of ski wax present on the
ski track to the fluff with resulting elimination of its effect,
an agent rejecting ski wax, e.g., polytetrafluoroethylene in
the form of grains 6, can be mixed intothe plastics material,
as is implied schematically in Figure 4. It has been noticed
that an appropriate quantity is 20 per cent by weight, but other
values may of course also be used. An extra advantage of
this solution is that the fluff is substantially retained with-
out re-grinding, in spite of wear, which wear, due to the
hardness of the plastics material, true enough, takes place
slowly but, nevertheless, cannot be avoided.
2~ Another possibility is to impregnate the plastics
material with, e.g., zinc stearate, appropriately in a quantity
of about 3 per cent by weight, whereby the zinc stearate also
counteracts formation of ice especially at temperatures of
about 0C to -1C.
