Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF T~E I~VENTION
This invention relates to an injection molded ski and
a method for producing the same. More particularly, the inven-
tion relates to a novel injection molded ski having excellent
properties and an improved injection molding method for produc-
ing the same in which the ski is produced by using thermoplastic
resin materials.
It is well known in the field of ski manufacturing that
skis are produced by means of injection molding of thermoplastic
resins. However, except simple and low-grade ones, it has been
considered to be quite difficult to produce skis integrally
through injection molding by using thermoplastic resins since
the attaching of steel edges is not easy.
Further, when steel edges are attached to both the side
edges of the sole plate or bottom running surface of a ski body
with set screws, stress is set up in screw holes, and if the
ski is bent too much, cracks are caused to occur in the portions
of screw holes to result in the damage of the ski. Accordingly,
even when a ski body and a sole plate are integrally formed
together by injection molding, the strength of such ski is
inferior to that of conventional ones and still more investi-
gation for producing the injection molded skis is required.
The inventor of the present application has made eager
. and extensive studies on the production of skis through injectio i
molding method, and as the result, the present invention has
been accomplished.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to
provide a plastic ski which is free from the above-mentioned
disadvantages caused to occur in conventional ones.
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Another object of the invention is to provide an
improved injection molded ski having excellent strength and
other characteristics.
Further object of the invention is to provide an
improved injection molding method for producing such skis, by
which method quite satisfactory skis can be produced with
neither difficulty nor troubles.
According to the present invention, the ski consists
of ski body, a sole plate and a pair of steel edges. These
members are put tightly together in injection molding process.
The ski body constituting the main portion of a ski is provided
with a pair of edge receiving portions on both the longitudinal
sides of the bottom surface. Each edge receiving portion is
provided with a plurality of projections generally formed at ~,
regular intervals, with which projections a steel edge is
attached to the ski body. Between the pair of edge receiving
portions on the bottom surface of the ski body is an uneven
abutting surface to receive thereon the above-mentioned sole
plate. After the steel edges are applied to the projections
formed on the edge receiving portions, the sole plate is formed
on the lower surface of the ski body, in which the sole plate
is firmly secured to the uneven lower surface of the ski body
and to the projections on the edge receiving portions with
interposing the steel edges.
In the method for producing plastic skis of the present
invention, the ski body having the edge receiving portions is
firstly made by injection molding, the die is then opened to
attach a pair of steel edges to the projections oh the edge
; receiving portions of ski body, and finally, the die is again
closed with another different half mold and the sole plate is
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then formed by injection molding.
In accordance with the method of the present invention,
the bonding of the ski body, sole plate and steel edges are
easily and reliably performed as compared with the conventional
method because the sole plate is adhered to the ski body in
fused state. Therefore, even when the ski of the present
invention is intensely bent in the use, the component parts
are hardly peeled off. Further, the steel edges are attached
to the ski body through the above-mentioned improved injection
molding process without using any set screws so that the edges
are easily secured to the ski body without the troublesome
work as that caused in the conventional method.
In addition to the above advantages, the skis produced
through the method of the present invention have other merits
in the excellence of several mechanical properties such as
bending strength, fatigue deformation, torsional rigidity, and
~` impact strength.
Thereare various kinds of thermoplastic resins appli-
cable to the above-disclosed injection molding method, however,
exemplified as the most ~ypical ones are ABS (acrylonitrile-
butadiene-styre~e) resin and glass fiber reinforced ABS resin.
Like the ordinary skis, those of the present invention may also
be finished on the surfaces thereof by using various kinds of
coating materials and coloring materials.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of the invention
will become more apparent from the following description taken
in connection with the accompanying drawings in which:
Fig. 1 is a longitudinal sectional view of an embodi-
ment of the ski of the present invention;
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Fig. 2 is a cross-sectional view of the same embodi-
ment~
Fig. 3 is a perspective e~ploded view of the same
embodiment taken from the under side;
S Fig. 4 is a cross-sectional view of a set of molds for
injection molding;
Fig. 5 is a cross-sectional view of the same molds which
are fed with the material for ski body;
Fig. 6 is a cross-sectional view of the female mold
carrying a molded ski body to which a pair of steel edges are
fitted;
Fig. 7 is a cross-sectional view of a set of molds in
which the female mold is applied with a male mold different
from that of Fig. 4 or 5;
Fig. 8 is a partial cross-sectional view of another
embodiment of a set of molds;
Fig. 9 is a schematic illustration of the state of bend-
ing tests;
Fig. 10 is a graphic chart showing the results of bend-
: ing tests;
Fig. 11 is a schematic illustration of the state of
fatigue deformation tests; and
Fig. 12 is a graphic chart showing the results of fatigue
deformation tests.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the accompanying drawings, some
embodiments of the present invention will be described in the
following.
A ski body 1 having a configuration similar to that of
conventional one is made by in]ection molding with using a
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therm~plastic resin, for exQmple, ~5 resin containing 10~ of
glass fiber. As shown in Fig. 2, the ski body 1 has a smooth
top surface and a corrugated or grooved bottom surface 3. The
grooves formed in the bottom surface 3 are arranged in a
plurality of rows along the longitudinal sides of the ski body
1. On both the longitudinal edge portions of the bottom surface
3 are formed edge receiving portions 2 which are provided with
a plurality of projections 5 as shown in Fig. 3. The projec-
tions 5 are generally formed at regular intervals for receiving
the apertures of the below-mentioned fixing pieces 4b of the
steel edges 4, and the length or height of each projection 5
is made somewhat larger than the thickness of the fixing piece
4b of the steel edge 4.
The steel edge 4 is made of a long, flat and angled
steel and the edge body 4a is provided with a plurality of fix-
ing pieces 4b at regular intervals interposing therebetween a
plurality of narrow cuts 4c. Formed in the middle portion of
each fixing piece 4b is an aperture 4d which is to be caught
by the above-mentioned projection 5. Thus when the steel edges
4 are attached to the ski body 1, the projections 5 on the edge
receiving portions 2 are fitted into the respective apertures 4d
of the fixing pieces 4b and the steel edges 4 are pressed
against the edge receiving portions 2. In order to attach the
. steel edges 4 firmly to the ski body- 1, if desired, the protrud-
ing ends of the projections 5 may be melted down into the form
like a rivet head.
Then the bottom surface 3 of the ski body 1 is applied
with a sole plate 6 by injection molding of a thermoplastic
resin as ABS resin. As shown in Fig. 2, the top or upper side
of the sole plate 6 adheres tightly to the grooved bottom
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surface 3 of the ski body 1 and the bottom surface, that is
the running surface, of the sole plate 6 is aligned with the
lowermost edges of the edge bodies 4a. When this sole plate
6 is formed by injection molding, the molten resin is brought
into contact with the grooved bottom surface 3 and the protrud-
ing ends of the projections 5 and then it is solidified as it
stands. Thus the steel edges 4 are tightly held between the
ski body 1 and the sole plate 6, in addition, they are firmly
fixed by the projections 5. With the above-disclosed structure,
the steel edges 4 are not released as far as the projections 5
are not damaged. Further, since the sole plate 6 is formed on
the under side of the ski body by injection molding, the sole
plate 6 can be firmly bonded to the ski body 1 and even when
the ski is bent, the sole plate 6 is not peeled off from the
ski body 1 and the steel edges 4. Therefore, the ski of the
present invention having the above-disclosed unified structure
is safe and durable in practical uses.
In the following, the injection molding method of the
present invention for producing the above-disclosed ski will be
: explained with reference to the accompanying drawings, especial-
ly to Figs. 4 to 8.
As shown in Fig. 4, a female mold 10 and a first mold
half 12 are closed by pùtting them together. The female mold
10 has mold surfaces for forming the top and both side surfaces
of a ski body 1. It is to be noted that the positioning of the
cavity 11 is upside-down relative to the foregoing Figs. 1 to 3.
The first mold half 12 has a mold surface 13 to form the bottom
surface 3 and the edge receiving portions 2 of the ski body 1.
Further, a plurality of holes 14 are formed along the longitudi-
nal sides (perpendicular to Fig. 4) of the mold surface 13.
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The mold surface 13 of the first mold half 12 is a little
lowered into the cavity 11 of the female mold 10. The distance
between the boundary plane of both the mold halves 10, 12 and
the surface to form the edge receiving portions (indicated by
"Q" in Fig. 5) coincides with the height of edges 4.
In the next step as shown in Fig. 5, the injection
nozzle 16 is brought into contact with the sprue 15 of the first
mold half 12 and molten thermoplastic resin (e.g. AsS resin
containing 10% of glass fiber) is then injected into the cavity
11 to form a preliminary molding of the ski body 1 having
integral parts of edge receiving portions 2 and a plurality of
projections 5.
In the above embodiment, the sprue 16 may be formed in
any portion of the ski body 1, however, it may be advantageous-
ly positioned at the tail end of the ski body 1 in order to
make the material flow unidirectional and to prevent the
~! occurrence of dead points of material.
The set of molds is then opened byremoving the first
mold half 12, and the female mold 10 with the molded ski body
1 is shifted to the position of a second mold half 17. A pair
~ of steel edges 4 are respectively fitted into the spaces 18
,i which are previously formed by the mold surface 13 of the first mold half 12. When the steel edges 4 are attached, the
apertures 4d of fixing pieces 4b are fitted to the projectlons
5 on the edge receiving portions 2 so that the lateral move-
ment of the edges 4 can be avoided. The bottom surfaces (upper
side in Fig. 6) of the edges 4 are positioned on the same level
as the upper surface (parting line) of the female mold 10.
Therefore, when the second mold half 17 is applied to the female
mold 10, the steel edges 4 are firmly and accurately placed on
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the edge receiving portions 2 of the ski body 1. '
In place of the above procedure, if desired, the molded
ski body 1 can be once taken out from the female mold 10 and
the steel edges 4 are fitted to the edge receiving portions 2
outside the female mold 10. And after that, the assembly may
be again inserted into the female mold 10 shifted under the
second mold half 17 or another similar female mold 10 under the
second mold half 17. With such process, a special molding
machine is not required since the shifting of the female mold
10 can be avoided.
Further, in another embodiment, the ski body 1 may be
prov,ided with a continuous ridge 5a on the inside of each edge
receiving portion 5 as shown in Fig. 8. With such structure,
~'~ the fitting of steel edges 4 can be made more reliable. Still
, 15 further, after the fitting of steel edges 4 to the edge receivin
. portions 2, the protruding end of each projection 5 may be
thermally pressed down like rivets as shown in Fig. 8. It will
be understood that these modified structures are effectual for
the reliable securing of the steel edges 4 to the ski body 1~
After the fitting of steel edges 4, the second mold half
17 is placed on the female mold 10 carrying the ski body 1 with
the steel edges 4 as shown in Fig. 7. The second mold half 17 ,
;` has a mold surface 19 that forms the running surface of the ski.
- The mold surface 19 has a flat face generally positioned on
the same level as the parting line between the molds, and a
middle longitudinal projection to form a cross-sectionally
arcuate groove in the running surface of a ski to be formed.
, After the closing of the second mold half 17, an injection nozzl
,, 21 is brought into contact with the inlet of a sprue 20 and
molten thermoplastic resin (for example ABS resin~ is injected
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into the space between the ski body 1 and the mold surface 19,
thereby forming a sole plate 6 of the ski. In this process, the
steel edges 4 are tightly secured between the longitudinal sides
of the sole plate 6 and the edge receiving portions 2 of the
ski body 1, at the same time, the protruding ends or flattened
ends of the projections 5 (and 5a) are well bonded to the
material of sole plate 6.
As disclosed above, the durability of ski is excellent
as compared with that of the conventional ones because the ski
body 1 and the sole plate 6 are integrally formed by using
thermoplastic resins without the use of any adhesive agent.
Further, the steel edges are also integrally secured between the
ski body and the sole plate by injection molding, accordingly,
the concentration of stress to attaching screws can be success-
fully avoided. Therefore, the ski of the present invention can
be prevented from the peeling of the sole plate and loosening
or breaking off of the steel edges. Furthermore, the integral
formation of the ski body and the sole plate can be performed
by using the same female mold in a continuous manner, so that
any special technique is not required and the injection molding
: of the ski body and the sole plate with different thermoplastic
materials can be quite easily carried out. Therefore, the
present invention is very useful in view of ski manufacturing.
Performance Tests
1. Flexural Rigidity and Maximum Bending Strength
~ The skis of the present invention were produced accord-
; ing to the above-disclosed method by using ABS resin reinforced
with 10~ by weight of glass fiber for ski body portions and sole
ABS resin for sole plates, and they were compared with commercial
ly available skis as follows:
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Table 1. Skis Used for Tests
Symbol Description Length L (below)
A Semi-plywood ski 110 cm 830 mm
B Fiber glass reinforced 110 cm 830 mm
plastic ski
C Ski of this invention 110 cm 830 mm
D Fiber glass rei,forced 140 cm 1130 mm
plastic ski
E Semi-plywood ski 140 cm 1130 mm
F Ski of this invention 140 cm 1130 mm
.
In the above Table 1, the skis A, B, D and E were
bought from the market. Each ski 30 was supported as shown by
the solid lines of Fig. 9, and a load 31 was applied to the
center of the ski 30 between the supports 32. The initial dis-
tance between the supports 32 was L cm. The ski 30 was gradually
bent down by the load 31 as shown by the dash lines in the same
figure and finally the ski 30 was broken.
The relation between the load (kg) and bending ~d, mm~,
and the maximum bending strength (kg) were measured, the result
of which are shown in Fig. 10. The numerals indicated at the
free ends of resultant curves are the maximum loads (kg) and the
,~ bendings (d, mm) when the skis were broken.
From the results shown in Fig. 10, it may be understood
that the skis of this invention are excellent in view of the
flexural rigidity and maximum bending strength as compared with
those of the conventional ones.
2. Fatigue Deformation
Each ski 30 was set as shown in Fig. 11 between the
supports 32 and it was bent by applying a load 31 for the stroke
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S mm. The bending operation was continually repeated at 45 to
50 cycles per minute and at each of 500, 1000, 2000, 3000, 4000
and 5000 bendings, the vertical distance between the horizontal
center of both supports 32 and the center of a ski (indicated
by the symbol dl in Fig. 11) was measured. Thus obtained value
d1 was compared with the initial arch bend do as shown in Fig.ll.
Thus the value of arch bend durability (~) was obtained
according to the following equation:
dl
- x 100 = Arch bend durability
The data of the skis used for the tests and some test
conditions are shown in the following Table 2.
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Table 2. Skis and Test Conditions
15Symbol Description Length (mm) (mm) (mm)
A Finly foamed poly- 110 830 7.4 80
styrene
, B Ski of this invention 110 830 7.2 80
C -do.- 140 1130 11.5 150
; D Semi-plywood ski 120 930 7.0 80
E Fiber glass reinforced110 830 4.0 80
plastic ski , , , ,
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The skis A, D and E were obtained from the market and
the skis B and C were made according to the method of this in-
vention by using ABS resin reinforced with 10% by weight of glass
fiber for ski bodies and ABS resin for sole plates. The results
of the tests are shown in Fig. 12. ~
The ski A was broken before 3000 bendings even though
the fatigue deformation of ski A was small.
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~urther, it will be understood from the res~lts shown in ~ig. 12
that the fatigue deformations of the skis of this invention are
very small as compared with those of the commercially available
ones.
3. Impact Resistance
In this test, each ski was loaded with a 20 kg weight,
then caused to glide on a horizontal plane by an air cylinder
and allowed to collide with a vertical solid wall surface at a
speed of 5.4 m/s (19.5 km/hr). In the tests, three kinds of 140
cm skis were used. A plywood ski was broken off at the point
near the front bent end. Another glass fiber reinforced plastic
ski was folded at a similar point. The ski of this invention
similar to those used in *he foregoing tests was bent to some e~tent
but it was not broken off.
From the abové tests, it will be understood that the
mechanical properties of the ski produced according to the pre-
sent invention are quite good. This is owing to the fact that
the ski body, sole plate and a pair of continuous steel edges
are integrally and firmly joined together by injection molding.
Although the present invention has been described in
connection with a preferred embodiment thereof, many variations
and modifications will now become apparent to those skilled in
the art. It is preferred, therefore, that the present invention
be limited not by the specific disclosure herein, but only by
the appended claims.
