Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
11 32~73~
1 BACKGROUND OF THE INVENTION
(FIELD OF TH~ INVENTION)
The present invention relates to an improvement
of a process for forming one or more insulated films on
the surface of a solid body such as an insulatlng coil
or a grip of a cutting pliers.
(DESCRIPTION OF THE PRIOR ART)
The present invention may be applied to any
articles or parts on which one or more insulated films
are coated an~ will be explained with reference to
the insulated conductor wherein an insulating film is
coated on a conductor.
Generally as the method for formir.g one or
more insulated films which will be covered on a bared
conductor, there are mentioned a variety of methods
such as coating an insulating paint on the surface
of a conductor, covering one or more insulated films,
which ha~e been previously formed in a cylindrical
shape (or a bag shape) over a conductor, winding an
insulating tape (or sheet) around a conductor to form
one or more insulated films on the surface of the
conductor and the like. Usually these methods are
appropriately selected and adopted depending on specific
forms of the articles or parts.
-- 1 -- *
~ 32:~73~
1 The present invention relates to the last
method among the above-mentioned ones, that is, a
method for forming one or more insulated films by winding
an insulating tape (or an insulating sheet) around a
conductor to form one or more insulated films.
The method for forming one or more insulated
films by winding an insulating tape, as disclosed also
in Japanese Patent Application Kokai (Laid-Open) No.
49455/77, is usually conducted by winding a certain
kind of an insulating tape around a conductor so as the
part of the tape to overlap, subjecting the tape to
resin impregnation (or winding the tape on which a
resin has previously coated around a conductor) and
curing the resin on the tape at the state by putting
external force through a plate on the external surface
(or heat-curing in the case of a thermosetting resin).
The method has almost no problem for forming
one or more insulated films used for popular applications,
but when it is adopted for forming the ones which may
be exposed to vigorous vibration or impact or on which
electrically excessive voltage or impulse voltage is
apt to be applied, the films tend to be weakened
mechanically or electrically. In other words, the one
or more insulated films having been cured by applying
external force to a plane through a plate seem apparently
to be formed uniformly in thickness because of the
flatness of the external surface. However, the conductor
itself has warpage or deformation~ to some extent, so
- 2 - ~
132173~
1 that the one or more insulated films may be pressed
unevenly by the pressure of the plate, that is to
say, adhesion between the conductor and the one or more
insulated films will not be uniform thus happening
peeling at the parts to which pressing force is applied
only weakly. Furthermore, the corner parts or curve
forming parts are at the worst in view of the adhesion,
and voids are likely to be formed and electrical proper-
ties are degraded at these parts where pressing force
is applied weakly.
In order to improve this point there has
recently been proposed a method for forming one or
more films, in which an insulating film (or tape) having
been wound around a conductor and subjected to resin
impregnation, of which the whole external surface
having been subjected to fluid sealing, is dipped into
an insulating oil in a sealed container and heat-cured
with pressure by raising the pressure and temperature
of the insulating oil.
The method presses uniformly the whole surface
of the one or more insulated films regardless of the
presence of the deformation, corner parts or curved
parts of the conductor, that is to say presses the
surface without any unevenness of the pressing force
and thus the adhesion is largely improved as compared
with the above-mentioned. However, as a result of our
detailed experiments, it was found that this method for
forming the one or more films has also the following
~ 32~73~
1 problems:
This method is conducted in oil, and thus
whole of the one or more insulated films placed on the
surface of a solid body is uniformly pressed. However,
air between the conductor and the film or within the
film layer will remains at the part in a compressed
state, so that the one or more insulated films cannot
exhibit satisfactorily the electrical properties which
are possessed intrinsically by the film. Moreover,
during operation or using of the products insulated by
this method, for a long time peeling is apt to be caused
by the remaining of the compressed air and thus the
film becomes weakened mechanically.
Thus, it is impossible to remove the air
remaining within the layer of insulating film, because
this method is conducted in compressed oil and the
air remains within layer of insulating film in a compres-
sed state.
SUMMARY OF THE INVENTION
~0 The present invention is conducted in view of
the above reason and the object of the present invention
is to provide a method for forming one or more insulated
films on a conductor (solid body) having a uniform
thickness and an excellent adhesion wherein no air will
remain between the conductor and the film or within a
film layer even if the conductor has warpage, deformation
or curved parts and a'l parts of the film are pressed
-- 4 --
132~73~
uniformly irrespective of the warpage, deformation or
curved parts of the conductor.
In other words, the present invention is a
method for accomplishing the expected object on curing the
impregnated resin in the above-mentioned film while
pressing the one or more films by providing densely a large
number of solid particle ~odies on the external surface of
the one or more insulated films, pressing the one or more
insulated films onto the surfaced of the solid body through
the solid particle bodies and curing the impregnated resin
in that state.
~ ccording to this method, whole of the one or
more insulated films provided on the surface of the solid
body is uniformly pressed by a large number of solid
particle bodies provided on that external surface, the air
between the insulated film and the solid body and within
the insulated film layer is expelled through the space
between the solid particle bodies to the exterior of the
layer in a state in which whole of the one or more
~0 insulated films are uniformly pressed and the impregnated
resin is cured in the state that the air is expelled, so
that the one or more insulated films formed on the surface
of the solid body will be the one which has a uniform
thickness and no remaining air therein and is excellent in
adhesion.
132~73~
According to one aspect of the invention there
is provided a process for forming one or more insulated
films on the surface of a solid body comprising pressing
towards said solid body one or more insulated films which
are so arranged as to cover at least a part of said solid
body and are impregnated with a resin and at the same time
curing said impregnated resin, characterized in that on
curing said impregnated resin while pressing said one or
more insulated films a large number of solid particle
bodies are densely provided on the external surface o~ said
one or more insulated films, said or more insulated films
are pressed onto the surface o~ the solid body through said
solid particle bodies and the impregnated resin is cured in
that state.
In accordance with another aspect of the
invention there is provided an apparatus for forming one or
more insulated films on the surface of a solid body
comprising pressing to the solid body one or more insulated.
films which are so arranged as to cover at least a part oP
~0 the solid body and are impregnated with a resin and at the
same time heat-curing said impregnated resin, characterized
in that a container Por receiving said solid body which is
covered with said one or more insulated films, said
particle bodies which are put in said container and in
5a
A
.. ` ` .. .. . . ~ . .
` ``." :. - `. : `
.
.
132173fi
which said solid body has been embedded and a pressing
means îor applying pressing force to said solid particle
bodies are provided, so that the pressing force by said
pressing means is applied to sai~ one or more insulated
films through said solid particle bodies.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a vertical section o:E an apparatus
5b
~32~ 736
l for forming one or more insulated films of the present
invention in order to illustrate an example of a process
for forming the one or more insulated films of the
present invention,
Fig. 2 is a vertical section which illustrates
only a container of Fig. l,
Figs. 3 - 5 illustrate the examples of the
process of the present invention sequentially, in which
Fig. 3 illustrates a perspective view of the insulated
conductor and Figs. 4 and 5 illustrate vertical sections
of the apparatuses,
Fig. 6 is a vertical section of the appara*us
for illustrating another example of the process of the
present invention,
Fig. 7 shows tan ~ - voltage characteristics
of the one or more insulated f ilms, and
Fig. 8 is a partly broken perspective view
of the insulating coil.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is explained in detail
with reference to the following examples.
E`igs. 3 and 4 illustrate the process for
forming the one or more insulated films of the present
invention sequentially.
These figures illustrate the case of forming
the one or more insulated films on the insulated connect-
ing conductor which is usually used for electric coupling
6 --
~321736
1 of the electric apparatuses at a power station or a
transforming station. First of all, as shown in Fig. 3,
an insulating tape 3 coated with a resin is wound
around a conductor 2 with overlapping a part of the tape
to form an expected film layer 4 on the surface of the
conductor 2. If a tape on which no resin is coated is
used, the film layer is subjected to resin impregnation
after winding the tape. The resin is generally
impregnated by vacuum pressure impregnation.
Next, the film layer 4 is molded by pressing
in a non-cured state of the impregnated resin, in which
the molding by pressing is conducted in the solid
particle bodies 5 as shown in Figs. 4 and 5.
That is to say, the insulated connecting
conductor 1 is embedded into solid particle bodies 5
such as sand or iron balls contained in a container 6
(Fig. 4), and these solid particle body, as shown in
Fig. 5, is pressed by a pressing means such as an oil
pressure piston 7 or the like. The sign 8 provided
right below the container 6 in the figure represents an
air ventilating apparatus, and the sign 9 represents a
filter for preventing the solid particle bodies 5 ~rom
expelling out of the container through the air ventilating
apparatus 8.
As mentioned above, to press the solid particle
bodies embedding the insulated connecting conductor 1
with the pressing means 7 means to apply external force
to the film layer 4 of the insulated connecting conductor
132~736
1 through the solid particle bodies 5. As the external
force is applied just through the particle bodies, it
is applied uniformly to all over the surface at fine
intervals, that is, pressing force is uniformly
added irrespective of the warpage or deformation of
the solid body (i.e. conductor 2 in this case). At
the same time, as the film is pressed through the
particle bodies, air within the film layer 4 is expelled
from the layer through the space between neighbouring
particles, and the air thus expelled or the air pressure
caused by the reduction of the container volume due
to the movement of the pressing means is expelled
externally through the air ventilating apparatus 8.
Accordingly, whole surface of the film layer
4 of the insulated connecting conductor (including corner
parts and plain parts) is pressed uniformly by a
predetermined pressure and the air existing within the
layer is expelled sufficiently to the external direction,
the contact surface of the film layer 4 and the conductor
2 and the interior of the film layer becomes the
satisfactorily closely adhered state and the thickness
of the film layer 4 itself becomes even. Finally the
film layer is heat-cured for a predetermined time to
give an insulated connecting conductor having an ideal
insulation layer.
In the above explanation, pressing of the one
or more insulated films through the solid particle bodies
is illustrated with reference to an example. However,
- 8 -
~3217~
1 for practical application there may be created a
variety of methods other than the above on consideration
of the kinds of resin, methods for ventilating air,
methods for pressing and the like.
Fig. 1 shows another example. In this example,
there may be obtained a stronger adhesion as compared
with the above-mentioned example, and elec~ric properties
may be improved by applying the process to ~he insulated
coil and the like. First of all, referring to circum-
ferential apparatuses thereof and then to the process,
there is a container 6 placed on a truck 10, in which
container a heat resistant solid particle bodies 5 and
an insulated coil la having previously been subjected
to resin impregnation are contained. Particularly, the
container is so formed as for a part of its wall to be
deformable. In other words, in this example there is
provided a heat resistant extensible member 11 such as
a polyester film wall at the upper part of the container
6. On the side wall of the container 6, there is also
provided a piping 12 for producing vacuum within the
container, which piping is connected to an external
pressure reducing means such as a vacuum pump 15 through
a flexible pipe 13 and a valve 14.
Moreover, the container 6 is arranged together
with the truck 10 within a heating oven. Within the
heating oven 16 a heating apparatus 17 is provided for
drying the inside of the heating oven.
Main apparatuses being as mentioned above, it
_ g _
132~73~
1 is important that not only the extensible member 11
provided at the upper part of the container 6 has a
strength for preventing itself from being broken when
the container has been made vacuum by a vacuum pump,
but also it can be deformed so that the solid particle
bodies 5 are pressed satisfactorily at a certain level
of vacuum, in other words, a means for pressing the
solid particle bodies must have a construction that
the container 6 is made vacuum and thus the solid
particle bodies are pressed by the deformation of the
extensible member (see Fig. 2), so that when the
extensible member is deformed it physically contacts
and presses the solid particle bodies. Therefore, it
is desirable for the solid particle bodies 5 to be
charged as much as possible in the container 6,
because the deformation degree of the extensible member
11 may be little.
A process for forming one or more films of an
insulated coil by using the apparatus is now explained.
The figure shows the state of the container 6
within which the insulated coil la is arranged. The
process is explained starting from preceeding processes
without illustration in figures. First of all, a coil
is made by winding a conductor and formed and then a
tape such as grass backed mica tape which has been
impregnated with an epoxy type semi-cured thermosetting
resin is wound around the coil to form an insulated
coil la.
-- 10 --
~ 32~L73~
1 Next, the insulated coil la is placed into the
container 6, wherein the insulated coil is embedded
deeply into the solid particle bodies 5 to ensure
that the insulated coil will not be exposed from the
solid particle bodies.
In this case, the extensible member 11 serves
as a closure of the container and thus the extensible
member 11 must be attached by providing a sufficient
sealing to ensure isolation of the inside of the
container from the outside after the insulated coil
has been inserted into the container.
Then the insulated coil is placed in the
heating oven 16 together with a container by a truck.
If the insulated coil la is so small in siz.e that an
operator can easily carry it by hand, the container
6 may be previously arranged within the heating oven
16 within which the insulated coil la is accommodated
in the container.
Next, if a vacuum pump 15 is operated to
reduce a reduced pressure within the container 6, the
extensible member 11 is deformed as shown in Fig. 2,
that is, atmospheric pressure P is applied to the
external side of the extensive member and the solid
particles receives the pressing force by the extensive
member, so that whole surface of the layer of the
insulating tape on the insulated coil is uniformly
pressed in the same way as in the aforementioned example
to improve the unlformity of the thickness and adhesion.
',
.
~32~736
1 Then, under this condition, the insulated
coil is heated and cured in the oven.
Particularly in case that the process for
forming a film conducted in this way is employed, not
only the same effect as the above-mentioned one is
generated since the process is also the pressing and
heating of the insulating film by solid particle bodies
as mentioned in the above example, but also air remaining
within the insulated coil is enforcedly drawn out of
the film simultaneously with the pressing of the solid
particles as the pressing means employs the deformation
of a container by vacuum within the container, that is,
voids are reduced and thus adhesion may be further
improved than in the above-mentioned example.
Fig. 6 shows a further example.
Pressing force is obtained by reducing pressure
(making a vacuum) within the container also in this
case, and explanation will be conducted only referring
to the different points from the above. There is a
tightly closed container 6, which is divided into two
rooms Rl and R2 up and down by the extensible member.
In the lower room R2, the solid particle bodies 5 and
the insulated coil la are received, and reduced pressure
is produced b~ a vacuum pump 15. On the other hand,
the upper room Rl is connected with a vacuum pump or
pressurizing pump 15a. Cooperation of the pressurizing
pump 15a and the vacuum pump 15 in the lower room makes
possible to press further stronger the solid particle
- 12 -
~32173~
1 bodies 5. Particularly if it is intended to make the
inside of lower room Rl extremely lower vacuum condition
and at the same time to retain the pressing force in a
relatively low level, pressure in the lower room is
reduced vigorously and a vacuum pump is connected also
to the upper room to reduce a pressure so as to obtain
the pressing force from the difference of the two
reduced pressures. Thus it will be possible to control
freely the degree of vacuum and the pressing force.
The present invention having been explained
with reference to the several examples above, there
ma~v also be used as the pressing means the expanding
force of a heat expanding body by the use of the heat
on heating a resin, the weight of the solid particle
bodies or the combination thereof. There may be also
considered a variety o~ methods such as compulsively
pushing a number of the solid particle bodies into a
tightly closed container having a predetermined volume
or the like.
As the solid particles, those having a particle
diameter of 10 - 800 ~ are optimal, and sand such as
molding sand is most inexpensive and practical. It
will be possible to employ any other particles such as
metal balls, glass beads or the like which form space
between the adjacent ones and retain air permeability
on gathering together.
Having explained for the case of parts wherein
one or more insulated films are formed on the surface
- 13 -
~ 32~73~
1 of a solid body and the one or more insulated films
and the solid body are integrally used, the present
invention is also applicable to the case of producing
an insulating plate or insulating molded article by
the use of a molding tool. That ls to say, when the
insulating plate having a wave shape is intended to
be produced, an insulating film having been impregnated
with a resin is placed on the solid body having a
wave-shaped surface and pressed in the solid particle
bodies in the same manner as the aforementioned examples.
In this case, as the solid body and the insulating
film are finally to be separated, it is needless ~o say
that a release agent is preliminarily provided between the
solid body and the insulating film. Insulating molded
articles produced according to the process have no void
in their layers and thus form a dense layer as those
mentioned above, and it is also possible to obtain a
layer having a uniform thickness along the shape of the
surface of a solid body.
Next, one or more insulated films produced by
the process of the present invention and the one
produced by the conventional process are compared from
the viewpoint of their effects.
Furthermore, it is difficult to evaluate the
insulated coils produced by these processes from the
viewpoint of their mechanical effects, that is, the
degree of peeling and the results cannot be expressed
specifically herein. However, it is well-known in the
- 14 -
11 3217~
l art that fewer voids in the insulating layer and uniform
thickness of the insulating film over the whole surface
will exhibit excellent properties in the insulated coil.
Fig. 7 is a test results of the insulated
coil formed by the process of the present invention
from the viewpoint of electri.c property which will
be largely effected by the presence of void and shows
the relationship between test voltage and tan ~ (%).
The insulated coil tested is a commutating-pole coil
used for a direct current traction motor for a car
(see Fig. 8), which has an oval shape with a total
length of 320 mm and a total width of 100 mm, a
rectangular section of 60 x 32 mm and a rated voltage
of 400 V.
lS In Fig. 7, the curve X represented by a dotted
line shows the test result of an insulated coil
produced by the conventional process for forming a
film, briefly saying, the one formed by pressing through
a plate on the external side of the one or more films,
wherein as i9 apparent from the figure tan ~ sharply
increases at the test voltage higher than 2.5 kV.
The curve represented by a chain line y shows the result
o~ an insulated coil produced by curing by applying
oil pressure in an insulated oil, wherein tan ~,
fluctuating little to the test voltage, is wholly in
a higher level. On the other hand, the curve Z represented
by a solid line shows a result of an insulated coil
produced by the process of the present invention, wherein
- 15 -
.
7 3 ~
1 as is apparent from the figure tan ~ remains wholly
in a low level and will not increase largely.
Table 1 shows the results of measurement for
evaluatin~ the uniformity of the insulation thickness
of coils (see Fig. 8 with reference to the measuring
point), wherein the thickness at the corner part
t3 ~mean value) and those at the plain side parts t
and t2 (mean value~ of the section of the insulated
coil are particularly compared.
As is apparent from the result, there is no
significant difference between the thicknesses at the
plain parts in the coils formed by the conventional
process and by the process of the present invention.
However, at the corner parts there is observed a
remarkable improvement for the coil formed by the
process of the present invention as compared with the
one formed by pressing through a plate, and the coil
produced by the process of the present invention has
the same uniform thickness as in the coil produced by
pressing in oil.
- 16 -
:~32~736
Table 1
_ Film formed by the
.conventional processFilm formed by
Measurlng the present
pointthrough Pressing invention
Interior1.5 mm 1.5 mm 1.5 mm
gide (t2) L 1~4 1.5 l.S
part (t3) ~ 1.4 1.4
1 Table 2 shows the test result of dielectric
breakdown voltages, which was carried out for four
coils each.
Measurement were conducted by putting an aluminium
foil as on electrode on the hollow part of Fig. 8, that
is, the interior wall, and applying a voltage between
the above electrode and a lead lb.
From the result, it will be apparent that the
film formed by the process of the present invention can
be resistant to a high voltage of about 10% higher than
that applied to the one or more conventional films.
- 17 - :
~321~36
Table 2
Film formed by the
conventional process
_ Fllm formed by
a plate Pressing the present
~... _ ._ .
18.0 19.0 21.5
Breakdown 18.0 20.0 22.0
voltage
(kV) 19.0 20.0 22.0
19.0 21.0 23.0
Mean
value 18.5 20.0 22.1
1 [EFFECTS OF THE INVENTION]
As mentioned above in detail, according to
the present invention when an impregnated resin in an
insulating film is cured while pressing the film a
large number of solid particle bodies are densely
provided on the external surface of the insulating film,
the insulating film is pressed onto the surface of
the solid body through the solid particle bodies and
the impregnated resin is cured in that state. Therefore,
the insulating film is uniformly pressed through the
surrounding solid particle bodies irrespect1ve of the
corner part, deformed part or curved part of the sol1d
body, and air between the insulating film and the solid :
body and within the insulating film layer is expelled
- 18 ~
~32:~36
1 out of the layer through the space between the solid
particle bodies, so that one or more insulated films
having a uniform thickness as a whole and no remaining
air and excellent in adhesion can be obtained.
- 19 -:
