Note: Descriptions are shown in the official language in which they were submitted.
54
SPECIFICATION
"MAGNETIC MATERIAL WIRE AND METHOD
OF PRODUCING SA~E"
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to an elongated magnetic material
element adapted to be wound around a conductor of an overhead
transmission line to prevent the freezing or icing thereof.
Prior Art
A conductor of an overhead transmission line is subjected
to icing and the deposition of snow in cold districts during
the winter. The snow or the ice on the conductor grows
upon lapse of time to increase the weight of the conductor
and a wind pressure to which the conductor is subjected,
thereby excessively increasing a tension of the conductor,
and a sag of the conductor between each adjacent pylons is
unduly increased. As a result, the conductor tends to be
broken off, and the steel pylons supporting the conductor
tend to fall. Further, there is a risk that lumps of snow
or ice drop from the conductor and hit a passer-by passing
beneath the transmission line. Even if the transmission
line is laid over agricultural lands, such fallen lumps
of snow or ice may give rise to dama~e to the crops and farm
acilities.
In order to prevent the conductor from being subjected
to the deposition of snow and the icing, it has been propos-
ed to temporarily pass a large amount of alternating current
~2~ i;4
-through the conductor to generate joule heat by which
the snow or ice on the conductor is melted. However, this
method can not be carried ou-t at all times because of -the
limitations on the operation of the transmission line.
Another method of overcoming the above-mentioned
difficulty is to mount rings on the conductor in spaced
relation to cause the snow on the conductor to drop there-
from. However, the rings often fail to cause the snow or
the ice to drop satisfactorily. Further, lumps of the
snow or ice caused to drop by the rings may injure a
passer-by or cause damage to the crops and the farm facili-
ties.
It has also been proposed to mount a magnetic material
element on the transmission line conductor so that the snow
or the ice on the conductor is melted by the heat due to
hys~eresis loss and eddy current loss generated by the
magnetic field developing in the magnetic material element
due to the flow of alternating current through the conductor.
The ma~netic material element includes a wire, a tape and
a rod all of which are adapted to be spirally wound around
the conductor, and a sleeve adapated to be fitted on the
conductor. Such magnetic material element should be as
ligntweight as possible to prevent the -transmission line
from becoming unduly heavy. ~lso, since the heat generat-
ed by the magnetic material element at temperatures causinq
no icing or snow deposition contributes to the loss of the
transmission power, the magnetic material element should
preferably be made of a low Curie point material of which
--2--
~z~s~
magnetic properties are lowered at high tempe~atuxes to
generate less heat. Generally, a low Curie point material
tends to be less magnetic even at low temperatures than a
high Curie point material. Therefore, -the melting of snow
or ice can not satisfactorily be achieved only by the heat
due to the hysteresis loss, and the heat due to the eddy
current loss must also be used together to achieve a desired
melting of the snow or ice.
Usually, the magnetic material element comprises a
magnetic material and a conductive metal sheathing covering
In the case of a magnetic material having a high Curie
point of not less than 300C, the heat due to the hysteresis
loss is greater than the heat due to the eddy current loss.
There~ore, the melting ef~ect is not so af~ected by the
thickness of the conductive metal sheathing covering the
magnetic material.
In the case of a magnetic material having a low Curie
point of not larger than 2~0C, the heat due to the eddy
current loss is greater than the héat due to the hysteresis
loss. Therefore, it is necessary to properly determine the
thickness of the conductive metal sheathing in order to
achieve a desired melting o~ the snow or ice.
The magnetic material element has been made of alloys
~5 having a Curie poin~ o~ 0 to 100C, such as an alloy con-
taining iron, nickel, chrominum and silicon and having a
Curie point of around room temperature. However, magnetic
properties of such alloys are liable to be affected by heat
~L2~1~@~i4
treatment c~nditions and other processing conditions. In
addition, such alloys have a poor reproducibility. For
example, the magnetic material element in the form of a
wire is manufactured by drawing. Magnetic properties
of the thus drawn wire are lowered due to the residual
strain of the wire irrespective of the reduction rate of
the drawing operation. If it is intended to use such a
wire for the purpose of melting the snow or ice on the
conductor, a large amount of wire must be wound around the
conductor to achieve the desired melting.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide
a magnetic material element comprising a core of magnetic
material having a low Curie point and a high conductive
metal sheathing of a uniform thickness covering the core,
the thickness of the metal sheathing being so determined
as to achieve the above-mentioned melting effect.
Another object is to provide such a magnetic material
element having a reduced residual strain.
According to the present invention, there is provided
a magnetic material wire comprising a core o~ magnetic
material having a Curie point of 70 to 250C, and a high
conductive metal sheathing of a uniform thickness covering
the core, the ratio of the metal sheathing to the wire in
cross-section being in the range of 15 to 40%.
If this ratio is less than 15%, the effect achieved
by the conductive metal sheathing is not satisfactory, and
particularly when this xatio is not less than 20%, a satis-
--4--
e~fect is achieved. On -the other hand, if this ratio
exceeds 40~, the heat generated becomes unduly small. Most
preferably, this ratio is 20 to 40~.
The core of magnetic material contains apart from
impurities 32 to 52% by wei~ht of nickel, 0.5 to 9% by
weight of chromium, 0.2 to 2~ by weight of silicon and
balance iron. The core has a low Curie point of 70 to 250C.
The high conductive metal sheathing is made of copper,
aluminum, zinc and their alloys.
In the case of the cold~drawing of a metallic material,
the residual strain tends to develop in the material, and
the amount of the strain becomes greater toward the outer
surface of the material because of the frictional contact
with the tools of the processing apparatus. It has now
been found that this residual strain adversely affects the
magnetic properties of a magnetic material. Generally, this
strain can be reduced by a heat treatment. However, in the
case of a magnetic material or alloy of the kind for the
above application, its magnetic properties can not suf-
ficiently be recovered by a heat treatment. In addition,
when such an alloy is heated at high temperatures, its
strength is lowered, and a layer of intermetallic compound
tends to be formed at the interface between the magnetic
material and the conductive metal sheathing. As a result,
electrical conductivity and magnetic properties are adverse-
ly affected.
According to a further aspect of the present invention,
the magnetic material element in the form of a wire is bent
--5--
~21~S4
in such a manner that the ratio of the radius (a half of
the thickness) of the core to a radius of curvature of the
bent wire is in the range of 2 to 9%, thereby reducing the
residual strain of the wire. With this method, the residual
strain can be satisfactorily reduced without the need for
a heat treatment.
The magnetic material wire according to this invention
may have any cross-sectional shape such as oval, square and
rectangular shapes.
BRIEF DY.SCRIPTION OF THE DRAWINGS
FIG.l is a graph showing ~he relation between the amount
of heat per 1 kg of an aluminum-sheathed wire and the ratio
of the aluminum sheathing to the wire;
FIG.2 is a graph showing the relation between the amount
of heat per 1 kg of a copper-sheathed wire and the ratio of
the copper sheathing to the wore;
FIG.3 is a graph showing the relation between a saturat-
ed magnetic flux density and a temperature;
FIG.4 is a graph showing the relation between a hyster-
esis loss and a temperature;
FIG.5 is a graph s'howing the relation between the amount
of heat per 1 kg of wire spirally wound on an ACSR and the
magnetic field;
FIG.6 is a triangular diagram showing the composition
of alloys cont~; n; ng Fe, Ni, Cr and Si; and
FIG.7 is a diagram similar to FIG.6 but showing some
examples of alloy compositions.
--6--
54
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The invention will now be illustrated by the following
examples:
Example 1
36% by weight of nickel, 3% by weight of chromium, 1%
by weight of silicon and balance iron ~apart from impurities)
were melted under vacuum and were cast under vacuum into an
alloy ingot of 30 mm diameter. The alloy ingot was subjected
to cold forging and was drawn into a wire core of 10 mm
diameter having a Curie point of around 150C. Then, the
surace of the wire core was subjected to polishing. Then,
0.3 to 2.0 mm thick aluminum sheathings in the ~orm of a
tube were fitted respectively on a plurality of wire cores
to form interm~diate products. ~hen, the intermediate
products were drawn into wires having diameters of 2.4 to
3.0 mm, respectively, so that each of the wire core was
xeduced into a diameter of 2.3 mm. The ratio of the aluminum
sheathing to the wire in cross-section was 10 to 49 %.
Comparative wires l and 2 were prepared according to
the above procedure except that the aluminum sheathing was
not applied to those wires, each o~ the wire having a dia-
metar of 2.3 mm. The comparative wire 2 was galvanized at a
final stage of the manufacture.
Then, the wires of this invention and the comparative
wires 1 and 2 were placed in an alternating magnetic field of
30 Oe (50H~), and the amount of heat generated by those
QQS~
wires was measured. The results obtained are shown in a
graph of FIG.l.
Because of the limitation of the weight of the wire
mounted on the conductor of the transmission line, the
heat required for the melting of snow or ice on the conduct-
or is at least 30 Watt per 1 kg of the wire in the magnetic
field of 30 Oe. As can be seen from the graph of FIG.l,
when the ratio of the aluminum sheathing to the wire in
cross-section is 15 to 40%, the amount of heat generated is
suficient to achieve a satisfactory melting effect.
Example 2
There was prepared a wire core made of an alloy compos-
ed of 36% by weight of nickel, 3.1% ~y weight of chromium, _
1~ by weight of silicon and balance iron, the wire core
having a Curie point of around 130C.
Another wire core was prepared from hard steel (JIS G
3506 SWRH 62 A).
Then, the alloy and steel cores were covered respective-
ly with sheathings made of aluminum for an electrical appli-
cation to produce wire 1 of this invention and comparative
wire 2a. In each case, the ratio of the aluminum sheathing
to the wire in cross-section was 25~.
Comparati~-wire 3 was prepared rom--the above-men*ioned
alloy and had no sheathing. Also, comparative wire 4 was
prepared from the above-mentioned hard steel and had no
sheathing~
Then, the wire 1 of this invention and the comparative
wires 2a, 3 and 4 were placed in an alternating magnetic
--8--
:~2~0S4
field of 50 Oe and 15 Oe (50Hz), and the amount of heat
generated by those wires at a temperature of 0C was
measured. The results obtained are shown in Table l in
which the amount of heat is indicated in terms of Wat-t
per l kg of each wire.
As can be seen from Table l, the comparative wire 2a
and the comparative wire 4 generated excessive heat. Thus,
in the case where the wire is made of hard steel regardless
of whether it has a conductive metal sheathing, undue loss
is produced.
The amount of heat generated by the wire l of this
invention was abo~t four times as much as the amount of heat
generated by the comparative wire 3. Thus, in the case
where the magnetic material element is made of an alloy
containing iron and nickel, a conductive metal sheathing
need to be provided.
_g_
Table 1
Ratio of Al Watt/kg Heat ratio Watt/kg Heat ratio
sh~athing to (50 Oe) of sheathed (15 Oe) of sheathed
core wire to non- wire to non-
sheathed wire sheatned wire
(50 Oe) (15 Oe)
Wire 1 of
this inven-25% 48 20
tion
4.4 3.2
wire 3 0~ 11 , 6.2 6
Comparative25% 105 9.8
1.3
0.93
Comparative
wire 4 0~ 82 10.5
s~
Example 3
Wire cores of an alloy composed of 54% by weight of
nickel, 9% by weight of chromium, 0.5% by weight of silicon
and balance iron were prepared according to the procedure
in Example 1. Then, copper sheathings were applied to five
wire cores so prepared so that intermediate products were
produced. Then, those five intermediate products were
drawn to a diameter of 2 mm to produce wires 3 to 7 of
this invention. The wires were processed to reduce the
residual strain thereof. The ratios of the copper sheathing
to the wire in corss-section in respect of the wires 3 to 7
of this invention were 15%, 25%, 33~, 40% and 47~.
Comparative wire 5 was prepared according to the above
procedure in this Example except that the copper sheathing
was not applied to ~he wire. The comparative wire 5 had
a diameter of 2 mm and was processed to reduce the strain
thereof.
Then, the wires 3 to 7 of this invention and the
comparative wire 5 were placed in an alternating magnetic
field of 30 Oe (50Hz) with the axes of those wires disposed
in the direction of the magnetic field, and the amount of
heat generated by those wires was measured. The results
obtained are shown in a graph of FIG.~.
As can be seen from the graph of FIG.2, in order to
obtain a heat amount of at least 30 Watt per 1 kg of the
wire, the ratio of the copper sheathing to the wire in cross-
section need to be 15 to 40%.
--11--
~,2~S~
Example 4
1200 g of electrolytic iron of 99.9 weight ~ purity,
720 g of nickel of 99~97 weight % purity, 60 g of chromium
of 99.3 weight % purity and 20 g of metallic silicon o 98
weight % purity were melted in a high-frequency vacuum
furnace to produce a molten material. Then, the molten
material was cast into an ingot having a diameter of 30 mm
and a length of 300 mm. Then, the ingot was subjected to
hot forging at temperature of 1100C to form a wire core
of 15 mm diameter. Then, the wire core was polished to
remove oxide scales therefrom and subsequently reduced to
a diameter of 6 mm by cold drawing Then, ~he wire core
was fitted in an aluminum sheathing in the form of a tube
to produce an intermediate product. Then, the intermediate
product was processed or reduced to a diameter of 2.6 mm
to produce a wire 8 of this invention in a manner not to
affect the magnetic properties thereof.
Example 5
43Z g of electrolytic iron of 99.9 weight % purity,
259.2 g of nickel of 99.97 weight % purity, 21.6 g of
chromium of 99.3 weight % purity and 7.2 of metallic silicon
of 98 weight % purity were melted in a high~frequency vacuum
furllace to produce a molten material. Then, the molten
material was cast into an ingot having a diameter of 20 mm
and a length of 300 mm. Then, the ingot was cold forged
to a wire core of 10 mm diameter. Then, the wire core was
fitted in an aluminum sheathing in the form of a tube to
-12-
~Z~Q5~
produce an intermediate product. Then, the interm~diate
product was drawn to a diameter of 2.6 mm in the same
manner described in Example 4, thereby producing a wire 9
of this invention.
Example 6
385.2 g of electrolytic iron, 266.4 g of nickel, 64.8 g
of chromium and 3.6 g of silicon were melted in a high-
frequency vacuum furnace to form an ingot. According to
the procedure in Example 5, there was prepared a wire 10
of this invention having a diameter of 2.6 mm and provided
with an aluminum sheathing. The wire core of this wire has
a low Curie point of about 90~C, and has a saturated magnetic
flux density of 4800 G and a hysteresis loss of 560 J/m3
at a temperature of 0C. The amoun~ of the heat generated
lS by the wire 10 of this invention in an alternating magn2tic
field of 15 Oe (50Hz) is 10 Watt per 1 kg of the wire, and
the amount of heat generated in the alternating magnetic
field of 30 Oe is 16 Watt per 1 kg of the wire.
Example 7
A wire core of 10 mm diameter was prepared according
to the procedure in Example 5. Then, the wire core was
fitted in a copper sheathing in the form of a tube to
produce an intermediate product. Then, the intermediate
product was drawn to a diameter of 2 mm to produce a wire 11
of tnis invention in a manner not to affect the magnetic
properties thereof. The wire core had the same composition
-13-
~2~S4
as the wire cores in Examples 4 and 5 and hence exhibited
the same magnetic properties. In the case where an
aluminum-sheathed wire and a copper-sheathed wire have
magnetic material cores of the same composition, the
amount of heat generated by the aluminum-sheathed wire is
substantially the same as the amount of heat generated by
the copper-sheathed wire, but since copper is heavier than
aluminum, the copper-sheathed wire is less than the alumi-
num-sheathed wire in the amount of generation of heat per
unit mass.
Also, for comparison purposes, comparative wires 6
and 7 were prepared. A hard steel wire (JIS G 3506 -
SWRH 57 B; analytical value by weight ~: C -0.58, Si 0.25,
Mn -0.80, P -0.02, S -0.01) having a diameter of 9.5 mm
was used as a wire core for the comparative wire 6. An
aluminum sheathing was fitted on the hard steel wire to
form an intermediate product. Then, the intermedia-te
product was drawn to a diameter of 2.6 mm to provide the
comparative wire 6. The ratio of the aluminum sheathing to
the wire in cross-section was 25~.
A soft steel wire (JIS G 3503 - SWRY 11; analytical
value by weight ~: C -0.08, Si -0.02, Mn -0.50, P -0.01,
Cu -0.05) having a diameter of 9.5 mm was used as a wire
core for the comparative wire 7. An aluminum sheathing was
itted on the soft steel wire to form an intermediate pro-
duct. Then, the intermediate product was drawn to a dia-
meter of 2.6 mm to provide the comparative wire 7. The
ratio of the aluminum sheathing to the wire in cross-~ection
QS~
was 25%.
The wires 8 to 11 of this invention prepared respec-
tively in Examples 4 to 7 and the comparative wires 6 and
7 were placed in an alternating magnetic field of 25 Oe
(50Hz), and the relation between the saturated magnetic
flux density (G) and the temperature (C) was observed.
The results obtained are shown in a graph of E'IG.3. As
can be seen from this graph, in respect of the wires 8 to
11 of this invention, the saturated magnetic flux density
becomes smaller with the increase of the temperature.
On the other hand, in respect of the comparative wires 6
and 7I the saturated magnetic flux density becomes greater
with the increase of the temperature. Thus, the wires of
this inven~ion have superior properties.
Also, the relation between the temperature 1C3 and
the hysteresis loss (J/m3) in respect of the wires 8 to 11
of this invention and the comparative wixes 6 and 7 placed
in the magnetic field of 25 Oe was observed. The results
obtained are shown in a graph of FIG.4. As can be seen
from this graph, in respect of the wires 8 to 11 of this
invention, the hysteresis loss becomes smaller with the
increase of the temperature~ On the other hand, in re-
spect of the comparative wires 6 and 7, the hysteresis
loss does not become smaller with the increase of the
temperature.
Also, the amount of heat, generated by each of the
wires 8 to 11 and comparative wires 6 and 7 wound at a pitch
oE 50 mm around a conductor (ACSR) through which current
s~
(50Hz) flows to produce an alternating magnetic field in
each wire, was observed. The conductor had a conductive
cross-sectional area of 810 mm . The results obtained
are shown in a graph of FIG.5. As can be seen from this
graph, when the magnetic field H is less than 20 Oe,
the amount of heat generated by the wires 8 and 9 of this
invention is greater than the amount of heat gen~rated by
the comparative wires 6 and 7, and in addition the wires
of this invention have a smaller degree o increase of heat
generation than the comparative wires.
Next, there was prepared a wire of 2.6 mm diameter
consisting of an aluminum sheathing and a wire core compos-
ed of 3~% nickel, 3% chromium, 1% silicon and balance iron
(% by weight). This aluminum sheathed wire was wound
spirally around a conductor (ACSR), having a conductive
cross-sectional area of 810 mm and a diameter of 38.4 mm
at a pitch of 50 mm. Then, snow was caused to deposit
on the ACRS with the spirally wound wire to carry out a
snow-melting test under the conditions shown in Table 2.
The results are also shown in Table 2.
-16-
~Zl~QS~
In
N J
o U~O O
~n o ~ a ~ ~
E~ ~ c~
~,
a) O U~a~ O ~1. .Y 3
U) ~ t' r-l U~
r~
O 1~ O r~ ~U
U~
'n
~ O U~ O O
a ~ ~ ~ o
r- E ~ t. ~ U~
~,~ rd ~ O U~ O O V
O r I H U~
~¢
~n~ O
O
r~l
a .~ ~
u. E~
S9~
As is clear from Table 2, when current of not less
than 300 A flows through the conductor, the snow deposited
on the conductor with the aluminum-sheath wire is complete-
ly melted. When the current is 200 A, the deposited snow
is not completely melted, but melted in a sherbet-like
manner, i.e., partly melted, so that the snow slides off
the conductor to achieve a substantial melting effect.
The magnetic material core of the wire of this inven-
tion contains, apart from impurities, 32 to 52~ by weight
of nickel (Ni), 0.5 to 9% by weight of chromium (Cr),
O.2 to 2% by weight of silicon (Si) and balance iron. When
the nickel content is 32 to 52% by weight, the Curie point
of the magnetic material core is lowered without deteriorat~
ing the magnetic properties, i.e., a saturated magnetic
flux density and a hysteresis loss. When the nickel
content does not fall within this range, a satisfactory
~ffect can not be achieved. In addition, when the nickel
content exceeds the upper limit-of 52%, processability
such as a drawing ability is lowered.
The addition of 0.5 to 9% chromium serves to improve
the magnetic properties to a satisfactory level and also
to lower the Curie point. When the chromium content
exceeds 9~, the magnetic properties are deteriorated.
The addition of silicon achieves similar effects as
the addition of chromium, and its content should be not
more than 2%. When its content exceeds 2%, processability
is adversely affected.
The above-mentioned composition range of the magnetic
-18-
~2~0S4
material core is indicated by a block in a triangular
diagram of FIG.6, the silicon content being 1%. Several
examples of magne-tic material cores are qualitatively
indicated by A, B, C, D and E in a triangular dlagram of
FIG.7. Although the sample A has increased saturated
magnetic flux density and hystexesis loss, its Curie point
is extremely high. The samples B and C are non-magnetic
at a temperature of around 0C. Although the sample D
has increased saturated magnetic flux density and hysteresis
loss, its processability is lowered. The sample E which
falls within the range of this invention has increased
saturated magnetic flux density and hysteresis loss at a
temperature of around O~C.
Example 8
Wire cores a,b,c and d having respective compositions
shown in Table 3 were prepared by casting ingots of 30 mm
diameter by the use of a vacuum furnace and then by reduc-
ing the ingots to a diameter of 10 mm by hot forging and
cold forging. Then, the wire cores were cleaned by remov-
ing scales of oxides and oil from their surfaces. Then,
sluminum sheathings in the form of a tube having an outer
diameter of 12 mm and a thickness of O D 8 mm were fitted
on the wire cores a, b, c, and d to produce intermediate
products. Then, the intermediate products were drawn to
a diameter of 2.6 mm to produce wires a', b' r c' and d'
having the wire core a, b, c, and d, respectively, the
aluminum sheathing and wire core of each wire being metal-
--19--
lZ~S~
lically bonded together. The sulfur and phosphorus
contents of each wire core are impurities.
The wires a', b', c~ and d' were bent to apply a
reverse strain to the entire outer peripheral portion of
the wire core to reduce the residual strain inherent in
the wire core. The ratio of the radius r of the wire core
to a radius R of curvature of the bent wire was 1.5~, 5.2
and 9.5~. The wires a', b', c' and d', sub`jected to this
bending operation and the wires a', b', c'~ and d' not sub-
jected to such bending were observed in respect of the
magnetic properties, using a DC magnetization measuring
device. The results obtained are shown in Table 4. As
seen from Table 4, the wires subjected to the bending
operation exhibited much improved ma~netic properties.
-20-
Table 3
(Wt-%)
~i Cr Si S P Fe
a 36.2 3.1 1.0 0.005 0.003 Balance
b 37.3 8.9 0.5 0.004 0~003
36.5 9.0 1.0 0.005 0.004
d 45.7 5.1 1.1 0.006 0.004 "
Table 4
IJ
\ No ben~;n~ operation T/R: 5.2~ r/R: 1.5% r/R: 9.5% 0
~ Bs(Gauss) Wh(J/m3) Bs(Gauss) (J/m3) Bs(Gauss) Wh~J/m ) BS(Gauss) ~ Wh(J/m33
a' 6,4801,055 9,260 1,210 6,5~0 1,070
b' 5,780719 7,480 738 5,840 725 mechanically
c' 5,210512 7,250 681 5,280 530
d' 8,7201,384 12,300 1,648 8,850 1,420
(Temperature: 0C; Magnetic field: 30 Oe)
5~
Example 9
According to the procedure in Example 8, there was
prepared an aluminum-sheathed wire of 2.6 mm diameter
having a wire core containing apart from impurities 62%
by weight of nickel, 3.1% by weight of chromium, 1% by
weight of silicon and balance iron. Seven samples 1 to 7
were prepared from the wire so formed and bent under the
conditions shown in Table 5 so that a bending strain (r/R)
was applied to the outer peripheral portion of the wire.
The magnetic properties of those samples were observed
according to the procedure in Example 8.
Samples 3 to 6 having a bending strain in the range of
2 to 9% ~xhibi~ed much improved magnetic properties. Sample
2 having a bending strain of less than 2% was not signif-
icantly improved in the magnetic propertiesO ~hen the bend-
ing strain exceeds 9%, the wire is subjected to a mechanical
damage such as meandering and ruptureO
-22-
Table 5
~ Bending strain(~) Bs (Gauss)Wh (J/m
Sample No. (r~R)
1 0 6,480 1,055
2 1.5 6,520 lrO70
3 2.3 8,970 lrl20
4 5.2 9,260 1,210
6.7 9,360 1,220
6 8.3 9,540 1,240
7 9.5 mechanically damaged
~2~5~
Example 10
Three kinds of aluminum-sheathed wires a", b~' and e
of 2.6 mm diameter were prepared using the wire cores a
and b in Table 3 and a wire core of carbon steel, respec-
tively. Samples were prepared from those wires and sub-
jected to a bending operation under the conditions shown
in Table 6. The amount of heat generated by each sample
in an alternating magne-tic field of 15 Oe (50Hz) at a
temperature of 0C was measured. The results obtained are
shown in Table 6. The heat amount is indicated in terms
of Watt per 1 kg of each sample.
For comparison purposes, the heat amount of the
samples not subjected to the bending operation was also
measured.
As seen from q1able 6, the samples a~' and b", having
the respective cores a and b and subjected to the bending
operation to reduce the residual strain, generated a much
larger amount of heat than those not subjected to the bend~
ing operation. On the other hand, the sample e having the
wire core of carbon steel was not improved in the genera-
tion of heat even though it was subjected to the bending
operation. Thus, only in the case of the magnetic material
wire having a core of an iron-nickel based alloy, the
reduction of the strain is efficient in improvement of the
magnetic properties and heat generation.
As described above, when the bending strain (r/R) is
less than 2~, a desired heat amount is not achieved. Also,
-2~-
Qg~
if the bending strain is more than 9%, the wire is me~
chanically damaged.
Therefore, the bending strain, i.e., the ratio of
the radius r of the wire core to the radius R of curvature
or the bent wire should be 2 to 9% in order to achieve
the desired heat amount for melting the snow without
sacrifice of the mechanical strength of the magnetic
material wire.
Table 6
Sample Bending Watt/kg
a" (strain reduced)5.2% 22.3
b" (strain reduced)5.2% 17.6
e (strain reduced)5.2% 9.6
a~' (no strain removed) - 10.2
b" (no strain removed) - 8.3
e (no strain removed) -- 9.5
a" ~strain reduced)1~5~ 12.2
b" (strain redu~ed~1.5% 10.4
-25-
