Abstrict
A heated tube with a electric heater comprising a braid structure
of bare strands of resistance wire connected in an arrangement to
form a number of resistance circuits in parallel in a zone formed
between exposed core portions of an electrical feeder line. The
electric heater is braided directly on a tube, or is braided in
a flat shape and then wound in a large spiral around a tube and
a feeder line with cores having exposed portions arranged along
the tube. When power is supplied to the feeder line, the electric
heater generates heat at each zone and a fluid flowing through the
heated tube is uniformly heated.
Claims
What is claimed is:
1. A heated tube comprising:
an electrically insulative tube through which a fluid may flow;
an electrical feeder line having a plurality of electrically conductive
cores which are arranged along the longitudinal direction of said
tube, insulation means covering each of said cores and having exposed
portion for exposing each core along the length thereof at regular
spaced apart intervals and in such an arrangement that said exposed
portions along any one core are longitudinally offset from the exposed
portions of other cores; an electric heater constructed of bare
strands having an electric resistance braided directly on said tube
into a tubular braid structure arranged along the longitudinal direction
of said tube with said braid structure being connected to said cores
of the feeder line through said exposed portions to form resistance
circuits between adjacent exposed portions and adapted to generate
a Joule heat during a current flowing through the cores of said
feeder line in order to heat the fluid to be heated; and an insulator
covering said feeder line and said electric heater around said tube.
2. A heated tube according to claim 1, further comprising a conductive
braid structured joint would around said exposed portions of the
cores of the feeder line for electrically connecting said electric
heater to said cores.
3. A heated tube according to claim 2, further comprising a fixing
piece provided with claws for forcibly griping said structured joint
in order to electrically connect said electric heater to said cores.
Description BACKGROUND OF THE INVENTION
Nowadays, transporting high-viscosity oil and the like through
pipes, the viscosity of the moving oil has been reduced by electrical-heating
of the pipe line in order to improve an efficiency of transportation
of oil. According to the prior art, such electrical heating system
is constructed, for example, by an electric heating cable consisting
of a feeder line and an electric heater, respectively are covered
by an inorganic insulating cover material, and a heat retaining
material made of calcium silicate and the like, the electric heating
cable is laid in straight or helically wound along a longitudinal
direction of an oil pipeline, consequently heat loss through the
pipe is prevented. According to other example of the prior art,
a small-diameter pipe is welded on the oil pipeline and an electric
heating cable is placed within the small-diameter pipe using a skin
current heating effect in the pipe. It is called a SECT (Skin Effect
Current Tracing) Method. Also, such electric heating cables are
used to prevent roads, pedestrian sidewalks, and pedestrian crossing
bridges in cold regions from freezing and being deposited of snow,
or heat buildings. In case that the electric heating cables are
installed in roads and sidewalks, the cables are buried in a serpentine
configuration under the ground of 50-100 mm in depth and cement
or asphalt concrete is cast in the direction of the serpentine cable.
Other than the electric heating cable above, heating tubes have
been used in order to sustain heat of the fluid flowing through
the tube and control the temperature of the fluid, which heating
tubes are made by integrally constructing or assembling a tube,
a feeder line, and the electric heater. The heating tube is usually
made of a thermal resisting tube of metal or non-metal and a fluid
flows therethrough, a feeder line extending along the thermal resisting
tube, and an electric heater wound around the assembly of the tube
and the feeder line helically or spirally in order to dielectrically
cover the tube. Such a heating tube has been employed in, for example,
a medical dialyser so as to sustain heat or temperature of the dialysis
liquid flowing in the tube at a human temperature. The electric
heater used in the electric heating cable and the heating tube generates
electrically heat due to Joule effect to heat the target material.
Next, disadvantageous features of the conventional electric heater
will be described with reference to FIG. 1 and FIG. 2(A), 2(B),
respectively showing the construction of the electric heating cable
and a heating tube formed according to the prior art.
As shown in FIG. 1 depicting an electric heating cable, it is constructed
by a feeder line 1, two cores 2 of the feeder line 1, insulating
covers 3, 4 and 9 made of insulation material, a resistance wire
5 wound around the insulating cover 4 spirally, and a shield 10.
The resistance wire 5 is an electric heating means. Ordinarily,
a diameter of the resistance wire 5 is AWG (American Wire Gauge)
about 36-42. The two cores 2 are developed through an exposed portion
7 formed in the insulation cover 4. The cores 2 and the resistance
wire 5 are connected each other at a connection point 8.
Such electric heating cables are attached to, for example, pipes
of installations in cold regions. In operation of such electric
heating cables, when an AC voltage is impressed to the cores 2,
respective resistance wire 5 connected in a zone section between
the two adjacent exposed portions 7 generates heat. Owing to the
heat of respective heat resistance wires 5, the piping for installations
are heated every zone section, so as to prevent a fluid flowing
through the piping for installations from freezing.
Another conventional heating tube disclosed in Japan Patent Application
Laid-Open No. Sho 56-85352 is shown as FIGS. 2(A) and 2(B).
The conventional heating tube consists of an inner layer of tube
1, a heat generating layer 2, an outer layer of tube 3, an electric
heating resin film 22, two tape-like metal foil conductors 23, and
a fluoroethylene plastics tape-like protective resin film 24. The
metal foil conductors 23 are positioned on the electric heating
resin film 22 and they are covered in turn by the protective resin
film 24 in a shape of sandwich in order to form a surface heating
member 21. The surface heating member 21 is wound around the tube
1 and the heat generating layer 2 is constructed. The assembly of
them is covered by a tube outer layer 3.
In general, the electric heating resin film 22 above is constructed
by a conductive polymer and the like having a positive thermal coefficient.
Ordinarily when a voltage is impressed between the metal foil conductors
23, the higher the temperature rises, the higher the resistance
becomes. An increase in the electric resistance causes the current
to decrease and accordingly the temperature of the heat generating
layer 2 decreases. As a result, the electric heater of this kind
belongs to a type of self-control.
Such heating tube has been used, for example, as a medical tube
in a medical installation. When AC is impressed to two tape-like
metal foil conductor 23, the electric heating resin film 22 is heated.
Heat generated by the film 22 warms the tube 1 to heat medical liquid
such as dialysis liquid, and medical gas flowing through the tube
1, sustaining them at a fixed temperature.
The conventional electrical heating cable shown in FIG. 1 and described
above uses a resistance wire 5 wound around the insulation shield
of the feeder line 1 in spiral as an electric heating means. The
resistance wire 5 mutually is connected to the core 2 at a junction
point 8. When a current is fed to the resistance wire 5, a joule
effect happens generating heat. When AC is impressed across the
resistance wire generating heat in a certain temperature cycle and
the cycle changes or an outside force such as a bending is applied
to the resistance wire 5, the wire is apt to be broken thus failing
to generate disadvantageously heat in a corresponding zone section.
Also, when a current flows through the resistance wire 5, it is
continuously heated causing its temperature to rise to a temperature
zone of more than 50.degree. C. at which the wire is no longer able
to sustain a load. In addition, because the single resistance wire
5 is joined to cores 2 at the junction point 8, it is possible that
a bad connection happens at the point 8.
The conventional heating tube shown in FIGS. 2(A) and 2(B) are
constructed as self control heaters to generate heat in the heating
resin film 22 which has a positive thermal coefficient by impressing
AC to two insulated tape-type metal foil conductor 23. Consequently,
a stable heat generation is limited in a low temperature zone and
it is disadvantageously difficult to obtain a stable generation
of heat at a temperature of more than 50.degree. C.
SUMMARY OF THE INVENTION
The electrically heated tube of the present invention comprises
a tube, an electrical feed line arranged along the tube consisting
of electrically conductive cores each of which is covered by an
insulator having exposed portions formed periodically at regular
spaced apart intervals to expose each core through each exposed
portion and an electric heater having a braided structure which
is arranged around the tube and electrically connected to the cores
through the exposed portions to form parallel resistance circuits
in a zone between exposed portions of the cores. In the case where
the heated tube with the electric heater is, for example, connected
to the route through which a fluid flows then when the switch is
turned on a voltage is impressed to the feeder line and a current
is fed to the braided electric heater which is electrically connected
to the cores at each of the exposed portions and a Joule heat is
generated in the heater. The Joule heat warms the tube which is
consequently transmitted to the fluid flowing through the tube for
preventing the fluid from freezing or for sustaining a fixed temperature
if necessary.
BRIEF DESCRIPTION OF THE DRAWING
FIGS. 1 and 2(A) and 2(B) are structural views of the conventional
electric heating cable and a heating tube;
FIGS. 3 and 4(A) and 4(B) are views of an embodiment of the present
invention;
FIG. 5 is a view of the electric heating cable of the first embodiment
or application of the present invention;
FIG. 6 is an exploded perspective view of a part of the arrangement
shown in FIG. 5;
FIG. 7(A), 7(B) and 7(C) are views of a fixing piece for connecting
the electric heater to the feeder line;
FIG. 8 is a schematic diagram of the electric heating cable;
FIG. 9 is a view of the electric heating cable of the first embodiment
which is used according to the present invention;
FIG. 10 is a view of the second embodiment in use according to
the present invention;
FIG. 11 is a sectional view of a part of the arrangement shown
in FIG. 10;
FIG. 12 is a longitudinal sectional view of the heating tube shown
in FIG. 10;
FIG. 13(A), 13(B) and 13(C) are exploded views of the connection
of the joint;
FIG. 14 is a schematic diagram of the heating tube shown in FIG.
10;
FIG. 15 is a view of another heating tube to which the present
invention is applied; and
FIG. 16 is a sectional view of a part of the arrangement depicted
in FIG. 15.
PREFERRED EMBODIMENT
As shown in FIGS. 3 and 4, the electric heater 5 consists of a
plurality of strands 50. The strands 50 are naked resistance wires
of diameters of about 0.08-0.1 mm. These strands 50 are arranged
in a manner of mutual-in-and-out and form a braid. FIGS. "3(A)"
and "3(B)" show one being braided of a single strand or
a plurality of strands 50 in a shape of band FIGS. "4(A)"
and "4(B)" respectively show another one being braided
of a single strand or a plurality of strands 50 around an electrically
insulating core member 51. Such constructed electric heater 5 is
used in various apparatuses as shown in FIGS. 5 to 16.
FIGS. 7(A), 7(B) and 7(C), respectively show views of fastener
pieces for joining the electric heater to the feeder line and show
the case in which the electric heater of the present invention is
applied to the electric heating cable for low and middle temperature
(0.degree.-50.degree. C., 50.degree.-120.degree. C.). In FIGS. 5-7,
the parts having the corresponding function to those of FIGS. 1
and 2 have the identical reference numerals and some parts will
be explained again in detail.
FIG. 5 shows the feeder line 1, two cores 2 of the feeder line
1, an insulator 3 covering the cores 2 and another insulator 4 for
both of the insulators 3. The cores 2 may be concentrated strands
consisting of high conductive metal such as copper or copper plated
with nickel or silver. The insulators 3 and 4 consist of fluoroethylene
plastics having high heat resistance.
The electric heater 5 according to the present invention has a
braided structure of bare strands 50 of resistance wire. A joint
6 has a flat band-shape and braided structure of strands which consist
of fine wires made of conductive metal like copper. The exposed
portion 7 is formed in each of the insulators 3 and 4 to expose
the core 2 and the exposed portion 7 is formed thereon to electrically
connect the core 2 at its exposed portion to the electric heater
5. It should be noted that the exposed portion 7 is formed alternately
to expose one of the two cores 2 at regular spaced intervals L along
the feeder line 1, and a joint 6 with a braided structure is wound
over each exposed portion of the cores. The joint 6 connects the
electric heater 5 to the cores 2 at respective joint portions 8
by pressing the electric heater 5 of a braid construction to cores
2 coming in contact through a number of points or lines. The heat
insulator 9 covers the joint 6 and other elements and the outer
shield 10 protects the insulator 9. As described above, an electric
heating cable C shown in FIG. 5 consists of the feeder line 1, the
electric heater 5, and the arrangement of braided joints.
For example, one manufacturing method of the electric heating cable
C above will be explained. First, the core 2 consisting of stranded
fine wires made of a conductive metal like silver plated copper
covered by the insulator 3. Two of the covered conductors are then
placed side by side and covered with insulator 4 and molded with
a plastic to make the feeder line 1 with two cores 2. Next, outer
portions of the insulators 3 and 4 are cut off in a half-cylindrical
shape so the two cores 2 may be alternately exposed at a regular
spaced interval L along the feeder line 1. Consequently, the cores
are exposed at the cut off portions with a fixed width, and exposed
portions 7 are formed. After the formation of the exposed portions
7, the bare strands 50 of resistance wires are braided around the
feeder line 1 so that the feeder line 1 may be wrapped in the braided
electric heater 5. In order to secure the electrical contact between
the electric heater 5 and the two cores 2, the electric heater 5
is bound at the exposed portions with the joints 6 which have a
braided structure with a little less width than that of the exposed
portion. A fixing member 11 of a C shape as shown in FIGS. 7(A)-7(C)
is applied on the braid of the joint 6 and an open portion of the
fixing member 11 is pressed from both sides of the member, so that
claws 12 provided on an inner face of the fixing member invade into
a gap between strands of the cores 2. As a result, the cores 2 are
fixed in a shape. A plurality of strands 50 consisting of the electric
heater 5 are pressed in points or lines and the electric heater
5 comes into contact with the cores 2 through a number of positions
joining them electrically. A principle of connection between the
electric heater 5 and the cores 2 is shown in FIG. 8. As apparent
from FIG. 8, a plurality of strands 50 constituting the electric
heater 5, respectively come into contact with the cores 2 through
multi-point and they are electrically connected firmly. After that,
the insulator 9 is extruded and plastic-molded so as to cover these
cores 2. If necessary, a shield 10 such as a braided fiber or a
stainless sheath is applied thereon to protect them.
The electric heating cable C manufactured according to the present
invention is used in an installation of, for example, an oil plant
as shown in FIG. 9.
As shown in FIG. 9, a main pipe 30 through which a fluid flows
has a branch pipe 31, a heat insulator 32 provided on a part of
the main pipe 30, and a manual control valve 33, and also a power
box 34 and a band 35 for fastening the power box 34. The electric
heating cable C according to the present invention is adapted to
be arranged along the main pipe 30 as shown. The cable C has a branch
portion separated from a suitable branch point c and extends into
the branch pipe 31. In particular, the electric heating cable C
is turned twice or triple on the manual control valve 33 to strengthen
a heating effect thereon. When an AC voltage is impressed from the
power box 34 to the electric heating cable C, the strands 50 of
respective braids of the electric heater 5 is heated by a Joule
effect. Consequently, the fluid flowing through the interior of
the main pipe 30 and the branch pipe 31 or the manual control valve
33 is heated by the hot electric heater 5 and the temperature of
the fluid is detected by a temperature detector (not shown) in order
to adjust the fluid flowing through the main pipe 30 and the branch
pipe 31 at a fixed temperature.
FIG. 10 is a construction explanation of the heating tube according
to the second embodiment of the present invention, FIG. 11 is a
section showing a part of FIG. 10, FIG. 12 is a longitudinal explanation
of the heating tube shown in FIG. 10, FIG. 13(A), 13(B) and 13(C)
are exploded explanation of connection of a joint, and FIG. 14 a
primitive layout of electricity of the heating tube shown in FIG.
10. FIG. 10 shows a heating tube T having a central tube t making
a fluid flown therethrough.
In FIGS. 10 and 11, the central tube t is a fluoric resin tube
or an insulation-treated metal tube. The heating tube T has a feeder
line 1, two cores 2 for the feeder line 1, an insulator 3 covering
both the cores 2, and another insulator 4 filling the gap or space
generated by existence of the feeder line 1 and making the whole
section of the tube T circular. Also, the heating tube T has the
electric heater 5 of a braid arranged around the tube t, a joint
6, and the exposed portion 7 of the two cores 2. The cores 2 and
the electric heater 5 are joined through the exposed portion 7 (see
FIGS. 10-13(C)).
The exposed portion 7 is formed mutually in the two cores 2 wound
around the tube t in a large spiral at a fixed interval L and the
joint 6 is fixed to the exposed portion 7. The insulator 4 and the
feeder line 1 are covered with an insulator 9, which is further
covered with a shield 10. The material used to make the cores 2,
the insulators 3 and 4, the electric heater 5 is the same as the
corresponding parts of the first embodiment of the present invention.
Therefore, as shown in FIG. 10, the tube t, the feeder line 1, and
the electric heater 5 and the other parts construct the heating
tube T.
The heating tube T above is manufactured by, for example, the following
steps.
First, the insulator 3 is laid around the cores 2 making a covered
conductor 1. The two covered conductors 1 are arranged side-by-side
and a two-core feeder line 1 is obtained. Portions of the insulator
3 at a regular interval L are mutually cut out. A circumferential
part of the insulator 3 is cut to expose a part of the cores 2 forming
the exposed portion 7 having a predetermined width.
Meanwhile a braid of the resistance line is arranged around the
tube t to form the electric heater 5 covering the tube t. The feeder
line 1 is then wound in a large spiral around the wrapped tube along
the longitudinal direction of the tube. In order to secure the electrical
contact between the electric heater 5 and the two cores, a joint
6 which has a braided structure with the substantially same width
as that of an exposed portion is applied over the braided electric
heater across each of the exposed portions 7 as shown in FIGS. 11
to 13. Similar to the case shown in FIG. 7, a C shape fixing piece
11 covers the exposed portion 7 and an open portion of the fixing
piece 11 is pushed from both the sides of the C shape fixing piece
11, thereby the claws 12 formed on the inner face of the fixing
piece 11 invade fixedly into the gap between strands of the cores
2. As a result, midportion of the ring-like joint 6 is squeezed
as shown in FIG. 13(B) and a plurality of strands 50 constructing
the electric heater 5 are pushed and come into contact forcibly
against the cores 2. In detail, due to such pressing, the joint
6 is certainly fixed on the cores 2 and the electric heater is electrically
connected through the joints 6 and exposed portions 7 to the feeder
line 1. The schematic connection of the electric heater 5 and the
cores 2 is shown in FIG. 14. In this case, a plurality of strands
50 as shown constructing the electric heater 5 come into contact
with the cores 2 through multi-point forming a complicated parallel
circuit. Then, the gap left by two feeder lines 1 wound in a large
spiral around the tube t is filled by the insulator 4. The deformed
section of the assembly is made neat in a circle. After the section
controlling step, the cover 10 covers the insulator 4 and the joint
6 and other parts so as to obtain the heating tube T.
It is noted that it is possible to construct the heating tube by
further providing a protective shield 10 on the insulator 9 as shown
in FIG. 11 by two-dot chain line.
FIG. 15 is a construction explanation of a usage of another heating
tube according to the present invention. The heating tube H shown
in FIG. 15 differs from that shown in FIG. 10 only in the structures
of the feeder line 1 and the electric heater 5. As shown, the feeder
line 1 and the electric heater 5 use a plurality of strands 50 to
form a flat braid. It is possible to omit the core 51 from the braided
band-like electric heater 5 similar to the cases shown in FIG. 3(A),
3(B) and FIG. 4(A) and 4(B). As shown in FIG. 15, according to the
embodiment of the present invention, two flat cores 2 having the
exposed portion 7 of the feeder line 1 are wound in a large spiral
at a distance of about 180 degree as shown or in a side-by-side
relation around the outer periphery of the tube t. The electric
heater 5 of a flat braid is laid thereon spirally. Then similar
to the embodiment of FIG. 10, the insulators 3 and 4 are plastic-
molded and the cover 10 is provided thereon. According to the construction
of the embodiment shown in FIG. 15, the feeder line 1 and the electric
heater 5 are both formed in flat, so that it is possible to obtain
the compact heating tube H.
Such heating tube H is used as a conduit of electric heating sustaining
fluid and of gas analyzer, and as a medical tube which is arranged
on the medical installation and the like. When a voltage is impressed
to two cores 2 of the heating tube H installed, a current is flown
to the electric heater 5 through the joint 6 generating a Joule
heat. The Joule heat generated in the electric heater 5 is transferred
to the tube t, thus a liquid or gas in the tube t is heated or sustained
at a fixed temperature.
Meanwhile, the electric heater 5 according to the embodiments described
above consists of strands 50 of resistance wires such as nickel
chrome wires.
However, it is possible to employ the wires made of self control
type material, such as a conductive polymer or semiconductive polycrystal
ceramic, carbon fiber wires, or a mixture of carbon fiber wires
and conventional resistance wires for the stands. Although an example
of a feeder line with two cores for use by a single phase AC is
shown above, it is also possible to use a feeder line with three
cores for use by a three phase AC.
Although an example of the electric heater 5 consisting of a plurality
of resistance wires was exemplified and explained, it is possible
to use a braid of a single wire, of a carbon fiber, or a carbon
fiber and ceramic material and plastics, or of a normal metal resistance
wire and a carbon fiber. In addition insulators 3 and 4 or an insulator
covering a metal tube for a central tube t may be made of a glass
fiber, a ceramic fiber or a polyamide film. An electric heater suitable
to a high temperature can be provided by constructing heat resisting
insulators in the shape of a sheath. Although a case of two cores
being used and a voltage being impressed thereon has been explained,
it is possible to use three cores, a three-phase AC being impressed
thereto.
In short, the electric heater of the present invention connected
to the feeder line so as to generate a Joule heat is constructed
by a braid of a plurality of strands of resistance wires, respectively
connected to the feeder line through a number of points.
Consequently, according to the present invention, it is possible
to obtain an electric heater having a wide usage range of temperature
without trouble in operation.
The heating tube and electric heater of the present invention has
a braided structure connected in an arrangement to provide a number
of multiple resistance circuits in parallel in a zone between each
of the adjacent exposed portions of the cores. Consequently, even
when a part of strands in the heater is broken because of externally
applied mechanical force or cyclic changes of temperature during
heating, a complete failure in generating heat in the zone to which
the broken part pertains hardly happens. In addition, since the
braid-structured electric heater is connected to the feeder line
at each of exposed portions of the cores having many contact points,
poor contact between the heater and the feeder line at the exposed
portion is prevented. Further, the joint in the braided structure
is electrically connected to the cores using a fixing piece with
claws which presses the joint to the core at each exposed portion
to secure the connection between the joint and the feeder line.
Accordingly, any difference in temperature along the tube is eliminated
and the fluid flowing in the tube is heated at a constant temperature.
Further, the electric heater according to the present invention
can be suitably used to sustain a temperature at the range from
middle level (50.degree. C.-120.degree. C.), because the generated
heat is distributed over the number of strands of a braided structure
when the electric heater generates heat. When the braided electric
heater is made of a heat resisting material, it is possible to provide
a heating tube with an electric heater durable to high temperature.
|