Note: Descriptions are shown in the official language in which they were submitted.
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HEATING E~W~ ND ~LET~OD OF M~NUFACTURE
R~cR~omN~ OF ~HE lNv~N~ oN
1. Field o~ Invention
This invention relates to heating elements, and more
particularly to heating elements which are soft, flexible, ~lat,
~trong, light and thin, and to their method of manufacture.
2. Description of the Prior Art
~ eating elements have extremely wide applications in household
items, construction, industrial processes, etc. Their physical
characteristics, such as thickness, shape, size, strength,
flexibility and other characteristics affect their usability in
1~ various applications.
Numerous types of thin and flexible heating elements have ~een
proposed, for example U.S. patent 4,764,665 to Orbat et al. This
heating element, however, is made of a solid piece of fabric with
metallized coating, it does not allow for flexibility in selection
of desired power density and is not economical due to metA~ ing
process. The '665 design is also not conducive to hermetic sealing
through the heater areas which can cause a short circuit through
puncture and admission of liquid. This element can't be used with
higher temperatures due to the damage that would be caused to the
metallized fabric.
Another prior art example is U.S. patent 4,538,054 to de la
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Dorwerth. However, the heating element o~ de la Dorwerth '054
suffers from the following drawbacks: its manufacturing is complex
requiring weaving of metal or carbon fibers into non-conductive
fabric in a strictly controlled pattern; the use of the metal wire
can result in breakage due to folding and crushing and it affects
softness, weight and flexibility of the finished heater; it can't
be manufactured in various shapes, only a rectangular shape is
available; only perimeter sealing is possible, which can result in
a short circuit due to puncture and admission of a liquid; the
method of interweaving of wires and fibers doesn~t result in a
strong heating element, the individual wires can easily shift
adversely affecting; the fabric base of the heating element is
fl~mm~hle and may ignite as a result of a short circuit; it is not
suitsble for high temperature applications due to destruction of
the insulating weaving fibers at temperatures exceeding 120~C.
U.S. patent 3,627,988 describes a method of assembling a
surface heater based on carbon fibers consisting of attAch~nt of
continuous non-woven carbon fiber material to contact electrodes
and to the shape forming layers of fabric by sewing with a thread.
The disadvantages of this method are as follows: this method
doesn~t allow the flexibility of creating heating elements of
various shapes and sizes; the manufacturing process is complex and
produces hazardous dust during the sewing operation; application
of pressure to the surface of the heating element, made of non-
woven carbon fa~ric, significantly increases its electro-
conductivity, which, in turn, changes its intended properties;
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after a period of use under the effect of mechanical forces the
non-~oven material tends to separate and to form localized lumps
af~ecting usability and performance; this method produces a heater
with significant thickness.
S Further, attempts have been made to fabricate electrically
heated systems from carbon fibers, yarns, and fabrics by coating
the carbon material with a protective layer of elastomer or other
materials to overcome carbon's extremely poor abrasion and kink
resistance (Carbon Fibers for Electrically Heated Systems, by David
Mangelsdorf, final report 6/74 - 5/75, NTIS). It was found that the
coating used in this method reduced the carbon material flexibility
and increased the difficulty of making electrical attachments to
it, and making electrically continuous seams. The poor flexibility
of coated carbon fabric made this material unsuitable for small and
complex assemblies, such as handware.
U.S. patent 4,149,066 to Niibe et al describes a sheet-like
thin flexible heater made with an electro-conductîve paint on a
sheet of fabric. This method has the following disadvantages: the
paint has a cracking potential as a result of sharp folding,
crushing or punching; the element is hermetically sealed only
around its perimeter, therefore lacking adequate wear and moisture
resistance; such an element can~t be used with high temperatures
due to destruction of the underlying fabric and thermal
decomposition of the polymerized binder in the paint; the assembly
has 7 layers resulting in loss of fle~ibility and lack of softness.
Additionally, a known method of achieving a flexible flat
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heating element is by surfacing threads of ~abric with carbon
particles and various polymers as disclosed in U.S. patent
4,983,814. The resulting heating elements have necessary electro-
physical characteristics, but their manufacturing is complex and is
ecologically unfriendly because of the use of organic solvents,
such as diethylphormamide, methylethylketone and others.
Furthermore, this method involves application of an electro-
conductive layer only to the surface of threads of fabrics. This
layer, electro-conductivity of which is achieved through surface
contact of extremely small particles, is susceptible to damage due
to external factors, such as friction, bending, etc.
Another prior art example is U.S. patent 4,309,596 to George
C. Crowley, describing a flexible self-limiting heating cable which
comprises two conductor wires separated by a positive temperature
coefficient (PTC) material. Said heating wires are disposed on
strands of nonconductive fibers coated with conductive carbon.
This method has the following disadvantages: (a~ the wires are
enveloped and separated by the tough PTC material which thickens
and hardens the heating element (b) the distance between the wires
is very limited, due to a nature of the PTC material having a high
electrical resistance, this prevents manufacturing of heaters with
large heat radiating surface; (c) the heater is limited only to one
predetermined highest temperature level, therefore, this heating
device i8 unable to bypass said temperature level when a quick
heating at the highest temperature is needed.
The present invention seeks to alleviate the drawbacks of the
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prior art and describes the fabrication of both a carbon carrying
fabric heating element and a non-metallic yarn which are econ~m;cAl
to manufacture; don't pose environmental hazards; and result in a
soft, flexible, flat, strong, thin,. and light heating element,
suitable for even small and complex assemblies, such as handware.
A significant advantage of the propo~ed patent is that it provides
for fabrication of heating elements of various shapes and sizes,
with predeterm;ne~ electrical characteristics; allows for a dura~le
heater, resistant to kinks and abrasion, and whose electro-physical
properties are unaffected by application of pressure, sharp
folding, punches, small punctures, small cuts and crushing.
SUMMARY OF THE lNv~NllON
The first objective of the invention is to provide a
significantly safe and reliable heating element which can function
properly after it has been subjected to sharp folding, kicking,
small punctures, punching or crushing, thereby solving problems
sssociated with conventional flexible heating wires. In order to
achieve the first obiective, the electric heating elementr of the
present invention, is made of a carbon carrying conductive fabric
or carbon/graphite electrically conductive yarns which possess the
following characteristics: (a) high strength; (b) high strength-to-
weight ratio; (c) high thermal and electrical conductivity; (d~
very low coefficient of thermal expansion; (e) non-flammability;
and ~f) softness. The proposed invention comprises continuous or
electrically connected separate strips of carbon carrying fabric,
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which radiate a uniform heat over the entire heating ~urface, thus
preventing occurrence of overheated spots. An additional
r~ho~l; m~t is comprised of continuous or electrically connected
~eparate strips, sleeves, ropes or strands of carbon/graphite
yarns, which radiate a uniform heat over the entire heating core
surface.
A second objective of the invention is to provide ~ m
flexibility and softness of the heating element. In order to
achieve the second objective, the electric heating element
comprised of carbon carrying conductive fabric is made of a very
thin (.1 to 3mm, but preferably within the range of ~.2-2.0mm)
woven or non-woven carbon carrying fabric, which is cut into
continuous or electrically connected strips and patterned to have
gaps between the strips. The electric heating element comprised of
carbon/graphite electrically conductive yarns contains thin (005 to
5.0 mm, but preferably within the range of 0.~-2.0 mm) threads,
which are woven or stranded into continuous or electrically
connected strips, sleeves/pipes, ropes or bundles, then arranged
and insulated to have gaps between the electrically conductive
--'; A . Furthermore, all the components of the multi-layer heating
element assembly are thin, soft and flexible materials.
A third objective of the invention is to provide for the
uniform distribution of heat without overheating and hot spots,
thereby solving the problem of over insulation and energy
efficiency. In order to achieve this ob~ective, one side of the
heatiny element includes a metallic foil or a metallized material
,, .
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to provide uniform heat distribution and heat reflection. A thin
layer of such electro-conducting heat reflecting material is placed
above the electro-insulating material prior to l~m; n~tion to
prevent direct electrical contact of metal with the conductive
fabric. It is also preferable that the soft heating elements of
the invention are made without thick cushioning insulation, which
~lows down the heat delivery to the surface o~ the heating
apparatus.
A forth objective of the invent.ion is to provide for ease in
the variation of heating power density utilizing the same type of
conductive fabric, thereby solving a problem of manufacturing
various heating devices with different electric power density
requirements. In order to achieve the forth objective, the carbon
carrying conductive fabric is stabilized by impregnation with soft
f; 1 1; ng substances and then cut to desired patterns. The soft
filling material can also be used to augment the electro-physical
characteristics of the carbon carrying fabric. In the modified
embo~;m~nt, the yarns in the heating element core are woven or
stranded into strips, ropes, sleeves/pipes or bundles with
2~ predeterm; n~ width, density of weaving and thickness. It is
preferable that the strips, sleeves/pipes, ropes or strands are
made of combination of yarns with dif~erent electrical resistance
and/or include electrically nonconductive high strength polymer or
ceramic fibers.
A ~ifth objective of the invention is to provide a reliable
and strong electrical contact of the conductive fabric with
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electrodes for electric power delivery, thereby solving a problem
of providing a sufficient electrical contact between soft
conductive fabric and metal electrodes during assembling of the
heating element. In order to achieve the fifth objective, the
contacts are made of thin metal foil, metallized polymer or thin
rigid conductive electrodes which are attached to the ends of the
carbon carrying fabric prior to lamination of insulating materials.
The electrical contacts are glued to the carbon carrying fabric
heating element core by the conductive adhesive and firmly attached
to the fabric to provide a sufficient electrical conductivity. It
is preferable that conductive adhesive is comprised of
carbon/graphite or silver or nickel ingredients.
A sixth objective of the invention is to provide for ease of
installation of the electric heating elements inside the heating
devices, thereby solving a problem of complicated attachment of
conventional heating wires over the desired working area of the
flexible heating devices. In order to achieve the sixth objective,
the insulated electric heating element is patterned and
manufactured prior to installation to fit the whole desired area of
the flexible heating device.
A seventh objective of the invention is to provide for ease in
manufacturing of the heating element core comprised of
carbon/graphite yarns, thereby eli m; n~ting a problem of
impregnation of the whole fabric with stabilizing or filling
materials to enable cutting to a desired pattern. In order to
achieve the fifth objective, all strips, sleeves/pipes, ropes and
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threads are woven or stranded into a desired stable shape prior to
the heating element manufacturing.
An eighth objective of the invention is to provide a
- temperature self-limiting properties to the heating element core if
dictated by the heater design th~reby ~lim;nAting a need for
thermostats. In order to achieve the sixth objective, the positive
temperature coefficient (PTC) material is utilized in the selected
areas of the heating element core.
The present invention compri~es a heating element which is
flat, thin, flexible, soft, strong and light. It i8 also highly
resistant to abrasion, punctures, cuts, punches, sharp folding and
crushing. It can be manufactured in various shapes and sizes, and
it can be designed for a wide range of parameters, such as input
voltage, desired temperature range, desired power density, type of
current (AC and DC) and method of electrical connection ( parallel
and series). In one em~odiment, a soft and flexible thin heating
element made of electrically conductive carbon carrying fabric is
impregnated with a soft filling material. The heating element is
shaped by pressing, heat treating and cutting the fabric into a
serpentine pattern. The electrodes are attached to the ends of the
serpentine strips which are electrically connected in parallel or
in series. The fabric heating element core is sealed to form a
multi-layer assembly comprising of at least two electrically
insulating layers which envelop each strip of the serpentine
2~ strips. The method of producing the soft and flexible heating
element is also disclosed.
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In a second ~oA; -nt, the heating element consists of
electrioally conductive carbon/graphite yarns woven or stranded
into strip~, ropes, sleeves/pipes or strands of threads. The
selected areas of the heating element core are conditioned to
5impart a variety of electrical properties in said core. The
conditioning of the soft woven heating element core may include a
positive temperature coefficient (PTC) material to impart
t~ A~ature self-limiting properties. The heating element core is
shaped hy folding or assem~ling of said conductive media into a
10predetermined pattern. The electrodes are attached to said heating
element core and are electrically connected in parallel or in
~eries. The soft heating element core is sealed to form an
assembly cont~;ning at least one electrically insulating layer
which envelops each strip, rope, sleeve/pipe or strand of threads.
BRIEF DESC~IPTION OF THE D~AWINGS
Fig. 1 is a schematic view of the process of manufacturing the
carbon carrying fabric with the soft filling material according to
the pre~ent invention.
20Fig. 2 is a perspective view of a heating element according to
the preferred o~ho~;~ont of the present invention.
Fig. 3 is an exploded view of the connection of the fabric,
contact electrodes, and power cord.
Fig. 4 is a plan view of heating elements connected in series
25according to an emh-odiment of the present invention.
Figs. 5a and 5b are plan views of heating elements connected
1~
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in parallel according to another embo~i -nt of the pre~ent
invention.
Fig. 6 is a cross section view of a l~;n~ted heating element
according to an alternate embo~; -nt of the present invention.
Fig. 7 is sectional view of a process of applying insulation
to a heating element according to an alternate embo~;m~nt of the
present invention.
Fig. 8 is a sectional view of an insulated heating element
according to an alternate ~ho~;m~rlt of the present invention.
Figure 9A shows a plan view of the heating element core
electrically connected in series according to the preferred
~h~l iment of the present invention.
Figure 9B is a perspective view of the end of the heating
element core showing connection of an electrode.
Figure 10A is a plan view of the heating element core
electrically connected in parallel, where individual strips are
shaped in zigzag pattern.
Figure lOB is a plan view of the heating element core
electrically connected in parallel according to the preferred
em~o~; -nt of the present invention.
Figure 11 is a perspective view of the insulated heating
element core electrically connected in parallel, having electrical
busses wrapped by the heating element core material and utilizing
cut outs.
Figure 12A i8 a perspective view of a fragment of the heating
element core electrically connected in parallel, having electrical
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busses made of woven strips sewn or stapled to the heating element
core and having PTC material incorporated longitll~inAlly into said
heating element core in selected areas.
Figure 12B is a perspective view of a fragment of the heating
element core, electrically connected in parallel having electrical
busses made of highly conductive threads or thin metal wires woven
or sewn into its body and having PTC material incorporated
longitll~; n~l ly into said heating element core in selected areas.
Figure 13 shows a plan view of the heating element core having
three bus conductors and a PTC material incorporated longit~ Ally
into the body of said heating element core so as to separate two of
three busses according to the preferred embodiment of the present
invention; said busses are connected to a power source through a
power controller.
Figure 14 shows a cross-section of the insulated heating
element including separate fragments of the heating element core,
having PTC material connecting said fragments and providing
electrical continuity.
Figure 15 shows a cross-section of the insulated heating
element including fragment of the heating element core where the
bus electrode is enveloped by the PTC material according to the
preferred embodiment of the present invention;
Figure 16 shows a perspective view of a fragment of the
heating element core made of a strand or a rope of non-metallic
fibers with varying electrical properties, having electrode
connector attached to its end by crimping.
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Figure 17A shows a perspective view of a sleeve/pipe shaped
heating element core, having bus electrodes and electrically
connected in series according to the preferred embodiment of the
present invention.
~igure 17B shows a perspective view of a sleeve/pipe shaped
heating element core, having bus electrodes and electrically
connected in parallel according to the preferred embodiment of the
present invention.
Figure 17C shows a perspective view of a sleeve/pipe shaped
heating element core, having bus electrodes, electrically connected
in parallel and having an optional PTC material incorporated into
said heating element core according to the preferred embodiment of
the present invention.
Figure 18A is a plan view of the back side of a garment
including a soft heating element according to the present
invention.
Figure 18B is a perspective view of a vehicle seat including
a soft heating element according to the present invention.
Figure 18C is a perspective view of a floor assembly including
a soft heating element according to the present invention.
Figure 18D iS a perspective view of a fragment of pipe
including a soft heating element according to the present invention
wrapped around the pipe.
2~ DETAILED DESCRIPTION OF THE 1NV~N~1~ION
The first ~hoA;~t of the present invention is detailed in
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Figures 1 through 6. As shown in Figure 1 a carbon carrying fabric
basis (11) is unrolled from the spool (17), advanced through the
driving rollers (30) and is saturated in the impregnation basin
(31) with a solution of soft filling material (21). The saturation
in the impregnation basin (31) can be successfully substituted by
spraying of the solution of soft filling material (21) or
application of thin polymer film of the soft filling material at
least from one side o~ carbon carrying fabric (11).
The excess soft filling material is than s~ueezed out by the
rollers (19) with an adjustable pressure function; this allows for
variation in the amount of the soft filling material left in the
carbon carrying fabric depending on design parameters. The carbon
carrying fabric (11) is then passed through the curing device (18)
where it is sub3ected to heat and, if necessary, pressure to
adequately set and cure the soft filling material (21~.
The soft filling material acts as fabric stabilizer and
enables cutting of the carbon carrying fabric into a desired shape.
In addition lt may be u~ed to augment the electro-conductive
characteristics of the base carbon carrying fabric (11).
Therefore, the soft filling material (21) can include conductive
particles like graphite, carbon black, or other metal carrying
compounds. It is preferable to use nonvolatile oligomeric or
polymeric compounds like starch, polyethylene,
csrboxymethylcellulose, polyurethane as soft filling materials
(21).
As shown in Figure 2, a serpentine shape heating element core
. . .
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(29) is cut out from the stabilized carbon fabric (11). It is
preferable that the strips of the carbon fabric serpentine core
(29) have an even width. The ends to which the electrodes shall be
attached are cleaned of non-conductive material and an optional
conductive adhesive or conducting filling material (16) is applied
to them. Thin contact electrodes (15) are then ~ttached to the
ends of the heating element core ~29).
As shown in Figure 3, the optional holding teeth (25) may be
used to achieve a better contact between the fabric and the
electrodes. A power cord (20), having a plug (26), is then
attached to the contact electrodes (15) utilizing male (23) and
female (24) connectors or other known methods which provide
sufficient electrical contact.
As shown in Figure 4 and Figure 5, the electrical connection
may be made in series or in parallel. An optional heat regulating
thermostat (27) and power output adjustment device (22), may be
installed, if required, by a listing agency or a design. The most
appropriate patterns which allow efficient and economical trimmlng
of the carbon carrying fabric (11) are zigzag and spiral shapes.
The parallel connection can be accomplished either by connecting
~eparate strips of the carbon carrying fabric (llj to a conductive
bus bar (33) as shown in Fig. Sa, or by cutting the assembly in
such a way that the carbon carrying fabric bus strips (34) located
at opposite ends of the heating strips are continuous to the
heating strips without a break in the carbon carrying fabric
material (11) from which they were cut out. (Fig. 5b) In order to
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provide for high electrical conductivit~ of the bus strips (34),
which is necessary to assure a uniform current distribution through
all strips of the heating core (29), the bus strips (34) can be
augmented by one or combination of the following methods: affixing
highly electro-conductive flexible strips (35) to at least one side
of each bus strip (34); interweaving or sewing highly electro-
conductive wires through each bus bar (34); or impregnating the bus
strips (34) with a highly electro-conductive ~ubstance, including
but not limited to graphite.
As shown in Figure 6, the assembly of heating element core
(29), contact electrode (15) and the power cord (20) is then
1~ inAted between at least two layers of electro-insulating
material (12) with an optional heat reflective layer (13) and a
protective layer (14) adhered to heat reflective layer (13). The
electro-insulating materials (12) envelop each strip of the heating
element fabric core (29), hermetically sealing the gaps between
3aid strips.
As shown in Fig. 7 and ~ig. 8, the complete heating element
assembly is then sealed by a pressure device (32) with or without
application of heat. ~he electro-insulating materials (12) envelop
each strip of the heating element fabric core (29) sealing the gaps
between said strips. A low temperature sealing consists of
application of electro-insulating materials (12) having heat
resistant adhesive (28) at least on one side of electro-insulating
materials (12) facing the heating element fabric core (29). A high
temperature sealing consists of heating of electro-insulating
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materials (12) which results in their fusing in the gaps between
the strips of the heating element fabric core (29).
A flexible-in-all-directions thin heating element can be
utilized for all varieties of commercial and industrial heaters
utilizing direct or alternative current. The main advantages of
the heating element are the high reliability and safety which are
provided by the tightly sealed soft and durable conductive fabric.
Furthe -re, the heating element has additional advantages in
that the thin fabric:
enables manufacturing of the thin, soft and uniform heaters
without installation of disturbing conventional heater wires;
provides high durability of the heating appliances which can
withstand sharp folding, punches, punctures, ~mall cuts and
compression without decreasing of electrical operational
1~ capabilities;
provides high tear and wear resistance owing to: ta) high
strength of the conductive fabric, (b) enveloping around all of the
fabric serpentine pattern with the polymer insulating material;
provides high moisture resistance owing to: ~a) impregnating
of ~he soft filling material which prevents or significantly 810ws
down penetration of the moisture through the fabric core, (b)
sealing of the gaps between the ~abric core serpentine by the
pol~mer insulating materials;
provides for manufacturing of corrosion and erosion resistant
heating element owing to: (a) high chemical inertness of the carbon
carrying fabric and (b) hermetic polymer insulation of the whole
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heating element including connection electrodes and temperature
control devices, in utilization in chemically aggressive industrial
or marine environments;
offers versatility of variation of the electrical conductivity
S of the fabric core owing to: (a) cutting of desired serpentine
pattern of the conductive fabric, (b) impregnation with the soft
filling material having different amount of conductive ingredient,
(c) carbon carrying fabric having different amount of conductive
fibers per unit volume tExample: different type and density of
weavingl, (d) carbon carrying fabric having different level of
carbonizing of the fibers;
provides for saving of electric power consumption owing to:
(a) installation of heat reflective layer and (~) possibility of
placing the heat element with less cushioning and insulation closer
~5 to the human body or to the heated obiect;
allows for manufacturing of heating element with electrical
connection of electrically conductive strips in parallel or in
series;
overcomes the problem of overheated spots owing to (a) high
heat radiating surface area of the fabric core, (b) uniform heat
distribution by the heat reflective and heat conductive layer
preventing the pos~ibility of skin ~urns or destruction of the
insulating polymer layers;
provides for extremely low thermal ~p~n~ion of the heating
element owing to the nature of the carbon carrying fabric. ~his
feature is extremely important for construction applications
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(Example:-concrete) or for multi layer insulation with different
t~er~l e~pAnsion properties;
consists of a non combustible conductive fabric which does not
cau~e arcing while being cut or punctured during electrical
operation;
offers high degree of flexibility and/or ~oftness of the
heating appliances depending on the type and thickness of
insulation; and
provides technological simplicity of manufacturing and
assembling of said heating element.
The process of manufacturing of the insulated heating element
can be fully automated, it utilizes the commercially available non
toxic and inexpensive products. The insulated fabric core can be
manufactured in rolls with subsequent cutting to desired sizes and
further attachment of electric power cords.
The aforementioned description comprises different embodiments
which should not be construed as limiting the scope of the
invention but, as merely providing illustrations of some of the
presently preferred embo~; -ntS of the invention. Additional
contemplated embodiments include: (a) the conductive fabric can
include other electrically conductive materials other than carbon,
such as electroplated copper, nickel or tin contA; n; ng coatings on
the surface of the carbon carrying fibers; (~) the electrically
conductive fabric can consist of ceramic fibers, such as alumina,
2~ silica, zirconia, chromia, magnesium, calcia or a combination
thereof, coated or impregnated with electrically conductive
19
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material 3uch a~ carbon; (c) the soft filling material can consist
of different oligomeric or polymeric compounds, such as
polyurethane, polyvinyl-con~A; n; ng products, etc.; (d) the
conductive fabric can be cut out into separate strips and
subsequently electrically connected to each other in a serpentine
form or other desired patterns, including ordinary straight or "U"
shaped strips; (e) the electric power cord can be attached to the
conductive fabric without electrodes by directly connecting of the
cord by conductive adhesive, conductive paint, conductive polymer,
etc.; (f) the conductive fabric heating element can be electrically
insulated by other soft non conductive fabrics by sewing, gluing,
fusing etc., forming a soft multi-layer assembly; (g) the
conductive fabric core of the heating element can be electrically
insulated by rigid non-conductive materials like ceramics,
concrete, thick plastic, wood, etc.; (h) the conductive fabric
heating element can be assembled in combination with other types of
known flexible heating elements like heating wires.
The second embodiment of the invention consists of a
non-metallic heating element core made by assembling yarns
comprising carbon/graphite fibers as shown in Figures 9-18. The
core is woven into various longitn~; n~l forms during textile
fabrication, such as strips, sleeves, pipes and ropes. It may also
take a form of a strand of threads. The heating element core may,
along with electrically conducting carbon/graphite fiber yarns,
contain other, electrically non-conducting, yarns in various
proportion and weaving patterns in order to augment its electrical
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resistance. Such yarns have at least one of t~e following
contents:
1. Yarns made of carbon/graphite carrying fibers with
similar electrical characteristics.
2. Yarns made of carbon/graphite carrying fibers with
varying electrical characteristics.
3. Yarns, as indicated in 1 or 2 above, with addition of
ceramic, including fiberglass, fibers.
4. Yarns, as indicated in 1 or 2 above, with addition of
synthetic polymer fibers.
5. Yarns, as indicated in 1 or 2 above, with addition of
ceramic fibers which were coated with a thin, up to ~.5 micron
~ayer of carbon/graphite.
It is preferable that the yarns consist of continuous filament
fibers.
The heating element core utilizes a woven product in its final
form, therefore el;m;nAting a step of treatment of the whole core
material with stabilizing substances, prior to cutting of patterns,
from the heating element manufacturing process.
Fig. 9A shows a woven electro-conductive heating element core
~111) in a form of a strip, folded and patterned as dictated by the
heating element design. Portions of the heating element core (111)
may be conditioned in various locat;ions to augment the electrical
resistance of the finished product, such conditioning is performed
by at least one of the following methods:
a. the use of electroconductive adhesive (122), preferably
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graphite based;
b. the use of non-electroconductive coating material (118),
preferably having adhesive properties.
c. making of cut outs of various shapes and sizes (117)
In order to control overheating, at least one power control
device (115) is placed along the length of the heating element
core.
The bends and folds along the length of the heating element
core are attached by at least one of the following shape holding
methods:
a. sewing (112) with electroconductive threads, preferably
carbon fiber based, or sewing with non-conductive threads;
b. stapling (112'~;
c. gluing
d. riveting
e. fusing or sealing by insulating material during
1 ~mi n;stion of the heating element core.
As shown in Fig. 9B the heating element core is energized
through a power cord (114) which is connected to the heating
element with electrodes (113), preferably having a flat shape, with
large contact area. The electrodes are attached to the ends of the
heating element core (111), conditioned with electroconductive
adhesive (122), said ends are folded over in order to have contact
with both sides of the electrodes (113), then the electrode
assembly is finished by sewing, stapling, riveting, or using a
toothed connector.
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In addition to the electrodes, the power cord has the
following attachments, shown in Fig. 9A:
a. electrical plug (116)
b. optional power control device (115)
Depending on the end use of the heating element, the
manufacturing process utilizes the following assembly operations in
any ~equence:
a. folding and shaping the core material into a
predeterm;nY~ shape;
b. attachment of the electrodes and the power cord;
c. 1 ~m; nAting between the insulating material layers;
It is preferable to utilize a heat radiating layer on one side
of the insulated heating element core if dictated b~ the heating
element design; such heat radiating layer may be an alllmi nl~m foil
or metallized polymer, electrically insulated from the
electroconductive heating element core.
Figure lOA shows the heating element core (111) in a form of
the strips, zigzagged by folding in order to vary the electrical
resistance and wound around the parallel longitll~inAl electrodes
(113). This enables the variation of the heating element's
electrical resistance without varying the heating element core
material. The ends of the strips (111) are attached to the
electrical busses (113) by sewing (112), stapling (112') or
riveting.
Electrode connectors (121) and a power cord (114) are attached
to the ends of the parallel bus electrodes (113). The lamination
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o~ the assem~ly between layers of electrically insulating material
i~ollows the connectJon of the electrode connector (121) to the ends
of the heating element core (111). In order to connect the
electrodes after the 1 A~; nAtion process, when dictated by the
heating element design, the insulating layer(s) shall be either
stripped at the points of connection or punctured by the electrode
connector (121).
Figure lOB demonstrates a variation of the heating element
shown in Figure lOA. However, instead of zigzagged strips (111),
folded and disposed between the electrical bus electrodes (113)/
the strips (111) have a straight run and are wound around the
parallel bus electrodes (113). The contact between the strip and
the busses is conditioned with a localized use of conductive
adhesive, preferably carbon/graphite based, then secured by
stapling (112) and/or sewing through the strip and the bus. The run
of the zigzag, the distance between the peaks, may vary even in the
~ame heating element, thereby varying the finished element
temperature density, as may be dictated by the heating element
design.
Figure 11 shows a heating element core (111) utilizing
cut-outs (117) in order to: (a) achieve the variation of the
electrical resistance (b~ to provide for tight and hermetic
l~inAtion of the heating element core by fusing the insulating
layers (123) through said cut outs. The cut outs (117) may also be
filled with conductive carbon carrying substances such as positive
temperature coefficient materials (PTC). The electrical bus
24
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e~ectrodes (113) are dispo~ed longitll~in~lly on the heating element
core. They are made of metal wires or woven non-metallic strips
with low electrical resistance or combination thereof.
~he high electrical resistance of the fabric of the heating
element core (111) can be achieved through addition of threads with
high electrical resistance during the fabric weaving process, and
through making cut-outs (117) in the body of the heating element
core. The electrodes (113) are wrapped with the woven heating
element core (111) and sewn with either conductive or
non-conductive threads capable o~ withst~n~i ng the ~; heat
generated by the heating element. Staples (112) can also be used
for this purpose.
It is preferable to apply a carbon/graphite carrying adhesive
to secure a good electrical contact between the bus electrodes
(113) and the woven non-metallic heating element core (111). The
heating element assembly is then followed by l~;n~tion with the
insulating materials and attachment of the electrode connectors and
power cord with an optional controller, to the bus electrodes
(113).
Figures 12A and 12B show variations of the electrical busses
designs and their attachments.
Figure 12A shows a detail of a heating element core (111),
prior to ~m; n~tion with insulating materials r having high
conductivity threads or thin metal wires woven or sewn into its
body to form the parallel electrical buss assembly (113~.
An optional positive temperature coefficient (PTC) material
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(119) may be incorporated longitudinally into the heating element
core (111) in selected areas. Such areas have the yarns woven in
such manner that the electrical resistance across said areas is
lower than the resistance of adiacent areas of the woven heating
element core (111).
As an example, in order to achieve lower electrical resistance
of said selected areas, the weaving process shall, for such
selected areas, use partially conductive or nonconductive yarns,
such as ceramic or polymers. Further, the incorporated P~C
material (119) introduces an additional self-limiting elec~rical
conductivity to said selected areas of the heating element core
(111). It is preferable to incorporate the PTC material
longitll~;n~lly either in the center of the heating element core or
next to the longitll~;n~l bus electrodes (113). Generally, the PTC
material i5 made of a polymer substance having electroconductive
carbon-carr~ing filler.
Figure 12B shows a detail of a heating element core (111),
prior to 1~ ;nAtion with the insulating materials, with optional
cut-outs (117), attached to woven bus strip electrodes ~113) with
low electrical resistance. Such an attachment is made by sewing
(120), stapling or riveting. It is preferable to condition the
place of said connection with electroconductive adhesive comprising
carbon/graphite particles prior to attachment. An optional PTC
material (119) may be utilized as described in ~igure 12A.
Figure 13 shows a fragment o~ the heating element, prior to
l~;n~tion with insulating materials, having at least three bus
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electrodes (113) and having the PTC material (119) longitu~;n~lly
disposed between one set of bus electrodes (113), said heating
element is electrically connected in parallel. The preferred
method consists of having no PTC material between one set of bus
5 electrodes and having PTC material (119) longit~l~;n~lly disposed
between another set of bus electrodes (113).
All three bus electrodes (113) are connected to one power
source through a power controller (115). This setup enables guick
gain in temperature by bypassing one bus electrode and a zone
comprising the PTC material (119). When the desired temperature of
the heated object is achieved, the electrical contact is switched
to the bus electrodes so as to provide the heater, by directing the
current through the PTC material (119), with self-limiting
temperature capabilities.
As an alternative a PTC materi~al with the same or different
temperature limit may be longitll~; n~l ly disposed in the area
indicated above as having no PTC material. This will provide for
a heater with two, preferably different, temperature zones, each
having the self-limiting temperature control capabilities. This
method allows for a heating element with multiple temperature zones
bordered by bus conductors.
As shown in Figure 14 the heating element core between the bus
electrodes (113) may contain two or more separate fragments of
woven electroconductive material (111~ having PTC material (119)
~5 connecting said fragments longit-l~; n~l ly and providing electrical
continuity. The location of the PTC material is dictated by the
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heating element design.
The two ad~acent fragments of the woven heating element core
(111) are first connected by sewing (120) to electrically
non-conductive connection strip (125), leaving a gap of
predetermined width between them. The gap is then bridged with
softened PTC material (119) so as to penetrate the matrix of the
woven fabric of the fragments of the heating element core (111) at
the edges. The sewn connection strip (125) provides desired
mechanical strength; the PTC material (119) provides electrical
continuity and desired se~f-limiting temperature control. An
insulating layer (123) envelops the assembly; it may also be used
for connecting said adjacent fragments of the heating element core
~111) instead of the connection strip ~125).
Figure 15 shows an optional detail of the heating element core
(111) attachment to a bus electrode (113). In this detail the bus
electrode iB embedded in the PTC material (119); the shape of the
PT~ material envelop (119) varies with the heating element design.
The edge o~ the heating element core (111) is then wrapped around
said bus electrode (113) and PTC material (llQ), and secured by the
shape holding means such as sewing (120), stap~ing or riveting.
The connection between the PTC material and heating element core
may also be heat sealed or fused. The insulation layer (123)
envelops the whole electroconductive assembly.
Figure 16 shows a fragment of the insulated heating element
core (111) comprising a strand of threads or a woven rope and a
preferred embodiment of its connection with a metal electrical
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conn~ctor (121) and a power cord (114). The heating element core
(111) consists of a strand or rope comprising electrically
conductive carbon/graphite or carbon/graphite coated ceramic
threads or combination thereof. The non-electroconductive ceramic
or polymer threads or combination thereof may be included in the
~trand or the rope of said core in order to impart additional
ch~n;c~l strength and electrical resistance.
The electroconductive core (111) is then enclosed by the
insulating sleeve (123). Due to a softness of the heating element
core (111), it is preferable to make the electrical connection with
the metal connector (121) by penetration of a thin part of the
connector, having shape of a thin insert (124), such as a tooth, a
screw or a needle, through a transverse cut of the insulated
heating element core. After penetration of such thin
electroconductive insert (124) into the body o~ the heating element
core (111), the electrode connector (121) and the insulated heating
element core are attached by crimping.
The sides of the electrode connector may also include teeth
(126) which penetrate into the body of the heating element core
(lll) by puncturing through the in~ulator (123) during crimping,
thus providing additional electrical connection. The electrode
connector (121) may be utilized to provide electrical continuity
between two segments of said heating element core or to connect one
segment of a power cord and a segment of said heating element core.
The same type of the electrical connection may be applied for the
insulated strip, sleeve or pipe heating element core described in
29
.
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this invention.
~ nother variation of the electrode attachment, proposed in
this invention, consists of stripping the insulation (123) from the
ends of the insulated heating element core (111) and attaching the
electrode connector ~121) to the core by crimping. It is
preferable to condition the ends of the threads with
electroconductive adhesive before attaching the electrode
connector. It is also preferable that electroconductive adhesive
compri~es carbon/graphite particles.
Figure 17A shows a perspective view of a sleeve/pipe shaped
heating element core (111) having bus electrodes (113'),
electrically connected in series according to the preferred
embo~;m~t of the present invention;
~igure 17B describes a perspective view of a sleeve/pipe
1~ shaped heating element core (111) having longit~l~; nA 1 ~us
electrodes (113'), electrically connected in parallel.
Figure 17C shows a perspective view of a sleeve/pipe shaped
heating element core (111), electrically connected in parallel,
having bus electrodes (113') and an optional PTC material (119)
incorporated longitn~;nAlly into said heating element core;
The installation of the bus electrodes (113'), the PTC
material (119) and lAm;n~tion with insulating materials may be
conducted as expl~;ne~ above for other types of heating elements.
For devices designed to heat pipe-type objects, it is preferable to
have one longitll~;nAl cut in the described sleeve heating element
core for ease of installation of the heating element on said
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pipe-type objects.
The proposed soft non-metallic heating elements may be
utilized in a variety of commercial and industrial heater
applications, using direct or alternating current. The main
advantages of the heating elements are the high reli~h;l;ty and
~afety which are provided by the tightly sealed soft and durable
electrically conductive yarns.
~ urther, the use of electrically conductive carbon/graphite
fibers, non-conductive ceramic or polymer fibers in the heating
element has the following additional advantages:
it enables manufacturing of thin, soft and uniform heaters
without utilizing conventional metal heater wires;
it provides high durability of the heating appliances which
can withstand sharp folding, small perforations, punctures and
compression without decreasing of electrical operational
capabilities;
it provides high tear and wear resistance owing to: (a) high
~trength of the conductive yarns and (b) tight hermetically
enveloping around all electrically conductive media with strong
insulating materials;
it provides for manufacturing of corrosion and erosion
re~istant heating element owing to: (a) high chemic~l inertness of
the carbon/graphite and ceramic yarns, (b) hermetic polymer
insulation of the whole heating element including connection
electrodes and temperature control devices, for u~ilization in
ch~m;r~lly aggressive industrial or marine environments;
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it offers versatility of variation of the electrical
conductivity of the heating element core owing to: (a~ weaving or
stranding of the electrically conductive carbon/graphite yarns to
the predet~rm;ned width and thickness of the strips, sleeves, ropes
or strands of threads; (b) weaving of the yarn~ to the
predete~ned density or type of weaving; (c) weaving or stranding
of the carbon/graphite yarns having different electrical
~o~ ctivity in one unit; (d) weaving or stranding of the
carbon/graphite yarns with nonconductive ceramic and/or polymer
threads or fibers; (e) - king cut outs of different shapes to vary
the electrical resistance of the heating element core; (f)
incorporating conductive carbon/graphite coated ceramic fibers or
threads;
it provides for saving of electric power consumption owing to:
(a) installation of heat reflective layer, and (b) possibility of
placing the heating element with less cushioning and insulation
closer to the human body or to the heated object;
it allows for manufacturing of heating element with electrical
connection of electrically conductive strips, ropes, sleeves/pipes
~0 or strands in parallel or in series;
it overcomes the problem of overheated spots owing to (a) high
heat radiating surface area of the heating element core, (b)
uniform heat distribution by the heat reflective layer, preventing
the possibility of skin burns or destruction of the insulating
~5 layers;
it provides for extremely low thermal expansion of the heating
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element owing to the nature of the carbon/graphite, polymer or
yarn~. This feature is extremely important for construction
applications (~xample:-concrete) or for multi-layer insulation with
- different th~r~-l ~p~n~ion properties;
it consists of a non-combustible electrically conductive
/graphite and carbon~graphite coated ceramic yarns which do
not cause arcing while being cut or punctured during electrical
operation;
it offers high degree of flexibility and/or softness of the
heating appliances depending on the type and thickness of
insulation; and
it provides technological simplicity of manufacturing and
as~embling of said heating element.
Further, a comh;n~tion of the electrically conductive
carbon/graphite carrying woven yarn.s and PTC material allows to:
(a) provide temperature self-limiting properties of the soft
heating appliances, el;~in~ting need for thermostats; (b) increase
the distance between the bus electrodes, decreasing the ris~ of
short circuit between said bus electrodes; (c) provide dissipation
of an excess heat through the highly thermally conductive
carbon/graphite fibers; (d~ provide larger heat radiating area
resulting in higher efficiency of the heater; (e) provide a barrier
for liquid penetration to the parallel bus conductors in the event
of puncturing the insulated heating element core.
The process of manufacturing of the insulated heating element
can be fully automated, it utilizes the commercially available non
33
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toxic, nonvolatile and inexpensive products. The insulated heating
core can be manufactured in rolls or spools with subsequent cutting
to desired sizes and further attachment of electric power cords and
optional power control devices.
Further, the proposed heating element can ~e utilized in, but
not limited to: (a) electrically heated blankets, pads, mattresses,
spread sheets and carpets; (b) wall, furniture, ceiling and floor
electric heaters; ~c) vehicle, scooter, motorcycle, boat and
aircraft seat heaters; (d) electrically heated safety vests,
garments, ~oots, gloves, hats and scuba diving suits; (e) food
(Example: pizza) delivery and sleeping bags; (f) refrigerator,
road, roof and aircraft/helicopter wing/blade deicing systems, lg)
pipe line, drum and tank electrical heaters, (h) electrical furnace
igniters, etc. In addition to the heating application, the same
car~on/graphite carrying heating element core may be utilized for
~n anti static protection.
Figure 18A shows a garment (128) including a soft heating
element according to one of the embo~ nts of the present
invention in its construction to provide a desired degree of
warmth. The soft heating element (127) is sewn (120) into the
garment in a predet~rm;neA location.
Figure 18B shows a vehicle seat (129) including a soft heating
element according to one embo~i -nt of the present invention. The
heating element (127) is placed under the seat upholstery.
Figure 18C demonstrates a floor assembly (130) utilizing one
of the embodiments of the present invention. The heating element
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(i27) is placed under the floor covering. An optional power
control device (115) can be utilized an any proposed heating
element assembly.
~ Figure 18D shows a length of pipe in~luding a soft heating
element (127) according to the present invention wrapped around the
pipe to provide a desired degree of heatin~.
The aforementioned description comprises different embo~; -ntS
which should not be construed as limiting the scope of the
invention but, as merely providing illustrations of some of the
presently pre erred embodiments of the invention. Additional
contemplated em~o~ ts include; (a) in addition to
carbon/graphite yarns the heating element core may include other
electrically conductive materials other than carbon, such as
copper, nickel or tin contAining materials; (b) heating element
core may include yarns made of ceramic fibers, such as alumina,
silica, boria, zirconia, chromia, magnesium, calcia, silicon
carbide or com~ination thereof; (c) heating element core may
comprise electrically conductive carbon/graphite coated ceramic
fibers, such as alumina, silica, boria, zirconia, chromla,
magnesium, calcia, silicon carbide or combination thereof; (d) the
strips can be soaked in a diluted solution of adhesives and dried,
to ease the hole cutting during manufacturing of the heating
element core and augmentation of its electrical properties; (e) the
heating element core may comprise the conductive strips, ropes,
~leeves/pipes or threads, having different electrical resistance;
(f) the heating element core may ~e formed into various patterns
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~uch a~ ~erpentine or other desired patterns, including ordinary
~traight, coil or "U" shaped forms; (g) the electric power cord can
~e directly attached to the conductive heating element core without
the use of electrodes, it is preferable to utilize electrically
S conductive adhesive, ~o~ ctive paint, conductive polymer, etc. to
assure good electrical connection; (h3 the conductive heating
element core can be electrically insulated by the soft non-
~n~n~tive fabrics or polymers by sewing, gluing, fusing etc.,
forming a soft multi-layer assembly; ~i) the conductive soft
heating element core can be electrically insulated by rigid
non-conductive materials like ceramics, concrete, thick plastic,
wood, etc.; (j) the ~hape holding means can be applied on any part
of the heating element core.
While the foregoing invention has been shown and described
with reference to a number of preferred embo~i -nts~ it will be
understood by those possessing skill in the art that various
changes and modifications may be made without departing from the
spirit and scope of the invention.
36
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