U.S. patent application number 09/829509 was filed with the patent office on 2002-04-11 for wound and themoformed element and method of manufacturing same.
Invention is credited to Schlesselman, John W., Von Arx, Theodore.
Application Number | 20020040898 09/829509 |
Document ID | / |
Family ID | 24575681 |
Filed Date | 2002-04-11 |
United States Patent
Application |
20020040898 |
Kind Code |
A1 |
Von Arx, Theodore ; et
al. |
April 11, 2002 |
Wound and themoformed element and method of manufacturing same
Abstract
A heating element for heating a flexible intravenous tube
includes a resistance heating wire having a pair of terminal ends
encapsulated within an electrically insulating polymeric layer. The
polymeric layer and the resistance heating wire are formed into a
plurality of turns defining a coil having a central axis. Each turn
of the coil is independently elastically expandable to surround a
portion of the flexible intravenous tube when the intravenous tube
is disposed axially through the coil such that the coil conforms to
the shape of the flexible intravenous tube.
Inventors: |
Von Arx, Theodore; (La
Crescent, MN) ; Schlesselman, John W.; (Fountain
City, WI) |
Correspondence
Address: |
WILLIAM H. MURRAY
DUANE MORRIS & HECKSCHER LLP
ONE LIBERTY PLACE
PHILADELPHIA
PA
19103-7396
US
|
Family ID: |
24575681 |
Appl. No.: |
09/829509 |
Filed: |
April 10, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09829509 |
Apr 10, 2001 |
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09642215 |
Aug 18, 2000 |
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Current U.S.
Class: |
219/535 ;
219/544; 392/472; 392/480 |
Current CPC
Class: |
B29K 2027/18 20130101;
B29K 2023/10 20130101; B29K 2079/08 20130101; B29K 2069/00
20130101; B29K 2079/085 20130101; B29K 2081/04 20130101; B29C
66/4326 20130101; B32B 2305/34 20130101; B29C 66/71 20130101; B29C
66/71 20130101; B29C 66/71 20130101; B29C 70/885 20130101; B29C
65/3412 20130101; B32B 37/206 20130101; B29C 65/02 20130101; B29C
66/73921 20130101; B29K 2023/12 20130101; B29C 66/71 20130101; B29C
66/729 20130101; B29K 2023/0683 20130101; B29K 2023/12 20130101;
B29K 2081/06 20130101; B29K 2071/00 20130101; A47J 36/2483
20130101; B29C 51/02 20130101; B29C 65/1464 20130101; B29C 65/342
20130101; B29C 66/71 20130101; H05B 2203/003 20130101; B29C 65/3428
20130101; B29C 66/4312 20130101; B29C 66/71 20130101; B32B 27/00
20130101; B29C 65/1406 20130101; H05B 2203/014 20130101; Y10T
29/49083 20150115; B29C 65/1458 20130101; B29C 66/81871 20130101;
B29C 66/91221 20130101; H05B 2203/002 20130101; B29C 65/3468
20130101; B29C 66/431 20130101; B29C 66/82661 20130101; Y10T
29/49085 20150115; B29C 51/12 20130101; B29C 66/45 20130101; B29C
66/71 20130101; B29C 66/91214 20130101; B29C 66/91655 20130101;
B29C 53/04 20130101; B65D 2581/3428 20130101; Y10T 29/49082
20150115; B29C 65/1445 20130101; B29C 66/133 20130101; B29L
2031/779 20130101; B32B 2310/022 20130101; B29C 65/3492 20130101;
B32B 2310/0806 20130101; B29C 66/71 20130101; B29C 65/3444
20130101; B29C 66/71 20130101; B29C 66/91411 20130101; B32B 1/02
20130101; B29C 70/82 20130101; H05B 2203/037 20130101; B29C 65/3488
20130101; B29C 66/71 20130101; H05B 3/36 20130101; B29C 66/83413
20130101; B29C 2793/0081 20130101; B32B 3/06 20130101; B32B 3/08
20130101; B65D 81/3476 20130101; H05B 2203/013 20130101; B29C
65/348 20130101; B29C 65/346 20130101; B29C 66/433 20130101; B29C
66/81831 20130101; B32B 37/06 20130101; H05B 2203/004 20130101;
H05B 2203/017 20130101; B29C 66/91421 20130101; B29C 51/00
20130101; B29C 65/3448 20130101; B29C 66/432 20130101; B29C 66/71
20130101; B29C 66/91645 20130101; B29C 66/91218 20130101 |
Class at
Publication: |
219/535 ;
219/544; 392/472; 392/480 |
International
Class: |
H05B 003/58 |
Claims
What is claimed:
1. A heating element for heating a flexible intravenous tube, said
heating element comprising: a resistance heating wire having a pair
of terminal ends, said resistance heating wire encapsulated within
an electrically insulating polymeric layer, said polymeric layer
and said resistance heating wire being formed into a plurality of
turns defining a coil having a central axis, wherein each of said
turns is independently elastically expandable to surround a portion
of said intravenous tube when said intravenous tube is disposed
axially through said coil such that said coil conforms to the shape
of said flexible intravenous tube.
2. The heating element of claim 1, wherein said coil includes at
least two sets of interconnected parallel turns.
3. The heating element of claim 2, wherein said coil includes two
sets of interconnected parallel turns, each of said sets
terminating at a different one of said terminal ends.
4. The heating element of claim 1, wherein said polymeric layer is
a tubular thermoplastic sheath and said resistance heating wire is
disposed axially through said tubular thermoplastic sheath.
5. The heating element of claim 1, wherein said polymeric layer is
extruded over said resistance heating wire.
6. The heating element of claim 5, wherein said heating element
includes a plurality of resistance heating wires connected in
series.
7. The heating element of claim 5, wherein said heating element
includes a plurality of resistance heating wires connected in
parallel.
8. The heating element of claim 1, further comprising a flexible
intravenous tube disposed axially through said coil.
9. A method of manufacturing a heating element for a flexible
intravenous tube, comprising the steps of: providing a resistance
heating wire having a pair of terminal ends; surrounding said
resistance heating wire with an insulating polymeric layer; and
forming said polymeric layer and said resistance heating wire into
a plurality of turns defining a coil having a central axis, wherein
each of said turns is independently elastically expandable to
surround a portion of said intravenous tube when said intravenous
tube is disposed axially through said coil such that said coil
conforms to the shape of said flexible intravenous tube.
10. The method of claim 9, wherein the step of forming said
polymeric layer and said resistance heating wire into a plurality
of turns includes the steps of wrapping said polymeric layer and
said resistance heating wire around a mandrel, heating said
polymeric layer and said resistance heating wire, and allowing said
thermoplastic sheath to cool to maintain said coil shape.
11. The method of claim 9, wherein said polymeric layer is a
tubular thermoplastic sheath and the step of surrounding said
resistance heating wire includes the step of disposing said
resistance heating wire axially through said tubular thermoplastic
sheath.
12. The method of claim 9, wherein the step of surrounding said
resistance heating wire includes the step of extruding said
polymeric layer over said resistance heating wire.
13. The method of claim 12, wherein the step of surrounding said
resistance heating wire includes the step of extruding said
polymeric layer over a plurality of resistance heating wires.
14. The method of claim 13, further comprising the step of
connecting said plurality of resistance heating wires in
parallel.
15. The method of claim 13, further comprising the step of
connecting said plurality of resistance heating wires in
series.
16. The method of claim 9, where in the step of forming said
polymeric layer and said resistance heating wire into a plurality
of turns includes the step of forming said polymeric layer and said
resistance heating wire into at least two sets of interconnected
parallel turns.
17. An expandable heating element, comprising: a resistance heating
material surrounded by an electrically insulating polymeric layer,
said polymeric layer and said resistance heating material being
formed into a plurality of turns defining a coil having an original
diameter and a central axis, wherein a plurality of said turns are
independently elastically expandable to a diameter greater than the
original diameter of said coil to surround a cylindrical body
disposed axially through said coil, at least a portion of said
cylindrical body having a diameter greater than the original
diameter of said coil.
18. The heating element of claim 17, wherein said resistance
heating material includes a resistance heating wire having a pair
of terminal ends.
19. The heating element of claim 18, wherein said resistance
heating wire is laminated between two sheets of thermoplastic.
20. The heating element of claim 18, wherein said polymeric layer
is extruded over said resistance heating wire.
21. The heating element of claim 20, wherein said polymeric layer
comprises a PTFE film.
22. The heating element of claim 17, wherein said resistance
heating material includes a resistance heating wire sewn to a
supporting substrate.
23. The heating element of claim 17, wherein said electrically
insulating polymeric layer includes a thermoplastic elastomer
material, the heating element further comprising a reinforcing
substrate fused with said electrically insulating polymeric
layer.
24. A method of manufacturing a flexible heating element,
comprising the steps of: providing a resistance heating material;
surrounding said resistance heating material with an electrically
insulating polymeric layer; and forming said polymeric layer and
said resistance heating material into a plurality of turns defining
a coil having a central axis and an original diameter, wherein a
plurality of said turns are independently elastically expandable to
a diameter greater than the original diameter of said coil.
25. The method of claim 24, wherein the steps of surrounding said
resistance heating material includes the steps of providing a first
and second thermoplastic sheets and laminating said resistance
heating material between said first and second thermoplastic
sheets.
26. The method of claim 25, wherein said forming step includes the
steps of wrapping said polymeric layer and said resistance heating
material around a mandrel, heating said polymeric layer and said
resistance heating material, and allowing said polymeric layer and
said resistance heating material to cool to maintain said coil
shape.
27. The method of claim 26, wherein said resistance heating
material includes a resistance heating wire having a pair of
terminal ends.
28. The method of claim 27, wherein said resistance heating wire is
sewn to a supporting substrate.
29. The method of claim 24, wherein the step of surrounding said
resistance heating material includes the step of extruding said
polymeric layer over said resistance heating material.
30. The method of claim 29, wherein the step of forming said
polymeric layer and said resistance heating material into a
plurality of turns includes the steps of wrapping said polymeric
layer and said resistance heating material around a mandrel,
heating said polymeric layer and said resistance heating material,
and allowing said polymeric layer and said resistance heating
material to cool to maintain said coil shape.
31. The method of claim 30, wherein said resistance heating
material includes at least one resistance heating wire.
32. The method of claim 24, wherein the step of forming said
polymeric layer and said resistance heating material into a
plurality of turns includes the steps of wrapping said polymeric
layer and said resistance heating material around a mandrel,
heating said polymeric layer and said resistance heating material,
and allowing said polymeric layer and said resistance heating
material to cool to maintain said coil shape.
Description
Cross-Reference to Related Applications
[0001] This application is a continuation in part of U.S. patent
application Ser. No. 09/642,215 to Theodore Von Arx, Keith Laken
and John W. Schlesselman, entitled "Formable Thermoplastic Laminate
Heated Element Assembly," filed on Aug. 18, 2000, the entirety of
which is hereby incorporated by reference herein.
[0002] This Application is also related to U.S. application Ser.
No. 09/369,779 of Theodore Von Arx, filed Aug. 6, 1999, entitled
"Electrofusing Of Thermoplastic Heating Elements And Elements Made
Thereby"; U.S. application Ser. No. 09/416,731 of John Schlesselman
and Ronald Papenfuss, filed Oct. 13, 1999, entitled "Heating
Element Containing Sewn Resistance Material"; U.S. application Ser.
No. 09/275,161 of Theodore Von Arx, James Rutherford and Charles
Eckman, filed Mar. 24, 1999, entitled "Heating Element Suitable For
Preconditioning Print Media" which is a continuation in part of
U.S. application Ser. No. 08/767,156 filed on Dec. 16, 1996, now
U.S. Pat. No. 5,930,459, issued on Jul. 27, 1999, which in turn is
a continuation in part of U.S. application Ser. No. 365,920, filed
Dec. 29, 1994, now U.S. Pat. No. 5,586,214, issued on Dec. 17,
1996; U.S. application Ser. No. 09/544,873 of Theodore Von Arx,
Keith Laken, John Schlesselman, and Ronald Papenfuss, filed Apr. 7,
2000, entitled "Molded Assembly With Heating Element Captured
Therein"; U.S. application Ser. No. 09/611,105 of Clifford D.
Tweedy, Sarah J. Holthaus, Steven O. Gullerud, and Theodore Von
Arx, filed Jul. 6, 2000, entitled "Polymeric Heating Elements
Containing Laminated, Reinforced Structures And Processes For
Manufacturing Same"; and U.S. application Ser. No. 09/309,429 of
James M. Rutherford, filed May 11, 1999, entitled "Fibrous
Supported Polymer Encapsulated Electrical Component" which are all
hereby incorporated by reference herein.
FIELD OF THE INVENTION
[0003] This invention relates to electric resistance heating
elements, and more particularly, to plastic insulated resistance
heating elements containing encapsulated resistance material and
shaped to surround tubular structures.
BACKGROUND OF THE INVENTION
[0004] A number of heating tapes have been developed that include
resistance heating elements and that are used primarily to heat the
exterior surface of tubes, pipes, containers and the like. Good
examples of these heating tapes include those described in R. M.
Combs, U.S. Pat. No. 2,719,907, issued Oct. 4, 1955; R. W. Logan et
al., U.S. Pat. No. 2,710,909, issued Jun. 14, 1955; and G. H.
Morey, U.S. Pat. No. 3,268,846, issued Aug. 23, 1966, which are all
hereby incorporated by reference herein.
[0005] R. M. Combs '907 discloses a heating tape in the form of a
flat elongated strip with a central core sandwiched between two
insulating layers. The core consists of a rubber supporting strip
that supports a Nichrome (Ni--Cr) wire coiled upon a rayon cord.
The wire is arranged in a series of loops extending from lateral
edge to lateral edge of the supporting strip and periodically
contacting a pair of lead wires. An outer cover of the heating tape
is grooved such that the grooves may be interlocked to secure
adjacent coils formed when the heating tape is wrapped around a
pipe.
[0006] R. W. Logan et al. '909 discloses a heating tape including a
plurality of parallel resistance wires connected in series and
sandwiched between two sheets of flexible reinforced dielectric
material, such as silicone rubber. The dielectric material is
covered by two sheets of glass cloth. Logan et al. teaches that the
heating tape may be wrapped around a pipe or other tubular body.
The tape may then be secured in the wrapped configuration by
overlapping an end of the heating tape with a portion of the body
of the heating tape.
[0007] G. H. Morey '846 discloses a flexible heating tape including
a plurality of ribbon like resistance heating elements arranged in
a parallel relationship and sandwiched between two thin plastic
strips.
[0008] Plastic welding sleeves have also been developed for use in
bonding two fitted thermoplastic pipes together. A good example of
a welding sleeve is disclosed in Blumenkranz, U.S. Pat. No.
4,436,999, issued Mar. 13, 1984, the entirety of which is hereby
incorporated by reference herein. Blumenkranz '988 discloses a
welding sleeve including two electrically conducting wires embedded
in a thermoplastic sheath. A length of the welding sleeve is wound
into a spiral pattern on a mandrel having substantially the same
diameter as an insert pipe of the two pipes to be fused together.
Each succeeding turn around the mandrel is wound as closely as
possible to the preceding turn, so that there is no space between
the turns. The adjacent turns of the welding sleeve are then fused
so that they are joined to form a self-sustaining spiral heating
element. The sleeve is fitted over the insert pipe, and the insert
pipe is then fitted into a second pipe and energized to fuse the
two pipes together.
[0009] The heated tape elements described above must all be
manually wrapped around an object to be heated, such as a pipe, and
then must be affirmatively secured in the wrapped configuration in
some manner, such as by overlapping the end of the tape with a
portion the heating tape or by interlocking specially designed
grooves. The heating tapes are not pre-formed into a configuration
that is capable of heating objects, such as pipes, that commonly
have different diameters without performing the above-described
wrapping and securing steps. The Blumenkranz heating element is
pre-formed to accommodate the general shape of a pipe structure and
does not need to be wrapped or independently secured to the pipe,
but the Blumenkranz heating element is designed for use only with
pipes having a diameter substantially matching that of the welding
sleeve heating element. Therefore, there remains a need for a
heating element that is adaptable to heat a plurality of heat
objects of different sizes but that does not need to be wrapped and
then secured around the object to be heated.
SUMMARY OF THE INVENTION
[0010] The present invention provides a heating element for heating
a flexible intravenous tube and a method of manufacturing the same.
The heating element comprises a resistance heating wire having a
pair of terminal ends. The resistance heating wire is encapsulated
within an electrically insulating polymeric layer. The polymeric
layer and the resistance heating material are formed into a
plurality of turns defining a coil having a central axis. Each of
the turns is independently elastically expandable to surround a
portion of the intravenous tube when the intravenous tube is
disposed axially through the coil such that the coil conforms to
the shape of the flexible intravenous tube.
[0011] The inventors of the heating element believe that the
heating element may be of great benefit in several medical
intravenous applications. For example, several dies used in
angioplasty procedures are very viscous at room temperature. The
timing of the injection of these dies must often be quite precise,
such as timing the injection of the die to occur in between heart
beats. These dies are often stored at reduced temperatures, and it
is believed that heating the die along the length of the tube may
reduce the viscosity of the die, thereby aiding in the control of
the timing of the injection. The heating element may also be used
to raise and regulate the temperature of other intravenous fluids,
such as blood plasma, from room temperature, or below room
temperature, to body temperature in a controlled manner (i.e.,
without overheating the blood plasma and destroying the red blood
cells) during procedures such as transfusions. These intravenous
fluids are often refrigerated prior to infusion to prevent
incubation of harmful organisms. Infusion of the fluid at these
reduced temperatures can induce thermal shock in a patient and
resulting in possible patient mortality. These heating applications
may be accomplished by the heating element of the present
invention, all while avoiding the shortcomings of prior art heating
elements that may be used to heat other tubular structures. There
is no need to manually wrap the heating element, coil by individual
coil, around the intravenous tube. The intravenous tube may simply
be inserted along the central axis of the coiled heating element.
There is also no need to independently secure the heating element
around the tube because the heating element is self-securing and
conforms to the shape of, and frictionally engages, the flexible
intravenous tube.
[0012] The utility of the present invention also extends past the
heating of intravenous tubes to the heating of other liquids or
devices, such as oil or fuel lines, food and beverage service
applications, etc. The present invention provides an expandable
heating element comprising a resistance heating material surrounded
by an electrically insulating polymeric layer. The polymeric layer
and the resistance heating material are formed into a plurality of
turns defining a coil having an original diameter and a central
axis. A plurality of the turns of the coil are independently
elastically expandable to a diameter greater than the original
diameter of the coil to surround a cylindrical body disposed
axially through the coil where at least a portion of the
cylindrical body has a diameter greater than the original diameter
of the coil.
[0013] The above and other features of the present invention will
be better understood from the following detailed description of the
preferred embodiments of the invention that is provided in
connection with the accompanying drawings.
A BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings illustrate preferred embodiments
of the invention, as well as other information pertinent to the
disclosure, in which:
[0015] FIG. 1 is a front plan view of a resistance heating element,
including a resistance wire disposed in a circuit path on a
supporting substrate and joined to a pair of electrical
connectors;
[0016] FIG. 1A is a front plan, enlarged view, of a portion of the
resistance heating element of FIG. 1, showing the preferred
cross-stitch attachment to the supporting substrate;
[0017] FIG. 2 is a rear plan view of the resistance heating element
of FIG. 1;
[0018] FIG. 3 is a front perspective view of a preferred
programmable sewing machine and computer for manufacturing
resistance heating elements;
[0019] FIG. 4 is a top plan view of a heated element assembly
including a resistance heating element according to the present
invention;
[0020] FIG. 5 is a cross-sectional view of the heated element
assembly of FIG. 4 taken along lines 1-1;
[0021] FIG. 6 is a cross-sectional view of a multilayered heated
element assembly according to the present invention;
[0022] FIG. 7a is a top plan view of a tubular shaped thermoplastic
body for providing thermoplastic sheets according to the present
invention;
[0023] FIG. 7b is a side elevational view of a tubular shaped
thermoplastic body for providing thermoplastic sheets according to
the present invention;
[0024] FIG. 8 is a partial, side elevational view of an exemplary
heating element according to the present invention;
[0025] FIG. 9 is a front elevational view of the heating element of
FIG. 8;
[0026] FIG. 10 is an enlarged, cross-sectional view of the heating
element of FIG. 8 taken along lines 10-10;
[0027] FIG. 11 is a partial, side elevational view of another
embodiment of an exemplary heating element according to the present
invention;
[0028] FIG. 12 is a rear elevational view of the heating element of
FIG. 11;
[0029] FIG. 13 is a top plan view of a planar resistance heating
element that may be formed into the heating element of FIG. 11;
[0030] FIG. 13A is a top plan view of the planar resistance heating
element of FIG. 13 shown with top polymeric layer removed;
[0031] FIG. 14 is a front elevational view of the planar resistance
heating element of FIG. 13;
[0032] FIG. 15A is an enlarged, cross-sectional view of an
exemplary resistance heating element including a plurality of
resistance heating wires that may be formed into the heating
element of FIG. 8;
[0033] FIG. 15B is a cross-sectional view of another exemplary
planar resistance heating element that may be formed into the
heating element of FIG. 11;
[0034] FIG. 16 is a partial, side elevational view of a heating
element according to the present invention having two sets of
interconnected parallel turns;
[0035] FIG. 17 is a partial, perspective view of the heating
element of FIG. 11 with individual turns expanded to surround a
pipe having diameter greater than the original diameter of the
heating element;
[0036] FIG. 18 is a partial, perspective view of a flexible
intravenous tube disposed axially through the heating element of
FIG. 8; and
[0037] FIG. 19 is a cross-sectional view of an exemplary
thermoplastic elastomer resistance heating element including
reinforcing substrates.
DETAILED DESCRIPTION OF THE INVENTION
[0038] As used herein, the following terms are defined:
[0039] "Laminate" means to unite laminae via bonding them together,
usually with heat, pressure and/or adhesive. It normally is used to
refer to flat sheets, but also can include rods and tubes. The term
refers to a product made by such bonding;
[0040] "Serpentine Path" means a path which has one or more curves
for increasing the amount of electrical resistance material in a
given volume of polymeric matrix, which is useful in controlling
the thermal capacity and expansion of the element;
[0041] "Melting Temperature" means the point at which a fusible
substance begins to melt;
[0042] "Melting Temperature Range" means the temperature range over
which a fusible substance starts to melt and then becomes a liquid
or semi-liquid;
[0043] "Degradation Temperature" means the temperature at which a
thermoplastic begins to permanently lose its mechanical or physical
properties because of thermal damage to the polymer's molecular
chains;
[0044] "Evacuating" means reducing air or trapped air bubbles by,
for example, vacuum or pressurized inert gas, such as argon, or by
bubbling the gas through a liquid polymer.
[0045] "Fusion Bond" means the bond between two fusible members
integrally joined, whereby the polymer molecules of one member mix
with the molecules of the other. A Fusion Bond can occur, even in
the absence of any direct or chemical bond between individual
polymer chains contained within said members;
[0046] "Fused" means the physical flowing of a material, such as
ceramic, glass, metal or polymer, hot or cold, caused by heat,
pressure or both;
[0047] "Electrofused" means to cause a portion of a fusible
material to flow and fuse by resistance heating;
[0048] "Stress Relief" means reducing internal stresses in a
fusible material by raising the temperature of the material or
material portion above its stress relief temperature, but
preferably below its Heat Deflection Temperature; and
[0049] "Flap" or "Flap Portion" means a portion of an element which
can be folded without damaging the element structure.
Resistance Heating Element
[0050] With reference to the Figures, and particularly FIGS. 1, 1A
and 2 thereof, there is shown a first embodiment of a resistance
heating element 10 having a diameter of about 11 cm. The preferred
resistance heating element 10 may include a regulating device for
controlling electric current. Such a device can include, for
example, a thermistor, or a thermocouple, for preventing
overheating of the polymeric materials disclosed in this invention.
The resistance heating elements 10 of this invention can take on
any number of shapes and sizes, including squares, ovals, irregular
circumference shapes, tubes, cup shapes and container shapes. Sizes
can range from less than one inch square to 21 in..times.26 in.
with a single sewing operation, and greater sizes can be available
if multiple elements are joined together. Greater sizes are also
available with continuous sewing where a substrate is fed from a
roll of substrate.
[0051] As shown in FIG. 1, the resistance heating element 10
includes a resistance wire 12 disposed in a helical pattern or
circuit path 18. The ends of the resistance wire 12 are generally
riveted, grommeted, brazed, clinched, compression fitted or welded
to a pair of electrical connectors 15 and 16. One circuit path is
illustrated in FIGS. 1 and 2. The circuit includes a resistance
heating material, which is ideally a resistance heating wire 12
wound into a serpentine path containing about 3-200 windings, or, a
resistance heating material, such as ribbon, a foil or printed
circuit, or powdered conducting or semi-conducting metals,
polymers, graphite, or carbon, or a conductive coating or ink. More
preferably the resistance heating wire 12 includes a Ni--Cr alloy,
although certain copper, steel, and stainless-steel alloys could be
suitable. A positive temperature coefficient wire ("PTC"), which is
self-regulating, may also be suitable. The resistance heating wire
12 can be provided in separate parallel paths, or in separate
layers. Whatever material is selected, it should be electrically
conductive, and heat resistant.
Substrates
[0052] As used herein, the term "supporting substrate" refers to
the base material on which the resistance material, such as wires,
are applied. The supporting substrate 11 of this invention should
be capable of being pierced, penetrated, or surrounded, by a sewing
needle for permitting the sewing operation. Other than this
mechanical limitation, the substrates of this invention can take on
many shapes and sizes. Flat flexible substrates are preferably used
for attaching an electrical resistance wire with a thread.
Non-plastic materials, such as glasses, semiconductive materials,
and metals, can be employed so long as they have a piercable
cross-sectional thickness, e.g., less than 10-20 mil, or a high
degree of porosity or openings therethrough, such as a grid, scrim,
woven or nonwoven fabric, for permitting the sewing needle of this
invention to form an adequate stitch. The supporting substrate 11
of this invention need not necessarily contribute to the mechanical
properties of the final heating element, but may contain high
strength fibers. Such fibers could contain carbon, glass, aramid
fibers melt-bonded or joined with an adhesive to form a woven or
non-woven mat. Alternatively, the supporting substrate 11 of this
invention may contain ordinary, natural, or synthetic fibers, such
as cotton, wool, silk, rayon, nylon, polyester, polypropylene,
polyethylene, etc. The supporting substrate may also comprise a
synthetic fiber such as Kevlar or carbon fibers that have good
thermal uniformity and strength. The advantage of using ordinary
textile fibers, is that they are available in many thicknesses and
textures and can provide an infinite variety of chemistry, porosity
and melt-bonding ability. The fibers of this invention, whether
they be plastic, natural, ceramic or metal, can be woven, or
spun-bonded to produce non-woven textile fabrics.
[0053] Specific examples of supporting substrates 11 useful in this
invention include non-woven fiberglass mats bonded with an adhesive
or sizing material such as model 8440 glass mat available from
Johns Manville, Inc. Additional substrates can include polymer
impregnated fabric organic fabric weaves, such as those containing
nylon, rayon, or hemp etc., porous mica-filled plate or sheet, and
thermoplastic sheet film material. In one embodiment, the
supporting substrate 11 contains a polymeric resin which is also
used in either the first thermoplastic sheet 110 or second
thermoplastic sheet 105, or both of a heated element assembly 100
described below. Such a resin can be provided in woven or non-woven
fibrous form, or in thin sheet material having a thickness of 20
mil. or less. Thermoplastic materials can be used for the
supporting substrate 11 which will melt-bond or liquefy with the
thermoplastic sheets 110, 105, so as to blend into a substantially
uniform structure.
Sewing Operation
[0054] With reference to FIG. 3, the preferred programmable sewing
machine 20 will now be described. The preferred programmable sewing
machine is one of a number of powerful embroidery design systems
that use advanced technology to guide an element designer through
design creation, set-up and manufacturing. The preferred
programmable sewing machine 20 is linked with a computer 22, such
as a personal computer or server, adapted to activate the sewing
operations. The computer 22 preferably contains or has access to,
embroidery or CAD software for creating thread paths, borders,
stitch effects, etc.
[0055] The programmable sewing machine 20 includes a series of
bobbins for loading thread and resistance heating wire or fine
resistance heating ribbon. Desirably, the bobbins are prewound to
control tension since tension, without excessive slack, in both the
top and bottom bobbins is very important to the successful
capturing of resistance heating wire on a substrate. The thread
used should be of a size recommended for the preferred programmable
sewing machine. It must have consistent thickness since thread
breakage is a common mode of failure in using programmable sewing
machines. An industrial quality nylon, polyester or rayon thread is
highly desirable. Also, a high heat resistant thread may be used,
such as a Kevlar thread or Nomex thread known to be stable up to
500.degree. F. and available from Saunders Thread Co. of Gastonia,
N.C.
[0056] The programmable sewing machine of this invention preferably
has up to 6-20 heads and can measure 6 foot in width by 19 feet
long. The sewing range of each head is about 10.6 inches by 26
inches, and with every other head shut off, the sewing range is
about 21 inches by 26 inches. A desirable programmable sewing
machine is the Tajima Model No. TMLG116-627W (LT Version) from
Tajima, Inc., Japan.
[0057] The preferred method of capturing a resistance heating wire
12 onto a supporting substrate 11 in this invention will now be
described. First, an operator selects a proper resistive element
material, for example, Ni--Cr wire, in its proper form. Next, a
proper supporting substrate 11, such as 8440 glass mat, is provided
in a form suitable for sewing. The design for the element is
preprogrammed into the computer 22 prior to initiating operation of
the programmable sewing machine 20. As with any ordinary sewing
machine, the programmable sewing machine 20 of this invention
contains at least two threads, one thread is directed through the
top surface of the supporting substrate, and the other is directed
from below. The two threads are intertwined or knotted, ideally
somewhere in the thickness of the supporting substrate 11, so that
one cannot view the knot when looking at the stitch and the
resulting resistance heating element 10. As the top needle
penetrates the substrate 11 and picks up a loop of thread
mechanically with the aid of the mechanical device underneath, it
then pulls it upward toward the center of the substrate 11 and if
the substrate is consistent and the thread tension is consistent,
the knots will be relatively hidden. In a preferred embodiment of
this invention, the resistance heating wire 12 is provided from a
bobbin in tension. The preferred programmable sewing machine 20 of
this invention provides a third thread bobbin for the electrical
resistance wire 12 so that the programmable sewing machine 20 can
lay the resistance wire 12 down just in front of the top needle.
The preferred operation of this invention provides a zig zag or
cross stitch, as shown in FIG. 1A, whereby the top needle
crisscrosses back and forth as the supporting substrate 11 is
moved, similar to the way an ornamental rope is joined to a fabric
in an embroidery operation. A simple looping stitch with a thread
14 is also shown. Sewing by guiding the top needle over either side
of the resistance heating wire 12 captures it in a very effective
manner and the process is all computer controlled so that the
pattern can be electronically downloaded into the computer 22 and
automatically sewn onto the substrate of choice.
[0058] The programmable sewing machine 20 can sew an electrical
resistance wire 12, 5 mil-0.25 inch in diameter or thickness, onto
a supporting substrate 11 at a rate of about 10-500 stitches per
minute, saving valuable time and associated cost in making
resistance heating elements.
[0059] The ability to mechanically attach resistive elements, such
as wires, films and ribbons, to substrates opens up a multitude of
design possibilities in both shape and material selection.
Designers may mix and match substrate materials by selecting their
porosity, thickness, density and contoured shape with selected
resistance heating materials ranging in cross-section from very
small diameters of about 5 mil to rectangular and irregular shapes,
to thin films. Also, secondary devices such as circuits, including
microprocessors, fiberoptic fibers or optoelectronic devices,
(LEDs, lasers) microwave devices (power amplifiers, radar) and
antenna, high temperature sensors, power supply devices (power
transmission, motor controls) and memory chips, could be added for
controlling temperature, visual inspection of environments,
communications, and recording temperature cycles, for example. The
overall thickness of the resistance heating element is merely
limited by the vertical maximum position of the needle end, less
the wire feed, which is presently about 0.5 inches, but may be
designed in the future to be as great as 1 inch or more. Resistive
element width is not nearly so limited, since the transverse motion
of the needle can range up to a foot or more.
[0060] The use of known embroidery machinery in the fabrication of
resistance heating elements allows for a wide variety of raw
materials and substrates to be combined with various resistance
heating materials. The above construction techniques and sewing
operation also provide the ability to manufacture multi-layered
substrates, including embedded metallic and thermally conductive
layers with resistance wires wrapped in an electrically insulating
coating, so as to avoid shorting of electric current. This permits
the application of a resistance heating wire to both sides of the
thermally conductive metallic layer, such as aluminum foil, for
more homogeneously distributing resistance heat.
Thermoplastic Laminate Heated Element Construction
[0061] FIG. 4 is a top plan view of a heated element assembly 100
according to the present invention. The heated element assembly 100
includes a first thermoplastic sheet 110 and a second thermoplastic
sheet 105 laminated to the first thermoplastic sheet 110. For
illustrative purposes, second thermoplastic sheets 105 is shown
partially removed from first thermoplastic sheet 110. A resistance
heating element 10, described above, is laminated between and to
the first and second thermoplastic sheets 110, 105 such that the
thermoplastic sheets 110, 105 substantially encompass the circuit
path 18, which includes resistance wire 12.
[0062] The supporting substrate of the resistance heating element
10 is preferably not thicker than 0.05 inch, and more preferably
0.025 inch. The supporting substrate should be flexible, either
under ambient conditions or under heat or mechanical stress, or
both. A thin semi-rigid heated element assembly 100 allows for
closer proximity of the resistance heating wire 12 to an object to
be heated when the heated element assembly is formed into a final
element assembly, such as a combination containment bag and heater.
Thin element assemblies according to the present invention provide
the flexibility to choose materials with lower RTI (Relative
Thermal Index) ratings because less heat needs to be generated by
the resistance heating element 10 to provide heat to the outer
surfaces of the heating element assembly 100.
[0063] The thermoplastic sheets 110, 105 are laminiated to each
other to secure resistance heating element 10 and to form a
reformable continuous element structure. The thermoplastic sheets
110, 105 may be heated and compressed under sufficient pressure to
effectively fuse the thermoplastic sheets together. A portion of
this heat may come from energizing the resistance heating element
10. Alternatively, a resistance heating element 10 may be placed
within a bag-shaped thermoplastic body (not shown) where the top
layer of the bag may be considered a thermoplastic sheet and the
bottom layer of the bag may be considered a thermoplastic sheet
(e.g., two thermoplastic sheets secured along mating edges, but
providing an opening for insertion of the resistance heating
element 10). Air from within the bag may be evacuated, e.g., by
pulling a vacuum, thereby collapsing the bag around the resistance
heating element 10, and then heat and/or pressure may be applied to
the collapsed structure to create a single heated element assembly
100. Also, heated element assembly 100 may be formed by extruding a
tubular shaped thermoplastic body 107 (FIGS. 7a and 7b), disposing
a resistance heating element 10 within the thermoplastic body 107,
and heating and compressing the body 107, particularly along edges
108, to secure the heating element 10 within the thermoplastic
body. Regardless of the initial form the thermoplastic sheets take,
thermoplastic sheets are preferably laminated such that a flexible
continuous element structure is created, including a resistance
heating element 10 and preferably with little air trapped between
the thermoplastic sheets.
[0064] Preferred thermoplastic materials include, for example:
fluorocarbons, polypropylene, polycarbonate, polyetherimide,
polyvinylidine fluoride, polyether sulphone, polyaryl-sulphones,
polyimides, and polyetheretherkeytones, polyphenylene sulfides,
polyether sulphones, and mixtures and co-polymers of these
thermoplastics. It is further understood that, although
thermoplastic plastics are most desirable for fusible layers
because they are generally heat-flowable, some thermoplastics,
notably polytetraflouroethylene (PTFE) and ultra
high-molecular-weight polyethylene (UHMWPE) do not flow under heat
alone. Also, many thermoplastics are capable of flowing without
heat, under mechanical pressure only.
[0065] Good results were found when forming a heated element
assembly under the conditions indicated in TABLE 1 as follows:
1TABLE THICKNESS OF SHEET PRESSURE TIME TEMP. MATERIAL (mil) (PSI)
(minutes) (.degree. F.) Polypropylene 9 22 10 350 Polycarbonate 9
22 10 380 Polysulfone 19 22 15 420 Polyetherimide 9 44 10 430
Polyethersulfone 9 44 10 460 where no vacuum was pulled,
"thickness" is the thickness of the thermoplastic sheets in mils (1
mil = .025 mm = .001 inch), "pressure" represents the amount of
pressure applied to the assembly during lamination, "temperature"
is the temperature applied during lamination, and "time" is the
length of time that the pressure and heat were applied.
[0066] The first and second thermoplastic sheets 110, 105 and
resistance heating element 10 of the heated element assembly 100
may also be laminated to each other using an adhesive. In one
embodiment of the present invention, an ultraviolet curable
adhesive may be disposed between the resistance heating element 10
and the first thermoplastic sheet 110 and between the resistance
heating element 10 and the second thermoplastic sheet 105, as well
as between areas of the thermoplastic sheets 110, 105 which are
aligned to be in direct contact. An ultraviolet curable adhesive
may be used that is activated by ultraviolet light and then begins
to gradually cure. In this embodiment of the present invention, the
adhesive may be activated by exposing it to ultraviolet light
before providing the second of the thermoplastic sheets 110, 105.
The thermoplastic sheets 110, 105 may then be compressed to
substantially remove any air from between the sheets 110, 105 and
to secure resistance heating element 10 between the thermoplastic
sheets 110, 105.
[0067] FIG. 6 illustrates that a heated element assembly 100a
according to the present invention may include a plurality of
heated layers. A second resistance heating element 10a may be
laminated between and to thermoplastic sheet 110 and a third
thermoplastic sheet 115.
[0068] The thicknesses of thermoplastic sheets 110, 105 and the
thickness of supporting substrate 11 and resistance heating
material 12 are preferably selected to form a reformable continuous
element structure that maintains its integrity when the element is
formed into a final element structure. The heated element assembly
100 according to the present invention, then, is a semi-rigid
structure in that it may be reformed, such as by simply folding or
folding under heat, pressure, or a combination thereof as required
by the chosen thermoplastics, into a desired shape without
sacrificing the integrity of the structure.
[0069] Similarly, one or both of the thermoplastic sheets of a
heated element assembly 100 or heated element assembly 500 may be
coated with a thermally conductive coating that promotes a uniform
heat plane on the heated element assembly. An example of such a
coating may be found on anti-static bags or Electrostatic
Interference (ESI) resistive bags used to package and protect
semiconductor chips. Also, thermally conductive, but preferably not
electrically conductive, additive may be added to the thermoplastic
sheets to promote heat distribution. Examples of such additive may
be ceramic powders, such as, for example, Al.sub.2O.sub.3, MgO,
ZrO.sub.2, boron nitride, silicon nitride, Y.sub.2O.sub.3, SiC,
SiO.sub.2, TiO.sub.2, etc. A thermally conductive layer and/or
additive is useful because a resistance wire typically does not
cover all of the surface area of a resistance heating element
10.
Wound and Thermoformed Element Construction
[0070] For purposes of this description, figures are not drawn to
scale. FIGS. 8-10 illustrate an exemplary heating element 400 for
heating a flexible intravenous tube. The heating element 400
includes a resistance heating wire 402, or plurality of resistance
heating wires 402 (as shown in FIG. 16A), encapsulated within an
electrically insulating polymeric layer 404. The polymeric layer
404 and resistance heating wire 402 are formed into a plurality of
turns 408 defining a coil having a central axis 410.
[0071] The terminal ends 406 of the resistance heating wire 402 may
be coupled to a pair of electrical connectors (not shown) using
known techniques such as riveting, grommeting, brazing, clinching,
compression fitting, or welding. The electrical connectors may then
be coupled to a power source.
[0072] The electrically insulating polymeric layer 404 may comprise
a thermoplastic, thermoplastic elastomer or thermosetting material
as long as each turn 408 is independently elastically expandable
along axes of elastic expansion 412, 414 to surround a portion of
an intravenous tube (not shown) when the intravenous tube is
disposed axially through the coil along central axis 410. The coil
conforms to the shape of the flexible intravenous tube, as shown in
FIG. 18, and may be bent, coiled or otherwise manipulated along
with flexible intravenous tube 700 during the normal use of the
flexible intravenous tube 700.
[0073] Preferred thermoplastic materials are described above in
connection with assembly 100. Some preferred thermosetting polymers
include epoxies, phenolics, and silicones. Preferred thermoplastic
elastomers include the Advanced Polymer Alloys ALCRYN series of
products, particularly ALCRYN No. 4080.
[0074] The resistance heating wire 402 may be surrounded by the
polymeric layer 404 in several ways. Polymeric layer 404 may be
provided as a tubular sheath, and the resistance heating wire 402
may be fed axially through the tubular sheath. Alternatively, the
polymeric layer 404 may be extruded over the resistance heating
wire(s) 402. If the polymeric layer 404 is extruded over the
resistance heating wire 402, polymeric layer 404 may need to be
partially stripped from the ends of heating element 400 to expose
the terminal ends 406 of the resistance heating wire 402. In one
embodiment of an exemplary heating element 400, a ground conductor
such as a copper wire or mesh may be wrapped around the polymeric
layer 404, and a second polymeric layer can surround the ground
conductor to provide a grounded heating element.
[0075] An exemplary electrically insulating polymeric layer 404
includes a PTFE film having a thickness of approximately
0.008-0.010" extruded around resistance heating wire 402 or a
polypropylene tube of the same thickness surrounding the resistance
heating wire 402. An exemplary resistance heating wire 402
comprises a Nichrome (80Ni-20Cr) wire or other alloy used in
resistive heating.
[0076] Once the resistance heating wire 402 is encapsulated within
the polymeric layer 404, the polymeric layer 404 and resistance
heating wire 402 may be formed into a plurality of turns 408 by
wrapping the polymeric layer 404 and resistance heating wire 402
around a mandrel (not shown) to form the coil shape shown in FIG.
8. The wrapping step may be accomplished manually or as a part of a
continuous, automated process. The polymeric layer 404 and the
resistance heating wire 402 are heated and then cooled to maintain
the coil shape formed by wrapping the polymeric layer 404 and
resistance heating wire 402 around the mandrel. In this
thermoforming process, the polymeric layer 404 and resistance
heating wire may be heated prior to being wrapped around the
mandrel, or the mandrel may provide the heat source. Cooling the
polymeric layer and resistance heating wire may occur passively,
i.e., by air cooling or through contact with the mandrel if the
mandrel does not supply the heat source, or the cooling step may
occur within an active cooling stage, e.g., within a cold water
circulation stage.
[0077] Regardless of the heating and cooling sources, the polymeric
layer 404 and resistance heating wire 402 are formed into a
plurality of turns 408 defining a coil having a central axis 410,
as shown in FIG. 8. The diameter of the mandrel is preferably the
same size as or smaller than the outer diameter of the preferred
flexible intravenous tube that is to be heated by the heating
element 400. It should be apparent that the interior diameter,
designated D, of the coil is substantially the same as the diameter
of the mandrel. In this manner, the heating element 400 is capable
of securing itself around a flexible intravenous tube having the
same or larger diameter as the heating element 400 when the
flexible intravenous tube is disposed axially through the heating
element 400. Because each turn 408 is independently elastically
expandable, each turn 408 locally secures itself to a portion of
the intravenous tube 700, thereby allowing the coil as a whole to
substantially conform to the shape of the intravenous tube 700.
Further, because the heating element 400 is thermoformed into the
coil shape, the heating element 400 does not rely upon the
resistance heating wire 402 to provide structural stability to the
heating element 400 or to maintain the coiled shape.
[0078] In one exemplary embodiment, the heating element 400 may
include a plurality of sets of interconnected parallel turns. For
example, as shown in the partial, side elevational view of the
heating element shown in FIG. 16, a first length of the polymeric
layer 404 and resistance heating wire 402 preferably comprises
approximately half of the total length of the polymeric layer 404
and resistance heating wire 402. This first length may be wrapped
around a mandrel to form a first set of turns 408a that terminates
at a first terminal end 406a. The remaining length of polymeric
layer 404 and resistance heating wire 402 shares a common
origination point with the first length. This length of polymeric
layer 404 and resistance heating wire 402 may then be wrapped
around the mandrel to form a second set of turns 408b that is
interconnected with and parallels the first set of turns 408a while
terminating at a second one of the terminal ends 406b. An even
number of sets of turns provides the advantage of terminal ends 406
that are close in proximity, thereby simplifying coupling the
terminal ends 406 to a power source (not shown).
[0079] Referring to the enlarged, cross-sectional view of FIG. 15A,
a heating element 400 may include a plurality of resistance heating
wires 402. A heating element 400 of a desired length, e.g., the
length of the flexible intravenous tube to be heated, may be
separated from an extended length of heating element 400, and the
ends 406 of the heating element may be stripped to expose the
terminal ends of the resistance heating wires 402. These terminal
ends may then be connected in series or in parallel depending upon
the desired heat characteristics for the heating element 400. The
wires 402 may be connected by twisting the wires, soldering the
wires, or by other coupling techniques known to those familiar with
manufacturing resistance heating elements.
[0080] FIG. 11 is a partial, side elevational view of another
exemplary expandable heating element 500. The heating element 500
includes a resistance heating material surrounded by an
electrically insulating polymeric layer. The resistance heating
material may be a resistance heating wire 504, as shown in FIGS.
11, 13, 13A and 14, but other forms of resistance heating materials
may be utilized, such as those described above in connection with
assembly 100. The resistance heating material may also be attached
to a supporting substrate, such as the 8440 glass mat via a sewing
operation as described above. The circuit path formed by the
resistance heating material may be grounded or ungrounded as the
application requires.
[0081] Still further, the resistance heating material may comprise
a woven or non-woven fibrous structure, with or without a
supporting substrate, including conductive fibers or fibers coated
with a conductive material such as graphite or carbon. The
resistance heating layer may also comprise a conductive polymeric
resistance heating layer comprising a polymeric layer having
conductive additives, such as graphite or carbon fibers or fibers
coated with a conductive material, that permit electricity to
conduct across or through the film and generates heat when
energized. Exemplary fibrous and polymeric resistance heating
layers are described in U.S. patent application Ser. No.
[D1349-00068] to Ted Von Arx, et al., entitled "Packaging having
self-contained heater," filed on Feb. 12, 2001, the entirety of
which is hereby incorporated herein by reference.
[0082] The resistance heating material is surrounded by an
electrically insulating polymeric layer preferably by laminating
the resistance heating material between two sheets 512a, 512bof an
electrically insulating polymeric material to form a planar element
550. Alternatively, the polymeric layer may comprise a film
extruded over the resistance heating material. The polymeric layer
may comprise a thermoplastic or thermoset material as described
above in connection with polymeric layer 404. In any case, an
exemplary expandable heating element 500 has a thickness "T," shown
in FIGS. 10 and 12, ranging from 0.010-0.250'. The appropriate
thickness is dictated in part by the RTI rating of the polymeric
material and the voltage source. The sheets 512a, 512b may be
configured such that they have different thermal characteristics.
For example, a sheet 512a or 512b which is oriented to be in
contact with the tube to be heated may be thinner than the other
sheet and/or include thermally conductive additives in order to
effectively bias generated heat toward the tube and away from the
environment surrounding the tube. If a polymeric layer is extruded
over the resistance heating material, the resistance heating
material may be disposed off-center such that it is closer to a
surface that contacts a tube that is to be heated.
[0083] The resistance heating material may comprise a plurality of
resistance heating wires 504 as shown in FIG. 15B. The resistance
heating wires 504 and polymeric layer may be formed into continuous
sheets that may be used to form the expandable heating element 500.
The terminal ends 502 of the wires 504 may be exposed and coupled
as desired, e.g., in series or in parallel. A pair of cold pins may
also be affixed to the terminal ends, the cold pins may then be
coupled to an appropriate power supply.
[0084] FIGS. 11, 13, 13A and 14 show a single resistance heating
wire 504 secured between two polymeric sheets 512a, 512b. The
resistance heating wire 504 is shown oriented in a simple "u"
shaped circuit path, but it should be apparent that the wire 504
may taken on any number of circuit paths, such as a zig-zag or
serpentine pattern, in order to occupy more surface area of the
final expandable heating element 500.
[0085] Once the resistance heating material is surrounded by the
electrically insulating polymeric layer, the polymeric layer and
resistance heating material may be formed into a plurality of turns
510 defining a coil having an original diameter, designated as "X,"
and a central axis 514. The electrically insulating polymeric layer
and resistance heating material of the expandible heating element
500 may be formed into the plurality of turns 510 by wrapping the
polymeric layer and resistance heating material around a mandrel
and thermoforming the polymeric layer and resistance heating
material into the coil shape of FIG. 9 by heating and then cooling
the polymeric layer and resistance heating material as described
above.
[0086] Turns 510 are each independently elastically expandable
along axes of elastic expansion 506, 508 to diameters greater than
the original diameter X of the expandable heating element 500 when
a cylindrical body having diameter greater than the original
diameter X is disposed axially along central axis 514. The heating
element 500, therefore, is particularly adapted to heat cylindrical
or tubular bodies, such as pipes and dispensing tubes used in the
food and medical industries or fuel lines in the automotive
industry, to name a few. Also, because each turn 510 is
independently elastically expandable, the heating element 500 may
be used to heat irregularly shaped articles, such as pipes having
diameters that vary along a central axis, pipes that are bent at
angles, and the like. Further, an individual heating element 500
formed on a single mandrel may be used to heat a plurality of pipes
each having different outer diameters.
[0087] FIG. 17 is a perspective view of a pipe 600 disposed axially
along the central axis 514 of a heating element 500. The pipe 600
has an outer diameter "Y" that is greater than the original
diameter X of the expandable heating element 500. Each turn 510 is
shown independently expanded to surround a different portion of the
pipe 600. A heating element 500 is preferably used to heat pipes
having diameters ranging from the original diameter X of the
heating element 500 to approximately three times the original
diameter X. The heating element 500, however, may be used to heat
objects having diameters even greater than three times the original
diameter X, but it should be understood that when a cylindrical
object is disposed axially through the heating element along the
central axis 514, the heating element 500 at least partially
uncoils to accommodate the larger diameter of the object, and the
distance, designated A, separating adjacent turns 510 on each side
of the object increases. This increase in turn separation distance
A increases the amount of surface area of the object that is not in
direct contact with the heating element 500 and, therefore, that is
not directly heated by the turns 510 of the heating element 500. It
should also be apparent that the length of the heating element 500
decreases as each turn expands to surround an object. This increase
in separation distance A and decrease in element length can be
accommodated through selection of an appropriate original diameter
X and heating element length.
[0088] FIG. 19 is a cross-sectional view of another planar element
structure 550b which may be formed into an expandable heating
element. If the electrically insulating polymeric layer include
thermoplastic elastomer materials, such as thermoplastic elastomer
layers 810, 812, one or both of the thermoplastic elastomer layers
810, 812 may further include a reinforcing substrate layer 804,
806. An exemplary reinforcing substrate layer includes an 8440
glass mat as described above fused with the thermoplastic elastomer
layers 810, 812, such as during lamination. Because thermoplastic
elastomer materials tend to stress relieve more easily than other
exemplary thermoplastic materials, the reinforcing substrate which
bonds with the thermoplastic elastomer layer provides additional
mechanical rigidity. This added rigidity enables the expandable
heating element to better secure itself to a tube or pipe when it
is expanded or uncoiled to surround the tube or pipe. As described
above, the resistance heating material may include a resistance
heating wire 802 sewn to a supporting substrate 808.
[0089] Although various embodiments have been illustrated, this was
for the purpose of describing, but not limiting the invention.
Various modifications which will become apparent to one skilled in
the art, are within the scope of this invention described in the
attached claims.
* * * * *