Technical Field
[0001] The invention relates to the field of electrical heating cables that comprise metal
filaments that act as heat generators when electrical current is sent through the
cable.
Background Art
[0002] Electrical heating cables comprising metal filaments are known. Important parameter
for the heating cable is its electrical resistance in ohm/meter length of the cable,
as it determines heat generation. Depending on the application, specific values for
the electrical resistance in ohm/meter length of the cable are required.
[0003] For a number of applications, e.g. for car seat heating applications, the flex fatigue
resistance (or flex life) of the heating cable is important. A number of patent documents
relate to heating cables with high flex fatigue, e.g. realized by means of appropriate
selection of the metal filaments used in the heating cable.
[0004] EP1337129 discloses an electrical heating element for heating units of seats and steering wheels.
The heating element comprises at least one conductor having at least one core-coated
wire. The coating comprises steel and the core comprises copper or a copper alloy,
or the coating comprises copper or a copper alloy and the core comprises steel.
[0005] Hybrid electrical heating cables comprising a number of metal filaments of different
types are known as well.
[0006] EP1705957 discloses a heating cable for car seat heating applications that has high flex fatigue
properties. The heating cable has outer strands wound around an inner strand that
is electrically conductive. The specific conductivity of the inner strand is smaller
than the specific conductivity of the outer strands. The inner strand is made of a
material having high tensile strength and/or high alternating bending strength than
a material from which the outer strands are made. The inner strands can e.g. be made
out of stainless steel filaments and the outer strands out of copper filaments.
[0007] DE10137976A1 discloses a heating cable for car seat heating. The heating cable comprises a combination
of several types of individual wires braided together. The individual types of the
individual wires have different electrical properties for setting desired electrical
characteristics of the heating cable. At least some of the types of individual wires
differ in terms of specific electrical resistance. The combination of copper (or copper
alloy) wires and aluminium (or aluminium alloy) wires is specifically favoured.
[0008] WO2012/136418A1 (and its corresponding US publication
US2014/0008351A1) discloses a heating cable comprising between seven and two hundred metallic monofilaments
of a first type. The metallic monofilaments of a first type have a diameter ranging
from 30 µm to 100 µm. The metallic monofilaments of a first type have a substantially
round cross section. The metallic monofilaments of a first type comprise a steel layer
with a chromium content of less than 10% by weight. The heating cable has an electrical
resistance ranging between 0.1 Ohm/m and 20 Ohm/m when measured at 20°C. A preferred
heating cable comprises a metallic monofilament of a second type or one or more bundles
of metallic monofilaments of a second type; wherein the second type differs in composition
from the first type.
[0009] DE19638372 discloses a lead wire for a sensor having a conductor unit including at least stainless
steel wires and copper wires. By setting the cross-sectional percentage of the stainless
steel wires in the conductor unit within the range of 30 to 70 percent, it is possible
to obtain a lead wire having low electrical resistance, and high flexibility, tensile
strength and elasticity.
[0010] The use of copper wires or copper filaments for heating wires is not always recommended,
as copper has a too high conductivity, leading to a high conductivity of the heating
cable. Therefore, when heating cables are required of lower conductivity, the use
of copper wires or copper filaments is not recommended. Copper wires and copper filaments
have low flex fatigue properties.
[0011] Electrical heating cables can be connected by means of crimp connectors. Such a crimp
connector can be used to connect the heating cable to another cable, e.g. the cable
supplying the electrical current. Such a crimped connection of a heating cable and
a supply cable is e.g. described in
DE202004018709U1 and in
US3324441.
[0012] Alternatively, the heating cable can be crimped alone in the crimp connector and
the electrical connection is realized e.g. by means of a plug or pin of the crimp
connector.
[0013] It is a problem that for a range of electrical heating cables that have a high flex
life, mechanical crimp connections - especially when the heating cable is crimped
alone in the crimp connector - cannot be decently nor reliably made.
Disclosure of Invention
[0014] The primary object of the invention is to provide a heating cable that has excellent
flex fatigue properties and that can be easily and reliably connected by means of
a mechanical crimp connection.
[0015] It is a specific objective to provide such a heating cable in the resistance range
of 0.1 - 5 Ohm/meter.
[0016] According to a first aspect of the invention an electrical heating cable is provided.
The electrical heating cable comprises two or more strands of metal filaments twisted
or cabled together. At least one, preferably at least two, and more preferably each
of the strands, comprises a first set of metal filaments and a second set of metal
filaments, both sets of metal filaments for conducting electrical current and generating
heat when the heating cable is in use. The metal filaments of the first set of metal
filaments comprise a steel layer. The metal filaments of the second set comprise a
steel layer. The metal filaments of the second set have an annealed microstructure,
involving that the steel layer of the metal filaments of the second set has an annealed
microstructure. The metal filaments of the first set have an end-drawn microstructure.
A strand is defined as a combination of filaments that are parallel to each and/or
are twisted together, whereby untwisting of the strand results in parallel filaments.
[0017] The first set of metal filaments and the second set of metal filaments will conduct
electricity and contribute to the heat generation when the heating cable is in use.
[0018] The heating cable of the invention has excellent flex fatigue resistance. It can
be crimped easily and reliably, with all metal filaments being properly crimped. This
is a consequence of the presence of the metal filaments of the second set that have
an annealed microstructure. The metal filaments of the second set are compressed during
crimping, ensuring good electrical contact between the metal filaments of the crimped
connection. Quality control of the crimp connections shows that a proper crimp connection
is made. An additional benefit is that the contact resistance of the crimped connection
is lower, certainly compared to similar crimp connections of other prior art heating
cables with high flex fatigue. A low contact resistance is beneficial as it avoids
overheating of the crimp connection due to heat generation at the crimp connector
when the electrical heating cable is in use.
[0019] The combination of metal filaments of two different types in one strand puts an additional
burden to the production of the strands. When combining the strand (e.g. when feeding
the different filaments together when twisting the filaments or before twisting a
strand) metal filaments of two different types have to be provided, e.g. unwound from
their respective spools, kept under appropriate tension and processed. Such processing
is more difficult - due to their differing mechanical properties - compared to the
processing of only one type of metal filaments.
[0020] Preferably, the specific electrical resistance of the metal filaments of the second
set is higher than the specific electrical resistance of the metal filaments of the
first set.
[0021] In a preferred embodiment, the equivalent diameter of the metal filaments of the
first set differs at maximum 20%, preferably at maximum 10%, and more preferably at
maximum 5%, from the equivalent diameter of the metal filaments of the second set.
The equivalent diameter is the diameter of a circle with the same surface area as
the cross section of the metal filament which is not necessarily round.
[0022] Preferably, the filaments of the first set of metal filaments and the filaments of
the second set of metal filaments are combined in the strand via twisting, wrapping,
or cabling.
[0023] In a preferred embodiment, the first set of filaments comprises between 5 and 150
filaments. More preferably more than 5, e.g. more than 10, e.g. more than 20, e.g.
more than 30, e.g. more than 50, e.g. more than 70, e.g. more than 90, e.g. more than
100. More preferably less than 150, e.g. less than 125, e.g. less than 100, e.g. less
than 80, e.g. less than 65, e.g. less than 50.
[0024] A preferred hybrid electrical heating cable has an electrical resistance in the range
of 0.1 - 5 Ohm/m, more preferably in the range of 0.1 - 3 Ohm/m.
[0025] Preferred for the filaments of the first set of metal filaments and/or for the filaments
of the second set of metal filaments are filament diameters between 35 µm and 100
µm, more preferably between 50 µm and 80 µm.
[0026] The heating cable can have a corrosion resistant sheath. The corrosion resistant
sheath can comprise a polymer layer. Preferred polymer layers comprise fluorine in
the polymer, resulting in superior corrosion resistance and high temperature resistance.
Further preferred, the corrosion resistant sheath of the heating cable comprises perfluoroalcoxy
(PFA), FEP (fluorinated ethylene propylene), TPE-C, PPS (polyphenylene sulfide) or
MFA (perfluoromethylalcoxy). The heating cable of such embodiments does - contrary
to heating cables made from hard drawn filaments only and having such a corrosion
resistant sheath - not show flaring after stripping of insulation coatings, facilitating
crimping of the heating cable.
[0027] In a preferred embodiment, the metal filaments of the first set of metal filaments
and the metal filaments of the second set of metal filaments are intermingled. With
the metal filaments of the first set and the metal filaments of the second set are
intermingled is meant that the metal filaments of the first set of metal filaments
are distributed in the strand in between metal filaments of the second set of metal
filaments, and the metal filaments of the second set of metal filaments are distributed
in the strand in between metal filaments of the first set of metal filaments.
[0028] The metal filaments of the first set of metal filaments have an end-drawn microstructure.
This has shown to provide excellent crimping in a crimp connector.
[0029] Preferably, in the cross section of the heating cable, the cumulated cross sections
of metal filaments of the second set is at least 25%, more preferably at least 30%,
and even more preferably at least 40 % - and preferably less than 70% - of the combined
cumulated cross sections of metal filaments of the first and second set.
[0030] Preferably, the specific electrical resistance, expressed in ohm*mm
2/m, of the metal filaments of the second set is at least 2 times, and more preferably
at least 3 times, more preferably at least 3 times, and more preferably at least 10
times higher than the specific electrical resistance of the metal filaments of the
first set.
[0031] An exemplary metal filament out of high carbon steel with a coating layer out of
zinc has a specific electrical resistance of 0.202 ohm*mm
2/m.
[0032] An exemplary metal filament out of low carbon steel with a coating layer out of zinc
has a specific electrical resistance of 0.110 ohm*mm
2/m.
[0033] An exemplary metal filament out of low carbon steel with a coating layer out of tin
has a specific electrical resistance of 0.124 ohm*mm
2/m.
[0034] A stainless steel filament has a specific electrical resistance of 0.682 ohm*mm
2/m.
[0035] An exemplary metal filament comprising a low carbon steel core and a copper cladding
has a specific electrical resistance of 0.043 ohm*mm
2/m.
[0036] An exemplary metal filament comprising a copper core and a stainless steel cladding
has a specific electrical resistance of 0.046 ohm*mm
2/m.
[0037] Preferably, the electrical conductivity of the heating cable is for more than 75%,
preferably for more than 85%, determined by the electrical conductivity of the metal
filaments of the first set.
[0038] In exemplary embodiments, the steel layer of the metal filaments of the first set
of metal filaments is a low carbon or a high carbon steel layer, preferably comprising
a corrosion resistant metal layer (e.g. zinc or nickel) around the low carbon or high
carbon steel layer.
[0039] In exemplary embodiments, the metal filaments of the first set of metal filaments
comprise a layer of a metal or metal alloy of specific electrical conductivity higher
than the specific electrical conductivity of the steel layer of the metal filaments
of the first set of metal filaments. In such embodiments, preferably the steel layer
of the filaments of the first set of metal filaments is a stainless steel layer or
a low carbon steel layer.
[0040] Preferably, the layer of a metal or metal alloy of specific electrical conductivity
higher than the specific electrical conductivity of the steel layer is concentric
with the steel layer.
[0041] The layer of a metal or metal alloy of specific electrical conductivity higher than
the specific electrical conductivity of the steel layer can be a copper layer or a
copper alloy layer.
[0042] For example, the metal filaments of the first set of metal filaments can comprise
a copper or copper alloy core and a - preferably circumferential - stainless steel
layer around it. Preferably, such metal filaments have an end-drawn microstructure.
[0043] Another example of the metal filaments of the first set is metal filaments comprising
a steel core (e.g. a low carbon steel core) and a - preferably circumferential - layer
of copper or of a copper alloy around it. Such filaments are known as copper cladded
steel filaments. Preferably, these metal filaments have an end-drawn microstructure.
[0044] In a preferred embodiment, the metal filaments of the second set of metal filaments
are stainless steel filaments, e.g. with polygonal cross section shape, e.g. bundle
drawn, or e.g. with substantially circular cross section, e.g. single end drawn.
[0045] In exemplary embodiments, the steel layer of the metal filaments of the second set
of metal filaments is a low carbon or a high carbon steel layer, preferably comprising
a corrosion resistant metal layer around the low carbon or high carbon steel layer.
[0046] For the invention, with high carbon steel is meant a steel grade with carbon content
between 0.30 and 1.70% by weight and a chromium content of less than 10% by weight.
For the invention, preferably high carbon steel grades with carbon content between
0.40 and 0.95% by weight are used, even more preferably high carbon steel grades with
carbon content between 0.55% and 0.85% by weight. The high carbon steel grades can
contain alloy elements; but for the invention, the high carbon steel grades preferably
have a chromium content of less than 2.5% by weight and a nickel content of less than
1% by weight, preferably a nickel content of less than 0.1 % by weight, even more
preferably a nickel content of less than 0.05% by weight. And preferably a chromium
content of less than 1% by weight.
[0047] The use of a high carbon steel grade has a number of additional benefits. The strength
of metal filaments comprising a high carbon steel layer is high, especially if the
metal filament has an end-drawn microstructure. The result is that heating cables
comprising such filaments have a high strength and a high flex life.
[0048] For the invention, with low carbon is meant a steel alloy where - possibly with exception
for silicon and manganese - all the elements have a content of less than 0.50 % by
weight, e.g. less than 0.20 % by weight, e.g. less than 0.10 % by weight. E.g. silicon
is present in amounts of maximum 1.0 % by weight, e.g. maximum 0.50 % by weight, e.g.
0.30 % by weight or 0.15 % by weight. E.g. manganese is present in amounts of maximum
2.0 % by weight, e.g. maximum 1.0 % by weight, e.g. 0.50 % weight or 0.30 % by weight.
Preferably for the invention, the carbon content ranges up to 0.20 % by weight, e.g.
ranging up to 0.06 % by weight. The minimum carbon content can be about 0.02 % by
weight. In a more preferred embodiment, the minimum carbon content can be about 0.01
% by weight. The low carbon steel composition has mainly a ferrite or pearlite matrix
and is mainly single phase. There are no martensitic phases, bainite phases or cementite
phases in the ferrite or pearlite matrix.
[0049] For use in the first set or in the second set of metal filaments, low carbon or high
carbon filaments are preferably provided with a corrosion resistant coating layer.
The corrosion resistant coating layer can e.g. be selected from the group consisting
of zinc, tin, silver, nickel, aluminum, or an alloy thereof. Preferably, the corrosion
resistant metal coating is between 1 and 10 % by weight of the metal filament. More
preferably, between 2 and 6 % by weight. Even more preferably between 3 and 5 % by
weight. As the metal coating layer is low in weight percentage of the metal filament,
it is not affecting the electrical resistance of the filament to a significant extent.
The benefit of the metal corrosion resistant coating on the steel filament is that
the steel filaments are better resisting staining and corrosion. This is of interest
for the production process of the heating cable of the invention and for storage of
half-products during the production process, but also during installation and use
of the heating cable.
[0050] Specific examples are the use of a nickel coating on steel filaments; the coating
layer being between 2 and 6% by weight of the steel filament. More preferably the
nickel coating is between 3 and 5% by weight of the steel filament. Specific examples
for a nickel coating layer are on a steel filament comprising low carbon steel or
comprising high carbon steel.
[0051] Another specific example is use of a zinc coating on a steel filament; the coating
layer being between 0.5 and 5% by weight of the steel filament. More preferably the
zinc coating is between 1.5 and 2.5% by weight of the steel filament. Specific examples
for a zinc coating layer are on a steel filament comprising low carbon steel or comprising
high carbon steel.
[0052] Preferably the metal filaments of the second set of metal filaments have been produced
by means of single end drawing.
[0053] Examples of preferred combinations of first and second set of metal filaments are
- first set of metal filaments out of high carbon steel or out of low carbon steel;
preferably with an end-drawn microstructure; and preferably with a corrosion resistant
coating layer, e.g. out of zinc or nickel; in combination with a second set of metal
filaments out of stainless steel, with an annealed microstructure. Preferably the
stainless steel filaments of the second set of metal filaments are single end drawn.
- first set of metal filaments comprising a steel core (preferably a low carbon steel
core) and a copper or copper alloy cladding, the filaments preferably have an end-drawn
microstructure; in combination with a second set of metal filaments out of stainless
steel, with an annealed microstructure. Preferably the stainless steel filaments of
the second set of metal filaments are single end drawn.
- first set of metal filaments comprising a copper or copper alloy core and a stainless
steel cladding or layer, the filaments preferably have an end-drawn microstructure;
in combination with a second set of metal filaments out of stainless steel, with an
annealed microstructure. Preferably the stainless steel filaments of the second set
of metal filaments are single end drawn.
- first set of metal filaments comprising a steel core (preferably a low carbon steel
core) and a copper or copper alloy cladding or layer, the filaments preferably have
an end-drawn microstructure; in combination with a second set of metal filaments out
of high carbon or low carbon steel, with an annealed microstructure; and preferably
with a corrosion resistant coating layer, e.g. out of zinc or nickel.
- first set of metal filaments comprising a copper or copper alloy core and a stainless
steel cladding or layer, the filaments preferably have an end-drawn microstructure;
in combination with a second set of metal filaments out of high carbon or low carbon
steel; with an annealed microstructure; and preferably with a corrosion resistant
coating layer, e.g. out of zinc or nickel.
- first set of metal filaments out of low carbon steel with an end-drawn microstructure;
and preferably with a corrosion resistant coating layer, e.g. out of zinc or nickel;
in combination with a second set of metal filaments out of out of low carbon steel
with an annealed microstructure; and preferably with a corrosion resistant coating
layer, e.g. out of zinc or nickel.
- first set of stainless steel filaments with an end-drawn microstructure; in combination
with a second set stainless steel filaments with an annealed microstructure. The stainless
steel filaments of the first set can e.g. be single end drawn; the stainless steel
filaments of the second set can e.g. be single end drawn
[0054] A second aspect of the invention is an assembly of a hybrid electrical heating cable
as in the first aspect of the invention and a crimp connector, wherein the hybrid
electrical heating cable is crimped in the crimp connector.
[0055] In a preferred assembly, the crimp connector is connectable to an electrical power
supply without overlap of an end portion of the heating cable with an end portion
of an electrical power supply cable, preferably via an alternative connection than
a crimp connection, e.g. via a pin or plug connector.
[0056] A preferred assembly comprises an electrical power supply wherein the crimp connector
is connected to the electrical power supply without overlap of an end portion of the
heating cable with an end portion of an electrical power supply cable, preferably
via an alternative connection than a crimp connection, e.g. via a pin or plug connector.
[0057] A preferred assembly comprises an electrical power supply wherein the crimp connection
is connected to the electrical power supply with an overlap of an end portion of the
heating cable with an end portion of an electrical power supply cable in the crimp
connector. Such an electrical power supply cable can advantageously comprise copper
filaments.
[0058] Crimping can be performed in a way that two crimps take place simultaneously, the
cable crimp and (if an insulation is present) the insulation crimp. The wire crimp
forms the mechanical-electrical connection between the heating cable and the terminal
(crimp connector). For a lot of applications, the connection must be gastight, meaning
that there should be no voids between the filaments of the heating cable and the terminal
(crimp connector) as corrosion could occur through such voids.
[0059] It is possible to strip an insulating coating layer fully or partly before crimping.
[0060] Several types of crimps exist and can be used for the invention. Examples are B-crimp
and O-crimp, wherein the name of the crimp is derived from the shape of the crimp.
[0061] The hybrid heating cable of the invention can e.g. be used in car seat heating systems
and in industrial heating systems
Brief Description of Figures in the Drawings
[0062] Figure 1 shows an example of a heating cable according to the invention. Figures
2 and 3 show examples of crimp connections comprising a heating cable of the invention.
Mode(s) for Carrying Out the Invention
[0063] Figure 1 shows an example of a heating cable 105 according to the invention. A strand
110 of 7 metal filaments has been twisted in a first twisting operation. In a second
twisting operation, 10 of such twisted strands 110 have been twisted together into
a cable with an outer diameter of 1.60 mm. The cable is extrusion coated with a PFA
coating layer 120, e.g. with a wall thickness of 0.22 mm. The strand 110 of 7 metal
filaments comprises a first set of metal filaments, wherein the set consists out of
two metal filaments 130 that have a copper core (36 % by weight of the metal filament)
and a stainless steel layer (64 % by weight of the metal layer), e.g. AlSl 316L. Preferably
the stainless steel layer has a substantially constant thickness over the full circumference
of the metal filament.
[0064] The strand 110 of 7 metal filaments comprises a second set of metal filaments, wherein
the set consists out of five metal filaments 140 which are single end drawn stainless
steel filaments (e.g. AlSl 316L).
[0065] The metal filaments of the first set 130 and the metal filaments of the second set
140 each have a diameter of 75 µm. The metal filaments of the first set 130 and of
the second set 140 had been randomly distributed in the strand 110, resulting in an
intimate blend in the strand 110 (and in the heating cable 105) of the two sets of
metal filaments and a homogeneous distribution over the heating cable of the two sets
of metal filaments. The stainless steel filaments (the filaments of the second set)
have an annealed microstructure; and the metal filaments of the first set can have
an end-drawn microstructure.
[0066] The electrical resistance of the heating cable is 0.46 Ohm/meter.
[0067] After stripping the insulating coating, the heating cable was crimped in a B-crimp
connector and via a plug connected to a power supply. The heating cable could be reliably
crimped in the crimp connector.
[0068] The heating cable showed excellent flex fatigue resistance.
[0069] A comparison of the contact resistance of the crimp connection of such a hybrid electrical
heating cable according to the invention compared to a similar heating cable but without
the second set of metal filaments (thus without the single end drawn stainless steel
filaments, e.g. AlSl 316L) showed that the contact resistance of the crimp connection
of the inventive heating cable was much lower than the contact resistance of the crimp
connection with the prior art cable: 3 mOhm with the inventive heating cable compared
to 30 mOhm with the prior art heating cable.
[0070] Another example of a hybrid electrical heating cable according to the invention comprises
9 strands twisted together, each of the 9 strands consists out of 7 metal filaments
twisted together. Three filaments of each strand are high carbon steel filaments with
a corrosion protecting coating of Zn and a diameter of 60 µm. The metal filaments
of the first set of filaments have an end-drawn microstructure. Four filaments (the
filaments of the second set of filaments) of each strand are single end drawn stainless
steel filaments of 60 µm diameter. The single end drawn stainless steel filaments
have an annealed microstructure. The position of the seven metal filaments in the
strand is random. The hybrid heating cable has a resistance of 2 Ohm/meter. The heating
cable was crimped in in a B-crimp connector and via a plug connected to a power supply.
The heating cable could be reliably crimped in the crimp connector.
[0071] Another example of a hybrid electrical heating cable according to the invention comprises
11 strands twisted together, each of the 11 strands consists out of seven metal filaments
twisted together. Five filaments of each strand are high carbon steel filaments (the
first set of metal filaments) with a corrosion protecting coating of Zn and a diameter
of 60 µm. The metal filaments of the first set of filaments have an end-drawn microstructure.
Two filaments (the filaments of the second set of filaments) of each strand are single
end drawn stainless steel filaments of 60 µm diameter. The metal filaments of the
second set of metal filaments have an annealed microstructure. The position of the
seven metal filaments in the strand is random. The hybrid heating cable has a resistance
of 1.2 Ohm/meter. The heating cable was crimped in in a B-crimp connector and via
a plug connected to a power supply. The heating cable could be reliably crimped in
the crimp connector.
[0072] Another example of a hybrid electrical heating cable according to the invention comprises
6 strands twisted together, each of the 6 strands consists out of seven metal filaments
twisted together. Two filaments of each strand are low carbon steel filaments with
a corrosion protecting coating of Zn and a diameter of 60 µm; these filaments are
forming the first set of metal filaments. The metal filaments of this first set of
filaments have an end-drawn microstructure. Five filaments (the filaments of the second
set of filaments) of each strand are single end drawn stainless steel filaments of
60 µm diameter. The metal filaments of the second set of filaments have an annealed
microstructure. The position of the seven metal filaments in the strand is random.
The hybrid heating cable has a resistance of 2.5 Ohm/meter. The heating cable was
crimped in in a B-crimp connector and the crimp connector has been connected to a
power supply via the plug of the crimp connector. The heating cable could be reliably
crimped in the crimp connector.
[0073] Another example of a hybrid electrical heating cable according to the invention comprises
twelve strands twisted together, each of the twelve strands consists out of seven
metal filaments twisted together. Two filaments of each strand are high carbon steel
filaments with a diameter of 60 µm (the first set of metal filaments). The metal filaments
of the first set of filaments have an end-drawn microstructure. Five filaments (the
filaments of the second set of metal filaments) of each strand are single end drawn
stainless steel filaments of 60 µm diameter. The metal filaments of the second set
of metal filaments have an annealed microstructure. The position of the seven metal
filaments in the strand is random. The hybrid heating cable has a resistance of 1.7
Ohm/meter. This is cable A for the comparison. The heating cable was crimped in a
B-crimp connector and via a plug connected to a power supply. The heating cable could
be reliably crimped in the crimp connector.
[0074] This hybrid electrical heating cable was compared with another inventive hybrid electrical
heating cable (cable B). The hybrid heating cable comprises 8 strands twisted together,
each of the 8 strands consists out of seven metal filaments twisted together. Five
filaments of each strand are high carbon steel filaments with a diameter of 60 µm
(the metal filaments of the first set of metal filaments). The metal filaments of
the first set of filaments have an end-drawn microstructure. Two filaments (the filaments
of the second set of filaments) of each strand are single end drawn stainless steel
filaments of 60 µm diameter. The metal filaments of the second set of metal filaments
have an annealed microstructure. The position of the seven metal filaments in the
strand is random. The hybrid heating cable has a resistance of 1.6 Ohm/meter.
[0075] The performance of cable A and cable B has been compared with the performance of
a prior art cable (cable C) comprising 6 strands twisted together, each of the 6 strands
consists out of 7 metal filaments twisted together; metal the filaments are high carbon
steel filaments with a diameter of 60 µm. The metal filaments have an end-drawn microstructure.
Cable C has a resistance of 1.6 Ohm/meter.
[0076] Comparative experiments with cables A and B (inventive cables) and cable C have shown
that
- cables A and B could be connected very well by means of a crimp connection; whereas
cable C did not show a good crimp connection; and
- a flex fatigue test showed that cable A had a lifetime of 11791 cycles to failure,
cable B had a lifetime of 7319 cycles to failure; whereas cable C only had a lifetime
of 5411 cycles to failure.
[0077] Figure 2 shows an example of a crimp terminal (or crimp connector) 200. A heating
cable 205 according to the invention is crimped in the crimp terminal 200. The crimp
terminal 200 has a pin 215 that is used to make contact with a power supply. Alternatively,
the crimp terminal can have a plug instead of a pin.
[0078] Figure 3 shows a cross section 303 of a heating cable 310 crimped in a B-type crimp
terminal 317. As an alternative to B-type crimp terminals, O-type crimp terminals
can be used as well.
1. Electrical heating cable (105) comprising two or more strands (110) of metal filaments
twisted or cabled together,
- wherein at least one of the strands (110) comprises a first set of metal filaments
(130) and a second set of metal filaments (140), both for conducting electrical current
and generating heat when the heating cable (105) is in use;
- wherein the metal filaments of the first set of metal filaments (130) comprise a
steel layer;
- wherein the metal filaments of the second set of metal filaments (140) comprise
a steel layer;
wherein the metal filaments (140) of the second set have an annealed microstructure;
characterised in that the metal filaments (130) of the first set have an end-drawn microstructure.
2. Electrical heating cable (105) as in the preceding claim, wherein the specific electrical
resistance of the metal filaments (140) of the second set is higher than the specific
electrical resistance of the metal filaments (130) of the first set.
3. Electrical heating cable (105) as in any of the preceding claims, wherein in the strands
(110) comprising metal filaments (130) of the first set and metal filaments (140)
of the second set, the metal filaments of the first set and the metal filaments of
the second set are intermingled.
4. Electrical heating cable (105) as in any of the preceding claims, wherein in the cross
section of the heating cable (105), the cumulated cross sections of metal filaments
of the second set is at least 25% of the combined cumulated cross sections of metal
filaments of the first and second set.
5. Electrical heating cable (105) as in any of the preceding claims, wherein the specific
electrical resistance, expressed in (ohm*mm2/m), of the metal filaments of the second set is at least 2 times higher than the
specific electrical resistance of the metal filaments of the first set.
6. Electrical heating cable (105) as in any of the preceding claims, wherein the electrical
conductivity of the heating cable (105) is for more than 75% determined by the electrical
conductivity of the metal filaments of the first set.
7. Electrical heating cable (105) as in claims 1 - 6, wherein the steel layer of the
metal filaments of the first set of filaments is a low carbon or a high carbon steel
layer.
8. Electrical heating cable (105) as in claims 1 - 7, wherein the metal filaments of
the first set of filaments comprise a layer of a metal or metal alloy of specific
electrical conductivity higher than the specific electrical conductivity of the steel
layer.
9. Electrical heating cable (105) as in claim 8, wherein the layer of a metal or metal
alloy of specific electrical conductivity higher than the specific electrical conductivity
of the steel layer is a copper layer or a copper alloy layer.
10. Electrical heating cable (105) as in claims 1 - 9, wherein the metal filaments of
the second set of metal filaments are stainless steel filaments.
11. Electrical heating cable (105) as in claims 1 - 9, wherein the steel layer of the
metal filaments of the second set of metal filaments is a low carbon or a high carbon
steel layer, preferably comprising a corrosion resistant metal layer around the low
carbon or high carbon steel layer.
12. Assembly of a hybrid electrical heating cable (205) as in any of the preceding claims
and a crimp connector (200), wherein the hybrid electrical heating cable (205) is
crimped in the crimp connector (200).
13. Assembly as in claim 12, comprising an electrical power supply and wherein the crimp
connector (200) is connected to the electrical power supply without overlap of an
end portion of the heating cable (205) with an end portion of an electrical power
supply cable.
1. Elektrisches Heizkabel (105), das zwei oder mehr Stränge (110) von Metallfilamenten
umfasst, die miteinander verdreht oder verdrillt sind,
- wobei mindestens einer der Stränge (110) einen ersten Satz von Metallfilamenten
(130) und einen zweiten Satz von Metallfilamenten (140) umfasst, die beide zum Leiten
von elektrischem Strom und Generieren von Wärme dienen, wenn sich das Heizkabel (105)
in Gebrauch befindet;
- wobei die Metallfilamente des ersten Satzes von Metallfilamenten (130) eine Stahlschicht
umfassen;
- wobei die Metallfilamente des zweiten Satzes von Metallfilamenten (140) eine Stahlschicht
umfassen;
wobei die Metallfilamente (140) des zweiten Satzes eine getemperte Mikrostruktur aufweisen;
dadurch gekennzeichnet, dass die Metallfilamente (130) des ersten Satzes eine endgezogene Mikrostruktur aufweisen.
2. Elektrisches Heizkabel (105) nach dem vorhergehenden Anspruch, wobei der spezifische
elektrische Widerstand der Metallfilamente (140) des zweiten Satzes höher als der
spezifische elektrische Widerstand der Metallfilamente (130) des ersten Satzes ist.
3. Elektrisches Heizkabel (105) nach einem der vorhergehenden Ansprüche, wobei in den
Strängen (110), die Metallfilamente (130) des ersten Satzes und Metallfilamente (140)
des zweiten Satzes umfassen, die Metallfilamente des ersten Satzes und die Metallfilamente
des zweiten Satzes einander durchsetzen.
4. Elektrisches Heizkabel (105) nach einem der vorhergehenden Ansprüche, wobei die kumulierten
Querschnitte der Metallfilamente des zweiten Satzes in dem Querschnitt des Heizkabels
(105) mindestens 25 % der kombinierten kumulierten Querschnitte der Metallfilamente
des ersten und zweiten Satzes betreffen.
5. Elektrisches Heizkabel (105) nach einem der vorhergehenden Ansprüche, wobei der spezifische
elektrische Widerstand der Metallfilamente des zweiten Satzes, ausgedrückt in (ohm*mm2/m), mindestens 2 Mal höher als der spezifische elektrische Widerstand der Metallfilamente
des ersten Satzes ist.
6. Elektrisches Heizkabel (105) nach einem der vorhergehenden Ansprüche, wobei die elektrische
Leitfähigkeit des Heizkabels (105) zu mehr als 75 % durch die elektrische Leitfähigkeit
der Metallfilamente des ersten Satzes bestimmt wird.
7. Elektrisches Heizkabel (105) nach den Ansprüchen 1 bis 6, wobei die Stahlschicht der
Metallfilamente des ersten Satzes der Filamente eine Schicht aus kohlenstoffarmem
oder kohlenstoffreichem Stahl ist.
8. Elektrisches Heizkabel (105) nach den Ansprüchen 1 bis 7, wobei die Metallfilamente
des ersten Satzes der Filamente eine Schicht aus einem Metall oder einer Metalllegierung
mit einer spezifischen elektrischen Leitfähigkeit umfassen, die höher als die spezifische
elektrische Leitfähigkeit der Stahlschicht ist.
9. Elektrisches Heizkabel (105) nach Anspruch 8, wobei die Schicht aus einem Metall oder
einer Metalllegierung mit einer spezifischen elektrischen Leitfähigkeit, die höher
als die spezifische elektrische Leitfähigkeit der Stahlschicht ist, eine Kupferschicht
oder eine Kupferlegierungsschicht ist.
10. Elektrisches Heizkabel (105) nach den Ansprüchen 1 bis 9, wobei die Metallfilamente
des zweiten Satzes von Metallfilamenten Filamente aus rostfreiem Stahl sind.
11. Elektrisches Heizkabel (105) nach den Ansprüchen 1 bis 9, wobei die Stahlschicht der
Metallfilamente des zweiten Satzes von Metallfilamenten eine Schicht aus kohlenstoffarmem
Stahl oder aus kohlenstoffreichem Stahl ist, vorzugsweise umfassend eine Schicht aus
korrosionsbeständigem Metall um die Schicht aus kohlenstoffarmem oder kohlenstoffreichem
Stahl herum.
12. Anordnung eines hybriden elektrischen Heizkabels (205) nach einem der vorhergehenden
Ansprüche und eines Crimpverbinders (200), wobei das hybride elektrische Heizkabel
(205) in den Crimpverbinder (200) gecrimpt ist.
13. Anordnung nach Anspruch 12, umfassend eine elektrische Energieversorgung, und wobei
der Crimpverbinder (200) mit der elektrischen Energieversorgung verbunden wird, ohne
dass ein Endabschnitt des Heizkabels (205) mit einem Endabschnitt eines Kabels der
elektrischen Energieversorgung überlappt.
1. Câble chauffant électrique (105) comprenant deux ou plus de deux brins (110) de filaments
métalliques torsadés ou câblés ensemble,
- au moins l'un des brins (110) comprenant un premier ensemble de filaments métalliques
(130) et un deuxième ensemble de filaments métalliques (140), à la fois pour conduire
le courant électrique et générer de la chaleur lorsque le câble chauffant (105) est
en cours d'utilisation ;
- les filaments métalliques du premier ensemble de filaments métalliques (130) comprenant
une couche d'acier ;
- les filaments métalliques du deuxième ensemble de filaments métalliques (140) comprenant
une couche d'acier ;
- les filaments métalliques (140) du deuxième ensemble ayant une microstructure recuite
;
caractérisé en ce que
les filaments métalliques (130) du premier ensemble ont une microstructure étirée
en bout.
2. Câble chauffant électrique (105) selon la revendication précédente, la résistance
électrique spécifique des filaments métalliques (140) du deuxième ensemble étant supérieure
à la résistance électrique spécifique des filaments métalliques (130) du premier ensemble.
3. Câble chauffant électrique (105) selon l'une quelconque des revendications précédentes,
dans les brins (110) comprenant des filaments métalliques (130) du premier ensemble
et des filaments métalliques (140) du deuxième ensemble, les filaments métalliques
du premier ensemble et les filaments métalliques du deuxième ensemble étant mélangés.
4. Câble chauffant électrique (105) selon l'une quelconque des revendications précédentes,
dans la section transversale du câble chauffant (105), les sections transversales
cumulées de filaments métalliques du deuxième ensemble étant au moins 25 % des sections
transversales cumulées combinées de filaments métalliques des premier et deuxième
ensembles.
5. Câble chauffant électrique (105) selon l'une quelconque des revendications précédentes,
la résistance électrique spécifique, exprimée en (ohm*mm2/m), des filaments métalliques du deuxième ensemble étant au moins 2 fois supérieure
à la résistance électrique spécifique des filaments métalliques du premier ensemble.
6. Câble chauffant électrique (105) selon l'une quelconque des revendications précédentes,
la conductivité électrique du câble chauffant (105) étant déterminée à plus de 75
% par la conductivité électrique des filaments métalliques du premier ensemble.
7. Câble chauffant électrique (105) selon les revendications 1 à 6, la couche d'acier
des filaments métalliques du premier ensemble de filaments étant une couche d'acier
à basse teneur en carbone ou à haute teneur en carbone.
8. Câble chauffant électrique (105) selon les revendications 1 à 7, les filaments métalliques
du premier ensemble de filaments comprenant une couche d'un métal ou d'un alliage
métallique ayant une conductivité électrique spécifique supérieure à la conductivité
électrique spécifique de la couche en acier.
9. Câble chauffant électrique (105) selon la revendication 8, la couche d'un métal ou
d'un alliage métallique ayant une conductivité électrique spécifique supérieure à
la conductivité électrique spécifique de la couche d'acier étant une couche en cuivre
ou une couche en alliage de cuivre.
10. Câble chauffant électrique (105) selon les revendications 1 à 9, les filaments métalliques
du deuxième ensemble de filaments métalliques étant des filaments en acier inoxydable.
11. Câble chauffant électrique (105) selon les revendications 1 à 9, la couche d'acier
des filaments métalliques du deuxième ensemble de filaments métalliques étant une
couche d'acier à basse teneur en carbone ou à haute teneur en carbone, comprenant
de préférence une couche métallique résistant à la corrosion autour de la couche d'acier
à basse teneur en carbone ou à haute teneur en carbone.
12. Assemblage d'un câble chauffant électrique hybride (205) selon l'une quelconque des
revendications précédentes et d'un connecteur à sertir (200), le câble chauffant électrique
hybride (205) étant serti dans le connecteur à sertir (200).
13. Assemblage selon la revendication 12, comprenant une alimentation électrique et le
connecteur à sertir (200) étant connecté à l'alimentation électrique sans chevauchement
d'une partie d'extrémité du câble chauffant (205) avec une partie d'extrémité d'un
câble électrique.