EP1484945A1 - Electrical heating cable or heating band - Google Patents

Abstract

Electrical heating cable or tape with insulating polytetrafluoro-ethylene (PTFE) sheaths in a layer structure, in which at least one of the PTFE layers is protected from shock by at least one adjacent insulating layer of melt-processable fluoropolymer (I).

Description

The present invention relates to an electrical heating line or an electrical Heating tape with insulating coatings arranged in the layer structure Polytetrafluoroethylene.

For a wide range of applications, for example also for Heating aggressive media are heating cables in a coaxial arrangement known (DE-A 28 50 722), in which the heating conductor of a fluoropolymer as Insulating material is enclosed. This insulation is covered by one Copper wire braid, using the individual wires to avoid corrosion are additionally nickel-plated. This network of copper wires is the electrical one Protective conductor of the line used to avoid accident hazards, for example also due to a short circuit in the electrically conductive part, within the line is provided. The protective conductor is covered by an external one Plastic sheath, which is used to protect against aggressive media in the environment, e.g. out is made of a fluoropolymer. Advantage of such a coaxial Arrangement is in addition to the wide range of use of this line due to resistant to high temperatures and insensitive to aggressive media Materials that such lines in practically any lengths with high Flexibility can be produced.

The same applies to known electrical heating tapes (GB 2 092 420 A, GB 2 130 459 A) which e.g. be used for so-called pipe trace heating or on steam-rinsed pipes for temperature maintenance or for a Ensure temperature increase. Finally, there are also so-called self-limiting Heating tapes with a semiconductor heating element in use. Because the heat emission here is controlled automatically depending on the ambient temperature such heating tapes for use in potentially explosive areas suitable.

Now it happens again and again that due to external operating conditions when using heating cables, for example in a coaxial version, with external ones Pressure load on the outer jacket is squeezed and the insulation from the Heating conductor is pushed away so that protective conductor and heating conductor touch each other or the insulating distance between the protective conductor and the heating conductor has become so small, that glow or spark discharges occur. Also at the Damage broken wires of the protective conductor get into the insulation and thus lead to failure of the entire heating cable. These are criteria that are to be taken into account particularly in the case of heating cables which explosion-proof systems are used and therefore special Safety requirements are placed as preventive explosion protection. These criteria must also be taken into account with regard to the applicable ones Standards (DIN VDE 0170/0171, EN 50014 and EN 50019), for example one Protective conductors require that the surface of the Conductor insulation guaranteed, as well as a separate squeeze test with a then testing the insulation capacity of the conductor insulation. A Reinforcement of the wall thickness of both the insulation and the outer jacket to avoid these difficulties does not help here, apart from the fact that these measures lead to a significant increase in the diameter of the whole Line as well as at an increased cost because of the larger Guide the amount of fluoroplastic material.

An electrical that is resistant to external mechanical loads Heating cable with a coaxial layer structure is already known (DE-ES 101 07 429). A glass ceramic tape layer in the layer structure above the conductor insulation this cable should work in conjunction with an air-permeable one Reinforcing layer offer protection against mechanical damage. both sides these two layers are air-impermeable layers of one extrudable fluoropolymer provided so that there is a between them Can form air cushions. Apart from this elaborate as well Layer construction that increases cable diameter leads to the deliberately created Air cushions in the interior of the cable significantly impair the Heat conduction away from the heating conductor to the cable surface and thus to one Deterioration of the efficiency of the heating cable itself.

In order to avoid this, however, according to the requirements of the applicable standards sufficient resistance to external impact or Sufficient pressure loads have already been proposed (EP 0 609 771 B1), below and / or above the protective conductor at one Generic electrical heating cable one or more layers of a tape made of mechanically high-strength plastics, such as polyimide. A such wrapping is able to withstand high pressure loads, external blows are absorbed dampened, damaging the Wire insulation is avoided.

Starting from this prior art, the invention takes a different path to protect the layer structure of a heating cable or heating tape existing coverings (conductor insulation, intermediate sheath, outer protective sheath ) made of polytetrafluoroethylene. even with the greatest mechanical force Impact or crushing stress.

According to the invention, at least one of the polytetrafluoroethylene coatings is by at least one adjacent insulating layer from a melt processable fluoropolymer shockproof. The invention is based on the Recognition that adequate protection against external mechanical Strains can be achieved through the juxtaposition of Polymer layers from the same polymer family, but different Polymer structure. So according to the proposal of the invention is the polytetrafluoroethylene with its fibrous, so-called fibril-containing, polymer structure through the neighboring thermoplastic polymer protected with its amorphous structure. This results from the fact that in contrast with impact or impact loads to the fiber structure the amorphous polymer structure has a shock absorbing effect.

An advantageous embodiment of the invention results in an electrical heating line in a coaxial arrangement with a central conductor, an insulation made of polytetrafluoroethylene and a protective conductor in the form of stranded or braided wires and an outer protective sheath when the polytetrafluoroethylene insulation has one or more layers. is shockproof by at least one adjacent insulating layer made of a fluoropolymer that can be processed from the melt.
A particularly advantageous embodiment of a heating line in a coaxial arrangement results according to the invention when the shock-absorbing insulating layer made of a melt-processable fluoropolymer is arranged below the polytetrafluoroethylene insulation surrounding the conductor, and thus directly on the conductor itself. Through the use of related materials for mechanical protection, the permanent temperature resistance, a necessary property for heating cables, is significantly increased compared to the known heating cables or lines. The heating cable according to the invention has no air cushions in the layer structure, the heating heat generated by the conductor thus reaches the cable / line surface without significant heat build-up, ie where it is also needed. The construction of the line is problem-free in terms of production technology; the extruded polymer protective layers allow the line diameter to be kept small.

As a rule, the polytetrafluoroethylene insulation is a heat treatment is subjected to for the purpose of sintering the polymer material the resulting shrinkage of the polytetrafluoroethylene compacting of the layer structure. The line is therefore, in contrast to the known Heating cable with air cushion, also longitudinally watertight, while known Glass fiber mesh, mica tapes or inorganic foils are another have unwanted wicking and therefore for an ideal Ensure moisture transport.

As stated above, in addition to the heating cables described in a coaxial design, electrical heating tapes of the most varied of embodiments are also used. If such a heating tape consists, for example, of parallel feed wires and a heating coil contacting the conductors of these feed wires at intervals and an intermediate jacket and / or an outer jacket made of polytetrafluoroethylene, then at least one jacket layer can be processed from the melt by at least one adjacent insulating layer in the implementation of the invention Shockproof fluoropolymer.
In another variant of a heating tape with parallel, non-insulated feed conductors and a heating wire guided parallel to these and contacted with the feed conductors at intervals and a common covering made of polytetrafluoroethylene, the covering is shock-protected according to the invention by at least one adjacent insulating layer made of a fluoropolymer that can be processed from the melt ,
Self-limiting heating tapes have proven to be advantageous for special applications, for example in explosion protection.These heating tapes with parallel, non-insulated feeders and a semiconducting sheath enclosing them, as well as common insulation and / or an outer protective jacket made of polytetrafluoroethylene, are in turn the common insulation and / or Protective sheath with shock protection according to the proposal of the invention.

The purpose of the longitudinal water-tightness and compactness of the heating lines or heating tapes according to the invention also serves to weld or glue the shock-absorbing insulating layers to the polytetrafluoroethylene sheathings. At the same time, the bending fatigue strength of such arrangements is significantly increased.
The thickness of the shock absorbing layer is 0.1 to 0.8 mm, preferably 0.2 to 0.5 mm. In the case of heating cables in a coaxial arrangement and the shock-absorbing insulating layer located directly on the conductor, the thickness to be selected essentially depends on the respective conductor diameter. For example, the shock absorbing layer with a conductor diameter of 1.5 mm is 0.2 mm.

The invention also offers particular advantages when the conductor insulation is made a polytetrafluoroethylene tape wrapped with overlap of the edges exists, for example with a rectangular cross section. In this case According to the invention the gusset formed by the winding of the tape with the Fluoropolymer filled the shock absorbing layer. The liability of adjoining layers is improved, the further gained thereby Compactness ensures high stability of the cable against kinking and bending.

The shock absorbing layer according to the invention consists of one of the Melt processable fluoropolymer. Since it is in a generic Heating line or a heating tape from their task to a high Permanent temperature resistance, possibly also under the influence of aggressive Media that arrives can advantageously be made from a shock absorbing layer Prepare tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (TFA / PFA). But also the tetrafluoroethylene / hexafluoropropylene copolymer (FEP) or the Polytetrafluoroethylene-perfluoromethyl vinyl ether copolymer, also known as the trade name HYFLON MFA, depending on the application, are advantageous Polymers for carrying out the invention.

Other known fluoropolymers that can be processed from the melt, such as polyvinylidene fluoride (PVDF) or ethylene tetrafluoroethylene (ETFE) can sometimes find an advantageous application.

A particularly advantageous embodiment of the invention results in a Polytetrafluoroethylene - wrapping from a wound polytetrafluoroethylene - Band if this has a plano-convex cross-sectional shape. Across from The plano-convex leads common belts with a rectangular cross-sectional shape Form after winding and sintering the polytetrafluoroethylene tape into one compact casing with closed smooth outer surface. This is from particularly advantageous when the outer surface of the aggressive media Environment is exposed.

Another beneficial way of improving insulation quality opposite to that of rectangular ribbons is that of the ribbon Form polytetrafluoroethylene in cross section as a flat profile, with from the center edge areas tapering to both sides and on the edges regular band course. After wrapping the tape with overlapping Edging and sintering of the strip material (PTFE) results from the leakage of the Band edges in the overlap area a particularly smooth, in itself closed insulating surface. The edges of the tape are advantageous Polytetrafluoroethylene broadly drawn, the edge width on both sides of the Band thickness determining middle range at least 45%, preferably 50 to 80% of the total width of the tape.

The thickness of the tape advantageously used according to the invention Polytetrafluoroethylene is 20 to 200 microns, preferably 40 to 160 microns. The The strip thickness decreases to 5 µm and less towards the edges. Doing so the bandwidth is expediently 5 to 50 mm, preferably 10 to 30 mm.

The same belt dimensions also apply with particular advantage if that in addition to the insulation, the outer protective jacket made of a wound Band consists of polytetrafluoroethylene.

In this case, it can sometimes be advantageous to leave underneath the winding layer (s) Polytetrafluorethylene is a shock absorbing insulating layer made from a To arrange melt processable fluoropolymer. Another beneficial one Embodiment of the invention would be the one or both sides of the protective conductor a shock-absorbing insulating layer made of a melt-processable To allow fluoropolymer to border, the protective conductor with these insulating layers include.

The invention is based on that shown in FIGS. 1 and 2 as particularly advantageous Embodiments of electrical heating cables in a coaxial arrangement closer explained.

To increase the flexibility of the heating cable according to the invention, the conductor is made 1, as shown in Figure 1, for example from a number of individual Resistance wires. The conductor insulation is labeled 2, it consists of a high temperature resistant polytetrafluoroethylene, the name "Polytetrafluoroethylene", as also above, such tetrafluoroethylene polymers includes that are provided with modifying additives, but in one Quantity that the polymer, like the PTFE itself, does not melt is processable.

In the preferred embodiment of the invention, the one used is Polytetrafluoroethylene from an initially unsintered strip or foil material, the wound in the unsintered state on the heating conductor, preferably with Overlap, for example up to 50%, and in the wound state an appropriate temperature treatment is sintered. The individual band layers are fused or welded into compact insulation.

The protective conductor 3 consists of individual metallic wires, for example nickel-plated copper wires that are roped on the insulation 2 or for achieving as far as possible over the circumference are.

To the outside, the heating line is closed by the jacket 4, the Appropriate, since such lines are also in the area of influence of aggressive media be used, for example in the chemical industry, from a corresponding suitable plastic material is made. As sheath materials have Fluoropolymers have also been found to be advantageous in extruded form be applied, or in that a winding from initially unsintered and wound sintered PTFE tapes forms the outer end of the heating cable.

In order to prevent the jacket 4 from being subjected to external pressure (impact) is squeezed and / or pushed away from the protective conductor 3, that is to say Damage to the heating cable and possibly line failures occurs provided the shock absorbing layer 5 below the jacket 4. This Layer of an extrudable fluoropolymer amorphous according to the invention dampens the impact energy applied from the outside and thus prevents one Cable damage or destruction.

FIG. 2 shows a particularly advantageous embodiment of the invention Heating line, again in a coaxial version, consists of the heating conductor 6, for example, from a large number of individual strands that are stranded or intertwined Resistance wires. The conductor insulation is designated 7, it consists in present embodiment of one or more layers of a tape made of polytetrafluoroethylene (PTFE). This tape in the unsintered state wound and sintered in the wound state forms after sintering the PTFE material is a compact, longitudinally watertight cover that can also be used against aggressive media is insensitive, but not due to the material structure is sufficiently suitable for impact or shock loads without damage take. To this heating cable also for use under extreme mechanical external loads, for example in sees the use of explosion-protected (endangered) systems Invention the shock absorbing layer 8 from a melt processable fluoropolymer. This layer covers conductor 6 directly, because of the smaller in relation to the diameter of the line Conductor diameter, the wall thickness of the layer 8 can be kept extremely thin become. Compared to the solution according to FIG. 1, this makes a significant difference Polymer material saved, moreover, this embodiment leads to one compared to the above embodiment, but especially compared to the state technology, reduced overall diameter.

Through the layer 8, which due to the material structure as it were as compliant Buffer layer acts on the line when impacted, the adjacent Conductor insulation 7 mechanically protected. The insulation is not removed from conductor 6 squeezed or pressed away, their insulating effect is retained. An outside Impact is absorbed dampened, the conductor insulation 7 is damaged not to fear. This line structure according to the invention reinforces the material-specific properties of PTFE and PFA (TFA, MFA) essential. The higher hardness of PTFE coupled with the higher elasticity of PFA For example, this composite construction leads to a considerable one Increase in pressure and shock resistance or stability.

Since the substructure remains undamaged when impacted, it also exists no risk of a wire break within the protective conductor 9 or a failure the heating cable due to broken wires which are damaged by insulation 7 could get through. The heating line according to the invention therefore fulfills all Safety requirements, especially those for explosion protection. About that In addition, this heating line according to the invention is inexpensive to manufacture, in some cases partly because of the simplified work steps compared to the prior art because of the smaller amounts of material, the same polymer family are to be assigned. A particular advantage when a high Permanent temperature resistance is required, for example in Steam cleaning systems with operating temperatures between 300 ° and 320 ° C.

The outer jacket 10 also consists of a in this embodiment Winding from PTFE tapes, in the wound state Subjected to temperature treatment and thus to a compact coating welded or fused. The special provided according to the invention Cross-sectional shape of the PTFE tape leads to a particularly smooth, in itself closed surface. Tearing open the individual layers of tape under impact or impact stress is a shock due to the solution according to the invention absorbent polymer layer from the same polymer family in the layer structure to arrange the heating cable avoided.

The heating line according to the invention shown in Figure 2 is also characterized by particularly favorable external dimensions. With a total diameter of z. B. 4.8 mm, the diameter of the conductor 6 is 1.4 mm, the wall thickness of the shock-absorbing layer 8 is 0.2 mm, the insulation 7 has a wall thickness of 0.6 mm, the thickness of the braid 9 is 0, 4 mm and the jacket 10 has a wall thickness of 0.5 mm.
Deviating from the preferred embodiment according to FIG. 2, other variants are also possible. For example, insulating layers made of PTFE and PFA can alternate in the layer structure of the heating cable, for example PTFE / PFA / PTFE or also PFA / PTFE / PFA. As in the exemplary embodiments, the prerequisite here is that these insulating layers each adjoin one another.

The effect of the invention can also be achieved if different from the Embodiments known heating cables or heating lines, too in embodiments deviating from the coaxial construction, against impact and pressure loads are to be strengthened and the PTFE coatings used there according to the invention insulating layers from the melt adjacent processible fluoropolymers.

Claims (22)

Electrical heating cable or electrical heating tape with insulating sheaths made of polytetrafluoroethylene arranged in the layer structure, characterized in that at least one of the polytetrafluoroethylene sheaths is shock-protected by at least one adjacent insulating layer made of a fluoropolymer that can be processed from the melt. Electrical heating cable according to claim 1 in a coaxial arrangement with a central conductor, an insulation made of polytetrafluoroethylene and a protective conductor in the form of stranded or braided metallic wires and an outer protective sheath, characterized in that the polytetrafluoroethylene insulation, one or more layers, by at least one adjacent insulating layer made of a melt-processible fluoropolymer is shockproof. Electrical heating cable according to Claim 2 in a coaxial arrangement with a single-layer insulation made of polytetrafluoroethylene surrounding the central conductor and a protective conductor covering this, as well as an outer protective sheath, characterized in that a shock-absorbing insulating layer consists of below the polytetrafluoroethylene insulation, and thus directly on the conductor a fluoropolymer that can be processed from the melt is arranged. Electrical heating tape according to claim 1 with parallel, consisting of insulated electrical conductors feed wires and a heating coil contacting the conductors of these feed wires at intervals as well as an intermediate jacket and / or an outer jacket made of polytetrafluoroethylene, characterized in that at least one jacket layer consists of at least one adjacent insulating layer the melt processable fluoropolymer is shockproof. Electrical heating tape according to claim 1 with parallel, non-insulated feed conductors and a heating wire guided parallel thereto and contacted with the feed conductors at intervals and a common covering made of polytetrafluoroethylene, characterized in that the covering is provided by at least one adjacent insulating layer made of a fluoropolymer that can be processed from the melt is shockproof. Electrical heating tape according to claim 1 with parallel, non-insulated feeders and a semiconducting sheath enclosing them and a common insulation and / or an outer protective jacket made of polytetrafluoroethylene, characterized in that the common insulation and / or the protective jacket by at least one adjacent insulating layer made of one of the Melt processable fluoropolymer is shockproof. Heating cable according to claim 2 or 3, characterized in that the thickness of the shock-absorbing insulating layer is 0.1 to 0.8 mm, preferably 0.2 to 0.5 mm, depending on the respective conductor diameter. Heating line or heating tape according to claim 1 or one of the following, characterized in that the shock-absorbing insulating layer is welded or glued to the polytetrafluoroethylene sheathing (insulation, jacket). Heating line or heating tape according to claim 1 or one of the following with a covering made of a polytetrafluoroethylene tape wound with an overlap of the edges, characterized in that the gusset formed by the winding of the tape is filled with the fluoropolymer of the shock-absorbing insulating layer. Heating line or heating tape according to claim 1 or one of the following, characterized in that the shock-absorbing insulating layer consists of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (TFA / PFA). Heating line or heating tape according to claim 1 or one of the following, characterized in that the shock-absorbing insulating layer consists of a tetrafluoroethylene / hexafluoropropylene copolymer (FEP). Heating line or heating tape according to claim 1 or one of the following, characterized in that the shock-absorbing insulating layer consists of a polytetrafluoroethylene-perfluoromethyl vinyl ether (MFA). Heating line or heating tape according to claim 1 or one of the following, characterized in that the polytetrafluoroethylene of the sheath is sintered. Heating line or heating tape according to claim 9, characterized in that the tape made of polytetrafluoroethylene has a rectangular cross-sectional shape. Heating cable or heating tape according to claim 9, characterized in that the tape made of polytetrafluoroethylene has a plano-convex cross-sectional shape. Heating line or heating tape according to claim 9, characterized in that the tape is made of polytetrafluoroethylene in cross section as a flat profile, with edge areas tapering from the center to both sides and a regular tape course on the edges. Heating line or heating tape according to claim 16, characterized in that the edges of the tape made of polytetrafluoroethylene are drawn wide, the edge width on both sides of the central area determining the tape thickness being at least 45%, preferably 50 to 80%, of the total width of the tape. Heating cable or heating tape according to claim 15 or one of the following, characterized in that the thickness of the tape made of polytetrafluoroethylene is 20 to 200 µm, preferably 40 to 160 µm, which decreases to 5 µm and less towards the edges. Heating line or heating tape according to claim 18, characterized in that the width of the tape made of polytetrafluoroethylene is 5 to 50 mm, preferably 10 to 30 mm. Heating line or heating tape according to claim 1 or one of the following, characterized in that the outer protective jacket consists of a wound tape made of polytetrafluoroethylene. Heating line or heating tape according to Claim 20, characterized in that a shock-absorbing insulating layer made of a fluoropolymer which can be processed from the melt is arranged below the winding layer (s) made of polytetrafluoroethylene. Heating line or heating tape according to claim 2 or one of the following, characterized in that a shock-absorbing insulating layer made of a melt-processable fluoropolymer adjoins the protective conductor on one or both sides.

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