Metal coil and method of its manufacture

Abstract

The present invention relates to a metal coil, in particular a tungsten coil. One aspect of the invention relates to a method of manufacturing said metal coil, a further aspect to the metal coil itself, and yet a further aspect to the use of the metal coil in a heat conduction vacuum gauge, a Pirani element, or as a glow filament.

Description

TECHNICAL FIELD

[0001] The present invention relates to a metal coil, in particular a tungsten coil. One aspect of the invention relates to a manufacturing method of said metal coil, a further aspect relates to the metal coil itself, and yet a further aspect relates to the use of the metal coil.STATE OF THE ART

[0002] A method of the manufacture of metal coils is known in the state of the art, whereby the starting material for the metal coil, a metal wire, is wound directly on a metallic core wire made of molybdenum. After a cutting of the core wire and the coiled metal wire, the metal wire is shaped in a reductive atmosphere and a metal coil is obtained that is still wound on the core wire. In order to free the metal coil from the molybdenum core wire and to obtain a usable metal coil, in the case of tungsten coils, the ensemble of molybdenum core wire and tungsten coil is treated with an acid and the auxiliary wires are etched away (www.de.wikipedia.org / wiki / Glühlampe, accessed on 26 Aug. 2024). Due to the different solubility behavior of these two metals, the molybdenum core is completely dissolved by aqua regia and a free tungsten coil is obtained. The isolation of the metal coil thus takes place at a time when the core wire carrier has been completely decomposed by the aqua regia and the tungsten coil has already been at least partially attacked by the acid. In an unfavourable case, such an attack by acid can endanger the usability or service life of a component in which the metal coil is used. Especially in applications where a high reliability is required, such a manufacturing method may possibly not be acceptable. This complex, time- and cost-intensive, difficult to control and dangerous working practice makes an automation of the method unattractive, especially for technical and economic reasons.DESCRIPTION OF THE INVENTION

[0003] A problem of the present invention is to provide a method of manufacturing a metal coil which is simpler to execute compared to the state of the art and / or provides metal coils of better quality. In particular, the task is to provide a safer, more reliable, more environmentally friendly, and / or more cost-effective method and / or a metal coil that is correspondingly easier to manufacture.

[0004] This problem is solved by the method with the features of claim 1. Further embodiments of the method, as well as of the metal coil and of the use of the metal coil are defined by the features of further claims.

[0005] The method of the invention is used for the manufacture of a metal coil, which in particular comprises or consists of the element tungsten (W) or its alloys.

[0006] In an embodiment, such tungsten alloys comprise an alloy of the element tungsten with one or more subgroup elements of the periodic table (subgroups IIIB to IIB of the periodic table), e.g. a tungsten-molybdenum alloy, a tungsten-rhenium alloy, a tungsten-nickel alloy, a tungsten-platinum alloy or a tungsten-copper alloy.

[0007] The method according to the invention comprises the following method steps, in particular in the given order:

[0008] a) winding a metal wire, in particular a metal wire comprising or consisting of tungsten (W) or a tungsten alloy, onto a carrier, in particular a rod-shaped carrier;

[0009] b) heating of the metal wire wound on the carrier; and

[0010] c) separating the heated metal wire from the carrier or a remaining remnant of the carrier, which carrier or remaining remnant of the carrier has a reduced diameter as a result of step b) compared to the carrier from step a), thereby obtaining the metal coil.

[0011] In an embodiment, the metal wire to be wound in step a) is tungsten wire, in particular with a degree of purity of more than 95.00%, 98.00%, 99.00%, 99.50%, 99.95% or 99.99%. In a further embodiment, the metal wire consists of an alloy of the element tungsten (W) with one or more subgroup elements of the periodic table (subgroups IIIB to IIB of the periodic table according to the CAS nomenclature, CAS: engl. abbreviation for “Chemical Abstracts Service”, subdivision of the “American Chemical Society”), e.g. a tungsten-molybdenum alloy, a tungsten-rhenium alloy, or a tungsten-copper alloy. The chemical composition of the metal wire in this embodiment corresponds to the chemical composition of the metal coil from step c), and can be verified, for example, by means of XPS analysis (photoelectron spectroscopy / ESCA), or other elemental analysis methods known to the skilled person. In further embodiments, the metal wire may consist of two or more than two adjacent metal components, for example of a metal component A, which forms the metal wire core inside the metal wire, and of a metal component B, preferably tungsten (W), which is arranged around the metal wire core, in particular enclosing the metal wire core.

[0012] The shape of the metal wire is to be chosen by the skilled person in such a way that it allows the wire to be wound around a correspondingly selected carrier. The metal wire to be wound can consist of a straight metal wire, for example, or of two or more metal wires twisted together, or comprise several metal wires twisted together.

[0013] In an embodiment, the metal wire has a diameter of less than 0.1 mm, for example 0.075 mm to 0.001 mm, 0.050 mm to 0.003 mm, 0.025 mm to 0.005 mm, or 0.01 mm.

[0014] According to step a), the metal wire is wound onto a carrier, in particular in such a way that the metal wire wraps around the carrier at least in sections. In an embodiment, the metal wire comprises at least three sections, a first, a second and a third section, which sections follow each other in the order mentioned. The first section of the metal wire is wound around the carrier continuously, i.e. along its total section length, the second section is not wrapped around the carrier, and the third section is wound around the carrier, analogously to the first section, continuously, i.e. along its total section length. In a further embodiment, the metal wire is wound continuously, i.e. along its entire wire length, around the carrier, along the carrier length.

[0015] The carrier is preferably rod-shaped, in particular having a constant diameter, or it comprises rod-shaped sections around which the metal wire can be wrapped. However, the carrier does not have to be rod-shaped and other geometric shapes are also possible. The carrier has a diameter perpendicular to a longitudinal extension of the carrier.

[0016] In the case of a rod-shaped carrier with, for example, an essentially oval, rectangular or circular cross-section, the said diameter corresponds to a maximum diameter of the cross-section. However, the cross-section can also have other, e.g. asymmetrical or irregular shapes.

[0017] In step b), which is preferably performed after step a), the metal wire wound onto the carrier is heated. In an embodiment, both the carrier and the metal wire are heated, e.g. by storing the carrier with the wound metal wire in a heating furnace, or only the metal wire is heated, e.g. electrically by contacting the metal wire with electricity. Both of the above-mentioned heating methods can also be combined with each other according to the invention. If only the metal wire is heated, it should be noted that the carrier can also warm up or heat up indirectly by heating the metal wire. If the metal wire is electrically heated, it is preferable to choose an electrically non-conductive carrier or a carrier having an electrically non-conductive surface.

[0018] In step c), which is preferably performed after step a) and step b), the heated metal wire is separated from the carrier, or a remnant of the carrier remaining after step b) and thus the metal coil is obtained—i.e. the metal coil is the product of the method. For the sake of clarity, it should be noted at this point that only after the separation of the heated metal wire from the carrier it is referred to as a “metal coil”. The separation in step c) can be achieved, for example, mechanically, in particular by pulling the metal wire off the carrier. The separation of the heated metal wire from the carrier, or any remnant of the carrier remaining after step b), can be carried out in particular after the carrier and / or the metal wire has cooled down, e.g. to room temperature, or in a heated state, e.g. if the carrier and / or the metal wire are heated.

[0019] It should be noted that step c) deliberately speaks of a

[0020] separation from the carrier or a remaining remnant of the carrier. Due to the direct or indirect effect of warmth or heat on the carrier in step b), i.e. when the metal wire wound onto the carrier is heated and indirectly transfers heat to the carrier, or when the wound metal wire and the carrier are heated simultaneously or sequentially, there is a change in the composition and / or structure of the carrier, e.g. to a decrease in the volume of the carrier, or a partial degradation of the carrier, in particular the degradation of an outer material layer of the carrier, around which the metal wire was wound in step a). It is important to note that for the purpose of the invention in step c) a carrier or a remnant of the carrier is separated out, which carrier or remaining remnant of the carrier has a reduced diameter compared to the carrier from step a).

[0021] This means that in step c) the carrier must either be completely or at least partially still present-a carrier that no longer exists, e.g. a completely burned, or a completely dissolved carrier does not fall under the wording “remaining remnant of the carrier” or “carrier with a reduced diameter” . In an embodiment of the method, the carrier or the remaining remnant of the carrier in step c) have a diameter equal to 99%, between 98% and 90%, 89% and 80%, 79% and 70%, 69% and 60%, 59% and 50%, 49% and 40%, 39% and 30%, 29% and 20%, 19% and 10%, or 9% and 1% of the diameter value of the carrier from step a). The remaining remnant of the carrier has in an embodiment of the method a mass corresponding to 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99% of the original mass of the carrier from step a).

[0022] In an embodiment of the invention, the metal coil is a metal coil spring, in particular a metal coil spring comprising tungsten (W) or a tungsten alloy or consisting of tungsten (W) or tungsten alloy having a diameter of less than 1.00 mm, preferably 0.15 mm.

[0023] In a further embodiment of the method, which may be combined with any of the embodiments or aspects already addressed or not yet addressed, unless in contradiction, the carrier comprises an organic material, optionally the carrier consists of an organic material, the material being in particular a natural or synthetic polymer, a non-polymer compound, or a mixture thereof.

[0024] Examples of organic materials according to the invention are synthetic resins, epoxy resins, polyurethane, acrylates, polyacrylates, polymethyl acrylates, cellulose esters, cellulose acetate, cellulose acetate butyrate, cellulose propionate, cellulose nitrate, polyamides, nylon, polyalkylenes, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl chloride, rubber linings, waxes, or PVC. In a preferred embodiment, the organic material does not form harmful degradation products, such as for example nitrous gases (in particular NO, NO2, N2O4, NOCl), Cl2, F2, Br2, I2, HCl, HF, HBr, or HI when heated or burned.

[0025] In a further embodiment of the method, which may be combined with any of the embodiments or aspects already addressed or not yet addressed, unless in contradiction, the carrier comprises an inorganic core and an organic material which organic material is arranged in the form of a sheath around the inorganic core, the inorganic core being in particular a glass fiber, a carbon fiber, a mineral fiber, a silica fiber, a ceramic fiber, or asbestos.

[0026] According to the invention, an inorganic core is understood to be a material inside the carrier, wherein the core extends essentially along the length of the carrier. The sheath can completely encase the inorganic core, i.e. form a kind of capsule around the core, or it can encase the core only along the longest length of the core, i.e. in the case of a rod-shaped carrier, it forms the mantle surface around a rod-shaped core. According to an embodiment of the invention, the carrier can be a glass fiber, carbon fiber, or ceramic fiber coated with an organic polymer.

[0027] In a further embodiment of the method, which can be combined with any of the embodiments or aspects already addressed or not yet addressed, unless in contradiction, the carrier of step a) consists of a material which material has a negative coefficient of thermal expansion, in particular a negative coefficient of thermal expansion under the heating conditions in step b).

[0028] In a further embodiment of the method, which may be combined with any of the embodiments or aspects already addressed or not yet addressed, unless in contradiction, the carrier of step a) comprises a material which material has a negative coefficient of thermal expansion, in particular a negative coefficient of thermal expansion under the heating conditions in step b), optionally wherein the inorganic core of the carrier comprises or consists of a material with a negative coefficient of thermal expansion.

[0029] Examples of materials with a negative coefficient of thermal expansion are for all embodiments, as long as not in contradiction, ZrW2O8, ZrV2O7, ZrMO2O8, HfMO2O8, HfW2O8, HfV2O7, HfV2, or optionally their alloys or compositions. By using such materials in or as carrier material, a contraction or a reduction in the carrier diameter can be achieved in step b), which facilitates the separation of the heated metal wire from the carrier or a remaining remnant of the carrier, in particular if the metal wire is Separated from the carrier at a time when the metal carrier is still contracted, further in particular when the carrier is still heated with respect to the room temperature by the heating in step b).

[0030] In the case of embodiments in which a carrier is used which carrier consists of or comprises a material with a negative expansion coefficient, the separation in step c) is performed in particular at a time when the carrier is still heated with respect to the room temperature by the heating in step b) or by a separate, later heating of the carrier with a metal wire wound around it.

[0031] In a further embodiment of the method, which may be combined with any of the embodiments or aspects already addressed or not yet addressed, unless in contradiction, the method comprises a further step d), which step d) is performed before step a), before step b), after step b) and / or after step c), optionally immediately after step b) and / or immediately after step c), and wherein step d) comprises a formation of a protective layer on a surface of the metal wire, in particular by means of burnishing.

[0032] Step d) can be performed either only once or multiple times during the method, creating a protective layer on the surface of the metal wire or the metal coil. The formation of such a protective layer ensures, for example, that the final metal coil has changed or improved properties, e.g. against corrosion. In addition, the protective layer can influence, for example, the colour, the reflection behaviour or the tribological properties of the metal coil and can be used by the skilled person according to the needs. In an embodiment of the invention, the protective layer may be an oxide, a nitride, and / or an oxynitride layer and / or be present on the entire surface or only on a part of the surface of the metal wire or the metal coil.

[0033] In a further embodiment of the method, which can be combined with any of the embodiments or aspects already addressed or not yet addressed, unless in contradiction, the heating in step b) is performed in a reducing atmosphere, in particular in a forming gas atmosphere, or in an inert gas atmosphere, in particular in an argon atmosphere, and the metal wire is heated to a temperature of 300° C. to 600° C., in particular 350° C. to 550° C., further in particular 400° C. to 500° C.

[0034] If the metal wire and the carrier are heat-treated in step b) in a reducing atmosphere, such as the forming gas atmosphere (N2:H2 mixture 70%: 30%, 80%: 20%, 90%: 10%, 85%: 15%, or 95%: 5%), the metal wire can be efficiently shaped and optionally stabilized. It is also possible to achieve good results in an inert gas atmosphere, such as an argon atmosphere with or without O2 traces.

[0035] In a further embodiment of the method, which can be combined with any of the embodiments or aspects already addressed or not yet addressed, unless in contradiction, the metal coil has a diameter of less than 1.00 mm, in particular a diameter in the range of 0.01 mm to 0.75 mm, further in particular 0.10 mm to 0.50 mm, or 0.10 mm to 0.25 mm.

[0036] The diameter of the metal coil indicates the diameter of the cross-section of the metal coil, which cross-section is defined as a plane perpendicular to a winding direction of the metal wire on the carrier. In the case of a circular cross-section, the diameter of the metal coil is constant for a cross-sectional area, and for an oval or rounded cross-section, it corresponds to the largest diameter of the cross-section. If the metal coil has several diameters, e.g. in a cone-shaped metal coil, or a metal coil which is simply wider in some places than in others, then the diameter according to claim 9 means the largest of the diameters.

[0037] In a further embodiment of the method, which can be combined with any of the embodiments or aspects already addressed or not yet addressed, unless in contradiction, the method is performed acid-free, in particular aqua regia free.

[0038] By avoiding acids, especially aqua regia, the skilled person is provided with a safer and less hazardous method to his health. This embodiment has in particular the further advantage that the metal wire or the metal coil is not exposed to acid (e.g. H2SO4, HNO3, H2SO5, a superacid, or HCl) or aqua regia (HNO3 / HCl 1:3). This means that the surface of the metal wire or the metal coil is not attacked by any acid, which characterizes the metal coil as a particularly high-quality product. In particular, in an aqua regia free method, a metal coil with an almost constant metal wire diameter, which metal wire diameter corresponds in particular the half of the coil core diameter or is less than half the coil core diameter, and / or a longer service life, is obtained in comparison to the state of the art. Avoiding aqua regia also offers the advantage that the effort involved in procuring, storing, processing and disposing of materials is significantly reduced compared to a method that uses aqua regia and / or a method is made possible that is much easier to automate on a small scale, e.g. by a robot or a system.

[0039] In a further embodiment of the method, which can be combined with any of the embodiments or aspects already addressed or not yet addressed, unless in contradiction, the procedure comprises the steps, in particular in the given order:

[0040] a) winding a metal wire, in particular a metal wire comprising or consisting of tungsten (W) or a tungsten alloy, onto a carrier, in particular a rod-shaped carrier;

[0041] b) heating of the metal wire wound on the carrier; and

[0042] c) separating of the heated metal wire from a remnant of the carrier remaining after step b), thereby obtaining the metal coil.

[0043] In a second aspect, which can be combined with the aspects and embodiments already addressed and not yet addressed, unless in contradiction, the invention relates to a metal coil obtainable by the method of the invention, wherein the surface of the metal coil in particular has no traces of etching, whereby the surface of the metal coil is further in particular free of chloride ions (Cl−) and / or optionally has a roughness with a Ra value of 4 μm to 1 μm.

[0044] In an embodiment of the invention, the surface of the metal coil obtained is essentially smooth, i.e. it does not show any clear traces of etching such as attacked grain boundaries, edges and / or steps. Whether such surface defects are present can be checked by the skilled person, for example, with the help of a microscopic examination of the metal coil surface, optionally with the help of optical filters. In addition, the surface of the metal coil obtained may be free of chloride ions, in particular immediately after step c) and / or immediately after step d). If the metal coil is used as a glow filament, the exit work can thereby be reduced compared to a chloride-afflicted surface, for example. Whether the surface of the metal coil is afflicted with chloride ions can be determined by the skilled person, for example, by photoelectron spectroscopy (XPS), or chemically, e.g. by chloride detection as AgCl precipitation after previous chloride ion extraction, or by means of an Elcometer® 134S chloride ion detection.

[0045] In a third aspect, which can be combined with the already addressed and not yet addressed aspects and embodiments, unless in contradiction, the invention relates to a use of the metal coil in a heat conduction vacuum gauge, in particular in a Pirani element, further in particular as a glow filament.

[0046] In a fourth aspect, which can be combined with the already addressed and not yet addressed aspects and embodiments, unless in contradiction, the invention relates to a heat conduction vacuum gauge having the metal coil prepared by the method of the invention, or with the metal coil of the invention. In an embodiment, the metal coil, in particular the tungsten coil, is connected in a Wheatstone measuring bridge, which is a part of the heat conduction vacuum gauge, in particular is an internal component of the heat conduction vacuum gauge. The metal coil can be thereby located in a measuring head of the heat conduction vacuum gauge, for example.SHORT DESCRIPTION OF THE FIGURES

[0047] Embodiments of the present invention are explained in more detail below by means of figures. These are for illustrative purposes only and are not to be interpreted restrictively. It shows

[0048] FIG. 1 Schematic step sequence of the method according to the invention as block diagram;

[0049] FIG. 2 Microscopic image of a metal wire wound on the carrier according to step a)-only a fragment is shown;

[0050] FIG. 3 Microscopic images of a metal coil which were obtained by the method of the invention.DETAILED DESCRIPTION OF THE FIGURES

[0051] FIG. 1 shows a schematic representation of four alternative exemplary step sequences of the method of the invention, from left to right. In the first embodiment, on the far left, steps a), b) and c) are performed immediately or not immediately after the start of the method, wherein the method is deemed to have ended immediately or not immediately after step c). In the other exemplary embodiments (2nd, 3rd and 4th from left), the method further comprises step d), step d) being performed either immediately or not immediately after step c), after step a) or after step b).

[0052] FIG. 2 shows a microscopic image of a metal wire wound on the carrier in front of a rough surface as background. A small section is shown, which illustrates a twist of the metal wire around the carrier. The surfaces of the carrier and of the metal wire are smooth. In the embodiment shown, the metal wire does not contact the carrier along the entire length of the metal wire, i.e. there are section-by-section areas where the wound metal wire does not contact the carrier. However, embodiments are possible in which the metal wire contacts the carrier in its entire length, does not contact, or contacts it in sections and / or does not contact it in sections.

[0053] FIG. 3 shows microscopic images of two tungsten coils according to the invention in front of a rough surface as background. The metal coils have an even and smooth surface, with no signs of etching or acid effect. The tungsten coils shown consist of a metal wire, which in turn comprises only one metal wire, i.e. the wire is not a wire twisted from several wires, although such an embodiment also falls within the scope of the invention. The metal coil shown in the bottom figure has a pitch of 50 μm and was cleaned in an ultrasonic bath with acetone after the separation from the rest of the carrier.

Claims

1. A method of manufacturing a metal coil, in particular a metal coil comprising or consisting of tungsten (W) or a tungsten alloy, wherein the method comprises the steps, in particular in the given order:a) winding a metal wire, in particular a metal wire comprising or consisting of tungsten (W) or a tungsten alloy, onto a carrier, in particular a rod-shaped carrier;b) heating the metal wire wound on the carrier; andc) separating the heated metal wire from the carrier or a remaining remnant of the carrier, which carrier or remaining remnant of the carrier has a reduced diameter as a result of step b) compared to the carrier of step a), thereby obtaining the metal coil.

2. The method according to claim 1, wherein the carrier of step a) comprises an organic material, optionally consists of an organic material, wherein the material is in particular a natural or synthetic polymer, a non-polymer compound, or a mixture thereof.

3. The method according to claim 2, wherein the carrier of step a) further comprises an inorganic core and the organic material is arranged in the form of a sheath around the inorganic core, wherein the inorganic core is in particular a glass fiber, a carbon fiber, a mineral fiber, a silica fiber, a ceramic fiber, or asbestos.

4. The method according to claim 1, wherein the carrier of step a) consists of a material, which material has a negative coefficient of thermal expansion, in particular under the heating conditions in step b).

5. The method according to claim 2, wherein the carrier of step a) comprises a material, which material has a negative coefficient of thermal expansion, in particular under the heating conditions in step b), optionally wherein the core of the carrier, in particular the inorganic core of the carrier, comprises or consists of a material, which material has a negative coefficient of thermal expansion, in particular under the heating conditions in step b).

6. The method according to claim 1, wherein the method comprises a further step d), which step d) is performed before step a), before step b), after step b) or after step c), optionally immediately after step b) or immediately after step c), and wherein step d) comprises the formation of a protective layer on a surface of the metal wire, in particular by means of burnishing.

7. The method according to claim 1, wherein the heating in step b) is performed in a reducing atmosphere, in particular in a forming gas atmosphere, or in an inert gas atmosphere, in particular in an argon atmosphere, and wherein the metal wire is heated to a temperature of 300° C. to 600° C., in particular 350° C. to 550° C., further in particular 400° C. to 500° C.

8. The method according to claim 1, wherein the metal wire wound on the carrier is heated in step b) thermically in a heating furnace, or electrically by a contact of the metal wire with electricity, in particular with alternating current or direct current.

9. The method according to claim 1, wherein the metal coil has a diameter of less than 1.00 mm, in particular a diameter in the range of 0.01 mm to 0.75 mm, further in particular 0.10 mm to 0.50 mm, or 0.10 mm to 0.25 mm.

10. The method according to claim 1, wherein the method is performed acid-free, in particular aqua regia-free.

11. A metal coil, in particular a metal coil comprising or consisting of tungsten (W) or a tungsten alloy, obtainable by the method according to claim 1, wherein the surface of the metal coil in particular has no traces of etching, wherein the surface of the metal coil is further free in particular of chloride ions and / or optionally has a roughness with a Ra value of 4 um to 1 μm.

12. A use of the metal coil manufactured according to claim 1, in a heat conduction vacuum gauge, in particular in a Pirani element, further in particular as a glow filament.

13. Heat conduction vacuum gauge having the metal coil manufactured according to claim 1.

14. A use of the metal coil manufactured according to claim 11 in a heat conduction vacuum gauge, in particular in a Pirani element, further in particular as a glow filament.

15. Heat conduction vacuum gauge having the metal coil manufactured according to claim 11.

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