Device for knitting precious metal wires

Abstract

Device for knitting precious metal wires in the form of a flat knitting machine, which has the following units: 1. at least one unit for wire feeding; 2. at least one wire tensioning unit; 3. at least one wire-guiding unit; and 4. a front and rear needle bed on which knitting can be carried out simultaneously with the at least one wire, the device being designed such that the unit under 2. creates a tension on the wire during the knitting process depending on the wire diameter, which is defined by the following formula (I): Voltage [g] = (0.11 × n) × wire diameter [μm] − 8 where n can take values ​​between 1 and 3 and the dimension [µm] -1 ] has.

Description

[0001] The present invention relates to a device for knitting precious metal wires. The invention describes flat knitting machines that are configured to maintain a specific yarn or wire tension during the knitting process.

[0002] Noble metal-catalyzed gas reactions, such as the oxidation of ammonia with atmospheric oxygen in nitric acid production (Ostwald process) or the reaction of ammonia with methane in the presence of oxygen to form hydrogen cyanide (Andrussow process), have long been of considerable industrial importance. These processes provide basic chemicals for the chemical industry and for fertilizer production on an industrial scale (Andreas Jess, Peter Wasserscheid: Chemical Technology; Wiley-VCH Verlag, Weinheim 2013, Chapter 6.4).

[0003] At the heart of these heterogeneously catalyzed gas reactions are precious metal catalysts in the form of gas-permeable three-dimensional structures on or within which the reaction takes place. For some time now, nets in the form of woven (DE4028916C2), knitted (DE4300791A1; EP606535A1) or crocheted (EP364153B1, DE4206199C1) structures made of fine precious metal wires have become established.

[0004] The catalyst meshes are typically arranged in a flow reactor in a plane perpendicular to the flow direction of the gas mixture. Conical arrangements are also known. It is advantageous to arrange several meshes one behind the other and combine them into a mesh stack.

[0005] The reaction gas or fresh gas (ammonia-air oxygen mixture with an ammonia content of 9 - 13 vol%) flows through the mesh stack under atmospheric or elevated pressure, whereby ignition of the gas mixture takes place in the inlet area and the combustion reaction to nitrogen monoxide (NO) and water covers the entire reaction zone: 4 NH3 + 5 O2 (air) → 4 NO + 6 H2O

[0006] Undesirable side reactions include the oxidation of ammonia to nitrogen and nitrous oxide (N2O), the former merely reducing the yield of NO, while the latter is also a potent greenhouse gas: 4 NH3 + 3 O2 (air) → 2 N2 + 6 H2O 4 NH3 + 4 O2 (air) → 2 N2O + 6 H2O

[0007] The NO in the outflowing reaction gas mixture subsequently reacts with the excess atmospheric oxygen to form NO2: 2 NO + O2 → 2 NO2

[0008] An undesirable side effect here is also the formation of nitrous oxide: 2 NO + ½ O2 → 2 N2O

[0009] The NO2 then reacts with water in a subsequent absorption process to form nitric acid, which is used, for example, in fertilizer production: 3 NO2 + H2O → 2 HNO3 + NO

[0010] For the production of precious metal meshes, precious metal wires made of platinum, rhodium, or alloys of these metals with other precious or base metals are used. Platinum-rhodium or platinum-palladium-rhodium alloys with 88 to 98 wt.% platinum are typical. Platinum is required to achieve the highest possible ammonia conversion rate, while rhodium improves the selectivity for NO, thereby reducing nitrous oxide emissions and increasing the mechanical strength of the meshes (GR Maxwell: "Synthetic Nitrogen Products - A Practical Guide to the Products and Processes", Springer Science + Business Media, Inc. 2005, p. 220). Palladium, in turn, is used to reduce precious metal loss by forming more stable alloys and, depending on current precious metal prices, to lower precious metal costs by replacing less platinum.

[0011] Several patent publications have already been released on the topic of precious metal meshes for ammonia oxidation. For example, US5266293A describes a knitted precious metal fabric in which the precious metal is selected from platinum group metals, gold and silver, and alloys thereof. EP544710A1 describes a knitting process for producing precious metal meshes, which offers several advantages over weaving.

[0012] The devices used for knitting precious metal meshes are generally known from textile knitting processes and can be adapted to the conditions of wire knitting (US5188813; WO9202301A; US5931023). Flat knitting machines are preferably used for knitting precious metal meshes (DE4206199C1). The flat knitting machine preferably has a front and a rear needle bed in which the tongue needles, which carry out the knitting process, are installed. The tongue needles pass through different positions depending on the machine's programming. The programming thus determines the structure of the knitted fabric. A special feature of the flat knitting machine compared to other fabric-forming machines is that knitted fabrics can be formed synchronously and independently on both the front and rear needle beds (single-bed fabric). The two knitted fabrics can be joined together by the knitting process (double-bed fabric).

[0013] The aforementioned DE4206199C1 relates to a process for producing gas-permeable meshes made of precious metals for the catalytic oxidation of ammonia. The precious metal meshes used are obtained by knitting wires, wherein the wires consist of platinum-rhodium alloys with 4 to 12 wt.% rhodium or wires of platinum-palladium-rhodium alloys with 4 to 38 wt.% palladium and rhodium. The wire diameters range from 50 to 120 µm. They can preferably be produced on flat knitting machines, with the needle pitch (distance between the needles on the flat knitting machine) between 3.63 mm and 1.81 mm and the stitch length between 2 and 6 mm. Multilayer meshes in mesh stacks can also be advantageously used for the oxidation reaction under consideration (EP680787A1).

[0014] Metal wires do not possess the same elasticity as other textile threads, such as polyester. This leads to mechanical stress on the wire during the knitting process, for example, of precious metal mesh on flat knitting machines. This stress is caused by jerky movements of the carriage and during the stitch formation process (pulling the needle on the wire loop). Such stress can lead to wire breakage and thus knitting defects. Therefore, the wire should be guided above the needle bed with as constant a tension as possible during knitting.

[0015] These and other problems that arise obviously from the available prior art for a person skilled in the art are solved by a device according to claim 1. The dependent claims of claim 1 relate to preferred embodiments of the device according to the invention.

[0016] By specifying a device for knitting precious metal wires in the form of a flat knitting machine, which has the following units: 1. at least one unit for wire feeding; 2. at least one wire tensioning unit; 3. at least one wire-guiding unit; and 4. a front and rear needle bed on which knitting can be carried out simultaneously with the at least one wire, the device being designed such that the unit under 2. creates a tension on the wire during the knitting process depending on the wire diameter, which is defined by the following formula (I): Voltage[g]=(0.11×n)×wire diameter[μm]−8 where n can take values ​​between 1 and 3 and the dimension [µm] -1By using this method, the problem can be solved advantageously. In a preferred embodiment, the value for n is between 1.5 and 2.5, and most preferably around 2. Preferably, the tension is 1-18 grams for thin wires with a diameter of 50-79 µm, 5-25 grams for medium wires with a diameter of 80-94 µm, and 8-40 grams for thick wires with a diameter of 95-150 µm (for information: 1 gram of tension = 0.98 cN; https: / / tradukka.com / unit / force / gram-force / centinewton / 10?hl=de). By adhering to the values ​​specified above during the knitting process, a more uniform knitting pattern is obtained. Furthermore, the entire knitting process is less prone to defects, as there are fewer wire breaks and less abrasion at the abrasion-prone areas. This applies in particular to the aforementioned compositions of the precious metal wires.

[0017] Flat knitting machines or flatbed knitting machines are already known to experts for knitting precious metal wire (DE4206199C1). The construction of the flat knitting machine is described in Fig. Figure 2 illustrates this. The flat knitting machine, unit 4, has a front (8) and a rear needle bed (9) into which the tongue needles (10) are installed. The yarn or precious metal wire is fed by a yarn guide or wire guide (13). If several yarn guides are used, multiple precious metal wires can be knitted simultaneously. The tongue needles pass through different positions depending on the machine's programming. The programming thus determines the structure of the knitted fabric via the movement of the tongue needles.

[0018] A special feature of the flat knitting machine compared to other fabric-forming machines is that knitted fabrics can be formed synchronously on both the front and rear needle beds independently of each other (single-bed fabric). Furthermore, spaced-spaced fabrics (double-bed fabric) can be produced, in which the precious metal wire alternately forms stitches or loops at the front and rear (EP1358010B2). The knitted fabric is worked downwards between the two needle beds (11). This is done by successively knocking off the individual formed stitches over the knock-off position and knock-off edge (12).

[0019] Knitted precious metal meshes offer several advantages over woven precious metal meshes, which is why they are now preferred in industrial applications. Firstly, knitting technology offers a high degree of flexibility with regard to knitting patterns, the thickness of precious metal wire used, and the resulting basis weight. Secondly, knitted precious metal meshes can be produced more economically, as knitting requires shorter setup times than weaving. This results in a significantly reduced amount of precious metal used in production. Precious metal meshes of any length can be produced on flat knitting machines. However, the minimum mesh size, i.e., the density of the knitted fabric, is limited by the maximum number of needles per given width.

[0020] The precious metal nets are stacked in the so-called net stack, which is placed in the reactor ( Fig. 1) The term "precious metal meshes" refers to the entirety of the catalyst and getter meshes. "Separation meshes" are meshes made of high-temperature-resistant steel, which are installed between the precious metal meshes to prevent them from sintering together. The mesh stack consists of the precious metal-containing catalyst meshes on the inlet side of the stack, and optionally the getter meshes on the outlet side, as well as the separation meshes, which may be installed between the precious metal meshes. In this context, "precious metals" refers to gold, silver, and the platinum group metals (Ru, Rh, Pd, Os, Ir, Pt).

[0021] The flat knitting machine has several essential units. At least one first unit is responsible for supplying the wire yarn or yarns at the required speed for the knitting process. Those skilled in the art know which devices are available for this purpose. The wire feeder(s) can preferably be simple rollers on which the wire(s) are wound and from which the at least one wire can be unwound. These can be electronically controlled or mechanically operated spoolers or unwinders, which are generally known from the textile industry. The spoolers or unwinders are commercially available in various designs for different spools and spool sizes, with speed, velocity, position, and length measurement, as well as tension control. For example, they can preferably be...Tangential unwinders or brush unwinding systems are used for the so-called overhead unwinding of the wire from the respective spool (e.g. https: / / www.mobac.de / wickelmaschinen / flyer-und-drahtablaeufe; https: / / wiretec.ch / ; https: / / www.winding-technology.com / ; or Flexible Automation Solutions for the Production of Winding Products, Author: Andreas Dobroschke, Fertigungstechnik Erlangen - ISBN 978-3-87525-317-7).

[0022] At least one second unit is provided in the device according to the invention to maintain the wire at a sufficient but not excessive tension. These wire tensioners are known to those skilled in the art from the textile knitting industry. Wire tensioning devices are also known in the winding technology of metal wires. The tension on the wire can preferably be applied by tension or compression. More preferably, a tensile tension is applied. This is set by so-called tension force regulators and can be controlled mechanically or electronically, such as electromagnetic dancers (Supertek; www.Supertek.de) for drawing, spooling, rewinding, or winding wire, fine wire, flat wire in various designs and alloys, fiber, synthetic fiber, glass fiber, textile fiber, stranded wire, micron tube, tape, foil, etc.The tension of the wire(s) is adjusted so that the wire does not break under tensile stress and is fed gently into the machine with a consistent pulling force. This reduces the use of guide rollers and the resulting friction. However, the tension must be high enough that the wire is not too loose and does not sag, as this could cause it to become entangled in the needle bed. The same applies to the use of a pressure regulator.

[0023] At least one other component is the wire guide or yarn guide. This serves to feed the precious metal wire to the needles. Precise positioning is crucial so that the needles can grip the precious metal wire and no insertion error occurs, which would result in a knitting defect in the product. Such devices are well known to experts in the field of knitting machines (see, for example, the links above). An advantageous yarn guide is mentioned, for example, in [reference to be added].

[0024] As already mentioned, the precious metal wire is subjected to bending stress and friction during the knitting process. In particular, the yarn guide (13), as unit 3, which is responsible for guiding the precious metal wire to the needles (10) in the correct position, and the wire tensioner, as unit 2, which must maintain tension on the wire, place stress on the precious metal wire. This is because the precious metal wire is deflected by approximately 90° at the wire exit via an eyelet and runs over the eyelet edge at high speed. This can damage the surface of the precious metal wire and possibly even lead to wire breakage. In any case, it contributes to wear on the yarn guide eyelet. Furthermore, due to its bending stiffness, precious metal wire is more difficult to hold in position than a textile thread, which can result in insertion errors during the stitch formation process of knitting. Advantageously, at least one wire guide of unit 3...and / or the wire tensioner of the unit under 2. is equipped with a deflection pulley for the wire.

[0025] A guide roller preferably consists of a wheel mounted on an axle with minimal friction, over which a precious metal wire is guided. This minimizes friction between the precious metal wire and the guide roller, thereby minimizing wear on the precious metal wire and reducing the risk of wire breakage. The yarn guide is advantageously moved back and forth above the tongue needles, so that the exit direction of the precious metal wire changes by 180° at each end of the knitting bed. Preferably, the yarn guide is equipped with two guide rollers at its end, the axes of which run parallel, with the precious metal wire exiting the yarn guide between the guide rollers. Fig. 3) Thus, the precious metal wire is preferably guided over a deflection pulley in both directions of movement without the need to rotate the thread guide.

[0026] The guide pulley should rotate as easily and quickly as possible to minimize friction between the precious metal wire and the pulley. Therefore, an advantageous version of the thread guide is equipped with guide pulleys featuring plain bearing bushings. Teflon or bronze are suitable materials for the plain bearing bushings because they run with low friction and ensure a long service life. Plain bearings have the advantage over roller bearings of being less sensitive to shocks and vibrations and less susceptible to contamination. Furthermore, their design is very simple.

[0027] However, the guide rollers are preferably equipped with rolling bearings, as these, although technically more complex, can further reduce the friction between the precious metal wire and the guide roller. Ball bearings are particularly preferred because they provide axial stability and can also reduce the friction generated by the axial forces acting on the guide roller. Steel is particularly suitable as a rolling bearing material because it is resistant to wear. For the same reason, steel is also very suitable for the guide roller. In this case, the guide roller can simultaneously serve as the outer ring of the rolling bearing.

[0028] Preferably, the deflection roller(s) are guide rollers which have a radially circumferential groove in the center of their outer running surface, preventing the wire or thread from slipping off the roller. Slippage of the wire necessitates an interruption of the knitting process and must be avoided at all costs. This groove preferably has a width of 0.2 to 2 mm. Preferably, the groove has a round cross-section with a radius of curvature of this cross-section greater than the groove width. Fig. 4) This prevents damage to the wire surface from the edges running on both sides towards the groove, thus preventing potential wire breakage.

[0029] Advantageously, after leaving the at least one wire feeding unit and preferably after leaving the at least one wire tensioning unit and before coming into contact with the at least one wire guiding unit, i.e., after leaving unit 1 or 2 and before reaching unit 3, the wire or wires are fed to unit 5 for the application of a lubricant, which is positioned so that the at least one wire can come into contact with the lubricant. The unit discussed here can be designed according to the specifications of a person skilled in the art. If in doubt, it is a container with the lubricant, e.g., a tub containing, for example, oil, through which the at least one wire is guided.By contacting the wire with a lubricant, the friction and thus the wear of the equipment of the device according to the invention and of the wire is minimized, which helps to minimize wire breakage and the abrasion of the other units of the device according to the invention.

[0030] In a highly preferred embodiment, the oil is an oil-water emulsion. The oil types mentioned above can be used. The emulsion should preferably contain 50-95 wt.%, preferably 70-90 wt.% water. Advantageously, further additives, such as emulsifiers, can be present in the emulsion. These are known to those skilled in the art (e.g., https: / / kluthe.com / magazin / emulgatoren-zur-herstellung-von-kuehlschmierstoffen / ). Others include, for example, petroleum sulfonates, alkali soaps, and amine soaps (e.g., triethanolamine salts of fatty acids).

[0031] The precious metal wire is guided from the at least one first unit, the wire feeder, via at least one wire tensioner to the wire guide, before the wire is picked up by a tongue needle of the flat knitting machine. The wire enters the wire tensioner, the second unit, at a specific speed. In a preferred embodiment, the device according to the invention is designed such that, during operation, the entry speed of the at least one wire into the wire tensioner is between 0.05 and 2 m / s, in particular between 0.20 and 1 m / s, preferably between 0.25 and 0.75 m / s. These speeds ensure that the wire is supplied quickly enough for an efficient knitting process without the risk of breakage.

[0032] As mentioned at the outset, the device according to the invention has at least one unit 2 for wire tensioning, which holds the wire at the specified tension during the initial setup. This is preferably done mechanically by pulling or pushing on a wire tensioner arm that encompasses the wire (e.g. Fig. 5) The expert knows how this can be done (https: / / www.karlmayer.com / de / produkte / kettvorbereitung / gatter / fadenspanner-waechter / ; https: / / www.supertek.de / produkte-und-services / wickeltechnik / zugkraftregler).

[0033] The tensioning of the wire in the at least one second unit is particularly preferably achieved by means of a spring or, for example, an elastic band. The specified tension of the at least one wire tensioner described in section 2 is particularly preferably maintained by a spring. Mechanisms familiar to those skilled in the art can be used to adjust the pressure or tension on the wire tensioner arm. For example, the spring can have a specific internal tension or a certain preload. The tension can be adjusted mechanically. However, it is advantageous if this preload can be adjusted automatically depending on the wire. In a further preferred embodiment, the tension of the wire is therefore adjusted automatically depending on the wire used and its thickness. Those skilled in the art know how this is to be done. For example, a device according to the invention equipped with a suitable computer program can be used here.

[0034] Instead of a tensioning device, the specified tension can alternatively be maintained by a counterweight. In this case, the wire preferably runs over a roller attached to a mechanical arm, which is pressed by a counterweight to exert the appropriate tension on the wire. The resulting pressure or tension holds the wire at the appropriate tension, which corresponds to the weight of the counterweight, less various frictional losses depending on the application. Fine adjustment of the wire tension [in grams] can be achieved, for example, by moving the weight along a mechanical arm. A pulley system allows for even finer adjustment of the weight.

[0035] To monitor the tension of the at least one wire tensioner, one or more sensors, preferably electrical, optical, or mechanical, can be used (https: / / www.hans-schmidt.com / produkte / handgeraete-mechanisch / ). Electrical sensors are preferred (https: / / www.hans-schmidt.com / produkte / stationaer-elektronisch / ). Alternatively, the tension can be monitored mechanically via a sensor. These sensors continuously monitor the wire tension and the wire tensioner during the knitting process and adjust the tension via computer control if the wire tension threatens to exceed the specified range. Preferably, a tensile force of 3–10 grams should be applied to the wire for thin wires with a diameter of 50–79 µm, 8–20 grams for medium wires with a diameter of 80–94 µm, and 15–35 grams for thick wires with a diameter of 95–150 µm.

[0036] To guide the wire and prevent it from jumping off any rollers present in units 2 and 3, and to keep it in position, guide loops made of, for example, ceramic or with a ceramic coating are preferably used. These loops are located between unit 1 and unit 3. They guide the wire and ensure that it is guided in the optimal position. These loops are known to those skilled in the art (https: / / www.steintex.de / portfolioitems / fadenfuehrer / ?portfolioCats=9 / #bundoesen-detail; https: / / www.webereibedarf.de / weberei-shop / keramik%C3%B6sen-fadenf%C3%BChrung-1 / ).

[0037] The present invention helps to establish an efficient and truly smooth knitting process with precious metal wires. Excessive tension on the wire puts stress on the needle hooks, which become indented due to friction with the wire. These indentations can later cause wires to snag and break. Furthermore, the tension must not be too low, as the wire will otherwise sag above the needle bed and catch on the edges of the needle bed, potentially breaking again. Accordingly, a tension as defined above must be selected for metal wires. Fig. 1: Construction of a flow reactor for the oxidation of ammonia. Fig. 2: Side view of a flat knitting machine for producing nets including yarn guide. Fig. 3: Detailed illustration of the thread guide. Fig. 4: Illustration of the deflection pulley with groove. Numbering: 1 flow reactor 2 Reaction zone 3 net stacks 4 catalyst mesh stacks 5 getter net stacks 6 Reaction gas 7 products 8 front needle bed 9 posterior needle bed 10 tongue needles 11 knitted product 12 Teeing-off edge 13 thread guides 14 pulleys 15 Nut 16 Radius of the groove's curvature Fig. 5: Wire tensioner 20 threads 21 Thread tensioner arm 22 spring 23 Thread deflection QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 4028916C2

[0003] DE 4300791A1

[0003] EP 606535A1

[0003] EP 364153B1

[0003] DE 4206199C1 [0003, 0012, 0013, 0017] US 5266293A

[0011] EP 544710A1

[0011] US 5188813

[0012] WO 9202301A

[0012] US 5931023

[0012] EP 680787A1

[0013] EP 1358010B2

[0018] Cited non-patent literature

[0000] Andreas Jess, Peter Wasserscheid: Chemical Technology; Wiley-VCH Verlag, Weinheim 2013, Chapter 6.4

[0002] GR Maxwell: “Synthetic Nitrogen Products - A Practical Guide to the Products and Processes”, Springer Science + Business Media, Inc. 2005, page 220

[0010] https: / / wiretec.ch / ; https: / / www.winding-technology.com / ;

[0021] Manufacturing of winding technology products, Author: Andreas Dobroschke, Manufacturing Technology Erlangen - ISBN 978-3-87525-317-7

[0021] https: / / www.karlmayer.com / de / produkte / kettvorbereitung / gatter / fadenspanner-waechter / ; https: / / www.supertek.de / produkte-und-services / wickeltechnik / zugkraftregler

[0032] https: / / www.steintex.de / portfolioitems / fadenfuehrer / ?portfolioCats=9 / #bundoesen-detail; https: / / www.webereibedarf.de / weberei-shop / keramik%C3%B6sen-fadenf%C3%BChrung-1 /

[0036]

Claims

[1] Device for knitting precious metal wires in the form of a flat knitting machine, which has the following units:

1. at least one unit for wire feeding; 2. at least one wire tensioning unit; 3. at least one wire-guiding unit; and 4. a front and rear needle bed on which knitting can be carried out simultaneously with the at least one wire, the device being designed such that the unit under 2. creates a tension on the wire during the knitting process depending on the wire diameter, which is defined by the following formula (I): Voltage[g]=(0.11×n)×wire diameter[μm]−8 where n can take values ​​between 1 and 3 and the dimension [µm] -1 ] has. [2] Device according to claim 1, characterized by , that the unit under 3. and / or 2. is equipped with a deflection pulley for the wire. [3] Device according to any one of the preceding claims, characterized by , that 5. a unit for the application of lubricant exists which is positioned such that the at least one wire can come into contact with the lubricant after leaving the unit under 1. and before reaching the unit under 3. [4] Device according to any one of the preceding claims, characterized by , that the device is designed such that the entry speed of the at least one wire into the wire tensioner during operation is between 0.05 - 2 m / s. [5] Device according to any one of the preceding claims, characterized by , that the wire tensioner under 2. maintains the specified tension by a spring. [6] Device according to any one of the preceding claims, characterized by , that the wire tensioner under 2. maintains the specified tension by a counterweight. [7] Device according to claim 5 and / or 6, characterized by that the voltage is electronically monitored via a sensor. [8] Device according to claim 5 and / or 6, characterized by that the voltage is mechanically monitored via a sensor. [9] Device according to any one of the preceding claims, characterized by , that the wire is guided into position with eyelets after leaving unit 1 and before reaching unit 3.

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