Device for knitting precious metal nets

Abstract

Device for knitting precious metal nets in the form of a flat knitting machine comprising: 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 back needle bed on which knitting can be done simultaneously with the wire; 5. A unit for applying a lubricant, positioned so that at least one wire can come into contact with the lubricant after leaving the unit under 1. and before reaching the unit under 3.

Description

[0001] The present invention relates to a device for knitting precious metal nets.

[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 mesh can, in principle, be borrowed from textile knitting processes (US5188813; WO9202301A; US5931023). Flat knitting machines are preferably used for knitting precious metal mesh (DE4206199C1). The flat knitting machine preferably has a front and a rear needle bed in which the tongue needles are installed. Depending on the machine's programming, the tongue needles move through different positions. 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 through 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] WO9202301A proposes applying a lubricant to a precious metal thread before knitting it on a knitting machine. However, it does not specify how this should be done.

[0015] The present invention addresses the question of how an apparatus for knitting precious metal meshes can be designed to achieve optimal interaction of all components involved. In particular, it aims to clarify how a lubricant should be applied to the precious metal wire to achieve an improved knitting result, e.g., by knitting without failure due to thread breakage or without excessive wear of the apparatus.

[0016] 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.

[0017] By specifying a device for knitting precious metal nets 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 back needle bed on which knitting can be done simultaneously with the wire; as well as 5. A unit for applying a lubricant, positioned such that the at least one wire can come into contact with the lubricant after leaving unit 1 and before reaching unit 3, advantageously solves the problem at hand. By lubricating the wire as precisely as possible after it leaves the wire-feeding unit and before reaching the wire guide, it is ensured that friction on the components necessary for knitting in a flat knitting machine, which come into contact with the precious metal wire, is minimized. This leads to significantly fewer failures due to wire breakage and a longer service life for the corresponding components, in particular, for example, the yarn tensioner, the yarn guide, and the needles. Preferably, the precious metal wire is lubricated between units 2 and 3.

[0018] 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 has, as shown in Figure 4, a front (8) and a rear (9) needle bed, 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.

[0019] 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).

[0020] 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.

[0021] 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).

[0022] 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).

[0023] At least one second unit is provided in the device according to the invention to maintain sufficient, but not excessive, tension on the at least one wire. 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. These so-called tension regulators can be controlled mechanically or electronically, such as electromagnetic dancers (e.g., from Supertek: https: / / www.winding-technology.com) for drawing, coiling, rewinding, or winding wire. These units are commercially available. The tension of the wire or wires is adjusted so that the wire does not break under tensile stress and is gently fed into the machine with a constant tensile force. This reduces the use of deflection units and the resulting friction.The tension must be sufficiently high so that the wire is not too loose and sags, as this could cause it to become entangled in the needle bed. Sufficient tension is characterized by the following tensile forces: for thin wires with a diameter of 50–79 µm, 1–15 grams; for medium wires with a diameter of 80–94 µm, 5–20 grams; and for thick wires with a diameter of 95–150 µm, 10–30 grams.

[0024] 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].

[0025] As already mentioned, the precious metal wire is subjected to bending stress and friction during the knitting process. In particular, the yarn guide (13), which is responsible for guiding the precious metal wire to the tongue needles (10) in the correct position, places a strain on the wire. This is because the 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 may even lead to its 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 of the wire guides in the unit described in section 3 is equipped with a deflection roller for the wire.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] Preferably, the deflection roller(s) or guide rollers have a radially circumferential groove in the center of their outer running surface, which prevents 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.

[0030] According to the invention, 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 a unit 5 for applying a lubricant, which is positioned such that the 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 tray containing oil, through which the 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.

[0031] A problem well-known to experts when knitting technical textiles with metal wires is needle wear. During the stitch formation process, the wire is guided through the needle hook and rubs against the needle surface. For this reason, the needles are usually chrome-plated. Nevertheless, after a certain period of use, indentations result from the friction between the wire and the needle hook. These indentations can lead to an uneven stitch pattern (due to the wire getting caught) and, in the worst case, to wire breakage. This risk is reduced by using a lubricant with a suitable application device.

[0032] Lubricating greases or oils suitable for this purpose can be used. Preferably, these are oils selected from the group of mineral oils, synthetic oils, or semi-synthetic oils, and preferably an oil-water emulsion. Lubricating oils for metalworking, such as those from the group of forming lubricants and cooling lubricants, are most preferably used. These are commercially available (e.g., https: / / www.klueber.com / de / de / produkte-service / produkte / klueber-silvertex-w-22 / 10157 / ).

[0033] 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).

[0034] Additives are primarily selected compounds from the group consisting of corrosion inhibitors (e.g., alkanolamines, fatty acids) or friction improvers. Examples include fatty acids, fatty acid derivatives, and organic amines. These highly polar molecules are adsorbed onto the metal surface, forming a friction-reducing surface film. Alternatively, anti-wear additives can be used: These are added to cooling lubricants to reduce direct contact between sliding surfaces (e.g., metals). They form plastically deformable layers with the metal surface. Zinc dialkyldithiophosphates and tricresyl phosphates are commonly used.

[0035] In an advantageous embodiment, the unit shown in section 5 comprises an absorbent soft material that is impregnated with the lubricant, in particular the oil or the emulsion ( Fig. 5) The unit is preferably designed such that the precious metal wire is in contact with the absorbent soft material directly after leaving the wire feeder. "Directly" in this context means that it does not contact any other unit of the device according to the invention beforehand. In a preferred embodiment, the absorbent soft material is selected from the group consisting of cloth, sponge, felt, nonwoven fabric, and foam.

[0036] This application method allows for precise wetting of the precious metal wire with the oil or oil-water emulsion. In a highly preferred embodiment, this unit is designed such that the wire is contacted on two sides, in particular with a felt, when the wire is drawn through a corresponding unit 5. Fig. 6) The oil-impregnated felt can, for example, be folded, and the wire runs between the pressed-together halves of the oil-impregnated felt. Other embodiments that ensure wetting of the wire on both sides with the oil or emulsion are known to those skilled in the art.

[0037] In another advantageous alternative, the oil or emulsion can be applied such that the wire is drawn through a unit below 5, in which the wire is dripped with oil from above ( Fig. 7) A person skilled in the art knows which dripping device can be used here. This can advantageously be done by using a drip hose or similar device that delivers the lubricating fluid to the wire surface. Such drip hoses are known to those skilled in the art (e.g., https: / / www.bj-aqua.de / ; https: / / ksrain.de / ).

[0038] In a preferred embodiment of the device according to the invention, the wire is guided through additional eyelets or around additional rollers to hold the wire in a precise position. Such devices are known to those skilled in the art (https: / / www.webereibedarf.de / ). It is advantageous if the eyelets or rollers are made of or coated with plastic or ceramic. These are commercially available (https: / / www.steintex.de / portfolio-items / fadenfuehrer / ?portfolioCats=9#bundoesen-detail). The coating serves to reduce friction when the wire slides past the eyelet or roller.

[0039] The device presented here allows for the knitting of precious metal meshes in a particularly advantageous manner. Measures to reduce friction during knitting protect both the wire and the otherwise highly abrasion-prone components of the device. The deflection rollers in the thread guide and the contact of the at least one wire with a lubricant result in surprisingly few wire breaks and a longer service life for, among other things, the needles, thanks to the device according to the invention. The extent of the improvement was surprising even to those skilled in the art. The device according to the invention surprisingly leads to 50% fewer wire breaks, and the needles have a 25% longer service life. The quality of the mesh pattern of the precious metal mesh also improves accordingly.

[0040] Figures: 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. Fig. 5: Representation of the unit under 5. With an oil-soaked felt. Fig. 6: Representation of the unit under 5 with a folded oil-soaked felt. Fig. 7: Drip device for wetting the wire 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 17 Drip device 18 wire 19 Direction of the wire 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, 0018] US 5266293A

[0011] EP 544710A1

[0011] US 5188813

[0012] WO 9202301A [0012, 0014] US 5931023

[0012] EP 680787A1

[0013] EP 1358010B2

[0019] 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 / ;

[0022] Manufacturing of winding technology products, Author: Andreas Dobroschke, Manufacturing Technology Erlangen - ISBN 978-3-87525-317-7

[0022] . Supertek company: https: / / www.winding-technology.com

[0023] https: / / www.klueber.com / de / de / produkte-service / produkte / klueber-silvertex-w-22 / 10157

[0032]

Claims

[1] Device for knitting precious metal nets in the form of a flat knitting machine comprising:

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 back needle bed on which knitting can be done simultaneously with the wire; 5. A unit for applying a lubricant, positioned so that at least one wire can come into contact with the lubricant after leaving the unit under 1. and before reaching the unit under 3. [2] Device according to claim 1, characterized by , that the unit under 3. is equipped with a deflection pulley for the wire. [3] Device according to any one of the preceding claims, characterized by , that the unit under 5. has an absorbent soft material or brush soaked in oil. [4] Device according to claim 3, characterized by that the wire is drawn through a device in which the wire is contacted with a felt on two sides. [5] Device according to claim 1, 3 or 4, characterized by that the oil is an oil-water emulsion. [6] Device according to claim 1 or 2, characterized by , that the wire is drawn through a unit under 5. in which the wire is dripped with oil from above. [7] Device according to claim 1 or 2, characterized by that the wire is guided through additional eyelets or around additional rollers to keep the wire in an exact position. [8] Device according to claim 7, characterized by that the eyelets or rollers are made of plastic or ceramic or are coated with it.

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