Yarn guide

Abstract

The utility model relates to a yarn guide (13) and a flat knitting machine used for knitting precious metal wires, in the flat knitting machine, one or more deflection rollers (14) are arranged at the end of the yarn guide (13), the precious metal wires are turned through the deflection rollers, and therefore at least one deflection roller is a guide roller, and the guide roller is a guide roller. According to the invention, the guide roller has, in the middle of the outer running surface thereof, a radially circumferential groove (15) which prevents the noble metal wire from slipping off the deflection roller, the groove (15) having a width of 0.2 mm to 2 mm, and the groove (15) having a circular cross-section, the radius of curvature (16) of which is greater than the width of the groove. The technical result consists in that this minimizes the friction between the noble metal wire and the deflection roller, thereby minimizing the wear of the noble metal wire, thereby reducing the risk of wire breakage.

Description

TECHNICAL FIELD

[0001] The present utility model relates to a yarn guide for a knitting machine for knitting a precious metal mesh, which is used for the catalytic oxidation of ammonia, in particular to NO, as it is used for the production of nitric acid. BACKGROUND

[0002] Gas reactions catalyzed by precious metals, such as the oxidation of ammonia using oxygen from the air (Ostwald process) in the production of nitric acid or the conversion of ammonia and methane to hydrogen cyanide in the presence of oxygen (Birkeland-Eyde process), have been of great industrial importance for a long time, as these gas reactions provide basic chemicals for the chemical industry and fertilizer production in a large-scale industrial manner (Andreas Jess, Peter Wasserscheid: Chemical Technology; Wiley-VCH Verlag, Weinheim 2013, Chapter 6.4).

[0003] The core of these heterogeneous catalytic gas reactions is the precious metal catalyst in the form of a gas-permeable spatial structure in which the reaction takes place. For some time, precious metal meshes made of fine precious metal wires in the form of woven fabrics (DE 40 28 916 C2) or knitted fabrics (EP 0 364 153 B1, DE 42 06 199 C1) have been successful in this regard.

[0004] In this case, the catalyst mesh is usually arranged in a flow reactor in a plane perpendicular to the flow direction of the gas mixture. Conical arrangements are also known. It is appropriate for several precious metal meshes to be arranged one after the other and combined into a mesh stack.

[0005] Figure 1 As an example of catalytic ammonia oxidation (Ostwald process), a reactor with a mesh stack installed inside is shown schematically, which functions as follows:

[0006] In the reaction zone (2) of the flow reactor (1), a mesh stack (3) is arranged in a plane perpendicular to the flow direction, which consists of several catalyst meshes (4) arranged one after the other on the inlet side and a separation and getter mesh (5) downstream. The mesh stack is held in place by clamping.

[0007] The reaction gas (ammonia-air-oxygen mixture with an ammonia content of 9 to 13 vol.%) (6) flows through the mesh stack (3) at atmospheric pressure or elevated pressure, wherein the ignition of the gas mixture takes place in the inlet region and the combustion reaction to form nitric oxide (NO) and water covers the entire reaction zone (2):

[0008] 4NH3+ 5O2 (air) → 4NO + 6H2O

[0009] The undesired side reactions are the oxidation of ammonia to nitrogen (N2) and nitrous oxide (N2O), where the former only reduces the yield of NO, but the latter is also a strong greenhouse gas:

[0010] 4NH3+ 3O2 (air) → 2N2+ 6H2O

[0011] 4NH3+ 4O2 (air) → 2N2O + 6H2O

[0012] The NO in the effluent reaction gas mixture then reacts with excess atmospheric oxygen to form NO2:

[0013] 2NO + O2→ 2NO2

[0014] The undesired side reaction here is the formation of nitrous oxide:

[0015] 2NO + 1 / 2O2→ 2N2O

[0016] NO2reacts with water in a downstream absorption process to form nitric acid, for example for fertilizer production:

[0017] 3NO2+ H2O → 2HNO3+ NO

[0018] The noble metal wire made of platinum, rhodium or alloys of these metals with other noble or base metals is used to produce the noble metal mesh. Here it is usually a platinum-rhodium alloy or a platinum-palladium-rhodium alloy containing 88 to 97% by weight of platinum. Platinum is necessary to achieve as high an ammonia conversion as possible, rhodium increases the selectivity for NO, thus reducing the emission of nitrous oxide, and increases the mechanical strength (G.R. Maxwell: "Synthetic Nitrogen Products - A Practical Guide to the Products and Processes", Springer Science+Business Media, Inc. 2005, page 220). Palladium is used to reduce the noble metal costs by replacing platinum depending on the noble metal prices.

[0019] The knitted noble metal mesh is produced using a flat knitting machine. The structure of a flat knitting machine is shown in Figure 2 The flat knitting machine has a front needle bed (8) and a back needle bed (9) in which latch needles (10) are mounted. The yarn or noble metal wire is fed by a yarn guide (13). The following description is limited to the knitting of noble metal wire.

[0020] If several thread guides are used, several noble metal threads can also be knitted synchronously. Depending on the programming of the machine, the needles pass through different positions. Thus, the structure of the knitted fabric is predetermined by the movement of the needles. One special feature of flat knitting machines compared to other fabric forming machines is that the knitted fabric can be formed independently on the front and back needle beds (single-bed fabric). In addition, spacer knitted fabrics (double-bed fabric) can be formed, in which the noble metal threads form loops or tuck stitches alternately in front and back (EP 1358010 B2). The knitted fabric is knitted downwards between the two needle beds (11). This is achieved by continuously cutting the individual formed stitches at the cutting position and the cutting tooth edge (12).

[0021] Compared to woven noble metal meshes, knitted noble metal meshes have many advantages, which is why they are preferred in today's industrial applications. On the one hand, the knitting technique offers the possibility of a high degree of flexibility in the knitting pattern, the thickness of the noble metal threads used and the resulting weight per unit area. On the other hand, noble metal knitted fabrics can be produced more economically, since the knitting technique requires less preparation time than the weaving technique. This is particularly desirable in view of a significantly reduced combination of noble metals in production.

[0022] Noble metal meshes of any length can be produced on flat knitting machines. However, the minimum stitch width, i.e. the density of the knitted fabric, is limited by the maximum number of needles per given width.

[0023] Important terms will be defined below:

[0024] Noble metals are gold, silver and platinum metals (Ru, Rh, Pd, Os, Ir, Pt).

[0025] A mesh that catalyzes the reaction of ammonia with oxygen is called a catalyst mesh.

[0026] A getter mesh is a mesh that is combined in the reaction gas stream on the outlet side of the catalyst mesh in order to capture volatile platinum oxides in order to recover them by alloying with the palladium of the getter mesh, thus minimizing the loss of platinum.

[0027] The ensemble of catalyst mesh and getter mesh is called a noble metal mesh.

[0028] A separation mesh is a high-temperature stable steel mesh that is installed between the noble metal meshes to prevent them from sintering together.

[0029] A mesh stack consists of a catalyst mesh on the mesh stack inlet side and optionally a getter mesh on the mesh stack outlet side and, if appropriate, separation meshes installed between the noble metal meshes.

[0030] A flow reactor is a reactor that ensures the passage of a reaction gas through a mesh stack installed therein.

[0031] The knitting process is performed using a latch needle. Each warp of the knitted fabric requires a latch needle.

[0032] The precious metal wire is fed to the latch needle via a yarn guide. In this case, precise positioning is crucial so that the latch needle can grasp the precious metal wire and avoid insertion errors, which would lead to knitting mistakes in the product.

[0033] Needle bed, single-bed fabric, double-bed fabric, connecting yarn: The needle bed is a component of a plain knitting machine that guides the latch needles. Plain knitting machines typically have a front needle bed and a back needle bed, on which a single-bed fabric can be knitted. If these two fabrics are knitted together during the knitting process via a connecting yarn (Polfaden), the resulting fabric is a double-bed fabric.

[0034] A tuft is created by connecting two loops. A tuft is a type of tuft that is inserted from one needle bed into the opposite needle bed in R / R knitting. "Tuft," "loop," and "R / R knitting" are all well-known terms to professionals in the field.

[0035] Coil rows and coil runs: A coil formed one by one from the same precious metal wire is called a coil row. Parallel coil rows are held together by winding the coils together in a coil run.

[0036] During knitting, precious metal wires are subjected to bending stress and friction. The yarn guide (13), in particular, which must feed the precious metal wire to the latch needle (10) at the correct position, represents the load on the precious metal wire, as it deflects approximately 90° at the wire exit and travels at high speed along the edge of the eyelet during this process. This leads to damage to the surface of the precious metal wire, potentially causing wire breakage and wear on the yarn guide eyelet. Furthermore, due to its bending stiffness, precious metal wire is more difficult to hold in place than woven yarn, thus insertion errors may occur during the loop formation process in knitting. Utility Model Content

[0037] Therefore, the purpose of this invention is to reduce wear on the precious metal wire and the yarn guide, and to improve the positioning of the precious metal wire so that it can be grasped by the latch needle. Therefore, the precious metal wire will always be referred to as the raw material. Hereinafter, steel wire or yarn can also be knitted if necessary.

[0038] This objective is achieved by a yarn guide for use in a plain knitting machine for knitting precious metal yarns, characterized in that the yarn guide is equipped with at least one deflecting roller at the yarn exit, via which the precious metal yarn is deflected, thus the at least one deflecting roller is a guide roller, the guide roller having a radially circumferential groove in the middle of its outer running surface, the groove preventing the precious metal yarn from slipping off the deflecting roller, the groove having a width of 0.2 mm to 2 mm, and the groove having a circular cross-section, the radius of curvature of the circular cross-section being greater than the width of the groove.

[0039] Advantageously, the yarn guide is equipped with two deflecting rollers at its end, the two deflecting rollers being centrally arranged on the same plane, and their axes being perpendicular to the plane and parallel to each other, so that the precious metal wire leaves the yarn guide between the two deflecting rollers.

[0040] Advantageously, the at least one deflection roller is equipped with a sliding bearing.

[0041] Advantageously, the deflection roller is equipped with a Teflon or bronze bushing as a sliding bearing.

[0042] Advantageously, the at least one deflection roller is equipped with a rolling bearing.

[0043] Advantageously, the rolling bearing is a ball bearing.

[0044] Advantageously, the rolling bearing is made of steel.

[0045] Advantageously, the deflection roller is made of steel.

[0046] Advantageously, the deflection roller is the outer ring of the rolling bearing.

[0047] Advantageously, the yarn guide is installed in the plain knitting machine such that the axis of the deflection roller is arranged at a right angle to the plane of motion of the yarn guide. Attached Figure Description

[0048] Figure 1 The reactor with an internal mesh stack is schematically shown using catalytic ammonia oxidation (Ostwald process) as an example.

[0049] Figure 2 This shows the structure of a plain knitting machine;

[0050] Figure 3 An example of the yarn guide of this invention is shown, in which the deflection roller can be seen; and

[0051] Figure 4 An example of the deflection roller of this invention as a guide roller is shown. Detailed Implementation

[0052] Figure 3 An example of the yarn guide of this invention is shown. The deflection roller (14) is clearly visible. The precious metal wire is deflected via the deflection roller, therefore the at least one deflection roller is a guide roller, which has a radially circumferential groove (15) in the middle of its outer running surface. The groove (15) prevents the precious metal wire from slipping off the deflection roller and has a width of 0.2 mm to 2 mm. Furthermore, the groove (15) has a circular cross-section, and the radius of curvature (16) of the circular cross-section is greater than the width of the groove.

[0053] The deflection roller consists of a wheel supported on a shaft with minimal friction, through which the precious metal wire is guided. This minimizes friction between the precious metal wire and the deflection roller, thereby minimizing wear on the precious metal wire and reducing the risk of wire breakage.

[0054] The yarn guide moves back and forth above the latch needle, causing the exit direction of the precious metal wire to change 180° at the end of the knitting bed. Preferably, the yarn guide is equipped at its end with two deflecting rollers extending in parallel axes, through which the precious metal wire exits the yarn guide. Thus, the precious metal wire is guided through the deflecting rollers in both directions of motion without requiring the yarn guide to be rotated.

[0055] The deflection roller should be able to rotate as easily and quickly as possible to keep the friction between the precious metal wire and the deflection roller as low as possible. Therefore, a variation of the yarn guide is equipped with a deflection roller featuring a sliding bearing bushing. Polytetrafluoroethylene (PTFE) or bronze is suitable as the sliding bearing bushing material because of its low friction during operation and long service life. Compared to rolling bearings, sliding bearings have the advantages of being less sensitive to shocks and vibrations, and less sensitive to contamination. Furthermore, their construction is very simple.

[0056] However, the deflection roller is preferably equipped with rolling bearings because, although these are technically more expensive, they can further reduce friction between the precious metal wire and the deflection roller. Ball bearings are particularly preferred because they keep the bearing axially stable and can also reduce friction caused by axial forces acting on the deflection roller.

[0057] Steel is particularly suitable as a material for rolling bearings because of its wear resistance. For the same reason, steel is also very suitable for deflection rollers. In this case, the deflection roller can also serve as the outer ring of a rolling bearing.

[0058] Preferably, the deflection roller is a guide roller with a radially circumferential groove at the center of its outer running surface, which prevents the filament or yarn from slipping off the roller. Slipping of the filament would cause an interruption to the knitting process and should be avoided under any circumstances. The groove preferably has a width of 0.2 mm to 2 mm.

[0059] The groove preferably has a circular cross-section with a radius of curvature greater than the groove width. This avoids damage to the filament surface at the edges extending to the groove on both sides, thus preventing potential filament breakage.

[0060] In the application of the yarn guide of this invention in a plain knitting machine for knitting precious metal yarns, the yarn guide is preferably installed in the plain knitting machine such that the axis of the deflector roller is arranged at a right angle to the plane of motion of the yarn guide. This ensures that the precious metal yarn is always at a right angle to the axis of the deflector roller, and through this arrangement, the friction between the precious metal yarn and the deflector roller and the risk of slipping off the deflector roller are minimized.

[0061] List of reference signs :

[0062] 1. Flow reactor

[0063] 2. Reaction zone

[0064] 3. Net stack,

[0065] 4. Catalyst mesh

[0066] 5. Getter net,

[0067] 6. Reaction gases

[0068] 7 products,

[0069] 8. Front needle bed,

[0070] 9. Rear needle bed,

[0071] 10. Tongue needles,

[0072] 11. Knitted products,

[0073] 12. Cut the edge of the toothed edge.

[0074] 13. Yarn guide,

[0075] 14 Deflection rollers,

[0076] 15 grooves,

[0077] 16. Radius of curvature of the groove.

Claims

1. A yarn guide for a flat knitting machine for knitting noble metal yarns, characterized in that, The thread guide is equipped at the thread exit with at least one deflection roller (14), via which the noble metal thread is diverted, therefore the at least one deflection roller is a guide roller, which has a radially encircling groove (15) in the middle of its outer running surface, which prevents the noble metal thread from slipping off the deflection roller, the groove (15) has a width of 0.2 mm to 2 mm, and the groove (15) has a circular cross section, and the radius of curvature (16) of the circular cross section is greater than the width of the groove.

2. The yarn guide of claim 1, wherein The thread guide (13) is equipped at the end with two deflection rollers (14), which are arranged centrally on the same plane, and their axes are perpendicular to the plane and parallel to each other, so that the noble metal thread exits the thread guide between the two deflection rollers.

3. A yarn guide according to claim 1 or 2, characterised in that The at least one deflection roller is equipped with a plain bearing.

4. A yarn guide according to claim 3, characterised in that The deflection roller is equipped with a Teflon or bronze bushing as a plain bearing.

5. A yarn guide according to claim 1 or 2, characterised in that The at least one deflection roller is equipped with a rolling bearing.

6. A yarn guide according to claim 5, characterised in that The rolling bearing is a ball bearing.

7. The yarn guide of claim 5, wherein, The rolling bearing is made of steel.

8. A yarn guide according to claim 1 or 2, characterized in that The deflection roller is made of steel.

9. The yarn guide of claim 5, wherein, The deflection roller is the outer ring of the rolling bearing.

10. A yarn guide according to claim 1 or 2, characterized in that The thread guide (13) is installed in the circular knitting machine in such a way that the axes of the deflection rollers are arranged at right angles to the movement plane of the thread guide.

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