METHOD FOR PRODUCING NOBLE METAL MESHES ON FLATBED KNITTING MACHINES

Abstract

A method for producing a two-layer noble metal mesh on a flatbed knitting machine which has a first and a second needle bed. The method comprises: providing at least one wire containing noble metal; and knitting the noble metal mesh. The first and second layers of the noble metal mesh are knitted simultaneously on the first and second needle bed, and a supporting mesh is knitted on the first and second needle bed using a supporting thread. An abutting edge of the supporting mesh is connected to the two layers of the noble metal mesh via connecting stitches and knitted via both needle beds in the knitting rows containing the connection.

Claims

1. A method for producing a two-layer noble metal mesh on a flat-bed knitting machine, the flat-bed knitting machine comprising a first and a second needle bed, the method comprising the steps of: providing at least one noble-metal-containing wire, providing at least one noble-metal-free support thread, knitting a first layer of the noble metal mesh on the first needle bed and a second layer of the noble metal mesh on the second needle bed, the first layer comprising the abutting edges S11 and S12 and the second layer comprising the abutting edges S21 and S22, the abutting edge S11 at least partially abutting the abutting edge S21 and the abutting edge S12 at least partially abutting the abutting edge S22, knitting a support mesh on the first and second needle bed using the at least one noble-metal-free support thread, the support mesh comprising an abutting edge SH and an edge KH opposite the abutting edge, the abutting edge SH abutting an abutting edge S11 and S21 of each of the two layers of the noble metal mesh, all of the knitting processes taking place simultaneously, wherein the abutting edge SH of the support mesh is connected to the respective abutting edges S11 and S21 of the two layers of the noble metal mesh via at least one knit stitch, and wherein the support mesh is knitted with connecting stitches from both needle beds in the knitting rows on which the abutting edge SH of the support mesh is connected to the respective abutting edges of the two layers of the noble metal mesh S11 and S21.

2. The method according to claim 1, wherein the at least one noble-metal-containing wire consists of platinum, a platinum alloy, palladium, or a palladium alloy.

3. The method according to claim 1, wherein the first and the second layer of the two-layer noble metal mesh are knitted from a noble-metal-containing wire or noble-metal-containing wires of the same composition.

4. The method according to claim 1, wherein the first and the second layer of the noble metal mesh are knitted from a noble-metal-containing wire or noble-metal-containing wires of the same diameter.

5. The method according to claim 1, wherein the first and the second layer of the noble metal mesh are knitted in the same knitting pattern.

6. The method according to claim 1, wherein the first and the second layer of the noble metal mesh are congruent.

7. The method according to claim 1, wherein the first layer and the second layer of the two-layer noble metal mesh are at least partially connected at their abutting edges by at least one connecting knit stitch.

8. The method according to claim 1, wherein the abutting edge SH of the support mesh has the same length as the abutting edges S11 and S12 of the first and second layers of the two-layer noble metal mesh.

9. The method according to claim 1, wherein the shape of the support mesh correlates with the shape of the first and second layers of the two-layer noble metal mesh.

10. The method according to claim 1, wherein the abutting edge SH of the support mesh is connected over its entire length to the respective abutting edges S11 and S21 of the first and second layers of the two-layer noble metal mesh.

11. The method according to claim 1, wherein the support mesh surrounds at least 50% of the sides of the first and second layers of the two-layer noble metal mesh.

12. The method according to claim 11, wherein the support mesh comprises a plurality of regions.

13. The method according to claim 12, wherein the method comprises a further step in which the support mesh is removed.

14. The method according to claim 1, wherein the method comprises a further step in which a connecting stitch or connecting stitches between the first and second layers of the noble metal mesh are removed on one side.

Description

[0069] The invention is explained in more detail below with reference to drawings and an example. However, it is not limited to these embodiments.

[0070] FIG. 1 is a schematic view of a flow reactor for the heterogeneous catalytic combustion of ammonia.

[0071] FIG. 2 is a schematic view of the thread guide of an exemplary right side row between the two needle beds of a flat-bed knitting machine.

[0072] FIG. 3 shows embodiments of two-layer noble metal meshes that can be produced using the method according to the invention on flat-bed knitting machines comprising two needle beds.

[0073] FIG. 1 is a schematic view of a vertically-positioned flow reactor 1 for the heterogeneous catalytic combustion of ammonia. The catalyst system 2 forms the actual reaction zone of the flow reactor 1. It comprises catalyst packing 3 and downstream catchment meshes 4. The catalyst system 3 comprises a plurality of catalyst meshes 6 arranged one behind the other in the flow direction 5 of the fresh gas.

[0074] Typically, the catalyst meshes 6 are knitted meshes that are produced, for example, from various platinum-rhodium alloys by knitting wire having a diameter of 76 m. Catchment meshes 4 can also be provided.

[0075] FIG. 2 is a schematic view of the thread guide in an exemplary right side row of a knitting row between two needle beds 10 and 11 of a flat-bed knitting machine. Needles that are used during the knitting process are highlighted and the direction of the thread guide is indicated by arrows. Each circle symbolizes a needle. FIG. 2 A illustrates the thread guide for a thread or wire 12 for a right side row in which only stitches are knitted on the first needle bed. In the event that only stitches are knitted on the first needle bed 10 in the wrong side row and all further complete knitting rows, a single-layer knitted fabric is obtained. If only stitches are knitted on the second needle bed 11 in the wrong side rows, a two-layer knitted fabric is obtained. The knitting pattern used in FIG. 2 A also contains a float: stitches are only formed on every second needle of the needle bed. FIG. 2 B shows the right side row for a single-layer knitted fabric in which stitches are knitted on the first and second needle bed 10 and 11 with the thread or wire 12.

[0076] FIG. 3 shows embodiments of two-layer noble metal meshes that can be produced using the method according to the invention on flat-bed knitting machines comprising two needle beds.

[0077] FIG. 3 A and B show a two-layer noble metal mesh 100 consisting of two rectangular layers 101 and 102, with only the first layer 101 being visible in the frontal view in FIG. 3 A. FIG. 3 B shows a view of the noble metal mesh 100 opened along the abutting edges 111 of the first layer 101 and the abutting edge 112 of the second layer 102, which abuts thereagainst. The abutting edge 112 of the first layer is congruent with the abutting edge 113 of the second layer 102. The opening is to be understood virtually at this point and serves to provide a better understanding of the invention. The two layers 101 and 102 are connected along their abutting edges 112 and 113 to the abutting edge 120 of a support mesh 130 (in the illustration in FIG. 3 B, the connection to the abutting edge 113 is not shown for better visualization). The support mesh 130 is knitted in a single layer from a support thread, preferably a cotton thread, from connecting stitches from the two needle beds. The edge 121 of the support mesh 130 opposite the abutting edge 120 does not abut any other sides or edges of the noble metal mesh 20.

[0078] FIG. 3 C shows a two-layer noble metal mesh 200 which is surrounded on two sides by a support mesh. Only the frontal view of a first rectangular layer 201 is shown, which lies congruently above a further layer. The two layers are connected to two support mesh regions 230 and 231 via their respective abutting edges (only the abutting edges (210 and 211) of the first layer 201 can be seen in the figure). The first region of the support mesh 230 is manufactured in a single layer. The second region 231 can be manufactured in one or two layers.

[0079] FIG. 3 D shows a view, analogous to FIG. 3 C, of a two-layer noble metal mesh 300 which is surrounded on two adjacent sides by a support mesh. In the case of a noble metal mesh of this embodiment, for example, the knitting of the lower region 331 of the support mesh can be started, after which the two layers of the noble metal mesh 300 and a further region 330 of the support mesh are produced simultaneously. In the corresponding knitting rows, stitches are thus formed from the support material and the noble-metal-containing wire. Expediently, the two regions of the support mesh 330 and 331 can be interconnected.

[0080] FIG. 3 E shows a view, analogous to FIG. 3 C, of a two-layer noble metal mesh 400 which is surrounded on all four sides by a support mesh. In the figure, the support mesh is expediently divided into the regions 430, 431, 432 and 433; these regions are preferably interconnected. In the embodiment shown in FIG. F, a two-layer noble metal mesh 500 is also surrounded on four sides by support mesh regions (530, 531, 532, 533). One of the support mesh regions 532 does not abut the noble metal mesh 500, but is spaced apart from the noble metal mesh by a gap 534. In this embodiment, too, all of the regions are produced simultaneously, i.e., during a single knitting process, in the knitting direction from bottom to top.

[0081] FIG. 3 G shows a view, analogous to FIG. 3 C, of a two-layer noble metal mesh 600 consisting of two semicircular layers (only the first layer 601 is visible). The two layers are connected on one side along the relevant abutting edge (610 in the case of the first layer 601) to the support mesh 630 via its abutting edge 620. FIG. 3 H also shows a two-layer noble metal mesh 700 formed from two semicircular layers, in which mesh the layers are surrounded by two support mesh regions 730 and 731 at both abutting edges.

EXAMPLE AND COMPARATIVE EXAMPLE

[0082] In the example according to the invention and in the comparative example, on a flat-bed knitting machine comprising two needle beds, a rectangular layer (100 cm wide, 200 cm long) was knitted on each needle bed using a PtRh5 wire (76 m diameter), the two layers being interconnected on one side. A cotton yarn was used as the support thread.

[0083] In the comparative example, a single-layer support mesh region was knitted using the cotton yarn on the unconnected side of both layers. A single-layer knitted fabric comprising two regions (noble metal layer and support mesh) was thus knitted on each of the two needle beds.

[0084] In the example according to the invention, a single-layer support mesh knitted across both needle beds was knitted on the unconnected side of the two layers. The two noble metal layers were therefore knitted only with stitches on one needle bed each, while the support mesh was knitted with stitches on both needle beds.

[0085] The knitted fabric of the example according to the invention had a more uniform structure than the knitted fabric of the comparative example. Such irregularities in the knitted fabric represent potential mechanical weak points that have a negative effect when the mesh is used in the reactor.

Definition of the Reference Signs Used

[0086] 1 Flow reactor [0087] 2 Catalyst system [0088] 3 Catalyst packing [0089] 4 Catchment meshes [0090] 5 Flow direction [0091] 6 Single-layer catalyst meshes [0092] 10 First needle bed [0093] 11 Second needle bed [0094] 12 Thread/wire [0095] 100, 200, 300, 400, 500, 600, 700 Noble metal mesh [0096] 101, 201, 301, 401, 501, 601, 701 First layer of the noble metal mesh [0097] 102 Second layer of the noble metal mesh [0098] 110, 210, 310, 410, 510, 610, 710 Abutting edges of the first layer of the noble metal mesh [0099] 111, 211, 311, 411, 511, 611, 711 [0100] 112, 113 Abutting edges of the second layer of the noble metal mesh [0101] 130, 230, 330, 430, 530, 630, 730 Support mesh [0102] 120, 220, 320, 420, 520, 620, 720 Abutting edge of the support mesh [0103] 121, 221, 321, 421, 521, 621, 721 Edge of the support mesh [0104] 231, 331, 431, 531, 731 Second support mesh region [0105] 432, 532 Third support mesh region [0106] 433, 533 Fourth support mesh region [0107] 534 Gap between noble metal mesh and support mesh