Use of a nozzle plate for the production of silica gel fibers

Abstract

Use of a nozzle plate comprising at least one nozzle with a nozzle opening, wherein the nozzle opening has a cross-sectional area of ​​size A1, wherein a separation edge with an angle β in the range of 5° to 90° extends around the nozzle opening, wherein the area which is directly adjacent to the nozzle opening outside the nozzle and extends around the nozzle opening has an area of ​​size A2, characterized in that - the ratio A2 / A1 is less than 1, - the nozzle plate comprises a number of nozzles ranging from 1 to 1000, and - the nozzles are designed as nozzle inserts that are inserted into corresponding openings in the nozzle plate to produce silica gel fibers.

Description

[0001] The present invention relates to the use of a nozzle plate for the production of silica gel fibers.

[0002] Patent DE 196 09 551 C1 and German patent application DE 10 2004 063 599 A1 disclose a process for producing silica gel fibers. The process comprises several steps. In a first step, a spinning mass is produced, which in a second step is forced from a pressure vessel through nozzles and emerges in the form of filaments. Depending on the size of the nozzles, the filaments have a diameter of approximately 10 to 100 µm.

[0003] German patent application DE 10 2004 063 599 A1 discloses details of the nozzles through which the spinning mass is extruded. A 7- or 19-hole nozzle plate is used. The pilot hole is 3.0 mm wide, and the hole diameter D is 0.15 mm. With a capillary length L of 0.45 mm, this results in an L / D ratio of 3. Fig. Figure 2 of the disclosure document schematically shows the nozzle plate and a single hole nozzle in cross-section.

[0004] US 4 724 109 A discloses a device with permanently installed nozzles.

[0005] DE 2 324 599 A discloses a spinneret plate with which a heating element and, if applicable, a temperature sensor is or are connected, achieving large heat transfer surfaces.

[0006] These nozzle plates described in the prior art have disadvantages. At the beginning of a pressing process of the spinning mass through a nozzle, as disclosed in DE 10 2004 063 599 A1, the emerging spinning mass wets the flat area around the nozzle opening. Spinning mass accumulates around the opening until, due to gravity, it gradually detaches from the nozzle opening and falls to the ground in the form of a droplet, trailing a silk thread behind it.

[0007] The individual nozzles exhibit different temporal behaviors. Some nozzles produce a thread immediately, but its thickness is initially inconsistent because some of the emerging spinning material adheres to the area around the nozzle opening and only detaches from the nozzle plate after varying intervals, leaving only a thin film. Other nozzles produce threads that break, and only after a certain time does a new, uniform thread form. In addition to this inconsistency, the spinning material around the nozzle opening can impair thread formation throughout the entire spinning process if it detaches only partially from the nozzle plate and the remaining material comes into contact with the thread. This leads to disruptions in thread formation and movement, potentially resulting in multiple threads becoming entangled or periodic dripping.

[0008] These problems, for example, lead to the discarding of the filaments initially emerging from the nozzles due to their inconsistency. If the filament production process is interrupted, uniform filaments can only be produced again after a significant start-up time and extensive cleaning of the nozzle plate. It is very frequently observed that spinning material, which inevitably remains as a thin film around the nozzle opening after the spinning mass detaches from the nozzle plate, causes the spinning mass to detach only very incompletely from the nozzle plate when the spinning process is restarted, meaning the nozzle plate must first be cleaned before it can be used again.

[0009] Based on the described state of the art, a person skilled in the art would therefore face the task of finding a solution to prevent the adhesion of spinning material to the nozzle openings and the associated initial formation of inconsistent threads. The solution should be particularly suitable for the production of silica gel fibers.

[0010] According to the invention, this problem is solved by using a nozzle plate according to claim 1. Preferred embodiments are found in the dependent claims.

[0011] The present invention therefore relates to the use of a nozzle plate comprising at least one nozzle with a nozzle opening, wherein the nozzle opening has a cross-sectional area of ​​size A1, wherein a separation edge with an angle β in the range of 5° to 90° extends around the nozzle opening, wherein the area which is directly adjacent to the nozzle opening outside the nozzle and extends around the nozzle opening has an area of ​​size A2, characterized in that - the ratio A2 / A1 is less than 1, - the nozzle plate comprises a number of nozzles ranging from 1 to 1000, and - the nozzles are designed as nozzle inserts that are inserted into corresponding openings in the nozzle plate to produce silica gel fibers.

[0012] A mass is forced out of the nozzle through the nozzle opening. The size of the nozzle opening determines the thickness of the extruded strand. The nozzle opening has a cross-sectional area of ​​size A1.

[0013] The spinning mass can be forced through the spinneret in various ways. In the prior art, a pressure vessel pressurized with gas is typically used. It is equally possible to force the spinning mass through the nozzle plate using a suitable pump. Depending on the application, a variety of pumps are suitable, such as piston pumps, gear pumps, eccentric pumps, and screw pumps. Gear pumps are preferred. It is also possible to force the spinning mass through the nozzles from a cylindrical container using a piston.

[0014] The spinning mass exiting through a nozzle opening should wet the area around the nozzle opening as little as possible, as otherwise an uncontrollable accumulation of material will occur around the nozzle opening. This accumulation leads to uneven thread formation, especially at the beginning.

[0015] Therefore, there is a tear-off edge around the nozzle opening, and the area extending around the nozzle opening outside of it is kept as small as possible.

[0016] A separation edge with a minimal surface area of ​​the nozzle area can in principle be achieved by designing the nozzle as a channel that runs vertically through the tip of a straight cone (see, for example, Fig. 3(a)). However, since for manufacturing reasons such an opening is always surrounded by a ring of finite width, the ratio A2 / A1 cannot be minimized arbitrarily. This is due to the Fig. 3(b) and Fig. 5 illustrates. Fig. Figure 3(b) shows the lower part of a nozzle in cross-section, in which a ring of finite width runs around the nozzle opening. Fig. Figure 5 shows the same nozzle from below in a top view. The nozzle opening has a cross-sectional area of ​​size A1, the ring has an area of ​​size A2. According to the invention, the ratio A2 / A1 is less than 1.

[0017] The ratio A2 / A1 is less than 1.

[0018] The angle β of the tear-off edge is preferably in the range of 10° to 90°, particularly preferably in the range of 20° to 90°, and most preferably in the range of 30° to 90°.

[0019] Preferably, the nozzle plate according to the invention has a plurality of identical nozzles with the features described above. The number of nozzles is in the range of 1 to 1000, preferably from 4 to 100.

[0020] The nozzles can be manufactured by drilling and / or milling into the nozzle plate. The nozzle plate has a modular design. This means that the nozzle plate has openings into which nozzle inserts can be inserted. For example, it is possible to shrink-fit or screw the nozzle inserts into the nozzle plate.

[0021] The nozzle plate according to the invention is suitable for the production of silica gel fibers, particularly in a dry spinning process as exemplified in DE 19609551 C1 and DE 10 2004 063 599 A1. The present invention therefore relates to the use of the nozzle plate according to the invention for the production of silica gel fibers.

[0022] Preferred embodiments of the nozzle plate according to the invention are described in more detail below, without, however, limiting the invention to these examples. The nozzle openings shown have a round cross-section. A round cross-section is always preferred, although it is also conceivable to design the cross-section in any other conceivable shape, in particular oval. It is also conceivable to combine features of individual embodiments shown to form further (not shown) embodiments according to the invention. Fig. Figure 1 schematically shows a preferred embodiment of a nozzle plate according to the invention in a top view. The nozzle plate is round and has 19 nozzles. Fig. Figure 2 schematically shows the nozzle plate made of Fig. 1 in cross-section along the dashed line. Each nozzle comprises a channel that narrows conically towards the bottom. Fig. Figures 3(a) to (e) schematically show different embodiments of nozzles. Fig. 1(a) The nozzle opening is formed by a channel that passes through the apex of a straight cone. A sharp trailing edge is thus formed around the nozzle opening. The angle β between the tapered cone and the vertical through the nozzle opening is in the range of 10° to 80°, preferably in the range of 20° to 70°, and particularly preferably in the range of 30° to 60°. In Fig. 3(b) The angle β of the demolition edge is 90°. A ring is located around the nozzle opening, which is grouted over the smallest possible width to ensure minimal wetting.

[0023] Regarding the nozzles of the Fig. 3(c) to 3(e) is the cylindrically extending section of the nozzle channel compared to the embodiments of the Fig. 3(a) and Fig. 3(b) has been extended. This results in a larger L / D ratio. The L / D ratio of the cylindrical area is in the range of 0.5 to 10, preferably in the range of 1 to 5, and particularly preferably in the range of 1.5 to 3.

[0024] In the Fig. In 3(b), (d) and (e), surfaces A1 and A2 run parallel to each other. However, it is also conceivable that surface A2 runs at an angle to surface A1. This is exemplified in Fig. 4(a) is shown. The angle ω is preferably in the range of 0° to 80°, particularly preferably in the range of 0° to 60°.

[0025] It is also conceivable that surface A2 is curved, as exemplified in Fig. 4(b) shown. However, it is important that an edge runs around the nozzle opening, which acts as a breaking edge for the filaments emerging from the nozzle opening. This edge is, in the example of the embodiment of Fig. 3(a) is illustrated, characterized by the angle β.

[0026] If the angle β is 90°, then the surfaces A1 and A2 run parallel to each other and, according to the invention, wetting of the surface A2 is minimized by the fact that the ratio A2 / A1 is less than 1.

[0027] Fig. Figure 5 schematically shows a nozzle according to the Fig. 3(b), Fig. 3(d), Fig. 3(e), Fig. 4(a) and Fig. 4(b) from below in the overhead view.

[0028] Fig. Figure 6 shows an enlarged section of the nozzle plate according to the invention. Fig. 1 and Fig. 2 in cross-section through the nozzles.

[0029] Fig. Figure 7 shows a preferred embodiment of a single nozzle. This is designed as a modular insert that can be inserted into a corresponding opening in a plate. The nozzle insert comprises a vertically extending channel. In the figure shown, the channel would be supplied with spinning material from above, which would then exit the channel in the lower region by means of pressure. The shape of the channel is initially cylindrical in the flow direction, then narrows conically at an angle γ to the vertical in the range of 10° to 80°, preferably in the range of 20° to 70°, particularly preferably in the range of 30° to 60°, until the diameter D of the channel cross-section is reduced to a size in the range of 0.05 mm to 0.5 mm, preferably in the range of 0.1 to 0.3 mm, particularly preferably in the range of 0.12 to 0.18 mm. A cylindrical region with a length L adjoins the conical region of the channel. For the in Fig. In the embodiment shown in section 7, the same preferred L / D ratios apply as in the example for Fig. 3 discussed.

Claims

[1] Use of a nozzle plate comprising at least one nozzle with a nozzle opening, wherein the nozzle opening has a cross-sectional area of ​​size A1, wherein a separation edge with an angle β in the range of 5° to 90° extends around the nozzle opening, wherein the area which is directly adjacent to the nozzle opening outside the nozzle and extends around the nozzle opening has an area of ​​size A2, characterized by , that - the ratio A2 / A1 is less than 1, - the nozzle plate comprises a number of nozzles ranging from 1 to 1000, and - the nozzles are designed as nozzle inserts that are inserted into corresponding openings in the nozzle plate to produce silica gel fibers. [2] The use of the nozzle plate according to claim 1, characterized by that the angle β of the tear-off edge is in the range of 10° to 90°, particularly preferably in the range of 20° to 90°, most preferably in the range of 30° to 90°. [3] The use of the nozzle plate according to one of claims 1 or 2, characterized by , that the nozzles comprise a channel which is initially cylindrical, then narrows conically in the direction of flow to a cross-sectional area of ​​size A1 and is again cylindrical up to the nozzle opening, wherein the cylinder adjacent to the nozzle opening has a length L and a diameter D, where the ratio L / D is: 0.5 ≤ L / D ≤ ​​10. [4] The use of the nozzle plate according to claim 3, characterized by that the L / D ratio is in the range of 1 to 5, preferably in the range of 1.5 to 3.

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