DISCHARGE TECHNOLOGY FOR PLASTIC FILTERS

Abstract

A discharge device is for a filtering device for separating impurities from a material melt, in particular a low-viscosity polymer melt. The discharge device includes a discharge shaft with a pressure screw conveyor and a discharge head. Also disclosed is a filtering device including a cylindrical drum filter, a scraper and such a discharge device.

Claims

1. A discharge device for a filtering device for separating impurities from a material melt, the discharge device being configured to discharge separated material from a filter chamber of the filtering device, the discharge device comprising: a discharge shaft with a pressure screw conveyor and a discharge head.

2. A discharge device according to claim 1, wherein the discharge head comprises a dosing discharge head.

3. A discharge device according to claim 1, wherein the discharge head is arranged at an end of the pressure screw conveyor.

4. A discharge device according to claim 1, wherein the discharge head seals off the filter chamber and/or the pressure screw conveyor from the environment.

5. A discharge device according to claim 1, wherein the pressure screw conveyor is configured to convey material into the discharge head while increasing the pressure.

6. A discharge device according to any claim 1, wherein the discharge head is configured to produce a portioned and/or intermittent discharge of material.

7. A discharge device according to any claim 1, wherein the discharge head comprises at least one discharge piston.

8. A discharge device according to claim 7, wherein the discharge piston is slidably mounted in the discharge head.

9. (canceled)

10. A discharge device according to claim 1, wherein the material discharge can be controlled, to provide a dosed material discharge, by the rotational speed of the discharge shaft and/or by the stroke of the at least one discharge piston in the discharge head.

11. A discharge device according to claim 1, wherein the discharge device comprises a discharge housing, wherein the discharge housing comprises at least one discharge opening, wherein the discharge opening is associated with a discharge piston.

12-15. (canceled)

16. A discharge device according to claim 1, wherein the discharge device forms an accumulation volume at the discharge head.

17. (canceled)

18. A discharge device according to claim 1, wherein the discharge head and/or the discharge housing and/or the at least one discharge piston, is configured to seal off the filter chamber from the environment.

19-21. (canceled)

22. A discharge device according to claim 1, wherein the pressure screw conveyor is arranged between the filter chamber and the discharge head.

23. A discharge device according to claim 1, wherein the pressure screw conveyor is configured to generate a pressure gradient between the filter chamber and the discharge head, from a filter pressure in the range from 10 to 20 bar to a discharge pressure in the range from 40 to 50 bar.

24. A discharge device according to claim 1, wherein the pressure screw conveyor is configured as a helix on the discharge shaft.

25. A discharge device according to claim 1, wherein the discharge head is arranged on the discharge shaft.

26. A discharge device according to claim 1, wherein the discharge head is detachably fastened to the discharge shaft.

27. (canceled)

28. A discharge device according to claim 1, wherein the pressure screw conveyor, is configured to generate an accumulation pressure at the discharge head.

29. A discharge device according to claim 1, wherein a stroke of a discharge piston is actuated by an accumulation pressure at the discharge head built up by means of the pressure screw conveyor, in particular increased with respect to the filter chamber.

30. A filtering device for separating impurities from a material melt, the filtering device comprising a housing, a filter, and a filter chamber at the surface of the filter, and a discharge device that is configured to discharge separated material from a filter chamber, the discharge device comprising: a discharge shaft with a pressure screw conveyor; and a discharge head.

31-38. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In the drawings:

[0043] FIG. 1 is a longitudinal sectional view through a filtering device (20) with a filter (30) and a discharge device (10);

[0044] FIG. 2 is a cross-sectional view of the filtering device (20) along the line of intersection A-A;

[0045] FIG. 3 is a cross-sectional view through the discharge device at the level of the discharge head (13) along the line of intersection B-B.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0046] Referring to the drawings, FIG. 1 shows a preferred embodiment of a filtering device (20). The filtering device (20) comprises a housing (21), a filter (30) with a filter shaft (31) and a discharge device (10).

[0047] The filter (30) is preferably configured as a rotating drum filter. The filter chamber (27) is formed at the surface of the filter (30) within the housing (21) of the filtering device. The typical material flow for filtering the molten material is shown in FIGS. 1 and 2. The feed material is conveyed under pressure into the filter chamber (27) by a material feed (25). Preferably, the material feed is from the outside, for example via a radial feed through the housing (21). The supplied material is distributed in the filter chamber (27) on the surface of the filter (30). The filter (30) preferably comprises a permeable filter screen (32), which is located on a rotating filter shaft (31).

[0048] The molten material is forced through the filter screen (32) under pressure, leaving impurities of the material at the surface of the filter screen in the filter chamber (27) due to their material properties. The filtered material passes through the filter screen (32) and flows in the direction of the material discharge (26). In the preferred embodiment, the filtered material is discharged through the filter shaft (31). For this purpose, the filter shaft (31) comprises suitable channels between the contact surface of the filter screen (32) and the internal material discharge (26).

[0049] In FIG. 2, the material flow (28) of the filtered material from the material feed (25) to the material discharge (26) is indicated by arrows.

[0050] At the surface of the filter screen (32), the substances separated from the starting material collect. Due to the rotation of the filter shaft (31) and the filter screen (32), the separated material is conveyed towards the discharge device (10) and the scraper (22). The scraper (22) presses on the surface of the filter screen (32). The scraper (22) is arranged like a scraper at the surface of the filter screen (32). Due to the rotation of the filter shaft (31), the material adhering to the surface of the filter screen (32) is removed by the scraper (22). Preferably, the discharge device (10) is arranged in the area of the scraper (22) on the filter chamber (27), so that the scraped-off material is picked up and conveyed away by the pressure screw conveyor (12).

[0051] The pressure screw conveyor (12) of the discharge device (10) is preferably formed by a circumferential helix at the surface of the discharge shaft (11). By rotating the discharge shaft (11) and the screw configured thereon, the material is conveyed in the axial direction of the discharge axis (A) out of the filter chamber (27) in the direction of the discharge head (13).

[0052] The discharge head (13) is preferably arranged in a discharge housing (14). The discharge housing (14) can be configured both as part of the housing (21) of the filtering device and as a separate discharge housing (14). The separate design of the discharge housing (14) is particularly advantageous for the maintainability and replacement of parts of the discharge device (10). Preferably, the discharge housing (14) is tightly attached to the housing and/or a cover of the housing (21) of the filtering device.

[0053] The discharge head (13) is preferably mounted in the discharge housing (14) so that it slides and seals against the ambient air. The discharge unit (10) forms an accumulation volume (18) in the area of the discharge head (13). The separated material is conveyed into the accumulation volume (18) by the pressure screw conveyor (12). In the accumulation volume (18), the pressure is increased to a sufficient level to overcome the static friction of the discharge pistons (16) in the discharge head (13).

[0054] Especially in the case of low-viscosity material melts, only by increasing the accumulation pressure at the discharge head (13) can the movement of the discharge pistons be ensured for metered material discharge.

[0055] FIG. 3 shows the stroke movement of the discharge piston (16) in a cross-section of the discharge head (13). Depending on the desired discharge volume and the periodicity of the discharge per revolution, one or more discharge pistons (16) can be provided.

[0056] With one rotation of the discharge shaft (11) and the discharge head (13), the discharge head takes up a stroke volume (H) from the accumulation volume (18), conveys it over a partial revolution in the direction of a discharge opening (17), and ejects the volume to the surroundings through the discharge opening (17) by an opposite stroke. Advantageously, the discharge opening (17) and the accumulation volume (18) are arranged opposite or slightly offset from each other so that the accumulation pressure in the accumulation volume (18) ensures ejection of the dirt cake through the discharge opening (17). With the stroke of the discharge piston (16), material is simultaneously taken up from the accumulation volume (18) and a corresponding volume is ejected through the discharge opening (17) on the opposite side.

[0057] The bores in the discharge head (13) and the discharge housing (14) are preferably designed in such a way that the discharge piston (16) is held positively in the discharge head (13) and cannot escape through the discharge opening (17).

[0058] The discharge housing (14) preferably comprises a cover (15). The discharge housing (14) can advantageously comprise an overflow channel on the bearing surface of the discharge head (13) in the discharge housing (14). Leakage material can flow off through the overflow channel.

[0059] In a particularly advantageous embodiment, the discharge device (10) is of modular design. Preferably, the discharge device (10) comprises a modular connection interface (19) between the pressure screw conveyor (12) and the discharge head (13).

[0060] Preferably, the discharge head (13) is detachably mounted on the discharge shaft (11). In a particularly advantageous embodiment, different pressure screw conveyors (12) and discharge heads (13) can be combined. The different embodiments of the pressure screw conveyor (12) and discharge head (13) have a uniform connection interface (19) for this purpose. In this way, for example, different discharge volumes and pressure gradients can be achieved by selecting and combining different pressure screw conveyors and discharge heads.

[0061] Preferably, the discharge head (13) is detachably arranged on the discharge shaft (11). Alternatively, the discharge shaft can be configured in one piece with the pressure screw conveyor (12) and the discharge head (13).

[0062] A particular advantage of the embodiment shown in FIG. 1 is the separation of the filter shaft (31) and the discharge shaft (11). The discharge shaft (11) is preferably arranged parallel to and radially offset from the filter shaft (31). With the separate discharge shaft (11), the material discharge through the discharge device (10) can be controlled separately from the rotational speed of the filter (30) and its filter shaft (31).

[0063] The combination of a rotating filter (30), in particular a drum filter, with a discharge device (10) with a discharge shaft (11) is also particularly advantageous for a precisely controllable filter process.

[0064] The discharge device (10) is preferably arranged on the outside of an externally loaded drum filter. It is particularly advantageous to combine the discharge device (10) with a filtering device with a static scraper (22) on a rotating filter screen (32).

[0065] With the discharge device (10) and the filtering device (20) according to the invention, even polymer melts that are difficult to filter, in particular PA or PET, can be filtered reliably and with precise control.

[0066] Compared to a previously known discharge device, the discharge device (10) disclosed here has the advantage that the continuously discharging pressure screw conveyor (12) conveys against an accumulation volume (18) which is sealed off from the ambient air by the discharge head (13), the discharge housing (14) and the discharge pistons (16).

[0067] The use of a discharge head with discharge piston alone, without an upstream pressure screw conveyor, would not build up sufficient internal pressure to actuate the discharge head in the case of low-viscosity polymer melts. A discharge screw alone, on the other hand, would not achieve sufficient sealing of the filter chamber (27) from the surrounding air. Especially in the case of low-viscosity polymer melts, conveying against a sealed accumulation volume is particularly advantageous.

[0068] Another particular advantage of the discharge device (10) disclosed here lies in the separation of the scraper function and the discharge function. The scraper (22) in contact with the rotating filter screen (32) is subject to particular mechanical stresses. A static scraper that is easy to position and replace is particularly advantageous in this respect. In the proposed invention, the discharge device (10) and the scraper (22) can be adjusted and maintained separately and/or together.

[0069] Preferably, the scraper (22) extends along the entire axial length of the filter screen (32). Preferably, the scraper (22) separates the filter chamber (27) in the tangential flow direction of the material along the surface of the filter screen (32) after approximately three quarters of the circumference starting from the material feed. In this way, the material deposited on the filter surface is collected along a large part of the filter rotation and reliably discharged by the discharge device (10). In the direction of rotation downstream of the scraper (22), the filter screen (32) is again free of separated material when it reaches the material feed (25).

[0070] The shown and/or described features and embodiments of the discharge device (10) and filtering device (20) can be used individually or in combination with each other. In particular, the invention is not limited to the embodiment shown. Individual features may be added, omitted, or substituted with the remaining features disclosed herein. Preferably, the invention is configured as a filtering device with the discharge device according to any one of the claims. However, the discharge device can also be used as a separate assembly, for example for retrofitting or converting a filtering device. Therefore, both a discharge device and a filtering device are claimed.

[0071] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

LIST OF REFERENCE NUMERALS

[0072] 10 discharge device [0073] 11 discharge shaft [0074] 12 pressure screw conveyor [0075] 13 discharge head [0076] 14 discharge housing [0077] 15 cover [0078] 16 discharge piston [0079] 17 discharge opening [0080] 18 Accumulation volume [0081] 19 connection interface [0082] 20 filtering device [0083] 21 housing [0084] 22 scraper [0085] 25 material feed [0086] 26 material discharge [0087] 27 filter chamber [0088] 28 material flow [0089] 30 filter [0090] 31 filter shaft [0091] 32 filter screen [0092] F filter axis [0093] A discharge axis [0094] H stroke