Extruder Comprising a Filter Element

Abstract

The invention relates to an extruder for processing pulverulent bulk material, in which at least one housing portion, which accommodates a filter element (5) located on a support frame (4), is configured in a feed region. According to the invention, the filter element (5) is formed from interconnected layers of sintered metal wire mesh screens, the filter element (5) containing at least one protective layer (27) which is directed against the screw and has a mesh size of 20-100 m, a filter layer (28) having a mesh size of <1 m, and a rear support layer, and the protective layer (27) being located at a safety distance of 0.5-2 mm from the outer diameter of the screw. The filter element (5) can be removed from the housing portion with the aid of the support frame (4) and is self-supporting and dimensionally stable.

Claims

1. An extruder for processing pulverulent bulk material, comprising an extruder housing which has at least one axially directed bore with an inner wall and a screw accommodated in the bore, at least one housing portion, which accommodates a filter element (5) for suctioning gaseous constituents of the bulk material, located on a support frame (4), being configured in a feed region of the extruder housing, the support frame (4) being detachably fastened to the extruder housing, characterized in that the filter element (5) is formed from interconnected layers of sintered metal wire mesh screens, the filter element (5) contains at least one protective layer (27) which is directed against the screw and has a mesh size of 20-100 m, a filter layer (28) having a mesh size of <1 m, and a rear support layer, the protective layer (27) being located at a safety distance of 0.5-2 mm from the outer diameter of the screw, and the filter element (5) can be removed from the housing portion with the aid of the support frame (4), the filter element (5) being self-supporting and dimensionally stable.

2. The extruder according to claim 1, characterized in that the position of the support frame (4) in the extruder housing can be adjusted radially to the at least one bore of the extruder.

3. The extruder according to claim 2, characterized in that the support frame (4) can be adjusted by means of an adjustable screw connection (14) between the support frame (4) and a cover plate (1) detachably fastened to the extruder housing in the radial direction of the extruder screw or the bores for the extruder screws.

4. The extruder according to claim 1, characterized in that the filter element (5) is fastened to the support frame (4) by means of clamping strips (6, 7, 8) running in the axial direction of the extruder or a clamping frame.

5. The extruder according to claim 3, characterized in that the screw connection (14) has a bore (25) running in the axial direction of the screw connection for connecting a suction channel.

6. The extruder according to claim 1, characterized in that the filter element (5) is fastened to the support frame (4) via a circumferential seal (9).

Description

DESCRIPTION OF THE DRAWINGS

[0023] The invention is explained in greater detail below with reference to an exemplary embodiment, wherein:

[0024] FIG. 1 shows a simplified perspective view of an insert part for accommodating a filter element,

[0025] FIG. 2 shows an exploded drawing of the insert part,

[0026] FIG. 3 shows a cross-sectional view of the insert part, and

[0027] FIG. 4 shows a microscopic view of the filter layer, viewed from the screw(s).

DESCRIPTION OF PREFERRED EMBODIMENTS

[0028] A substantially cuboidal insert element shown in FIG. 1 is configured so that it can be inserted into a housing portion of the feed region of an extruder. It has a cover plate 1 furnished with a gas passage, which cover plate can either be fastened onto an edge portion of the gas-permeable wall portion of the extruder housing by means of a screw connection via boreholes 3 on the corner side, or which rests on a recessed shoulder in the wall region of the wall portion and is fastened thereto by means of screws, as a result of which the surface of the cover plate can run in the plane of the outside of the extruder housing.

[0029] A flat seal 2 for sealing the cover plate 1 against the extruder housing is located between the cover plate 1 and the extruder housing.

[0030] A screw connection 14 depicted in detail in FIGS. 2 and 3 connects the cover plate 1 to a support frame 4 via a filter cover 13. The support frame 4 has double-bend side walls on the front side for a twin-screw extruder, the arcuate shape of which side walls represents partial arcs which run concentrically to the circumference of two screws located in a double extruder. The front side of the filter element 5 directed against the screws rests in the radial direction of the screws via a seal 9 at the edge of the arc-shaped side walls and in the axial direction of the screws on straight edge portions of the support frame 4 and is fastened to the support frame 4 by means of clamping strips 6, 7, 8.

[0031] When the filter element is fixed to the screws, the filter construction lies snugly in contact with the circumference of the screws.

[0032] FIG. 2 shows an exploded view of the insert element for insertion into an extruder housing. The cover plate 1 has a central bore 16 in which there is an annular seal 24 which is directed against a smooth-cylindrical region 22 of the screw connection 14 which is guided through the bore 16. The front end of the screw connection 14 carries an external thread 23, via which the screw connection 14 can be screwed into an internal thread 20 of a plate-shaped filter cover 13 which forms the rear part of the support frame 4.

[0033] The enlarged shoulder 22 adjoins the thread 23 of the screw connection 14, on which the cover plate 1 placed thereon can be displaced in the axial direction. A flat seal 29 is located on the front side of the shoulder 22. An external thread 21 is configured in the axially central region of the screw connection 14. As soon as the screw connection is fastened to the filter cover 13 via the thread 23 and the cover plate 1 having the bore 16 is pushed onto the enlarged shoulder 22, a lock nut 15 can be screwed onto the thread 21, which makes it possible to position the support frame 4 in relation to the cover plate 1 as a function of the axial position of the lock nut on the thread 21.

[0034] The axial position of the screw connection 14 and therefore the position of the filter unit, which comprises the filter cover, the support frame and the filter element, can be locked with respect to the cover plate 1 in relation to the screws. This can be achieved in that the lock nut 15 can be fixed with respect to the cover plate 1 via clamping screws which are guided through the lock nut 15 through slots 18 running in the circumferential direction of the lock nut 15 and are screwed into the cover plate 1. If the clamping screws are loosened again, the lock nut can be twisted and therefore the position of the entire filter unit can be changed with regard to the cover plate 1.

[0035] Guide pins fastened to the cover plate 1 or the support frame 4, which are inserted into blind holes of the opposite support frame 4 or, respectively the cover plate 1, can be used to prevent the support frame 4 from twisting with respect to the cover plate 1.

[0036] The screw connection 14 is configured as a hollow screw having a bore 25. A quick-release coupling of a gas discharge channel or hose can be flanged to the bore 25 on the outside of the screw connection.

[0037] The front, open end of the screw connection 14 protrudes into the internal space 19 of the support frame 4, so that a gas-conducting channel into the internal space 19 of the support frame is formed via the screw connection 14.

[0038] The annular seal 24 and the flat seals 2 and 17 serve to seal the internal space of the filter element with respect to the ambient air of the extruder.

[0039] The flat seal 17 is located between the filter cover 13 and the support frame 4. The support frame is formed from two longitudinal walls and two transverse walls, the transverse walls having double-bend surfaces on the front side for a twin-shaft extruder and single-bend surfaces on the front side for a single-shaft extruder, while the longitudinal walls are substantially rectangular with planar surfaces on the front side.

[0040] The filter element, which has a shape corresponding to the circumferential surfaces, is applied to the circumferential surfaces of the support frame 4. It is fastened to the surfaces with the aid of screws, which are guided through the longitudinally running clamping strips 6, 7, 8 into blind holes 10, 11, 12 of the side walls or, respectively a central web 26. A flat seal 9 following the shape of the filter element 5 is provided between the filter element 5 and the surfaces on the front side of the support frame 4 in order to provide a seal between the filter element 5 and the support frame 4.

[0041] The hollow space 19 between the back of the filter element 5, the insides of the support frame 4 and the filter cover 13 is directly connected to a suction channel via the bore 25 in the screw connection 14, so that gases entering the hollow space 19 can be suctioned without any problems via the filter element 5.

[0042] The filter element is self-supporting and rigid. It substantially contains three layers, namely a front protective layer 27, a filter layer 28 and a rear support layer. All three layers are configured as sintered metal screen layers, with the filter layer 28 having a mesh size of <1 m, preferably 0.5 m. The protective layer 27 has a mesh size of approximately 20-100 times that of the filter layer 28, while the support layer preferably likewise has a mesh size of 20-100 m. To increase the rigidity, the support layer can also be formed from multiple layers sintered together having different mesh sizes.

[0043] FIG. 4 shows a microscopic photograph of the filter element, which shows the protective layer 27 and the filter layer 28 lying underneath. The thickness of the protective layer 27 is so small that the filter layer 28 can be located at a distance of 0.5-2 mm from the course of the outer circumference of the screws. This ensures that no filtercake can be configured in practice between the filter layer and the outer circumference of the screws. Consequently, neither a pressure pulse through the filter layer to break down a filtercake nor brushing is required. This increases the service life of the extruder and avoids downtimes.

[0044] A precise distance adjustment of the filter layer 28 with respect to the circumference of the screws can be achieved by suitably adjusting the screw connection 14.

[0045] The invention is not limited to deployment on twin-screw extruders, but can also be used with an adapted shape in the same way in the case of single-screw extruders.

REFERENCE NUMERALS

[0046] 1 Cover plate [0047] 2 Flat seal [0048] 3 Bore [0049] 4 Support frame [0050] 5 Filter element [0051] 6 Clamping strip [0052] 7 Clamping strip [0053] 8 Clamping strip [0054] 9 Flat seal [0055] 10 Bore [0056] 11 Bore [0057] 12 Bore [0058] 13 Filter cover [0059] 14 Screw connection [0060] 15 Lock nut [0061] 16 Bore [0062] 17 Flat seal [0063] 18 Slot [0064] 19 Hollow space [0065] 20 Internal thread [0066] 21 External thread [0067] 22 Shoulder [0068] 23 Thread [0069] 24 Annular seal [0070] 25 Bore [0071] 26 Central web [0072] 27 Protective layer [0073] 28 Filter layer [0074] 29 Flat seal