Extruder containing filter elements

Abstract

The invention relates to an extruder for processing comminuted bulk material, the feed area of ​​which is configured with at least one housing part housing a filter element (5) arranged on a support frame (4). According to the invention, the filter element (5) is formed from interconnected layers of sintered metal wire mesh screens, the filter element (5) comprises at least one protective layer (27) facing the thread and having a mesh size of 20-100 μm, a filter layer (28) having a mesh size of less than 1 μm and a rear support layer, the protective layer (27) being arranged at a safety distance of 0.5-2 mm from the outer diameter of the thread. The filter element (5) can be removed from the housing part with the help of the support frame (4) and is self-supporting and dimensionally stable.

Description

[Technical field]

[0001] The present invention relates to an extruder for processing comminuted bulk material, comprising a filter element according to the preamble of claim 1. [Background technology]

[0002] As a general rule, extruders for producing and processing polymers contain in their feed area a housing part that accommodates a replaceable filter element through which the volatile components of the bulk material fed in comminuted form can be sucked in. Such filter elements are often embodied as porous plates or screens. A problem that often occurs is that such filter elements are prone to clogging.

[0003] One approach consists in applying a counter gas pressure surge to the filter element through suction channels in a gas-permeable housing part, sucking the volatile components therefrom and freeing the front side of the filter element facing the extruder screw axis from the powder cake deposited there. It is also conceivable to mechanically peel off the powder cake, but this is only possible during production shutdowns.

[0004] An extruder disclosing the basic principle of venting the feed area of ​​the extruder is shown in DE 1729395B. There, a vent is shown which is equipped with a fine mesh screen and constructed as a sintered metal plate. To avoid the powder being sucked out of the vent, the screen is at a relatively large distance from the screw axis, so that a cushion acting as a very fine mesh filter can be constructed. The filtering properties of the cushion depend strongly on the particle size and properties of the powder material. However, the filtering performance decreases as the cushion becomes larger.

[0005] DE 3310676 A1 describes a porous plate in the form of a sintered metal plate containing pore openings of 5 to 200 μm and having a porosity of 25 to 60% for filtration, the plate being at a distance from the screw shaft that corresponds to half the distance of the screw shaft from the inside of the extruder housing.

[0006] Extruders with a vent equipped with a filter element made of sintered metal arranged at a distance from the screw axis and forming a gap with a thickness of 2 mm to 30 mm are shown in DE 202007011767 U1 or EP 1977877 B1, respectively. The filter cake accumulated in the gap is removed by a pressure pulse delivered through a pressure purge line.

[0007] EP1400337B1 discloses an extruder vent, in which a metal wire mesh composite sheet having two or more layers is fixed, with the progressively finer mesh layers being arranged on a support layer of coarsely woven larger mesh, with the finest mesh layer being arranged on the product-related side. The mesh size of the finest mesh layer is between 1 μm and 500 μm. Each layer of the metal wire mesh composite sheet can be sintered. The composite sheet can be cleaned by backwashing, brushing or calcination.

[0008] EP2218568B1 discloses an extruder having a vent that houses an insert having a filter unit having a filter fineness of 1 μm to 10 μm and configured as a metal nonwoven fabric supported on a base body via a support and a drain fabric.

[0009] DE102013208993B4 shows a filter insert for an extruder, in which a protective element having at least two separate protective areas with through openings is arranged upstream of the filter element, each protective area being assigned a central channel for gas supply in order to enable separate flushing.

[0010] DE202012001277U1 discloses an extruder for processing comminuted bulk material, the housing of which is configured with a housing part that accommodates a filter element arranged on a support frame. The support frame is removably fixed to the extruder housing. The filter element has a filter layer with a mesh size of less than 1 μm and includes a rear support layer. The filter element can be removed from the housing part by the support frame. Summary of the Invention

[0011] There is a need for further improvement and simplification of extruder filter devices.

[0012] It is an object of the present invention to equip an extruder with a filter element which has a small mesh width, is simple in construction and does not require periodic backwashing of the filter side.

[0013] This object is achieved by the invention as set forth in the claims. Advantageous further developments of the invention are disclosed in the subclaims.

[0014] The invention proceeds from an extruder of the type indicated in the preamble of claim 1.

[0015] According to the invention, the filter element formed from interconnected layers of sintered metal wire mesh screens preferably has a mesh size of less than 1 μm, the filter layer being held between a protective layer facing the threads and a back support layer. The protective layer is held at a safe distance of 0.5-2 mm from the outer diameter of the threads. The filter element is fixed in a holding device so that it can be removed from the gas-permeable wall.

[0016] The filter element used in the present invention preferably consists of only three layers: a wide-mesh protective layer that prevents damage to the actual filter layer, especially when it has a very small mesh size of less than 1 μm and is correspondingly sensitive. Behind the filter layer, a support layer is provided to stabilize the filter unit. The structure of each layer and each filter element is connected by sintering each layer and by connecting each layer to each other.

[0017] In the case of the subject matter of the present invention, since there is no filter cake involved, the provision of a safety distance only serves to protect against tolerances in the circumference of the screw and in the construction of the extruder housing.

[0018] The filter element formed from the above-described layers is self-supporting and dimensionally stable, and can be removed from the gas permeable wall portion by releasing the retaining device that carries the filter element so that it can be removed from the extruder housing for maintenance.

[0019] The radial position of the retaining device in the extruder housing relative to the screw is preferably configured to be adjustable. In particular, adjustability can be realized in that the retaining device can be adjusted by means of an adjustable screw connection between the retaining device and a cover plate that is removably fixed to the extruder housing.

[0020] The filter element is preferably screwed or clamped to the holding device by means of fastening strips, which serve to fix the filter element in place and compress the seal between the filter element and the holding device to avoid warping or displacement of the filter element due to high shear forces during operation of the extruder. The fastening strips also allow the filter element to be easily separated from the holding device. A self-supporting clamping frame for accommodating the filter element can also be provided without screw fastening as an alternative to fastening or clamping strips.

[0021] The gas flowing through the filter layer is preferably sucked in via a bore in the screw connection, to which the suction channel is flanged via a coupling, the bore of the screw connection opening into a hollow space of the holding device behind the filter layer.

[0022] To prevent gas from escaping through a gap between the retainer and the cover plate of the gas permeable housing portion within the extruder housing, the retainer preferably has a peripheral seal. A flat seal extending to the peripheral housing portion may also be provided between the retainer and the filter layer, also creating an airtight seal there. [Brief description of the drawings]

[0023] The invention will now be explained in more detail with reference to exemplary embodiments: [Figure 1] FIG. 1 is a simplified perspective view of an insert for receiving a filter element; [Diagram 2] Figure 2 shows an exploded view of the insert parts. [Diagram 3] FIG. 3 is a cross-sectional view of an insert part; [Figure 4] FIG. 4 is a micrograph of the filter layer seen from the screw. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The roughly cubic insert element shown in Fig. 1 is designed to be inserted into a housing part in the feed area of ​​an extruder. It has a cover plate 1 with gas passages, which is fixed to the edge of the gas-permeable wall of the extruder housing by means of a screw connection via a corner bore hole 3 or rests on a concave shoulder in the wall area of ​​the wall and is fixed by means of screws, so that the surface of the cover plate can run in the outer plane of the extruder housing.

[0025] Between the cover plate 1 and the extruder housing there is arranged a flat seal 2 for sealing the cover plate 1 to the extruder housing.

[0026] A screw connection 14, which is depicted in detail in Figures 2 and 3, connects the cover plate 1 to the support frame 4 via the filter cover 13. The support frame 4 has a double-bent side wall at the front for the twin-screw extruder, the arcuate shape of which represents a partial arc running concentrically around the two screws arranged in the double extruder. The front side of the filter element 5 facing the screws rests in the radial direction of the screw via a seal 9 at the end of the arcuate side wall and in the axial direction of the screw at the straight end part of the support frame 4 and is fixed to the support frame 4 by clamping strips 6, 7, 8.

[0027] When the filter element is secured to the screw, the filter structure fits snugly around the screw.

[0028] 2 shows an exploded view of the insert element for insertion into the extruder housing. The cover plate 1 has a central bore 16 in which there is an annular seal 24 facing a smooth cylindrical area 22 of the screw connection 14 guided through the bore 16. The screw connection 14 is provided at its front end with an external thread 23, via which the screw connection 14 can be screwed into an internal thread 20 of the plate-shaped filter cover 13 forming the rear part of the support frame 4.

[0029] The enlarged shoulder 22 adjoins the thread 23 of the screw connection 14, on which the cover plate 1 arranged can be displaced in the axial direction. A flat seal 29 is arranged in front of the shoulder 22. The screw connection 14 is formed with an external thread 21 in its axially central area. As soon as the screw connection is fastened to the filter cover 13 via the thread 23 and the cover plate 1 with the bore 16 is pressed against the enlarged shoulder 22, the locking nut 15 can be screwed onto the thread 21, which makes it possible to position the support frame 4 relative to the cover plate 1 as a function of the axial position of the locking nut on the thread 21.

[0030] The axial position of the screw connection 14, and therefore the position of the filter unit including filter cover, support frame and filter element, can be locked relative to the screw with respect to the cover plate 1. This can be achieved in that the locking nut 15 can be fixed relative to the cover plate 1 via a clamping screw which passes through the locking nut 15 through a circumferentially running slot 18 in the locking nut 15 and is screwed into the cover plate 1. If the clamping screw is loosened again, the locking nut can be twisted and thus the position of the entire filter unit can be changed relative to the cover plate 1.

[0031] Guide pins fixed to the cover plate 1 or the support frame 4 can be inserted into blind holes in the opposing support frame 4 or cover plate 1, respectively, and can be used to prevent the support frame 4 from twisting relative to the cover plate 1.

[0032] The screw connection 14 is configured as a hollow screw having a bore 25. A quick release coupling for a gas exhaust channel or a hose can be flanged into the bore 25 on the outside of the screw connection.

[0033] The front open end of the screw connection 14 projects into the interior space 19 of the support frame 4 so that a gas-conducting channel is formed via the screw connection 14 to the interior space 19 of the support frame.

[0034] The annular seal 24 and the flat seals 2,17 serve to seal the interior space of the filter element from the ambient air of the extruder.

[0035] A flat seal 17 is arranged between the filter cover 13 and the support frame 4. The support frame is formed of two longitudinal walls and two transverse walls, the transverse walls having a double bending surface at the front in case of a twin-shaft extruder or a single bending surface at the front in case of a single-shaft extruder, while the longitudinal walls are approximately rectangular with a flat surface at the front.

[0036] The filter element, which has a shape corresponding to the peripheral surface, is applied to the peripheral surface of the support frame 4. The filter element is fixed to the surface through longitudinally running clamping strips 6, 7, 8 with the help of screws guided in blind holes 10, 11, 12 in the side walls or, respectively, in the central web 26. To effect a seal between the filter element 5 and the support frame 4, a flat seal 9 is provided between the filter element 5 and the front surface of the support frame 4, which follows the shape of the filter element 5.

[0037] The hollow space 19 between the back of the filter element 5, the inside of the support frame 4 and the inside of the filter cover 13 is directly connected to the suction channel via the bore 25 of the screw connection 14, so that the gas that enters the hollow space 19 can be sucked in without any problems through the filter element 5.

[0038] The filter element is self-supporting and rigid. It essentially comprises three layers, namely a front protective layer 27, a filter layer 28 and a rear support layer. All three layers are constructed as sintered metal screen layers, the filter layer 28 having a mesh size of less than 1 μm, preferably less than 0.5 μm. The protective layer 27 has a mesh size of about 20-100 times that of the filter layer 28, and the support layer preferably has a mesh size of 20-100 μm as well. To increase rigidity, the support layer can also be formed from a sintered body of several layers with different mesh sizes.

[0039] Figure 4 is a micrograph of the filter element, showing the protective layer 27 and the underlying filter layer 28. The thickness of the protective layer 27 is so small that the filter layer 28 can be placed at a distance of 0.5-2 mm from the periphery of the thread. This ensures that no filter cake forms between the filter layer and the periphery of the thread. As a result, no pressure pulses or brushing through the filter layer are required to break up the filter cake. This increases the life of the extruder and avoids downtime.

[0040] By properly adjusting the threaded connection 14, precise distance adjustment of the filter layer 28 relative to the circumference of the threads can be achieved.

[0041] The invention is not limited to deployment in a twin screw extruder, but can be adapted for use in a single screw extruder as well. [Explanation of symbols]

[0042] 1 Cover plate 2 Flat seal 3 Bore 4 Support frame 5 Filter Elements 6 Clamp Strips 7 Clamp Strips 8 Clamp Strips 9 Flat seal 10 Bore 11 Boa 12 Bore 13 Filter cover 14 Threaded Connection 15 Lock nut 16 Bore 17 Flat seal 18 Slots 19 Hollow Space 20 Internal Thread 21 External Thread 22 Shoulder 23 Threads 24 Annular seal 25 Bore 26 Central Web 27 Protective layer 28 Filter Layer 29 Flat seal

Claims

1. An extruder for processing a comminuted bulk material, comprising an extruder housing, the extruder housing comprising at least one axially oriented bore having an inner wall, a screw accommodated in the bore, and at least one housing part accommodating a filter element (5) for aspirating gaseous components of the bulk material, arranged on a support frame (4) arranged in a feed area of ​​the extruder housing, the support frame (4) being removably fixed to the extruder housing, The filter element (5) is formed from interconnected layers of sintered metal wire mesh screen; said filter element (5) comprises at least one protective layer (27) facing said thread and having a mesh size of 20-100 μm, a filter layer (28) having a mesh size of less than 1 μm, and a rear support layer, said protective layer (27) being arranged at a safe distance of 0.5-2 mm from the outer diameter of said thread; The extruder, wherein said filter element (5) can be removed from the housing part with the aid of said support frame (4), said filter element (5) being self-supporting and dimensionally stable.

2. 2. The extruder of claim 1, wherein the position of the support frame (4) within the extruder housing is radially adjustable relative to the at least one bore of the extruder.

3. 3. The extruder according to claim 2, wherein the support frame (4) is adjustable in the radial direction of the extruder screw or of the bore for the extruder screw by means of an adjustable threaded connection (14) between the support frame (4) and a cover plate (1) removably fixed to the extruder housing.

4. 2. Extruder according to claim 1, characterized in that the filter element (5) is fixed to the support frame (4) by clamping strips (6, 7, 8) or clamping frames running in the axial direction of the extruder.

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

6. 2. The extruder of claim 1, wherein the filter element (5) is fixed to the support frame (4) via a peripheral seal (9).

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