DE102008005794B4 - Filter medium for filtering a substance and device with such a filter medium - Google Patents

Abstract

Filter medium (4) with permeable filter element sections, which flows against a substance in order to filter it, with a fiber fleece (6) through which flow can take place during the filtering process and a fabric structure (7) which is designed in such a way that the smallest particles not retained by the fiber fleece (6), which have a particle size of less than 100 µm, to filter off, a multi-layer structure being implemented, characterized in that the fabric structure (7) has pores with a nominal pore size of less than 10 µm to 1 µm, with two layers of fabric structure (5, 7 ) are present, with a first fabric structure (5) in front of the fiber fleece (6), so that the fiber fleece (6) is present between the fabric structures (5, 7), with the fiber fleece (6 ) follows and then the above-mentioned second fabric structure (7), the first fabric structure (5) having a lower filter fineness than the second fabric structure (7) and the first fabric structure has a pore size of up to 100 µm.

Description

State of the art

Devices for filtering substances such as liquids or gases are known in a wide variety of technical fields. The substances to be filtered flow through, for example, a filter medium or a filter means with openings, with substance components being retained in or on the filter medium. A filter medium can comprise, for example, a screen, a fabric, a porous plate or a non-woven fabric.

When used as a filter, non-woven fabrics are characterized by a comparatively large absorption capacity for substances to be filtered, in particular very small particles. In particular, the non-woven fabric has a multiple layering of fiber pieces, with the structure showing hundreds of layers, for example. After the fibers have been connected, for example by a sintering process, the fleece arrangement or a "web" obtained can be pressed, for example with rollers, in order to obtain a desired pore geometry. The pores of a fiber fleece are relatively large in relation to the desired filter fineness. The filtration effect of the fiber fleece is mainly due to the accumulation of the particles to be filtered on the fibers. Van der Waal's forces in particular play a role here. Due to the comparatively large pores of the nonwoven fabric, a relatively low pressure drop can be observed when liquids or gases flow through the nonwoven fabric.

The state of the art EP 1317949 A1 and the CH584038A5 to call.

Object and advantages of the invention

The object of the present invention is to improve a filter medium, which has a nonwoven fabric, in an economically advantageous manner with regard to the filter performance.

This object is solved by claims 1 and 8. Advantageous developments of the invention are shown in the dependent claims.

The invention is based on a filter medium with permeable filter element sections which flow against a substance for filtering, with a fiber fleece through which flow can take place during the filtering process and a woven structure. The essence of the invention lies in the fact that the fabric structure is designed in such a way that the smallest particles not retained by the nonwoven fabric, which have a particle size of less than 100 μm, are filtered out. The nominal pore size or nominal filter fineness of the fabric structure is 100 µm. The pore size distribution or the pore sizes of the fiber fleece are in particular significantly larger than that of the fabric structure and can be selected differently depending on the filter task.

In particular, better filter performance can be achieved with the proposed filter medium compared to previous arrangements using a fiber fleece and a woven structure in a filter medium. The defined or reproducible structure of the filter medium with regard to the pore size of the fabric structure is particularly advantageous. With the new filter medium, the previously uncontrollable disadvantages in filtration tasks with regard to the filter performance of the fiber fleece or the woven structure can be eliminated. For example, the fibers present in the fiber fleece can break off or become detached and become mobile as a result of mechanical stress or pulsation, so that the particles can get into the filtrate without a retaining structure. According to the invention, such particles can be held back by the fabric structure with the comparatively small pore size or the low filter fineness.

So far, when using nonwoven fabrics, it has not been possible in an economically justifiable manner to prevent pieces, in particular of the fibers of the nonwoven fabric, from becoming detached and escaping from the filter or getting into the filtrate, which is undesirable. So far, the use of fiber fleece for a number of applications was impossible.

With the previous use of fabric structures in filter media, it is disadvantageous that these lead to a comparatively strong increase in pressure during filtration and have a relatively low absorption capacity for the substances to be filtered off. The advantages of the fabric structures, which also exist, e.g. the defined filter fineness, the regular pore geometry or the mechanical strength, could not be used for all interesting applications in the filter area.

With the proposed filter medium, the disadvantages of the fiber fleece can be eliminated by the combination with the woven structure and vice versa, the respective disadvantages of the woven structure can be eliminated by the fiber fleece, with the advantages of fiber fleece and woven structure being fully retained. Overall, a compact filter medium can thus be provided for a number of demanding filter tasks, eg for solid, liquid or gas flows or for filter flows mixed therefrom with large material flows of the material to be filtered. Such filters are, for example, in the chemical or pharmaceutical used in the chemical industry or in machines or systems, e.g. for high-performance units such as combustion engines in the aerospace industry.

According to the invention, the fabric structure has pores with a nominal pore size of less than 100 μm. With the proposed corresponding nominal filter fineness or the comparatively small pores or through-flow openings of the fabric structure, a reliable retention or filtration of corresponding material fractions can be achieved. The woven structure prevents small particles from escaping through the filter medium, in particular fibers or fiber fragments from the fiber fleece. The fabric structure can be adjusted in particular by the type or production of the fabric in such a way that a desired nominal pore size, in particular of less than 100 μm, can be specified exactly and consistently. In particular, such fabric structures can be produced in precision wire weaving mills using modern weaving processes.

The nominal pore size of a filter medium or the nominal filter fineness is obtained when a filter is used in practice. It is defined, for example, in such a way that 98 percent of the particles in the substance to be filtered or e.g. in a suspension that are greater than or equal to the nominal filter fineness are retained. This separation performance is influenced not only by the filter medium itself, but also by the environmental conditions.

The fabric structure preferably has pores with a nominal pore size of less than 40 μm to 1 μm. Substances or particles with the smallest particle dimensions or with average particle diameters in the specified size range can thus be reliably retained in the filter medium.

The fabric structures also give the filter medium an advantageously increased mechanical stability, since the fabric structure is positioned on the outside and inside of the fiber fleece of the filter medium.

In principle, the proposed nominal pore size can be used to filter particles that have different particle shapes or particle materials. It is also possible to retain elongate, thin particles with the corresponding tissue structure, for example broken or non-bonded fibers of the fiber fleece, which can be elongate and thin, for example having a thickness of approximately 5 to 10 μm.

It is of particular advantage that the fabric structure is designed as a dutch weave, in particular as a twill dutch weave. A dutch fabric, like any other fabric, consists of weft threads and warp threads aligned transversely to them. A dutch fabric is characterized by its very small pore size or low filter fineness. A dutch weave is made with a plain weave (1/1). The warp threads can be woven with greater spacing than the weft threads. Advantageously, the surface of the dutch weave is closed, so that the filtration can take place at the point where the warp and weft threads are tied. Compared to other fabrics, this can result in significantly higher mechanical strengths. In addition, dutch fabrics are characterized by a very regular fabric structure with the smallest of pores.

The so-called twill weave fabric, which has a twill weave (2/2) and is realized by weaving warp threads with a larger number of weft threads, can be used particularly advantageously. With a twill weave, for example, relatively dense, e.g. light-tight fabrics can be produced. With a proposed twill weave, a nominal pore size of the twill weave of approximately 1 µm to over 50 µm, e.g. up to approximately 100 µm, can be realized. Due to the comparatively high material density in twill weave fabric, a very robust fabric is produced in comparison to the pores or openings provided with it. A filter medium which comprises a twill weave fabric can thus be used in a wide variety of technical areas. An example area of application is exhaust gas cleaning.

In principle, as an alternative to the dutch fabrics, other fabric structures or types of weave are also conceivable in order to form the fabric structure with pores of the desired relatively small nominal pore size.

It is further proposed that a multi-layer structure with two layers of fabric structures and one layer of the non-woven fabric be formed. This comes close to a minimum equipment of the filter medium, with which a reliable and high filter performance can be realized.

According to the invention, a layer formed from a fabric structure follows in the flow direction after a fabric structure and a layer formed from the nonwoven fabric. In this way, a combination filter medium can be implemented that particularly reliably prevents the escape of very small particles from the filter medium during filtering.

With the fiber fleece from a variety of fiber layers can in particular a comparatively large surface area for an accumulation of the filtering substance are provided. With a corresponding thickness of the non-woven fabric layer, a depth filter can be implemented which, due to the fabric structure, also exhibits the properties of a surface filter, with which, for example, a combined surface-depth filter can be provided.

In the subject of the invention, a multi-layer structure is implemented, with two layers of the fabric structure being present, between which a layer of the fiber fleece is arranged. In this way, in particular, a filter medium can be provided which can advantageously be used in opposite filter flow directions or filter directions. In addition, the filter medium can be precisely matched to a preferred inflow direction.

In the flow direction, after a first fabric structure, there follows a fiber fleece and then a second fabric structure, the first fabric structure having a lower filter fineness than the second fabric structure. In principle, instead of one layer with the fiber fleece, a multi-layer fiber fleece can also be used, in which case the individual layers of the fiber fleece can be designed differently, e.g. can have different pore dimensions.

Alternatively or in combination with a dutch or twill weave fabric, a micro-perforated perforated plate with a nominal pore size or filter fineness comparable to the proposed dutch or twill weave fabric can be provided. The micro-perforated perforated plate can be arranged, for example, in the direction of flow through the filter medium in front of the non-woven fabric and/or behind the non-woven fabric. In the case of a three-layer filter medium structure with a fiber fleece in the middle, it is conceivable, for example, to arrange the micro-perforated perforated plate on one side and the arrangement of a dutch fabric on the other side of the three-layer filter medium.

The fabric structure advantageously comprises weft threads and warp threads, the warp threads having a larger diameter than the weft threads. The warp threads can be about 20 to 40% larger in diameter than the weft threads, which is particularly advantageous with regard to the production and the stability of the fabric structure.

It is also advantageous that the fabric structure is formed from metallic fibers, in particular from high-grade steel. With a metallic material, in particular made of a high-quality alloy, the fabric can be particularly resistant to chemical, thermal and/or mechanical influences.

As an alternative to the metallic fibers forming the fabric structure, fibers made of other materials can also be used. For example glass fibres, mineral fibers or plastic fibers or structures which comprise such fibres. Alternatively, different materials can be woven into a fabric structure, e.g. the warp threads consist of a different material than the weft threads.

The fabric structure preferably consists of monofilament fibers, although the use of multifilament fibers is also conceivable.

In addition to metal fibers, alternatively multifilament glass, mineral and/or plastic materials can also be used for the fibers.

Furthermore, it is preferred that a sintered connection is formed between the fabric structure and the nonwoven fabric. This is a particularly effective and stable type of connection for woven or nonwoven structures. In principle, other types of connection can also be advantageous, for example press, welded, adhesive or soldered connections.

It is particularly advantageous that the fiber fleece comprises metallic fibers. In particular, a metal fiber fleece with comparatively short and individual very thin pieces of wire is preferred. The pieces of wire can have a thickness of approximately 10 to less than 8 μm, for example. Such a metal fiber mat can be formed by joining the short, very thin pieces of wire together. The respective bonds are usually comparatively weak or loose.

The invention also relates to a device for filtering a substance with a filter medium which is designed in accordance with the above.

The advantages mentioned above can thus be achieved in a device for filtering, for example a filter module or a filter apparatus.

character list

• 1 einen Ausschnitt aus einem Vergleichsbeispiel eines Filtermediums in Schnittansicht und
• 2 einen Ausschnitt aus einem weiteren erfindungsgemäßen Filtermedium in Schnittansicht.

The invention is explained in more detail using two exemplary embodiments, which are shown very schematically. In detail shows:

• 1 a section of a comparative example of a filter medium in a sectional view and
• 2 a section of a further filter medium according to the invention in a sectional view.

1 shows a cross section of a comparative example of a filter medium 1 in a highly schematic manner. A substance to be filtered (not shown) flows against the filter medium 1 in the inflow direction according to arrow S1, the filtrate (not shown) emerging from the filter medium 1 according to arrow S2 being obtained on the opposite outflow side of the filter medium 1. The substance to be filtered first passes through a first layer of the filter medium 1, here a non-woven fabric 2, with fibers 2a, indicated as dashed lines, in different orientations. The fiber fleece 2 is followed by a second layer of the filter medium 1, here a fabric 3 designed as a twill weave fabric with parallel warp threads 3a and weft threads 3b that are bent over several times and are aligned transversely thereto. The diameter of the warp threads 3a, which are round in cross section, is approximately 30% larger than the diameter of the weft threads 3b.

The two layers of non-woven fabric 2 and fabric 3 are connected by sintering. The thickness of the fabric 3 can typically be, for example, in the range from about 50 μm to more than about 250 μm, and the thickness of the fiber fleece 2 can be, for example, in the range from about 0.5 mm to more than 1.5 mm.

The non-woven fabric 2 can in particular be made from many individual, very thin and short pieces of wire, as a result of which a comparatively large number of particles, in particular small ones, can accumulate in the non-woven fabric. Particles which penetrate the non-woven fabric 2 are held back by or on the fabric 3 . The fabric 3 can thus act, so to speak, as a protective filter against the escape of the smallest particles. By the combination shown according to 1 With the fiber fleece 2, which is followed by the fabric 3 in the inflow direction or through-flow direction, fibers 2a or parts thereof that become detached can also be held back securely in the fabric 3.

2 shows a highly schematic cross section of a filter medium 4 according to the invention. The filter medium 4 comprises a first fabric 5 in the inflow direction according to the arrow S1, then a nonwoven fabric 6, to which a second fabric 7 is connected. The fabric 5 and the fabric 6 are designed as twill weave fabrics with the same type of weave, in particular made of stainless steel warp and weft wires. The fabric 7 has larger wire diameters than the fabric 5. The fabrics 5 and 7 can thus differ from one another, in particular in terms of their filtration effect.

The fiber fleece 6 is constructed in particular as a metal fiber fleece with metallic fibers 6a made of stainless steel. The fabrics 5 and 6 are arranged on both sides of the fiber fleece 6 and are sintered to the fiber fleece 6, for example. With the arrangement according to 2 Particles can be separated on the fabric 5 according to the inflow direction S1, with further, in particular fine, particles being able to be deposited within the fiber fleece 6. Filtrate (not shown) emerges from the filter medium 4 on the outflow side according to arrow S2, the filtrate being free of very small particles since these are retained in the fabric 7, for example also thin fibers 6a detached from the fiber fleece 6 or fragments thereof.

Typical pore sizes for fabrics 3, 5 and 7 are in the range from 1 μm to 100 μm.

The diameters of the threads of the fabrics 3, 5 and 7 are in the range from approx. 20 μm to approx. 100 μm for the warp threads and in the range from approx. 15 μm to over approx. 70 μm for the weft wires.

Basically, it is also conceivable that instead of a fiber fleece, for example, a fabric with multifilament fibers is formed. With this arrangement, the non-woven fabric can be replaced more cost-effectively if necessary.

Reference List

1

filter medium

2

non-woven fabric

2a

fiber

3

tissue

3a

warp thread

3b

weft thread

4

filter medium

5

tissue

6

non-woven fabric

6a

fiber

7

tissue

Claims (8)

Filter medium (4) with permeable filter element sections, which flows against a substance in order to filter it, with a fiber fleece (6) through which flow can take place during the filtering process and a fabric structure (7) which is designed in such a way that the smallest particles not retained by the fiber fleece (6) which have a particle size of less than 100 µm, to filter off, a multi-layer structure being implemented, characterized in that the fabric structure (7) has pores with a nominal pore size of less than 10 µm to 1 µm, with two layers of fabric structure (5, 7 ) are present, with a first fabric structure (5) in front of the nonwoven fabric (6), so that the nonwoven fabric (6) between the fabric structures (5, 7) is present, with the fiber fleece (6) following a first fabric structure (5) in the direction of flow and then the above-mentioned second fabric structure (7), the first fabric structure (5) having a lower filter fineness than the second fabric structure (7) and the first fabric structure has a pore size of up to 100 µm. filter medium claim 1 , characterized in that the fabric structure (5, 7) is designed as a dutch weave, in particular as a twill dutch weave. Filter medium according to one of the preceding claims, characterized in that the fabric structure (5, 7) comprises warp threads and weft threads, the warp threads (3a) having a larger diameter than the diameter of the weft threads. Filter medium according to one of the preceding claims, characterized in that the fabric structure (5, 7) is formed from metallic fibers, in particular from high-grade steel. Filter medium according to one of Claims 1 - 3 , characterized in that the fabric structure is formed from non-metallic fibers, eg glass fibers, mineral fibers, plastic fibers. Filter medium according to one of the preceding claims, characterized in that a sintered connection is formed between the fabric structure (5, 7) and the fiber fleece (6). Filter medium according to one of the preceding claims, characterized in that the fiber fleece (6) comprises metallic fibers. Device for filtering a substance with a filter medium according to any one of the preceding claims.

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