DE9318673U1 - Hollow cylindrical filter element and filter unit made with it - Google Patents

Description

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Reinfried Frhr. v. Schorlemer

34117 Kassel Brüder-Grimm-Platz 4 Telephone (O561) 153 35

EN 6625

Jochen Deichmann, 36179 Bebra

Hollow cylindrical filter element and filter unit made from it

The invention relates to a filter element and a filter unit according to the preambles of claims 1 and 3 and to a method for producing the filter element.

Filter elements in the form of bag filters are often used for dust separation (DE 39 39 645 Al), which have a diameter of 150 mm and a length of 4000 mm, for example, and are made of fabrics, e.g. felt, in particular needle felt, which can be made of natural, but also synthetic fibers such as polyester fibers, or also of a fiber fleece. These filter elements are arranged in a raw gas chamber and raw gas flows through them from the outside to the inside. Their interior is connected to a clean gas chamber which is operated at a lower pressure than the raw gas chamber and from which the cleaned gas leaves the filter system.

The dust particles or other contaminants that accumulate on the outer walls of the filter elements form a filter cake, the thickness of which increases more and more during operation. Therefore, the filter elements, if they are used for dust extraction systems, are assigned blow lines, by means of which compressed air can be supplied to their interior at preselected intervals. The sudden overpressure generated by this causes the filter cake adhering to the outer walls to be thrown off and thus the filter elements to be cleaned. With the help of valve controls, depending on the respective operating conditions,

It can be determined how often and for how long the compressed or purge air flow is switched on.

The known bag filters are made of flabby, non-self-supporting, easily deformable materials. To achieve the described function, support baskets made of metal, for example, are inserted into them. The only task of these support baskets is to prevent the filter elements from collapsing, even when the differential pressure of, for example, 10-30 mbar prevails during operation between the raw gas and clean gas sides.

Support baskets of this type contribute significantly to the overall costs of a hose filter system, which can have several hundred or thousand filter elements. They also mean that the filter elements, which are radially inflated when the flushing air is blown in for a short time, e.g. only 50 msec, contract again abruptly when the compressed air is suddenly switched off and the pressure difference prevailing during normal operation is restored, and thus hit the support baskets. This can also result in accelerations so high that the dust particles sitting on the outer walls gradually migrate through the hose material and enter the clean gas chamber, which increases the dust content in the clean gas chamber. In addition, the service life of the filter elements is reduced due to mechanical damage.

In addition to the hose filters described, self-supporting filter elements have also become known that do not require support baskets (DE 9111 939 Ul). They consist of a nonwoven, needle felt or fabric material that is solidified by processing with heat and/or pressure, adding chemicals, applying binding agents or the like in such a way that a self-supporting, hollow cylindrical tube can be formed. Although such rigid body filter elements can in principle be used as hose filters without support baskets, they have the problem that they are not suitable for all desired differential pressures and when compressed air is supplied for flushing they tend to be radially inflated as a whole, which impairs their durability and reduces the backwash properties.

The invention is based on the object of producing and designing the filter elements and filter units equipped therewith of the types described at the beginning in such a way that they can be operated with higher negative pressures and have better backwash properties.

The characterizing features of claims 1 and 3 serve to solve this problem. The inventive method for producing the filter elements results from the following description.

The invention is based on the surprising discovery that the seam areas obtained by overlapping when the material web is wound spirally or helically can be stiffened by the joining method selected in each individual case in such a way that a spiral or helical strip is created which has a noticeably greater stiffness than the other areas of the tube and thus forms a helical, very slightly flexible support body. One consequence of this is that the filter material, when subjected to pressure, is no longer moved back and forth as a whole, but only in zones between adjacent stiffening webs of the filter element. This means that the filter element can be subjected to higher pressures, which increases its durability. The zones of different stiffness also promote the shedding of the filter cake adhering to the outer walls, which means that the filter element has better backwash properties.

Further advantageous features of the invention emerge from the subclaims.

The invention is explained in more detail below in conjunction with the accompanying drawings using an exemplary embodiment. They show:

Fig. 1 shows a schematic front view of a filter unit for a dust extraction system equipped with filter elements according to the invention;
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Fig. 2 and 3 each show a side view and a top view of the feed unit according to Fig. 1;

Fig. 4 shows an enlarged section "X" of a filter element according to the invention; and Fig. 5 shows an enlarged section "Y" of a filter element according to the invention.

Fig. 1 to 3 show one of a plurality of tubular filter elements according to the invention.

elements 1, in which the filter elements 1 are arranged one behind the other. The filter unit 2 contains a holding plate 3, in which a number of passages corresponding to the number of filter elements 1 is formed. The holding plate 3 preferably consists of a U-shaped sheet with webs projecting downwards and with a crossbar lying between the upper ends of these webs, in which a series of holes is formed that extend practically over the entire width of the crossbar. Sleeves are inserted into these holes, which are firmly connected to the holding plate 3, in particular welded to its webs. The sleeves can, for example, be flush with the top of the crossbar.

While the upper ends of the filter elements 1 are open, their lower ends are closed with welded or otherwise attached bases 9 (Fig. 2). In addition, the holding plate 3 can be provided with holes 10 or the like at its ends, which serve for its installation, for example in a dust extraction system.

Filter elements and filter units made from them are generally known to those skilled in the art and therefore do not need to be explained in more detail. To avoid repetition, the content of DE 9111 939 Ul is hereby expressly made the subject of the present disclosure.

The filter elements 1 consist of a preferably surface-coated fabric, a nonwoven or needle felt material, whereby the fabrics can consist of plastic or cotton threads and the fibers of natural or synthetic fibers. In contrast to known filter elements, however, these materials are solidified in such a way that they do not produce flexible hoses, but rather self-supporting tubes that are essentially rigid and are not or only insignificantly compressed radially at the differential pressures that usually prevail, e.g. 10 - 30 mbar. The use of additional support baskets when assembling them according to Fig. 1 to 3 is therefore unnecessary.

The required dimensional stability and strength of the filter elements 1 is achieved on the one hand by the fact that the fabric or needle felt material from which they are made is mechanically, thermally and/or chemically strengthened using means known per se.

in particular, all known processes for the consolidation of nonwoven fabrics or felts can be used, for example needling, processing with heat and pressure on a calender, the addition of chemicals that have a swelling and/or plasticizing effect or the application of binding agents or the like. A surface coating with, for example, Teflon or the like is also possible if the materials have additional special properties and are intended, for example, to make cleaning easier. The material to be used in each individual case is to be determined based on the required filter properties, air flow rates, etc., and the type of consolidation chosen should ensure that the filter properties are impaired as little as possible.

Of the commercially available materials suitable for the purposes of the invention, one material in particular should be mentioned which is sold by Gebr. Roder AG, D-29614 Soltau, under the name "Soltafilt" PES 228/30-A5b. This material not only has the desired dimensional stability, but also the properties required for filter systems such as air filter systems for fine dust, in which filter elements of the type described are preferably used.

On the other hand, the desired dimensional stability is ensured by giving the filter elements a shape that promotes dimensional stability over their entire length. For this purpose, the filter elements 1 are preferably provided with a circular cross-section throughout. Although known tubular filter elements also have predominantly circular cross-sections, the special shape is only important in terms of other properties, but not with regard to dimensional stability due to their manufacture from fabrics, needle felts or nonwovens.

To produce the filter elements 1 according to the invention, it is preferable to start from a material that is already sufficiently solidified, e.g. the "Soltafilt" specified above, which is cut into a strip-shaped material web. Such a material web, which preferably has straight and parallel longitudinal edges, is wound spirally or helically from one end to the other onto a cylinder, whereby web sections 4 lying next to one another are obtained on the cylinder. These web sections 4 are laid with an overlap as shown in Fig. 4, i.e. two adjacent web sections 4 have common edge regions lying one above the other, which form a single, double-layered

• ■ · · S ·

Form a strip 5 which extends in a helical manner from one end of the cylinder or feed element 1 to the other.

After being wound onto the cylinder, the overlapping edge areas are connected to one another by a suitable connection method, e.g. welding or gluing, in such a way that the strip 5 forms an area of increased rigidity between adjacent, more flexible zones, which consist only of the respective web section 4. As a result, the strip 5 forms a helical support body extending over the length of the entire filter element 1, to which less rigid zones of the tube forming the filter element 1 are connected on both sides. One consequence of this is that when the filter unit according to Fig. 1 to 3 is in operation, only the more flexible zones contract due to the internal negative pressure, while the support webs in between, formed from the strip 5, largely retain their shape. Conversely, the parts of the web sections 4 located between the strips 5 are bulged radially outwards or contracted again when an internal overpressure is suddenly applied only between the individual support webs. This has a surprisingly positive effect on the desired removal of the adhering filter cake. It is assumed that the cylindrical tube does not expand or contract radially as a whole uniformly, i.e. by an essentially constant amount, which would result in a low cleaning effect, but that individual zones of the filter material are expanded and contracted by different amounts at a large number of points, with the strip 5 remaining practically undeflected. As a result, the filter cake is subjected to different pressures in different zones and therefore falls off quickly.

The filter elements 1 are preferably manufactured using a material that has already been fully solidified, so that only a connection of the overlapping edge areas is required during or after winding onto the cylinder. Alternatively, however, it would also be possible to wind a material that has not yet been solidified or has not yet been sufficiently solidified in a helical manner onto a cylinder and to process it during or after this using a roller or the like that causes the solidification, whereby the required connection of the individual edge areas could also be carried out.

Finally, when using very soft, flexible materials, it would be conceivable

to additionally insert a strip of a sufficiently rigid material, e.g. a steel wire or the like, between the overlapping edge areas in order to bring about the desired flexural rigidity in the area of the strip 5. This could be done at the same time as the material web is wound up.
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In particular, the preferred method, which starts from a material web that is already sufficiently solidified 4, has the advantage that it can easily be carried out continuously, for example, by gradually pulling the pipe sections that are produced one after the other on a rotating cylinder from one end of the cylinder and, for example, immediately cutting them to the desired length.

In all the variants described, the resulting self-supporting tube is finally provided with the base 9, which can be attached by welding or sewing, but also in other ways, e.g. by gluing. It is particularly advantageous to cast a molded part made of plastic onto the lower end of the filter element in a manner known per se (DE 91 03 538 Ul). Similarly, molded parts in the form of holding plates can be cast onto the other end of the filter element, which are required for sealing and fastening in a dust extraction device. Alternatively, molded parts made of metal can also be provided if this is necessary due to excessively high temperatures or due to a lack of chemical resistance.

In a particularly preferred embodiment, holding bodies 11, as shown in Fig. 5, are cast onto the filter elements 1. These are conically widened outwards towards the free end, provided with a circumferential groove 12 in the widened area and made of a flexible material. This makes it possible to insert the filter elements 1 in Fig. 1 from above, i.e. from the clean gas side, into openings in the holding plate 3 or the usual hose carrier plate until the edges 14 delimiting these openings snap into the circumferential groove 12. The holding plates 3, together with the ends of the filter elements 1 adjacent to them, give way elastically. If, however, it is desired or necessary to attach the filter elements 1 in Fig. 1 from below, i.e. from the raw gas side, to the holding plate 3 or the like, they are preferably inserted into a mounting plate analogously to Fig. 5 and then, by suitably arranging and fastening them, their upper ends are pressed against the

Holding plate 3 or similar. Sealing rings can be used for sealing, which are inserted into grooves 15 formed in the upper end faces of the holding bodies 11. This makes it easy to install the filter elements 1 either from the clean gas side or from the raw gas side, depending on the local conditions.

The invention is not limited to the described embodiments, which can be modified in many ways. This applies in particular to the described filter units and the assembly of the filter elements 1 in the filter units. It is also understood that the described dimensional stability or flexural rigidity is not only achieved when the filter element is a completely geometrically rigid body. Rather, within the scope of the invention, precisely those filter elements are desired that expand radially to a small extent during the cleaning process due to the internal overpressure or contract radially to a small extent during normal operation due to the internal negative pressure, but otherwise do not require any additional parts, in particular not the usual support baskets. Therefore, the dimensional stability sufficient for the purposes of the invention is always achieved when the filter elements can be used as intended without the use of support baskets. Accordingly, the shape of the filter elements according to the invention can be changed, for example, by giving them a slightly oval, elliptical or similar cross-section instead of an exactly circular one.

cross-section is given, provided that such a cross-section can also avoid the use of support cages.

Claims (6)

Expectations 1) Hollow cylindrical filter element for dust extraction systems in the form of a self-supporting tube, which is made from a material web wound in a helical shape and with overlapping edge regions at its edges, which consists of a consolidated nonwoven, needle felt or fabric material, characterized in that the edge sections are connected to one another to form a strip (5) of increased rigidity. 2) Filter element according to claim 1, characterized in that the edge sections are connected to one another by gluing or welding. 3) Filter element according to claim 1 or 2, characterized in that it is provided at one end with a cast-on holding body (11) which has a circumferential groove (12) and consists of a flexible material. 4) Filter element according to claim 3, characterized in that the holding body (11) widens conically towards its free end and the circumferential groove (12) is formed in the widened area 5) Filter element according to claim 3 or 4, characterized in that the holding body (11) is provided on its free end face with a groove (15) intended for the insertion of a sealing ring. 6) Filter unit with at least one hollow cylindrical filter element (1) which is releasably attached to a holding plate (3) hanging downwards, characterized in that the filter element (1) is designed according to one of claims 1 to 5.