Sludge Filter

Abstract: A woven filter medium for sludge dewatering consists of longi­ tudinal threads (A-D) and transversal threads (1-12) in one or several layers, whereby the longitudinal threads are bind­ ing with the transversal threads according to any known pattern of weaving. In order to facilitate the formation of the cakes and to re­ lease these is at least the section of the longitudinal threads (A-D) flattened in the plane of the woven fabric and the longitudinal and transversal threads are made of monofilament of plastic, e.g. unsaturated polyester plastic, polyamide, tetrafluorpolyethylene, polyetherketone, poly­ thenylensulphidepolypropen or the like.

Description: This invention relates to a woven filter medium for sludge dewatering consisting of longitudinal and transversal threads of monofilament of plastic in two layers, whereby the cross section shape of the longitudinal threads is flattened, and whereby the longitudinal threads bind with the transversal threads according to any pattern to form a fabric. Filtration of sludge containing liquids requires a high standard of the used filter medium. It shall have an adequate permeability, a surface and a system of pores giving quick formation of cake and a surface which renders release of cakes possible without the material being adhered to the filter. The filter must have a certain mechanical stability and chemical resistance. Woven structures of synthetic yarns and filament are used to an increasing extent. The use of solid-drawn, circular threads of a thermoplastic resin (circular monofilament) are normally used when weaving a filter media for sludge filtration. The degree of free area and the smothness of the surface can be graded by choice of the thread count and thickness of the filament. The possibilities to vary this are, however, not so many as desirable when using only circular filaments. These have among other things the tendency to be enbedded so completely by the filter cake that the disengagement of it will be difficult and the material will adhere to the filter. However CH-608 975 discloses that the warp threads are flattened in contrary to circular threads. However, these circular warp threads do not form the surface of the fabric and will therefore not facilitate the disengagement of the filter cake. Further, this fabric is of metal threads. A metal thread fabric cannot be woven so that the warp threads pass over more than one weft thread which means that there is no floating for the warp threads. DE-A-2 531 222 also discloses flattened threads but the design of the fabric is not so that the disengagement will be facilitated. It is an object of the invention to eliminate this drawback and facilitate the formation of the cakes. The invention is hereby characterized in that the longitudinal threads are located to form surfaces along parts in their longitudinal direction, said surfaces being dominantly extended in the plane of the fabric, and that the first layer of the transversal threads are of spun yarns or multifilaments and the transversal threads of the second layer are circular monofilaments of plastic, whereby the pattern is chosen such that said surfaces of the flattened threads to the largest extent are exposed on the side of the first layer on which a cake is to be formed Because of the flattened cross section of the longitudinal threads, the degree of free area of the filter is easier to grade, since the open space in a woven fabric consisting of flat threads are smaller than when the woven fabric consists of circular threads. The formation of cakes will also be formed faster, because the solid sludge particles will adhere to a flat surface easier than on a round surface because of the geometry and the way of flow. As mentioned above, the release of cakes will be easier as flat threads will not be enbedded by the cake and for the same reason the filter will remain cleaner after the release of cakes. The embodiments of the invention will be described in the following with reference to the enclosed drawing. Fig. 1 is a transversal section of a double layer woven fabric according to the invention. Fig. 1 shows a double layer woven fabric and the longitudinal threads A, B, C and D are flat filaments. The transversal threads 1, 2, 4, 5, 7, 8, 10 and 11 are soft yarns or multifilament. The remaining transversal threads 3, 6, 9 and 12 are circular monofilament. Thus, a smaller degree of free area is achieved by adding softer multifilament or spun yarns to the filaments. Over the reduction of the degree of free area, the soft threads will fill up the space between the filament in the filter surface if they are taken up,and will hereby contribute to a better and a cleaner release of cakes. For a woven fabric having longitudinal flattened filament and transversal circular filaments with soft filler yarns in both directions, the weaving pattern may be chosen so that the flattened threads and the filler yarns to the largest extent are exposed on the side of the filter on which the filter cake shall be formed.

Claims: Woven filter medium for sludge dewatering consisting of longitudinal and transversal threads of monofilament of plastic in two layers, whereby the cross section shape of the longitudinal threads is flattened, and whereby the longitudinal threads bind with the transversal threads according to any pattern to form a fabric which is characterized in that the longitudinal threads are located to form surfaces along parts in their longitudinal direction, said surfaces being dominantly extended in the plane of the fabric, and that the first layer of the transversal threads are of spun yarns or multi filaments and the transversal threads of the second layer are circular monofilaments of plastic, whereby the pattern is chosen such that said surfaces of the flattened threads to the largest extent are exposed on the side of the first layer on which a cake is to be formed. Filter medium according to claim 1, characterized in that the cross section of the longitudinal threads has a horizontal rectangular shape. Filter medium according to claim 1, characterized in that the cross section of the longitudinal threads has a horizontal oval shape. Filter medium according to any of claims 1, 2 and 3, characterized in that the threads are of thermoplastic material. Filter medium according to claim 4, characterized in that the longitudinal threads or the transversal threads are of any kind of polyester plastic. Filter medium according to claim 4, characterized in that the longitudinal threads of the transversal threads are of any kind of polyamide plastic. Filter medium according to claim 4, characterized in that the longitudinal threads or the transversal threads are of tetrafluorpolyethene plastic. Filter medium according to claim 4, characterized in that the longitudinal threads or the transversal threads are of any kind of polyetherketone plastic. Filter medium according to claim 4, characterized in that the longitudinal threads of the transversal threads are of any kind of polyphenylensulphide plastic. Filter medium according to claim 4, characterized in that the longitudinal threads or the transversal threads are of any kind of polypropene plastic.

Inventors: ALMHEM ROLF, ALMHEM, ROLF
Applicants: SCANDIAFELT IT AB
Application year: 1987
Main classification: B01D39
IPC codes: B01D39, D03D15