Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/14—Other self-supporting filtering material ; Other filtering material
  • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
  • B01D39/2027—Metallic material
  • B01D39/2041—Metallic material the material being filamentary or fibrous
  • B01D39/2044—Metallic material the material being filamentary or fibrous sintered or bonded by inorganic agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/10—Filter screens essentially made of metal
  • B01D39/12—Filter screens essentially made of metal of wire gauze; of knitted wire; of expanded metal

Definitions

• the invention relates to a filter element comprising a filter medium and a reinforcing structure.
• the invention further relates to the use of such a filter element and to a method of manufacturing a filter element.
• Filter elements comprising a filter medium made from a metal or metal alloy such as a metal fiber fleece are known in the art. They are used for several filtration applications, such as gas or liquid filtration. As a metal fiber fleece has a limited strength, it is necessary to support the metal fiber fleece by means of a reinforcing structure. For this purpose, a metal fiber fleece may be welded or sintered to a wire mesh or to a perforated metal sheet.
• particles are retained on the surface of the filter medium. Some particles may enter the pores of the filter medium and are caught in the porous structure of the filter medium. To avoid that the filter medium is clogged and as a consequence, the filtration flux decreases to very low levels or even to zero, the retained particles are to be removed from the filter medium or out of the porous structure of the filter medium at regular times. This may be done by reverse pulses.
• the particles are pulsed, e.g. blown or pushed backwards and removed from the filter medium or out of the porous structure of the filter medium.
• These severe pulses may damage the metal fiber fleece If a metal fiber fleece is not supported, the repetitive reverse pulses may cause fatigue failures of the metal fiber fleece.
• a filter element comprises a filter medium and a reinforcing structure.
• the reinforcing structure is provided with open areas.
• the filter medium is made of a metal or a metal alloy and is covering the open areas of the reinforcing structure.
• the reinforcing structure comprises at least an outer layer of a thermoplastic material.
• connection between the filter medium and the reinforcing structure is obtained by inserting the filter medium at least partially in the at least partially softened thermoplastic polymer material.
• the thermoplastic polymer material can be softened by melting.
• the filter medium may comprise a mesh, such as a woven or welded mesh.
• the filter medium comprises a non-woven metal fiber
• the reinforcing structure may extend beyond the filter medium.
• the reinforcing structure may be made completely of a thermoplastic polymer material or may be made of another material comprising an outer layer of a thermoplastic polymer material.
• An outer layer of a thermoplastic polymer material can for example be obtained by spraying a layer of a thermoplastic polymer material on a reinforcing structure, by applying powder on a reinforcing structure or by applying strips on a reinforcing structure.
• thermoplastic polymer material is meant that at least the outer surface of the thermoplastic polymer material is softened.
• the filter medium is pressed towards the reinforcing structure and the filter medium is at least partially inserted in the at least partially softened thermoplastic polymer material.
• thermoplastic polymer material can be softened or melted in many different ways.
• a first way to melt the thermoplastic polymer material at least partially comprises the heating of the reinforcing structure by means of a heating element.
• a heating element all heating elements known in the art can be used.
• a preferred technique to melt the thermoplastic polymer material is by using a stream of hot air.
• Alternatives comprise the use of an induction coil or an infra-red heater.
• An alternative way to obtain a connection between the filter medium and t e reinforcin structure is b heatin he f ter medium and ressin this heated filter medium to the at least partially softened thermoplastic polymer material.
• the reinforcing structure will melt due to the heat of the filter medium. After cooling, a strong connection between the reinforcing structure and the filter medium will be obtained.
• connection between the filter medium and the reinforcing structure comprise welding techniques such as friction welding, ultrasonic welding, high frequency welding, ...
• thermoplastic material may be used to provide the reinforcing structure.
• thermoplastic polymer material has a melting point ranging between 80 and 250 °C and more preferably between 80 and
• polymer materials having a melting point higher than 300 °C can be used.
• An example of such a polymer material is poly-ether-ether ketone
• melting point has to be understood as glass transition temperature.
• thermoplastic materials examples include polyolefins such as polyethylene (PE) or polypropylene (PP), polyolefin derivates, polystyrene (PS), polyvinylchloride (PVC), poly(methyl methacrylate)
• PE polyethylene
• PP polypropylene
• PS polystyrene
• PVC polyvinylchloride
• PLC poly(methyl methacrylate)
• the thickness of the reinforcing structure may range between 1 and 50 mm. Preferably, the thickness of the reinforcing structure is between 1 and 25 mm, for example between 3 and 10 mm.
• the reinforcing structure is provided with open areas.
• An "open area” is to be understood as a zone of the reinforcing structure, where the thermoplastic material has been removed or an aperture or perforation has been provided.
• An open area may have any shape, it may for example have a circular, triangular, square, rectangular, trapezoid, parallelogram-like or hexagonal, shape.
• the open areas in the reinforcing structure may be provided by any technique known in the art, for example by perforation, laser cutting, drilling, die cutting, punching or milling.
• a reinforcing structure provided with open areas is obtained by injection moulding.
• the total open area of the reinforcing structure is preferably more than 25 % compared to the surface of the filter medium which covers the open areas.
• total open area of the reinforcing structure is meant the sum of the surfaces of all open areas present at the surface of the reinforcing structure and which are covered by the filter medium.
• the total open area is more than 50 %, most preferably more than 70 % or even more than 85 %. To maintain a reinforcing effect however, it is preferred that the total open area of the reinforcing structure is not more than 90 %.
• the filter medium may comprise a mesh, such as a welded or a woven mesh.
• any type of metal or metal alloy may be used to provide the mesh.
• Preferred alloys are stainless steel alloys such as AISI 300- or AISI 400- decade alloys as for example AISI 316L or AISI347.
• alloy comprising and/or nickel and 0.05 to 0.3 % by weight of yttrium, cerium, lanthanum, hafnium or titanium (known as Fecralloy® may be used.
• the filter medium comprises a non-woven metal fiber fleece.
• the metal fiber fleece preferably comprises metal fibers having a diameter ranging between 0.5 and 100 ⁇ m, e.g. between 2 and 25 ⁇ m. With equivalent diameter is meant, the diameter of an imaginary circle, said circle having the same surface of the surface of a radial or cross section of the metal fiber.
• the metal fibers can for example be obtained by bundle drawing or by shaving techniques (e.g. as described in US4930199), or by any other process known in the art.
• the metal fiber fleece is sintered.
• Ni-fibers or stainless steel fibers are used, e.g. stainless steel fibers from AISI 300- or AISI 400-serie alloys such as AISI 316L or AISI347, or alloys comprising Fe, Al and Cr, stainless steel comprising chromium, aluminum and/or nickel and 0.05 to 0.3 % by weight of yttrium, cerium, lanthanum, hafnium or titanium are used, such as Fecralloy®.
• the metal fiber fleece may comprise only one layer of metal fibers, or may be a stack of different fiber layers, each fiber layer comprising metal fibers with a specific equivalent fiber diameter, fiber density and weight of the layer. This weight of each layer is expressed in g/m 2 , and will hereafter be referred to as "specific layerweight".
• the different layers of the metal fiber fleece may be sintered separately.
• the stack comprising the different layers may be sintered.
• the reinforcing structure is present at side of the filter medium where the filtrate (filtered liquid) leaves the filter medium.
• the reinforcing structure is present at the flow in side of the filter medium.
• the flow in side of the filter medium is defined as the side of the filter medium where the liquid to be filtered enters into the filter medium.
• a third group of filter elements comprises filter elements comprising two filter media, one at each side of the reinforcing structure.
• a preferred technique to remove the retained particles is by reverse flow cleaning. This can for example be realised by applying pressure pulses during a short time period.
• the reverse flow cleaning may bend or deform the filter medium in a direction towards the flow in side of the filter medium. If the reinforcing structure is located at the flow in side of the filter medium, the filter medium is supported during reverse flow cleaning. No damage of the filter medium can be observed.
• the reinforcing structure may absorb the energy provided by the reverse flow cleaning. In case the reinforcing layer is located at the flow out side of the filter medium, the filter medium is not supported at the flow in side during reverse flow cleaning.
• the filter medium is not disconnected from the reinforcing structure.
• the connection between the reinforcing structure and the filter medium is sufficiently strong so that the energy provided by reverse flow cleaning such as high pressure liquid cleaning can be absorbed without bending or deforming the filter medium.
• the dimensions of the open areas are preferably chosen in such a way that the distance between a point of an open area and the edge of the open area is less than 100 mm. More preferably this distance is less than 70 mm, or even less than 40 mm, such as 30 mm.
• the dimensions of the open areas are chosen in such a way that for at least one point of the open area, its distance to the edge of the open area is larger than 0.5 mm or even larger than 1 mm, such as larger than 2 mm or even larger than 3 mm.
• the smallest distance between the edge of an open area, closest to the edge of the filter medium, and the edge of the filter medium is more than 3 mm or even more than 10 mm.
• the filter medium and the reinforcing structure have a common zone with a width of at least 3 mm at the edge of the filter medium. These zones will hereafter be referred to as "common zones".
• the presence of a common zone is preferred to avoid non filtered liquid by-passing the filter at the edge of the filter medium.
• the edge of the filter medium may be subjected to a compressing operation, to close the pores of the filter medium at its edge, in order to avoid bypass of liquid via the edge of the filter medium.
• a metal wire mesh such as a woven or braided mesh may be added to the metal fiber fleece.
• the metal wire mesh is located between two layers of metal fibers.
• a metal wire mesh is present at one side of the metal fiber fleece, for example at the side of the metal fiber fleece opposite to the side to which the reinforcing structure is located.
• a filter element according to the present invention may have any shape; it may for example be a flat filter element or a tubular filter element.
• a preferred embodiment of a filter element as subject of the present invention comprises a filter plate. Such a filter plate comprises both at its upper side and at its lower side a non-woven metal fiber fleece bonded to a reinforcing structure.
• the metal fiber fleece may be located at the outer surface or at the inner surface of the filter plate.
• a spacer layer e.g. a mesh, foam or stretch metal (expanded metal sheet) is positioned between the two metal fiber fleeces bonded to a reinforcing structure.
• Such a filter plate may be placed horizontally or vertically during filtering operations.
• a filter element as subject of the invention has several advantages to filter elements known in the art.
• a filter element according to the present invention has a high strength.
• the reinforcing structure is giving the necessary support to the filter medium. Even larger filter surfaces may be mounted in horizontal or vertical direction, without the need for extra support as compared to the presently known metal fiber filter surfaces.
• filter elements are characterised by a low weight.
• liquids or gasses may flow in opposite direction through the filter plate.
• such filter plates as subject of the invention are used for filtering food liquids such as wine, beer, juice or oil such as olive oil.
• a method of manufacturing a filter element comprises the steps of - providing a filter medium made of a metal or metal alloy; providing a reinforcing structure comprising at least an outer layer of a thermoplastic material, said reinforcing structure being provided with open areas; heating at least part of the thermoplastic polymer material to soften at least the outer surface of said thermoplastic polymer material; inserting said filter medium into the at least partially softened thermoplastic polymer material to connect the non-woven metal fiber fleece to the reinforcing structure.
• the filter medium may comprises a woven or welded mesh or may comprise a non-woven metal fiber fleece.
• the metal fiber fleece is positioned on the reinforcing structure thereby covering all open areas of the reinforcing structure.
• thermoplastic polymer material may be provided at least in the contact zone between the thermoplastic polymer material and the non-woven metal fiber fleece.
• the use of an inert or reducing atmosphere may avoid surface deterioration of the metal fiber fleece. This is particularly important in case a polymer material with a high melting point such as PEEK is used.
• thermoplastic polymer material and/or the metal fiber fleece For high melting polymer materials it is necessary to heat the thermoplastic polymer material and/or the metal fiber fleece to a temperature higher than 300 °C, and possibly to a temperature higher than 400 or 500 °C. At these high temperatures the metal fiber fleece may suffer from surface deterioration which may have a negative influence on the filter performance.
• the inert or reducing atmosphere may for example comprise argon or hydrogen or a mixture of argon and hydrogen.
• a great advantage of the method according to the present invention is that no complicated and expensive equipment is necessary to manufacture a filter element.
• a filter element according to the present invention can be made transparent by using a transparent thermoplastic polymer material. For many applications a transparent filter element is interesting as it allows to see the filtration process.
• thermoplastic polymer material By the choice of the thermoplastic polymer material, additional features such as impact resistance or flexibility can be given to the filter element according to the present invention.
• thermoplastic polymer with a high impact resistance such as acrylonitril- butadiene-styrene (ABS) can be used.
• ABS acrylonitril- butadiene-styrene
• a flexible thermoplastic polymer can be used.
• Filter elements according to the present invention furthermore show the advantage that they can easily be mounted in a filter system.
• a further advantage of a filter element according to the present invention comprises the possibility to integrate other parts of the filter system in the filter element as for example handles, connections, ... Injection moulding for example is a suitable technique to provide a reinforcing structure provided with other parts of the filter system.
• a filter element according to the present invention for the filtration of liquids or gases is provided.
• Such a filter element is in particular suitable to be used as filter element in reverse pulsing filtration operation.
• It may for example be used for the filtration of waste water, for the filtration of cooling liquids of for example metal milling apparatuses, for the filtration of liquids containing vulnerable or noble or precious metals or particles, or for the filtration of liquids such as food liquids and beverages as for example wine, beer, juice or olive oil. It is understood that the dimensions of the filter medium and the reinforcing structures will be chosen in order to meet the requirements of the different filter applications.
• FIGURE 1 schematically shows a filter element as subject of the invention
• - FIGURE 2 schematically shows a cross-section of the filter element shown in FIGURE 1
• - FIGURE 3 and FIGURE 4 schematically show a tubular filter element as subject of the invention
• FIGURE 5 schematically shows a tubular filter element with open areas having different sizes
• FIGURE 6a and 6b schematically show a cross-section of a filter plate as subject of the invention
• FIGURE 7 schematically shows a front view of a filter plate as subject of the invention.
• a flat filter element as subject of the invention is shown schematically in Figure 1.
• the filter element comprises a reinforcing structure 11 made of polypropylene.
• the reinforcing structure 11 has several open areas 13.
• the metal fiber fleece 12 (drawn in dashed line) is bonded to the reinforcing structure 11 by heating the reinforcing structure 11 so that the outer surface of this reinforcing structure is softened and by inserting the filter medium 12 into the softened reinforcing structure 11.
• the filter medium 12 is thereby covering all open areas 13 of the reinforcing structure 11.
• the reinforcing structure 11 has a part 15, which extends beyond the filter medium 12.
• the edge 16 of an open area closest to the edge 17 of the filter medium defines a common zone with a width 18 of at least 10 mm. Alternatively, the width of this common zone may be smaller.
• the edge of the filter medium is sealed by closing the pores of the filter medium at its edge for example by compression of the edge.
• the open areas 13 may have any shape.
• the open areas as shown in figure 1 have square shapes having a side of 40 mm. Between each adjacent sides of adjacent square open area 13, an area
• the total open area is thus more than 85% of the total surface of the metal fiber fleece.
• Figure 2 shows a cross-section of the filter element shown in Figure 1 , after it has been connected to the other parts of a filter unit, e.g. a filter chamber 21.
• the filter element is connected to the filter unit at the part
• Liquid or gas, loaded with particles 22 flows towards the filter element 11 in the direction as indicated with arrow 23. Filtered liquid or gas flows away from filter element as indicated with arrow 24.
• the side 25 of the filter element is called flow in side
• the side 26 of the filter element is called flow out side.
• a pressure pulse is given in the direction as indicated with arrow 27. Due to the strong connection between the reinforcing structure and the filter medium over the whole and essentially flat surface 28 of the metal area 14, the filter medium 12 is not disconnected from the reinforcing structure 11. It is not necessary to support the filter medium at its flow in side. Particles 24 being retained at the flow in side may be removed uniformly by reverse pulses and are not hindered or stuck by a reinforcing structure being present at the flow in side.
• the filter medium comprises a non-woven metal fiber fleece.
• the metal fiber fleece comprises for example three layers of AISI 316L fibers
• a first layer, of the metal fiber fleece, being present at the flow in side of the metal fiber fleece comprises a layer of 2 ⁇ m equivalent diameter fiber, with a specific layerweight of 450 g/m 2 .
• a second layer, being present beyond this first layer comprises 4 ⁇ m equivalent diameter fibers. This second layer has a specific layerweight of 300 g/m 2 .
• a third layer of metal fibers, being present beyond the second layer and facing the flow out side of the metal fiber fleece, consists of a layer with a specific layerweight of 600 g/m 2 of fibers with equivalent diameter of 6.5 ⁇ m. These three layers are sintered to each other.
• a filter element with absolute filter rating of 2 ⁇ m may be obtained.
• the metal fiber fleece is sintered first. Possibly, the sintered metal fiber fleece is compressed to obtain the required filter efficiency. This sintered and compressed metal fiber fleece may then be bonded to the reinforcing structure.
• An alternative embodiment comprises a reinforcing structure as described above and at both sides of the reinforcing structure, a metal fiber fleece.
• the metal fiber fleeces comprise for example a stack of layers as described above.
• a tubular filter element 300 as subject of the invention is shown in
• the filter element as shown in Figure 3a comprises a tubular reinforcing structure 302 provided with open parallelogram-like areas 303 and a filter medium 304.
• the filter medium 304 is bonded to the inner surface of the tubular reinforcing structure 302 by heating the reinforcing structure 302 so that the outer surface of this reinforcing structure is softened and by inserting the filter medium 304 into the softened reinforcing structure
• two parts 305 and 306 of the reinforcing structure 302 extend beyond the filter medium 304.
• the filter medium 304 may be connected to the tubular reinforcing structure 302 at the outer surface of this reinforcing structure or at the inner surface of the reinforcing structure. In the embodiment of Figure 3, the filter medium 304 is located at the inner surface of the reinforcing structure 302 whereas in the embodiment of Figure 4, the filter medium
• zone 305 is used to receive a filter cap 307 to close this side of the filter element.
• the liquid to be filtered enters the filter element as indicated by arrow 310.
• the filtered liquid is evacuated in axial way as indicated by arrow 312.
• the particles, being retained at the outer surface of the tube, may be blown or pushed off by using reverse pulses.
• a reinforcing structure with unequal open areas over its surface may be used to provide a tubular filter element as subject of the invention.
• a reinforcing structure 502 provided with e.g. 3 different open areas is used.
• the reinforcing structure has a maximum reinforced zone 506, a normal reinforced zone 508 and a minimum reinforced zone 510.
• the zone 512 can be used to receive an end cap.
• the filter plate 901 as subject of the invention is shown in Figure 6a, Figure 6b and Figure 7.
• the filter plate 901 comprises two filter element 902 and preferably a spacer layer 903, e.g. an expanded metal sheet or woven metal wire mesh.
• Figure 6a shows an embodiment having two filter element 902, having their reinforcing layer 904 pointing to the outer side of the filter plate 901.
• the filter media 905 of both filter elements 902 are pointing inwards of the filter plate 901.
• Figure 6b shows an embodiment having two filter elements 902, having their reinforcing layer 904 pointing to the inner side of the filter plate 901.
• the filter media 905 of both filter elements 902 are pointing outwards of the filter plate 901.
• a sealing means 906 is provided at the edge of the filter plate, in order to seal the edges of the filter plate, so avoiding by-passes of unfiltered liquid or gas when the filter plate is used.
• Both filter elements 902 are clamped to the sealing means 906, for example by using a polymer strip or a set of bolts and nuts 907, which are located in appropriate openings in both the filter elements 902 and sealing means 906.
• an appropriate outlet means 908 is provided, e.g. a conical tubular element. This outlet means 908 may be used to mount the filter plate 901 to a corresponding inlet means 909 of the evacuation duct 910.
• a wire mesh or other permeable means may be provided at the outer side of the filter plate, in order to prevent mechanical damages to the filter medium 905, either present at the outer side of the filter plate 901 , or present at the outer side at the openings of the reinforcing structure 904.
• the presence of parts of the reinforcing layer 904, extending beyond the metal fiber fleece 905 are an advantage for construction reasons.
• Such zones 913 may be used e.g. to clamp the seal 906, to provide evacuation channels 911 (zone 914), or to fix, e.g. by welding, the outlet means 908 to the filter element 902 (zone 915).
• Liquids e.g. wine, beer, olive oil or juice
• Liquids may be filtered by forcing the liquid to flow from the outer side of the filter plate 901 , via the openings in the reinforcing structure 904, via the metal fiber fleece 905, possibly via the spacer layer 903, possibly via evacuation channels 911 into the evacuation duct 910, as indicated with arrows 912.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Inorganic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Filtering Materials (AREA)

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• 2003
  • 2003-06-26 EP EP03762688A patent/EP1519780A1/de not_active Withdrawn
  • 2003-06-26 AU AU2003251723A patent/AU2003251723A1/en not_active Abandoned
  • 2003-06-26 WO PCT/EP2003/050269 patent/WO2004004868A1/en not_active Application Discontinuation

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