Filter element

Abstract

The invention relates to a filter element having inherent stability and being porous to permit flow therethrough, comprising a filter body which forms a porous sintered structure and is constructed with filter body particles which are at least in part polysulfide particles. In addition, the invention relates to a method of manufacturing such a filter element.

Claims

1. A filter element (30) being porous to permit flow therethrough, comprising a filter body (20) which forms a porous sintered structure and is constructed with filter body particles (10, 14) which are at least in part polysulfide particles (10), wherein: the polysulfide particles (10) contain a tempered polysulfide; and the tempering is carried out at a temperature of 255° C. to 275° C. over a period of time from 7 to 24 hours prior to sintering.

2. The filter element (30) of claim 1, wherein the polysulfide particles (10) are polyphenylene sulfide particles.

3. The filter element (30) of claim 1, wherein all filter body particles contain polysulfide.

4. The filter element (30) of claim 1, wherein at least part of the filter body particles consists of polysulfide.

5. The filter element (30) of claim 4, wherein all filter body particles consist of polysulfide.

6. The filter element of claim 1, wherein the polysulfide particles (10) contain at least two polysulfides of different configuration.

7. The filter element (30) of claim 1, wherein the filter body particles (10) have a melt flow index of at the most 500 g/10 min.

8. The filter element (30) of claim 1, wherein the polysulfide particles (10) contain unfilled polysulfide.

9. The filter element (30) of claim 1, wherein the polysulfide particles (10) contain at least one tempered polysulfide and at least one untempered polysulfide.

10. The filter element (30) of claim 1, which has a porosity of at least 30%.

11. The filter element (30) of claim 1, wherein the filter body (20) is formed such that the pressure loss across the filter element (30), measured with respect to an air flow without foreign matter load at a volumetric flow rate of 12.011 m.sup.3/(m.sup.2×min) and with an air flow-through area of the filter body (20) of 256 mm×256 mm with a thickness of 4 mm, is at the most 2000 Pa.

12. The filter element (30) of claim 1, wherein the polysulfide particles (10) have an average size of 50 to 500 μm.

13. The filter element (30) of claim 1, wherein the filter body (20) comprises, in addition to the polysulfide particles (10), particles that are not polysulfide particles.

14. The filter element (30) of claim 1, wherein the filter element (30), on an inflow side (22) thereof, is provided with a coating (24) constructed with additional particles (28), said coating (24) having a smaller pore size than the filter body (20).

15. The filter element (30) of claim 1, wherein the filter body (20) in a tensile test reveals a tensile strength of at least 1 N/mm.sup.2.

16. The filter element (30) of claim 1, wherein the filter body (20) in a tensile test has an elongation at break of at least 0.2 mm.

17. The filter element (30) of claim 1, wherein the filter element is a lamellar filter element.

18. The filter element (30) of claim 17, further comprising a filter head (36) and a filter foot (34), which are constructed with the same material as the filter body (10).

19. The filter element (30) of claim 1, which is capable of withstanding a temperature in the range from 50 to 200° C.

20. A method of manufacturing a filter element (30) having inherent stability and being porous to permit flow therethrough, said method comprising steps of: Providing filter body particles comprising polysulfide particles (10), at least part of said polysulfide particles tempered at a temperature of 255° C. to 275° C. over a period of time from 7 to 24 hours, and sintering the filter body particles to form a porous sintered filter body (20) of the filter element (30).

21. The method of claim 20, wherein the polysulfide particles are polyphenylene sulfide particles.

22. The method of claim 20, wherein the sintering takes place at ambient pressure.

23. The method of claim 20, wherein the sintering takes place at a temperature of 290° C. to 350° C.

24. The method of claim 23, wherein the sintering takes place over a period of time from 5 min to 180 min.

25. The method of claim 20, wherein at least two polysulfides of different configuration are used for providing the filter body particles.

26. The method of claim 25, wherein the provided filter body particles comprise tempered polysulfide and untempered polysulfide particles.

27. The filter element (30) of claim 16, wherein the tensile test is performed according to DIN EN ISO 527-2 (2012-06) at a test speed of 80 mm/min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a sectional view of a section of a filled mold, for the production of a filter element, illustrating the state before sintering.

(2) FIG. 2 shows a sectional view of a section of a filter element without surface coating;

(3) FIG. 3 shows a sectional view of a section of a filter element, after application of a surface coating;

(4) FIG. 4 shows an embodiment of a filter element according to the invention with a filter head which is held on an upright partition between raw fluid space and clean fluid space;

(5) FIG. 5 shows a sectional view of the filter element at the position marked V-V in

(6) FIG. 4;

(7) FIG. 6 shows a sectional view of the filter element at the position marked VI-VI in FIG. 4; and

(8) FIG. 7 shows a microscopic image of a sintered filter body according to the first example.

DETAILED DESCRIPTION

(9) FIG. 1 illustrates a section of a mold 2 enclosing a mold cavity 4. Filter body particles, in this case polysulfide particles 10, i.e. particles of a polysulfide material as described herein, have been introduced into the mold cavity 4. The filter body particles constitute the starting material for a filter body 12. In addition, FIG. 1 reveals hollow glass globules 14 which as fillers fill spaces between the polysulfide particles 10.

(10) FIG. 2 illustrates the state after vibration of the mold 2 and heating of the same to a sintering temperature for a suitable period of time. The polysulfide particles 10, at contact points between adjacent polysulfide particles 10, i.e. at locations where adjacent polysulfide particles 10 contact each other or almost contact each other, have formed sintering necks 16. At the sintering necks 16, the polysulfide particles 10 have grown together, so that a flow-porous sintered structure, i.e. a sintered structure that is porous to permit flow therethrough, is formed which constitutes a coherent, but still flow-porous filter body 20. Upon cooling of the filter body 20, the sintered structure thus produced forms an inherently stable solid structure, so that the now sintered together filter body 20 can be removed from the sintering mold 2 shown in FIG. 1 as well. FIG. 2 illustrates the filter body 20 after removal of the same from the opened sintering mold 2.

(11) FIG. 3 finally shows a state in which, after removal from the sintering mold 2, a coating 24 for surface filtration has been applied to the filter body 20 on a side 22, that is the right side in FIG. 3, which forms the inflow side during operation. The coating 24 contains fine-grain plastics particles 28. The plastics particles 28 typically have anti-stick properties and may be, for example, polytetrafluoroethylene particles. The average size of the plastics particles 28 may be between 0.3 and 30 μm, depending on the application. In the case of polytetrafluoroethylene particles, the particles form polytetrafluoroethylene agglomerates. The particles 28 can be applied, in particular, by first spraying an adhesive onto the relevant surface of the raw filter body 20 and then blowing on the particles 28. Alternatively, it is also possible to firstly blow on the particles 28 and then spray on a liquid adhesive. The coating can also be applied as a liquid, e.g. consisting of an aqueous emulsion of particles and adhesive. The adhesive may be a thermosetting plastic, which then cures at room temperature or at an elevated temperature.

(12) The hollow glass globules 14 are optional. In principle, the filter body 20 could also be constructed of the polysulfide particles 10 only.

(13) FIG. 4 shows a filter element 30 according to the invention, comprising a filter body 20 having the construction described hereinbefore, as well as a filter foot 34 integrally formed on the filter body 20 and a filter head 36 integrally formed on the filter body 20. The filter element 30 shown in FIG. 4 is held on a vertically arranged or upright partition 32, with the longitudinal direction of said filter element 30 between filter head 36 and filter foot 34 extending in the horizontal direction. FIG. 4 shows the filter element 30 as viewed in the direction towards one of two large, zig-zag-shaped or wavy first side walls 38. Narrow, second side walls 40 laterally connect the first side walls 38 to each other so as to form a box-like structure. The partition 32 is part of a filter device, not shown in more detail, and separates a raw fluid side 42 of the filter device from a clean fluid side 44.

(14) The filter element 30 is “laterally” attached with its filter head 36 to the upright partition 32. FIG. 4 illustrates the so-called clean-fluid-side installation of the filter element 30, in which a lateral surface of the filter head 36 projecting beyond the side walls 38, 40 and facing towards the filter foot 34 is attached to the partition 32 on the clean fluid side 44, and the filter body 20 of the filter element 30 projects through an opening in the partition 32. Between the filter head 36 and the partition 32, there can be seen a seal 44 as a sealing member between the raw fluid side 42 and the clean fluid side 46. This permits replacement of the filter element 30 from the “clean” clean fluid side 44. Alternatively, the so-called raw-fluid-side installation of the filter element 30 is also possible, in which the filter head 36, with the lateral surface thereof opposite to the filter foot 34, is attached to the partition 32 from the raw fluid side 42. Installation and removal of the filter element 30 then take place via the raw fluid side 42. It is, of course, also possible to mount the filter element 30 in suspended form, instead of being attached laterally. The partition 32 is then provided transversely in the manner of an intermediate floor in the filter device between an e.g. lower raw fluid side 42 and an upper clean fluid side 44. Also in this suspended installation position of the filter element 30, there may be provided either a clean-fluid-side or raw-fluid-side installation of the filter element 30.

(15) During operation of the device, the medium to be filtered is sucked into the device through an opening, not shown, or urged by positive pressure into the device and flows from the raw fluid side 42 through the porous side walls 38, 40 into the hollow interior of the filter element 30 and is sucked from there through a through-flow opening 48 in the filter head 36 onto the clean fluid side 44. From there, it is discharged through an opening, also not shown, back to the outside of the filter device. The solid particles to be separated from the medium to be filtered are retained by a fine porous layer on the surface of the filter element 30 and remain partially adhered thereto. This layer of adhering solid particles is cleaned off at regular intervals by blasting off, e.g. by a pressurized air surge which is opposite to the direction of flow, and then falls to the ground on the raw fluid side 42 of the device.

(16) FIG. 5 illustrates the space 50 between the two first side walls 38 which is confined in zig-zag-like or wavy manner and continues in the flow passage 48 through the filter head 36 to the clean fluid side 44. In contrast to FIG. 4, FIG. 5 shows the installation of the filter element 30 on the raw fluid side.

(17) The side walls 38 of the filter element 30 are flow-porous structures consisting of sintered together polysulfide particles 10 as described herein. On the upstream or inflow side of the filter element 30, there may be applied finer porous coating 24, for example, of finer-grain polytetrafluoroethylene particles, whereby the surface filtration properties can be controlled particularly well and can be adapted particularly well to the substances to be filtered.

(18) The filter head 36 as well as the filter foot 34 are made of a plastic material which is matched to the polysulfide material of the filter body 20, and are integrally formed on the filter body 20, e.g. by injection molding. In the transition shown in FIG. 2 between the filter body 20 and the filter head 36, the side walls 38 of the filter body are enclosed on the outside by the filter head 36 with a first part 52 of its height, while a second part 54 of the height of the filter head 36 surmounts the side walls 38 upwardly and covers the same at the upper ends thereof. Thus, the connecting area between the side walls 38 and the filter head 36 becomes particularly large.

(19) In principle, any synthetic resin is suitable for molding the filter head 36 and the filter foot 34 onto the side walls 38 of the filter element 30. However, it is particularly advantageous when the material of filter head 36 and filter foot 34, with respect to thermal stress, behaves as similar as possible as the material of the filter body 20. It is therefore recommended that the molded filter head 36 or filter foot 34 be formed from possibly the same polysulfide plastics as the filter body 20. However, filter head and filter foot do not need to be porous to permit flow therethrough. The filter head 36 and filter foot 34, respectively, and the filter body 20 then expand to the same extent under thermal stress.

(20) Basically, FIG. 5 shows the section through the filter element 30 at a position of the filter element 30 where the zig-zag-like first side walls 38 come close to each other. However, on the right side of FIG. 5 there is also shown, in broken lines, the outermost, underlying wall portion of the course. In this case, it is also shown how the through-flow passage 48 extends from a substantially rectangular flow cross section in the upper region of the filter head 36 into the interior of the filter element 30, which is advantageous in terms of flow. The transition extends from the innermost wall portions in funnel-shaped manner obliquely upwards in outward direction, while it extends from the outermost wall portions in substantially rectilinear manner or with a slight inclination only.

(21) The sectional view shown in FIG. 6 illustrates in part two first side walls 38 and a narrow, second side wall 40. It can also be seen that the filter element 30 is formed from two halves 38, 38 which are joined together along their longitudinal axis 56. The two halves 38, 38 may be joined together by, for example, gluing, sintering, welding or otherwise. Of course, an integral manufacture of the filter element 30 is possible as well.

(22) The two halves 38 and 38, except for the second narrow side walls 40, are also connected to each other between the same along wall portions 58, preferably from the filter head 36 to the filter foot 34. This leads to a subdivision into smaller, box-like elements or cells, which increases the strength of the filter element 30 in total, as the individual cells themselves already are of relatively high strength.

(23) The first side walls 38 have a substantially zigzag-like course and are formed of successive first and second wall sections arranged following each other. FIG. 6 very nicely illustrates the “fir-tree” shape of the filter element 30, which forms a lamellar filter.

(24) In addition to the box-like shape of the filter body shown in FIGS. 4 to 6, filter elements with differently shaped filter bodies are also possible, for example tubular filter elements in which the filter body has a substantially cylindrical shape.

EXAMPLES

(25) In the following, there are indicated some examples of filter elements according to the invention:

Example 1

(26) Coarse-grain plastics powder of polyphenylene sulfide (PPS) particles having an average grain size of 100 μm was thoroughly mixed and filled into a tempering mold. The PPS powder had the following properties: density according to ASTM D792: 1340 kg/m.sup.3; water absorption at 23° C. per 24 h according to ASTM D570: 0.05%, tensile modulus according to ISO 527-2: 3400 MPa, melting point according to ISO 11357-3: 280° C.; glass transition temperature according to ISO 11357-2: 90° C. The tempering mold was vibrated during the filling in of the plastics particles.

(27) The particles in powder form filled into the mold were tempered in an air circulating oven for 11 hours at a temperature of 270° C. in an ambient air environment. After tempering, discoloration of the polyphenylene sulfide particles to brown color could be observed. The particle size distribution of the polyphenylene sulfide particles did not change significantly by the tempering process.

(28) For both the untempered particles and the tempered particles, the melt index was determined at 316° C. per 5 kg according to ASTM D 1238-13, Procedure B. This determination yielded a melt index of 100 g/10 min for the untempered polyphenylene sulfide particles. After tempering, the melt index of the filter body particles dropped so much that it was no longer measurable by the method used.

(29) The tempered polyphenylene sulfide particles were filled, after cooling and re-sieving, into a sintering mold with dimensions of 300 mm×480 mm×4 mm. The average grain size of the polyphenylene sulfide particles was still 100 μm. The sintering mold was vibrated during filling to achieve a sufficiently dense packing of the polyphenylene sulfide particles. The polyphenylene sulfide particles filled into the sintering mold were then sintered in a sintering furnace for 60 min at a sintering temperature of 310° C.

(30) Upon removal from the sintering furnace, the sintered filter body plate was removed from the mold and tested for its mechanical properties. A micrograph of a section of the filter body plate after sintering at thirty times magnification is shown in FIG. 7.

(31) Various test pieces were cut out from the plate and tested for mechanical properties or porosity.

(32) A first test piece of 110 mm×10 mm was subjected to a tensile test according to DIN EN ISO 527-2 (2012-06) at a test speed of 80 mm/min. Here, a stress-strain diagram revealed a tensile strength of the test piece of 1.77 N/mm.sup.2 and a maximum elongation of the test piece of 0.34 mm until breakage.

(33) A determination of the pore size distribution on another test piece with dimensions of 250 mm×250 mm yielded a porosity of 65%.

(34) Another test piece measuring 280 mm×280 mm was used to determine the pressure loss. In this case, a pressure loss of 1000 Pa was determined, measured with respect to a flow of air without foreign matter load at a volumetric flow rate of 12.011 m.sup.3/(m.sup.2×min) and with an air flow-through area of the test piece of 256 mm×256 mm.

Example 2

(35) Coarse-grain plastics powder of polyphenylene sulfide (PPS) particles having an average grain size of 100 μm was thoroughly mixed and filled into a tempering mold. The PPS powder had the following properties: density according to ASTM D792: 1340 kg/m.sup.3; water absorption at 23° C. per 24 h according to ASTM D570: 0.05%, tensile modulus according to ISO 527-2: 3400 MPa, melting point according to ISO 11357-3: 280° C.; glass transition temperature according to ISO 11357-2: 90° C. The tempering mold was vibrated while the plastics particles were filled in.

(36) The particles in powder form filled into the mold were tempered in an air circulating oven for 11 hours at a temperature of 270° C. in an ambient air environment. After tempering, discoloration of the polyphenylene sulfide particles to brown color could be observed. The particle size distribution of the polyphenylene sulfide particles did not change significantly by the tempering process.

(37) For both the untempered particles and the tempered particles, the melt index was determined at 316° C. per 5 kg according to ASTM D 1238-13, Procedure B. This determination yielded a melt index of 100 g/10 min for the untempered polyphenylene sulfide particles. After tempering, the melt index of the polyphenylene sulfide particles dropped so much that it was no longer measurable by the method used.

(38) A mixture of 20 percent by weight of the untempered PPS particles and 80 percent by weight of the tempered PPS particles was prepared after cooling and re-sieving of the tempered polyphenylene sulfide particles. The average grain size of polyphenylene sulfide particles after sieving still was 100 μm. The mixture was filled into a sintering mold with dimensions of 300 mm×480 mm×4 mm. The sintering mold was vibrated during filling to achieve a sufficiently dense packing of the polyphenylene sulfide particle mixture. The polyphenylene sulfide particles filled into the sintering mold were then sintered in a sintering furnace for 60 minutes at a sintering temperature of 305° C.

(39) After removal from the sintering furnace, the sintered filter body plate was removed from the mold and tested for its mechanical properties.

(40) Various test pieces were cut out from the plate and tested for mechanical properties or porosity.

(41) A first test piece of 110 mm×10 mm was subjected to a tensile test according to DIN EN ISO 527-2 (2012-06) at a test speed of 80 mm/min. Here, a stress-strain diagram revealed a tensile strength of the test piece of 4.46 N/mm.sup.2 and a maximum elongation of the test piece of 0.44 mm until breakage.

(42) A determination of the pore size distribution on another test piece with dimensions of 250 mm×250 mm yielded a porosity of 63%.

(43) A further test piece measuring 280 mm×280 mm was used to determine the pressure loss. In this case, a pressure drop of 1160 Pa was determined, measured with respect to a flow of air without foreign matter load at a volumetric flow rate of 12.011 m.sup.3/(m.sup.2×min) and with an air flow-through area of the test piece of 256 mm×256 mm.

Example 3

(44) Coarse-grain plastics powder of polyphenylene sulfide (PPS) particles having an average particle size of 100 μm was thoroughly mixed and filled into a tempering mold. The PPS powder had the following properties: density according to ASTM D792: 1340 kg/m.sup.3; water absorption at 23° C. per 24 h according to ASTM D570: 0.05%, tensile modulus according to ISO 527-2: 3400 MPa, melting point according to ISO 11357-3: 280° C.; glass transition temperature according to ISO 11357-2: 90° C. The tempering mold was vibrated while the plastics particles were filled in.

(45) The particles in powder form filled into the mold were tempered in an air circulating oven for 11 hours at a temperature of 270° C. in an ambient air environment. After tempering, discoloration of the polyphenylene sulfide particles to brown color could be observed. The particle size distribution of the polyphenylene sulfide particles had not changed significantly by the tempering process.

(46) For both the untempered particles and the tempered particles, the melt index was determined at 316° C. per 5 kg according to ASTM D 1238-13, Procedure B. This determination yielded a melt index of 100 g/10 min for the untempered polyphenylene sulfide particles. After tempering, the melt index of the polyphenylene sulfide particle dropped so much that it was no longer measurable by the method used.

(47) A mixture of 25% by weight of expanded glass globules and 75% by weight of the tempered polyphenylene sulfide particles was prepared after cooling and re-sieving of the polyphenylene sulfide particles. The average grain size of polyphenylene sulfide particles after sieving still was 100 microns. The mixture was filled into a sintering mold with the dimensions of 300 mm×480 mm×4 mm. The sintering mold was vibrated during filling to achieve a sufficiently dense packing of the mixture of polyphenylene sulfide particles/expanded glass globules. The polyphenylene sulfide particles filled into the sintering mold were then sintered in a sintering furnace for 60 min at a sintering temperature of 315° C.

(48) After removal from the sintering furnace, the sintered filter body plate was removed from the mold and tested for its mechanical properties.

(49) Various test pieces were cut out from the plate and tested for mechanical properties or porosity.

(50) A first test piece of 110 mm×10 mm was subjected to a tensile test according to DIN EN ISO 527-2 (2012-06) at a test speed of 80 mm/min. Here, a stress-strain diagram revealed a tensile strength of the test piece of 3.71 N/mm.sup.2 and a maximum elongation of the test piece of 0.39 mm until breakage.

(51) A determination of the pore size distribution on a further test piece with dimensions of 250 mm×250 mm revealed a porosity of 52%.

(52) Another test piece measuring 280 mm×280 mm was used to determine the pressure loss. In this regard, a pressure loss of 3030 Pa was determined, measured with respect to an air flow without foreign matter load at a volumetric flow rate of 12.011 m.sup.3/(m.sup.2×min) and with an air flow-through area of the test piece of 256 mm×256 mm.