POROUS PANEL

Abstract

A porous panel with a surface area of at least 0.5 m.sup.2 has a first layer of metal fibers of an average equivalent diameter between 8 and 65 m. The cross-section of the metal fibers has two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides. The metal fibers are bonded to each other by metal bonds; where the metal of the metal fibers of the first layer is the bonding agent forming the metal bonds. The filter has a second layer of metal fibers. The average equivalent diameter of the metal fibers of the second layer is smaller than the average equivalent diameter of the metal fibers of the first layer. The first layer and the second layer are bonded to each other by metal bonds.

Claims

1-9. (canceled)

10. A porous panel with a surface area of at least 0.5 m.sup.2, comprising a first layer of metal fibers of average equivalent diameter between 8 and 65 m; wherein the metal fibers of the first layer of metal fibers have a cross-section, wherein the cross section has two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides; and wherein the metal fibers of the first layer of metal fibers have an average length of at least 6 mm; wherein the metal fibers of the first layer of metal fibers are bonded to each other by means of metal bonds; wherein the metal of the metal fibers of the first layer is the bonding agent forming the metal bonds; a second layer of metal fibers; wherein the average equivalent diameter of the metal fibers of the second layer of metal fibers is smaller than the average equivalent diameter of the metal fibers of the first layer of metal fibers; and wherein the first layer of metal fibers and the second layer of metal fibers are bonded to each other by means of metal bonds; wherein the metal of the metal fibers of the first layer of metal fibers and of the second layer of metal fibers is the bonding agent forming the metal bonds.

11. The porous panel as in claim 10, wherein the metal fibers of the first layer of metal fibers have a standard deviation between fibers of the equivalent fiber diameter of less than 25% of the equivalent fiber diameter.

12. The porous panel as claim 10, wherein the second layer of metal fibers comprises at least two sub-layers, wherein the metal fibers of the at least two sub-layers differ in average equivalent diameter; wherein a sub-layer closest to the first layer of metal fibers comprises metal fibers of higher average equivalent diameter than a sub-layer further away from the first layer of metal fibers.

13. The porous panel as in claim 10, further comprising a metal wire mesh, wherein the metal wire mesh is bonded in the panel by means of metal bonds.

14. The porous panel as in claim 13, wherein the metal wire mesh is bonded by means of metal bonds to the second layer of metal fibers, at the side of the second layer of metal fibers opposite to the side of the first layer of metal fibers.

15. The porous panel as in claim 10, wherein the second layer of metal fibers comprises metal fibers having a hexagonal cross section.

16. The porous panel as in claim 10, wherein the second layer of metal fibers comprises metal fibers that have a cross section, wherein the cross section has two neighbouring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides.

17. The porous panel as claim 10, wherein the porosity of the first layer of metal fibers is between 50% and 80%.

18. The porous panel as in claim 10, wherein the porous panel comprises at both of its outer sides a wire mesh bonded into the porous panel by means of metal bonds.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 shows the cross section of a porous panel according to the invention.

[0039] FIGS. 2-7 show examples of fiber cross sections of metal fibers that can be used for the first layer of metal fibers of the filter

[0040] FIG. 8 shows an exemplary set up for fiber machining to manufacture metal fibers of an average length of at least 6 mm and that have a cross-section that has two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides.

[0041] FIG. 9 shows a filter of a circular shape that can be made using the porous panel according to the invention.

[0042] FIG. 10 shows a filter with a half moon shape that can be made using the porous panel according to the invention.

MODE(S) FOR CARRYING OUT THE INVENTION

[0043] FIG. 1 shows the cross section 10 of a porous panel according to the invention. The porous panel comprises a first layer 12 of metal fibers. The metal fibers of the first layer of metal fibers have a cross-section having two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides. The metal fibers of the first layer of metal fibers have an average length of at least 6 mm, e.g. of 8 mm.

[0044] The first layer 12 has been built up by superimposing a number of webs of such metal fibers, e.g. five webs 13. It is clear however that the first layer 12 can be made by using one web or by using any other number of webs superimposed on top of each other. The metal fibers of the first layer of metal fibers are bonded to each other by metal bonds; e.g. by means of sintering, although welding is an alternative technique that can be used, e.g. capacitive discharge welding (CDW).

[0045] The porous panel 10 comprises a second layer of metal fibers 15. The average equivalent diameter of the metal fibers of the second layer of metal fibers 15 is smaller than the average equivalent diameter of the metal fibers of the first layer 12. In the example, the second layer 15 comprises two sub-layers 16, 17. The metal fibers of the two sub-layers 16, 17 differ in average equivalent diameter. The sub-layer 16 closest to the first layer 12 of metal fibers comprises metal fibers of higher average equivalent diameter than the sub-layer 17 further away from the first layer of metal fibers.

[0046] The filter 10 comprises a metal wire mesh 18. The first layer 12, the second layer 15 and the metal wire mesh 18 are bonded to each other by metal bonds; e.g. by means of sintering, although welding is an alternative technique that can be used, e.g. capacitive discharge welding (CDW).

[0047] FIGS. 2-7 show examples of fiber cross sections of metal fibers that can be used for the first layer of metal fibers of the filter. The fiber cross sections have two neighboring straight lined sides 110, 120 with an included angle of less than 90 and one or more irregularly shaped curved sides 130. Metal fibers having such cross-sections can also be used in the second layer of metal fibers. Such fibers can be made according to the method described in WO2014/048738A2. Such fibers for the first layer of metal fibers (and for embodiments of the second layer of metal fibers)fibers that have a cross-section that has two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sidescan be made according to the method comprising the steps of: [0048] fixing on a lathe a metal piece (or work piece), for instance an ingot, from which the metal fibers will be cut; [0049] mounting a tool on a tool holder and sliding the tool holder with a feed rate along the axis of the lathe; [0050] imposing a vibration upon the tool thereby cutting metal fibers from the metal piece; [0051] measuring the rotational speed of the lathe and using the measurement signal in order to dynamically synchronize (preferably steer and synchronize) the vibration frequency of the tool with the rotational speed of the lathe by means of an electronic control circuit.

[0052] The vibration of the tool can be obtained by means of a piezomotor, the frequency of which is controlled. This method results in metal fibers with a cross-section having two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides. This follows from the way the tool cuts fibers out of the work piece. A previous cut formed two straight lines, during cutting the fiber, the first will be deformed in an irregularly shaped curve the second stays straight and forms an included angle of less than 90 with a newly formed straight edge. The latter is formed by the cutting action on the cutting plane of the knife. The one or more irregularly shaped curved sides are formed by upsetting/bulging of a side not in contact with the cutting tool during the cutting process, by the compressive forces in the material being cut.

[0053] This way, metal fibers can be made that have a low standard deviation between fibers of the equivalent fiber diameter.

[0054] Fibers of discrete length are produced by exiting the cutting tool each vibration cycle out of the tool. This way of working has the benefit that fibers with low variation in length can be produced.

[0055] Preferably, a ball bearing, and more preferably a pre-tensioned ball bearing, is used to slide the tool holder along the axis of the lathe. This feature further ensures low variation between fibers of the equivalent diameter of the fibers.

[0056] Alternatively, the sliding of the tool holder along the axis of the lathe can be realized by means of a direct drive by means of a linear motor, meaning that no reduction of motor speed nor clutch is required.

[0057] Preferably, the tool holder set up and/or tool mounting is such that displacement of the tool due to bending of the tool holder during fiber cutting is less than 5 m, preferably less than 2 m. This feature improves the uniformity of the equivalent diameter of the fibers that are produced.

[0058] Preferably, the tool holder and/or the tool is supported in order to minimize or prevent bending of the tool holder due to the cutting forces.

[0059] Preferably, the tool holder and/or the tool is supported by a mechanical support, more preferably the mechanical support is connected to the block onto which the tool holder is mounted. The tool and/or the tool holder can e.g. vibrate in a bush. With this embodiment, it is possible to obtain metal fibers with even lower variation between fibers of the equivalent fiber diameter.

[0060] FIG. 8 shows a cross section of an exemplary set up for the fiber cutting for fiber machining to manufacture metal fibers of an average length of at least 6 mm and that have a cross-section that has two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides. A block 810 is provided.

[0061] Block 810 will slide with a constant speed along the axis of the lathe (not shown in the figure). The sliding movement can be provided via a pre-tensioned ball bearing.

[0062] A housing 815 is fixed to the block 810. The housing 815 comprises a piezomotor 820.

[0063] The vibration frequency of a few thousand Hertz is synchronized via electronic means (using an appropriate controller) with the revolving speed of the lathe, via measurement of the revolving speed of the lathe. A tool holder 830 is connected via a connection 840 to the piezomotor, hence the tool holder 830 will vibrate in the bush 845 thanks to the action of the piezomotor. A chisel (cutting tool) 850 is fixed by means of a clamp 860 and a bolt 870 onto tool holder 830. A supporting piece 880 which is fixed to the block 810 is supporting the tip of the chisel 850 as it is supporting the tool holder 830 under the position of the tip of the chisel 850.

[0064] The dimensions of the cross section of the metal fibers can be determined via image analysis.

[0065] As an example of the invention, a porous panel has been made of size 1.5 m by 1 m. In making the porous panel, a first layer of 3000 g/m.sup.2 of stainless steel fibers of average equivalent diameter of 35 m with a cross-section having two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides, with an average length of 8 mm and with a standard deviation between fibers of the equivalent fiber diameter of 18.1% of the equivalent fiber diameter is provided. This first layer of metal fibers can e.g. be built up by superimposing 5 webs of 600 g/m.sup.2 each. The webs have been made by means of a dry-laid nonwoven production process wherein panels of 1.2 m by 1.5 m have been made. It is also possible to manufacture rolls of web.

[0066] The panels are put on top of each other to build the first layer of stainless steel fibers. As an alternative to dry-laid nonwovens, wet laid webs can be used, or any other technology to make a stainless steel fiber nonwoven web.

[0067] In the first layer, instead of fibers of 35 m equivalent diameter, fibers of other equivalent fiber diameters can be used, e.g. 50 m, 22 m, 12 m or 8 m; e.g. in AISI 316 steel grade.

[0068] A second layer of stainless steel fibers is provided. The second layer comprises two sub-layers.

[0069] The sub-layer that will be closest to the first layer of stainless steel fibers comprises 450 g/m.sup.2 of stainless steel fibers of 22 m equivalent diameter and the sub-layer that will be positioned further away from the first layer of stainless steel fibers comprises 900 g/m.sup.2 stainless steel fiber of 12 m equivalent diameter. Both sub-layers comprise bundle drawn stainless steel fibers and thus fibers of hexagonal cross section.

[0070] Alternatively however, it is also possible to use stainless steel fibers that have a cross-section that has two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides, e.g. fibers of an average length of at least 6 mm. Each of the sub-layers is made by means of carding, wherein panels of 1.2 m by 1.5 m have been made. It is also possible to manufacture rolls of web. The panels for the sub-layers have been superimposed in the correct order on the first layer.

[0071] A woven stainless steel wire mesh, a K-mesh, has been provided and put on top of the second layer. This way, a porous panel is built up.

[0072] After putting all the layers on tops of each other, the porous panel was bonded by means of sintering in a sinter oven in order to obtain a panel of size 1.5 m by 1 m according to the invention. Alternatively the panel can be bonded by means of capacitive discharge welding, welding the stainless steel fibers to each other and to the woven wire mesh at cross over contacting points.

[0073] The obtained porous paneland also the filters punched out of ithad a thickness of 1.75 mm, a weight of 5650 g/m.sup.2, a porosity of 59.8%, an air permeability of 42.4 litre/(dm2*min) as measured at a differential pressure of 200 Pa and according to ISO4022; and a bubble point pressure of 2240 Pa, as measured according to ASTM E128-61. Tests have shown that the filters provided excellent shearing results.

[0074] As an alternative for making the porous panel via superimposing and sintering panels of a certain size, e.g. 1.5 m by 1 m; it is also possible to unwind web layers from rolls, and superimpose them, together with the appropriate mesh layer, if required, in order to make a porous panel that can be sintered.

[0075] If such porous panel is made in continuous length, continuous sintering or welding (e.g. capacity discharge welding) is possible in order to bond the superimposed layer. After bonding, the porous panel can be cut to a size to enable its transport, e.g. to a panel size of e.g. 1.5 m by 1 m.

[0076] An alternative exemplary porous panel according to the invention comprises a first layer of 675 g/m.sup.2 of stainless steel fibers of average equivalent diameter of 8 m with a cross-section having two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides and a length of 10 mm. The porous panel comprises a second layer of stainless steel fibers, comprising a sub-layer of 300 g/m.sup.2 of stainless steel fibers with hexagonal cross section (made via bundled drawing) of average equivalent diameter 8 m; a sub-layer of 150 g/m.sup.2 of stainless steel fibers with hexagonal cross section (made via bundled drawing) of average equivalent diameter 6.5 m; and a sub-layer of 300 g/m.sup.2 of stainless steel fibers with hexagonal cross section (made via bundled drawing) of average equivalent diameter 4 m.

[0077] The porous panel can comprise a stainless steel wire mesh. The first layer of stainless steel fibers, the second layer of stainless steel fibers and the meshif presentare bonded by means of sintering. The porous panel can also comprise a stainless steel wire mesh at its both sides; e.g. bonded in the porous panel by means of sintering or welding.

[0078] Such porous panels are especially suited for production of filters for gel shearing and filtration of molten polymers using leaf disks in polymer film extrusion.

[0079] A yet alternative porous panel according to the invention comprises a first layer of stainless steel fibers of 1200 g/m.sup.2, comprising a first sub-layer of 900 g/m.sup.2 of stainless steel fibers of average equivalent diameter of 22 m with a cross-section having two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides and a length of 10 mm; and a second sub-layer of 300 g/m2 of stainless steel fibers of average equivalent diameter of 12 m with a cross-section having two neighboring straight sides with an included angle of less than 90 and one or more irregularly shaped curved sides and a length of 10 mm. The porous panel comprises a second layer of stainless steel fibers, comprising a sub-layer of 300 g/m.sup.2 of stainless steel fibers with hexagonal cross section (made via bundled drawing) of average equivalent diameter 8 m.

[0080] The porous panel can comprise a stainless steel wire mesh at one of its sides. The stainless steel wire mesh can e.g. be bonded by means of metal bonds (e.g. sinter bonds) to the second layer of stainless steel fibers, at the side of the second layer of stainless steel fibers opposite to the side of the first layer of stainless steel fibers. The porous panel can comprise a stainless steel wire mesh at both sides of the porous panel.

[0081] The first layer of stainless steel fibers, the second layer of stainless steel fibers and the mesh or meshesif presentare bonded by means of sintering. Such a porous panel is especially suited for production of a filter for gel shearing and filtration of molten polymers using leaf disks in polymer film extrusion.

[0082] Out of the porous panels of the invention, filters of various shapes can be cut or punched.

[0083] FIG. 9 shows a filter 90 punched out of the porous panel of the invention and has a circular surface shape with diameter D1, e.g. 80 mm. FIG. 10 shows a filter 100 punched out of the porous panel of the invention and that has a half moon shape, e.g. with dimensions H 80 mm and B 40 mm. Other shapes for the filter are possible, e.g. the shapes that are known and in use for polymer filtration. The filters made this way has shown to provide excellent shearing properties and excellent filtrations performanceremoval of dirt particlesin filtering molten polymer.