GB2202461A

GB2202461A - Edge filters

Info

Publication number: GB2202461A
Application number: GB08807330A
Authority: GB
Inventors: Michael Victor Wafforne
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-03-26
Filing date: 1988-03-28
Publication date: 1988-09-28
Anticipated expiration: 2008-03-28
Also published as: GB8707290D0; GB2202461B; GB8807330D0

Abstract

In an edge filter comprising a stack of discs clamped together, the discs are each moulded from rubber or plastics such as polythene or polystyrene and have staggered recesses 14, 16 in opposite faces which provide extended inlet/outlet spaces where solids may collect. The discs may have other discs made of absorbent material clamped between them and effectively filling the recesses. After use the plastics discs may be cleaned and the absorbent discs discarded. The filter is used for dielectric fluid in spark/wire erosion apparatus. <IMAGE>

Description

Title: "Filter" Description of Invention This invention relates to filters, such as are used in the filtration of fluids, and is primarily concerned with filter assemblies of the kind (hereinafter referred to as being of the kind specfied) which comprise a plurality of generally planar filter elements arranged in succession in faceto-face relationship, and with filter elements for such assemblies.

In such an assembly, the filter elements lie closely adjacent to each other and the fluid undergoing filtration flows in gaps which nonetheless exist between the surfaces of successive elements either in a generally radially inward direction e.g., towards a generally central axial region which may communicate with an outlet, or in a generally radially outward direction e.g.

from an inlet in the vicinity of said axial region to an outlet adjacent to outer edges of the filter elements.

Such filters are used in the field of "spark erosion" or "wire erosion" processes in which a substantial electric current is passed between an electrode and a work-piece immersed in a dielectric fluid to enable the electrode to "burn" an indentation or orifice corresponding to the shape of the electrode in the work-piece. The filters are used for filtering the dielectric in order to remove by-products of such processes to enable the dielectric to be continuously recirculated and hence reused. The invention is not however limited to this field of use.

Conventionally, such filter assemblies have comprised filter elements in the form of simple cardboard or paper disks including suitable apertures and/or perforations, the disks being arranged in succession along an axis in alternate different orientations so that said apertures lie adjacent to unapertured parts of adjacent disks, so forming cavities in which sediments will be collected.

Typically spark or wire erosion apparatus comprises two such filter assemblies, each utilising about 300 such card or paper elements, and it has been found that in many applications such filters rapidly become clogged and are only useful for about 40 hours or so.

The paper or card elements, by virtue of their number and intrinsically low strength may not readily be cleaned, and so it is conventional practice to throw them away, when they have become clogged, and install new filter assemblies comprising new such elements. This is very wasteful, and in the long run very expensive.

It is an object of the invention to provide a new and improved filter element and a new and improved filter assembly.

According to a first aspect of the invention, there is provided a filter element suitable for use in a filter assembly of the kind specified wherein the filter element is formed by moulding thereof from rubber and/or rubberlike and/or plastics material.

In this manner, the durability of the filter elements may be increased compared with conventional filter elements, and, importantly, cleaning of the filter elements becomes relatively easy.

Thus by utilising filter elements in accordance with the invention, it is possible to re-use the filter elements a great many times, and so although filter elements in accordance with the invention may be more expensive than.

(say) conventional paper filter elements, they will be more economical in the long run. It is envisaged that this cost advantage of the invention will be particularly important to relatively small business concerns, where it is generally more economical to devote time to attempting to clean existing equipment rather than merely replacing it.

The filter elements may be made from rubber, which is particularly suitable where the dielectric is water, or from a "hard" plastic such as polystyrene if there will be no reaction thereof with the fluid undergoing filtration, or from a "soft" plastic such as "polythene" (polyethylene).

In a particular application of the filters for filtering the dielectric fluid in spark/wire erosion apparatus, polythene is much preferred, since it is not caused to perish by paraffin/oil dielectrics such as are commonly used in such apparatus.

Preferably the filter element comprises depressions in at least one side thereof for trapping sediment.

Preferably such depressions are formed in both sides of the filter element, and the depressions in one side of the element may be located intermediate the depressions in the other side of the element, the depressions then conventiently being about one half of the element thickness in depth.

The surface of the element may be provided with a roughened texture to facilitate adherence of sediment thereto, and to ensure that flow routes are available for the fluid undergoing filtration even when the elements are maintained either tightly against each other or tightly in close proximity to each other where absorbent sub-elements (see below) are employed between the filter elements.

The invention also provides disposable absorbent sub-elements, for example of a suitably absorbent paper or other porous material, which if desired may be located at least in said depressions prior to or during assembly or reassembly of the filter assembly.

Such sub-elements may have a natural, uncompressed thickness at least as great as the depth of the depressions, and may conveniently be of such size and shape as to span more than one depression.

Preferably each such sub-element is in the form of an annul us of the absorbent material, preferably of a size such that all of the depressions defined between two successive filter elements may be occupied simultaneously by a single such sub-element.

Said depressions may correspond in size and general shape to the through-apertures which have hitherto been provided in paper filter elements, but advantageously they are of a superior shape e.g. generally radial elongate indentations which facilitate trapping of sediment.

According to another aspect of the invention, there is provided a filter assembly comprising a plurality of generally planar filter elements disposed in face-to-face succession between two end plates provided at respective opposite ends of the assembly, and clamping means acting between at least one of the end plates and a connecting means extending between the end plates, to urge the end plates towards each other and hence compress the filter elements against each other.

The terms "face-to-face" and "against each other" as used herein are to be interpreted broadly as including both the possibility that the filter elements are in direct succession, and the possibility that successive filter elements have disposed between them absorbent sub-elments such as have been described in relation to the first aspect of the invention.

The connecting means may for example comprise a perforated tube, preferably extending through the filter elements, having threaded ends which receive clamping means in the form of respective nuts, or the connecting means may comprise a plurality of rods which extend through the end plates and filter elements, with nuts at opposite ends thereof, to compress the filter elements between the end plates. The connecting means may be provided as an alternative or addition to any existing means for maintaining the filter elements in alignment.

Preferably the clamping means is arranged to act on inner regions of the filter elements e.g. in the vicinity of central apertures therein, which arrangement is particularly suited to fluid flow in a radially inward direction, or alternatively the outside edges of the filter elements could be clamped, which would be particularly suitable for flow in the opposite direction.

Preferably the clamping means is adjustable to permit the clamping pressure to be adjusted, and hence permit control of the rate of flow for a given fluid pressure difference across the filter.

Several embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which, Figure I is a plan view of a first filter element in accordance with the invention; Figure 2 is a plan view of a second filter element in accordance with the invention; Figure 3 is a cross sectional elevational view of a filter assembly embodying the invention; and Figure 4 is a plan view of a third filter element in accordance with the invention, to a larger scale than Figures I and 2.

Referring first to Figure I of the drawings, a first filter element 10 in accordance with the invention is in the form of a generally planar plasticsmoulded disk 12.

Depressions 14 are moulded in one face of the disk 12, and correspondingly shaped depressions 16 #are moulded (shown in broken lines) in the opposite face of the disk 12, but at locations intermediate those of the depressions 14 on the first face of the disk. The depth of the depressions is approximately half the thickness of the element 10. The element 10 comprises a central aperture 18 and further apertures 20 and cut outs 22 which facilitate alignment and mounting of the element 10 in a filter assembly and facilitate fluid flow.

In use, a plurality of such filter elements 10 are placed face-to-face in direct succession (or with sub-elements, such as are herein described, disposed therebetween), successive filter elements 10 being similarly orientated and with corresponding faces facing the same way, along a direction herein referred to as the axial direction. The thus closely adjacent filter elements are held against (or in close proximity to) each other under mechanical pressure but have roughened surfaces so that there nonetheless exist fluid flow gaps and passages between adjacent filter elements.

The depressions 14 and 16 in this embodiment are not through apertures, unlike similarly shaped formations in conventional paper-type filter elements, and so in order to ensure that the required sediment collection cavities are obtained, it is merely necessary to arrange successive filter elements 10 at a similar orientation, rather than having to arrange successive filter elements at alternate different orientations. The depressions have particularly rough surfaces, to assist trapping of sediment.

In use, the completed filter assembly is located within a chamber, around a perforated outlet tube which extends through the central apertures 18, so that fluid admitted to the chamber must flow through gaps between the filter elements in order to reach the outlet.

Any sediments in the fluid, during such flow, will generally be deposited and trapped in the cavities afforded by the depressions, and will thus be removed from the fluid undergoing filtration.

Such fluid may for example be dielectric fluid e.g. paraffin, oil or water such as may be used in a spark or wire erosion process which requires recirculation and re-use of the fluid. Such processes are described in the introduction to this specification, to which reference is expressly directed.

In such fields of use, the aforesaid "sediments" are the "by-products" of such processes which must be removed from the fluid.

Eventually, the filter assembly will become clogged with such sediments, and it is then re-assembled and the relatively durable filter elements 10 are then rinsed and/or brushed in order to be cleaned, the elements then being re-assembled to provide what to all intents and purposes is a fresh filter. In the long term, this re-use can represent a considerable cost saving over conventional filter assemblies comprising a plurality of cardboard or paper disk elements which are very difficult to clean (to the extent that they are often simply thrown away wastefully) and are prone to damage.

In the example illustrated, the filter element is made from a relatively "soft" and flexible plastics material, namely polythene (polyethylene) material, but may alternatively be made from a relatively "hard" plastics material such as polystyrene (where this does not react with fluids undergoing filtration) or from rubber or some rubber-like material (especially suitable where the fluid concerned is water or the like.) An alternative such filter element 110 is shown in Figure 2, being otherwise numbered so as to correspond to the filter element 10 of Figure I.

In this alternative element 110, the depressions of the filter of Figure I are replaced by a greater number of depressions, occupying similar regions, but being of different shapes particularly suitable to collection of sediment.

These superior depressions are in the form of generally radial elongate indentations.

If desired, any such filter elements may be fractionally (eg. about 5%) thicker in the vicinity of their central apertures than in the vicinity of their outer peripheries, to facilitate fluid flow into a filter assembly formed from such filters, where such flow is radially inward, or may be thicker by such a fraction in the vicinity of their outer peripheries where flow is radially outward. Any change of thickness may be progressive or stepped.

Disposable absorbent sub-elements (in contrast to the generally nonabsorbent material for filter elements in accordance with the invention) are preferably included in the depressions prior to or during assembly or reassembly of the filter assembly.

Such sub-elements may be of a suitably absorbent paper or any other suitably porous material, for example a synthetic foam or sponge material, or a fibre or textile material, and may have a natural uncompressed thickness at least as great as the depth of the depressions. Such sub-elements serve the purpose of collecting and trapping sediment during use.

Conveniently each sub-element is of such a size and shape as to span more than one depression in use (which depressions may be depressions on the same filter element, or depressions on successive filter elements.) In a particular preferred embodiment, each absorbent sub-element is in the form of an annul us of the absorbent material having a central hole of a size slightly greater than that of the central apertures of the filter elements, and an outer diameter slightly less than that of the filter elements. Such an annul us may be of uniform thickness and density throughout prior to use, and so is easy to manufacture.

In use, when such an annular sub-element is placed between two successive filter elements during the assembly or re-assembly of a filter assembly, and the aforesaid mechanical pressure is applied to press the filter elements towards each other, those portions of the subelement which overlie depressions on one or other of the filter elements are caused to occupy those depressions and remain relatively uncompressed or are compressed only to a thickness slightly greater than the depth of the depressions, whilst those portions of the sub-element which do not overlie any such depression are compressed to a very much greater extent, lying between surface portions of the respective filter elements which would touch each other in the absence of the sub-element.

In this manner all of the depressions concerned may be occupied simultaneously by a single such sub-element disposed between the filter elements. Where the filter assembly is held together by the aforesaid plurality of rods, both the filter elements and said annular sub-elements are provided with corresponding through-holes through which the rods may pass.

Typically each filter element has a total thickness of approximately 2 mm to 5 mm or so, preferably about 4 mm, an outer diameter of approximately 150 mm to 160 mm or so, and a central aperture of approximately 30 mm to 40 mm width, whilst each annular sub-element would typically be of approximately 10 mm natural uncompressed thickness (compressing to a fraction of a millimetre in use where it does not overlie a depression) and would have an outer diameter of approximately 145 mm to 155 mm and a central hole of diameter approximately 30 mm to 40 mm.

Where the aforesaid plurality of rods is employed, two such rods each of diameter about 6 mm may for example be employed, at respective diametrically opposite positions about 40 mm from the central axis of the assembly.

Referring now to Figure 3 of the drawings, a filter assembly 200 comprises a plurality of generally planar filter elements 210 (for example filter elements each the same as that of Figure I and/or Figure 2 and/or Figure 4 (see later) clamped together between two end plates 220 in face-toface succession. The filter elements are shown in cross-section in Figure 3, from which their small thickness compared with their diameter will be apparent. For the sake of clarity, details of cross-sectional shape due to depressions in the filter elements are omitted from this drawing. The filter assembly 200 compares about one hundred such elements. For convenience of illustration, the repetitive details of the middle portion of the assembly are omitted from Figure 3, and the region indicated by broken lines may in fact be of indefinite length, to suit a given application.

The clamping of the filter elements is achieved by mounting the filter elements 210 on a perforated tube 222 additional to a perforated outlet tube 224 which is conventionally provided within a filter chamber. The tube 222 receives clamping means i.e. large nuts 226,226 at each threaded end of the tube 222, which nuts 226 may be tightened to urge the end plates 220 towards each other and hence compress the filter elements against each other, thereby changing the size of any gaps between adjacent faces of the filter elements, and thereby changing the resistance offered to fluid flow by the filter assembly 220.

Alternatively, instead of using such an additional tube 222, a plurality (e.g. two or three) of rods (not shown) provided with nuts (not shown) at opposite ends may be used to clamp the end plates 220, and hence the interposed filter elements 210, together. The rods may pass through the end plates and the filter elements.

It will be appreciated that such clamping means may be adjusted accurately e.g. by being tightened to a specified torque, to enable a particular filtering characteristic to be achieved.

In this example, clamping due to the tube 222 and the nuts 226 occurs in the vicinity of the central apertures of the filter elements, which is particularly suited to fluid flow in an inwardly radial direction. Flow routes into and out of the assembly are indicated schematically by arrows F in Figure 3. It is to be appreciated that clamping of the outer peripheral regions of the elements may be appropiate should radially outward fluid flow be desired.

An alternative, preferred, filter assembly in accordance with the invention is identical or similar to the assembly 200, except that the abovedescribed annular absorbent subelements are employed between successive filter elements, and between the end-most filter elements and the end plates.

Such sub-elements are renewed whenever the assembly is re-assembled after cleaning of the filter elements.

Instead of the relatively heavy duty end plates 220 illustrated, alternative end plates may be employed. Each such alternative end plate may have a flat annular surface portion which, in use, lies against an endmost filter element, and ribs on the reverse side thereof to reinforce said surface portion against distortion. Such ribs may include central and outer circumferential reinforcing ribs, and radial reinforcing ribs. Portions of increased thickness may be provided where any clamping means engages the end plate.

A third filter element 310 in accordance with the invention is shown in Figure 4, and is otherwise labelled so as to correspond to the elements already described in detail.

The filter element 310 may be of the same or similar materials to the elements 10,110, 210, but each side thereof is provided with seven depressions as shown,the depressions 14 on one side being disposed intermediate the depressions 16 on the other side. Although not indicated in Figure 4, these depressions have roughened surfaces. These depressions occupy virtually the full area of the element, so maximising sedimenttrapping ability of the element. There are no through apertures corresponding to the through apertures 20 hereinbefore described, and the central aperture 18 is in the shape of a square with truncated corners increase strength. Cut outs 22 are of a modified form, and the depressions 16 approach these cut-outs very closely, which facilitates entry of fluid.

Disposable sub-elements of the kind hereinbefore described may be used in relation to the depressions 14 and 16.

It is to be appreciated that filter elements in accordance with the invention may be used in filter assemblies other than that of Figure 3, and that the filter assembly of Figure 3 need not necessarily use filter elements such as those of Figures 1, 2 and 4.

It is to be understood that filter elements and filter assemblies substantially as hereinbefore described but intended for uses other than filtration of dielectric in spark/wire erosion processes, will remain within the scope of the invention.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS:

I. A filter element suitable for use in a filter assembly of the kind specified wherein the filter element is formed by moulding thereof from rubber and/or rubber-like and/or plastics material.
2. A filter element according to Claim I made from a "hard" plastic material.
3. A filter element according to Claim 2 wherein said plastic is polystyrene.
4. A filter element according to Claim I made from a "soft" plastic.
5. A filter element according to Claim 4 wherein said plastic is "polythene" (Polyethylene).
6. A filter element according to any one of the preceding claims comprising depressions in at least one side thereof for trapping sediment.
7. A filter element according to Claim 6 wherein such depressions are formed in both sides of the filter element.
8. A filter element according to Claim 7 wherein the depressions in one side of the element are located intermediate the depressions in the other side of the element.
9. A filter element according to Claim 8 wherein the depressions are about one half of the element thickness in depth.
10. A filter element according to any one of the preceding claims wherein the surface of the element is provided with a roughened texture.
II. A filter element according to any one of the preceding claims wherein said depressions correspond in size and general shape to the throughapertures which have hitherto been provided in paper filter elements.
12. A filter element according to any one of Claims I to I I wherein said depressions are in the form of generally radial elongate indentations.
13. For or in combination with one or more filter elements in accordance with any one of Claims I to 12, a disposable absorbent sub-element which may be located at least in one or more of said depressions prior to or during assembly or re-assembly of a filter assembly formed from the filter elements.
14. A sub-element according to Claim 13 having a natural, uncompressed thickness at least as great as the depth of the depressions.
15. A sub-element according to Claim 13 or Claim 14 which is of such size and shape as to span more than one depression.
16. A sub-element according to Claim 15 which is in the form of an annul us of the absorbent material.
17. A subelement according to Claim 16 wherein the sub-element is of a size such that all of the depressions defined between two successive filter elements may be occupied simultaneously by a single such sub-element.
18. A filter assembly comprising a plurality of generally planar filter elements disposed in face-to-face succession between two end plates provided at respective opposite ends of the assembly, and clamping means acting between at least one of the end plates and a connecting means extending between the end plates, to urge the end plates towards each other and hence compress the filter elements against each other.
19. A filter assembly according to Claim 18, further comprising absorbent sub-elements in accordance with any one of Claims 13 to 17 between successive filter elements.
20. A filter assembly according to Claim 18 or Claim 19 wherein the connecting means comprises a perforated tube having threaded ends which receive clamping means in the form of respective nuts.
21. A filter assembly according to Claim 20 wherein the perforated tube extends through the filter elements.
22. A filter assembly according to any one of Claims 18 to 21 wherein the connecting means comprises a plurality of rods which extend through the end plates and filter elements, with nuts at opposite ends thereof, to compress the filter elements between the end plates.
23. A filter assembly according to any one of Claims 18 to 22 wherein the connecting means is provided as an alternative or addition to any means for maintaining the filter elements in alignment.
24. A filter assembly according to any one of Claims 18 to 23 wherein the clamping means means is arranged to act on inner regions of the filter elements e.g. in the vicinity of central apertures therein.
25. A filter assembly according to any one Claims 18 to 23 wherein the clamping means clamps the outside edges of the filter elements.
26. A filter assembly according to any one of Claims 18 to 25 wherein the clamping means is adjustable to permit the clamping pressure to be adjusted.
27. A filter assembly according to any one of Claims 18 to 26 wherein the filter elements are in accordance with any one of Claims I to 12.
28. filter element according to any one of Claims I to 12, or a disposable absorbent sub-element according to any one of Claims 13 to 17, or a filter assembly according to any one of Claims 18 to 27, for use in filtering dielectric fluid in spark/wire erosion apparatus.
29. A filter element, disposable absorbent sub-element, or filter assembly substantially as hereinbefore described with reference to and/or as illustrated in the accompanying drawings.
30. Any novel feature or novel combination of features disclosed herein and/or illustrated in the accompanying drawings.