GB2288751A

GB2288751A - Filter element

Info

Publication number: GB2288751A
Application number: GB9407736A
Authority: GB
Inventors: Philip Arthur Mullins
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-04-19
Filing date: 1994-04-19
Publication date: 1995-11-01
Also published as: GB9407736D0

Abstract

The invention provides a filter element for use in an air extraction assembly, the filter element comprising a pleated filter membrane 401, wherein the spaces between the pleats 402 on the downstream side of the membrane 401 are filled with a porous solid packing 403, the packing 403 being sufficiently dense to prevent collapsing of the pleats 402 as air is drawn therethrough, but sufficiently porous to permit air to flow freely therethrough. The invention is particularly applicable to V-pleated filters. In a further aspect the invention provides a filter assembly comprising the filter elements of the invention. In addition, the invention provides an air extraction assembly comprising a filter assembly incorporating a filter element of the invention. The packing may be inert or chemically reactive to treat the air. <IMAGE>

Description

FILTER ELEMENT This invention relates to filter elements, filter assemblies containing the filter elements, and extraction systems incorporating the filter assemblies.

It is known to provide extraction systems for extracting and filtering air to remove air-entrained particulate matter and gases in a wide variety of industrial situations, for example in the electronics and pharmaceutical industries. For example, work stations on an assembly line at which fume and/or dust generating operations are carried out on e.g. electrical components such as circuit boards, will require an extraction system.

Fume and dust extraction systems for use in this sort of environment can comprise an articulating arm assembly, a number of articulating arm assemblies from different work stations being linked together by appropriate pipework to a pump/filter assembly. Examples of such fume extraction assemblies are those sold by the present applicant under the names HI-TECH and PUREX.

The filter assemblies used in extraction systems of this type typically consist of a box-pleated or V-pleated filtering membrane for removing particulate matter, and a chemical filter for removing fumes. The chemical filter can be, for example, activated charcoal or aluminium oxide impregnated with potassium permanganate.

The pleated filtering membranes, which are generally known by the term High Efficiency Particle Arrestors (HEPA) can be formed from borosilicate fibre.

A problem with the known filtering elements incorporating box-pleated or V-pleated filtering elements is the tendency for adjacent folds of the filter to collapse together thereby increasing resistance to air flow therethrough which in turn can lead to rupturing of the filter along the fold lines.

Attempts have been made to overcome this problem by reinforcing the pleated membrane with a stiffening material. Such an approach has however been found only to provide a partial solution to the problem in that collapsing of the filter still takes place in time.

Moreover, applying a stiffening layer in this way adds a further level of complexity and cost to the filters of known type.

It is an object of this invention to provide a filter which has increased resistance to collapsing, is simple and efficient to manufacture, and which has a prolonged life relative to known filter types.

Accordingly, in a first aspect, the invention provides a filter element for use in an air extraction assembly, the filter element comprising a pleated filter membrane, wherein the spaces between the pleats on the downstream side of the membrane are filled with a porous solid packing, the packing being sufficiently dense to prevent collapsing of the pleats as air is drawn therethrough, but sufficiently porous to permit air to flow freely therethrough.

The porous packing may take the form of a continuous matrix, for example a suitable porous foam matrix, but may also be defined by a particulate packing. Preferably the packing is of particulate form, and can be for example a packing formed from glass balls, glass beads or beads formed of any heat resisting particulate medium.

In one embodiment, the porous packing can take the form of a chemical filter, for example a particulate chemical filter such as aluminium oxide spheres impregnated with potassium permanganate.

The invention is applicable to both box-pleated filters and V-pleated filters, but preferably the filters of the present invention are V-pleated filters.

In a further aspect, the invention provides a filter assembly comprising a filter housing having secured therein a filter element according to the present invention. In a particular embodiment, the filter housing also contains a chemical filter on the downstream side of the filter membrane, the chemical filter being defined either by the porous packing, or by means of a separate chemical filtering element.

It is preferred that the packing on the downstream side of the filter membrane extends in a downstream direction beyond the folds in the membrane so as to support the membrane in the vicinity of the fold.

In a still further aspect, the invention provides an air extraction assembly comprising a housing within which is disposed a filter assembly as hereinbefore defined, inlet means for directing air from an extraction conduit to the filter, a pump downstream of the filter assembly for drawing air through the filter, and outlet means for exhausting filtered air.

The invention will now be illustrated, but not limited, by reference to the accompanying drawings of which: Figure 1 is an isometric elevation of a filter/pump unit; Figure 2 is an isometric view of a known type of boxpleat filter element; Figure 3 is a plan view of the filter element of Figure 2; Figure 4 is an isometric view of another known type of filter element; Figure 5 is a schematic isometric view of a filter element according to one embodiment of the invention; Figure 6 is a schematic, partly sectioned isometric view of a filter assembly incorporating the filter element of Figure 5; Figure 7 is a side sectional elevation of the filter assembly shown in Figure 6; and Figure 8 illustrates schematically a side elevation of a filter element according to a second embodiment of the invention.

Referring now to Figure 1, it can be seen that a filter/pump unit for a fume extraction system comprises a housing 101 containing an inlet 102 for receiving fume- or particle-contaminated air; a pre-filter 103, a filter assembly 104 a pumping system 105 and a purified-air outlet 106. In use, contaminated air passes through the inlet 102 from a fume extraction conduit mounted at a work station, and is directed firstly through pre-filter 103 which removes coarser particles from the air, and then through the main filter assembly 104 which removes finer particles and chemical fumes. The purified air is then vented to atmosphere through outlet 106.

Filter/pump units of this type are well known, and are commercially available, and details of their construction and operation need not be given here.

A known type of filter element used in the filter assemblies of fume extraction systems of this type is illustrated in Figures 2 and 3. Thus, in Figure 2 there is shown a filter element having a box-pleat structure in which the opposing folds 201 of the filter are spaced apart by corrugated cardboard or aluminium reinforcing elements 202.

Although the corrugated strengthening elements 202 do provide some resistance against collapsing of the pleats of the filter, over a period of time there is nevertheless a tendency for the walls of the filter to become compacted against the reinforcing elements 202. Airflow through the filter is thus substantially impeded, and the resulting pressure differential within the filter can cause rupturing of the membrane at the end folds 203.

Another known type of filter element is shown in Figure 4. This type of filter element has a V-pleated structure rather than box pleats, and the folds 301 are reinforced with a laminated plastics material to enhance their resistance to collapsing. The advantages of this type of V-pleated structure aver the box-pleated structure lie chiefly in its ability to withstand higher pressure differentials, and in the fact that it provides a greater filter surface area in a given space than the box-pleated filter elements. However, such filter elements do nevertheless have a tendency to collapse over a prolonged period and, moreover, are not ideally suited for filtering hot gases, due to the plastics reinforcing layer.

A filter element of the present invention is illustrated in Figure 5, from which it can be seen that the filter comprises a V-pleated membrane 401 through which, in use, contaminated air is directed from direction B. The membrane 401 is formed of a borosilicate fibre material.

The membrane collects 100t of particles to 0.3 micron and 95% of particles to 0.01 micron. On the downstream side of the membrane 401, in the spaces between adjacent folds 402, is disposed a porous packing 403, which can be for example a porous foam, but more preferably is a particulate packing comprising glass beads, glass balls, or a chemical filtering medium such as aluminium oxide impregnated with potassium permanganate or the like. The packing is disposed so as to extend to a position 404 downstream of the fold lines 405 in the pleated filter membrane. In this way, the packing 403 serves to support and strengthen the filter membrane at the location 405 and reduce the likelihood of the filter from splitting at this point.

The construction of a filter assembly incorporating a filter element of the general type illustrated in Figure 5 is shown in Figures 6 and 7. Thus, the filter assembly comprises a metal casing 501 within which is located the filter element 502, which has a particulate packing 503 on the downstream side of the filter membrane 504. Upstream of the filter element 502 and secured to the metal casing 501 by means of an adhesive is a perforated metal shield 505 which provides mechanical protection for the filter element 502 but allows passage of air into the filter. On the downstream side of the filter element 502 are disposed spaced apart perforated metal plates 506 and 507 which are likewise secured by means of an adhesive to the metal casing 501. Extending around the periphery of the casing, and serving to strengthen the joint between the perforated metal plates 506 and 507 and the casing 501 is a strengthening member 508 of channel section. Located between the metal plates 506 and 507 is a chemical filter medium 509, which may, for example, be an activated charcoal, or an aluminium oxide impregnated with potassium permanganate.

Disposed between the perforated metal plates 506 and 505, and lining the walls of the metal casing 501 is a heat resistant sealing moulding 510 formed of a heat resistant silicone rubber or other heat resisting polymer.

The filter element 502 is located within the heat resistant sealing moulding, the folds 511 of the element being secured to the metal shield by means of a suitable silicone based adhesive, arranged in strips or bands across the metal plate.

In a modification to the filter assembly shown in Figure 6 and 7, the separate chamber between plates 506 and 507 could be omitted, the particulate packing 503 then serving as the chemical filter.

An alternative embodiment of the invention is illustrated in Figure 8 where there is shown a filter 601 having a box-pleat structure, the spaces between opposing folds 602 being filled with a particulate packing substance 603 such as glass spheres.

The advantages of the filter assembly of the present invention are that it should have an extended life compared with filter assemblies of known type, in which there is a tendency for the folds of the filter to collapse thereby leading to reduced airflow therethrough, and rupturing of the filter membrane. Moreover, since the need to provide a plastics backing or stiffener to the back of the filter membrane is avoided, the construction of the filters is made considerably simpler and cheaper. In addition, by replacing the plastics, corrugated or paper or aluminium stiffening with a particulate packing, e.g. formed from glass beads or balls or a chemical filtering medium, the filter is far more resistant to high temperatures and pressures, and can therefore be used in conjunction with flow soldering machines, infra red ovens, and any other industrial air filtering processes where high pressures and temperatures are experienced, applications for which filters of known type incorporating plastics or paper backing material are not particularly well suited.

It will readily be apparent that numerous modifications and alterations may be made to the forms of construction shown in the accompanying drawings without departing from the principles underlying the invention.

All such modifications and alterations are intended to be embraced by this application.

Claims

1. A filter element for use in an air extraction assembly, the filter element comprising a pleated filter membrane, wherein the spaces between the pleats on the downstream side of the membrane are filled with a porous solid packing, the packing being sufficiently dense to prevent collapsing of the pleats as air is drawn therethrough, but sufficiently porous to permit air to flow freely therethrough.

2. A filter element according to Claim 1 wherein the porous packing is in the form of a continuous matrix.

3. A filter element according to Claim 2 wherein the porous packing is a porous foam matrix.

4. A filter element according to Claim 2 wherein the porous packing is a particulate packing.

5. A filter element according to Claim 4 wherein the particulate packing is constituted by glass balls, glass beads or beads formed of any heat resisting particulate medium.

6. A filter element according to Claim 1 wherein the porous packing takes the form of a chemical filter.

7. A filter element according to Claim 6 wherein the chemical filter is constituted by aluminium oxide spheres impregnated with potassium permanganate.

8. A filter element according to any one of the preceding Claims wherein the pleated filter membrane forms a V-pleated filter.

9. A filter element according to any one of the preceding Claims wherein the packing on the downstream side of the filter membrane extends in a downstream direction beyond the folds in the membrane so as to support the membrane in the vicinity of the fold.

10. A filter element substantially as described herein with reference to the accompanying drawings Figures 5 to 8.

11. A filter assembly comprising a filter housing having secured therein a filter element according to any one of the preceding Claims.

12. A filter assembly according to Claim 11 wherein the filter housing contains a chemical filter on the downstream side of the filter membrane, the chemical filter being defined by the porous packing.

13. A filter assembly according to Claim 11 wherein the filter housing has a separate chemical filtering element on the downstream side of the filter membrane.

14. An air extraction assembly comprising a housing within which is disposed a filter assembly as defined in any one of Claims 11 to 13, inlet means for directing air from an extraction conduit to the filter, a pump downstream of the filter assembly for drawing air through the filter, and outlet means for exhausting filtered air.