GB2333468A - Filter cartridge containing pleated filter element with projecting ribs - Google Patents

Abstract

A filter cartridge comprises an annular pleated filter element 3 the walls of the pleats of which are indented to provide projections, or elongate ribs 5, in the outwardly opening pockets 4 and corresponding recesses in the inwardly opening pockets 6. The ends of the pleats at at least one end of the element are sealed by moulding into an annular end plate of elastomeric material 8, with an annular projection 9 which is arranged to seal against a collection pipe 10A, 10B of the filter. Projections on adjacent faces of adjacent pleats engage one another in order to increase the spacing apart of the other pleats (fig 2). This allows the pleats to have greater radial extent, causing dirt to be deposited evenly on the surfaces of the outwardly projecting pleats. The elastomeric material of the end plates may have a Shore hardness of less than 60, and the filter cartridge may be used to clean the working liquid recirculated form an electric discharge cutting machine.

Description

FILTER CARTRIDGB This invention relates to filters for cleaning fluids, particularly working liquid, such as deionised water, recirculated from an electric discharge metal cutting machine (EDM machine).

A conventional filter for this purpose, hereinafter referred to as a filter of the kind described, comprises an outer cylindrical housing which contains a filter cartridge, incorporating an annular pleated paper filter element and positioned around a perforate collection tube.

The space between the housing and the radially outer side of the filter cartridge forms an inlet plenum which is fed with the dirty fluid. The fluid passes radially inwardly through the element and is discharged through the collection tube which forms an outlet plenum. The paper may be impregnated with, or at least partially formed of a synthetic material, such as a phenolic resin.

The pressure difference across the element can be as high as 3 bar, particularly when the cartridge has been in use for some time and is becoming clogged with dirt.

Consequently it has been usual for the axial zig zag ends of the pleats to be sealed to an annular end plate at at least one end of the element, to avoid fluid bypass around the ends of the pleats. This is usually achieved by embedding the ends of the pleats in a layer of resin adhesive attached to one face of the end plate, or moulding the ends of the pleats into the end plate itself if the end plate is made of plastics material.

Also, in order to avoid fluid bypass around the end plate from the inlet plenum to the outlet plenum, or between adjacent end plates if two or more cartridges are threaded onto a common collection tube within a common housing, it is important that the inner peripheral rim of the annular end plate provides a fluid tight seal against an unperforated portion of the collection tube. This seal has previously been provided in a number of ways. In a first way, when the annular end plate is made of metal, the seal has been provided by an annular, externally grooved, rubber grommet which fits into the end plate with the inner peripheral rim of the end plate engaging in the external groove in the grommet. However, this requires an additional part to provide the seal and an additional assembly step, and the seal between the grommet and end plate is not always secure.

When the end plate has been moulded from a rigid plastics material, an alternative way in which the seal with the collection tube has been provided is by moulding into the end plate an 0 sealing ring of elastomeric material. However the moulding operation is unreliable as it is difficult to support the soft, readily distortable, small 0-ring in the mould during the creation of the end plate.

With pleated filter elements, there has been an accepted minimum internal diameter for the element based on the understanding that if the diameter is too small, the radially inner folds of the pleats will be so tightly bunched together as to provide an unacceptably high pressure difference across the element and, eventually, so called 'blinding' when the flow is impeded completely. It is because of the accepted minimum internal diameter of the element that the end plate, when moulded of a plastics material, has been made of a rigid material since the element provides no support for the annular portion of the end plate extending radially between the collection tube and the inner periphery of the element, and this portion has to resist buckling under the pressure difference.

Contrary to what is understood by some, the life of a pleated filter element, before it needs to be changed, or cleaned by back washing, does not depend entirely on the aggregate area of the pleated material. It depends upon the spacing of the walls of adjacent pleats and the manner in which dirt can be deposited evenly so as to contribute to the filtering effect. In the light of this we have developed an annular pleated filter element in which the pleats have been permanently indented to provide projections on the pleat faces opening radially outwardly and corresponding depressions on the pleat faces opening radially inwardly. The projections on the adjacent faces of adjacent pleats are preferably opposed to one another so that they engage one another to increase the spacing apart of the rest of those pleat faces opening radially outwardly. No corresponding spacing apart occurs in the radially inwardly opening pockets of the element.

Surprisingly this enables the pleats to have a greater radial extent because there are fewer pleats per unit angular extent around the element, the dirt being comparatively evenly deposited in the outwardly openly pockets so as to contribute to the filtering effect and compensate for the fewer pleats per angular extent.

Taking all these factors into account, we have now appreciated that there may be provided an efficient and long life filter cartridge for a filter of the kind described, if the cartridge comprises an annular pleated filter element the walls of the pleats of which are indented to provide projections in the outwardly opening pockets and corresponding recesses in the inwardly opening pockets, the ends of the pleats at at least one end of the element being moulded into an annular end plate of elastomeric material providing integrally at its inner periphery with an annular projection which is arranged to seal, in use, against the collection pipe of the filter.

The use of the filter element with the indented pleat walls enables the inner diameter of the element to be reduced so that the element will support the end plate radially inwardly to closely around the projection tube, thereby enabling the end plate to be made of a more flexible material than previously, and hence with the integral sealing ring. At a stroke both the efficiency and life of the filter element are increased and the provision of the sealing ring on the end plate does not require an additional part or manufacturing step.

The elastomeric material from which the end plate is now moulded may typically have a shove hardness of less than 100, preferably less than 60.

An example of a filter cartridge constructed in accordance with the present invention is illustrated in the accompanying drawings, in which: Figure 1 is an elevation, partly broken away in section, of one end of the cartridge; and Figure 2 is a perspective view of a portion of the filter element with the pleats shown open.

The cartridge has an annular pleated paper filter element 3, the walls of the pleats of which are embossed to provide, on the wall faces defining the radially outwardly opening pockets 4, a series of elongate ribs 5, the height of which increases in the radially outward direction.

Corresponding recesses are formed on the wall faces defining the radially inwardly opening pockets 6.

Consequently, when the element is folded into the annular configuration, with the pleat walls forming, as seen in the axial direction, a zig zag arrangement, the radially outwardly opening pockets are held slightly open by the abutting ribs of adjacent pleats to a radially outwardly increasing extent. In use this allows dirt to be deposited evenly on the wall surfaces of the radially outwardly opening pockets whereby the dirt contributes to the filtering effect.

In the annular configuration of the filter element 3, the inner cylindrical surface of the element is stabilised by an expanded metal support tube 7. At the upper end of the cartridge, as seen in figure 1, the zig zag ends of the pleats of the element 3, together with the upper end of the supporting tube 7, are moulded into an elastomeric annular end plate 8. The internal periphery of this end plate is provided integrally with a radially inwardly projecting annular projection 9. It will be seen that the internal diameter of the element 3 is only slightly larger than the diameter of a collection tube lOA,lOB so that only a small annular area of the plate 8 remains unsupported from below.

In use the cartridge will be threaded onto the collection tube, which has a perforate portion 10A within the element 3 and an imperforate portion lOB within the end plate 8. Upon assembly, the tube is slid through the central opening in the end plate 8, slightly deforming the projection 9, which takes the place of the conventional 0-ring, until the fully assembled position has been reached. The projection 9 then forms an adequate fluid tight seal against the imperforate portion lOB of the tube.

In use the cartridge, assembled around the collection tube, will be inserted in a cylindrical housing and the fluid to be filtered will flow radially inwardly through the element 3, through the holes in the support tube 7, through the perforations in the collection tube portion lOA, and hence axially out through the collection tube.

Claims (3)

1. CLAIMS 1. A long life filter cartridge for a filter, the cartridge comprising an annular pleated filter element the walls of the pleats of which are indented to provide projections in the outwardly opening pockets and corresponding recesses in the inwardly opening pockets, the ends of the pleats at at least one end of the element being moulded into an annular end plate of elastomeric material providing integrally at its inner periphery with an annular projection which is arranged to seal, in use, against the collection pipe of the filter.
2. 2. A cartridge according to claim 1, wherein the elastomeric material from which the end plate is moulded has a Shore hardness of less than 100.
3. 3. A cartridge according to claim 1, wherein the elastomeric material from which the end plate is moulded has a Shore hardness of less than 60.