WO1989009644A1

WO1989009644A1 - Filter disc

Info

Publication number: WO1989009644A1
Application number: PCT/GB1989/000351
Authority: WO
Inventors: David Amey; Peter Pickard; John Sexton
Original assignee: Fairey Microfiltrex Limited
Priority date: 1988-04-07
Filing date: 1989-04-05
Publication date: 1989-10-19
Also published as: GB8808100D0; AU3366589A

Abstract

A filter capsule, for example for filtering molten polymers, comprises upper and lower generally flat annular filter media members (40, 40'), welded together at their common outer circumferences (42). Loosely held between the filter media members is an intermediate grooved support plate (48). In use, the polymer to be filtered passes through the media members (40, 40'), into the grooves (50, 50'), and into a mounting tube (not shown) around which the capsule is located. When the media members (40, 40') become clogged with polymer, they are machined off by cutting around the circumference (42). The support plate (48) is then cleaned and re-used with new filter media members.

Description

Filter disc .

The present invention relates to filter capsules, and in particular capsules suitable for filtering solution polymers or molten polymers.

Three known types of filter capsule are shown in cross-section in Figures 1 to 3 which, respectively, show a welded (or hard) hub capsule, a floating hub capsule, and a hubless (or soft hub) capsule. The vertical dimension in each of the drawings is exaggerated, for clarity.

Each of the three types of known capsule comprises a pair of upper and lower generally flat annular filter media members 10, 10' welded together around their common circumference 12. Between the filter media members there are upper and lower apertured annular support plates 14, 1 ', and between these plates is an annular support mesh 16. The apertured support plates 14, 14' are also welded together at the circumference 12.

In use, the polymer to be filtered passes from outside the capsule, through the upper and lower filter media members 10, 10' , through the upper and lower apertured support plates 14, 14' and into the support mesh 16. From there, it passes radially inwardly to be discharged around the inner circumference of the capsule, and into a cylindrical apertured mounting tube (not shown) around which the capsule is located. In practice, a plurality of capsules will surround a single tube, with adjacent capsules having some means of sealing against each other, at their inner circumferences, so that polymer outside the assembly can reach the interior of the mounting tube only by passing through, and being filtered by, one of the filter capsules.

The various known ways of sealing the inner circumferences of the filter capsules will now be described. Figure 1 shows an arrangement known as a welded or hard hub design. With such an arrangement, a solid cylindrical hub 18, having a plurality of radially-extending bores 20 is provided, to which the filter media members and the support plates are welded at 22. Sealing between adjacent capsules is effected by means of intermediate crush-metal washers 24. Alternatively, metal 0-»ring seals 25 may be used, as are illustrated at the lower left hand side of Figure 1.

An alternative design, shown in Figure 2, is known as a floating hub design. Here, the filter media members and the support plates are not welded together around their inner circumference 28, and the hub 26 is left free. Sealing between adjacent capsules is achieved by the use of intermediate crush-metal washers 30 which are of such a size as to trap the inner circumferential edges of the filter media members and support plates between themselves and an outwardly- extending shoulder of the hub 26. When sufficient pressure is applied, the relatively soft material of the washer 30 (usually aluminium) will be forced into the interstices of the filter media members and the support plates, so sealing the exterior of the capsule from the interior.

A third possible variation, shown in Figure 3, is known as the hubless or soft hub capsule. In this version, the hub is omitted entirely, and instead the inner circumference of the filter media members and support plates are provided with respective annular swaged lands 32. Sealing is effected simply by virtue of the abutment between the upper land of one capsule, and the lower land 34 of an adjacent capsule, usually via an interposed metal gasket (not shown). With the hubless design, high differential pressures cannot be achieved since the fact that the support mesh 16 is not entirely rigid, and can only take a limited axial load, limits the amount of compression that can be applied to a stack of capsules. In addition, because of the non- rigidity of the lands 32 it is not possible to use metal O-ring seals. •

Depending upon the polymer that is being filtered, capsules of the type shown in Figures 1 to 3 can sometimes be re-used, after appropriate cleaning to remove polymer and contaminant that has become clogged in the filter media members. However, cleaning tends to be a difficult, lengthy and expensive process, largely due to the complexity of the fluid flow path within the support mesh 16, and the fact that the interstices within this mesh are not easily accessible.

Even if the polymer being filtered is one which is susceptible to cleaning, there comes a time when the filter media members become so clogged that further cleaning becomes impossible or uneconomic to carry out. With certain polymers, this may happen even after the first use of the capsule. It is then necessary to throw the entire capsule away, and replace it. This means that one has to dispose of not only the clogged filter media members, but also the substantially more expensive support plates and support mesh and hub. Because the support mesh 16 provides a tortuous flow path for the polymer being filtered, the polymer is always subjected to large shear forces. Although this is desirable for many polymers, there are certain polymers for which lower shear forces would be preferable something which cannot be achieved with present filter capsule designs.

It is an object of the present invention at least to alleviate some of the disadvantages of the prior art.

According to a first aspect of the invention there is provided a filter capsule comprising upper and lower annular filter media members secured together along their outer peripheries-, and an annular support member received between the filter media members but not fixedly secured thereto.

According to a second aspect of the invention there is provided a filter capsule comprising upper and lower annular filter media members, and an annular support member therebetween, the filter media members being secured together in a peripheral region which is spaced from the outer periphery of the support member.

With such a filter capsule, the upper and lower annular filter media members can be removed, when they become clogged, and the annular support member cleaned, retained, and used in the construction of a new filter capsule (along with replacement upper and lower filter media members). Thus, the expensive support member is not thrown away when the filter media becomes clogged.

Preferably, each of the filter media members has, around its inner peripheral edge, a hub. The support member (which is desirably rigid) may extend between the upper and lower hubs. This provides a rigid annular region of the filter capsule which, in combination with an adjacent capsule, can be used to achieve effective sealing between the exterior of the capsule and the interior of a mounting tube around which the capsule is received, in the manner of the known solid hub capsules of Figures 1 and 2. If the support member is itself rigid, then high axial forces can be applied to the stack of capsules without the necessity of having a single central hub (as shown in Figures 1 and 2) which extends the entire depth of the capsule. In addition, conventional metal O-ring seals (of the type shown in Figure 1 ) can be used.

Conveniently, the support member may be a generally flat slotted plate, having grooves which open along its inner peripheral edge. The grooves could be radial, or zig-zag, or otherwise convoluted. Alternative arrangements could include grooves that merge in a tree-like configuration, or grooves that spiral inwardly. It would also be possible for the grooves to be defined between a plurality of individual upstanding lands on the plate, so that, when seen from above, the plate appears stippled. All of these possibilities are easily effected if the plate is cast, for example from a suitable metal alloy, and it is therefore an easy matter to choose a configuration which provides a suitable level of shear for the particular polymer which is to be filtered.

According to a third aspect of the invention there is provided a filter capsule comprising upper and lower annular filter media members secured together around their outer peripheries, and a one-piece annular support member between the filter media members, the support member have channel means for channelling a liquid being filtered to the inner periphery of the support member.

The invention also extends to a method of re¬ conditioning a filter capsule, as previously defined, comprising removing the filter media members from the support member, cleaning the support member, and using the support member together with new filter media members in the construction of a new filter capsule.

The invention may be carried into practice in a number of ways and one specific filter capsule and its method of use will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a cross-section through a known welded hub capsule; «

Figure 2 is a cross-section through a known floating hub capsule;

Figure 3 is a cross-section through a known hubless capsule;

Figure 4 is a plan of a filter capsule embodying the present invention, with part of the filter media member being shown cut away; and

Figure 5 is a cross-section through the capsule of Figure 4.

A capsule embodying the present invention is shown in Figures 4 and 5. It comprises upper and lower generally flat annular filter media members 40, 40', the outer circumferences of which are slightly dished and are welded together at 42. Typically, the filter media members may comprise sintered metal powder or sintered metal fibres, held within a fine mesh for the capsule. A typical diameter is about 8 cm.

Welded to the inner circumference 44, 44' of each of the members 40, 40' there is an annular slave hub 46, 46*, desirably made of stainless steel.

Located between the filter media members 40, 40', and having an inner circumference approximately that of the slave hubs 46, 46', there is an integral central support plate 48. The plate is secured neither to the filter media members nor to the slave hubs, and accordingly is retained loosely within the interior of the capsule.

The upper and lower surfaces of the plate are provided with radially-extending grooves or channels 50, 50', which open into the inner circumferential edge of the plate. The grooves desirably become a little deeper near the inner circumferential edge, as is shown in the right-hand part , of Figure 5, where the cross- section is taken through corresponding upper and lower channels.

The plate 48 is desirably cast, and the channels may either be radial, as shown, or in any other configuration suitable for the polymer which is to be filtered. The channels could, for example, comprise a tree-like structure with the branches merging as they approach the inner edge of the plate. Alternatively, zig-zag or other convoluted channels could be provided if it is desired to subject the polymer to be filtered to a substantial amount of shear. It would even be possible, if the circumstances warranted it, to replace the support plate 48 with a support mesh 16 of the known type shown in Figures 1 to 3; such a mesh may consist of several separate parts.

The filter capsule shown in Figures 4 and 5 is used for filtering in an identical way to those shown in Figures 1 to 3. The filter passes from the outside of the capsule, through the upper and lower filter media members 40, 40', into the channels 50, 50', from the inner ends of which it enters the central mounting tube (not shown). When the filter media members 40, 40' become clogged with polymer, however, instead of

the entire capsule being thrown away, it is returned for cleaning and re-use.

The steps involved in cleaning and re-using the capsule are as follows. First, the capsule is preliminarily cleaned with solvent, to remove the worst of the residue from the exterior surfaces. Then, the filter media members 40, 40' are machined off by cutting around the outer circumferential edge of the capsule, just inside the welding 42. This causes the capsule to split into three parts, the upper media member 40 and slave hub 46, the lower media member 40' and slave hub 46', and the support plate 48. The first two of these are disposed of, but the support plate is retained and thoroughly cleaned. Since the grooves 50 in the plate are now exposed, cleaning (for example by means of a suitable solvent) is a relatively quick and easy process.

Replacement filter media members and slave hubs are now provided, and these are circumferentially welded together outside the outer periphery of the support plate, to produce effectively a new capsule.

Thus, the inner support plate 48 (by far the most expensive part of the capsule) is retained and re-used.

Claims

1. A filter capsule for polymer filtration comprising upper and lower annular metallic filter media members secured together along their outer peripheries, and a rigid annular support member received between the filter media members but not fixedly secured thereto, the support member extending between respective rigid hubs at the inner peripheries of the filter media members.

2. A filter capsule for polymer filtration comprising upper and l 1ower annular metallic filter media members each having a rigid hub around the inner periphery thereof, and an annular rigid support member received between the filter media members and the respective hubs, the filter media members being secured together in a peripheral region which is spaced from the outer periphery of the support member.

3. A filter capsule as claimed in any one of the preceding claims in which the support member is a generally flat slotted plate.

4. A filter capsule as claimed in Claim 3 in which the plate is cast.

5. A filter capsule as claimed in Claim 3 or Claim 4 in which the plate is slotted on both its upper and lower surfaces.

6. A filter capsule as claimed in any one of the preceding claims in which the upper and lower filter media members are dished adjacent their respective outer peripheries.

7. A method of re-conditioning a filter capsule as claimed in any one of Claims 1 to 6 comprising removing the filter media members from the support member, cleaning the support member, and using the support member, together with new filter media members, in the construction of a new filter capsule.

8. A method as claimed in Claim 7 in which the filter media members are removed by cutting through them along a line which is outwardly spaced from the outer periphery of the support member.

9. A filter capsule for polymer filtration comprising upper and lower annular metallic filter media members secured together around their outer peripheries, and a one-piece annular support member between the filter media members, the support member having channel means for channelling a liquid being filtered to the inner periphery of the support member.

10. A filter capsule as claimed in Claim 9 in which the support member is a generally flat slotted plate.

11. A filter capsule as claimed in Claim 10 in which the plate is cast.

12. A filter capsule as claimed in Claim 10 or

Claim 11 in which the plate is slotted on both its upper and lower surfaces.