FIELD OF THE INVENTION

The present invention relates to a method of producing small diameter, porous metallic membrane bundles and, in particular, bundles which are suitable for welding to a face plate of a filter module. The invention further relates to a membrane bundle produced by said method for use in a filter module.

BACKGROUND OF THE INVENTION

Porous filter membranes are used in numerous industries to separate particulates from fluid and gas. The membranes can be constructed from various materials including metal, plastic and ceramics. Stainless steel membrane technology was first developed more than twenty years ago, however, has not been widely implemented compared to other cross flow membranes, and is only typically used when other membranes fail.

The main reason for the slow market up take has been cost, when compared to say polysulfone or polyvinyl which sells for around 6% / m 2 and ceramic for around 25% / m 2 of the cost of metallic membrane. This is partly due to the raw material cost, however, the most expensive component is by far the high labour content.

A typical metallic membrane is manufactured by the known art of Isostatic Pressing. The green membrane produced is subsequently sintered, welded into the required lengths, coated with the appropriate inner membrane, and then re-fired. This process requires time and manpower which contribute to the significant costs.

Lumen standard commercial metallic membranes are produced having diameters of around 17- 19mm, which contributes to their expense and foot print. Smaller diameter metallic membranes would reduce the cost and foot print, and also provide other benefits, but they have not been developed to date. This is because of the difficulty associated with terminating and jointing bundles of small diameter tubular membranes for placement inside filter modules.

A known termination method for standard metallic membranes of 12-20mm is for each membrane to be welded to the face plate of filter modules. However, the smaller in diameter the membrane becomes, the more difficult and time consuming the welding process is. For membranes of say 3mm diameter, welding is virtually impossible and considering that some filters may require thousands of such membranes, it would be far too time consuming and costly to have to weld each membrane individually to the face plate. Further issues envisaged when welding small diameter membranes include:

• the heat zone produced adjacent to the weld will cause damage to the membrane due to heat and oxidation, and it will become prone to corrosion; and

• due to the high welding temperatures used (up to 2200°C), the fine inner coat that is the active membrane is damaged, causing a change in the micron size and porosity of the membranes.

Because of these problems, such membranes cannot be classified as being "absolute" in terms of their properties, instead they can only be described as "nominal".

It is therefore an object of the present invention to overcome at least some of the aforementioned problems or provide the public with a useful alternative. SUMMARY OF THE INVENTION

Therefore in one form of the invention there is proposed a Therefore, in one form of the invention there is proposed a method of manufacturing porous metallic membranes of a diameter between 1mm and 20mm, said method including the steps of:

(a) mixing two or more metal powders of varying sizes depending on micron finish required with one or more binders;

(b) heating or cooling the mixture depending on the binder(s) selected;

(c) extruding the mixture to form a tubular membrane of a predetermined diameter between 3mm and 20mm;

(d) curing the extruded membrane using a heating or cooling source depending on the

binder(s) selected;

(e) cutting the extruded and cured membrane into required lengths; and

(f) sintering the membranes. Preferably said method includes the further steps of:

(a) applying an inner coating to the membranes; and

(b) re-sintering the membranes.

In a further form of the invention there is proposed a porous metallic membrane manufactured according to the above method.

In a still further form of the invention there is proposed a metallic membrane bundle for use in a filter module including end face plates, said metallic membrane bundle comprising:

a plurality of tubular metallic membranes having a diameter of between 1mm and 20mm; and end components which terminate said plurality of tubular metallic membranes such that each membrane extends in a spaced apart, substantially parallel arrangement, said end components having a lower melting point than said membranes and being adapted for welding to said filter module end face plates.

In a still further form of the invention there is proposed a metallic membrane bundle for use in a filter module, said bundle including a first end component adapted for welding to a face plate of said filter module, and a second end component adapted for joining said bundle with the first end component of a second bundle such that said joined bundles extend along a common longitudinal axis end to end.

In a yet further form of the invention there is proposed a method of manufacturing end components adapted for terminating a plurality of metallic membranes in a spaced apart and parallel arrangement for welding to a filter module metallic surface, said method including pressing or compacting two or more fine metal powders to form a solid end component and cutting/boring the end component into a shape suitable to terminate ends of the plurality of metallic membranes.

In a still further form of the invention there is proposed an end component used to terminate a metallic membrane manufactured in accordance with the above method.

In a yet further form of the invention there is proposed a filter membrane bundle for use in a filter module, said bundle comprising:

a first end member adapted for receiving at one end a first end of a plurality of spaced apart, parallel filter membranes and adapted to engage at the opposed end a filter module face plate such that liquid adapted to pass through said filter travels through the end member into the plurality of membranes; and

a second end member adapted for receiving at one end a second end of the plurality of filter membranes and adapted to receive in the opposed end the first end member of a second bundle such that said liquid is adapted to travel through the second end member and into the first end member of the second bundle.

Preferably said bundle includes spacer members spaced along the plurality of membranes for maintaining the membranes in a spaced apart, parallel arrangement.

In a yet further form of the invention there is proposed a method of manufacturing a filter membrane bundle including the steps of:

(a) forming a plurality of metallic membranes of a diameter of between 1mm and 20mm;

(b) forming two end sleeve members by pressing or compacting one or more fine metal powders to form a cylindrical structure;

(c) boring out holes into one end of each end sleeve to receive ends of the membranes;

(d) boring out a single hole into the opposed end of each end sleeve to a diameter sufficient to appropriately receive one end of either a stub or joiner end component;

(e) softening each of the end sleeves and stub and/or joiner component ends;

(f) inserting the smaller diameter components into the larger diameter components using a screwing motion;

(g) drying the components;

(h) sintering the components.

Preferably step (e) involves placing approximately 10mm of the part to be joined into a solution of water for a period of 2-3 minutes.

In preference step (f) involves inserting the stub end into a first sleeve.

In preference step (f) involves inserting one end of each membrane into the first sleeve bores. Preferably step (f) involves inserting the opposite ends of each membrane into a second sleeve.

Preferably step (f) involves inserting the joiner and/or stub end into the second sleeve.

In preference step (g) involves placing the components on drying racks where they are constantly rotated until completely dry. In a still further form of the invention there is proposed a filter membrane bundle manufactured according to the above method.

In a yet further form of the invention there is proposed a filter module including a filter membrane bundle, small diameter filter membranes, or filter membrane end components as defined above. BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawings, which are incorporated in and constitute a part of this

specification, illustrate several implementations of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings:

Figure 1 illustrates an exploded perspective view of a metallic membrane bundle produced by the

method of the present invention; and

Figure 2 illustrates a longitudinal cross sectional view of the metallic membrane bundle of

Figure 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description of the invention refers to the accompanying drawings.

Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. Wherever possible, the same reference numbers will be used throughout the embodiments and the following description to refer to the same and like parts. The present invention provides a means of utilizing small diameter (3- 12mm) metallic membranes, having known benefits in terms of filtration, which hitherto have not been useable in filter modules because of difficulties associated with fitting such membranes into modules. As mentioned in the preamble of the invention, larger diameter membranes are typically welded to filter module face plates but this is not practical or perhaps even possible for small diameter membranes. The present invention provides a method of terminating and jointing small diameter membranes, to thereby produce a bundle of such membranes suitable for welding in a manner which will not damage the membranes, and render the membrane "absolute" rather than

"nominal".

Figure 1 illustrates a metallic membrane bundle 10 including seven tubular, small diameter metallic membranes 12. In the embodiment shown, there is a central membrane with six further membranes radially disposed by equal angles about the central membrane. It is to be understood that there could be more or less membranes 12 per bundle, and they could be arranged in an alternative manner.

The plurality of membranes 12 are terminated at ends thereof using an end sleeve 14 and joiner end 16 at one end, and an end sleeve 18 and stub end 20 at the opposed end. Whilst these components appear to be individual in the exploded view, it will become apparent that after the sintering process described, the end sleeve 14 and joiner end 16 become an integral component, as do the end sleeve 18 and stub end 20. It is to be understood that these end components are shaped like so to suit a particular filter module face plate, but may well be shaped differently as required. The main function of the end components is to provide a larger diameter at the ends to enable welding of the membranes, whilst still utilizing the smaller diameter membranes. The end components 14, 16, 18 and 20 of the bundle 10 are constructed from a material suitable for welding to a filter module face plate (not shown). Notwithstanding the fact that small diameter membranes cannot be welded without compromising the membranes, the skilled addressee would realize that use of such bundles 10 will reduce the number of welds into the tube face. Once the bundles 10 are constructed they can be welded in the same manner that individual larger diameter membranes (not shown) are welded.

The end components are manufactured from a material having a lower melting point than the membrane material to ensure they are weldable without causing damage to the membranes. In a preferred embodiment, the end components are manufactured from fine powders that enable them to solid sinter, for example, either nickel or stainless steel or a mixture of both. There are many other materials with a lower melting point than the main membrane that may be used to cause a solid state effect, however, due to their high costs may not be suitable. Figure 2 illustrates the internal shape of the various end components. Each of the end sleeves 14 and 18 are of a cylindrical construction having a large hole 22 bored out from one end to approximately halfway along the sleeve, and a plurality of holes 24 bored out from the other end such that they extend all the way through to hole 22. The joiner end 16 includes an outer diameter along a portion 26 extending approximately 80% of its length which corresponds with the inner diameter of hole 22 of sleeve 14 such that the portion 26 is to be received inside hole 22 of sleeve 14. Similarly, the stub end 20 includes an outer diameter along a portion 28 extending less than 50% of its length which corresponds with the inner diameter of hole 22 of sleeve 18 such that the portion 28 is to be received inside hole 22 of sleeve 18. In a preferred embodiment, each of these diameters is equal at both ends.

The joiner end 16 further includes a portion 30 of greater internal and external diameter to that of portion 26, and which provides a means of abutment for sleeve 14. The stub end further includes a portion 32 of less internal and external diameter to that of portion 28, portion 32 having an outer diameter which corresponds with the inner diameter of portion 26 of the joiner end 16 such that the stub end 14 of one bundle 10 can be coupled to the joiner end 16 of another bundle to increase the total length of the membrane. Thus, as well as providing a means of terminating bundles of membranes, the end components provide a means of jointing membrane bundles end to end.

Where there are multiple bundles 10 joined end to end, as described above, obviously the final bundle will have two stub ends 20, one for jointing to the second to last bundle, and the other for terminating with the opposed end face plate.

The skilled addressee would realize that in terminating bundles of membrane in this way, the stub end 20 and hence the plurality of small diameter membranes become weldable to a filter module face plate as per known methods. Each stub end 20 is of a similar diameter to the larger 12-20mm diameter membranes of the prior art.

Positioned along the length of the bundle 10 are one or more spacers 34 which are circular discs preferably constructed of the same material as the end components and which include a plurality of holes adapted to accommodate each membrane 12 there through. In the embodiment shown, there are two spacers 34 spaced equally along the length of the membranes. Turning now to the method of manufacturing the bundle 10 of the present invention, each of the small diameter metallic membranes are preferably constructed as follows:

(a) Metal powders of various sieve sizes (depending on micron finish required) are mixed with various binders and are either heated or cooled depending on the binder selected;

(b) The mix is then extruded using specially designed die heads (single or multi head dies) of various diameters from 3mm to 20mm or greater;

(c) As the membrane is extruded from the die head the material is cured using a heating or cooling source, again depending on the binder selected (typically either hot air, induction heating or a cooling media);

(d) The membranes are cut to length and by the known art of sintering are sintered;

(e) An inner coating is applied to the membranes either in a high vacuum furnace or a low hydrogen continuous furnace; and

(f) The membranes are re- sintered.

The preferred method of manufacture of each of the stub end and joiner end components is by pressing the fine metal powders mentioned earlier, and then boring holes into and milling the components into their required shape. The method of pressing provides several advantages, including speed of production, the high level of compaction which results in a dense (solid) final product, and the resulting high green strength enabling ease of handling.

The preferred method of manufacture of each of the end sleeves is as follows: (a) forming a member, in the embodiment shown into a cylindrical shape, by pressing of fine metal powders as per the stub and joiner end construction;

(b) boring out holes into one end of each end sleeve so as to receive the small diameter

membranes;

(c) boring out a single hole into the opposed end of each end sleeve to a diameter sufficient to appropriately engage either the stub end or the joiner end as described below. The preferred method of assembling each bundle, after each of the end components is manufactured, is as follows:

(a) one end of each piece to be joined is first softened by placing approximately 10mm of the part into a solution of water for a period of 2-3 minutes;

(b) inserting the smaller dimensioned components into the larger dimensioned components using a screwing motion, that is, the stub end into the first sleeve, one end of each membrane into the first sleeve; the opposite ends of each membrane into the second sleeve, the joiner end into the second sleeve, and the stub end of a second bundle into the joiner end of the first bundle (if applicable);

(c) drying the components by placing them on drying racks where they are constantly rotated until completely dry; and

(d) sintering the components by the known art of sintering.

It is to be understood that the abovementioned steps are described by way of preferred example. The drying step (c) for example need not necessarily be achieved as described above but by some other suitable drying method.

The present invention thus enables the use of small diameter membranes of 3mm or greater diameter in filter modules, which in the past could not be used. There are a number of benefits in using such metallic membranes, including:

• increased surface area in the same size module (up to 10 times the surface area);

• increased shear providing better self cleaning of the membrane;

• smaller circulation pumps required to move liquid through the filter and hence less power consumption;

• smaller hold-up volume, reducing waste;

• reduced manufacturing costs;

• reduced land fill due to long life expectancy of membrane, which is in excess of 10 years. Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus.

In any claims that follow and in the summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.