Improvements relating to filters

Abstract: Bundles (2) of continuous fibres impregnated with resin are wound in controlled helical patterns over a sheet (1) of filter medium laid down over a rotating mandrel. The tension in the fibres is controlled in such a way that the resin is forced through the filter medium to impregnate it at the point of contact. When the resin sets the fibres (2) become bonded to parts of the filter sheet (1) whilst leaving portions of the filter material in the openings between the fibres. Strengthening ribs at the ends could be formed by building up the thickness of the fibres in a ring shape.

Description: Problems arise in providing adequate support for filter structures, particularly where the filters have a large surface area and/or have to operate at high pressures so that conventional support members become complex, heavy and expensive to fabricate. US-A-3815341 discloses a supported filter comprising a fibrous knitted fabric of meshed structure serving as a support base for fixing a filtering material which is synthetic flock fibres. A coat of an adhesive, such as a synthetic resin, is impregnated or otherwise applied onto the meshed support base and then the filter material is applied against said base. The supported filter is then dried and cured in order to bond the support base to the filter material. DE-A-240643 discloses a reinforced filter comprising a layer of filter material integrated with an open-grid reinforcing frame which is glued, or otherwise adhered, on to filtering material. The reinforcing frame may be made of a textile or any suitable system of fibres. Neither of these arrangements is capable of creating a rigid support structure for filter structures which may be of various shapes. According to one aspect of the present invention there is provided a method of forming a supported filter, wherein a layer of filter material is laid over a table or around a mandrel and individual bundles of resin impregnated fibres are laid over the filter member and overlaid over one another to create an open grid stucture under controlled tension so that some of the resin is impregnated into the filter material, whereby the fibres create a support structure for the filter material, after curing. According to a further aspect of the invention there is provided a method of forming a supported filter, wherein individual bundles of resin impregnated fibres are laid over a table or around a mandrel and overlaid over one another to create an open grid structure under controlled tension and a layer of filter material is laid over the fibres under tension so that some of the resin is impregnated into the filter material, whereby the fibres create a support structure for the filter material, after curing. The integration of the filter material with the support structure by bonding these two parts together results in a very secure support of the filter material whilst the support structure itself can be relatively light in weight. The support structure could be in the form of a cage, perforated tube or frame for supporting a filter of cylindrical or flat form or a filter having a non-symmetrical shape or topography. In most constructions it is envisaged that the openings in the support structure will generally be in the form of diamonds or rectangles. The foraminous material for the filter medium may be of any convenient form and may for example be constructed as woven or non-woven cloth, mesh or tissue or any filter-type fabric. One possibility is a plastic, ceramic or other similar material which is applied directly to the mandrel by, for example spraying, which is finely porous by nature or becomes porous during its application. Such a sheet with minute holes is particularly advantageous for fine filtration operation. For added strength or for particular purposes the support structure and filter material could be built up in multiple layers. Thus, for example, a layer of filter material can be carried between two support structure layers. Alternatively, layers of filter material can be supported on either side of a single support structure. Many more layers may be built up if desired. For increased strength, layers of fibre bundles can be built up one on top of the other. In order to combat the possibility that several such layers of fibre bundles might tend to flatten out the arrangement could be such that one fibre bundle is pre-wound around another fibre bundle. If desired, external pressure could be applied to force the resin into the filter material. The invention may be performed in various ways and a preferred embodiment will now be described, by way of example, with reference to the accompanying drawings, in which:- Figures 1 and 2 are perspective views of two alternative views of a supported filter structure in accordance with this invention. In the arrangement shown in Figure 1 a sheet of filter medium 1 is laid down, wound round or sprayed onto a rotating mandrel so as to create a complete sleeve. Bundles or tows 2 of continuous fibres (for example, glassfibre, carbon aramide, thermoplastic or other fibres) are impregnated with a suitable resin and are wound or laid in controlled helical patterns at a predetermined pitch and under controlled tension. This creates openings of a generally diamond shape between the impregnated fibres. The tension of the resin impregnated fibres is controlled in such a way that the resin is forced through the filter medium onto the supporting mandrel so as to impregnate those parts of the filter medium. As the resin sets, the fibres 2 become bonded to parts of the filter sheet 1 whilst leaving portions of filter material within the diamond openings. As an alternative, the fibres can be wound first onto the mandrel and then the layer of filter material can be laid over the top under tension so that the resin will soak up from underneath. In the arrangement shown in Figure 2 the fibres are laid down firstly in longitudinal rows around the mandrel and secondly as circumferential rings, so as to create rectangular spaces. It is also possible to build up several layers of filter fabric each sandwiched between impregnated fibres to form multi layer filters. In order to provide sufficient strength for the larger filters of say 6m diameter, multiple 'tows' of fibres can be introduced and a progressive build-up of the cage structure can be achieved by local reinforcement at strategic points. When these multiple 'tows' become large in cross section they tend to flatten out due to the controlled tension. This can be prevented by using a secondary winding operation which lays or winds another 'tow' of fibres circumferentially around the primary tow in advance of it being laid onto the mandrel. This effectively prevents the primary tow from spreading out due to the tension applied onto the surface of the mandrel. Local reinforcement may be particularly necessary at the ends and in the drawings this is illustrated at 3 where progressive build-up of fibres has been created.

Claims: A method of forming a supported filter, wherein a layer of filter material is laid over a table or around a mandrel and individual bundles of resin impregnated fibres are laid over the filter member and overlaid over one another to create an open grid structure under controlled tension so that some of the resin is impregnated into the filter material, whereby the fibres create a support structure for the filter material, after curing. A method of forming a supported filter, wherein individual bundles of resin impregnated fibres are laid over a table or around a mandrel and overlaid over one another to create an open grid structure under controlled tension and a layer of filter material is laid over the fibres under tension so that some of the resin is impregnated into the filter material, whereby the fibres create a support structure for the filter material, after curing. A method as claimed in Claim 1 or Claim 2, wherein external pressure is applied to force the resin into the filter material. A method as claimed in any one of Claims 1 to 3 wherein extra layers of filter material and/or support structure are built up onto the base construction of a layer of filter material and a support structure.

Inventors: WILLIAMS ANTHONY CAREY, WILLIAMS, ANTHONY CAREY
Applicants: CAMPLAS TECHNOLOGY, CAMPLAS TECHNOLOGY LIMITED
Application year: 1993
Main classification: B01D39
IPC codes: B01D29, B01D39