GB2266850A

GB2266850A - Making a filter sleeve

Info

Publication number: GB2266850A
Application number: GB9310072A
Authority: GB
Inventors: Roy Bennett
Original assignee: Scapa Group Ltd
Current assignee: Scapa Group Ltd
Priority date: 1992-05-16
Filing date: 1993-05-17
Publication date: 1993-11-17
Also published as: GB9310072D0

Abstract

A filter sleeve is made by winding a strip of filter fabric helically and overlapping and securing the edges of adjacent together turns by welding or adhesive. A helical reinforcing wire of metal or plastics is incorporated between the overlapping sections as they are secured together. The sleeve may comprise a single strip of filter fabric or two strips wound side by side (Figs. 1, 6).

Description

METHOD OF MAKING A FILTER SLEEVE The present invention relates to a method of making filter sleeves.

One known filter sleeve comprises a tube of filter fabric. A plurality of support rings are situated along the length of the tube. The rings prevent the tube from collapsing under the slight pressure differentials which exists when the filter sleeve is in use. These sleeves are made by securing together the longitudinal sides of a rectangular piece of filter fabric so as to provide the tubular construction. The ring supports are subsequently affixed on the outside of the tube.

The present invention seeks to provide an improved method of making filter sleeves.

According to a first aspect of the present invention there is provided a method of making a filter sleeve comprising the steps of winding at least one length of filter fabric into a helix and securing the adjacent edges of adjacent windings of the helix together, wherein a reinforcing structure is provided in the sleeve as said edges are secured together.

This single operation manufacturing process allows the filter sleeve to be produced in a very cost efficient manner.

According to a second aspect of the present invention there is provided a filter sleeve comprising at least one helix of filter fabric, the adjacent edges of adjacent windings of the helix being secured together, wherein a reinforcing structure is provided inbetween said edges.

The reinforcement is preferably helical and may comprise a length of wire. The wire may be made from any material which may be formed into a helical shape such as plastics or metal, provided that the wire suits the conditions in which the tube is to operate.

In a preferred embodiment of the invention the interior overlapping edges and any interior flaps resulting from the overlapping edges extend in the same direction. Likewise the exterior overlapping edges and any exterior flaps resulting from the overlapping edges preferably extend in the same direction. This may be achieved by using a single length of filter cloth.

The adjacent edges may be secured together by fusion bonding and/or by using adhesive or by sewing.

In order that the present invention may be more readily understood specific embodiments thereof will now be described by way of example only with reference to the accompanying drawings in which: Fig. 1 is a side elevation of one filter sleeve in accordance with the present invention; Figs. 2 and 3 show the filter sleeve of Fig. 1 being manufactured; Fig. 4 shows a longitudinal cross sectional view of the filter sleeve of Fig. 1; Fig. 5 is a magnified view of part of Fig. 4; and Fig. 6 shows an alternative embodiment of the invention.

Referring to Figs. 1 to 5 a filter sleeve 10 comprises a single length of filter fabric 11 arranged in a helical fashion. The adjacent edges of adjacent windings are secured together by fusion bonding. This is achieved by feeding the length of fabric into the joining zone of a fusion bonding machine as shown in Figs. 2 and 3. This machine produces a stream of hot air which serves to temporarily soften or melt the surface of the filter fabric to facilitate fusion bonding. This bonding process is particularly applicable to bonding thermoplastic fibres such as polyester fibres. "Non thermoplastic"filter materials such as Nomex and acrylics may be bonded by hot air welding. Alternatively these materials may be bonded using an adhesive applied either in liquid state or as a hot melt which would run into both fabric surfaces creating a strong bond.Suitable adhesives include thermoset polyurethanes which may be in any form such as powders, granules, aqueous dispersion and aqueous pastes. A latent adhesive (supplied by Latent Bondings Ltd) may be used particularly in relation to non-thermoplastic filter materials. This is a relatively low-melt polyurethane film which melts or becomessticky at around 50-60 C and in this state bonds well both to itself and to most textile materials. By raising the temperature to in excess of 1100C the polyurethane cross links, transforming itself into a thermoset structure which is capable of withstanding operating temperatures up to about 2000 C.

It is noted that the cross linking can also be effected by dielectric or ultrasonic heating rather than impingement of direct heat.

During manufacture a plastics or metal reinforcing wire 12 is received inbetween the edges of adjacent windings as those edges are being bonded together. The reinforcing wire 12 therefore adopts a helical structure which extends along the length of the filter sleeve 10.

It is noted that the filter sleeve 10 comprises a plurality of overlapping regions 13 where the edges of adjacent windings are bonded together. Here the overlapping regions 13 comprise flaps 14 on the outside of the sleeve 15 and flaps on the inside of the sleeve. By using a single length of fabric all of the flaps 15 on the interior of the sleeve extend in the same direction and all of the flaps on the exterior of the sleeve extend in the opposite direction.

If air being filtered flows in the sleeve extend in the direction "A" as illustrated the air flow will move the flaps 15 inwardly and any dust 16 in the air will tend to accumulate in the groove 17 defined by the flap 15. This accumulation will not take place if the direction of air flow is in the opposite direction, "B", as illustrated as air flow in that direction tends to urge the flaps outwardly eliminating the groove. Thus if all of the flaps exposed to the air flow extend in the same direction as shown and if the sleeve is arranged in relation to the direction of air flow such that the flaps are not disposed to inward movement (i.e air flow in direction "B") then this problem may be overcome.

It is noted that the dust can be collected on either the inside or outside of the fabric's surface.

This will depend upon the type of filter sleeve involved. It is important to know whether collection is to be on the outside or inside of the sleeve during assembly since extra care should be taken in eliminating the overlapping flap to prevent excessive cake build up at that location.

Ideally the full breadth of the overlapping edges should be glued to the adjacent winding in order to eliminate the flaps. If the full width of the overlapping edge has been adhered to the adjacent winding then the problem of dust accumulation will be reduced, but dust may still accumulate at the shoulder formed at the joint. Thus it is still desirable to use a single length of cloth to eliminate dust accumulation. The height of the flap should be reduced in order to still further reduce dust accumulation. This may be achieved by compressing the overlapping edges with a presser roll since the fabric is thermoplastic and deformable. Manufacture of the sleeve preferably comprises the steps of using a cardboard tube making or like machine using fusion bonding to melt the mating surfaces of the adjacent windings of the filter fabric.

Referring to Fig. 6 a further filter sleeve 20 comprises two lengths of filter fabric each of which is wound into a helix 21,22. The windings of the first helix 21 are provided between the windings of the second helix 22. The left hand edge, as illustrated, of the first helix 21 is fusion bonded to the right hand edge of the second helix 22. A synthetic reinforcing wire 23 is wound in a helical manner between these two edges and held in position by the bonded edges. The opposite edges of the helices are secured together by means of two rows of monofilament stitching.

During manufacture the two lengths of fabric 21,22 are first secured together with stitching. A length of plastics wire is fed between the edges of adjacent windings as they are fusion bonded together during which time the fabrics are rotated to form the helix structure described above. The reinforcement wire is captured between the bonded edges of the fabrics.

It is noted that this embodiment provides both inner and outer flaps in opposing directions. For the reason specified above the embodiment as described with reference to Figs 1 to 5 is therefore preferred.

It is to be understood that the above described embodiment have been described by way of example only.

Many modifications and variations are possible.

Claims

1. A method of making a filter sleeve comprising the steps of winding at least one length of filter fabric into a helix and overlapping and securing the adjacent edges of adjacent windings of the helix together, wherein a reinforcing structure is provided in the sleeve as said edges are being secured together.

2. A method of making a filter sleeve as claimed in claim 1, wherein the reinforcing structure is captured between the overlapped edges of the adjacent windings.

3. A method of making a filter sleeve as claimed in claim 1 or claim 2, wherein the reinforcing structure is helical.

4. A method of making a filter sleeve as claimed in claim 1, claim 2 or claim 3, wherein the reinforcing structure comprises a length of wire.

5. A method of making a filter sleeve as claimed in any of claims 1 to 4, wherein the overlapping edges of fabric provided on the interior of the filter sleeve extend in the same direction.

6. A method of making a filter sleeve as claimed in any of claims 1 to 5, wherein the overlapping edges of fabric provided on the exterior of the filter sleeve extend in the same direction.

7. A filter sleeve comprising at least one helix of filter fabric, the adjacent edges of adjacent windings of the helix being overlapped and secured together, wherein a reinforcing structure is captured inbetween said overlapped edges.

8. A filter sleeve as claimed in claim 7, wherein the reinforcing structure is helical.

9. A filter sleeve as claimed in claim 7 or claim 8, wherein the reinforcing structure comprises a length of wire.

10. A filter sleeve as claimed in any of claims 7 to 9, wherein the overlapping edges of fabric provided on the interior of the filter sleeve extend in the same direction.

11. A filter sleeve as claimed in any of claims 6 to 18, wherein the overlapping edges of fabric provided on the exterior of the filter sleeve extend in the same direction.

12. A filter sleeve substantially as described herein with reference to the accompanying Figs. 1 to 5 or 6.