GB2239663A

GB2239663A - Improvements in or relating to textile filter sleeves

Info

Publication number: GB2239663A
Application number: GB9026884A
Authority: GB
Inventors: Subhash Chander Anand; Philip John Lawton
Original assignee: Scapa Group Ltd
Current assignee: Scapa Group Ltd
Priority date: 1989-12-12
Filing date: 1990-12-11
Publication date: 1991-07-10
Also published as: ZA909994B; FR2655664A1; AU6800090A; DE4039609A1; GB8928050D0; GB9026884D0; CA2031988A1

Abstract

A filter sleeve for use in dust extraction is of circular single-jersey knit construction and has inlay yarns extending in the coursewise direction, the inlay yarns serving to make the fabric isotropic. The inlay yarns may be of polyester. <IMAGE>

Description

i t 1 - :;2: 'D C=, CS::3 IMPROVEMENTS IN OR RELATING TO TEXTILE FILTER

SLEEVES The invention concerns improvements in or relating to textile filter sleeves, and has more particular reference to such sleeves of circular knit construction.

The essential principle of fabric filtration is to cause, say, dusty gas to flow through elements of permeable textile fabric by pressure or by suction, and to retain the dust on the fabric. At intervals the collected dust is discharged by flexing of the element, with the dust falling into a collecting hopper, thus to restore the filtering ability of the fabric.

Textile filter sleeves for industrial dust collection purposes are traditionally manufactured from fabrics of woven or needlefelt construction. These fabrics, after suitable finishing processes, provide a high filtration efficiency coupled with a dimensional stability which enables them to withstand the mechanical forces experienced during cleaning.

In dry filtration in general and dust filtration in particular needlefelt constructions have steadily replaced woven fabrics as filter media for a number of reasons.

needlefelt constructions exhibit a greater . thickness, and of the finished fabric surface, and also give rise to cheaper production costs.

However, in the case of woven as well as needlefelt fabrics, elaborate and costly seaming operations have to be carried out to produce filter bags.

For example, flexibility in area density It is known that circular knitted fabrics have certain advantages for industrial applications,' for example (a) circular knitting is unquestionably among the fastest and simplest systems for conversion of yarn to fabric;_ (b) by virtue of appropriate stitch selection, correct yarn utilisation and finishing techniques, fabrics can be specifically engineered to meet an infinite number of end-use requirements; and (c) the tubular nature of the knitted construction gives a unique advantage in that this shape is oftenthat required for industrial end-uses.

For instance, the tubular nature of the fabric is particularly significant for textile filter sleeves which, when produced from needlefelt or woven fabrics, have to be seamed to produce a tube dimensioned to fit the filter cages. Seaming is labour intensive and can result in potentially weak places down the sleeve, and additionally leads to a reduction in air permeability which may result in an uneven filter performance of the sleeve. Notwithstanding the above mentioned advantages, knitted fabrics are not inherently suitable for use in filtration. More particularly, there are a number of limitations of a weft knitted fabric, such as high extension and low recovery when subjected to pressure, as well as the anisotropic nature of the fabric properties, which will render it unsuitable for use as a filter medium.

t 1 i In an endeavour to utilise the benefits of knitting it has been proposed to use a circular knit pile fabric, whether of terry loop or other pile construction, as a filter medium, the ground and pile stitches being said to be locked against undesirable distortion and opening of the fabric, but such fabrics have been found to be susceptible to loads, particularly in the coursewise (or width) direction, and to be highly anisotropic. A typical such structure is disclosed in U.S. specification No. 4284507.

The present invention is predicated upon the appreciation that, contrary to previous thinking, it is possible to provide a circular knit fabric, and in particular a singlejersey fabric, which has physical and filtration characteristics comparable with those of fabrics more traditionally used in the manufacture of filter sleeves and it is the primary object of the present invention to provide a single-jersey knit structure of ready and useful application to the context of phase separation, for example industrial dust collection.

According to the present invention there is proposed a filter fabric, and more particularly a filter sleeve, comprising a single-jersey circular knit structure including inlaid yarns extending in the coursewise (or width) direction thereof, thus to impart a substantially isotropic characteristic to the structure.

The invention will now be described further, by way of example only, with reference to the accompanying stitch diagrams illustrating several forms of flat single-jersey fabrics constructed in accordance therewith. In the drawings Figure 1 shows a 1 x 1 Cross Inlay, Figures 2 to 6 respectively show a 1 x 2 Inlay, alx3 Inlay, alx2Cross Inlay, alx 3 Cross Inlay, and a 2 x 2 Cross Inlay,. whilst Figure 7 is a graph illustrative of load elongation characteristics of a conventional knitted loop-pile filter fabric and the fabric shown in Fig. 1.

Referring now to Figure 1, the flat single-jersey circular knit fabric shown therein is a 1 x 1 Cross Inlay identifiable as follows Knitting Yarn 74 tex medium or high tenacity staple-fibre polyester. 90,4 tex medium or high tenacity staple-fibre polyester.

Non-knitting yarn or inlay Finished courses per cm Finished wales per cm 8.8 Finished width 22 cm flat tube Finished area density: 517 grams metre -2 A fabric constructed as aforesaid has been found to have low percentage elongation under specified loads in both the machine and width directions and to be substantially isotropic.

Comparative performance figures for a conventional knitted loop-pile filter fabric, for example a fabric constructed 13 t 1 5 in accordance with the U.S. specification aforesaid and the fabric of the present invention are as follows Knitted Loop- 1 x 1 Cross Pile Fabric Inlay Fabric Finished courses per em: 26 13 Finished wales per cm 13 9 Finished area density (g/M2): 590 517 Unused air permeability (M3/m2/min at 12.7 mm Water Gauge): 11.5 7 Percentage elongation under load Walewise (or machine) direction 20Newtons 36 12.4 50Newtons 56 22.5 100Newtons 87 34.7 Coursewise (or width) direction 20Newtons 9 10.5 50Newtons 21 22.4 100Newtons 39 31.0 Dust Emission long term tests (Mg/M3) 1 0.3 Pressure Drop A P)(m.bar) >15 <5 i - 6 Flex Abrasion Resistance No. of flexes (X 103) Walewise Coursewise 1011.0 3405.7 261.2 '118.9.

It will be seen that, whereas the percentage elongation of the flat single-jersey fabric of the invention in the coursewise (or width) direction thereof is comparable with that of the known knitted loop-pile fabric, a most significant improvement is shown in machine direction (that is to say walewise) percentage elongation with the fabric of the invention, the graph of Fig. 7 being relevant in this regard.

However, in total contradistinction to the known knitted loop-pile fabric, the fabric of the present invention is substantially isotropic.

The percentage elongation characteristics and the substantially isotropic nature of the flat single-jersey fabric of the invention shows such fabric to be superior to the conventional knitted loop-pile fabric currently used in dust extraction, and thus of ready application in lieu thereof.

The stitch diagrams in Figs. 2 to 6 show alternative fabric structures to that shown in Fig. 1, such structures being thought to exhibit characteristics similar to those of the fabric shown therein, and likewise being of advantageous use in dust collection.

1 1 - 7 By means of the present invention we are able to take advantage of the high rate of production. of circular knitting machines and can, at the same time, avoid the need to seam a woven or needled fabric to bring the same into sleeve form and the adverse effect of such a seam on filter performance. Indeed the fabric of the present invention may be produced at a higher rate than the fabric illustrated in U.S. specification No. 4284507.

The geometry of the finished structure is dictated by the inlay yarns rather than the knitting yarns, and thus the "finished width" dimension will be greater than that of the conventional knitted loop-pile fabric.

The invention is not limited to the precise detail of the embodiment hereinbefore described, since alternatives will readily present themselves to one skilled in the art. Thus, for example, by utilising the technique of the present invention it is possible to utilise inlay yarns of any requisite characteristic, Or indeed to include yarns of respective characteristics in combination

Claims

1. A filter fabric comprising a single-jbrsey circular knit structure including inlaid yarns extending in the coursewise (width) direction and imparting a substantially isotropic char acteristic to the structure.

2. A filter fabric as claimed in claim 1, wherein said fabric is in sleeve form.

3. A filter fabric as claimed in claim 1 or 2, wherein the inlaid yarns exist as a cross-inlay.

4. A filter fabric as claimed in any one of the preced ing claims, wherein the inlaid yarns comprise medium or high tenacity polyester yarns.

5. A filter fabric as claimed in any one of the preced ing claims, wherein the inlaid yarns are heavier than the knitting yarns.

6. A filter fabric substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.

Published 1991 at 7be Patent Offlcc, State House. 66/71 HighHolborn. London WC I R41P. Further copies my be obtained frorn Sales Branch, Unit 6. Nine Mile Point Cwrnfelinfach. Cross Keys. Newport NPI 7HZ. Printed by Multiplex techniques lid, St Mary Cray, Kent 11 i 1