EP1377382A1

EP1377382A1 - Air-cleaning filter

Info

Publication number: EP1377382A1
Application number: EP02718757A
Authority: EP
Inventors: Evert Krantz
Original assignee: Freshman Flimmer AB
Current assignee: Freshman Flimmer AB
Priority date: 2001-04-12
Filing date: 2002-04-04
Publication date: 2004-01-07
Anticipated expiration: 2022-04-04
Also published as: EP1377382B1; ATE456400T1; SE0101336D0; WO2002083314A9; DE60235228D1; WO2002083314A1; SE0101336L; SE518972C2

Abstract

The invention relates to an air-cleaning filter of the type that comprises a set of soft threads (4) of an electrostatically chargeable material and a thread-carrying body (3), having a round basic shape, which comprises gaps (6) defined by curve-shaped walls (5) through which air may pass into and through the thread set. According to the invention, gaps (6) located near the periphery of the body are thinner than gaps located closer to the centre of the body. In this way, an even distribution of the threads in the thread set is obtained.

Description

AIR-CLEANING FILTER

Technical Field of the Invention

This invention relates to an air-cleaning filter of the type that comprises a set of soft threads of an electrostatically chargeable material and a thread-carrying body having a round basic shape, which comprises gaps, defined by curve- shaped walls, through which air may pass from outside into and through the thread set.

Prior Art

An air-cleaning filter of the,_.above generally mentioned kind is previously known by WO 95/33567 (priority from SE 9401950-2) . The thread-carrying body of this known air-cleaning filter is manufactured by a work piece consisting of two stiff, although elastically flexible bands or sheets of plastic, which initially are parallel to each other and united by a large number of spaced-apart intermediate flanges, which together with . the bands define cross-section-wise quadrangular ducts in the work piece. At the manufacture, parallel slots are cut in one of the bands, more precisely between nearby intermediate flanges, and then the other band may be bent and formed as a spiral-like coil. The intermediate flange^'s remaining after the slotting individually receive a T-shaped cross-section profile. The electrostatically chargeable threads are fastened on the smooth side of the band, which is opposite the intermediate flanges. Characteristic of the previously known filter is that all intermediate flanges have one and the same height, something that means that the air gap between nearby walls in the spiral coil receives a uniform width all the way from the centre out towards the periphery. During practical development work, it has turned out that the fact that the air gap is of a uniform width along the entire extension thereof gives rise to an uneven distribution of the threads in the thread set. More precisely, the thread count in the parts of the thread set which are peripherally located becomes smaller than the thread count in the centrally located parts. This means that the particle-separating ability of the thread set decreases in the direction from the centre towards the periphery. Objects and Features of the Invention

The present invention aims at obviating the above-mentioned disadvantage and at providing an improved air-cleaning filter of the type initially mentioned. Therefore, a primary object of the invention is to create a filter in which the distribution of the threads in the thread set is in all essentials even along the entire cross-section area of the filter. An additional object is to create a filter that may be manufac- tured having a round or cylindrical basic shape in a simple, efficient and inexpensive way.

According to the invention, at least the primary object is attained by the features defined in the characterizing clause of claim 1. Preferred embodiments of the filter accord- ing to the invention are furthermore defined in the dependent claims .

Brief Description of the Accompanying Drawing In the drawing: Fig 1 is a perspective exploded view of a filter composed of a casing and a filtration unit consisting of a thread set and a carrying body, Fig 2 is a schematic end view of the thread-carrying body according to a first embodiment of the invention, and Fig 3 is an analogue end view of a body according to an alternative, preferred embodiment of the invention.

Detailed Description of Preferred Embodiments of the Invention In fig 1, two components included in a filter accord- ing to the invention are illustrated in a separated state. One of the components consists of a casing 1 and the other component of a filtration unit in its entirety designated 2, which in turn is composed of on one hand a form-stiff body 3, and on the other hand a thread set in which the individual threads are designated 4. The casing 1 as well as the filtration unit 2 is of a round or cylindrical basic shape, the shape of the filtration unit being determined, by the shape of the stiff body 3. In the body 3, gaps are included which are delimited by curve- shaped walls and through which air may pass. In the example according to fig 1, the body is shown in a horizontal plane with the threads 4 hanging down from the bottom side of the body. In this case, air (or another gas) may be taken in in the direction from above and then pass into and through the thread set positioned downstream the body. In this connection, it should be pointed out that the body may be positioned in another way than in a horizontal plane.

The threads 4 consist of an electrostatically chargeable material, e.g. polypropene or the like, and are soft by nature. The threads may be of varying lengths and be utterly fine.

Advantageously, cross-section-wise rectangular threads having the size of 0,001 x 0,004 mm, are used.

The casing 1 may advantageously - though not necessarily - be of the same length as the filtration unit 2. By having a cylindrical or cross-section-wise circular basic shape, the filter according to the invention is suitable for mounting in circular air ducts or passages.

As far as the shown filter has been described hitherto, the same is in all essentials previously known by WO 95/33567. . The body 3 shown in fig 2 includes a plurality of rings 5a, 5b, 5c, 5d and 5e. The ring 5a defines a central hollow space 6a. Outside this hollow space, the rings define in pairs ring-shaped air gaps 6b, 6c, 6d, and 6e, respectively. Thus, the rings serve as. curve-shaped partition walls between the air gaps. In the example, the rings are circular, i.e. the individual curve shape of the wall is constituted by a circle. In fig 2 is seen how the rings are arranged concentrically in each other. The rings are held together at determined distances from each other by means of spacing members 7, which in the example consist of two bars or needles 7, arranged perpendicularly to each other, which intersect the rings. In practice^ other arbitrary distance members may be used for holding the rings in place in the body.

The rings may in practice consist of thin cylinder walls of plastic having a suitable axial extension (e.g. within the range of 10-40 mm) . The wall thickness may advantageously be within the range of 0,5-1,5 mm. The threads 4 are applied on the rings and evenly distributed along the same. For instance, threads may be welded on one of the sides of the ring wall (e.g. the inside) or on both sides of the same. It should also be mentioned that the number of rings may be considerably larger than five.

If the air gaps 6 would be of a uniform width according to prior art, the relation between the cross-section area of the outer air gap 6e and the circumference (360°) of the ring 5e positioned outside would become proportionally larger than the relation between the cross-section area of the air gap 6d and the circumference of the ring 5d. This is due to the fact that the cross-section area of the air gaps increases exponentially in relation to a radius increase, while the circumference of the individual ring increases rectilinearly in relation to a radius increase. By the fact that the threads 4 are evenly distributed along the periphery of the rings, the same there- fore become more sparsely distributed in the outer air gaps than in the inner air gaps .

In order to solve the above-mentioned problem, the body according to the invention is formed in such a way that the relation between on one hand the circumference of a given wall portion having the arc length of 1 turn (360°), and on the other hand the area of a section of the air gap positioned inside said wall portion, is in all essentials constantly independent of the radial position of the wall portion in question. Suppose that the ring 5a has the radius R. The ring 5b should then have the radius 1,62 R, the ring 5c the radius 2,19 R, the ring 5d the radius 2,75 R, and the ring 5e the radius 3,30 R. In other words, the width of the different air gaps is reduced successively in the direction from within and out towards the periphery. In this way, the cross-section areas of the air gaps are adapted to the circumference of the appurtenant, thread- carrying ring in such a way that the threads in the thread set are distributed in all essentials evenly in the cross-section. In fig 3, an alternative embodiment is shown according to which the curve-shaped walls that define air gaps 6 consti- tute part of a stiff band 5 having a spiral-like shape. In this connection, the width of the single air gap 6 may advantageously - though not necessarily - decrease continuously in the direction outwards towards the periphery of the body. This reduction of width is achieved according to the same principle as has been described above.

In the embodiment according to fig 3, the body comprises teeth or projections 9, which protrude from one side of the band 5 and serve as distance members between the different band portions in the spiral coil. Said teeth 9 are of different height. More precisely, the teeth located closest to the centre of the body are higher than the teeth located closest to the periphery of the body. The tooth height may vary continuously, i.e. so that all teeth are somewhat shorter than each tooth positioned inside counted from the centre towards the periphery. It is, however, also feasible to vary the tooth height batchwise in such a way that two or more teeth in a set closest to the centre have a maximum height, and then two or more teeth in a subsequent tooth set have a reduced height, etc.

Feasible Modifications of the Invention

The invention is not solely restricted to the embodiments described above and schematically illustrated in the drawing. For instance, it is possible to spare the distance members in the helical body according to fig 3. Thus, the partition wall formed by the helical band may be manufactured with a predetermined shape and from a material, e.g. plastic, having a certain inherent elasticity which enables an insertion of the body into the casing with a certain press fit.

Claims

1. Air-cleaning filter, comprising a set of soft threads (4) of an electrostatically chargeable material and a thread-carrying body (3) having a round basic shape, which comprises gaps (6) defined by curve-shaped walls (5) through which air may pass from outside into and through the thread set, c h a r a c- t e r i z e d in that gaps (6e) located near the periphery of the body are thinner than gaps (6b) located closer to the cen- tre of the body.

2. Air-cleaning filter according to claim 1, c h a r a c- t e r i z e d in that the curve-shaped walls constitute part of at least one band (5) having a spiral-like shape, which defines a continuous air gap (6) .

3. Air-cleaning filter according to claim 1, c h a r a c- t e r i z e d in that the width of the air gap (6) decreases continuously in the direction outwards towards the periphery of the body. .

4. Air-cleaning filter according to claim 1, c h a r a c- t e r i z e d in that the curve-shaped walls of the body (3) consist of separate, circular rings (5) having different radii, which are arranged concentrically in each other and define ring-shaped air gaps (6).

5. Air-cleaning filter according to any one of the preceding claims, c h a r a c t e ri z e d in that the relation between on one hand, the circumference of a given wall portion (5) having an arc length of 1 turn (360°) , and on the other hand the area of a wall portion positioned inside said section of the air gap (6) is in all essentials^' constantly independent of the radial position of the wall portion in question.

6. Air-cleaning filter according to any one of the preceding claims, c h a r a c t e r i z e d in that the same comprises one or more spacing members (7, 9) in order to hold the curve- shaped walls (5) at predetermined distances from each other.

7. Air-cleaning filter according' to claim 6, c h a r a c- t e r i z e d in that the spacing members consist of a plurality of projections (9) that protrude from one side of the individual wall (5) and are of varying heights, more precisely in such a way that projections located near the centre of the body have a larger height than projections located closer to the periphery of the body.