IE20100788A1

IE20100788A1 - A method of manufacturing a filter medium

Info

Publication number: IE20100788A1
Application number: IE20100788A
Authority: IE
Inventors: Donal Richard Mcgoey
Original assignee: Donal Richard Mcgoey
Priority date: 2007-06-18
Filing date: 2008-05-02
Publication date: 2011-02-16
Also published as: GB2460187A; GB2450395A; GB0808068D0; GB2450395B; IES20070433A2; IE20080352A1; GB2460187B; GB0910450D0

Abstract

A method of manufacturing a filter medium (1) which has a number of V-shaped pleats (11), with an upstream side (12) and a downstream side (13). The angle of each pleat (11) is selected within a range of between 4 degrees and 12 degrees. The filter is formed by pleating sheets of filter medium and applying strips of semi-liquid hot-melt material to the filter medium, allowing the hot-melt material to harden by directing a stream of cooling gas to the pleats and adjusting the angle of each pleat by regulating the strength of the stream of gas. <Figure 1>

Description

The invention relates to a method of manufacturing a filter medium for filtering gas, such as air but not limited thereto.

Filters usually contain a filter medium, such as glass paper, micro spun bonded polypropylene or cotton fibre mat. Such filter medium is used particularly for filtering air from dust or other undesired particles. To achieve a high filtering effect, i.e. to retain as many particles as possible in the filter medium, the sheets of filter medium are pleated in a zigzag manner to form a plurality of V-shapes or U-shapes. Typical filter medium consists of numerous interwoven fibres having spaces therebetween. During filtering, a proportion of incoming particles is captured in the filter medium by sticking to or between the filter fibres and remains in the filter medium. Some particles however may pass through the spaces between the fibres and exit the filter at the downstream side thereof. The ratio between the number of particles captured by the filter medium and a certain total number of incoming particles is referred to in the art as filter efficiency. Various factors exist which influence filter efficiency, such as for example, size of incoming particles, material of the filter medium, age of the filter, configuration of the filter medium, electric charge (or absence thereof) of the incoming particles, flow rate (volume of gas or air pumped through the filter in a unit of time), etc. It is known that efficiency of a typical filter tends to increase over time. This phenomenon occurs as more and more particles remain captured in the filter leaving fewer spaces between filter fibres for new particles to pass through. Although beneficial in that greater proportion of undesired particles remains captured in the filter, more energy is required to maintain the same flow rate through the filter. In order to increase filter efficiency from the beginning of exploitation of a new filter, it is known to install ionisation means at an upstream side of the filter for appropriately charging incoming particles in order to increase attraction between the incoming particles and the filter fibres. However, ionisation is only useful at low flow rates. At high flow rates the effect of ionisation decreases dramatically.

It is therefore an object of the present invention to overcome the aforementioned problems and to provide a filter means having high efficiency from the beginning of the use of a new ’ filter throughout its life, lower energy consumption and longer fife. It is a further object of the present invention is to provide a filter which is capable of maintaining high efficiency at fe ιΟ 07 8 8 high flow rates. It is yet a further object of the invention to provide a filter with low pressure loss at various modes of operation.

Accordingly, the invention provides a method of producing a filter medium comprising the 5 steps of: (a) pleating sheets of filter medium to form a plurality of substantially V-shaped pleats; (b) applying a semi-liquid hot melt stabilizing material onto the filter medium in form of a plurality of strips crossing the pleats ofthe filter medium; (c) allowing the stabilizing material to harden by directing a stream of cooling gas towards the filter medium while keeping the filter medium in the desired contour; and (d) adjusting the angle of each pleat by regulating the strength of the stream of gas applied to the stabilizing material to cause the pleats of the filter medium to move relative each other thus achieving the selected optimal angle of each pleat.

Preferably, fans are used for providing streams of air for hardening (i.e. cooling) the stabilising means.

Conveniently, the use of polypropylene as the material for both the filter medium and the stabilizing means provides for more precise control of the cooling step thereby allowing to achieve more precise pleat spacing compared to other materials.

Accordingly, such a filter comprises a filter medium which has been pleated to form a plurality of substantially V-shaped pleats, the filter medium having an upstream side and a downstream side and an ionising means positioned adjacent the upstream side of the filter medium for electrically charging incoming particles, thereby increasing attraction of the particles to the filter medium, wherein the angle of each pleat (i.e. the angle between surfaces of the filter medium defining each V-shape) is selected within a range of 4° and 12°.

Preferably, the depth of the pleats (i.e. the shortest distance between an apex of a pleat on one side of the filter and a plane spanning pleat apices on the other side of the filter medium) is selected between 22mm and 94mm. Further preferably, the pitch (i.e. the shortest distance between adjacent pleat apices on the same side of the filter medium) is selected between 3.5mm and 5.5mm.

IB 1 Ο Ο 7 8 8 Ideally, for pleat depth of 22mm the pleat angle is selected from a range between 10° and 12° and for pleat depth of 94mm the pleat angle is selected from a range between 4° and 6°.

It is considered that the provision of a certain optimal angle between the pleats of the filter medium for a particular pleat size, in combination with the ionising means provides for significant increase of filter efficiency from the beginning of use of a new filter throughout its life (in contrast to known filters whose efficiency starts at a lower level and increases over time), even at high flow rates, such as for example 5000 m3/hr, and even for small particle size (e.g. 0.3-0.5pm) while at the same time causing low pressure loss. Such an arrangement provides for lower energy consumption in order to pump the gas being filtered through the filter and for longer life of the filter. The use of polypropylene as the material for the filter medium, further enhances the above described effects. The use of polypropylene fibres coated with a layer of fluorocarbon as the material for the filter medium even further enhances the above effects. It will be nevertheless appreciated that other materials or combinations of materials may be used, such as for example, glass fibre or a mix of polypropylene/polyester mixture.

Although the preferred filtered medium is air, the filter is suitable for filtering other gases or gaseous mixtures.

In a preferred arrangement, the ionising means comprises at least one and preferably a series of ionising brushes positioned at selected locations adjacent the upstream side of the filter medium, the brushes being connected to a source or sources of voltage for electrically charging incoming particles. Since the voltage applied to the brushes is related to the efficiency of the filter, it is preferred that the voitage applied to the brushes can be varied to adjust the efficiency of the filter. Due to the unique combination of the optimised pleat angles and ionisation, irrespective of the voltage applied to the brushes and subsequent efficiency, the same pressure loss is maintained at the various voltage levels.

Preferably, the filter comprises stabilizing means in the form of lines of hardened hot melt material crossing the pleat lines. Such a stabilizing means is described in EP 1 034 024 B. Such stabilizing means is formed by applying lines of semi-liquid material onto the pleated filter medium and allowing the lines to harden in a shape, according to the contour of the filter medium. The stabilizing means subsequently retain their shape after hardening independently of the desired form of the filter medium and become firmly connected with the filter medium after hardening. The stabilizing means may be applied in the form of one or more substantially parallel strips crossing the pleat lines of the filter medium or, alternatively, in the form of one or more non parallel strips thereby forming a grid. For best results, the stabilizing means is made from the same material as the filter medium. By using the same material, for example polypropylene, for the stabilizing means and for the filter medium very good bonding characteristics are obtained, which are far superior to the adhesive characteristics of the commonly used glue. The use of such stabilizing means allows the filter contour to remain firm after hardening and does not require any further retaining means.

It is important that during the manufacture of the filter medium according to the invention the necessary optimal pleat angle is obtained. Too wide or too narrow pleat angle results in increased pressure loss. In a filter medium having the above described stabilizing means, the selected optimal pleat angle is achieved during the manufacture the filter medium in accordance with the method of the invention? Accordingly, the invention provides a method of manufacturing a filter medium as defined in the appended claims.

The invention will now be described more particularly with reference to the accompanying drawings which show by way of example only one embodiment of the invention. In the drawings: Fig. 1 shows a perspective view of a filter medium pleated in a zigzag-manner; Fig. 2 is an enlarged view of area C of Figure 1 showing an ionising brush; Fig. 3 is an enlarged partial front view of the filter medium of Figure 1 in the direction of arrow A; and Fig. 4 is a cross-sectional view of Figure 3 along lines B-B.

Referring initially to Figure 1, the filter manufactured according to the method of the invention is indicated generally by reference numeral 1. The filter 1 comprises a filter medium 10 made from a sheet of material suitable for filtering, such as fibre-glass, polyester, polyethylene, cotton or the like. In this particular embodiment (but not in any way limited thereto) the sheet material is micro spun polypropylene which has excellent filtering characteristics for filtering air and which is particularly suitable for use with a polypropylene stabilizing means. The sheet of filtering material has been pleated in a zigzag manner to form a plurality of substantially V-shaped pleats 11 in order to improve the filtering capacity. This is well known and need not be described here in detail. The number of V-s depends on the material used for the sheet, its thickness and various other parameters. The filter medium 10 has an upstream side 12 from which the gas to be filtered approaches the filter and a downstream side 13 from which filtered gas exits the filter medium. The filter 1 also has one or more ionising brushes 14 (only one shown in Figures 1 and 2) positioned adjacent the upstream side 12 of the filter medium. The brushes are connected to a source or sources of voltage (not shown) for electrically charging, for example negatively, particles approaching the filter 1 at its upstream side 12 thus increasing attraction of the particles to the filter medium 10. The filter can be provided with regulation means to adjust the voltage applied to the brushes to set up a desired filter efficiency.

The filter of the presently described embodiment is particularly suitable for filtering air, but it will be appreciated that its use is not limited to air only and the filter can be found useful in filtering other gases or gaseous mixtures.

With reference to Figure 4, the angle a of each V-shaped pleat 11 (i.e. the angle between sides 11 a and 11 b of each V-shape) is selected within a range of 4° and 12°. It has been discovered that selection of a particular optimal angle a for a particular pleat size provides for significant increase of filter efficiency, from the start of exploitation of the filter throughout its life (in contrast to known filters whose efficiency starts at a lower level and increases over time), even at high flow rates, such as for example 5000m3/hr, and even at low particle size, e.g. in the range about 0.3pm to 0.5pm while at the same time causing low pressure loss. It has been further discovered that the filter provides for lower energy consumption in order to pump the gas being filtered through the filter and for longer life of the filter.

For example, it has been found that for pleat depth D (see Figure 4) of 22mm the pleat angle a is selected from a range between 10’ and 12° and for pleat depth of 94mm the pleat angle a is selected from a range between 4° and 6°.

It is preferred that the filter comprises a stabilizing means 20 (Figures 1, 3 and 4) in the form of lines of hardened hot melt material crossing pleat lines, such as described in EP 1 IE 1 0 0 7 88 034 024 B. The use of such stabilising means has been found particularly efficient in maintaining the optima! angle a.

The stabilizing means 20 is formed from a strip of polypropylene which has been applied 5 to the filter medium in a semi-liquid form. In Figures 1, 3 and 4 a plurality of substantially parallel strips 20 is shown. In another modification (not shown), the strips 20 may cross each other as well as the pleat lines thereby forming a grid. Strips 20 may be applied either to one side or the filter medium 10 (either upstream 12 or downstream 13) or to both sides 12,13.

When heated and melted stabilizing means 20 is applied onto the pleated filter medium 10, the stabilizing means repeats the contour of filter medium 10 whereby the corners of the V-s are reached. As the melted stabilizing means 20 is allowed to harden, the material of the filter medium is welded to the material of the stabilizing means. For best results, the stabilizing means is made from the same material as the filter medium, and most preferably from polypropylene. After cooling down the stabilizing means 20 fixes the filter medium 10 in its configuration. The pleat angles a are then fixed and maintained throughout the use of the filter medium 10.

Hardening of the stabilizing means material is assisted by directing a stream of cooling gas (e.g. air) towards the filter medium while keeping the filter medium in the desired contour.

The desired optimal angle a of each pleat is obtained by regulating the strength of the stream of gas applied to the stabilizing material thereby causing the pleats of the filter medium to move relative each other, thereby narrowing or widening the angle therebetween until the desired angle a is obtained. One or more cooling fans may be used for blowing streams of air onto the stabilising means.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention as defined in the appended claims.

Claims

CLAIMS:

1. A method of producing a filter medium comprising the steps of: 5 (a) pleating sheets of filter medium to form a plurality of substantially V-shaped pleats; (b) applying a semi-liquid hot melt stabilizing material onto the filter medium in form of a plurality of strips crossing the pleats of the filter medium; (c) allowing the stabilizing material to harden by directing a stream of cooling gas towards the filter medium while keeping the filter medium in the desired contour; and 10 (d) adjusting the angle of each pleat by regulating the strength of the stream of gas applied to the stabilizing material to cause the pleats of the filter medium to move relative to each other thus achieving the selected optimal angle of each pleat.

2. A method as claimed in Claim 1, the method further comprising the step of: (e) using fans for providing streams of air for hardening the stabilizing means.

3. A method as claimed in Claim 1 or Claim 2 comprising the step of: 20 (f) positioning an ionising means adjacent an upstream side of the filter medium for electrically charging incoming particles, thereby increasing attraction of the particles to the filter medium, and selecting the angle of each pleat from within a range of between

4. ’ and 12”. 25 4. A method as claimed in Claim 3, comprising the step of: (g) selecting the depth of the pleats from within a range of 22mm and 94mm and the pitch is selected from within a range of 3.

5. Mm and 5.5mm. 30 5. A method as claimed in Claim 3 or Claim 4, comprising the step of: (h) for a pleat depth of 22mm, selecting the pleat angle from a range between 10° and 12°. 35

6. , A method as claimed in Claim 3 or Claim 4, comprising the step of: IE 1 0 07 88 (i) for a pleat depth of 94mm, selecting the pleat angle from a range between 4° and 6°.

7. A method as claimed in any of Claims 3 to 6, comprising the step of: (j) providing one or more ionising brushes at selected locations adjacent the upstream side of the filter medium; and (k) connecting the brushes to one or more source of voltage for electrically charging incoming particles.

8. A method as claimed in any preceding claim, comprising the step of: (l) selecting the material of the filter and the stabilizing means to be polypropylene. 15

9. A method of producing a filter medium substantially as herein described with reference to the accompanying drawings.

10. A filter medium manufactured in accordance with the method of any one of Claims 1 to 9.