FILTER FOR SEPARATING PARTICLES FROM AIR

Abstract: The present invention relates to a filter for separating particles from air, more precisely down to submicron particles, said filter comprising on one hand a set (10; 10'; 10''; 10''') of elongated, flexible or floppy elements of electrostatically chargeable material being assembled at their ends, and on the other hand a frame structure (12; 12'; 12''; 12''') for said set of elements (10; 10'; 10''; 10'''), said filter being intended to operate in a duct where flowing air is passing through said filter in order to generate static electricity having the task of attracting particles from the air to the elements. The purpose of the invention is to define a simplified frame structure compared to SE-C-500 636. The filter according to the present invention is characterized in that the frame structure (12; 12'; 12''; 12''') consists of a homogeneous, air-pervious material having low air resistance.

Description: FILTER FOR SEPARATING PARTICLES FROM AIR Technical Field of the Invention The present invention relates to a filter for separating particles from air, more precisely down to submicron particles, said filter comprising on one hand a set of elongated, flexible or floppy elements of electrostatically chargeable material being assembled at their ends, and on the other hand a frame structure for said set of elements, said filter being intended to operate in a duct where flowing air is passing through said filter in order to generate static electricity having the task of attracting particles from the air to the elements . Prior Art From WO 95/00248 is previously known a device for separating submicron particles from air. This device is characterized in that a frame structure supports a multitude of threads or strips, the air to be cleaned bypassing said threads or strips, static electricity being generated on one hand due to the friction of the air relative to the fibres and on the other hand due to the fact that the fibres are rubbed against each other. The frame structure is formed from a flexible band formed into loops, the strips being affixed on said band. The frame structure also includes a plurality of pipe- or tube forming means for distributing the air flow through the frame structure . Objects and Features of the Invention The present invention aims at proposing an alternative design of the frame structure, said design being essentially more simple to manufacture than the frame structure according to SE-C-500 636, said frame structure being for instance composed of a known standard material or being designed integral with the strips. The material of the frame structure should have good air permeability and low pressure drop without the need for special arrangements . Brief Description of the Drawings In the drawings : Figure 1 is a longitudinal section through an embodiment of a filter according to the present invention; Figure 2 is an end view along II -II in figure 1; Figure 3 is a longitudinal section through an alternative embodiment of a filter according to the present invention; Figure 4 is an end view along IV- IV in figure 3; Figure 5 is a longitudinal section through a further alternative embodiment of a filter according to the present invention; Figure 6 is an end view along VI -VI in figure 5 ; Figure 7 is a longitudinal section through a further alterna- tive embodiment of a filter according to the present invention; and Figure 8 is an end view along VIII-VIII in figure 7. Detailed Description of Preferred Embodiments of the Invention An embodiment of a filter according to the present invention is shown in figures 1 and 2. The filter comprises a set 10 of elongated, flexible or floppy elements, which set in turn includes a number of partial sets 11 of said elements. The elements are preferably fibres of polypropylene having cross- sectional dimensions of 10-40 μm. In this connection it should be pointed out that the elements may consist of fibres from at least two different materials or types of materials having different polarity, e.g. a first material having a strongly positive charge and a second material having a strongly negative charge. The first material may be chosen from the group of wool, cotton or the like, while the other may be a plastic polymer in the shape of polypropylene. In the set of elements 10 elements/fibres of electret-type as well as metal fibres, e.g. copper fibres, may be included. The filter also comprises a frame structure 12 that in the shown embodiment consists of a homogeneous, open fibre material having low air resistance, i.e. the pressure drop is small when the air passes through the frame structure 12. As is most clearly shown in figure 2 the frame structure generally has a circular cross-sectional shape, a number of slots 14 being provided in the frame structure 12. Said slots 14 are through-going, i.e. they extend along the entire axial extension of the frame structure 12. Further the slots 14 extend parallel to each other in the axial direction of the filter. As can be seen from figure 2 the slots 14 have a fixed extension in a direction that is defined by the two-way arrow 16 in figure 2, while the slots have a varying extension in a direction perpendicular to the direction according to the two- way arrow 16. The slots 14 receive the partial sets 11 in such a way that a partial set 11 is mounted in each slot 14. The partial sets 11 are thus assembled in the portion that is received in the slots 14, especially in a direction transverse to the lon- gitudinal direction of the slots 14. The connection between the frame structure 12 and the partial sets 11 may be carried out in different ways. For exemplifying, but non-restricting purposes adhesive bonding and induction welding, e.g. by the aid of UV light, may be mentioned. As is apparent from figure 1 the frame structure 12 has a certain extension LI in the axial direction and the portion of the set 10 that is located outside of the frame structure 12 also has a certain extension L2 in the axial direction. Preferably L2 is several times LI and for exemplifying, but non-restricting purposes it is stated that L2 may be 2-10xLl. The axial extension is of importance for guaranteeing proper securing of the partial sets 11 in the frame structure 12. In the embodiment shown in figures 3 and 4 the filter comprises a set 10' of elongated, flexible or floppy elements, said set 10' including a number of partial sets 11' of said elements. The filter also comprises a frame structure 12', which, in the disclosed embodiment, consists of a homogeneous, open fibre material having low air resistance. Preferably the material of the frame structure 12 ' is the same as the material of the frame structure 12. The principal difference between the embodiment of figures 3 and 4 and the embodiment of figures 1 and 2 is that the frame structure 12' of the first-mentioned embodiment has a square cross section, while the frame structure 12 in the embodiment according to figures 1 and 2 has a circular cross section. This means that the slots 14' in the frame structure 12 ' of the embodiment according to figures 3 and 4 have mutually corresponding dimensions and consequently the partial sets 11' are given mutually corresponding dimensions. As regards the securing of the partial sets 11' in the frame structure 12 ' reference is made to what has been said above in connection with the embodiment according to figures 1 and 2. In the embodiment shown in figures 5 and 6 the filter also comprises a set 10" of elongated, flexible or floppy elements, said set 10" having the shape of a continuous band of such elements extending transverse to the longitudinal direction of the band. The set 10" of elements is secured in a frame structure 12" included in the filter, said frame structure 12" being, in the shown embodiment, composed of a homogeneous, open fibre material having low air resistance. The frame structure 12" is also in the shape of a band, the width of the band forming the frame structure 12" being essentially smaller than the width of the band forming the set 10" of elements. When manufacturing a filter according to the embodiment of figures 5 and 6 the two bands are connected with each other in an area along a common longitudinal edge. Said connection may for instance be carried out by adhesive bonding or induction welding. The band package formed in such a way is then wound up in order to create a filter according to figures 5 and 6, a suitable adhesive, e.g. glue or tape, being used to maintain the helical shape according to figures 5 and 6 after the winding-up is completed. In connection with the winding-up the portion of the set 10" of elements that is covered by the frame structure 12" will be somewhat compressed. This is evident from figure 6 since from said figure it can be learnt that the helical band portions of the set 10" of elements (dotted in figure 6) that are received in the helical frame structure 12" have an essentially smaller extension in the radial direction than the corresponding portions of the frame structure 12". The embodiment of a filter shown in figures 7 and 8 comprises a set 10'" of elongated, flexible or floppy elements, said set 10"' at the top of figure 7 being transferred into a frame structure 12"'. This frame structure 12"' is inte- gral with the set 10'", i.e. the frame structure 12'" comprises the same elongated elements as the set 10'", the difference being that the portion of the elements that is part of the frame structure 12'" are more assembled than the portion of the elements that are suspending freely. In order to maintain the assemblage of the portion of the fibres that forms the frame structure 12'" an induction welding may for instance be applied to the outside of the frame structure 12'". It is also possible that a thin casing is applied to the outside of the portion of the filter that forms the frame structure 12"', said casing being connected with the elements by for instance induction welding. What has been said above in connection with the embodiment according to figures 1 and 2 regarding the elements, i.e. material and dimensions, is also valid for the other embodiments. It should also be pointed out that the relation between the measures LI 1 and L2 ' in figure 3, LI" and L2 " in figure 5 and LI'" and L2 '" in figure 7 normally is in accordance with what has been said regarding LI and L2. It is generally valid that the different embodiments of the frame structure 12; 12'; 12"; 12'" described above are manufactured from a homogeneous, air-pervious, porous material, e.g. polypropylene, said material normally being so open that no special arrangements are necessary to further increase the air permeability, i.e. the pressure drop is at a low level. By homogeneous material should in this connection be understood a material having a uniform structure throughout its entire volume. For exemplifying purposes it should be mentioned that the fibres included in the frame structures 12; 12'; 12 ' ' may have a diameter of 0,3-2 mm. As regards the frame structure 12"' the dimensions of the fibres of course correspond to those of the set 10'" of elements since the frame structure 12"' and the set of elements are integral with each other. The filters described above are intended to be mounted in an air duct, the cross section of the filters being adapted to the cross section of the air duct, i.e. the frame structure 12; 12'; 12"; 12'" of the filter seals against the walls of the air duct. For a more complete description of the structural design of a device, in which the filter according to the pre- sent invention may be incorporated, reference is made to SE-C- 500 636, especially figure 1 and the appurtenant part of the description. In this connection it should be pointed out that in order to achieve a proper degree of separation the material of the walls of the air duct should have a low dielectric constant, e.g. said material could be polyethylene, acrylic or the like. The filters according to the present invention function in the following way. The air flowing through the ducts ini- tially meets the frame structure 12; 12; 12"; 12'", said air exclusively flowing through the material of the frame structure 12; 12'; 12"; 12'" itself when passing through said frame structure 12; 12'; 12"; 12'", this being indicated by the arrows 18. When the air flow passes the freely suspending portion of the flexible, floppy elements/fibres static electricity is generated on one hand due to the friction of the air relative to the fibres and on the other hand due to the fibres being rubbed against each other. This results in that the fibres attract submicron particles from the air. The arrows 20 in figure 1, 3, 5 and 7 symbolize cleaned air that exits from a filter according to the present invention. Although the invention is described and defined in the claims as suitable in connection with separation of submicron particles from air it is evident that the invention is useful for the same purposes also in connection with other gases than air.

Claims: Claims 1. Filter for separating particles from air, more precisely down to submicron particles, said filter comprising on one hand a set (10; 10'; 10"; 10"') of elongated, flexible or floppy elements of electrostatically chargeable material being assembled at their ends, and on the other hand a frame structure (12; 12'; 12"; 12'") for said set of elements (10; 10'; 10"; 10'"), said filter being intended to operate in a duct where flowing air is passing through said filter in order to generate static electricity having the task of attracting particles from the air to the elements, c h a r a c t e r i z e d in that the frame structure (12; 12'; 12"; 12'") consists of a homogenous, air-pervious material. 2. Filter according to claim 1, c h a r a c t e r i z e d in that the material of the frame structure (12; 12'; 12"; 12'") has a fibre diameter substantially in the range of 0,3-2 mm. 3. Filter according to claim 1 or 2 , c h a r a c t e r i z e d in that the frame structure (12; 12') has slots (14; 14') that each receives a partial set of the set (10; 10') of elements. 4. Filter according to claim 1 or 2 , c h a r a c t e r i z e d in that the frame structure (12") consists of a helically wound band, the set (10") of elements also being band shaped, and that a portion of the set (10") of elements is wound up in said helically wound frame structure (12") . 5. Filter according to any of the claims 1-4, c h a r a c t e r i z e d in that the set (10; 10'; 10") of elements is connected with the frame structure (12; 12'; 12") by means of an adhesive. 6. Filter according to claim 1 or 2 , c h a r a c t e r i z e d in that the frame structure (12'") constitutes an integral portion of the set (10'") of elements, said elements/fibres included in the frame structure (12'") are more assembled than the rest of the elements/fibres. 7. Filter according to claim 6, c h a r a c t e r i z e d in that the assemblage is achieved by means of an adhesive applied to the outside of the frame structure (12'") . 8. Filter according to any of the preceding claims, c h a r a c t e r i z e d in that the axial extension (L2; L2 ' ; L2 " ; L2"') of the portion of the set (10; 10'; 10"; 10'") of elements located outside the frame structure (12; 12'; 12"; 12"') is several times the axial extension (LI; LI'; LI"; LI'") of the frame structure (12; 12'; 1"; 12'"). 9. Filter according to claim 8, c h a r a c t e r i z e d in that the axial extension (L2; L2 ' ; L2 " ; L2 '") of the portion of the set (10; 10'; 10"; 10"') of elements located outside the frame structure (12; 12'; 12"; 12"') is 2-10 times the axial extension (LI; LI'; LI"; LI'") of the frame structure (12; 12'; 1"; 12'") .

Inventors: VON GLEHN ANDREAS, VON GLEHN, ANDREAS
Applicants: FRESHMAN AB, VON GLEHN ANDREAS, VON GLEHN, ANDREAS
Application year: 1998
Main classification: B03C3
IPC codes: B01D46, B03C3