The present invention relates to a filter device, comprising a filter cabinet, at least one filter chamber provided in the filter cabinet and filter elements pro- vided in the filter chamber, wherein air streams mixed up with particles are fed into the filter chamber and into the filter elements such that particles present in the air streams adhere to the outer sides of the filter elements while air purified by the filter elements leaves or is discharged therefrom, wherein a filter cleaning device includes a compressed-air device and a device for directing blows of compressed air into the filter elements for momentary expansion or dilatation thereof and thereby shake off particles adhering thereto, wherein a pre-separator is provided to separate coarse particles from the air stream mixed up with particles before said air stream is fed to the filter elements in the filter chamber, and wherein the pre-separator includes at least one nozzle which is provided to direct the air stream mixed up with particles and flowing to the pre-separator, into a separating space in which the air stream is de- flected in such a direction that the coarse particles are deposited from the air stream by mass forces genera- ted during the deflection.

Filter devices of the abovementioned type but without pre-separators are known from the publication DE 1 407 944.

It is however, also previously known to provide filter devices of this type with pre-separators for separating coarse particles before the air stream reaches the filter elements. Such prior art pre-separators often have limi- ted ability to separate coarse particles.

The object of the present invention is primarily to further develop prior art pre-separators in order to, inter alia, improve their separating capacity. According to the invention these problems have been remedied by pro- viding the abovementioned filter device with the characte-

rizing features of primarily subsequent claim 1.

Since the filter device includes pre-separators ha- ving at least one nozzle with said characterizing fea- tures, a less turbulent air stream is generated and thus, an improved ability to separate coarse particles.

The invention will be further described below with reference to the accompanying drawings, in which fig. 1 is a section through the filter device accor- ding to the invention; fig. 2 is a perspective view of parts of the filter device of fig. 1; and fig. 3 is a perspective view of an alternative em- bodiment of the filter device according to the invention.

The filter device illustrated in fig. 1 is adapted to separate coarse as well as fine particles from air streams mixed up with particles, e. g. such air streams which are generated in connection with different methods of treatment, e. g. in the form of welding fume during welding or grinding dust during grinding. The filter de- vice includes at least one unit 1, consisting of a filter cabinet 2, at least one filter chamber 3 provided in the filter cabinet 2 and communicating with an air inlet pipe 4 and an air outlet pipe 5. At the back, the filter chamber 3 is defined by a rear wall 6, on the sides by two opposing side walls 7 of the filter cabinet 2 and at the front by a front wall 8. Furthermore, the filter chamber 3 is at the top defined by the upper side 9 of the filter cabinet and it has an opening 10 down below.

A plurality of horizontally mounted filter elements 11 are provided between the front and rear walls 6,8. These filter elements 11 are tubular in a manner known per se and they have in a manner known per se inner support wires 12 and an outer, folded filter material 13, the folds 14 of which extend in the longitudinal direction of the filter elements 11 between the rear and front walls 6,8. The filter elements 11 are closely connected to the rear wall 6 and they are provided with front openings 15

which connect closely to the front wall 8 around ope- nings 16 therein.

These filter elements 11 operate such that air streams 17 mixed up with particles are brought to flow into the filter elements 11 so that the particles therein adhere to the outer side of the filter material 13. The pure air 18, free from particles, is brought to flow out of or exit the filter elements 11 through their front openings 15 and through the openings 16 in the front wall 8 into a pure-air chamber 19 and through said cham- ber out of the filter cabinet 2 through the air outlet pipe 5. The pure-air chamber 19 is located at the front in the filter cabinet 2 and it is sealed preferably by a door 20 which can be opened and which when closed de- fines or forms part of the front side of the filter cabi- net 2. On the door 20 or in any other suitable manner there is provided a filter cleaning device 21 in the pure- -air chamber 19. This filter cleaning device 21 includes a compressed-air device 22 and a device connected thereto for directing blows of compressed air into the filter elements 11. Said latter device includes here magnetic valves 23 and cleaning tubes 24 connected thereto. The cleaning tubes 24 extend vertically in front of the front wall 8 of the filter chamber 3 and each cleaning tube 24 is associated with a filter element 11 and has air dis- charge openings, preferably in the form of slits (not shown) through which blows of compressed air are directed into the filter elements 11 through the openings 16 and 15 such that the filter material 13 of said filter elements 11 is momentarily expanded or dilated, whereby particles adhering to the outer side thereof are shaken off and brought to fall downwards and out through the opening i0.

The filter material 13 is momentarily expanded or dilated by folding outwards in the folds 14 during the blow of compressed air, and folded inwards in said folds 14 after said blow.

The abovementioned cleaning procedure is controlled

by opening of the magnetic valves 23 during and at cer- tain times, which might occur during and/or after opera- tion of the filter device.

The compressed-air device 22 may include a tube in which compressed air is stored and this tube can be moun- ted at the top on the inner side of the door 20. Down below on the inner side of the door 20 there may be pro- vided brackets 26, to which flattened end portions 27 of the cleaning tubes 24 are attached by means of mounting screws 28 which may be threaded through holes in said end portions 27.

At the back in the filter cabinet 2 itself there is provided, in the embodiment shown, a pre-separator 31 in which coarse particles 32 are separated from the air stream 17 mixed up with particles before said air stream reaches the filter elements 11 in the filter chamber 3.

This pre-separator 31 is a dynamic dust separator or dust collector, in which the air stream 17 mixed up with particles preferably is accelerated to high speed and deflected such that the coarse particles 32 are depo- sited or precipitated by mass forces generated during the deflection.

The rear wall 6 of the filter chamber 3 can define a front wall of the pre-separator 31, a rear wall 33 of the filter cabinet 2 can define a rear wall of the pre- -separator 31 and the opposing side walls 7 of the filter cabinet 2 can define opposing side walls of the pre- -separator 31.

The pre-separator 31 includes an air guide means 34 which can connect to the rear wall 33 of the filter cabi- het 2 such that an air inlet part 35 is defined between said air guide means 34 and said rear wall 33. The air guide means 34 further defines an air through-flow part 36 in upper portions of the pre-separator 31, and beneath the air inlet part 35 and air through-flow part 36 there is provided a separating space 37 in which coarse partic- les 32 are separated from the air stream 17.

The particle-loaded air stream 17 flowing in through the air inlet pipe 4 is brought to flow downwards through the air inlet part 35 and out of said air inlet part 35 in downwards direction through a downwardly directed nozzle 39 defined by the air guide means 34, preferably together with the rear wall 33. Since the air guide means 34 includes a member 38 which is directed obliquely down- ward towards the rear wall 33 and located upstream rela- tive to the nozzle 39, the through-flow area of the air inlet part 35 diminishes in downwards direction, which means that the flow speed of the particle-loaded air stream 17 increases when it flows downwards from the nozzle 39 into the separating space 37. This separating space 37 is shaped to deflect the air stream 17, within an area 40 beneath the nozzle 39, in upwards direction into the air through-flow part 36 such that said separa- tion of the coarse particles 32 occurs within said area 40.

The air stream 17, free from coarse particles 32 but still loaded or mixed up with finer particles, is brought to flow through the air through-flow part 36 and there- from through a through-flow opening 41 in the rear wall 6 into the filter chamber 3. Therein, the air stream 17 mixed up with particles is brought to flow as stated in- to the filter elements 11, whereupon finer particles ad- here to or deposit on the outer sides thereof.

The nozzle 39 preferably includes one or more, e. g. four, air guide members 42, e. g. air guide plates, which extend in parallel with the particle-loaded air stream 17 flowing through the nozzle 39. These air guide members 42 divide the nozzle 39 in a number of, e. g. five, smaller nozzles 43 for the air stream 17, such that a less tur- bulent flow is obtained beneath the nozzle 39, in and/or downstream thereof. Said smaller nozzles 43 extend in parallel with each other and they preferably have a grea- ter length than width.

In order to obtain a particularly advantageous sepa- rating effect in the separating space 37, the nozzle 39

may have a fixed width or diameter C. Furthermore, there may be provided an air guide screen 44 in the separating space 37, on the rear wall 6, and extend backwards there- from. The air guide screen 44 is preferably mounted such that its rear edge 45 is located at a level beneath the nozzle 39, situated a distance D therefrom. Additionally, an air gap 46 having a width E is preferably defined between the rear edge 45 of the air guide screen 44 and front parts of the nozzle 39. By dimensioning the width C, distance D and width E in a certain proportion to each other and to the speed of the particle-loaded air stream 17 leaving or exiting the nozzle 39, said advantageous separating effect can be obtained.

The air guide means 34 may be located on a cover 47 defining or forming part of the upper side 9 of the filter cabinet 2, such that said air guide means 34 is removed with said cover 47. Hereby, the inner members of the pre- -separator 31 are released in a simple manner by removing the cover 47.

In fig. 3, an embodiment of the filter device is shown, wherein at least two units 1 with filter chambers 3 are placed on top of each other. In this embodiment, the pre-separator 31 may be common to both units 1 or several units 1. If the pre-separator 31 forms part of the filter cabinet 2, parts 31a of the pre-separator 31 may be loca- ted behind each filter chamber 3 and when the units 1 are placed on top of each other, said parts 31a define toget- her a pre-separator 31 which is common to both units 1.

In the pre-separator 31, the air inlet part 35 may form part of the upper unit 1 and there may be a through-flow opening 41 to the filter chamber 3 only in the upper unit 1 or eventually in every unit 1.

The invention is not limited to the embodiments de- scribed above and illustrated in the drawings. As alterna- tives not described, please note that the expression"air streams"may include air-containing gases of another type than welding fume, grinding dust or similar, from which

particles need to be filtered or separated, the pre-sepa- rator 31 may be located outside the filter cabinet 2, the air guide means 34 may be a completely circular tube which is e. g. embedded between the walls 6 and 33, the air guide screen 44 may be constructed otherwise than shown, there may be more than two units 1 placed on top of each other, which together define a common pre-separa- tor 31, the nozzles 43 may be defined by other air guide members than air guide plates 42 and the nozzle 39 need not be located above the separating space 37, but may be oriented otherwise in relation thereto.