Abstract:
An air filtration unit, includes a filter cartridge ( 4 ) of the filtration bag ( 6 ) type, the bags ( 6 ) being arranged vertically and held extended by appropriate fixing elements ( 16, 17 ), between two support structures ( 12, 13 ). The upper ends ( 15 ) of the bags ( 6 ) are fixed to an upper support structure ( 13 ), in the form of a perforated sheet and the lower ends thereof ( 14 ) are fixed to a lower support structure ( 12 ), in the form of a grille. According to the invention, the fixing elements ( 16, 17 ), for the filtration bags ( 6 ), are embodied to permit the tensioning of the bags ( 6 ) at the upper end ( 15 ) thereof. The invention further relates to a particular method for assembly of a filtration bag within a unit as above, a tool for tensioning bags, embodied to be suitable for the unit.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an improvement made to air filtration plants fitted with filter sleeves. It also concerns an assembly process of a filter sleeve within the plant, as well as a tool for tensioning said sleeves suited to said plant. 
   BACKGROUND OF THE INVENTION 
   Plants of such type are described for example in the documents EP-0 343 061 and FR-2 514 669. 
   The corresponding apparatus ensure extraction of elements in suspension in a drawn atmosphere of particular premises, for example in production, treatment or storage facilities of powdery products, or of certain industries causing the release of waste such as very volatile sawings or chippings. 
   Such apparatus are formed conventionally of three main elements generally centred on the same vertical axis: 
   an upper body, cylindrical or truncated, wherein the air to be de-dusted arrives tangentially, 
   a settling chamber, in the form of a funnel or cylindrical, arranged beneath the upper body; this chamber is fitted with waste recovery means at the lower section thereof, and 
   a filter cartridge formed of vertical filter sleeves extending between said settling chamber and the cover of the apparatus where the filtered air is exhausted. 
   The corresponding filter sleeves are generally cylindrical in shape and they are made conventionally of a material such as needled felt. Such sleeves are stretched vertically within the filter cartridge between two adapted supporting structures: their lower ends are interconnected on a lower supporting structure, for example in the form of a grid, which is situated above the settling chamber, and which provides access to the contaminated air on the outer side of the filter sleeves; their upper ends are interconnected to an upper supporting structure, generally in the form of a plate fitted with circular openings, for exhausting the air filtered. 
   The assembly of each filter sleeve within this kind of plant is described for example in the document U.S. Pat. No. 4,244,718. Such assembly consists first of all in interconnecting the upper end of the sleeves at one of the openings of the upper plate; such interconnection is obtained traditionally an integrated member in the form of a ductile ring (of &lt;&lt;snap ring&gt;&gt; type). 
   The lower end of the sleeves is then attached to the lower supporting structure; appropriate means are provided at this lower end for reliable tensioning of each sleeve. 
   By reason of the structure of the current filtration plants, the operator should be able to access the lower supporting structure to carry out most of the assembly and maintenance operations relative to the filter sleeves. 
   Still, the corresponding interventions are not really convenient because of the small space requirements encountered. Moreover, they are conducted in dusty and dirty environments; besides, they are not totally harmless to the operator further to the dusts in presence, in particular within the framework of items of equipment processing atmospheres with explosive or flammable characteristics. 
   SUMMARY OF THE INVENTION 
   The purpose of the present invention is to remedy these shortcomings while providing an air filtration plant whereof the original structure facilitates the assembly and maintenance operations for the out-call staff. 
   The air filtration plant, according to the invention, is of the type described above in that it includes a filter cartridge formed of filter sleeves stretched vertically; it is characterised in that the upper and lower fastening means of the filter sleeves are suited to enable adjustment of the tension of each sleeve at the upper end thereof. 
   The operator may consequently conduct most of the assembly and maintenance operations at the upper supporting structure of the sleeves, and this in a secured and little polluted atmosphere. 
   According to a particular provision of the invention, the fastening means of the upper end of the filter sleeves, at the upper supporting structure, consist of a add-on member in the form of a ductile ring; such add-on member is designed for a location within the sleeves once the latter have been attached to the lower supporting structure, and stretched, so as to hold said sleeves in this stretched condition by clamping against the contour of the openings of the upper supporting structure. 
   Preferably, the corresponding add-on ductile ring includes an annular groove extending over the external contour thereof, intended for being embedded on the internal contour of the openings of the upper supporting structure, so as to clamp the sleeves against these openings. 
   Preferably still, the upper end of the filter sleeves is fitted with a structural element for easier gripping thereof, manually or mechanically, in particular for a reliable tension thereof. 
   According to a particular embodiment, the corresponding structural element is in the form of a rigid collar integrated to the structure of the sleeve. 
   The filter sleeves may have a circular section constant over the whole length thereof; according to an embodiment variation, they may comprise an upper end portion generally truncated in shape, with an end rigid collar of diameter greater than that of the openings of the plateau. 
   This particularity enables the sleeves to run through the openings of the upper supporting structure more easily, from the cover of the apparatus, while avoiding any accidental fall of the whole sleeve into the filter cartridge. 
   According to another provision of the invention, the lower end of the filter sleeves is provided with a bottom cup, fitted with a protruding rod comprising a catching element; such catching element is designed for co-operating with a supporting profile of matching shape, provided at the lower supporting structure. 
   Preferably, the lower supporting structure includes at least one supporting profile, in the form of folded sheet metal, formed of a central part extending vertically, and whereof the upper end is extended by a return element extending over the whole length thereof. The corresponding return element is fitted with several open slots each letting through a rod for catching a sleeve and locating the catching element of said rod. 
   Preferably still, the upper end of the supporting profile(s) includes a return element formed of two parts forming a dihedron. One of said parts, designated &lt;&lt;horizontal section&gt;&gt;, extends at right angle or substantially at right angle from the upper end of the central part of the supporting profile; the other of said parts, designated &lt;&lt;tilted section&gt;&gt;, extends slantwise downwards. Such return element is fitted with a plurality of open slots each letting through a rod for catching a sleeve, the catching element of said rod being designed for a location beneath the horizontal section aforementioned. 
   The present invention also relates to a particular tensioning tool of filter sleeves, pour an air filtration plant as described above. 
   The corresponding tensioning tool includes: 
   a seating element intended for being located on the upper supporting structure of the plant, 
   a stretching means of the upper end of a filter sleeve, and 
   a means for manoeuvring the traction means. 
   Preferably, the manoeuvring means in question assist mechanically the driving of the traction means. 
   The manoeuvring means then consists advantageously of at least one gas, pneumatic or hydraulic jack-operated device; this or these manoeuvring means are arranged between the seating element and the traction means, so as to enable assisted manoeuvring thereof when being deployed. 
   Still according to a particular embodiment, the stretching means consist of generally U-shaped element, intended for location beneath an element in the form of a collar provided at the upper end of the sleeves. 
   The purpose of the present invention is still a particular assembly process of a filter sleeve within the air filtration plant, subject matter of the invention. Such process consists mainly: 
   in attaching the lower end of the filter sleeve, via an appropriate fastening means, to the lower supporting structure, 
   in tensioning the filter sleeve by a vertical upward traction, and 
   in attaching the upper end of the filter sleeve to the upper supporting structure via a suitable fastening means. 
   On the other hand, the invention also concerns a particular filter sleeve suitable to equip the air filtration plant described above, which sleeve includes a hooking member at its lower end, and a structural element for easier gripping thereof at its upper end. The structural element in question may be in the form of a rigid collar. 
   In a particular embodiment, the upper section of this filter sleeve is generally truncated in shape delineated by two rigid collars, the upper rigid collar having a diameter greater than that of the lower rigid collar. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     But the invention will still be illustrated, without being limited thereto, by the following description of a particular embodiment of an air filtration plant according to the invention, given solely for exemplification purposes, and illustrated by the appended drawings, wherein: 
       FIG. 1  is a schematic elevation view of an air filtration plant fitted with a filter sleeves, according to the invention; 
       FIG. 2  is a perspective view of a section of the plant of  FIG. 1 , detailing the fastening means of the lower end of a filter sleeve to the lower supporting structure; 
       FIG. 3  is a side view still detailing the fastening means of the lower end of a filter sleeve to the lower supporting structure; 
       FIGS. 4A ,  4 B and  4 C illustrate schematically the main steps for interconnecting the upper end of a sleeve to the upper supporting structure; 
       FIG. 5  is a side view showing an embodiment variation of the filter sleeves; 
       FIG. 6  is a perspective view of a tool suitable for tensioning the filter sleeves; 
       FIGS. 7A ,  7 B and  7 C are schematic views which illustrate the tensioning tool illustrated on  FIG. 6 , according to the main arrangement for stretching a filter sleeve according to the invention. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
   The air filtration plant represented as a schematic elevation view on  FIG. 1 , includes elements of circular shape which are centred on the same vertical axis, i.e. mainly:
         an upper body  1 , in the form of a cylindrical ferule, fitted with a tangential supply  2  of the air to be de-dusted;   a settling chamber  3 , here of truncated shape, arranged in the alignment and beneath the upper body  1 ; this chamber  3  includes in its lower section particle and/or dust recovery means, not represented, deposited thereon   a filter cartridge  4 , interconnected with the upper body  1  by means of a annular ring  5 ; this filter cartridge  4  includes a set of filter sleeves  6 , for example made of a material such as needled felt, possibly fitted with several reinforcement rings arranged over the length thereof.       

   The corresponding filter cartridge  4  extends for example substantially half in the upper body  1 , and the other half above this very corps  1 . The upper section of the filter cartridge  4  includes a cover  7 , fitted with an opening  8  for exhausting the filtered air; this cover  7  may be equipped with an automatic filter cleaning device  9 , conventional, well known in the technical field affected. 
   This filter cartridge  4  is delineated laterally, above the upper body  1 , by a cylindrical wall or shroud  10 ; it is delineated in its lower section, at the upper body  1 , by a shroud  11  in the form of a skirt which is intended to form a screen for protecting the lower section of the sleeves  6  arranged at the tangential supply  2  of the air to be de-dusted. 
   The cartridge  4  is still delineated by two supporting structures, one lower  12  and the other upper  13 , between which the filter sleeves  6  are held stretched vertically. 
   The lower supporting structure  12  is in the general form of a grid; it is situated above the settling chamber  3  and it is held in position by attachments  19  interconnected with the lower section of the skirt  11 . The upper supporting structure  13  is, for its own part, in the form of a plate fitted with a plurality of circular openings; it is arranged at the upper section of the cylindrical shroud  10 , attached conveniently. 
   The lower  14  and upper  15  ends of the filter sleeves  6 , are interconnected respectively with the supporting structures  12  and  13  by fastening means marked  16  and  17 . 
   According to the invention, such fastening means  16  and  17  are suited to enable tensioning of the sleeves  6  at the upper ends thereof  15 . 
   The fastening and tensioning means aforementioned enable particular cinematic assembly of the filter sleeves  6  within the filter cartridge  4 . Indeed, each of the sleeves  6  may be mounted in the plant according to the following procedure: 
   first of all, the lower end  14  of the sleeve  6  is interconnected with the lower supporting structure  12  by dint of the associated fastening means  16 ; 
   this sleeve  6  is then tensioned by a vertical upward traction exerted on its upper end  15 ; 
   the sleeve  6  held stretched is finally interconnected with one of the openings of the plate  13  by actuating the associated fastening means  17 . 
   For disassembly of the sleeves  6 , the operator should simply deactivate successively the fastening means  16  and  17 , in an order appropriate to the situation. 
   The fastening means  16 , for interconnection of the lower end  14  of the sleeves  6 , are adapted for being activated by an operator located at the upper supporting structure  13 ; and tensioning of the sleeves may also be realised at the upper supporting structure  13 . 
   Consequently, the out-call staff may then conduct all the maintenance operations, and notably the assembly/disassembly operations of the sleeves  6 , from said upper supporting structure  13 , and this in a clean environment or at least a little polluted environment. 
   Obviously, the operator may access such upper plate  13  by any appropriate means. Such access may in particular consist of a manhole, a pivoting vaulted cover or similar, for example provided in the upper cover  7 . 
   A particular embodiment of the fastening and tensioning means of the filter sleeves  6  is represented on  FIGS. 2 to 7 . 
   The fastening means  16  of the lower end  14  of the sleeves to the structure lower  12  are detailed on  FIGS. 2 and 3 ; they are implemented after running the sleeve  6  into one of the openings of the upper plate  13 . 
   First of all, it should be noted on  FIGS. 2 and 3  that the lower end  14  of the sleeve  6  is provided with a bottom cup  20 , conventional, fitted with a central rod  21  extending axially, and comprising at its end a catching element  22 ; such catching element  22  consists here of an element of nut-brake type, screwed on a thread provided on the end of the rod  21 . More generally, any type of particular hooking system, such as a single-block hook, a snap-on structure, magnet or other, arranged at the end of the rod  21  may be contemplated. 
   As can be noted on  FIGS. 2 and 3 , the lower supporting structure  12  is constituted of a plurality of parallel profiles  23 , attached to reinforcement  24  arranged at the lower end of the skirt  11 ; the attachment in question is realised by means of the linking plates  19 . 
   The supporting profiles  23  are made of folded sheet metal they are each constituted of a vertical central part  25  delineated by an upper end rim  26  and a lower end rim  27 . The lower end rim  27  is extended over its whole length by a return element  28  at right angle, for increased rigidity of the profile. 
   The upper end rim  26  is, for its own part, fitted with an upper return element  29 , in the form of a dihedron, formed of two sections marked  30  and  31 . The section  30  extends at right angle from the end  26  of the central part  25 , along a horizontal or substantially horizontal plane; the section  31  of the return element  29  extends the section  30  tilted downwards aforementioned. 
   As may be observed on  FIG. 2 , the return element  29  exhibits several open slots  32 , extending transversally over both sections  30  and  31  of said upper return element  29 . The end  33  of each slot  32  is generally V-shaped at the opening; the other end  34  only extends partially over the horizontal section  30  of the return element  29 . 
   The catching element  22  of the sleeves  6  is designed for co-operating with one of the slots  32  provided on the supporting profiles  23 . 
   When assembling a sleeve  6  on the supporting profile  23 , the rod  21  is located at the flared end  33  of the slot  32  affected, the catching element  22  being arranged beneath the end of the section  31  of the return  29 ; the V-shape of this end  33  facilitates the insertion of the rod  21  into the slot  32 . 
   It then suffices for the operator to exert an upward traction to the sleeve  6  for final positioning, as may be observed in detail on  FIG. 3 . Indeed, the tilted shape of the section  31  of the return element  29  enables the catching element  22  to travel up to a position against the lower face of the horizontal section  30 . Moreover, this tilted section  31  of the upper return element  29  forms a kind of stop, intended for holding in position the catching element  22  against the horizontal section  30 , when the sleeve  6  is held stretched; this tilted section  31  also enables to prevent disconnection of the catching element  22  in case of slight release of the sleeve  6 . 
   To deactivate the attachment of the lower end  14  to the lower supporting structure  12 , the operator simply needs to suppress the tension exerted upon the sleeve  6  and to disengage the rod  21  from the open slot  32 . 
   As indicated above, the corresponding hooking operation may be realised from the upper zone of the cartridge  4 , at the cover  7 . To do so, the operator holds the upper end  15  of the sleeve  6  and initiates slight oscillation of this sleeve so as to locate the catching element  22  into one des slots  32 . It should be understood that the attachment of the lower end of the sleeves  6  to the lower supporting structure  12  takes place quite simply and without requiring any particular tooling. 
   Once the lower end of the sleeve  6  has been attached, the assembly of said sleeve  6  continues with the tensioning thereof and with the attachment of its upper end  15  to the plate fitted with openings  13 . The corresponding fastening means  17  are detailed on  FIGS. 4A to 4C . 
   First of all, on these  FIGS. 4A to 4C , it should be noted that the upper end  15  of the sleeve  6  is fitted with two rigid collars, one lower  35  and the other upper  36 , delineating a cylindrical upper end portion  37 , at which the fastening means  17  are intended for location; these rigid collars  35  and  36  are in the form of rings of plastic or metallic material integrated to the structure of the sleeve  6 , for example in sewn sheaths. 
   The fastening means  17  are in the form of a add-on ductile ring  38 , of &lt;&lt;snap ring &gt;&gt; tube, whereof the external contour is fitted with an annular groove  39 ; such member  38  is intended for clamping and holding the upper end portion  37  of sleeve  6  on the plate fitted with openings  13 , as will be described more in detail below. 
   After locating the upper end  15  of the sleeve  6  in the affected opening  40  of the plate  13  ( FIG. 4B ), said sleeve  6  is stretched by an upward traction; the assembly is finalised by locating the annular member  38  within the sleeve  6  stretched, as illustrated on  FIG. 4C . 
   To do so, the annular flexible member  38  inside the upper end portion  37  of the sleeve  6 , so that the annular groove  39  is placed on the contour  41  of the orifice  40 ; a circular zone of the upper end portion  37  of the sleeve  6  is then clamped or pinched between said ductile member  38  and the contour  41  of the orifice  40  of the plate  13 . The flexibility characteristics of the annular member  38  are adapted for optimum clamping and holding of the upper end of the sleeve  6  stretched. 
   This type of interconnection ensures efficient tightness between the sleeve  6  and the plate fitted with openings  13  this still prevents the risks of rotation of the sleeve  6 . Moreover, the close contact between the sleeve  6  and the plate fitted with openings  13  ensures efficient electrostatic conductibility, enabling to reduce the risks of electrostatic discharge without requiring the use of conductibility beads. 
   It appears from this description, in relation to  FIGS. 2 to 4 , that the assembly and the disassembly of the filter sleeves  6 , within the cartridge, may take place quickly and simply from the upper cover  7 . 
   More generally, the fastening means  16  and  17  of the sleeves  6  are suited to enable tensioning of said sleeves by acting solely upon their upper end  15 , without acting upon their lower end  14 , contrary to the plants of this kind know to the state of the art. 
   According to a derived embodiment, illustrated on  FIG. 5 , the filter sleeve  6  may include an upper end portion  37 , arranged between the rigid collars  35  and  36 , generally truncated in shape. In this case, the upper rigid collar  36  has a greater diameter than that of the lower rigid collar  35 , but also in relation to the diameter of the openings  40  of the upper supporting structure  13 ; the remainder of the length of these sleeves, in the alignment of the lower rigid collar  35 , is cylindrical, of diameter smaller than or equal to that of the openings  40  aforementioned. 
   The assembly of such a sleeve within the plant involves running the lower end thereof through an opening  40  of the upper supporting structure  13 , and this from the upper cover  7 . 
   After fastening its lower end  14  to the supporting structure  12 , the sleeve  6  is stretched and fastened at its upper end portion  37  to the upper supporting structure  13 . It appears that by reason of the particular diameter of the upper rigid collar  36 , the operator conducting the assembly or the disassembly of these sleeves cannot drop them by accident, in particular in the lower section of the filter cartridge  4 . 
   The tensioning of the upper section of the filter sleeves  6  may take place manually or assisted by an appropriate tooling. 
   A particular embodiment of a mechanical tensioning means of the sleeves is represented on  FIGS. 6 and 7 . 
   The corresponding tensioning tool  45  ( FIG. 6 ) is constituted of the following main elements: 
   a seating  46 , intended to rest on the plate fitted with openings  13 , 
   a traction structure  47 , adapted for co-operating with the upper end  15  of a sleeve  6 , and 
   a manoeuvring system  48 , intended for assisting the displacement of the traction structure  47 . 
   The seating  46  includes two longitudinal girders  50  extending parallel to one another, and whereof the ends  51  and  52  are connected by crosspieces  53 ,  53 ′. The ends  51  of each of the longitudinal girders  50  are fitted each with a vertical stanchion  54 , on which the traction structure  47  is hinged. 
   This traction structure  47  is here constituted of a set of two arms  56 , supporting a gripping member  57  of the sleeve  6 . One of the ends of these arms  56  is hinged along a horizontal axis  58  on the vertical stanchions  54 ; the other end of these arms  56  is connected by a crosspiece  59  whereon an element in the form of a sleeve  60  fitted with two hooking structures  61  is hinged; both these hooks  61  are arranged so as to co-operate with the crosspiece  53  provided on the side of the end  52  of the longitudinal girders  50 . 
   The gripping member  57  is hinged on the arms  56 , along an axis  62  parallel to the pivoting axis  58  aforementioned. Such gripping member  57  is formed of two lateral walls  63 , co-operating with the arms  56  by lugs  64 , connected by a generally U-shaped floor  65 ; moreover, a crosspiece  66  is provided between the lateral walls  63  for increased global rigidity. 
     FIG. 6  also shows the manoeuvring system  48  of the traction structure  47 , here illustrated in the form of two gas-operated springs; these gas-operated springs  48  extend each from a longitudinal girder  50  of the seating element  46  to the manoeuvring arm  56  arranged opposite. 
     FIGS. 7A to 7C  illustrate the use of the tool  45  for tensioning a sleeve  6 . 
   As can be noted on  FIG. 7A , the tensioning tool  45  is first of all located at an opening  40  of the upper supporting structure  13 ; more precisely, the longitudinal girders  50  of the seating  46  are located on both sides of the corresponding opening  40 . 
   The hooks  61  co-operate with the crosspiece  53 , situated on the end  52  side of the longitudinal girders  50 ; the gas-operated springs  48  of the manoeuvring system are then in a retracted position. 
   Moreover, the gripping member  57  is toggled around its axis  62 , in order to release the central space and facilitate the passage of the upper end  15  of the sleeve  6  through the opening assembly  40 . 
   Once the end  15  of the sleeve  6  has been sufficiently stretched upward manually, the gripping member  57  is pivoted so as to adopt a resting position, i.e. with the floor element  65  horizontally ( FIG. 7B ). 
   When the gripping member  57  pivots round the axis  62 , the U-shaped floor element  65  is located just beneath the lower face of the collar  36 . 
   The sleeve  6  is then stretched by manual deactivation of the hooks  61  ( FIG. 7C ). Indeed, the gas-operated springs  48  impart a thrust and they can deploy automatically; this cause the arms  56  to be hinged around their axis  58 , and consequently vertical or substantially vertical displacement upwards of the gripping member  57 . 
   The upper collar  36  is then stretched upwards, over a few millimeters or a few centimeters, in order to stretch the sleeve  6  correctly. 
   The gas-operated springs  48  hold the corresponding tension without involving the operator&#39;s intervention; the latter may then locate the ductile ring  38  so as to clamp the upper portion  37  of the sleeve  6  against the contour  41  of the opening  40 , as described previously in relation to  FIG. 4C . 
   To separate the tool  45  from the sleeve  6 , the operator actuates downwards the sleeve  60 , so as to re-actuate the hooks  61 ; he may then cause the gripping member  57  to pivot easily and thereby to clear the upper collar  36 . The tool  45  may then be displaced at another opening  40  to stretch another sleeve. 
   This tool  45  enables to assist the operator in tensioning the sleeves  6 ; once such a tool has been located correctly, the operator should also deactivate the hooks  61 , and the gas-operated springs  48  stretch the sleeve automatically. When this sleeve  6  is stretched, the operator may concentrate on the location of the lock ring  38  without adjusting the tension of the sleeve. 
   The strength of the gas-operated springs  48  will be adapted to provide each of the sleeves with regular and constant tension, for example of the order of 40 kg. 
   It will be noted that the filter sleeves of the plant may have sections others than circular ones, for example oval or polygonal; the form of the openings  40  of the upper plate  13  will then be adapted consequently.