Abstract:
A sorbent type filter assembly (10) which is made by sequentially placing a first resilient perforated plate (40), a first retention filter (36), a sorbent bed (34), a second retention filter (38), a second resilient perforated plate (42), and a cover (14) within the cylindrical portion (16) of a canister shell (12). The cover (14) is forced downwardly to compress the sorbent bed (34) and to resiliently spring bias or stress the first resilient perforated plate (40). While the parts are held together under compression, an annular edge portion of the cylindrical shell is rolled into a circumferentially extending groove on the canister cover to hermetically and mechanically hold the parts together in their assembled and compressed relationship.

Description:
TECHNICAL FIELD 
     The present invention relates generally to filter assemblies, and more particularly to a sorbent type filter assembly for a respirator and a method of making the filter assembly. 
     BACKGROUND OF THE INVENTION 
     Sorbent type filter assemblies for respirators are well known in the art. The filter assemblies customarily have a sorbent bed formed from a granular material which could be, for example, activated charcoal. In order to prevent the sorbent bed from shifting during use, which shifting could lead to early breakthrough of noxious gases, it is customary to maintain the sorbent bed under compression. In a typical application this is achieved by providing a spring which is biased against a perforated plate or screen to hold the perforated plate or screen against a retention filter which is in turn biased into contact with the sorbent bed on one side, the other side of the sorbent bed also being retained by a retention filter and perforated plate or screen. 
     Sorbent bed filters may also be associated with particulate filters for filtering out airborne particles. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide a novel sorbent type filter assembly having a minimum number of parts and which can be handled in a normal manner without undue damage to the filter assembly. 
     More particularly, it is an object of the present invention to provide a sorbent type filter assembly which includes a sorbent bed disposed within the cylindrical portion of a canister shell, the sorbent bed being maintained under compression by retention means which includes a resiliently stressed perforated plate. 
     It is another object of the present invention to provide a method for assembling a sorbent type filter assembly. The method includes the steps of sequentially placing a first resilient perforated plate, a first retention filter, a sorbent bed, a second retention filter, a second resilient perforated plate and a cover within the cylindrical portion of a canister shell. The cover is forced downwardly to compress the sorbent bed and to resiliently spring bias or stress the first resilient perforated plate. While the parts are held together under compression, an annular edge portion of the cylindrical shell is rolled into a circumferentially extending groove on the canister cover to hermetically and mechanically hold the parts together in their assembled and compressed relationship. 
     The foregoing objects and other objects and advantages of this invention will become more apparent after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which one of the preferred forms of this invention is illustrated. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is an end view of a sorbent type filter assembly of this invention. 
     FIG. 2 is a sectional view taken generally along the lines 2--2 of FIG. 1. 
     FIG. 3 is the other end view of the filter assembly shown in FIGS. 1 and 2. 
     FIGS. 4, 5, and 6 illustrate sequentially a portion of the method of assembling the filter assembly shown in FIGS. 1, 2, and 3, FIG. 6 corresponding to the section indicated in FIG. 2. 
     FIG. 7 is an enlarged detail view of a portion of FIG. 2 as indicated in the drawings. 
    
    
     DETAILED DESCRIPTION 
     Referring first to FIG. 2, a cross section of a sorbent type filter assembly is illustrated, the assembly being indicated generally at 10. The filter assembly is formed from two exterior components which are a canister shell 12, formed from drawn aluminum or the like, and a canister cover 14, which is formed of a suitable injection moldable plastic. The plastic should have good dimensional stability, creep resistance, resistance to various chemicals, and good thermal characteristics. Examples of such plastics are certain types of ABS and polyphenylene oxides. The canister shell is provided with a generally cylindrical portion 16 and an end portion 18 provided with a passageway therein, which passageway may be in the form of a plurality of equally spaced apart relatively small apertures 20. The canister cover includes an integrally formed central fitting 22 provided with internal threads 24, the fitting providing a passageway for the egress of purified air from the canister. The canister cover is further provided with an axially extending peripheral portion 26. The peripheral portion is provided with a circumferentially extending V-shaped groove, best shown in FIG. 4, the V-shaped groove being provided with upper and lower ramp surfaces 28, 30, respectively. The parts are secured together by forming an annular edge portion 32 of the cylindrical portion 16 of the canister shell 12 into the V-shaped groove in a manner which will be more fully described below. 
     The filter assembly further includes a sorbent bed 34 which can be any one of a number of suitable compounds which are selected for filtering out various vapors and gases, one common form of sorbent bed being activated charcoal granules. Because the sorbent bed is of a granular material, it is necessary to maintain it between retention means. In the embodiment illustrated, the retention means includes a pair of oppositely disposed first and second retention filters 36, 38 respectively, and a pair of oppositely disposed first and second resilient perforated plates 40, 42, respectively. These plates, which may be formed from aluminum, are maintained in intimate contact with the retention filters and maintain the sorbent bed in a compressed state therebetween. The assembly may additionally include a particulate filter, and one such filter is indicated at 44 in FIGS. 2 and 7. It should be noted, however, that in some filter designs there may be no requirement for a particulate filter, and thus the particulate filter may be eliminated. In the design illustrated, when a particulate filter is employed, the periphery of the particulate filter will bear against the step 46 which is formed between the cylindrical portion 16 of the shell and its end portion 18. If no particulate filter is employed, the periphery of the first resilient perforated plate will bear against such step. An inhalation valve 48 may be also provided, the inhalation valve laying over the apertures 20 and being secured in place by a rivet 50. Finally, the filter assembly may be provided with a gasket 52 which is disposed within the central fitting 22 for insuring a proper seal between the fitting 22 and an inlet fitting on a respiratory device to which the central fitting may be secured. 
     It should be appreciated that in the operation of such a filter it is desirable that no noxious gases bypass the seam between the canister cover and the canister shell. It is also important that the sorbent bed 34 be maintained under compression to prevent it from shifting, which shifting could lead to an early breakthrough of noxious gases. Additionally, the filter should be capable of working in a wide variety of temperatures and to withstand temperature ranges from below 0° F. to well above 100°F., the thermal expansion and contraction not damaging the seam between the canister shell and the canister cover. It is also desirable that a minimal number of parts be employed in the construction to simplify the design of the filter assembly and to improve its reliability. These objectives have been achieved through applicant&#39;s novel design and method of assembly. Thus, when the parts are to be assembled, the canister shell is initially positioned so that the generally cylindrical portion 16 extends upwardly to its terminal edge 54, the portion initially being free of any indentations. This will permit the various parts to be assembled within the canister. The second resilient plate 42 is initially incorporated into the cover 14. This has been accomplished by providing an internal annular groove 56 within the peripheral portion 26, the second resilient perforated plate 42 being so sized that it can be force fit into the annular groove 56. To this end, it should be noted that the groove 56 is provided with a tapered leading surface 58 to facilitate the insertion of the plate 42 into the groove. The canister cover 14 is also provided with four equally spaced apart ribs 60, the lower surfaces of which lie in a plane which correspond to the planar surface of the groove 56 so that when the plate 42 is assembled within the cover, it is maintained in a planar condition. After the cover and perforated plate subassembly has been completed, it may be inserted into the canister shell. However, it is first necessary to assemble the particulate filter 44, if one is to be used, the first resilient perforated plate 40, the first retention filter 36, and the bed of sorbent material 34 into the canister shell. The bed may be placed in by any of a variety of techniques which are well known to those skilled in the art to achieve a level, uniform bed of an acceptable packing density. After the sorbent has been placed within the canister shell 12, the second retention filter 38 is then placed over the sorbent bed. At this time the parts are now ready to be finally assembled together and a bead of sealing compound 62 is placed on the lower ramp surface 30 of the V-shaped groove in the axially extending peripheral portion 26 of the canister cover 14. The cover is now placed within the open end of the canister shell and, acting through the second plate 42, bears against the second retention filter 38 and the material within the sorbent bed 34 to place it under compression. To this end, an axial force of 40 to 50 pounds is applied to the cover (in a design configuration having a diameter of approximately 5 inches) to maintain the sorbent bed under compression and, at the same time, to cause the unsupported central portion of the first resilient perforated plate to be bowed downwardly, as viewed in FIG. 2, to resiliently stress the perforated plate 40. While this force is being applied, the parts will be sealed together. To this end, a first roller (not shown) is run around the upper periphery of the assembly to force the annular edge portion 32 into the V-shaped groove until it attains the position illustrated in FIG. 5, thus forming a corresponding radially inwardly extending V-shaped surface 64 which is in intimate contact with the V-shaped groove in the peripheral portion of the cover to the extent permitted by the sealing compound 62. To complete the assembly operation another roller is rolled around the upper periphery of the assembly to force the terminal edge 54 into contact with a radiused upper edge 66 of the peripheral portion 26 of the canister cover while the surface 64 is maintained in contact with the V-shaped groove. The process outlined above provides a good mechanical and hermetic seal between the canister shell and the canister cover. It also causes the first resilient perforated plate 40 to maintain the sorbent bed 34 under compression after the compressive force to the cover 14 is released.