Patent Publication Number: US-6905529-B2

Title: Wire Filter cage

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The current application is a continuation of U.S. patent application Ser. No. 10/645,859 filed on Aug. 21, 2003, entitled “Wire Filter Cage,” now U.S. Pat. No. 6,790,250, which is a continuation of U.S. patent application filed on Dec. 31, 2001, entitled “Wire Filter Cage” having Ser. No. 10/137,319, now U.S. Pat. No. 6,626,970, which claims the benefit of U.S. Provisional Application No. 60/258,674, filed Dec. 29, 2000, and U.S. Provisional Application 60/295,333, filed on Jun. 1, 2001, all of which are hereby incorporated herein in their entirety by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to an air filtration system suitable for use within the ventilation system of a building. More particularly, the invention relates to improved filter cages used for supporting elongated filtration bags or socks within such a filtration system. 
   BACKGROUND OF THE INVENTION 
   Air filtration systems utilized in large ventilation systems often employ banks of elongated filtration bags or socks supported by wire filter cage assemblies. The filtration bags are positioned over the filter cages and remove particulates from the air circulated through the bag. The wire filter cages support the bags and prevent the bags from collapsing as air is drawn through the bags. Filter media exclude particulates from passing through the bag along with the air, and the particulates accumulate on the outside of the bags as air is drawn through the bag and filter cage combination. 
   Wire filter cages supporting filtration bags are commonly used in large-scale filter assemblies. A large-scale filter assembly structure includes a large enclosure. The large enclosure is divided by a horizontal partition plate that separates an upper clean air compartment from a lower dirty air compartment. The partition plate is formed with a large number of openings arranged in a pattern. Each such opening supports a wire filter cage and its associated fabric filter bag. Thus, the air flow passes from the lower dirty air compartment through the suspended filter bags and wire filter cages through the openings in the partition plate and into the upper clean air compartment. 
   Filter bags are periodically cleaned by shaking or by creating a backflow of air from the inside of the filter bags outward. After an extended period of use it becomes necessary to remove the filter cages and filter bags from the partition plate in order to replace the filter bags. If a one-piece filter cage is employed it is necessary that the upper clean air compartment have sufficient overhead height for the entire length of the filter cage to be accommodated. Wire filter cages can be as long as 26 feet. Thus, it is preferred, with lengthy filter cages, that the filter cages be partitioned into two or more sections to allow for a shorter overhead height in the clean air compartment. This shorter overhead height can result in large cost savings in material and construction of large filter assemblies. 
   Fine dust can form an explosive mixture with air. Dust collectors are thus vented to prevent an accumulation of fine dust. Larger collector volume requires a greater vent area. A reduction in overhead height and consequently volume in the upper compartment leads to a lower venting cost and associated operating cost. 
   A variety of techniques have been used to connect multiple sections of wire filter cages. Wire filter cage section connections should be secure and easily assembled and disassembled, preferably without tools. In addition, it is desirable that the inner connections be made without leaving any exposed wire ends or other sharp. Fabric filter bags are relatively vulnerable. If they are snagged on exposed wire ends they may be torn thereby causing particulate leaks and requiring replacement of the bags sooner than would otherwise be necessary. 
   It is also desirable that wire filter cage sections be assembled without the need for fine motor dexterity. Workers replacing filter bags and handling wire filter cages wear heavy protective clothing including heavy gloves to protect them. Thus, it would be beneficial if wire filter cage sections could be assembled and disassembled without the need for fine manipulation. 
   U.S. Pat. Nos. 5,173,098 and 3,747,307 are example of wire filter cage assemblies having exposed ends that may tear filter bags. Other prior art approaches also may expose wire ends, which may cause damage to fabric filter bags. 
   The approach to connecting wire filter cage sections disclosed in U.S. Pat. No. 5,173,098, issued to Pipkorn, reveals a connection technique utilizing two sheet metal sleeves and two wire clips. This approach provides a secure interconnection that is relatively easy to assemble and disassemble, however it utilizes two sheet metal sleeves which add expense and two wire clips which require relatively fine manipulation to connect. In addition, the presence of the two sheet metal sleeves reduces the surface area available for filtration by inhibiting air flow. 
   It would be desirable to have a multi-section wire filter cage that can be easily assembled and disassembled without the need for tools, and that minimized potential damage to fabric filter bags from exposed wire ends. Further it is desirable that the wire filter cage that could be easily manipulated by gloved hands. 
   SUMMARY OF THE INVENTION 
   The present invention in large measure solves the above-indicated problems by providing a new structure and technique for connecting wire filter cage sections. The present invention includes formed wire guides to create a snap latch joint. The wire guides protrude from the interior of a first wire filter cage section. The wire guides are inserted into the open end of a second wire filter cage section to join the sections. When the two sections are assembled together on a common axis, the resistance to bending of the wire guides presses the ends of the wire guides against the annular rings of the second wire filter cage, thus aligning the two cages axially and holding the two cages snugly together. 
   The present invention reduces the overall costs of assembling wire filter cage joints by elimination of sheet metal sleeves. Better welds may be achieved and there is no need for arc welding of the joints. The ability to use resistance welding equipment to assemble the joints eliminates the need for buffing of welding flash thereby reducing cost. The wire guides do not need adjustment of the spread of these assemblies prior to assembling wire filter cage sections. The use of wire guides also eliminates the need for any additional latching or any retaining assembly in the joint. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cutaway perspective view of a large-scale filter assembly that can utilize a plurality of wire filter cages in accordance with the present invention; 
       FIG. 2  is a partial perspective view illustrating the fastening of a filter element within a filter assembly; 
       FIG. 3  is a partial, side sectional view taken along line AA of  FIG. 2 ; 
       FIG. 4  is a partial perspective view illustrating an alternative fastening of a filter element within a filter assembly; 
       FIG. 5  is a perspective view of two sections of a wire filter cage in accordance with the present invention; 
       FIG. 6  is a plan view of one embodiment of a wire guide in accordance with the present invention; 
       FIG. 7  is an elevational view of the wire guide depicted in  FIG. 6 ; 
       FIG. 8  is a plan view of an alternate embodiment of a wire guide in accordance with the present invention; 
       FIG. 9  is an elevational view of the wire guide depicted in  FIG. 8 ; 
       FIG. 10  is a plan view of another embodiment of a wire guide in accordance with the present invention; 
       FIG. 11  is a detail view of the wire guide depicted in FIG.  10  and depicting grip angle and grip range; 
       FIG. 12  is a partial elevational view of a wire filter cage including two wire guides; 
       FIG. 13  is a sectional view of a wire filter cage including two wire guides; 
       FIG. 14  is a plan view of an alternate serpent head embodiment in accordance with the present invention; 
       FIG. 15  is a plan view of an alternate arrowhead embodiment of the present invention; 
       FIG. 16  is an elevational view of the arrowhead embodiment depicted in  FIG. 15 ; 
       FIG. 17  is a plan view depicting alternate angular embodiments of the arrowhead embodiment of the invention; 
       FIG. 18  is a plan view of another embodiment of the wire guide adapted for use with circular filter cages; 
       FIG. 19  is a partial plan view of two circular filter cage sections joined with the wire guide embodiment of  FIG. 18 ; 
       FIG. 20  is a sectional view taken along section line BB of  FIG. 19 ; 
       FIG. 21  is a sectional view taken along section line CC of  FIG. 19 ; 
       FIG. 22  is an alternate embodiment of the wire guide depicted in  FIG. 10 ; 
       FIG. 23  is a sectional view of a wire filter cage assembly utilizing an alternate embodiment of a wire guide; 
       FIG. 24  is a sectional view of a wire filter cage assembly utilizing an alternate embodiment of a wire guide; 
       FIG. 25  is a sectional view of a wire filter cage assembly utilizing two alternate embodiments of the wire guide; 
       FIG. 26  is a perspective view of a wire filter cage assembly utilizing the embodiment of the wire guide depicted in  FIG. 24 ; 
       FIG. 27  is a perspective view of the wire guide depicted in  FIG. 24 ; 
       FIG. 28  is a perspective view of a wire filter cage assembly utilizing the embodiment of the wire guide depicted in  FIG. 24 ; and 
       FIG. 29  is a perspective view of a wire filter cage assembly utilizing the embodiment of the wire guide depicted in FIG.  24 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a plurality of filter elements are depicted as installed in an air filtration unit  11 . The air filtration unit  11  broadly includes plenum enclosure  12 , base frame  14 , air filtration assembly  15 , filtered exhaust duct  16 , and air intake duct  17 . Air filtration unit  11  is utilized, for instance, in power or nuclear plants, coal dumping facilities, grain handling facilities and buildings where refining operations may take place. Typical ventilation systems used in these environments may range in height from fifty to one hundred feet. An access ladder  18 , surrounded by safety cage  20 , leads up to catwalk  22 , providing access to plenum enclosure  12  through access door  24 . Filtered exhaust duct  16  and air intake duct  17  may be attached to and integral with plenum enclosure  12 . Air filtration assembly  15  is positioned within plenum enclosure  12 . Plenum enclosure  12  is positioned on base frame  14 . 
   Base  14  may include frame  30 , legs  32 , and braces  34 . Base  14  may vary in size and proportion, depending on the size of the plenum enclosure  12  to be supported on base  14 . Base  14  can be made of a variety of high strength, durable materials such as structural steel. Those of skill in the art will recognize that a variety of materials may be employed without departing from the scope of the present invention. 
   Plenum enclosure  12  may be a large, generally cylindrical structure, ranging from twenty-five to fifty feet in height. Plenum cover or roof  36  is positioned over plenum enclosure  12 . Dust collection funnel  38  tapers downwardly toward dust discharge mouth  40 . The funnel  38  is positioned underneath plenum enclosure  12 , residing within the space below base frame  30  and between legs  32  and braces  34 . 
   The air filtration assembly  15  is contained mainly within plenum chamber  42 . Air filtration assembly  15  comprises an air pressure pump  44 , pressurization nozzle input duct  46 , nozzle arm  48 , and numerous filter elements  50  having air permeable hanging filter media bags or socks  52  surrounding filter cages  54 . In a typical large capacity air handling system, often employing multiple air filtration units  11 , as many as twenty thousand filter bags  52  and twenty thousand wire filter cages  54  may be utilized. Air pressure pump  44  is connected to nozzle duct  46 . Nozzle arm  48  is positioned beneath nozzle duct  46 , and has suction nozzles  56  opening in a downwardly direction, directed toward bag mouths  58  of filter elements  50 . 
   Filter media bags or socks  52  are attached to bag mouths  58 . Bag mouths  58  are positioned below bag nozzles  56 . Bag mouths  58  rest on and are supported by bag hanger deck  62 . Filter media bags  52  are positioned over and supported by wire filter cages  54 . Unfiltered air enters air filtration unit  11  through intake duct  17  so as to be processed through air filtration assembly  15 . Filtered air is expelled from air filtration unit  11  through filtered exhaust duct  16 . 
   Referring now to  FIGS. 2 and 3 , filter element  55  is shown ready for fastening to hangar deck  62 . Bag mouth  58  and filter bag  52  may be held in position against bag hanger deck  62  by O-rings  78 ,  78   a  which are positioned inside over-deck bead  80  and under-deck bead  82  of bag  52 . O-rings  78 ,  78   a  snap into place so as to restrain filter bag  58  and provide a tight seal, so that no particulate or filtered matter enters plenum chamber  42 . Bag mouth  60  is securely fastened to bag hanger deck  62  through mounting hole  79  using washer  81  and bolt  83 . 
   Referring now to  FIG. 4 , another embodiment of bag mouth  58 ′ is illustrated. In  FIG. 4 , bag mouth  58 ′ is positioned on filter cage  54  such that longitudinal wires  84  terminate below the surface of mouth rim  77 . Bag mouth  58 ′ is positioned on bag hanger deck  62 , and is simply pressed into place and engages with bag hanger deck  62  by friction. No bolt is utilized to hold bag mouth  58 ′ to bag hanger deck  62 . 
   Thus a ventilation system  11  includes a plurality of filter elements  50 . Each filter element includes a filter cage  54  and a filter bag  52 . As will be appreciated, the filtration unit  11  depicted in  FIG. 1  can accommodate conventional filter units, filter units in accordance with the present invention, or a combination of conventional filter units and units in accordance with the present invention. 
   Referring to  FIG. 5 , an improved wire filter cage  120  in accordance with the present invention includes a first section  122  and a second section  124 . First section  122  presents a male end  126  and second section  124  presents a female end  128 . Each section  122 ,  124  includes a plurality of circular or oval form wires  130  connected by a plurality of generally parallel longitudinal wires  132 . First section  122  may further include a large junction form wire  134  at the end thereof. First section  122  includes two guides  136  presenting male end  126  adapted to be received into female end  128  of second section  124 . Wire guides  136  can be made out of wire or another suitable material having sufficient elastic memory to return to a relaxed state after deformation. 
   Each wire guide  136  includes a pair of generally parallel legs  137 , and a circular end  139 . As can be seen in  FIG. 5 , the wire guides  136  are positioned at opposed ends of the generally race track in cross-section wire filter cage section  122 . 
   Wire guides  136 , form wires  130  and longitudinal wires  132  are preferably joined by resistance welding though other joining methods may be employed. Whatever joining method is employed, it is desirable that the finished product be smoothly finished to prevent snagging or damage to filter bags  52 . 
   Generally, a wire filter cage  120  will be formed of metal wires. However, it is specifically contemplated that the invention disclosed here may be used with any type of filter cage or filter support. Examples include but are not limited to filter cages made from plastics, composites and perforated sheet materials. 
   Referring to  FIG. 5 , in operation, wire filter cages  120  are assembled from a first section  122  and a second section  124  by aligning the first section  122  and the second section  124  coaxially and pressing the two sections together. In the assembly process, as depicted in  FIGS. 5 and 13 , wire guides  136  engage form wires  130  to secure the joint. In this embodiment of the invention wire guides  136  engage form wires  130  primarily by friction and outward biasing force. 
   A worker disassembling a wire filter cage  120  generally works from above the wire filter cages  120 . The worker lifts a wire filter cage  120  to expose the entire length of first section  122  and secures second section  124  to prevent it from falling. The worker then grasps first section  122  and pulls parallel to the longitudinal axis thereof, in order to overcome the retaining force created by wire guides  136 . Once the retaining force is overcome, first section  122  and second section  124  separate. Second section  124  is then lifted from its position below the worker. If a wire filter cage  120  employs more than two sections, the disassembly process is repeated for each succeeding pair of sections. 
   Referring to  FIGS. 6 and 7 , an alternative embodiment of wire guide  138  is depicted. Hairpin wire guide  138  is preferably formed of a single piece of stiff resilient wire and has two generally parallel legs  140  and a semicircular end  142 . Semicircular end  142  is of the same diameter as the separation of legs  140 . Referring to  FIG. 7 , hairpin wire guide  138  may further include offset  144 . Forming will generally be accomplished by bending but may also be accomplished by other techniques. 
   Hairpin wire guide  138  provides ease of assembly and disassembly but is limited to applications requiring primarily alignment and a low retention force. It displays relatively low weak side axial stability. 
     FIGS. 8 and 9  depict another embodiment of wire guide  146 . Rabbit ear wire guide  146  generally includes parallel leg segment  148 , diverging leg segment  150  and rounded end  152 . Referring to  FIG. 9 , rabbit ear wire guide  146  may further include offset  154 . 
   In operation, rabbit ear wire guide  146  is engaged and disengaged in a similar manner to hairpin wire guide  138 . Rabbit ear wire guide  146  provides a somewhat greater frictional retentive force than hairpin wire guide  138  due to the diverging nature of diverging leg segments  150 . 
   Referring to  FIG. 10 , the embodiment of wire guide  136  is depicted in greater detail. Keyhole wire guide  136  includes generally parallel legs  137  and circular end  139 . The arc of circular end  139  extends to greater than about one hundred eighty degrees and less than about 300 degrees. Circular end  139  forms a retaining head. 
     FIG. 11  shows further detail of wire guide  136 . Wire guide  136  presents a grip angle  162  and a grip range  164 . Grip range  164  extends from closed joint ideal location  166  to acceptable joint location  168 . Wire guide  136  may also be modified into another embodiment  136 ′ as depicted in  FIG. 22  by removing a portion of the wire at the end of circular end  160 . 
   Again referring to  FIG. 5 , female end  128  of second section  124  comprises a generally race track shaped wire  130  having opposed parallel sides  159 , and opposed generally circular ends  160 . The diameter of the retaining head  139  is sized such that it can be received between the two parallel sides  137  of wire  130  of female end  128  of section  124 , but can be snapably retained within its respective form wires  130  of female end  128 . As can also be seen  FIG. 5 , the wire guides  136  are positioned in first section  122  such that the retaining heads  139  are received within the form wires  130  of female end  128  of second section  124 , when the two sections are joined together. Because the retaining heads  139  are of a larger diameter than the distance between the sides of form wire  130  of female end  128  of the second section  124  at their initial contact point, the retaining heads  139  are urged inwardly as the two sections are pushed together, where the distance between the wires  159  is greater, and then received through the female end  128 . Once received through the female end  128 , the retaining heads  139  snap outwardly behind form wire  130 , thus engageably retaining the first section  122  with the second section  124 . 
   Note that a cross sectional view of any wire filter cage  120  has at least a first width and a second width. Even a circular cross section has a greatest chord which is the diameter and a plurality of lesser chords all of which are less in linear dimension than the greatest chord. The guides of the present invention all have significant memory, such that, when urged out of their rest position they are biased to return to the rest position. When the wire guides  136 , for instance, of first section  122  are inserted into second section  124 , form wires  130  of second section  124  urge the wire guides  136  towards each other. Once the semicircular head  139  is received past the form wire proximate the female end  128  of section  124 , the guides  136  are urged back to their rest position and snapably couple the first and second sections together. The other embodiments act in a similar manner. 
     FIG. 14  depicts another embodiment of wire guide  136  as employed in the present invention. Serpent head wire guide  170  includes serpent shaped head  172  and generally parallel legs  173 . Serpent shaped head  172  presents a widening taper  174  followed by a narrowing taper  175 . 
   In operation, serpent head wire guide  170  is operated in a manner similar to the foregoing embodiments. The serpent head wire guide  170  displays ease of insertion because of widening taper  174  and a retention force similar to keyhole wire guide  156  because of narrowing taper  175 . The serpent head wire guide  170 , however, requires more complex tooling to manufacture. 
   As depicted in  FIG. 15  arrowhead wire guide  176  generally includes arrowhead shaped head  178  and generally parallel legs  179 . Arrowhead wire guide  176  presents shallow widening taper  180  and steep narrowing taper  181 . Arrowhead wire guide  176  may also include offset  182  as depicted in FIG.  12 . Referring to  FIG. 17 , Arrowhead wire guide  176  may be constructed with a variety of arrowhead angles  184 . A variety of angles  184  similarly may also be applied to serpent head wire guide  170 . 
   In operation, arrowhead wire guide  176  is operated in a manner similar to the foregoing embodiments. The arrowhead wire guide  176  displays ease of insertion and a retention greater than keyhole wire guide  156  because of shallow widening taper  180  and steep narrowing taper  181 . The arrowhead wire guide, however, requires more complex tooling to manufacture. 
   Referring to  FIGS. 18 through 21 , another embodiment of the wire guide  186  is depicted. This embodiment of the wire guide  186  is particularly well adapted for use with wire filter cages  192  of circular cross section. Those skilled in the art will recognize that the cage may take many different arcuate or polygonal cross-sections without departing from the scope of the present invention.  FIGS. 19 ,  20  and  21  depict wire guide  186  as utilized with wire filter cages  192  of circular cross section. 
   Referring to  FIG. 24 , an alternative embodiment of wire guide  186 ′ is depicted. Guide wire  186 ′ is similar to guide  186 , but includes additional curvatures. In this embodiment the head or end of the wire guide  186 ′ includes curve  200  such that the wire guide  186 ′ contacts form wire  130  in an approximately radial orientation. Wire guide  186 ′ further includes engagement portion  194 , arcuate portion  196  and curve  200 . 
   Curve  200  may be applied to any of the previously described hairpin wire guide  138 , rabbit ear wire guide  146 , keyhole wire guide  156 , serpent head wire guide  170 , arrowhead wire guide  176  or circular cage wire guide  186 .  FIG. 24  depicts curve  200  as applied to circular cage wire guide  186 ′. Referring to  FIG. 25  curve  200  may be replaced with bend  202  or double bend  204 . Other configurations will be readily appreciated by those skilled in the art and the illustrated embodiments should not be considered to be limiting.  FIGS. 26 ,  27 ,  28  and  29  further depict curve  200  as applied to circular cage wire guide  186 ′. 
   It is noted that resistance to bending of the wire guides is a major factor in joint retention force. Grip angle is a smaller factor. Regardless of the shape of the wire guide employed, when assembled the wire guide grips a form wire  130  of female end  128  of second section  124 . The retention force of wire guides is a function of the spring constant of the wire, the preset width separating the two wire guides in a joint and the outside dimension of the retention head of the wire guide. The spring constant depends upon the diameter and metallurgical qualities of the wire employed. 
   Referring to  FIG. 11 , grip range  164  extends from closed joint ideal location  166  to acceptable joint location  168 . Grip angle  162  provides a force tending to hold the connection between first section  122  and second section together even if the wire guide is not engaged with form wire  130  to the closed joint ideal location  166 . 
   Referring to  FIGS. 23 and 24 , it is notable that in embodiments of the wire guide including curve  200 , the retention force of the wire guide is enhanced because the force vector created by the spring action is directed more nearly normal to form wires  130  than wire guides without curve  200 . As depicted in  FIG. 25 , it is noted that wire guide can be formed in other ways to acquire the desired angle of contact between wire guide and form wires  130 . These are specifically contemplated to be embodiments of the present invention. 
   The multi-sectional nature of the filter cage  120  hereof, and in particular the ease and reliability with which the sections can be snapped together and pulled apart, facilitate the conservation of space within filter housings. Because the length of the sections is less than the length of the whole, the upper, clean portion of filter housings can be reduced in height. 
   The present invention may be embodied in other specific forms without departing from the spirit of the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.