Wire filter cage

An improved filter support structure for supporting filter media. The support structure includes two sections removably coupled together with an improved coupling assembly. The first section has a cross section presenting a first width spaced apart from a second width, the second width being less than the first width. The coupling assembly includes an element carried by the second section, and presents an engagement width that is greater than the second width and less than or equal to the first width such that the element may be shiftably received within the first section at the first width, and can be removably engaged at the second width.

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 structures. 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.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, a plurality of filter elements are depicted as installed in an air filtration unit11. The air filtration unit11broadly includes plenum enclosure12, base frame14, air filtration assembly15, filtered exhaust duct16, and air intake duct17. Air filtration unit11is 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 ladder18, surrounded by safety cage20, leads up to catwalk22, providing access to plenum enclosure12through access door24. Filtered exhaust duct16and air intake duct17may be attached to and integral with plenum enclosure12. Air filtration assembly15is positioned within plenum enclosure12. Plenum enclosure12is positioned on base frame14.

Base14may include frame30, legs32, and braces34. Base14may vary in size and proportion, depending on the size of the plenum enclosure12to be supported on base14.

Base14can 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 enclosure12may be a large, generally cylindrical structure, ranging from twenty-five to fifty feet in height. Plenum cover or roof36is positioned over plenum enclosure12. Dust collection funnel38tapers downwardly toward dust discharge mouth40. The funnel38is positioned underneath plenum enclosure12, residing within the space below base frame30and between legs32and braces34.

Referring toFIGS. 2,3and4, The air filtration assembly15is contained mainly within plenum chamber42. Air filtration assembly15comprises an air pressure pump44, pressurization nozzle input duct46, nozzle arm48, and numerous filter elements50having air permeable hanging filter media bags or socks52surrounding filter cages54. In a typical large capacity air handling system, often employing multiple air filtration units11, as many as twenty thousand filter bags52and twenty thousand wire filter cages54may be utilized. Air pressure pump44is connected to nozzle duct46. Nozzle arm48is positioned beneath nozzle duct46, and has suction nozzles56opening in a downwardly direction, directed toward bag mouths58of filter elements50.

Filter media bags or socks52are attached to bag mouths58. Bag mouths58are positioned below bag nozzles56. Bag mouths58rest on and are supported by bag hanger deck62. Filter media bags52are positioned over and supported by wire filter cages54. Unfiltered air enters air filtration unit11through intake duct17so as to be processed through air filtration assembly15. Filtered air is expelled from air filtration unit11through filtered exhaust duct16.

Referring now toFIGS. 2 and 3, filter element55is shown ready for fastening to hangar deck62. Bag mouth58and filter bag52may be held in position against bag hanger deck62by O-rings78,78awhich are positioned inside over-deck bead80and under-deck bead82of bag52. O-rings78,78asnap into place so as to restrain filter bag58and provide a tight seal, so that no particulate or filtered matter enters plenum chamber42. Bag mouth60is securely fastened to bag hanger deck62through mounting hole79using washer81and bolt83.

Referring now toFIG. 4, another embodiment of bag mouth58′ is illustrated. InFIG. 4, bag mouth58′ is positioned on filter cage54such that longitudinal wires84terminate below the surface of mouth rim77. Bag mouth58′ is positioned on bag hanger deck62, and is simply pressed into place and engages with bag hanger deck62by friction. No bolt is utilized to hold bag mouth58′ to bag hanger deck62.

Thus, a ventilation system11includes a plurality of filter elements50. Each filter element includes a filter cage54and a filter bag52. As will be appreciated, the filtration unit11depicted inFIG. 1can 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 toFIG. 5, an improved wire filter cage120in accordance with the present invention includes a first section122and a second section124. First section122presents a male end126and second section124presents a female end128. Each section122,124includes a plurality of circular or oval form wires130connected by a plurality of generally parallel longitudinal wires132. First section122may further include a large junction form wire134at the end thereof. First section122includes two guides136presenting male end126adapted to be received into female end128of second section124. Wire guides136can be made out of wire or another suitable material having sufficient elastic memory to return to a relaxed state after deformation.

Each wire guide136includes a pair of generally parallel legs137, and a circular end139. As can be seen inFIG. 5, the wire guides136are positioned at opposed ends of the generally race track in cross-section wire filter cage section122.

Wire guides136, form wires130and longitudinal wires132are 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 bags52.

Generally, a wire filter cage120will 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 toFIG. 5, in operation, wire filter cages120are assembled from a first section122and a second section124by aligning the first section122and the second section124coaxially and pressing the two sections together. In the assembly process, as depicted inFIGS. 5 and 13, wire guides136engage form wires130to secure the joint. In this embodiment of the invention wire guides136engage form wires130primarily by friction and outward biasing force.

A worker disassembling a wire filter cage120generally works from above the wire filter cages120. The worker lifts a wire filter cage120to expose the entire length of first section122and secures second section124to prevent it from falling. The worker then grasps first section122and pulls parallel to the longitudinal axis thereof, in order to overcome the retaining force created by wire guides136. Once the retaining force is overcome, first section122and second section124separate. Second section124is then lifted from its position below the worker. If a wire filter cage120employs more than two sections, the disassembly process is repeated for each succeeding pair of sections.

Referring toFIGS. 6 and 7, an alternative embodiment of wire guide138is depicted. Hairpin wire guide138is preferably formed of a single piece of stiff resilient wire and has two generally parallel legs140and a semicircular end142. Semicircular end142is of the same diameter as the separation of legs140. Referring toFIG. 7, hairpin wire guide138may further include offset144. Forming will generally be accomplished by bending but may also be accomplished by other techniques.

Hairpin wire guide138provides 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.

In operation, rabbit ear wire guide146is engaged and disengaged in a similar manner to hairpin wire guide138. Rabbit ear wire guide146provides a somewhat greater frictional retentive force than hairpin wire guide138due to the diverging nature of diverging leg segments150.

Referring toFIG. 10, the embodiment of wire guide136is depicted in greater detail. Keyhole wire guide136includes generally parallel legs137and circular end139. The arc of circular end139extends to greater than about one hundred eighty degrees and less than about 300 degrees. Circular end139forms a retaining head.

FIG. 11shows further detail of wire guide136. Wire guide136presents a grip angle162and a grip range164. Grip range164extends from closed joint ideal location166to acceptable joint location168. Wire guide136may also be modified into another embodiment136′ as depicted inFIG. 22by removing a portion of the wire at the end of circular end160.

Again referring toFIG. 5, female end128of second section124comprises a generally race track-shaped wire130having opposed parallel sides159, and opposed generally circular ends160. The diameter of the retaining head139is sized such that it can be received between the two parallel sides159of wire130of female end128of section124, but can be snapably retained within its respective form wires130of female end128. As can also be seenFIG. 5, the wire guides136are positioned in first section122such that the retaining heads139are received within the form wires130of female end128of second section124, when the two sections are joined together. Because the retaining heads139are of a larger diameter than the distance between the sides of form wire130of female end128of the second section124at their initial contact point, the retaining heads139are urged inwardly as the two sections are pushed together, where the distance between the wires159is greater, and then received through the female end128. Once received through the female end128, the retaining heads139snap outwardly behind form wire130, thus engageably retaining the first section122with the second section124.

Note that a cross sectional view of any wire filter cage120has 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 guides136, for instance, of first section122are inserted into second section124, form wires130of second section124urge the wire guides136towards each other. Once the semicircular head139is received past the form wire proximate the female end128of section124, the guides136are urged back to their rest position and snapably couple the first and second sections together. The other embodiments act in a similar manner.

FIG. 14depicts another embodiment of wire guide136as employed in the present invention. Serpent head wire guide170includes serpent-shaped head172and generally parallel legs173. Serpent-shaped head172presents a widening taper174followed by a narrowing taper175.

In operation, serpent head wire guide170is operated in a manner similar to the foregoing embodiments. The serpent head wire guide170displays ease of insertion because of widening taper174and a retention force similar to keyhole wire guide156because of narrowing taper175. The serpent head wire guide170, however, requires more complex tooling to manufacture.

As depicted inFIG. 15arrowhead wire guide176generally includes arrowhead-shaped head178and generally parallel legs179. Arrowhead wire guide176presents shallow widening taper180and steep narrowing taper181. Arrowhead wire guide176may also include offset182as depicted inFIG. 16. Referring toFIG. 17, Arrowhead wire guide176may be constructed with a variety of arrowhead angles184. A variety of angles184similarly may also be applied to serpent head wire guide170.

In operation, arrowhead wire guide176is operated in a manner similar to the foregoing embodiments. The arrowhead wire guide176displays ease of insertion and a retention greater than keyhole wire guide156because of shallow widening taper180and steep narrowing taper181. The arrowhead wire guide, however, requires more complex tooling to manufacture.

Referring toFIGS. 18 through 21, another embodiment of the wire guide186is depicted. This embodiment of the wire guide186is particularly well adapted for use with wire filter cages192of 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. 19,20and21depict wire guide186as utilized with wire filter cages192of circular cross section.

Referring toFIGS. 21,24,27,28and29an alternative embodiment of wire guide186′ is depicted. Guide wire186′ is similar to guide186, but includes additional curvatures. In this embodiment the head or end of the wire guide186′ includes curve200such that the wire guide186′ contacts form wire130in an approximately radial orientation. Wire guide186′ further includes engagement (or bridging) portion194which provides an abutment surface195, acute portion196and curve200.

Curve200may be applied to any of the previously described hairpin wire guide138, rabbit ear wire guide146, keyhole wire guide156, serpent head wire guide170, arrowhead wire guide176or circular cage wire guide186.FIG. 24depicts curve200as applied to circular cage wire guide186′. Referring toFIG. 25curve200may be replaced with bend202or double bend204. Other configurations will be readily appreciated by those skilled in the art and the illustrated embodiments should not be considered to be limiting.FIGS. 26,27,28and29further depict curve200as applied to circular cage wire guide186′.FIGS. 28 and 29also exemplify a reticulation of structural members comprising circular form wires130connected by a plurality of generally parallel longitudinal wires132. The wires defining first side410and second side420of the reticulation and enclosing flow passageway440. Form wire130exemplifies an inner peripheral edge430bounding the flow passageway440.

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 wire130of female end128of second section124. 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 toFIG. 11, grip range164extends from closed joint ideal location166to acceptable joint location168. Grip angle162provides a force tending to hold the connection between first section122and second section together even if the wire guide is not engaged with form wire130to the closed joint ideal location166.

Referring toFIGS. 23 and 24, it is notable that in embodiments of the wire guide including curve200, 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 wires130than wire guides without curve200. As depicted inFIG. 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 wires130. These are specifically contemplated to be embodiments of the present invention.

The multi-sectional nature of the filter cage120hereof, 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.

FIG. 30depicts a wire filter cage192of circular cross section including guide wire186and racetrack stiffener206. Racetrack stiffener206includes curved ends208and straight sides210. Curved ends208are fixedly connected to form wires130preferably by resistance welding. Racetrack stiffener206may be secured to form wires130by other joining methods as well. Racetrack stiffener206serves to stiffen form wire130to reduce flexion and increase the retaining force with which wire guide136grips form wire130.

FIG. 31depicts a wire filter cage192of circular cross section including four wire guides136. Utilizing four wire guides136instead of two increases the retention force with which wire guides136removably secure first section122to second section124.

Referring toFIG. 32, a filter cage section having four wire guides136is depicted engaged to a filter cage section including four wire guides136and double racetrack stiffener212. In this embodiment of the invention, two racetrack stiffeners206that are at substantially right angles to one another are secured to form wires130of circular cross section. In this embodiment, double racetrack stiffener212stiffens form wire130as well as providing for engagement with wire guides136.

Referring toFIG. 33, double racetrack stiffener212is depicted as engaged with two wire guides136. Note that in this embodiment of the invention, wire guides136do not engage directly with form wires130.

FIG. 34depicts yet another embodiment of the invention. Here, wire filter cage120includes a second section124including cloverleaf stiffener214. Cloverleaf stiffener214, as depicted, includes four U-shaped members216. Cloverleaf stiffener may also be formed with three U-shaped members216or a greater number than four U-shaped members216. In this embodiment of the invention, the U-shaped members216are joined to longitudinal wires132, preferably by resistance welding, though other welding techniques or other attachment approaches may be employed. Either racetrack stiffener206, double racetrack stiffener212or cloverleaf stiffener214may be secured either to form wires130or to longitudinal wires132.

In another embodiment of the invention depicted inFIGS. 35 and 36, wires guides136further include at least one, but preferably two engagement notches218. Engagement notches218may be sized and positioned to receive form wires130, racetrack stiffener206, double racetrack stiffener212or cloverleaf stiffener214. The presence of engagement notches218significantly increases the holding force when wire guides136are engaged to form wires130or racetrack stiffener206, double racetrack stiffener212or cloverleaf stiffener214. In one test, the use of engagement notches218increased the pulling force required to separate first section122from second section124from 50 pounds to greater than 160 pounds.

Referring toFIG. 37, another embodiment of the invention is depicted. Independent wire guide assembly220generally includes independent form ring222and two or more double-ended wire guides224. Double-ended wire guides224are secured to independent form ring222substantially at the center226of double-ended wire guides224. The ends of double-ended wire guides224may be shaped in a similar fashion to any other wire guide discussed in this application.

In operation, independent wire guide assembly220is inserted into a first section122of wire filter cage120and the other end of independent wire guide assembly220is inserted into second section124of wire filter cage120.

Referring toFIG. 38, another embodiment of the invention including another wire guide end shape is depicted. Acute angle wire guide228generally includes tapered shaft portion230and engagement portion232. Engagement portion232includes tapered tip234. Tapered tip234may have a closed end236or an open end238. Engagement portion232meets tapered shaft portion at acute angle portion240.

In operation, acute angle wire guide engages form wire130or racetrack stiffener206, double racetrack stiffener212or cloverleaf stiffener214at acute angle portion240, providing great retention force.

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.