FIELD OF THE INVENTION 
       [0001]    The present invention relates to filters used in air filtration generally and is more specifically related to pulse-jet filter elements and filter-cage assemblies, and to cartridge filters, of the type typically used in industrial applications. 
       BACKGROUND OF THE INVENTION 
       [0002]    Filter elements in use have cylindrical filter bags, mounted onto cylindrical wire cages, which are installed by means of snap-ring fittings in the housing. Air is drawn through the filter bags during the filtration process. In pulse-jet filter applications, the air flow direction is reversed during the cleaning cycle. 
         [0003]    The filter bags are closed on the bottom and open on the top. The dust laden air is drawn through the filter bag from an exterior of the filter bag, and the dust particles are retained on the surface of the filter bag. The air-to-cloth ratio, dust particle size, electrostatic properties of dust and filter cloth, can velocity, dust retention and cake-release of a given filter material and the filtration surface texture determine the efficiency of a filter. Pulse-jet filter bags are limited by the length and circumference of the filter bags and the can velocity due to the small open space between the circular filter bags and bag housing. Improving efficiency by increasing the size of the filter housing, or increasing the number of filter bags, is expensive and is often impractical. The circular, sewed-on bottoms often protrude beyond the sides of the filter elements and become obstacles that catch and collect dust, which later impedes dust release in the cleaning cycle, and creates a negative impact on the can velocity at the bottom of the filter elements. 
         [0004]    Similarly, cartridge filters have the disadvantage of being limited in temperature resistance and in length, which typically may not exceed two meters. High differential pressure causes the pleats to concave at the tips of the pleats, thereby reducing the effective filter area at this point. In addition, dust and other undesirable particles build up on the outside between the pleats and, in some cases, completely clog the cartridge filter. The extruding rim of the bottom plate of the cartridge filter is frequently an obstacle that catches and retains dust, preventing the collected dust from falling down into the hopper. 
       SUMMARY OF THE INVENTION 
       [0005]    The filter has radially extending fingers or rays that yield a filter bag having a propeller-shaped cross section. The present invention significantly increases the filtration surface while using the same number of filter elements at the same gas volume, and also using the same bag diameter and bag length of conventional pulse-jet filter bags. Additionally, the structure of the invention reduces the air to cloth ratio, can velocity and differential pressures, which leads to significant efficiency gains with respect to emission values and energy consumption. 
         [0006]    Radially extending portions of the filter elements lend a propeller shape to the device of the invention. The sides of the bag are formed to allow an easy collection of dust. and the propeller-shaped bottom of the bag has no obstacles that accumulate falling dust, thus enhancing dust-cake release during the cleaning cycle. By substituting normal pulse-jet filter elements with frusto-conical, propeller-shaped moulded bottom filter elements in a jet-filter bag-housing, this invention substantially increases the filter capacity of the bag housing, while simultaneously significantly reducing energy consumption and operating costs. The number of filter elements, as well as space needed for the new filter housing, is substantially reduced. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a 6-ray frusto-conical propeller-shaped embodiment of the fabric filter used in a filtration process. 
           [0008]      FIGS. 2 ,  3 ,  4 , and  5  are cross-sectional views of different embodiments of frusto-conical propeller-shaped bottoms projected into the top open circle of the corresponding filter element (cell plate and gasketing size), demonstrating the frusto-conical form of each of these frusto-conical, propeller-shaped filter bags. 
           [0009]      FIG. 4   a  demonstrates additional open space gained between the bottoms of frusto-conical filter elements in comparison to using cylindrical filter elements. 
           [0010]      FIG. 6  is a cross-sectional view of the basic support element before forming to a required size (diameter of cage), with standardized ring and 8 standardized rays with eyes. 
           [0011]      FIG. 7  is a cross-sectional view of the ring and one ray with eye of  FIG. 6  bent 90° to the diameter size of the frusto-conical propeller-shaped support cage. 
           [0012]      FIG. 8  is a plan view of two typical, but dimensionally different, frusto-conical propeller-shaped filter elements with accompanying inner propeller-shaped support cages. 
           [0013]      FIG. 9  is a plan view of a frusto-conical propeller-shaped filter element with an integrated flange to replace a typical pleated cartridge filter element. 
           [0014]      FIG. 10  is a perspective view of a propeller-shaped moulded bottom or boot. 
           [0015]      FIG. 11  is a side view of the top of a 8-ray frusto-conical propeller-shaped filter element without pleats and with ring cuff. 
           [0016]      FIG. 12  is a side view of the top of a 6-ray frusto-conical propeller-shaped filter element with box pleats and snap-band cuff. 
           [0017]      FIG. 13  is a side view of the cylindrical top part of a 8-ray frusto-conical propeller-shaped filter element with a ring cuff, which is preferred when using interior venturis. 
           [0018]      FIG. 14  is a side view of the top part of a 8-ray frusto-conical propeller-shaped filter element, whereby a cylindrical cuff with a snap-band is sewed onto a propeller-shaped filter element with box pleats, which is preferred when using interior venturis. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]      FIG. 1  is a perspective view of a 6-ray frusto-conical propeller-shaped embodiment of filter bag  10 . The filter bag is shown as used during a filtration process under negative differential pressure. A horizontal, circular band  12  may surround the filter bag. The filter bag  10  is comprised of filter cloth  11  which has a circumference that is materially larger than the circumference of the circular band  12 . The circular band is preferred to be circumferentially attached in regular intervals by fasteners such as staples  13  or seams, or other techniques to the filter fabric  11 , thereby holding the filter bag  10  permanently in a propeller shape  40 . This design allows the filter cloth  11  known in the art, such as needled felt, non-woven material, woven material, warp-knitted, circular knitted, micro-filament or micro-fiber fabric, fiberglass and/or woven metal or monofilament filter material to form over the longitudinal wire pairs  31  of the inner cage  30  into a propeller shape during filtration, and hold this position during the reversal of air or gas flow during the cleaning cycle. 
         [0020]    In a preferred embodiment, the propeller-shaped filter bag  10  is placed over a frusto-conical propeller-shaped support cage  30 . This support cage is preferred to be formed by supports  32  and pairs of laterally offset frusto-conical longitudinal wires  31  that form the frusto-conical cage.  FIG. 8 . The longitudinally, evenly spaced supports  32 , as shown in the embodiment of  FIG. 6 , are comprised of a ring  33  with radially-outwardly-in-equal-distance-arranged rays with eyes  34 , which are bent to the proper diameter needed ( FIG. 7 ), and may be connected by blind rivets  35  to the washers  36  holding together each pair of wires  31  and so forming a ray  14  of the frusto-conical propeller pattern. The filter bag as shown ends in a moulded propeller-shaped bottom  15  ( FIG. 10 ), and may be installed by means of a ring  16 , snap-band  17  or other fixture integrated in a top portion of the assembly, as shown in  FIGS. 11-14 . 
         [0021]      FIG. 2  shows a propeller-shaped metal end piece  37  of a 4-ray cage embodiment of the invention. This will support, for example, a 110/95 mm  frusto-conical propeller shaped bag  10  rendering, for example, about 54% more filtration area than a 110 mm  pulse-jet filter bag of the same length as previously known. 
         [0022]      FIG. 3  shows an embodiment of the invention having a propeller-shaped metal end piece  37  of a 6-ray cage. A 140/115 mm  frusto-conical propeller-shaped bag  10  of this embodiment offers about 64% more filtration area in comparison to a 140mm  pulse-jet filter bag  44  of equal length as previously known. 
         [0023]      FIG. 4  shows an embodiment of the invention having a propeller-shaped metal end piece  37  of a 8-ray cage. A 150/130 mm  frusto-conical propeller-shaped bag  10  of this embodiment renders 100% more filtration surface than a 150 mm  pulse-jet filter bag  44  of the same length as previously known. 
         [0024]      FIG. 4   a  shows a foot print demonstrating the additional open space  41  gained when replacing 150 mm  pulse-jet filter bags previously known with 150/130 mm  frusto-conical propeller-shaped filter bags  10  having moulded propeller-shaped bottoms  15 .  FIG. 4 . In this embodiment, the gain of additional open space between the bags is 35%, reducing the can velocity by the same percentage, with a constant gas volume. By cutting the air to cloth ratio in half, the differential pressure will be reduced by about 40% or more. A mean diameter  42  of 100 mm  in connection with the propeller form  40  significantly reduces the particle migration from row to row of filters during the cleaning cycle. As a result, cleaning pressure can be lowered, for example, to as low as 2.2 bar, which will lead to higher filtration efficiency, and reduce particle-migration after the pulse-jet cleaning cycle. Energy savings of as much as 50% or more yields substantial economic gains, less wear-and-tear on the filter elements and, therefore, extended life-span of the filter elements. 
         [0025]      FIG. 5  shows a propeller-shaped metal end piece  37  of a 9-ray cage for a 170/145 mm  frusto-conical propeller-shaped filter bag  10  rendering 100% more filtration area in comparison to a 170 mm  pulse-jet filter bag  44  of equal length. 
         [0026]      FIG. 6  shows a support element  32  comprised of a ring  33  with 8 radially outwardly and equally-spaced-apart rays with eyelets  34 . For all known bag diameters  44  of this embodiment, the same ring  33  and the same rays with eyelets  34  can be used, which will be bent to the required diameter as shown in  FIG. 7 . 
         [0027]      FIG. 7  discloses an embodiment comprising pairs of laterally offset and frusto-conical longitudinal wires  31  that are connected by means of blind rivets  35 . The wire pairs are separately made to length by spot welding special washers  36  in-equal-distance to both wires. 
         [0028]      FIG. 8  shows an embodiment of two typical frusto-conical propeller-shaped filter elements  10  without box-pleats  18  at the top, and with moulded propeller-shaped bottoms  15 . One filter element is a 4-ray version with snap band cuff  17  and one filter element is an 8-ray version with ring cuff  16 . The corresponding frusto-conical propeller-shaped support cage  30  is shown beside its filter element. 
         [0029]      FIG. 9  shows an embodiment of a frusto-conical propeller-shaped cartridge filter element  20  without box-pleats  18  at the top, with top ring cuff  16  and with a moulded propeller-shaped bottom  15  mounted on an exchangeable frusto-conical, propeller-shaped support cage  30  with a top flange  38 . The much higher air to cloth ratio of this cartridge filter element will more than compensate for the smaller filtration area in comparison to a star-like pleated cartridge filter. The moulded propeller-shaped bottom  15  and the drop-off sides  43  reduce the can velocity, improve the cleaning efficiency, and will not allow the filter element to clog up as is so often experienced with conventional pleated cartridges with agglomerating dust, e.g. wet paper dust, and dust from plasma welding or laser cutting. 
         [0030]      FIG. 10  shows an embodiment of a typical 8-ray moulded propeller shaped bottom or boot  15  with open drop-off sides  43 . This boot can be economically produced and attached to the main filter body, such as by sewing a horizontal seam  21 .  FIG. 9 . 
         [0031]      FIG. 11  shows a preferred version of a top without pleats  18 , and having a ring cuff  16 . 
         [0032]      FIG. 12  shows another version of a top with box pleats  19  and snap-band cuff  17 . 
         [0033]      FIG. 13  shows an embodiment showing cylindrical top with ring cuff  16  and inner overlap seams  22  as recommended for interior venturis. 
         [0034]      FIG. 14  shows a cylindrical top with snap-band cuff  17  sewed with a horizontal seam  21  onto a propeller-shaped filter corpus with box pleats  19 , which is preferred for interior venturis. 
         [0035]    In the preferred embodiment shown in  FIGS. 9 and 11 , the filter cartridge and filter bag are without pleats at the top and have a moulded bottom. Both filter elements are open at the top and closed on the bottom. The bottom piece of the frusto-conical propeller-shaped fabric filter is moulded in the exactly required radially extending propeller form and may be secured by fasteners such as metal clamps or staples. 
         [0036]    Polyurethane, silicone or other mouldable material may be used to form the moulded bottom of the filter bags. The very top of a preferred filter bag is not propeller-shaped, but is cylindrical. Snap-band rings with double-beaded gasketing, felt strips, rings or other conventional installation methods may be employed for mounting the filter bags. The open top can therefore be made to fit any standard cell plate and gasketing size. 
         [0037]    The filter media may be chosen from many materials used for industrial dust filtration, and may be needled felt, non-woven, woven material, warp-knitted, circular knitted fabric also out of micro-filament yarn and fibers, fiberglass and/or metal-fabrics, and others. The length and diameter of the filter bag is variable in accordance with the needs in line of the filter housing dimensions. A preferred filter element of the invention comprises filter media which can withstand temperatures up to 280° C. 
         [0038]    Interior venturis or special types of filter material (e.g. glass, woven, light-weight-spun-bond material) may make it desirable to deviate from the preferred pleat-free open top form and to use a box-pleat design sewed onto a tubular top  FIG. 14  or an inner overlap-seam design, forming a tubular top.  FIG. 13 . 
         [0039]    Bands on the exterior of the filter bag may be used to give the filter element the multi-propeller-blade shape, and also prevent the filter bag from expanding too much during the pulse-jet cleaning cycle. The bands are placed horizontally around the filter bag at calculated intervals along the length of the bag. The smaller outer-circumference of the filter element is created by matching marks on the band to proportionally-greater-distanced marked points on the bags. These marks are then joined together by sewing, stapling, or other techniques. 
         [0040]    The filter bag must have an inside support, which may be a cage. To meet the needs of the individual application, this cage is preferred to be constructed of rigid materials such as steel or stainless steel, whereby all steel parts can be treated or coated as required. The cage may have, for each propeller-blade, a pair of wires forming a frusto-conical shape along the length of the cage from the riveting points of the supports, which are placed at regular intervals down the length of the cage. The filter material is preferred to touch the cage only along the edges of the wires, which minimizes mechanical abrasion and also allows full use of the filter material as a filtration surface. 
         [0041]    The filter cages may be constructed as a single piece or they may be delivered in an assembly set, to be mounted together on the location site with fasteners such as rivets. Long cages may be constructed in two pieces, with tubular inner joints, to be assembled during installation. 
         [0042]    The invention as disclosed in this embodiment may be used to replace cartridge filters, with the definitive advantage of having drop-off sides that have no obstacles to catch and retain dust and polluted particles. The cage with the preferred top flange is reusable when the frusto-conical, propeller-shaped fabric filter bag is replaced. 
         [0043]    The filter bag according to the invention achieves a filtration surface which is 1.5 to 2 times as large as a conventional pulse-jet filter bag of the same top diameter and length. Moreover, when the resulting filter bag is stabilized by a frusto-conical, propeller-shaped support cage  30  and circular bands  12 , the filter material  11  is moved more gently at lower pressure during the pulse-jet cleaning cycle. The frusto-propeller shaped design has less inner-bag air volume (as in comparison to conventional cylindrical filter elements) which reduces the compressed air and energy consumption needed during the pulse-jet cleaning cycle, permitting that the frusto-propeller-shaped filter bags and cartridges can be cleaned less aggressively in comparison to conventional pulse-jet filter elements. 
         [0044]    The advantages gained in using the preferred filter elements are: 
         [0000]    lower differential pressures
 
lower can velocity
 
less particulate migration after pulse cycle
 
meeting highest emission standards due to better fine dust retention
 
enhanced dust-release due to propeller form, flex motion and slick drop-off sides  43 
 
mountable frusto-conical propeller-shaped support cage  30  substantially facilitates and reduces the cost of transportation
 
This frusto-conical propeller shaped filter bag  10  with a moulded propeller-shaped bottom or boot  15  according to the invention, will substantially lower energy cost substantially, increase the capacity and usable life span of filter elements, thereby reducing operating cost.
 
         [0045]    Thus the many aforementioned objects and advantages are most effectively attained. Although preferred embodiments of the invention have been disclosed, and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims. 
       LIST OF ELEMENTS NUMBERED IN THE DRAWINGS: 
       [0000]    
       
           10  Frusto-conical propeller-shaped filter bag 
           11  Filter cloth or filter fabric 
           12  Circular band 
           13  Band attachment (seam, staple and others) 
           14  Ray or propeller blade 
           15  Moulded propeller-shaped bottom or boot 
           16  Ring cuff 
           17  Snap-band cuff 
           18  Top without pleats 
           19  Box-pleats 
           20  Frusto-conical propeller-shaped cartridge filter element 
           21  Horizontal seam 
           22  Inner over lap seam 
           30  Frusto-conical propeller-shaped support cage 
           31  Frusto-conical longitudinal wire pair 
           32  Support element 
           33  Ring 
           34  Ray with eye 
           35  Blind rivet 
           36  Washer 
           37  Propeller-shaped metal end piece with holes for blind rivets 
           38  Top flange 
           40  Propeller form 
           41  Open space 
           42  Mean diameter 
           43  Drop-off side 
           44  Top bag diameter, cell plate fit
A filter element is longitudinally formed in a frusto-conical shape The filter element has a plurality of radially extending members that form a propeller shaped cross-section, and a propeller-shaped moulded bottom that enhances dust fall from the exterior. A frusto-conically-shaped inner cage facilitates the shape of the filter element.