Abstract:
Apparatus and method for forming an axial flow filter element from a fan or sectorial shaped sheet having parallel curved ends, straight sides converging at an angle less than 180° and a plurality of curved ridges and valleys extending between the sides parallel to the curved ends. Holding wedges are inserted into the valleys in the upper side of the sheet while the latter is supported on a table. The pitch between the holding wedges is then reduced uniformly to reduce the radial length of the sheet. The sheet is then partially rounded into a semi-circular shape to increase the central angle of the sectorial shape sheet to as much as 180° by forcing the wider convex end of the reduced sheet toward a circular post centrally engaging the midpoint of the smaller concave end of the sheet. The partially rounded sheet, then is reformed to impart true circular arcs to the ridges and valleys by inserting reforming wedges into the valleys in one side of the sheet and sliding the wedges along those valleys along fixed predetermined circular arcs.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an axial flow filter element which removes dust and other particles from air or oil. More especially the present invention relates to a method and apparatus for forming a semi-circular filter element from a fan or sectorial shaped sheet of filter material, e.g. non-texture cloth. 
     BRIEF DESCRIPTION OF THE CONVENTIONAL METHOD 
     The conventional method for forming a filter element is depicted in FIGS. 8(a)-(c), namely a sectorial shaped sheet 2 of non-texture cloth is combined with a fan or sectorial shaped wavy elastic film, such as thermoplastic polyethylene film 1 having alternating ridges and valleys extending between the straight sides parallel to the curved ends of the sector. Then the sheet 2 is conformed to the film 1 by hand as a first step (shown in FIG. 8(a)). Then the smaller concave end of the fan shaped wavy sheet 2 is engaged with a pin 3 which is fixed on a table, and the wavy sheet is rounded by hand in such a manner that both sides of the sheet are moved toward each other, as shown in FIG. 8(b). After that the sheet is completely rounded in order to abut both sides thereof against each other, as shown in FIG. 8(c). These hand manipulations shown in FIG. 8(b) and FIG. 8(c) are carried out as a second step. 
     SUMMARY OF THE INVENTION 
     These conventional steps described above, however, have a defect, e.g. requiring a long time to perform because of the resiliency of the sheet 2. Namely, it is very difficult to control the resiliency of the sheet 2 while the sheet 2 is rounded. According to the present inventors&#39; experience, about thirty seconds are required to round the filter element when the final diameter thereof is about 300 mm, for example. Furthermore, since the filter element is produced by hand, product quality can not be maintained within a good range so that the pitch between adjacent ridges or valleys becomes irregular and hinders the filtering effect of the element. 
     The present invention has the object to provide an advanced automatic apparatus which produces a sectorial shaped wavy filter sheet with a central angle as large as 180°. In order to attain this object, the method of the present invention includes the following steps: 
     providing a fan or sectorial shaped sheet of filter material which has parallel curved ends, straight sides converging toward the smaller concave end and a plurality of uniformly spaced concentric arc-like wavy portions or curved corrugations, i.e. alternating arc-shaped ridges and valleys, extending between the sides parallel to the curved ends of the sheet; 
     holding or retaining the fan shaped sheet in its corrugated configuration by inserting a plurality of narrow curved holding wedges in and at the midlength of the valleys in one side of the sheet; 
     reducing the radial length of the sectorial corrugated sheet by uniformly reducing the pitch between adjacent holding wedges; 
     rounding the fan shaped corrugated reduced sheet until the central angle thereof becomes as large as 180° by forcing the convex end of the fan shaped sheet toward the concave end while the midlength of the latter is fixed in position; and 
     reforming the shape of the corrugations of the rounded fan shaped sheet to true arcs of a circle by sliding reforming wedges along predetermined circular paths in the valleys in one side of the sheet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side view showing the apparatus of the present invention. 
     FIG. 2 is a perspective view of the sectorial shaped wavy sheet which is used in the apparatus shown in FIG. 1. 
     FIG. 3 is a perspective view of the final product of the apparatus shown in FIG. 1. 
     FIG. 4 is a schematic view showing the relationship between the pantograph and the cam plate of the apparatus shown in FIG. 1. 
     FIG. 5 is a plan view showing the shape of the holding wedges and their relationship with the valleys in one side of the sheet shown in FIG. 2. 
     FIG. 6 is a plan view showing the main structure of the rounding means of the apparatus shown in FIG. 1. 
     FIG. 7 is a plan view showing the main structure of the reforming means of the apparatus shown in FIG. 1. 
     FIGS. 8(a)-8(c) are perspective views showing the steps for forming a filter element by the conventional method. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention is described hereinafter with reference to the drawings. 
     FIG. 2 shows a fan shaped sheet 2 of non-textured cloth which is used as the starting material in the apparatus of the present invention. This sheet 2 has been bent or creased to make a plurality of curved wavy portions, i.e. uniformly spaced alternating ridges and valleys extending between the straight sides parallel to the curved ends of the sheet. The angle between the sides of a valley preferably is about 90° with a predetermined pitch between ridges of p&#39;. Apparatus and method for making wavy portions in a flat sectorial sheet is disclosed in U.S. Pat. No. 4,659,323. That sheet is then reduced in its radial length by the reducing step of the present invention and then rounded to make a semi-circular shaped element as shown in FIG. 3. After the sheet is rounded to a semi-circular shape, the sheet is then rounded further by another rounding machine (not shown) to attain a completely semi-circular shape as shown in FIG. 8(c). 
     As shown in FIG. 1, the apparatus of this invention has a horizontal working table 11 for carrying the sheet 2 and movable reducing means X located under a fixed frame 13 which is above and parallel to the working table 11. The reducing means X has an elevating frame 15 that is carried and movable vertically by the rod of an upright cylinder 14 fixed to the frame 13. The elevating frame 15 also supports a rodless horizontal cylinder 16 and a rod 17 and a cam plate 18 below and parallel to the rodless cylinder 16. The rod 17 is supported by the elevating frame 15, via depending end brackets 19 and 20, and a plurality of pieces 21 are mounted to slide along the rod 17. Each sliding piece 21 carries a narrow arcuate holding wedge 22 at the lower end thereof which fits into, at the midlength of, a corresponding valley in the sheet 2 except the left most and right most wedges which engage the opposite ends of the sheet at the midlength thereof. Each sliding piece 21 is connected to a crossing pivot of a common pantograph 23 having an equal pitch between adjacent sliding pieces 21. The left most sliding piece 21a is connected with a slider 24 of the rodless cylinder 16. Accordingly, each sliding piece 21 and corresponding holding wedge 22 is moved while keeping a predetermined equal interval between the wedges when the slider 24 of the rodless cylinder 16 is moved in the C direction indicated by the double ended arrow C-D shown in FIG. 1. 
     When the slider 24 is so moved, the right most sliding piece 21b is not moved but maintains a fixed position until a predetermined shortening of the pantograph 23 as described hereafter. Since all the pieces 21 are connected with the pantograph 23, all the pieces left of the right side piece 21b travel rightward when the pantograph reduces the interval between adjacent pieces 21 as the left most piece 21a is moved to the right by the slider 24. After the pitch between the adjacent holding wedges is reduced to a predetermined pitch p (shown in FIG. 3) of the sheet 2, the distance between two rollers 25 carried on the side apices at the right most end of the pantograph becomes the same as the largest width M of the cam plate 18, so that the entire pantograph 23 and all the sliding pieces 21, including the right most piece 21b, start to move in the C direction. 
     At the right end of the table 11 and slightly spaced therefrom is an auxiliary working table 30 flush with the table 11. The table 11 has a central slot extending inward from the right hand end toward the left hand end. Disposed below the slot and the small gap between the tables 11 and 30 is rounding means Y which can be elevated to prevent the right hand concave edge 2a of the sheet 2 from dropping into the gap between the tables 11 and 30 as the sheet is moved off the table 11 onto the table 30 as described hereinafter. 
     As shown in FIG. 5, the cross-sectional shape of the holding wedges 22 is a short arc shape in order to fit the arc-shaped valleys and end edges of the sheet 2, and the width of the holding wedges 22 gradually reduce from the larger curved end toward the smaller concave end of the sheet 2. Namely, the width of the right hand holding wedge 22 is smaller than that of the left hand holding wedge 22 as shown in FIG. 5. The pitch of the holding wedges 22 initially should be the same as the pitch p&#39; of the wavy portions of the sheet 2 as shown in FIG. 2. The pitch p&#39;, of course, can be varied according to variations of the configuration and dimensions of the sheet 2. 
     The operation of the reducing means is explained hereinafter. First, the fan shaped sheet 2 which has wavy portions, as shown in FIG. 2 is placed on the working table 11 with the smaller concave end 2a to the right as shown in FIG. 1. Then, the elevating frame 15 is moved downward (the direction A indicated by the double ended arrow A-B in FIG. 1) by the cylinder 14. The rodless cylinder 16, the rod 17, the sliding pieces 21 and the holding wedges 22 are also moved downward with the elevating frame 15, so that the lower end portions of the intermediate holding wedges 22 are inserted into the valleys of the wavy portions for holding the sheet 2 on the working table 11, as shown in FIG. 1. At the same time the left and right end wedges 22 respectively engage the larger convex and smaller concave ends of the sheet 2. Then the rodless cylinder 16 begins to move the slider 24 in the C direction shown in FIG. 1. The movement of the slider 24 causes all the holding wedges 22, except the right most which is held against moving by engagement of the rollers 25 with shoulders on the cam plate 18, to move rightward and thus reduce the radial length of the sheet 2, i.e. the distance between the convex and the concave ends. Such movement also reduces the pitch between the ridges in the sheet 2 until the pair of rollers 25 (FIG. 4) move apart a distance sufficient to embrace the wide part M of the cam plate 18. At that time the right hand wedge 22 moves together with all the others so that the reduced sheet is pushed off of the table 11 to a predetermined position 2&#39; on the table 30. 
     The sheet 2 on the auxiliary working table 30 is then rounded. The rounding means Y is disposed below the working table 11 when inoperative or stowed and raised to an operative or working position above the auxiliary working table 30 only when required. The rounding means Y is mounted on a slide base 34 which slides on a pair of rails 32 via slide bearings 33. The rails 32 are mounted on a base 31. The auxiliary working table 30 also is mounted on the slide base 34 via columns 35. An upright cylinder 36 mounted to and below the slide base 34 has its rod fastened to a sub-base 37 of the rounding means Y to raise and lower the latter (in the directions G and H indicated by the double ended arrow in FIG. 1) between its inoperative and operative positions. 
     The main structure of the rounding means Y is shown in FIG. 6. The rounding means Y has a pair of horizontal upper and lower cylinders 38 and 39, respectively, which are fixed to the sub-base 37. A U-shaped bracket 40 is fixed on the end of the rod of the lower cylinder 39, and a pair of links 42, on the ends of which rollers 41 and 41a are provided, are pivotally connected at their midpoints to the ends of the bracket 40, as at 48, so that the bracket 40, a link 42 and its pivot pin 43 make an arm 44. A rotor 45 is mounted to the end of the rod of the upper cylinder 38. The ends of a belt 46 are secured to the two rollers 41 with the intermediate portion of the belt 46 being trained over the rollers 41a and 45 as shown in FIG. 6. 
     The operation of the rounding means will now be explained. After a reduced sheet 2 is moved onto the auxiliary working table 30, the rounding means Y is raised by the cylinder 36 to its operative or working position. After that, the cylinder 39 extends its rod to move the arms 44 to the right and cause the links 42 to rotate and the rollers 41 to move in a curved path in the direction E indicated by the double ended arrows E-F in FIG. 6. This movement of the rollers 41 makes the belt 46 engage the convex edge of the sheet 2 and constrict and partly round it as shown by the dotted lines in FIG. 6. 
     A two-part upright stop plate 47, which engages the sides of the partly rounded sheet, limits the central angle of the partly rounded sheet 2, and an upright pin 48 which engages the midpoint of the concave edge of the sheet 2, are mounted on the auxiliary working table 30, as best shown in FIG. 6. Since the rollers 41 travel beyond the stop plate 47, the convex edge of the sheet 2 is pressed by the belt 46 and the sheet is partly rounded until the central angle of the sheet 2 becomes as large as 180°. During the pressing and rounding operation of the belt 46, the tension force of the belt 46 is controlled by movement of the rod of the cylinder 38, and the tension force of the belt 46 is modified in accordance with the number of ridges and valleys in the sheet. 
     After that, the sheet is reformed in order to make the shape of the wavy portions more truly circular. The reforming means Z is located under the auxiliary working table 30. As shown in FIG. 1, the reforming means Z, like the rounding means Y, has a vertical cylinder 50 mounted to and beneath the slide base 34. A sub-base 51 is mounted to the end of the rod of the cylinder 50, and a horizontal cylinder 52 mounted to and above the sub-base 51. As shown in FIG. 7, a holder 54 is connected to the end portion of the rod of the cylinder 52 via a bracket 55. The holder 54 has three parts which carry sets of upright aligned reforming wedges 53a, 53b and 53c, respectively. The reforming wedges of each set 53a, 53b and 53c are so arranged that the pitch therebetween is the same as the pitch of the wavy portions of the sheet which has already been partly rounded. The center set of wedges 53b is movable only vertically by the cylinder 50. The parts carrying the reforming wedges 53a and 53c located at right side and left side of the center reforming wedges 53b are, on the other hand, linked with the holder 54 in such a manner that both sets of the reforming wedges 53a and 53c are rotated in opposite directions away from the center set of wedges 53b, i.e. in the directions M indicated by the double ended arrows M-N in FIG. 7, when the holders 54 is moved by the cylinder 52. 
     A plurality of arcuate slots 56, which are aligned with and serve as guides for the sets of reforming wedges 53a and 53c during their rotations are provided in the auxiliary working table 30. The valleys in the underside of the partly rounded sheet are aligned with these slots 56. 
     The operation of this reforming means Z is now described. The sets of reforming wedges 53 are elevated from their lower position through the slots 56 by operation of the cylinder 50, so that the top of the reforming wedges 53 are inserted into the valleys in the underside of the sheet 2. At the same time, the holding wedges 22 which had retained the form of the sheet 2 start to move up, by movement of the frame 15, for returning to their starting position. Then the cylinder 52 moves the bracket 55 in the direction K indicated by the double ended arrow K-L in FIG. 7 and such movement makes the parts of the holder 54 carrying the wedge sets 53a and 53c rotate clockwise and counterclockwise respectively. Such rotation moves the wedge sets 53a and 53c in true circular arcs along the valleys in the underside of the partly rounded sheet to correspondingly shape such valleys. 
     After that the reforming wedges 53 are withdrawn downward from the sheet 2, the rollers 41 retracted and the rounding means Y and reforming means Z returned to their lower inoperative positions. The table 30 carrying the reformed sheet 2 then is moved to the position &#34;2&#34;&#34;, shown in dotted lines in FIG. 1 by operation of a cylinder 57 which is connected to the left side of the slide base 34 in order to carry the reformed semi-circular sheet 2 to the next station (not shown) where it is made completely circular. 
     According to the present invention a portion of the process for forming a filter element which has heretofore been done manually can be performed automatically. Furthermore, the operation of the reforming wedges not only forms the ridges and valleys into true arcs but also makes the density of the filter element more uniform. The method and also the apparatus of the present invention obviously can be adapted for use to form filter elements having different sizes and/or different numbers of ridges and valleys.