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Inventors
Stoyell, Richard C.
Williamson, Kenneth M.
Hopkins, Scott D.
Geibel, Stephen A.
Wolff, Terry L.
Application #
660413
Filed
Jun-7-1996
Published
Nov-25-1997
Current US Class
055/500
055/521
156/218
156/69
210/493.2
210/493.5
210/509
493/941
International Classes
B65B 007/00; B01D 027/06
Field of Search
210/493.1 210/493.5 210/493.2 210/509 493/941 55/500 55/521 156/218 156/69
Assignee
Pall Corporation (East Hills, NY)
Examiners
Walker; W. L.
Attorney, Agent or Firm
Leydig, Voit & Mayer, Ltd.
US Patent References
| 5130023 |
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Filter cartridge with... |
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Referenced by:
View Backward References
Citation
Cite This Patent
More From Subclass 521
More From Class 055
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Abstract
A filter includes a cylindrical filter element having a longitudinal axis, first and second end surfaces, and a plurality of longitudinal pleats. Each of the pleats has a pair of legs with first and second surfaces. The pleats are in a laid-over state in which the first surface of each leg is in intimate contact with the first surface of an adjoining leg and the second surface of each leg is in intimate contact with the second surface of an adjoining leg over substantially the entire height of each leg and over a continuous region extending for at least approximately 50% of the axial length of the filter element. An impervious end cap is connected to the first end surface of the filter element.
Claims
What is claimed is:
1. A method of assembling a filter comprising:
repairing a corrugated filter composite comprising a filter medium having upstream and downstream sides and at least one of an upstream drainage layer on the upstream side of the filter medium and a downstream drainage layer on the downstream side of the filter medium;
forming the composite into a cylindrical filter element having a center and pleats extending along a longitudinal axis, each pleat having first and second legs, each leg having first and second surfaces;
forming the pleats of the cylindrical filter element into a laid-over state in which the first surface of one leg of one pleat is in intimate contact with the first surface of an adjoining leg of said one pleat and the second surface of said one leg is in intimate contact with the second surface of an adjoining leg of an adjoining leg of an adjacent pleat over substantially the entire height of said one leg and over a continuous region extending for at least approximately 50% of the length of the filter element;
retaining the pleats in the laid-over state; and
capping at least a first end of the pleated, laid-over cylindrical filter element to prevent axial flow through the pleats at the first end.
2. The method of claim 1 wherein forming the pleats into a laid-over state includes twisting the pleats to lay the pleats over.
3. The method of claim 2 wherein retaining the pleats includes disposing the laid-over pleats inside a cage.
4. The method of claim 1 wherein forming the pleats into a laid-over state includes passing the cylindrical pleated filter element through a funnel-shaped tool.
5. The method of claim 4 wherein retaining the pleats includes disposing the laid-over pleats inside a cage.
6. A method assembling a filter comprising:
preparing a corrugated filter composite comprising a filter medium having upstream and downstream sides and at least one of an upstream drainage layer on the upstream side of the filter medium and a downstream drainage layer on the downstream side of the filter medium, the composite having a plurality of parallel pleats each having a pair of legs, each leg having first and second surfaces;
forming the pleats into a laid-over state in which in the first surface of one leg of one pleat is in intimate contact with the first surface of an adjoining leg of said one pleat and the second surface of said one leg is in intimate contact with the second surface of an adjoining leg of an adjacent pleat over substantially the entire height of said one leg and over a continuous region extending for at least approximately 50% of the length of the composite;
forming the composite with the pleats in the laid-over state into a cylindrical filter element;
retaining the pleats in the laid-over state; and
capping at least a first end of the pleated, laid-over cylindrical filter element to prevent axial flow through the pleats at the first end.
7. The method of claim 6 wherein forming the pleats into a laid-over state includes pressing the corrugated composite between two flat surfaces to lay the pleats over.
8. A method of making a filter comprising laying over and arranging a plurality of pleats including a filter medium into a cylindrical configuration to form a filter element having axially extending pleats, including intimately contacting a first surface of a first leg of one pleat with the first surface of an adjoining leg of said one pleat and a second surface of said first leg with the second surface of an adjoining leg of an adjacent pleat over a substantial portion of the height of the first leg and over a continuous region extending for at least approximately 50% of the axial length of the filter element, and sealing at least a first end of the filter element to prevent axial flow along the pleats at the first end.
9. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming the plurality of pleats into a cylindrical configuration and then laying over the pleats.
10. The method of claim 8 wherein laying over and arranging the plurality of pleats includes laying over the pleats and then forming the plurality of pleats into a cylindrical configuration.
11. The method of claim 10 wherein laying over the pleats includes forming each pleat with a first leg and a second longer leg.
12. The method of claim 8 further comprising forming a smooth radius at the crest of each pleat.
13. The method of claim 12 wherein forming the smooth radius includes removing a strip-out layer from the pleats.
14. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including a filter medium and a drainage layer which comprises an extruded mesh having first and second sets of parallel strands, the first set of parallel strands being disposed between the filter medium and the second set of parallel strands and the first set of parallel strands having a strand count of at least about 10 strands per inch, and corrugating the composite to form the plurality of pleats.
15. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including an upstream drainage layer, a downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance, and corrugating the composite to form the plurality of pleats.
16. The method of claim 8 wherein layer over and arranging the plurality of pleats includes forming the plurality of pleats into a cylindrical configuration and then laying over the pleats and wherein the method further comprises forming a smooth radius at the crest of each pleat.
17. The method of claim 8 wherein laying over and arranging the plurality the pleats includes forming a composite including a filter medium and a drainage layer which comprises an extruded mesh having first and second sets of parallel strands, the first set of parallel strands being disposed between the filter medium and the second set of parallel strands and the first set of parallel strands having a strand count of at least about 10 strands per inch, corrugating the composite to form the plurality of pleats, forming the plurality of pleats into a cylindrical configuration, and then laying over the pleats.
18. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite having an upstream drainage layer, a downstream drainage layer and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance, corrugating the composite to form the plurality of pleats, forming the plurality of pleats into a cylindrical configuration, and then laying over the pleats.
19. The method of claim 8 wherein laying over and arranging the plurality of pleats includes laying over the pleats and then forming the plurality of pleats into a cylindrical configuration and wherein the method further comprises forming a smooth radius at the crest of each pleat.
20. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including a filter medium and a drainage layer which comprises an extruded mesh having first and second sets of parallel strands, the first set of parallel strands being disposed between the filter medium an the second set of parallel strands and the first set of parallel strands having a strand count of at least 10 stands per inch, corrugating the composite to form the plurality of pleats, laying over the pleats, and then forming the plurality of pleats into a cylindrical configuration.
21. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including a filter medium and a drainage layer which comprises an extruded mesh having first and second sets of parallel strands, the first set of parallel strands being disposed between the filter medium and the second set of parallel strands and the first set of parallel strands having a strand count of at least about 10 stands per inch, corrugating the composite to form the plurality of pleats, including laying over the pleats by forming each pleat with a first leg and a second longer leg, and then forming the plurality of pleats into a cylindrical configuration.
22. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including an upstream drainage layer, a downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance, corrugating the composite to form the plurality of pleats, laying over the pleats, and then forming the plurality of pleats into a cylindrical configuration.
23. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including an upstream drainage layer, a downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance, corrugating the composite to form the plurality of pleats including laying over the pleats by forming each pleat with a first leg and second longer leg, and then forming the plurality of pleats into a cylindrical configuration.
24. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including a filter medium and a drainage layer which comprises an extruded mesh having first and second sets of parallel strands, the first set of parallel strands begin disposed between the filter medium and the second set of parallel strands and the first set of parallels strands having as strand count of at least about 10 strands per inch corrugating the composite to form the plurality of pleats, forming the plurality of pleats into a cylindrical configuration, and then laying over the pleats and wherein the method further comprises forming a smooth radius at the crest of each pleat.
25. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including an upstream drainage layer, a downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance, corrugating the composite to form the plurality of pleats, forming the plurality of pleats into a cylindrical configuration, and then laying over the pleats and wherein the method further comprises forming a smooth radius at the crest of each pleat.
26. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including an upstream drainage layer, a downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance and at least one of the upstream and downstream layers comprising an extruded mesh having first and second sets of parallel strands, the first set of parallel strands being disposed between the filter medium and the second set of parallel strands and the firs set of parallel strands having a strand count of at least 10 strands per inch, corrugating the composite to form the plurality of pleats, forming the plurality of pleats into a cylindrical configuration, and then laying over the pleats.
27. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including a filter medium and a drainage layer which comprises an extruded mesh having first and second sets of parallel strands, the first set of parallel strands being disposed between the filter medium and the second set of parallel strands and the first set of parallel strands having a strand count of at least about 10 strands per inch, corrugating the composite to form the plurality of pleats, laying over the pleats, and then forming the plurality of pleats into a cylindrical configuration and wherein the method further comprises forming a smooth radius at the crest of each pleat.
28. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including an upstream drainage layer, an downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance, corrugating the composite to form the plurality of pleats, laying over the pleats, and then forming the plurality of pleats into a cylindrical configuration.
29. The method of claim 8 wherein the laying over and arranging the plurality of pleats includes forming a composite including an upstream drainage layer, a downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance and at least one of the upstream and downstream drainage layers comprising an extruded mesh having first and second sets of parallel strands, the first set of parallel strands being disposed between the filter medium and the second set of parallel strands and the first set of parallel strands having a strand count of at least about 10 strands per inch, corrugating the composite to form the plurality of pleats, laying over the pleats, and then forming the plurality of pleats into a cylindrical configuration.
30. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including an upstream drainage layer, a downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance, corrugating the composite to form the plurality of pleats including laying over the pleats by forming each pleat with a first leg and a second longer let, and then forming a plurality of pleats into a cylindrical configuration.
31. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including an upstream drainage layer, a downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance and at least one of the upstream and downstream drainage layers comprising an extruded mesh having first and second sets of parallel strands, the first set of parallel strands being disposed between the filter medium and the second set of parallel strands and the first set of parallel strands having a strand count of at least about 10 strands per inch, corrugating the composite to form the plurality of pleats, forming the plurality of pleats into a cylindrical configuration, and then laying over the pleats and wherein the method further comprises forming a smooth radius at the crest of each pleat.
32. The method of claim 8 wherein laying over and arranging the plurality of pleats includes forming a composite including an upstream drainage layer, a downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, the upstream and downstream drainage layers having substantially the same edgewise flow resistance and at least one of the upstream and downstream drainage layers comprising an extruded mesh having first and second sets of parallel strands, the first set of parallel strands being disposed between the filter medium and the second set of parallel strands and the first set of parallel strands having a strand count of at least about 10 strands per inch, corrugating the composite to form the plurality of pleats, laying over the pleats, and then forming the plurality of pleats into a cylindrical configuration.
33. The method of claim 8 further comprising retaining the pleats by disposing the pleats in a perforated cage.
34. The method of claim 8 further comprising retaining the pleats by wrapping the pleats with a wrap.
35. The method of claim 8 further comprising tightly wrapping the pleats with a wrap to pre-compress the pleats.
36. The method of claim 35 wherein tightly wrapping the pleats includes pre-compressing the pleats such that during filtration additional compression will be no greater than about 5%.
37. The method of claim 8 further comprising forming a composite including a first drainage medium, a second drainage medium, and a filter medium disposed between the first and second drainage media, the first drainage medium being thicker than the second drainage medium.
38. The method of claim 37 wherein the first drainage medium comprises an upstream drainage medium and the second drainage medium comprises a downstream drainage medium.
39. A method of making a filter comprising forming a composite including a filter medium and a drainage layer, corrugating the composite to form a plurality of pleats, arranging the plurality of pleats into a cylindrical configuration, laying the pleats over, intimately contacting a first surface of a first leg of each of the plurality of pleats with the first surface of an adjoining leg of said pleat and a second surface of said firs leg with the second surface of an adjoining leg of an adjacent pleat over a substantial portion of the height of the first leg and over a continuous region extending for at least approximately 95% of the axial length of the pleats to form a filter element, and sealing at least a first end of the filter element to prevent axial flow along the pleats at the first end.
40. A method of making a filter comprising forming a composite including an upstream drainage layer, a downstream drainage layer, and a filter medium disposed between the upstream and downstream drainage layers, corrugating the composite to form a plurality of pleats, arranging the plurality of pleats into a cylindrical laid-over configuration to form a filter element having axially extending pleats, including intimately contacting a first surface of a first leg of each pleat in the filter element with the first surface of an adjoining leg of said pleat and a second surface of said first leg with the second surface of an adjoining leg of an adjacent pleat over substantially the entire height of the first leg and over a continuous region extending for at least approximately 50% of the axial length of the filter element, and sealing at least a first end of the filter element, and sealing at least a first end of the filter element to prevent axial flow along the pleats at the first end.
41. A method of making a filter comprising arranging a plurality of pleats to form a filter element wherein the height of each pleat is greater than (D-d)/2, D being the outer diameter at the crest of the pleat and d being the inner diameter at the root of the pleat, including intimately contacting a first surface of a first leg of one pleat with the first surface of an adjoining leg of said one pleat and a second surface of said first leg with the second surface of an adjoining leg of an adjacent pleat over a substantial portion of the height of the first leg and over a continuous region extending for at least approximately 50% of the axial length of the pleats of the filter element, and sealing at least a first end of the filter element to prevent axial flow along the pleats at the first end.
42. The method of claim 41 further comprising forming a composite including a filter medium and a drainage medium and corrugating the composite to form the plurality of pleats.
43. The method of claim 42 wherein forming the composite includes forming a composite comprising a filter medium which includes a porous film and a drainage medium which includes a non-woven fabric.
44. The method of claim 43 wherein the continuous region extends for at least approximately 95% of the axial length of the pleats of the filter element.
45. The method of claim 44 wherein corrugating the composite includes forming pleats having equal length legs and wherein arranging the plurality of pleats includes transforming the pleats into pleats having unequal length legs.
46. The method of claim 45 further comprising retaining the pleats by disposing the pleats in a perforated cage.
47. The method of claim 45 further comprising retaining the pleats by wrapping the pleats with a wrap.
48. The method of claim 44 wherein corrugating the composite includes forming pleats having unequal length legs.
49. The method of claim 48 further comprising retaining the pleats by disposing the pleats in a perforated cage.
50. The method of claim 48 further comprising retaining the pleats by wrapping the pleats with a wrap.
51. The method of claim 42 wherein forming the composite includes forming a composite comprising a filter medium which includes a fibrous medium and a drainage medium which includes a mesh.
52. The method of claim 51 wherein the continuous region extends for at least approximately 95% of the axial length of the pleats of the filter element.
53. The method of claim 52 wherein corrugating the composite includes forming pleats having equal length legs and wherein arranging the plurality of pleats includes transforming the pleats into pleats having unequal length legs.
54. The method of claim 53 further comprising retaining the pleats by disposing the pleats in a perforated cage.
55. The method of claim 54 wherein forming a composite further includes forming a composite comprising a cushioning layer which includes a non-woven fabric disposed between the fibrous medium and the mesh.
56. The method of claim 53 further comprising retaining the pleats by wrapping the pleats with a wrap.
57. The method of claim 56 wherein forming a composite further includes forming a composite comprising a cushioning layer which includes a non-woven fabric disposed between the fibrous medium and the mesh.
58. The method of claim 52 wherein corrugating the composite includes forming pleats having unequal length legs.
59. The method of claim 58 further comprising retaining the pleats by disposing the pleats in a perforated cage.
60. The method of claim 59 wherein forming a composite further includes a forming a composite comprising a cushioning layer which includes a non-woven fabric disposed between the fibrous medium and the mesh.
61. The method of claim 58 further comprising retaining the pleats by wrapping the pleats with a wrap.
62. The method of claim 61 wherein forming a composite further includes forming a composite comprising a cushioning layer which includes a non-woven fabric disposed between the fibrous medium and the mesh.
63. The method of claim 41 further comprising forming a composite including a first drainage medium, a second drainage medium, and a filter medium disposed between the first and second drainage media and corrugating the composite to form the plurality of pleats.
64. The method of claim 63 wherein the first drainage medium is thicker than the second drainage medium.
65. The method of claim 64 wherein the first drainage medium comprises an upstream drainage medium and the second drainage medium comprises a downstream drainage medium.
66. The method of claim 63 wherein forming the composite includes forming a composite comprising a first drainage medium which includes a polymeric mesh, a filter medium which includes a fibrous medium, and a second drainage medium which includes a polymeric mesh.
67. The method of claim 66 wherein the continuous region extends for at least approximately 95% of axial length of the pleats of the filter element.
68. The method of claim 67 wherein corrugating the composite includes forming pleats having equal length legs and wherein arranging the plurality of pleats includes transforming the pleats into pleats having unequal length legs.
69. The method of claim 68 further comprising retaining the pleats by disposing the pleats in a perforated cage.
70. The method of claim 68 further comprising retaining the pleats by wrapping the pleats with a wrap.
71. The method of claim 67 wherein corrugating the composite includes forming pleats having unequal length legs.
72. The method of claim 71 further comprising retaining the pleats by disposing the pleats in a perforated cage.
73. The method of claim 71 further comprising retaining the pleats by wrapping the pleats with a wrap.
74. The method of claim 41 further comprising tightly wrapping the pleats with a wrap to pre-compress the pleats.
75. The method of claim 74 wherein tightly wrapping the pleats includes pre-compressing the pleats such that during filtration additional compression will be no greater than about 5%.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
this invention related to pleated filter elements. Methods of assembling filter elements methods and apparatus for manufacturing pleated filter elements and methods for precoating and backwashing filter elements.
2. Description of the Related Art
Cylindrical filter elements having radially-extending, longitudinal pleats are among the most common types of filter elements and are used to filter innumerable fluids, i.e., liquids or gases. (throughout this application "filter" and "filtration" include both the removal of particulates, e.g., by sieving or trapping within a porous medium, and the removal of impurities, e.g., by ion exchange resins or sorbents). In a typical cylindrical pleated filter element, a plurality of pleats are arranged around a tublar core to defind a cylinder. As viewed in a transverse cross-section, the individual pleats of such a filter element extend radially outward from the core toward the outer periphery of the filter element. It is good design practice to have enough pleats in a cylindrical filter element so that adjoining pleats contact one another along the circumference of the core, However, because of the radial geometry of the pleats, the spacing between adjacent pleats necessarily increases as the distance from the center of the core increases. Accordingly, in a typical cylindrical pleated filter element, there is a great deal of unused space between adjacent pleats.
Making a filter element larger to compensate for the unused space between adjacent pleats is frequently not possible. In the filter industry today, the dimensions of filter housings within which the filter elements are enclosed have become fairly standardized. Accordingly, a major challenge of filter designers is to increase the filtering capacity of a filter element, i.e., the usable surface area, without altering its external dimensions so that it can be employed with existing filter housings.
While cylindrical pleated filter elements are very common, they have typically not be used as precoat filters. A precoat filter is a type of filter in which a slurry is applied as a cake, called a precoat, to the exterior of a non-pleated, porous support structure called a septum. After the precoat is applied to the septum, a fluid to be filtered is then directed through the precoat and the septum where this precoat serves to filter the fluid. Pleated filter elements have not been used as supports for septa because the pleats tend to collapse as the precoat is applied or as the fluid flows through the precoat.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a filter which has a greater filtering capacity than a conventional filter of the same external dimensions.
It is another object of the present invention to provide a filter having good strength and resistance to handling.
It is a further object of the present invention to provide a precoat filter having a pleated filter element.
It is yet another object of the present invention to provide an apparatus and method for forming a material into pleats of a form particularly suitable for a filter according to the present invention.
The present invention provides a filter including a cylindrical filter element having an end surface and an impervious end cap connected to the end surface. The filter element has a plurality of longitudinal pleats, each of the pleats having a pair of legs. Each of the legs has a first surface and a second surface. The pleats are in a laid-over state in which the first surface of each leg is in intimate contact with the first surface of an adjoining leg and the second surface of each leg is in intimate contact with the second surface of an adjoining leg over substantially the entire height of each leg and over a continuous region extending for at least approximately 50% of the axial length of the filter element.
The present invention also provides a filter comprising a cylindrical filter element having an inner radius, outer radius, and a plurality of longitudinal pleats. Each pleat has a height greater than the difference between the outer and inner radii. The filter further comprises a wrap member wrapped around the filter element.
Because the pleats are in a laid-over state or because the height of each pleat is greater than the difference between the out and inner radii, the height of the pleats is much large than that of a conventional filter of the same dimensions. As a result, the surface area of a filter according to the present invention usable for filtration, which is proportional to the pleat height, can be greatly increased, resulting in a longer lifespan.
A filter embodying the present invention may have a hollow center and a cylindrical outer periphery. It can be used for outside-inflow in which a fluid to be filtered flows from the outer periphery through the filter element into the hollow center, or it can be used for inside-out flow in which fluid flows from the hollow center through the filter element to the outer periphery.
The present invention also provides a pleating apparatus which may form a material into pleats having unequal legs. The pleating apparatus includes a pleating member and a stripper member having unequal legs. The pleating apparatus includes a pleating member and a stripper member having pleating surfaces spaced by a gap. At least one of the pleating surfaces is curved or extends at an acute angle to a support surface for supporting a material to be pleated. The pleating member and the stripper member are moved relative to each other to compress the material within the gap and thereby form a pleat, which may have unequal legs. As a result of the pleats having unequal legs, they can readily be formed into a laid-over state. A pleating apparatus according to the present invention can be used to pleat not only single-layer materials, but can also be used to pleat multi-layer composites.
The present invention further provides a precoat filter including a pleated filter element having a longitudinal axis and a plurality of longitudinal pleats. A septum adapted to support a precoat layer is wrapped around and bears against a periphery of the filter element.
In preferred embodiments, the pleated filter element of the precoat filter is cylindrical and has laid-over pleats extending non-radially with respect to the longitudinal axis of the filter element. Alternatively, the pleats may extend radially, with adjoining pleats pressed into intimate contact with one another by wedges or the like. A flow straightener such as a mesh may be disposed around the septum to prevent turbulence from damaging the precoat layer.
The pleated filter element of a precoat filter according to the present invention can have a large surface area, so it can trap fines which pass through the precoat layer and prevent them from flowing to the downstream side of the filter. By having its pleats in a laid-over state or pressed into intimate contact with one another, the filter element can provide a more stable support for the septum and thereby prevent cracking of the precoat layer in response to fluctuations in the pressure across the filter.
Additionally, the present invention provides methods of assembling a filter and filtering methods, all as defined by the attached claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cut-away perspective view of a filter.
FIG. 2 is a transverse cross-sectional view of a portion of the filter of FIG. 1.
FIG. 3 is an enlarged cross-sectional view of one of the pleats of FIG. 2.
FIG. 4 is a schematic perspective view of a portion of a filter composite having an insert strip at one end.
FIG. 5 schematically illustrates one method of forming the pleats of a filter element into a laid-over state.
FIG. 6-11 are schematic views illustrating a method and apparatus for forming a filter element.
FIG. 12 and 13 are schematic views illustrating another method and apparatus for forming a filter element.
FIG. 14 is an enlarged side view of one of the pleats of FIG. 9.
FIG. 15 is a side view of a pleating apparatus.
FIG. 16 is a plan view of the pleating apparatus of FIG. 15.
FIG. 17 is a side view of another pleating apparatus.
FIG. 18 is a side view of another pleating apparatus.
FIG. 19-21 are schematic views illustrating a method and apparatus for assembling a filter element.
FIG. 22 is a cut-away perspective view of another filter.
FIG. 23 is a cross-sectional view of a precoat filter.
FIG. 24 is a cross-sectional view of another precoat filter.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 illustrates a first embodiment of a filter according to the present invention. This embodiment is generally cylindrical in form and includes a pleated filter element 10 having a plurality of longitudinal pleats 11. A cylindrical core 20 may be coaxially disposed along the inner periphery of the filter element 10, and a cylindrical cage or wrap 30 may be disposed along the outer periphery of the filter element 10.
As shown in FIGS. 2 and 3, each pleat 11 has two legs 11a which are joined to one another at the crown 11b of the outer periphery of the filter element 10 and which are joined to a leg 11a of an adjacent pleat 11 at the root 11c of the inner periphery of the filter element 10. Each leg 11a has an internal surface 11d which opposes the internal surface 11d of the other leg 11a in the same pleat 11, and an external surface 11e which opposes the external surface 11e of a leg 11a of an adjacent pleat 11. When the filter element 10 is being used such that fluid flows radially inwardly through the element, the internal surfaces 11d of the legs 11 a form the downstream surface of the filter element 10, while the external surfaces 11 c form the upstream surface of the filter element 10. Alternatively, when the filter element 10 is being used such that fluid flows radially outwardly through the element, the internal surfaces 11 d and the external surfaces 11e respectively form the upstream and downstream surfaces of the filter element 10.
As shown in the figures, the opposing inner surfaces 11d of the legs 11a of each pleat 11 are in intimate contact with one another over substantially the entire height h of the legs 11a and of the pleat 11 and over a continuous region extending for a significant portion of the axial length of the filter element 10. In addition, the opposing external surfaces 11e of the legs 11a of adjacent pleats 11 are in intimate contact over substantially the entire height h of the adjacent pleats 11 and legs 11a and over a continuous region extending for a significant portion of the axial length of the filter element. Here, the height h (shown in FIG. 2) of the pleats 11 and the legs 11a is measured in a direction along the surfaces of the legs 11a and extends from the inner periphery to the outer periphery of the filter element 10. The condition illustrated in FIGS. 2 and 3 in which the surfaces of the legs 11a of the pleats 11 are in intimate contact and in which the height h of each pleat 11 is greater that the distance between the inner and outer peripheries of the filter element 10 (i.e., ›D-d!/2 in FIG. 2) will be referred to as a laid-over state. In the laid-over state, pleats may extend, for example, in an arcuate or angled fashion or in a straight, non-radial direction, and there may be is substantially no empty space between adjacent pleats, and virtually all of the volume between the inner and outer peripheries of the filter element 10 may be occupied by the filter element 10 and can be effectively used for filtration.
Because the filter element 10 is formed from a material having a finite thickness t, at the radially inner and outer ends of the pleats 11 where the filter element 10 is folded back upon itself to form the pleats 11, the pleats 11 will be somewhat rounded. As a result, at the radially inner ends of the pleats 11, small triangular gaps 11f are formed between the opposing internal surfaces 11d of adjoining legs 11a, and at the radially outer ends of the pleats 11, small triangular gaps 11g are formed between the opposing external surfaces 11e of adjoining legs 11a. However, in the present invention, the height of these gaps 11f and 11g as measured along the height of the pleats is preferably extremely small. The height of the gaps 11f adjoining the inner diameter of the filter element 10 is preferably no more than approximately t and more preferably no more than approximately 1/2t, wherein t is the thickness of the material forming the filter element 10, as shown in FIG. 3. The height of the gaps 11g adjoining the outer diameter of the filter element 10 is preferably no more than approximately 4t and more preferably no more than approximately 2t. The sharper the pleats 11, i.e., the less rounded are their radially inner and outer ends, the smaller can be the heights of the gaps 11f and 11g and the greater can be the percent of the volume between the inner and outer peripheries of the filter element 10 which is available for filtration.
The opposing surfaces of adjoining legs 11a of the pleats need not be in intimate contact over the entire axial length of the filter element 10, but the greater is the length in the axial direction of the region of intimate contact, the more effectively used is the space between the inner and outer periphery of the filter element 10. Therefore, adjoining legs 11a are in intimate contact over a continuous region which preferably extends for at least approximately 50%, more preferably at least approximately 75%, and most preferably approximately 95-100% of the axial length of the filter element 10.
The filter element 10 includes a filter medium and drainage means disposed on at least one side, preferably the upstream side, and more preferably on both the upstream and downstream sides of the filter medium. The drainage means prevents opposing surfaces of the filter medium from coming into contact with one another and enables fluid to evenly flow to or from substantially all portions of the surface of the filter medium when the pleats are in the laid-over state. Thus, virtually the entire surface area of the filter medium may be effectively used for filtration.
In the embodiment of FIG. 1, the filter element 10 comprises a three-layer composite of a filter medium 12, upstream drainage means in the form of an upstream drainage layer 13 disposed on the upstream surface of the filter medium 12, and downstream drainage means in the form of a downstream drainage layer 14 disposed on the downstream surface of the filter medium 12. Here, upstream and downstream surfaces when the filter is being subjected to radially inward fluid flow or to interior and exterior surfaces when the filter is being subjected to radially inward fluid flow or to interior and exterior surfaces when the filter is being subjected to radially outward fluid flow.
There are no particular restrictions on the type of filter medium which can be employed in the present invention, and it can be selected in accordance with the fluid which is to be filtered and the desired filtering characteristics. The filter medium 12 can be used to filter fluids such as liquids, gases, or mixtures thereof. The filter may comprise a porous film or a fibrous sheet or mass; it may have a uniform or graded pore structure and any appropriate effective pore size; it may be formed from any suitable material, such as a natural or synthetic polymer, glass, or metal.
The filter medium 12 may comprise a single layer, or a plurality of layers of the same medium may be disposed atop one another to a desired thickness. Furthermore, it is possible for the filter medium to include two or more layers having different filtering characteristics, e.g., with one layer acting as a prefilter for the second layer.
The upstream and/or downstream drainage layers may be regions of a single, unitary porous sheet having a finely-pored center region, which serves as a filter medium, and coarsely-pored upstream and/or downstream regions which serve as the drainage layers. However, the drainage layers are preferably distinct layers separate from the filter medium.
The upstream and downstream drainage layers 13 and 14 can be made of any materials having suitable edgewise flow characteristics, i.e., suitable resistance to fluid flow through the layer in a direction parallel to its surface. The edgewise flow resistance of the drainage layer is preferably low enough that the pressure drop in the drainage layer is less than the pressure drop across the filter medium, thereby providing an even distribution of fluid along the surface of the filter medium. The drainage layers can be in the form of a mesh or screen or a porous woven or non-woven sheet.
Meshes or screens (also called netting) come in various forms. For high temperature application, a metallic mesh or screen may be employed, a metallic mesh or screen may be employed, while for lower temperature applications, a polymeric mesh may be particularly suitable. Polymeric meshes come in the form of woven meshes and extruded meshes. Either type may be employed, but extruded meshes are generally preferable because they are smoother and therefore produce less abrasion of adjoining layers of the filter composite. An extruded mesh may have a first set of parallel strands and a second set of parallel strands intersecting the first set of strands at an angel. Extruded meshes may be classified as either symmetrical or non-symmetrical. In a symmetrical mesh, neither of the first or second sets of strands extends in the so-called "machine direction" of the mesh, which is the direction in which the mesh emerges from a mesh manufacturing machine. IN a non-symmetrical mesh, one of the sets of strands extends parallel to the machine direction. IN the present invention, it is possible to use either symmetrical or non-symmetrical meshes. Non-symmetrical meshes have a somewhat lower resistance to edgewise flow per thickness than do symmetrical meshes. Therefore, for a given edgewise flow resistance, a non-symmetrical mesh can be thinner than a symmetrical mesh, so the number of pleats in a filter element 10 using a non-symmetrical mesh can be larger than for a filter element of the same size using a symmetrical mesh. One the other hand, symmetrical meshes have the advantage that they are easier to work with when manufacturing a pleated filter element 10.
Meshes may be characterized by their thickness and by the number of strands per inch. These dimensions are not limited to any particular values and can be chosen in accordance with the desired edgewise flow characteristics of the mesh and the desired strength. Typically, the mesh will have a mesh count of at least 10 strands per inch.
In embodiments of the present invention, the opposing surfaces of the pleats are in intimate contact. Consequently, the strands of the drainage mesh of each leg of the pleats are pressed against the strands of the drainage mesh of an adjacent leg of the pleats. If the strands of the mesh on two opposing surfaces are parallel to one another, the strands may have a tendency to "nest", i.e., to fit between one another rather than to lie atop one another. This degrades the drainage properties of the mesh and decreases its ability to properties of the mesh and decreases its ability to provide drainage for the filter medium. With a non-symmetric mesh, care must be taken that the machine direction strands are on the side of the mesh facing toward the filter medium rather than away from it so as to prevent nesting of the strands when the filter element 10 is corrugated. With a symmetric mesh, however, there are no machine direction strands, so it does not matter which surface of the mesh faces the filter medium, and less care is required in assembly of the filter element 10.
Regardless of whether a mesh is symmetric or non-symmetric, the strands of the meshes can be prevented from nesting if the meshes are oriented as follows. Assuming that the first set of strands is on the side of a mesh facing toward the filter medium and the second set of strands is separated from the filter medium by the first set of strands, the second set of strands can be prevented from nesting when the pleats are in a laid-over state if the second set of strands extends along lines intersecting the longitudinal axis of the filter element at an angle between 0 and 90 degrees. If the second set of strands extends along lines intersecting the axis at an angle of either 0 or 90 degrees, i.e., if the second set of strands is either parallel or perpendicular to the axis of the filter element, it is possible for the second set of strands to nest. However, at any angle between these limits, the second set of strands will lie atop each other without nesting.
If the mesh is so oriented, when the pleats 11 assume a laid-over state, a surface which is tangent to the second strands of the mesh on each leg of a pleat will be in intimate contact with a surface which is tangent to the second strands of the mesh of an adjoining leg.
Specific examples of suitable extruded polymeric meshes are those available from Malle Plastics (Austin, Tex.) under the trade names Maltex, Zicot, and Ultraflo.
Meshes are particularly suitable as drainage layers when the filter medium is a fibrous laid-down medium. On the other hand, when the filter medium is a membrane, a woven or non-woven fabric is more suitable for use as the drainage layer because a fabric is usually smoother than a mesh and produces less abrasion of adjoining layers of the filter composite. An example of a suitable non-woven fabric for use as a drainage layer is a polyester non-woven fabric sold under the trade designation Reemay 2011 by Reemay, Inc.
The upstream and downstream drainage layers 13 and 14 can be of the same or different construction. It has been found that the pressure drop across the filter medium 12 may be lowest and filter life may be longest when both drainage layers 13 and 14 have substantially the same edgewise flow resistance. Therefore, regardless of whether the drainage layers 13 and 14 are made of the same material, they are preferably selected so as to have substantially the same resistance to edgewise flow. For ease of manufacture, it is convenient to use identical materials for both drainage layers 13 and 14, thereby assuring the same edgewise flow resistance through both drainage layers.
Alternatively, the upstream and downstream drainage layers 13 and 14 may have different characteristics and these characteristics may be varied to provide a desired effect. For example, where the thickness of the filter composite is fixed, e.g. in order to fix the surface area of the filter medium within an envelope, the thickness of the upstream drainage layer may be greater than the thickness of the downstream drainage layer. This may provide greater cake space on the upstream side of the filter medium, but is may sacrifice even flow distribution on the downstream side of the filter medium.
The filter composite forming the filter element 10 may include other layers in addition to the filter medium 12 and the drainage layers 13 and 14. For example, in order to prevent abrasion of the filter medium due to rubbing contact with the drainage layers when the pleats expand and contract during pressure fluctuations of the fluid system in which the filter is installed, a cushioning layer can be disposed between the filter medium and one or both of the drainage layers. The cushioning layer is preferably made of a material smoother than the drainage layers and having a higher resistance to abrasion than the filter medium 12. For example, when the drainage layers are made of an extruded nylon mesh, an example of a suitable cushioning layer is a polyester non-woven fabric such as that sold under the trade designation Reemay 2250 by Reemay Corporation.
The layers forming the filter element 10 can be formed into a composite by conventional filter manufacturing techniques, either prior to or simultaneous with corrugation.
In the prior art, in order to ensure adequate drainage in a filter element with closely spaced pleats, it was necessary to form large surface irregularities, such as grooves, in the surface of the pleats in order to create drainage passageways. These grooves, typically formed by a method such as embossing, greatly reduced the volume of a filter element which was available for filtration in the present invention, the drainage layers can provide adequate drainage even when in intimate contact with one another, so large surface irregularities in the pleats are not necessary. Therefore, each of the layers in the filter composite forming the filter element 10 may have a substantially flat surface.
The core 20 supports the inner periphery of the filter element 10 against forces in the radial direction and also helps to give the filter axial strength and rigidity against bending. The core 20 may be of conventional design and may be made of any material having sufficient strength and which is compatible with the fluid being filtered. Openings are formed through the wall of the core 20 to permit the passage of fluid between the outside and the center of the core 20.
When the filter element 10 is being subjected to outside-to-inside fluid flow, the presence of a core 20 is usually desirable. However, depending upon the forces acting on the filter element 10 during filtration, it may be possible to omit the core 20. For example, when the fluid flow through the filter element 10 is primarily form the inside to the outside thereof, radially inward forces on the filter element 10 may be absent or so low that a core 20 becomes unnecessary, enabling a reduction in the weight of the filter.
A filter according to the present invention preferably includes means for retaining the pleats of the filter element 10 in a laid-over state. In the present embodiment, this means comprises the outer cage 30 which surrounds the filter element 10. The cage 30 may be of conventional design with openings formed therein for the passage of fluid. The material of which the cage 30 is made can be selected based on the fluid being filtered and the filtering conditions.
Usually, a filter according to the present invention will be equipped with end caps 40 (only one of which is shown in FIG. 1) at one or both ends of the filter element 10. The end caps 40 can be either blind or open end caps, and the material of which they are formed on their shape can be selected in accordance with the filter conditions and the materials of the members to which the end caps are to be joined. Preferably, the end caps 40 are attached to the filter element 10, but they may also be attached to the core 20 or the cage 30. Conventional techniques can be used to attach the end caps to the filter element 10, such as by use of an epoxy, by polycapping (as taught, for example, in U.S. Pat. No. 4,154,688), or by spin welding.
In order to prevent leakage of fluid at the ends of the filter element 10, it is desirable to obtain a good seal between the end caps 40 and the end surface of the filter element 10 so that fluid is prevented from passing through the end surfaces of the filter element 10. However, it may be difficult to obtain a good seal when the filter element 10 and the end caps 40 are made of materials having poor affinity for one another. In such cases, an insert in the form of a strip of material having a good affinity for the end cap material can be corrugated into the ends of the filter element 10. FIG. 4 schematically illustrates a portion of a filter element having an insert 15 corrugated between two of the layers of the filter composite. When the end caps 40 are attached, the insert 15 enables the creation of a good seal between both ends of the filter element 10 and the end caps 40. For example, when the end caps are made of a fluoropolymer, a strip of another fluoropolymer, such as a fluorinated ethylene-propylene (FEP) resin, can be corrugated into the ends of the filter element 10 as the insert 15. The insert 15 need only be wide enough to bond the filter medium to the end cap, and therefore, as shown in FIG. 4, it normally extends for only a portion of the axial length of the filter element 10. A typical width for the insert 15 is approximately 0.5 inches.
The filter element 10 illustrated in FIG. 1 can be manufactured by a variety of techniques. In one technique, the filter composite is first corrugated to form a corrugated sheet, cut to a suitable length or suitable number of pleats, and then formed into a cylindrical shape. The lengthwise edges of the corrugated sheet are then sealed to each other by conventional means to form a cylindrical filter element 10. The pleats of the filter element 10 are then laid over as the filter element 10 is inserted into a cage 30. After the filter element 10 has been fit into the cage 30, a core 20 is inserted into the hollow center of the filter element 10, and then end caps 40 are attached to the ends of the filter element 10 to form a completed fiber.
FIG. 5 illustrates one method of laying over the pleats. In this method, the filter element 10 is inserted lengthwise into the mouth of a funnel-shaped tool 60 having an exit (the left end in FIG. 5) adjoining a cage. As the filter element 10 is pushed into the tool 60, it is simultaneously twisted, either by hand or by machine, thereby causing the pleats to lay over against one another. The dimensions of the tool 60 are selected so that at the exit, the filter element 10 has an outside diameter small enough for the filter element 10 to slide into the cage 30.
It is also possible to form the pleats of a corrugated sheet 10 into a laid-over state before forming the pleats into a cylindrical form. For example, after the filter composite is passed through a corrugator to form a substantially planar corrugated sheet, the sheet can be pressed between two flat surfaces to flatten the sheet and cause the pleats to lay over against one another. The thus flattened corrugated sheet can then be bent into cylindrical form and the ends of the sheet sealed to one another to form a cylindrical filter element 10.
It may be easier to lay over the pleats of the filter element 10 if there is a smooth radius on the outside pleat crest as opposed to a sharp crease. One method of creating a smooth radius is to place a disposable layer of paper, referred to as a strip-out paper, on the downstream side of the filter corrugated composite during corrugation. The strip out paper becomes part of the pleats and produces a desired smooth radius. The strip-put paper is then stripped off the composite after the completion of corrugation and before the composite id formed into a cylinder. The material used for the strip-out paper is not critical. An example of a suitable material is a smooth paper. The thickness of the strip-out paper can be selected based on the desired bending radius of the corrugated composite, taking into consideration the thickness of the other layers of the composite.
Another technique for manufacturing the filter element 10 allows the formation of pleats in which the adjoining legs have slightly different lengths. For many filter elements, especially those formed from a multilayer composite, it is easier and more reliable to form the filter element into a laid-over state if the adjoining legs of each pleat have slightly different lengths. Such pleats will be referred to as pleats with unequal legs.
Preferred embodiments of a pleating method and apparatus according to this aspect of the present invention will now be described with reference to FIGS. 6-11, which schematically illustrate one cycle in a pleating method of the present invention. As shown in these figures, pleats are formed atop a support, such as a planar pleating table 100, by a pleater member and a stripper member. In accordance with one aspect of the invention, the pleats are formed between surfaces of the pleater member and the stripper member which are curved or extend at an acute angle from the pleating table 100, preferably substantially less than 90.degree., more preferably within the range from about 15.degree. to about 75.degree., and most preferably within the range from about 30.degree. to about 60.degree., e.g., 45.degree.. For example, the pleater member may be a wedge-shaped member referred to as a pleating wedge 101 and the stripper member may be a thin plate referred to as a stripper knife 102. The pleating wedge 101 can be raised and lowered with respect to, and moved back and forth parallel to, the top surface of the pleating table 100, while the stripper knife 102 can be raised and lowered with respect to the pleating table 100. For convenience, the surface of the pleating table 100 is usually level, but a level surface is not necessary for the method of the present invention.
The material 103 to be pleated may be dispensed onto the pleating table 100 by any suitable means, such as a reel 104. The material 103 may be a single sheet or layer, or it may be a composite of a plurality of layers, such as a filter medium and one or more drainage layers. The layers may be formed into a composite prior to being stored on the reel 104, or the individual layers may be stored on separate reels and simultaneously fed to the pleating table 100 so that the composite is formed as the layers are pleated.
As shown in the figures, the front surface 101a of the pleating wedge 101 and the rear surface 102a of the stripper knife 102 (the surface which opposes the pleating wedge 101) are both sloped with respect to the pleating table 10 by similar but not necessarily equal acute angles. It is because these surfaces extend at acute angels, or because they are curved, that the method of the present invention is able to form pleats having adjoining legs of unequal lengths.
FIG. 6 illustrates the start of the pleating cycle, in which the pleating wedge 101 is locate at a point A in the figure. At this position, the front surface 101a of the pleating wedge 101 is spaced from the rear surface 102a of the stripper knife 102 by a predetermined distance which depends upon the height of the pleats which are to be formed. The lower surface of the pleating wedge 101 is in frictional contact with the material 103 to be pleated, and the lower edge of the stripper knife 102 is pressed against the material 103 to be pleated so as to restrain it.
The pleating wedge 101 is then moved from point A towards the stripper knife 102 in the direction of the arrow in FIG. 7 while the lower surface of the pleating wedge 101 remains in frictional contact with the material 103 to be pleated. At the same time, the stripper knife 102 is maintained stationary. Due to the frictional contact between the pleating wedge 101 and the material 103 to be pleated, the movement of the pleating wedge 101 towards the stripper knife 104 causes the portion of the material 103 disposed between the pleating wedge 101 and the stripper knife 102 to bend upwards from the surface of the pleating table 100 in the form of a bulge 105.
As the pleating wedge 101 is moved still closer to the stripper knife 102, the bulge 105 in the material 103 to be pleated begins to fold into the shape of a pleat 11, as shown in FIG. 8. The pleating wedge 101 is advanced further to a point B in FIG. 9, in which the material 103 is compressed between the front surface 101a of the pleating wedge 101 and the rear surface 102a of the stripper knife 102, thereby forming a single pleat 11.
The stripper knife 102 is then raised from the pleating table 100 and simultaneously pivoted in the clockwise direction in the figures. As the stripper knife 102 rises, its rear surface 102a slides along the pleat 11 which was just formed, further pressing the pleat 11 against the front surface 101a of the pleating wedge 101. When the rear surface 102a of the stripper knife 102 clears the upper end of the pleat 11, the rear surface 102a of the stripper knife 102 may then contact the front surface 101a of the pleating wedge 101, as shown in FIG. 10. The stripper knife 102 is then lowered, and its rear surface 102a slides along the front surface 101a of the pleating wedge 101 between the pleating wedge 101 and the pleat 11 just formed until the lower edge in FIG. 11. During the raising the lowering of the stripper knife 102, the pleating wedge 101 may be maintained substantially stationary.
Next, while the stripper knife 102 is maintained stationary, which in turn holds the material 103 stationary, the pleating wedge 101 is returned to point A to complete the pleating cycle. The path of the pleating wedge 101 as it travels from point be back to point A is such that the lower surface of the pleating wedge 101 is raised above the surface of the material 103 to be pleated so that the material 103 will not be pulled backwards. For example, the pleating wedge 101 can be moved along a path with straight sides indicated as B-C-D-A in FIG. 6. Alternatively, the pleating wedge 101 can move along an arcuate path in going from point B to point A. Upon the wedge 101 returning to point A, the above process is repeated.
Each time the cycle illustrated in FIGS. 6-11 is performed, a new pleat 11 is formed, and it is moved by the stripper knife 102 to the right to join the pleats 11 which have already been formed and which accumulate on the right side of the stripper knife 102 in the figures. The entire group of completed pleats 11 is incrementally pushed to the right by the movement of the stripper knife 102. Any desired number of pleats can be formed by repeating the above-described cycle a corresponding number of times. The group of completed pleats may be conveniently rolled off the end of the pleating table 100.
FIGS. 12 and 13 are schematic illustrations showing the operation of a creaser bar 109. These figures are analogous to FIGS. 6-11 except the pleating apparatus further includes a creaser bar 109 which moves up and down through a gap 110 in the pleating table 100. In these figures, as the pleating wedge 101 begins to move toward point B from point A, the creaser bar 109 is made to protrude through the gap 110 in the pleating table 100 and above the surface of the pleating table 100. When the creaser bar 109 protrudes above the surface of the pleating table 100, it contacts the material 103 and forces the material 103 to bulge upwards properly, e.g., without any wrinkles. The upper edge of the creaser bar may also form a crease in the material which may become the crest or root of the pleat. As the pleating wedge 101 moves closer to point B, the creaser bar 109 is retracted beneath the surface of the pleating table 100 so that the pleating wedge 101 can pass over the gap 110 in the pleating table 100. The pleating process is otherwise the same as described with respect to FIGS. 6-11.
FIG. 14 is an enlarged view of a pleat 11 which can be formed by the process illustrated in FIGS. 6-13. The pleat has two legs 11a', 11a", one of which contacts the front surface 101a of the pleating wedge 101 and the other of which contacts the rear surface 102a of the stripper knife 102. Because the front surface 101a of the pleating wedge 101 is sloped with respect to the pleating table 100 by an acute angle, the length L1 of the leg 11a' contacting the front surface 101a of the pleating wedge 101 may be shorter than the length L2 of the adjoining leg 11a " of the same pleat 11, wherein the lengths may be measured between the points where the material 103 being pleated is folded back upon itself. If the front surface 101a of the pleating wedge 101 is sloped with respect to the surface of the pleating table 100 by an angle .theta..sub.1 and the thickness of the material 103 to be pleated is t, then the difference between the lengths L1-L2=2t/tan.theta..sub.1. The difference in length can be set to a desired value by suitably selecting the angle of the pleating wedge 101. Due to the difference in length, pleats formed by the method of the present invention can be easily formed into a laid-over state.
Many of the components of a pleating apparatus according to the present invention are similar to those of commercially available push bar type pleating machines, such as a Model No. 10148 pleating machine manufactured by Chandler Machine Company of Ayer, Mass. Pleating is performed atop a pleating table 100, as shown in FIGS. 15 and 16. In a typical pleating machine, the pleating table 100 has two sections 100a and 100b which can be moved with respect to each other in the horizontal direction to form a gap of a desired size between the two sections. When the movable sections 100a and 100b are separated by a gap, the creaser bar 109 can be moved up and down in the gap by an unillustrated drive mechanism to assist in the pleating process. If the creaser bar 109 is not employed, the two sections 100a and 100b of the pleating table 100 are made to abut, or the pleating table 100 can be made in one piece and the creaser bar can be omitted.
In the embodiment of FIG. 15, the material being pleated is a filter composite 103 of three different layers 103a, 103b, 103c dispensed onto the pleating table 100 from three different reels 104a, 104b, 104c, respectively. The layers 103a, 103b, 103c can be made of the same of different materials. In this example, the material 103b on the middle reel 104b is a filter medium, while the materials 103a and 103con the top and bottom reels 104a and 104c are extruded meshes which serve as drainage layers for the upstream and downstream surfaces of the filter medium 103b.
The pleating apparatus is equipped with a bar which has a generally L-shaped cross section and which is referred to as a pusher bar 111. The pusher bar 111 is movably disposed atop the pleating table 100 so as to move along a closed path, at least one portion of which extends parallel to the surface of the pleating table 100. In this embodiment, the pusher bar 111 is driven along a four-sided closed path, indicated by points A'-B'-C'-D' in FIG. 15, by a drive mechanism 112. While a pusher bar 111 need not be employed in a pleating apparatus according to the present inve |