Stacked Sheet Filter Assembly

Abstract

A plurality of flexible metal sheets, each too thin to be self-supporting, are selectively etched so as to have projections on one surface, and such projections have roughened lateral surfaces. Such sheets are stacked and compressed to form a rigid structure, which is placed in a housing so that entering fluid must pass between the edges of the stacked sheets to reach an outlet. The roughened surfaces and projections trap undesired particles of extremely small size. Housings include threaded locking elements for the stack with passages for equalizing pressures thereon, and grooves or ribs for cooperative locking engagement with the filter elements.

Parent Case Text

This application is a continuation of Ser. No. 688,938, which is a continuation of Ser. No. 562,043, which is a continuation-in-part of my copending application, Filter, Ser. No. 218,642, filed Aug. 22, 1962, all now abandoned.

Description

The present invention relates to filters and, more particularly, to a filter for removing solid contaminants from a fluid that is utilized by downstream components.

There is a continuing need for the improvement of filters for the removal of solid particles from liquid or gaseous media. In recent times, this need has become acute in connection with the separating of particles of less than 100 micron size from hydraulic fluids, fuels and other fluids utilized in missiles and aircraft.

Heretofore, wire mesh and sintered filters have usually been employed for the separation of particles smaller than 100 microns. However, these types inherently have disadvantages whereby they give very short service lines at the level of efficiency indicated by their absolute and nominal ratings. For example, the manufacturing processes used inherently involve a high level of filter element contamination resulting from the sintering or weaving process; the filters have poor resistance to vibration stresses; the filters have an inerently low capacity to resist high pressure differentials; the filters have an unsatisfactory temperature range of operation; and the filter elements cannot be cleaned after use and therefore are not reusable.

The foregoing and other disadvantages of previously available filters are eliminated by my invention.

More specifically, one of the important objects of the invention is to provide a filter element of unitary or integral one-piece structure that can be manufactured and placed into use in an absolutely clean condition with no manufacturing contaminant remaining thereon. As a result, when filter elements of this type are placed into use, they do not release portions of themselves downstream in the effluent even when subjected to extreme sonic vibration, shock or excessive pressure differentials.

Another object of the invention is to provide a filter utilizing a stack or stacks of such unitary filter elements that are compressively loaded to constitute a rigid column which will stand extremely great pressure differentials. Additionally, the stack arrangement of filter elements provides an edge of filtration in combination with a depth type of filtration, the latter type of filtration serving to entrap elongated contaminants while the edge or surface type of filtration captures spherical particles or the like.

Yet another object of the invention is to provide a filter that can be sold in an absolutely clean condition and which can be recleaned under field service conditions after having been in service. In this connection, the filter of my invention has a removable cartridge and a stacking arrangement of filter elements permitting loosening of the compressive force on the elements whereby every individual element can be readily be cleaned while the stack is in the loosened condition. Furthermore, individual filter elements of the stack, if found defective under a bubble test, may be removed and replaced whereas with sintered or wire mesh filters, defects found after bubble testing are brazed or soldered, thus adding material which can be lost in the effluent.

These and other objects and advantages of the invention will be apparent from the following description, when taken in conjunction with the annexed drawings.

FIG. 1 is a perspective view of a filter assembly incorporating the invention, the assembly being longitudinally sectioned on a diametral plane to disclose details of interior construction;

FIG. 2 is a perspective view of the filter cartridge utilized in the assembly of FIG. 1;

FIG. 3 is a transverse sectional view of the filter assembly taken on the line 3--3 in FIG. 1;

FIG. 4 is a partial plane view of the area 4 of FIG. 3, on an enlarged scale, to show details of the configuration of one side of a filter element;

FIG. 5 IS A sectional view on the line 5--5 of FIG. 4, on a further enlarged scale;

FIG. 6 is a plan view of an alternative configuration of filter element for use in the assembly of FIG. 1;

FIG. 7 is an axial sectional view of an alternative embodiment of filter assembly;

FIG. 8 is a transverse sectional view on the line 8--8 of FIG. 7;

FIG. 8a is a partial plan view of one surface of one of the filter elements of the assembly of FIG. 7;

FIG. 9 is a longitudinal sectional view of a radiator type filter assembly embodying the invention;

FIG. 10 is a sectional view taken on the line 10--10 of FIG. 9;

FIG. 11 is a partial plan view of the area 11 of FIG. 10, on an enlarged scale, showing the configuration of one side of a filter element;

FIG. 12 is an axial sectional view of an alternative embodiment of an in-line filter assembly;

FIG. 13 is a transverse sectional view taken on the line 13--13 of FIG. 12, showing the dual inlet arrangement for the influent;

FIG. 14 is a sectional view on the line 14--14 of FIG. 12;

FIG. 15 is a partial plan view of the area 15 of FIG. 14, on an enlarged scale;

FIG. 16 is a sectional view on the line 16--16 of FIG. 14;

FIG. 17 is a transverse sectional view of a filter cartridge containing another configuration of filter element;

FIG. 18 is a partial plan view of an inner area of thin sheet metal having a resist pattern thereon to illustrate a step in the process of making a filter element;

FIG. 19 is a view of the resist pattern on the other side of sheet metal piece shown in FIG. 18;

FIG. 20 is a sectional view on the line 20--20 OF FIG. 18, schematically indicating another step in the process of etching filter elements;

FIG. 21 is a partial plan view of another embodiment of a filter element of my invention;

FIG. 22 is an enlarged fragmentary plan view of the filter element of FIG. 21; and

FIG. 23 is a partial plan view of a still further filter element of my invention.

FIG. 1 shows a T-type filter assembly 20 in which is mounted a filter cartridge 21, such as is seen in FIG. 2. This assembly includes a generally cylindrical housing 22 which may be formed integrally with an upper end wall 23 closing the upper end of the housing. The housing defines a generally cylindrical chamber 24 having a smooth land 25 at its lower end adapted to slidably receive a cylindrical cage 26 of the cartridge 21. The upper end or roof of the chamber 24 has a downwardly protruding index pin 27 adapted to seat in a blind index bore 28 formed in the upper face of an integral flange 29 of the upper end of the cage 26. The cartridge 21 is thus held in predetermined angular relationship within the housing 22. At its lower end, the chamber 24 is internally threaded, as indicated at 30, to threadably receive a locking disc 3-1 by means of which the filter cartridge is securely held against the roof of the housing 22. Beneath the internal threads 30, the chamber 24 is formed with a smooth counterbore 32 to slidably receive a cylindrical boss portion of a cap 33 that closes the lower end of the housing. This cap may be held in place by a plurality of bolts 34, or other suitable fastening means, to seal the lower end of the housing 22, The lower end of the chamber is bevelled, as indicated at 35, to receive an O-ring 36 that is mounted around the boss of the cap 33.

The filter cartridge 21 defines an annulus with the housing 22 to which the fluid to be filtered is introduced through an inlet port 37 and intermediate passage 38. The cartridge 21 contains a coaxially arranged stack of ring shaped filter discs 40 defining a hollow core for the filter cartridge. Thus, the fluid passes radially inwardly from the annulus, between discs 40, thereafter to be passed through the hollow core of the cartridge and exhausted from an outlet port 41 of the housing. To insure that none of the fluid bypasses the filter cartridge 21, a circular groove 42 is formed in the upper end flange 29 of the filter cage 26 to hold an O-ring 43.

Each of the filter elements is made of an impervious material, preferably sheet metal that has been etched, cut, rolled, coined or otherwise formed. For critical applications where it is desired, for example, to make a filter having an absolute rating of 25 microns, the filter elements preferably comprise stainless steel sheet which is completely formed by etching.

More specifically, let it be assumed that the filter 20 has an absolute rating of 25 microns. Each of the identical filter discs 40 is them made from stainless steel sheet by etching the sheet into the ring like configuration shown, and to leave on one surface of the disc an array or pattern of protrusions 40a integrally with an impervious base portion 40b. The stainless steel sheet from which the discs 40 are etched has an original thickness of 0,002 inch and is partially etched on one face to a depth of 0.001 inch whereby the protrusions 40a extend 0.001 inch above the base section 40b. The discs 40 may be etched with unbroken inner and outer peripheral edges, if desired, but in this instance, in order to increase the edge filtration area, the discs have been etched to leave a crenelated outer edge 40c and may also have an inner crenelated edge 40d. An alternative inner end outer edge configuration for another form of disc 40' is shown in FIG. 6 having sawtooth inner and outer edges 40d' and 40c', respectively, etched in the disc.

As is shown in FIG. 5, the discs 40 are stacked one on top of the other with the protrusions 40a of one disc in engagement with the smooth unetched surface of another disc 40 so that there is a gap at both the inner and outer edges of an adjacent pair of discs of 0.001 inch. Accordingly, when a stack of the discs 40 is compressively and coaxially held, as in the cartridge 21, edge filtration occurs at the outer edge of the discs 40 so that particles exceeding 25 microns in diameter are kept from passing radially inwardly through the stack. Inwardly of the outer surface of the stack, a depth type of filtration occurs due to the presence of the protrusions 40a which will capture such elongated particles, having a diameter of 25 microns or smaller which have managed to pass inwardly of the outer surface of the stack. Such elongated particles, as for example, cotton linters, will not be capable of following the sinuous path between the closely spaced protrusions 40a and therefore will be caught.

As is shown in FIG. 4, the protrusions 40a are Y-shaped and are closely spaced together. More specifically, each protrusion 40a has the arms of the Y opening radially outwardly of the disc with the stem of the Y disposed substantially in a radial direction of the disc. A stagnation cavity 46 is thus defined by the pair of arms of each Y-shaped protrusion 40a which will capture a substantial part of all spherical and fibrous particles smaller than 25 microns which pass the edge filtration action of the stack of discs. It should also be noted that the gap between the stem portions of an adjacent pair of Y-shaped protrusions 40a is interrupted by a stagnation cavity 46 of another protrusion 40a positioned behind the adjacent pair of protrusions. For example, in FIG. 4 an adjacent pair of protrusions x and y have the gap between their stem portions interrupted by the stagnation cavity of another protrusion. With this arrangement, not only is a very sinuous path defined for the entrapment of elongated particles, but the clearance between protrusions 40a can be held to a very small value to arrest the passage of such particles, smaller then 25 microns, as may not be entrapped in the stagnation cavities 46.

The discs 40 have an outer diameter to be slidably receivable within the cage 26 and an innner diameter corresponding to the diameter of the effluent opening through the flange 20 in the upper end of the cage. When the cartridge 21 is assembled, all of the discs 40 are oriented in the manner shown in FIG. 5, i.e., with the protrusions 40a of each disc abutting the underside or unetched surface of the disc 40 just above or adjacent. For a 25-micron filter, 400 of the discs 40 are utilized for each inch of filter, measured axially of the stack of filters discs. The required number of discs are placed within the cage 26 to be seated, at one end of the stack, on the flange 29 of the upper end of the cage. At intervals of about 1 inch, rigid washers 65 are placed in the stack of discs to aid in holding the discs against turning when torque is applied at one end of the stack to compress it into a rigid column and, also, to prevent the disc tilting out of planes normal to the axis of the stack, which could occur due to an accumulation of tolerances of the discs or accumulation of slightly bent discs.

The lower end of the case 26 is tapped to receive a nut 49 to clamp the stack of discs 40 against the flange 29. The discs 40, before clamping, may not be perfectly flat and the loosely contained stack of discs and washers will have slack to occupy an over-all length greater than the finished length. After tightening of the nut 49, all slack between discs will be taken up and there will be approximately 500 discs per inch and the entire stack has the characteristics of a relatively incompressible loaded structural column. In this connection, the close spacing of the protrusions 40a is important, and the pattern of distribution of the protrusions, in order to insure that a large proportion of protrusions will not penetrate into or bend the surface of another disc. Care should be taken to insure that a majority of the protrusions of a disc have bearing contact with areas of an adjacent disc that are also the bases of protrusions of the adjacent disc to define columnar areas through the superposed protrusions or superposed areas of protrusions.

After the nut 49 has been tightened, a lock nut 50 is screwed onto the tapped lower end or skirt of the case 26. The cartridge 21 is then ready for placement within the housing 22 to be held in place by the nut 31 that bears against the lower end of the cage 26.

As is shown in FIG. 2, the wall of the cage 26 is cut away between the lower end skirt and the upper end of the cage leaving four longitudinally extending bars 51, 52, 53, and 54 between which the outer edges 40c of the discs 40 are exposed, as the edge filtration area of the filter cartridge. The opening between the bars 51 and 52 is of shorter length than the other openings to provide a deflector 55. Because of the index pin 27, the cartridge 21 is set within the housing 22 in a predetermined angular relationship whereby the deflector 55 is positioned opposite the passage 38 from the inlet 37 of the housing 22. Thus as the fluid to be filtered enters the housing 22 and leaves the passage 38, the particles therein do not impinge on the edges of the discs 40 behind the deflector 44. Accordingly, wear of the outer edges of this group of discs 40 is avoided and the particulate matter within the fluid is uniformly dispersed throughout the annulus defined around the filter cartridge.

To counterbalance the fluid pressure exerted on the holding nuts, a system of pressure relief ports is provided in the nuts 49, 50 and 31. The nut 49 has a plurality of ports 60 extending from the upper surface at the outer edge of the nut downwardly and radially inwardly to open into the undersurface of the nut. The upper surface of the nut 50 is formed with a shallow cylindrical cavity 61 and the spanner wrench holes 62 of the nut 50 extend through the nut so that fluid reaching the cavity 61 from the ports 60 can pass through the nut 50. Similarly, the nut 31 has through spanner holes 63 to pass fluid to the space between the nut 31 and the heavy cap 32 for the housing 22. In this manner, pressures tend to be equalized on the nut 31, nut 50 and nut 49.

In FIG. 7, the invention is embodied in an inline filter assembly 70. In this assembly, a tubular housing 71 is formed with an interior integral partition 72. On the downstream side of the partition, an annular recess 73 is formed to receive a ring 74 that is one end of a cage to contain a stack of filter discs 75. The other end of this cage comprises a ring 76 disposed in a plane diametrically to the axis of the stack of filter discs 72 and interconnected to the ring 74 by a plurality of ribs 77.

The discs 75 may also be made of a very thin sheet metal which is first die formed into conical configuration and then etched to leave the ring-like plan configuration shown, with inner and outer edges 75a and 75b, respectively. Then, one face of the disc is etched to the desired depth, leaving circular protrusions 75c integral with an imperforate base portion 75d. For example, it it is desired to have a filter with an absolute rating of 25 microns, the filter discs are made from 0.002 -inch sheet and one face is etched to leave the protrusions 75c extending 0.001 inch above the base section 75d. With respect to FIGS. 7, 8, and 8a, it will, of course, be appreciated that the thickness of the filter discs and the apparent area and height of the protrusions 75c and the spacing between the protrusions have been greatly exaggerated for clarity of illustration, just as in the case of the other filter elements illustrated in the drawings.

The filter discs 75 are arranged in a stack as shown in FIG. 7 so that the etched surface of one disc abuts the unetched surface of an adjacent disc. The stack of filter discs 75 is thereafter compressed to achieve the desired structural column effect and to achieve the desired gap of 0.001 inch between outer edges 75d for edge filtration.

The downstream side of the partition 72 is formed with a frusto-conical nose 80 to seat the concave face of the disc 75 at that end of the stack of the discs. The cage for the filter discs 75 is inserted first with the ring 74 in place on the shoulder 73. Thereafter, the loose stack of discs 75 is inserted through the opening in the ring 76 and the stack is thus held in coaxial alignment by the cage. The downstream end of the housing 71 is interiorly tapped, as indicated at 81, to threadly receive a downstream end fitting 82, formed with a circumferential groove 83 to seat an O-ring 84 to effect a fluid seal between the fitting and the housing. The end fitting 82, at its inner end, has a flat end face 85 adapted to abut the ring 76 of the disc retaining cage. Within the flat end 84, the fitting 82 is formed with a frusto-conical seat 86 to seat the convex face of the disc 75 at that end of the stack of filter discs. Tightening of the end fitting 82 causes compression of the stack of filter discs 75 against the disc seat formed on the nose of the partition 72. In this connection, the annular recess 73 provides clearance to permit full or complete compression of the stack of filter discs. The end fitting 83 is itself exteriorly threaded to receive a lock nut 87 that can be run up against the corresponding end of the housing 71 to retain the end fitting 82 in clamping position. The end fitting 82 has an axially extending outlet port 88 communicating with an outlet port adapter 89 that is threadedly received in the end fitting. An O-ring 90 is retained between the adapter 89 and the tapped bore of the end fitting 82 to effect a fluid seal.

The partition 72 is formed with a plurality of spaced passages 91 to receive the influent fluid from an inlet end fitting 92 threaded to the inlet end of the housing 71, as indicated at 93, The inlet end fitting 92, at its inner end, is formed with a circumferential groove 94 to seat an O-ring 95 to effect a fluid seal between the housing and the inlet end fitting. The inlet end fitting also has an axially extending inlet 96 that is tapped to receive an inlet port adapter 97. An O-ring 98 is retained under the head of the adapter 97 to effect a fluid seal between the adapter and the fitting 92.

In the operation of the filter assembly 70, the influent enters the fitting 92 and is distributed by the ports 91 of the partition 72 into the annular spaced defined between the stack of filter elements 75 and the wall of the housing 71. Edge filtration of particulate matter occurs on the outer edges of the filter discs 75, the edge spacing determining the absolute rating of the filter assembly 70. The fluid then passes inwardly to the hollow core of the stack of filter discs in the frusto-conical paths dictated by the configuration of the filter discs 75, and depth filtration occurs whereby elongated particles of smaller diameter than the edge gap become entrapped by the protrusions 75c . The filtered effluent is then passed outwardly from the hollow core of the stack of filter discs 75 through the bore 88 in the outlet fitting 82. Thus, the filtering action of the filter assembly 70 is very much like that in the filter assembly 20. However, a lesser pressure drop will be encountered with the filter assembly 70 due to the frusto-conical configuration of the filter discs, and the corresponding passage configuration, which gives an axial component to the flow of fluid through the filter.

In FIG. 9, the invention is embodied in a radiator type filter assembly 110. The filter housing has a body 111 whose lower end is sealed by a gasket 112 held in place beneath a bottom cap 113 that is retained by a plurality of suitable bolts or other fasteners 114. The upper end of the body 111 has its edge sealed by another gasket 112, beneath a removable cover plate 115 that is retained by a plurality of bolts 114 also. An inlet port 116 is provided in one end wall of the body 111 and in the opposite end wall there in an outlet port 117.

The filter assembly 110 has a stack of identical filter elements 120. As is shown in FIG. 10, each of these elements is an elongated rectangularly shaped strip, preferably of stainless steel, that has been etched into the rectangular shape shown and also etched to produce front and rear edge spaced compression pads 120d and Y-shaped protrusions 120a shown in an exaggerated scale in FIG. 11. As in the case of the filter elements 40 of the filter assembly 20 of FIG. 1, for a 25-micron rating, each of the filter elements 120 has an over-all thickness of 0.002 inch, being the total of a base section 120b thickness of 0.001 inch and a height of the protrusions 120a, above the base section, of another 0.001 inch. The gap between forward edges 120c of an adjacent pair of filter elements 120 is thus 0.001 inch in the spaces between pads 120d whereby all particles above 25 microns in size are excluded from the radiator bank of filter elements. The Y-shaped protrusions 120a are arranged in the same type of pattern is employed in the filter discs 40 of FIG. 3, so that a stagnation cavity 121 of each rearward line of protrusions is behind the gap between front edge pads 120d or between an adjacent pair of protrusions immediately in front of the stagnation cavity. Also, the spacing between adjacent protrusions 120a is preferably held to 0.001 inch, i.e., the space between opposed arms of an adjacent pair of Y's. The arms and stem of each Y may have a width on the order of 0.003 inch and each Y may have an over-all length of 0.030 inch and an over-all width of 0.020 inch.

As is shown in FIG. 10, the bank of filter elements 120 is held in place within the body 111 by a pair of vertically extending slots 123 formed in opposite side walls of the body. If desired, a sealing gasket or the like may be employed within each groove 123 to prevent unfiltered fluid being passed around the ends of the bank of filter elements 120. However, such seal means may be eliminated if the filter elements 120 are of a length to give a press fit within the slots 123, or longer than the span between floors of the grooves 123 by a distance of 0.001 inch. A clamping bar 124 is seated on top of the bank of filter elements 120 and is also of a length to have its ends received within the grooves 123. The opposite ends of the bar 124 may be provided with a fluid seal means or may also have a very close fit within the slots with a clearance tolerance no greater, over-all, than the rating of the filter.

When the cover plate 115 is fastened down the clamping bar 124, it fully compresses the bank of filter elements 120, eliminating all slack so that a solid vertical column is achieved with approximately 500 of the filter elements 120 within each inch of height of the radiator bank. For holding the bank of filter elements 120 against the operating differential pressure of the filter, a pair of support columns 125 abuts the downstream side of the bank of filter elements. As is shown in FIG. 10, these vertically extending columns 125 preferably have flat bearing surfaces to contact the rear side of the bank of filter elements. Referring to FIG. 9, it can be seen that each column at its lower end has an integrally formed pin 126, that is seated within a complementary socket formed in the upper surface of the bottom plate 113. At its upper end, each column 125 has an integrally formed cylindrical flange 127 that is receivable within a complementary pocket 128 formed in the lower face of the top cover 115. A spring 129 is seated within the cylindrical flange 127 and pocket 128 to bias each column 125 downwardly into a secure seat of the pin 126 on the lower end into its socket. This arrangement allows clearance at a shoulder 130 defined between the collar 137 and the upper end of the column 125 to insure that the height of the columns 125 will not prevent completely clamping the cover 115 down onto the bar 124, to fully compress the stack, and, also, to insure that the gasket 112 at the upper end of the body 11 is tightly clamped in place.

In FIG. 12, the invention is embodied in another configuration of in-line filter assembly 130. A cylindrical housing 131 at one end has a frustoconical shaped dome 132 that develops into an inlet port 133. This dome is interiorly tapped to receive an inlet pipe 134 coaxially with the housing the other end of the housing 131 is formed with an exterior circumferentially extending flange 135 on which a base plate 136 of a removable filter cartridge is seated. A suitable O-ring 137 is mounted between the flange 135 and base plate 136. The base plate 136, in turn, seats a mounting flange 138 of a cap member 139 which has a tapped outlet port 140 to receive an outlet pipe 141. An O-ring 142 is mounted between abutting faces of the mounting flange 138 and base plate 136 to effect a fluid seal between these parts. The flange 135, base plate 136 and mounting flange 138 are formed with alignable bores for the reception of suitable bolt fasteners 143 to hold these parts together.

The filter cartridge is carried on the base plate 136 and can be removed along with the base plate after the bolts 143 and cover member 139 have been removed from the housing 131. The cartridge includes a plurality of identical filter discs 145, a plurality of longitudinally extending tie rods 146 anchored at one end in the base plate 136, and at the other end threadedly engaged with a pressure plate 147. Also included in the filter cartridge are a plate 148, that is retained by the tie rods 146, and a pressure screw 149, threadedly engaged with the plate 147 and acting to clamp the filter discs 145 between the plate 148 and the base plate 136.

More specifically, the filter discs 145, for a 25-micron filter, are made from 0.002-inch stainless steel sheet that is etched in the plan view configuration shown in FIG. 14. Each disc is generally circular in shape having a central opening 145a and a saw-toothed outer edge 145b. This outer edge is not continuous but at positions spaced 90.degree. apart is formed with semicircular notches 145c adapted to receive the tie rods 146. The filter discs 145 are thus indexed into a desired angular orientation, relative to each other and to the base plate 136. Each of the filter discs 145 is formed with four circularly spaced apart arcuately shaped grooves or openings 145d and the base plate 136 is formed with openings 150 of the same configuration and similarly spaced apart.

After the filter discs 145 have been etched to the plan configuration just described, they are etched to produce the surface configuration schematically shown in FIG. 14. Thus, one surface of each disc is etched to a depth of 0.001 inch to leave the illustrated pattern of Y-shaped protrusions having an altitude of 0.001 inch above a base section 145f of a thickness of 0.001 inch and, also, leaving four elongated pads of pad areas 145g extending radially from the center hold 145a. In order words, the pad areas 145g and the Y-shaped protrusions 145e are unetched while the balance of the surface of the disc is etched to a depth of 0.001 of an inch. The Y-shaped protrusions are arranged in accordance with the scheme previously described.

In the filter assembly 130, the influent enters the inlet port 133 and enters the stack of filter elements 145 both from the annular space between the stack of filter elements and the wall of the housing 131 and also from within the hollow core defined by the inner edges 145a of the stack of filter discs. As is shown in FIG. 13, the plate 148 is formed with a plurality of radially extending passages 152 having their inner ends in communication with an axially disposed orifice 153 having the same diameter as the diameter of the filter openings 145a and communicating with the hollow core defined by the holes 145a. Accordingly, the influent passes radially inwardly from the outer edge of the stack of filter discs 145 and also passes radially outwardly from the hollow core of the stack. The filtered effluent, i.e., the fluid in the arcuate passages 145 d is then drawn axially from the filter stack through the base plate passages 150, the outlet port 140 and pipe 141.

Referring to FIG. 14, it will be noted that in each of the quadrants or separate areas of the filter discs 145, the Y-shaped protrusions 145e, positioned radially outwardly from the arcuate openings 145d are arranged to dispose their stagnation cavities 155 facing outwardly. In each quadrant of the filter discs 145, those Y-shaped protrusions 145e that are radially inwardly from the arcuate openings 145d are oriented with their stagnation cavities facing radially inwardly. In connection with the scale of the drawings, it will be appreciated again that the relative size of the protrusions is greatly exaggerated for clarity of illustration.

As with the previously described filter assemblies, so too in the filter assembly 130, the filter discs 145 are stacked with the etched face of one disc in abutment with the smooth unetched face of an adjacent disc. These congruent discs are assembled with each of the discs being indexed by the tie rods 146 whereby the pads 145g, protrusions 145e and the openings 145d are congruently superposed. The openings 145d register with the openings 150 in the base plate 136 while the hollow core defined by the holes 145a registers with the port 153 of the plate 148.

As is shown in FIG. 13, the tie rods 146 extend through suitably located openings in the plate 148, these openings having a sliding fit on the tie rods. The plate 147 is also formed with openings to slidably receive the tie rods 146 and is held in place on the tie rods by cap nuts 157 threadedly engaging the ends of the tie rods. The clamping screw 149 is threadedly engaged with a tapped bore in the center of the clamping plate 147 and the inner end of the screw bears against the center of the plate 148 to remove all slack and fully compress the stack of filter discs between the plate 148 and the base plate 136. Once again, assuming a 25-micron rating for the filter, when the stack of filter discs 145 is fully compressed there are substantially 500 of the discs per inch of axial length of the stack. In this connection, it is important to note, as is shown in FIG. 16, that the pads 145g are protrusions 145e are exactly superposed so that when the stack is fully clamped, the stack has rigidity and structural column characteristics like a thick-walled tube.

FIG. 17 illustrates another embodiment of the invention that is adapted to prevent placing any filter disc into a cartridge in a reverse position, i.e., with the protrusions of the filter disc abutting the protrusions or etched side of another filter disc. In this instance, there is a filter cartridge or cage 161 generally similar in overall configuration to the cage 26 shown in FIG. 2, having a spaced pair of longitudinally extending bars 162 and 163 extending between opposite ends of the cage. While bars 162 and 163 are relatively distantly spaced, another pair of relatively small cross-sectional area bars 164 and 165 are relatively closely spaced to define a keyway 166 therebetween. This keyway receives a compression pad area 167 that protrudes radially outwardly from a filter disc 168 and the disc has a plurality of integral protrusions 169 on one surface, in the area between outer edge 168a and inner edge 168b of the ringlike disc.

It will be noted that the outer edge 168a of the filter disc is formed with a substantially semicircular notch 168c that is located generally oppositely to the compression pad 167 but offset from a diameter which would intercept the compression pad. An index rod 170 is mounted in the filter cage 161 in a corresponding position in the gap between the bars 162 and 163 to register with the indexing notch 168 of the filter element. If the filter disc is reversed, it cannot be received into the cartridge because the indexing notch 168c would not register with the index rod 170 even if the compression pad 167 were positioned within the keyway 166. Thus, there is no possibility that any single filter disc 168 can be inserted into the cartridge in reversed position and the desired edge gap between discs will always be maintained since there is not possibility of the protrusions 169 of one disc seating on protrusions 169 of an adjacent disc.

As has already been indicated, it is highly preferable that the filter elements be made by etching the filter element from a thin sheet of metal, so as to provide an absolutely clean filter media, no part of which can be displaced to be lost downstream in the filter effluent. This process may be carried out as indicated in FIGS. 18, 19 and 20 which show, by way of example, steps in the formation of the filter disc 168 shown in FIG. 17.

FIG. 18 shows a corner area of a thin sheet of metal 175 which may be assumed to have an original thickness of 0.002 inch. For convenience, that side of the sheet of metal 175 shown in FIG. 18 will be referred to as the upper side, corresponding to what may be termed the upper side of the filter disc 168 depicted in FIG. 17. The reverse side of the sheet metal 175 is shown in FIG. 19. In FIGS. 18 and 19, the shaded areas represent a suitable etchant resist material which may be applied by silk screen or photographic process to block out or protect those areas of the sheet which are to remain unetched. Thus, in FIG. 17, the circular raised protrusions 169 and the compression pad area 167 are the only unetched areas of the upper side of the filter disc 168. The same reference numerals are used in FIG. 18 to represent corresponding areas of the sheet 175 which are covered with resist material so as not to be removed from the upper surface of the sheet by the etchant. In similar fashion, in FIG. 18, the reference numerals 168a and 168b show edges of masked areas of the sheet 175 corresponding to outer and inner edges 168a and 168b of the filter disc 168 shown in FIG. 17. On the bottom or reverse side of the sheet 175, as shown in FIG. 19, the entire surface of the sheet is masked by the resist except for the outer edge 168a, including the indexing notch 168c and compression pad 167, and the completely circular inner edge 168b.

It will be observed that the outlines of the several filter elements marked on the upper surface in FIG. 18 are in mirror image relationship to the outlines of the filter elements marked on the bottom surface in FIG. 19, and the patterns on the opposite sides of the sheet are of course exactly superimposed. Accordingly, when the resist-coated sheet 175 is immersed in an etchant, the exposed areas of the sheet are attached by the etchant simultaneously on both sides of the sheet. This is indicated schematically in FIG. 20 where it will be seen that metal has been removed between the masked protrusions 169, around the outer edge 168a, and around the inner edge 168b, the etched areas being attacked simultaneously from opposite sides of the sheet. It is to be understood that in the representation of FIG. 20, the etchant has not yet fully penetrated but the etchant, in the given example of a sheet of 0.002 inch thickness, is of sufficient strength to penetrate to a depth of 0.001 inch whereby each of the filter elements 168 will be fully severed from the sheet 175 along the edges 168a and 168b, and one surface only of each filter element will have the metal removed between the protrusions 169a on one side of the sheet only.

In the event filter elements of the configuration of the element 75 of FIG. 8 are desired, a sheet of metal like the sheet 175 in FIGS. 18, 19 and 20 can first be frustoconically dimpled by forming dies and the resist then applied to etch the filter elements with their protrusions from the preformed sheet. Alternatively, flat filter elements may be made from a thin sheet metal by first piercing the blanks of desired plan configuration from the sheet with piercing dies, and thereafter applying a resist to the filter element blanks to accomplish the removal of metal from one surface in order to leave the desired configuration and distribution of protrusions. However, etching to sever the filter disc blank or fully formed disc from the sheet is highly preferable since it does not involve the possibility of producing slivers and chips and tears of metal, such as could result from piercing the sheet with piercing dies.

FIGS. 21-23 illustrate filter elements having etch patterns uniquely shaped to cause fluid passing through a filter to be subjected to a swirl, and causing particles to be carried into and lodged in crevices. Referring to FIGS. 21 and 22, a thin metallic ring 181 is etched to provide curved channels 182 through which fluid passes to the interior of the ring.

As best seen in FIG. 22, the etched channel 182 in the arrangement shown has an unbroken curved wall 183, and a curved wall 184 that has a folded-back portion 185 extending into the channel and toward the outer edge of the ring.

With a stack of filter elements of this construction, fluid forced through the channels is subjected to a swirl, or centrifugal force, which tends to carry particles into the crevices formed between the walls 184 and the extensions 185.

FIG. 23 illustrates a ring 186 with an etch pattern which serves the same purpose as for the element of FIGS. 21 and 22. The channels 187 in FIG. 23 are shaped so that one wall 188 thereof is provided with a number of spaced reentrant portions 189.

In FIGS. 21-23, it should be observed that the etching causes the floors and walls of the channels to be roughened. Hence, the floor and wall surfaces themselves serve to trap particles which would pass through if these surfaces were smooth. The degree of roughness can be controlled as desired, and may be such that the surfaces are relatively jagged to enhance trapping of particles to be filtered out of the fluid.

From the foregoing description it will be apparent that the filter media of my invention may be embodied in a wide variety of configurations. Additionally, as the filter media is of integral or unitary construction, there is no possibility of media migration, i.e., removal and displacement of portions of the filter media which can be passed into the effluent. Furthermore, as no foreign matter is manufactured into the filter element, as is the case with sintered or wire mesh or screen filter media, there is no possibility of such foreign matter being released into the effluent as a result of vibration of the like.

With the present invention, a filter cartridge can be subjected to a bubble test prior to installation of a filter assembly. Then if any defective surface area be found, the stack of filter elements may be loosened and the individual defective filter discs or layers may be removed and replaced by other filter discs and the cartridge may then be reassembled. This procedure completely eliminates the necessity for any bracing, as is common with screen or sintered types of filters, in which brazing to close unacceptable voids results in the addition of foreign matter which can be lost in the effluent and also reduces the filtration area.

The filter of my invention may be more effectively cleaned by sonic or mechanical vibration as such vibration will not result in the removal and displacement of any portion of the filter media. Furthermore, as a filter cartridge may be removed from the filter assembly after a period of use and loosened to effect a spacing between filter elements, it is now possible to clean the depth filtration space of the filter as well as the edge filtration area.

While several embodiments of my invention have been hereinabove described in detail, it is to be understood that I do not mean to be limited to the specific details of construction set forth, but only by the spirit and scope of the following claims.

Claims

I claim:

1. A stack of substantially identical, very thin, flexible metal sheets, each sheet having portions etched from one surface thereof to leave a plurality of spaced projections in a prescribed pattern integral with an imperforate base section of the sheet, said base section and the lateral surfaces of the upstanding portions of said projections having minute rough surfaces, each sheet also having an etch-roughened peripheral edge surface;

a housing for said stack;

and means for compressing said stack in said housing to form a rigid stack of said flexible sheets resistant to vibration and with said pattern of projections and said rough surfaces arranged to trap particles in fluids that flow between said sheets.

2. A filter as defined in claim 1, wherein each sheet has a central opening therein, and wherein the edge surface of the sheet around said opening is etch-roughened.

3. A filter as defined in claim 1, wherein said housing has opposed grooves and each sheet is a rectangular element nesting at its ends in said grooves;

a pair of rigid rod-like members supported in said housing and abutting one side of the stack;

and means to introduce fluid into said housing on the side of the stack opposite said rods.

4. A filter as defined in claim 1, wherein each sheet has a tab and a notch along its periphery which are angularly spaced so as not to be diametrically opposed, and wherein said housing has a longitudinal rib and a longitudinal groove for mating with the respective notches and tabs of said sheets.

5. A filter as defined in claim 4, wherein said rib is formed of a second longitudinal groove in said housing confronting the notches in said sheets and an index rod extending through the opening defined by said second longitudinal groove and said confronting notches.

6. A filter comprising:

a stack of substantially identical flexible metal sheets, each sheet being etch-roughened on one surface and with a pattern of projections on said one surface;

a housing for said stack;

a body having inlet and outlet ports at one end to admit fluid into said body and through which fluid passes out of said body;

means positioning said housing in said body with one end of the stack adjacent said one end of said body, said housing having openings therein to permit fluid entering said body to pass laterally between said sheets into the center openings thereof, said body having a passageway through which fluid entering said center openings passes out of said outlet port;

a pair of rigid washers at each end of said stack, one of said washers abutting one end of said housing;

a first nut engaging the other washer and threaded into said housing for compressing said sheets;

a second nut threaded into said housing for locking said first nut in place;

a locking disc threaded into said body for locking said housing therein;

and passages interconnecting the opposite surfaces of said nuts and said disc with said inlet port for equalizing pressures therebetween.

7. A filter cartridge for use in a filter housing placed in the path of a fluid containing particles to be trapped, said cartridge comprising:

a stack of substantially identical flexible metal sheets, each sheet having one roughened surface and a plurality of spaced projections in a prescribed pattern integral with said surface, the lateral surface portions of said projections being minutely roughened;

a housing for said stack;

means for compressing said sheets in said housing to make a rigid stack, whereby to permit said stack to resist vibration, and whereby said pattern of projections and said roughened surfaces serve to trap particles in a fluid that flows between said sheets.

8. A filter as defined in claim 7, wherein said means for compressing said sheets includes a member supported in said housing and having passages interconnecting its opposite surfaces for pressure equalization.