U.S. patent application number 10/829211 was filed with the patent office on 2004-10-07 for methods of making a filter element.
This patent application is currently assigned to Pall Corporation. Invention is credited to Hartmann, Thomas.
Application Number | 20040195170 10/829211 |
Document ID | / |
Family ID | 32314250 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040195170 |
Kind Code |
A1 |
Hartmann, Thomas |
October 7, 2004 |
Methods of making a filter element
Abstract
Methods of making a filter element may comprise inserting end
portions of a filter and a core into a liquid bonding material of
an end cap. The end portions may be inserted into the liquid
bonding material at the same time or at different times. Inserting
the end portion of the core into the liquid bonding material may
include separating some of the liquid bonding material from the end
portion of the filter. The end portion of the filter is bonded to
the end cap, while the core may or may not be bonded to the end
cap. The inner periphery of the end portion of the filter near the
bond may be supported by an outer wall of the core.
Inventors: |
Hartmann, Thomas;
(Huntington Station, NY) |
Correspondence
Address: |
LEYDIG VOIT & MAYER, LTD
700 THIRTEENTH ST. NW
SUITE 300
WASHINGTON
DC
20005-3960
US
|
Assignee: |
Pall Corporation
East Hills
NY
|
Family ID: |
32314250 |
Appl. No.: |
10/829211 |
Filed: |
April 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10829211 |
Apr 22, 2004 |
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09720196 |
Apr 2, 2001 |
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6739459 |
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09720196 |
Apr 2, 2001 |
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PCT/US99/14357 |
Jun 25, 1999 |
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60090909 |
Jun 26, 1998 |
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Current U.S.
Class: |
210/450 ;
210/457 |
Current CPC
Class: |
B01D 2201/0415 20130101;
B01D 29/232 20130101; B01D 2201/0407 20130101; B01D 29/111
20130101; B01D 2201/291 20130101; B01D 29/21 20130101 |
Class at
Publication: |
210/450 ;
210/457 |
International
Class: |
B01D 027/06 |
Claims
What is claimed is:
1. A method of making a filter element comprising: inserting an end
portion of a filter into a liquid bonding material of an end cap;
inserting a narrow edge at an end portion of a core into the liquid
bonding material, including separating some of the liquid bonding
material from the end portion of the filter; bonding the end
portion of the filter to the end cap; and supporting an inner
periphery of the end portion of the filter by an outer wall of the
core near the bond.
2. The method of claim 1 wherein the end portion of the filter and
the end portion of the core are inserted into the liquid bonding
material simultaneously.
3. The method of claim 1 wherein the end portion of the filter and
the end portion of the core are inserted into the liquid bonding
material at different times.
4. The method of claim 1 wherein inserting the narrow edge of the
core into the liquid bonding material and separating some of the
liquid bonding material from the end portion of the filter includes
directing liquid bonding material away from the end portion of the
filter.
5. The method of claim 4 wherein directing liquid bonding material
away from the end portion of the filter includes directing liquid
bonding material into an annular recess in the end portion of the
core, the method further comprising solidifying liquid bonding
material in the recess.
6. The method of claim 1 further comprising venting gas in the
recess through vents in the core.
7. The method of claim 1 further comprising solidifying bonding
material in contact with or facing an interlock arrangement at the
end portion of the core.
8. The method of claim 7 further comprising not fixing the core to
the end cap and arranging the core to move with respect to the end
cap.
9. The method of claim 8 wherein the core is arranged to move
axially but not rotationally with respect to the end cap.
10. The method of claim 1 further comprising not fixing the core to
the end cap.
11. The method of claim 1 further comprising fixing the core to the
end cap.
12. The method of claim 1 wherein supporting the inner periphery of
the filter includes arranging the filter and the core such that the
inner periphery at the end portion of the filter intimately faces
the outer wall of the core.
13. The method of claim 1 wherein supporting the inner periphery of
the filter includes contacting the inner periphery at the end
portion of the filter and the outer wall of the core.
Description
[0001] This application claims the priority of U.S. patent
application Ser. No. 09/720,196, filed Apr. 2, 2001, which
application is incorporated by reference in its entirety.
BACKGROUND
[0002] A filter element may include a hollow cylindrical filter
pack, where a filter pack may be defined as any structure that
includes a filter medium. The interior of the filter pack may be
supported by an internal core and the exterior of the filter pack
may be supported by an external cage. One or both ends of the
filter pack are typically bonded to a closure such as an end cap.
The end of the filter pack may be bonded to the end cap by any
suitable technique which provides sufficient filter integrity,
including melt bonding or the use of a potting material, such as an
epoxy, a urethane, or a hot melt adhesive.
[0003] When a filter pack is bonded to an end cap, an end portion
of the end cap may be liquefied, for example, by heating it until
the end portion melts, and the filter pack may be inserted into the
molten portion. Alternatively, a liquid potting material may be
applied to the end cap and the end of the filter pack may be
inserted into the potting material. The liquid bonding material,
e.g., either the molten portion of the end cap or the potting
material, then solidifies or hardens, forming a bond between the
filter pack and the end cap.
[0004] In a typical melt bonding and/or potting material bonding,
the end of the core and/or the end of the cage may be inserted into
the liquid bonding material along with the end of the filter pack.
Unfortunately, the end of the core and/or cage then displaces a
significant amount of the liquid bonding material. This displaced
bonding material may be forced into the bonding area between the
end cap and the end of the filter pack, resulting in excess bonding
material. The excess bonding material may cause improper bonding
and compromise the integrity of the bond between the end cap and
the end of the filter pack. The excess bonding material may also be
drawn deep into the end of the filter pack, where it may damage or
blind the filter medium or bond the filter pack to the core.
[0005] The liquid bonding material displaced by the end of the core
and/or cage may also be forced onto the outer or inner surfaces of
the filter element, where it can resolidify as globules or ridges.
Not only are these globules or ridges unsightly; they can also
interfere with the fit of the filter element into a housing and
with the flow of fluid around and through the filter element.
[0006] Another problem with conventional cylindrical filter
elements is that pressures exerted on the filter pack at the bond
during filtration and backwashing or blowback stress the bond
between the filter pack and the end cap. Expansion or contraction
of the filter pack due to the effects of temperature and/or
moisture can also stress the bond between the filter pack and the
end cap. Repeated stress on the bond may cause the bond to fail,
allowing unfiltered fluid to bypass the filter pack and contaminate
fluid that has been treated by the filter element.
SUMMARY OF THE INVENTION
[0007] In accordance with one aspect of the invention, methods of
making a filter element may comprise inserting an end portion of a
filter into a liquid bonding material of an end cap and inserting a
narrow edge at an end portion of a core into the liquid bonding
material, including separating some of the liquid bonding material
from the end portion of the filter. The end portions of the filter
and the core may be inserted into the liquid bonding material at
the same time or at different times. The methods further comprise
bonding the end portion of the filter to the end cap. The end
portion of the core may or may not be bonded to the end cap. The
methods also comprise supporting an inner periphery of the end
portion of the filter near the bond by an outer wall of the
core.
[0008] Embodiments of the invention represent a considerable
advance in the state of the art. For instance, methods which
provide for supporting the periphery of a filter by an outer wall
of a core at the bond and separating excess liquid bonding material
from the end of the filter provide for several advantages over the
prior art. For example, when the end of a filter pack and the end
of the core are inserted into the melted region of an end cap or a
liquid potting material in an end cap, excess liquid bonding
material displaced by the end of the core is not forced into the
bonding area nor onto the inner surfaces of the filter. Rather, the
displaced bonding material may be separated from the end of the
filter, enhancing the integrity of the bond and the effectiveness
of the filter element. In addition, because the filter is supported
by the outer wall of the core at the bond, less stress is placed on
the bond between the filter and the end cap. Thus, the likelihood
of stress failure at the bond and the opportunity for untreated
process fluid to leak through a failed bond and contaminate treated
fluid are virtually eliminated.
BRIEF DESCRIPTION OF THE FIGURES
[0009] FIG. 1 is a side view of one example of a core partially in
cross section invention.
[0010] FIG. 2 is a top view of the core in FIG. 1.
[0011] FIG. 3 is a cross sectional view along the recess of the
core in FIG. 1.
[0012] FIG. 4 is a cross sectional view of a portion of a filter
element.
[0013] FIG. 5 is a cross sectional view along a recess of a second
example of a core.
[0014] FIG. 6 is an isometric cross sectional view along a recess
of a third example of a core.
[0015] FIGS. 7a and 7b are side and top views of one example of a
cage.
[0016] FIG. 7c is a cross sectional view along the recess of the
cage of FIGS. 7a and 7b.
DETAILED DESCRIPTION
[0017] In some embodiments of the invention, the filter element
comprises a core disposed in a hollow filter pack and an end cap
bonded to the filter pack. As shown in FIGS. 1-3, the core 10
includes a perforated cylindrical body 11 which may be disposed
inside the hollow filter pack to support the filter pack against
forces directed radially inwardly through the filter element during
filtration and backwashing or blowback. For example, during
filtration process fluid may flow generally radially outside-in
through the filter, through the apertures 12 in the perforated core
10 to the interior hollow portion of the filter and the core 10 and
then axially to an outlet at one or both ends of the core 10.
Alternatively, during filtration, process fluid may flow generally
radially inside-out from the hollow interior through the apertures
12 in the perforated core 10 to the filter pack.
[0018] The core body may be configured in a variety of ways. For
example, the core body is preferably cylindrical and has a
generally circular cross section, but it may alternatively have a
polygonal cross section. The core supports the filter pack against
pressurized outside-in flow and prevents the element from
collapsing inwardly. Consequently, the core preferably has a
configuration similar to the filter and an outer diameter that
corresponds to the inner diameter of the filter. The core body may
have an even, smooth outer surface except for the apertures or the
outer surface may have one or more grooves 13 or other textures to
channel fluid to or from the apertures. The apertures may have any
shape. For example, the apertures may be circular or rectangular
shaped. The apertures are spaced sufficiently apart so that fluid
may readily pass between the filter pack and the core with little
or no pressure drop.
[0019] At least one end, and preferably both ends, of the core 10
include a recess 14 where liquid material, such as waste or
extraneous material formed during bonding of the end cap to the
filter pack, may be confined. The recess 14 may have any suitable
configuration. For example, as shown in FIGS. 1-3, the recess 14
may comprise a groove 15 in the end face at a first end 14 of the
core 10. The groove 15 may be defined by an outer wall 20 and an
inner wall 21 and may be unbounded on only one side, e.g., the end
face of the core 10. Both the outer wall and the inner wall may be
the same height or they may have different heights. For example,
the inner wall may be shorter than the outer wall. The outer wall
and the inner wall may have the same thickness or the thicknesses
may differ. For example, the thickness of the outer wall may be
greater than the thickness of the inner wall, providing a strong
outer wall to support the filter pack. The edges of the inner and
outer walls may be flat or inclined and they may be even or
textured. The outer wall is preferably continuous while the inner
wall may be continuous or discontinuous.
[0020] As illustrated in FIGS. 1-3, both the outer wall 20 and the
inner wall 21 have the same height, and the inner surface 22 of the
outer wall 20 and the outer surface 23 of the outer wall 21 are
each generally continuous. Further, the inner surface 22 of the
outer wall 20 and/or the outer surface 23 of the inner wall 21 may
be tapered and define a V-shaped groove 15 having a narrow base 24
at the intersection of the inner and outer surfaces 22, 23. In a
preferred embodiment, the outer wall 20 has a narrow edge and a
tapered inner surface which neatly divides the liquid material at
insertion and directs the liquid bonding material at the end of the
core inward away from the bonding area between the end cap and the
end of the filter pack. However, the groove may have any suitable
shape which is capable of receiving and containing liquid bonding
material when the core is inserted into the liquid bonding
material. For example, the outer and inner surfaces of the inner
and outer walls may extend axially parallel to one another to
define a generally U-shaped groove having a relatively wider
base.
[0021] The recess may include a variety of other features. For
example, one or more vents may communicate with the recess and
allow gas to escape as liquid bonding material flows into the
recess. For example, as shown in FIGS. 1-3, a plurality of vent
holes 25 extend through the outer wall 20 of the core 10 near the
base 24 of the groove 15. Alternatively or additionally, vents may
be located in the inner wall or the base.
[0022] An interlock arrangement comprising one or more structures
may be formed at one or both ends of the core, preferably in the
recess, to aid in the prevention of rotational and/or axial
movement of the core relative to the end cap and/or the bonded
filter pack. For example, one or more of the inner wall, the outer
wall, or the base of the groove may include surface textures, such
as bumps, or contoured features, such as indentations, or holes,
such as the vents, in or around which the liquid bonding material
may solidify. Alternatively, the structures may comprise
protrusions, such as partition walls, which extend into the recess
and around which the bonding material may solidity. For example,
one or more ribs, lands, or walls may protrude into the groove from
the outer wall, the inner wall, and/or the base. As shown in FIGS.
1-3, several partition walls 30 protrude radially inward from the
inner surface 22 of the outer wall 20. The partition walls 30
preferably extend radially completely across the groove 15 to the
inner wall 21 but may terminate prior to the inner wall 21.
Further, the partition walls 30 preferably extend axially from the
base 24 all the way, or most of the way, to the edge of the outer
and/or inner wall 20,22, and the top edge of each partition wall 30
is preferably tapered. Generally, however, the protrusions are not
restricted to any particular shape or orientation. The protrusions
may protrude from the outer wall, the inner wall, and/or the base
in a direction parallel to or at an angle to the radius and/or the
axis of the core.
[0023] The interlock arrangement may include one or more regular or
irregular surfaces 30 which are arranged to contact solidified
bonding material to prevent relative movement between the core and
the end cap and/or the bonded filter pack in one or more
dimensions, e.g., axially or circumferentially (i.e., in the theta
direction of a cylindrical coordinate system). In many embodiments,
the interlock arrangement may comprise protrusion or indentation
including one or more surfaces which have a significant
circumferential projection and which are arranged to prevent
relative rotation between the core and the end cap. For example, in
the embodiment illustrated in FIGS. 1-3, each partition wall 30
includes opposing surfaces 31a, 31b which are arranged to face
generally circumferentially and prevent relative rotation between
the core and the end cap and/or the bonded filter pack when the
surfaces contact solidified bonding material.
[0024] At least one end, and preferably both ends, of the core
include an outer wall structure which is dimensioned to support the
inner periphery of the filter pack in the vicinity of the bond
between the filter pack end the end cap. The outer wall structure
may 10 be configured in a wide variety of ways. For example, as
shown in FIGS. 1-3, the outer wall structure at an end of the core
10 may comprise a continuous outer wall surface 33 having an outer
diameter which corresponds to the inner diameter of the inner
periphery of the filter pack at the end. A continuous outer wall
surface 33 enables the end of the core 10 to completely support the
entire inner circumference of the filter pack in the vicinity of
the bond between the filter pack and the end cap. Consequently, a
continuous outer surface is preferred. However, discontinuities in
the outer wall structure may be provided so long as the inner
periphery of the filter pack in the vicinity of the bond between
the end cap and the filter pack is substantially supported.
Supporting the end of the filter pack in the vicinity of the bond
serves to relieve and/or prevent undue stress on 20 the bond during
filtration and/or backwashing. As a result, the bond between the
filter pack and the end cap is less likely to fail, reducing the
likelihood that untreated fluid may bypass the filter pack.
[0025] The core may comprise any sufficiently rigid material which
is compatible with the fluid to be processed and which has
sufficient structural integrity to support the filter pack. For
example, the core may be made of a thermoplastic resin, a metal
mesh, a perforated sheet of metal such as steel or aluminum, a
porous ceramic or anyone of a number of porous rigid materials
adapted to form a support for a cylindrical filter element.
Polymeric materials are preferred. Particularly preferred is a core
made of polypropylene or polyethylene. Additionally, the
cylindrical body 11 of the core 10 is preferably perforate and
includes apertures directing fluid through the cylindrical body 11
to or from the hollow interior of the cylindrical body. However,
the cylindrical body may be fashioned from a porous material as,
for example, a hollow or solid porous cylinder or from an
impervious, imperforate material having channels formed in its
outer surface. Each of these cores is preferably arranged to not
only support the filter pack but also provide little or no pressure
drop for fluid flowing through the filter element.
[0026] The core may be fashioned in a wide variety of ways. For
example, the core may be injection molded, it may be extruded, or
it may be machined. The core may preferably comprise a unitary,
one-piece structure. Alternatively, the core may comprise a
multiple piece structure, e.g., an integral two or three piece
structure in which, for example, the cylindrical body of the core
is injection molded and one or two separately molded or machined
end pieces containing the grooves and the continuous outer wall
surface are fixed to the ends of the body, for example, by welding
or bonding. Rather than being fixed to the body, the end pieces may
be coupled to the ends of the body in a manner which allows the end
pieces to move axially and/or rotationally with respect to the
body.
[0027] The shape of the filter pack is preferably cylindrical and
hollow. The filter pack may be configured in a variety of ways. For
example, it may comprise a hollow or solid fibrous mass, or
helically wrapped layers of a filter medium and/or a drainage
material. Preferred, however, is a hollow, pleated configuration.
An example of a suitable pleated configuration for the filter pack
may be a cylindrical configuration having a straight radial pleat
design. More preferred is a pleated filter having a laid-over
configuration, as disclosed, for example, in U.S. Pat. No.
5,543,047, herein incorporated by reference in its entirety.
[0028] Various types of filter media may be used with the present
invention. The filter media used in the filter element may include
any material capable of forming a porous structure suitable for
filtering liquids or gases, including porous metal media, porous
ceramic media, porous media comprising organic and/or inorganic
fibers such as carbon and/or glass fiber media, and/or porous
polymeric media. The filter media may include fibrous media such as
a mass of fibers, fibrous mats, woven or non-woven fibrous sheets,
and fibrous depth filters made by a variety of means including melt
blowing, Fourdrinier deposition, or air laying fibrous materials.
In addition, the filter media may include a porous film or
membrane. The porous filter media of the present invention are not
restricted to any particular pore sizes or structures. Microporous
and ultraporous media are preferred. Additionally, the filter
medium may comprise one or more layers, each layer having the same
or different filtering characteristics. For example, the filter
medium may comprise two or more layers. One of the layers,
preferably an upstream layer, may be more coarse than the other
layer, thereby serving as a prefilter.
[0029] The filter pack may also contain one or more additional
layers such as upstream and/or downstream drainage layers and a
cushioning layer. The upstream and downstream drainage layers are
disposed on the upstream and downstream surfaces of the filter
medium, respectively. The upstream and downstream drainage layers
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 woven or non-woven
porous sheet.
[0030] The cushioning layer may be disposed between the filter
medium and one or both of the drainage layers. The cushioning layer
helps prevent abrasion of the filter medium due to rubbing contact
with the drainage layers during pressure fluctuations of the fluid
system in which the filter is installed. 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. For
example, of a suitable cushioning, layer may be a polymeric
non-woven fabric.
[0031] The filter element may have one or more closures, including
end caps such as open end caps, blind end caps, and joiner caps,
bonded to the filter pack. The end caps may be fashioned from any
suitably impervious material, such as a metallic, ceramic, or
polymeric material, which is compatible with the material to be
filtered. For example, the end cap material may be a metal such as
aluminum, stainless steel, or carbon steel or a ceramic or even a
fiber reinforced product such as fiberglass reinforced
polypropylene, polyamide, such as nylon, or polyester resin.
Preferably, the end cap is made from a polymeric material such as
polypropylene, polyamide (e.g. nylon), or a polyester. The end cap
need not be made of the same material as the core.
[0032] The end caps may be of any desired configuration,
appropriate to the requirements of the filter pack and the filter
element. Usually, at least one of the end caps will be provided
with an aperture to allow flow of filtered fluid from or unfiltered
fluid to the interior of the filter element. In many instances,
both end caps will be apertured, particularly where a plurality of
filtered elements are to be connected together at joiner caps to
form a long tubular element.
[0033] The core, the filter pack, and the end cap may be assembled
to form the filter element in a wide variety of ways. For example,
the filter pack and the core may be arranged to contact one another
such that at least in the vicinity of one end, or preferably both
ends, the inner periphery of the filter pack intimately faces or
contacts the outer wall structure of the core, the outer wall
structure having an outer diameter corresponding to the inner
diameter of the filter pack. The end cap may be bonded to the
filter pack, the liquid bonding material flowing into and being
contained in the recess of the core and/or contacting the interlock
arrangement.
[0034] The inner periphery of a filter pack may be contacted with
the core in a variety of ways. For example, the filter pack may be
positioned so that the core may be inserted in the inner hollow
portion of the filter pack, or the core may be positioned so that
the filter pack may be slid over the core. In the vicinity of one
end, preferably both ends, the inner periphery of the filter pack
contacts the outer wall structure of the core. The outer wall
structure of the core and the inner periphery of the filter pack
contact one another when they are in actual physical contact or
when they are sufficiently proximate that the core supports the
filter pack.
[0035] The filter pack may be bonded to an end cap in any suitable
manner which prevents fluid bypass. For example, the ends of the
filter element may be bonded to the end caps by a potting material,
e.g., a bonding agent such as an adhesive, a solvent, an epoxy, a
urethane, or a silicone. As another example, the filter element may
be bonded to the end cap by melt bonding. Melt bonding and the use
of potting material are preferred methods, but less preferred
methods include spin welding and sonic welding.
[0036] In melt bonding, a thermoplastic end cap may be heated to
liquefy one entire surface or more preferably a region, such as an
annular region, of one surface of the end cap, forming a softened
or molten plastic. One end of the filter pack and core may be
placed into the liquefied plastic of the end cap, where the liquid
plastic flows into the interstices of the filter pack. When the
plastic solidities, the filter pack is securely joined to the end
cap. A conventional melt bonding method is disclosed in U.S. Pat.
No. 3,457,339, herein incorporated by reference in its
entirety.
[0037] In potting, a potting material is placed on one surface or
in a cavity of the end cap, a potting material being a material
that is liquid under filter pack assembly conditions but solid or
firm under normal operating conditions. Typically this may be a hot
melt adhesive, a molten polymer, a plastisol, an epoxy resin, a
wax, a urethane, a silicone, a liquid polymer or elastomer that can
quickly be cured to a solid or firm state, or some such similar
material. One end of the filter pack and core may be placed in the
potting material on the end cap, where the potting material flows
into the interstices of the filter pack. When the potting material
solidities, e.g., hardens or firms up, the filter pack is securely
joined to the end cap, sealing the end of the filter pack to the
end cap.
[0038] When the end of the filter pack and the end of the core are
inserted into the liquid bonding material, e.g., the molten portion
or the end cap or the potting material, the liquid bonding material
displaced by the end of the core is preferably not forced into the
bonding area between the end of the filter pack and the end cap.
Rather, liquid bonding material displaced by the end of the core is
directed to and contained in the recess and/or around the interlock
arrangement at the end of the core. In particular, the narrow edge
of the outer wall of the core slices into, divides, and separates
the liquid bonding material at the end of the filter pack from the
liquid bonding material at the end of the core. The inner surface
of the outer wall, especially a tapered inner surface, directs the
liquid bonding material at the end of the core away from the
bonding area between the end of the filter pack and the end cap.
Thus, the liquid bonding material at the end of the core is not
forced into the bonding area, where as excess bonding material it
can compromise the integrity of the bond between the filter pack
and the end cap. Nor is it forced far up into the filter pack or
between the filter pack and the core where it can damage or blind
the filter medium or bond the core directly to the filter pack.
Rather, the liquid bonding material at the end of the core is
directed into the recess and/or around the interlock arrangement at
the end of the core, where it is contained. Gas, such as air, in
the recess may be vented through the vents, e.g., the vent holes,
as the liquid bonding material flows into the recess. Once the
liquid bonding material solidities, not only is the filter pack
securely bonded to the end cap but the bonding material displaced
by the core material is neatly confined in the recess and/or around
the interlock arrangement. By confining the bonding material at the
end of the core, little or none of the bonding material solidifies
as globules or ridges on the inner surfaces of the end cap or the
inner surfaces of the body of the core.
[0039] As described above, the ends of the filter pack and the core
are preferably simultaneously inserted into the molten plastic of
the end cap or into the liquid potting material. Alternatively, the
end of the filter pack and core may be positioned adjacent to the
end cap, and then the end cap may be heated or the liquid potting
material may be applied to the end cap and the filter pack. In
another alternative, the end of the filter pack may be inserted
into the molten plastic of the end cap or into the liquid potting
material, and then the core may be inserted into the hollow
interior of the filter pack and into the molten plastic of the end
cap or the liquid potting material. In still another alternative,
the end of the filter pack may be positioned adjacent to the end
cap, the end cap may be heated or the liquid potting material may
be applied to the end cap and the filter pack, and then the core
may be inserted into the hollow interior of the filter pack and
into the molten plastic of the end cap or the liquid potting
material. In each case, the inner periphery of the filter pack is
supported by the core in the vicinity of at least one end, and the
filter pack is bonded to the end cap. Any liquid bonding material
at the end of the core will flow into the recess of the core and/or
around the interlock arrangement, where it is contained, and gas
may be vented through the vent holes.
[0040] In the embodiment of the filter element illustrated in FIG.
4, liquid bonding material produced during the bonding of the end
cap 41 to the filter pack 42 was directed into the recess of the
core 10, i.e., the groove 15, by the outer and inner walls 20, 21
of core 10. Vent holes 25 communicating with groove 15 allowed air
to vent from the groove 15 as the liquid material at the end of the
core 10 entered the groove 15. When bonding material 40 cooled or
hardened, it solidified and was confined in the recess of the core
10 and around the partition walls 30.
[0041] The size of the recess, e.g., the height and/or width of the
groove, may vary depending on many factors, including the volume of
the bonding material to be contained in the recess. This, in turn,
depends, for example, on the bonding technique used to join the end
cap to the filter pack. In spin welding, very little melt is
produced and much of it is forced radially outwardly due to
centrifugal force. Consequently, the recess of the core may be
sized relatively small to accommodate the relatively small volume
of material. In potting, the volume of potting material applied to
the end cap and the filter pack may be closely controlled.
Consequently, the recess of the core may be intermediately sized to
accommodate a small to intermediate volume of bonding material. In
melt bonding, the volume of molten plastic produced is more
variable. Consequently, the recess of the core 30 may be sized
relatively large to accommodate a potentially large volume of
bonding material. Regardless of the bonding technique, the recess
may be oversized for the volume of bonding material available to
the recess, allowing the bonding material to be more fully
contained within the recess. Alternatively, the recess may be
undersized for the volume of bonding material available to the
recess, allowing the bonding material to more fully contact the
interlock arrangement, for example, by forcing the bonding material
into and through holes, such as the vents. For example, the volume
of the recess may be R times the volume of the bonding material
available to the recess, where R is any rational number less than
or equal to about 5 and greater than or equal to about 0.5. Thus,
the volume of the recess may be about 5 or about 3 or about 2 or
about 1.5 or about 0.75 times the volume of bonding material
available to the recess.
[0042] In each of the embodiments of the invention, at least one
end, and preferably both ends, of the filter pack are bonded to the
end cap in a manner that fixes and substantially seals the filter
pack to the end cap. The core, on the other hand, may be arranged
with the end cap either in a manner which fixes the core to the end
cap or in a manner which allows the core to move or float relative
to the end cap in one or more dimensions, e.g., axially or
circumferentially.
[0043] The end of the core may be fixed to the end cap at the same
time, or at a different time, and in the same manner, or in a
different manner, that the end of the filter pack is fixed to the
end cap. For example, the core may be made of a material which is
similar to or which has a lower melting point than the end cap.
Inserting the end of the core into the molten plastic of the end
cap, either before or after but preferably as the end of the filter
pack is inserted into the molten plastic, may cause portions of the
end of the core to melt. Thin portions of the core, such as thin
walls, tips, or other thin core structures, are particularly prone
to melting. When the melt, including both molten end cap and molten
core portions, solidities, the core, filter pack, and end cap may
all be fixed to one another.
[0044] Alternatively, the core and the end cap may be fixed to one
another by a potting material which bonds the core and the end cap.
Again, the end of the core may be inserted into the potting
material either before or after but preferably as the end of the
filter pack is inserted into the potting material. When the potting
material solidifies, hardens, or otherwise firms up, the core,
filter pack, and end cap may all be fixed to one another.
[0045] The interlock arrangement, such as the partition walls 30,
may supplement the fixed bond between the end cap and the core. For
example, the partition walls 30 may each include a generally
circumferentially facing surface, preferably a pair of oppositely
disposed circumferentially facing surfaces 31a, 31b. As the liquid
bonding material at the end of the core 10 flows into the recess,
it flows along the partition walls 30 adjacent to the opposite
circumferentially facing surfaces 31a, 31b. When the bonding
material 40 solidifies, it forms correspondingly circumferentially
facing surfaces intimately facing or contacting the
circumferentially facing surfaces 31a, 31b of the partition walls
30. Thus, these facing and/or abutting surfaces of the partition
walls 30 and the solidified bonding material are not only bonded to
one another but are also arranged to mechanically resist any
rotational movement of the end cap clockwise or counter clockwise
with respect to the core.
[0046] Instead of being fixed to the end cap, the core may not be
bonded to the end cap but may be arranged with the end cap in a
manner which allows the core to move or float with respect to the
end cap in one or more dimensions. This may be preferable where the
filter pack has a different coefficient of expansion than the core.
For example, a nylon filter medium expands axially due to the
effects of moisture and/or temperature much more than a
polypropylene core. This expansion is most pronounced in a densely
pleated filter pack, such as a filter pack having a laid-over
configuration. If the filter pack and the polypropylene core are
both fixed to the end cap, the nylon filter medium may buckle
outwardly as it expands, stressing the bond between the end cap and
the filter pack. Consequently, it is frequently preferable to fix
the filter pack to the end caps but allow the core to float axially
with respect to one or both end caps.
[0047] While it may be preferable to allow the core to float
axially with respect to one or both end caps, it is frequently
desirable to prevent relative rotational movement between the core
and the end caps. For example, one end cap, often the open end cap,
may include a fitting which mechanically interlocks the filter
element with the housing. The fitting is rotated by grasping the
opposite end cap, often the blind end cap, and twisting it one
direction or the other. Torque is preferably transmitted from the
blind end cap to the open end cap along the core rather than along
the filter pack. Transmitting torque along the filter pack can
stress the bond at one or both end caps and potentially compromise
the integrity of the seal between filter pack and the end caps. To
provide for torque transmittal along the core, the core and the end
caps are preferably arranged to prevent relative rotation between
them.
[0048] Thus, the core may be arranged with one or both end caps to
float axially but not circumferentially. For example, the core may
be made of a material which has a higher melting point than the end
cap. Inserting the core into the molten plastic of the end cap does
not melt any portion of the core. Consequently, when the melt
solidifies, the core and the end cap may not be bonded to one
another. Alternatively, the core may be made of a material that
does not bond to the potting material. Inserting the core into the
potting material and allowing the potting material to solidify may
not bond the core to the end cap.
[0049] Further, as shown in FIGS. 1-3, the core may also include an
interlock arrangement having opposite circumferentially facing
surfaces 31a, 31b but no undercut axially facing surfaces. Not only
is the core then not bonded to the end cap, but the interlock
arrangement does not prevent axial movement of the core with
respect to the end cap or the filter pack, because the interlock
mechanism does not have any undercut axially facing surfaces which
could abut solidified bonding material and mechanically prevent
axial movement between the core and the end cap. Consequently the
core is free to slide axially with respect to the end cap(s) and
the filter pack. However, the core and the end cap rotate together
because the solidified bonding material abuts the oppositely
disposed circumferentially facing surfaces 31a, 31b of the
interlock arrangement, mechanically preventing any clockwise or
counterclockwise movement of the end cap or filter pack with
respect to the core. Torque may then be conveniently transmitted
from one end cap along the core to the opposite end cap.
[0050] In alternative embodiments, the interlock arrangement may
include one or more undercut surfaces having a significant axial
projection as well as circumferentially facing surfaces. For
example, as shown in FIG. 5, the partition walls 30 may each
include a generally axially facing undercut surface 32 in addition
to the oppositely facing circumferential surfaces 31a, 31b. As the
liquid bonding material at the end of the core 10 flows into the
recess it also flows along and under the partition walls 30
adjacent to the opposite circumferentially facing surfaces 31a, 31b
and the axially facing undercut surface 32. When the bonding
material solidifies, it forms corresponding circumferentially
facing surfaces and axially facing surfaces intimately facing or
contacting the circumferentially facing surfaces 31a, 31b and the
axially facing surface 32, respectively, of the partition wall 30.
The axially facing and abutting surfaces of the partition walls 30
and the solidified bonding material mechanically resist any
movement of the end cap away from the core while the
circumferentially facing and abutting surfaces mechanically resist
any rotational movement of the end cap with respect to the
core.
[0051] In other alternative embodiments, the interlock arrangement
may include one or more undercut axially facing surfaces but no
circumferentially facing surfaces. If the core does not bond to the
end cap, the end cap and the filter pack may then be able to move
circumferentially but not axially with respect to the core. In
other embodiments, the core may not include any interlocking
arrangement. If the core does not bond to the end cap, the end cap
and filter pack may then be free to move both circumferentially and
axially with respect to the core. In still other embodiments the
vents may function as the interlock arrangement and restrict axial
and/or rotational movement of the core with respect to the filter
pack and the end cap. Liquid overflow material may flow into and
completely or partially fill the vents. When the overflow material
solidifies, the solidified overflow material may abut any axially
facing surfaces and/or circumferentially facing surfaces of the
vents, restricting the axial and rotational movement of the core
relative to the filter pack and the end cap.
[0052] Although the core may be arranged to float, e.g., axially,
with respect to one or both end caps, the core, the end cap(s), and
the filter pack are preferably arranged such that that outer wall
structure of the core always supports the filter pack at the bond.
This may be accomplished in any suitable manner. For example, the
end of the core and the end of the filter pack may be offset such
that the end of the core extends beyond the end of the filter pack.
The offset distance may be designed to be greater than the maximum
distance that the core is expected to float away from the end cap.
Alternatively, or additionally, the depth of the bond (i.e., the
depth that the filter pack is inserted into the molten plastic or
the potting material) may be designed to be greater than the
maximum distance that the core is expect to float away from the end
cap. In any event, as the core floats axially with respect to the
end cap, the outer wall structure of the core preferably always
supports the filter pack at the bond with the end cap against the
inwardly directed forces of the process fluid.
[0053] While the overflow recess shown in FIGS. 1-3 comprises a
groove 15 defined by outer and inner walls 20, 21, the overflow
recess may be differently configured. For example, the overflow
recess shown in FIG. 6 comprises an annular space 16 defined by an
outer wall 20 and a base 24 of the core 10. The inner surface 22 of
the outer wall 20, which may extend parallel to the axis of the
core, has an inner diameter greater than the minimum inner diameter
of the interior of the core 10, e.g., the inner diameter of the
body of the core. However, the inner wall is eliminated and the
space 16 is unbounded on two sides, e.g., at the end face and
radially inwardly. Otherwise, features of the core 10, including
the outer wall 20 and the interlocking arrangement, may be
identical to many of the embodiments of the core previously
described.
[0054] The method for applying the core 10 of FIG. 6 to an end cap
may be similar to the method of applying any of the previous
embodiments of the core to an end cap. However, when the core 10 of
FIG. 6 is arranged against the end cap, e.g., inserted into the
molten plastic or the potting material, a retainer post is
preferably disposed inside the core 10. The retainer post
preferably has an outer diameter substantially equal to the inner
diameter of the core 10 at the open edge of the base 24. The
retainer post may extend axially to or beyond the end of the outer
wall 20 and may be formed from a material which does not bond to
the end cap or the potting material. Consequently, the retainer
post prevents the bonding material from flowing radially inside the
edge of the base 24, maintaining the bonding material within the
recess. However, the retainer post may be conveniently removed
after the bonding material solidifies.
[0055] Although the present invention has been described in terms
of several exemplary embodiments which include a core, it is not
limited to those embodiments. For example, the filter element may
include a cage disposed around the exterior of the filter pack with
or without a core disposed in the interior of the filter pack.
Thus, the filter element may comprise a hollow fiber unit where the
filter pack includes a plurality of hollow fibers extending from
one or more end elements. A cage may be joined to the end
element(s) and disposed around the hollow fiber filter pack to
protect the hollow fibers. However, the filter element need not
include a core.
[0056] A cage serves to protect the filter pack during handling and
to support the filter pack against forces directed inside out
through the filter element during filtration and backwashing or
blowback. The cage, which may be thinner than the core, nonetheless
may include a perforated cage body and at one or both ends of the
cage an inner wall, an outer wall and a recess between the inner
wall and the outer wall. The inner and outer walls of the cage are
analogous to the previously described outer and inner walls,
respectively, of the core, and the features previously described
with respect to the core may also be features of the cage, with
this reversal in geometry. For example, the inner wall of the cage
includes an inner wall structure which is dimensioned to support
the outer periphery of the filter pack in the vicinity of the bond
between the filter pack and the end cap. The outer wall of the cage
may have a height less than or equal to the height of the inner
wall. The recess of the cage may have any suitable shape between
the inner and outer walls; including a V- or a U-shaped
configuration. Further, the cage may include an interlock
arrangement and/or vents at one or both ends of the cage,
preferably in the recess. The cage may be bonded to the end cap(s)
as preciously described with respect to the core, and the cage may
be mechanically fixed to the end cap(s) or may float in one or more
dimensions as previously described with respect to the core. The
cage may be formed from any of the materials using any of the
techniques previously described with respect to the core. Thus, the
present invention is also directed to a filter element which
comprises a cage disposed around a hollow filter pack and an end
cap bonded to the filter pack.
[0057] One example of a cage 60 is shown in FIGS. 4, 7a, 7b, and
7c. The cage 60 includes a cylindrical perforated polymeric body 61
having apertures 62. At least one end, and preferably both ends, of
the cage 60 include an inner wall 63, an outer wall 64, and a
recess 65 between the inner and outer walls. The inner wall 63
includes an inner wall structure 70, and the outer wall 64 is
preferably less high than the inner wall 63. The recess 65
preferably has a U-shaped configuration defined between the inner
wall 63, the outer wall 64 and a base 71.
[0058] The cage 60 further comprises an interlock arrangement which
includes one or more ribs or lands 72. The ribs 72 extend radially
outwardly from the inner wall 70 to the outer wall 64 and axially
from the top of the inner wall 63 to the base 71. Thus, each rib
has oppositely disposed circumferentially facing surfaces 73a, 73b
but preferably no undercut axially facing surface. The inner wall
structure of the cage 60 preferably comprises a continuous inner
wall surface 74 having an inner diameter which corresponds to the
outer diameter of the outer periphery of the filter pack in the
vicinity of the end.
[0059] The cage, the filter pack, and the end cap may be assembled
to form a filter element according to any of the techniques
previously described with respect to the core, the filter pack, and
the end cap. For example, the cage and the filter pack may be
arranged to contact one another such that at least in the vicinity
of one end, and preferably both ends, the inner wall structure of
the cage supports and/or contacts the outer periphery of the filter
pack. The end of the filter pack and the end of the cage may be
inserted into the liquid bonding material. The liquid bonding
material displaced by the end of the cage is not forced into the
bonding area between the end of the filter pack and the end cap as
excess bonding material. Rather, the narrow edge of the inner wall
of the cage slices into, divides, and separates the liquid bonding
material at the end of the filter pack from the liquid bonding
material at the end of the cage. The outer surface or the inner
wall directs the liquid bonding material away from the bonding
area, neatly confining it in the recess and/or around the interlock
arrangement. The cage may be arranged with the end cap either in a
manner which fixes the cage to the end cap or in a manner which
allows the cage to move or float relative to the end cap in one or
more dimensions, e.g., axially or circumferentially. In particular,
fixing the cage at least mechanically to prevent relative rotation
between the cage and the end cap allows torque to be transmitted
from one end cap to the other via the cage.
[0060] In the embodiment of the filter element illustrated in FIG.
4, the liquid bonding material was directed into the recess 65 and
around the ribs 72. When the bonding material 40 solidified, it was
confined in the recess and formed circumferentially facing surfaces
intimately facing or contacting the circumferentially facing
surfaces of the ribs 72. Preferably, the nature of the bonding
material and the cage is such that the cage does not bond to the
bonding material. The circumferentially facing surfaces of the
solidified bonding material and the ribs abut one another and
mechanically resist any rotational movement of the end cap
clockwise or counterclockwise with respect to the cage, but the
cage is free to float axially with respect to the end cap. An outer
flange section 43 of the end cap 41 may be provided. The flange 43
and the outer wall 65 prevent the bonding material from flowing
radially outside the cage 60. Preferably, the flange section 43 is
not removed after the bonding material solidifies and remains as a
portion of the end cap 41.
[0061] Filter elements embodying the invention may include a cage
but no core or a core but no cage. Many embodiments, however,
preferably include both a cage and a core. With the inner wall
structure of the cage and the outer wall structure of the core
completely supporting the end(s) of the filter pack for
360.degree., a highly uniform pack end is presented to the liquid
bonding material. Further, none of the liquid bonding material at
the end of the cage or the end of the core is directed into the
bonding area as excess bonding material, enhancing the integrity of
the bond between the end of the filter pack and the end cap.
[0062] Although the present invention has been described in terms
of exemplary embodiments, it is not limited to these embodiments.
For example, in bonding the end of the filter pack to the end cap,
tooling may be substituted for the core and/or the cage. In one
embodiment, an inner cylindrical tool may be inserted into the
interior of the filter pack and/or an outer cylindrical tool may be
slid along the exterior of the filter pack. The inner cylindrical
tool may have an outer wall structure including a narrow edge and
an outer diameter corresponding to the inner diameter of the filter
pack. The outer cylindrical tool may have an inner wall structure
having a narrow edge and an inner diameter corresponding to the
outer diameter of the filter pack. The narrow edge of the inner
cylindrical tool, the end of the filter pack, and the narrow edge
of the outer cylindrical tool may be inserted into the liquid
bonding material, where the narrow edges of the inner and outer
cylindrical tools slice into, divide, and separate the liquid
bonding material. Liquid bonding material at the end of the inner
cylindrical tool and the end of the outer cylindrical tool is thus
directed away from the bonding area by the narrow edges of the
cylindrical tools, preventing excess bonding material from being
forced into the bonding area. The cylindrical tools are preferably
formed from a material that does not bond to the liquid bonding
material or to the end cap. Consequently, once the liquid bonding
material solidifies, the cylindrical tools may be removed, leaving
a high integrity bond between the filter pack and the end cap.
[0063] Clearly, alternative embodiments, examples, and
modifications which would still be encompassed by the invention may
be made by those skilled in the art, particularly in light of the
foregoing teachings. For example, the present invention encompasses
the combination of one or more features of any of the embodiments
previously described or illustrated with the features of the other
embodiments. The present invention also encompasses any of the
embodiments previously described or illustrated where one or more
features of the embodiment are modified or deleted. Therefore, the
following claims are intended to cover any alternative embodiments,
examples, modifications, or equivalents which may be included
within the spirit and scope of the invention as defined by the
claims.
* * * * *