Compound layer resin bonded filter cartridge

A hollow, cylindrical, resin-bonded filter cartridge has an inner, depth-type filter media with a graded density which decreases (becomes porous) in the radial direction from the inner surface to the outer surface. An outer strip of filter media is then wound in a spiral or helix around the inner filter media. The outer filter media is also a depth type of filter media and has uniform density and is wound with adjacent windings abutting one another such that a continuous groove or channel is provided along the length of the cartridge. The groove or channel provides a greater effective surface area on the outer surface of the filter cartridge. The outer strip of filter media preferably comprises a lengthwise-extending body panel with a pair of leaves extending along either edge of the body panel. The leaves are folded against the lower surface of the outer filter media to provide a multi-layer outer filter media structure.

FIELD OF THE INVENTION 
The present invention relates generally to filter cartridges and methods 
for making filter cartridges. 
BACKGROUND OF THE INVENTION 
Filter cartridges which are porous, hollow, cylindrical, resin-bonded 
structures are known in the art for high temperature and/or high strength 
applications. Particulate matter is entrapped within the pores of the 
filter media in the cartridge as fluid or gas flows radially inward or 
radially outward through the media. Various filter media structures have 
been developed in an attempt to provide an efficient, low-cost and 
long-lasting filter cartridge. One known filter media structure has a 
stepped or graded density in the radial direction through the filter 
cartridge. The density of the filter media increases in the direction of 
fluid flow (radially inward or radially outward) to trap the larger 
particulate matter in the more porous (less dense) areas, while the 
smaller particulate matter is retained in the less porous (more dense) 
areas. Such filter cartridges are preferable to a single, high density 
filter cartridge because larger particulate matter contacting the surface 
of a high density filter may completely plug or fill the small spaces or 
voids in the media. Such filter media structures are shown in U.S. Pat. 
Nos. 5,122,270; 3,347,391; 4,661,132; 5,269,921; 3,450,632; 4,240,864; 
5,340,479; 4,731,184; 4,629,474; 3,399,516; 4,111,815; and 3,347,391. 
The filter media for such cartridges can be formed in many different ways, 
for example the media can be blown as fibers onto a spinning mandrel, or 
the media can be formed in a mat, such as by a needling machine. In the 
latter case, the mat can be wound around the mandrel in a single winding, 
or built-up in a number of windings. Harwood, et al., U.S. Pat. No. 
5,039,413 describes a multi-layer filter cartridge wherein a mat of filter 
media is wound in a strip around the cartridge such that each individual 
winding overlaps onto an adjacent winding at least 50% of the width of the 
wrap. The overlapping of the windings is provided for strengthening the 
filter cartridge. 
It is also known to increase the exposed surface area of a filter cartridge 
by pleating (see e.g., U.S. Pat. No. 4,731,184) or by cutting into the 
exterior surface of the filter media so as to form circumferential grooves 
(see e.g., U.S. Pat. No. 3,347,391). Increasing the exposed surface area 
of a filter cartridge can increase the useful life of the cartridge 
because the cartridge can collect and retain a larger amount of large 
particulate matter. The above techniques of pleating and cutting, however, 
can require additional manufacturing steps which can increase the overall 
cost of the filter cartridge, while the technique of cutting can also 
waste material. 
It is therefore believed that there is a demand in the industry for an 
efficient, low-cost and long-lasting filter cartridge which i) does not 
require additional manufacturing steps such as cutting or pleating to 
increase the exposed surface area of the cartridge, and ii) does not waste 
material during manufacture. 
SUMMARY OF THE INVENTION 
The present invention provides a novel and unique structure for an 
efficient, low-cost and long-lasting filter cartridge, and a method for 
making the filter cartridge. 
The filter cartridge includes an inner, depth-type tubular filter media 
preferably formed from needled mat material. The inner filter media is 
impregnated with a resin for strength and is wound around a mandrel in a 
plurality of windings to an appropriate diameter. The wound mat of inner 
filter media has a density which decreases (becomes more porous) in the 
radial direction from the inner surface to the outer surface. The density 
of the inner filter media can be controlled by compression rollers as the 
inner filter media is being wound around the mandrel. A polyester wire or 
string can be wound around the inner filter media to retain the inner 
filter media on the mandrel. 
An outer filter media is then disposed around the inner filter media. The 
outer filter media is preferably a depth-type, needled-fibrous mat 
material in strip or ribbon form. The outer strip of filter media 
preferably has a uniform density which is significantly less (more porous) 
than the inner filter media such that the outer filter media acts as a 
pre-filter. The outer filter media is also preferably formed with a 
lengthwise-extending body panel and a pair of leaves extending along 
either edge of the panel. The leaves are folded against the lower (inner) 
surface of the outer filter media to provide a multi-layer outer filter 
media structure. 
The outer filter media is spirally or helically wrapped around the inner 
filter media. The outer filter media is preferably wrapped in a single 
layer around the inner filter media such that the edges of adjacent 
windings abut each other. A continuous groove or channel is provided 
between the adjacent windings of the outer filter media because of the 
multi-layered structure of the outer filter media. The groove or channel 
provides a greater effective surface area for particle entrapment along 
the length of the filter cartridge. The ends of outer layer of filter 
media can be secured to the inner filter media in an appropriate manner, 
for example with an adhesive. 
The present invention as described above provides an efficient, low-cost 
and long-lasting filter cartridge which does not require additional 
manufacturing steps (such as pleating or cutting) to increase the exposed 
surface area of the cartridge, and does not waste material during 
manufacture. 
Other features and advantages of the present invention will become further 
apparent upon reviewing the following description and accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, and initially to FIGS. 1-4, a filter cartridge 
constructed according to the principles of the present invention is 
indicated generally at 9. The filter cartridge 9 has a tubular or 
cylindrical body 10 with opposite flat end faces 11, 12. The dimensions of 
the filter cartridge (inner and outer diameter, length, etc.) can vary 
depending upon the particular application as should be apparent to those 
skilled in the art upon reading the following description of the 
invention. 
The filter cartridge 9 includes an inner filter media wrap 13 and an outer 
filter media wrap 14. As can best be seen in FIG. 2, the inner filter 
media 13 is a depth-type filter and has a graded density which varies from 
the inner surface 15 to the outer surface 16 of the inner filter media. 
Preferably, the inner filter media has a density which is greater (less 
porous) toward the inner surface and is less (more porous) toward the 
outer surface. The density of the inner filter media preferably varies in 
a uniform manner radially outward from the inner surface to the outer 
surface, although the variation in density can be tailored for the 
particular application (e.g., the density can be stepped, exponential, 
etc.). 
The inner filter media 13 is preferably formed from a conventional 
material. One preferred material for the inner filter media is an acrylic, 
however, other appropriate materials include polymers, such as polyester, 
polyamide, polyvinyl chloride or polyacrylonitrile; or polyolefins such as 
polyethylene or polypropylene. Other less preferred materials include 
wool, esparto, yucca, cellulose, glass, rayon or admixtures thereof. 
Methods for manufacturing the inner filter media material into an 
appropriate porous structure are also conventional and well-known to those 
skilled in the art. One preferred method is to form a needled-fibrous mat 
of material. The mat can be formed by a needling machine which weaves the 
fibers into a matrix. 
The inner filter media is preferably impregnated with a heat-fusable resin 
to impart strength and rigidity to the media such that the media can 
withstand high temperatures and pressures, and to waterproof the fibers. 
The resin employed in the inner filter media is also conventional, and can 
be a thermosetting resin such as water-based phenol formaldehyde 
condensation products, urea formaldehyde condensation products, or 
melamine resins. Thermoplastic resins such as polystyrene may also be 
used. The methods for impregnating fibers with resin are also conventional 
and well-known to those skilled in the art. One preferred method of 
impregnating the inner filter media is to pass the mat through a pair of 
transfer rollers in a nip coater, although another appropriate method is 
to dip-coat the mat. The inner filter media is then located in a pre-cure 
oven until the inner filter media has a relatively stable form, but has a 
certain amount of flexibility. 
The mat is then cut to an appropriate length and wound around a mandrel "M" 
(FIG. 3) by automated machinery into a multi-layer tubular form. 
Preferably, three outside compression rollers are used to direct the mat 
around the mandrel. The rollers vary the density in the mat and control 
the diameter of the inner filter media by varying the compression on the 
mat. As indicated previously, the rollers preferably provide a wound mat 
with a density which is maximum at the inner surface and decreases 
(becomes more porous) radially outward from the inner surface to the outer 
surface. The number of layers of inner filter media wound around the 
mandrel can vary depending upon the initial thickness of the inner filter 
media, the amount of compression provided by the rollers on the mat, and 
the desired overall diameter of the filter cartridge. 
After the inner filter media is wound onto the mandrel, a string or wire 17 
(e.g., a polyester or acrylic tire cord) can be wrapped around the inner 
filter media to hold it temporarily on the mandrel. Alternatively, 
adhesive can be applied along the free edges of the inner filter media to 
hold the inner filter media together. 
The outer filter media wrap 14 is then disposed around the inner filter 
media 13. The outer filter media can also be formed of the same 
depth-type, needled-fibrous mat material as the inner filter media, and 
can be resin impregnated in the same manner as described previously. 
Preferably the density (porosity) of the outer filter media is uniform and 
is significantly less (more porous) than the density of the inner filter 
media. As an example, the density of the inner filter media might vary 
from about 5 .mu.m at the inside diameter to 75 .mu.m at the outside 
diameter, while the density of the outer filter media layer might be at 
least 125 .mu.m. The outer filter media thereby is designed to act as a 
pre-filter for the inner filter media. As with the inner filter media, the 
density of the outer filter media can be chosen depending upon the 
particular application. 
The outer filter media preferably comprises a lengthwise-extending body 
panel 18 having a pair of leaves 20 along either edge of the body panel. 
The leaves 20 are folded lengthwise against the inner (lower) surface 21 
of the main body panel 18 to create a strip or ribbon form. Preferably, 
the leaves 20 of the outer filter media are each about half the width of 
the main body panel 18 such that when the leaves are folded inwardly, an 
outer filter media structure is provided with substantially two complete 
layers (see e.g., FIG. 4). The leaves can be folded as the outer filter 
media layer is disposed around the inner filter media layer such as by 
feeding the outer filter media through a funnel "F" to impart a C-shaped 
form to the strip. 
Preferably, the outer filter media 14 is wound in a helical or spiral 
fashion in a single layer along the length of the cartridge, as 
illustrated in FIG. 3. Winding equipment (e.g., funnel F) is positioned 
substantially perpendicular to the axis of the mandrel and traverses the 
length of the cartridge in a single pass. A roller "R" then compresses the 
strip of outer filter media as it is being applied to the inner filter 
media to provide a substantially flat outer filter media structure. When 
the outer filter media is wrapped around the inner filter media, the 
inwardly-directed surface 22 of the leaves 20 is in surface-to-surface 
contact with the outer surface 16 of the inner filter media 12. The ends 
of the outer filter media strip can then be secured to the inner filter 
media such as by a hot melt adhesive or other appropriate means. 
The outer filter media is wound in such a manner that the edges of the 
individual windings abut each other along the length of the filter 
cartridges, as best shown in FIG. 4. In so doing, a thin V or U-shaped 
groove or channel 27 is provided between the individual windings 
continuously along the length of the filter cartridge at the interface 
locations between the windings. The groove or channel 27 is caused by the 
rounded edge structure of each winding formed as a result of the 
multi-layered outer filter media structure. The groove or channel extends 
part-way through the outer filter media structure. Alternatively, the 
outer filter media can be wound in such a manner that a space is provided 
between adjacent windings and the groove or channel exposes the inner 
filter media 12. In either case, the groove or channel provides a greater 
effective surface area on the exterior surface of the cartridge. 
The filter cartridge is then given a final cure to set the resin in the 
inner and outer filter media. The final cure also causes the windings of 
the outer filter media (if they are abutting each other) to adhere to one 
another along their side edges to form a strong integral outer layer. The 
cartridge is then removed from the mandrel and sheared or cut to an 
appropriate length, if necessary, to provide the flat end surfaces. 
A schematic illustration of a portion of the machinery for forming the 
filter cartridge of the present invention is shown in FIG. 5. The inner 
filter media is provided in mat form on roll 30, and passed through a 
cutter/splicer 32 and resin-coater 34. The resin-impregnated mat is then 
pre-cured in oven 36 and cut to an appropriate length by cutter 38. The 
cut mat is then fed through a mat winder 40 and wound around a mandrel 41 
to an appropriate diameter. Mat winder 40 can introduce a wire or string 
to hold the inner filter media on the mandrel. 
After the inner filter media 13 is wound around mandrel 41, the strip of 
outer filter media 14 is unwound from roll 42 and fed through winding 
equipment 49 (e.g., the funnel) to wrap the inner filter media on the 
mandrel. The funnel traverses the length of the filter cartridge as it 
applies the spiral or helical winding of outer filter media material. The 
outer filter media is then cut as appropriate and attached (such as with 
adhesive) at its ends to the inner filter media. The filter cartridge is 
then removed from the mandrel, cut to an appropriate length, and given a 
final cure. 
The filter cartridge described above provides a greater effective surface 
area along the outer surface of the filter cartridge by virtue of the 
exterior channel or groove along the windings on the cartridge. Fluid 
flowing through the cartridge is generally drawn to the groove or channel 
because of the less flow resistance in this area. As the filter media in 
the groove or channel becomes filled with particulate matter, the fluid 
begins to flow primarily through the body portion of the outer filter 
media. The increased surface area on the cartridge increases the service 
life of the cartridge and is provided without additional manufacturing 
steps such as pleating or cutting, and without wasting outer filter media 
material. Further, the outer filter media, being of a larger porous 
structure, traps larger particulate matter, which thereby also extends the 
life of the filter cartridge. The wrapping of the inner filter media with 
a spiral or helical layer of outer filter media further improves the 
strength of the filter cartridge by tightly retaining the layers of the 
filter cartridge. The diameter of the filter cartridge can also be 
carefully controlled by compression rollers such that post-grinding of the 
cartridge is not necessary. 
The assembled filter cartridge described above can then be further 
integrated into a filter assembly. The structure of the filter assembly 
can vary depending upon the particular application, and is not described 
herein for sake of brevity. As should be apparent from the above, the 
filter cartridge of the present invention is intended to be used where the 
contaminated fluid or gas passes radially inward through the filter 
cartridge to take advantage of the porous structure of the outer 
pre-filtration layer, the increased filter area provided by the continuous 
groove or channel in the outer layer, and the varying density in the inner 
filter media. 
Thus, described above, the present invention provides an efficient, 
low-cost and long-lasting filter cartridge which does not require 
additional manufacturing steps to increase the exposed surface area, and 
which does not waste material during manufacture. The principles, 
preferred embodiments and modes of operation of the present invention have 
been described in the foregoing specification. The invention which is 
intended to be protected herein should not, however, be construed as 
limited to the particular form described as it is to be regarded as 
illustrative rather than restrictive. Variations and changes may be made 
by those skilled in the art without departing from the scope and spirit of 
the invention as set forth in the appended claims.