Note: Descriptions are shown in the official language in which they were submitted.
Field of the Invention
This invention relates to improvements in the construction
of filtering devices. It particularly relates to precision
wound filter tubes comprising helically wound layers of yarn or
5 roving.
Description of Prior Practices
It has been long known that filters may be formed by
constructing a tubular element comprising a foraminous core
precisiQn wound with a multiplicity of layers of spaced con-
lo volutions of strand applled in criss-cross fashion to form a
plurality of diamond shaped filtering passages through the
sidewall of the element ~hrough which the fluid to be filtered
is caused to pass. The fluid passing through khe filter is
clarified as particles in fluid adhere to the fibrous strands.
15 The cartridge may be napped durlng winding to create additional
loosely held fibers which occupy the passages and capture dirt
partlcles. Reissue Patent No. 22,651 to Hastings et al is an
example of such a filter. Such filters suffer from the disad-
vantage that when being used the filter suffers failure by
20 excessive pressure drop prior to the fibers being totally or
predominantly coated with the particles being filtered from the
fluid. The loading of the filter is generally thought to occur
by large particles which coat and block the outer portion of
the filter. Ordinarily the filtering direction is from the
25 outside to the inner portion of the filter.
1-
i11) 1'7
It has also been known to wind filter cartridges using
yarns made from fibrlllated f`ilms ordinarily of polypropylene.
While these cartridges of polypropylene are advantageous in
that they do not have a finish on the fiber and therefore are
very suitable for filtering food materials, they suffer from
the disadvantage that they do not have the ability to trap as
large an amount of dirt in the cartridge as a cartridge wound
with textile roving and further they do not have as high an
efficiency which means that they do not filter as much dirt,
especially fine particles, from the material fed to the
cartridge as would be desirable.
U.S. Patent No. 3,~28,934 to Green et al suggests that
filters can be wound using a filter material composed of fibers
attached to a substrate, such as by flocking. The method
disclosed by Green et al calls for providing a windable strand
material with a plurality of fibers attached thereto by one
fiber end only. The fibers are attached to the strand by an
adhesive. Choice of the adhesive must vary according to the
chemical nature of the fluid being filtered to avoid situations
wherein the fluid being filtered would dissolve the adhesive.
In addition, the cost of adhesively bonding the fibers to the
strands has been found to be economically prohibitive.
Therefore, there is a need to provide a highly fibrillated
winding material that is both economically viable and which can
be used for filtering a broad variety of chemically active
fluids while still providing good filtration performance and
filter medla integrity.
In addition to the wound cartridges utilitzing fibrillated
film yarn, there also has been proposed such as shown in United
States Patent ~o. 3,904,798 to Vogt et al that filters of
variable density be formed by extrusion of flbers dlrectly onto
a rotating collection device. However, such a process is
expenslve to control for unlrormity, the process is llmited to
extruded ~lbers rather than roving or napped fibers and the
S process does not readlly lend ltself to the formatlon of well
defined efficiency rating categories in comparison to the con-
ventional filters produced on the presently available winding
equipment used to form precislon wound cartridges.
In ~eneral, precislon wound ~ilters are formed by mounting
the core, horizontally, on a motor driven spindle. One end Or
the strand of filtering material can be tled or otherwise fixed
to one end of the sidewall of that core. The strand passes
through a guide which is set up, through a gear train or simi-
lar arrangement to maintain a precise relationship between
rotations of the core and traverse o~ the ~uide, to move back
and forth along the length of the core, as the core is rotated.
As the guide travels in one directlon along the rotating core, ~
a spiral of strand is wrapped around the core from one end to
the other. When the gulde reaches the far end of the core, it
reverses in direction and travel~ back to the beginning point.
During this travel in the reverse direction, the core contlnues
to rotate in the same direction. Thus a reverse spiral of
strand is laid down on the core overlaying the original strand
spiral, forming a succession of diamond patterned layers.
Brief Description of the Drawlngs
Fig. l illustrates the complete diamond pattern layer of a
precision wound filter cartridge whlch has been split longitu-~
dinally along one surface of the cartridge, opened up and laid
rlat .
Fig. 2 is a pro~ection illustration of a diamond ~rom the
diamond pattern of Fig. l, showing the arrangement of the
filter strand overlays.
Fig.l 3 ls a side view Or Fig. 2 illustrating the depth
dimension of a diamond as well as the arrangement of the filter
strand overlays.
V~7
Fig. 4 is a cross sectional view of a conventional filter
cartrid~e sectioned in a plane perpendicular to its longltudi-
nal axis.
Flg. 5 is an lllustration of an enlarged section of an
example of standard ~ibrlllated polypropylene film.
Fig. 6 is an illustration o~ an enlarged section of an
example of highly ~ibrillated fllm accordin~ to the present
inventlon.
The diamond pattern, as it is wound on the core as described
above, is illustrated in Fig. 1 of the drawings.
Fig. l shows a cylindrical core which has been cut axially
alon~ one wall and then rlattened out. Keeping in mind that
the strand is continuous, each strand spiral wound on the core,
by the traverse of the gulde ln a single direction, is
designated by~ a letter. The order in which each strand spiral
-3a-
n.~ ~
has been wound is alphabe-tical. Thus, beglnning in the lower
left hand corner of Fig. 1, the strand is tied to the end o~
the core and is designated as spiral a. It is wound around the
core as the guide moves in a direction from the bottom of Fig.
1 to the top. Thus it will be noted, in Fig. 1, that every
fourth line sloping upwardly from left to right is designated
as spiral a. When the guide reaches the far end of the core,
represented by the top of Fig. 1, the end of spiral a is
reached and spiral b begins as the guide reverses direction.
This is designated as a-~b at the top of Figo 1. Spiral b ls
wound in the reverse direction from spiral a and is shown by
lines sloping downwardly from left to right, and every fourth
of these lines is designated as spiral b.
When spiral a has been wound and spiral b has been wound
in overlay on top o~ spiral a, the guide has traveled the
length of the core twice, from the beginning end of the core to
the far end, then revers~ng directions, back to the beginning
end. Thus the guide has traveled through one cycle, from its
beginning point back to that same end of the core. It will be
noted that spiral a has made precisely 3-5/6 complete winds on
the core and that spiral b also has made precisely 3-5/6
complete winds. Adding this together, it will be apparent that
the core has been rotated precisely 7-2/3 tirnes during one
cycle of the guide.
Again referring to Fig. 1, the guide, during one complete
cycle, returns to the beginning end of the core, however, not
to the same point on the circumference of the core at which it
began. Along the bottom of ~ig. 1, it will be noted that
spiral b does not end at the same point at which spiral a
began; spiral b transcends into spiral c, designated as b-~c,
at a polnt which is to be precisely two-thirds of the circum-
ference away from the beginning of spiral a in the direction of
rotation of the core. At this point, the guide direction of
traverse again reverses, winding splral c. At the far end of
the core, the guide direction again reverses and spiral d is
wound to complete the second cycle of the guide. Again, the
core has rotated precisely 7-2/3 times during this second cycle
of the guide~ for a total of precisely 15-1/3 revolutions for
precisely two guide cycles. Spiral c transcends into spiral d,
designated as c-~d, at the far end o~ the core9 at the top of
Fig. l, and spiral d is wound in the re~erse direction of
spiral c. At this point four spirals have been wound, spirals
a and c being in the same direction and generally parallel to
each other, and spirals b and d being in the same direction,
opposite to the direction of spirals a and c, and also
generally parallel to each other, as depicted in ~ig. 1. And
spiral d ends at a point-which is to be precisely two-thirds of -
the circumference away from the beginning of spiral c in the
direction of rotatlon of the core.
At the end of the second cycle of the guide traverse,
spiral d transcends into spiral e, designated as d~e at the
bottom of Fig. 1 and a third guide traverse cycle begins,
winding spiral e which transcends into spiral f at e-~f as
shown at the top of Fig. 1. Again, the guide reverses its
direction of traverse at the far end of the core and winds
spiral f in the opposite direction to the winding of spiral e.
At the end of the third guide traverse cycle, spiral f ter-
minates at a point which is to be at precisely the same point
on the beginning end of that core where spiral a began. At
this point one complete layer of diamond patterns has been
i~ )l'7
wound. During the thlrd cycle of spindle traverse, the core
has, again, been rotated precisely 7-2/3 times, now totalling
precisely 23 revolutions for three complete guide traverse
cycles.
In the parlance of the filter lndustry, the "wind number"
of the filter cartridge shown in Fig. 1 is three, equal to the
number of guide traverse cycles required to wind one complete
layer of diamond patterns. The number of circumferential
diamonds which appear on the filter cartridge is equal to the
wind number. Another term that ls used in the industry is
"wind ratio". This ratio is set up as a fraction with the
"wind number" on the bottom and the number of revolutions,
which were turned by the core during the winding of one
complete layer of diamond patterns, being on top. The filter
cartridge shown in Fig. l was rotated 23 times, during three
guide traverse cycles, to form one complete diamond pattern.
Thus the "wind ratio" is-23/3 or 7-2/3~ This is equal to pre- -
cisely the number of revolutions which the core turned to
complete a single guide traverse cycle, from one end to the
other and back along the rotating core.
It turns out that the number of "axial diamonds", or the
number of diamonds along the longitudlnal axis of the filter
cartridge, is one-half of the number of times the core was ~`
rotated to wind one complete diamond pattern layer. For the
filter cartridge illustrated in Fig. 1, the core was rotated 23
times to wind one complete diamond pattern layerg thus the
number of 'laxial diamonds" is meant to be precisely 11 1/2. It
also turns out that the total number of diamonds on the face or
surface of the cartridge is the product of multiplying the
number of revolutions required to wind one complete diamond
pattern layer, with the number o~ guide traverse cycles
required to wind one complete diamond pattern layer. For the
filter cartridge illustrated in Fig. 1, the core was rotated
precisely 23 times and the guide went through precisely three
traverse cycles to form one complete diamond pattern layer.
Thus 23 x 3 = 69, precisely the number of diamonds to be formed
on the surface of the filter cartridge, including half diamonds
at the ends of the core.
Again, referring to Fig. lg initially, spiral a was wound,
followed by spiral b in a reverse directionP This formed a
diamond pattern which was three times the size Or the diamonds
which ultimately form the first diamond pattern layer. This is
shown in dotted outline about the vertical center of FigD 1.
Spiral b overlaps spiral a. Next spirals c and d were wound,
with spiral c overlapping spirals a and b and spiral d
overlapping spirals a, b and c. What was then formed within
that original large diamQnd pattern were two parallelograms,
one small diamond and another diamond twice its size. This is
shown in dashed outline in combination with the dotted outline
of Fig. 1. Flnally spirals e and f were wound, with spiral e
overlapping all of the foregoing spirals and spiral f
overlapping all those other spirals including spiral e. What
was finally formed are nine essentially equivalent diamonds
within the original large diamond. This is shown in dot-dash
outline, combined with the dotted outline and dashed outline of
Fig. 1. One of those diamonds, having the letter "d" appearing
on it, was formed of spiral a, crossed by spiral b, which in
turn were both crossed by spiral c, and finally spirals a, b
and c were crossed by spiral do This criss-cross formation is
illustrated in Fig. 2, in enlarged section, projection view.
Ii~1017
Because of this criss-cross formation, a third dimension,
depth, is added to the diamond pattern, each diamond
approachingg in depth, about an average of 2-1/2 times the
nominal diameter of the strand material of each spiral, as
illustrated in Fig. 3 which shows an elevational, or side view,
of the diamond illustrated in Fig. 2.
Typical filter cartridges have a core with an outside
diameter of about 1~ inches and an outside diameter of about
2~7/16 inches with a filtering medlum, or build up of strands,
that is about 11/16 inch thick, give or take about 1/16 inch on
all dimensions. The filter is wound in a range of approx-
imately 15~ to 200 guide traverse cycles, and for the standard
ten inch long filter, the ratio of circumferential diamonds to
a~ial diamonds is usually within the range of about two to
about five. That is, for each circumferential diamond, there
are about two to five axial diamondsO Among the commonly
available filters, the coarsest winds have a wind number of
about six and the finest winds have a wind number of about 39,
and the number of complete diamond pattern layers ranges from
as many as about 25 to as few as about four.
Of course, as each successive complete diamond pattern
layer is wound on the one before it, the overall diameter of
the cartridge increases, and the distance around the circum- ~-
ference increases, but the number of diamonds around the cir-
cumference remains constant, because the wind number, or number
of guide traverse cycles, is set as a constant at the
beginning, as is the number of core rotations for each complete
diamond pattern layer. The shape of the diamond changes as
the diameter of the filter cartridge increases with each suc-
cessive complete diamond pattern layer. Referring to Fig. 1,
the diamonds increase in length, sideways, as the circumference
dimension lncreases, but the height of the diamonds remains
constant because the length of the cartrid~e does not change.
Thus, the cross sectional areas of the diamonds increase,
As viewed from the circular end of a filter cartridge, or
more precisely, looking towards the cut end of a cartridge
which had been sectioned perpendicular to the longitudinal axis
of the cartridge, as shown in Fig. 4, it is noted that the
diamonds, in addition to increasing in size along the circum-
ference of the cartridge, as each successive complete diamond
pattern layer is wound, also are symetrically displaced. The
centers of each successive diamond, going from the center of
the core to the outside diameter of the cartridge, are not
aligned on a radius line. Rather, the centers are displaced to
~orm a compound curve, or a helix, generally analogous to a
snail shell as shown in Fig. 4. Thus the centerline of the
passageway formed by the_successive diamond layers, from the
core to the outside diameter of the filter cartridge, does not
track a straight line, but rather~ follows the helix curve.
This phenomenon is caused by the displacement of the transition
points, one spiral to the other, about the circumference of the
filter cartridge, as each successive complete diamond pattern
layer is wound. Such filter cartrldges are referred to as
"helical" cartridges or "helically" wound cartridges. It is
believed, by those with skill in the art, that this helix pat-
tern of displacement of`the diamonds serves to create a tortuous
path in the flow of fluids therethrou~h, thus aiding in the
exposure of the diamond sidewalls to more particles of dirt,
resulting in the entrapment of more dirt particles aOainst
those sidewalls. Thus, as the theory goes, dirt particles
O17
which would otherwise pass through a larger diamond cross sec-
tional area, would tend to cling to the sidewalls of that
diamond, while the fluid flows on through. This is thought to
increase ~ilter cartridge life by trapping, in the larger
diamonds, dirt particles which would otherwise more rapidly
clog up the lesser cross sectional areas of the smaller
diamonds ln the layers nearer the cartridge core.
For each successive complete diamond pattern layer, one on
top of the other, the cross sectional areas of the diamonds
increase, and the voids inside of each diamond increase in
size, resulting in additional space, in each such layer, for
the pass-through of dirt particles to the layers beneath.
Where the diamond cross sectional areas become too large, for
example where the overall diameter of the filter cartridge is
increased too much, in comparison with the core diameter, the
filter cartridge is known to loose its ability to trap dirt
particles within those cQ~plete outer layers of diamond pat- -
ternsO Simply, the dirt particles are too small and the holes
through which they travel are too big. This problem can be
overcome, generally, by using fibrillated strand material wikh
fibrils extending from the strands to position a portion of the
filterin~ media within the voids of the complete outer layers
of diamond patterns. However, strand fibrillation has been a
costly and difficult process as detailed in the above mentioned
prior art. There remains a need for an economical improved
highly ~ibrillated film cartridge of great efficiency, extended
life and dirt holding capacity.
Summary of the Invention
It is an ob~ect of this invention to overcome disadvan
tages of prior filters made from fibrillated film yarns and
processes using these filters.
It is an additlonal obJect of this lnvention to create an
improved helically wound fibrillated film cartrldge.
It is an addltional obJeet of this invention to provlde
improved dirt holdlng eapaeity ln a wound fibrillated film
S fllter cartrldge.
It is another further obJeet of thls lnvention to provlde
a fibrillated fllm eartridge of lncreased effieiency.
These and other ob~ects of the inventlon are generally
accomplished by providing filters of the preeislon wound type
in whieh the strands are of a yarn formed from hlghly
flbrillated film.
¦ In a particularly preferred form of the invention a eon-
¦ ventional filter cartridge of about 2-7~16 inch overall
I diameter on a core of about 1-1/18 inch dlameter was prepared
¦ by windlng a highly ribrillated film yarn of 10,000 total
bundle denler J having a f~bril denler of less than 50 and con
taining greater than three percent broken fibrils, onto a
cartridge Or any desired length. This cartrldge exhibits much
higher llfe and efficiency than previously available
fibrlllated film filter cartridges.
Detailed Descrlption of the Invention
The filter cartridge and filtering process of the inven-
tion has a decided advantage over pr~or art fibrillated film
cartridges. The cartridges of the invention have up to about 3
times longer llfe while exhibiting greater efficiency than pre-
vious cartridges using standard fibrillated fllm yarns as shown
in Fig. 5. The cartridges have greater dirt holding capacity
and are able to trap more fine particles of matter from the
fluid passing through it ~han prlor cartridges. Further the
lo instant cartridges have the advantage that the technique of
forming the cartrldge remains the same as for prior wound
cartridges, therefore making the increase ln performance
possible wlth no addltional capital outlay for winding
equipment.
In the instant specification the following terms of art
are utllized ln accordance wlth the deflnitlons below which are
considered to be in accordance with their accepted meaning in
the cartridge filtering art:
efficiency (particle size) percentage removal of a
given size particle as
determined from the ratio
of downstream number or
~ 7
weight of partlcles of that
particular size to the
number or weight of that
particular si~e particle ln
S the upstream fluid from a
filter. An efficiency
rating would be stated 9 for
example~ as "90% at 10
microns".
wind number number of circumferential
diamonds on the surface of
a cartridge taken at the
locus of points creating a
circle in a plane perpen-
dicular to the axis of the
filter.
wind ratio _ equals spindle revolutions -
divided by guide traverse
cycles (complete traverse
cycles of the guide mecha
nism up and back to the
starting end of the core).
dirt holding capacity (DHC) the amount or quantity of ~
dirt fed to a filter
cartridge up to the point
where the pressure drop
between the inlet and
outlet of that filter
reaches 30 psi. (also
referred to as life of the
cartridge). This term does
not mean the amount of dirt
held by the cartridge as of
the point where the
pressure drop reaches ,
30 psi,
pressure drop the change in pressure
between input fluid and
fluid exiting a cartridge
during filtering.
diamond the area defined by a first
pair of adjacent, spaced-
apart substantially
parallel strands and a
second pair of adjacent,
spaced-apart substantially
_ parallel strands that
crosses said ~irst pair in
. a precision wlnding on a
filter cartridge. The
extension of this defini-
tion to fractional half-
diamonds at the end of the
filter cartridge will be
apparent.
diamond pattern is the complete winding to
form one layer of circum-
ferential diamonds, i.e.,
13 cycles of the traverse
are required to form a
101~ ~
complete diamond pattern
for a 13 I'wind number"
cartridge.
flbrillated film yarn a yarn made by orienting a
polymeric film suf~iciently
to cause it to separate
into a fibrous structure
(fibrils). The geometry
and degree of separating
into fibrils can be
controlled and/or enhanced
by several techniques known
to those in the art, such
as embossing or perforating.
highly fibrillated film yarn a fibrillated film yarn in
whi.ch about 3% or more of
- the auxiliary fibrlls are
broken on one end from the
main fibril strands, in
which the auxiliary fibrils
are about one-half lnch
(1.25 cm) or more in length
and are of an average
denier of about 70 or less.
~5 It is known that in a precision wound filter, increasing
the number of circumferential diamonds (finer winding) provides
higher efficiency, but that it usually shortens the cartridge
life. Conversely decreasing the number of circumferential
diamonds (coarser winding) provides greater cartridge life but
with lower efficiency.
.017
By way of example only the following table provides a com-
parison of the properties of typical highly fibrillated yarns
as compared to typical standard fibrillated yarns.
PROPERTY HIGHLY FIBRILLATED STANDARD FIBRILLATED
Yarn denier lO,OOO average 10,000 average
Total fibrils in 200-600 50-75
cross section
Total main 8-25 percent 30~50 percent
fibrils
Total aux. 75-92 percent 50 70 percent
fibrils
Aux. fibril 1/2 in. to 3/1~ in. 1/8 in. to 3/8 in.
length
Aux. fibrils 6-10 1-4
per inch of
main fibril
Percentage of 3-50 percent 0-1 percent
broken aux.
fibrils
~ilm thickness l.O to 1.75 mil 2.0 to 2.5 mil
avg. 3~ micrometers avg. 57 micrometers
avg. ~i5 mil avg. 2.25 mil
It is well ~nown that reducing the average cross-sectional
area (denier) of a fibrous assemblage reduces 1ts bending modu-
lus (stiffness). Ordinary fibrillated film yarns are usually
produced such that the bending modulus is reduced while main-
taining tensile properties of the strands. The highly
fibrillated film yarns used to make the cartridges of the pre-
sent invention are produced with stretching of the film to an
extent sueh that only tensile properties sufficient to permit
winding are retained while significantly reducing the average
cross-sectional area (denier) of the individual fibrils. Thus
the preferred highly fibrillated film yarns have an average
fibril denier less than about 50 and more than 3 percent of the
fibrils are broken. The total bundle denier may be any denier
``\ ~ o~
that gives good filter performance. A total bundle denier of
about lO,000 has been found to be satisfactory.
Filter cartridges made from highly fibrillated yarns have
been found to be much more efficient in removing particles than
cartridges of the same wind number made with ordinary
fibrillated film yarn. Additionally, the life of the highly
fibrillated film yarn cartridge usually increases relative to
those made with ordinary fibrillated film yarns. It has been
found that a significant increase in life without loss in effi-
ciency is achieved with highly fibrillated film yarns when the
wind number is reduced (coarser winding). Improvements in life
of up to threefold that of those made from ordinary fibrillated
film yarn are possible. This amount of improvement in both
life and efficiency generally can be achieved be forming the
highly fibrillated cartridges at one or kwo wind numbers lower
(coarser) than those made with ordinary fibrillated film yarn.
The preferred highl~ fibrillated film yarns of the inven- -
tion may be formed of any film forming polymer. Typical are
polyesters, polyethers, polyethylenes, polysulfides, polyacry-
lics, fluorinated polymers, polyvinyl chlorides, polypropy-
lenes, rubberized styrenes and polyamides. A preferred
material has been found to be the polyolefins as they are low
in cost, are easily fibrillated and are suitable for use in
food products. The optimum material has been found to be
polypropylene as it is lowest in cost and is easily worked to
form fibrillated films and is safe for food products.
It has been found that for the conventional, about 2-7/16"
diameter, cartridges a wind number of between about lO and
about 13 is preferred, for A.C. coarse test dust, as the
highest performance is in this range with greatly increased
life and higher efficiency. As is apparent from the above set
~ 7
for~h definitions a specific wind number cartridge has that
specific number of circumferential diamonds at any circumferen-
tial circle, i.e. a 13 wind number cartridge has 13 circum-
ferential dlamonds. The ratio of axial diamonds to circum-
ferential diamonds per 10 inch length of the cartridge is typi-
cally kept about between about 2 and about 5. The preferred
ratio is between 2.5 and about ~ for good filtering perfor-
mance. The optimum ratio is between about 3 and about 3.5 as
this ratio gives the best filtering performance and ease of
winding.
Because fibrillated film yarns are derived ~rom films,
even though the yarns may be nearly circular in cross section,
¦ when they are wound under tension, they tend to flatten out.
Thus, the effeckive strand width is greater than textile
lS rovings and the opening of any given diamond, vis-a-vis a
corresponding textile roving diamond, is smaller for
fibrillated fllm yarn where comparable bundle deniers and the
same wind numbers are used. Above about 13 wind number, lOgO00
total denier fibrillated film yarn produces overlapping
diamonds because of this flattening phenomenon and filtration
performance (life) is significantly reduced. By using a
fibrillated film yarn with a relatively smaller cross-section
(lower total denier) it is believed that more definite but ~-
relatively smaller diamonds (greater wind number) would be
possible. It is believed that highly fibrillated film yarns of
even lower denier could be utilized at even higher wind numbers
as the packing of the finer yarns would not be as tight.
The following examples illustrate the dramatic improvement
in performance obtained by the instant invention,
Three different fibrillated film yarns were made by
extruding polypropylene films, orienting (stretching) the
~ilms, generally contactin~ the films with embosslng rolls to
cause separations into a fiberous-like structure
(fibrillation), slitting the films into appropriate widths to
yield lO,OOO total bundle deniers, and winding the yarns onto
supply bobbins.
The first yarn was used to make standard fibrillated film
yarn filter cartridges which are identified as "ORD" in the
following examples. It was made from a polypropylene film
about 0.00225 inches thick (2.25 mil approx.) Orientation and
embossing produced a network of main support strands and auxi-
liary fibrils about as shown in Fig. 5, the main strands
averaging about 173 denier There were about four auxiliary
fibrils per linear inch of main strand. The auxiliary fibrils
averaged about 22.5 denier and were about 3/8 inch long~
Essentially all of the auxiliary fibrils were connected at both
ends between main strands as shown in Fig. 5. The yarn pro-
duced with this film is similar to yarns available, for
example, from Blue Mountain Industries, Anniston, Alabama (Type
1300) and EB Industries, Inc., Senisbury, Connecticut (Type
6700).
The second yarn was used to make the fibrillated film yarn
cartridges which are identified as "HIGH" in the following
examples. It was made from a polypropylene film about 0.0015 ~
inches thick (1.5 mil approx.). Orientation and embossing were
essentiall~ identical to that used to produce the first film
yarn as described above. However, the orientation and
embossing produced a network of main strands and auxiliary
fibrils about as shown in Fig. 6. The main strands averaged
about 107 denier. There were about eight auxiliary fibrils per
~ ~ 7
linear inch of main strand. The auxiliary ~ibrils averaged
about 5/8 inch in length and were about 22.4 denier.
Approximately 10% of the auxiliary fibrils were broken from the
main strands on at least one end.
A third yarn was used to make the fibrillated film yarn
cartridges which are identified as "EXTRA HIGH" in the
following examples. It was also made from a polypropylene film
about 0~0015 inches thich (1.5 mil approx.). Orientation was
essentially identical to that used to produce the first and
second film yarns. However, the contact area of the embossing
rolls with the film was increased. This resulted in main
strands which averaged about 107 denier, as in the second yarn
described above. -There were about eight auxiliary fibrils per
linear inch of main strand. However, the auxillary fibrils
averaged only about 12 denier and were about 7/8 inch in
length. And about 50% of the auxiliary fibrils were broken
from the main strands on~at least one end.
A series of precision wound filter cartridges were formed
from each of the three yarns described above utilizing a
cartridge core of per~orated tinned steel of a diameter of
about 1-1/8 inch, The cartridges were wound in 10 inch lengths
to an overall dlameter of about 2-7/16 inches. All of the
cartridges were formed at a spindle speed of about 650 rpm.
The cartridges were formed with a ratio of total diamonds of
between 3 and 3.5 axial diamonds to circumferential diamonds on
the 10 inch cartridge. The roving tension was between about
400 and 800 grams for winding of all cartridges. The winder
was a Leesona winder which utilized a back plate which pressed
against the turning cartridge after about the formation of the
first 8th inch of windings. The cartridges average about 200
gms of yarn. Back plate pressure was adjusted to give finished
`~` ~ 7
cartridges with air density as shown ln the table below~ ~ir
density is the pressure drop measured in inches of water at 3.9
scfm airflow.
After formation, each cartridge was tested in flow.ng
water containing A.C. Coarse Test Dust from the A.C. Spark Plug
Company. A.C. Coarse Test Dust as available from A.C. Spark
Plug Company contains particle size distribution as follows:
weight percent at micrometer: 12% at 0-5; 12% at 5-10; 14% at
10-20; 23% at 20-40; 30% at 40-80; 9% at 80-200. The water was
flowing at a rate of about 3.5 gallons per minute during
testing and the test was stopped at a pressure drop across the
cartridge of about 30 pounds or when no increase in the
pressure drop was occuring. The test results f'rom each
cartridge are displayed in the listing below. This listlng
illustrates that highly fibrillated film yarn filter cartridges
exhibit greater efficiency and generally greater dirt holding
capacity than those made ~ith ordinary fibrillated film.
Additionally, when the wind number of the highly fibrillated
film yarn filter cartridges is reduced as much as two values
both the efficiency and dirt holding capacity are still higher
relative to the finer wound ordinary fibrillated film
cartridges.
-\ ~ 7
Chart No. 1
EFFICIENCY
Yarn (Percent at
Fibrillation Wind Air Micrometers)
Ex. Degree No. Density DHC~ 5~m 10~m ?0~m 30~m 50~m
la ORD 8 0.3 no Too low to measure
lb EXTRA HIGH8 0.4 2 PSID 10 14 20 25 30
2a ORD 10 0.4 0.2PSID -- 9 12 15 18
2b HIGH 10 1.0 227g 2040 55 62 75
2c HIGH 9 o.6 5PSID 2025 30 38 56
3a ORD 11 o.6 3PSID 2023 28 32 35
3b HIGH 11 1~5 35g 8996 9999.4 99O9
4a ORD 13 3.3 13g 3744 5458 64
4b EXTRA HIGH13 5.1 57g 6894 98100 100
4c HIGH 12 2.0 79g 5465 7679 89
*Dirt Holding Capacity (DHC) is expressed in grams fed to
achieve 30 psld (pounds per square inch drop). Some cartridges
do not achieve 30 psid. In such cases cartridges achieving
higher pressure drop are considered to have higher dirt holding
capacity. Those not achieving 30 psid substantially cease to
provide filtering and me~ely pass dust fed after trapping an
initial amount. In chart No. l, where filter cartridges failed
to reach 30 psid, DHC is expressed in psid reach rather than
grams fed to achieve 30 psid.
In Chart No. 1, examples la through 4c each illustrate
that, at a given wind number, use of a highly fibrillated film
yarn increases life (DHC) and concurrently provides signifi-
cantly increased particle removal efficiency. In example 4,
the highly fibrillated film yarn wound cartridges (4b and 4c)
exhibit greater than four times the DHC, in comparison to those
wound with standard fibrillated film yarn (4a), and, con-
currently, about twice the particle removal efficiency.
Examples 2 and 4 demonstrate that because of the improved
filtering characteristics of the highly fibrillated film yarn
of the present invention~ filter cartridges can be made at wind
numbers which are lower than those used for standard
fibrillated film yarn` cartridges and still provide more effi-
ciency and life (DHC) in comparison. By comparlng example 4a
with 3b and example 3a with 2c, it can be seen that a filter
cartridge made from a highly fibrillated film yarn provides a
greater life (DHC) and a greater efficiency than a filter
cartridge wound from standard fibrillated film yarn at two wind
numbers higher.
Numerous modifications of this invention may be made
without departing from the spirit and scope of the invention.
For instance, the cartridges may be formed in irregular shapes
I rather than onto tuhes. ~urther, while the invention is set
forth primarily with the conventional 2-7/16 nominal diameter
filter tube, the invention is viable for any diameter tubeO
Further, the invention is viable for any length tubular filter
and the invention may be utilized with highly fibrillated yarns
of materials other than the demonstrated polypropylenes such as
polyethylenes or polyestersO Further highly fibrillated yarns
may be utilized of higher or lower total bundle denier which
would result in a shift of wind number values to account for
the change in dimensions of the diamond opening caused by yarn~
size difference. For instance lower bundle denier highly
fibrillated yarns would be expected to reach best filter per-
formance at higher wind numbers. The important factors of high
fibrillated yarns which are low average fibril denier and the
presence of broken fibrils are present at other total bundle
deniers.
These and other modifications will be apparent to the per-
son with skill in the filter art. For instance, the core
1.~
material also could be modified ko be other than tin material
such as plastic or stainless steel, both of which are par-
ticularly desirable in the food industry. Such modifications
are within the scope of the invention. Accordingly, the inven
tion is not to be limited except as set forth in the appended
claims.
