Note: Descriptions are shown in the official language in which they were submitted.
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FILTER MATERIAL
Field of the Invention
The present invention relates to a filter material comprising fabric of
ceramic
oxide fibers and vermiculite particulate. The filter material can be
incorporated, for
example, into filter bag, pleated filter cartridge, and molded or pressed
filter
constructions.
Description of Related Art
It is generally known that fiberglass fabrics and (crystalline) ceramic
fabrics
can be employed in filter bags for use at higher temperatures than filter bags
made
of polymeric fibers. A drawback associated with fiberglass filter fabrics is
the need
to protect the fibers from self abrasion (i.e. abrasion resulting from fibers
rubbing
together) and abrasion by material being filtered (e.g., dust). Abrasions on
the
surface of the glass fibers cause a decrease in the strength of the fiber.
Further, periodic cleaning of the bags, for example, by periodic pulses or
blasts of air, or by mechanical shaking, results in substantial fiber to fiber
contact,
and fiber flexing. Under such conditions, fiberglass filter bags would quickly
fail.
Although it is common in the industry to address the fiber abrasion problem by
coating the fibers with polytetrafluoroethylene, the usefulness of such
coating is
limited by the decomposition temperature of the polytetrafluoroethylene, which
is
about 260 C (500 F).
There are industry needs, however, for filtering gas streams at temperatures
in excess of 260 C (500 F). Crystalline ceramic metal oxide fiber filter bags
have
been developed for such applications and are recommended for use up to about
760 C (1400 F). The typical cost of the crystalline ceramic metal oxide
fibers,
however, has impacted and limited their use in such applications.
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More than one year prior to the filing of the present application, the
assignee
showed a vermiculite coated fabric having a gas permeability of zero I/min/cm2
(zero Udm2=min) to at least one third party. The woven (5-harness satin weave)
fabric was a 50:50 by volume blend of 11 diameter aluminoborosilicate fiber
(available from the 3M Company under the trade designation "NEXTEL 312" and
magnesium aluminosilicate glass fiber (available under the trade designation
"S2
GLASS" from Owens-Corning Fiberglas Corp. The intended use of the
vermiculite-coated fabric was as a gas tight fire barrier.
Summary of the Invention
The present invention provides a filter material comprising fabric of ceramic
(metal, including Si) oxide fibers and vermiculite particulate, the fibers
collectively
having an outer surface (i.e., each fiber has an outer surface, and the sum of
these
outer surfaces provides a "collective" outer surface), at least a portion of
the outer
surface being covered by a sufficient amount of vermiculite particulate such
that the
filter material has an increased flexural endurance over the fabric without
the
presence of the vermiculite, of at least 100 percent (preferably at least 200
percent,
more preferably at least 500 percent, and most preferably at least 1000 or
even at
least 5000 percent), the filter material having a gas permeability of at least
0.15
1/min/cm2 (preferably at least 0.3 1/min/cm2).
For most fiber fabric applications, the filter material according to the
present
invention preferably has a gas permeability of less than 2 Umin/cm2 (200
Udm2=min;
33.3 cm3/sec/cm2; 2000 cm3/min/cm2; 65 CFM/ft2), more preferably less than 1.5
1/min/cm2, and most preferably less than 0.81/min/cm2. In general, for most
fiber
fabric applications, the filter material according to the present invention
preferably
has a gas permeability in the range from 0.15 to 2 Umin/cm2, more preferably,
0.30
to 1..5 L/min/cm2, and most preferably, 0.3 to 0.81/min/cm2.
Preferably, the filter material according to the present invention has the
increased flexure properties even after exposure to temperatures of about 315
C
(preferably about 538 C) for at least seven days, preferably at least one
year. In
certain preferred embodiments of the present invention, the ceramic oxide
fibers are
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glass fibers made of glass having a softening point in the range from about
600 C
to about 875 C, more preferably in the range from about 750 C to about 875 C.
In this application:
"ceramic" refers to crystalline ceramics, glasses, and glass-ceramics;
"gas permeability" refers to the average of four gas permeability values
which are determined as described in the working examples;
"Umin/cm2i refers to liters per minute per centimeter squared;
"Vdm2=min" refers to liters per decimeter squared=minute;
"cm3/sec/cm2" refers to cubic centimeters per second per centimeter
squared";
"cm3/min/cmZ" refers to cubic centimeters per minute per centimeter
squared;
"CFM/ft2i refers to cubic feet per minute per foot squared";
"softening point" refers to the temperature at which a glass in the form of a
0.235 mm long fiber having a 0.55-0.75 mm diameter, at a heating rate of 5
C/min,
elongates at a rate of I mmlmin under its own weight;
"fiber" refers to a filament structure having a length of at least 100 times
its
diameter;
"continuous fiber" refers to a fiber which as infinite length compared to its
diameter (see, e.g., U.S. Pat. No. 4,047,965 (Karst et al.);
"flexural endurance" is determined as described in the working examples
section below; and
"filter bag" refers to a filter material in the form of a tube open on at
least
one end, which may be seamless but preferably has a seam.
The filter material according to the present invention can be incorporated
into conventional filter constructions including filter bags, pleated filter
cartridges,
and molded or pressed filters.
Description of Preferred Embodiments
The fabric of ceramic oxide fibers can, for example, be woven, (e.g., with
plain weave, twill weave, drill weave, satin weave, etc.), braided, knitted,
or non-
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woven. Suitable fabrics for making the filter material according to the
present
invention include those employing alumina fibers, titania fibers, silica
fibers and
zirconia fibers. Useful fabric is available, for example under the trade
designation
"DUST FILTRATION FABRICS" from Burlington Glass Fabric Co. of
Greensboro, NC.
The fabric can also be made by techniques known in the art. For example,
woven fabric can be formed using a loom to interlace warp (iengthwise) yarns
with
filling (crosswise) yarns. Knitted fabric can be constructed using a needle(s)
to
interloop yarn or fiber loops. Braided fabric can be made by intertwining
fibers or
yarns with a braiding machine to provide tubular structure.
Non-woven ceramic metal oxide fiber fabric, which has no predetermined
intertwining or pattern of fibers or yarns, can be formed from non-continuous
fibers
or yarns using paper processing methods or air laying methods. The strength
and
integrity of non-woven ceramic oxide (fiber) fabrics may be increased by the
presence of organic (e.g., polyvinyl acetate, polyvinyl alcohol, polyvinyl
pyrrolidone, and polyethylene glycol) or inorganic (e.g., colloidal silica)
binders, or
by entangling the fibers by needle-punching, hydro-entanglement or air
entanglement, or by stitch-bonding. For further details regarding methods for
making non-woven fabrics see, for example, U.S. Pat. No 5,380,580 (Rogers et
al.).
Fibers used to make fabric are typically available in continuous tows (also
referred to as rovings (i.e., an assembly of one or more strands of ceramic
fibers
without twist) or yarns. Useful continuous ceramic metal oxide fibers include
aluminosilicate, aluminoborosilicate fibers, alumina fibers, titania fibers,
and zirconia
fibers. Preferred aluminosilicate fibers, which are typically crystalline,
comprise by
weight, on a theoretical oxide basis, A1Z0, in the range from about 67 to
about 77
percent, and Si02 in the range from about 33 to about 23 percent. Sized
aluminosilicate fibers are available, for example, under the trade
designations
"NEXTEL 550" and "NEXTEL 720" from the 3M Company of St. Paul, MN.
Aluminoborosilicate fibers preferably comprise by weight, on a theoretical
oxide basis, Al2o, in the range from about 55 to about 75 percent, Si02 in the
range
from less than about 45 to greater than zero (preferably, less than 44 to
greater than
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zero) percent, and B203 in the range from less than 25 to greater than zero
percent
(preferably, about I to about 5%). The aluminoborosilicate fibers preferably
are at
least 50 percent by weight crystalline; more preferably, at least 75 percent;
and most
preferably, about 100%. Sized aluminoborosilicate fibers are available, for
example,
under the trade designations "NEXTEL 312" and "NEXTEL 440" from the 3M
Company. Preferred alumina fibers are alpha-alumina fibers available, for
example,
under the trade designation "NEXTEL 610" from the 3M Company. Fabrics made
from these fibers are also commercially available.
Further, suitable aluminosilicate fibers, aluminoborosilicate fibers, and
alumina fibers, can be made by techniques known in the art including those
disclosed in U.S. Pat. Nos. 3,795,524 (Sowman), 4,047,965 (Karst et al.), and
4,954,462 (Wood et al.). Useful zirconia fibers, yttria-alumina fibers, and
titania
fibers can be made as described, for example, in U.S. Pat. Nos. Re. 35,143
(Funkenbusch, et al), 5,348,918 (Budd et al.), and 4,166,147 (Lange, et al).
Preferred glass fibers include magnesium aluminosilicate glass fibers such as
those available under the trade designation "S2-GLASS" (softening point of
about
860 C) from Owens-Corning Fiberglas Corp. of Granville, OH. Such preferred
glass fibers comprise by weight, on a theoretical oxide basis, SiO2 in the
range from
about 64 to about 66 percent, A1203 in the range from about 24 to about 26
percent, MgO in the range from about 9 to about 11 percent, and other oxides
such
as CaO, Na20, K20, and Fe203. Another preferred glass fiber is a silicate
fiber
available, for example, under the trade designation "E GLASS" (softening point
of
about 846 C from Owens-Corning Fiberglas Corp. This latter fiber comprises by
weight, on a theoretical oxide basis, SiO2 in the range from about 52 to about
56
percent, A1203 in the range from about 12 to about 16 percent, CaO in the
range
from about 16 to about 25 percent, up to about 5 percent MgO, B203 in the
range
from about 5 to about 10 percent, and other additives such as Na20, K20, Ti02,
and Fe203. Further, quartz fibers are available, for example, under the trade
designation "ASTROQUARTZ" from J.P. Stevens, Inc., of Slater, N.C.
Ceramic metal oxide fibers also are available as "mineral wool" fibers, which
tend to be short, fine diameter (i.e., 2-3.5 micrometers) fibers. Mineral wool
fibers
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can be employed in the fabric, particularly when combined with other, longer,
fibers
(e.g., the continuous alumina, aluminosilicate, or aluminoborosilicate fibers
described above). Mineral wool fibers, which are typically aluminosilicate,
are spun
from molten material. Such fibers are available, for example, under the trade
designations "FIBERFRAX" from Carborundum Co., Niagara Falls, NY, and
"CERWOOL" from Premier Refractories and Chemicals, Inc., King of Prussia, Pa.
Preferably, the ceramic oxide fibers diameter in the range from about 3 to
about 25 micrometers; more preferably, from about 4 to about 15 micrometers.
Fibers having diameters greater than about 25 micrometers are useful, but
fabrics
made from such fibers tend to be less efficient for use in filtration
applications, and
tend to have lower flexibility than those made with smaller diameter fibers.
Fibers
having a diameter less than about 3 micrometers may also be useful but tend to
be
avoided because of the small diameter.
Although the fibers used to prepare the fabric can be sized or unsized, the
fibers are typically available in their as-received condition with a size
coating
present. Typically, continuous fibers are treated with organic sizing
materials
during their manufacture to provide lubricity and to protect the fiber strands
during
handling. It is believed that the sizing tends to reduce breakage of fibers
and reduce
static electricity during handling and processing steps. When making a non-
woven
fabric by wet-lay methods, the sizing tends to dissolve away. Sizing also can
be
removed after fabrication of the fabric at high temperatures (i.e., 300 C).
Preferably, the sizing is removed before applying the vermiculite to the
fabric.
It is within the scope of the present invention for the fabric to employ one
of
several types of fiber, including utilizing fibers of different compositions.
Typically,
the fabric comprises at least 75 percent by volume (preferably at least 90,
95, or
even 100 percent by volume) ceramic oxide fiber, based on the total fiber
volume of
the fabric.
Preferably, the fabric has a thickness in the range from about 0.2 mm (0.008
inch) to about 1.3 mm (0.05 inch), or, in another aspect, expressed as weight
per
unit area, as from about 271 g/m2 (8 oz/yd2) to about 847 g/m2 (25 oz/yd2).
Generally, fabrics less than about 0.2 mm tend to be weak and not wear as well
as
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heavier fabrics. Fabrics exceeding about 1.3 mm in thickness tend to be
excessively
expensive, and have a lower permeabilities than the lighter weight fabrics.
The fabric can comprise up to about 25 percent by weight (based on the
total weight of the fabric) fugitive material (e.g., heat fugitive materials
such as
thermoplastic, nylon, and rayon fibers, powders, films, and webs, and water
soluble
materials such as polyvinyl alcohol). Fugitive fibers or particles can be
burned or
dissolved out of the fabric to provide a desired structure or porosity.
Fugitive
materials can be incorporated into the fabric using conventional techniques
including soaking or spraying the fabric with fugitive material. Binders can
be
incorporated into the fabric, for example, by saturating or spraying the
fabric with
binder.
Vermiculite is a hydrated magnesium aluminosilicate, micaceous mineral
found in nature as a multilayer crystal. Vermiculite typically comprises by
(dry)
weight, on a theoretical oxide basis, about 38-46% Si02, about 16-24% MgO,
about 11-16% A1Z0,, about 8-13% Fe203, and the remainder generally oxides of
K,
Ca, Ti, Mn, Cr, Na, Ba, etc. "Exfoliated" vermiculite refers to vermiculite
that has
been treated, chemically or with heat, to expand and separate the layers of
the
crystal, yielding high aspect ratio vermiculite platelets. These platelets can
be
ground up to produce small particulate, typically ranging in size (i.e.,
length and
width) from about 0.3 micrometer to about 100 micrometers, with a mean size of
about 20 micrometers. The thickness of the platelet typically ranges from
about 10
Angstroms to about 4200 Angstroms. In another aspect, the vermiculite
platelets
may have a bi-modal distribution of particle sizes.
The vermiculite can be applied to the fabric by dispersing vermiculite
particulate in a liquid medium (typically water), and applying (e.g., coating)
the
dispersion onto the fabric. Aqueous vermiculite particle dispersions are
available,
for. example, from W.R. Grace of Cambridge, MA, under the trade designation
"MICROLITE 963". The desired concentration of the dispersion can be adjusted
by removing or adding liquid media thereto.
It is preferred that any sizing present on the fibers of the fabric be removed
before the vermiculite is applied. The sizing can be removed conventional
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techniques including heating the fabric to burnoff or decompose the size
material
(e.g., heating the fabric for 24 hours at a temperature in the range from
about 204
C (400 F) to about 400 C (750 F)). Removal of the sizing is believed to
increase
the wetting of the fibers by 'the dispersion, as well as to contribute to the
homogeneity of the resulting vermiculite coating.
The vermiculite can be applied to the fabric using conventional techniques
such as dip coating, spray coating, and brush coating. Preferably, the
vermiculite is
"worked into" or uniformly distributed into the fabric. For example, the
vermiculite
can be forced into the fabric by pressure (e.g., by using a conventional hand
held
roller; by hand flexing the coated fabric back and forth; and/or by passing
the
vermiculite coated fabric between two opposed rolls positioned, or capable of
being
positioned, such that the gap therebetween is less than the thickness of the
coated
fabric). Optionally, the vermiculite dispersion can be heated to a temperature
below
the boiling point of the liquid media before it is applied to the fabric.
Further, the
coated fabric can be at an elevated temperature (e.g., a temperature at or
above the
boiling point of the liquid media in the dispersion) before, and/or while the
pressure
is being applied.
A preferred method for coating the fabric is to dip the fabric into a
vermiculite dispersion for at least several seconds, remove the fabric from
the
dispersion, allow excess dispersion material to drain off, and then dry the
coated
fabric, for example, in an oven (e.g., at 110 C for 2 hours). Affter drying,
the
resulting filter material is ready for use.
In another method for making fabric material according to the present
invention, vermiculite can be applied to the fabric using conventional
techniques,
and prior to drying, the vermiculite coated fabric can be run between two
opposed
rolls positioned, or capable of being positioned, such that the gap
therebetween is
less than the thickness of the coated fabric. Preferably, the coated fabric is
at an
elevated temperature (e.g., a temperature at or above the boiling point of the
liquid
media in the dispersion) before, and/or while it is passed between the rolls.
Although not wanting to be bound by theory, it is believed individual
coating of the fibers with the vermiculite is preferred as compared to
vermiculite
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coatings were there is bridging of vermiculite or the like (e.g., a film)
between
individual fibers.
Filter material according to the present invention is useful, for example, for
the removal of entrained particulate from fluid streams. The filter material
can be
incorporated into conventional filter constructions including hot gas filters
and filter
bags (see, e.g., U.S. Pat. No 3,884,659 (Ray). A particularly useful filter
utilizing
fabric material according to the present invention is a bag filter in the
shape of a
tube. Typically, bag filters range in diameter from about 10 cm to about 31
cm, and
in length from about 1.2 meters to about 9 meters, although other sizes may
also be
useful, depending upon the particular use requirements and bag construction. A
tubular filter bag is typically made from filtration fabric cut to the
appropriate length
and width for the desired filter bag. Preferably, any sizing present on the
fabric is
removed prior to treating the fabric with vermiculite. The fabric can be sewn
lengthwise to form a tube before or after the vermiculite treatment. A cuff
may be
sewn on one or both ends, and a closing cap may be sewn on one end. Metal
rings
for attachment and support may be added. The finished bag is attached to a
support
structure, which forms a seal between the clean and dirty sections of a
"baghouse".
A baghouse is a filtering apparatus having a multiplicity of tubular filter
bags
mounted in a filter housing. The filtering apparatus allows for the removal of
dust
or particulate entrained in a fluid (e.g., hot gas) stream. Each filter bag
has a
tubular supporting frame or cage which holds the filter bag in an open tubular
configuration. A particulate-laden gas stream flows into the bag and the
particulate
gradually becomes deposited on the exterior surface of the filter bag, due to
the
flow of gas from the outside to the inside of the bag.
Baghouses are typically equipped with a dust removal hopper. The
accumulated particulate on the outside of the bag is removed by mechanical
shaking
or by reverse jet flow (i.e., a burst of pressurized air applied to the
opening in the
bag, causing the bag to billow out, resulting in dislodgment of particulate
from the
bag surface). The interval between cleanings can be a few minutes to hours,
depending upon the rate of particulate collection.
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Objects and advantages of this invention are further illustrated by the
following examples, but the particular materials and amounts thereof recited
in
these examples, as well as other conditions and details, should not be
construed to
unduly limit this invention. All parts and percentages are by weight unless
otherwise indicated.
Examples 1-4 and Comparative Example I
Glass fabric (722 g/m2 (21.3 oz/sq yd), 3x1 twill, 48x40 yarn count,
texturized fill, filament size "DE", nominal 6 micrometer diameter; available
under
the trade designation "E GLASS" from Owens-Corning Fiberglas Corp. of Toledo,
OH) was heated at 400 C for 1 hour in a conventional oven to burn off the
sizing
present on the as-received fabric.
Vermiculite dispersions of 1%, 2%, 2.5% and 3% by weight vermiculite
were prepared by diluting a commercially available vermiculite dispersion
(7.5%
solids in water; viscosity of 550 cps; mean particle size of about 20
micrometers;
available under the trade designation "MICROLITE 963" from W.R. Grace of
Cambridge, MA) with deionized water. The as-received fabric was cut into 17.8
cm x 50.8 cm (7 in x 20 in) pieces which were coated with one of the
vermiculite
dispersions as follows. The fabric was placed into the vermiculite dispersion
then
repeatedly folded back and forth on itself for about 10 seconds (i.e., the top
major
surface of the fabric was folded back upon itself at an angle of about 180 ,
unfolded, then folded back, etc.). The fabric was turned over and again dipped
and
folded in the vermiculite dispersion for about 10 seconds. The coated fabric
was
then dried at 110 C for two hours.
The gas permeability of the vermiculite-coated fabrics were determined
using ASTM D737-75 ("Standard Test Method for Air Permeability of Textile
Fabrics"), wherein a suction fan drew air though a known area of fabric
defined by a
circular orifice (6 mm in diameter) and a vertical manometer measured the rate
of
air flow though the test area of fabric. The sample to be tested was clamped
into
the test apparatus (i.e., into a rubber-faced specimen holder) assuring that
it was
free of tension. The motor to the test apparatus was started and its speed
slowly
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adjusted using the rheostat to maintain the oil level in the inclined
manometer at
12.5 mm (0.5 in.). The oil level in the vertical manometer was recorded. If
while at
an oil level of 12.5 mm (0.5 in.) on the inclined manometer, the oil level in
the
vertical manometer was off scale (i.e., either high or low) the size of the
circular
orifice was changed as appropriate.
The gas permeability was calculated by measuring the rate of flow of air
passing through the test area of the sample from the level of oil in the
vertical
manometer. The gas permeability of a heat cleaned (i.e., 400 C for 1 hour)
fiberglass fabric ("E GLASS") having no vermiculite on it was also measured.
The
gas permeability values, which are based on an average of three runs, are
reported
in Table 1, below.
Table 1
Conc. of vermiculite Gas permeability
Example dispersion. wt. % Umin/cm2 (CFM/ftZ)
Comp. I ---- 0.89 (29)
1 1% 0.89 (29)
2 2% 0.77 (25)
3 2.5% 0.74 (24)
4 3% 0.34 (11)
The flexural endurance of Examples 1-4 and Comparative Example I was
evaluated as described in ASTM D-2176-89 ("Standard Test Method for Folding
Endurance of paper by the M.I.T. Tester"), using a 1 kg load. This test, which
is
designed to simulate the flexing that filter bags experience during the
cleaning cycle,
involved successively folding the sample until failure (i.e., until all the
yarns in the
fill direction broke).
More specifically, the flexural endurance of Examples 1-4 and Comparative
Example I was evaluated using a Tinius Olson M.I.T. Folding Endurance Tester
(available from Tinius Olson of Willow Grove, PA). Samples of each example
were
cut into 1.9 cm (0.75 inch) by 11.43 cm (4.5 inch) pieces. The fabric ("E
GLASS"
was unraveled to 1.25 cm (0.5 in) in width (11 fill yarns wide).
For each sample, the bottom oscillating folding head (jaw) of the tester was
rotated so that its opening was vertical. The fold counter was set at zero.
One end
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of the sample was clamped firmly and squarely into the top head of the tester.
The
plunger was depressed into the position corresponding to a one kilogram dead
weight load. Without touching the portion of the sample to be folded, the
bottom
of the sample was clamped firmly and squarely into the bottom head of the
tester,
with the sample lying flat, and without either side of the sample touching
toughing
the oscillating head mounting plate. The sample was folded through an angle of
135 , and at a uniform rate of 175 25 double folds/min until failure.
In addition, the flexural endurance of Exampies 1-4 further heat treated at
316 C or 425 C for 15 minutes were also evaluated to at least in part simulate
in-
use conditions for the fabric. Under some conditions, heat treatment can
contribute
to the strength of the fabric; alternatively, heat can also cause the fibers
in the fabric
to be have reduced strength. The results of the flexural endurance tests are
shown
in Table 2, below.
Table 2
Conc. of Flexural endurance,
vermiculite number of
Example. dispersion, wt.% Heat treatment, C double folds
Comp. I ---- ---- 16
1 1% 110 66
IA 1% 316 59
1B 1% 425 15
2 2% 110 318
2A 2% 316 406
2B 2% 425 104
3 2.5% 110 622
3A 2.5% 316 362
3B 2.5% 425 229
4 3% 110 936
4A 3% 316 892
4B 3% 425 662
Examples 5 and 6
A 46 meter (50 yds) long by 1.24 meter (49 in) wide piece of glass fabric
(722 g/m2 (21.3 oz/sq yd), 3x 1 twill, 48x40 yarn count, texturized fill,
filament size
"DE", nominal 6 micrometer diameter; available under the trade designation "E
GLASS" from Owens-Corning ) was heat cleaned in a conventional oven for 24
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hours at 204 C and 24 hours at 371 C to remove the sizing present on the as-
received fabric. The heat-cleaned fabric was threaded into a dip coating
machine
equipped with a 9.1 meter (30 ft) tall vertical drier. Twenty three meters (25
yds)
of the fabric was fed into a coating tray filled with a 1.7% vermiculite
dispersion
(prepared by diluting a commercially available vermiculite dispersion
("MICROLITE 963") with deionized water), and passing underneath a 10 cm (4 in)
diameter stainless steel roll located at the bottom of the coating tray, the
roll being
completely submerged in the dispersion. The fabric exited vertically from the
dispersion, passing through two coating knives set at a gap of 0.96 mm (0.038
inch), and then continuing into the bottom of the vertical drier. The bottom
section
of the vertical drier was at a temperature of about 107 C, the top section at
about
177 C. The fabric passed through the drier over a top roller, then back down
through the drier, and then exited the drier and was wound on a core. The web
speed was 91 m/hr (100yds/hr).
Example 6 was prepared as described for Example 5 (above), except the
concentration of the dispersion was 2% vermiculite.
The gas permeabilities of the Example 5 and 6 vermiculite-coated fabrics
were 1.25 Umin/cm2 and 1.28 1/min/cm2, respectively. The gas permeability of
the
heat cleaned fabric (without the vermiculite coating) was 1.13 1/min/cm2, and
the
flexural endurance value was 16 double folds.
The flexural endurance of Examples 5 and 6, as well as samples of these
examples further heat treated at 316 C or 425 C for 15 minutes are reported in
Table 3, below.
Table 3
Conc. of Additional Flexural endurance,
vermiculite Heat number of
Exam le disQersion, wt % treatment, C double folds
5 1.7 --- 182
5A 1.7 316 54
5B 1.7 425 30
6 2 --- 204
6A 2 316 57
6B 2 425 23
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Examples 7-10
A 61 cm (24 inches) long by 18 cm (7 inches) wide piece of glass fabric
(722 g/m2 (21.3 oz/sq yd), 3x1 twill, 48x40 yarn count, texturized fill,
filament size
"DE", nominal 6 micrometer diameter; available under the trade designation "E
GLASS" from Owens-Corning ) was heat cleaned in a conventional oven for about
1 hour at 400 C to remove the sizing present on the as-received fabric.
Vermiculite
dispersions of 1%, 1.67%, 2% and 2.5% by weight vermiculite were prepared by
diluting a commercially available vermiculite dispersion ("MICROLITE 963")
with
deionized water. Heat-cleaned fabric was dipped in a tray filled with one of
the
vermiculite dispersion for about 20 seconds. The fabric was removed from the
dispersion, and excess dispersion was allowed to drain off for about 5
seconds. The
soaked fabric was then placed between two sheets of silicone coated paper and
fed
into laboratory scale laminator. The temperature of the laminator's nip rolls
was set
at 115.5 C (240 F). The gap between the rolls was slightly less than the
combined
thickness of the paper/fabric/paper. The roll pressure was at approximately
34.5
kPa (5 psi). For the 1% vermiculite dispersion example (i.e., Example 7), the
paper/fabric/paper sandwich was passed through two heated nip rolls five
times.
For the 1.67%, 2%, and 2.5% vermiculite dispersion examples (i.e., Examples 8,
9,
and 10, respectively), the paper/fabric/paper sandwiches were passed through
two
heated nip rolls nine times for each example. The fabric was then allowed to
completely dry at room temperature.
The flexural endurance of Examples 7-10, as well as samples of these
examples further heat treated at 316 C for 15 minutes are reported in Table 4,
below.
Table 4
Conc. of Additional Flexural endurance,
vermiculite Heat number of
Example dispersion, wt % treatment, C double folds
7 1 --- 218
7A 1 316 131
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8 1.67 --- 513
8A 1.67 316 312
9A 2 --- 580
9A 2 316 287
10 2.5 --- 639
IOA 2.5 316 417
Example 11 and Comparative Example II
This example illustrates the flex performance of filter bags made from the
fabric of this invention in a simulated baghouse test.
Two 50.8 cm (20 inch) by 152.4 cm (60 inch) pieces of fiberglass fabric
(fabricated from "S2 GLASS" yarns, and commercially available from Clark-
Schwebel of White Plains, NY, as Style 6781; 8-Harness Satin, 57x54 yarn
count,
306 g/m2 (8.90 oz/yd2); no texturized yarns) were each sewn into filter bags
1.22
meters (4 feet) long and 11.7 cm (4.62 inch) in diameter using quartz thread
(Q-18;
commercially available under the trade designation "ASTROQUARTZ" from J.P.
Stevens, Inc.) to provide a conventional french felled seam having 2 stitches
per cm
(5 stitches per inch). The bags were heat cleaned at 315 C (600 F) for 1 hour.
The
heat-cleaned bags were dipped into a 1.67% by weight vermiculite dispersion
(diluted with deionized water from "MICROLITE 963"). The vermiculite
dispersion was worked into the fabric using a hand held rubber roller. The
resulting
vermiculite-coated bags were dried at 93.3 C (200 F) for 4 hours. The
resulting
bags (Example 8) were installed on wire cages for testing in a baghouse.
The baghouse testing was run for 400 hours at a temperature of 493 C.
Each bag was subjected to a repeated pulse (2-5 pulses/minute) of room
temperature air at pressure of 420 Pa (60 psi) down the center of the bag to
simulate the type of pulsing done in actual use conditions to clean filter
bags.
Two other bags (Comparative Example II) were prepared as described for
Example 8 except for the addition of vermiculite.
The Comparative Example II bags each failed after not more than 112,000
pulses. The Example 8 bags, however, did not fail even after 333,000 pulses.
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Various modifications and alterations of this invention will become apparent
to those skilled in the art without departing from the scope and spirit of
this
invention, and it should be understood that this invention is not to be unduly
limited
to the illustrative embodiments set forth herein.
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