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Патент USA US3090113

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May 21, 1963
w. P. CRAWLEY
3,090,103
HEAT RESISTANT FIBROUS PRODUCTS CONTAINING CERAMIC
FIBERS AND METHOD OF‘ MAKING THE SAME.‘
Filed Oct. 24, 1957
I20 ' \
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ASBESTOS FABRIC
\<5_ (GRADE AAA)
(STlERbNsGIL)H
CERAMIC
ASBESTOS BLENDED
4O '
FIBER FABRIC
2O "
\\
O
700
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l
I
l
l
l
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J
800
900
I000
IIOO
I200
I300
I400
I500
TEMPERATURE (°F)
INVENTOR.
WlLLlAM P. CRAWLEYv
EATTORNEY
3'90g?,1'3'
Patented May 21, 1963
2
ethylene ?bers, polyamide ?bers, vinyl ?bers, and protein
3,090,163
I-EAT RESETANT FTBROUS PRQDUCTS CQNTATN
lNG
ENG TILE
CEIC
SAMEFIBERS AND METH'DD OF
?bers.
The invention can best be understood by reference to
several speci?c embodiments of the invention that are
William P. Crawley, Tonawanda, N.Y., assignor to The
described in the following examples.
The drawing provides a graphical representation of the
Carhorundum Company, Niagara Falls, N.Y., a cor
properties of a fabric made according to the embodiment
poration of Delaware
Filed Oct. 24, 1957, Ser. No. 6%,2?5
5 Claims. (Cl. 28-78)
of the invention described in Example I. The drawing
comprises a pair of curves, each’ curve showing graphical
10 ly the relationship between tensile strength and heat re
sistance of the fabric.
This invention relates to ?brous products that have
EXAMPLE I
unusual characteristics of strength and heat resistance.
The ceramic ?bers of the aluminum silicates that are
Fibrous Products Made From Intimate Blends of
now available have outstanding heat resistance, but their
physical characteristics have restricted their use. These 15
ceramic ?bers are straight and discontinuous. They have
no natural twist and are brittle and delicate.
The ?bers
are smooth-surfaced, so that there is little or no cohesion
between the ?bers, and because there is no crimp or curl
Ceramic Fiber and Asbestos Fiber
An intimate blend of “Fiberfrax” aluminum silicate
long staple, “medium” ceramic ?ber and carded asbestos
?ber, Cassiar grade AAA, a chrysotile asbestos, was made
acconding to the method that is described in the co-pend
to the ?bers, they do not cling together. Moreover, the 20 ing patent application of John W. Weber, Serial No.
658,582, ?led May 13, 1957, and now Patent 3,012,289.
?bers have low extensibility. Because of these character
“Fiberfrax” is a registered trademark of The Carborun
istics, these ceramic ?bers will not card on conventional
dum Company, Niagara Falls, New York. The long
machinery, but fall out of the machine.
staple grade of “Fiberfrax” ceramic ?ber contains about
Fabricated items such as paper, batts, roving, yarn,
cord, rope, cloth, and non-woven structures made from 25 51.3% silica, about 45.3% alumina, and about 3.4%
Zirco-nia. Fiber length is about 13/8" average, but varies
various conventional ?bers, both organic and inorganic,
considerably. The diameters of the “medium” ?bers are
are much more limited in their resistance to heat, accord
predominantly in the range 8 to 14 microns, With a mean
ing to the heat resistance of the speci?c ?bers used in
diameter of about 10 microns (about 2 denier). The
these items.
I have found that certain combinations of ceramic ?ber 30 speci?c gravity of the ?bers is about 2.73 gin/cc. As
produced, the ?ber contains up to about 65% of non
of an aluminum silicate with conventional ?bers can be
?brous solids or shot.
made in the form of intimate blends that can be carded
According to the Weber method, the asbestos ?bers
on textile machinery. Fibrous products that are made
were carded to form a continuous web. The Web of as
from these blends are characterized by unexpected com
35 bestos carrier ?bers was divided into four widths. A
binations of strength, heat resistance, and heat dissipa
mass of the ceramic ?bers was opened to make a plurality
tion.
of small tufts, and these tufts were deposited onto each
Accordingly, one object of this invention is to provide
of the widths of the carrier ?bers, so that there were a plu
?brous products that have materially increased heat re
rality of tufts of ceramic ?bers distributed upon each width
sistance.
40 of the web of carrier ?bers. The widths of the carrier
A related object of the invention is to provide an inti
web, with the tufts of the ceramic ?bers distributed there
mately blended ?brous mixture of ceramic ?bers of an
on, were superposed to form a pile. The pile was then
aluminum silicate and carrier ?bers, that can be formed
carded to form a blended web of carrier ?bers and ce
into ?brous products that have substantially increased heat
resistance over products formed from the carrier ?bers 45 ramic ?bers. The proportions of asbestos carrier ?ber
and ceramic ?ber were carefully regulated so that the
alone, and that have appreciable strength.
blended web comprised about 44% by weight of asbestos
Another object of the invention is to provide ?brous
?ber and about 56% by Weight of- ceramic ?ber. Sub
products that have greater strength at high temperatures
stantially no organic impurities were present.
than ?brous products previously available.
The non-?brous material, or shot, was separated from
According to the present invention, ?brous products,
the ceramic ?bers before the tufts of ceramic ?bers were
including non-woven, woven, and knitted products, are
deposited on the web of asbestos carrier ?bers.
made from intimate ?ber blends that contain, by weight,
, The blended ?ber web was divided into several widths,
between about 10% and about 95% of ceramic ?ber,
to form rovings which were spun to make yarn. The
the remainder being a carrier ?ber that will permit the
ceramic ?ber to be processed on conventional machinery. 55 yarn was woven into a six inch Wide twill weave tape.
Several pieces were cut from the tape for testing pur
While ceramic ?ber that is made from substantially
poses. Similar test pieces were obtained from grade
pure aluminum silicate is the preferred ceramic ?ber for
AAA asbestos tape of substantially the same Weight and
use in accordance with the teachings of this invention, it
construction, to provide a standard of comparison. The
is contemplated that certain other heat-resistant ceramic
?bers could also be used, such as, for example, ?bers that 60 several test pieces were then placed in ovens, in pairs of
‘one piece of asbestos tape and one piece of blended ?ber
contain aluminum silicate together with certain other in
tape, at different temperatures for 24 hours. Thereafter,
organic oxides, such as, for example, boron oxide, thoria
the tensile strength, ASTM grab method, of the warp was
and zirconia. Ceramic ?bers of this type are produced
determined for each of these. The results were plotted,
by processes similar to those used for mineral Wool or
were reproduced in the drawing.
staple glass ?bers, except that the melting point (33%0 65 andAsthethecurves
drawing indicates, the asbestos fabric has supe
F.) is so high that the heat of an electric arc furnace is
rior tensile strength up to a temperature between 1000°
required. The molten mix is formed into ?bers ‘by blow
F. and 1100" F. At temperatures above 1000° F., the
ing with steam or air, or by spinning from mechanical
tensile strength of the fabric made from the blend of
rotors. Resistance to high temperatures is unexcelled by
70 ceramic ?ber and asbestos ?ber had a considerably supe
any ?ber with the possible exception of pure silica.
rior tensile strength. Even at 1500" F., the fabric from
Some of the carrier ?bers that may be used are acrylic
the blended ?ber had appreciable tensile strength.
?bers, rayon, cotton, Wool, asbestos, glass, tetrafluoro
3,090,103
a
For the ?eld of use at temperatures between about
1000“ F. and 1500“ F., therefore, the fabric from the
blended ?ber is markedly superior to asbestos.
Representative points on the curves are as follows:
TABLE I
Tensile strength, lbs.
Time, hrs.
Temp., ° F.
Unheated tapes _________________ __
24 ___________________________ __
Asbestos
cloth
Cloth from
blended
159v 0
55.0
85. 0
35. 0
13. 5
__________ _ _
RJI‘.
1, 000
24. _
1, 150
24. _
1, 300
24____
1,500
2.0
20.0
__________ __
10. 5
cut, the tape undoubtedly would resist destruction under
static load for a considerable period of time.
On the basis of the data that is outlined above, and on»
the basis of the results of other tests with other blends of‘
asbestos ?ber and aluminum silicate ceramic ?ber, andi
experience with such blends, certain proportions of as-*
bestos ‘to ceramic ?ber appear to be best for making in-timate blends for products for use in certain temperature-'
ranges. Thus, for the range 1000“ F. to 1400" F., blends?
10 that contain ‘60% to ‘90% asbestos, and the balance alu-‘
minum silicate long staple ceramic ?ber, would o?er a‘.
good combination of heat resistance, strength, and econ-'
omy. ‘In the range 1400" F. to 1800” F., blends of 40%
to 60% asbestos with the balance ceramic ?ber would be
15 most practical. In the range 1~800° F. to 2300“ F., blends
of 10% to 40% asbestos with ceramic ?ber would be most
The entries under the temperature column in Table I indi
practical. Typical applications for ?brous products made
cate the temperature at which the respective samples were
from intimate blends of asbestos ?ber and ceramic ?ber
held for 24 hours, before their tensile strength was deter
include heat barriers of all types, such as for example,
mined. The superiority of the asbestos fabric is evident 20 furnace curtains, lagging, ?reshields, ?re screens, heat in
until temperatures on the order of about 10000 are
sulating materials, and the like. Felted products made
reached, but above 1100” F., the cloth from the blended
from these intimate blends of ?bers are useful for high
?ber is markedly superior in strength, appearance, and
temperature gas ?ltration, as Well as for many other pur
hand.
poses.
One sample of the asbestos tape, and one sample of the 25
EXAMPLE II
tape made from the blended ?ber, were held in a furnace
Blends
0)‘
Ceramic
Fiber and Acrylic Fiber
for 24 hours at 1000" F. The weights of these samples
were recorded before and after furnacing. The results are
presented in Table H, below.
Fibrous products made from cotton, nylon, acrylic ?ber,
and cellulose acetate ?ber would have a much more broad
30 ?eld of use, if the temperature resistance were increased
TABLE II
even moderately. For example, in the ?ltration ?eld, the
manufacture of collector bags consumes a large amount of
Weight, in grams
Sample
Before
Blended sample ____ __
Asbestos tape _______ __
special cloth annually. For example, ?lament glass cloth
_'
After
iurnacing
iurnacing
36. 56
26. 08
35. 67
21. 58
Percent
loss
2. 4
17. 2
treated with a silicone resin is used extensively in the
35 manufacture of dust collector bags for carbon black col~
lection. This cloth is resistant to continuous temperatures
of 400° F., and has a useful life of between 12 and 18
months. Considerable processing economies would be
available if a fabric were available that could be used to
The difference in weight loss is attributable in part to the 40 make these bags, and that could Withstand temperatures
Organic ?ber content of the asbestos tape, which burned
in the range of 500° F. up to 550° F.
oif during furnacing.
According to the present invention, such fabrics can
In an additional test, the tape made from the blended
readily be prepared by making cloth from intimate ?ber
?ber was subjected to even higher temperatures. Test
blends that have predetermined proportions of acrylic car
pieces of the tape were held for two hours at several
rier ?ber and ceramic ?ber of an aluminum silicate.
45
different high temperatures, and thereafter, the strength
A blend can be prepared of 25% by weight “Fiberfrax”
characteristics were determined, as summarized below in
long staple, medium ceramic ?ber and 75% by weight
Table III.
“Orion” acrylic ?ber. “Orlon" is a registered trademark
TABLE III
of the E. I. du Pont de Nemours Co., Inc., Wilmington,
50 Delaware,_for an acrylic ?ber made from polymerized
Load in lbs. Percent of the
acrylonitrile. The intimate blend of ?bers can be spun
Temp, ° F.
at the break
original
point;
to form a yarn. The yarn has good strength and unusual
heat resistance up to around 300'’ F. It can be woven
strength
retained
to form insulating cloth, ?lter elements, gaskets, and pack
23. 5
16.0
15. 0
a 1 Completely melted.
25
17
l4
55 ings, of unusual heat resistance.
Woven products made from this intimate ?ber blend
can be heat treated at temperatures above about 320° F.,
and preferably in the range of 400°F. to 600° F., in
circulating air or other oxidizing atmosphere, for su?i
In another test, two one-inch wide ravelled strips of the 60 cient time to permit the acrylic ?ber to undergo a change
tape were loaded with Weights, one with three pounds
in character to a non-?ammable state. An exothermic
(approximately 5% of breaking load at room tempera
reaction takes place under these conditions, and it is be
ture), and the other with nine pounds (approximately
lieved that the acrylic ?ber is converted to linear, hetero~
15% of breaking load at room temperature). The two
cyclic form. The ?brous product must be held above
strips were then heated gradually in an oven. After 95 65 320“ F., in contact with air, for su?icient time to permit
minutes of heating, and at a temperature of 2310" F., the
the reaction to be completed, otherwise, the product will
strip with the nine pound load failed. After 110 minutes
be ?ammable. Ordinarily, for woven fabrics, periods
of heating, and at 2360° F., the strip with the three pound
from one-half hour to three hours are suf?cient. When
load failed.
the acrylic ?ber has been heat treated in this manner, as
On the basis of the foregoing data, it is apparent that
described in detail in a copending patent application Serial
temperatures in the neighborhood of 2350° F. are critical
No.
692,206, ?led October 24, 1957, ?reproof ‘fabrics are
with regard to the load breaking properties of this par
obtained that have excellent heat resistance. Thus, the
ticular tape. At temperatures up to about 2000° F., the
yarn above can be woven to form a fabric weighing ten
material exhibits reasonably good resistance to static load
stresses, and if vibrations or shearing action are not pres 75 oz./sq. yd. When this fabric is heat treated as described,
it can be used for ?ltration bags and for active ?lter ele
3,090,103
5
ments, and in other applications, at continuous tempera
@
?lling. This cloth had excellent heat resistance and made
tures up to about 600° F. Even higher service tempera
tures are permissible when the ?ber blend contains a
greater proportion of ceramic ?ber.
EXAMPLE III
Fibrous Products Made Fram. Blends of Ceramic
an excellent material for use as press cloth material.
Another blended web was prepared that contained 15%
by weight of ceramic ?ber and 85% by weight of rayon.
This blended web was formed into yarn that was spun
to form a light weight fabric that had excellent heat re
sistance. This fabric had characteristics that made it a
superior material for use for ironing board covers, and
for similar applications where enhanced resistance to heat
Fiber and Organic Fiber
Several intimate blends containing 70 parts by weight 10 and scorching is important.
of “Fiberfrax” long staple “medium” ceramic ?ber and
‘Intimate blends of rayon ?bers and ceramic ?bers of
30 parts by weight of carrier ?ber were prepared. The
an aluminum slicate have excellent textile properties, par
carrier ?bers were as follows:
ticularly where the rayon ?bers comprise 70% to 85% by
weight of the blend. Fibrous products from such blends
Fiber:
Description
Cotton ___________ _. 1%" staple, from picker lap.
Nylon ___________ __ 3 denier, garnett stock.
“Dynel”1acrylic ?ber- 3 denier, 11/2" staple.
Cellulose acetate ___~ 3 denier, 11/2" staple.
1“Dynel” is a registered trademark of Union Carbide Cor
poration for its acrylic ?ber, made from a copolymer of vinyl 20
chloride and acrylonitrile.
The ?ber blends were made by hand picking the com
ponent ?bers and making a sandwich-type mix. The mix
was then broken down vertically and re-sandwiched. This
was repeated for a total of three blendings. The stock
was then hand fed to a single cylinder card equipped with
ring doffers and rub aprons.
An examination of the blended webs from the card in
dicated that the blended Webs that contained cotton and
nylon had a fair degree of ?ber blending, and that the
acrylic ?ber and cellulose acetate ?ber blends had a better
have enhanced heat resistance with very little sacri?ce in
hand, appearance, and strength.
The foregoing examples illustrate certain speci?c em
bodiments of the invention. It should be appreciated that
many other combinations of carrier ?ber with the ceramic
?ber are possible, and are contemplated within the scope
of this invention. For example, the asbestos ?ber-ceramic
?ber blends described in Example I can be modi?ed, for
special purposes, by incorporating still other ?bers in the
intimate blend.
Generally, the ceramic ?bers range in size from about
2 to about 20 microns, although ?bers with diameters up
to about 80 microns can be used successfully. In general,
the ceramic ?ber constitutes at least about 10%, and
preferably at least 15%, by weight of the ?ber blend, to
achieve a substantial upgrading of heat resistance. The
maximum proportion of ceramic ?ber that can be em
Fibrous products made from the blended webs serve ad 35
ployed, under the best possible conditions, with the most
suitable machinery now available approaches 95% by
weight of the blend. For most high temperature appli
cations, however, the preferred amount of ceramic ?ber
mirably for high temperature packing and for thermal
insulation.
Since roping and yarn strength depend primarily upon
in a blend of ?bers is on the order of 80% to 90%, that is,
about 10% to 20% by Weight of the blend comprises
carrier ?bers.
selected for further processing, and were formed into yarn
on a woolen spinning frame. The resulting yarns from
both types of ?ber blends were satisfactory, although there
were indications that better results would be obtained
from mechanically blended ?bers. Drafts as high as 1.25
were used successfully in making the yarns.
of this type are readily available in a variety of deniers.
degree of ?ber blending.
All of these blended webs were characterized by en
hanced heat resistance and good yarn-making properties.
The ceramic ?bers that can be used, in accordance with
the carrier ?ber, good ?ber blending is necessary for mak
ing satisfactory roping and yarn. Since the blended webs 40 the teachings of this invention, contain a major propor
tion of aluminum silicate, together with small amounts
containing the acrylic ?ber and the cellulose acetate were
of boric oxide, zirconia, or other ?uxes. Ceramic fibers
characterized by good ?ber blending, these webs were
For good processing characteristics, the longer ?bers, of
large diameter, are preferred. The ?ber diameters prefer
ably should be predominantly in the range between 2
and 20 microns.
While certain carrier ?bers have been described above
in relation to speci?c embodiments of the invention, it
All four blended webs, that is, the hand-picked, carded,
blends of ceramic ?ber and cotton, nylon, acrylic ?ber, 50 will be understood that many suitable carrier ?bers can
be used. Rayon is a highly desirable carrier ?ber for
and cellulose acetate, respectively, were also hand-twisted
many purposes where resistance to extremely high tem
to form ropings or yarns. The twisted ropings were sus
peratures is not required, because rayon is a precision
pended vertically, and a small weight was then attached
?ber. The acrylic ?bers and other synthetics are also
to each at its lower end. The ?ame of a match was
rought into contact with each strand. The carrier ?bers 55 precision ?bers, so that processing can be facilitated by
selecting, for blending with the ceramic ?ber, a carrier
of nylon and cotton burned, leaving parted strands indi
?ber that will have, consistently, optimum carrier char
cating no residual strength. The acrylic ?ber and cellu
lose acetate ?ber blacknened and shrank, but the residues
acteristics. However, the natural ?bers, such as, for ex
apparently provided a bonding action which held the un~
ample, wool and cotton, can also be used.
burned ceramic ?bers together, since some yarn strength 60
Some of the organic carrier ?bers that can be em
ployed tend to shrink at elevated temperatures. In the
remained.
EXAMPLE IV
?brous products p epared according to this invention,
however,
?ber shrinkage upon exposure to heat is often
Blended Rayon Fiber and Ceramic Fiber
not a serious problem. This is particularly true where
Yarn was made by carding and spinning a blend of 80 65 the ceramic ?ber constitutes the major proportion of the
parts by weight of rayon and 20 parts by weight of “Fiber
?ber blend.
frax” long staple, “medium” ceramic ?ber. The rayon
In any woven ?brous product made according to the
was 1.5 denier, 11/2” staple ?ber. The ceramic ?ber had
teachings of this invention, the ?bers are bound together
a mean diameter of about 4- microns, with a minimum of
by twist and ?ber to ?ber cohesion, and therefore, tensile
about 2 microns, and a maximum of about 40 microns 70
strength is not substantial at high temperatures. Higher
(average, about 055 denier). Staple length of the ceramic
tensile strength can be obtained by inserted material such
?ber averaged about 1%", with some variation between
as alloy wire. Under many conditions, a glass ?lament
individual ?ber lengths.
yarn, or an asbestos yarn insert, provide adequate
The ?bers were carded and spun to form an eight oz./
sq. yd. cloth that had a yarn count of 15/2 warp and 75 strength, but for extremely high temperature applications
7
3,090,103
where the temperature limitations of these inserts are ex
ceeded, wire is necessary. Nickel-chrome alloy wire and
stainless steel Wire are good insert Wires for high tem
perature applications.
The ?brous products of this invention can be formed
readily in substantially any desired fabricated form. For
example, herringbone Weave cloth, twill Weave tape, tu
bular Woven fabric with a stainless steel Wire insert, pa
3. A strong, heat-resistant fabric, adapted for service
'at temperatures in the range from about ‘1000" F. to
about 1400“ ‘F. which involves maintenance of substan
tial tensile strength, said fabric being woven from yarns
consisting essentially of carded and spun, intimate mix
tures of staple, inorganic, siliceous, ceramic ?bers con
taining a major proportion of aluminum silicate and
staple carrier ?bers consisting essentially of asbestos, said
per, batts, blankets, roving, yarn, cord, rope, and the
ceramic ?bers constituting from about 10% to about
like, can be produced readily.
10 40% by weight of said fabric.
The ceramic ?bers provide heat-resistant and heat
4. A strong, heat-resistant fabric, adapted for service
di?’using members in the products, and thus upgrade the
at temperatures in the range from about 1400° F. to
heat resistance. The ceramic ?ber offers particular ad
about 1800" F. which involves maintenance of substan
vantages in products where previous failures had been
tial tensile strength, said fabric being woven from yarns
caused by a surface or localized heat condition.
15 consisting essentially of carded and spun, intimate mix
' Speci?c ?brous products that may be improved, ac_
tures of staple, inorganic, siliceous, ceramic‘ ?bers con
cording to the teachings of this invention, include lami—
taining a major proportion of aluminum silicate and
nating paper for high temperature applications, laundry
staple carrier ?bers consisting essentially of asbestos, said
cloths, and many other textiles for high temperature ap
?bers constituting from about 40% to about
plications. Many other speci?c ?brous products are 20 ceramic
60% by Weight of said fabric.
mentioned above. ,
_ While the invention has been described in connection
5. A strong, heat-resistant fabric, adapted for service
at temperatures in the range from about 1800° F. to
with speci?c embodiments thereof, it will be understood
that it is capable of further modi?cations, and this ap
‘about 2300° F. which involves maintenance of substan
adaptations of the invention following, in general, the
principles of the invention and including such departures
consisting essentially of carded and spun, intimate mix
tures of staple, inorganic, siliceous, ceramic ?bers con
taining a major proportion of aluminum silicate and
tial tensile strength, said fabric being woven from yarns
plication is intended to cover any variations, uses, or 25
from the present disclosure as come Within known or
customary practice in the art to which the invention per
tains and as may be applied to the essential features
herein before set forth, and as fall within the scope of the
invention or the limits of the appended claims.
I claim:
1. A blended, ?brous product characterized by a high
degree of strength retention at temperatures between 35
‘staple carrier ?bers consisting essentially of asbestos, said
ceramic ?bers constituting from about 60% to about
90% by weight of said fabric.
References Cited in the ?le of this patent
UNITED STATES PATENTS
2. A strong, heat-resistant fabric, adapted for service
451,115
1,486,800
2,132,702
2,266,907
2,306,781
2,401,389
2,424,743
2,467,889
at temperatures in the range from about 1000° F. to
' 2,557,834
McMullen ____ __' ____ __ June 19, 1951
about 2300" F. which involves maintenance of substan
tial tensile strength, said fabric being woven from yarns
consisting essentially of carded and spun, intimate mix
tures of staples, inorganic, siliceous, ceramic ?bers con~
2,626,213
2,643,437
Novak ______________ __ Jan. 20, 1953
Parker ______________ __ June 30, 1953
540,018
764,417
Canada ______________ __ Apr. 23, 1957
Great Britain ________ __ Dec. 28, 1956
1000’ F. and 2000° F. and consisting essentially of an
intimate carded mixture of staple, inorganic, siliceous,
ceramic ?bers containing a major proportion of alumi
num silicate and’staple carrier ?bers consisting essen
tially of asbestos,'said ceramic ?ber constituting from
about 10% to about 90% by weight of said product.
taining a‘major proportion of aluminum silicate and
staple carrier ?bers consisting essentially of asbestos, said
ceramic ?bers constituting from about 10% to about
90% by weight of said fabric,
Emsley ______________ __ Apr. 28,
Riesenberg __________ __ Mar. 11,
Simpson ______________ __ Oct. 11,
Riehl _______________ __ Dec. 23,
Francis ______________ __ Dec. 29,
Truitt ______________ __ June 4,
Davis _______________ __ July 29,
Harter et al. _________ __ Apr. 19,
1891
1924
1938
1941
1942
1946
1947
1949
FOREIGN PATENTS
OTHER REFERENCES
“Modern Textiles,” September 1957, page 61.
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