US3090103A - Heat resistant fibrous products containing ceramic fibers and method of making the same - Google Patents

Description

May 21, 1963 TENSILE STRENGTH (lbs) w. P. CRAWLEY 3,090,103 RESISTANT FIBROUS PRODUCTS CONTAINING CERAMIC FIBERS AND METHOD OF MAKING THE SAME. Filed Oct. 24, 1957 HEAT ASBESTOS FABRIC 80 (GRADE AAA) CERAMIC- ASBESTOS BLENDED 4O FIBER FABRIC O l I l l l I l J 700 800 900 I000 IIOO I200 I300 I400 I500 TEMPERATURE (F) INVENTOR.

WlLLlAM P. CRAWLEY EATTORNEY 3,090,163 I-EAT RESETANT FTBROUS PRQDUCTS CQNTATN- lNG CEIC FIBERS AND METH'DD OF ENG TI E SAME William P. Crawley, Tonawanda, N.Y., assignor to The Carhorundum Company, Niagara Falls, N.Y., a corporation of Delaware Filed Oct. 24, 1957, Ser. No. 6%,2fi5 Claims. (Cl. 28-78) This invention relates to fibrous products that have unusual characteristics of strength and heat resistance.

The ceramic fibers of the aluminum silicates that are now available have outstanding heat resistance, but their physical characteristics have restricted their use. These ceramic fibers are straight and discontinuous. They have no natural twist and are brittle and delicate. The fibers are smooth-surfaced, so that there is little or no cohesion between the fibers, and because there is no crimp or curl to the fibers, they do not cling together. Moreover, the fibers have low extensibility. Because of these characteristics, these ceramic fibers will not card on conventional machinery, but fall out of the machine.

Fabricated items such as paper, batts, roving, yarn, cord, rope, cloth, and non-woven structures made from various conventional fibers, both organic and inorganic, are much more limited in their resistance to heat, according to the heat resistance of the specific fibers used in these items.

I have found that certain combinations of ceramic fiber of an aluminum silicate with conventional fibers can be made in the form of intimate blends that can be carded on textile machinery. Fibrous products that are made from these blends are characterized by unexpected combinations of strength, heat resistance, and heat dissipation.

Accordingly, one object of this invention is to provide fibrous products that have materially increased heat resistance.

A related object of the invention is to provide an intimately blended fibrous mixture of ceramic fibers of an aluminum silicate and carrier fibers, that can be formed into fibrous products that have substantially increased heat resistance over products formed from the carrier fibers alone, and that have appreciable strength.

Another object of the invention is to provide fibrous products that have greater strength at high temperatures than fibrous products previously available.

According to the present invention, fibrous products, including non-woven, woven, and knitted products, are made from intimate fiber blends that contain, by weight, between about 10% and about 95% of ceramic fiber, the remainder being a carrier fiber that will permit the ceramic fiber to be processed on conventional machinery.

While ceramic fiber that is made from substantially pure aluminum silicate is the preferred ceramic fiber for use in accordance with the teachings of this invention, it is contemplated that certain other heat-resistant ceramic fibers could also be used, such as, for example, fibers that contain aluminum silicate together with certain other inorganic oxides, such as, for example, boron oxide, thoria and zirconia. Ceramic fibers of this type are produced by processes similar to those used for mineral Wool or staple glass fibers, except that the melting point (33% F.) is so high that the heat of an electric arc furnace is required. The molten mix is formed into fibers by blowing with steam or air, or by spinning from mechanical rotors. Resistance to high temperatures is unexcelled by any fiber with the possible exception of pure silica.

Some of the carrier fibers that may be used are acrylic fibers, rayon, cotton, Wool, asbestos, glass, tetrafluoro- 3'90 fl,1 3' Patented May 21, 1963 ethylene fibers, polyamide fibers, vinyl fibers, and protein fibers.

The invention can best be understood by reference to several specific embodiments of the invention that are described in the following examples.

The drawing provides a graphical representation of the properties of a fabric made according to the embodiment of the invention described in Example I. The drawing comprises a pair of curves, each curve showing graphically the relationship between tensile strength and heat resistance of the fabric.

EXAMPLE I Fibrous Products Made From Intimate Blends of Ceramic Fiber and Asbestos Fiber An intimate blend of Fiberfrax aluminum silicate long staple, medium ceramic fiber and carded asbestos fiber, Cassiar grade AAA, a chrysotile asbestos, was made acconding to the method that is described in the co-pending patent application of John W. Weber, Serial No. 658,582, filed May 13, 1957, and now Patent 3,012,289. Fiberfrax is a registered trademark of The Carborundum Company, Niagara Falls, New York. The long staple grade of Fiberfrax ceramic fiber contains about 51.3% silica, about 45.3% alumina, and about 3.4% Zirco-nia. Fiber length is about 1 /8" average, but varies considerably. The diameters of the medium fibers are predominantly in the range 8 to 14 microns, With a mean diameter of about 10 microns (about 2 denier). The specific gravity of the fibers is about 2.73 gin/cc. As produced, the fiber contains up to about 65% of nonfibrous solids or shot.

According to the Weber method, the asbestos fibers were carded to form a continuous web. The Web of asbestos carrier fibers was divided into four widths. A mass of the ceramic fibers was opened to make a plurality of small tufts, and these tufts were deposited onto each of the widths of the carrier fibers, so that there were a plurality of tufts of ceramic fibers distributed upon each width of the web of carrier fibers. The widths of the carrier web, with the tufts of the ceramic fibers distributed thereon, were superposed to form a pile. The pile was then carded to form a blended web of carrier fibers and ceramic fibers. The proportions of asbestos carrier fiber and ceramic fiber were carefully regulated so that the blended web comprised about 44% by weight of asbestos fiber and about 56% by Weight ofceramic fiber. Substantially no organic impurities were present.

The non-fibrous material, or shot, was separated from the ceramic fibers before the tufts of ceramic fibers were deposited on the web of asbestos carrier fibers.

, The blended fiber web was divided into several widths, to form rovings which were spun to make yarn. The yarn was woven into a six inch Wide twill weave tape.

Several pieces were cut from the tape for testing purposes. Similar test pieces were obtained from grade AAA asbestos tape of substantially the same Weight and construction, to provide a standard of comparison. The several test pieces were then placed in ovens, in pairs of one piece of asbestos tape and one piece of blended fiber tape, at different temperatures for 24 hours. Thereafter, the tensile strength, ASTM grab method, of the warp was determined for each of these. The results were plotted, and the curves were reproduced in the drawing.

As the drawing indicates, the asbestos fabric has superior tensile strength up to a temperature between 1000 F. and 1100" F. At temperatures above 1000 F., the tensile strength of the fabric made from the blend of ceramic fiber and asbestos fiber had a considerably superior tensile strength. Even at 1500" F., the fabric from the blended fiber had appreciable tensile strength.

a For the field of use at temperatures between about 1000 F. and 1500 F., therefore, the fabric from the blended fiber is markedly superior to asbestos.

Representative points on the curves are as follows:

TABLE I Tensile strength, lbs. Time, hrs. Temp., F.

Asbestos Cloth from cloth blended Unheated tapes RJI. 159v 85. 0 24 1, 000 55.0 35. 0 24. 1, 150 13. 24. 1, 300 2.0 20.0 24 1,500 10. 5

The entries under the temperature column in Table I indicate the temperature at which the respective samples were held for 24 hours, before their tensile strength was determined. The superiority of the asbestos fabric is evident until temperatures on the order of about 1000 are reached, but above 1100 F., the cloth from the blended fiber is markedly superior in strength, appearance, and hand.

One sample of the asbestos tape, and one sample of the tape made from the blended fiber, were held in a furnace 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.

TABLE II Weight, in grams Sample Before After Percent iurnacing iurnacing loss Blended sample 36. 56 35. 67 2. 4 Asbestos tape 26. 08 21. 58 17. 2

TABLE III Load in lbs. Percent of the Temp, F. at the break original point; strength retained a 1 Completely melted.

In another test, two one-inch wide ravelled strips of the tape were loaded with Weights, one with three pounds (approximately 5% of breaking load at room temperature), and the other with nine pounds (approximately 15% of breaking load at room temperature). The two strips were then heated gradually in an oven. After 95 minutes of heating, and at a temperature of 2310" F., the strip with the nine pound load failed. After 110 minutes of heating, and at 2360 F., the strip with the three pound load failed.

On the basis of the foregoing data, it is apparent that temperatures in the neighborhood of 2350 F. are critical with regard to the load breaking properties of this particular tape. At temperatures up to about 2000 F., the material exhibits reasonably good resistance to static load stresses, and if vibrations or shearing action are not prescut, the tape undoubtedly would resist destruction under static load for a considerable period of time.

bestos to ceramic fiber appear timate blends for products for omy. In the range 1400" F. to 1800 F., blends of 40% to 60% asbestos with the balance ceramic fiber would be most practical. In the range 1-800 F. to 2300 F., blends of 10% to 40% asbestos with ceramic fiber would be most practical. Typical applications for fibrous products made from intimate blends of asbestos fiber and ceramic fiber include heat barriers of all types, such as for example, furnace curtains, lagging, fireshields, fire screens, heat insulating materials, and the like. Felted products made from these intimate blends of fibers are useful for high temperature gas filtration, as Well as for many other purposes.

EXAMPLE II Blends 0 Ceramic Fiber and Acrylic Fiber Fibrous products made from cotton, nylon, acrylic fiber, and cellulose acetate fiber would have a much more broad field of use, if the temperature resistance were increased even moderately. For example, in the filtration field, the manufacture of collector bags consumes a large amount of special cloth annually. For example, filament glass cloth treated with a silicone resin is used extensively in the manufacture of dust collector bags for carbon black collection. 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 make these bags, and that could Withstand temperatures in the range of 500 F. up to 550 F.

According to the present invention, such fabrics can readily be prepared by making cloth from intimate fiber blends that have predetermined proportions of acrylic carrier fiber and ceramic fiber of an aluminum silicate.

A blend can be prepared of 25% by weight Fiberfrax long staple, medium ceramic fiber and 75% by weight Orion acrylic fiber. Orlon" is a registered trademark of the E. I. du Pont de Nemours Co., Inc., Wilmington, Delaware, for an acrylic fiber made from polymerized acrylonitrile. The intimate blend of fibers can be spun to form a yarn. The yarn has good strength and unusual heat resistance up to around 300' F. It can be woven to form insulating cloth, filter elements, gaskets, and packings, of unusual heat resistance.

Woven products made from this intimate fiber blend can be heat treated at temperatures above about 320 F., and preferably in the range of 400F. to 600 F., in circulating air or other oxidizing atmosphere, for suflicient time to permit the acrylic fiber to undergo a change in character to a non-flammable state. An exothermic reaction takes place under these conditions, and it is believed that the acrylic fiber is converted to linear, heterocyclic form. The fibrous product must be held above 320 F., in contact with air, for sufiicient time to permit the reaction to be completed, otherwise, the product will be flammable. Ordinarily, for woven fabrics, periods from one-half hour to three hours are sufficient. When the acrylic fiber has been heat treated in this manner, as described in detail in a copending patent application Serial No. 692,206, filed October 24, 1957, fireproof fabrics are obtained that have excellent heat resistance. Thus, the yarn above can be woven to form a fabric weighing ten oz./sq. yd. When this fabric is heat treated as described, it can be used for filtration bags and for active filter elements, and in other applications, at continuous temperatures up to about 600 F. Even higher service temperatures are permissible when the fiber blend contains a greater proportion of ceramic fiber.

EXAMPLE III Fibrous Products Made F ram. Blends of Ceramic Fiber and Organic Fiber Several intimate blends containing 70 parts by weight of Fiberfrax long staple medium ceramic fiber and 30 parts by weight of carrier fiber were prepared. The carrier fibers were as follows:

Fiber: Description Cotton 1%" staple, from picker lap. Nylon 3 denier, garnett stock. Dynel acrylic fiber- 3 denier, 1 /2" staple. Cellulose acetate 3 denier, 1 /2" staple.

Dynel is a registered trademark of Union Carbide Corporation for its acrylic fiber, made from a copolymer of vinyl chloride and acrylonitrile.

The fiber blends were made by hand picking the component fibers 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 indicated that the blended Webs that contained cotton and nylon had a fair degree of fiber blending, and that the acrylic fiber and cellulose acetate fiber blends had a better degree of fiber blending.

All of these blended webs were characterized by enhanced heat resistance and good yarn-making properties. Fibrous products made from the blended webs serve admirably for high temperature packing and for thermal insulation.

Since roping and yarn strength depend primarily upon the carrier fiber, good fiber blending is necessary for making satisfactory roping and yarn. Since the blended webs containing the acrylic fiber and the cellulose acetate were characterized by good fiber blending, these webs were selected for further processing, and were formed into yarn on a woolen spinning frame. The resulting yarns from both types of fiber blends were satisfactory, although there were indications that better results would be obtained from mechanically blended fibers. Drafts as high as 1.25 were used successfully in making the yarns.

All four blended webs, that is, the hand-picked, carded, blends of ceramic fiber and cotton, nylon, acrylic fiber, and cellulose acetate, respectively, were also hand-twisted to form ropings or yarns. The twisted ropings were suspended vertically, and a small weight was then attached to each at its lower end. The fiame of a match was rought into contact with each strand. The carrier fibers of nylon and cotton burned, leaving parted strands indicating no residual strength. The acrylic fiber and cellulose acetate fiber blacknened and shrank, but the residues apparently provided a bonding action which held the unburned ceramic fibers together, since some yarn strength remained.

EXAMPLE IV Blended Rayon Fiber and Ceramic Fiber Yarn was made by carding and spinning a blend of 80 parts by weight of rayon and 20 parts by weight of Fiberfrax long staple, medium ceramic fiber. The rayon was 1.5 denier, 1 /2 staple fiber. The ceramic fiber had a mean diameter of about 4- microns, with a minimum of about 2 microns, and a maximum of about 40 microns (average, about 055 denier). Staple length of the ceramic fiber averaged about 1%", with some variation between individual fiber lengths.

The fibers were carded and spun to form an eight oz./ sq. yd. cloth that had a yarn count of /2 warp and filling. This cloth had excellent heat resistance and made an excellent material for use as press cloth material.

Another blended web was prepared that contained 15% by weight of ceramic fiber and by weight of rayon. This blended web was formed into yarn that was spun to form a light weight fabric that had excellent heat resistance. 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 and scorching is important.

Intimate blends of rayon fibers and ceramic fibers of an aluminum slicate have excellent textile properties, particularly where the rayon fibers comprise 70% to 85% by weight of the blend. Fibrous products from such blends have enhanced heat resistance with very little sacrifice in hand, appearance, and strength.

The foregoing examples illustrate certain specific embodiments of the invention. It should be appreciated that many other combinations of carrier fiber with the ceramic fiber are possible, and are contemplated within the scope of this invention. For example, the asbestos fiber-ceramic fiber blends described in Example I can be modified, for special purposes, by incorporating still other fibers in the intimate blend.

Generally, the ceramic fibers range in size from about 2 to about 20 microns, although fibers with diameters up to about 80 microns can be used successfully. In general, the ceramic fiber constitutes at least about 10%, and preferably at least 15%, by weight of the fiber blend, to achieve a substantial upgrading of heat resistance. The maximum proportion of ceramic fiber that can be employed, under the best possible conditions, with the most suitable machinery now available approaches 95% by weight of the blend. For most high temperature applications, however, the preferred amount of ceramic fiber in a blend of fibers is on the order of 80% to that is, about 10% to 20% by Weight of the blend comprises carrier fibers.

The ceramic fibers that can be used, in accordance with the teachings of this invention, contain a major proportion of aluminum silicate, together with small amounts of boric oxide, zirconia, or other fluxes. Ceramic fibers of this type are readily available in a variety of deniers. For good processing characteristics, the longer fibers, of large diameter, are preferred. The fiber diameters preferably should be predominantly in the range between 2 and 20 microns.

While certain carrier fibers have been described above in relation to specific embodiments of the invention, it will be understood that many suitable carrier fibers can be used. Rayon is a highly desirable carrier fiber for many purposes where resistance to extremely high temperatures is not required, because rayon is a precision fiber. The acrylic fibers and other synthetics are also precision fibers, so that processing can be facilitated by selecting, for blending with the ceramic fiber, a carrier fiber that will have, consistently, optimum carrier characteristics. However, the natural fibers, such as, for example, wool and cotton, can also be used.

Some of the organic carrier fibers that can be employed tend to shrink at elevated temperatures. In the fibrous products p epared according to this invention, however, fiber shrinkage upon exposure to heat is often not a serious problem. This is particularly true where the ceramic fiber constitutes the major proportion of the fiber blend.

In any woven fibrous product made according to the teachings of this invention, the fibers are bound together by twist and fiber to fiber cohesion, and therefore, tensile strength is not substantial at high temperatures. Higher tensile strength can be obtained by inserted material such as alloy wire. Under many conditions, a glass filament yarn, or an asbestos yarn insert, provide adequate strength, but for extremely high temperature applications where the temperature limitations of these inserts are exceeded, wire is necessary. Nickel-chrome alloy wire and stainless steel Wire are good insert Wires for high temperature applications.

The fibrous products of this invention can be formed readily in substantially any desired fabricated form. For example, herringbone Weave cloth, twill Weave tape, tubular Woven fabric with a stainless steel Wire insert, paper, batts, blankets, roving, yarn, cord, rope, and the like, can be produced readily.

The ceramic fibers provide heat-resistant and heatdifiusing members in the products, and thus upgrade the heat resistance. The ceramic fiber offers particular advantages in products where previous failures had been caused by a surface or localized heat condition.

' Specific fibrous products that may be improved, ac cording to the teachings of this invention, include lami nating paper for high temperature applications, laundry cloths, and many other textiles for high temperature applications. Many other specific fibrous products are mentioned above.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come Within known or customary practice in the art to which the invention pertains 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, fibrous product characterized by a high degree of strength retention at temperatures between 1000 F. and 2000 F. and consisting essentially of an intimate carded mixture of staple, inorganic, siliceous, ceramic fibers containing a major proportion of aluminum silicate andstaple carrier fibers consisting essentially of asbestos,'said ceramic fiber constituting from about 10% to about 90% by weight of said product.

2. A strong, heat-resistant fabric, adapted for service at temperatures in the range from about 1000 F. to about 2300" F. which involves maintenance of substantial tensile strength, said fabric being woven from yarns consisting essentially of carded and spun, intimate mixtures of staples, inorganic, siliceous, ceramic fibers containing amajor proportion of aluminum silicate and staple carrier fibers consisting essentially of asbestos, said ceramic fibers constituting from about 10% to about 90% by weight of said fabric,

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 substantial tensile strength, said fabric being woven from yarns consisting essentially of carded and spun, intimate mixtures of staple, inorganic, siliceous, ceramic fibers containing a major proportion of aluminum silicate and staple carrier fibers consisting essentially of asbestos, said ceramic fibers constituting from about 10% to about 40% by weight of said fabric.

4. A strong, heat-resistant fabric, adapted for service at temperatures in the range from about 1400 F. to about 1800" F. which involves maintenance of substantial tensile strength, said fabric being woven from yarns consisting essentially of carded and spun, intimate mixtures of staple, inorganic, siliceous, ceramic fibers containing a major proportion of aluminum silicate and staple carrier fibers consisting essentially of asbestos, said ceramic fibers constituting from about 40% to about by Weight of said fabric.

5. A strong, heat-resistant fabric, adapted for service at temperatures in the range from about 1800 F. to about 2300 F. which involves maintenance of substantial tensile strength, said fabric being woven from yarns consisting essentially of carded and spun, intimate mixtures of staple, inorganic, siliceous, ceramic fibers containing a major proportion of aluminum silicate and staple carrier fibers consisting essentially of asbestos, said ceramic fibers constituting from about 60% to about by weight of said fabric.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Modern Textiles, September 1957, page 61.

Claims (1)

1. A BLENDED, FIBROUS PRODUCT CHARACTERIZED BY A HIGH DEGREE OF STRENGTH RETENTION AT TEMPERATURES BETWEEN 1000* F. AND 2000* F. AND CONSISTING ESSENTIALLY OF AN INTIMATE CARDED MIXTURE OF STAPLE, INORGANIC, SILICENOUS,

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