Asbestos is a nonmetallic mineral fiber, which is nonflammable. It is a very important industrial fiber that serves the textile industry in a number of useful ways. Asbestos is a natural silicate fiber of mineral origin. It occurs in the form of a natural rock composed of tightly packed fibrous crystals. These are generally constituted of silicates of either magnesium or its combination with other elements such as calcium, iron, and sodium.
Asbestos fiber does not have detectable odor or taste and is chemically inert. Therefore it is an excellent material used to produce heat and chemical resistant fabrics. This material had been used in different applications like heat insulation, sound absorption, in brake shoes, clutch plates and fire protection.
Among their beneficial properties are extreme durability and resistance to fire and most chemical reactions, especially the alkalis of the cement environment, all of which promoted their use for many years in different commercial and industrial capacities, including the building and construction industries. The strength of asbestos combined with its resistance to heat and the relatively low cost of its fibers made it an ideal material for use in a variety products, including roofing shingles, floor tiles, siding, flat and corrugated sheets, and other cement compounds.
In addition, the low-cost production methods of asbestos–cement-based components and their applicability in rapid construction techniques promoted their wide use in lightweight housing and industrial buildings.
The fiber is woven into fabrics and used for theater curtains and industrial uses where flame-resistant materials are needed. The fibrous form of several minerals and hydrous silicates of magnesium. The name may also be applied to the fibrous forms of calcium and iron. Asbestos fibers can be molded or woven into various fabrics. Because it is nonflammable and a poor heat conductor, asbestos has been widely used to make fireproof products such as safety clothing for fire fighters and insulation products such as hot-water piping.
Of the naturally occurring fibers asbestos is the most peculiar. Unlike other rocks that crystallise during their formation, asbestos is derived from a rock that crystallizes in the form of fibers that are closely packed together giving the surface a grainy appearance.
The application of asbestos has not been popular as it has been determined as carcinogenic to humans by the IARC (International Agency for Research on Cancer).
History of Asbestos Fiber:
Asbestos is the only natural fiber of mineral origin. When asbestos was first discovered it was called cotton stone by French-Canadians. The first fibers to be commercially used in cement-based composites were made from asbestos, which is comprised of a set of six naturally occurring silicate minerals, all of which consist of long (roughly 1:20 aspect ratio), thin, microscopic fibrous crystals. The first recorded use of the word asbestos is by Pliny the Elder in the 1st century ad, although the substance itself was known as early as the 2nd century BC. The Romans made cremation cloths and wicks from it, and centuries later Marco Polo noted its usefulness as cloth.
Asbestos is recovered from the rocks which have crystallized in the fibrous form, was regarded as textile fiber as early as 1950, and was commercially produced in the year 1860. It is found that the technique of spinning and weaving of asbestos was known to Indians as early as 1724.
Asbestos mining began more than 4000 years ago, but did not start largescale until the end of the 19th century, when manufacturers and builders began using asbestos because of its desirable physical properties, viz. sound absorption, average tensile strength, its resistance to fire, heat, electrical and chemical damage, and affordability. It was used in such applications as electrical insulation for hotplate wiring and in building insulation. When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement or woven into fabric or mats. These desirable properties made asbestos a very widely used material, and its use continued to grow throughout most of the 20th century until the carcinogenic effects of asbestos dust caused its effective demise as a mainstream construction and fireproofing material in most countries.
Manufacturing Process of Asbestos:
Asbestos is of two principal classes, the amphiboles and the serpentines, the former of relatively minor importance. Chrysotile, in the serpentine class, constitutes most of the world supply of asbestos. Countries that have produced asbestos include South Africa, Russia, Kazakhstan, China, Brazil, and Canada.
Asbestos is obtainable by various underground mining methods, but the most common method is open-pit mining. Only about 6 percent of the mined ore contains usable fibers.
The fibers are separated from the ore by crushing, air suction, and vibrating screens, and in the process are sorted into different lengths, or grades. The most widely used method of grading, the Québec Standard Test Method, divides the fibers into seven groups, the longest in group one and the shortest, called milled asbestos, in group seven. The length of the fibers, as well as the chemical composition of the ore, determines the kind of product that can be made from the asbestos. The longer fibers have been used in fabrics, commonly with cotton or rayon, and the shorter ones for molded goods, such as pipes and gaskets.
The compressed fibrous mass of raw asbestos is subjected to preliminary crushing (fibrising) to open and loosen the fibers from the compact mineral mass. Care is taken to avoid or minimize breakage of the fibers.
After the preliminary crushing, the fibrous mass of asbestos are further opened by passing through a toothed roller type machine. Dirt and powdered rock are removed at this stage. The opened asbestos fibers are now ready for carding.
Carding is affected by combing with rotating brushes having steel bristles. Impurities and short fibers further separate out and the longer asbestos fibers take the form of a loose sheet or web and delivered as narrow ribbons or rovings. The rovings are spun to yarns using flyer or ring spinning frames. Asbestos fibers may be mixed or blended with selected other fibers before spinning. The length ranges between 0.5-12 inch. They are somewhat polygonal or circular in cross-section.
Application / Uses of Asbestos Fiber:
Asbestos fibers have been used in a broad variety of industrial applications. Asbestos is highly resistant to heat, acids, alkalies, and other chemicals. It is also resistant to microorganisms and insects. It is used primarily in applications such as conveyor belts for transporting hot materials, electrical installations, fireproof clothing, break linings, heat resistant felts, tapes and cloth for gloves, industrial packagings and gaskets.
Asbestos is also used in brake pads, cloth behind fuses, filters, fire blankets, pipe insulation, rope seals for boilers and stage-safety curtains. Asbestos has been used in building-construction materials, textiles, missile and jet parts, asphalt and caulking compounds and paints, and in friction products such as brake linings. Asbestos fibers also have been used to reinforce plastic products made from PVC, phenolics, polypropylene, nylon, etc.
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.