Inorganic Fibres

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  • 8/3/2019 Inorganic Fibres



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    Introduction Inorganic fibers, both metal and non metal ones, are moreresistant, more rigid, have an higher melting point and are more

    heat resistant than traditional fibers.

    They are also totally uninflammable, but, except for the metalones, they are fragile. Their textile importance is also

    limited, whereas they are widely used as reinforcement incomposite materials.

    They are usually excellent in high temperatures and in acorrosive surrounding.

    Real fibers with an area transversal section lower than 0,005mm2 and a thickness lower than 0,25 mm are carried out. We can get them as wiskers (= mono crystalline materials)and as real fibers, both continuous and cut in cluster.

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    Their diameter changes from 5 to 15 nm, but otherones are much thicker, like the ones got throughvapor deposition on the fibers, such as borate fibers

    and silicon carbide fibers (100-150 n).

    The diameter of the fiber is critical compared to itsresistance: like all fragile materials their resistanceincreases when their transversal size reduces.

    Fibers in cluster can be produced directly or throughthe cutting of continuous filaments.

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    Ancient Egyptians made containers of coarse fibers drawnfrom heat softened glass.

    The French scientist, Reaumur, considered the potential offorming fine glass fibers for woven glass articles as early asthe 18th century.

    Continuous glass fibers -1930sRaw materials such as silicates, soda,

    Clay limestone, boric acid, fluorspar or various metallic oxidesare blended to form a glass batch which is melted in a furnace.

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    The molten glass flows to platinum/ rhodium alloy bushingsand then through individual bushing tips andorifices ranging from 0.76 to 2.03 mm (0.030 to 0.080 in)

    and is rapidly quenched and attenuated in air (to preventcrystallization) into fine fibers ranging from 3 to 35 m.

    Mechanical winders pull the fibers at lineal velocities up to61 m/s over an applicator which coats the fibers with anappropriate chemical sizing to aid further processingand performance of the end products.

    High strength glass fibers like S-2 Glassare compositions

    of alumino silicates attenuated at higher temperatures intofine fibers ranging from 5 to 24 m.

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    ECRGLASS Calcium alumino silicate glasseswith a maximum alkali content of 2 wt. % usedwhere strength, electrical resistivity, and acid

    corrosion resistance are desired. AR GLASS Alkali resistant glasses composed

    of alkali zirconium silicates used in cementsubstrates and concrete.

    R GLASS Calcium alumino silicate glassesused for reinforcement where added strength andacid corrosion resistance are required.

    S-2 GLASS Magnesium alumino silicateglasses used for textile substrates orreinforcement in composite structural applicationswhich require high strength, modulus, and stabilityunder extreme temperature and corrosiveenvironments.

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    Glass Fiber Manufacturing

    Glass fiber manufacturing is the high-temperatureconversion of various raw materials (predominantly borosilicates) into a homogeneous melt, followed by thefabrication of this melt into glass fibers.

    Glass fiber production can be segmented into 3 phases:

    Raw materials handling,

    Glass melting and refining, and

    Textile and wool glass fiber production.

    Raw Materials Handling

    The primary component of glass fiber is sand, but it also

    includes varying quantities of feldspar, sodium sulfate,

    anhydrous borax, boric acid, and many other materials.

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    The materials are weighed according to the desired productrecipe and then blended well before their introduction into themelting unit.

    The weighing, mixing, and charging operations may beconducted in either batch or continuous mode.

    Glass Melting and Refining

    In the glass melting furnace, the raw materials are heated totemperatures ranging from 1500 to 1700C (2700 to 3100F)and are transformed through a sequence of chemicalreactions to molten glass.

    In operation, raw materials are introduced continuously on top

    of a bed of molten glass, where they slowly mix and dissolve.

    Mixing is effected by natural convection, gases rising fromchemical reactions, and, in some operations, by air injectioninto the bottom of the bed.

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    Glass melting furnaces can be categorized by their fuel source

    and method of heat application into 4 types:


    Regenerative, unit, and

    Electric melter.

    Regenerative furnaces use a lattice of brickwork to recoverwaste heat from exhaust gases.

    In the initial mode of operation, hot exhaust gases are routedthrough a chamber containing a brickwork lattice, whilecombustion air is heated by passage through anothercorresponding brickwork lattice.

    About every 20 minutes, the airflow is reversed, so that thecombustion air is always being passed through hot brickworkpreviously heated by exhaust gases.

    Electric furnaces are either hot-top or cold-top.

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    Electric furnaces are currently used only for wool glass fiberproduction because of the electrical properties of the glassformulation.

    Unit melters are used only for the "indirect" marble meltingprocess, getting raw materials from a continuous screw atthe back of the furnace adjacent to the exhaust air discharge.

    In the "indirect" melting process, molten glass passes to a

    forehearth, where it is drawn off, sheared into globs, andformed into marbles by roll-forming. The marbles are then stress-relieved in annealing ovens,cooled, and conveyed to storage or to other plants for later

    use. In the "direct" glass fiber process, molten glass passes fromthe furnace into a refining unit, where bubbles and particlesare removed by settling, and the melt is allowed to cool to theproper viscosity for the fiber forming operation.

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    Glass Fiber Production Process.

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    Textile Glass Fiber Forming and Finishing

    Molten glass from either the direct melting furnace or theindirect marble melting furnace is temperature-regulated to a

    precise viscosity and delivered to forming stations. At the forming stations, the molten glass is forced through

    heated platinum bushings containing numerous very smallopenings.

    The continuous fibers emerging from the openings aredrawn over a roller applicator, which applies a coating of awater-soluble sizing and/or coupling agent.

    The coated fibers are gathered and wound into a spindle.

    The spindles of glass fibers are next conveyed to a drying

    oven, where moisture is removed from the sizing andcoupling agents.

    The spindles are then sent to an oven to cure the coatings.The final fabrication includes twisting, chopping, weaving,and packaging the fiber.

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    Glass fiber manufacture both staple fiberand continuous filament process

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    Physical properties of glass fibers

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    Chemical properties of Glass fibers Effect of acids: Excellent resistance to organic and

    inorganic acids. Effect of alkalis: Good to fair resistance

    Effect of sunlight: Poor Resistance.

    Effect of Dyeability: Poor Dyeabilty

    Effect of heat and thermal insulation properties:Excellent to Good resistance.

    Effect of mildew: Good resistance for long time.

    Effect of electrical conductivity: Poor conductor ofelectricity.

    Effect of corrosion resistance: Excellent resistanceto corrosion.

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    USES Sports cars, micro cars, karts, body shells, boats, flat roofs,

    lorries, wind turbine blades. Minesweeperhulls

    Pods, domes and architectural features where a light weight isnecessary.

    Bodies for automobiles body.

    FRP tanks and vessels: FRP is used extensively tomanufacture chemical equipments and tanks and vessels. UHF-broadcasting antennas are often mounted inside a

    fiberglass cylinder on the pinnacle of a broadcasting tower Most commercial Velomobiles

    Large Commercial Wind Turbine Blades