M.HABIB SOFIA

07BTT14

The basic component of glass fibers is silica, SiO2. In its pure form it exists as a polymer, (SiO2)n.

It has no true melting point but softens up to 2000°C, where it starts to degrade.

It is usual to introduce impurities into the glass in

the form of other materials to lower its working temperature.

In the polymer it forms SiO4 groups which are

configured as a tetrahedron with the silicon atom at the center, and four oxygen atoms at the corners.

These atoms then form a network bonded at the

corners by sharing the oxygen atoms.

Density -2.50-2.55 g/cc Diameter -10-20 µm Tenacity -6.3-11.7 g/den Extension at break (%) -2.5 % Tensile strength (MPa) -2000-3500 Young’s modulus (GPa) -73 Melting Point -700C

There are two popular manufacturing processes for glass fibers.

1. Preparation of marbles, which are remelted in the fiberisation stage.

2. Direct melting route, in which a furnace is continuously charged with raw materials which are melted and refined.

Glass fibers are produced by rapid attenuation of the molten glass exuding through nozzles under gravity.

A solid intermediate stage (glass marbles) is thereby eliminated which, in particular, brings about a reduction in the specific energy costs.

It is common practice to melt E-glass (alkali-free glass) in spinning baths heated by natural gas with recuperative heat recovery to achieve melting capacities of 6–20 t/day.

The rate of fiber production at the nozzle is a function of the rate of flow of glass, not the rate of attenuation, which only determines final diameter of the fiber.

As the melt cools, it increases in viscosity, which varies along the nozzle making exact predictions of the flow rate difficult. Iterative procedures can be used to determine the dimensions of a nozzle of a selected design.

Direct melt spinning is more predictable because of the complexities introduced by remelting preformed marbles.

a) Discontinuousb) Continuous

After cooling, glass fibers immediately assume a solid state. The more quickly cooling takes place, the more their structure corresponds to that of the glass melt.

Structural changes in the fiber are caused by ageing or reheating; disassociation (micro-heterogeneity), in particular, increases which, at the same time, causes the density to rise but also initiates contraction phenomena.

For standard reinforcing materials, fiber diameters of 9–11 μm are generally employed although, for economic reasons, there is a tendency to increase the range to 13–15 μm.

Very high tensile strength Excellent resistance to sunlight and UV Excellent FR properties Good dimensional stability Zero moisture absorbance Resistant to mildew, rotting and insects Excellent UV stability Glass textiles are of comparatively

relatively low price (1.25 Euro/kg) so they have found wide applications.

Adhesion difficulties. Relatively heavy. Glass fibres if breathed into the lungs

can promote fatal cancerous growth.

Brittle, poor flexing properties. Poor abrasion resistance.

Glass fabrics are used for interior furnishings wherever high demands are placed on safety, e.g. in ships, hotels, cinemas, wall coverings, etc.

Glass woven fabrics are use as bases for PTFE coatings for industrial uses, such as calender belts and building structures.

Fiberglass reinforcing sheets are used in PVC-backed carpet tiles.

The fiberglass prevents creep of the PVC.

Nonwoven glass and polyester fabrics are widely used in roofing applications.

Glass fibres are almost universally used in place of asbestos.

Glass fibers are also heat-resistant materials.

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