History……. Ancient Egyptians made containers of coarse fibers drawn from heat softened glass. Napoleon’s funeral coffin was decorated with glass fiber textiles. By the 1800s, luxury brocades were manufactured by co-weaving glass with silk, and at the Columbia Exhibition of 1893. The scientific basis for the development of the modern reinforcing glass fiber stems from the work of Griffiths. The French scientist, Reaumur, considered the potential of forming fine glass fibers for woven glass articles as early as the 18th century. Continuous glass fibers were first manufactured in substantial quantities by Owens Corning Textile Products in the 1930’s for high temperature electrical applications. Raw materials such as silicates, soda, clay, limestone, boric acid, fluorspar or various metallic oxides are blended to form a glass batch which is melted in a furnace and refined during lateral flow to the fore hearth.
Introduction Glass in the form of fibers has found wide and varied applications in all kinds of industry because it is the most versatile industrial materials known today. All glass fibers derived from compositions containing Silica, which are available in virtually unlimited supply. They exhibit useful bulk properties such as Hardness, Transparency, Resistance To Chemical Attack, Stability, and Inertness, as well as Desirable Fiber Properties such as Strength, Flexibility, and Stiffness. Glass fibers are used in a number of applications which can be divided into four basic categories: (A) Insulations, (B) Filtration Media, (C) Reinforcements, And (D) Optical Fibers.
Types of Glass Fiber As per ASTM C 162 the glass fiber were classified according to the end use and chemical compositions.E, Electrical Low Electrical ConductivityS, Strength High StrengthC, Chemical High Chemical DurabilityM, Modulus High StiffnessA, Alkali High Alkali Or Soda Lime GlassD, Dielectric Low Dielectric Constant
A GLASS – Soda lime silicate glasses used where the Strength, Durability, And Good Electrical Resistivity. C GLASS-- Chemical Stability In Corrosive Acid Environments. D GLASS – Borosilicate glasses with a Low Dielectric Constant For Electrical Applications. E GLASS – Alumina-calcium-borosilicate glasses with a maximum alkali content of 2 wt.% used as general purpose fibers where strength and High Electrical Resistivity are required.
ECRGLAS® – Calcium aluminosilicate glasses with a maximum alkali content of 2 wt.% used where strength, electrical resistivity, and acid corrosion resistance are desired. AR GLASS – Alkali Resistant Glasses composed of alkali zirconium silicates used in cement substrates and concrete. R GLASS – Calcium aluminosilicate glasses used for reinforcement where added strength and acid corrosion resistance are required. S-2 GLASS® – Magnesium aluminosilicate glasses used for textile substrates or reinforcement in composite structural applications which require high strength, modulus, and stability under extreme temperature and corrosive environments.
More than half the mix is Silica Sand, Other ingredients are Aluminum, Calcium and Magnesium.Oxides, and Borates
The fiber manufacturing process has effectively two variants. One involves the preparation of marbles, which are re-melted in the fiberisation stage.The other uses the direct melting route, in which a furnace is continuously charged with raw materials which are melted and refined as that glass reaches the forehearth above a set of platinum–rhodium bushings from which the fibers are drawn.The two processes are described in Figures 6.2 and 6.3.2 Glass fibers are produced by rapid attenuation of the molten glass exuding through nozzles under gravity.The glass viscosity between 600 and 1000P.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.
The molten glass flows to platinum/ rhodium alloy bushings and then through individual bushing tips and orifices ranging from 0.76 to 2.03 mm (0.030 to 0.080 in) and is rapidly quenched and attenuated in air (to prevent crystallization) into fine fibers ranging from 3 to 35 μm. Mechanical winders pull the fibers at lineal velocities up to 61m/s over an applicator which coats the fibers with an appropriate chemical sizing to aid further processing and performance of the end products.
Furnace The temperature is so high > 1600 °C that the sand and other ingredients dissolve into molten glass. The inner walls of the furnace are lined with special "refractory" bricks that must periodically be replaced.
Bushings The molten glass flows to numerous high heat-resistant platinum trays which have thousands of small, precisely drilled tubular openings, called "bushings."
Design and Manufacture of Bushings for Glass Fiber Production
Filaments This thin stream of molten glass is pulled and attenuated (drawn down) to a precise diameter, then quenched or cooled by air and water to fix this diameter and create a filament.Bunker,Bushing,Cooler
Sizing The hair-like filaments are coated with an aqueous chemical mixture called a "sizing," which serves two main purposes: 1) Protecting the filaments from each other during processing and handling, 2) Ensuring good adhesion of the glass fiber to the resin.Sizing thickness ~ 50 nanometers
Immediately after cooling with water the fibers are coated with an aqueous size (usually an emulsion) in contact with a rubber roller. The size (or finish) is crucial to the handle ability of the fibers and their compatibility with the matrix. The ‘finish’ therefore may consist of:1. lubricant(s),2. surfactant(s),3. antistatic agent(s), and4. an optional polymeric binder (emulsion or powder) used for fiber mats
Strands After the sizing is applied, filaments are gathered together into twine-like strands that go through one of three steps, depending on the type of reinforcement being made.
Chemical Resistance The chemical resistance of glass fibers to the corrosive and leaching actions of acids, bases, and water is expressed as a percent weight loss. The lower this value, the more resistant the glass is to the corrosive solution.
Thermal Properties The viscosity of a glass decreases as the temperature increases. Note that the S-2 Glass fibers’ temperature at viscosity is 150-260°C higher than that of E Glass, which is why S-2 Glass fibers have higher use temperatures than E Glass.
Radiation Properties E Glass and S-2 Glass fibers have excellent resistance to all types of nuclear radiation. Alpha and beta radiation have almost no effect. But some times it produce 5 to 10% decrease in tensile strength. E Glass and C Glass are not recommended for use inside atomic reactors because of their high boron content.
Composite Properties Application of glass fiber composite materials depends on proper utilization of glass composition, size chemistry, fiber orientation, and fiber volume in the appropriate matrix for desired mechanical, electrical, thermal, and other properties.
Strength and stiffness For glass this will be about 7GPa, but the practical strength would be significantly less at about 0.07GPa. A typical E-glass fiber can have a strength of 3GPa.
Static Fatigue Glass fibers are subject to static fatigue, Which is the time-dependent fracture of a material under a constant load, as opposed to a conventional fatigue test where a cyclic load is employed
Environmental Stress Corrosion Cracking (ESCC) E-glass fibers have a reduced lifetime under load and this is more severe in an acidic environment. This is generally referred to as environmental stress corrosion cracking or ESCC. Here, a synergism between stress and chemistry occurs as described in the previous section under II. At low loads and in alkaline environments, chemical corrosion dominates but is stress assisted.
These are fibers which have been chopped to lengths of 1.5 to 50mm, depending on the application. These are combined with thermoplastic or thermosetting resins for molding compounds. Chopped strands are either soft- or hard-sized, depending on the molding application.