Glass Fiber: Types, Properties, Manufacturing Process and Uses

Last Updated on 19/08/2021

Introduction of Glass Fiber:
Glass is a non-metallic fiber, widely used as industrial material these days. The art of spinning glass yarns to make fabrics is very old, dating back to 1713. In 1893, a glass dress made for the Broadway actress, Georgia Cayvan, which was exhibited at the World’s Columbian Exposition in Chicago, was made from bundles of spun glass fiber held together by silk threads. However, the fabric was too cumbersome to be worn because it was too stiff to drape. The base ingredients of glass fibers are forms of silica, mainly sand, limestone, stone ash and borax.

glass fiber
Fig: Glass fiber (chopped strands)

Glass fiber also called fiberglass. It is material made from extremely fine fibers of glass. Fiberglass is a lightweight, extremely strong, and robust material. Although strength properties are somewhat lower than carbon fiber and it is less stiff, the material is typically far less brittle, and the raw materials are much less expensive. Its bulk strength and weight properties are also very favorable when compared to metals, and it can be easily formed using molding processes. Glass is the oldest, and most familiar, performance fiber. Fibers have been manufactured from glass since the 1930s. Glass fiber products are categorized into four major groups; chopped strands, direct draw rovings, assembled rovings, and mat products

Types of Glass Fiber:
As to the raw material glass used to make glass fibers or nonwovens of glass fibers, the following classification is known:

1. A-glass: With regard to its composition, it is close to window glass. In the Federal Republic of Germany it is mainly used in the manufacture of process equipment.

2. C-glass: This kind of glass shows better resistance to chemical impact.

3.D- Glass: An important type of glass fiber is D-type glass fiber. Boron contains the trioxide compound intensively. Boron trioxide is used as a starting material for the synthesis of other boron compounds such as boron carbide in the production of fluids for glass and enamels, and in the production of heat resistance and thermal shock resistance borosilicate glasses.

4. E-glass: This kind of glass combines the characteristics of C-glass with very good insulation to electricity. E-glass is basically a calcium alumino-borosilicate glass containing less than 1% alkali calculated as Na2O.

5. AE-glass: Alkali resistant glass.

6. ECR-glass: It is also called electronic glass fiber. It has a good waterproofing ratio, high mechanical strength, electrical acidic and alkali corrosion resistance. It shows better properties than E-Type glass fiber. The biggest advantage is a more environmentally friendly glass fiber.

7. AR-glass: Alkali Resistant (AR: Alkali Resistant) Glass Fibers are specially designed for concrete construction. They contain alkaline zirconium silicates. They are effective to prevent concrete cracking. This adds strength and flexibility to concrete. They are also used for asbestos changes. They have alkali strength and strength. It is very difficult to dissolve in water. Not affected by pH changes. They are easily added to stainless steel and concrete mixtures. Intensive Magnesium and Calcium added fibers. Ideal for applications with high acidic strength and mechanical strength.

R-glass, S-glass or T-glass fibers are trade names of equivalent fibers having better tensile strength and modulus than E-type glass fibers. Higher acidic strength and wetting properties are obtained with a smaller filament diameter.

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Generally, glass consists of quartz sand, soda, sodium sulphate, potash, feldspar and a number of refining and dying additives. The characteristics, with them the classification of the glass fibers to be made, are defined by the combination of raw materials and their proportions. Textile glass fibers mostly show a circular.

Physical and Mechanical Properties of Glass Fiber:
Glass fibers are useful because of their high ratio of surface area to weight. However, the increased surface area makes them much more susceptible to chemical attack. By trapping air within them, blocks of glass fiber make good thermal insulation, with a thermal conductivity of the order of 0.05 W/(mK).

Glass fibers have outstanding mechanical properties, such as less fragility, extreme strength, less stiffness, and lightweight. Some physical and mechanical properties of glass fibers are listed below table.

Table: Different types of glass fibers and physical and mechanical properties

physical and mechanical properties of glass fibers

The strength of glass is usually tested and reported for “virgin” or pristine fibers those which have just been manufactured. The freshest, thinnest fibers are the strongest because the thinner fibers are more ductile. The more the surface is scratched, the less the resulting tenacity. Because glass has an amorphous structure, its properties are the same along the fiber and across the fiber. Humidity is an important factor in the tensile strength. Moisture is easily adsorbed, and can worsen microscopic cracks and surface defects, and lessen tenacity.

In contrast to carbon fiber, glass can undergo more elongation before it breaks. There is a correlation between bending diameter of the filament and the filament diameter. The viscosity of the molten glass is very important for manufacturing success. During drawing (pulling of the glass to reduce fiber circumference), the viscosity should be relatively low. If it is too high, the fiber will break during drawing. However, if it is too low, the glass will form droplets rather than drawing out into fiber.

Manufacturing Processes of Glass Fiber
Idea of manufacturing glass fiber and yarn is centuries old. The raw materials for glass are primarily silica sand and limestone, with small amount of other compounds such as aluminium hydroxide, sodium carbonate and borax. After the initial process of melting glass and passing it through spinnerets, continuous filaments or staple fibers of glass are manufactured by two different methods.

Flow diagram showing glass fiber manufacture
Fig: Flow diagram showing glass fiber manufacture

Continuous Filament Process
In this process, continuous filaments of indefinite length is produced. The molten glass passes through spinnerets having hundreds of small openings. These strands of multiple filaments are carried to winder revolving at very high speed of more than 2 miles per km. This process draws out the fibers in parallel filaments of the diameter of the openings. A sizing or a binder is applied to facilitate the twisting and winding process and to prevent breakage during yarn formation. After winding, filaments are further twisted and plied to make yarns by methods similar to those for making other continuous filament yarns. The sizing is removed through volatizing in an oven. These yarns are used for making such items as curtains and drapes.

Staple Fiber Process
Fibers with long-staple qualities are manufactured through staple fiber process. There are many methods for producing such fibers.

In one of such methods, the molten glass flows through the small holes of bushing, where jets of compressed air shake the thin streams of molten glass into fine fibers. These fibers vary in length ranging from 8 to 15 inches. The fibers fall through a spray of lubricant and a drying flame onto e revolving drum where they form into a thin web. These fibers in the form of web are gathered from the drum into a sliver. Yarn is then made from this sliver by similar methods that are adopted for making cotton or wool yarns. These yarns are used for fabrics for industrial purposes where insulation is required.

In yet another method, the ends of the glass rods are melted from which drops of glass fall away drawing off glass filaments after them onto a speedily revolving cylinder where they are wound parallel to each other. A web of sliver is formed if the cylinder moves sideways. Sometimes, the staple may be thrown off the cylinder onto a stationary sieve where it forms a sliver. In either conditions, the sliver is then converted into spun yarn.

The staple fiber, if subjected to oven, is compressed to the desired thickness and the binder which was earlier applied, is cured. This permanently binds the fibers.

Glass Fiber Production:
The subsequent manufacture of glass fibers may be executed to the direct melting process. However, in most cases glass rods or balls are made first which then may undergo a variety of further processes.

Manufacture of glass melt
Fig: Manufacture of glass melt

Nozzle-Drawing:
As can be seen in below Fig, the glass fed in is melted in a heated melt tub at 1250–1400oC. Then, it emerges at the bottom of the melt tub from nozzle holes of 1–25 mm diameter and it is taken off and drawn. The filaments solidify and are finished and wound. One can find them in the shops as various kinds of “glass silk”. To make them into webs, the filaments are cut to length (mostly, between 6 and 25 mm).

Processes to make glass fibers
Fig: Processes to make glass fibers

Nozzle-Blowing:
The same as with nozzle-drawing, glass balls are melted in the tub. The melt emerging from the nozzle holes is then taken by pressed air, which draws the liquid glass so as to make fibers of 6–10 um diameter. A fluttering effect is caused by the flow of pressed air, which results in fibers of lengths from 50 to 300 mm. A lubricant is put on and the fibers are laid down on a sieve drum which sucks them in. The dry web received is held together by the long fibers, the short ones lying in between them as a filling material. Then, the slivers of glass fiber material are cut.

Rod-Drawing:
By means of a burner, bundles of glass rods are melted at their bottom ends. This results in drops which, as they fall down, draw filaments after them. The filaments are taken by a rotating drum, a squeegee laying them down onto a perforated belt. Thus, a dry web is received which can be wound as glass fiber slivers. – Machine performance being limited by the number of glass rods fed in, the rotating drum may be combined with nozzle-drawing, which results in drum-drawing. This multiplies machine performance. The dry web is again laid down onto a perforated belt and solidified or, after winding it so as to receive slivers, cut for further processing on machines producing wetlaid nonwovens. Using and processing glass fibers is not without any problems. For example, fine pieces of broken fibers may disturb if the work place is not well prepared for the purpose. Using the nonwovens to manufacture glass-fiber reinforced plastics, it is important the surface of the plastic material is fully even. Ends of fiber looking out may be pulled out or loosened by outward stress (temperature, gases, liquids), which may influence material characteristics. In some cases, it is
advisable to cover up such layers of glass fiber with suitable chemical fibers.

Application / End Uses of Glass Fiber and Yarn:
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.

Glass fiber is manufactured in a wide range of fine diameters. Some of them are so fine that they can be seen only through a microscope. This quality of fineness contributes greatly to the flexibility of glass fibers. Various manufacturers produce different types of glass fibers for different end uses. Glass fibers them are used for various purpose.

  • For making home furnishings fabrics;
  • For making apparels and garments; and
  • For the purpose tires and reinforced plastics.

There are certain glass fibers that can resist heat upto 7200oC and can withstand forces having speed of 15,000 miles per hour. These types of glass fibers are used as:

  • Filament windings around rocket cases;
  • Nose cones;
  • Exhaust nozzles; and
  • Heat shields for aeronautical equipment

Some other types of glass fibers are embedded into various plastics for strength. These are used in:

  • Boat hulls and seats;
  • Fishing rods; and
  • Wall paneling

Some other types of glass fibers are used for reinforcing electrical insulation. Yet other types are used as batting for heat insulation in refrigerators and stoves. Glass fiber is also used in furnishings (such as upholstery and curtains); insulation, conveyor belts, circuit boards, protective clothing for military troops, ropes and meshes in shipbuilding and aircraft construction.

Conclusion:
Using glass fiber as a reinforcing agent in the composite industry shows a big trend since the price of the glass fiber is low in comparison to carbon fiber or Kevlar. For general-purpose application E-glass is seen to be a best choice and also for high technology applications various types of glass fiber like S glass or ECR glasses were introduced to the market. Glass fiber products have the advantages that it can be used either in the traditional composite manufacturing processes (hand layup) or it can be used in high technology composite manufacturing techniques like RTM.

In the transportation and automotive industries the idea of lightweight vehicles is the driving force for glass fiber composite manufacturers and according to the demand of customers glass fiber is widely used since it fulfills the composite market needs by considering low cost and availability in the glass fiber market. By looking at the growth of light vehicle sales to about 50% from 2010 to 2015, increasing the glass fiber production can also be considered.

References:

  1. High-Performance Fibres by J W S Hearle
  2. Introduction to Textile Fibres by V. Sreenivasa Murthy
  3. Fibres to Fabrics by Bev Ashford
  4. Hybrid Fiber Composites: Materials, Manufacturing, Process Engineering By Anish Khan, Sanjay Mavinkere Rangappa, Mohammad Jawaid, Suchart Siengchin and Abdullah M. Asiri
  5. Fiber Technology for Fiber-Reinforced Composites Edited by Ozgur Seydibeyoglu, Amar Mohanty, Manjusri Misra
  6. Textile Engineering – An Introduction Edited by Yasir Nawab
  7. Handbook of Textile Fibre Structure | Volume 2: Natural, Regenerated, Inorganic and Specialist Fibres Edited by S.J. Eichhorn, J.W.S. Hearle, M. Jaffe and T. Kikutani

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  8. Recent Developments in High Performance Fibers

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