Glass Fiber: Manufacturing Process, Types, and Properties

By Eman Abdallah Kamel

Eman is a writer and engineer. She received her bachelor’s degree in textile science from the Faculty of Applied Arts.

Glass fiber is an important material. In this article, you will learn the meaning of “glass fiber,” how it is manufactured, its types, properties, and uses.

Glass Fiber

Glass fiber is a material composed of extremely fine glass fibers. Glass fibers are made by passing molten glass through holes and then allowing it to solidify. Their flexibility makes them suitable for use as fibers. Their diameters range from 5 to 24 micrometers. It possesses mechanical properties nearly identical to those of other fibers, such as polymers and carbon fibers. It is significantly cheaper and less brittle when used in composite materials. Therefore, glass fiber is used as a reinforcing agent in many polymer products to create very strong and lightweight composite materials. Various types of glass fibers are commercially available.

Properties

Glass fibers are generally known for their good impact resistance.
Their density is higher than that of carbon fibers and aramid fibers.
These fibers are transparent to radio waves and are thus used in radars and antennas.
Glass fiber-reinforced composite materials are excellent electrical and thermal insulators.

Types

Glass fiber is divided into two categories:

General, low-cost fibers
Premium fibers for specialized applications.

Did You Know?

Over 90% of all glass fiber products are general-purpose.

1. General, low-cost fibers

The most common type of E glass contains 5 to 6% boron oxide by weight. Commercial boron-containing E glass is available in two forms:

One is derived from the tetramer SiO₂-Al₂O₃-CaOMgO,
The other is derived from the tertiary complex SiO₂-Al₂O₃-CaOMgO.

To remove boron from gases emitted by boron-containing molten metals, costly emissions-control systems must be installed in accordance with stringent environmental regulations. Alternatively, boron-free E glass is required. These molten metals do not contain boron and therefore do not release it into the environment during manufacturing.

Did You Know?

Fiberglass Corporation (Owens Corning Corporation, Toledo, Ohio) recently introduced a boron-free E glass product to the market under the Advantex brand.

Difference between boron-free E-glass and boron-containing E-glass:

The corrosion resistance of boron-free E glass is seven times higher than that of boron-containing E glass when tested at room temperature for 24 hours in 10% sulfuric acid. It is comparable to the corrosion resistance of ECR glass fibers.
Boron-free E glass has a higher refractive index and coefficient of linear expansion than boron-containing E glass fibers.
Boron-free E glass has a slightly higher density (2.62 g/cm³) than boron-containing E glass (2.55 g/cm³).
Boron-free E glass has a slightly higher dielectric constant (7.0) than boron-containing E glass (5.9 to 6.6) when measured at room temperature and a frequency of 1 MHz. Consequently, boron-containing E glass fibers are used in electronic circuit boards and aerospace applications.
The modulus of elasticity of boron-free E-glass is approximately 5% higher than that of boron-containing E-glass.

2. Premium fibers

Special-purpose fibers include:

High-corrosion-resistant glass fibers (ECR glass);
High-strength fibers (S, R, and Teglass);
Fibers with low dielectric constants (D glass);
High-strength fibers and fibers made of pure silica or quartz, which can be used at extremely high temperatures.
Other special-purpose fibers include A-glass, C-glass, hollow fibers, two-component fibers, and three-lobed fibers.

Manufacturing process

Glass is a solid material formed by rapidly cooling the molten material to prevent crystallization. When the molten material is cooled slowly, crystallization can occur at or below the liquidus temperature, where the crystals and liquid are in equilibrium. Therefore, glass fibers are manufactured at high cooling rates. Chemically, glass consists of a silica network. Other oxides facilitate melting, homogenization, removal of gaseous impurities, and fiber formation at optimal temperatures.

The general melting and forming process required for boron-free E-glass is similar to that required for boron-containing E-glass, except that the viscosity/temperature curve differs.

The glass fiber manufacturing includes the following stages:

Mixing and Melting in a Batch
Fiberizing and Sizing

Glass melting furnace.

1. Mixing and Melting in a Batch

The glass melting process begins by weighing and mixing the raw materials. In modern fiberglass plants, this process is fully automated, using computerized weighing units and closed material handling systems. Individual components are weighed and transferred to the mixing station, where the batch components are thoroughly mixed before being sent to the furnace.
The batch is transferred to the furnace section for melting, degassing, and homogenization.
The molten glass then flows into the refining section, where its temperature is reduced from 1370°C to approximately 1260°C.
Finally, the molten glass moves to the forehearth section, located directly above the fiber-forming stations.

2. Fiberizing and Sizing Process

Molten glass flows through a bushing made of a platinum-rhodium alloy, containing a large number of holes from 400 to 8,000 in typical production.
The bushing is electrically heated, and the temperature is precisely controlled to ensure that the glass viscosity remains constant.
When the fibers exit the bushing, they are drawn down and rapidly cooled.
A sizing layer is applied to the surface of the fibers by passing them over an applicator that rotates continuously through the sizing bath to maintain a thin layer through which the glass fibers pass.

Did You Know?

The components of the sizing impart strand integrity, lubricity, resin compatibility, and adhesion to the final product, thereby tailoring the fiber properties to specific end-use requirements.

After sizing, the filaments are bundled into a single strand before reaching the collection device. Multiple collection devices are used if small bundles of yarn are required.

Consider the following:

Fiber Diameters: Bushing temperature, glass viscosity, and pressure head over the bushing all affect fiber diameter. The most common take-up device is the forming winder, which uses a rotating collet and a traverse mechanism to distribute the strand randomly as the forming package expands in diameter.
Yarn Designation: In the fiberglass industry, the diameter of a given yarn is indicated by a specific alphabetical code. Microfibers, used in textile applications, typically have diameters ranging from D to G. Fine fibers provide sufficient flexibility for the yarn to be processed in high-speed winding and weaving operations. Traditional plastic reinforcement uses yarns with diameters ranging from G to T.

Uses

Fiberglass is commonly used to make thermal, electrical, and acoustic insulation fabrics, as well as highly durable, abrasion-resistant fabrics. It is also used to reinforce a variety of materials, including tent poles, hockey sticks, surfboards, and boat hulls. It’s used in medical splints. They are used in the production of various car components, including the body, seat covers, door panels, and frame supports. Open-weave fiberglass mesh is used to reinforce asphalt pavements. Glass fiber reinforced plastic (GFRP) is commonly used in the production of circuit boards, computers, televisions, mobile phones, wires, and cables.

Sources

Glass Fiber
Glass Fibers. Frederick T. Wallenberger, James C. Watson, and Hong Li, PPG Industries, Inc., pdf
Thermo-Mechanical Properties and Applications of Glass Fiber-Reinforced Polymer Composites

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