2015-04-14 10:42:44

Fiberglass brief introduction

History of fiberglass

Fiberglass is the original fiber reinforcement of modern composites. Though the ancient Phoenicians,
Egyptians and Greeks knew how to melt glass and stretch it into thin fibers, it wasn’t until the 1930s that the process evolved into commercial-scale manufacturing of continuous fibers, which would later be used as
structural reinforcements. Patent applications filed between 1933 and 1937 by Games Slayter, John Thomas and Dale Kleist, employees of Owens-Illinois Glass Co. (Toledo, Ohio), record the key developments that
step-changed the industry from producing discontinuous-fiber glass wool to making continuous glass
filaments with diameters as small as 4 microns (4 millionths of a meter) and thousands of feet long.
Ensuing breakthroughs made the process commercially viable and cost-competitive. The last two patents in
the series, entitled “Textile Material” and “Glass Fabric,” foreshadowed the future of glass fiber as a textile
reinforcement. The patents were awarded in 1938, the same year that Owens-Illinois and Corning Glass
Works (Corning, N.Y.) joined to form Owens-Corning Fiberglas Corp. (OCF). The new company marketed
its glass fiber under the trade name Fiberglas, which was the genesis of the common generic reference to
fiberglass. It was not long before a number of other manufacturers entered the market and, through
numerous process and product innovations, contributed to a worldwide structural composite reinforcements market of roughly 4 to 5 million tons per year.

What is fiberglass made of?

Textile-grade glass fibers are made from silica (SiO2) sand, which melts at 1720°C/3128°F. SiO2 is also the basic element in quartz, a naturally occurring rock. Quartz, however, is crystalline
(rigid, highly ordered atomic structure) and is 99 percent or more SiO2. If SiO2 is heated above
1200°C/2192°F then cooled ambiently, it crystallizes and becomes quartz. Glass is produced by altering the temperature and cooldown rates. If pure SiO2 is heated to 1720°C/3128°F then
cooled quickly, crystallization can be prevented and the process yields the amorphous or randomly ordered atomic structure we know as glass. Although continuously refined and improved, today’s glass fiber manufacturers combine this high heat/quick cool strategy with other steps in a
process that is basically the same as that developed in the 1930s, albeit on a much larger scale. This process can be broken down into five basic steps: batching, melting, fiberization, coating
and drying/packaging.


Elements

C glass

E glass

ECR glass

S glass

Silicone Dioxide

64~66%

53~55%

59~62%

64~66%

Calcium Oxide

13~14%

16~23%

20~24%

-

Aluminum Oxide

4~5%

13~16%

12-15%

24~26%

Boron Oxide

4~6%

0-10%

-

-

Sodium and Potassium Oxide

3-10%

0-1%

2.4%

-

Magnesium Oxide

3-4%

0-5%

1~4%

9~11%


How to fiberglass form?

1.Batching

Although a viable commercial glass fiber can be made from silica alone, other ingredients are added to
reduce the working temperature and impart other properties that are useful in specific applications. For
example, E-glass, originally aimed at electrical applications, with a composition including SiO2, AI2O3
(aluminum oxide or alumina), CaO (calcium oxide or lime) and MgO (magnesium oxide or magnesia), was
developed as a more alkali-resistant alternative to the original soda lime glass. Later, boron was added via
B2O3 (boron oxide) to increase the difference between the temperatures at which the E-glass batch melted and at which it formed a crystalline structure to prevent clogging of the nozzles used in fiberization (Step 3,
below). S-glass fibers, developed for higher strength, are based on a SiO2-AI2O3-MgO formulation but
contain higher percentages of SiO2 for applications in which tensile strength is the most important property.

In the initial stage of glass manufacture, therefore, these materials must be carefully weighed in exact
quantities and thoroughly mixed (batched). Batching has become automated, using computerized weighing
units and enclosed material transport systems. For example, in Owens Corning’s plant in Taloja, India, each
ingredient is transported via pneumatic conveyors to its designated multistory storage bin (silo), which is
capable of holding 70 to 260 ft³ (1.98 to 7.36m³) of material. Directly beneath each bin is an automated
weighing and feeding system, which transfers the precise amount of each ingredient to a pneumatic blender in the batch house basement.


2. Melting:

From the batch house, another pneumatic conveyor sends the mixture to a high temperature (≈1400ºC/2552ºF) natural gas-fired furnace for melting. The furnace is typically divided into three sections, with channels
that aid glass flow. The first section receives the batch, where melting occurs and uniformity is increased,
including removal of bubbles. The molten glass then flows into the refiner, where its temperature is reduced
to 1370ºC/2500ºF. The final section is the forehearth, beneath which is located a series of four to seven
bushings that, in the next step, are used to extrude the molten glass into fibers. Large furnaces have several channels, each with its own forehearth.

3. Fiber forming

Glass fiber formation, or fiberization, involves a combination of extrusion and attenuation. In extrusion, the
molten glass passes out of the forehearth through a bushing made of an erosion-resistant platinum/rhodium alloy with very fine orifices, from 200 to as many as 8,000. Bushing plates are heated electronically, and their temperature is precisely controlled to maintain a constant glass viscosity. Water jets cool the filaments as they exit the bushing at roughly 1204ºC/2200ºF. Attenuation is the process of mechanically drawing the
extruded streams of molten glass into fibrous elements called filaments, with a diameter ranging from 4 μm
to 34 μm (one-tenth the diameter of a human hair). A high-speed winder catches the molten streams and,
because it revolves at a circumferential speed of ~2 miles/~3 km per minute (much faster than the molten
glass exits the bushings), tension is applied, drawing them into thin filaments.

4. Sizing coating

In the final stage, a chemical coating, or sizing, is applied. (Although the terms binder, size and sizing often
are used interchangeably in the industry, size is the correct term for the coating applied, and sizing is the
process used to apply it. 

5. Drying

Finally, the drawn, sized filaments are collected together into a bundle, forming a glass strand composed of   51 to 1,624 filaments. The strand is wound onto a drum into a forming package that resembles a spool of
thread. The forming packages, still wet from water cooling and sizing, are then dried in an oven, and
afterward they are ready to be palletized and shipped or further processed into chopped fiber, roving or yarn. Roving is a collection of strands with little or no twist. An assembled roving, for example, made from 10 to
15 strands wound together into a multi-end roving package, requires additional handling and processing
steps. Yarn is made from one or more strands, which may be twisted to protect the integrity of the yarn
during subsequent processing operations, such as weaving.