How is fiberglass made?
Background
Fiberglass refers to a group of products made from individual glass
fibers combined into a variety of forms. Glass fibers can be
divided into two major groups according to their geometry:
continuous fibers used in yarns and textiles, and the discontinuous
(short) fibers used as batts, blankets, or boards for insulation
and filtration. Fiberglass can be formed into yarn much like wool
or cotton, and woven into fabric which is sometimes used for
draperies. Fiberglass textiles are commonly used as a reinforcement
material for molded and laminated plastics. Fiberglass wool, a
thick, fluffy material made from discontinuous fibers, is used for
thermal insulation and sound absorption. It is commonly found in
ship and submarine bulkheads and hulls; automobile engine
compartments and body panel liners; in furnaces and air
conditioning units; acoustical wall and ceiling panels; and
architectural partitions. Fiberglass can be tailored for specific
applications such as Type E (electrical), used as electrical
insulation tape, textiles and reinforcement; Type C (chemical),
which has superior acid resistance, and Type T, for thermal
insulation.
Though commercial use of glass fiber is relatively recent, artisans
created glass strands for decorating goblets and vases during the
Renaissance. A French physicist, Rene-Antoine Ferchault de Reaumur,
produced textiles decorated with fine glass strands in 1713, and
British inventors duplicated the feat in 1822. A British silk
weaver made a glass fabric in 1842, and another inventor, Edward
Libbey, exhibited a dress woven of glass at the 1893 Columbian
Exposition in Chicago.
Glass wool, a fluffy mass of discontinuous fiber in random lengths,
was first produced in Europe at the turn of the century, using a
process that involved drawing fibers from rods horizontally to a
revolving drum. Several decades later, a spinning process was
developed and patented. Glass fiber insulating material was
manufactured in Germany during World War I. Research and
development aimed at the industrial production of glass fibers
progressed in the United States in the 1930s, under the direction
of two major companies, the Owens-Illinois Glass Company and
Corning Glass Works. These companies developed a fine, pliable,
low-cost glass fiber by drawing molten glass through very fine
orifices. In 1938, these two companies merged to form Owens-Corning
Fiberglas Corp. Now simply known as Owens-Corning, it has become a
$3-billion-a-year company, and is a leader in the fiberglass
market.
Raw Materials
The basic raw materials for fiberglass products are a variety of
natural minerals and manufactured chemicals. The major ingredients
are silica sand, limestone, and soda ash. Other ingredients may
include calcined alumina, borax, feldspar, nepheline syenite,
magnesite, and kaolin clay, among others. Silica sand is used as
the glass former, and soda ash and limestone help primarily to
lower the melting temperature. Other ingredients are used to
improve certain properties, such as borax for chemical resistance.
Waste glass, also called cullet, is also used as a raw material.
The raw materials must be carefully weighed in exact quantities and
thoroughly mixed together (called batching) before being melted
into glass.
The Manufacturing Process
Melting
Once the batch is prepared, it is fed into a furnace for melting.
The furnace may be heated by electricity, fossil fuel, or a
combination of the two. Temperature must be precisely controlled to
maintain a smooth, steady flow of glass. The molten glass must be
kept at a higher temperature (about 2500 F [1371 C]) than other
types of glass in order to be formed into fiber. Once the glass
becomes molten, it is transferred to the forming equipment via a
channel (forehearth) located at the end of the furnace. Forming
into fibers
Several different processes are used to form fibers, depending on
the type of fiber. Textile fibers may be formed from molten glass
directly from the furnace, or the molten glass may be fed first to
a machine that forms glass marbles of about 0.62 inch (1.6 cm) in
diameter. These marbles allow the glass to be inspected visually
for impurities. In both the direct melt and marble melt process,
the glass or glass marbles are fed through electrically heated
bushings (also called spinnerets). The bushing is made of platinum
or metal alloy, with anywhere from 200 to 3,000 very fine orifices.
The molten glass passes through the orifices and comes out as fine
filaments. Continuous-filament process
A long, continuous fiber can be produced through the
continuous-filament process. After the glass flows through the
holes in the bushing, multiple strands are caught up on a
high-speed winder. The winder revolves at about 2 miles (3 km) a
minute, much faster than the rate of flow from the bushings. The
tension pulls out the filaments while still molten, forming strands
a fracti
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