FIBRE GLASS and glass fibre is a kind of
syntetic material made from extremely serat kaca yang baik.
It is used as a reinforcing agent for many polymer products;
the resulting composite material, properly known as
fiber-reinforced polymer (FRP) or glass-reinforced plastic (GRP),
is called "fiberglass" in popular usage.
Glassmakers throughout history have experimented with glass
fibers, but mass manufacture of fiberglass was only made
possible with the advent of finer machine-tooling. Pada tahun 1893,
Edward Drummond Libbey exhibited a dress at the World's
Columbian Exposition incorporating glass fibers with the
diameter and texture of silk fibers. What is commonly known
as "fiberglass" today, however, was invented in 1938 by
Russell Games Slayter of Owens-Corning as a material to be
used as insulation. Produk ini dipasarkan dalam perdagangan dengan nama Fiberglas, yang kemudian menjada nama dagang generik.
Formation
Glass fiber is formed when thin strands of silica-based or
other formulation glass is extruded into many fibers with
small diameters suitable for textile processing. Kaca berbeda dengan polimer lain, yakni, it has
little crystalline structure (see amorphous solid). The
properties of the structure of glass in its soft stage are
very much like its properties when spun into fiber. One
definition of glass is "an inorganic substance in a
condition which is continuous with, and analogous to the
liquid state of that substance, but which, as a result of a
reversible change in viscosity during cooling, has attained
so high a degree of viscosity as to be for all practical
purposes rigid." [1]
Teknik pemanasan dan pembentukan kaca menjadi serat yang halus diyakini telah dicoba selama ribuan tahun; however, the
concept of using these fibers for textile applications is
more recent. Produksi fiberglas untuk komersil yang pertamakali adalah di tahun 1936. Pada tahun 1938, Owens-Illinois Glass Company dan
Corning Glass Works bergabung membentuk Owens-Corning
Fiberglas Corporation. Until this time all fiberglass had
been manufactured as staple. When the two companies joined
together to produce and promote fiberglass, they introduced
continuous filament glass fibers. [1] Owens-Corning is still
the major fiberglass producer in the market today.
COMPOSITION
Material of textile grade glass fibers is silica, SiO2. In
its pure form it exists as a polymer, (SiO2)n. It has no
true melting point but softens up to 2000°C, where it starts
to degrade. At 1713°C, most of the molecules can move about
freely. If the glass is then cooled quickly, they will be
unable to form an ordered structure. [2] In the polymer it
forms SiO4 groups which are configured as a tetrahedron with
the silicon atom at the center, and four oxygen atoms at the
corners. These atoms then form a network bonded at the
corners by sharing the oxygen atoms.
The vitreous and crystalline states of silica (glass and
quartz) have similar energy levels on a molecular basis,
also implying that the glassy form is extremely stable. In
order to induce crystallization, it must be heated to
temperatures above 1200°C for long periods of time. [1]
Molecular Structure of Glass
Molecular Structure of Glass
Although pure silica is a perfectly viable glass and glass
fiber, it must be worked with at very high temperatures
which is a drawback unless its specific chemical properties
are needed. It is usual to introduce impurities into the
glass in the form of other materials, to lower its working
temperature. These materials also impart various other
properties to the glass which may be beneficial in different
applications. The first type of glass used for fiber was
soda-lime glass or A glass. It was not very resistant to
alkali. A new type, E-glass was formed that is alkali free
(< 2%) and is an alumino-borosilicate glass [3]. This was
the first glass formulation used for continuous filament
formation. E-glass still makes up most of the fiberglass
production in the world. Its particular components may
differ slightly in percentage, but must fall within a
specific range. The letter E is used because it was
originally for electrical applications. S-glass is a high
strength formulation for use when tensile strength is the
most important property. C-glass was developed to resist
attack from chemicals, mostly acids which destroy E-glass.
[3] T-glass is a North American variant of C-glass. A-glass
is an industry term for cullet glass, often bottles, made
into fiber. AR-glass is alkali resistant glass. Most glass
fibers have limited solubility in water but it is very
dependent on pH. Chloride ions will also attack and dissolve
E-glass surfaces. A recent trend in the industry is to
reduce or eliminate the boron content in the glass fibers.
Since E-glass does not really melt but soften, the softening
point is defined as , "the temperature at which a 0.55 –
0.77 mm diameter fiber 9.25 inches long, elongates under its
own weight at 1 mm/min when suspended vertically and heated
at the rate of 5°C per minute". [4] The strain point is
reached when the glass has a viscosity of 1014.5 poise. The
annealing point, which is the temperature where the internal
stresses are reduced to an acceptable commercial limit in 15
minutes, is marked by a viscosity of 1013 poise. [4]
Properties
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 0.05
W/m-K.
Glass strengths are usually tested and reported for "virgin"
fibers which have just been manufactured. The freshest,
thinnest fibers are the strongest and this is thought to be
due to the fact that it is easier for thinner fibers to
bend. The more the surface is scratched, the less the
resulting tenacity is. [3] Because glass has an amorphous
structure, its properties are the same along the fiber and
across the fiber. [2] Humidity is an important factor in the
tensile strength. Moisture is easily absorbed, and can
worsen microscopic cracks and surface defects, and lessen
tenacity.
In contrast to carbon fiber, glass can undergo more
elongation before it breaks. [2]
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
Melting
There are two main types of glass fibre manufacture and two
main types of glass fibre product. First, fiber is made
either from a direct melt process or a marble remelt
process. Both start with the raw materials in solid form.
The materials are mixed together and melted in a furnace.
Then, for the marble process, the molten material is sheared
and rolled into marbles which are cooled and packaged. The
marbles are taken to the fiber manufacturing facility where
they are inserted into a can and remelted. The molten glass
is extruded to the bushing to be formed into fiber. In the
direct melt process, the molten glass in the furnace goes
right to the bushing for formation. [4]
Forming into Fibres
The bushing plate is the most important part of the
machinery. This is a small metal furnace containing nozzles
for the fiber to be formed through. It is almost always made
of platinum alloyed with rhodium for durability. Platinum is
used because the glass melt has a natural affinity for
wetting it. When bushings were first used they were 100%
platinum and the glass wetted the bushing so easily it ran
under the plate after exiting the nozzle and accumulated on
the underside. Also, due to its cost and the tendency to
wear, the platinum was alloyed with rhodium. In the direct
melt process, the bushing serves as a collector for the
molten glass. It is heated slightly to keep the glass at the
correct temperature for fiber formation. In the marble melt
process, the bushing acts more like a furnace as it melts
more of the material. [1]
The bushings are what make the capital investment in fiber
glass production expensive. The nozzle design is also
critical. The number of nozzles ranges from 200 to 4000 in
multiples of 200. The important part of the nozzle in
continuous filament manufacture is the thickness of its
walls in the exit region. It was found that inserting a
counterbore here reduced wetting. Today, the nozzles are
designed to have a minimum thickness at the exit. The reason
for this is that as glass flows through the nozzle it forms
a drop which is suspended from the end. As it falls, it
leaves a thread attached by the meniscus to the nozzle as
long as the viscosity is in the correct range for fiber
formation. The smaller the annular ring of the nozzle or the
thinner the wall at exit, the faster the drop will form and
fall away, and the lower its tendency to wet the vertical
part of the nozzle. [1] The surface tension of the glass is
what influences the formation of the meniscus. For E-glass
it should be around 400 mN per m. [3]
The attenuation (drawing) speed is important in the nozzle
design. Although slowing this speed down can make coarser
fiber, it is uneconomic to run at speeds for which the
nozzles were not designed. [1]
Continuous Filament Process
In the continuous filament process, after the fiber is
drawn, a size is applied. This size helps protect the fiber
as it is wound onto a bobbin. The particular size applied
relates to end-use. While some sizes are processing aids,
others make the fiber have an affinity for a certain resin,
if the fiber is to be used in a composite. [4] Size is
usually added at 0.5–2.0% by weight. Winding then takes
place at around 1000 m per min. [2]
Staple Fiber Process
In staple fiber production, there are a number of ways to
manufacture the fiber. The glass can be blown or blasted
with heat or steam after exiting the formation machine.
Usually these fibers are made into some sort of mat. The
most common process used is the rotary process. Here, the
glass enters a rotating spinner, and due to centrifugal
force is thrown out horizontally. The air jets pushes it
down vertically and binder is applied. Then the mat is
vacuumed to a screen and the binder is cured in the oven.
[5]
Uses
End uses for regular fiber glass are mats, building
insulation, thermal insulation, reinforcement, heat
resistant fabrics, corrosion resistant fabrics, high
strength fabrics, aircraft bodies, cars and boat frames. A
famous user in the UK was the Reliant Motor Company, which
used fiberglass for many of its vehicles. Fiberglass is also
used in orthopedic casts as an alternative to plaster casts.
See also
* Basalt fiber
* Carbon fiber
* Fiberglass molding
* Glass microsphere
* History of fiberglass
* Optical fiber
Notes and references
1. ^ a b c d e f Loewenstein, K.L. (1973). The Manufacturing
Technology of Continuous Glass Fibers. New York: Elsevier
Scientific, 2-94. ISBN 0-444-41109-7.
2. ^ a b c d Gupta, V.B.; V.K. Kothari (1997). Manufactured
Fibre Technology. London: Chapman and Hall, 544-546. ISBN
0-412-54030-4.
3. ^ a b c d Volf, Milos B. (1990). Technical Approach to
Glass. New York: Elsevier. ISBN 0-444-98805-X.
4. ^ a b c d Lubin, George (Ed.) (1975). Handbook of
Fiberglass and Advanced Plastic Composites. Huntingdon NY:
Robert E. Krieger.
5. ^ Mohr, J.G.; W.P. Rowe (1978). Fiberglass. Atlanta: Van
Nostrand Reindhold, 13. ISBN 0-442-25447-4.
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