Note: Descriptions are shown in the official language in which they were submitted.
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WO 00/15567 PCT/US99/16585
SYSTEM FOR DELIVERING COOLANT AIR
TO A GLASS FIBER ATTENUATION ZONE
TECHNICAL FIELD AND INDUSTRIAL
APPLICABILITY OF THE INVENTION
This invention relates to a system for delivering coolant air to a glass fiber
attenuation zone of a glass fiber mechanical drawing process. More
particularly, this
invention relates to the method and apparatus for delivering non-intrusive
coolant air to
the attenuation zone of a glass drawing process where the flow of the coolant
air is
determined by the speed at which the glass filaments are drawn. A localized
vacuum is
created by the fiber motion induces airflow at nominal velocities and allows
the glass
fibers to entrain coolant air as required without variation in fiber diameter.
The apparatus
provides the required coolant air supply to at least the front and rear of the
bushing used
to draw the glass, and preferably around the entire periphery of the tip
plate.
BACKGROUND OF THE INVENTION
The present invention relates to glass filament forming and more particularly
to
the apparatus and method for providing a uniform thermal environment at the
attenuation
zone below a plurality of orificed filament forming tips on a heated glass
fiber forming
bushing.
It is well known in the art to produce filaments from glass by flowing a
stream of
molten material from a plurality of orificed tips provided on the bottom of a
heated
bushing. The streams are attenuated, usually by mechanical means, into
filaments. The
filaments are gathered into strands and may, subsequently, be processed into a
variety of
commercial products. More particularly, in the production of glass fiber
strands, molten
glass flows from a suitable source into the heated bushing assembly. This
bushing is
generally an elongated channel having side and end walls and a generally
planar bottom
which carries a large number of nozzles or tips through which the molten glass
passes. In
the zone immediately below these tips, the molten glass is formed into
filaments. This
3o zone is the attenuation zone, in which the glass fibers are cooled, may
have a sizing
applied to them, and are gathered into a strand. Finally, the strands are
wound on a spool
into a glass package. The environment in the zone directly below these tips is
crucial in
the formation of the filaments because it is in this area that then molten
glass cools. As the
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strand filaments cool, their mechanical properties and physical dimensions are
established.
For a more detailed description of a method and/or apparatus for making
filaments
reference is made to U.S. Patents Nos.4,118,210; 3,040,377; 2,300,736;
4,018,586;
4,636,234; 4,622,054; 4,325,722; and 4,866,536, incorporated herein by
reference.
There are four principal factors in the forming region which effect fiber
formation.
These are air, fibers, fins and the tip plate. The tip plate temperature
distribution governs
the glass throughput in each of the tips. Glass flows by gravity through the
tips and is
attenuated to the final diameters with the winder sustaining the tension. As
the glass jets
attenuate from their initial diameter to their final diameter, they lose heat
by radiation to
the fins and convection to the air around it. Also, air drag pulls air from
the surroundings
into the fiber fan. The air penetrates the fibers starting at the edge of the
tip plate and
works its way to the middle. During this process, there is heat exchange
between the air
and the fins, air and fibers as well as air and tip plate. The air gets
progressively hotter
towards the middle of the tip plate. Further, the velocity component parallel
to the tip
plate gets smaller (it is highest at the edge of the tip plate) as the
entrained air is pulled
downward by the fibers and is eventually "squeezed out" of the fiber fan. It
is the
attenuating history (local fiber diameter, velocity and temperature) of each
of the fibers
that dictates the air entrainment.
The entrained air cools the tip plate. As a result of the changing air
temperatures
and velocities, the heat transfer coefficient below the tip plate can be a
function of local
position. This implies that the air can contribute to tip plate temperature
gradients, which
in turn means variations in glass flow from tip to tip. In addition, air
influences fiber
attenuation history (fiber diameter, velocity and temperature as functions of
the
attenuation direction). Since the entrained air is cooler at the tip plate
periphery and hotter
in the middle of the tip plate with changing velocities, air may be cooling
part of the fins
while heating the remainder of the fin.
As has been observed, fiber attenuation contributes to the fin heat load,
affects the
air temperature and entrainment. Fiber attenuation is strongly influenced by
glass physical
properties. These physical properties include viscosity, surface tension,
density, specific
heat, emissivity (hemispherical total), and thermal conductivity. It will be
appreciated that
since glass is an absorbing-emitting medium, the hemispherical total
emissivity (which
determines the radiative heat loss from the fiber) and thermal conductivity
(which
2
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determines conduction in the fiber) are dependent on absorption coefficient
versus wave
length data. These data are temperature dependent. Furthermore, both
hemispherical total
emissivity and thermal conductivity are governed by the optical thickness
(absorption
coefficient times distance) and temperature.
Fins exchange radiative heat with the tip plate and attenuating fibers. They
also
participate in convection and conduction heat exchange with air. The fin
location/orientation below the tip plate can be very important since radiation
exchange
view factors as well as air flows can be impacted. The heat transfer
coefficient in the fin
manifold influences fm heat removal and impacts the forming process.
1 o The tip plate, which determines the tip exit glass conditions, exchanges
radiative
heat with fins and convective and conductive heat transfer with air. It will
be appreciated
that air flow and temperature fields can lead to varying (from position to
position) tip
plate temperatures.
It will be appreciated that due to the entrained air flow and temperature
fields,
15 each fiber experiences a different thermal environment and its attenuating
history is
therefore different. This means that the initial cone angle for each fiber can
be different
which, in turn translates to different glass throughputs since the throughput,
among other
quantities, also depends on the initial cone angle. Temperature fluctuations
in this zone
will result in diameter variations in the strands. Furthermore, if the
environment in the
2o zone immediately under the bushing tip is overcooled, the filaments formed
by the
bushing will have larger diameters and may not withstand the gathering and
winding
forces applied to them causing breakage of the filament. Conversely, filaments
which are
undercooled may break due to instability.
Additionally, stray air currents can carry unwanted materials into the
attenuation
25 zone thereby breaking the filaments and decreasing production efficiency.
Production
efficiency is measured by the break rate or short term yardage. The production
efficiency
may also be measured in terms of reducing the required inputs, i.e. material,
energy, time,
and equipment to achieve the same break rate. It is also well known that
forcing air into
the attenuation zone, perpendicular to the fiber flow, may spread the fibers
into random
30 streams as compared to orderly filaments. The random streams are then
collected on a
rotating drum for use as a staple textile fiber. In a properly controlled
environment,
without a forced air stream, the ordered filaments may be combined into a high
quality
strand that may be wound onto a spool as a glass package.
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One typical use for such strand is in the formation of glass fabrics. In order
that a
satisfactory woven fabric be produced, it is imperative that the diameters of
each glass
strand be consistent. Variations in the diameters of glass strands along the
length thereof
results in a fabric that will not lie flat but rather becomes "puckered." Such
a fabric is
unacceptable.
Problems associated with prior art cooling apparatus include, for example, low
production rate due to a high breakage, inequitable distribution of molten
material to each
tip, poor quality fabric due to glass strand diameter variation, inefficiency
due to high
process costs, and inefficiency due to high capital equipment investment.
Compared to the
1o heretofore known practice of blowing coolant air at the fibers, it will be
appreciated that
an air curtain in accordance with the present invention is non-intrusive and
has the
potential of aerodynamically isolating one position from the other.
In view of the foregoing, it is an object of the present invention to provide
an
apparatus to produce high quality glass fiber. It is another object of the
present invention
15 to provide an apparatus to produce a glass fiber with reduced breakage
rate. Another
object is to provide an apparatus for producing glass fiber of simplified
design and
generally lower cost than prior art apparatus of the same type. Yet another
object of the
present invention is to provide an apparatus for producing glass fiber that
efficiently
utilizes coolant air. Still another object of the present invention is to
provide a method for
2o producing glass fiber using the apparatus as disclosed.
SUMMARY OF THE INVENTION
Briefly, there is provided a method and apparatus for forming continuous glass
fibers. The method includes the steps of supplying a plurality of streams of
molten glass
25 from a bushing, drawing the streams into continuous glass filaments,
providing a stream
of coolant air parallel to the direction of draw of the streams of continuous
glass filaments
in at least the front and back of the bushing to entrain the coolant air
wherein the
entrainment of the coolant air is determined by the speed at which the glass
filaments are
drawn; and then collecting the continuous filaments.
3o The apparatus for delivering non-intrusive coolant air to an attenuation
zone of a
glass drawing process of a bushing including a bushing tip plate having a
plurality of
bushing tips includes at least two plenum chambers having inlets into which
coolant air is
fed under pressure at a selected flow rate to discharge outlets. The discharge
outlets
4
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extend a longitudinal length of the bushing tip plate to provide coolant air
to a front and
back of the tip plate. The entrainment of the coolant air is a function of the
speed at which
the glass filaments are drawn.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and other objects and advantages will become clear from the
following detailed description made with reference to the drawings in which:
FIG. 1 is a bottom view of a bushing including a coolant air delivery
apparatus in
accordance with the present invention;
i0 FIG. 2 is a cross sectional view of the bushing of FIG. 1 taken along line
2-2;
FIG. 3 is a cross sectional view of the bushing of Fig. 1 taken along line 2-2
utilizing another coolant air delivery apparatus in accordance with the
present invention;
FIG. 4 is a cross sectional view of the bushing of Fig. 1 taken along line 2-2
utilizing another air delivery apparatus in accordance with the present
invention; and
15 FIG. 5 is a cross sectional view of the bushing of Fig. 1 taken along line
2-2
utilizing another air delivery apparatus in accordance with the present
invention.
DETAILED DESCRIPTION AND PREFERRED
EMBODIMENTS OF THE INVENTION
2o Referring to the figures where like reference characters represent like
elements,
there is shown a system and apparatus 10 for delivering connective coolant air
12 to a
glass fiber attenuation zone of a hushing 14. As is well known in the art,
molten glass 16
is drawn through bushing tips 18 of the bushing 14. A plurality of bushing
tips 18 are
positioned in an array on the bushing tip plate. As the molten glass 16 is
attenuated
25 through the bushing tips 18, cones of glass are foamed. Upon further
attenuation these
cones are formed into filaments 20 which are later gathered into composite
strands.
It will be appreciated that although the present invention is shown in the
figures in
cooperation with a single bottom bushing the invention may also be used with
equal
facility with a double bottom bushing, i.e. two tip plates separated by a gap,
of a type well
30 known in the art.
The bushing tips 18 are typically cooled by means of a plurality of cooling
fins 22
operatively attached to a liquid cooled manifold 24. The cooling fins 22 are
operatively
attached to the manifold 24 so that heat may be removed from the area
surrounding the
CA 02343896 2001-03-13
24 ~8 2Q~~ ~~T~~~'I ~~ i~E~~
bushing tips 18. As shown in Fig. 1, the cooling fins 22 are arranged between
rows of
bushing tips 18. FIG. 1, also illustrates the connection of the cooling fins
22 to the
manifold 24 and the direction of travel of the coolant within the manifold 24.
The heat is
removed through the cooling fins 22 and ultimately removed by the flowing
liquid in the
manifold 24. As shown in the figures, the manifold 24 may be a hollow pipe or
the like
and the cooling fins 22 may be in the form of solid fin members. In an
alternate
embodiment, a second manifold 24a may be operatively connected to an opposing
side of
the cooling fins 22 as shown in FIG. 5. Notwithstanding, it will be
appreciated that the
exact means employed for such cooling is not important to the operation of the
instant
1 o invention and are well known in the art.
Referring to the figures, the system and apparatus 10 includes at least two
plenum
chambers 26 into which a coolant gas such as air is fed under pressure at a
suitable flow
rate. In a preferred embodiment, the coolant air is at a temperature no
greater than
ambient temperature for efficient operation. However, the coolant air may be
chilled as
15 desired. The coolant air enters the plenum chambers 26 through inlets 28
and exits the
system through discharge outlets 30. The discharge outlets 30 extend the
longitudinal
length of the tip plate 14 on both sides of the tip plate to provide
satisfactory coolant air
coverage. The discharge outlets 30 are designed to provide between 150 - 300
cfm (cubic
feetlminute) of coolant air for yarn and reinforcement type bushings having a
throughput
20 of about 50 - 300 lbs/hr. However, it will be appreciated that the amount
of coolant air
may be adjusted as desired for the type of bushing design employed. The
openings in the
discharge outlets 30 comprise less that 1% of the total surface area of the
outlet.
Referring to FIGS. 2-5, there are shown alternate embodiments of the apparatus
for providing coolant air to the attenuation zone at both the front and rear
of the tip plate
25 14, and preferably the entire periphery of the tip plate. The plenum
chambers 26 may be
rectangular shape (FIGS. 4 and 5) or the plenum chambers may be "boot shape"
(FIGS. 2
and 3). The plenum chambers 26 may include vanes (not shown) for directing the
coolant
air flow perpendicular to the tip plate 14. The outlets 30 may be positioned
above a plane
formed by the cooling fins 22 (FIG. 4), below the plane formed by the cooling
fins (FIGS.
30 2, 3 and 5) or parallel to the plane formed by the cooling fins (FIGS. 5,
shown in phantom
line). In a preferred embodiment, the discharge outlets 30 of the plenum
chamber 26 are
positioned about 0 - 4 inches from the horizontal edge of the tip plate 14 and
no more
than about 3 inches from the bottom of the tip plate. The coolant air exits
the outlets 30
6
AMENDED SHEET
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substantially vertically downward into the attenuated zone directly adjacent
the tips 18 to
form an air curtain on at least the front and rear of the bushing, preferably
the entire
periphery of the bushing. A localized vacuum is created by the fiber motion
and induces
coolant airflow at nominal velocities and allows the glass fibers to entrain
coolant air as
required without variation in fiber diameter. It will be appreciated that a
perforated screen
(not shown) mounted on or located upstream of the discharge outlets 30 may be
used to
reduce turbulence in the coolant gas and also act as a filter to prevent any
particulate
matter from coming into contact with the glass fiber filaments being formed.
It will be
appreciated that the air curtain delivers a majority of the coolant air
substantially
1o vertically downward on at least the front and rear of the tip plate 14,
preferably the entire
periphery of the tip plate, to allow the attenuating fibers to entrain the
necessary quantity
of coolant air as dictated by the movement of the fibers. A minor component of
the
coolant air may also be angled at the glass fibers so as to not disturb the
attenuating zone.
Compared to the heretofore known practice of blowing coolant air at the
fibers, it will be
is appreciated that the air curtain is non-intrusive and has the potential of
aerodynamically
isolating one position from the other. Furthermore, it has been found that
only providing
coolant air parallel to the direction of flow of the glass fibers an on at
least both the front
and rear of the tip plate 14 a reduced amount of coolant air is required over
heretofore
known systems to achieve the same coolant effect and, in addition, as a
further benefit
20 short term yardage is improved.
In operation, the bushing is supplied with molten glass which passes through
the
tips 18. The fin plates 22 are properly positioned below the tip plate 14 and
a liquid
coolant is passed through the manifold at a desired flow rate to extract heat
from the fin
plates. The coolant air is introduced into plenum chambers 26 passes through
diffuse
25 screens and flow in a non-turbulent manner parallel to the direction of
pull of the glass
fibers on both sides of the tip plate. The coolant air is drawn into the
attenuated zone so
that the filaments are attenuated in a uniform environment.
The Patents and documents herein are hereby incorporated by reference.
Having described presently preferred embodiments of the invention it will be
3o appreciated that the invention may be otherwise embodied within the scope
of the
appended claims.
AMENDED SHEET
P r~~tec~ 28 08 ~t~~~J
