Note: Descriptions are shown in the official language in which they were submitted.
39~
~his invention pertains to mineral fibers and
the manufacture of mineral fibers for such uses as
textiles, reinforcements, construction ma-terials, and
insulating materials. With respect to this invention, the
term "mineral fibers" means fibers of glass, rock, slag or
basalt. In one of its more specific aspects, this
invention pertains to non-circular mineral fibers and, in
particular, non-circular glass fibers.
The production of wool gla~s fibers by means of
lo the rotary process is well known. In general, molten
glass is fed into a spinner which revolves at high speeds.
The spinner has a peripheral wall c?ontaining a
multiplicity of orifices. Molten glass passed by
centrifugal force through the orifices of the peripheral
wall forms small diameter molten glass streams.
Positioned circumferentially about the spinner is an
annular blower for turning the fibers downwardly and, in
some cases, for further or secondary attenuation of the
original or primary fibers to produce fibers of smaller
diameter. As the streams of molten glass are emitted from
the orifices, they are still sufficiently nonviscous that
surface tension forces pull or shape each of the molten
`~ streams into substantially circular cross-sections,
regardless of the cross-sectional shape of the streams as
2~ they are emitted from the orifices. Further, rotary
fiberizers are typically equipped with annular burners or
other sources of hot gases for secondary attenuation of
the primary fibers; thes~ hot gases keep the
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1 glass sufficiently fluid or nonviscous that fibers of
substantially circular cross-section result.
The production of textile or continuous glass
fibers by mechanicall~ drawing molten streams of glass from
orifices in the bottom wall of a bushing or feeder is also
well known. Non-uniformities in the roundness of the molten
streams tend to be corrected by surface tension forces prior
to the cooling and hardening of the molten streams into
glass fibers. Thus, as in the case of wool glass fiber
production, it has not been possible to produce
significantly non-circular continuous fibers using shaped
orifices in a bushing.
There has long been a need for producing fibers,
both in the rotary process and in the continuous fiber
process, that have significantly non-circular
cross-sections. With respect to reinforcement of resin `
matrices, such non-circular fibers would be useful in
imparting greatly increased transverse strength and improved
shear strength qualities. Non-circular fibers for use as
insulation materials would be advantageous in that the
increased surface a~ea per unit volume of glass would lower
the thermal conductivity of insulation made from such
fibers.
A measure of the non-circularity of mineral fibers
is the "mod ratio", which is deined as the ratio of the
diameter of the smallest circle into which the fiber
cross-section fits to the diameter of the largest circle
which can fit inside the fiber cross-section. As employed
herein, fibers having a mod ratio of less than 1.2 are
referred to as circular fibers; fibers having a mod ratio
greater than or e~ual to 1.2 are referred to as non-circular
fibers.
One attempt to make non-circular glass fibers was
by Warthen, as described in U.S. Patent No. 3,063,094
Warthen's method employs mechanical perturbation of the
glass stream while it is still in a plastic, ~eformable
state. Warthen teaches that to cxeate a non-circular fiber,
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7~39'1
1 the glass stream, initially in a conical shape with a
circular cross-section, should be distorted at a region
where the viscosity of the stream is sufficiently high as to
become rapidly chilled or solidified during attenuation of
the streams to a continuous fiber whereby a similar
distortion in the cross-sectional configuration is retained
in the attenuated solidified fiber. Warthen also teaches
that a heat sink is to be applied to the glass stream by
direct contact. This raises the viscosity of the molten
glass to better enable retention and perpetuation of the
non-circular cross-sectional character of the mechanically
perturbed molten glass stream.
In the art of producing organic fibers, it is a
common practice to use quenching methods to solidify molten
streams o organic material into non-circular cross-sections
which are similar to the shapes of the non-circular
orifices. However, these methods are practical under
conditions which differ greatly from conditions associated
with forming mineral fibers. The production of organic
non-circular fibers can be facilitated by pressurization of
the bushings, whereas pressurization of bushings containing
molten glass presents severe operating problems. The
melting points of glass and organic compositions differ by
1500F (815C) or more. The mineral material of this
invention will have a liquidus temperature greater than
about 1200~F (649-C), whereas organic compositions soften
- and/or decompose at much lower temperatures.
The differences in physical characteristics can be
clearly understood by comparing the ratio of
viscosity-to-surface tension ~or glass with the same ratio
for organic fiber formin~ material. The
viscosity-to-surface tension ratio ~poises/(dynes/cm)) of
polymers lies within the range of from about 25 to about
- 5000. The ratio for glass is within the range of from about
0.1 to about 25, preferably within the range of from about
~25 to about 15, and most preferably within the range of
from about 0.4 to about 10. The viscosity of molten glass
~7~
at fiber forming temperatures is typically about 300 poi~e
whereas the viscosity of the molten organic material is
typically on the order of about 1000 to about 3000 poises.
~150, the surface tension forces of glass (on the order of
about 250 to about 300 dynes/cm) are an order of magnitude
greater than those of the organic material (about 30
dynes/cm). The lower viscosity and higher surface tension
of glass make it about 100 times more difficult to preven-t
the shaped glass fibers from re-forming into glass fibers
having circular cross-sections.
In spite of pa.st attempts to manufacture non-
circular mineral fibers, there has never been a
commercially successful method or apparatus for achieving
the goal of making non-circular fibers from non-circular
orifices.
Accordingly, one aspect of the invention
provides the method of making non-circular ~ineral fibers
having a mod ratio greater than about 1.2 comprising
discharging molten mineral material having a liquidus
greater than about 1200~F (649C) from non-circular
orifices to produce molten streams of non-circular cross-
section, said non-circular orifices being positioned in a
wall of a container for holding a body of molten mineral
material and the mineral material in said streams having a
low enough initial viscosity that said steams would assume
circular cross-sections in the absence of quenching, and
quenching said streams to harden them into mineral fibers
having a non-circular cro~s-sectional shape similar to the
shape of said orifices before the stream~ can assume
circular ~ross sections.
Another aspect of the invention provides
apparatus for making non-circular mineral fibers having a
mod ratio greater than about 1.2 comprising an orifice
bushing wall for discharging one or more stream6 of molten
mineral material having a liquidus greater than about
1200F (649C), said orificed bushing wall being
positioned in a container for holding a body of molten
mineral material and the mineral material in said strea~s
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having a low enough initial viscosity that said streams
would assume circular cross-sections in the absence of
quenching, the or~fices having a mod ratio within the
range of from about 1.3 to about 25, and means for
quenching said streams to form mineral f ibers having a
non-circular cross-sectional shape similar to the ~hape of
said orifices.
Thus, it has now been found that mineral fibers,
such as glass fibers, can be produced with non-circular
cross-sections by dischargin~ streams of molten mineral
material from non-circular ori~ices and forcibly quenching
the steams sufficiently fast to harden them into non-
circular mineral fibers. This forcible cooling of the
streams hardens them into fibers with non-circular cross-
sections beore surface ten~ion forces can cause the
stream~ to assume circular cross-sections. The rapid
cooling aspect of this invention e~ables the production of
mineral fibers having higher mod ratios than those
practically feasible with the processes of the prior art.
The invention can be employed in both the rotary process
and in a continuous fiber process.
Although the preferable means for quickly
quenching the streams is a relatively cold (e.g. room
temperature) gaseous flow, such as air, directed into
contact with ~he st~eams, any suitable means for rapidly
cooling the streams, such as fluid flow, water spray,
liquid bath, ultr~sonics or fin shields, can be employed.
Streams having greater mod ratios will, in general, h~ve
greater surface areas ~i.e., greater perimeter of the
stream cross-section) and hence greater heat transfer
characteristics (and quench rates) than those streams with
lesser mod ratios. When using a cooling gas, the
temperature and velocity of the cooling gas flow al50
a~fect the quench rate, as does the velocity of the
streams and the time required for passage of the streams
throu~h the quenching gas flow as well as the distance
traveled before the streams are hardened in-to fibers.
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The mineral fiber forming process of this
invention can be effected by numero~ variables, including
inertia forces (hydrostatic head or pressurization in a
textile process; hydrostatic head forces in a rotary
procecs), body force~ in a rotary process, initial
temperature and viscosity of the mineral material,
thickne~s or depth of the non-circular orifice, surface
tension characteristics of the molten mineral material,
- speed at which the streams are -traveling, and the rate a-t
which the streams are quenched.
Pressurization of the body of molten glass, or
the inertial force on the glass from the spinner, or the
mechanical pulling force in a continuous fiber process,
can affect the ultimate mod ratio of the mineral fibers.
To the extent that surace tension forces start to act to
re-form the streams into circular cross-sections before
the streams reach the cooling gas flow, the source of
which may be positioned some distance below the non-
circular orifices, the time for the streams -to each the
region of the cooling gas flow may be critical.
As mentioned above, the method of making non-
circular mineral fibers comprises discharging molten
mineral material from non-circular orifices to produce
streams of non-c.ircular cross-section, and cooling the
streams to harden them into fibers having a non-circular
cross-sectional shape similar to the shape of the orifices
before the streams can assume a circular cross-section. A
plurality of such orifices can be positioned in a wall of
a container for a body of molten mineral material. The
container can be, for example, a spinner or a feeder.
: In one embodiment of the invention, the
quenching of the mineral material is effecte~ by directing
a cooling fluid into contact with the glass stream in an
amount and at a locus sufficient to prevent the material
from assuming a circular cross-section.
The apparatus of the invention for making non-
circular mineral fibers comprises an orificed bushing for
discharging one or more streams of molten mineral
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~7~
material, the orifices advantageously having a mod ratio
greater than about 1.2, and mean~ for quenching th2
streams to form mineral fibers having a non-circular
cross-sectional shape similar to the shape of the
orifices. Preferably, the orific~s have a mod ratio
within the range of from about 1.2 to about 50, more
preferably within the range of from about 1.3 to about 25,
and most preferably within the range of from about 1.7 to
about 10. The orifices can be trilobal, with the three
lobe~ being generally, evenly, angularly spaced from each
other.
Embodiments of the invention will now be
described, by way o~ example, with reference to the
accompanying drawing3, in which:
Figure 1 is a schematic view in elevation of one
apparatus for forming continuous non-circular glass fibers
from a bushing according to the principles of the
invention;
Figure 2 is an upward plan view of a bushing
bottom plate containing an array of non-circular orifices;
Figure 3 is a perspective view of a non-circular
orifice of Figure 2, and a non-circular glass fiber being
formed;
Figure 4 is a graph of fiber charac-teristics as
a function of distance from the bushing;
E'igure 5 is a schematic vlew in elevation of a
non-circular orifice according to the pri~ciples of the
invention;
Figures 6 through 9 illustrate non-circular
cross-sections of glass fibers made under various
conditions of quenching;
Figure 10 is an enlarged cross-sectional view of
the trilobal glass fiber of Figure 9;
Figure 11 is a graph indicating the relationship
between the mod ratlo and quench velocity;
Figure 12 is an isometric view in perspective of
a resin matrix reinforced with non-circular fibers;
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~a
Figure 13 is an enlarged isometrlc view in
perspective of three of the trilobal fibers of Figure 12;
Figure 14 is an upward plan view of a bushing
bottom wall containing both circular and non-circular
orifices;
Figure 15 is a schematic cross-sectional view in
elevation of the invention applied to a rotary process;
Figure 16 is a schematic view in elevation of
the spinner of Figure 15;
Figure 17 is an enlar~ed cross-sectional view of
a crescent-shaped fiber produced on the apparatus of
Figures 15 and 16; and
Figure 18 is a plan view of an embodiment of a
tipped non-circular orifice.
This invention will be described in terms of a
glass fiber forming process and apparatus, and products
made therefrom, although it i-q to be understood that the
process is suitable for fibers of other mineral materials,
particularly of such mineral materials as rock, slag and
basalt.
As shown in Figure 1, molten ~lass streams 10
are emitted from orificed bushing bottom wall 12 of feeder
or bushing 14, and are drawn into fibers 16 by any
- suitable means, such as by the mechanical action of winder
18. Gathering shoe 20 and size applicator 22 can be
employed in the manner well known in the art. The bushing
contains a body of molten glass 24 from which the streams
of molten
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~7~35a~
1 glass are drawn. As illustrated, air nozzles 26, which are
means for quenching the streams of molten glass, are
positioned to direct air into contact with the molten
streams as they are emitted from the bushing bottom wall.
The air flow cools the molten streams quickly enough into
glass fibers so that they retain the general non-circular
shape o~ the molten streams. Other sui~able cooling fluids,
such as carbon dioxide, nitrogen, steam or water, can be
employed to forceably cool the streams.
As shown in Figures 2 and 3, the bushing bottom
wall contains trilobal orifices 28, having the lobes
positioned evenly around the periphery. The orifices and
the resulting ibers can be of various shapes, such as, for
example, cross-shaped, star-shaped, pentalobal, octalobal,
or rectangular.
In order to ~uantitatively describe the formation
of non-circular glass fibers, it is useful to consider a
time constant r for the decay of the shape from
non-circular cross-section back to circular cross-section.
As soon as a molten glass stream of non-circular
cross-section flows from a non-circular orifice, surface
tension forces act on the stream to change it into a
circular cross-section. Opposing these forces are viscous
forces, which tend to resist changes in the shape of the
stream. The viscous forces increase extremel~ rapidly
because of cooling as the molten glass in the stream moves
away from the orifice. In order to successfully make
non-circular fibers, the viscous forces (i.e., the
viscosity) must be increased quickly enough to retard the
effect of the surface tension forces.
The time constant is believed to be the function
of the viscosity of the glass, the e~uivalent radius of the
glass stream, and the surface tension, according to the
e~uation: r - ~r/ ~ . This equatior. can be transformed
- 35 with a velocity ~actor to enable integration over distance
along the fiber, i.e., vertical distance downward from the
orifice, instead of with respect to time. In operation,
741;~
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1 when only a few time constants pass prior to the hardening
or greatly increased viscosity of the glass, the fiber still
main-tains its non-circular shape. When many time constants
pass, however, prior to reaching high viscosity, the glass
stream returns to a circular cross-section and produces a
circular fiber. When the inverse of the time constant is
integrated over the distance to 100~ attenuation, the ratio
of the time-to-become-viscous to the
time-to-revert-to-a-circular-cross-section is obtained.
This ratio, di~icult to measure exactly, can be estimated
by the ratio Z, as given by the following equation:
750~0~rO reo) (l/vo) * l/(MRo -1)
where:
X75 is the distance from the bushing at 75 percent
attenuation (cm);
is the initial viscosity (poise);
reO is the initial equivalent fiber radius (cm);
is the initial surface tension of the mineral
material (dynestcm);
~ 20 vO is the initial velocity (cm/sec) through the
-~ orifices; and
MRo is the initial mod ratio of said streams.
The factor 1/(MRo -1) is a ~actor indicative of
the mod ratio of the hole, and hence the initial mod ratio
of the glass stream. It has been found that this equation
correlates very well with theoretical considerations as
shown in Figure 4 where the curve represents the reciprocal
of the time constant as a function of distance from the
bushing. The integral is the area underneath the curve, and
the smaller the area underneath the curve, the smaller the
number o~ time constants experienced by the stream before
hardening and therefore the greater the mod ratio. It has
been found that in order for the final ~iber to be
non-circular, Z should be less than or equal to 2, and
preferably less than or equal to 1.
The inertia ~orces or glass pressure at the
ori~ices can af~ect the extent to which non-circular ~ibers
'7~3~a~
1 can be formed. The pressure can be produced by any means,
such as the hydrostatic head of the molten glass, gas
pressurization of the feed~r, or a combination of both. For
the production of continuous glass fibers, the hydrostatic
pressure is preferably within a range of from about 0.4 psig
(2,800 Pascals) to about 100 psig (690,000 Pascals). Most
preferably, the molten mineral material will be subjected to
a hydrostatic pressure within the range of from about 0.7
psig (4,800 Pascals) to about 5.0 psig (34,000 Pascals).
Although the bushing shown in Figures 1~3 contains
tipless orifices, the invention can be performed with tipped
orifices as well. The orifice in Figure 5 has depth "t".
It has been found that shallower or less deep ori~ices
enable an improvement or increase in the mod ratio of the
non-circular fibers. Preferably, the depth of the orifices
is within the range of from about .001 in. (.025 mm) to
about .250 in. (6.4 mm).
The mineral fibers produced according to this
invention will, in general, have equivalent diameters within
the range of from about .2xlO 5 in. (.05 microns) to about
300xlO 5 in. (76 microns), although non-circular fibers
outside this range are possible. Preferably, the mineral
fibers are within the range of B to Y filaments, i.e.,
within the range of from about lOxlO 5 in. (2.5 microns3 to
about 120xlO in. (30 microns). Most preferably, the
mineral fi~érs of this invention are G through T ~ilaments,
within the range of from about 35xlO 5 in. (8.9 microns) to
about 95xlO 5 in. (24 microns).
Figures 6 through 9 illustrate cross-sections of
four non-circular fibers produced from apparatus similar to
that shown in Figures 1-3. These fiber cross-sections are
all similar in shape to the trilobal orifice. The apparatus
was controlled at substantially constant operating
conditions except for the velocities of the quenching fluid.
The velocities were different for each of the ~ibers. It is
believed that the rate at which the molten glass streams is
cooled is a function of the velocity of the ~uenching medium
,
~27~3~
11
1 when all other conditions are equal. Fiber 16a in Figure 6
was produced with a quench air velocity at the bushing
orifice of approximately 1~ meters per second, and has a mod
ratio of about 1.35. Non-circular fiber 16b shown in Figure
7 was produced with a quench rate of approximately 15 meters
per second, and has a mod ratio of about 1.45. Fiber 16c
shown in Figure 8, having a mod ratio of about 1.75, was
produced with a quench rate of approximately 20 meters per
second. Non-circular fiber 16d shown in Figure 9, having a
~ mod ratio of about ~.70, was produced with a ~uench rate of
approximately 30 meters per second. Although quench
velocities of up to 60 meters per second, or more, could
possibly be used with the invention, it has been found that
the preferred quench velocity of room-temperature
(approximately 80 F, 27 C) air is below about 40 meters per
secon~. Most preferably, the quench rate is within the
range of from about S to about 30 meters per second. These
quench velocities are in contrast to those used in normally
operating air-quenched bushings used to prevent flooding,
which have quench rates at the bushing tips on the order of
about 2 to 4 meters per second.
As shown in Figure 10, the dimensions of
non-circular fiber 16d can be characterized by using the mod
ratio, which is the outer diameter Do divided by the inner
diameter Di. The outer diameter is the smallest circle into
which the entire cross-section can be placed. The inner
diameter is the largest circle which can be positioned
within the fiber cross-section.
As shown in Figure 11, the mod ratio in~reases
with an increase in the quench velocity. It is also shown
that when the bushing is pressurized, the mod ratio
increases.
As shown in Figures 12 and 13, continuous trilobal
fibers 16d can be made and positioned in a matrix, such as
plastic resin 3~, for reinforcement. The mineral fibers o~
this invention can be used to rein~orce any organic or
inorganic matrix suitable for use with other types of
12
1 reinforcement. For example, thermoplastic or thermoset
resins, such as polyesters or epoxies, could be used.
Cements, low melting point metals, and silicate matrices
could also be reinorced. Matrices reinforced with
non-circular mineral fibers of this invention could also be
simultaneously rein~orced by any other suitable
reinforcement, such as circular mineral fibers or organic
fibers.
As shown in Figure 14, the bushing bottom wall 12
can contain both non-circular orifices 28a and circular
orifices 34 to produce strands of fibers, some of which have
circular cross-sections and some of which have non-circular
cross-sections.
As shown in Figure 18 a tipped bushing can be used
to produce non-circular fibers of the invention. The three
legs 54 of the orifice have enlarged leg ends 56. The
orifice is formed in the bottom end of a ciosed end tube tip
58.
When the invention is carried out using the rotar~
process, the "container" is a spinner rather than a feeder
or bushing, and the non-circular orifices are positioned in
the spinner peripheral wall rather than in the bushing
bottom wall.
As shown in Figure 15, molten glass 40 can be
supplied to rotating spinner 42. The molten glass impinges
on bottom wall 44 of the spinner and flows outwardly by
centrifugal force to the spinner peripheral wall 46. The
spinner peripheral wall contains non-circular orifices 48
through which molten streams of glass 50 emanate. The
relative motion of the glass streams emanating from the
spinner and the air surroundiny the spinner results in a
quenching of the molten streams into glass fibers 52. To
some extent, the rate of quenching can be controlled by the
rotational rate of the spinner. An annular blower, such as
3~ blower 54, can be positioned concentrically around the
spinner to turn the fibers down for collection of the
fibers, which can be by conventional means.
~7~ 4
13
1 The spinner can be adapted with non-circula~
orifices of various shapes, such as slots or crosses, and in
various configurations. As shown in Figure 16, the spinner
can be adapted with crescent-shaped orifices to produce
glass fiber 52 having the cross-sectional shape shown in
Figure 17.
EXAMP1E I
Continuous E glass trilobal fibers having an
average mod ratio of about 2.3 were made from a tipless
bushing having 20 trilobal orifices under the following
conditions:
Trilobal Qrifice size:
depth: .015 in. (.38 mm)
width of each leg: ~009 in. (.23 mm)
length of each leg
to center of orifice: .027 in. (.69 mm)
Glass temperature = 2190 F (1200 C)
Glass type: 200E
Bushing pressure (total): 8.7 psig (60 KPa)
Glass flow rate: .034 lb/hr/hole (0.26 g/min/hole)
Number of filaments: 20
Hole pattern: 2 rows, 10 holes/row, staggered pattern
sp~cing between rows: .125 inch (3.18 mm)
hole spacing along row: .120 inch (3.05 mm)
Quench medium: air at 80F (27C)
Quench nozzle size: 1.5 in. (38.1~n) horizontal ~ .25 in.
(6.35mm) vertical
Quench nozzle position: 1 inO (25mm) from center line of
bushing (center line between two
rows)
15 degree angle ~rom horizontal
Quench nozzle flow rate: 300 scfh (10.2 kg/hr)
Quench velocity: 32 ft/s (9.8 mts~ at ~uench nozzle
29-32 ft/s (8.8-9.8 m/s) at bushing center
line (very little velocity decay, if any)
Winder speed: 1550 ft/min (7.87 m/s)
~ ;~74~
14
1 Average fiber diameter: M filament 65 HT 116.5 microns)
based on cross-sectional area
EXAMPLES II & III
Continuous E glass trilobal fibers were made with a 14 hole
tipped bushing using finshield quench. The tips were closed
end tube tips with orifices of the design shown in Figure 18
machined in the tip bottom. The particular dimensions of
the design used determined the final fiber mod ratios. The
following conditions pertained to all tips:
Tip tube diameter: 0.130 in. (3.3 mm)
Tip tube length: 0.240 in. (6.1 mm)
Tip end thickness (depth of orifice): 0.011 in. tO.28 mm)
Tip pattern: 2 rows, 7 tips/row, straight pattern
spacing between rows - 0.030 in. (7.6 mm)
tip spacing along row - 0.23 in. (5.8 mm)
Finshield geometry: fin thickness - 0.055 in. (1.4 mm)
fin height - 0.625 in. (15.9 mm)
fin length - 1.68 in. (42.7 mm)
fin blade spacing - 0.23 ln. (5.8 mm)
Glass type: 20OE
Glass temperature: 2250F (1230C)
Bushing pressure (total): 1.1 psig (7.6 KPa)
Winder speed: Approximately 750 ft/min (3.81 m/s)
This varied somewhat during the ;
experiments.
EXAMPLE II
Hole dimensions: D - 0.025 in. iO.64 mm)
P - 0.020 in. ~0.51 mm)
W - 0.010 in. (0.25 mm)
Glass flow rate: 0.018 lb/hr/hole (0.14 gm/min/hole)
Average fiber diameter: N filament, 70 HT (17.8 microns)
Average mod ratio: 2.2
EXAMPLE III
Hole dimensions: D - 0.025 in. (0.64 mm)
3~ P - 0.020 in. (0.51 mm)
~ - 0.005 in. (0~13 ~n)
~7~3~
1 Glass flow rate: 0.0141b/hr/hole (0.106gm/min/hole)
Average fiber diameter: 1 filament, 59 HT (14.9
microns)
Average mod ratio: 5.3
It will be evident from the foregoing that various
modifications can be made to this invention. Such, however,
are considered as being within the scope of the invention.
INDUSTRIAL APPLICABILITY
-
This invention will be found to be useful in the
production of glass fibers for such uses as thermal and
acoustical insulation products, and reinforcements for resin
matrices.
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