Note: Descriptions are shown in the official language in which they were submitted.
~036~Z:~
This is a division of application No. 217,563, filed
January 8, 1975, "Method and Apparatus for the Manufacture of Glass
Fibers".
BACKGROUND OF THE INVENTION
In recent years, there has been considerable interest in
the production of glass fibers. Due to the tremendous usages of
glass fibers, this interest has been particularly focused on inc-
reasing the production of individual fiber drawing stations. In
the production of fibers, molten glass is typically passed through
nozzles or orifices in a bushing to create individual fibers. In
addition to the problem of increased production, the apparatus used
in such processes is typically quite expensive as it often times
involves the use of inordinate amounts of platinum, complex
orifices, high pressure generating equipment, pressure resistant
bushings, etc.
To increase the yield of the drawing stations, the obvious
but difficult approach is to increase the number of orifices per
bushing through which the molten glass is directed and from which
the individual fibers are formed. A few years ago, a standard
bushing produced 204 fibers. After considerable expense and research,
the capacity of the bushing has been increased to 2,000 orifices and,
through a recent breakthrough in the art, arcuate bushings have been
developed which are used in conjunction with high pressure glass and
are capable of handling 6,000 orifices. While the total number of
bushings per drawing station could, of course, be increased to raise
the production of the station, such an approach would be self-
limiting, increase the bulk of the station, complicate the operation
as well as increase the costs and result in the decrease of unifor-
mity of the individual fibers over the entire station. Therefore, it
is the individual bushing orifice function and capacity which is a
substantial limiting factor in the production of a high volume of
quality fibers from a drawing station.
A single bushing 10-inch square, incorporated in the
method and apparatus hereinafter to be described, can support
~L
- 1 - "'~
1036821
102,400 orifices. This represents 51.2 times the number of glass
fibers which can be produced by the best of the current standard
systems and 17 times more than the aforementioned arcuate bushing
system are capable of producing. In spite of this tremendous
gain, the present invention is remarkably sim~le both in concept
and construction. It utilizes the simplest of bushings containing
a minimum zmount of platinum, the base of which is formed into a
generally flat, thin horizontal orifice plate with just plain
holes therein.
Plain holes in flat, wettable alloy plates have been
utilized in the past, however, they have been quite limited with
respect to the proximity of adjacent orifices. If the hole edges
are closer than about l/2-inch apart, the glass will often times
creep through capillary action along the underside of the plate
to join and break an adjacent fiber. Such flow will continue
in an ever-widening cycle resulting in a flooding of the entire
bushing. The underside of the plate will become coated with a
single, useless glob of glass. With non-wettable alloys, where
the wetting an~le is 55 or more, plain holes can~ of course,
be closer together, but the spacing nevertheless is limited to
the diameter of the drops passing therethrough. Even with the
best of non-wettable alloys, should two drops touch, they will
immediately flow together to form a single larger drop and be
forced to wet the plate. This wetting cycle will continue
between the remaining orifices resulting in a totally unusable
bushing.
There are other systems which employ plain holes in
a flat bushing wherein a burnable gas is directed at the bushing
and the forming cones. Upon contact with the high temperature
of the issuing glass and of the bushing, the gas deccmposes to
deposit a carbon coating on the plate and glass. Due to the
poor wetting characteristics of glass on carbon and graphite,
103~8Zl
the carbon which coats the glass drops allows the drops to be
pushed together without coalescing. Despite the increased
proximity within which the orifices may be placed in such a
system, the overall production of the system i5 still quite
limited due in part to the degrading effect of carbon on the
glass. Moreover, such systems are unreliable because once
flooding occurs, it is very difficult to effect separation
thereafter. Other systems actually employ carbon inserts coaxial-
ly disposed around each orifice. Such systems occupy a greater
amount of space and the carbon must be employed in an inert
atmosphere. This, of course, further increases the cost of such
a system and the inert gas along with the exposure of the carbon
may have a damaging effect on the surface of glass fibers which
desireably should be disposed in an oxidizing atmosphere. Such
systems, therefore, do not present a satisfactory solution to
the problem of increasing production.
United States Letters Patent No. 3,573,014 discloses
a method and apparatus for producing fibers from glass which in-
corporates an arcuate bushing of the type referred to above.
The system disclosed therein utilizes pressure on the glass
substantially above a nominal pressure head to cause separation
and prevent flooding of the bushing. To withstand such pressures,
the bushing must have a pressure resistant configuration. This
configuration is provided by the arcuate bushing. In such a
system, separation is caused by what was originally termed the
shower head effect wherein the molten glass is forced at high
pressure through the apertures in the bushing and the formed jet
overwhelms any thin film on the bushing and in fact suc~s the
surrounding area dry thereby preventing flooding and thereafter
maintaining individual separated glass fibers. This high pres-
sure as well as requiring additional equipment for its generation,
dictates the configuration of the bushing used in such a system
which in turn limits the number of fibers which can be produced
by such a system. r .
10368Zl
In providing an economical system with increased
fiber production, in addition to developing a bushing with a gr-
eater number of orifices therein, it is necessary first to cause
separation and thereafter to maintain the separation of each of
the formed fibers. ~,lass has an unusually high surface tension
and, therefore, a droplet is constrained to a generally spherical
configuration. To distort th~ drop into a fiber forming cone
requires the application of stress. As molten glass passes
through an orifice and i8 forced to form into a fiber, the base
of the fiber assumes the shape of a fiber forming, asymptote-like
cone. ~s long as there is sufficient stress to maintain the
geometry of the cone, i.e., to cause some concavity, an equili-
brium between the fiber and its glass source will prevail.
However, such fibers cannot be sustained without exercising
considerable control over the asymptotic geometry of the feeding
cone.
There are several means for cooling glass fibers.
The standard means comprises one or two rows of orifices sandwic-
hed between fins which in turn are cooled by liquid or air. Var-
iations include several hundred individual streams of air, eachone of which cools a single fiber base or row of fibers either
through holes in fins or by air piped through hundreds of hyper-
dermic needle-like tubes to direct air at or in between each
fiber. Such fins are sometimes perforated to cause an overall
oozing of air streams to impinge at or near the fiber roots. Such
systems either cross the fibers at 90 with respect to their
axis or blow in a downward direction. An example to the con-
trary is found in United States Letters Patent No. 3,695,858
which apparently incorporates a pair of air jets for each
formed filament, i.e., 20 air jets for each 10 fibers. Each
of the air jet orifices are located only a few thousandths of
an inch from each fiber and are downwardly and upwardly directed
103~8Zl
at 45. The pairs of iets work in unison ostensibly to cause
a controlled turbulence to cool a row two tips wide within a
hooded enclosure. In such systems, the physical positioning of
the air orifices is extremely critical and necessarily complex.
Such systems have several problems which the herein-
after described system eliminates. Jets, fins and hoods must be
located adjacent to both bushing and orifices which in turn re-
quires very careful positioning and position maintenance. They
absorb considerable energy in cooling the bushing, occupy val-
uable space on the bushing and, therefore, substantially decreasethe number of orifices which can be employed. In addition, these
jets, fin~ and hoods become a recepticle for condensates from the
molten glass which cause fiber breaking "flys" and which degrades
the cooling efficiency and necessitates frequent cleaning. Fin-
ally, such systems have a most serious weakness in that they are
limited to cooling but a few rows of orifices. When air blows
across several rows of orifices at 45 or less, a primary and con-
tiguous layer hugs the plate in a laminar flow and blankets the
plate to prevent additionally directed air from penetrating the
blanket to cool the cones. The air tends to laminate to create
successive layers which quickly become too deep to have any cooling
effect on the very short fiber forming cones. Consequently, the
air at the cone level over cools the first rows of fiber and
under cools the successive rows. For this reason, air directed
from 90 to 45 to the fiber axis is quite limited in the width
of its quenching effect.
To constrain the cone to its fiber forminq shape by
cooling is not difficult with a single fiber because of 360
cooling nor is cooling difficult with any number of rows of fibers
one or two fibers wide. However, when there is a press of thou-
sands of orifices tightly grouped together in a single flat
bushing, a continuous and identical geometrical constraint on
1036i8Zl
each of these thousands of cones present~ a substantial cooling
problem. Should just one of the thousand~ of forming cone~
loose its shape, the force of wetting would at once dominate
and the glass would creep to an adjacent cone which would then
break, the cycle of breakage and wetting continuing thereafter
in an ever-widening ring until the bushing would become flooded.
'rherefore, in addition to providing an economical system for
incrcased glas~ fiber production which incorporate~ a bushing
having an increased number of orifices therein, it is neces-
~ary to provide a temperature control for the creation and main-
tenance of the asymptotic geometry of the fiber forming cones.
DESCRIPTION OF THE INVENTION
It is one object of this invention to provide an
improved apparatus for producing fibers from a high tempera-
ture molten material.
It is another object of this invention to provide
an improved apparatus for the production of glass fibers.
It i~ yet another object of thi~ invention to pro-
vide an improve~ apparatus for increasing the production of
glass fibers from a single station.
It is still another object of this invention to pro-
vide an improved apparatus for increasing the production of
glass fibers from a single bushing.
It is a further object of this invention to pro-
vide an inexpensive and economical apparatus for the production
of glass fibers.
It is yet a ~urther object of this invention to
provide an apparatus for the production of glass fibers which
incorporates a bushing having a high density of orifices.
3~ It is still a further object of this invention to
provide an apparatus for the production of glass fibers having
improved temperature balance across the bushing and fibers
pultruded therethrough. 6
i~
1036~21
In accordance with one aspect of this invention
there is provided an orifice plate for forming glass fiber
filaments including a generally flat orifice area having a
plurality of orifices therein, and capillary grooves in the
underside of the orifice plate connecting adjacent orifices.
Each of the orifices is adaptsd for the formation of a fiber-
forming cone of molten gla6s. With this arrangement, control-
lcd 100ding occurs between adjacent orifices connected by a
capillary when a fiber drawn from one of the orifices breaks.
The orifice plate is used in a method which in-
volves:-
(a) passing separate streams of molten glass through
the generally flat orifice plate having at least four rows
of orifices therein, with orifices spaced in flooding relation-
ship;
~b) drawing fibers from cones of molten glass
formed at each said orifice; and
~c) directing a bulk flow of rapidly moving gas
upwardly to the orlfice area in said plate:
Ii) to cool said cones to provide a
stable cone formation and to maintain separation of cones thus
preventing flooding;
~ii) to impinge on said plate essentially
to eliminate stagnant gas adjacent said plate and to cause
gas to move outwardly along said plate in all directions from
said orifice area, and
(iii) to supply a source of ga~ suc~ed
downwardly by the fibers~
1036BZl
Other aspects of this invention are described
below.
The advantages to be achieved from the present
invention are manifold. As a threshold matter, the orifice
plate or bushing is simple to manufacture and employs less
extremely expensive metal alloy than commercial bushings in
use today. Compared to conventional practice employing ori-
fices with tips, the radiant heat given off by the bushing
employed in this invention is less and therefore the operator
i~ subjected to less exposure to radiant heat. Inasmuch as
there i8 less radiation, the present invention affords the pos-
sibility of employing less electrical energy. The above is
particularly dramatic when comparing bushings of equal through-
put.
Since high orifice densities may be realized, the
present invention provides increased production per unit area
of orifice plate. Moreover, there is more throughput per
orifice than is realized in conventional practice employing
tip~, because of a ~kin effect pumping action due to the cones
being cooled by air, the shcrter orifice length and the higher
exit temperature from the orifice. The fibers have good uni-
formity and do not require complex manufacturing apparatus.
This invention does not require the use and complexity of fins,
hood enclosures, expensive, non atmospheric gas mixed with
carbon plating gases to create a
10368Zl
non-wettable carbon barrier, arcuate pressure bushings, high
pressure systems and does not require non-wettable alloys. In
addition, it utilizes the simplest of cooling means. From a
gas (e.g., air) source located below and relatively far from the
orifices, a stable environment is forced upon thousands of fibers
to maintain the stability of each of the formed fibers. With
this system, thousands of orifices can be croweded into a single
bushing which is very small in proportion to its yield yet has
virtually no length and breadth limitation and wherein the hole
edges can be as close as ,001 of an inch. In contrast, the
~tandard bushings have virtually reached their economic limit
at 2000 orifices. A system free from such limitations greatly
increases the yield and lowers production costs over the systems
heretofore available.
This invention also provides considerable flexibility
with regard to the number of fibers to be drawn from a bushing.
~he number of fibers required for final product application
readily may be drawn from a single orifice area. Final products
may require bushings producing strands having 1600, 2000, 3200,
20 4000~ 20~000~ or more fiber~. The present invention has the
potential of eliminating roving operations.
This invention further provides more flexibility in
choosing windup speeds because commercially acceptable production
rates (lbs. of glass) may be achieved employing more orifices and
lower windup speeds which tend to reduce the risk of fiber break-
age. Even at higher windup speeds, it has been found that "snap-
outn, wherein a large multitude of fibers break at essentially the
same time, does not occur. Since the orifice plate is overwhelmed
with high velocity upwardly moving gas, which moves outwardly
along the orifice plate, no adjacent ambient gas (which may carry
impurities that contaminate the fibers and cause fiber breaking)
is drawn around the cones so that the enviroNment around the
cones is cleaner. 9
10;~68Zl
With a relative high density of fibers passing over
the dressing fluid (binder) applicator roll~ there is less loss,
and therefore less consumption, of dressing fluid than experienced
in conventional commercial processes. Interfiber scrubbing action
appears to prevent excess pick up of dressing fluid by individual
fibers so that later sling off of dressing fluid by the fibers
is materially reduced. Reduced sling off of dressing fluid will
result in a reduction of sizing in the air and both equipment
and the work area will stay cleaner, thereby affording a better
environment for the operator. Rapid quench of the glass also
will reduce the content of glass volatiles in the surrounding
environment, and the cooling gas which moves laterally outwardly
from the bu~hing readily can be removed from the operating area
to keep the operating area cooler.
Finally, this invention provides high quality glass
fibers. Rapid glass quench ~order of magnitude 100:1 compared
to conventional type bushings), with a reduced loss of volatiles
from the glass, results in a fiber more nearly corresponding to
the composition of the glass in the molten bath. Moreover, the
sub~tantially greater cooling of the glass in the cones by
conduction and convection, rather than cooling by radiation,
provides a more tempered glass fiber.
This invention readily may utilize conventional glass
furnaces, and conventional auxiliary equipment, such as bushing
heaters, dressing fluid applicators and windup equipment. Ex-
isting glass fiber operations may be converted for the practice
of this invention by modification of the bushing and provision
of proper cooling gas means.
This invention easily may be practiced with the head
of glass normally maintained in a conventional glass furnace,
which generally is from about 8 to about 14 inches of molten
glass. Indeed, the present invention can be practiced with a
10368Zl
glass head of only about 1 inch or less. Although pressures
in excess of those provided by a head of glass require expensive
equipment that may be difficult to maintain, such pressures may
be employed if desired. The temperature of the molten glass in
the bath obviously will depend upon the type of glass being used.
With type E glass, the temperature wiil be about 2100F to about
2400F (1150-1315C). The choice of the temperature for the
molten glass bath in the glass furnace for any type of glass is
routinely established in conventional practice and is easily
within the skill of the art.
The orifice plate used in this invention may be made
of any alloy acceptable for operation under glass fiber forming
conditions. The alloy may be wettable or non-wettable. A
standard platinum alloy of 80~ platinum and 20% rhodium, or an
alloy of 90% platinum and 10% rhodium, readily may be employed.
Zirconia grain stabilized platinum alloys which have creep
resistance may also be employed.
The surface of the orifice plate is generally flat.
Plates which have small dimples or are in the form of gentle
concave and/or convex configurations may be used without ad-
versely affecting the practice of this invention. Heat warpage
of a flat orifice plate may result in convex and/or concave areas
within the plate but such distortions can readily be tolerated. If
desired, the orifice plate may be reinforced with ribs or a
honeycomb structure on the molten glass side of the bushing.
With commercial tips, the gas (e.g., air) cools the
tips substantially below the bulk temperature of the bushing.
As the tips cool, the glass flowing through the tips is also
cooled and becomes more viscous and flows less readily so that
the tips act as a thermal valve which decreases glass throughput.
In the practice of this invention, the metal temperature adjacent
the orifice during operation should not become substantially less
10368;~
than the bulk temperature of the orifice plate so that significant
adverse thermal valve effects are avoided.
The thickness chosen for an orifice plate will be a
function of bushing size, alloy strength, orifice size, orifice
density, and the like. Generally the orifice plate need not be
greater than 0.06 inches thick and orifice plate 0.04 inches
thick have been successfully employed. The orifice area in the
bushing readily may have a minimum dimension of at least about
1/2 inch with minimum dimensions of at least about 1 inch being
quite feasible. Orifice areas of 10 inches x 10 inches are
po~sible. In accordance with the conventional practice, the
orifice plate or bushing is provided with heating means. General-
ly heating is accomplished by electrical resistance means.
The Grifices in the orifice plate will generally be
less than about 0.1 inch in diameter and may be as small as
about 0.020 inches in diameter. The arrangement of holes is a
matter of choice and orifices may be arranged in a square, hex-
agonal or any other desired arrangement. In order to obtain
maximum utilization of bushing area the orifices generally will
be spaced not more than about 2 diameters, center-to-center,
with spacings of from about 1.25 to about 1.7 diameters, center-
to-center, being preferred. With smaller orifices, the metal
between adjacent orifices may be as little as 0.001 inch. It
is apparent that the orifice spacing will depend in part on the
thickness of the orifice plate alloy. If desired, periodic spaces
having no orifices can be provided to add strength to the bushing.
Care should be exercised, however, to avoid uneven air flow in
the event such spacings are employed.
The orifice plates used in the practice of the pre-
sent invention are at least 4 rows of orifices, preferably areat least about 10 or 11 rows of orifices, and most desirably are
at least about 15 rows of orifices wide (i.e., in any direction~.
This 1 ~
- ~0368Zl
invention permits the orifices to be spaced closely together
with orifices in each row being spaced from orifices in its row
and in adjacent rows in flooding relationship which, of course, is
diametrically opposed to present practice. An orifice plate which
would normally flood and would not maintain cone separation for
practical production at operating glass pressure and temperatures
can readily be employed in this invention since the bulk gas
movement establishes and maintains cone separation. Even though
an orifice plate may flood and foreclose sustained production
under normal operating conditions of glass pressure and glass
temperature ~ust over the plate, such plate can be employed
adopting the practice of this invention. In production, at least
90% production efficiency is generally desirable. Such rates
and more can readily be attained by this invention.
Generally, for practical production, orifice density
will be at least about 50 orifices per square inch, preferably
at least about 100 orifices per square inch, and most desirably
about 200 holes per square inch of the orifice area in the
bushing. With very small orifices, the densities may fange from
20 about 500 to about 1000 orifices per square inch. The greater
the density of a given orifice size, the greater the production
that can be achieved per square inch per orifice area. Although
orifice densities are given in orifices per square inch, it
should be understood that the area occupied by the orifices may
be less than 1 square inch.
Air is particularly preferred for this invention
and can be at ambient temperature, or can be heated or cooled.
Steam, finely dispersed water, other liquid droplets or the like
can be added in the air~if desired to increase its cooling capa-
city. Other gases such as nitrogen, carbon dioxide or the like
may be employed in combination with air or instead of air. A non-
reducing gas or gaseous fluid, i.e., one that does not provide
- 13
10368Z~
a reducing atmosphere at the cones and orifice plate i8 general-
ly preferred. While a reducing gas is not preferred, such gas
(e.g. methane, ethane, or the like) may be employed if desired,
but because of the essential requirement of this concept: a
large cross section of rapidly moving gas to constrain the cones
to their asymtotic-like configuration to prevent flooding,
would require a great deal of expensive gases and not have
any advantages over air. Since the gas is employed for cooling
purposes it i8 preferred to employ gases of temperatures of
about ambient temperature or less ~e.g. about 100F or less).
It should be understood, however, that the benefits of this
invention can also be achieved by warmer gas which may be,
for example, even at 500F, providing the volume of air is
increased accordingly.
For ease of presentation the description herein is
couched in terms of air. It is to be understood, however, that
the description is equally applicable to other gases.
In one method of start-up of the method described
herein, albeit one having a slower start-up, the orifice plate
temperature which i9 about 1000C from the previous shutdown i8
elevated to about the range of devitrification temperature,
between about 1083C and 1105C for E type glass. This will
also cause a thin layer of glass inside and above the orifice
plate to be raised to this temperature. The mass of glass
inside the bushing which has been maintained at a temperature
of about 1150C to 1315C is not affected. When the small
quantity of glass adjacent the plate passes through the orifices,
it will pass therethrough as separated streams without wetting
and without flooding the plate even though the plate may be
constructed of a wettable alloy. This cooler glass is no
longer a pure Newtonian liquid but has some crystalline growth
therein. While the resulting fibers are brittle, if handled
carefully and slowly withdrawn, while increasing the plate
temperature well ¦ ~
~03~8Zl
above the devitrification range and while simultaneously adjus-
ting the air cooling, the small amount of devitrified glas~ can
be quickly and completely rinsed out, at which time the glass can
be handled in the standard fashion.
In somewhat different operation to speed start up,
the temperature of the glass adjacent the plate is increased by
increasing the temperature of the orifice plate itself so that
the glass therefrom beco~es less viscous and under the pressuxe
of the head of molten glass within the bushing quickly begins
to pass through the orifices in the bushing or orifice plate.
Due to the wetting properties of the glass and the close prox-
imity of orifices, the underside of the plate begins to flood.
As soon as the volume of flooded glass is heavy enough to fur-
nish the initial attenuating force, it is necessary to reduce
the flow of the glass through the orifices, otherwise, separation
cannot occur. In one preferred embodiment of this invention,
this flow rate regulation is accomplished through temperature
control of the orifice plate. In yet another preferred embodi-
ment, the current flow to the plate can be kept constant, and
the glass flow through the plate reduced to allow separation to
occur by directing a steady flow of air to the plate thereby re-
ducing the plate temperature. Once separation is achieved, this
air flow can be reduced to allow the plate to heat up and func-
tion as described above.
As the glass drops flow through the orifices and
flood the underside of the orifice plate, it is necessary to re-
duce the temperature of the orifice plate into or at the edge of
the glass devitrification temperature whereby the orifice plate
functions as a molten glass thermic flow valve. This temperature
30 reduction of about 50C to 150C virtually stops the flow of
glass through the orifice and allows for the flooding glass to
flow or he drawn from the underside of the plates into individual
10368Z~
glass fibers. If the glass is slowly withdrawn, separation will
occur with the formation of a cone at each orifice with a fiber
extending from each cone. An alternative to free flow is to
contact the flooding drops with a glass rod or the like and
slowly withdraw the rod from the plate. The heat of the molten
glass causes the coalesced flooding drops to be welded to the
rod and, therefore, the withdrawal of the rod causes the giant
flooding drop or drops to form into individual fibers extending
from the several orifices.
The early withdrawal rate should proceed generally
at about 1/2 inch per second to avoid glass starvation of the
forming fibers and to allow the surface glass to be slowly pulled
into the enlarged main stream of attenuation without accidental
pinch-off. Such a deliberate and slow rate of pull should continue
until the underside of the plate is unflooded and separation is
obtained.
A considerable drag will be experienced as the plate
is be~ng cleaned up by the glass tendency to adhere to the plate.
The tensile strength and self-wetting energy of the glass is
stronger than its plate wetting energy so that the dynamic glass
will pull almost all of the static surface glasq on the plate
into its moving column and the plate will almost completely clean
up leaving only a layer of glass about .001 inch thick. If pul-
ling is carefully and slowly continued without interruption, a
very fine fiber will extend from each hole in the orifice plate
when there is no more surface glass available and when the glass
which is being pulled through each of the orifices becomes the
fibers final and sole source. At this point, it is again neces-
sary to prevent fiber starvation and pinch-off by an increase
in the glass flow rate through the orifices by a slight warming
to the plate. As the warming of the thermic gate proceeds to
permit a renewed but limited flow rate through the
16
1036821
individual orifices, the glass fibers which extend therefrom
can be wound around a very slowly rotating collet. The rotational
speed of the collet and the temperature of the plate which con-
trols the flow therethrough can be simultaneously and gradually
increased while the air cooling (to be discussed) is coordinately
reduced in pressure until a maximum drawing speed at a maximum
temperature is reached.
In increasing the rate of production from the initial
~tart up of the apparatus, at which time the fibers are withdrawn
at about 1/2 inch per second to the desired attenuation rate,
careful regulation and correlation of the temperature of the
orifice plate, velocity of quench air, and the speed of with-
drawal is accomplished. Since glass wets itself more readily
than it does even a wettable orifice plate, as long as the
forming cone under each orifice is maintained in an asymptotic
configuration, the glass will continue to flow and is drawn
through the orifices constrained in this manner to form into
glass fibers as opposed to its tendency to run along the under-
side of the orifice plate and thereby floodin~ the plate. The
molten glass passlng through the oriice i8 continuously sucked
into the fibers and cannot flood. In a simple implementation
of this invention, a microscope with about 7 to 20 diameters
of power can be placed near the underside of the orifice plate
to view these cones while manually controlling the parameters.
Continual viewing of thecones allows an operator carefully to
correlate the temperature and rate of draw increases while
controlling the air velocity visually to maintain the asymptotic
configuration of the fiber forming cones. Of course, after
considerable testing, such correlations should be computer
actuated thereby saving considerable adjustment time and further
increasing the production of the individual stations, however,
an experienced operator can reach full attenuation speed as
- ~7
10361~Z~
quickly as the plate-temperature can stabilize, in about 30
seconds or less. Generally speaking, by properly maintaining
the above described concavity of the forming cones, the atten-
uation rate can be increased to the limits of stress on the
winding or other accumulating equipment. During operation, as
glass passes through an orifice, a stress is provided by the
forces of attenuation which are resisted by the viscosity drag
of the glass through the cone, the base of which is fastened
to the rim of the orifice by surface tension, the wetting
energy of the glass and the partial vacuum inside the cone.
Through this dynamic sucking stress, more glass is pulled through
the orifice than would flow by gravity alone and there is a
continuous flow of glass toward the filament and flooding is
avoided.
As hereinafter noted, to maintain this asymptotic
geometry of the fiber forming cones and therefore maintain
separation of the individually formed fibers, it is necessary
to cool substantially identically each of the fibers and the
fiber forming cones as well as maintain the proper correlation
between the rate of withdrawal, the temperature of the orifice
plate and the flow rate through the individual orifices. In
order uniformly to cool each of the individual fibers and cones,
an air source is disposed below the orifice plate. The distance
of the source from the plate depends upon the area of the ori-
fices, size of the air nozzle or nozzles and the like. The dis-
tance is generally between 1 and 20 inches and with the particular
size nozzle described below is between 2 and 4 inches. Preferably
the upwardly moving air is introduced at a distance of from
about 2 to about 12 inches from the bushing. With larger orifice
areas the source of upwardly moving air will often be at least
about 4 inches from the plate so that the air stream readily
can impact on the entire orifice area.
18
~03~8Zl
The upwardly quenching air flow moves in between
the individual fibers to each of the hundreds or thousands of
cones. While it may appear that a tremendous number of fibers
emanating from the orifices would prevent air travel therethrough,
there may be, however, paradoxically over 40,000 times more air
cross section than glass cross section which is considerably more
open space than occupied space. For example, on a 3 x 10 inch
bushing using a C filament whose cross-sectional area is
2.54 x 10 8 square inches~ 30~000 orifices (0,020 in. dia, on
0.032 in center) can be drilled. This represents 7.6 x 10 4
~quare inches for the entire 30,000 fibers, which move through
30 square inches of open space to leave a vast unopposed open-
ness for the air to move upwardly through the fibers to the form-
ing cones. Despite the small area occupied by the fibers, the
fast moving filaments will entrain the air and begin to function
as an air pump. Within the first fractions of an inch from the
orifices, however, the skin drag of the fibers is unable to
accelerake the skidding air vortices thereby to a speed at which
this entrainment pump becomes effective. But as the fibers are
brought closer together and the air skids faster along the
fiber boundary layers, this pumping effect rapidly increases.
ordinarily, fill-in quenching air is sucked immediately across
the plate and into the first few inches of fiber strands
wherein the glass fiber pump becomes more effective closer to
the plate. Accordingly, it appears as though this pumping
action which begins at once would make it quite difficult to
quench the fiber forming cones. However, as soon as air is
directed upwardly between the fibers, this sucked in air is
stopped and cooling air therefore is able to pass virtually
unopposed upwardly between the fibers through generally quiescent
air to the orifice plates. There is nevertheless sufficient
downward skidding of air in the immediate vicinity of the fiber
19
10368Zl
boundary layers between the bushing and the air nozzle to cause
the rapid upwardly moving air to invert and flow inwardly and
downwardly in the direction of the high speed moving fibers.
This air increases in speed as it assumes an umbrella-like shape
in the cone area whose analogous handle is a rapidly descending
trumpet-shaped tube of air which cascades 360 around the fiber
forming cone, cooling the cone from its plate secured base to
the extended fiber apex. When the ascending turbulent air
reaches the interstices between the orifices, it splits to form
a hexagonal star, the moving points of which flow toward the
area between the fibers while the remainder is perfectly pro-
portioned, providing even 360 cooling of the fiber orming
cones. As this cool air turns downwardly, hugging the convex
shape of the cone as well as hugging and skidding the full fiber
length, it accelerates to a very high speed as it follows the
filament into the high pumping zone. A continuous mixing of
cool ascending air with hot turbulent air in the vortices
caused by the skin effect surrounding the descending fibers
provides a uniform and stable environment over the entire length
of the formed fiber. Through such cooling, the asymptotic
geometry of hundreds or thousands of fiber forming cones can
be continually maintained thereby allowing for a large increase
in fiber production from a relatively very small orifice plate.
The upwardly directed air, in addition to cooling
the surface of the cones and providing air to be drawn down the
fibers, also serves to prevent pockets of stagnant air on the
underside of the bushing which can result in local hot spots
and cause flooding. The upwardly directed bulk air movement
impinges on the underside of the bushings and tests indicate
that a portion of that air moves laterally outwardly in all
directions from the orifice area. The macro-cooling with the
upwardly moving bulk air establishes and maintains cone and
fiber separation. 2 ~
1036821
Diametrically opposed to a conventional bushing with
tips, it has been determined that, at a constant windup speed
and constant plate temperature, more cooling by the air will
provide a larger diameter fiber. Apparently the skin cooling
in the cone creates a pumping action as the fiber is drawn from
the cone. In this regard it should be noted that cooling occurs
by extremely rapid conduction so that the skin of the fiber-
forming cone is cooler than the interior. In conventional
practice with fins, cooling is largely by radiation so that the
interior of the transparent cone tends to be at more nearly the
same temperature as the skin.
In proper operation the cone lengths are stable to
the eye and the visual length of the cone is very short, general-
ly not more than about 2-1/2 times the orifice diameter and, in
any event, generally not longer than about 1/8 inch. In pre-
ferred operation the cone length is not more than about 1-1~2
times the orifice diameter. Many times, the pumping action
caused by the cooled skin of the cone results in the base of the
cone receding part way up the side of the orifice in the bushing.
The glaqs temperature at the tip of the cone will be approx-
imately the annealing temperature of the glass, and generally
will be from about 1400F (760C~ to about 1700F (927C).
The angle of air flow will vary somewhat depending
on the number of rows and the density of orifices. Generally,
process control is best maintained by positioning the air as
vertical as possible consistent with the needs to draw fibers.
While with extremely close control, the air may be directed
upwardly at an angle of about 40 from horizontal, tests with
a 17 row orifice plate and a 10 row orifice plate have indicated
that for realistic control in commercial operation, the angle
of the air should be at least about 45 or 46 degrees from the
horizontal, but preferably at least about 60 degrees from the
2~
10368Z~
horizontal. With only a few rows the angles may be somewhat
less critical. The term horizontal is employed here to mean
the plane in which the orifice plate generally lies.
Any mechanical arrangement that provides a bulk flow
of air (i.e., a generally single upwardly moving air column at
the cone and plate area~ that impinges on the orifice plate
is satisfactory for this invention. Multiple nozzles or a
nozzle with a slit can be employed. Deflector plates which
deflect air to an upward path can also be employed. While
introduction of the upwardly moving air from one side of the
orifice plate is entirely satisfactory and is preferred, the
air can, if desired, be introduced from two or more sides of
the bushing. The cross-sectional size of the air stream at the
orifice plate should be at least as large as the orifice area
in the orifice plate. The fibers can be pulled somewhat off
to one side to accommodate the mechanical arrangement for
introducing the air. The same benefit can be obtained by pull-
ing the fibers vertically and tilting the bushin~ slightly.
The air pressures to be employed may readily be
determined by the routineer and may vary from 2 inches of water
to 5 psig or 10 psig or more depending on nozzle size, nozzle
location and the li~e. Pressures from about 1 to about 5 psig
are generally preferred, particularly for bushing of 10 rows
or more. Generally the linear velocity of the air leaving the
nozzle will be at least about 100 feet per second and preferably
at least about 200 feet per second. Air velocities on the order
of 400 feet per second and higher are readily employed in this
invention. The velocity or pressure chosen, as noted above,
will depend, in part, on the particular arrangement chosen.
In any event the air flow should be sufficient to cool the cones
and provide stable separated cones, to impinge on the plate
essentially to eliminate stagnant air adjacent the plate and to
22
103682~
provide a source of gas sucked downwardly by the fibers. It
is apparent that cooling should not be so pronounced that fi-
ber production is materially adversely affected.
While the above represents the preferred embodiment
of cone stabilization~ another method of in-mass cooling is pro-
vided by a series of thin curtains of cool air which sweep across
orifice plate in rapid succession. These curtains should be
aimed at an angle of 46 to 9C~ to the plate surface to sweep
in a broom-like fashion removing the hot stagnant air from
the plate. By controlling the rate and frequency of the sweep
and the velocity of the air, an average ideal temperature can
be maintained across the fibers and fiber forming cones. These
curtains of quenching air can be created by an air nozzle hav-
ing one or more orifice slits therein, which nozzle is continual-
ly rotated at 90 to the fiber axis to provide the described
broom effect of these curtains of air.
Other variations in cooling such as the utilization
of a staccato series of controlled annular vortices moving onto
and generally normal to the face ~f the bushing can also be
lncorporated. The 510w moving donuts of air with high internal
angular momentum would continuously exchange the heated air from
the plate, sweeping it into its annular vortex to scrub the pl-
ate surface while growing in size continuously to replace stag-
nant hot air. If these annular vortices of air are repeated at
rapid intervals, the effect is to maintain an average desirable
temperature over the length of formed fibers including the vital
forming cones. Similarly, spiraling air currents could be
employed whose vortices rotate generally in a plane with the
plate similar to that produced by a fan blade. These spiraling
cool vortices act to sweep away the hotter s~agnant air remain-
ing on the surface of the bushing. In each of these systems, the
air is directed substantially parallel and in an opposite
23
10368Zl.
direction to the motion of the f~bers so that the air is able
to pass generally unopposed between the fibers and to utilize
a substantial pumping effect created by the formed fibers. Early
pumping created by the rapidly moving fibers is easily over-
whelmed and throu~h the vast open spaces cool air reaches each of
the forming cones rigidly to maintain its re~uired configuration.
The close orifice spacing and the stability of the
cones can result in self-correction of localized flooding, should
such flooding occur during operation, If a fiber breaks and the
orifice floods to an adjacent fiber, that fiber will exert an
increasing amount of attenuating force on the flooded glass to
reinstitute cone and fiber formation from the flooded orifice.
If necessary, localized cooling air as known in the art, for
example, from a hand air lance may be applied to the multiple
coalesced fibers to correct the flooding and reinstitute nor-
mal operation.
A slight instability may appear in the cones along
the periphery of the orifice area. This occurs because the plate
and glass are cooler due to heat losses to the exposed edges of
the bushing, Stability can be improved providing the peripheral
orifices are made slightly larger (for example, from about 0.001
to about 0.003 inches in diameter larger) than the interior
orifices. Such adjustment will provide a more stable operation
without materially affecting uniformity of fiber size. Since
the volume of glass, not just its skin, flowing through the
peripheral orifices is cooler, glass will flow through the
orifice less readily so that use of a slightly larger orifice
will compensate for the reduced abi~ity of the glass to flow.
In order to insure that molten glass from an orifice
will controllably flood if the fiber breaks, one embodiment
of this invention contemplates the provision of capillary grooves
between orifices. These capillary grooves will cause the plate
2~
1036t~21
to act as though it had a controlled but perfect wettability.
Since only a small volume of glass from the oozing orifice will
first contact a neighbor fiber, the increase of acceleration
load will be gradual, as the whole fiber pulls more glass out
of the groove its own cross section enlarges and become stronger
until a single larger fiber is fed by two orifices. It is
described elsewhere how to separate such single fibers into
two ~ibers. In this embodiment, each orifice ~s joined to at
least two adjacent orifices so that if a fiber breaks, controlled
flowing of the ~lass to the adjacent orifice is virtually assured.
The grooves may be as wide as the orifices but preferably about
one-third of the diameter of the orifice and may have a depth
of around one-half the thickness of the bushing plate. Since
the outer orifices may tend to flood more often than interior
orifices, only outer orifices may be provided with grooves.
Viewed in the context of start-up and self-correction of flood-
ing, a bushing made of a highly wettable alloy,which more easily
floods, is preferable to a bushing made of a so-called non-
wettable alloy. All alloys, of course, will flood if the temp-
erature of the glass is sufficiently high to cause the glassto be quite fluid.
The cooled fibers are coated with a dressing fluid
or sizing by contacting the fibers with an applicator roll or
the like, and the fibers then may be wound up on a package. The
drawing or windup speeds of the fibers may vary widely from,
for example, of about 100 ft. per minute up to about 13,000 ft.
per minute or more. Determination of wind-up speeds or atten-
uation force for any given set of conditions is within the skill
of the art. Windup speeds of over about S000 feet per minute
are employed in conventional processes and may readily be employ-
ed here. Low draw off speeds may permit matching of fiber prod-
uction with the rate of fiber usage in the manufacture of a
103~8Z~
final product so that the fiber or strand could be employed
directly in the final production~ In view of the orifice den-
sity such procedures would still be within the range of practical
production. Dressing fluids, dressing fluid applicators and
windup apparatus are conventional in the art and will not fur-
ther be described here.
Good quality glass fibers are manufactured by the
method as described. As a threshold matter, the extremely rapid
quench of the molten glass below the orifices results in less
0 1058 of volatiles from the glass so that the glass composition
of the fiber will closely conform to the glass composition in
the glass bath. Moreover, this invention permits the production
of tempered fibers. With a super quench due to the inwardly
flowing air, the surface is cooled more rapidly than the inter-
ior glass and the temperature gradient is greater above the an-
nealing temperature than below. As a result, the surface of the
final fiber is under compression. In a conventional process em-
ploying long tips quite the reverse occurs. The temperature grad-
ient is greater below the annealing temperature than above. In
conventional processes, snap-out sometimes occurs wherein the
fibers at temperatures below the annealing temperature break
substantially at the same time. Snap-out has been attributed
to circumferential and length-wise temporary tensional forces.
As noted earlier, snap-out has not been observed in the method
of this invention, and logically so.
While a conventional glass furnace and auxiliary
equipment readily can be employed in the practice of this in-
vention a particular apparatus wherein the head of glass can be
maintained independent of the level of the glass bath is shown
in the attached drawings.
Figure 1 is a schematic view of the glass fiber
filament production equipment.
~6
1036t~Z:l
Figure 2 is an enlarged sectional view of the bus-
hing and orifice plate illustrated in Figure 1.
Figure 3 is an enlarged sectional view taken along
Line 3-3 of Figure 1 showing the bushing and orifice plate.
Referring now in detail to the drawings, an appara-
tus 10 for producing glass fibers 12 is illustrated in Figure 1.
As shown therein, a head of molten glass 14 is maintained with-
in a bushing 16. The bushing is comprised of a tubular reser-
voir portion 18 which can be square, rectangular or cylindrical
in ~hape and an enlarged base portion 20 which terminates at the
lower end thereof in a flat orifice plate 22. The orifice plate
has a plurality of tightly spaced plain holes 24 therein. As
an example, in a 2,000 hole orifice plate 2.7 inches square,
the holes or orifices are .04 inches in diameter and spaced
.06 inches from center line to center line. Typically, the
lengths of the holes in the orifice plate vary from .03 inches
to .06 inches and T-shaped reinforcing bars 26 or, alternative-
ly, a honeycomb structure (not shown) may be provided on the ori-
fice plate to add strength thereto and to prevent plate sag. It
is also entirely feasible to employ a generally flat orifice
plate without any reinforcing.
A valve 28 which communicates the interior of the
bushing with a liquid glass supply 30 can be disposed atop
bushing 16 to permit a change in fiber diameter, with high heads
tending to provide somewhat larger filaments. By opening
and closing valve 28, glass is allowed to flow from the supply
30 into the reservoir portion of the bushing 16 thereby main-
taining the desired head of the glass within the bushing. Of
course, the fiber withdrawal rate, cooling air and plate temper-
ature also are adjusted to obtain a stable fiber~ To facilitatethe regulation of the glass head within the bushing, an elongated
platinum tube 32 extends upwardly from the interior of the
27
103Gt~2~
bushing, through valve 28 to a sonic depth indicator 34. The
sonic depth indicator is coupled with a valve regulator 36
which reacts to signals therefrom to move the valve 28 upwardly
or downwardly on the bushing thereby opening and closing the
valve and allowing the liquid glass to pass thereby.
In the embodiment illustrated in Figure l, the valve
28 is in threaded contact with regulator 36 by means of a
threaded bar 37. Rotating the bar 37 causes the valve to move
vertically with respect to valve seat 39 thereby regulating
the flow of glass into the bushing 16. In this manner, a desired
head o glass is continually maintained within the bushing as
the glass fibers are drawn through the orifices 24 in the
orifice plate 22.
The majority of applications will require no head
control, therefore an envelope geometry of a bushing may be
employed that is a duplicate of a conventional configuration,
one that can exactly fit into a standard forehearth position.
Because this geometry is well known in the art, further des-
cription is redundant.
As shown in Figure 1, a platinum bus bar 38 commun-
icates with an electrical source of about 3 volts and l,000 amps
with the orifice plate whereby the temperature of the plate can
be increased. A water cooled copper bus bar 40 is provided on
the platinum bus bar 38 to make the electrical contact between
the platinum bus bar 38 and the electrical source and reduce
the necessary length of the platinum bus bar thereby reducing
costs. The copper bus bar 40 is water cooled to reduce the
temperature at the point of contact between the two bus bars
and thereby preserve the copper and is spaced a minimum distance
of about 1.5 inches from the orifice plate 22 so as to have a
minimal effect on the temperature of the plate while limiting
the length of the platinum bus bar. It can be seen that by
28
~0368Z~
controlling the electrical flow through a regulator 41, the
temperature of the orifice plate can be carefully regulated. As
an alternative to the above described plate heating method, it
should be noted that the temperature of the orifice plate can
also be controlled through induction heating without the need
for the aforesaid bus bars. In general, orifice plate temp-
eratures will range from about 2050F (1120C) to about 2300F
(1260C) during operation.
Upwardly directed air 49 flows thxougn nozzle 45
disposed on the end of supply hose 47, through connection 44.
A row of nozzleq can, of course, be employed to provide a sub- .
stantially single column of air that impinges on the orifice
plate and cools the cones to maintain them in a stable config-
uration. The attenuation of the fibers is effected by rotating
drum 42.
In addition to the aforementioned temperature re-
gulation controls of the orifice plate, fibers and cones, ad-
ditional insulation and heating is provided to prevent tempera-
ture loss from the system which would necessarily effect the
viscosity of the molten glass and consequently, the forming of
the glass fibers. As shown in Figures 1 and 2, the base portion
cf the bushing is surrounded by a ceramic support 46 which, in
addition to providing support for the bushing, further insulates
the exterior position thereof which is adjacent the orifice plate.
The ceramic support 46 and tubular reservoir portion 18 of the
bushing are surrounded by a layer of insulation material 48
which additionally extends between the platinum copper bus bars
and the supply of li~uid glass. The insulation material 48
terminates short of the walls of the bushing to provide an
annular area 50 about the reservoir portion of the bushing in
which a heating coil 52 is disposed to provide compensation
for heat loss due to conduction through the insulation. The
29
1036~Z~
heating coil is connected to a thermocouple 53 to control the
current therethrough and thereby regulate the compensating heat
generated thereby. A second layer of insulation material 54
is disposed over and spaced from the liquid glass supply 30
thereby providing an insulation gap 56, as shown in Figure 1.
Of course, the above represents merely an exemplary embodiment
of an insulation and supplementary heating configurations and
other varying configurations could be employed to adequately
maintain the desired temperatures. ~or example, to compensate
for heat loqs from the bushing due to conduction, resistance
heating could be employed using the bushing as an element of
an isolated circuit. In such an embodiment, a 400 cycle gen-
erator has been found to be an excellent power source.
Lastly, as shown in Figure 1, a sizer 58 is provided
to size the individual fibers with a standard lubricant type
material such as starch to reduce abrasion between adjacent
fibers and to assist resin wetting for future laminating. A
roll sizer may al o be employed to reduce consumption of sizing.
The following examples are included for illustrative
purposes only and are not intended to limit the scope of the
invention.
EXAMPLE I
A conventional tipless bushing was employed in this
example made from a 0.040 inch thick platinum alloy (80%
platinum - 20~ rhodium) flat sheet. Orifices 0.052 inches in
diameter were drilled in the flat plate in a hexagonal pattern
on 0.070 in. centers. The rectangular orifice area in the
bushing was approximately 1.25 in. wide and approximately 2.85
in. long with alternating 17 and 18 orifice rows. Each row
contained about 46 orifices.
Type E ~lass was melted in a conventional glass fur-
nace to provide about a 10 in. deep glass bath having a temp-
erature of approximately 2300F and glass fibers were manufac-
1036821
tured employing the above plate, The plate was equipped with aheater and maintained a temperature of about 2100F, A stan-
dard sizing was applied by a roll to the fibers which were wound
at a speed of about 3,000 ft. per minute.
In order to maintain fiber separation, air was dir-
ected upwardly from the long side of the orifice area at an
angle of approximately 15 degrees from vertical through six
1/4in, diameter nozzles arranged in a row on one side of the
orifice area about 5 inches below the orifice plate. Air pres-
~ure within the range of 3-5 psig was employed.
Fibers were successfully drawn in stable operation
and filament separation was maintained.
During usage the orifice plate exhibited some war-
page and developed both concave and convex areas. The warpage
of the orifice plate did not hamper fiber manufacture.
EXAMPLE II
In order to illustrate the benefits of this inven~
tion, the performance of the orifice of Example I is ccmpared to
the performance of two conventional tip bushings, (designated A
and B) employing fin coolers, The overall bushing face areas
were the same in each case but the orifice section of the
bushing of Example I covered less than 1/4 of the entire face
of the bushing. In each case Type E glass was used.
31
10368Z:~ Bushing
Ex. I A B
No. Holes 804 390 390
Hole Dia (in.) .052 .078 .090
Throughput (lb/hr) 65.0 39.0 51.6
Area of Each Hole (in2 x 10 4) 21.23 47.78 63.62
Hole Area Ratio 1 2.25 3
Orifice Plate Area (in2) 3.56 15.62 15.62
Throughput ~lb.in2/hr) 18.3 2.5 3.3
10 Holes per inch2 of Bushing 226 25 25
The above demonstrates that this invention provides more through-
put per unit of bushing area in the bushing as compared to con-
ventional practice. This invention also provides more through-
put per hole area as compared to conventional practice. More
clearly to envision the magnitude of difference, if an equal
size of orifice section were used, Example I bushing would have
produced 3527 fibers with a throughput of 285 pounds per hour.
EXAMPLE III
The bu~hing employed in this example was made from
20 a 0.060 inch thick platinum alloy ~80% platinum - 20% rhodium)
flat sheet. One thousand six hundred and seventy orifices were
drilled in the flat plate in a hexagonal pattern on 0.070 inch
centers. The rectangular orifice area in the bushing wax approx-
imately 1-1/8 inch wide and approx imately 6-1/2 inches long.
The peripheral orifices were 0.049 inches in diameter and the
remaining orifices were 0.047 inches in diameter.
Type E glass was melted in a conventional glass fur-
nace to provide a~out a 10 inch deep glass bath having a tem-
perature of approximately 2300F and glass fibers were manufac-
30 tured employing the above plate. The plate was e~uipped with a
heater and maintained a temperature of about 2240F. A standard
sizing was applied by a roll to the fibers which were wound at a
32
~036821
speed of about 2,500 feet per minute.
In order to maintain fiber separation, air was
directed upwardly from the long side of the orifice area at an
angle of approximately 20 degrees from vertical through twelve
1/4 inch diameter nozzles arranged in a row on one side of the
orifice area about 5 inches below the orifice plate. Air pres-
sure within the range of 3-5 psig was employed.
Fibers were successfully drawn in stable opera-
tion and filament separation was maintained. The peripheral
cones were quite stable.
Changes and modification may be made in carrying
out the present invention without departing from the spirit and
scope thereof. Insofar as these changes and modiications are
within the purview of the appended claims, they are to be con-
sidered as part of the invention.
33
