Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relates to a method and apparatus
for forming fibers from molten mineral material such as
glass and, in particular, to a rotary fiberizing apparatus
and method for producing a strand or rope comprising contin-
uous or very long fibers of 7 microns diameter or less without
using the conventional external hot gas attenuating technique.
The fiberization of molten mineral material such as
glass can be accomplished by several known methods. One
conventional method is rotary fiberi~ation. At least as
early as 1933 it was known to produce glass fibers by centri-
fugally forcing molten glass through perforations in the `
periphery of a rapidly rotating spinner or rotor followed by
ripping the fibers apart by an annular air current traveling
transverse to the emerging fibers, as evidenced by German
Patent l~o. 571,807. It has also been known, at least since
19~0t to make glass fibers purely by the action o~ a rotary
spinner, as shown by U.S. Patent No. ~,192,944. After leaving
the perforations in the periphery of the rotor, the fibers
were attenuated somewhat due to their engagement with the
relatively quiescent air surrounding the rotor, but, as repor-
ted in U.S. Patent No. 2,431,205, the degree of ~ttenuation
caused by this effect is very limited. To increase the
degree of attenuation and thus reduce the fiber diameter,
this latter patent proposed to anchor the streams or fibers
at a point removed fro~ the rotor. In U.S. Patent No.
2,497,369 it wais proposed to heat certrifugally formed primary ~ -
fibers externally of the rotor to further attenuate the fibers.
None of the above mentioned references revealed
the diameter of the glass fibers produced by the disclosed
processes, but later reEerences evidenced tllat the ~iber
diameter was at least 5 microns greater than was possible
rw/
~0'7~
using the more costly flame attenuation fiberizing
technique, e.g., see U.S. Patent Nos. 2,609,566 and Re
24,708. The former patent proposed to correct ~his defi-
ciency by subjecting the centriugally drawn out primary
fibers to further attenuation by the action of a transverse
blast of hot gas. This gas had to have a temperature and
a velocity sufficient to soften and attenuate the primary
fibers. The gas blast was provided by the combustion of
substantial quantities of fuel to produce a gaseous stream
having a velocity of at least 1,200 feet per second and a
temperature of at least 3,000F.
As disclosed in U.S. Patent Nos. 3,040,377 and
3,0~0,736, it is also known to make continuous glass fibers
by rotary fiberization, but these processes also included
hot gas attenuation externally of the rotor.
From the issuance of Patent No. 2,609,566 in
; 1952 and until the present time a large number of advance-
ments ha~e been made in the rotary fiberization field, but
none have accomplished the manufacture of glass fibers hav-
ing an average diameter below 7 microns, and particularly
below 5 microns, without the necessity of also using a ~ -
relatively high temperature gaseous blas~ to attenuate the
primary fibers. It would be highly desirable to eliminate
the hot gas blast or equivalent high energy usage attenuation
step without sacrificing the desirably small fiber diameter
it produces, particularly in view of the energy crisis and
the resultant rapid increase in the prices of all fuels.
For example, in a typical rotary fiberization process as
much as about 7,000 to 8,000 cubic feet of natural gas, or
an equivalent amount of other fuel, is required for external
jet blast attenuation for every ton of glass fiber produced. ~- ;
- 2 - ;
rw/
7~ ~L8
In a typical rotary fiberization process making 4-7
micron fibers by forcing the glass through 24 mil ori~ices
in the rotor and attenuating the primary fibers with such
a hot gaseous blast, the fiber diameter jumps to 10 to
15 microns when the burners providing the heat for the -
hot gaseous blast are turned off.
It has also been suggestea in U.S. Patent No.
3,511,306 to make the orifices in the rotor as small as
10 mils to make staple fiber having a diameter of 4 to
1~ 10 microns, but it was not recognized that, by carefully
controlling the relationship between the process vari-
ables, the hot blast attenuation could be eliminated.
This reference, typical of the prior art, included hot
gas blast attenuation as one of the process steps.
While some of the above prior art processes pro-
duce fibers ha~ing diameters of 7 microns or less, these
processes present several problems. The larye volume of
fuel such as natural gas utilized by such processes is
not always readily available and acute shortages are fore-
cast. ConsequPntly, production can be interrupted or
slowed by the unavailability of sufficient natural gas
~or the process and other gaseous fuels such as propane or -~
butane increase the operating costs substantially.
It is desirable to eliminate the additional
expense of providing the blast of hot gases for attenu-
ation plus the maintenance and related problems associated
with the burners used in the attenuating apparatus. Also,
every fuel burning step produces pollutants that must be
dealt with causing an additional operating expense.
Finally, the additional heat added by the attenuating
burners must be absorbed in the collection chamber prior
to winding the strand or rope into a packaye.
~ 3
rw/
According to the present invention, there is
provided a method of producing continuous or long fibers
having an average diameter of less than about 7 microns
from molten glass material, the method including the
steps of introducing the molten material at a rate of
hundreds of pounds per hour into a rotating rotor internal
of a peripheral wall of the rotor, the peripheral wall
containing orifices having a diameter no greater than
about 18 mils. The molten material is passed through the
orifices, and the relationship of design and operational
parameters, consisting essentially of density, viscosity
and rate of flow through the rotor of the molten material,
peripheral wall thickness, interior diameter, rotational
speed of the rotor, number and diameter of orifices in the
; rotor, head of molten material on the in-terior surface of
the peripheral wall of the rotor are so controlled as to
form the fibers having an average diameter of no more than
about 7 microns without using additional attenuating means
externally of the rotor.
It is an object of the invention to produce
continuous fibers having diameters of 7 microns or less
; solely by passing molten material through orifices of a
rotor into a relatively cool environment, thus eliminating
the hot gas blast used in the prior art and the fuel usage
associated therewith.
Applicants have discovered that it is possible
to make continuous glass fibers having an average diameter
of 7 microns or less, preferably 5 microns or less, and
most preferably 4 microns or less by passing molten mineral
material such as glass through orifices in a peripheral
wall of a rotor and into a relatively cool environment.
Rotors having a large number of orifices, each having an
_
sb/)i)
.: . .. . . .. ... . . . . .
~L~7~
initial diameter of less than about 18 mils, are able
to form primary fibers having diameters of less than 7
microns, e.g., 3 to 5 microns, if the relationship
between the process variables are controlled in accordance
with particular
B 4a -
sb/ ' ;~
~.~7~
1 relationships. It is even possible to produce sub-micron
fibers using rotors whose orifice diameters are 2 mils
or less.
With this arrangement, primary continuous
fibers issue from the orifices, are twisted into a
rope or strand by the spinning action of the rotor,
and the rope or strand is pulled downward and wound
into a package or further processed. Because of the
relatively low temperature of the ambient air sur-
rounding the rotor, at least the surfaces of the
glass fibers are quickly cooled below the softening
point of the glass. The continuous fibers are quickly
cooled by the relatively cool environment surrounding
the rotor. Unlike the prior art processes, the con-
tinuous fibers are not heated, or their rate of cooling
reduced, externally of the rotor to cause attenuation
- in the present process.
The continuous fibers formed by the process
and apparatus of the present invention have a narrower
diameter distribution than the fibers produced by the
prior art processes using hot gas blast attenuation~
For the purpose of this application, the
term "average diameter" when referring to the fiber
diameter is used in the sense of the conventional
arithmetic or mean diameter obtained by averaging
results of a microscopic determination.
Detc~iled Description of The Invention
The drawing illustrates the preferred apparatus
of the present invention. The apparatus is supported
on conventional framework, but to better illustrate the
apparatus the supporting framework has been omitted
rom the drawing.
~' ~ - ,:
'
., ~ . ~. . . .
The apparatus comprises a drive shaft 32
which carries a spinner or rotor 34. The drive shaft
is supported by, and rotatably mounted within, a tubular
housing 36 by means of a pair of conventional bearing
assemblies that are mounted in the tubular housing 36
in a conventional manner. The upper portion of the
drive shaft 32 is provided with a sheave 40. The sheave
is connected to a variable speed motor 42 or other con-
ventional drive means by belt drive 44. Thus the
rotation of the spinner 34 is affected by the motor 42
ich drives the drive shaft 32.
- The rotor 34 comprises a bottom wall 46, a
peripheral wall ~7 containing orifices 48, and a re-
inforcing upper wall ring 50 extending inwardly from
the upper edge of the peripheral wall 47. The rotor is
typically 12, 15, 18, 24 or more inches in interior
diameter and has a centrally located aperture through
which a threaded portion of the drive shaft 32 passes.
Smaller diameter rotors are operable, but are not
de~irable because the output per unLt of height of the
peripheral wall is undesirably low. A nut 52 on the
threaded portion of the drive shaft plants the bottom
wall of the rotor between itself and a shoulder on the
drive shaft in a conventional manner. The bottom wall
46 forms the floor of the rotor. The lower edge portion
of the peripheral wall 47 can be welded or otherwise
affixed to the periphery of the bottom wall 46 and the
upper edge portion of the peripheral wall 47 can be
welded or otherwise secured to the upper reinforcing
wall 50 which lends needed strength to the rotor when it
is rotating at high speed at temperatures which tend -to
~, ' .
rw/ _ 6 _ -
. . . . . . . . . .
~L~7~ ,y
weaken the metal of the peripheral wall. The rotors
ean be a one piece casting made by known casting techniques,
such as investment casting, and this is preferred.
The peripheral wall 4~ of the rotor.is pro- -
vided with a plurality of orifices 48 with the longitu-
dinal axis of the orifices extending radially through
the peripheral wall 47. In order to form continuous
fibers having an average diameter of 3 to 5 microns by
passing glass through the orifices at a rate of at
least 600 lbs. per hr. and into a relatively cool
environment, it is preferred to have at least 40,000
to 100,000 orifices in the peripheral wall with each
orifice having an initial diameter ranging up to about
18 mils, preferably 12 mils, and most preferably up to
about 10 mils or less. The spacing between orifices
is typically about 36 mils, plus or minus about 10 mils.
Hot gasses from the burners 28, usually three
such burners are sufficient, are directed onto the
interior of the peripheral wall 47 of the rotor to
maintain the peripheral wall at temperatures sufficient
to maintain the glass at the proper viscosity to produce
the desired fiber diameter in accordance with the present
invention. For typical glass compositions presently being
used, the interior peripharal wall is usually maintained
at a temperature in the range of about 1700F. to 2100F~ ;
A combustible mixture is supplied to the burners 28 by
conventional means.
The molten glass feed 26 flows rom a suitable
source (not shown~ such as a forehearth, or oth~r con-
rw/
- .
. ~
~7~
ventional glass melting and/or refining means, e.g. an
electric furnace. The molten glass feed 26 enters the rotor
at a point offset from its center. Due to the centrifugal
forces generated by the rotation of the rotor, the molten
glass flows toward the peripheral wall of the rotor and up
the interior surface of the peripheral wall. When a sufficient
head "h" has been built up on the interior wall of the rotor,
and when the other operational and design parameters are
properly controlled, the molten glass is forced through the
orifices by the centrifugal force of the rotor to form contin-
uous fibers having an average diameter of 7 microns or less.
The magnitude "h" can be controlled by controlling the rate of
molten glass feed 26, the interior temperature of the rotor,
and the rotational speed of the rotor.
A guard ring 54 surrounds the rotor for safety
purposes and also to eliminate any disturbances in the fiber
flow that might be caused by air currents in the plant.
The temperature of the environment within the guard
member 54 is not critical so long as the temperature is below
that that would be required to soften and thus attenuate the
primary fibers. Normally some plant air is inherently drawn
into the opening between guard 54 and the peripheral wall of
the rotor 47 by the downward movement of the fibers.
Any heat c-ontained in the environment within ring
54 because of the continuous flow of hot fibers therethrough,
is purely coincidental because the advantage of the present
invention is thal: it is not necessary to heat this~environ-
ment to a temperature sufficient to
jrr:~
.
.
:' '. ~ : .
1 promote and permit attenuation of the fibers. Its
sole function is to cool the continuous or long fibers.
In operation, the burners 28 heat both the
bottom wall 46 and the interior of the peripheral wall
4% of the rotor to a temperature sufficient to main-
tain the molten glass within the rotor 34 at the proper
viscosity to produce fibers having the desired dia~
meter. While many glass compositions conventionally
used to form glass fibers are suitable for use in the
present invention, it is preferred to use a glass
composition having a relatively low temperature
~ softening point and having suitable fiberizing visco-
; sities at relatively low temperatures. Such a glass
composition permits lower temperature rotor operation
which extends the life of the rotor. The rotor life
is dependent upon operating temperature, thus it is
desirable to operate the rotor at as low as temperature
as possible.
The continuous or long glass fibers 56 are
collected at a point 58 located below the rotor 34
and are twisted into a rope or strand 60 by the spin-
ning of the rotor. m e rope or strand is removed and
collected or processed in conventional ways, e.g.,
see U.S. Patent No. 3,040,377.
The strand or rope product of the present
in~ention has many uses, e.g., it can be used as a g
caulking or sealing material, can be used in rein-
forcing rovings, and can be chopped into lengths to
make fiber mat or air blown insulation.
Cr:itical to the manufacture of continuous
or very long fibers having diameters of less than 7 ;
microns by rotary fiberization without using hot gas
~--
... . . .
;~r~
1 blast attenuation is the maintenance of particular
relationships between the process design and opera-
tional variables. These variables are glass viscosity,
glass density, total flow of molten glass to and from
the rotor, orifice diameter, rotor speed (RPM), thickness
of the glass layer or head "h" on the interior of the
peripheral wall of the rotor, thickness of the peripheral
wall of the rotor (orifice length), interior diameter
of the rotor, and the total number of the orifices in
the peripheral wall of the rotor. Some of these variables
are design parameters, e.g., orifice diameter, number
of orifices, and rotor diameter. Other of the variables
such as glass viscosity, glass density, rotor speed,
and total flow rate of molten glass in the form of
fibers from the rotor are operational parameters.
Because of the erosion caused by the molten
- glass flowing through the orifices, the orifice dia-
meter increases during the life of the rotor. To
compensate for this change and to maintain the dia-
meter of the fibers within the desired range, it
becomes necessary during at least a portion of the
rotor life to effectively decrease the height of the -
peripheral wall of the rotor. Techniques for achieving
this result will be described in detail later in the
specification.
The particular relationships critical to the
formation of small diameter primary fibers of no more
than 7 microns are represented by the following three
formulas:
(1) do = 2 / F
~ ~ pDfN
. ,~,,, ~ .
.
r~fphl 1/2
(2) do = .25 L - ~ d2
(3) h = 64 vFl
7r 3p2Df 2d~N --
Where do = the average diameter of the fiber product;
= 3.14;
p = glass density at room temperature
v = glass viscosity at operating temperature of
the rotor;
F = total glass flow through the rotor per unit
of time;
1 = thickness of the peripheral wall of the rotor;
D = interior diameter of the rotor;
- f = rotor speed;
d = diametar of the orifices; ;~
h = glass head on the wall of the rotor; and
N = ~otal number of orifices in the rotor.
; In determining the design and operational parameters
necessary to produce primary fibers having the desired
- diameter without hot gas blast attenuation the following
procedure is used.
First, a suitable glass composition is selected for
use in the process. A viscosity versus temperature curve
and the glass density for this glass are determined using
well know techniques. Next, working with Formula (1) above,
values for various parameters are selected on the basis
of the results desired and the desired operating conditions.
For example, the desired diameter of the primary fibers,
do, is selected. The glass density is known. A suitable
rotor speed, f, is selected, the rate of primary fiber
production, E', is selected, and finally the diameter of the
rotor D, is selected. ~aving selected these parameters,
'
sb/ o
~Q'7'~
Formula (1) above is then solved to determine the total
number of holes or orifices, N, needed in the peripheral
wall of the rotor. At this point, if the total number
of holes, N, is
:
L' ~
lla - ~:
sb/~
~o~
e~cessive to permit adequate spacin~ between orifices it will
be necessary to go back and select another set of parameters,
differing in at least one respect from the initial set select-
ed. It will be readily apparent to one skilled in the art,
having the benefit of the disclosure of Formula ~1), how to
modify the selection of the parameters to produce a smaller
N value.
Once a suitable N value has been determined, a rotor
operating temperature is selected and the corresponding vis-
cosity of the glass at that temperature is taken from theviscosity versus temperature curve. Then using Formula ~3)
above, and after selecting a peripheral wall thickness which
typically should fall between 50 and 250 mils, and selecting
an "h" value which typically should fall between 1/32" and 1~2"
Formula (3) is solved to determine the orifice diameter, d.
For current rotor capabilities a peripheral wall thickness of
about 124 mils and an "h" value of about 1/8 inch ~ 1/16 inch
are preferred. This diameter should be less than 18 mils,
preferably within the range of about 6 to 13 mils, and most
preferably about 8 to 12 mils.
- As will be apparent to one skilled in the art
from the above relationshlps there are several combinations
of variables which will produce the desired primary fiber
diameter. This feature offers flexibility to select specific
values for those parameters which are the most critical to
economical fiberization and to adjust the other parameters
accordingly to produce the desired fiber diameter.
The following examples illustrate two embodiments
utilizing the method and apparatus of the present invention.
The first embod:iment represents the preferred mode of oper_
ation and the second example represents one of numerous ~lternative
embodiments that can be practiced.
- 12 _
jrr:~
.
~)7'~
EX~PLE 1
Three to five micron diameter fiber was produced
using the apparatus illustrated in the drawing. The apparatus
included an 18" diameter rotor having a peripheral wall height
of 1 1/4" and a peripheral wall thickness of about 125 mils.
The rotor contained 50,000 orifices, each having an average
diameter of about 10 mils. The initial rotor speed was set
at 2200-2300 RPM and the molten glass feed was adjusted to
1000 lbs/hr, which was sufficient to produce an h value
nominally of 1/8 inch and which varied between 1/16 and 3/16
inch. The burners heating the interior of the rotor were
- adjusted to produce an initial rotor interior temperature of
about 1850-1900F.
The glass composition used in this example contain-
ed on an oxide weight basis, 55.1% silica, 17.1~ soda, 13%
lime, 9.3% B203, 3.5~ alumina, .9% potash, .6% magnesia,
.1% iron oxide and .1% sulphur trioxide with the remainder
being made up of traces of other oxide impurities. ~his
glass has a glass density of 2.G gm/cc, a softening point
of 1217F, and a viscosity at 1850-1900F of about 500-325
poise respectively and the rotor was made of an alloy
typically containing about 0.28% carbon, 27.8% chromium,
2.5% nickel, 5.8% molybdenum, 1.8% iron,and the balance ;
cobalt, on a weight basis.
Operating under these design and operational
parameters this apparatus and process produced about
. ' :'
- 13 - ~
. ' , .
jrr~ <-- ~
1 1000 lbs. per hour of fi~er strand with the individual
fibers having an average diameter in the range of 3-5
microns.
EXAMPLE 2
Using the same glass composition and rotor
material as described in Example 1, a 15" diameter rotor
having a 2" high peripheral wall 125 mils thick and con-
taining 50,000 orifices of 10 mil diameter produced
essentially the same product and at essentially the same
rate as the apparatus and process of Example 1. It was
necessary to increase the initial rotor speed to a value
in the range of about 2800-3000 RPM but the rotor
interior temperature, h value, glass density, and vis-
cosity and molten glass flow rate were at the same
values used in Example 1.
In selecting the rotor diameter, the rotor
peripheral wall thickness, and the materials to be used
in making the rotor for use in the present invention
several factors must be considered. First, as evidenced
from Formulas (1) and ~3) above, the rotor diameter can be
adjusted to allow adjustment in other operational
parameters. Second, as the rotor diameter is increased
the area of the peripheral wall also increases if the
peripheral wall height is not changed. Thus, the height
of the peripheral wall can be decreased as the diameter
increases, to hold the area constant. This factor is
very important because as the height of the peripheral
wall increasles there is more of a tendency, due to the
centrifugal forces developed during operation and the
high temperature at which the rotor must operate, for
the peripheral wall to deform outwardly at its center.
When this happens the orifice diameters change, the
,~
~~
''' "
~ 07i~
1 "h" value no longer remains constant, and the useful
life of the rotor is essentially endecl. Thus, it is
desirable to keep the height of the peripheral wall as
low as possible.
In selecting the thickness of the peripheral
wall one must balance the strength that increased thick-
ness provides with the increased mass that accompanies
an increased thickness. An increased peripheral wall
mass increases the tendency for the peripheral wall to
warp or deform at operational speeds and temperatures.
A suitable operating range for the peripheral wall thick-
ness, with the alloy disclosed in Example 1, has been
found to be in a range of about 50-250 mils. A peri-
pheral wall thickness of less than about 50 mils does
not produce the desired structural strength in the
rotor, and a peripheral wall thickness greater than
about 250 mils is not only difficult to penetrate by
conventional laser drilling techniques, or other equi-
; valent techniques of forming the orifices, but also
.
adds excessive weight or mass onto the peripheral wall,
reducing its ability to maintain structural integrity
at operating conditions.
The preferred alloy for use in making the
rotor is disclosed in Example 1 and represents a balance
between high temperature structural strength and resis-
tance to erosion and corrosion by the molten glass
passing through the orifices. Other alloys are avail-
able that have greater resistance to high temperature
creep or deformation under stress. While rotors of ~;
such alloys could be operated at higher RPMs, higher
temperatures, and/or greater peripheral wall heights
without deformation, the orifices were eroded faster
, ~ ~ j .
< ~
.. ' ' '
~ '
.. , . . , , . - . ~ . . . , : .
~)774~
1 by the glass flow through the orifices, thus reducing
the life of the rotor. Some alloys tested had greater
resistance to erosion by the molten glass, but their
creep resistance was insufficient to resist the
deformation tendencies at operating temperatures for
sufficient periods of time.
The design and operational parameters selected
according to the above described procedures are initial
parameters. As mentioned earlier, one of the design
parameters, orifice diameter, changes as the rotor life
increases, and thus one or more other parameters must be
; changed accordingly to compensate for the change in the
orifice diameter in order to retain the desired diameter
in the fiber produced. Formula (2) above is useful in
determining which parameter(s) should be changed, and
how much they should be changed, to compensate ~or the
change in the orifice diameter, d. Looking at Formula
(2) it can be seen that as d increases it is necessary
to either decrease the rotor speed and/or to increase
the viscosity of the glass in order to keep do constant.
The glass density and the thickness of the peripheral
wall are not adaptable to modification during the operation
of the rotor. To compensate for an increasing orifice
diameter during the life of the rotor, it is preferred
to first increase the glass viscosity by lowering the
temperature on the interior of the rotor, to maintain
a constant ~iber diameter in the fiber product, until
that temperature is reached which is just above a
temperature that would cause devitrification problems ;
in the molten glass in the rotor, i.e., just above
the liquidus temperature. Once that point is reached
the rotor speed is increased to compensate for the
., .. . ,. . -
... ~
~o~
1 reduction in the number of holes emitting primary
filaments, N, due to increasing d value (See Formula 1).
The "h" value must be maintained above a minimum value
of about 1/32 inch to maintain the desired fiber diameter.
When a maximum practical rotor speed is reached it is
then necessary to put on a new rotor in order to continue
to make primary fibers having the desired diameter of 7
microns or less. Experience has shown that, when the
process parameters are so adj~lsted to produce a maximum
rotor life, fibers are being formed from the orifices
in only about the lower one-half of the peripheral wall
during the final stage of the rotor life. Thus during
the latter portion of the rotor life the effective
height of the peripheral wall is reduced.
The fibers produced by the present invention
are not all continuous since some o~ the fibers break
off in the bending path and during twisting. However,
the major portion of the broken fibers are long, com- -
pared to the lengths of conventional staple glass
fibers, e.g., at least about 5 times as long. Because
of the extreme difficulty of isolating individual fibers
without causing additional breaks the average lengths
of the fibers is not known.
` In describing the invention certain embodiments
have been used to illustrate the invention and the
practice thereof. However, the invention is not limited
to these specific embodiments as other embodiments and
modifications within the spirit of the invention will ~ -
readily occur to those skilled in the art on reading
this specification. The invention is thus not intended
to be limited to the specific emhodiments disclosed,
but instead it is to be limited only by the claims
appended hereto.
``. '.. ,7
--~ .. ... .
- . . . .
.
