Note: Descriptions are shown in the official language in which they were submitted.
6;~
ME~IOD AND APPARATUS FOR PRODUCI~ UNL~O~M
STRANDS ~RO~ A SPLIT FI~ER GLASS ~US~IING
Background of the Invention
&lass fibers are produced by drawing multiple stre~ms of molten
~lass at a given rate of speed through orifices or nozzles located in a
heated container known in the fiber glass industry as a bushing. The bush-
ings containing the molten glass are electrically heated and maintained at
given temperatures to provide molten glass at the orifices or nozzles at
a desired viscosity. Ihe maintenance of uniform temperature across the
bushing face i.e., the area of the bushing on which the orifices or nozzles
are located is important in providing uniform fiber formation from each
orifice or nozzle. The fibers drawn from the orifices or nozzles are
gathered after they solidify into one or more strands and are collected on
a collet into one or more forming packages.
In recent years bushings have increased in size so that in indus-
try today bushings having 800 to 2,000 or more orifices or nozzles ar~
commonplace. It is also cGmmon practice to produce more than one strand
from these larger bushings by winding, for example, two strands on a single
collet using a single bushing. Typically this is accomplished by using one
side of a bushing to produce one strand and the other side to produce a
similar second strand. Splitting the bushing in this manner to produce
more than one strand requires precise control of the bushing temperature
from side to side on the bushing io that the strands produced and collected
on a collet have the same yardage, i.e., the same yards per pound of glass,
or viewed in another way the same weight of glass strand per package col-
lected on the collet for a given period of time.
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To provide good control of bushing temperatures on each side of a
split bushing where two strand~, one fr~m each side are pro~uce~ it is also
desirable to provide a control method which caQ be easily adjusted by an
operator without recourge to the uge of detailed and expensive control
systems and equipment. In practice today,variationg in temperature in
split bushings as evidenced by a substantial variation in forming package
weights on a winder used to collect two packages fr~m a split bushing are
compensated for ~y operators adjusting air flows to the bushing, adjusting
fin cooler placement under the bushing orifices and/or terminal clamp posi-
tioning on the bushing. This system, as will be appreciated by the artisan
is at best a ~unction of operator skill which falls short of being satis-
factory since such changes are manual, time-consuming, and of necessity not
precise.
In U.S. patent 4,024,336, a system is described which controls
two sides of a bushing by using two full wave variable impedance devices to
regulate current transmitted to the bushing by a power transformer. While
the relative yardage of two strands produced from a split bushing using
this device may be manipulated, it has not always been effective because as
change on one side of the bushing occurs it is always accompanied by a
change on the other side. Further the system described requires the use of
a temperature controller on each side of the bushing as well as two full
wave variable impedance devices; which are c08tly on a per bushing basis
considering that a modern fiber glass furnace forehearth can have 70 to 100
bushings positioned on it.
A need therefore exists for a simple system, easily adjustable
by an operator, to control the two halves of a split fiber glass bushing
producing two or more strands. The instant invention supplies that need.
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In accordance with thig invention, a simple elec~rical system is
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provided to regulate the temperature to each half/o~ a split fiber gla8s
bushing and maintain each side of the bu8hing subgtantially canstant in
temperature. The invention involves measuring the temperature of the bush- -
ing across its length at one or more distinct pointg, controlling the power
supply to the bushing using measured temperature3, providing a shunt having
an impedance therein in parallel with the bushing power supply and varying
the current input to the bushing on each side by varying the impedance in
each side of the shunt. Preferably the shunt impedance employed i8 a
variable resistor.
Brief Description of ~he Drawings
In the accompanyiag drawings;
FIG 1 is a diagrammatic flow sheet showing ths apparatus of the
instant invention and the relationships of each of the devices used to
control the temperature of a fiber glass forming bushing;
FIG 2 is a line diagram of the temperature averaging device uti-
lized tc average temperatures measured at the bushing;
and FIG 3 is a flow diagram showing the temperature averaging
device, the rheostat and their relationship to the power transformer Eor
the bushing.
Detailed Description of the Drawings
Referring to FIG 1, there is 3hown input power lines 1 and 2
feeding into a power pack 5 which has two electrical leads 3 and 4 which
feed current into the primary coil 7 of a power transformer generally
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indicated at 8. Se~ondary coil 9 of t~le tr~l)gfonner 8 is connected across
electrical lines 11 and 12. Connected in parallel with the secondary coil
9 of the transformer 8 is line 13 which ha3 a variable impedance 14, a
poeentiometer as shown, associated therewith utilizing a wiper arm 1~ con-
nected to bushing 17. Lead lines 11 and 12 feed electrical connectors 18
and 19 which feed current to a fiber glass bushing 17.
Lines 40, 41, 42, 43, 44, 45, 46 and 47 shown leaving the bushing
17 feed signals fro~ thermocouples associated with them in response to
temperatures measurements made in the bushing 17 to a temperature averag-
ing device 22 which is more fully described in FIG 2. The average tem-
perature sensed by the device 22 produces signals that are fed through
lines 23 and 24 to a bushing temperature controller 25. m e ternperature
controller 25 in response to the signal received from averaging device 22
produces signals which are sent to the power pack 5 through lines 26 and
27 and the power pack 5 by virtue of its operation adjusts current fed to
the primary coil 7 of the transformer 8 in response to signals from the
temperature controller 25 to thereby alter the current input to the bush-
ing 17.
FIG 2 as shown illustrates a temperature averaging device which
utilizes four thermocouples 31, 32, 33 and 34. These thermocouples 31, 32,
33 and 34 are typically placed on the face plate of the bushing across its
length, preferably equidistant from each other, to measure temperatures
generated at the plate surface. The temperatures sensed produce signals in
the thermocouples which are carried by electrical lead lines which are
associated with each of the thermocouples.
In thermocouple 31 the signals are carried by lead lines 40, 41,
;n thermocouple 32 by lines 42 and 43, in thermocouple 33 lines 44 and 45
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and in thermocouple 34 by lines ~6 and 47. Resistors are placed in each of
the aforementioned lead lineg. Thus, resigtorg 4~' and 41' are in lines 40
and 41 respectively, 42' and 43' are in lines 42 and 43 respectively,
resistors 44' and 45' are in lines 44 and 45 respectively and resistors 46'
and 47' are in lines 46 and 47 respectively. The resistors 40', 41', 42',
43' 44', 45', 46', and 47' are sized such that the differences in the
resistances of the platinum wires from the thermocouples to the outlet
aver~ged signal carried in lines ~e and ~ are essentially masked. By
providing resistors large enough t~ ignore the small differences in the
potential drop across the various wqres caused by length and thickness
variations in wires 40, 41, 42, 43, 44, 45, 46, and 47 a true average can
be obtained. More importantly, the resistors prevent the shunting of large
amounts of current through the thermocouple wires themselves. The averaged
signal produced by the four thermocouples is fed via lines 23 and 24 into
the temperature controller 25. This controller produces a signal trans-
mitted by lines 26 and 27 to the power pack 5 of FIG 1. The power pack 5
then adjusts the power feed to the primary coil 7 of the transformer 8
which then adjusts current fed to the bushing 17.
FIG 3 is another diagrammatic illustration of the thermocouple
averaging device showing the bushing 17 as a resistor element. Since the
bushing is constructed of platinum, it acts as a resistance heating element.
Thus, current is fed to the bushing 17 and the resistance across the heat-
ing element or bushing 17 i9 the mechanism by which the metal is heated to
maintain the glass contained in the bushing 17 in a molten state. The
variable resistor 14 is utilized to shunt current in lines 11 and 12 to the
bushing proper. By manipulation of the wiper arm 16 the current fed to
each side of the bushing 17 is altered by the shunt, i.e. line 13, element
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14 and arm 16. Thu8, movement of the arm 16 to the left or to the right as
a result of observation of unequal weights of forming packages being fvrmed
from the b~ushing 17 ~n a single winder, chal1ges the current flow to each
bushing half/via the shunt and consequently the degree of heating of each
bushing half.
In a practical embodiment of the instant invention, the power
pack 5 used for controlling transformer 8 is typically an SCR circuit con-
structed and arranged to regulate the voltage input to the transformer pri-
mary. An SCR control power pack rated at forward current of 30 to 40 amps
with an average of 35 amps is preferred and can be selected to have a
forward blocking voltage from 800 to 1200 volts. Ihe particular power
pack controller utilized in conducting an experiment utili~ing the instant
invention was a Model 110 controller purchased from Control Systems Inc.,
Fairmont, West Virginia. m e resistors utilized in the averaging device
were 10 ohm resistors having a variance of ~2~. In the preferred embodiment
the impedance 14 employed was a 0.5 ohm resistor.
In order to prepare the system to render it operative for form-
ing department operators so that adjustments could be made manually, an
examination of a typical fiber glass split bu~hing was made. m e amount of
current change required to produce a given change in the front package
weight and the back package weight of two packages being for~ned from a
single 9pl it bushing on a single winder was determined. In general, ~or a
complete understanding of the terminology and for purposes of thi~ specifi-
cation, the bushing as viewed by the operators is divided into a left half
and a right half. m e fibers drawn in the left hal~ of the bushing are
gathered in a gathering shoe and wound onto the front half of a collet
which is positioned at a 90 angle to the longitudinal axis of the bushing.
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The fibers from the right half of the bushing are gathered into a strand
and are wound on the winder on the back half.
A split bushing, in this instance a double G 75, was operated for
three consecutive call downs to obtain base line data. Current changes
were then made to determine the effect of a current change on front and
back package weights. In the first test the wiper arm 16 was centered on
the resistor 14 of FIG 3 to produce zero current through arm 16. In a
second test, arm 16 was moved in one direction until a 10 a~np current
appeared in anm 16. In a third test the arm 16 was moved in the opposite
direction to the second test arm movement until a 10 amp current appeared.
In the fourth test the second test was repeated. Currents were measured by
a clamp on ammeter. In each of the tests forming package weights from
front and back were made. This data was recorded and is shown in table 1.
_ABLE I
Weights AfterWeights AfterWeights After
Base Line Weights10 Amp Change10 Amp Ghange10 Amp Change
in Lbs. In Lbs. In Lbs. In Lbs.
_ _ __ __
Front 22.10 22.48 21.73 22.38
Back 22.15 21.98 22.43 21.97
The above table indicates that a 10 amp change in current produces
a .541 lb. average change in the front to back weight of the packagea wound
on the winder from the spli~ bushing. Recognizing from the data obtained
in table 1 that a 10 amp change can have the effect demonstrated by the
table, a double G 75 bushing was then operated to approximate the base line
weights of 22.10 lb. and 22.15 lb. Based on the results of the base line
data obtained in Table I, the current was set on the bushing to give equal
weighta on front and back packages.
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In the first runs, eleven consecutive call down~ were made which
yielded an average front weight of 22.12 pounds and a back weight of 2Z.15
pounds. These runs are listed in Table II. A second set of experiments
was run with a slightly different current setting but designed to give
equal weights on the front and back packages and thirteen additional runs
were made. The average package weights of the8e runs were 22.26 lbs and
22.23 lbs front to back. These runs are tabulated below in table III.
Table IIr~ble Ill
Package Wt. in Lbs. Package Wt. in Lbs.
_ _
Front BackFront Back
_
22.05 lbs 22.05 lbs 22.30 lbs 22.34 lbs
22.00 22.0022.45 22.40
22.10 22.1022.40 22.40
22.20 22.2022.25 22.20
22.20 22.0522.35 22.25
22.10 22.1022.40 22.40
22.20 22.30Z2.25 22.20
22.00 22.2022.30 22.25
22.25 22.1522.15 22.05
22.15 22.3522.20 22.00
22.10 22.1522.20 22.20
22.05 22.05
~vg. 22.12 22.1522.10 22.20
Avg. 22.26 22.23
As can be readily appreciated, the variation of weight from front
to back was minimal in both sets of runs and the runs clearly demonstrate
that the control device works effectively to limit yardage variation on
front to back packages collected on a single winder from a single split
bushing. The device is simple to operate and requires only the adjustment
of a single dial controlling the wiper arm and consequently the resistance
on each side Oe the shunC to accomplish the necessary result of equalizing
package weights front to back on a winder collecting two or more packages
fr~n a single split bushing. Checks of the current can be made from time
to time by the operators. ~lhe amount of adju~tment required on the poten-
tiometer, i.e. the impedance 1~ and wiper 16 can be monitored by observing
the current change to the center tap by using a clamp on amineter or by
marking the wiper arm 16 control with a suitable dial. While in the pre- -
ferred embodiment of the invention a temperature averaging device of spe-
cific construction was used in conjunction with the potentiometer and shunt
system used to control the bushing halves, the shunt and potentiometer
alone can be effective. If used ~Jithout a temperature averaging device the
current adjustment to the bushing halves is first made to equalize them and
then the temperature control of the whole bushing is adjusted to the
desired temperature. l`hus, for example, in a double bushing if one half of
a bushing is operating at 2215F and the second half is operating at 2230F
and the desired package weight is that produced by the high temperature
half of the bushing the wiper arm 16 is moved to provide more resistence to
the colder side of the bushing to produce a 15 change. The bushing con-
troller is then further adjusted as required to maintain the total bushing
temperature at 2230F.
It will be obvious to the skilled artisan that other modifications
can be made to the present invention without seriously departing from the
basic concept. Thu9, the number of thermocouple taps utilized to average
temperatures from the bushing in the preferred embodiment can be increased
over the four shown in the illu5tration of FIG. 2 or decreased without
changing the basic concept of the invention. The measured bushing tempera-
tures coupled with the utilization of a variable impedence element in the
power feed lines to the bushing can be controlled by a potentiometer or
other similar mechanism such as coils, capacitors and the like to shunt
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current from one side of the buslling to the other to achieve substantially
uniform package weight9, front to back f~r two stratlds tnade frotn a split
bushing. This has no deleterious effect on fiber Eormation so long as the
currents are balanced to produce substantially the same weights front to
back on the winder since the fiber9 and the strands made from these fibers
as they are gathered are all traveling at the same 9peed. The only differ-
ence, therefore, front to back on the winding collet, will be the weight of
the glass. By virtue of the instant invention that weight i~ equalized.
While the invention has been described with respect to certain
specific examples, it is not intended to be limited thereby except insofar
as it appears in the accompanying claim.
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