Note: Descriptions are shown in the official language in which they were submitted.
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Back~round and Summary of the Invention
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; The present invention relates to apparatus for heat-
softening and attenuating glass material into fibers, and more
particularly to an electrical resistance furnace known in the art
as a bushing. A bushing is used to melt, condition and fiberize
the glass material.
Prior art bushings, whether utilized in a direct-melt
or marble-melt configuration, are almost always constructed of
platinum-rhodium alloys. Such alloys are used because they are
highly corrosion resistant and can accommodate high operating
;''h temperatures in excess of 2450 Fahrenheit. In prior art marble-
melt bushings, it has generally been the practice to provide
substantially greater temperatures in the melting and condition-
ing of glass material than is actually necessary for fiberiza-
tion. Specifically, as set forth in U.S. patents 3,013,095 and
` 3,048,640, molten glass must be heated at a temperature upwardly
of 2300 F. This same teaching is also set forth in U.S. patent
-- 3,615,314 wherein it is stated that a bushing must be maintained
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generally at a temperature of about 2400-2500 F. It must be
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emphasized that if the glass is to be maintained at such tem-
peratures, upwardly of 2300 F., the side walls of the bushing,
as well as the top wall, will be at an even higher temperature.
However, it has been determined that actual fiberiza-
, tion temperature of most common glasses is not in excess of
2250 F. Prior art bushing constructions have required that the
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side wall temperatures be several hundred degrees higher than the
base plate temperature in order to maintain the base plate
temperature at the fiberization temperature, which may be in the
-~ order of 2000-2250 F. Higher side wall temperatures are re-
quired because the base plate will radiate heat off into the
atmosphere. However, the overall effect is to provide a bushing
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which is of "hight heat" mode, i.e., a bushing in which tempera-
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tures above 2250 occur.
; Prior art bushing constructions, in the marble-melt
bushing mode, also generally utilize a construction in which the
side walls are joined at a seam at their upper ends to a basket.
The basket serves to retain glass material during the melting
phase. However, the seam does not generally contact glass
material and therefore provides a juncture of extremely high
temperature. This can lead to bushing failures especially in the
; case where it is desired to construct a bushing of a nonplatinum-
-~ 10 rhodium alloy.
Accordingly, it is a general object of the present
invention to provide an electrical resistance bushing for use in
an apparatus for heat-softening and attenuating glass material
into fibers, and more particularly, it is an object to provide a
low temperature bushing. This is achieved by a construction
which ensures that the base plate and side walls are maintained
in approxima~ely the same temperature range, i.e., in the range
of approximately 2000-2250 F. Maintaining this temperature
range is accomplished by a novel dimensioning of the relative
thicknesses of the base plate and side walls. In the case of a
~, marble-melt bushing, dimensioning of the top wall relative to
.~ the base plate is also an important criteria.
Specifically, a low temperature bushing of the present
invention is accomplished in the direct-melt mode by dimensioning
the base plate with an average thickness at least four times
greater than the average thickness of each side wall. With
respect to a marble-melt bushing having a top wall, the present
invention contemplates that the base plate will be dimensioned
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with an average thickness of at least eight times the average
' ,~ 30 thickness of an upper section of each side wall over at least
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~` about fifty percent of the vertical dimension, measured along
the length of the bushing. The base plate is also dimensioned
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to be at least eight times as thick as the average thickne~s of
the top wall.
; ~ith the above set forth dimensions as a criteria for
'~, direct-melt and marble-melt bushings, it has been found that the
base plate and side walls may be maintained at approximately the
fiberization temperature for most common glasses. This results
; in a low temperature bushing enabling the use of materials
alternative to platinum-rhodium alloys. Exemplary materials may
include nickel-chromium alloys, stainless steels, nickel-tungsten
~`~ 10 alloys, etc.
- Another object of the present invention is to provide
a direct-melt or marble-melt bushing with a relatively thick base
plate, as described above, with the additional provision of
auxiliary end plates mounted adjacent each end wall of the
bushing. Specifically, each auxiliary end plate will be spaced
~ from its adjacent end wall and secured to an adjacent terminal
: and to the base plate. Because each auxiliary end plate is
spaced from its adjacent end wall, electric current will be
~; channeled from the terminal directly to the base plate without
stray,ing through the lower corners of the side uall thereby
eliminating deleterious effects on the temperature pattern of the
bushing. This also results in a substantially ~niform base plate
temperature.
Still another object of the present invention is to
provide a marble-melt bushing, dimensioned as described above,
~- with a plurality of material-directing funnels which are mounted
on the top wall of the bushing. Surrounding a peripheral
, portion of the funnel, adjacent its connection to the top wall,
is a cooling means provided for maintaining a temperature which
will prevent glass material from adhering or accumulating in a
region adjacent its entry through an opening into the interior
of the bushing. It is contemplated that a collar will be
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positioned between the end o~ the ~unnel and the opening in the
top wall which is cooled by the coolin~ means.
A still further object of the present invention is to
provide a marble-melt bushing, dimensioned as described above,
with opposed side walls which are inclined and extend upwardly
and outwardly from the base plate. Each of the side walls is
joined, at its upper end, to an upper side wall section which is
inclined inwardly toward the lon~itudinal axis of the bushing.
This construction results in the provision of a relatively
narrow top wall. Furthermore, the outwardly inclined side walls
provide a structure which serves to "bridge" molten material as
it is being melted from a solid condition to a more viscous
condition.
These and additional objects and advantages of the
present invention will be more readily understood from a con-
sideration of the drawings and the detailed description of the
.
preferred embodiment.
The part, improvement or combination which is claimed
as the invention herein is, in an apparatus for heat-softening
and attenuating material into fibers, an electrical resistance
bushing mounted in a frame. The bushing comprises a horizontally
positioned base plate having aperture means for fiber-forming
extending through it. Spaced-apart side walls are joined into
the base plate and extend upwardly from it. A top wall is pro-
' vided, with an opening interconnecting the side walls adjacent
their upper portion. Opposed end walls interconnect the base
plate and the side walls. Each of the end walls includes a
terminal extending from it. The base plate is dimensioned with
an average thickness at least eight times greater than the
average thickness of an upper section of each side wall overat least 50% of the height of the side wall measured along the
length of the side wall. Additional claims specify in further
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detail various preferred properties and characteristics of the
components of the bushing.
Brief Description of the Drawings
Fig. 1 is an end elevation view, taken in cross-
section, of a marble-melt bushing used in an apparatus for
heat-softening and attenuating material into glass fibers, glass
fibers shown being drawn onto a rotatable drum disposed there-
beneath;
Fig. 2 is a end elevation view, taken in cross-
section, of a direct-melt bushing used in an apparatus for
heat-softening and attenuating material into glass fibers;
Fig. 3 is a side elevation view, shown partially in
cross-section of another embodiment of a marble-melt bushing in
accordance with the present invention;
Fig. 4 is an end elevation view, taken in cross-
section, along lines 4-4 of Fig. 3;
Fig. 5 is a view taken along lines 5-5 of Fig. 3 and
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illustrates mounting of a cooling tube adjacent entry of material
into the bushing and is shown adjacent Fig. 2;
Fig. 6 is a perspective view of a portion of a bushing,
having a relatively thick base plate, illustrating current paths
from a bushing terminal along the bushing's end, side and bottom
walls and is shown adjacent Figs. 1 and 2;
Fig. 7 is an end elevation view of a portion of a
bushing according to the present inven~ion illustrating use of
an auxiliary end plate adjacent the terminals so that electrical
current will be channeled to the base plate;
Fig. 8 is a side elevation view, reduced in size from
the other drawings, showing the construction of a long bushing,
in the range of 6-8 feet, including a plurality of material
directing funnels and cooling tubes;
Fig. 9 is a perspective view, illustrating another
embodiment of the present invention including an elongate con-
tinuous funnel for directing material into the bushing; and
Fig. 10 is an end elevation view of a bushing, taken in
cross-section, showing an embodiment including an internal core
for enhancing melting of glass by virtue of improved radiation
resulting from the relative closeness of the walls of the internal
core and the side walls of the bushing.
Detailed Description of the Preferred Embodiments
Turning now to the drawings, and referring initially
to Fig. 1, a bushing according to a first embodiment of the
present invention is generally designated at 10. Bushing 10 is
mounted in an apparatus, known in the art as a direct-melt
furnace, (though it could be used for melting cullet, etc.) for
heat-softening and attenuating glass material into fibers.
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`` 112~601
Bushing 10 includes a horizontally po8itioned ba8e pl~te 12
having a plurality o~ ~ibe~ fo~ming apertures 13 extending there-
through. A pair of opposed, spaced-apart side walls 14, 16 are
joined to base plate 12 and extend vertically upwardly therefrom.
Side walls 14, 16 include flanges 14a, 16a respectively which are
mounted into associated refractory material 18, 18a and 20, 20
respectively. An outer supporting frame (not shown) mounts the
insulating material.
Although only a portion of a direct-melt apparatus is
shown in Fig. 1, it must be remembered that molten material
indicated at 22 would normally be channeled or fed into bushing
10 from a forehearth. Thus, bushing 10 would normally be pro-
vided with an open-top construction as illustrated. Further
considering Fig. 1, it can be seen that heat softened material
from the molten material is directed downwardly through aperatures
13 and wound onto a rotatable drum 24 in conventional manner. A
gathering shoe is schematically shown at 25.
According to the present invention, the specific dimen-
sions of a direct-melt bushing such a bushing 10 are critical if
the bushing is to function as a low temperature bushing. As
mentioned previously, known bushings are generally constructed
from platinum-rhodium alloys such as ten percent rhodium-platinum
or twenty percent rhodium-platinum. It is also known to con-
;~, struct bushings for specialized applications of zirconiums-stabil-
' ized platinum ~hich is highly resistant to distortion. Such
bushings would be "high temperature" bushings, i.e., bushings in
which upper wall temperatures may rise to 2300 F. and above.
However, the present invention contemplates that base
plate 12 will be dimensioned ~ith an average thickness at least
four times greater than the average thickness of each side wall
14, 16. Furthermore, it has been found advantageous to provide
a bushing wherein bushing 10, when viewed in transverse cross-
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section, includes base plate 12 with a cross-sectional area
in the range of at least forty-five percent of the total cro~s-
sectional area of side walls 14, 16 and base plate 12 taken
together.
With the above construction, it is possible to main-
tain a base plate temperature in a certain fiberization range
without the side wall temperatures greatly exceeding that range.
Prior art bushing constructions necessarily required that precious
metals be used because the side walls would reach significantly
higher temperatures than the base plate. Stainless steels or
nickel-chromium alloys could not be employed because they could
not sustain the high side wall temperatures required to maintain
a relatively thin base plate at a desired temperature. However,
with the above construction, the relatively thin side walls draw
much less electrical current and therefore genera~e much less
heat and consequently enjoy low operating temperatures. With the
average thickness of base plate 12 being at least four times
greater than the average thickness of side walls 14, 16, it is
possible to maintain both the base plate and the side walls in
the range of about 2000-2250 F. which is necessary for proper
conditioning of glass in an attenuating process. The bushing
can then be accurately referred to as a "low temperature" bushing.
It has been found that if base plate 12 were not dimensioned with
a thickness at least four times greater than the average thick-
ness of side walls 14, 16, side wall temperatures could exceed
2250 which would prevent the construction of a stainless steel
or nickel-chromium alloy bushing. Nickel-chromium bushings would
experience rapid oxidation and deterioration if temperatures
exceeded the range of about 2250 F.
Additionally, base plate 12 is significantly stronger
because of its relatively thick dimension and also permits
greater lengths and widths to be manufactured without accompa-
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nying warpage or distortion during high operating temperatures.
A thick base plate is also easily cast with nozzels in situ
thereby saving fabrication costs. Another advantage resides in
the fact that nozzles may be machined into the base plate for
extending from aperatures 13. Specifically, through machining
an annular cavity surrounding a portion of an aperture, the
bottom of the base plate may be formed so that a nozzle extends
outwardly. Additionally, press-fit nozzle tips may be premanu-
factured on a screw machine or turret lathe and mounted in an
individual aperture because the thick base plate provides a
substantial material thickness for accommodating a press-fit.
Also, tips may be spot welded or attached by adhesive ceramic
to the base plate. It is to be noted that press-fit nozzles
could be made of different alloys, i.e., could be constructed
of a more corrosion-resistant material than the base plate itself.
Additional advantages of a relatively thick base plate
reside in the fact that convection currents, which are normally
associated with the molten mass held by a bushing do not appreci-
ably influence the base plate. For instance, a thin base plate
would not retain as much heat as a thick base plate and therefore
convection currents would more readily disturb a thin base plate's
temperature. Also, it is to be noted that a thick base plate is
less effected by external temperature influences because the
base plate has a higher heat content due to its thickness. An
even temperature is provided at the meniscus or the point at
which a fiber forms after passing from an aperture or nozzle. A
relatively thick base pla~e also provides more intense thermal
conditioning as glass passes through the apertures and reduces
the probability of crystals being passed out~ardly.
Some bushing constructions require that coaling fins be
located adjacent the meniscus. In conventional bushing
constructions, if the bushing base plate becomes warped, it
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could contact the cooling fins and upset the heat content of
the base plate. ~lowever, with a relatively thick base plate, as
set forth above, signi~icant widths may be provided which enable
the apertures or nozzles to be spread far apart and thus reduce
the radiation from one nozzle to another. It has been found that
nozzles can be placed in excess of one-half inch apart on a
relatively thick base plate and this facilitiates restart if
fibers should become broken in a fiber forming process. Widely
spaced nozzles reduce the probability that a bead which has
formed after a fiber has broken will contact and break other
fibers.
Wîth reference now directed to Fig. 2, another embodi-
ment of the present invention is illustrated and pertains to a
bushing generally indicated at 26 used in a marble-melt process.
Specifically, bushing 26 is used in a process in which marbles,
cullet, rod or other material are deposited into the interior of
the bushing for melting. Bushing 26 is of the electrical resist-
ance type and includes a horizo~tally positioned base plate 28
having a plurality of fiber-forming apertures 30 extending there-
through. Opposed, spaced-apart side walls are provided, each of
which may include wall sections having d~fferent side wall thick-
nesses, when viewed in cross-section. For instance, base plate
28 is secured to a side wall 32 which includes a section 33 from
which upwardly extends a less thick, upper section 34. Similarly,
a side wall 36 is secured to the other side of base plate 28 and
includes a section 37 from which upwardly extends a less thick,
upper section 38.
The bushing construction shown in Fig. 2 refers to a
bushing used for melting heat-softenable material and contem-
plates that base plate 28 will be dimensioned with an averagethickness at least eight times greater than the average thickness
of each upper section 34, 38. Furthermore, each of the upper
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llZ~601
sections with the above-described thickness i8 contemplated a8
occupying at least fifty percent of its associated side wall
height measured from end to end in the bushing. The base plate
thickness dimension is also at least eight times greater than the
average thickness o~ a top wall which is indicated at 40. It is
noted that it is necessary to provide base plate 28 with a
thickness at least eight times greater than the thickness of -
upper sections 34, 38 as well as top wall 40 in order to keep the
current flow in the upper section and top wall approximately one-
eighth or less than the current flow in the base plate so that
the side walls and top wall do not become overly hot. The
reason for the eight to one ratio resides in the fact that a base
plate is not encased in refractory and is highly disposed to heat
losses through radiation whereas side walls are encased in
refractory and are thus not disposed to high radiant heat losses.
The bottom portion of the side walls can radiate a significant
quantity of heat through the base plate. According to the
present invention, the upper side wall sections are dimensioned
thin, relative to the base plate, so that they will generate less
heat.
Bushing 26 also includes a collar 42. Extending up-
wardly from collar 42 is a funnel means indicated at 44. A
cooling means such as a cooling tube 46 surrounds collar 42 for
preventing marble or cullet material from sticking to collar 42
or in interior walls adjacent to the region cooled by cooling
tube 46. Details of collar 42, funnel means 44 and cooling
tube 46 will be more fully described hereinafter with reference
to a third embodiment shown in Figs. 3 and 4. Also, a baffle
means indicated at 48 will receive a more detailed discussion at
a later point.
Turning now to Figs. 3 and 4, another embodiment of the
present invention contemplates a marble-melt bushing indicated at
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50. Bushing 50, as shown in Fig. 4, includes a base plate 52
horizontally positioned and including a plurality of flber form-
ing apertures 54. Opposed, spaced-apart side walls are generally
indicated at 55, 57. Extending upwardly from base plate 52 and
inclined outwardly relative thereto are lower side wall sections
56, 58. Each side wall 55, 57 includes an upper side wall
section such as section 56a, 58a joined at obtuse angles to
lower side wall sections 56, 58 respectively. A relatively
narrow top wall 60 extends between sections 56a, 58_ and joins
them. A frame having opposed sides 51, 51a supports the bushing
in suitable refractory material.
As shown in Fig. 3, additional upper side wall sections
62, 64 are inclined upwardly toward top wall 60. Top wall 60 is
provided with an opening 66 (other openings are also provided as
shown in Fig. 3~ and a collar means 68, preferably of circular
periphery, is mounted on top wall 60. Mounted to and extending
upwardly from collar means 68 is a funnel means 70. Depending
upon the length of bushing 50, a plurality of funnel means are
provided at spaced-apart locations as suggested by Fig. 3. It
~, 20 should also be noted that a fluid-conducting coolant tube 7Z
surrounds collar means 68. Details and advantages of coolant
tube 72 will be described at a later point.
Returning to Fig. 4, it can be seen that base plate 52
is dimensioned with an average thickness at least eight times
greater than the average thickness of upper side wall sections
' 56a, 58a, and a portion of lower side wall sections 55, 58 for at
least fifty percent of the height of side walls 55, 57 measured
from end to end in the bushing. The base plate thickness dimen-
sion is also at least eight times greater than the average
thickness of upper side wall sections 62, 64 and top wall 60.
The purpose of such an eight to one ratio is substantiall~ as set
forth for the previously described marble-melt bushing
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embodiment, i.e., to ensure that a low temperature bushing iR
provided wherein the side walls and base plate are maintained
within approximately the same temperature range. It is to be
noted that marble or cullet material generally designated at M,
is funneled down through funnel means 70 from a feeder assembly
generally designated at 74 into a region defined by collar means
68.
As shown in Fig. 5, collar means 68 is substantially
surrounded by coolant tube 72. An inlet is indicated at 72a and
an outlet at 72b. Thus, with coolant fluid being continuously
circulated through coolant tube 72, (any suitable coolant fluid
may be used) it can be appreciated that collar means 68 will be
maintained at a relatively cool temperature when compared with
side walls 56, 58 and upper side wall~sections 56a, 58a. Addi-
tionally, top wall 60 while being somewhat hotter than collarmeans 68, will nonetheless not achieve a significantly high
temperature. Thus, as material M descends downwardly through
funnel means 70, it will not stick or build up on the interior
periphery 68a of collar means 68 or on the interior surface of
top wall 60 beneath coolant tube 72. The material will descend
generally at an angle represented by the sloped lines 76 into the
:. interior of bushing 50. Because of the relatively cool tempera-
tures of collar means 68 and top wall 60, no material will stick
thereto but rather will be channeled into contact with upper
sections 56a, 58a. The upper sections are maintained at general-
ly the fiberization temperature and cause rapid melting of the
material.
It must be appreciated that the sloped wall configura-
tion of bushing 50, i.e., as shown in Fig. 4, provides several
distinct advantages. For instance, it is preferable to increase
the area of glass contact and decrease the area which is not in
glass contact. For instance, in conventional bushings, there is
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provided a large top wall surface which can become hot and cause
rapid oxidation and deterioration of the top wall alloy. The
increased glass contact with the side walls, a~ shown in Fig. 4
of the present invention ensures relatively uniform melting of
material M with only a small region not actually in contact with
the material.
Bushing 50, which includes angled or inclined side
walls 56, 58 ensures that there is a "bridging effect". More
specifically, it can be seen that obtuse angles A, B defined by
walls 56, 56a and 58, 58a respectively, enable a narrow top
wall 60 to be provided plus a structure in which softened materi-
al in a region C may be at least temporarily supported to ensure
that complete melting of the material results. Furthermore, it
is to be noted that a baffle means such as indicated at 78 is
provided directly beneath collar means 68 and funnel means 70.
Baffle means 78 includes an apertured plate mounted on legs above
base plate 52 and is provided to reduce hydrostatic pressure over
apertures 54 and to retard the downward movement of unmelted
glass. This may be required when it is needed to improve the
fiber forming characteristics at the meniscus.
It has been found that it may be necessary to retard
downward pressure and downward movement of particulate glass
because material may be in too solid of a condition adjacent the
' interior portion of bushing 52. The material will be reduced to
a molten state adjacent the side walls, but additional retarding
of downward pressure may be required in order to ensure that
adequate heat input is directed to the material located interior-
ly of the bushing. It has been found that even downward flow
across a horizontal gradient will be optimized by providing
funnel means 70, the inclined wall structure, and baffle means
78. It is to be noted that a baffle means will be provided
beneath each funnel means and top wall opening.
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~ nother feature of the present invention, and one which
may be employed in each of the above embodiments, is the pro-
vision of an auxiliary end plate provided on opposite ends of the
bushing. Such end plates 80, 81 are shown in Figs. 3 and 7.
Beore a discussion of the details and advantages of the end
plates are pursued, reference to Fig. 6 is required. A bushing
82 having a relatively thick base plate is shown in perspective
from beneath in Fig. 6 and includes terminals 84, 84_. During
input of electrical current through the terminals, it has been
found that the current ~ill be directed across end wall 86
generally in the current pattern as shown. The current will
follow the path of least resistance and therefore a high portion
of the current will be directed to the edge of end wall 86 and
across the side wall as shown in generally curved gradient lines
which increase in concentration toward the region occupied by a
base plate. This concentration will result in localized "hot
spots" such as indicated at 88, 89 and 90. Similar "hot spots"
are located on the other side as only one-half of the gradient
lines are shown for purposes of clarity. These "hot spots",
occur,ring as shown, will greatly increase the temperature of the
side walls and central base plate portion thereby providing a
result which can only be accommodated by a platinum or platinum
alloy bushing. In order to alleviate such "hot spots" the
present invention includes the additional improvement of pro-
viding auxiliary end plates 80, 81 as shown in Figs. 3 and 7.
Specifically, as shown in Figs. 3 and 7 end plate 80 is
constructed with inclined sides 80a, 80b and is provided with a
notch or recess 80c so that it may be welded, along the recess,
to a terminal such as terminal 91 provided on bushing 50.
Another weid is indicated at 92 and secures the bottom of end
plate 80 to a position adjacent base plate 52. It is to be noted
that an air space or gap, indicated at 94 is provided between the
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interior face of end plate 80 and an end wall 96 of the bushing.
It is imperatlve to have such an air space or to provide insulat-
ing material in the space so that current will be channeled from
terminal 91 through end plate 8Q directly into base plate 52. No
welds other than those indicated should be provided because the
object of such a construction is to enæure that the path of
conductivity to the side walls is eliminated with conductivity
being channeled only to the base plate.
Current is directed into base plate 52 so that the
overall heat content of base plate 52 is maintained. It may or
may not be necessary to provide insulating material between the
inside face of end plate 80 and the outside face of an end wall
depending upon the oxidation characteristics of a particular
metal. The important thing to remember, however, is that the
provision of the novel auxiliary end plates will serve to channel
electrical current directly into the base plate from its ends
thereby maintaining the base plate at a substantially uniform
temperature.
Returning to Figs. 3 and 4, it will be appreciated that
the r~latively thîck base plate construction of the present
invention, in all of the above emobidments, enables the connec-
tion thereto of a bushing supporting mechanism including a
support rod 98 and transversely extending brace 100. Support
rod 98 is anchored to the base plate and extends upwardly there-
from. Brace 100 includes a yoke member 101 which is slidably
mounted on rod 98. Opposed nuts 99, 99a are threadably engaged
with the rod on opposite sides of the yoke. Elements 100a, 100b
are provided on opposite ends of the brace and are slidable along
flanges provided on opposed sides 51, 51a of the fxame.
Thus, the rod and brace define a "dynamic support" in
that adjustment of the nuts may be made to compensate for expan-
sion of the bushing as it heats up. Adjustments in the vertical
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direction, lengthwise and transversely are accommodated by the
supporting mechanism. Further, it i8 to be noted that the rod
could be a thermocouple sheath if desired. A thermocouple pro-
vided for measuring the temperature of base plate 52 may be
secured to the base plate at its upper surface between aperatures
54. The thermocouple may be insul~ted with MgO and sheathed in a
heat and corrosion resistant alloy. The relatively thick con-
struction of base plate 52 permits the use of such a MgO thermo-
couple because it allows the use of nozzles spaced-apart far
enough to permit the thermocouple to be secured to the base plate
between nozzles. ~lso, the thickness of the base plate permits
the drilling of a thermocouple receiving bore. It may be advis-
able to provide a multiplicity of spaced-apart thermocouples, ~ ;
extending generally in the longitudinal direction of the bushing
for monitoring base plate temperature. Further, each of the
thermocouples may be appropriately secured to a bracing member
thereby adding structural integrity to the bushing proper.
Another embodiment of the present invention is shown in
Fig. 8 and includes an extremely long bushing, when cansidered in
view of the prior art, generally designated at 102. Bushing 102
may be provided with a length as much as 6-8 feet or more because
of the relatively thick base plate construction and other novel
features of the present invention. As shown, a plurality of
dynamic supporting mechanisms may be provided for structural
integrity. The base plate is substantially more rigid than
existing bushing base plate constructions and enables substantial
bushing lengths to be feasible especially when employed with the
above-described dynamic supporting mechanism. Additionally, it
can be appreciated that a plurality of separate funnel means may
be provided beneath a material dispensing feed assembly. Each of
the funnel means is directed into the top wall of the Dushing via
a collar means as previously described. Each of the collar means
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is provided with a coolant tube ~or the purposes as outllned with
reference to Figs. 3 and 4.
Turning to Fig. 9, another embodiment of the present
invention contemplates the provision of a relatively long bushing
wherein a continuous funnel means is provided. Specifically, a
bushing 104 includes a feeding or funnel means 106 which extends
substantially the length of the bushing. Funnel means 106 is
supported from above (not shown) and is not connected to collar
means 110. Bushing 104 is provided with a top wall 108 having a
continuous opening on whcih is mounted an elongate collar means
110. Surrounding collar means 110 is a continuous coolant tube
112. The bushing shown in Fig. 9 includes a portion broken away
in order to better illustrate the provision of a plurality of
baffle means disposed beneath funnel means 106. As shown, each
of the baffle means is spaced a small distance apart from
adjacent baffle means in order to break the path of end to end
f conductivity and thereby prevent substantial heat build up on the
baffle means. Of course, the baffle means may be constructed of
relatively nonconductive material, if desired, so that electrical
curre,nt is not channeled into the baffle means from the base
plate. The continuous funnel means will ensure continuously even
downward pressure and movement of particulate material across
horizontal gradients thus improving fiber forming characteristics.
A last embodiment of the present invention is illus-
trated in cross-section in Fig. 10 and includes a bushing pro-
' vided with a core. The bushing includes a base plate and side
wall construction utilizing an eight to one ratio similar to
~, that described for the embodiments of Figs. 2-4. As illustrated,
a bushîng generally indicated at 114 is provided with circular or
curved side walls 116, 118 which extend upwardly from a rela-
tively thick base plate'120. Mounted internally of bushing 114
is a cylindrical member or core 122 which defines an internal
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1~21~;01
space 124. Core 122 is provided in order to enhance melting of
glass through improved radiation because of the relative closeness
of walls 116, 118 and the outer surface of core 122. It must be
remembered that core 122 conducts electricity and is therefore
heated. The use of core 122 is primarily effective in the
situation prior to establishing a regular fiber throughput
pattern. For instance, it is known that bushings can become
relatively hot along their upper side wall sections prior to
throughput being established. This is because a flow of incoming
cold glass is not established during startup. The glass is
initially residing in the bushing and is not moving. After move-
ment of the glass starts (i.e. when throughput is initiated) heat
may be reduced. During the startup phase, it may be advisable to
transfer some type of cooling fluid through a region 124 so that
side walls 116, 118 may be cooled during the startup phase. Once
throughput is initiated, it is contemplated that the cooling
fluid through region 124 would be eliminated or reduced and then
the walls of core 122 and side walls 116, 118 would simultaneous-
; ly radiate heat towards each other in order to substantially
improve the thermal characteristics and heating capabilities ofthe bushing. While it has been disclosed to provide some type
,~ of cooling fluid to channel through region 124, it must be
i~ remembered that the basic concept disclosed in Fig. 10 contem-
plates the provision of a heat sink in order to provide cooling
~ for the upper wall portions of the side walls when they become
'~ too hot prior t~ the establishment of throughput.
-~ The above-description, with reference to the preferred
embodiments, sets forth both direct-melt and marble-melt bushings
having relatively thick base plates compared to the thickness of
~,
the bushing's side walls. It is known that many repeated
attempts have been directed toward developing bushings made of
less expensive, alternative materials from the conventional
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l~Z1601
platinum or platinum-rhodium alloy bushings but none have been
practical, primarily because they have required auxiliary heat
sources which result in higher operating costs. However, the
present invention provides a startling breakthrough in bushing
construction because it enables the use of nonprecious metal
alloys to be advantageously used. Stainless steels or nickel-
chromium alloys may be readily employed in either a direct-melt
or marble-melt bushing as long as the base plate and side wall
thickness dimensions, as described above, are employed. Sub-
stantial savings in fabrication and operating costs are realizedwhen a nonprecious metal bushing is used. Also from the above,
it should be clear that the present invention enables bushings
of nonprecious metals to be constructed which are extremely
rugged and adapted to perform without substantial deformation or
warpage over extended operating periods.
There are other significant advantages present in the
bushing construction utilizing a relatively thick base plate as
outlined above. For instance, because the bushing operates at a
relatively low temperature, it will enjoy a longer life. This
concept could be readily employed with conventional platinum-
rhodium alloy bushings. Additionally, the long life is accom-
:1 panied by an extremely rugged construction. For instance, if the
bushing is to be constructed of a nickel-chromium alloy, damage
would not result if other metals contacted the bushing. Con-
versely, platinum tends to readily alloy with other metals when
at high temperatures. Therefore, if cooling fins or other
objects inadvertently come in contact with the nozzles of a
platinum bushing, irreparable damage usually occurs.
The ruggedness of a bushing utilizing the relatively
thick base plate of the present invention also permits blocked
nozzles to be readily rodded. This refers to the use of a thin
wire or rod which is inserted through a plugged orifice in the
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nozzle. Such rodding may advantageously be used in a nickel-
chromium alloy bushing but cannot be used with platinum-rhodium
alloy bushings.
Another advantage of the present invention resides in
the use of a nickel-chromium alloy bushing having a relatively
thick base plate whih can fiberize scrap window glass cullet.
Such cullet is generally contaminated with lead putty and alum-
unium extrusion scraps which cannot be segregated with magnets or
other readily available means. Such contaminants would ruin a
conventional platinum-rhodium alloy bushing but can be withstood
in a nickel-chromium alloy bushing or bushing constructed of
some nonprecious metal alloys.
Still another advantage of the present invention
resides in the use of the auxiliary end plates, as described
above, to remove "hot spots" at the lower corners of the side
walls and on the middle region of the base plate. The result is
a very uniform base plate temperature which enables the attenua-
tion of uniformly dimensioned fibers. A uniform base plate
temperature, at the fiberization temperature, ensures that uni-
form quality fibers will be drawn.
In conventional marble bushings, a problem resides inthat convection currents may be present within the molten mass of
the bushing. The convection currents can cause problems in that
colder glass may be present in areas of the base plate directly
beneath an inlet funnel. Another problem resides in the fact
that pockets of stagnation may occur between convection currents
and in areas outside of their path. However, with the low
, temperature bushing of the present invention, convection currents
are substantially eliminated. This is achieved because a highly
molten bath is not required in the mid-section of the bushing
because glass descends toward the base plate in an even downward
flow steadily increasing to fiberization temperature. There are
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llZ16(~i
no convection currents because the glass i8 too viscous to flow
in currents until it hits the baae plate where it immediately
passes through the orifices and i8 fiberized. This concept is
known as using liquid zones of progressively decreasing Vi8C08i-
ties and can be readily achieved with the relatively thick base
plate construction utilized with the other features, aæ outlined
above, for ending convection currents, pockets or stagnation and
attendant crystalization. An advantage of having no convection
currents, no pockets of stagnation and no attendant crystaliza-
tion resides in the fact that a bushing, constructed as outlinedabove, may be brought up to perating conditions much faster than
conventional bushings.
Still another advantage of the present invention
resides in the fact that the relatively thick base plate will not
be affected by heat variations caused by extraneous thermal
influences. This is because the relatively thick base plate
retains a high heat content and a low thermal conductivity.
Thus, even if menici cooling tubes come in contact with the base
plate, no adverse affects result on the base plate.
It should also be noted that automatic temperature
controls generally are not necessary for a low temperature
bushing constrcuted in accordance with the principles of the -.
present invention in most applications. This is because the
bushing is not as susceptible to extraneous thermal influences as
high temperature bushings are.
While the present invention has been described with
j reference to the foregoing preferred embodiments, it will be
apparent to those skilled in the art that other changes in form
: and detail may be made within the scope of the present invention
as defined in the appended claims.
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