CA1096626A - Control apparatus and system for closely spaced heating elements for forming glass fibers and method of using same - Google Patents

Abstract

CONTROL APPARATUS AND SYSTEM FOR
CLOSELY SPACED HEATING ELEMENTS

Thomas H. Jensen Abstract of the Disclosure In an electrical heating element apparatus and control system for tubular glass fiber bushings wherein a plurality of bushings are each individually temperature controlled by a compact power supply and control system and means are provided for mounting and holding the orifice tube fiber units in proper relationship, while at the same time providing the required electrical connection to them. The heating elements or the orifice tubes are connected in parallel across the secondary of a single transformer, and individual control elements are connected in series with each element on the secondary side of the transformer. A special fluid control system is used to provide for differential flow of cooling fluid across the face of the orifice tube.
The cooling fluid is controlled along the length of the orifice tube by segmented units, that can be individually controlled to provide for varying cooling fluid flow along a given length of the orifice tube.

Description

Bac_ground of the Invention In conventional fiber glass producing arrangements, molten glass is delivered to an electrically heaeed busiling which includes a plurality of tips having orifices theretllrougll for the passage of glass streams. The glass streams are attenuated into fibers which are grouped together as a strand and collected as a package. Cenerally, the busllings are constructed of an alloy, sucll as 90 percent platinum and 10 percent rhodium. The tips are painstakingly built up by dropping molten alloy onto a bushing plate, and then drilling the built-up alloy to form the orifices. This arrangement, although commonly used, has a serious limitation in that only a relatively small number of orifices can be provided in a given space.
Another and later approacll is to drill small, closely spaced holes in the wall of a metal pipe and deliver molten glass under pressure to the pipe so as to extrude glass through the holes. It has been found that the number of the holes per unit of area of pipe far exceeds the number of tips for a like area of a conventional bushing. Further, the cost of an orifice tube of the type just described is considerably less than the cost of conventional bushing. In such devices, it is customary to provide at least a partial shroud for the orifice tube and to deliver a controlled atmosphere to the shroud to envelop the tube and be discharged near the holes to provide cooling to the filaments and, for certain embodi-ments protect the tube against oxidation.
By utili~ing high pressures up to perhaps several hundred pounds per square inch in the orifice tube, as opposed to convcntional one pound pcr square inch pressure, the fibers may be attenuated from smaller .

orifices wllile producing less tension in the filament than was the case witll prior, larger, orifice bushings producing an equivale]-t filament at comparable speeds. Such a higll pressure orifice tube fiberizing unit is disclosed and claimed in U. S. Patent ~o. 3,625,025 assigned to the assignee oE the present application In conventional fiberizing systems, the bushillg generally requires from 1500 to 3000 amperes at operating conditions. To provide this power, a step-down transformer is generally used to provide a high-current, low voltage circuit from which the current is supplied to tlle bushings, with the high-voltage side of the transformer providing the control. Thus in conventional systems the primary side of the transformer may include a saturahle core reactor or a solid state semiconductor system for regulating the flow of power to the buslling to control the temperature thereof. How-ever, because oE the physical size of the components of such a control system, this means of control becomes extremely impractical when con- -sidered for load elements such as the orifice tubes described above, particularly when they are placed in close proximity, for the small size of the orifice tube only requires about one-tenth the space required for a comparable conventional bushing. Further, the orifice tube requires only about one-fifth the power to operate than is required for conventional devices and thus the size of the conventional power supply and controller is not necessary for orifice tube fiberizers.
It has been conventional practice in operating orifice tubes of this type to surround the tubes with a fluid cooling system typically an air supply system to assist in providing close temperature control over the oriEices. 'rhis is typically accomplishe(l with a plenum chamber con-structed nnd arranged to deliver the air across the orifice tube from .., ' : :
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~96~6 both sides from one end to the other. Since some orifices along the length may require more or less cooling fluid to operate eEEectively, this system has been found to be unsatisfactory in some instances.

SUMMARY OF THE INVENTION
Accordingly, the present disclosure relates to an improved means for regulating the temperature of an orifice tube fiberizing unit.
Also disclosed is a compact, convenien-t, more efficient heating control system for glass fiber orifice tubes while providing more individual control of the cooling of the orifice tips along the length of the tube.
Still further there is disclosed an improved heating control apparatus which is adapted to the reduced power requirements produced by the small size of an orifice tube fiberizing unit, and which is designed to provide means for conveniently mounting and holding the fiberiziny units in proper relationship.
Also disclosed is a heating element control system for a plurality of glass fiber orifice tubes~ wherein the heating elements of all of the tubes are connected in parallel with the secondary winding of a single supply transformer, with each element being individually controlled at the trans-former secondary.
Briefly, a presently disclosed arrangement comprises an orifice tube fiberizing unit mounted in compression between a combination clamp and spring-loaded electrical connector and a high pressure glass source which provides molten glass for the unit. The fiberizing unit , .. . , ~ . .
' inclutles a tube having a multitude of small orifices formed in a portion Or its surrace through which a heat softened material such as glass is extruded. ~t one end of the tube is a flanged connector designed to seat in a mating recess on the glass source, while the other end of the oriEice tube is engaged by a clamp which includes an electrical connector for the tube. The clamp and the connector are adjustably attached to a fixed bus bar which serves both to provide a rigid mount for the entire assembly and to supply power to the unit.
The bus bar is connected at one encl to a transformer oE sufficient power capacity to handle all of the fiber units that can be secured to the bus bar. Embedded within the bus bar and contacting the electrical connector Eor each Ullit is a pair oE half-wave thyristors througll which Elows the current from the bus bar to the connector, and which serve to regulate the current to provide the power required to maintain the desired temperature in the orifice tube. The bus bar and connector assembly are water cooled to protect the semiconductive thyristors, and the connector includes a finned cooling block to prevent overheating.
~ thermocouple on each orifice tube provides a signal proportional to its temperature, this signal being fed to a suitable control system to produce an output wllicll regulates the operation of the corresponding thyristors. The control system, which may be a conventional three mode system, provides the necessary control action to maintain each individual orifice tube at a predetermined level, or set point. Each of the many orifice tubes tllat may be connected to a single bus bar are connected in electrical pa~allel to the secondary of the transformer, an(l each tube is provided witll an individual controller to regulate the power expended in accordance with the requirements of the respective tube. The power and control system is compact and efficient, allowing close spacing of , 10~ ii21~

adjacent orifice tube units, ancl is operable from the secondary of a power supply transformer, thus substantially reducing the bulk and expense of the power and control system.
According to the present invention the orifice tube is surrounded on either side by a cooling fluid delivery system which delivers Eluid across the long axis of the orifice tube. The fluid delivery system is provided with means to adjust the quantity of fluid deli~-ered across a given segment of the tube to thereby provide for variable cooling along the length of the orifice tube at given points to allow for more individual control of cooling at the multiplicity of orifices.

Brief Description of the Drawings The foregoing and additional objects, features and advantages of the present invention will be apparent to those of skill in the art from a con-sideration of the following detailed description, taken with the accompanying drawings, in which:
FIG. 1 is a front elevation in partial section of an orifice tube, clamp, and electrical connector in accordance with the present invention as viewed along line 1-1 of FIG. 2;
FIG. 2 is a side elevation of the device of FIG. 1 along line 2-2 of FIG. 1 in partial section and showing in addition a second orifice tube clamp and connector assembly similar to the assembly of FIG. l;
FIG. 3 is a partial schematic and partial block diagram of the control system of the present invention;

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l~tG. 4 is a front elevation in partial section o~ another cmbodim~nt o~ the invention having an orifice tube and ~:lectrical con~
ncction tllereto as well as the glass delivery system; and I~IG. 5 is a cross section of FIG. 4 taken along lin~ 5-5 of FIG. 4 to show tlle internal fluid control passages in the air chamber 413 of ~IG. 4.

Description of a Preferred Embodiment Turning now to a consideration of ~IGS. 1 and 2, there are illustrated at 10 and 12 two orifice tube Eiberiæing units each having a plurality of orifices therein for extruding streams of molten glass delivered under pressure to the tubes from a pressure source 14. ~s described more fully in the aforesaid V. S. Patent No. 3,625,025, the orifice tube 16 of fiberi~ing unit 10 is made of platinum or platinum alloy with a plurality of orifices being formed in the lower portion of its ~all, generally at 18, in a closely spaced arFay. One end 20 of tube 16 is closed, while the other end 22 is open and provided with a flanged coupler 24 to mate with a complementary coupler 26 on a supply conduit 28 which serves to supply molten glass to the tube. The tube 16 is heated by passing an electric current therethrougll, as will be described.
The orifice tube 16 is shrouded by a manifold 30 to which cooling air is delivered by way of an inlet conduit 32 (FIC. 1). The manifol(l partlally covers the orifice tube and terminaLes at an opening 3~, the eclges of which are slightly spaced from the orifice tube , . .~

~or the passage oE cooling air as may be seen in the sectional view of the Eil)eri~.ing unit in ~IG. 2. This air flows down througll the manifold 30 and is blown Erom opposite sides across the ori~ices formed at 18, eventually following the streams of glass and the resultant fi~ers down and vut opening 34. The air cools the fibers as they are being [ormed, and insures stable attenuation of the fibers.
To protect tlle orifice tube from (listorting or rupturing under tlle rela~ively high pressure exerted on it by the glass feed, a shield tube 36 partially surrounds tube 16, but is separated tllerefrom by a layer of insulating material 38 which serves to isolate tube 16 fro~ the cooling air in maniEold 30. The shield tube 36 and the insulating material may extend beyond the ends of the maniEold 30, as shown in FIG. 1, to cover the tube 16 outside the manifold. t~n air shield 40 over the shield tube 36 ~urther assists the shield tube in diffusing the coolin~ air, so that cooling of the orifice tube is avoided. With this structural arrangement, variations in the flow rate or temperature of the cooling air have sub-stantially no effect on the temperature of the orifice tube. In order to diffuse tlle alr flowing out of manifold 30 and distribute it along the length of the orifice tube, a plurality oE diffusing screens and baffles 42 are located within the manifold between the supply tube 32 and the manifold outlet 34 as is more fully described in said ~.S. Patent No. 3,625,025.
P.ecause of the small si~e of the orifice tube construction9 it is possible to obtain substantial savings in the space required for producing a given numl)er of fibers; in some cases up to ten orifice tubes can be used in the ~space normally required for a single conventional bllslling producing a comparable amount of fiber. In order to ta~e advantage of this considerable space savings, the present invention contemplates the provision of a unique ... . ,, . .. . , .. .. , . ~

means ~or mounting the orifice tube, whicll means include a novel electrical connector arrangement and incorporates an electrical control circuit that takes advalltage of the substantially reduced power requ;rements of the orifice tuhe construction. ~s illustrated in FIGS. 1 and 2, the fiberi~ing unit 10 is secured at one end to the source 14 of high-pressure molten glass, by means of the flanged connector 24. ~le opposite encl of the unit is secured in an elongate clamping bar ll4, with the end 20 oE orifice tube 16 passing there-through for contact with a spring-loaded electrical connector 46. The connector is pressed against the end of the tube to malce a good electrical contact, whereby an electrical current of selected amp:Litu(le is introduced into tlle orifice tube, flowing thro-lgh the tube to a ground point at colmector 26 to heat the orifice tube to the selected temperature.

Clamping bar 44 is adjustably attached to, but is electrically insulated from, a fixed bus bar 43 which serves to provide a rigid mount for a plurality of fiherizing units as well as a common power source for the units so connected. A bolt 50 secures the clamping arm in place, the bolt passing through a spring arm 52 (FIG. 1), a first leg portion 54 of a curved contact arm 56, an upper elongated slot 53 in the bus bar, a second leg-portion 60 of the contact arm 56, an opening in a spacer plate 62, and the clamping arm. The bolt 50 is surrounded by an electrically insulative sleeve 53. ~n electrically insulative bushing 64 spaces the bolt 50 from arm 44, and a nut 66 and washer 68 secure the bolt.
second bolt 70 provides a pivot point for the clamping arm, bolt 70 being spaced from bolt 50 and passing through spring arm 52, leg portion 54 of the contact arm, through a lower elongated slot 72 in the bus bar, through Llle secolld leg portion 6C of arm 56, and througll spacer plate 62. The ell(l oE l-olt 70 is tllreaded into an electrically insulating pivot block 74 which may be secured to spacer plate 62. ~olt 70 serves to clamp the .. .. .. ~

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spring arm an(l contact arm assembly together and to bllS bar 48, as well as to provicle a pivot point for clamp arm 44. I~en nu~ 66 is threadecl onto holt 50, it tends to pull the top o:E clamp arm 44 (as seen in FIG. 1) toward the curved contact arm 56 and the bus bar 48. The middle portion of the clamping arm abuts the insulating spacer 74, whicll prevents it from coming into contact with the contact arm; accordingly, tighteninp, of nut 66 tends to move the lower portion of arm 44 away from contact arm 56, and into contact with the fiberi~ing unit 10. I~lus, the Eiberizing unit may be firmly clamped between the bus bar 48 and the glass supply source 14 by the clamping arm,- thereby securing the fiberizing unit in a selected position. The slots 58 and 72 in the bus bar allow adjustment of the exact location oE the Eiberizing unit an(l allow close spacing oF adjacent units, as may be seen in FIG. 2. Further, an individual fiberizing unit ~lay easily be removed or installed without disturbin~ adjacent ~mits~ merely by loosening nut 66 and by releasing the electrical contact 46.
Contact arm 56 is generally "J"-shaped, the J-shaped arm being inverted and positioned over the bus bar 48 so that the shorter depending leg portion 54 is adjacent one side of the bus bar and the longer depending leg portlon is adjacent the other side of bus bar 48. ~lounted in corre-sponding depressions 76 and 78 formed on opposite sides of bus bar 48 are a pair of thyristor elements 80 and 82, respectively. These elements are thicker than the depth of the depressions in which they are located so that one surface of each thyristor extends above the surface of the corresponding side oE the bus bar. Thus, the outer surface of thyristor 80 extends ahove the bus bar at depression 76 and is adapted to contact the inner surEace oE leg portion 54 oE connector 56. Simiarly, the outer surface of thyristor 82 extencls above the surface of tlle bus bar 48 at depression 78, ancl is adapted to contact the inner surface oE leg portion 60 of the connector arm.

I'rotrusion~s X4 and 86 are formed on opl~os:ite s:kles of the bus bar in the center of depressions 76 an(l 78, respectively, and ~it into corresponding hollows in the center of the thyristors 80 and 82 to center the thyristors in the bus bar depressions. The contact arm 56 similarly is provkle~ with protrusions 88 and 90 which engage corresponding hollows in the outer surfaces of thyristors 80 and 82 whereby the contact arm assembly is positioned with respect to the thyristors and bus bar. The bolts 50 and 70 hold the various elements tightly togetller in firm electrical contact, clamping tlle inner surfaces of the contact arm against the outer surfaces of the thyristors, and holding the thyristors tiglltly against the bus bar, whereby current may flow from the bus bar through one or the other of thyristors 80 and 82, depending on which is conductive, into the corresponding leg of contact arm 56.
The longer leg 60 of contact arm 56 extends downwardly and supports at its lower end 92 the electrical connector 46 wllich is adapted to provide electrical contact with orifice tube 16. Connector l~6 includes a contact block 9~ secured to tlle end 92 of leg 60, the block having on one side a cavity 96 adapted to receive the closed end 20 of the orifice tuhe. S~cured to the otller side of block 9~ hy means of screws 98 and 100 is a finned cooling block 102 which insures that the contactor will remain within acceptable temperatures, while yet avoiding excessive cooling of the orifice tube.
~djustment of the pressure of connector 46 against orifice tube 16 is by means of spring arm 52, the upper end 10~ of which is secured tightly to the bus bar by bolts 50 and 70. The spring arm tapers down at shoulder 106 to Eorm a thin, relatively flexible central portion 108.
The sprillg arm extencls downwardly as far as the orifice tube, with the bottom portion 110 being thickened and provided with a threaded llole through whicll extencls a pressure adjusting screw 112. This screw is al:igned approximately with the axis of the ori~ice tube,' and extends througll the lower portion 110 of the spring arm into contact with the connector hlock 46. I'referably, the end oE the screw extends into an , .. . , . , . , ............ .. _ _. .. . . _ ~' ' ' ~ ' ' .

6;~
opellin~ ll4 formecl in t~e coolin~, rins 102 Qn~l contacts a pacl 116 in the bo ttom thereor.
~ len the screw 112 is threaciecl into the spring arm its end presses against the contact block, tending to separate tile block 46 from the end llO of the sl~ring arm. The spring action of arm 52 tends to force contact block 46 against the end of the oriEice tube, with a Eorce depending upon the strength of the arm 52 and the amount that the acljusting screw is threaded into the lower end portion 110.
As indicatecl in FIC. 2, a temperature measuring device such as, Eor example, a Pt-PtRh thermocouple, 118 is placed on the orifice tube 16 to provide an output signal on lines 120 and 122 proportional to the temperature of the glass being extruded. A control system including a temperature controller 124 provides the necessary control action to maintain the oriEice tuhe 16 at a predeterniined level, or set point. The controller regulates a thyristor firing circuit 126 in known manner by way of lines 128 nncl 130, with the output of the firin~ circuit being applied by way of lines 132 nnd 134 to thyristors 80 and 82, as shown in FIG. 3.
The control system is of conventional type, and preferably is oE the three mode type well known in the prior art. As shown in FIGS. 2 ancl 3, each of the fiberiæing units 10, 12, etc., are substantially identical, and are individually controlled by corresponding control systems.
Thus, the unit 12 is shown in FIG. 2 as being mounted closely adjacent unit 10, with all of the units being ad~justably secured to the bus bar 48 by means of slots 58 and 720 In practice, it has been found that numerous UllitS may be placed in electrical parallel on a single bus bar, with the center-to-center spacing being on the order of 1-1/2 inches or less. In FIC. 2 and FIG. 3, the elements of fiberizing unit 12 that are duplicates of similar elements on fiberizing unit 10 are similarly numbered, but primcd.
~ s shown in FIG. 3, the bus bar 48 is connected to the secondary wincling 13G of a power supply transformer 138 selected to have a rating . _ sufficiellt to handle the maximum ret~uirements all oE the Eiberizing units that can be connected to tlle bus bar. The transformer primary winding 140 is energized from a voltage source (not showll) which may be variable to provide the desired voltage level on bus bar 48. ~ach of the fiberi2ing units 10, 12, etc., are connected across the trans- -fonner second~ry winding 136, being connected at one end to bus bar 48 and at the other end to a ground reference point 142 or by means of grounded coupler 26. The two thyristors 80 and 82 are half wave devices connected in parallel with each other with one end oE the thyristor combination being connected to bus bar 48 and the other end of the com-bination being connected through connector 56 to the orifice tube 16, represented here as a lleating resistance elemellt 144.
Thermocouple 118 senses tlle te~perature of orifice tube 16, and provides a signal to three-mode temperature controller 124, whicll may be energized by power lines 146, 148, and which compares the measured temperature signal with a precision reference voltage representing the set point, or desired temperature. Any difference between these signals is ampliÇiecl and applied to a conventional three mode control device, which feeds a signal to the firing circuit 126 to regulate the length of time during each half cycle of the AC input voltage from transformer 138 each thyristor will conduct. This regulation is carried out by applying appropriate control signals to the gate circuit of the thyristors 80 and 82 by way of lines 132 and 134, respectively, in known manner. In similar manner, each fiberi~inR unit that may be connected to transformer 138 is corlllectetl to tlle secondary, ancl is individually controlled, whereby fully indepen(lent control is obtained Çor each orifice tubt?.

6~ 6 It will be seen from the ~oregoing that a~ter securing tlle desired nnlnl~er of fiberizing units to tlle bu~s bar, the volta~,e at the sccondary o~ tile transFonner is adjusted to a level that will provide surricicnt excess volta~e to allow aclequate control for all of the units, and the voltage is thereaEter held constant. I~en the temperature of the orifice tuhe 16 deviates from the set point, the cnntroller 124 acts through the ~irin~ circuit 126 to cause the thyristors ~3n and 82 to alternately conduct, during a lar~er or smaller portion of eacl~ half cyc]e of the supply current, as the case may be, thereby passing a con-10 trolled amollnt oE current througll the orifice tube. This current --regulatioll adjusts the temperature oE the ori~ice tube until the set point is reached, and the overall effect i~s to maintain the orifice tube at the des;red set point. ~s long as the primary power system maintains a constant volta~,e across secondary windillg 136, each individual fiberizing unit may be regulated from zero to mQximum power, independently of adjacent units.
Tlle hus bar 4~ is shown in FI~. 2 as bein~ secured by means of suitahle holts 150 and 152 to a stud 154 on transfonner 13~, which stud provides a connection to the secondary windin~, and thus serves as an output terminal for the transformer.
In FIG. 4, an apparatus similar to F:[~. 1 is shown but having certain inllovative modifications tllerein in the electrical system utilized to ~eed current to closely spaced orifice tubes. Thus in FI~.. 4 there is sllown a glass delivery tube 414 suitably insulated with reEractory 415 wllich delivers molten glass from a furnace, not shown, to a horizontally oriellte(l mal~ l(l tul)e 419 ~s!lown in ~section. ~long one ~side o~ tlle hori-zont~l tul)e 419 therc is provided a plurality o~ cone sl~aped nipples, one of which i9 sllo~n as 420 in section. These nipples 420 are shaped to .

~66~

I)rovklc a mating, locatlng and ~sealillg sur~ace l~etween the or:ifice tube 416 and the molten glass source 414, and thereby insure t11e constant supply of molten ~las9 to the tube 4:L6. ~urrounding the nipple 420 is a ring Inem~er 424 constructed to firmly hold nipple 420 in a surrounding relatioll~sllil) and provicled with a lower pivotecl arm member 426. The ring 424 has secured to its upper end througll holt 428 antl 425 provided at its ~ree end with a stationary pin member 427 whicll protrudes inwardly.
clarlp 431 is provided whicil engages orifice tube 416 and is provided on its upper extremity with a curved slot 432 constructed to engage the pin 427. At its lower end arm 431 is provided with a slot For insertion of arm 42G therein. The arm 426 is threaded to receive nut 469 wllich wllen tirhtened urge~s clalllp 431 in a direction to~ard the molten glass source wllicll in turn ~irmly seals orifice tube 416 against ti~e nipple 420. The oriEice tube 416 is ritted with a circular conductor 422 whicll has a correspon-lillg cone shape at its point o~ connection to orifice tube 416 and extenlls bac~ along the tube. ~n electrical watercooled clamp 433 surrounds the circular conductor 422 with a corresponding support ring ~23 to provide necessary clamping support. An annular space is provided hetween the ring 423 and orifice tube 416 to allow sufficient insulation 470 and insure unrestricted movement of the orifice tuhe ~or a sealed connection with the glass source. ~n insulator 421 is provided between tlle conductor ring 422 and the nipple 420. This insulator 421 isolates the electrical system used to individually control the ori~ice tube 416 in accordance with this invention from the electrical supply, not shown, whicll is used to maintain the glass in the glass deliver-ing system in a ~oL~ c~ll(litioll. -' .

Oriflce tube hollsing 410 is physically positioned at its extren~ityopposite the glass source by a hallger 436 secured to bo]ts and 443 by a connector plate which supports the entire assembly. The end oE tube 416 is firmly connected by a clamp 454 to a connector 453 having leads 435 connected thereto. Leads 435 are held at their other e~tremity in a concluctive block 437 bolted to plate 439 which plate is in electrical contact w4th connector 448. The connector 448 is horseshoe shaped and is in electrical communication with thyristors 449 and 450. Plate 451 and 452 on the right side of the unit and plates of similar design on the left side of the unit, through bolts 442 and 443 and their associated nuts 444, 446, 445 and 447 clamp tightly against the bus bar 459 to insure good electrical contact between the thyristors 449 and 450 and the connector 448. Bolt 442 is provided with an insulated sleeve 440 and bolt 443 with a similar insulated sleeve 441. This clamping also insures good electrical contact between the connector 448 and the electrically conductive plate 439 which feeds current from the transformer, not shown, to the orifice tube 416.
Current at the other end of tube 416 is passed through the ring 422 to the clamp 433 secured to connector 434 through bolt 468. This unit is similar to the electrical system utilized in the embodiment of the invention as is shown in FIG. 3. Thus, the bus bar 459 is connected to the secondary winding 136 of a power supply transformer 140. The winding 140 is of course energized by a voltage source not shown and which may be adjustable to provide the desired voltage level on bus bar 459. The fiberizing unit 416 is connected across the transformer secondary winding 136, being connected to bus bar 459 at one end and terminal 142 at the other end.

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In this embodiment, of course, thyristors 449 and 450 are half ~ave devices connected in parallel Witil each other with one end of the thyristor combination connected to bus bar 459 and the other end oE the combination being connected through connector 448 to the orifice tube 416.
The operation of the control circuitry is as described hereinbefore in discussing FIG. 3.
~hile only one fiberizing tube 416 is shown in FIG. 4 it is, of course, understood that the plurality of these tubes may be used with each tube 416 being controlled Erom a common power transformer by providing each tube with a thyristor system such as shown above.
It will be understood that, if desired, various additional cooling means may be provided for the apparatus to prevent overheating of the thy-ristors. Thus, for example, cooling ducts may be provided in the bus bar 459 through which cooling water may be circulated. ~s may be seen in FIG. 1, the source 14 of molten glass may feed not only the parallel orifice tubes of orifice tube fiberizing units 10 and 12, but an additional row of tubes 156 extending in the opposite direction from the feeder. ~ similar arrange-ment can be made in FIG. 4 by providing suitable nipples 420 on the opposite side of the glass delivery tube 419.
As can be seen from the drawings, particularly FIGS. 4 and 5, the orifice tube 416 is insulated by refractory 417 in an air manifold housing 410. The manifold housing 410 is provided with an air supply inlet 411 and air chamber 413. The air in chamber 413 is distributed along the oriEice tube 416 by passing the air through the chamber 413 down through the restricted air passages 472 through filtering means, for example, screens 471 and out across the orifice tube 416. The screw type elements 473 are used to control the opening of the passages 472 by inserting the tapered ~ - ~

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end 474 of each of the elements 473 to any desired length into the passages 472 thus increasing or decreaslng the amount of air that can be fed through each Or these passages 472. The air distribution elements 477 are placed in the plenum or air chamber 413 in surrounding relationship to the orifice tube and along the length of the chamber 413 in side by side relationship to each other. Each of the elements 473 controls the air flow across the orifice tube 416 for a length of about 1.5 inches (3.81 centimeters). Sufficient of the elements 473 are provided for a given length oE orifice tube 416. Thus, for example, with an orifice tube 416 having a length o~ 18 inches (45.72 centi-meters~ eleven opposite pairs of elements 473 are used so that incremental lengths of 1.5 inches (3.81 centimeters) are individually controlled. When any discrepancy or erratic performance of a group of orifices along the length of the tube 416 is observed, the cooling at that location can be readily adjusted by moving the pin 474 into or out of its mating passage 472 until the condition is corrected. Tllus, a method is provlded to achieve more accurate temperature control over the multiplicity of orifices contained along the elongated orifice tube 416 to insure more uniform operation thereof.
In lieu of the air distribution system described above, the system described hereinbefore with respect to FIG. 2 can be employed.
Thus there has been disclosed an apparatus for providing fully inde-pendent temperature control of a multitude of closely spaced heating elements by a technique which eliminates the need for space-consuming step-down transformers and saturable reactors for each unit, as now used on conventional bushing systems.
A single power source is used to power a plurality of such elements, through a connector arrangement which provides means for conveniently and quickly removing and installing , .. ~. .

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individual fiberi~ing units. ~lthough the invention has been described and illustrated in terms of a preferred embodiment thereof, it will be apparent to those skilled in the art that numerous varlations and modifi-cations can be made without depart:ing from the true spirit and scope thereof, as defined in the following claims.

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Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a glass fiber forming system in which glass fibers are formed from an elongated bushing operating under positive pressure other than glass head pressure and in which the elongated bushing is electrically controlled, the improvement comprising providing along incremented lengths of the bushing cooling fluid zones which are adjustable, and adjusting one or more of said zones in response to a need for more or less cooling fluid to that zone during operation of the bushing.

2. In an elongated fiber glass bushing having a cooling fluid source which projects fluid across the surface of said elongated bushing during operation thereof the improvement comprising a plurality of fluid adjustment means positioned along the length of said elongated bushing, each of said adjustment means being individually controllable so as to deliver cooling fluid from a common fluid source across an incremental portion of the length of said elongated bushing.

3. The apparatus of claim 2 wherein means are provided to filter said cooling fluid before releasing it to said elongated bushing.