WO2001083389A2

WO2001083389A2 - Method and apparatus for controlling heating and cooling in fiberglass bushing segments

Info

Publication number: WO2001083389A2
Application number: PCT/US2001/013887
Authority: WO
Inventors: Paul S. Sanik; Eugene C. Varrasso
Original assignee: Advanced Glassfiber Yarns, Llc
Priority date: 2000-05-01
Filing date: 2001-04-30
Publication date: 2001-11-08
Also published as: AU2001257434A1; WO2001083389A3

Abstract

A method and apparatus for controlling the temperature of a multiple segment glass fiber bushing by providing a main current and a supplemental current having a heating and cooling circuit and directing the cooling circuit to a bushing segment 180° out-of-phase with the main current to effect enhanced cooling of the segment.

Description

METHOD AND APPARATUS FOR CONTROLLING HEATING AND COOLING IN FIBERGLASS BUSHING SEGMENTS

FIELD OF THE INVENTION The present invention relates in general to the control of glass fiber forming bushings and, more particularly, to an improved method and apparatus for controlling the temperature of a fiberglass bushing by providing supplementary heating or cooling.

BACKGROUND OF THE INVENTION Glass fibers are commonly produced by drawing multiple streams of molten glass through nozzles or holes located in a heated container known in the industry as a bushing. The bushing is electrically resistance heated by passing high current therethrough. Since the temperature of the bushing is one important factor in determining the characteristics of the glass fibers produced using the bushing, a variety of temperature control arrangements have been devised. Known fiberglass bushing control circuits are based on either current diversion around all or one or more segments of a multiple segment bushing, or current injection into one or more segments or a multiple segment bushing.

Temperature control using current diversion around a bushing, or one or more segments of a multiple segment bushing is disclosed, for example, in U.S. Patent No. 4,594,087. In that disclosed arrangement, a controller diverts current around a bushing or segments of a bushing using variable impedance circuits. The diverted current reduces the temperature of the bushing, or segment of the bushing from wliich the current was diverted. U.S. Patent No. discloses a bushing controller using an auxiliary transformer in each of the variable impedance circuits of the type of controller shown in U.S. Patent No. 4,594,087, to increase the current capacity of the controller. Temperature control using current injection to a bushing is disclosed, for example, in U.S. Patent No. 4,780,120. This patent discloses injecting current into all but one segment of a multiple segment bushing and adjusting the supply of electrical energy to the entire bushing to control temperature of each segment of the bushing.

Many of the known prior arrangements are able to control fiberglass bushings to produce high quality glass fibers. There is an ongoing need for improvement in controlling fiberglass bushings to improve their operation and efficiency.

SUMMARY OF THE INVENTION According to one embodiment, the present invention provides a method for controlling the temperature of a multiple segment fiberglass bushing by providing a main current and coupling the main current to the bushing. A supplemental current comprising a heating and a cooling circuit is provided and coupled to the bushing. The supplemental current from the cooling circuit is directed to the bushing 180 degrees out-of-phase with the main current.

In a further embodiment, the present invention is directed to the aforementioned method and further comprises generating a control signal for said segment of the fiber glass bushing, and determining whether the control signal commands heating or cooling of the fiber glass bushing segment.

In a further embodiment, the present invention relates to a method for heating and cooling fiber glass bushing segments by providing a main current and coupling the main current to the bushing. A supplemental current comprising a heating and a cooling circuit is provided and coupled to the bushing. The supplemental current from the cooling circuit is directed to the bushing 180 degrees out-of-phase with the main current by achieving phase reversal of the current needed for the heating circuit. Such reversal is accomplished, in one embodiment, by reversing the connections on the main current. In a still further embodiment, the present invention is directed to a method for controlling the temperature of a multiple segment fiber glass bushing by providing a main current and coupling the main current to the bushing. A supplemental current comprising a heating and a cooling circuit is provided and coupled to the bushing. The supplemental current from the cooling circuit is directed to the bushing 180 degrees out-of-phase with the main current. The method further comprises operating the heating and cooling circuit to heat a fiber glass bushing segment by connecting supplemental current to the segment of the fiber glass bushing when a control signal commands heating, and cool the segment by directing the supplemental current from the cooling circuit to the segment 180 degrees out-of-phase with the main current when a control signal commands cooling.

In yet another embodiment, the present invention is directed to an apparatus for controlling the temperature of a fiber glass bushing segment comprising a primary power source for delivering a main current to a bushing segment along a main circuit and a secondary power source for delivering a supplemental current comprising a heating and a cooling circuit along a supplemental circuit to a bushing segment, the supplemental circuit having a phase controller for controlling the supplemental current to a phase the same as or different from the main current. In a preferred embodiment, the phase controller directs the supplemental current to run 180 degrees out-of-phase with the main current.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows schematic representation of a controller for a bushing system;

Figure 2 shows a schematic representation of a current-injection bushing system;

Figure 3 shows a schematic representation of the combined current-injection and current-shunting heating and cooling system;

Figure 4 shows a schematic representation of a five segment bushing showing the limitation on the capacity for cooling;

Figure 5 shows a schematic representation of the active-cooling arrangement according to one embodiment of the present invention; Figure 6 is a diagram showing the outcome if the conduction angle of the supplemental current, in the cooling mode, exceeds the conduction angle of the main bushing current;

Figure 7 is a diagram showing how the voltage cycles are varied to vary the bushing current; Figure 8 is a diagram showing voltage control using phase-angle control of the conduction time of each half cycle of incoming AC; and Figures 9 and 10 are phase diagrams showing the supplemental current regulated by phase-angle firing.

DETAILED DESCRIPTION OF THE INVENTION The heat-cool form of current-injection was developed to provide automatic, desired compensation for changes in the heat pattern of a bushing. Bushings are normally set up mechanically to provide a "level" heat distribution across the bushing. A level heat pattern is one in which the temperature of the glass in the tips (nozzles or apertures) of the bushings, is approximately equal at all locations on the bushing tip- plate. This heat pattern produces filaments of equal diameter from any point on the bushmg. Leveling a bushing is understood to be the process where adjustments in the cooling fins and the power attachment clamps are made to adjust the heat flow, into or out of the bushing, to achieve a heat balance that results in a uniform temperature of the glass in the tips. Such "leveling" has been accomplished by adjusting cooling fins along the bushing and by adjusting the position of the clamps that provide electrical connections to the bushing ears. In this "static" system, any subsequent changes that affect heat transfer in the bushing will change the final heat pattern in the bushing. The standard automatic control system can change the bushing power to return the center-section thermocouple reading back to its setpoint, but the temperatures of the end section may change.

Current injection allows for the adjusting of one component of the heat input to the end sections of the bushing, which regulates end-section temperatures. Known current injection bushings source current to the bushing at from 0 to 200 amps. According to one embodiment of the present invention, current injection rods are built into the bushing at intervals about one-third the distance along the bushing. In other words, for example, a bushing 24 cm in length would have the rods located at a point on the bushing located 8 cm inward from each end of the bushing. A further preferred embodiment contemplates a "four way split" with the rods occurring at on-quarter intervals along the bushing length. In other words, a bushing 24 cm in length would have rods inserted at the 6 cm, 12 cm, and 18 cm points on the bushing. In this way the three inserted rods separate the rod's length to provide four regions or zones. The rods protrude through the bushing side- wall to provide one of the electrical contacts in the circuit, with the other contact being the bushing ear.

In one embodiment, the rods are oriented on the same side of the bushing, however the rods may be positioned in any desired orientation to achieve the desired effect. In this way, the current path exists between the rod and the ear, and allows an auxiliary current to flow only to the end section of the bushing. In another embodiment, rods may be placed on both sides of the bushing.

In the current-injection embodiment of the present invention, the bushing is mechanically leveled with half of the maximum injection current supplied to the end section. After that, the end-section control loop either adds more current to "heat" the section, or sources less current to "cool" the section.

In the heat-cool current injection embodiment of the present invention, the "heat" mode works by sourcing additional current to the end section. To "cool" the bushing section, some of the current that would normally flow through the bushing from the main power controller is diverted around the end section. Current is shunted from the ear terminal connection and returned through the current-injection rod in the end section. In essence, a heat-cool power pack provides a controllable electrical short around the end section that is, in reality, a series of phase fired silicon controlled rectifiers (SCRs) controlled so that they conduct for only a portion of each line cycle. However, this system of cooling has limitations that cannot be overcome by merely increasing current.

According to the present invention, an "active cooling" system has been discovered. To provide heating, a supplemental current is driven in-phase with the main heating current. To provide cooling, a supplemental current is driven out-of- phase with the main current. This has the effect of reducing the net current in the zone when cooling is desired. Accordingly, one advantage of the method of the present invention provides a system that is not dependent on the voltage drop along the bushing between the attachment points of the supplemental system (the voltage between current-injection rods, or between an ear and a current-injection rod) to drive the diversion current. Line voltage, stepped down appropriately through a transformer, is used to drive the out-of-phase current. The applied voltage can be selected to handle the circuit resistance of the rods and cables so that they are not the limiting factors with respect to cooling.

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. Figure 1 shows a schematic representation of the temperature regulation system for bushings used to manufacture glass fiber. In this system 10, an electrical voltage is applied across the bushing 12 through the secondary 11 of a transformer 13. The voltage to the primary 9 of the transformer 13 is adjusted via phase angle controlled SCRs 14a, 14b on power pack 14 in order to vary the bushing voltage on the secondary 11. The main power delivery system 15 is attached to the bushing 12 via clamps (not shown) to "ears" 18, 20 that are provided at the ends 17, 19 of the bushing 12. The temperature of the bushing 12 is monitored by a process controller 22 which receives a temperature representative voltage signal from a thermocouple 23 to adjust the SCR firing angle which regulates the bushing temperature. If the primary side of the bushing transformer of Figure 1 were connected directly to the power lines, a current would flow in the bushing 12, causing it to heat. However, there would be no means of controlling the temperature. To provide temperature control, some means of regulating the current flow through the bushing is required. This is most easily accomplished by modifying the voltage applied to the primary of the bushing transformer. This in turn modifies the voltage developed at the secondary, and thus the current that subsequently flows in the bushing. The voltage applied to the transformer primary is usually modified in one of two ways described below. Either method can be accomplished by the proper control of the SCRs 14a and 14b in the power-pack 14. See Figure 1. One method alternately applies or skips some number of complete cycles of the incoming "AC" voltage. The ratio of the number of "on" cycles to the total number of cycles available in a particular interval determines the fraction of the incoming line voltage that is actually applied to the transformer in that interval. By varying the number of "on" cycles in the interval, the primary voltage is varied, and thus the bushing current is varied. Figure 7 illustrates this in a simplified fashion. Another method of modifying the voltage applied to the transformer is by phase-angle control of the conduction time during each half-cycle of the incoming "AC" voltage. In this method, the SCRs wait some adjustable period of time after the "zero crossing" of the voltage wave before they begin to conduct current. The SCRs then conduct until the current goes to zero. This procedure is repeated for each half- cycle of the incoming AC wave. By adjusting the time delay after the zero crossing, the voltage applied to the transformer is varied, and thus the bushing current is varied. The technique is illustrated in Figure 8.

The magnitude of sine wave is given by the function: V-=Vpeak*sin(theta), where theta is an angle between 0 and 360 degrees. This is equivalent to the equation: V=Vpeak*sin(omega*t), where omega is the frequency in radians per unit time, and "t" is the time, starting at zero. For a fixed value of omega, (as is the case with the normal line voltage), specifying "t" is equivalent to specifying theta. Although the power-control technique generally uses time as the reference to control the SCRs, it is called "phase-angle" firing because, on a cycle-by-cycle basis, it is easier to visualize the SCRs firing at a particular angle in the sine function. Figure 2 shows a schematic representation of a current-injection bushing temperature regulation system. In this system 40, a multi-segment bushing 41 is depicted. A current-injection system is shown to help customize the temperature achievable in a particular segment. Bushing 41 comprises segments 42, 44, and 46. Current injector rods 58 and 60 are attached to the same side of bushing 41. Ends 54 and 56 of the supplemental circuit are attached to bushing ears 51 and 52. The other ends of the supplemental circuit are attached to current-injection rods 58, 60 that are built into bushing 41 located on the same side adjacent to bushing sections 42, 44, and 46. The circuit is phased such that the supplemental current from supplemental transformers 57, 59 flows in phase with the main current from the main bushing transformer 70. The power controllers 62, 64 and 66 isolate the main and supplemental circuits such that the currents are shared only in the segment of interest. SCRs 62a, 62b, 64a, 64b and 66a, 66b are associated with power controllers 62, 64, and 66 respectively.

Figure 3 shows the "heat-cool" embodiment of the present invention. The schematic representation shows a current injection system with a current shunting system. The arrows indicate the current direction that achieves the heating or cooling necessary. The heating function is achieved in the same manner as disclosed with the current injection system of Figure 2. For cooling, however, another set of SCRs 84a, 84b, 86a and 86b are added across the primary 57a, 59a of the supplemental transformers 57, 59 and made through a connection that is "downstream" of the heating SCRs 62, 64. When these cooling SCRs 84, 86 are conducting, they create a short across the primary 57a, 59a that is reflected to the secondary 57b, 59b, and provide a current path around the associated segment (from the ear 51, 52 to the current injection rod 58, 60). The amount of current that is shunted is determined by the voltage drop across the segment, the resistance of the shunting circuit, and the amount of time that the SCRs conduct (the conduction phase angle). With this system, the bushing can be leveled with no current flowing in the heat and cool system. For heating, twice the current that could be delivered from the same current- injection only system is available, and an equal amount of current can be shunted (assuming the other system elements permit it). Figure 4 shows a conventional heat-cool system applied to a bushing with more than single end sections of supplemental control. In essence, this figure shows the effect that the voltage drop (induced in a shared current-injection rod) can have on an adjacent cooling zone. This figure illustrates the limitations found in trying to apply conventional heat-cool techniques to adjacent zones of control in bushings. A bushing 100 is divided into sections 102, 104, 106, 108 and 110. Zone injection rods 112 and 118 are "shared" by adjacent heat-cool sections. Center segments are controlled from a thermocouple at a bushing center (not shown), and the end segments are controlled from thermocouples on those segments (not shown). Injection rods are shown inserted on the same side of bushing. However, problems arise when a bushing is divided into more segments, for example four or more, (and heat/cool is applied to adjacent segments), when one is left to be controlled by the main power system. Indeed, problems could arise with as few as three segments if the main power is fixed, and a supplemental system is attached to each segment or zone.

First, with more segments, the voltage across each segment is smaller. This means that, for a fixed external-circuit resistance, the maximum current that may be shunted is also smaller. Further, if a current-injection rod is shared, the voltage drop along the rod created by the heating-current flowing in one zone is phased such that it further reduces the voltage available at the neighboring zone to drive the shunt current. Therefore, when one zone is adding a significant amount of heat, the neighboring zone maybe incapable of cooling at all. See Figure 4. The schematic representation shown in Figure 4 assumes a desire to heat one segment 102, but cool another adjacent segment 104. The voltage available to drive the shunt current (V_x) is shown by the following equation:

If the V_rod = VS₂, then I_cooι = zero. Therefore, according to conventional schemes, situations could arise where no cooling could be achieved in segment two. Potential cures for this deficiency include using larger diameter current-injection rods to reduce the voltage drop along the rod, and to reduce the external circuit resistance. However, the rod becomes a significant heat sink and could distort the heat pattern across the bushing. Additionally, independent rods could be used for each zone, but that introduces more cables, clamps, and complexity to an already confined space, and further distorts heat distribution. This results in a non-uniform distribution of fiber diameters that is not acceptable in a useable product. Still further, independent current-injection rods could be used to avoid the voltage drop due to the shared current. However, this also risks further distorting the heat pattern and introduces more large cable connections in an already confined space.

These problems are solved by the "active cooling" system of the present invention. Figure 5 shows a conventional bushing heating circuit 81, and two active- cooling circuits 83, 84 that can supply either supplemental heating or cooling to bushing sections 42, 46 respectively. The arrows in Figure 5 indicate relative directions of current flow relative to the instantaneous flow in the main bushing- heating circuit. Figure 5 illustrates the condition of supplemental heating of the bushing segment 42, and supplemental cooling of bushing segment 46. Figure 5 is for illustration purposes only. It is understood that in practice either segment may be heated or cooled independently of the other.

The supplemental heating shown for bushing segment 42 is accomplished according to the methods shown in Figures 2 and 3 wherein supplemental current is driven through the bushmg segment in-phase with the main bushing-heating current. The amount of supplemental current that flows is regulated by the phase-angle firing of the SCRs 150a, 150b. The resulting currents are shown in greatly simplified and exaggerated form in Figure 9.

Instead of simply shunting current to achieve cooling, as is done in Figure 3, the supplemental cooling shown for bushing segment 46 in Figure 5 is accomplished by driving a current through the bushing segment that is 180 degrees out-of-phase with the main bushing-heating current. This results in a net reduction of the current through the segment that achieves the necessary and desired cooling. The amount of supplemental current that flows is regulated by the phase-angle firing of the SCRs 152 a, 152b. The resulting currents are shown in greatly simplified and exaggerated form in Figure 10.

As shown in Figure 6, for the circuit of Figure 5, it is critical that the conduction angle of the active cooling circuit 83, 85 be less than the conduction angle of the main bushing-heating system 81 during the cooling mode. As long as this condition is met, the active cooling system provides a net reduction of the current in the bushing segment to be cooled. Since the cooling mode works by effectively "canceling out" part of the main bushing-heating current, if the conduction angle of the supplemental cooling current exceeds that of the main bushing-heating current, there will actually be an increase in the net current in the bushing segment over that achieved when the conduction angles were just equal. In this instance, the segment will begin to heat rather than cool. This happens because during the interval before the main SCRs 66a, 66b begin to conduct, there is no current flowing in the main bushing circuit 81. If supplemental current is allowed to flow during this interval it will be the only current flowing in the segment since there is no main bushing-current to cancel out as yet. The resulting Joule heating will increase the segment temperature, rather than reduce it. Under closed-loop control, the process controller will see this increase in heating, and further increase the conduction angle in an attempt to cool the segment. This increase in conduction angle will only exacerbate the situation and result in a "run-away" condition of the control loop.

This situation can be avoided. One method is to feed the supplemental active- cooling circuits 83, 85 with the voltage applied to the primary of the main bushing- transformer (XI -X2) in circuit 81. In this way, the supplemental circuit can never supply current if the main current is not already conducting. A second way of avoiding the overlap problem is to provide the main bushing-transformer voltage as an input signal to the control portion of the active-cooling circuits 83, 84. The control circuits can then use this signal as a reference to electronically limit the conduction angle of active-cooling circuits' SCRs.

The average amount of current that flows in a supplemental circuit is a function of both the amount of time that it is allowed to flow (the conduction angle of the SCRs), and voltage applied from the supplemental transformer's secondary. If, in practice, the conduction angle of the supplemental cooling circuit begins to approach that of the main bushing-heating circuit (a condition to be avoided as noted above), the same average current can be achieved while simultaneously reducing the conduction angle of the supplementary circuit by changing to a transformer turns-ratio that provides a higher secondary voltage (a change in the tap setting of the transformer). In other words, a larger amount of current (from the higher voltage) is supplied for a shorter time.

To achieve the relative 180 degree phase reversal of the current, as compared to the main bushing-heating current in section 81 and the supplemental heating- current in section 85, the connections of section 83 to the power source can be reversed when cooling is desired. This is most easily accomplished on the primary side of the supplemental transformers. Such reversal can be done with a relay, as illustrated in Figure 5. However, for long term use, a solid-state mechanism is preferred. The relay position in section 85 is shown in the position that provides in- phase current to bushing section 42, and thus provides supplemental heating. The relay position in section 83 is shown in the position that provides out-of-phase current to bushing section 46, and thus provides supplemental cooling. The position of the relay is selected by the control circuit that is associated with the active-cooling circuit. This determines whether heating or cooling is being demanded. The control circuit is the same as that employed in the heat-cool controller of U.S. Patent No. 5,785,728, which is incorporated by reference herein as though made a part of the present specification.

By using an active-cooling circuit rather than a simple current-diversion circuit, a large enough voltage can be supplied from the supplemental transformer to overcome the losses encountered in the external circuit, and the voltage drops along the current-injection rods 58, 60. This allows the active-cooling circuit to be effective in situations where the earlier heat-cool circuit was not effective

While the rods are shown oriented on the same side of the bushing, the present invention contemplates orienting the rods at any point about the circumference of the bushing to obtain the desired effects. The transformer primaries 81, and supplemental active-cooling circuits 83, 84 control the voltages to the main bushing heating circuit by adjusting the conduction angle (time of firing) of SCRs 66, 150 and 152 respectively. That is, the main circuit is adjusted with SCRs 66. The two active- cooling circuits are adjusted with SCRs 150 and 152. As both the main bushing heating circuit 81 and the supplemental-active cooling circuits 83, 84 adjust their voltages by controlling the amount of time that their respective SCRs 150, 152 conduct (phase angle firing), it is critical that the conduction angle of the active cooling system 83, 84 during the cooling mode be less than the conduction angle of the main bushing heating system 81. If this is not accomplished, the cooling controller will actually begin to apply heat to the segment 46 that is undesirable. In effect, active cooling works by "canceling out" some of the main current. If the main current is zero, as it will be during the first part of the line voltage cycle before the SCR 66 begins to conduct, and the supplemental system sources a current, there will be no main current to cancel out, and the supplemental current will heat. This is shown in Figure 6. This could be avoided by feeding the supplemental active cooling circuits 83, 84 with the main circuit's 81 primary voltage XI -X2. In this way, the supplemental circuit current cannot conduct when the main circuit is not conducting. A similar effect can be obtained with smart controllers that communicate their firing signals to one another.

Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

THAT WHICH IS CLAIMED:

1. A method of controlling the temperature of a multiple segment glass fiber bushing comprising the steps of: providing a main current to a circuit; coupling the main current to the bushing; providing a supplemental current comprising a heating and a cooling circuit; coupling the heating and cooling circuit to the bushing; directing the supplemental current from the cooling circuit to the bushing 180 degrees out-of-phase with the main current.

2. The method according to Claim 1, further comprising the step of generating a control signal for said segment of the glass fiber bushing.

3. The method according to Claim 2, further comprising the step of determining whether the control signal commands heating or cooling of the glass fiber bushing segment.

4. The method according to Claim 1 , wherein the bushing comprises a plurality of segments.

5. The method according to Claim 1, wherein the cooling circuit comprises a process controller.

6. The method according to Claim 1, wherein the heating circuit comprises a process controller.

7. The method according to Claim 1, further comprising the steps of achieving phase reversal of the current to reverse the heating and cooling circuits.

8. The method according to Claim 7, wherein the phase reversal is achieved by reversing the connections to the main current source.

9. The method according to Claim 1, further comprising the steps of operating the heating and cooling circuit to heat a glass fiber bushing segment by connecting the supplemental current to a segment of the glass fiber bushing when a control signal commands heating, and cooling the segment by directing the supplemental current from the cooling circuit to the segment 180 degrees out-of-phase with the main current when a control signal commands cooling.

10. An apparatus for controlling the temperature of a glass fiber bushing segment comprising: a primary main power source for delivering a main current to a bushing segment along a main circuit; and a secondary power source for delivering a supplemental current comprising a heating and a cooling circuit to a bushing segment along a supplemental circuit, the supplemental circuit having a phase controller for controlling the supplemental current to a phase the same as or different from the main current.

11. The apparatus according to Claim 10, wherein the supplemental current is provided to the bushing 180 degrees out-of-phase with the main current provided to the bushing for cooling a bushing segment.