FI66257C - FARING REQUIREMENTS FOR VARIABLE ELECTRICAL EQUIPMENT WITH JEWELLE EFFECTIVE WASHING MATERIAL IN MATERIAL MATERIAL - Google Patents

Description

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Patana · odi ragirtarrtyulaan '' Aw »lan ta <dod / edjJtr ^^ 31-05.84 (32X33X31) ^ r« «er« »oikmn-Λ ^ βΗ prior * · '15-10.74 USA (US) 514549 (71) Owens -Corning Fiberglas Corporation, Fiberglas Tower, Toledo,

Ohio 43659, USA (72) Eugene Camillo Varrasso, Heath, Ohio, USA (74) Oy Kolster Ab (54) Method and device for warning of incipient electrode dies when heating a thermoplastic agent by the Joule effect - Förfarande och anordning för varning av begynnande elektrodfel vid Joule-effekt-uppvärmning av i värme mjuknande material Electrically heating thermally softenable materials using the Joule effect involves providing an electrical current connection through this material from the electrodes. A typical heat-softenable material, glass, has previously been maintained at or near operating temperatures of about 1425 ° C by immersing one or more pairs of electrodes in molten glass and passing controlled pulses of electrical power from the electrodes through that glass. Often, these electrodes have considerable portions of their glass-contacting surfaces spaced apart from the walls of the glass of this container or furnace in order to reduce the heat applied to these walls and increase the life of the walls. One shape of the electrodes includes a straight circular cylinder that is elongated. Passing it through the bottom of this furnace. Although a number of solutions have been used to protect this electrode and the refractory material at the bottom has been found, there is a tendency for the electrodes to corrode in the area of this wall from which they pass.

66257

In the case of cylindrical electrodes, coolable sheaths are installed around these electrodes below the bottom of this furnace to reduce the temperature of the electrodes outside this furnace to a level that is not exposed to the interfering effects of atmospheric parts. It is still not uncommon to maintain an inert atmosphere within this sheath and around the electrodes so that it is partially protected from the length at which the temperature approaches that inside the furnace. Even with such precautions, the electrodes tend to corrode generally at or slightly below the interface between the bottom of the furnace and the molten glass. Such corrosion may result in rupture of the electrode in the melt.

When the electrode breaks the wall of this furnace in the vicinity of the remaining lump, it is etched and leaks unless corrective action is taken quickly.

The present invention relates to a method and apparatus for monitoring electrodes used in the melting of thermosetting substances, wherein a pulsating voltage is periodically applied over electrodes which are electrically in contact with the molten substance. The goal is to detect the expected electrode failure conditions and point these situations out. Such an indication allows corrective action to be taken in a timely manner.

The expected electrode failure has been found to be demonstrable as an increase in the resistance value between a pair of electrodes that supply electrical power for this heating with the Joule effect.

One aspect of the present invention is based on determining the rms value of the voltage across the electrodes and the rms value of the current flowing to the electrodes, determining the electrical resistance based on the rms voltage and current rms values obtained, and detecting the electrode current initially depending on a predetermined resistance value.

Another feature of the invention includes enhancing the accuracy of the resistance value, which is accomplished by detecting the rms values of current and voltage and using them to determine the resistance value.

Another aspect of the invention includes optionally connecting a resistance measuring device to a pair of electrodes using the Joule effect from among such pairs of electrodes and using an expected failure detector and an electrode pair detector to indicate the pair from which the detector then operates.

Figure 1 is a flow chart of a procedure for monitoring the expected failure of electrodes in a Joule effect heater applied to an electrically conductive, thermally softenable material.

Fig. 2 is a schematic representation of the structure of a glass melt with the electrode pairs formed as individual electrode portions and in which the 3 66257 electrode pairs consist of electrodes having a plurality of portions, and a schematic circuit diagram for a typical pair of each type.

According to the present invention, it has been found that the expected failure of an electrode embedded in a fluid in a fluidizable material when electrical power or current is applied to the fluid for heating with the Joule effect can be demonstrated by an increase in resistance between the electrode pairs transmitting this current. This phenomenon is believed to originate from corrosion of the electrode which reduces its cross section and the formation of fractures in the area narrowed by this corrosion.

Since a substantial increase in resistance value between electrode pairs has been observed as much as 24 hours before electrode failure, it has been concluded that the onset of the event that ultimately results in failure occurs as a decrease in cross-sectional area along the electrode length. This reduction, or inward constriction, has most often been observed to occur in the area of the electrode in the vicinity of the area of immersion from its refractory wall to the tank for molten material. Typically, the rate of flattening of the resistance value increases with time. It has been found that an increase of 20% (20) is a reliable indication of the expected interference, as a result of which such an increase has been used as a criterion for activating the interference detector.

It should be noted that in the long-term plans of Joule-heated tanks, some electron corrosion occurs over relatively long periods of time. This prolonged corrosion and the associated long-term increase in resistance between the electrode pairs is not indicative of the expected electrode failure. Accordingly, in the case of a glass smelter using sodium borosilicate type glass in the manufacture of glass wool and heated to a melt temperature and a refining temperature of about 1425 ° C, the resistance value between the vertical, straight circular cylindrical molybdenum electrodes with diameters of 3 is through a base containing glass more than twenty inches in length is about 0.04 ohms when they are spaced six feet apart along this base.

The observed increase in resistance value to 0.03 ohms in a relatively short period of time has been used to indicate expected failure. In order to minimize false alarms, there has been a period of operation of 4 66257 in which normal corrosion leaching changes have not been compensated for about 3 months. Thus, when the resistance value between the pairs of electrodes is compared with a certain setpoint value, this point of the setpoint value can be redefined by sixty percent above the then resistance value every three months.

The operation of the detector according to this system may be enabled in order to implement an automatic power cut-off for a pair of electrodes from which increased resistance is detected. However, the preferred practice is to use the alarm continuously until the alarm is acknowledged and instruct the appropriate personnel to act on the alarm by inspecting the electrodes, circuit and oven to determine the cause of the change and then either correct the cause, turn off the power to the area or no problem exists.

A set of variables that affect the resistance value of a pair of electrodes exist for any given system in which the above method of monitoring is used. In the case of glass, there is a steep temperature resistance coefficient in the temperature range in question for melting, cleaning and machining. The Coalition of Glass is also relevant in determining resistance. The size of the electrodes and the conditions as mentioned above also have an effect on the resistance value. In normal practice, the glass assembly and temperature are stabilized and can therefore be disregarded. The initial size of the electrodes is predetermined and the gradual change in size can be taken into account as it changes the resistance value of the pair of electrodes as mentioned above. Thus, a relatively sudden change in the resistance of a pair of electrodes is correlated with a rapid change in the state of the electrode.

In practice, the Joule phenomenon is used to heat glass with a set of electrode pairs. The electrodes of these pairs can be made of one or more parts. Effective control of this system involves optional control of the resistor from each set of electrode pairs. This is accomplished by observing the pairs periodically. If a plurality of parts are used for the electrodes in a pair, the individual parts of the electrodes can be inspected in pairs with another electrode or part of the electrode. This control of the parts is desirable because the increase in the resistance value due to changes in the state of a particular part is overlapped with respect to the parts connected in parallel with it. Such parallel-connected electrode parts tend to collect for themselves the current previously carried by the associated part as this part deteriorates and increases in resistance.

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Another factor that should be considered when monitoring the resistance of a pair of electrodes is the current flow between the pairs and the complex waveform in the furnace input power, from which the current and voltage values for indicating the resistance value are obtained. The current flow between the pairs can be ignored in a stable system. Waveforms, especially those generated by phase or time control of the input power, differ from the pure sinusoidal shape. Those signals that represent voltage and current can be processed to correspond to true rms values for accurate determination of the resistance of a pair of electrodes. This is especially the case when heating with glass with the Joule effect, where essentially the entire impedance is of the resistance type.

If computer resistance calculation is used, the actual effective current and voltage values can be selected on a scale to suit the input needs of this computer.

As represented in the control case of Figure 1, when illuminating the expected electrode failure, it can be accomplished by generating a mismatch value of the electrode pair that includes this electrode and comparing this resistance value to a certain setpoint, which triggers the error detecting apparatus. Resistance is determined by looking at the voltage or its dimensional portion applied over a pair of electrodes to use Joule heating in a molten material to be treated and measuring the current or a measured portion thereof as it passes through the pair of electrodes. This voltage and current control can be implemented in cables or,: conductors leading to these electrodes,

The illustrated comparison with the setpoint is suitable for automatic detector operation, a memorizing pressure device, or a change in process control, however, direct expression as a read predetermined fading value can also be implemented as an indication of an expected fault.

An apparatus for heating molten glass with the Joule effect is shown in Figure 2, which includes multi-electrode pair monitoring device information that is automatically swept, measuring the curing value and indicating alarm levels, current values, and voltage values for each code-identified pair. The glass furnace is shown provided with five pairs of electrodes 12, 13, 14, 15 and 16 as they protrude upwards through its base 17 and immersed in molten glass 18. Each pair of electrodes 16 has two electrode parts 21, 22 and 23 and 24. 12-15 and for paired electrode parts 21,22 and 23 and 24.

* "6 66257

Each of the electrode pairs 12-16 is connected to an input source of electrical power pulses having alternately opposite polarities such as via parallel opposed polar rectifiers 26 and 27 to the pair 12 adjusted by a trigger control 28 which may be provided with current limiters (not shown) to optionally, the SCR rectifiers would be triggered when alternating current is supplied through the power transformer 29. In the case of a pair of electrodes 12, the conductors 31 and 32 transfer power to these electrodes. In the case of a pair of electrodes 16, the electrode parts are connected to the AC power supply from the transformer 33 via SCR rectifiers 34 and 33, the trigger control 36 of which corresponds to part 28. Parallel conductors 37) 38 and 41 and 42, respectively, pass to electrode parts 21, 22 and 23 and 24 Controlled power supply sources with pulsed opposite polarities (not shown) corresponding to transformer 29, SCR rectifiers 26 and 27 and trigger control 26 are also provided for electrode pairs 13) 14 and 15.

The resistance value of the electrode pair 12 is determined by measuring the voltage across the electrodes from conductors 31 and 32 using transducer 44, one half of which is grounded and the other half is connected via conductor 43 and contact 46 from relay R1 to rail 47 · Rail 47 supplies voltage waveform to DC , which in a typical case is a type 4128 true power to DC voltage transformer manufactured by Burr Brown.

The DC converted signal representing the effective voltage is input to the computer 51 from the conductors 32 and 33 from the converter 46 and processed by the computer with the rated signal representing the effective current generating a flux value for the electrode pair 12. 18 is detected by a current transformer 34 having a winding around the conductor 32, which feeds a signal to the converter 33 · When dimensioning this current the reverse voltage signal representing the power value current is applied from the conductors 62 and 63 to the computer 51 as a resistance value to be processed there. The normal resistance value for a pair of electrodes can be obtained by calculation or measurement.

Once the equilibrium handling conditions have been established in the furnace 11, the resistance value can be generated from the computer-determined effective voltage and the effective current value. The setpoint is formed as the threshold value for this residual alarm and is set as an input value for a comparator inside the computer. The second input to the comparator is the processed resistance value (R - E / l), which is obtained from the effective voltage and the effective current.

The functions of the transducers in parts 4S and 61 as well as the processing functions in the computer 51 are in use for a number of electrode pairs, several of which must be monitored. This is done in the manner of either time alternation or multiplexing, which is internally programmed into the computer and the computer periodically assigns an address code to several different circuits from which the resistor is to be monitored. Typically, an IBM 1800 computer is used, which is applied to a number of other process controls and control tasks by connecting the multiplexing circuit to the electrode pairs in each turn. When observing each pair of electrodes, the observation typically includes a time interval of about two seconds. During this two-second interval, the effective voltage and the effective current are read and the calculation of the resistance value is performed. The coded output is then input so that the multiplexing circuitry is next connected to the circuit being monitored. The computer may be provided for continuous sweep rescheduling of the circuits being viewed, for complete timelines of these sweeps over time, or optionally for viewing certain circuits at more frequent intervals than other circuits.

The circuit address codes are provided by the computer 51 in the form of four binary characters on wires 64,65,66 and 67 to the interpreter 68. The interpreter 68 provides individual relay triggers for those relays that have normally open cords in their circuits. between for voltage signals and between the current signal input source and the rms value converter 61 for each pair of electrodes for the corresponding code. Thus, the relay R1 is actuated by closing the tips 46 and 53 and switching on the electrode pair 12 to calculate the resistance value. Similarly, other electrode pairs are monitored by energizing the relays in the alternating order of monitoring. When the code of a certain pair is entered from the computer 51, it also enters a pair of code, which may be digital or interpreted as another code such as a number or letter display 71, such as a window 72, while displaying current and voltage values in windows 7? j * 74 *

In the event that the resistance value is too high for the monitored zone at a given time, the alarm indication may be displayed in window 75 and / or the printer's printing device or light display may be arranged to display a message such as "electrode pair no. 1, turn off the power". leave and call the supervisor ".

Since the resistance between the pairs of electrodes or between the pairs of electrode parts may be different, each pair could be provided with a separate set point. This setpoint is obtained from the memory of the computer 51 when the pair in question is being monitored. It may have been set in an appropriate manner (e.g., from 120 to 96 of the normal resistance value) for the alarm threshold to indicate electrode failure in that pair.

It can be seen that although the Fifth pair of 16 electrodes or the Fifth Joule phenomenon, the heating zone numbered from left to right in Fig. 2 is provided with two portions of closely spaced straight circular cylindrical rods running vertically upwardly through the bottom of this furnace. Thus, although the common power of the supply source for heating with the Joule effect in zone 5 is electrically connected to the individual parts in parallel, only one such oea is monitored at each polarity during a given sweep interval.

The parts 21 and 23 are monitored by their voltage at the transformer 76 over the conductors 37 and 41 and their current is monitored in the winding 77 at the conductor 37 to the transformer 78.

This monitoring is performed when indicated by the interpreter 68 exclusively energizing the relay R5 and closing the tips 81 to the actual rms converter 46 for the voltage arm and the contacts 82 for the actual rms converter 61 to the current. At this point, the computer calls up the resistance values of the setpoints over the parts of this electrode pair and turns on the display. Furthermore, a separate scan monitoring time interval is formed for the pairs of electrode parts 22 and 24 in zone 5 when the computer in turn indicates that the relay R6 is energized.

The programming of the computer 51 may include an expected electrode disturbance alarm subroutine. Such a subroutine retains the display as a result of an alarm condition triggered as a result of the resistance value being at the threshold level. In this way, the code of the electrode pair from the pair indicating the alarm condition and the detected current and voltage are continuously stored in the display. Alternatively, the computer may retain the address of the electrode pair at which the alarm condition is indicated, causing changes in current and voltage to be excreted on displays 73 and 74 as they change later after the alarm condition begins.

Although some specific conditions have been set forth in the foregoing description for the use of electrode pairs of the order of 3000 amps at a voltage of 150 volts for heating to Joules on glass and thus having about 0.05 ohms, it is to be understood that the invention is applicable to other thermosetting agents having other electrical parameters for heating with the Joule effect. It is further to be understood that the functions of the computer that have been proposed can be modified to allow for other indications or control measures such as reading the actual resistance values of the electrode pair. Accordingly, the foregoing description is to be construed as illustrative of the present invention and not as limiting.

Claims (12)

A method for monitoring electrodes used in the melting of thermoplastics, wherein a pulsating voltage is periodically applied over electrodes in electrical communication with the molten material, characterized by determining the rms value of the voltage across the electrodes and the rms value of the current flowing to the electrodes. based on the rms values of voltage and current obtained and that the electrode fault is initially detected depending on a predetermined resistance value. Method according to Claim 1, characterized in that the electrical resistance is determined at periodic intervals and that the electrode fault is detected as a function of a predetermined change in resistance from a predetermined value. Method according to Claim 1, characterized in that the predetermined resistance value corresponds to an increase in resistance of 20%. Method according to Claim 1, characterized in that the rms values of voltage and current are sensed periodically. Method according to claim 1, characterized in that when monitoring several electrode pairs, the rms values of current and voltage over certain electrode pairs are collected in a predetermined periodic order and that an identification message is issued for the electrode pair in which the electrode fault is detected. A method according to claim 5, characterized in that a resistance reference value is determined for each electrode pair, that the determined resistance of each electrode pair is compared with the corresponding reference values of these pairs and that the electrode fault is detected when the determined resistance of a pair has a predetermined relationship with that pair. The method of claim 1, wherein the plurality of elements form a single electrode pair operating electrode, characterized in that the current flowing to the individual electrode element is determined and the electrical resistance is determined based on the current of the individual electrodes, and the electrode fault 66257 is detected as a function of current , which flows into a single electro-dielement. Device for monitoring electrodes used in the melting of thermoplastic substances by a method according to any one of claims 1 to 8, wherein a pair of electrodes (12-16) are adapted to be immersed in the thermoplastic substance and connected to a pulsating voltage source (29), characterized by 44) for monitoring the voltage between said electrode pairs and for monitoring the current from the device (54) to the electrodes, the device (51) for calculating a resistance value based on the rms values of the monitored voltage and current, and the detector device (71) for detecting an electrode fault initially depending on a predetermined resistance value. Device according to Claim 8, characterized in that the current monitoring and voltage monitoring devices comprise a converter (48) for converting the actual rms value of the pulsating current into a direct voltage value. The device of claim 8, having at least a first and a second pair of electrodes, characterized by at least the first and second devices (44, 76) for monitoring the voltage between the first pair of electrodes, respectively, at least the first and second devices (54, 77). a current to monitor the current from the electrodes of the second pair, respectively, and to simultaneously sweep the respective voltage and current monitoring devices of each electrode pair from the device (68). 10 66257 Device according to claim 10, characterized by a device (71, 75) operating independently of the scanning device (68) for signaling for corresponding predetermined resistance values of the individual electrode pairs. Device according to claim 10, characterized by a device (51, 71, 72) dependent on the scanning device (68) for providing an electrode pair identification signal for the respective individual electrode pairs depending on predetermined resistance values of the respective individual electrode pairs. 12 66257