JPS5917051B2 - Method and device for monitoring initial electrode damage during Joule effect heating of thermosoftening substances - Google Patents

Description

BACKGROUND OF THE INVENTION 0 Field of the Invention The present invention relates to the monitoring of processing equipment, particularly the initial monitoring of electrodes or refractory walls in heating and melting equipment for thermoplastic materials heated by the Joule effect. This invention pertains to a method and apparatus for monitoring conditions indicative of serious damage.

5. Description of the Known Art Electrical heating of thermoplastic materials by the Joule effect consists in establishing electrical current communication with the material through electrodes.

A typical thermosoftening material, glass, is processed at normal processing temperatures by immersing one or more pairs of electrodes into the molten glass and passing controlled pulsed electrical power from the electrodes through the glass. is about 2600°F (1426°C)
Or even longer. Often these electrodes move a substantial portion of their surfaces in contact with the glass away from the walls of the glass vessel or furnace to reduce the heat imparted to the walls and extend the life of the walls. ing.
One type of electrode includes a perfectly round cylinder extending through the bottom of the furnace. Although a number of measures have been used to protect the electrode and the bottom refractory wall, it has been found that the electrode tends to erode in the area of the wall where the electrode penetrates. In the case of cylindrical electrodes, a cooling jacket is installed around the electrode just below the bottom of the furnace to reduce the temperature of the electrode outside the furnace to a point where it is not attacked by atmospheric components. Furthermore, it is common practice to maintain an inert atmosphere within this jacket and around the electrodes, so that the electrodes are protected over the length where the temperature reaches the furnace temperature.

Even with these precautions, the electrodes usually tend to erode in the area of the furnace floor-to-molten glass interface and slightly below it. Such erosion destroys the electrode into a molten state. If the electrode breaks, the furnace wall near the broken portion will erode and leakage will occur unless immediate repair action is taken.

SUMMARY OF THE INVENTION The present invention relates to a method and apparatus for monitoring apparatus for Joule effect heating of molten material to detect incipient failure conditions of electrodes and to indicate these conditions during repair procedures. be carried out in a timely manner.

It has been found that initial electrode failure is indicated by an increase in resistance between the pair of electrodes that is being powered to heat by the Joule effect.

One feature of the present invention is to sense the current and voltage in the circuit of the electrode pair and actuate the indicator upon sensing a predetermined resistance value to determine the resistance value. Another feature of the invention is that the current and voltage R. m. By sensing the value of s and using these values to recognize the resistance value,
The purpose is to increase the accuracy of the perceived resistance value.

Another feature of the invention is. selectively associating a Joule effect electrode pair resistance measuring means with the plurality of electrode pairs, an incipient failure indicator and an electrode pair indicator to determine the plurality of electrode pairs at which the indicator is actuated; It is to identify.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, initial failure of an electrode immersed in a bulk fluid of thermoplastic material through which an electric current is passed for heating by the Joule effect will result in It has been shown that this is indicated by an increase in the resistance between the sending electrode pair.

This phenomenon is believed to be due to the erosion of the electrode reducing its cross section and the formation of cracks in the narrowed region. A significant increase in resistance between the electrode pairs may cause electrode failure.
Since it has been observed for several hours, it is inferred that the beginning of the process that ultimately leads to failure is a reduction in the cross-sectional area along the length of the electrode.

This reduction or thinning is most frequently observed in the region near where the electrode emerges from the refractory wall of the vessel of molten material. This characteristic is that the rate of increase in resistance increases with time. It has been found that a 20% increase in resistance is a reliable indicator of incipient trouble and therefore such an increase is used as the standard for activating a trouble indicator.

It should be understood that during long-term operation of vessels heated by the Joule effect, some erosion of the electrodes will be experienced over a relatively long period of time.

This long-term erosion and associated long-term increase in resistance between the electrode pairs does not represent initial electrode failure. Thus, in the case of a glass melter for sodium borosilicate type glass for the production of glass wool heated to a melting and refining temperature of about 2600 F (1426 C), the furnace It extends through the bottom of the
0c! The resistance between a vertical, perfectly circular cylindrical molybdenum electrode 7.5 cm (3 in) in diameter in contact with the glass over a length n (20 in) across the bottom of the furnace is 180
approximately 0.04 ohm when spaced 6 feet apart. A sensed resistance increase of up to 0.05 ohms over a relatively short period of time has been used to indicate incipient failure.

To reduce false readings, the operating period during which resistance changes due to normal erosion are compensated for is approximately three months. Therefore, if the resistance between the electrode pairs is compared against a set value, this set value is equal to 20% of the then current resistance every three months. It is reset above. Operation of the indicator with this system can be used to automatically shut off power to the electrode pair when increased resistance is sensed.

However, the preferred practice is to activate the alarm continuously until the alarm is noticed and in response to this alarm order the responsible person to inspect the electrodes, circuits and furnace to ascertain the cause of the change and troubleshoot the problem. This means cutting off power to the affected area and having the cause repaired or confirming that there is no problem in itself. For any given system to which the above monitoring method is applied, there are numerous variables that affect electrode pair resistance.

In the case of glass, there is a sharp temperature coefficient of resistance in the temperature range of interest for melting, refining and processing. The composition of the glass is also important in determining resistance.
Electrode dimensions and conditions as described above also affect resistance. Usually the composition of the glass and the temperature are kept constant and therefore these can be ignored. The initial electrode dimensions are predetermined and the gradual change in dimensions can be accommodated in changing the resistance of the electrode pair as described above. Therefore, a relatively rapid change in the resistance of an electrode pair can be correlated with a rapid change in electrode condition. In practice, Joule effect heating of glass is performed with multiple electrode pairs.

These pairs of electrodes may be made of a single element or multiple elements. The actual monitoring of the system is to selectively monitor the resistance of each of the plurality of electrode pairs. This is done by scanning the electrode pairs in a repeated sequence. When multiple elements are used in an electrode pair, individual electrode elements can scan when paired with other electrodes or electrode elements. Monitoring of such elements is desirable since increases in resistance due to changes in the state of one element are counteracted by the elements connected in parallel. Such parallel connected electrode elements tend to pick up the current previously carried by the combined element even as it deteriorates and increases its resistance. Other conditions that must be considered when monitoring the resistance of an electrode pair are the complex waveform of the furnace power and the current between the pair from which the current and voltage values indicating resistance are derived.

The current between this pair is negligible in a stable system. In particular, waveforms generated by controlling applied power proportional to phase or time differ from pure sine waveforms. Signals representing voltage and current are used to determine the true R. m. It can be processed so that it becomes the s value. This is especially true in Joule effect heating of glass where the total impedance is resistive in nature. If computer calculations are involved, the true R. m. The s value can be converted to suit computer input requirements.

As shown in Figure 1, initial electrode failure monitoring involves determining the resistance of the electrode pair, including the electrodes, comparing this resistance to a set point, and when they match, triggering the failure response mechanism. This can be achieved by working.

The resistance value is determined by the voltage applied between the pair of electrodes and its equivalent for the Joule effect heating of the molten material being treated, and by the electric current passing through the electrode pair and its equivalent. It is generated accordingly. This voltage and current monitoring takes place in the cables or conductors leading to the electrodes. Although comparisons to setpoints such as those shown are convenient for automatically activating an indicator, printing mechanism, or process control changer, it is useful to use a direct indicator reading of a given resistance as an initial It can also be used as an indication of damage.

The device for Joule-effect heating of molten glass includes automatic scanning, generation of resistance values and indication of current and voltage values and alarm levels for code-identified pairs;
2 with a multi-electrode pair monitoring device operated by.

Glass furnace 11 is shown with five electrode pairs 12, 13, 14, 15 and 16 projecting upwardly through its bottom surface 17 and immersed into molten glass 18. Each electrode of the electrode pair 16 has two electrode elements 21, 22 and 23, 24. Resistance monitoring is performed using electrode pairs 12 to 15 and paired electrode elements 21, 22 and 23, 24.
It is done for. Each electrode pair 12-16 is connected to an alternating polarity pulsed power supply through parallel oppositely polarized SCRs 26 and 27 for pair 12, controlled by an ignition controller 28. The ignition controller may be provided with current limiting means (not shown) for selectively igniting the SCR when AC is applied via the power transformer 29.

In the case of electrode 12, leads 31 and 32 deliver power to the electrode. In the case of electrode 16, the electrode element is connected to ignition control device 28.
SCR 34 and 3 with ignition control device 36 corresponding to
5, the secondary side of the transformer 33 is connected to a source of AC power. Parallel leads 37, 38 and 41, 42 extend to electrode elements 21, 22 and 23, 24, respectively.
Transformer 29, SCR 26 and 27 and ignition control device 2
A pulse controlled power supply (not shown) of opposite polarity corresponding to 8 is provided for electrode pairs 13, 14 and 15. The resistance of the electrode pair 12 is connected to the lead 31 by a transformer 44.
A transformer 44 is connected to ground on one of its secondary sides and connected to bus 4 through lead 45 and contacts 46 of relay R1 on the other side.
7 is connected.

This bus 47 is a true R. m. The voltage waveform is applied to a converter 48 that converts the value of s to direct current, typically a true R. m. s-DC converter 4128. R. m. A DC-reduced signal representing the s voltage is sent from converter 48 to lead 52.
and 53 to the computer 51, and in this computer R. m. s is processed together with a scaled signal representing the current to generate a resistance value for the electrode pair 12. The current supplied from a power source to electrode pair 12 for Joule effect heating of molten material 18 is sensed by current transformer 54 having a winding around lead 32, which transmits a signal to transformer 55. supply. In converting the current signal, a resistor 56 is connected across the secondary of the transformer 55 between the ground terminal and a lead 57 which is connected to the true R. m. A relay R1 is connected to a bus 59 connected to a converter 61 that converts the value of s into DC.
The signal is passed through the contact 58 of. R. m. The scaled DC signal representing the s current is passed by leads 62 and 63 to computer 51 and processed into a resistance value. The typical resistance value of the electrode pair can be established by calculation or measurement. When balanced process conditions are established in the furnace 11, the resistance value increases to the perceived R. m. s voltage value and R. m. can be generated by a computer from the s current value.

The set point is then established as the alarm threshold and set as one input to the computer's internal comparator. The other input to this comparator is R
．． m. s voltage and R. m. is the processed resistance E value (R-) derived from the s current.

I Conversion action of converters 48 and 61 and computer 5
One processing action is used for multiple electrode pairs if multiple electrode pairs are to be monitored.

This is done on a time-sharing or multiplexed basis when scheduled within the computer, where the computer issues address codes periodically to the multiple circuits whose resistances are to be monitored. A typical IBM 18OO computer, which is used for many other process monitoring and control functions, is used with multiplexing circuitry connecting the electrode pairs one after the other. Evaluation of each electrode pair during scanning is typically performed at approximately 2 second intervals. In these two seconds, R. m. s voltage and R. m. s current is read and a resistance calculation is made. The coded output is then issued and the multiplexing circuit is connected to the next circuit to be evaluated. The computer may selectively evaluate some circuits at more frequent intervals than others, or it may continuously scan the circuits undergoing evaluation in complete scan cycles spaced in time. Can be configured.
The address code for the circuit is issued by computer 51 to decoder 68 in four binary signals on leads 64, 65, 66 and 67. The decoder 68 includes a voltage signal source and a voltage signal R. m. s converter 48 and between the current signal source and the electrode pair of each cord. m. An individual relay activation signal is issued to the relays, each having a normally open contact, in the circuit between it and the S converter 61. Therefore, relay R
1 is energized to close contacts 46 and 58 and connect electrode pair 12 for resistance calculation. Other electrode pairs are similarly monitored by energizing relays in scan order. While the pair code is issued by the computer 51, the computer issues either a digital pair code or a pair code to the window 72 of the display 71 which is later converted into another code such as a numeric value; windows 73 and 74
The current and voltage values are displayed. If the degree of resistance is excessive for the area currently being monitored, an alarm indication will be displayed on window 75 and/or the tie writer will print, or the CRT display will shut off power to electrode pair #1. It may be configured to issue a message such as 0 to call the administrator.

Since the resistance values between pairs of electrodes or pairs of electrode elements can be different, each pair can be provided with a separate setting value.

This setting is recalled from the memory of computer 51 when that electrode pair is under monitoring. This can be offset appropriately (to 120% of the normal resistance value) with respect to the alarm threshold for indicating failure of that pair of electrodes. The fifth pair 16 of electrodes, ie the fifth Joule effect heating region counted from left to right in FIG. It should be noted that the electrode elements are paired in order to allow individual elements to be monitored.

The common power supply for this region 5 of Joule effect heating is therefore electrically connected to the individual elements in parallel, but only one element of each polarity is monitored in one scan interval. Elements 21 and 23 are monitored for voltage in transformer 76 between leads 37 and 41 and in lead 3.
In winding 77 of 7 the current to transformer 78 is monitored. This monitoring is accomplished by decoder 68 exclusively energizing relay R5 to determine the true R. m. Contact 8 to s converter 48
1 and true R.1 for current. m. Contact 8 to s converter 61
Acts when addressed to close 2 and 2. At this time, the computer retrieves the set resistance value between the electrode element pair and activates the display. Additionally, when the computer sequences the addresses to energize relay R6, the pair of electrode elements 22, 24 in region 5 is given another scan spacing. The computer 51 program includes an initial electrode breakage alarm subroutine. The subroutine maintains the display in response to the alarm being activated by sensing the resistance at the alarm threshold. In this manner, the pair of electrode pairs indicating the alarm condition and the sensed current and voltage are maintained on the display. Alternatively, the computer may maintain the address of the electrode pair exhibiting the alarm condition, thereby displaying changes in the current and voltage at 73 and 74 as the voltage and current change following the onset of the alarm condition. Good too. Although the foregoing description has described the specific condition of the electrode pair operating at 3000 amperes, 150 volts, and therefore about 0.05 ohms for Joule effect heating of glass, other electrical sources for Joule effect heating It should be understood that it is also applicable to other thermosoftening materials with specific parameters.

Furthermore, it is clear that the proposed computer action can be modified to provide other indications or control actions, such as reading the actual resistance of the electrode pair. Accordingly, the above description is merely illustrative of the invention and is not intended to be limiting.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the procedure for monitoring incipient electrode failure in a Joule effect heating device for conductive pure softening materials; and FIG. 2 shows an electrode pair made of individual electrode elements. 1 is a plan view of a glass melter having electrode pairs made of multi-element electrodes, and a schematic wiring diagram monitoring representative pairs of each type; FIG. 11... Glass furnace, 12, 13, 14, 15,
16... Electrode pair, 18... Molten glass, 21, 22, 23, 24... Electrode element, 44
......Transformer, 54...Current transformer, 46,
58... Contact, 47, 59... Bus,
48, 61...Converter, 51...
Computer, 68... Decoder, 71...
...Daisbrae.

Claims (1)

[Claims] 1. To achieve Joule effect heating of the glass, a pulsed voltage is repeatedly applied between electrodes in electrical communication with the molten glass; the effective value of the voltage between the electrodes is recognized; Recognizing the effective value of the current flowing through the electrode; recognizing the electrical resistance value based on the recognized effective value voltage and effective value current;
and a method for monitoring initial failure of an electrode used for Joule effect heating of molten glass, comprising the step of instructing early electrode failure according to a predetermined resistance value. 2 at least a first and second pair of electrodes placed in the glass; a power source; means for connecting the power source to said electrodes;
at least first and second means for monitoring voltages between the pair of electrodes and between the second pair of electrodes, respectively; one of the first pair of electrodes and one of the second pair of electrodes; means for respectively monitoring the supplied current; means for scanning the voltage and current monitoring means for each of said plurality of pairs of electrodes; means for determining a resistance value based on the monitored voltage and current from said monitoring means; An electrode for use in Joule effect heating of molten glass, comprising means for generating a signal in response to a predetermined resistance value; and means for generating an electrode pair identification signal in response to the scanning means. equipment to monitor early damage.