DE2813739A1 - DETECTOR FOR MONITORING ELECTRODE BREAKAGE IN ARC FURNACES - Google Patents

Description

Patent attorneys Dipl.-Ing. Curt Wallach Dipl.-Ing. Günther Koch

·. .- ^ Dipl.-Phys. Dr Tino Haibach

Dipl.-Ing. Rainer Feldkamp

D-8000 Munich 2 Kaufingerstraße 8 Telephone (0 89) 24 02 75 Telex 5 29 513 wakai d

Date: 30. Mar Z 1978

Our reference: 16 I98 - K / Ap

Applicant: British Steel Corporation

Grosvenor Place
London, SWI,
England

Name: Detector for monitoring a

Electrode break in an electric arc furnace

809840/1055

The invention relates to a detector for detecting a broken electrode, in particular but not exclusively to a detector for use in a vacuum arc degassing furnace for steel treatment.

In vacuum arc degassing furnaces, a ladle is filled with molten metal, such as steel, from an arc furnace in arranged in a tank, which is then sealed with a lid through which the electrodes protrude or in a vacuum-tight manner instead, the pan itself can be closed in a vacuum-tight manner by means of a lid. Then the melt is electric arc heated, which are drawn between the electrodes and the conductive melt, and a vacuum is applied and the melt is set in motion, for example, by a gas blown in or by electromagnetic means, whereby gaseous impurities are driven off and the melt is refined. Various alloy components can also be used at this time can be added.

The system can instead be used as a heating furnace only, using the arc heating that Keeping the melt in a specific temperature range.

The electrodes made of graphite or carbon are consumed to some extent during this process and they are exposed to severe stress from vibration, etc. subject to electromagnetic forces to which they are exposed. With the introduction of long, slender electrodes, the possibility of breakage due to these stresses increases increases and this can be very risky, especially with vacuum arc degassing units where the electrodes are enclosed in a telescopic sleeve. In these cases, the break can occur within the sleeve and in the past Control systems used may be the absence of the arc, the

809840/1055

is recognized by these systems, cause a reaction, through which the electrode is driven down and again an arc from the top of the broken electrode section pulls. In this case, the arc is drawn inside the sleeve and restored, which is the most favorable In the event of serious damage to the sleeve and, in the worst case, an explosion.

The invention is based on the object of creating a detector for detecting broken electrodes through which this problem is avoided.

The invention is based on a device for detecting broken electrodes in an electric arc steel treatment furnace and solves the problem in that a circuit monitors the current through the electrode and that the The circuit includes a timer stage which is selectively operable when current flows through the electrode for a period of time is interrupted, which exceeds a predetermined period of time, whereby a warning signal is generated which the Indicates electrode breakage and thereby the drive of the electrode is blocked in the sense of a re-ignition of the arc.

The timer circuit preferably has a first and a second timer, the first timer having a delay » has time that ignores normal power interruptions in operation (due to the inconsistent nature of the arc), while the second timer has a time delay which corresponds to the predetermined value and indicates the electrode break.

According to the invention, a detector is provided that the current flow monitors and creates a simple, reliable and permanent solution to the problem, and also through the furnace environment remains unaffected.

8O9840 / 10S5

An exemplary embodiment of the invention is described below with reference to the drawing. In the drawing show:

1 shows a schematic representation of a vacuum arc degassing system;

FIG. 2 is a circuit diagram of the system according to FIG. 1.

FIG. 1 shows a vacuum tank 1 with a cover 2 and a melting pan 5 standing in it. The pan contains a steel melt 4 and has a slide valve 5 for withdrawing the melt. Inert gas is passed through a porous plug 6 introduced into the melt. The air is sucked out through an opening 7 in the tank and various deoxidizers and Alloy additives etc. can be introduced through a feeding device.

Three graphite electrodes 10 protrude through the cover and each is carried by an arm 12 which is supported in a sleeve IJ which shields the electrode. This sleeve 13 is Telescopically movable over an inner sleeve 14 and a sliding vacuum seal is provided at 15.

The electrodes and thus also the sleeve IJ become progressive moved downwards or upwards in the direction of the double-headed arrow l6 by a drive mechanism, not shown, that the arc drawn between the electrode and the melt is maintained. A current transformer I7 monitors separate the current flowing through each electrode.

According to FIG. 2, two timers T1 and T2 are provided, and these are prepared for operation by applying a voltage source. The timers are activated by closing a Contact CR when a current through the current transformer I7 (Fig. 1)

80984Ö / 10SS /

flows.

The timer Tl has a time constant of 2 see and er therefore switches off when CR is open for longer than 2 seconds and in the same way the timer T2 is switched off when CR is open for more than 5 seconds. This latter period of time from 5 see is considered to be indicative of an electrode break, while the 2 see period takes normal arc interruptions into account.

If Tl works, then the contact TIl closes and it becomes one Control relay SR energized via a normally closed contact ARl of an alarm relay AR. This circle remains via a holding contact SRI's Control relay and the normally closed contact RRl of an electrode lift relay, not shown, to voltage. Simultaneously causes the actuation of T2 that the contact T21 opens (the contact SR2 of the control relay has a closing delay), whereby the Alarm relay is switched off under these circumstances. The alarm relay AR is locked when energized so that it can be unlocked this relay is provided with a separate circuit with a reset button RS.

In operation, contact CR often opens and closes during normal arc interruptions, but both Timers T1 and T2 remain activated if the power interruptions do not exceed a duration of 2 see. The through the Delay provided by the timer T1 prevents the relay contact T1 from opening and closing together with the CR contact. However, if CR is open for longer than 2 seconds, then TIl opens. This contact closes again if CR does not remain open for longer than 3 more seconds.

If CR is open for longer than 5 seconds, the contact closes T21 and locks the relay AR, producing an audible and

809840 / 10B5

visible alarm signal is generated and it becomes the drive mechanism stopped to lower the electrode. The contact ARl opens and de-energizes the control relay SR. this shows the breakage of an electrode.

Then the electrode is raised, whereupon the lifting relay is excited and its contact RR1 opens. The relay AR remains locked until after unlocking by manually resetting the R button, the circuit returns to the normal position. Of the Contact TIl was of course after the initial 2 see Delay after loss of power open.

Raising the electrode during normal operation of the arc automatically resets the circuit, since the contact RRl opens and the control relay contacts SRI and SR2 open as soon as the current is interrupted for longer than 2 seconds.

The circuit is thus activated when an arc is drawn at the beginning of the procedure and normal current interruptions, resulting from the non-uniform nature of the arc are ignored and a loss of arc performance is registered as a broken electrode if this interruption exceeds a defined period of 5 seconds. Then the downward movement of the electrode is automatically stopped and the alarm is triggered. The circuit must be reset manually after an electrode is broken. Then the circuit will automatically return to its Active position transferred when the electrodes are raised under normal manual control.

The invention has been described above with reference to a specific embodiment. However, it is clear that various modifications can be made without departing from the scope of the invention. The special time intervals

809840/1055

valle are not critical and can be dependent on Practical requirements are changed. Other circuits may also be provided which are capable of the Detect interruption of the arc current during a predetermined period of time »

809840/1055

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Claims (1)

Patent attorneys D i ρ I.-1 Π g. C U rt Wal laughs Dipl.-Ing. Günther Koch Dipl.-Phys. Dr Tino Haibach Dipl.-Ing. Rainer Feldkamp D-8000 Munich 2 Kaufingerstraße 8 Telephone (0 89) 24 02 75 Telex 5 29 513 wakai d Date: 30 "Mar 2 I978 Our reference: l6 I98 - K / Ap Claims Detector for detecting broken electrodes in an electric arc steel treatment furnace, characterized by the fact that a circuit (Pig »2) is provided which enables the Monitored electrode current and has a timer circuit (Tl, T2) which selectively according to a current interruption responds, which exceeds a predetermined period of time and provides a warning signal, which indicates the electrode break and the drive of the electrode in the sense of a renewed pulling of the Arc locks. 2. Detector according to claim 1, characterized in that the timer circuit has a first (Tl) and a second timer (T2), the first timer providing a delay period which is normal Corresponds to current interruptions of the current flowing through the electrode and the detector sequence can not trigger, and that the second timer provides a delay period that the predetermined Corresponds to the time interval. 809SAO / 1055 ./. ORIGINAL INSPECTS ^ 5. Apparatus according to claim 1 or 2, characterized in that the timer circuit has contacts arranged in a loop of the circuit, wherein a control relay (SR) is provided so that the circuit when an arc is drawn through the Electrodes of a steel treatment furnace made effective will. 4. Detector according to one of claims 1 to 3, characterized in that the circuit can be manually reset (RS) after an electrode break has been detected, and that an automatic reset takes place according to a lifting of the electrode in normal operation. 5. Detector according to one of claims 1 to 4, characterized in that the warning signal is visual and / or audible. 6. Detector according to claims 1 to 5, characterized in that the treatment furnace is an arc vacuum degassing furnace is. 809840 / 1Ό5Β