EP0059181B1 - Method and apparatus for controlling the melting rate of an electrode by electroslag remelting - Google Patents

Description

The invention relates to a method and a device for regulating the melting rate of a self-consuming electrode in a slag bath during electro-slag remelting.

AT-PS 345 487 has already proposed to keep the current required for remelting constant by changing the lowering speed of the electrode to be melted in the event of deviations from the setpoint, etc. If the current is too low, the lowering speed is increased and if the current is too high it is reduced. Furthermore, with such a constant current, if the lowering speed is too low compared to a preselected lowering speed, the bath voltage is increased in order to supply more active power and thus to be able to increase the melting rate and thus the lowering speed. In the opposite case, the bath tension is reduced.

According to this method, there is no specifically proportional influence on the melting rate, because the bath depth also changes the immersion depth, e.g. an increase in voltage with a constantly regulated current would result in a reduction in the immersion depth of the electrode in the weld pool, but as a result the melting rate generally does not increase proportionally. Due to metallurgical reactions in the weld pool, the bath resistance changes over the course of the melting time. If the bath voltage and current are kept constant, the electrode is e.g. Immerse the increasing bath resistance deeper into the weld pool, which also changes the melting rate.

The effects described do not allow remelting conditions to remain constant. For metallurgical reasons, however, a controllable, e.g. Constant melting rate of great importance, because the influencing factors on the melting rate and immersion depth of the electrode are very diverse and cannot be calculated exactly, the melting rate and immersion depth would have to be monitored using control engineering methods.

For example, in DE-PS 1 934 218, the melting weight of a self-consuming electrode is regulated according to a weight-time function without regard to an electrode spacing to be maintained. In DE-PS 2 456 512 the immersion depth is regulated according to the bath resistance or its gradient without monitoring the melting rate. The reasons given above already show that immersion depth control according to the bath resistance is very imprecise.

The known methods for regulating the melting rate each have the disadvantage that the regulation takes place only via the feed rate of the electrode, the voltage or the current intensity. However, the position of the electrode in the slag bath and its distance from the melt level are not taken into account. However, the thermal conditions during solidification are of great importance for the metallurgical properties of the block to be melted. The deeper the electrode is immersed in the slag bath, the higher the temperature of the still liquid block and the lower the sump made of liquid metal formed in the block. Furthermore, the melting rate is not linearly dependent on the immersion depth, which means that the immersion depth is an important control variable.

The method according to the invention for regulating the melting rate of a self-consuming electrode during electroslag remelting in a slag bath, the lowering speed of the electrode to be remelted, which is determined by a length measurement, being regulated in relation to compliance with a target value of the melting rate and the current intensity and / or the voltage , consists essentially in the fact that the weight of the portion of the electrode immersed in the slag bath is continuously determined from the actual total electrode weight and the length of the electrode above the slag bath surface and compared with a target value and, if the quotient of U _target and J _so deviates, changes the product remains constant and the actual melting rate is compared with a target melting rate and in the event of a deviation the product of J _{so "} and Us _o n is changed accordingly. From the difference in the weighted electrode weight, which can also be determined via the weight of the block that has already melted, and the length of the electrode above the slag bath surface, which is used to calculate the weight of the electrode above the slag bath, the weight fraction of the electrode can be calculated located in the slag bath can be easily calculated, the resistance being changed in the event of a deviation, but the product of the current strength and voltage being kept constant. Then the actual melting rate, that is the molten weight of the electrode per unit of time, is compared with a target melting rate and if there is a deviation, the product is changed accordingly.

In principle, the remelting process is equivalent to a 2-size controlled system, with bath voltage U _WB and current J as input variables (manipulated variables) and the melting rate and electrode immersion depth Δb or immersion weight AG as output variables. In general, separate regulators for maintaining voltage U _WB and current J are provided, the setpoints of which can be set separately.

die Spannungs- und Stromsollwerte U_WBS, Js für die Regler errechnet, erfolgen, C_u, C_j sind Korrekturwerte für Nichtlinearitäten des Widerstandes R_B.In order to keep the electrode immersion depth in the weld pool constant with a subsequent change in the effective bath power P _WB , a decoupling of the control variables is necessary. This can be done with the help of a control computer, which from the given active bath power P _wBs and melt _{pool active resistance} R _B according to the relationships

the voltage and current setpoints U _WBS , Js are calculated for the controllers, C _u , C _j are correction values for non-linearities of the resistor R _B.

According to a further feature of the invention, the lowering speed of the electrode is controlled via the nominal value of the current strength. It must be taken into account here that the block grows against the electrode as it melts. Controlling the lowering speed by means of the current strength ensures that the speed is maintained more precisely, as a result of which the melting conditions can be maintained even more precisely.

According to a preferred feature of the invention, the weight of the electrode is weighed, which gives the most accurate possible weight determination, and weight measurements such as power supply lines, the electrode holder, buoyancy of the electrode in the slag bath, etc. are easily possible via the weight measurement.

A device according to the invention for carrying out the method, in which a current or voltage regulator connected to an actuating device for lowering the electrode and a voltage regulator connected to an actuating device for adjusting the tap of a variable transformer supplying the remelting system, essentially consists in the fact that the The current and voltage regulator is connected to a control computer which calculates the setpoints for these regulators and is in turn connected to a resistance value calculator which serves as a reference variable for determining the current and voltage setpoints and a melting rate regulator which is preferably influenced by a power value transmitter. This enables a particularly advantageous decoupling of the controlled variables, with both the resistance and the melting rate being easily controlled, so that the desired temperature conditions in the liquid block can be maintained.

If the resistance value calculator is connected to a position controller that compares the position of the electrode with respect to the slag bath surface with a setpoint value, which in turn is connected to a calculator for determining the melting weight from the melting length of the electrode and a measuring device for directly determining the melting weight of the electrode, one can particularly precise control of the portion of the electrode immersed in the liquid slag can be carried out based on a setpoint.

The position controller contains a correction device which, when a certain difference between the directly determined and the melting weight determined from the melting length of the electrode is exceeded. B. holds on to the last determined value, then automatic control is also possible if the electrode contains large cavities, since the electrode is not pulled out of the slag bath due to the seemingly too high melting rate.

For the continuous measurement of the electrode weight between a lifting and lowering device for adjusting the electrode, a force measuring device is interposed, which is able to tare dead loads, such as electrode holder, etc., to zero and is at least approximately the same as the time differential of the measured value Signal-emitting device connected to the melting rate controller, both the weight of the electrode can be precisely determined on the one hand, and the melting rate can also be precisely determined and maintained via the device mentioned, since the weight measurement of the electrode takes the current conditions during remelting particularly carefully into account. This accuracy is particularly important at the end of the remelting process, since there is usually only a relatively small and therefore low-weight electrode, and depending on the operational requirements, a relatively low melting rate should also be maintained.

• Fig. 1 ein Blockschaltbild einer Einrichtung zur Durchführung des erfindungsgemässen Verfahrens;
• Fig. 2 schematisch mehrere mögliche Anordnungen von Einrichtungen zur Ermittlung des Absenkweges der Elektrode;
• Fig. 3 schematisch verschiedene Anordnungen von Messeinrichtungen zur direkten Gewichtsmessung der Elektrode und
• Fig. 4 bis 16 verschiedene Möglichkeiten der Anordnung der Gewichtsmesseinrichtungen bei verschieden ausgestalteten Elektrodenhalterungen.

The invention is explained in more detail below with reference to the drawings. Show it:

• 1 shows a block diagram of a device for carrying out the method according to the invention;
• 2 schematically shows several possible arrangements of devices for determining the lowering path of the electrode;
• Fig. 3 shows schematically different arrangements of measuring devices for direct weight measurement of the electrode and
• Fig. 4 to 16 different ways of arranging the weight measuring devices with differently designed electrode holders.

In the embodiment according to FIG. 1, the current regulator 1 and the voltage regulator 2, which are connected to actual value transmitters and adjusting devices (not shown), are optionally via the switch 3 with a current setpoint generator 4 or a voltage setpoint generator 5 or a control computer 6 connected. The actuating device connected to the current regulator 1 acts on a lifting and lowering device for actuating the electrode for setting the lowering speed thereof, whereas the actuating device connected to the voltage regulator 2 acts on the tap of a regulating transformer which melts the electro-slag remelting device, not shown known type supplied. The control computer 6 is connected to a resistance computer 7 and via 12, 13 to a power value _transmitter 8 and supplies the current or voltage regulator 1, 2 with setpoints Js ° y or U _{So1 which are} dependent on the required power value and the resistance value coming from the resistance value _{computer 7} ".

In the control computer 6, not shown, there are still the adjustable limits for the upper and lower limits of the active bath power. The proportion of the signal supplied by the power value transmitter 8 to the control computer 6 can be adjusted by the signal mixer 12, 13 to which the manipulated variable output of the melting rate controller 14 is also connected. The regulating and control component (R / S) is set by the signal mixer. With a 100% tax share, the signal from the power value transmitter 8 comes into full effect in the control computer 6 and vice versa.

The resistance value calculator 7 is connected to the setpoint generators 4 and 5 and uses these values to calculate a basic resistance value R _o , which is based on and coming from the position controller 9 the switch 10 feedable signal is corrected. The position controller 9 is in turn connected to an immersion weight and immersion depth (position) setpoint device 11 and an actual immersion weight or immersion depth (position) transmitter, and the weight of the immersed portion of the electrode is calculated from these values. which is compared with the target values, the quotient of U _target and J _{target being} changed in the event of a deviation, but the product is kept constant. In addition, the position controller 9 also contains the correction logic and arithmetic device (not shown) which evaluates the two oil melting rates from the weight or length measurement and, if a certain difference is exceeded, carries out corrections, for example, to the last determined value.

The meltdown rate controller 14 receives its setpoint from a meltdown rate generator 15 and its actual value from the meltdown rate calculator 16, which preferably provides a signal corresponding to the actual meltdown rate by differentiating or forming differences in finite time intervals of the preferably directly determined meltdown weight of the electrode.

2 schematically shows various possibilities for arranging the measuring devices for determining the lowering path of the electrode.

On the cable winch stage 17, the cable winch 18 and its drive 19 and a cable guide roller 20 are arranged, via which the cable 23 provided for adjusting the electrode carriage 21 along the guide column 22, which is attached to the electrode carriage 21, is guided. Furthermore, sensors 24 for monitoring the adjustment movement of the electrode are arranged on the cable winch stage 17 or, as indicated by dashed lines, on a cantilever arm connected to the guide column 22. These transducers 24 are connected to the electrode carriage 21 via measuring chains 25, which expediently run exactly vertically, so that each of the measuring transducers 24 corresponds to the same changes in the height of the electrode by the same angular amounts due to the rotation of a sprocket engaged with the measuring chain 25.

With regard to the installation locations of a transducer 24, designated I, 11, 111, the installation location designated 1 provides the most accurate measurement values, since with this method the measurement chain 25 practically runs in the electrode axis 26 and therefore deflections of the electrode carriage 21, which occur during the melting of the Reduce the electrode, do not go into the measurement result, which is increasingly the case for installation locations 11 and 111.

Fig. 3 shows schematically the possibilities for the attachment of force transducers. For example, a force transducer designed as a tensile load cell 27 can be installed in a pulley-like guidance of the rope 23 directly in the rope strand held at a fixed point (arrangement IV) or, where apart from the negligible weight of the rope strand, which of course changes during the course of the lowering of the rope strand Electrode 28 or the electrode carriage 21 changes, and apart from frictional forces between the electrode carriage 21 and the guide column 22 detects half the weight of the electrode carriage 21 together with the electrode 28. It is of course possible to balance the weight portion of the electrode carriage 21 in a downstream evaluation circuit and to form the time differential or the difference in finite but very small time intervals from the corrected signal.

On the other hand, a tensile load cell 27 remains unaffected by the change in the cable weight if, like at installation location V, it is interposed between the loose pulley of the pulley-like cable guide and the electrode carriage 21, although it must absorb the full weight of the electrode carriage 21 together with the electrode 28 . At this installation location V, the force transducer must also absorb a high tare weight, the electrode carriage 21.

At the installation locations VI, on the other hand, pressure measuring sockets 27 'are provided, which are supported on the electrode carriage 21 and carry a weighing platform 29, on which in turn the electrode 28 is supported. This results in a comparatively significantly lower tare weight than in the installation locations IV and V and, moreover, there is no influence by frictional forces between the electrode carriage 21 and the guide column 22.

4 to 15 schematically show possibilities for holding and contacting the electrode 28, which likewise influence the measurement result of the direct weight measurement of the electrode to determine the actual melting rate to a greater or lesser extent.

In the embodiment according to FIGS. 4 and 5, which is shown in elevation and plan view, the contact jaws 30 are attached to a pressing device with the interposition of insulation 31, which are essentially connected by two levers connected via a hydraulic cylinder 32 and articulated to a rocker bearing 33 34 is formed. The rocker bearing 33 enables the levers 34 to pivot about the longitudinal axis of the rocker bearing, which is fastened to the electrode carriage 21. The electrode 28 is lifted from its support on the electrode carriage 21 by means of the lifting hydraulics 35 mounted on the electrode carriage 21 via the cable 23, into which a tensile load cell 27 is installed, and an insulated hook 37. The lifting is necessary in order to prevent force shunts by a to eliminate electrode head resting on the electrode carriage 21. The electrode 28 itself is raised and lowered with the electrode carriage 21.

The indicated weighing platform with the pressure load cells 27 'represents an alternative to weighing with tensile load cells. When the electrode 28 is attached, the pressure load cells 27' must be relieved.

The current supply lines 36 are connected directly to the contact jaws 30 and are preferably extremely flexible.

In this embodiment, the weight measurement of the electrode 28 is loaded only by a very low tare weight, since the weight of the contact jaws 30 together with the portions of the lever 34 on the contact jaw side is approximately the weight of the Hydraulic cylinder 32 together with the hinged portions of the lever 34 corresponds. However, frictional forces occurring in the joints of the pressing device are included in the weight measurement.

In the embodiment according to FIGS. 6 and 7, flexible copper strips 36 'are welded to the head of the electrode 28 and can be connected to contact jaws 30 which are seated on an insulation 31 attached to the electrode carriage 21 and which can be closed via hydraulic cylinders 32'. The current leads 36 to the contact jaws 30 can be stiff since they are not included in the measurement. As in the embodiment according to FIGS. 4 and 5, the electrode 28 hangs on an insulated hook 37, which is connected to the lifting hydraulics via a rope provided with a tensile load cell, or is supported on a weighing platform 29. This results in only a very low tare weight, namely the hook 37 and the rope or weighing platform 29, as well as part of the weight of the copper strips 36 'and the protective box 38 covering them. However, changes in the bending stiffness of the copper strips 36' are caused by the heating unavoidable, which go into the measurement, but this embodiment is characterized by a particularly low tariff load and simplest structure.

A further embodiment, in which there is a very low tare load on the force measuring transducers, and therefore those with a correspondingly small measuring range can be used, which also respond more sensitively to changes in force, are shown in FIGS. 8 and 9. In this embodiment, FIG Electrode 28 is provided with an anchor rod 39 which passes through a sleeve 40 supported on electrode carriage 21. The contact jaws 30 engage the sleeve 40, which is connected to the electrode 28 via flexible copper strips 36 ′, which are covered with a protective box 38. In this embodiment, the electrode 28 is weighed by means of the weight measuring device, which acts via an insulated hook and has a tensile load cell. The electrode is raised and lowered via the electrode carriage 21, on which the sleeve 40 or the contact jaws 30 are supported.

With this construction, the protective box 38 is also no longer included in the measurement, since it is supported on the sleeve 40.

In the embodiment according to FIGS. 10 and 11, the lifting and lowering device provided with the force measuring device 27 or 27 ', which is formed either by the separate lifting hydraulics 35 or by the cable winch of the electrode carriage, not shown in these FIGS. 10 and 11, engages if a weighing platform 29 and pressure load cells 27 'are used on the contact jaw 30', which is supported on the or by means of the insulation 31 from the weighing platform 29 or directly from the electrode carriage. The contact jaw 30 'is e.g. tapered, self-adjusting surface, in which contact blocks 41 are arranged, but a slot 42 corresponding approximately to the diameter of the rod of the electrode 28 is provided, through which the one e.g. rod having a conical head of the electrode 28 can be inserted laterally into the conical contact jaws. If the weight of the electrode 28 is not sufficient to achieve a perfect electrical contact in the contact jaw 30 ', the contact pressure of the conical head of the electrode 28 on the contact blocks 41 of the contact jaw 30' can be increased by means of the clamping arms 44 which can be actuated via the hydraulic cylinders 43.

The contact jaw 30 'is expediently gimbaled via these tensile load cells 27 on the lifting hydraulics 35 or supported on the weighing platform. To increase the measuring accuracy, it is expedient in this embodiment to use copper strips which are as flexible as possible for the power supply.

A similar embodiment is shown in FIGS. 12 and 13, only that instead of the one conical contact jaw 30 ', two contact jaws 30 are provided, which are provided with cylindrical surfaces and can be moved relative to one another by means of two hydraulic cylinders 32', between which the head of the electrode 28 can be clamped. When using tensile load cells 27, which, as can be seen from FIG. 13, can also be found with one, the ropes connected to these or these engage on a holder 45 guiding the contact jaws 30, on which also the hydraulic cylinders 32 'are attached. If pressure load cells 27 'are used, these can possibly be engage directly on the bracket 45 or support it.

The embodiment according to FIGS. 14 and 15 provides a head of the electrode 28 which is provided with an axial and two non-circular bores 50 and 49 running transversely thereto, on which the insulated hook of the weight measuring device, which has tensile load cells (not shown), also engages . In this case, the contact jaws 30 ″ are penetrated by a pull rod 47 provided with a hammer head 46, which is acted upon by a spring 48. This spring 48 is accommodated in a housing 51 and is relieved of the pull rod 47 via a sleeve 52 and a rocker 53. A rotating device 54, which is connected to the pull rod 47 and which enables the pull rod 47 to be rotated by 90 °, is fastened to the housing 51 in order to be able to insert it into the non-circular bores 49 and then to rotate it, so that after unlocking the Spring 48 the hammer head 46 of the pull rod rests against the wall of the bore 50 and presses the contact jaws 30 "against the head of the electrode 28, the contact jaws 30" being only loosely guided by the base plate 55.

In this embodiment, there is reliable self-clamping contacting, which is without force shunt in terms of weight measurement.

• G_G ⁼ Gr_T + G_KOKT - Gs - GBo
  • T = Bezug auf die Nulltarierung des leeren Kokillen- und Blockwagens.

16 shows an alternative to direct electrode weighing. The entire block is weighed here and the melted block weight is determined via the block weight increase. The weighing device consists of load cells under the cooled block wagon. With lifting molds, there are considerable forces conclusions between block and mold that falsify the weighing result. For this reason, either the mold carriage must be weighed, in a similar way to the electrode carriage in FIG. 3, or even better the mold itself, using weight measuring cans. The measured values G _BO block weight after the last electrode, G _E current displayed apparent block weight, G _s and G _{KOK are the} current apparent weight of the lifting mold. The current melting weight G _{G of} the electrode results in:

• G _G ⁼ Gr _T + G _KOKT - Gs - GBo
  • T = reference to the zero taring of the empty mold and block wagon.

The effort here is greater than with the devices previously, but with the advantage that it is not influenced by current leads.

Claims (10)

1. A method of regulating the melting rate of a consumable electrode in electro-slag remelting in a slag bath, in which the lowering speed of the electrode to be melted, whose length is determined, is regulated with respect to maintaining a nominal value of the melting rate and the current intensity and/or the voltage, characterized in that the weight of the part of the electrode immersed in the slag bath is continually determined from the actual overall weight of the electrode and the length of the electrode above the surface of the slag bath, and is compared with a nominal value and is altered if there is a variation in the quotient of the voltage U_nomina_l and the current intensity J_nominal, the product remaining constant, and in that the actual melting rate is compared with a nominal melting rate and, if there is a variation, the product of Jnominal and Unominal is altered accordingly.

2. A method according to claim 1, characterized in that the lowering speed of the electrode is controlled via the nominal value of the current intensity.

3. A method according to claim 1 or 2, characterized in that the electrode is weighed.

4. Apparatus for carrying out the method according to one of claims 1 to 3, in which a current regulator, connected to an adjusting device for lowering the electrode, and a voltage regulator, connected to an adjusting device for adjusting the tap of a regulating transformer, supplying the remelting system, are provided, characterized in that the current and the voltage regulators (1; 2) are connected to a control calculator (6) which calculates the nominal values for these regulators (1; 2) and in turn is connected to a resistance value calculator (7) supplying a resistance value which is used as the reference value for determining the current and voltage nominal values and to a melting rate regulator (14), influenced preferably by a power value indicator (8).

5. Apparatus according to claim 4, characterized in that the resistance value calculator (7) is connected to a position regulator (9) which compares the position of the electrode (28), in reaction to the surface of the slag bath, with a nominal value, and which in turn is connected to a calculator for determining the melting weight from the melting length of the electrode and to a measuring device for directly determining the melting weight of the electrode.

6. Apparatus according to claim 5, characterized in that the position regulator (9) contains a limiting circuit which makes corrections if a specific difference value between the directly determined melting weight and the melting weight which has been determined from the melting length of the electrode is exceeded.

7. Apparatus for carrying out the method according to claim 1 or 2, characterized in that in order to measure the electrode weight continually there is interposed between a lifting and lowering apparatus for displacing the electrode (28), a force measuring device (27, 27') which is connected to the melting rate regulator (14) by way of a device which emits a signal corresponding at least approximately to the time differential of the measured value.

8. Apparatus according to claim 7, characterized in that the lifting and lowering apparatus for the electrode (28) is loaded by way of the force measuring device and a device for contacting the electrode, the current being supplied to the contacting device by way of flexible copper bands (36').

9. Apparatus according to claim 7 or 8, characterized in that the electrode (28), provided with a penetrating tie rod (39), at which contact jaws (30) engage, hangs on a draw hook and is connected to the sleeve (40) by way of flexible copper bands (36').

10. Apparatus according to claim 7, characterized in that the electrode (28) is connectable by way of flexible copper bands (36') to contact jaws (30) supported at the electrode carriage (21), and the lifting and lowering apparatus provided with the force measuring device (27, 27') engages directly at the electrode (28).

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