DE1183613B - Program control for electric arc furnaces - Google Patents

Description

Program Control for Electric Arc Furnaces The invention relates to focuses on electric ovens and focuses in particular on control circuits for regulation the operation of such furnaces, especially electric arc furnaces and furnaces with multi-voltage taps. Because long arcs in the arc furnaces of the furnace lining and furnace roof harm, if not covered by the batch, must occur during the melting period care must be taken to ensure that the electrical input power is used to protect the heat-resistant lining is reduced at the right moment. For a given Current grows the arc length with the voltage, so that at a certain point in time usable voltage is influenced by the nature and condition of the furnace lining will.

The aim of the invention is to create a control circuit for automatic Change in the power of an electric furnace under the given conditions.

A control system for an electric furnace according to FIG Invention heat-sensitive device, which one the heat development in the furnace regulating regulator controls automatically.

According to a preferred embodiment of the invention, the system contains a heat-sensitive device for controlling an electric arc furnace, the amount of heat emanating from the temperature and / or from the furnace lining responds, and a regulator operated by the thermosensitive device, which responds as soon as the temperature reaches a certain level, and thereby the Input to the furnace electrodes changes to a desired value.

In one embodiment of the invention, the system includes a multi-position switch, a thermosensitive device, an electrical input control circuit to the arcs and a timing device so arranged and switched is that when the melting process is initiated, the power input is automatic is increased progressively in steps at times indicated by the timer are determined. Towards the end of the melting period when the temperature or the the amount of heat impinging on the lining reaches a certain first value the input power is automatically and gradually reduced in stages. During the purification period, during which the temperature has a second predetermined When the value is reached, the input power is further reduced progressively.

In some ovens, especially when using low specific Weighted scrap that. Batch can be added in more than one serving. In this case, the first two stages of control can be used for each melting process be repeated.

In the following, the invention is intended to make it easier to understand of an embodiment of a control system for an electric arc furnace are described in more detail. The drawings show in FIG. 1 (A) and 1 (B) taken together a circuit diagram of the control system according to the invention, FIG. 2 the power supply to the contacts switching the electrodes, FIG. 3 the circuit breaker, furnace transformer and the electrodes.

In the ovens in question, the ceiling temperature rises during of melting at a steep rate until essentially the entire batch melted, whereupon the temperature of the ceiling begins to rise rapidly as it is now directly exposed to the radiation coming from the arc.

The temperature rise at this stage can be about 50 ° C per minute be. At the end of the melting period, the input power is reduced, and the temperature drops briefly, as the purification process continues, the However, temperature rise again and often reaches a maximum, just before the oven is tapped.

In the case of ceiling temperature measurements carried out on these ovens, found that the temperature at the end of the melting period was in the range between 1520 and 1650 ° C. Even if the ceiling temperature is at the lower end of this Range, the bath temperature is significant, so the high performance that allowing the ceiling temperature to rise to 1650 ° C, becoming a waste electrical energy, destruction of the refractory lining and overheating of the molten charge.

After switching off the input power, the actual steel production process begins. The arches are then no longer shielded from the scrap, and neither is the furnace lining is exposed to direct radiation and convection through the arches. Consequently the general temperature level of the lining increases until for a given Input power enters a stable state.

In the special embodiment according to the drawings, the electrical Input power through multiple voltage taps and a tap selector switch S 11 changed (see Fig. 2). The program is set using a Number of tap changers, each consisting of a number of fixed contacts and an associated movable contact, which successively in its movement establishes the connection with the fixed contacts. Such switches are called often as multi-position switches or, more generally, as uniselectors.

Uni selectors usually contain a number of solid, arched shapes arranged contacts and a radial sliding arm as a movable contact. in the During operation, the grinding arm is advanced in stages and thus performs a certain Movement from touching a firm contact to touching one fixed neighboring contact in accordance with separate excitation or stepping signals by.

Such uniselectors are also available as step switches with several switching levels available, d. H. in the form of a large number of corresponding contact arcs and grinding arms, wherein the grinding arms respond collectively to common step signals to determine certain maintain geometric positions with respect to their fixed contacts. A university selector Z of this particular embodiment is shown in FIG. 1 of the drawings and has seven different levels Z1 to Z7.

The program to be followed is established by connecting the appropriate fixed contacts of the various uniselector levels with associated circles like this set that when connecting the uniselectors sliding contacts to a certain Set of corresponding fixed contacts the associated circles the predetermined, perform the functions required for this stage of the program. These functions include, for example, as will be apparent from the explanation below, the interruption the power supply, raising the furnace electrodes, changing the power supply connection, lowering the furnace electrodes and switching on the mains again.

Having performed the functions for such a program level are, the clock 12 determines a predetermined minimum time period after which the uniselector advances to the appropriate functions for the next Initiate stage of the given program.

In accordance with the second feature of the invention, this is Embodiment additionally provided with temperature-sensitive devices that are arranged in such a way that they are used by the clock for certain stages of the program specific, minimal periods of time but only under certain conditions.

To control the oven in the manner described above, two devices 10, 11 are provided which respond to the temperature of the oven ceiling or oven wall and to the speed with which the heat is absorbed by the ceiling or the wall. These devices close contacts HL and LL when the temperature and the amount of heat have reached predetermined values. The temperature-sensitive device 10 can consist of a thermocouple which is housed in a heat-resistant tube in the ceiling or wall, or of a radiation pyrometer which is observed through the furnace wall in the vicinity of the ceiling. The device 11 responsive to the absorption of heat can consist of a heat quantity meter which is preferably arranged in the ceiling or, if possible, on the upper part of the wall.

The two devices 10, 11 can consist of a single thermocouple or a radiation pyrometer, provided that the usual potentiometer recording controller associated with the thermocouple or pyrometer is equipped with an auxiliary device which responds to the rate of rise of the temperature to be measured. In this case, the contacts LL can close if the rate of increase in temperature exceeds the value of 20 ° C. per minute for longer than 45 seconds, for example.

If necessary, two temperature-sensitive devices or a single temperature-sensitive device can be arranged in such a way that the contacts LL and HL close when different temperature levels, for example of 1100 ° C. and 1600 ° C., are reached. In this case, the contacts LL switching at the lower temperature are arranged in such a way that they close at a temperature at which, as experience has shown, the rate of rise of the temperature is reached.

In the example shown, the furnace electrodes E (FIG. 3) are supplied via alternating current lines 30 by a contactor B and a transformer TR, which has eight voltage taps. A switch S 11 (FIG. 2) is coupled directly to the tap changing mechanism with switches R, W, which when energized changes the tap up or down in a known manner between numbers 1 to 8, however causes positions not shown as such. These taps are successively selected in a predetermined order under the control of the uniselector Z, and each time the uniselector advances to a new position, the corresponding contact R or W is actuated to change the tap to a value determined by the new uniselector position . While the actual taps of the transformer TR, which can be selected by the switch S 11, are not shown, some of the contacts of the uniselector Z are provided with the reference numerals 1 to 8 in order to indicate which tap positions belong to them. The movement of the uniselector Z from one position to the next is normally initiated by a timing circuit consisting of a solenoid T and the clock 12, which determines the minimum period of time for which a particular tap is effective. In certain positions of the switch, the movement is caused by the aforementioned contacts LL and HL .

The uniselector Z is spooled in opposite directions ZF, ZR driven, moving in forwards or backwards direction through corresponding pulses are generated at the coils ZF and ZR.

The voltage taps 1 through 8 are represented by the lines L 1 through L 8 in FIG. 2 and can be connected to the supply line L through the switch S 11. Each voltage tap is assigned to one of the eight relays EA, EB ... EH , which are connected to their corresponding tap lines L 1 to L 8 in FIG. 1 (B) are turned on. It can be seen that for each of these lines L 1 to L 8, the associated relay is energized through the terminals L to N with the aid of the switch S 11 during operation. The slide of the switch S11 is driven by the tap changing device, so that, for example, when the fourth tap is used, the line L 4 is energized and the relay ED is actuated.

At this point it should be pointed out that the reference symbols used in the drawings to designate the relays are used in the usual manner, ie the relay reference symbols contain numbers which reflect the number of contacts actuated by this relay. For example, relays EA through EH are labeled EAl4 through EH / 4 in the drawings to indicate that each of these relays operates four contacts. Each of the relays EA to EH has a pair of contacts EA 1, EA 2,. . . , EH1, EH2 connected in series. The contacts of Z 1 are connected to this chain at locations selected according to the voltage tap required in each successive period of the process. For example, the tap 5 is required to initiate the melting period, and therefore the first contact of Z 1 between the contacts EE 1, EE 2 of the relay EE corresponding to the tap 5 is switched on.

To initiate the control cycle of the furnace, an alternating current source is connected to terminals 13, while a direct current source is connected between terminals 14 and 15 and then between terminals 14 and 16 when a switch formed by contacts S 1 A and S 1 B , which is sometimes generally referred to as switch S1, is brought into the "on" position so that the contacts S2A toggle from the displayed off "position and the contacts S1B close. The tap of the uniselector is in each step Z1 to Z 7 on the first of the contacts shown. In stage Z 1, a negative potential is applied to tap i via the closed switch contacts S 1A and thus to contacts EE 1, EE 2. The ends of the chain of contacts EA 1 to EH 2 are connected to relays D and U, which are connected to positive terminal 14 on their other sides. If the contacts EE 1, EE 2 are not open, ie if the relay EE is not energized and the fifth tap is not used, then one or the other relay D, U is energized, depending on which of the relays EA to EH is in operation causing the interruption in the chain of contacts EA 1 to EH 2. The actuation of the relay D or U has the consequence that the tap changes by closing the corresponding contact D 1 or U 1 (Fig. 2) to energize the switch W or R until the fifth tap is reached. The first contact of stage Z1 is isolated by opening contacts EE1, EE2. When the fifth tap is reached, the excitation of the relay EE also closes the contact EE3, which, as can be seen, is also switched on at the first contact of stage Z3. The relay O is excited by a circuit that leads from terminal 15 via contacts S 1 A, C3, ZF 0, stage Z 3, contact EE3, relay O to terminal 14.

When the relay O is energized, it operates by closing its contacts 02 a switch G (FIG. 2) via the auxiliary switch contacts By. The switch D causes the oil breaker switch to close switch J, causing through Close its contacts to the AC power source via switch B and the furnace transformer TR is connected to the electrodes E (Fig. 3), so that these are downwards Lower into the batch and initiate the arc.

The contacts O 3 also close when the relay O is energized is to operate the timing circuit, which consists of a coil T and a clockwork 12 consists, which are excited at the same time. When excited by switching on the terminals 13 engages the coil T in the gear of the clock 12, so that the time period which has been previously set on the dial of the watch. At the end the time period, the contacts T 1 are automatically closed while the contacts T2 can be opened. Closing contacts T1 initiates the next stage of the oven cycle one, as it makes a circle from terminal 14 via the contact arm of level Z2, the Coil ZF, the contacts T1, the normally closed contacts ZR 0 and S 1 A to terminal 15 closes. The Uniselektor is therefore by the coil ZF in Operated to switch to the second contact, which is the tap setting of 6 corresponds.

When the Uniselektor switches over to the second contact, the above-mentioned circuit in stage Z3 for contacts EE3 to relay O is interrupted. If the relay O is de-energized, the timer circuit is reset by opening the contacts 03 and the coil T is thus de-energized. Closing the contacts O 1 (FIG. 2) results in the switching contact K being excited via the closed switching contact S1B on the alternating current supply line L, N. Closing the contacts K l causes the switching contacts M to be energized, as a result of which the furnace electrodes E are raised and, after a certain, previously set time within the range of 0 to 30 seconds, for example 10 seconds, are sufficient for the arcs to be raised of the electrodes are interrupted, the contacts M 1 close so that the circuit breaker trip coil X is energized. Circuit breaker B opens and power to the furnace is cut off. When the circuit breaker is triggered, auxiliary contacts BX open and the coil X is de-energized. The circle can now change over to a new tap that is selected by the second position of the uniselector.

In the second stage, the contact arm on stage Z1 connects terminal 15 to the connection of contacts EF 1, EF 2 and via contacts EF 2 to EH2 to relay U. Relay U is energized, contacts U 1 close, and the contact switch R is actuated. If the tap 6 is reached, the contacts EF2 open and de-energize the relay U, so that a further tap change is prevented. At the same time the contacts EF 3 close and cause the relay O to be excited by a circuit similar to the one above, but via the plane Z3 and the contacts EF3 instead of the contacts EE3. As a result, the contact switch G is again energized, which operates the breaker closing the contact switch, and the current is again supplied through the oil circuit breaker B to the electrodes E, the timer circuit being reset as at the end of the first tap change.

At the end of the period set by the timer the uniselector moves to the third position; there is a change in tapping to tap 7, and the power supply to the electrodes in this tap position occurs for the time period set by the timer. At the end In the third stage, the uniselector moves to its fourth position and chooses the tap 8 off, and the timer circuit is put into operation again, however unlike the previous stages, the period of this tapping is not just through the timing is determined, but also by the temperature or the speed the heat flow to the furnace ceilings or furnace walls, which with the help of the sensor 11 and can be determined by actuating the contacts LL. At the end of the Timing device for a certain period, the contacts T1 close as before, however, the excitation circuit to the coil ZF is not closed until the contacts LL are closed and thus energize relay A.

When the low temperature responsive device is actuated and contacts LL close, relay A is energized and is kept energized by contacts A 1 for the remainder of the oven period. When the contacts A 2 close, the excitation circuit for the coil ZF from the terminal 14 via the contact arm of level Z 2, the fourth contact in this level, contacts A 2, coil ZF, contacts T 1 (which are closed) and contacts ZR 0 closed to terminal 15. If the contacts HL responsive to the higher temperature level are to close before the contacts LL, then the excitation circuit for the coil ZF is closed directly via the contacts HL and the normally closed contacts A 3 to close the contacts A 2 during their closure by actuating the Bridge relay A as described above.

If the coil ZF is excited, the uniselector moves into the fifth position, which corresponds to the seventh tap. The tap change in downward direction occurs, and in each of the following three stages In the furnace cycle, the tap is successively changed from 7 to 3 by the switching device reduced.

The first four stages in the furnace cycle correspond to the initiation of the melting period, during which the output increases progressively. The next five stages correspond to the end of the melting period, during which performance gradually decreases. The following stages correspond to the purification period when, as will be explained later, the performance decreases again. During the ninth stage, the period for which tap 3 is used is determined by the timing circuit in conjunction with the contacts HL located on the highest stage, since contacts A 3 are switched off for the remainder of the furnace cycle by energizing relay A via the Contacts LL opened earlier. At the end of the period determined by the timer circuit, the contacts T 1 close, but as long as the contacts HL are closed, the circuit to the coil ZF remains open. As soon as the furnace temperature reaches the higher value, the contacts HL close, and the coil ZF is excited via a circuit that is supplied by terminal 14, the contact arm of level Z2, the ninth contact in this level, the contacts HK, the coil ZF, the closed contacts T1, ZR 0 and the closed switch contacts S 1 leads to terminal 15. The uniselector therefore moves to the tenth position and the tap 2 is selected by the device described above. The power at this tap is usually available for the remainder of the refining period, but after the contacts T1 are closed at the end of the time interval, if the temperature again reaches the value at which the contacts HL are closed, the coil ZF is energized again over the circle described above; and causes the uniselector to move to the eleventh position and select the lowest tap 1 for the remainder of the operation if the current regulator of the power control system, not shown, provides suitable control.

At the end of the furnace cycle, switch 1 is manually switched to the "off" position, which applies negative potential to the contact arm of stage Z6 and thus to one side of relay C, the other side of which is connected to the positive terminal. The resulting excitation of the relay C closes the contacts C1 and C2 and switches the contacts C3 from the position shown, so that the contacts ZFO are connected in series with the stage Z6 and the coil ZF via the terminals 15, 16 and the Uniselektor returns to the first position in the forward direction as soon as relay C is de-energized.

The operation of the control system is indicated by two sets of lamps 17, 18 numbered according to the voltage tap to which they relate. The lamps 17 are switched on at the subsequent contacts in stage Z7 in such a key that at each stage the selected lamp corresponds to the desired tap of this stage. The second row of lamps is switched on individually via contacts EA4 to EH4 and therefore light up after each tap is in operation. If the lamps in the two series 17, 18 match, then the worker knows that the tap change has been made correctly.

This is due to the special preselected assignment of the voltage taps The program selected for the contacts in level Z1 can be activated by pressing Switches S2 to S7 can be modified, which are connected to selected contacts of level Z 4 be switched on. Correct actuation of these switches enables the in series with the coil ZF lying time switch contacts T1 are short-circuited, and. the The progress of the uniselector is made before the end of the by the timer initiated period. For example, if the Uniselektor on the second Contact is made, then when the switch S 2 is closed, a circuit becomes the coil ZF from terminal 15, contacts C3, the. Kon =, clock ZF 0, the contact arm of the Level Z4, the switch S2, the coil ZF, the contact arm of the level Z2, the terminal 14 closed and the uniselector moves forward one step. A simultaneous Pressing the switches S2 and S3 causes the system to jump to the fourth Step. This relief can be applied at the start and / or at the end of the melting process, so that various voltage taps are skipped if desired will.

In some furnaces that use low-density scrap, the batch must be added in more than one portion. In such cases it will modified the program to correctly repeat the initial melting steps will.

Sometimes it is necessary to use extremely high power during the refining period to melt the second slag or for other purposes. This is done by actuating the push button PB 1, as a result of which the uniselector runs back, for example from the tenth position corresponding to tap 2 into the ninth position corresponding to tap 3. If the button PB 1 is pressed, the normally open contacts 19 are bridged and the left coil 20 of the relay Y is energized. A hold circuit is closed across contacts Y1 and contacts Y2 are closed to create a circuit for relay coil 21 of relay Y. If the button PB 1 is released, then the normally closed contacts 22 are bridged, so that the coil 21 is switched against the coil 20 and the relay Y resets itself. While coil 20 of relay Y remains energized, coil ZR is energized via a circuit that runs from terminal 15 to contacts C 3, the contact arm of level Z 5, contacts Y3 (closed), coil ZR to terminal 14 leads. A pulsation of the coil ZR causes - that the uniselector runs back.

If one considers in general the mode of operation of the subject matter of the invention compared to the particular exemplary embodiment given above, then the furnace has a power source for supplying power with a large number of different, specific values. This current source is not shown in detail in the exemplary embodiment, but is indicated by the transformer TR (FIG. 3), which can be set between eight different tapping points labeled 1 to 8. The programming device has the form of the uniselector Z, each stage of which is assigned a predetermined, special power input value, ie the corresponding tap point of the transformer TR, which is automatically set to the predetermined tap point at each program stage, as described above with particular reference to the individual relay EA to EH associated with special tapping points would be described. The duration of each switching stage of the uniselector Z is set up so that a minimum duration prescribed by the timer in the form of the timer circuit with the clock 12 is present: The arrangement is such that the uniselector advances by one step at the end of this minimum duration, as it does described above. ; .

In at least one stage of the program device, for example the third stage in the above example, devices operate which extend the prescribed minimum duration of the program stage in question in order to achieve a predetermined temperature characteristic of the furnace. These devices practically consist of the relay A, whose contacts A 2 or A 3 are in a circle for switching the Uniselectors Z at the end of the relevant stage. In particular, these contacts are arranged in such a way that the uniselector cannot actually be switched further until the relay A is energized, regardless of the end of the prescribed minimum duration. The excitation of the relay A depends on the closing of the contacts LL when a predetermined rate of temperature rise is achieved for the furnace walls or ceiling.

Claims (4)

Claims: 1. Program control for electric arc furnaces with a current source from which a large number of different, specific current values are supplied, that is, the program control controls the power supply to the furnace in stages and each stage of program control a predetermined precise power input value is assigned to that a timer (12) provided for maintaining a minimum duration for each level of program control and that responsive to the furnace wall or ceiling temperature or temperature change Facilities (10,11) the duration of at least one preselected program level in accordance expand with a predetermined temperature characteristic of the furnace or its batch, once this characteristic does not meet the prescribed value for the selected Level reached within the minimum level duration. 2. Program control according to claim 1, characterized in that the heat-sensitive device on two or more different temperature characteristics, for example the temperature and the Speed of heat flow, responses and duration over a selected one Program stage is extended and this stage ends in accordance with the first Occurrence of one of the different prescribed characteristics. 3. Program control according to claim 1 or 2 for an electric arc furnace with devices (M) for lifting the furnace electrodes, devices (M, XB) for interrupting the electrical circuit for the electrodes, devices (T, R) for changing the supplied by this circuit Services, devices (J, B) for producing this circuit and devices (J) for lowering the electrodes, characterized by connections (O) from the program device for operating the furnace in a predetermined sequence during at least each intermediate program stage and further characterized in that the clock is switched so that it simultaneously connects the electrical circuit to the electrodes during such stages. 4. Program control according to claim 3, characterized in that the device for interrupting the Electrode supply circuit switched on after lifting the electrodes is and that delay devices (M, M 1) are provided which the temporal Distance between the activation of the electrodes and the interruption of the supply, determine a circle. Publications considered: German Patent No. 760 645; U.S. Patent No. 2,556,450; "Steel and Iron", 1953, issue 23, p. 1441 to 1446; 1954, issue 2, pp. 82 to 95.