EP0042609A1 - Process for lowering the electrodes of an electric arc furnace - Google Patents

Abstract

Method for releasing the graphite electrodes (4) carried by vertically displaceable electrode holders and penetrating the lid (3) of an electric arc furnace vertically, the furnace lid (3) first being pivoted completely sideways away from the furnace vessel (1) and then the free lengths of the electrodes (4) below the electrode clamps (5) to the dimension ensuring a stable arc. The free lengths of the electrodes (4) below the electrode clamps (5) are set by means of a lifting device (8). The electrodes (4) are connected at their upper ends to the lifting device (8); After loosening the electrode clamps (5), the free lengths are adjusted by lowering the electrodes (4), whereupon the electrode clamps (5) are clamped again and the electrodes are released from the lifting device (8). Alternatively, if there is no possibility of moving the electrode arms with the furnace lid swung out, the height-adjustable support plates (11) are brought up to the electrodes (4) until contact and after the electrode clamps (5) have been loosened, the free lengths corresponding to the Support plates (11) supporting electrodes (4) by lowering the support plates (11) to the desired size, whereupon the electrode clamps (5) clamped back to the electrodes (4) and the support plates (11) by further lowering out of contact with the electrodes (4) are brought.

Description

The invention relates to a method for releasing the electrodes of an electric arc furnace releasably clipped by vertically displaceable electrode arms.

As is known, the electrodes of an electric arc furnace are subject to erosion, with the result that the length of the electrodes decreases continuously in the course of a melt. It is therefore necessary after exhaustion of the adjustment stroke, which can be regulated as a function of the burn-up speed, of the electrode arms releasably gripping the electrodes, lifting the clasping, then releasing the electrodes relative to the electrode arms and then re-tightening the electrode arms on the electrodes in order to continue to regulate the tracking Ensure electrodes during the subsequent melting process.

The electrodes can be released in a known manner, for example before the first basket filled with scrap is charged.

In this case, the electrode arms are first moved to the lowest position with the furnace lid remaining restricted above the furnace vessel. Then a crane picks up the electrode carrying nipple, so that the clasping of this electrode can be released.

The electrode is then lowered by the crane by a predetermined amount, which restores the correct removal of the electrode tip from the bottom of the furnace vessel. The electrode arm in question can then be clamped to the electrode again. The crane can now be used to release the other electrodes.

The advantage of this method is that the electrodes can be released exactly. However, the high is a disadvantage Loss of time because the furnace vessel is not accessible while the electrodes are releasing and therefore charging is not possible.

In practice, in order to reduce the loss of time when the electrodes are released, the electrodes have been released using a crane as soon as the electrodes have worked their way through the scrap and the electrode arms have reached the lowest position. This method is used in particular where only a single crane is available for an electric arc furnace.

In this case, after the electrode has been picked up by the crane, the clasping of the electrode is released and the electrode arm is then moved upwards by an amount which must necessarily be estimated by the melter. Once the height determined by the melter has been reached, the electrode arm is clamped to the electrode again and the other electrodes are then released.

A major disadvantage of this method is that it is only a matter of the ability of the melter to estimate how exactly the relaxation of each individual electrode is carried out and its height is brought into line with the height of the other electrodes.

For example, if the relaxation is too short, the arc between the electrode tip and the material to be melted will lead to an unstable arc, which inevitably increases the melting time and increases the energy consumption. On the other hand, the stove lining can be easily damaged if an electrode has been worn too much.

Finally, in order to reduce the decay time, the electrodes were decayed when the first scrap basket had been charged and the arc was present at all electrodes. The arc furnace is then switched off and the electrodes are loosened together or in succession.

Depending on the type of clasping, the electrodes slide or fall down until the electrode tips hit the scrap. The electrode arms are then raised by an amount which in turn can only be estimated by the smelter for each electrode. When the selected height is reached, the electrode arms are clamped back to the electrodes and the arc furnace is switched on.

The easing of the electrodes with the support of the scrap is associated with the least loss of production time, but has the disadvantage of a very imprecise adjustment of the electrodes to the melt. In addition, the electrodes can be damaged relatively quickly if the electrode tips hit oblique, sharp-edged shot parts.

The invention is therefore based on the object of providing a method for releasing the electrodes of an electric arc furnace, by means of which an exact release of the electrodes is ensured without loss of production time while avoiding the risk of electrode damage.

The solution to this problem is seen in the features listed in the characterizing part of claim 1.

The essence of the inventive concept is the possibility of having work processes run in parallel, which previously could only be carried out one after the other. The electrodes are now released when the furnace lid is swung out in the end position, that is to say next to the furnace vessel.

Swinging out the furnace lid is an already necessary process to enable charging. Consequently, during the charging of the first scrap basket, the electrodes next to the furnace vessel are released at the same time. In view of the high minute costs of an electric arc furnace, production time is saved due to the simultaneous work processes, which is therefore noticeable in a higher economic output.

Another advantage of the invention is that the electrodes can now be released with absolute precision. For this purpose, in addition to the furnace vessel, stops arranged according to the number of electrodes, that is to say support plates, can be used, which can be adjusted sensitively, that is to say exactly in height.

An exact height adjustment, however, in turn ensures an exact decrease of the electrodes, which are usually burned to different extents. It is possible that the stops, that is, support plates, are only fixed to a single estate height. The burned electrodes are then lowered using the electrode arms until the electrode tips touch the stops. This lowering can be carried out absolutely softly, so that no damage to the electrodes is to be expected. Then stand the electrodes on the stops, that is to say support plates, the electrode arms are detached from the electrodes, brought up to the intended extent with the utmost precision and braced again on the electrodes.

This method can be used in particular where the furnace construction allows the electrode arms to be moved downwards when the furnace cover is pivoted out. The investment costs are also reduced.

If there is no possibility of moving the electrode arms when the furnace lid is pivoted out, the invention provides that the stops are adjustable in height. In this case, the stops in the form of support plates can be raised and softly brought into contact at the electrode tips. After the clasping is released, the stops are lowered to the intended heel height together with the electrodes standing on them. When the intended height of reduction is reached, the electrode arms are fixed to the electrodes again.

With regard to a device for releasing the electrodes of an electric arc furnace releasably clasped by vertically displaceable electrode arms, which has a pivotable furnace cover which is penetrated vertically by the electrodes, the solution to the objective part of the task is characterized by the pivoted-out position of the furnace cover Stops arranged below the electrodes, also variable in height and lockable in the preselected height, in the form of support plates.

These stops arranged in the form of support plates next to the furnace vessel have the particular advantage that they are largely independent of the warm area of the arc furnace. They can therefore be designed to be comparatively simple. If the stops are fixed at a certain height, for example in the form of a support table, which is advantageous in furnace designs in which the electrode arms can be moved downwards when the furnace cover is pivoted out, the investment is low since no moving parts have to be provided.

If it is not possible to lower the electrode arms when the furnace lid is swung out, the height of the stops in the form of individual support plates is adjustable and lockable at the preselected height. The means for adjusting the stops can be controlled sensitively, so that the stops cannot hit the electrode tips hard with the risk of damage.

It is also conceivable in this context that after the contact of the electrode tips with the stops, be it with locally fixed stops, the support table or with height-adjustable stops, the support plates the subsequent processes, such as loosening the clasp, relative displacement of the electrode arms and Re-tensioning, are triggered automatically.

The invention is explained in more detail below with reference to exemplary embodiments shown in the drawings.

• Fig. 1 einen Elektro-Lichtbogenofen, bestehend aus Ofengefäß mit ausgeschwenktem Ofendeckel und in der Länge unterschiedlich abgebrannten Elektroden,
• Fig. 2 den ausgeschwenkten Ofendeckel mit einer Hubvorrichtung, bei der eine der drei Elektroden am Kragennippel erfaßt, in oberer Stellung dargestllt ist,
• Fig. 3 wie Fig. 2, jedoch ist die Elektrode über die Hubvorrichtung in der gewünschten Länge nachgelassen, dargestellt,
• Fig. 4 den ausgeschwenkten Ofendeckel mit drei unterschiedlich abgebrannten Elektroden, die von einzelnen Stützplatten von unten unterstützt, dargestellt sind,
• Fig. 5 wie Fig. 4, jedoch sind die drei Elektroden um die vorgesehene Länge nachgelassen, indem die Stützplatten mit den aufstehenden Elektrodenspitzen auf die vorgewählte gleiche Höhe abwärts gefahren, dargestellt sind,
• Fig. 6 den ausgeschwenkten Ofendeckel mit unterschiedlich abgebrannten Elektroden und darunter befindlichem Stütztisch,
• Fig. 7 wie Fig. 6, wobei die Elektrodenarme die angeklammerten Elektroden soweit abwärts gefahren haben, bis die Elektrodenspitzen auf dem Stütztisch aufstehen,
• Fig. 8 wie Fig. 7, wobei die Elektroden mit den Spitzen auf dem Stütztisch aufstehen, die Elektrodenklammern gelöst sind und auf gleiches Höhenmaß hochgefahren, dargestellt sind,
• Fig. 9 wie Fig. 8, die Elektrodenarme fahren mit den wieder angeklammerten Elektroden um ein vorgewähltes Maß hoch, damit der Ofendeckel samt Elektroden-Trageeinrichtung bereit zum einschwenken auf das Ofengefäß, dargestellt ist.

Show schematically in section:

• 1 shows an electric arc furnace, consisting of a furnace vessel with the furnace lid swung out and electrodes that have burned up differently in length,
• 2 the swung-out furnace cover with a lifting device, in which one of the three electrodes is gripped on the collar nipple, is shown in the upper position,
• 3 as in FIG. 2, but the electrode has been reduced in the desired length via the lifting device,
• 4 shows the pivoted-out furnace cover with three differently burned electrodes, which are supported by individual support plates from below,
• 5 as in FIG. 4, but the three electrodes have been reduced by the intended length in that the support plates with the rising electrode tips are moved down to the preselected same height,
• 6 the pivoted-out furnace cover with differently burned-off electrodes and a support table underneath,
• 7 as in FIG. 6, the electrode arms having moved the clamped electrodes downwards until the electrode tips stand on the support table,
• 8 like FIG. 7, the electrodes with the tips standing on the support table, the electrode clamps being released and being raised to the same height, are shown,
• Fig. 9 as Fig. 8, the electrode arms move up with the electrodes clipped on again by a preselected amount, so that the furnace lid together with the electrode carrying device is shown ready to be pivoted onto the furnace vessel.

Fig. 1, the furnace vessel 1 and the pivoted furnace cover 3 shows an electric _- arc furnace 2 in section. In order to explain the method clearly, the devices and devices shown in FIG. 1 and the following drawings are only shown schematically.

The furnace vessel 1 can be closed by a furnace lid 3, which can be adjusted in height by means not shown in the drawing, and which can be pivoted horizontally about a vertical axis (not shown).

The furnace cover 3 is penetrated vertically by three electrodes 4 arranged offset by 120 ° to one another. These electrodes 4 are moved by an electrode lifting and carrying device, not shown in the drawing, via support arms and releasably clipped by means of electrode clamps 5. The electrode support arms carrying the electrode clips 5 can be displaced vertically when the furnace cover 3 is pivoted out.

In order to maintain the clarity of the drawing, the electrical feeds to the electrodes 4 via the electrode clamps, which usually consist of a mounting ring and contact jaws, are not shown in the drawings.

Fig. 1 shows the electrodes 4 after a series of melting processes and it can be seen that due to different erosion, the electrode tips 6, 6 'and 6''have burned differently.

During the releasing process, the electrodes, which have different lengths after the previous erosion, are relieved, so that their tips are then relieved at a height which is indicated by the line 7.

2 and 3, the easing of the electrodes 4 is shown schematically by means of a lifting device 8 with the furnace cover fully pivoted out. The electrodes 4 are connected with the carrying nipples 9 located at their upper end via suspension hooks to the lifting device 8 assigned in the electrode position when the cover is pivoted out. After the electrode clips 5 have been released, the free lengths of the electrodes 4 are reduced to a preselectable length below the electrode clips 5. The electrode tips 6, 6 'and 6 "are lowered to the same height, which corresponds to line 7.

After reconnecting the electrode clamps 5, the connection to the lifting device 8 is released.

When using this lifting device, the observation and coordination of the height of the electrode tips 6, 6 'and 6 "at about the height of line 7 is left to the melter. The advantage, however, is that the length of the electrodes that pass through the pivoted-out furnace lid is free of the furnace vessel and can be set by the melter without thermal impairment.

In the method for releasing the electrodes shown schematically in FIGS. 4 and 5, a releasing device 10 with three mutually independent support plates 11 and associated lifting elements 12 with control elements is provided exactly in the extension of the electrode axes of the furnace cover 3 pivoted out in the end position.

After the furnace lid 3 has been swung out into its end position for charging, the height-adjustable support plates 11 are moved sensitively from below up to contact with the electrode tips 6 via individual lifting elements 12. As soon as the support plates 11 touch and support the electrodes during their upward movement, the electrode clips 5 are released. Now the support plates 11 with the electrodes are opened with the electrode clamps 5 down to a fixed position, that is to the drop position 13, the support plates 11 being lowered together with the upstanding electrodes 4. When the reduction position 13 according to FIG. 5 is reached, the electrode clips 5 are clamped again. After the three electrode clips have been disconnected, the electrode arms with the electrode clips 5 and the clamped electrodes are moved back into the upper starting position; the support plates 11 are moved back into the lower starting position, so that the furnace lid can be swiveled in again over the furnace vessel after the charging process has been completed.

Since the electrode clamps are in the uppermost position and the support plates 11 with the electrodes are moved into the defined reduction position 13, the set electrode length A - that is, the distance from the electrode tips 6 to the lower edge of the electrode clamp 5 is constant for sufficiently long electrodes for each melt. The upward movement of the support plates 11 is stopped as soon as a slight pressure is applied to the inflation system, and damage to the electrodes is excluded.

Some furnace designs allow the electrode arms to be moved downwards when the furnace lid is swung out. With these furnace designs it is not necessary that the height of the support plates can be moved.

After the furnace cover 3 has been swung out into its end position, the electrode arms with the clamps 5 holding the electrodes are moved down until the electrode tips 6, 6 ′ and 6 ″ touch the support table 14. This is illustrated schematically in FIGS. 6 and 7.

As soon as the electrode tips 6 come into contact with the support table 14, the downward movement of the individual electrode arms with the clamped electrodes 4 is stopped and the electrode clamps 5 are released. After all three electrodes stand on the support table 14 and the clamps 5 are loosened, the electrode arms with the electrode clamps 5 are raised to a fixed height, the estate height 15. This is shown in Fig. 8. The clamps 5 are then closed and the electrode arms with the electrode clamps which clamp the electrodes are moved back into the uppermost position according to FIG. 9. Now the furnace lid 6 can be swiveled in again after the charging process has been completed.

The two methods described last differ in principle in that, according to FIGS. 4 and 5, the electrode tips, which are at different levels of burnup, are carefully approached from below by individual support plates. In the other case, due to a special furnace construction, the electrode arms are suitable for moving the electrodes into the lowest position until the electrode tips sit on the support table by carefully moving them down. It is of course also included that instead of this support table common to all electrodes, a support plate which is firmly fixed in height can also be provided for each electrode.

The detailed representation of the devices in the drawing is deliberately omitted, since, for example, both hydraulic cylinders or motor-driven support columns can be used for the intended, sensitive displacement of the support plates. The devices only have to meet the two conditions of the switchable speed control. The upstroke must be delicately provided with an overload switch that stops the upstroke when it comes into contact with the electrode tips. The automatic downward stroke must be limited to a lower reduction position 13. If the electrode length is no longer sufficient, the downward stroke is controlled by hand.

List of reference symbols

• 1 oven vessel
• 2 arc furnaces
• 3 furnace covers
• 4 electrodes
• 5 electrode clips
• 6 electrode tips (6, 6 'and 6 ")
• 7 line
• 8 lifting device
• 9 carrying nipples
• 10 release device
• 11 support plate
• 12 lifting element
• 13 estate position
• 14 support table
• 15 estate amount

Claims (5)

1. A process for releasing the graphite electrodes carried by vertically displaceable electrode holders, vertically interspersed with the lid of an electric arc furnace, characterized in that the furnace lid (3) is first pivoted completely sideways away from the furnace vessel (1) and then the free lengths of the electrodes ( 4) below the electrode clamps (5) to the dimension ensuring a stable arc. 2. The method according to claim 1, characterized in that the free lengths of the electrodes (4) below the electrode clips (5) are adjusted by means of a lifting device. 3. The method according to claim 2, characterized in that the electrodes (4) are connected at their upper ends with a lifting device (8) and that after loosening the electrode clips (5) the free lengths are set by lowering the electrodes (4) , whereupon the electrode clamps (5) are clamped again and the electrodes are released from the lifting device (8). 4. The method according to claim 1, characterized in that on the electrodes (4) adjustable in height support plates (11) up to the contact and after loosening the electrode clips (5) the free lengths of the support plates (11) are supported Electrodes (4) by lowering the support plates (11) can be set to the desired size, whereupon the electrode clamps (5) are clamped again to the electrodes (4) and the support plates (11) are brought out of contact with the electrodes by further lowering. 5. The method according to claim 1, characterized in that the electrodes clamped on the electrode clamps (5) to the electrode arms (4) by means of conventional electrode holders first lowered to the height-fixed support table (14) and then the electrode clamps (5) released and the free lengths are then adjusted by moving the electrode holder upwards relative to the electrodes (4) and then the electrode clamps (5) are clamped again to the electrodes.

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