EP1536900A1

EP1536900A1 - Method and device for commencing a casting process

Info

Publication number: EP1536900A1
Application number: EP03798105A
Authority: EP
Inventors: Gerald Hohenbichler; Gerald Eckerstorfer
Original assignee: Voest Alpine Industrienlagenbau GmbH
Current assignee: SIEMENS VAI METALS Technologies GmbH
Priority date: 2002-09-12
Filing date: 2003-08-18
Publication date: 2005-06-08
Anticipated expiration: 2023-08-18
Also published as: US20050224210A1; EP1536900B1; AT411822B; ATA13672002A; EP1536900B2; AU2003258624B2; WO2004028725A1; KR101143384B1; US7156153B2; KR20050057316A; CN1681613A; AU2003258624A1; DE50301955D1; MXPA05002697A; CN100577326C

Abstract

The invention relates to a method for improving the conditions at the commencement of a casting process in a twin-roll casting device, which does not use a dummy bar, said method comprising the following steps: an operating casting thickness is set and the casting rolls are rotated at a casting-roll peripheral speed, which corresponds to a reduced commencing casting speed in relation to the casting speed for stationary operation; molten metal is fed into one of the rotating casting rolls and into the molten metal chamber that is configured from lateral plates lying against the rolls and a cast metal bar with an essentially constant, predetermined cross-sectional size is formed, whilst the casting speed is simultaneously increased to a strip forming casting speed; the casting speed is subsequently increased to a strip separating speed, which is significantly higher than the speed sufficient to cause solidification and the metal strip that has been cast up to this point is separated; the stationary operation casting speed is set; the following cast metal strip is deviated onto a strip transport unit and the stationary casting operation commences. The invention also relates to a twin-roll casting device for carrying out said method.

Description

Method and device for starting a casting process

The invention relates to a method for starting a casting process in a two-roll casting device without using a start-up strand and a device for carrying out this method.

To produce a continuously cast metal strand of indefinite length, essentially chilled molds with a continuous mold cavity are used, in which the molten metal introduced on the inlet side solidifies, at least in the contact area with the mold cavity walls. On the output side, a substantially solidified metal strand is pulled out of the mold. At the start of the casting process, an initial filling of the mold cavity with molten metal is to be carried out, with a completely rigid starting piece having to be achieved in particular with a predominantly vertical alignment of the mold cavity, so that the molten metal does not flow uncontrollably through the mold and exit from it. The casting thickness of the metal strand to be produced, the solidification conditions and the amount of heat that can be dissipated through the mold cavity walls during the short residence time are of particular importance.

In order to reliably prevent the uncontrolled escape of molten metal from the mold in the start phase of the casting process, a start-up line is usually introduced into the mold before the start of casting, which largely but not necessarily completely closes the exit cross section of the mold cavity and only after a firm connection of the introduced melt has been formed with the start-up strand head and a pronounced strand shell of sufficient thickness along the mold cavity walls with a pair of drive rollers from the mold. This start-up procedure requires at least one new start-up head to be coupled to the start-up line each time the casting system is restarted. Such a start-up strand, as is used in strip steel casting molds formed by broad side walls and narrow side walls, is known, for example, from US Pat. No. 4,719,960. A start-up strand for the special application in a two-roll casting installation is described in EP-A 208642. This start-up line contains a start-up head with two flanges formed by thin sheet metal strips, which abut the lateral surfaces of the casting rolls and thus form a space for receiving the incoming molten metal. Immediately after the first strand shell has been formed, the starting strand and the cast strip are conveyed out of the casting gap formed by the casting rolls.

In the case of very small casting thicknesses, preferably below a casting thickness of 5.0 mm, a start-up strand is not absolutely necessary, since the open casting gap is bridged within a very short time due to the rapid solidification of the molten metal on the mold walls. Starting procedures in which no starting line is required are also known several times.

For example, a starting method is known from JP-A 61-266 159, in which the two co-operating casting rolls are brought into a starting position before the start of casting, in which there is no casting gap and the casting rolls stand still. Immediately after the melt feed begins and a first strand shell is formed on the two lateral surfaces of the casting rolls, they are moved apart onto the operating casting gap (strip thickness) and the casting speed is brought up to the operating casting speed along a ramp-up curve. A starting process with stationary casting rolls is, however, very unreliable because the actual casting level in the melt chamber cannot be measured with the necessary accuracy up to the narrowest cross section between the casting rolls. Neither an increase in force between the two casting rolls nor the degree of filling of the mold can therefore be regulated reasonably. A different degree of solidification of the melt along the bandwidth and especially in the vicinity of the side plate can cause substantial wedge formation due to solidified metal above the narrowest cross section and subsequently lead to side plate damage. Furthermore, with such a starting method with upright casting rolls, there is an increased risk of section shell adhesives on the lateral surface of the casting rolls.

From WO 01/21342 a casting process for a two-roll casting device is known, in which the casting gap between the two casting rolls is set to a value which is reduced compared to the operating casting gap before the melt is supplied. The melt is supplied with rotating casting rolls, the Casting speed is set so that the thickness of the strip produced is greater than the previously set casting gap. In principle, the tendency to drip through molten metal is reduced by a reduced casting gap. On the other hand, the disadvantages described above with regard to JP-A 61-266 159 increasingly occur in the case of small casting gaps, in particular the tendency to damage side plates.

Further casting processes for conventional two-roll casting machines with special procedural instructions for the course of the casting speed in the starting phase or the selection of a favorable starting casting thickness in relation to the operating casting thickness are described in JP-A 63-290654, JP-A 1-133644 or JP-A 6- 114504 already known. EP-A 867 244 describes a control with which, in the starting phase of the casting process, the successive time periods of the casting rolls are first regulated as a function of a bath height measurement in the melt pool between the casting rolls and then the molten metal supply as a function of a roll speed measurement.

The object of the present invention is therefore to avoid the disadvantages of the prior art described at the outset and to propose a method for starting a casting process in a two-roll casting device and a device for carrying out the method, the passage of molten metal through the casting gap being kept low can and at the same time the tendency to wedge formation and thickening at the beginning of the cast strip is avoided as far as possible. At the same time, a separation of a first piece of the cast strip, which does not meet the quality requirements of a continuous production, from the strip subsequently produced under largely stationary operating conditions, is to be achieved without the need for mechanical separation devices.

This object is achieved by the method according to the invention with the following steps:

Setting an operating casting thickness and rotating the casting rolls at a casting roll circumferential speed which corresponds to a reduced starting casting speed compared to a stationary operating casting speed, Feeding metal melt into a melt space formed by the rotating casting rolls and the side plates adjoining them, and forming a cast metal strip with a substantially constant, predetermined cross-sectional format while simultaneously increasing the casting speed to a strip formation casting speed,

Subsequently increasing the casting speed to a strip cutting casting speed which is significantly higher than a casting speed which meets the current solidification conditions and cutting off the previously cast metal strip,

Setting the stationary operating casting speed,

• Deflection of the subsequent cast metal strip to a strip transport device and start of a stationary casting operation.

The casting speed is always determined by the casting roll circumferential speed, since the strand shells formed and adhering to the casting roll shells are transported at this speed through the narrowest cross section between the casting rolls and are connected to one another.

The starting casting speed is a low casting speed, at which, due to the longer dwell time of the strand shells that form in the melt chamber, an increased strand shell growth occurs and the casting gap which is open at the bottom can therefore be bridged particularly quickly.

The band formation casting speed is a casting speed which is dependent in particular on the current liquid metal casting level and also on the solidification conditions and the casting roll separation force required by the steel analysis, at which band formation and the removal of the formed strip takes place downwards and at which the band forming conditions remain largely unchanged can be. During the transition from the starting casting speed to the band forming casting speed, the continuous filling of the melt space with molten metal takes place to the level of the operating casting level, the band forming casting speed increasing continuously with increasing casting level. Since the casting gap in the claimed process is kept at the value of the operating casting thickness during the entire starting process, there are additional advantages: a reduced starting casting speed means that a low strip throughput is achieved until the target operating casting level is completely reached, and thus the proportion of rejects is kept low , Furthermore, the operational casting thickness, which is not reduced in the start-up phase, leads to fewer disturbances, which, as a result of solidification on the narrow side walls, lead to widening of the casting gap when passing through the casting cross section and possibly uncontrolled tearing of the cast strand. The elimination of a radial displacement of the casting rolls, which occurs when the starting process is started with a starting casting thickness that is smaller than the operating casting thickness, furthermore causes a reduction in the parasitic solidifications which occur in the relatively cold, released zones on the side plates would form.

In order to achieve a sufficiently rapid strand shell growth on the lateral surfaces of the casting rolls and thus a rapid bridging of the casting gap by solidified metal melt, the starting casting speed is chosen to be less than half the operating casting speed, the casting rolls usually rotating. In the case of casting thicknesses of more than 3 mm, the start phase can also be initiated with upright casting rolls, so that the starting casting speed is still 0 m / min at the start of the supply of molten metal and the casting rolls are then accelerated quickly.

Particularly favorable conditions for the rapid bridging of the casting gap due to solidified metal melt in the starting phase result when the starting casting speed is less than 12 m / min. A start casting speed in this range enables a good timing between the melt feed until the operating casting level is reached and the starting casting speed is increased to a band forming casting speed which corresponds approximately to the operating casting speed. This is achieved by a moderate, steady increase in the casting roll peripheral speed to a banding casting speed that matches a measurable target casting level, in order to ensure reliable banding (strand shell formation on the casting roll surfaces in the melt pool). Accordingly, the band formation casting speed is set or regulated in accordance with a measurable target casting level. A further possibility of setting the band formation casting speed in the best possible way is that the band formation casting speed is regulated as a function of the separating force occurring between the casting rolls. For a given casting gap, the separating force between the two casting rolls is a measure of the strand shell thickness and the current state of solidification in the narrowest cross section between the casting rolls. It is higher the further the solidification process has progressed in this area. The metal bath level, which predominantly rises in the start-up phase and which has a significant influence on the formation of strand shells, is also taken into account here.

The measured values of a bath level measurement and a separation force measurement in combination can also be used to regulate the banding casting speed.

The strip separation casting speed is to be understood as the casting speed at which the first part of the cast metal strip, which was produced under transient casting conditions in the starting phase of the casting process and is therefore to be regarded as scrap material, is separated from the continuously following metal strip produced under largely stationary casting conditions. According to a possible embodiment, this separation takes place exclusively under the influence of the dead weight of the starting piece of the cast metal strip, which leaves the narrowest cross section between the casting rolls and hangs down by tearing it off in the casting gap. By increasing the casting speed to the strip separating casting speed, the solidification conditions and thus the mechanical properties of the cast strip in the casting cross section, in particular by reducing the tensile strength, are changed so that the strip breaks off in this cross section without additional mechanical measures.

Alternatively, the cast metal strip can be separated at the strip separation casting speed under the influence of a strip tension which is increased compared to the force of gravity and is applied by a driver arrangement which is arranged on the outlet side below the casting gap of the two-roll casting device. An improvement in the separation conditions can be achieved if the increase in the casting speed to the strip separation casting speed is overlaid with a brief increase in the casting thickness of 5 to 40%.

The belt separation casting speed is higher than the operating casting speed, preferably it is 5% to 40% higher than the operating casting speed.

This strip separation casting speed is set briefly as soon as almost stationary casting conditions are reached. It is preferred that a constant strip quality is already ensured. The strip separating casting speed is expediently set in the starting phase when the molten metal in the melt chamber has essentially reached the desired operating casting level.

In order to ensure a continuous transition to stationary casting conditions and thus to stationary solidification conditions on the casting rolls and in the casting gap, it is expedient if the casting speed is increased to approximately the operating casting speed in the melt chamber before the desired operating casting level is reached.

The proposed method enables the stationary casting operation to be achieved within 5 to 60 seconds after the start of the supply of molten metal into the melt chamber.

In the case of very thin strips in particular, it is advantageous that when starting a casting process, a starting casting thickness that is larger than the operating casting thickness is set, and this starting casting thickness is reduced to the operating casting thickness at the earliest after forming a cast metal strip with a constant cross-sectional format. This method is preferably used for casting thicknesses below 2.5 mm, since the difficulties described at the outset with side plate solidifications and wedge formation and subsequent uncontrolled band breaks can occur especially in this thickness range and the band following the band separation thus has a better inherent rigidity for guiding through the system.

To ensure an automated sequence of the starting process, it is useful that at least reference data of the current casting speed and the instantaneous casting level of the molten metal in the melt space and / or the instantaneous separating force between the pouring rollers and / or the gap width between the pouring rollers and / or the strip thickness of the cast metal strip during the start of casting and continuously fed to a computing unit and from this reference data including one Mathematical models for the starting process are generated for the casting speed, for the position of a strip guiding device and for the transport speed of the cast metal strip in a strip transport device and are transmitted to the drive units of these devices.

In addition, the separation conditions for the separation of the first piece of the cast metal strip in the casting cross-section are improved if, based on current input data, such as steel quality, operating casting thickness, temperature conditions, quality-related solidification conditions, etc., an additional manipulated variable for the spacing positioning of the two casting rolls to one another, in particular an increased starting casting thickness, is generated.

The quality of the metal strip produced can generally and continuously be optimized during the casting process and adapted to changing operating conditions if the mathematical model comprises a metallurgical model for forming a certain structure in the cast metal strip and / or for influencing the geometry of the cast metal strip.

A two-roll casting device for carrying out the described method for starting a casting process without a starting strand consists of two casting rolls which are coupled with rotary drives and rotate in opposite directions and side plates which bear against the casting rolls and which together form a melt space for receiving the metal melt, as well as at least one displaceable strip guide device and at least one strip transport device. It is characterized by

a speed measuring device for determining the instantaneous casting speed is assigned to the casting rolls,

a level measuring device for determining the instantaneous level of the metal melt is assigned to the melt chamber,

- That the speed measuring device and the level measuring device by Signal lines are connected to an arithmetic unit and - the arithmetic unit is connected by signal lines to the rotary drive of the casting rolls, to a position adjusting device of the strip guiding device and to the drive of a strip transport device. The two casting rolls can also be coupled to a common rotary drive with the interposition of a transfer case.

A two-roll casting device equipped in this way enables current production data from the steel production process to be taken over and processed together with measurement data on the casting device in a computing model to optimize the starting process.

An appropriate course of the method according to the invention is also possible if, instead of continuously measuring the level of the casting level in the melt chamber with a level measuring device, alternatively a separating force measuring device for determining the instantaneous separating force between the two casting rolls, which is essentially caused by the banding, or a position measuring device for determining the current gap width between the casting rolls or a measuring device is used to determine the current strip thickness. Each of these measurements provides reference data that, at least indirectly, establish a mathematically describable connection with the strand shell formation in the melt pool and thus with the metal strand formation in the narrowest cross-section between the casting rolls and which can therefore be used in a mathematical model to calculate manipulated variables in order to minimize or minimize the starting process to optimize the shape and manageability of the tear-off edge. A further improvement of the starting method can be achieved by combining at least two of these measurement methods, the measurements being carried out simultaneously and processed in a correspondingly expanded mathematical model.

A further optimization of the method results if at least one of the two casting rolls is coupled to a casting roll adjusting device and the computing unit is additionally connected to a casting roll adjusting device by means of a signal line for setting a starting casting thickness. As a result, for predetermined production parameters, such as, in particular, the steel quality, the casting format, preferably the operating casting thickness, and also characteristic data adopted from steel production, such as, for example, the superheating temperature of the melt, and from Measurement data on the system in the process model, a specific higher starting casting thickness is determined and set on the casting system.

The present method and the associated two-roll casting installation are suitable for the casting of metal melts, preferably Fe-containing metal alloys, in particular for steels.

Further advantages and features of the invention emerge from the following description of non-limiting exemplary embodiments, reference being made to the accompanying figures, which show the following:

1 is a schematic representation of a two-roll casting device for performing the method according to the invention,

2a shows a schematic representation of the solidification conditions in the casting gap at the operating casting speed,

2b shows a schematic representation of the solidification conditions in the casting gap at strip separation casting speed,

Fig. 3 shows the course of the casting speed, the casting gap, the

Casting level signal and the casting roll separation force during the start of a casting process for a steel of quality AISI 304.

A two-roll caster with the facilities necessary for carrying out the method according to the invention is shown schematically in FIG. It consists of two casting rolls 1, 2 which are arranged at a distance from one another in a horizontal plane and are equipped with internal cooling (not shown). These are rotatably supported in shaft bearings 3, 4 and coupled to rotary drives 5, 6 which rotate the casting rolls 1, 2 in opposite directions Casting roll axes 1 ^' , 2 ^' with an adjustable peripheral speed that corresponds to the casting speed. To determine the current casting speed, at least one of the casting rolls 1, 2 or the associated rotary drives 5, 6 or even the cast metal strip itself is assigned a speed measuring device 34. One of the two casting rolls 2 is slidably supported in the horizontal plane transversely to the casting roll axis 2 ^' and is coupled to a casting roll adjusting device 7, whereby the distance between the two casting rolls 1, 2 to one another is adjustable adjustable. At the end of the casting rolls 1, 2, side plates 8 are pressed, which, together with a section of the lateral surfaces 9, 10 of the rotating casting rolls, form a melt space 11 for receiving metal melt 12. The molten metal 12 is introduced from an intermediate vessel 13 through a dip tube 14 into the melt chamber 11 continuously and in a controlled manner, so that during the stationary casting operation, the melt is supplied through the dip tube outlets in submerged form, ie always below a pouring level 15 which is kept at a constant level. The level of the casting level is continuously monitored by means of a level measuring device 16 arranged above the melt chamber 11.

On the output side, the melt space 11 is delimited by the casting gap 18, which is defined by the distance between the two casting rolls 1, 2 and determines the casting thickness D of the cast metal strip. The solidified strand shells 19, 20 formed on the lateral surfaces 9, 10 of the casting rolls in the melt chamber 11 are connected in the casting gap 18 to form a largely solidified metal strip 21, which is conveyed downward from the casting gap 18 by the rotational movement of the casting rolls 1, 2, by a downstream one pivotable belt guide device 22 and belt guide rollers 23 are deflected in a largely horizontal transport direction and a belt transport device 24 formed by a pair of drive rollers is conveyed out of the two-roll casting device. The arcuate tape guide 22 is connected to a drive unit 25, which enables the tape guide 22 to be pivoted from a retracted position A to an operating position B and back. During the starting process of the casting process, the strip guide device is in the retracted position A and, after a first piece of the cast metal strip has been cut off, is pivoted into the operating position B and can remain there during the entire stationary production process. A scrap pick-up carriage 26 is arranged vertically below the casting gap 18, in which at most metal melt which initially drips through and the first section of the cast strip can be collected and, if necessary, transported away.

The scrap pick-up truck can also be designed without wheels. It can be positioned within a chamber wall that surrounds the path of the cast metal strip from the casting rolls to the first driver. This too must the first section of the cast strip does not necessarily fall directly into the scrap pick-up carriage, but can also be fed indirectly to it.

After the cast metal strip emerges from the strip transport device 24 equipped with a drive unit 27, it is refined in further treatment devices 28 (not shown in any more detail) and finally wound into coils 29 and / or divided into sheets. The further treatment devices 28 can be formed, for example, by rolling stands, trimming devices, surface treatment devices, thermal treatment devices of various types, such as heating devices, holding furnaces, temperature compensation furnaces, and cooling sections.

The two-roll casting device is equipped with an arithmetic unit 36, which makes it possible to carry out the starting process in an automated manner as a function of predefined input variables and current measured variables determined on the device. With characteristic data fields and / or a mathematical model, optimal manipulated variables such as the start casting speed v _gSt , the position of the strip _{guiding device} , the drive speed of the strip transport device and, if applicable, the starting casting thickness D _st and other manipulated variables are generated in the computing unit and the starting process is continuously regulated and supervised.

Actuating variables that are generated from the computing unit 36 to carry out the starting process are based on currently collected measurement data from the casting installation, which are directly or indirectly related to the strand shell growth. The instantaneous level of the casting level 15 is predestined for this, ie the level of the casting level in the melt chamber 11, which can be determined continuously using a level measuring device 16. The separating force F _Tr between the two casting rolls 1, 2 represents a reaction force on the strand shells passed through and likewise provides a reference value for the degree of solidification in the narrowest cross section between the casting rolls. It is to be determined with a separating force measuring device 30, which is assigned to the casting roll bearings 3, 4 or is installed in the casting roll adjusting device 7. A further possibility for determining a reference quantity is provided by the instantaneous gap width G between the casting rolls, which is closely related to the separating force F _Tr , since a higher separating force causes the casting rolls 1, 2 to deflect from one another radially or to deform them. This can be done directly through a position measuring device 31 can be measured on the casting rolls or indirectly via a strip thickness measuring device 32. The simultaneous measurement and processing of the measurement data from several of the measuring systems described minimizes the time required to start the system and in particular increases the quality of the strip tear-off edge of the subsequent metal strip with regard to its geometry and its manageability through the system, as well as the quality of the product produced from the start of production.

The solidification conditions on the lateral surfaces 9, 10 of the two casting rolls and in the casting gap 18 at a steady operating casting speed and at a strip cutting casting speed are compared in FIGS. 2a and 2b. At a steady operating casting speed (FIG. 2a), the two casting rolls 1, 2 are set on a casting gap 18 which corresponds in particular to the stationary casting level and the operating casting thickness D of the desired cast metal strip. Here, on each of the lateral surfaces 9, 10 of the casting rolls, an increasingly thicker strand shell 19, 20 is formed in the direction of rotation of the casting rolls, thus oriented towards the casting gap 18. The two strand shells 19, 20 are joined together in the casting cross section 18 and a solidified metal strip is formed under stationary casting conditions. The V-shaped lines 37 here illustrate the transition from 100% melt to a mixing area with an increasing solid content and the V-shaped line 38 illustrates the transition to 100% solid content, thus the solidified strand part. 2b shows the changed solidification conditions at a strip separation casting speed which is increased compared to the operating casting speed. This means that the peripheral speed of the casting rolls is increased. The cooling conditions were not changed here. As a result, the available strand shell formation time in the melt space and thus the strand shell growth is reduced, so that the solidification point 39 shifts in the casting direction and in the casting cross section there is either still an increased proportion of liquid body fraction and / or the average strip temperature is at least higher than at the operating casting speed. In both cases, the tensile strength of the hanging metal strip piece at the strip separation casting speed is reduced to such an extent that the metal strip breaks off in the casting cross section under the influence of its weight.

In a preferred embodiment, the casting speed is increased to such a high strip separation casting speed and then immediately lowered again, that temporarily no separation force is measured. In this short phase, molten metal flows into the space below the narrowest cross-section between the casting rolls due to the lack of connection between the two strand shells and under the effect of the ferrostatic pressure. This leads to local bulging of the metal strip and considerable rewarming of the strip layers near the surface, and tearing under the influence of the strip's own weight hanging downwards.

FIG. 3 shows the sequence of the method described for starting a casting process in a two-roll casting plant for a stainless steel AISI 304 with an operating casting thickness D = 2.5 mm and an operating casting speed V _gB et _r = 60 m / min. Before the melt feed, the operating casting gap is set to 2.5 mm and the casting rolls are driven at a peripheral speed which corresponds to a starting casting speed v _gSt = 10 m / min. With the start of the melt feed, the casting speed v _{g is} continuously increased up to the banding casting speed v _gBb , which corresponds approximately to the operating casting speed v _gBe t _r = 60 m / min. Shortly after the melt feed begins, the casting gap which is open at the bottom is bridged by the strand shells which form and the casting speed is still very low. This can be seen from the briefly sharply rising curve for the casting gap position G and the casting roll separation force F _Tr , which correlate directly. The casting gap position G is measured on the hydraulic piston of an AGC system. With increasing casting speed v _g , the tendency of an increasing separating force reverses again, since the strand shell formation also decreases due to the shorter residence time of the strand shell in the melt space. The mold level h _Gsp can only be measured after a certain degree of filling has been reached, since the melt chamber is narrowed in a funnel shape towards the pouring cross-section due to the arrangement of the casting rollers and level measurement in this very narrow area is not technically feasible. After a period of about 5 to 15 seconds, which can be selected variably, the operating casting level h _Bβ t _{r is} reached and kept at this level. This means that almost constant casting conditions are achieved and the casting speed is increased for a short period of 0.2 seconds to the strip separation casting speed v _gTr = 80 m / min, which is 20 m / min higher than the stationary operating casting speed v _gBθtr . At this strip separation casting speed, the cast metal strip tears under the influence of its own weight in the narrowest cross section between the casting rolls. Here falls the Casting roll separation force F _Tr briefly returns to zero. When the casting speed is reduced to the value of the operating casting speed v _gBe tr = 60 m / min, the casting roll separating force F _{Tr increases} immediately to the value before the casting speed was increased to the strip cutting casting speed. This means that the conditions for a stationary casting operation are met and the production of a steel strip of consistent quality is guaranteed.

Claims

claims

1. Method for starting a casting process in a two-roll casting device without a starting strand, characterized by the following steps:

• setting an operating casting thickness (D) and rotating the casting rolls (1, 2) having a casting-roll circumferential velocity which is opposite to a stationary operation the casting speed (v _GBE t _r) decreased start casting speed (v _g s _t) corresponds to a,

• Feeding molten metal (12) into a melt space (11) formed by the rotating casting rolls (1, 2) and the side plates (8) abutting them and forming a cast metal strip (21) with an essentially constant, predetermined cross-sectional format with simultaneous increase the casting speed (v _g ) to a banding casting speed (v _gB b),

Subsequently increasing the casting speed (v _g ) to a strip cutting casting speed (Vg _Tr ) which is significantly higher than a casting speed (v _g ) which meets the current solidification conditions and cutting off the previously cast metal strip (21),

Setting a stationary operating casting speed (v _gBθtr ),

• Deflection of the subsequent cast metal strip (21) to a strip transport device (24) and start of the stationary casting operation.

2. The method according to claim 1, characterized in that the starting casting speed (v _g s _t ) is less than half the operating casting speed

(VgBetr) -

3. The method according to claim 1 or 2, characterized in that the starting casting speed (v _g s _t ) is less than about 12 m / min.

4. The method according to any one of claims 1 to 3, characterized in that the starting casting speed (v _gS t) at the beginning of the supply of molten metal is still 0 m / min and is subsequently accelerated.

5. The method according to any one of the preceding claims, characterized in that the banding casting speed (v _gBb ) is set in accordance with a measurable target casting level (h _Gsp ).

6. The method according to any one of the preceding claims, characterized in that the banding casting speed (v _gBb ) substantially corresponds to the stationary operating casting speed (v _gBet r).

7. The method according to any one of the preceding claims, characterized in that the banding casting speed (v _gBb ) is _controlled as a function of the separating force (F _Tr ) occurring between the casting rolls.

8. The method according to any one of the preceding claims, characterized in that the strip separation casting speed (v _gTr ) is higher than the strip forming casting speed (v _gBb ) and / or the operating casting speed (v _gTr ).

9. The method according to any one of claims 1 to 7, characterized in that the strip separation casting speed (v _gTr ) is 5% to 40% higher than the strip formation casting speed (v _gB ) and / or the operating casting speed (v _gBθtr ).

10. The method according to any one of the preceding claims, characterized in that a short increase in the casting thickness (D) by 5 to 40% is superimposed on the increase in the casting speed to the strip separation casting speed (v _gTr ).

11. The method according to any one of the preceding claims, characterized in that the strip separation casting speed (v _gTr ) is set as soon as the molten metal in the melt _chamber (11) has substantially reached the target operating _casting level (h _Gsp ).

12. The method according to any one of the preceding claims, characterized in that the separation of the cast metal strip at strip separation casting speed (v _gTr ) by tearing off the cast strip under the effect of the weight of the metal strip in the casting gap (18) between the casting rolls (1, 2) he follows.

13. The method according to any one of the preceding claims, characterized in that the separation of the cast metal strip at strip separation casting speed (v _g τ _r ) takes place under the action of an increased strip tension.

14. The method according to any one of the preceding claims, characterized in that at least in a period of time before reaching the target operating casting level (h _gsp ) in the melt chamber (11) the casting speed (v _g ) increases to approximately the operating casting speed (v _gBetr ) becomes.

15. The method according to any one of the preceding claims, characterized in that the stationary casting operation is achieved within 5 to 60 seconds after the initial supply of the molten metal into the melt space (11).

16. The method according to any one of the preceding claims, characterized in that when starting a casting process for the production of a very thin metal strip, a starting casting thickness (D _St ) which is increased compared to the operating casting thickness (D) is set and this starting casting thickness is formed at the earliest after formation of a cast metal strip with an essentially constant, predetermined cross-sectional format is reduced to the operating casting thickness (D).

17. The method according to any one of the preceding claims, characterized in that at least reference data of the instantaneous casting speed (v _g ) and the instantaneous casting level of the molten metal and / or the instantaneous separating force (Fr _r ) between the casting rolls and / or the gap width (G) between the casting rolls and / or the strip thickness of the cast metal strip are continuously determined during the casting start and fed to a computing unit (36) and from these reference data, including a mathematical model for the starting process, manipulated variables for the casting speed, for the position of a strip guide device (22) and for the transport speed of the cast metal strip is generated in a strip transport device (24) and transmitted to the drive units (5, 6, 25, 27) of these devices.

18. The method according to claim 15, characterized in that a manipulated variable for the spacing positioning of the casting rolls (1, 2) to one another, in particular a starting casting thickness (D _St ), is additionally generated from the mathematical model.

19. The method according to claim 15 or 16, characterized in that the mathematical model comprises a metallurgical model for forming a certain structure in the cast metal strip and / or for influencing the geometry of the cast metal strip.

20. Two-roll casting device for carrying out a method for starting a casting process without a starting strand according to one of the preceding claims 1 to 19, consisting of two casting rolls (1, 2) coupled with rotary drives (5, 6) and rotating in opposite directions and side plates (8 ), which together form a melt space (11) for receiving the metal melt (12), as well as at least one displaceable strip guide device (22) and at least one strip transport device (27), characterized in that

- A speed measuring device (34) for determining the instantaneous casting speed (v _g ) is assigned to the casting rolls (1, 2);

- The melt chamber (11) is assigned a level measuring device (16) for determining the current casting level height (h _gsp ) of the molten metal,

- and / or one of the casting rolls (1, 2) is assigned a separating force measuring device (30) for determining the instantaneous separating force (F _Tr ) between the two casting rolls (1, 2),

- and / or the casting rolls (1, 2) are assigned a position measuring device (31) for determining the instantaneous gap width (G) between the casting rolls (1, 2),

a strip thickness measuring device (32) for determining the instantaneous strip thickness (D) of the metal strip (21) leaving the casting rolls (1, 2) is arranged on the casting roll (1, 2) and

- The speed measuring device (34) and the level measuring device (16) and / or the separating force measuring device (30) and / or the Position measuring device (31) and / or the strip thickness measuring device (32) are connected to a computing unit (36) by signal lines, -the computing unit (36) by signal lines to the rotary drives (5, 6) of the casting rolls (1, 2) a position adjusting device (25) of the tape guide device (22) and the drive (27) of a tape transport device (24) is connected.

21. The apparatus according to claim 20, characterized in that at least one of the two casting rolls (1 or 2) coupled to a casting roll adjusting device (7) and the computing unit (36) additionally through a signal line with the casting roll adjusting device (7) for adjustment an increased starting casting thickness (D _St ) is connected to the operating casting thickness (D).