EP1365873A1

EP1365873A1 - Method for determining the characteristics of an oscillation system in an oscillating continuous casting mould

Info

Publication number: EP1365873A1
Application number: EP02719905A
Authority: EP
Inventors: Peter Müller; Horst Von Wyl; Thomas Fest; Frank Weissbuch; Michael Schwarz
Original assignee: Salzgitter AG; SMS Demag AG
Current assignee: Salzgitter AG; SMS Siemag AG
Priority date: 2001-03-02
Filing date: 2002-02-23
Publication date: 2003-12-03
Anticipated expiration: 2022-02-23
Also published as: DE50200631D1; DE10110081A1; WO2002070172A1; EP1365873B1

Abstract

The invention relates to a method for determining the characteristics of an oscillation system in an oscillating casting mould, which is displaceable on an elevation path x by means of a lifting drive. The elevation path x of the oscillating mould (1) and the drive force FA required for displacing the cast in an elevating manner are detected. In order to determine real characteristics with high precision, particularly the frictional force between the walls of the mould and the casting shell, a hysteresis-curve (H1, H2) of the elevation path is determined as a function of the drive force on a lifting cycle.

Description

Method for determining characteristics of an oscillating system of an oscillating continuous casting mold

The invention relates to a method for determining characteristic data of an oscillation system of an oscillating continuous casting mold, which can be moved by a stroke drive over a stroke path x, the stroke path x of the oscillating mold and the driving force FA for the mold stroke movement being detected. In addition, the invention relates to a continuous casting device for casting metal, in particular steel, comprising an oscillation system with an oscillating mold.

In continuous casting production, in particular in the casting process known as CSP (Compact Strip Production) for the production of thin slabs, the melt jet is introduced in a known manner from a ladle through a shadow pipe, a distributor and an immersion pipe into the mold. For comparatively high casting speeds, special casting powder is used to produce a lubricating film between the mold walls and the strand which is solidifying. This, as well as the use of an oscillation system - also in conjunction with an optimal mold geometry - enables optimal strip surfaces to be achieved.

The mold oscillation is therefore an essential part of the continuous casting process of metals. It enables the required lubricating effect of the lubricant and thus reduces the coefficient of friction or the frictional force occurring between the strand shell and the mold walls and thus the strand shell adhering to the mold walls. Insufficient friction conditions reduce the quality of the strand product, which is particularly noticeable in longitudinal cracks and irregular and deep lifting marks. A direct measurement of the frictional force is not yet known due to the inaccessibility of the source of this force. For this reason, the frictional force is calculated. The basis for most of the known methods for determining the frictional forces is the measurement of the driving force of the oscillation device and the fact that this driving force or excitation force of the oscillation system can be broken down into three basic components according to the basic differential equation of a linear oscillator:

F _E (t) = ma (t) + dv (t) + cs (t) or F _E (t) = m ds ² / dt ² + d ds / dt + es

with: m: oscillating mass a (t) acceleration of the system at time t dv (t) the desired, speed-dependent proportion of friction force c spring constant s (t) the position of the system at time t

F _E (t) the excitation force or driving force of the system at time t.

In general, it is now assumed that this equation is solved for the frictional force or the frictional force component dv (t) by measuring the excitation force or driving force at the time of observation. The product of mass and current acceleration and - if not neglected - the product of spring constant and stroke position is subtracted from this driving or excitation force. A prerequisite for such a calculation is that the parameters m, a (t), c and s (t) are known or can be neglected. The acceleration is also measured or derived from the stroke position. A disadvantage of this method is that the mass and the spring force are assumed to be constant. In particular, in the case of small casting molds with relatively low oscillating masses, namely Additional weights, such as changeable attachments and installations, operating personnel on the swinging cover, different settings of dead weight compensation, wear, fatigue etc. significantly influence the evaluation result.

In addition, on the basis of the mathematical model, these calculations assume an ideal sinusoidal oscillation of the linear single-mass oscillator, from which real mold oscillations deviate more or less. In real mold oscillations, for example, it is observed that these fall into different typical vibration modes, so-called eigenmodes. These can appear in isolation or in combination and overlay the basic form in a way that is difficult to predict. To make it more difficult for a numerical or arithmetical determination of the frictional force, the fact that the frictional force itself influences the frequency position of this natural oscillation by damping it.

A mathematical calculation based on an oscillation system is based, for example, on the method for determining the frictional force according to WO 96/33035. For the reconstruction of the friction force, it is proposed to continuously measure the mold lifting movement and the driving force for the mold movement and to process the measurement results in a special arithmetic circuit in order to calculate the friction force as an absolute variable.

JP 610 52 972 proposes to predict the breakdown of a strand in a mold by measuring the amplitude value of the oscillation movement. An inhibiting influence of the frictional force on the mold stroke is assumed.

The invention is based on the object of providing a method and a continuous casting device according to or with the characteristics of

Oscillation system, especially the actual frictional force, with high Accuracy can be determined and are available for use in machine and process control or optimization.

According to the method, this object is achieved in that a hysteresis curve of the stroke distance as a function of the drive force - or a hysteresis curve of the drive force as a function of the stroke distance - is determined over a stroke cycle and that current characteristic data are determined via the oscillation system by means of this hysteresis curve , A hysteresis curve over one stroke cycle or the curves over several stroke cycles can be determined. The values of the driving force and the stroke distance in the sense of the respective stroke position are recorded synchronously by measurement.

The heat loss WR through the area of the hysteresis curve is preferably determined as characteristic data. The actual frictional force F _R between the mold walls and the strand shell can be determined from this heat loss WR or the area determined, which is enclosed by the hysteresis curve. For this purpose, it is proposed to determine a friction force value F _Ry from the ratio of the work dissipation W _R and the stroke amplitude value y _x as the maximum stroke.

The invention makes use of the phenomenon that the acceleration-proportional mass or inertial force as well as the travel-proportional spring force of the oscillation or oscillation system describe a reversible process and completely compensate for each individual completed stroke cycle. This is not the case with friction. This is an irreversible process in which the mechanical energy is irretrievably converted into heat. This loss of energy can be visualized using the hysteresis curve. In this case, the area enclosed by the hysteresis curve in the coordinate system driving force-stroke distance or stroke distance-driving force corresponds to the work dissipation W _{R of} the process, which is used as a measure of the friction force FR. The principle of using the hysteresis curve as the basis for determining characteristic data in an oscillation system, in particular the frictional force, thus enables the actual frictional force to be determined. Even if the hysteresis curve of an irreversible process is overlaid with the trajectory curves of reversible processes, the lossy part can still be clearly determined by the enclosed area of the hysteresis curve. The knowledge gained from this of the actual frictional force allows defects in the casting process to be recognized at an early stage and thus increases operational reliability.

By calculating a frictional force value FR _Y with the help of the ratio of dissipation work WR and stroke amplitude value y _x , the frictional force value becomes completely independent of changing boundary conditions and can be determined without any additional mathematical assumptions. Neither harmonics of the oscillation system nor stochastic disturbances from the environment influence the evaluation result.

According to a preferred method variant, the stroke amplitude value yx is averaged to form a stroke amplitude mean value y _x , preferably by means of a moving averaging within a stroke amplitude. Likewise, the determined friction force values FR _{Y should be} subjected to a smooth smoothing - over several lifting cycles. In this way, errors due to electrical interference that could distort the minimum and maximum values are eliminated.

In addition to the energy loss as the area enclosed by the hysteresis curve or the friction force, characteristic data can also be determined from the individual curve profile of the hysteresis curve. Information about the state of wear of the oscillation system is preferably obtained on the basis of the individual curve shape. A comparative method of visualized hysteresis curves is particularly useful here, whereby hysteresis curves are one that is free of play and one that is free of play due to wear Differentiate drivetrain significantly. Quantitative differences can be determined using an image recognition method.

In addition, characteristic data can be determined from the — preferably mean — slope or slope of the hysteresis curve; in particular, information about the mold suspension is hereby obtained. The reason for this is that the shift in the proportions of superimposed force components from acceleration and spring forces is included in the average slope of the hysteresis curve. For example, the breakage of one or more articulations of the oscillation system can be recognized by a proportional rotation of the hysteresis slope. Just as a comparison of the individual curve profiles can be carried out, the comparison of the inclinations of several successive hysteresis curves leads to qualitative statements about the oscillation system.

According to the method, the driving force and the stroke or the oscillation position of the lifting drive must be detected, preferably by measurement. This measurement should take place at measuring frequencies f _me ss of 2-100 times the oscillation frequency f. At the longest, a measurement is required after half a stroke cycle of the oscillation to be assessed. In practice, sampling frequencies of 10-100 times the oscillation frequency have proven their worth.

As a preferred embodiment of the method, it is also proposed that an idle measurement be carried out to determine the idle losses of the oscillation system. The reason for this is that the determination of the friction losses includes both the friction losses between the mold and the train as well as the mechanical friction losses in the suspension and the drive train. An idling measurement is therefore carried out in order to determine the mechanical friction losses in advance and to subtract them later from the total value determined in order to determine an effective value of the friction force. Here is a calculation using individual value differences, mean value differences or Difference hysteresis curves possible. It is advisable to carry out various idle measurements of the oscillation system with different oscillation parameters before the start of casting and / or during a pause in casting. The determined values can also be processed statistically.

According to a development of the method, the determined characteristic data and / or the hysteresis curves are visualized and registered, and control data for the corresponding change of the current oscillation parameters, such as negative strip, healing time, i.e. the time in which the lubricant penetrates into the gap between the strand shell and the mold wall, stroke amplitude and stroke frequency as well as the shape of the oscillation, as well as for changing the current casting parameters, such as cooling parameters and casting powder use, to achieve target conditions.

According to the device, the object is achieved by a generic continuous casting device which comprises a computer unit for determining a hysteresis curve from the stroke as a function of the driving force over a stroke cycle and for determining current characteristic data via the oscillation system on the basis of this hysteresis curve.

According to a preferred embodiment, this continuous casting device further comprises signal lines which connect devices for measuring the driving force F _A and the stroke x with the computer unit, the computer unit calculating corresponding control signals from the determined characteristic data, and command lines between the computer unit and control devices for controlling the Oscillation system and / or the casting parameters depending on the determined characteristic data and calculated control data.

In an oscillation system that is provided with a hydraulic drive unit, the respective drive force is preferably determined from the measured chamber pressures of the respective hydraulic cylinders of the drive train. averages. The device for determining the stroke travel includes position meters for measuring the current position of the respective cylinder piston of a cylinder unit of the hydraulic drive unit. Hysteresis curves are formed for each of the separate cylinder units or, if necessary, averaged over several cylinder units. In the case of mechanical lever drives, the drive forces can be determined using strain gauges or load cells on the connecting rods, and the stroke lengths are calculated back from the angles of rotation.

Preferably, the proposed method for resonance molds, i.e. molds stored in spring packs can be used.

Further details and advantages of the invention result from the following description of the figures. In addition to the combinations of features listed above, features alone or in other combinations are also essential to the invention. Show it:

Figure 1 is a schematic representation of an oscillating mold with the attacking forces.

2 shows a schematic illustration of a continuous casting device according to the invention for determining the frictional force;

3 shows two hysteresis curves, represented as a stroke (mm) as a function of the driving force (kN);

FIG. 1 schematically gives an overview of a mold 1, shown here with two walls 1 a, b, with strand 2 solidifying therein, as well as an overview of the attacking forces. In order to enable casting with a high surface quality, the mold 1 is set into an oscillating or oscillating movement (according to the direction of the arrow) and for this purpose a driving force F _{A is} applied. Due to the oscillating movement of the mold, the friction force FR in this vibrating system between strand shell and mold walls 1a, b.

FIG. 2 shows an illustration of an oscillation system 3 and a continuous casting device according to the invention. The oscillation system 3 comprises a lifting table 4 which receives the mold 1 in a positive and non-positive manner. This lifting table 4 is freely swingably mounted on hydraulic cylinders - one of these hydraulic cylinders is shown here as a cylinder unit 5 as an example - and is guided by a spring system 6 in a vertical direction of vibration. Each cylinder unit 5 has a working piston 9 arranged between an upper pressure chamber 7 with a pressure p ₀ and a lower pressure chamber 8 with a pressure p _u , the upper and lower working surfaces of which can be acted upon by the working medium of the upper or lower pressure chamber 7, 8. These pressures p ₀ and p _u are measured by means of corresponding measuring devices 10, 11 and corresponding signals are fed via signal lines 12, 13 directly into a central computer unit 14 in order to calculate the resulting driving force FA for the respective cylinder.

Based on the movement of the working piston 9, the stroke x is determined by means of a position meter 15 in synchronism with the pressures p ₀ and p _u . The measured values are likewise fed into the central computer unit 14 via a corresponding signal line 16. This computer unit 14 uses the drive forces F _A and the respective stroke position x to determine a hysteresis curve over a stroke cycle, specifically for each hydraulic cylinder. With the help of the characteristic data determined from the respective hysteresis curve or from the comparison of several temporally following hysteresis curves, in particular the friction force, whereby both the hysteresis curves and the characteristic data are visualized on a monitor, control signals are calculated which are transmitted via Command lines 17 for controlling control devices for the oscillation system 3 or for setting the casting parameters are transmitted to the corresponding control devices. The control device 18 for setting the casting speed v is shown here by way of example. The pouring speed should be reduced if there is a risk of breakage, so that the strand shell becomes thicker and more stable again. Knowledge of the frictional force can also be used for process control and process monitoring with regard to an automated supply of casting powder or the addition of lubricant or with regard to a taper adjustment of the side walls in the case of adjusting molds, by the supply of casting powder when the friction increases and the taper of the side walls in the case of abnormal friction conditions is adjusted. The continuous casting device shown here is only one example for determining the driving force of the oscillating movement of continuous casting molds. Measurements by means of strain gauges, load cells in mechanical drives and the measurement of motor currents in electrical drives are of course also conceivable.

3 shows the determined hysteresis curves Hi, H _{2 of} two lifting cylinders by plotting the respective measured stroke in mm over the respective, synchronously measured, driving force FA. The area enclosed by the respective hysteresis curve corresponds to the heat loss WR due to friction losses. From this, the frictional force can be determined based on a stroke value. In the specific example, the mold is moved approximately between +2, 5mm and -2.5mm. The period or one stroke cycle is 0.466 seconds or reciprocally a frequency of 2.146 Hz. The slope of the left hysteresis curve is 3.84 kN / mm, that of the right hysteresis curve 3.27 kN / mm. The hysteresis is 5.70 kN on the left hysteresis curve and 4.94 kN on the right hysteresis curve.

Characteristic data, in particular for determining the actual frictional force FR, can be determined both from the area enclosed by the hysteresis curves, from the special curve shape and from the slope or inclination of the individual curves.

Claims

claims:

1. A method for determining characteristics of an oscillation system of an oscillating continuous casting mold, which can be moved by means of a stroke drive over a stroke path x, the stroke path x of the oscillating mold (1) and the driving force F _A for the mold stroke movement being detected, characterized in that a Hysteresis curve (H-ι, H ₂ ) of the stroke is determined as a function of the driving force over a stroke cycle and that current characteristic data are determined via the oscillation system by means of this hysteresis curve.

Method according to Claim 1, characterized in that the loss work WR is determined as the characteristic data by the area of the hysteresis curve.

3. The method according to claim 2, characterized in that the frictional force FR between the mold walls (1 a, b) and the strand shell is determined from the determined area of the hysteresis curve.

4. The method according to claim 3, characterized in that a friction force value F _{Ry is determined} from the ratio of the heat loss WR and the stroke amplitude value y _x .

5. The method according to claim 4, characterized in that the stroke amplitude value yx to a stroke amplitude mean value y _x and the friction force value F _Ry to a friction force mean value

F _{Ry be} averaged.

6. The method according to any one of claims 1 to 5, characterized in that characteristic data are determined from the individual curve profile of the hysteresis curve.

7. The method according to claim 6, characterized in that information about the state of wear of the oscillation system (3) is obtained with the aid of the characteristic data determined from the individual curve profile of the hysteresis curve.

8. The method according to any one of claims 1 to 7, characterized in that characteristic data are determined from the slope of the hysteresis curve.

9. The method according to claim 8; characterized in that information about the mold suspension is obtained with the aid of the characteristic data determined from the slope of the hysteresis curve.

10. The method according to any one of claims 6 to 9, characterized in that a comparison of the individual curves and / or slope is carried out by several hysteresis curves.

11. The method according to any one of claims 1 to 10, characterized in that a measurement of the driving force F _A and the stroke x with measuring frequencies i _meSs of 2 to 100 times, preferably 10 to 100 times, the oscillation frequency f he follows.

12. The method according to any one of claims 1 to 11, characterized in that an idle measurement is carried out to determine the idle losses of the oscillation system (3).

13. The method according to claim 12, characterized in that different idle measurements of the oscillation system (3) are carried out during a casting break with different oscillation parameters.

14. The method according to any one of the preceding claims, characterized in that the determined characteristic data and / or the hysteresis curves are visualized and registered and that control data for the corresponding change in the current oscillation parameters and the current casting parameters are determined to achieve target conditions.

15. Continuous casting device for casting metal, comprising an oscillation system (3) with an oscillating mold (1), which can be moved by means of a stroke drive over a stroke path x, and means for detecting the driving force F _A and the stroke path x, characterized by a computer unit (14) to determine a hysteresis curve from the Stroke x as a function of the driving force F _A over a stroke cycle and to determine current characteristic data via the oscillation system (3) on the basis of this hysteresis curve.

16. Continuous casting device according to claim 15, characterized by

Signal lines (12, 13, 16), which connect the devices for detecting the driving force F _A and the ones for detecting the stroke x with the computer unit, the computer unit (14) calculating corresponding control signals from the determined characteristic data, by command lines (17) between the computing unit (14) and

Control devices (18) for controlling the oscillation system and / or the casting parameters depending on the determined characteristic data and calculated control data.

17. Continuous casting device according to claim 16, characterized in that the oscillation system (3) is provided with a hydraulic drive unit and that the device for determining the driving force FA is a measuring device (10, 1 1) for the different chamber pressures (p ₀ , p _u ) each of the chambers (7, 8) comprises a cylinder unit (5) and / or that the device for determining the stroke travel includes a position meter (15) for measuring the current position of the respective working piston (9) of a cylinder unit (5) of the hydraulic drive unit includes.