JPS6061150A - Foreseeing method of breakout in continuous casting - Google Patents

Abstract

PURPOSE:To enable foreseeing of breakout by taking out the oscillation input and output signals of an oscillating system for a casting mold by an acceleration sensor of oscillation and issuing an alarm when the transmission function of the specific higher harmonic component in a resonance frequency band exceeds a reference range. CONSTITUTION:Oscillation input and output signals are respectively taken out by an acceleration sensor 10 secured to an arm 9 for exciting a casting mold 1 and an acceleration sensor 15 secured to the mold 1 and the acceleration waveforms of both signals are Fourier-transformed to a basic wave and the higher harmonic corresponding to the same by a spectrum analyzer 18. An amplitude ratio and a phase difference are continuously analyzed with respect to the frequency component existing in the resonance frequency band of the oscillation system in the Fourier spectrum and the monitoring signal thereof is inputted to a microcomputer 19 by which the signal is compared with a reference value. An alarm device 21 for breakout is triggered when either of the amplitude ratio or the phase difference exceeds the reference range. The foreseeing of the breakout is thus made possible with extremely high probability.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting breakout accidents in advance during continuous casting of molten metal, such as molten steel, without applying vibration to a mold.

In continuous casting of molten steel, a breakout accident (steel leakage due to rupture of the solidified shell) is the most serious accident in continuous casting operation. The impact on the steelmaking process is enormous. recent years.

Maintenance-free continuous casting slabs and direct rolling are progressing, but in this case, casting conditions are subject to various restrictions and breakouts tend to occur more easily. Therefore, in order to satisfy these casting conditions and continue safe operations,
There is a strong desire to establish a technology that constantly monitors the thermal conditions between the mold and the slab, predicts breakouts in advance, and prevents them from occurring.

Up to now, various proposals have been made for predicting this breakout or for monitoring abnormalities in lubrication between the mold and the slab, but none have been technically established yet. The categories of what has been proposed so far are as follows.

(1), Measurement of vibration strain using a strain gauge (2), Vibration waveform measurement using a differential transformer (3), Mold vibration measurement using an accelerometer (4), Mold support force measurement using a load cell (5), Mold using a thermocouple There are advantages and disadvantages to each prescription for temperature measurement, but basically (11,
(2), (41) and (5) have problems with the reliability of the measurement results because the detected values depend on the mechanical strength and structure of the mold vibrating device, especially when detecting extremely small changes. However, it would be risky to make quantitative judgments based on this.On the other hand, the method (3) of monitoring the vibration status of the mold using an accelerometer and detecting abnormalities from the waveform analysis is It can be said that it is the most reliable.There are two known examples that are considered to belong to this prescription, for example, JP-A-57
There are methods described in Japanese Patent Application Laid-Open No. 57-3'2866, Japanese Patent Application Laid-Open No. 57444456.

In principle, the present invention also uses this accelerometer to monitor the vibration status of the mold and predict breakout, but by adopting a principle different from the prescription described in the above publication, breakout can be stably and reliably predicted. We have developed a method to predict outs. That is, 1 the present invention extracts a vibration input signal to the mold during continuous casting using a vibration acceleration sensor fixed to a vibrating arm that applies vibration to the mold, and also extracts a vibration input signal to the mold during continuous casting using a vibration acceleration sensor fixed directly to the mold. Extract the vibration output signals of the 9 signals, Fourier transform the acceleration waveforms of both signals, and continuously measure the amplitude transfer function (amplitude ratio) and/or phase transfer function (phase difference) from the fundamental wave component to its harmonic components using a spectrum analyzer. The present invention is characterized in that an alarm is issued when the amplitude ratio and/or phase difference of a certain frequency among the harmonic components exceeds a reference range.

The present invention will be explained in detail below, but it will be noted that the vibration input signal to the mold is taken out from an acceleration sensor fixed to the vibration arm of the vibration device, and that some of the harmonic components of the transfer function The point that an alarm is issued when the amplitude ratio and/or phase difference of a specific frequency exceeds a reference range is disclosed in the aforementioned Japanese Patent Application Laid-Open No. 57-25269, No. 57-32866, and Japanese Patent Laid-Open No. 57-57. This is a unique prescription employed in the present invention, which is not described in Publication No. 44456, etc., and allows breakouts to be predicted accurately and with sufficient advance notice with an extremely high probability. .

FIG. 1 shows an example of a device for applying vibration to a mold in continuous casting equipment for molten steel. As is well known, when pulling a slab out of a mold, the mold is given a vertical reciprocating motion at a predetermined period in order to prevent sticking between the inside of the mold and the slab. It is generally adopted because it is mechanically simple and has few problems. Figure 1 is an example of this.

A vibration system consisting of a mold 1 and a vibration table 2 that integrally supports the mold 1 (installed so as to be movable up and down via a balancer 3) is supplied with rotational power from a motor 4 to a transmission gear 5 and a crankshaft 6. After converting into linear reciprocating motion via the crank arm 7, vertical vibration is applied via the link mechanism. In the present invention, the part of such a vibrating device that makes linear reciprocating motion, more specifically.

An acceleration sensor 10 is fixed to the vibrating arm 9. In FIG. 1, 11 is a fulcrum pin, and 12 is a parent pin.

13 indicates a stroke adjustment mechanism.

The acceleration sensor 10 uses a servo type.

By attaching this to the linear reciprocating motion part (link motion part) of the vibration excitation device, specifically the vibration arm 9, it is possible to extract vibration input signals to the vibration system (mold) during continuous casting. There is one feature of the present invention. On the other hand, the vibration output signal of the vibration system is detected by an acceleration sensor 15 directly fixed to the copper plate of the mold 1 (both copper plates on the long side).
This can be retrieved directly by

FIG. 2 systematically shows an example of a typical apparatus used to predict breakout in accordance with the method of the present invention from vibration input and output signals from single acceleration sensors 10 and 15. 1 to 15 in FIG. 2 are the same device elements as explained in FIG. 1, 16 is a vibration amplifier, 17
is an isolated amplifier, 18 is a spectrum analyzer, 19
2 shows a microcomputer, 20 a D10 converter, and 21 an alarm device. In other words, 2 car acceleration sensor 1
The input signal to the vibration system from 0 and 15 and the output signal of the vibration system are simultaneously sampled to the multi-channel spectrum analyzer 18 via the vibration amplifier 16 and the isolation amplifier 17, and the transfer function of the vibration system is measured over time. Learn from series data. More specifically, both jaw speed sensor 1
The acceleration waveforms measured at 0 and 15 are Fourier-transformed into a fundamental wave and harmonics corresponding to this fundamental wave using the spectrum analyzer 18, and the frequency components in the mold vibration system resonance frequency band of the Fourier-transformed Fourier spectrum are The amplitude ratio and phase difference between the two are continuously analyzed and recorded.

The microcomputer 19 performs input/output of various data regarding casting conditions as well as calculation and control of control input/output.

The present inventors have been monitoring mold vibration conditions for many years using this equipment configuration, recording signals during operation, and determining whether there is any warning signal before a breakout occurs. was analyzed and discussed in detail. As a result, we found that the transfer function (amplitude ratio and phase difference) of a specific frequency component in the resonance frequency band of the mold vibration system showed fluctuations compared to when it was stable. The specific frequency component in which this fluctuation appears varies depending on the operating conditions, but for example, the vibration frequency (fundamental frequency) of the mold is 63.8 cpm (= 1.061
1z) When continuously casting stainless steel, 14.
Large fluctuations appear only in the harmonic components of 211z.

Figures 3 and 4 show this relationship, and among the many harmonic components, 11.0.12.0.13.0.14.
Only the frequency component of 2°15.2 tlz is extracted, and the amplitude ratio (Fig. 3) and phase difference (Fig. 4) in the time period 240 seconds before breakout are plotted.

However, slab cross section: 155 x 1035 mm, casting temperature i: 1552°C, casting speed: 0.70 m/m
in, mold vibration frequency; 63.8 cpm (= 1.061
This is data when 5tlS430 stainless steel was cast with 1z). As is clear from both figures, 14.211
Only for the frequency component of z, the breakout is about 60
2 seconds ago, the amplitude ratio was far out of the range of +50% of the reference value, and the phase difference had returned to the range of the reference value again after being far out of the range of -40° (degrees) than the reference value.

Therefore, under this operating condition, the harmonic 14.211z
constantly monitors fluctuations in the amplitude transfer function (amplitude ratio) and/or phase transfer function (phase difference) of the frequency components, inputs the monitoring signal to the microcomputer 19 and compares it with a reference value, When the value is out of the reference value range, an alarm signal is output and this is sent to the D10 converter
If the alarm device 21 is activated after 0, a breakout can be predicted approximately 60 seconds before the breakout occurs.
Breakout can be prevented by lowering the drawing speed of the slab or adjusting the amount of mold powder supplied.

Even if the operating conditions are different from the previous example, if you know in advance which harmonic component transfer function changes before breakout for each operating condition, you can constantly monitor this and use the same method as the previous example. A breakout can be predicted. According to the experience of the present inventors, 2 In accordance with the present invention, a vibration input signal to the mold during continuous casting is extracted by a vibration acceleration sensor 10 fixed to a vibrating arm that applies vibration to the mold, and vibration acceleration directly fixed to the mold is detected. When the sensor 15 is used to extract the vibration output signal of the mold during continuous casting, the resonance frequency band of the mold vibration system is 10 to 10.
It has been found that breakage l- can be predicted with extremely high probability by monitoring fluctuations in the amplitude transfer function (amplitude ratio) and/or phase transfer function (phase difference) in harmonic frequency components in the range of 1511z. In other words, these 10~
It was found that abnormal fluctuations in the transfer function of harmonic frequency components in the 15 Hz range are highly reliable as a signal corresponding to abnormal lubrication of the mold and slab before breakout.

As described above, according to the present invention, breakout, which is the most serious operational trouble in continuous casting, can be reliably predicted in advance of sufficient time to take measures to prevent breakout. This makes it possible to avoid large losses due to breakout occurrences, and to constantly monitor the lubrication status of the mold and slab during continuous casting, making a significant contribution to this field.

[Brief explanation of the drawing]

FIG. 1 is an equipment layout diagram showing an example of a vibration system in a continuous casting apparatus and a vibration device that applies vibration to the vibration system. Fig. 2 is an equipment layout system diagram showing an example of equipment for implementing the method of the present invention, Fig. 3 is a diagram showing fluctuations in amplitude ratio before breakout of a specific harmonic component, and Fig. 4 is a diagram showing a variation in the amplitude ratio before breakout of a specific harmonic component. FIG. 3 is a diagram showing fluctuations in phase difference before component breakout. 1. Mold, 2. Vibration table, 3. Balancer,
4...Motor, 5...Transmission gear, 6...
Crankshaft, 7...crank arm, 9...vibration arm. 10 and 15... Acceleration sensor. 16...Vibration amplifier, 17...Isolation amplifier. 18...Spectrum analyzer. 19...Microcomputer, 20...D10 converter, 21...Alarm device. 1 Figure 1

Claims (1)

[Claims] A vibration acceleration sensor fixed to the vibration arm that applies vibration to the mold extracts the vibration input signal to the mold during continuous casting, and a vibration acceleration sensor fixed directly to the mold extracts the vibration output signal of the mold during continuous casting. 9. Fourier transform the acceleration waveforms of both signals to obtain the amplitude transfer function (amplitude ratio) from the fundamental wave component to the harmonic component and /
Alternatively, the phase transfer function (phase difference) is continuously analyzed using a spectrum analyzer, and an alarm is issued when the amplitude ratio and/or phase difference of a certain frequency among harmonic components exceeds a reference range. Breakout prediction method in continuous casting.