JPS63115660A - Predicting method for breakout in continuous casting - Google Patents

Abstract

PURPOSE:To restrain the generation of cast slab having low quality and to improve the yield and the productivity by measuring mold temps. at two positions in the mold for continuous casting, calculating the changing ratio per unit time by finding the temp. difference and predicting the breakout by comparing a calculated value with a standard value. CONSTITUTION:The ends of temp. sensing elements 11, 12 are buried at two points along drawing direction at lower position than the molten surface in the mold 3. And, the mold temps. TU, TL measured by each element 11, 12 are converted to A/D by a converter 13 and inputted into a subtracter 14. The subtracter 14 finds the difference T(=TL-TU) of the mold temps. TU, TL and also stores, and the newest stored signal and the stored signals of four pitches before it are inputted into a differentiation circuit 15. The differentiation circuit 15 finds the changing ratio d( T)/dt per unit time for the temp. difference T of mold at the intermediate time in the stored signals, and inputs to a comparator 16. In the comparator 16, the standard value d( T)/dt>K (providing K=positive constant) is set, and in case of satisfying this, the breakout is predicted at high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for predicting breakouts occurring during casting by utilizing temperature changes in a continuous casting mold.

[Prior art]

If a breakout occurs in continuous casting equipment and unsolidified molten steel inside the slab leaks, stop casting, drain the slab that has caused the breakout, and replace equipment such as rolls to which the molten steel has adhered. necessary, and will be forced to suspend operations for a considerable period of time. For this reason, breakout is the biggest operational trouble in continuous casting, and it has been desired to establish measures to prevent it.

By the way, the solidified shell of the slab that is being drawn sticks to the mold and breaks, and molten steel leaks out from the bottom of the mold before it is sufficiently cooled, resulting in what is called a restraining breakout. In this case, it is known that the temperature of the mold gradually increases in the part of the mold through which the broken part of the solidified shell passes before passing the broken part, and gradually decreases after passing the broken part.

For this reason, temperature measuring elements such as thermocouples are embedded in the copper plate of the mold to measure the temperature of the copper plate of the mold (hereinafter referred to as mold temperature).
and the change in the measured mold temperature per unit time,
It is possible to predict a breakout by determining the ratio and monitoring the magnitude of that value and a reference value (Japanese Patent Laid-Open No. 115962/1983).

[Problem that the invention seeks to solve]

However, the mold temperature is not always stable during continuous casting, and there are fluctuations in the scene inside the mold, large and small drawing speeds, uneven inflow of lubricating powder into the mold, and contact between the mold and slab. It varies depending on factors such as the size of the area.

For this reason, when using the conventional method, breakout is often predicted even when no breakage of the solidified shell has actually occurred, resulting in a lack of reliability. Furthermore, if a breakout is predicted, the drawing process is generally stopped or the drawing speed is slowed considerably, resulting in poor operational stability and deterioration in slab quality.

The present invention has been made in view of these circumstances, and it is an object of the present invention to provide a method that can predict breakout with high accuracy.

[Means for solving problems]

The present invention measures the mold temperature at two positions to determine the temperature difference, calculates the rate of change of the temperature difference per unit time, and predicts a breakout by comparing the calculated value with a reference value. .

That is, the breakout prediction method in continuous casting according to the present invention measures the mold temperature at two positions of the continuous casting mold, calculates the difference in the two measured mold temperatures, and calculates the rate of change per unit time, It is characterized by predicting a breakout by comparing the calculated value with a reference value.

[Effect]

In the present invention, when passing through the solidified shell fracture part, the temperature of one mold rises once, and then when it falls, the temperature of the other mold rises, so the change in the difference in the temperature of both molds per unit time The ratio is greater than that of the respective mold temperature. In addition, when temperature changes occur due to uneven inflow of powder, etc., the movement speed does not decrease due to the broken part sticking to the mold in the case of solidified shell breakage, and the time difference in temperature measurement of the same slab part does not occur. is small, so the temperature difference between the two molds changes gradually. Therefore, breakouts can be predicted with high accuracy.

〔Example〕

The present invention will be specifically explained below based on the drawings.

FIG. 1 is a schematic diagram showing the state of implementation of the present invention, in which molten metal 1 such as molten steel stored in a tundish (not shown) is vibrated up and down at a constant period through an immersion nozzle 2 installed below. The mold 3 is charged. The molten metal 1 in the mold 3 is primarily cooled through the powder film formed by the lubricating powder 6 flowing along the inner wall of the mold 3 to form a solidified shell 5, which is used as the surrounding wall of the mold. The piece 4 is pulled downward by a pinch roll (not shown).

Below the scene level of mold 3, there is a pull-out direction (arrow direction).
The tips of temperature measuring elements I2 such as thermocouples are buried in two places along /digital conversion and applied to the subtracter 14. Regarding the buried position of the temperature measuring element IL 12, it is preferable to embed the temperature sensor IL 12 at a position below the lower 5° level of the scene level in order to reduce the effects of uneven inflow of powder and scene fluctuations.

The subtracter 14 receives two input signals from the A/D converter 13 at a predetermined pitch (Δt) of, for example, 0.5 seconds to 1 second. Regarding this input signal, in order to eliminate the influence of noise caused by an electromagnetic stirring device etc. installed around the mold 3, an A/D
For example, the average value of a plurality of signals output from the converter 13 at a pitch of 10 milliseconds is used.

Then, the subtractor 14 calculates the two mold temperatures TU and TL that have been taken in.
The difference ΔT (""Tt Tu) is determined and stored, and the latest stored signal and the stored signals for 4 consecutive pitches before it, that is, the stored signals for a total of 5 pitches, are provided to the differentiating circuit 15.

The differentiating circuit 15 stores the mold temperature difference (Δ1゛) per unit time at the intermediate point of the signal for 5 pitches, that is, if the capture pinch is 0.5 seconds, 1 second before the current measurement point. In order to obtain the rate of change d(ΔT)/dt, the following well-known formula (1) is set.

d(ΔT)/dt= d(TLf2)−Tu (21
) /dt=1/(12・Δt)・((TL (41
Tu (4)) - 8 (TL (3) - TU (31) + 8 (TL (1) - TO (111 - (TL (0
) -TU(0) ) )...(1) However, TL (0) TO(0), TL (1)
Tu (11,...

TL (4) Tu (4): The difference differential circuit 15 between TL and TLl for each of five consecutive pitches including this from the current measurement time is (d(ΔT) calculated based on equation 11)
/dt to the comparator 16.

It goes without saying that d(ΔT)/di may be calculated using a general formula for calculating a differential coefficient instead of the above formula (1).

The following equation (2) is set in the comparator 16, and the comparator 16 receives a signal related to the input d(ΔT)/dt as shown in (2).
If the formula is satisfied, the alarm 17 issues an alarm and an abnormality occurrence signal is output to a control device (not shown).

d(ΔT) /dt>K...(
2) However, K: positive constant When the above control device (not shown) receives an abnormality occurrence signal, it drives the sliding nozzle part 7 provided in the middle of the immersion nozzle 2 with a hydraulic cylinder 8, and controls the immersion nozzle 2. When it is completely closed, the rotation of the pinch roll (not shown) is stopped. In this regard, the immersion nozzle 2 may be left slightly open and the drawing speed may be considerably reduced.

In the present invention using such a device, breakout can be predicted with high accuracy because the temperature difference between the upper and lower molds is as follows. This will be explained below.

Figure 2 shows time on the horizontal axis and mold temperature on the vertical axis.
It is a diagram showing the transition of the mold temperature at the upper and lower two positions when the solidified shell fracture part moves downward, where the solid line indicates the upper mold temperature and the broken line indicates the lower mold temperature. As can be understood from this figure, the points at which temperature changes occur due to passage of the solidified shell fractured portion are shifted between the upper and lower two positions.

Therefore, T rises with a delay as shown in FIG.

The temperature difference (-
Dot-dashed line) is the rate of change dT/ of T, , TL when the temperature rises.
dt (see Figure 2), the change when the temperature rises ff
1d(ΔT)/dt becomes significantly large. At this time, d
(ΔT)/dt is a positive value.

Therefore, in the present invention, (d(ΔT) by equation 11)
/dt, and determine whether the constant, which is an empirically determined threshold so that breakout can be predicted with high accuracy, and the calculated value satisfy the formula (2). Breakouts can be predicted with higher accuracy. The above value is the mold position of the temperature measuring element.

It varies depending on the burial depth, continuous casting operating conditions, etc., but 1.
Approximately 5 to 15 (c/sec) is appropriate.

Furthermore, it is known that when a restraining breakout occurs, the rate at which the solidified shell ruptures descend within the mold is significantly lower than the rate at which it is pulled out by the pinch rolls, making it difficult to obtain the temperature difference described above. It is possible. However, even if a temperature change occurs due to causes such as the uneven inflow of powder mentioned above, the descending speed of the temperature changing part is the same as the drawing speed.
Mold temperature Tu, TL detected by upper and lower temperature measuring elements
As shown in Figure 4(a), the time difference becomes smaller, and the mold temperature change T also becomes smaller as shown in Figure 4(b), so the differential value of the mold temperature difference becomes a significantly smaller value. .

As described above, in the case of the present invention, the behavior of mold temperature changes when solidified shell rupture occurs, which is the cause of breakout, is taken into consideration, and temperature changes due to causes such as uneven inflow of powder are taken into account. However, it is possible to accurately detect only solidified shell rupture without predicting it incorrectly, and has excellent detection accuracy.

In addition, in the above example, the differential value of (TL - TO) is K
(>0), a breakout is predicted, but the present invention is not limited to this.
It can also be implemented by calculating the differential value of -TL) and predicting a breakout if the calculated value is smaller than -.

Further, in the above embodiment, the two temperature measuring elements are provided in the mold so as to be spaced apart in the drawing direction, but the present invention is not limited to this, but the temperature measuring elements are spaced apart in the width direction or thickness direction of the mold. It can be implemented even if it is installed. That is, in the case of restraint breakout, when a solidification shell rupture occurs, molten steel leaks out and becomes stuck to the mold. Even in this state, since the slab is pulled out by the pinch rolls, a new fracture portion is generated in the width direction or thickness direction of the slab in the fixed solidified shell portion. Therefore, breakout can be predicted with high accuracy according to the present invention even if the temperature measuring elements are installed apart in the width direction or thickness direction of the slab, or in a diagonal direction that has both these directions and the drawing direction. .

Further, in the above description, two temperature measuring elements are installed spaced apart in the vertical direction, two width directions, and the thickness direction, but the present invention is not limited to this, and a large number of temperature measuring elements are installed in advance in the mold. Alternatively, two temperature measuring elements may be arbitrarily selected and the mold temperature measured using the two temperature measuring elements may be used.

However, as for the position where the temperature measuring element on the lower side (sometimes at the same height) is installed, it should be placed at the lower 5th level of the scene level.
In addition to setting the position below 011, it is also a position where there is enough time to actually prevent the breakout even if the operating conditions such as the pulling speed are changed after predicting the breakout, that is, the lower position. The position is set so that the time required for the hard shell fracture to descend from the temperature measuring element to the lower end of the mold is longer than the time required to change the operating conditions.

〔effect〕

With conventional methods, false alarms are often issued;
The alarm accuracy rate, expressed as the ratio of the number of alarms based on solidified shell rupture to the total number of alarms, was as low as about 40%. In contrast, in the case of the present invention, the alarm accuracy rate was doubled to about 80%.

As detailed above, in the case of the present invention, the mold temperature at two positions of the continuous casting mold is measured, the difference in the two measured mold temperatures is calculated, the rate of change per unit time is calculated, and the calculated value is Since breakout is predicted by comparing the size of the steel plate with the standard value, highly accurate prediction is possible.This reduces the number of times the drawing must be stopped or the drawing speed is reduced, and the generation of low-quality slabs can be suppressed. The present invention has excellent effects such as improving yield and productivity.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the implementation state of the present invention, Fig. 2 is a diagram showing the transition of the upper and lower mold temperatures, Fig. 3 is an explanatory diagram of the breakout prediction principle according to the present invention, and Fig. 4 is a diagram showing the powder failure. FIG. 3 is a diagram showing the transition of upper and lower mold temperatures and the mold temperature difference when the mold temperature changes due to uniform inflow, etc. 3... Mold 5... Solidified shell 11.12... Temperature measuring element 14... Subtractor 15... Differential circuit 16...
・Comparator Time Xu Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Noboru Kono Ukimon ＼ Z Ku Nisshu Kaige 3 Ku V, 4IB

Claims (1)

[Claims] 1. Measure the mold temperature at two positions of the continuous casting mold, find the difference between the two measured mold temperatures, calculate the rate of change per unit time, and compare the calculated value with the reference value to determine breakout. A breakout prediction method in continuous casting, characterized by predicting breakout.