JPS6152973A - Method for predicting breakout in continuous casting - Google Patents

Abstract

PURPOSE:To predict surely the breakout of the unsolidified billet to be drawn from a casting mold by measuring the differential pressure of the oil pressure between the push side and push back side of a hydraulic cylinder which oscillates the mold and knowing the lubricating condition of the mold and solidified shell from the change in the differential pressure thereof. CONSTITUTION:Oil gages 8a, 8b which measure the oil pressures on the push side 6a and push back side 6b of a reciprocating hydraulic cylinder 6 of an oscillation 5 for oscillating the casting mold 2 are provided to pipings 7a, 7b which are connected to the push side 6a and the push back side 6b and in which a working oil passes in continuous casting of the steel. The difference in the oil pressure between the push side and push back side is continuously measured by the gages 8a, 8b. The lubricating condition between the solidified shell 10 of the molten steel 9 poured into the mold 2 and the mold 2 is known from the change in the difference of the oil pressure and the generation of the breakout of the unsolidified billet 11 to be drawn from the mold 2 is predicted therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for predicting breakouts in continuous steel casting, which can detect the occurrence of breakouts in advance.

[Prior art and its problems]

In continuous casting operations, higher casting speeds are required to improve productivity. However, when continuous casting is performed at high speeds, breakouts tend to occur in the unsolidified slab directly under the mold, and the occurrence of breakouts is a major technical obstacle to increasing the casting speed.

Generally, breakouts are caused by delayed growth of the shell within the mold, and breakouts are caused by the frictional force between the unsolidified slab and the mold exceeding the high-temperature strength of the unsolidified slab.

In continuous casting, as is well known, mold powder is added to the surface of molten steel in a mold. This powder melts and flows uniformly between the mold and the unsolidified slab, thereby providing a lubricating effect that facilitates the downward drawing of the unsolidified slab.

However, if the flow of molten powder between the mold and the unsolidified slab becomes uneven or the amount of the inflow decreases, the frictional force between the mold and the unsolidified slab increases.
Breakout occurs when the frictional force exceeds the high temperature strength of the unsolidified slab.

Therefore, various measures have been taken to prevent this type of breakout, but at present, sufficient effects have not yet been obtained.

[Purpose of the invention]

In view of the above-mentioned current situation, the present invention makes it possible to predict the breakout of unsolidified slabs pulled from the mold and prevent the breakout from occurring. The purpose of this paper is to provide a method for predicting breakout in continuous casting.

[Summary of the invention]

The breakout prediction method in continuous casting of this invention continuously measures the difference in oil pressure between the pushing side and the pushing back side of the hydraulic cylinder used to vibrate the mold, and detects changes in the oil pressure difference. , is characterized in that it knows the lubrication state between the solidified shell of molten steel injected into the mold and the mold, and thus predicts the occurrence of breakout of the unsolidified slab to be pulled out from the mold.

[Structure of the invention]

The present inventors have conducted extensive research in order to prevent the breakout that occurs when the above-mentioned frictional force between the unsolidified slab and the mold exceeds the high temperature strength of the unsolidified slab. As a result, in a mold that is vibrated by hydraulic pressure, the difference in hydraulic pressure between the pushing side and the pushing back side of the hydraulic cylinder that gives vibration to the mold increases, as the frictional force between the mold and the unsolidified slab increases.
In order to try to keep the amplitude and frequency of the mold constant,
If you measure the difference in this oil pressure, therefore, it increases.
It was discovered that the lubrication state between the mold and the unsolidified slab can be determined from changes in the oil pressure difference, and the occurrence of breakout can be predicted. This invention was made based on the above findings.

Next, the present invention will be explained based on the drawings.

FIG. 1 is an explanatory diagram showing one embodiment of the present invention.

In FIG. 1, 1 is a water box for a water-cooled mold 2, 3 is a mold frame for the mold 2, 4 is a mold support frame for supporting the mold 2, and 5 is an oscillation frame for vibrating the mold 2. At one end of the oscillation frame 5,
As shown in FIG. 2, a reciprocating hydraulic cylinder 6 is attached, and piping 7a, 7b connected to the push side 6a and push-back side 6b of this hydraulic cylinder 6 and through which hydraulic oil passes are connected to the push-side 6a and the push-back side. Oil pressure gauges 8a and 8b are provided for measuring the oil pressure of oil pressure 6b. The molten steel 9 injected into the vibrating mold 2 generates a solidified shell 10 in the mold 2, becomes an unsolidified slab 11, and is pulled out from the mold 2 while being supported by slab support rolls 12.

In this invention, changes in the difference in oil pressure between the pushing side 6a and the pushing back side 6b of the hydraulic cylinder 6 are monitored, and thereby the lubrication state between the mold 2 and the solidified shell 10 is known, and the unsolidified cast This is because it predicts the breakout in piece 11.

That is, when the lubrication state between the mold 2 and the solidified shell 10 in the mold 2 is good and the unsolidified slab 11 is normally pulled out from the mold 2, the push side measured by the oil pressure gauge 8a The difference ΔP between the oil pressure at 6a and the oil pressure at the push-back side 6b measured at 8b hardly changes. On the other hand, when the lubrication state between the mold 2 and the solidified shell 10 deteriorates and the frictional force between the mold 2 and the unsolidified slab 11 increases, the oil pressure difference ΔP increases. Steady value ΔPo of this oil pressure difference ΔP
The amount of variation Δ(ΔP)=ΔP−ΔPo is determined by the magnitude of the frictional force between the mold 2 and the unsolidified slab 11. Therefore, from this amount of variation Δ(ΔP),
It is possible to know the lubrication state between the two, and to detect breakout of the unsolidified slab 11 in advance.

The difference ΔP in the hydraulic pressure of the hydraulic cylinder 6 when the frictional force causes a risk of breakout in the unsolidified slab 11 varies depending on the model of the continuous casting machine and the casting conditions, but it is determined based on experience in actual operation. For example, the steady value △P is 120 to 130
It has been confirmed that it is sufficient to select %. Therefore, the upper limit of the oil pressure difference ΔP is 120 to 13 of the steady value ΔPa.
By setting the pressure to 0%, it is possible to selectively remove only the dangerous situation in which the unsolidified slab 11 breaks out.

As described above, when the occurrence of a breakout in the unsolidified slab 11 is predicted from the change in the difference in oil pressure between the pushing side and the pushing back side of the hydraulic cylinder 6, the time from this prediction to the occurrence of the breakout is 1. There is a time margin of about 2 minutes, so if measures such as stopping the injection of molten steel 9 into the mold 2, lowering the injection speed, and changing the powder are taken during this time, the occurrence of breakout can be prevented. be able to.

[Embodiments of the invention]

Next, the present invention will be explained with reference to examples.

A 40 kg class slab with a thickness of 250 μm and a width of 1750 mm having the composition shown in Table 1 was cast using a 10.5 mH curved continuous casting machine, and the push side and push back side of the hydraulic cylinder in between were cast. The hydraulic pressure difference ΔP between the two was continuously measured.

Table 1 (wt, %) FIG. 3 graphically shows the measurement results of the differential pressure ΔP.

As can be seen from FIG. 3, the differential pressure ΔP gradually increases from points a and a' and reaches a steady value P at point b.

It became 0.120-130%. At this point, when the casting speed was lowered from 1.4 frL/min to 0.4 m/m1n, the differential pressure △P decreased and reached a steady value (0 point) after 2 minutes.
When the slab was observed after the completion of casting, it was confirmed that the solidified shell had fractured in the mold at the time when the differential pressure ΔP increased.

〔Effect of the invention〕

As explained above, according to the present invention, the hydraulic pressure difference between the pushing side and the pushing back side of the hydraulic cylinder that vibrates the mold is measured.

Since the lubrication state between the mold and the solidified shell is known from changes in the differential pressure, it is possible to reliably predict the breakout of unsolidified slabs pulled from the mold, and prevent the occurrence of breakouts. Can be done. Therefore, excellent industrial effects are brought about, such as making it possible to increase the casting speed, which has been hampered by the occurrence of breakouts.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of the method of the present invention, Fig. 2 is an explanatory diagram showing the method of Fig. 1, in which the difference in oil pressure of the hydraulic cylinder that vibrates the mold is measured, and Fig. 3 is an explanatory diagram showing the method of Fig. 1. It is a graph which shows an example of the measured value when the difference image of the oil pressure of a hydraulic cylinder is measured in the method of this invention. In the drawings, 1...Water box, 2...Mold, 3...T18m7V-m, 4...Mold support frame, 5...Onration frame, 6...Hydraulic cylinder, 6a...Press side, 6b・
...Push back side, 7a, 7b...Piping, 8a, 8
b... Oil pressure gauge, 9... Molten steel, 10... Solidified shell, 11... Unsolidified slab.

Claims (1)

[Claims] In continuous casting of steel, by continuously measuring the difference in oil pressure between the pushing side and the pushing back side of a hydraulic cylinder used to vibrate the mold, changes in the oil pressure difference can be used to determine the inside of the mold. Breakout in continuous casting, characterized by knowing the lubrication state between the solidified shell of molten steel injected into the mold and the mold, and thus predicting the occurrence of breakout in the unsolidified slab drawn from the mold. Prediction method.