JPS59125252A - Predicting method of breakout in continuous casting - Google Patents

Abstract

PURPOSE:To predict the generation of breakout and to increase its casting speed by monitoring electrically the contact condition of a casting mold and a molten steel in the casting mold. CONSTITUTION:The current value of an ammeter 8 hardly changes when the contact condition between a casting mold 1 and a molten steel 2 is normal and a billet is stably drawn from the mold 1. If abnormality arises in the contact condition between the mold 1 and the steel 2 and when the billet or molten steel contacts locally the inside surface of the mold 1, the current values increases sharply. When the generation of breakout is predicted from the change in the current or voltage between the mold 1 and the steel 2, measure such as stopping of casting into the mold, decreasing of the casting speed, changing of powder or the like is taken since the prediction until the generation of breakout, whereby the breakout is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for predicting breakout in continuous casting, which can detect the occurrence of breakout in continuous casting.

In order to improve productivity, it is required to increase the casting speed in slow reading... Therefore, the occurrence of this breakout is a major technical obstacle to increasing the casting speed.

Breakout generally occurs due to two types of breakouts: one is caused by delayed growth of the shell in the $j mold, and the other is when the frictional force between the slab and the mold exceeds the high-temperature strength of the slab, leading to breakage of the slab. It occurs due to two causes.

The present inventors have devoted themselves to research into means for preventing the occurrence of breakout due to the latter cause. In continuous steel casting operations, as is well known, mold mogu is added to the surface of the molten steel in the mold. This powder melts and flows uniformly between the mold and the slab, thereby exerting a lubricating effect that facilitates the downward drawing of the slab. However, if the amount of molten iE powder flowing between the mold and the slab is reduced, the slab may locally come into direct contact with the inner surface of the mold, or The slab breaks in the mold, causing local direct contact between the molten steel and the inner surface of the mold, leading to breakout. Therefore, inventor #(c)1 discovered that it is possible to predict the occurrence of breakout in advance by electrically detecting the contact state of molten steel or slab with the inner surface of the mold as described above. .

This invention was made based on the above first observation, and
In continuous casting of steel, a DC or AC voltage is applied between the mold and the molten steel poured into the mold, or a DC or AC electric current is passed between the mold and the molten steel. The change in current or voltage flowing through "i" is measured, and from the change in current or voltage, the state of contact between the mold and the molten steel is determined, thus predicting the occurrence of breakout. It has certain characteristics.

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 the drawings, 1 is a water-cooled mold, 2 is a solidified shell poured into the mold 1, and 3 is a solidified shell.

The mold 1 is fixed to a mold support frame 4, which is attached to an orion frame 5. The mold 1 and the molten steel 2 are connected by a conducting wire 6, and a DC constant voltage generator 7 and an ammeter 8 are provided in the middle of the conducting wire 6.

In this invention, 1. Changes in the ammeter 8 are monitored, thereby detecting the state of electrical contact between the mold 1 and the molten steel 2. That is, when the contact state between the mold 1 and the molten steel 2 is normal and the slab is stably pulled out from the mold 1, the current value (1) of the ammeter 8 hardly changes.

However, if an abnormality occurs in the contact state between the mold 1 and the molten steel 2 and the slab or molten steel locally contacts the inner surface of the mold 1, the current value (1) increases rapidly.

Steady value of current value (1) ■. The amount of variation ΔI (I-I
O) is determined depending on the degree of direct contact, so the current value (
If a certain upper limit is set for 1), only dangerous conditions that may cause a breakout are selectively extracted, thereby making it possible to prevent a breakout from occurring.

The upper limit of the current value (I) mentioned above varies depending on the nuclide in continuous casting and the casting conditions, but according to the experience in actual operation, it is good to select 120 to 130% of the steady value. has been confirmed.

Note that the slab pulled out from the mold l is placed between support rolls 9 and j.
However, since it is technically difficult to insulate the support roll 9 and the vibration table, the vj type support frame 4 and the oscillation frame 5 are separated by the insulator 10.
It is necessary that the bit be set.

In the example described above, a voltage is applied between the mold and the molten steel, and changes in the current value are detected. However, a DC constant current generator is provided in place of the DC constant voltage generator described above, and the voltage is applied between the mold and the molten steel. The contact state between them may be detected by a change in voltage.

Further, the power source is not limited to direct current, and alternating current may be used.

According to the above, when the occurrence of a breakout is predicted from a change in the current or voltage between the mold and the molten steel, there is a time margin of about 1 to 2 minutes between this prediction and the occurrence of the breakout. During this time, breakouts can be prevented by taking measures such as stopping pouring into the mold, slowing down the pouring speed, and changing the powder.

Next, the present invention will be explained using examples.

A 40 kg slab for a thick plate having a thickness of 250 IuL and a width of 1750 mja and having the composition shown in the table below was cast using a 10.5 mR curved continuous casting machine.

A DC voltage is applied between the molten steel in the mold and the mold, (wt,
h) The change in the current flowing at that time was measured. FIG. 2 shows the change in current over time at this time. As can be seen from the drawing, the current value gradually increased past point A and rose to 1.25 times the steady value at point B. At this point, when the casting speed was lowered from 1.2 m/rnin to 0.4 m/min, the current value decreased, and after 2 minutes it reached a steady value (6 m/min).
point).

When the slab was observed after casting, it was detected that the solidified shell broke in the mold when the current value increased, and the molten steel was in direct contact with the mold.

As explained above, according to the present invention, by electrically monitoring the contact state between the mold and molten steel in the mold, it is possible to predict the occurrence of breakout in advance, thereby increasing the casting speed. It has excellent industrial effects such as speeding up the process.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG. 2 is a graph of current values showing an example of when a current change is detected by the present invention. In the drawing, 1. Mold 2. Molten steel 3. Solidification/L 4 Mold support frame 5. O/
ration frame 6 Conductor 7... DC constant voltage generator 8.
...Ammeter 9...Support roll 10...Insulator applicant Natsuo Shioya, representative of Nippon Koukan Co., Ltd. (and 2 others)

Claims (2)

[Claims] (1) In continuous casting of steel, a voltage of DC or 2 AC υ■L is applied between the mold and the molten steel injected into the t=+4 mold, thereby causing the mold and the -molten steel to The method is characterized in that a change in the current flowing at the same time as the molten steel is measured, and from the change in the current, the fluctuation of fMj between the νj type and the molten steel is known, and thus the occurrence of a breakout is predicted. , A method for predicting break-at in A construction. − (2) f: (In mixed casting, direct or alternating current is applied between the mold and the old steel poured into the mold,
As a result, the change in the 1L pressure θIC between the mold and the molten steel is measured, and from the change in the voltage, the contact state between the mold and the molten steel can be determined, thus preventing the occurrence of breakout. A breakout prediction method in continuous casting, characterized by predicting breakout.