JPH04172159A - Method for detecting abnormality in immersion nozzle in continuous casting - Google Patents

Abstract

PURPOSE:To accurately decide nozzle clogging and inclusion dropping by detecting the change with the lapse of time in difference between the theoretical value of a gate opening degree based on molten steel surface level in a tundish, molten steel surface level in a mold and drawing velocity and the gate opening degree at the time of actually casting. CONSTITUTION:The molten steel 2 is received into the tundish 3 from a ladle 1 and poured into the mold 6 through an immersion nozzle 5 while adjusting flow rate with the gate 4. The drawing velocity, the molten steel surface level in the mold, the molten steel surface level in the tundish, cross sectional area of the mold and opening degree meter signal of the gate, are inputted in a calculater. Based on these values, the theoretical opening degree of gate 4 is calculated, and by the change with the lapse of time in the difference from the actual opening degree, conditional variation of the immersion nozzle 5 is decided. In the case the stuck inclusion in the immersion nozzle 5 is dropped, the difference is reduced and in the case the immersion nozzle is clogged, the difference is made large.

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention is intended to prevent immersion problems such as "immersion nozzle clogging" and "falling of inclusions attached to the immersion nozzle into the mold" during continuous casting. The present invention relates to a method for accurately detecting an abnormality in a nozzle.

<Prior art and its problems> In continuous casting, the problem has been that inclusions such as AN 203 adhere to the immersed nozzle installed in the tundish. The falling of clogging inclusions into the mold has a major negative impact on casting work and product quality, so understanding the situation inside the immersion nozzle has become an extremely important issue.

However, several proposals have been made so far regarding means for detecting the falling of inclusions adhering to the inside of the nozzle in case of nozzle clogging, and the following method is a typical example.

fat A method of determining that a sudden change in the level of molten steel in the mold under conditions where the drawing speed and the level of molten steel in the tundish are stable is ``exfoliation and falling of inclusions'' (Japanese Patent Application Laid-Open No. 62-227564).

(b) A method of determining "separation and falling of inclusions" based on a signal of a sudden decrease in the opening of an injection valve opening meter that detects the flow of molten steel from the tundish (Japanese Patent Laid-Open No. 159956/1983).

(The absolute value of the difference between the ideal opening degree and the actual opening degree of the C1 molten steel inflow adjustment gate exceeds a predetermined value is called “Inclusions peeling off and falling.”)
A method for determining this (Japanese Patent Application Laid-open No. 192246/1983). Note that the ideal opening degree in this proposal was determined by the following calculation formula. That is, Q, -c, 5b-r”i-dingr
Crime ・・・・・・(1) Mouth n -5n
・v,l
...The equation (2) holds true, where -Ill.

Since there is a relationship, the following holds true. Then, if the cylinder stroke that adjusts the opening area of the gate is a, and the radius of the opening is b, then Sb = 2 d ``cos-'(-) -2a, /
TT' - Dingman (4) holds true, and the cylinder stroke (ie, "ideal opening degree") a is determined from the relationship of equation (4).

However, methods (a) and (b) above can only determine whether the inclusions are peeling off or falling when the operation is stable, such as when the drawing speed is constant, the steel is molten in the tundish, and the heat is also constant. Only when doing so. Moreover, "the level of molten metal in the mold suddenly changes (rapidly)", which is the criterion for the above-mentioned +al method.
Is it in the mold? This is also caused by disturbances to the gtiA level meter (for example, powder is thrown into the radiation type level meter, conductive material approaches the sensor in the electromagnetic induction type), and therefore, the above-mentioned (BL method) prevents the falling of inclusions. It was difficult to make an accurate judgment.Furthermore, the Cbl method was also explained earlier (al. It must be said that it is difficult to accurately judge the falling of inclusions for the same reason as in the case of the law.

On the other hand, as the absolute value of the difference between the ideal opening degree and the actual opening degree of the molten steel inflow adjustment gate exceeded a predetermined value, “inclusions were peeled off and fell.”
(For the C1 method, when the gate opening is new, if the flow coefficient is correct, the actual opening and the theoretical opening will usually be approximately equal, so an appropriate judgment can be made. However, in actual operation There was a problem in that the gate opening was eroded over time, which caused a difference between the theoretical opening and the actual opening, making it impossible to make accurate judgments.

Means for Solving the Problems> The present invention solves the above-mentioned problems pointed out in the conventional method for determining abnormalities inside a submerged nozzle, and eliminates "nozzle clogging" and "falling of inclusions into the mold." This method was designed to provide a means for accurate determination. [A gate with an opening and an immersion nozzle are provided in the tundish, and the opening area of the gate is adjusted so that the molten steel level in the mold is kept constant. In continuous casting when pouring into a mold, the difference between "the gate opening obtained from the theoretical value calculated based on the steel level in the tundish, the molten steel level in the mold, and the drawing speed" and the "gate opening during actual pouring" is determined. The major feature is that it is possible to accurately detect abnormalities in the immersed nozzle during continuous casting by detecting changes in the situation inside the immersed nozzle based on changes in the difference over time.

That is, the present invention detects "nozzle clogging" and "intervention" by chronological changes (relative changes) in the difference between the actual opening of the gate during operation and the theoretical opening based on information obtained during operation. The present invention is designed to be able to appropriately determine whether an object has fallen into a mold, and the present invention will be described in more detail below with reference to Examples.

FIG. 1 is a schematic diagram of an example of a continuous casting apparatus suitable for carrying out the method of the present invention, in which molten steel (2) is produced from a ladle (1).
is received in the tandish (3) and sent to the gate (4).
In the continuous casting equipment (numeral 7 in the figure indicates a pinch roll) that injects into the mold (6) through the immersion nozzle (5) while adjusting the flow rate in step 1, there is an abnormality in the immersion nozzle including the "calculator". A device equipped with a detection mechanism is shown.

During casting operations using such continuous casting equipment, the computer records operating data such as "pulling speed,""molten metal level in the mold,""molten steel level in the tundish (which can also be determined from the tundish weight)," and "mold cross-sectional area ( ``mold thickness, mold width)'', ``gate opening degree meter signal for comparison with theoretical value'', and ``level control start signal'' are captured.

The signal acquisition period of the computer may be about 100m5 to 1 second, but considering the processing power of computers normally used in this type of operation, about 1 second may be practical.

Next, the theoretical opening degree is determined from the captured data using the following formula. That is, Qc = c -5ciτHt ・-・
・・−(5)L Qll=V, 1・WD+WD−・・・・・・・
(6) Since t holds, the theoretical gate opening area is determined from the relationship Qc=Q,1.

Here, in order to match the polarity of the gate opening degree, if "+" in the "Level fluctuation" section is changed to "-", the above (7
) is the formula.

Then, if the cylinder stroke for adjusting the opening area of the gate is degree)xm (this may be obtained by calculation, or the relational curve may be made into a table and the opening degree corresponding to S may be obtained).

Next, the difference Xx between the actual opening X and the theoretical opening x1
xl and -xs are determined, and their changes over time are monitored to detect changes in the situation inside the immersion nozzle.

The change in the situation inside the immersion nozzle is the difference between the actual opening and the theoretical opening
has the following impact on

A) tjQ nozzle second mall
As shown in the figure, when an inclusion falls, the subsequent actual gate opening X becomes smaller by the amount that the clogging inclusion has fallen, and therefore the difference between the subsequent actual opening and the theoretical opening. Naturally, X also becomes smaller.

B)? ? llA measured by the nozzle As shown in Figure 3, the actual gate opening X gradually increases as inclusions adhere and accumulate, so naturally the difference X between the actual opening and the theoretical opening also gradually increases. becomes larger.

For this reason, "Shikii Direct" is LM (negative).

Assuming LP (positive), as shown in Figure 4, XL-x,
The case where ≦L8 is defined as "falling of inclusions", and as shown in Fig. 5, xo-X@≧L.

Each case is determined to be a "nozzle clogging", and the corresponding alarm and lamp are outputted accordingly.

As for computer processing, signals may be captured all the time, but it is also necessary to determine whether there is an abnormality in the immersion nozzle (each calculation for determination).
The process starts after the mold level is automatically controlled (if a controller, etc. is used).
It is preferable to take in the signal, process it, and make a judgment only when the mold scene level control is automatic.

In addition, if automatic mold scene level control is turned off during operation for some reason, initialize all the values being calculated and start calculation again when automatic control is turned on (manual level control (Do not refer to current information).

Furthermore, Figure 6 shows the accuracy of abnormality detection in a submerged nozzle using the method of the present invention and the conventional method (method according to JP-A-62-192246).
Figure 6 shows the results of a comparison between
It is clear that the method of the present invention allows for a sufficiently appropriate determination of abnormalities within the nozzle.

(Summary of Effects) As explained above, according to the present invention, the melt level in the mold and the drawing speed are included in the formula for calculating the theoretical opening.

Since the molten steel level in the tundish is incorporated and used, the determination of abnormalities in the immersed nozzle is less affected by external disturbances, and the above determination is made based on time-series changes (relative changes) in the difference between the theoretical opening and the actual opening. In addition, erroneous judgments due to operational fluctuations are reduced, and nozzle clogging and falling inclusions can be accurately judged, which brings about industrially useful effects.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of a continuous casting apparatus suitable for carrying out the method of the present invention. FIG. 2 is a graph showing the behavior of each piece of information when an inclusion falls. FIG. 3 is a graph showing the behavior of each information in the case of nozzle clogging. FIG. 4 is a graph illustrating the "time-dependent change in the difference between the actual opening and the theoretical opening" which is determined to be the falling of an inclusion. FIG. 5 is a graph illustrating the "change over time of the difference between the actual opening and the theoretical opening" which is determined to be nozzle clogging. FIG. 6 shows the results of comparing the accuracy of abnormality detection in a submerged nozzle between the method of the present invention and the conventional method. In the drawings, 1... Ladle, 2... Container steel. 3...Tandish, 4...Gate. 5... Immersion nozzle, 6... Mold. 7...Pinch roll.

Claims (1)

[Claims] In continuous casting, a gate with an opening and an immersion nozzle are provided in the tundish, and molten steel is injected into the mold while adjusting the opening area of the gate so that the molten steel level in the tundish remains constant. It is characterized by detecting changes in the situation inside the immersion nozzle based on the change over time in the difference between the "gate opening obtained from a theoretical value calculated based on the molten steel level and drawing speed" and the "gate opening during actual pouring". A method for detecting abnormalities inside an immersion nozzle during continuous casting.