KR20010017607A - Method For Predicting The Unevenness Of Solidified Shell - Google Patents

Abstract

PURPOSE: A method for estimating thickness nonuniformity of a solidified shell is provided to estimate qualities such as surface crack of steel billet as well as center segregation by measuring variation of bulging (abnormal bulging) according to time due to thickness nonuniformity of a solidified shell in a casting direction during continuous casting using a pinch roll deformation measuring equipment. CONSTITUTION: A method for estimating thickness nonuniformity of solidified shell using a pinch roll deformation measuring equipment during continuous casting comprises the processes of installing equipment capable of measuring a pinch roll deformation during continuous casting on stand of a continuous casting and frame of a pinch roll, measuring abnormal bulging values which are occurred by thickness nonuniformity of solidified shell during casting, and estimating on line the thickness nonuniformity of solidified shell based on the measured abnormal bulging values. Thickness nonuniformity of solidified shell is effectively estimated by measuring abnormal bulging (in which a bulging amount varies according to time) generated by nonuniformity of solidified in the casting direction.

Description

{Method For Predicting The Unevenness Of Solidified Shell}

The present invention relates to a method for predicting the degree of non-uniformity of the solidification cell thickness during continuous casting by measuring abnormal bulging online using a displacement measuring device of the pinch roll during continuous casting, in particular, the surface cracks, internal quality (center crack) , Center segregation) or to predict the degree of non-uniformity of solidification cell thickness during continuous casting.

Currently, as a method of predicting the non-uniformity of the solidification cell thickness online during continuous casting, there is a method of measuring the temperature at the corresponding position by installing thermocouples at various positions of the mold. This method is mainly used to predict solidification unevenness or breakout in the width or thickness direction of the cast, and is not suitable for online prediction of solidification thickness nonuniformity in the casting direction.

In other words, when the thermocouple is used to predict the non-uniformity of the coagulation cell thickness, the thermocouple should be replaced every time mold replacement is performed. Also, the thermocouple may be measured only at the local position where the thermocouple is inserted, rather than the average coagulation non-uniformity. Have

Accordingly, an object of the present invention for solving this problem is to measure the average coagulation nonuniformity of the whole coagulation cell, there is no hassle when measuring coagulation nonuniformity, and effectively measure the coagulation nonuniformity of the coagulation cell surface of the cast steel It is to provide a method for measuring nonuniformity of the coagulation cell thickness that can predict internal quality such as cracks or central cracks and central segregation.

In order to achieve the above object, the solidification cell thickness non-uniformity measuring method according to the present invention is installed by the pinch roll displacement measuring device in the frame on which the standard stand and the pinch roll of the continuous casting machine is seated, generated by the continuous casting solidification cell thickness non-uniformity By measuring the abnormal bulging is characterized in that the solidification cell thickness non-uniformity of the casting direction is predicted online.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a block diagram of a pinch displacement measuring means used in the present invention.

2 is a conceptual diagram showing the displacement of the pinch according to the bulging change (abnormal bulging) during casting.

Figure 3 is a graph showing the displacement of the pinch roll measured during abnormal bulging.

4 is a view showing the results of directly measuring the degree of non-coagulation cell thickness nonuniformity.

Figure 5 is a graph predicting the degree of coagulation unevenness and the degree of coagulation unevenness by steel type by abnormal bulging measurement.

<Description of the code | symbol about the principal part of drawing>

1: Lower unit

2: upper unit

3: connection

4: sensor holder

5: displacement sensor

6: sensor target

7: spring

12: target axis

18: cast

Figure 1 is a schematic view showing a pinch roll displacement measuring apparatus used in the present invention, a detailed description thereof will be omitted. The sensor 5 was installed in the upper unit 2 upside down to indirectly measure the movement of the driving roll, and prevented foreign matter from accumulating between the sensor 5 and the sensor holder 4.

In the lower unit 1, the target 6 in contact with the sensor 5 was manufactured in an appropriate size in consideration of the zigzag movement when opening and closing the driving roll. It is also very important to keep the target 6 horizontal during measurement since the sensor 5 may not be located at the center of the target 6. Therefore, the shaft 12 supporting the target 6 was manufactured in three axes so that the shanghai-dong could be desired while the target 6 was horizontal during casting. When opening and closing the driving roll, the cylinder stroke is much larger than the casting cap or the measuring range of the sensor 5, so that the spring 7 is applied to the target shaft 12 to protect the sensor 5 and to allow a large stroke. Installed.

That is, the spring 7 is designed to operate when the movement of the driving roll exceeds the measurement range. At this time, when the spring 7 moves during casting, the reliability of the measurement data drops rapidly, so that the elastic modulus of the spring 7 is sufficiently increased. Thereby, the spring 7 was to be operated only when the movement of the drive roll exceeds the measurement range.

In addition, to prevent thermal expansion of the system, to protect the displacement sensor and durability of the system to utilize the field air line to purge the inside of the device for 24 hours. It can be adjusted by using a needle valve to take a little pressure, and it is manufactured to install the air gauge separately so that the pressure state inside the device can be optimally adjusted.

The connecting portion 3 is a portion connecting the upper unit 2 and the lower unit 1, and the casting direction movement of the driving roll during the casting, the driving roll opening, the zigzag movement at the closing, and the casting gap as described above. The bellows were used to allow very large cylinder strokes, and the silicone rubber was coated on the bellows surface to prevent deterioration with prolonged use.

2 is a conceptual diagram showing the displacement of the pinch roll moving in accordance with the abnormal bulging in the slab. Here, reference numeral 19 denotes the position of the pinch roll when the bulging is the maximum, reference numeral 20 indicates the position of the pinch roll when the bulging is the minimum, reference numeral 21 indicates the pinch roll displacement when the maximum bulging occurs during abnormal bulging. And reference numeral 22 represents pinch roll displacement at the time of abnormal bulging and minimum bulging occurs. That is, since the pinch roll displacement is determined by balancing the hydraulic pressure of the pinch roll and the bulging force of the unsolidified steel in the slab, they are sensitively moved by the change of the bulging of the slab.

In detail, abnormal bulging occurs due to the nonuniformity of the solidification cell thickness during continuous casting, which in turn causes fluctuations in the surface of the mold, affecting not only the vertical, horizontal and corner cracks but also internal quality such as center segregation. Thus, prediction of solidification cell thickness non-uniformity during casting is essential. In addition, in the case of abnormal bulging caused by the non-coagulation cell, the degree of amplification varies depending on the roll roll design state of the player, thereby providing important information in terms of future player design technology.

On the other hand, when measuring the abnormal bulging directly in the demonstration cycle, since the measuring device directly contacts the surface of the cast steel, the device is complicated and has a problem in durability, while the thickness of the solidified cell is measured by measuring the movement of the pinch roll that is sensitive to the cast steel. Abnormal bulging caused by nonuniformity can be measured indirectly and efficiently and has the advantage of being easily applied to the site.

Hereinafter, the effects of the present invention will be described through examples.

Example 1

3 is a graph showing indirect measurement results of bulging by pinch rolls. It can be seen that in the mold containing 0.09 to 0.11% C after the start of casting, abnormal bulging of as much as about ± 0.5 mm occurs over about 12200 seconds. However, in a mold containing about 0.15% C, a very clean bulging curve was measured after 12200 seconds without occurrence of abnormal bulging.

As can be seen in this example, it was confirmed that such abnormal bulging occurs in the mold containing 0.09 to 0.12% C and the API material (Line pipe material) of this composition range, such that there is a very distinct steel type dependency.

Moreover, it turned out that the frequency of the roll rotation by 0.02 to 0.025 Hz by the casting bow roll and the roll pitch period of 0.06 to 0.08 Hz appear by the frequency analysis result. In particular, it was confirmed that the main peak appeared in the vicinity of 0.02 to 0.25 Hz near the period of about 4.4 seconds. Until now, no measurement of such abnormal bulging cycles has been reported. However, Lamant et al. (Proc. 6th International Iron and Steel Congress, ISIJ, 1990, 317p) analyzed 0.08 to 0.11% C in the mold cycle. In the case of the mold, the frequency of 0.1 to 0.5 Hz, especially 0.3 Hz was measured, which is reported to be related to the deep oscillation mark due to coagulation cell unevenness.

That is, in the present embodiment, the abnormal bulging of 0.2 to 0.25 Hz is caused by the nonuniformity of the solidification cell thickness of the cast steel, which can be confirmed in more detail in Example 2. In conclusion, in the present invention, the abnormal bulging measurement by the displacement measurement of the pinch is shown to be an effective method of predicting the nonuniformity of the coagulation cell thickness.

Example 2

In the present embodiment, in order to measure the profile of the solidification cell in the mold during casting, 0.095% C mold with abnormal bulging was severely measured, and FeS powder was filled into the Cu tube at the end of casting of the API material, and then it was put into the molten metal. Then, the results observed by the Sulphur printing method are shown in FIG.

As a result, it can be seen that very severe coagulation cell nonuniformity is formed in the casting direction, and from this coagulation cell nonuniformity period, abnormal bulging at a frequency of 0.2 to 0.25 Hz is caused by casting coagulation cell nonuniformity.

Example 3

Figure 5 shows the degree and frequency of non-uniformity of the coagulation cell thickness predicted by steel type abnormal bulging measurement. As mentioned in Example 1, among the 0.09 to 0.12% C-containing molds, Nb and V added API materials (Line pipe material, V11XDBEH, V09XWBEH) always generate coagulation cell unevenness, which is larger than other steel grades. Able to know. From the above results, it can be confirmed once again that the degree and frequency of coagulation cell thickness nonuniformity according to the steel grade can be predicted by abnormal bulging measurement by the pinch displacement measurement.

Therefore, in the case of displacement measurement pinch according to the present invention can be measured for a long time without the need for thermocouple replacement, and because the abnormal bulging depends on the overall degree of non-coagulation cell thickness non-uniformity provides more accurate information.

In addition, according to the present invention, by measuring the abnormal bulging caused by the solidification unevenness in the casting direction (the amount of bulging changes with time) has the advantage that the solidification cell thickness unevenness can be effectively predicted.

The foregoing merely illustrates preferred embodiments of the present invention, and those skilled in the art to which the present invention pertains may make modifications and changes to the present invention without departing from the scope and spirit of the appended claims.

Claims (1)

Installing a device capable of measuring the displacement of the pinch roll during continuous casting in the frame of the player stand and the pinch roll, Measuring abnormal bulging caused by non-uniformity of solidification cell thickness during casting; Predicting the solidification cell thickness non-uniformity on the basis of the measured abnormal bulging value on the basis of the pinch during continuous casting characterized in that the solidification cell thickness non-uniformity prediction method by displacement measurement.