JPH04178253A - Method and device for evaluating flowing state at inner part of casting mold for continuous casting - Google Patents

Abstract

PURPOSE:To evaluate the state of flow at the inside of a casting mold by detecting the temperature difference between the inlet and outlet sides of the cooling water supplied into the casting mold respectively on the downstream side in the direction of flow of the poured metal from each poured metal hole. CONSTITUTION:Inlet side thermometers 12, 13 and outlet side thermometers 14, 15 are arranged respectively to detect the inlet side temperature and the outlet side temperature of the cooling water supplied to cool the inside wall of the casting mold 1 respectively on the downstream side in the flowing direction of the molten metal 3 from each pouring hole 2a, 2b, that is, on both of these short sides in the casting mold 1 for slab. Difference of these detected temperatures, that is, the temperature difference generated between the inlet side and the outlet side of the cooling water as the result of cooling of the casting mold 1 on the downstream side in the flowing direction of the molten metal 3 from each pouring hole 2a, 2b are found and when these temperature differences are compared mutually, the flowing state at the inside of the casting mold can be evaluated. Then, mixture of inclusion in a product ingot caused by the biased flow in the casting mold 1 and generation of a defect in a succeeding stage can be prevented.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is particularly applicable to continuous casting equipment for slabs, in which melt is poured into the mold from a submerged nozzle having a plurality of pouring ports. The present invention relates to a method for quantitatively evaluating the flow state inside a mold in order to detect on-line the occurrence of one-sided flow in the long side direction of the mold, which causes unilateral flow in the longitudinal direction of the mold, and an apparatus used to implement this method.

[Conventional technology]

In the continuous casting method, molten metal is continuously injected into a mold with openings on the top and bottom, is cooled and solidified by contact with the water-cooled inner wall of the mold, and is poured from the bottom opening with the outside covered with a solidified shell. It is continuously drawn out and further cooled, and when solidification has progressed to the inside, it is cut into appropriate dimensions to obtain product slabs that will be used in subsequent processes such as rolling.

In such a continuous casting method, a product slab with a shape corresponding to the cross-sectional shape of the mold is obtained, so when manufacturing slabs that will be the raw material for plate rolling, a mold with a rectangular cross-section corresponding to the cross-section of the slab is used. It is being

Incidentally, in recent years, there has been a strong desire to further increase the casting speed to improve productivity, but as mentioned above, in continuous casting equipment for slabs that uses molds with rectangular cross sections, it is especially important to use molds with a high slenderness ratio. When used, there is a limit to the realization of the above-mentioned high speed due to the occurrence of non-uniform flow of the molten metal in the long side direction. Conventionally, continuous casting equipment for slabs has been used to pour metal into a mold from multiple pouring ports, such as by using a submerged nozzle equipped with a pair of pouring ports that open toward both short sides of the mold. By pouring molten metal, the flow of the molten metal along the long sides is strengthened and uneven flow is alleviated, thereby increasing the casting speed.

[Problem to be solved by the invention]

However, when multiple pouring ports are installed in this way, the degree of clogging that occurs between the pouring ports varies as the operation progresses, or the clogging occurs unevenly on the inner wall of the nozzle, making it difficult to pour from each pouring port. There is a risk that the balance of the amount of molten metal will be disrupted, and the flow of molten metal from the spout on the side where there is less clogging will become stronger, causing a one-sided flow inside the mold, and solidification of the molten metal on the side where the flow is stronger will be inhibited, resulting in an unrestricted state. - In addition to causing the occurrence of breakouts due to solidification, the depth of inclusions and bubbles brought into the molten metal increases on the side where the flow is stronger, and their inclusion increases the incidence of defects in product slabs. There were additional difficulties. In particular, blistering defects that occur on the surface of cold-rolled galvanized steel sheets are caused by alumina A1 inside the continuously cast slab used as the raw material.
The main causes are inclusions such as 203 and Ar bubbles, and it is important to quantitatively evaluate the flow state inside the mold in order to detect the occurrence of the one-sided flow as described above as early as possible. There is.

Conventionally, the method for evaluating flow conditions is to obtain the temperature distribution in the depth direction on both short sides of the mold using the detection results of a large number of thermocouples embedded in both short sides of the mold, and then perform evaluations based on these results. Generally, two methods are used: one is to measure the scene changes that occur inside the mold near both short sides of the mold, and the evaluation is performed based on a comparison of these. However, in the former method, the variation in sensitivity between each thermocouple affects the evaluation accuracy, so it takes a lot of effort to manage the sensitivity of a large number of thermocouples. The configuration of the signal processing system to process the output of
Since maintenance of this system also requires a great deal of effort, it has been difficult to stably evaluate the flow state with high accuracy over a long period of time.

On the other hand, in the latter method, a clear correspondence between scene changes on the surface of the molten metal and flow conditions inside the molten metal was not established, making it difficult to evaluate the flow conditions with high accuracy. .

Furthermore, in Japanese Patent Application Laid-Open No. 61-150762, a thermocouple housed in a case made of refractory is inserted into the molten metal and is placed to face each of a plurality of pouring ports, and the temperature of the poured metal from each pouring port is measured by the thermocouple. At the same time, the dynamic pressure of the molten metal flowing out from each pouring port and acting on the case is measured using a strain gauge attached to the supporting part of the case, and the flow state is evaluated based on these measurement results. A method is disclosed. However, in this method, the temperature measurement result by the thermocouple is affected by the thickness of the peripheral wall of the case, and this thickness is reduced by the erosion caused by contact with the molten metal, so it is difficult to obtain accurate temperature measurement results over a long period of time. The case must be replaced frequently, and the output of the strain gauge is affected by the high temperature of the molten metal in the vicinity, making it difficult to accurately measure the dynamic pressure based on this output. There is an accuracy problem in that it is difficult to
There are many drawbacks to the operation, such as the mixing of the melted metal from the case into the molten metal, which causes new defects.

The present invention has been made in view of the above circumstances, and provides a flow condition evaluation method capable of evaluating the flow condition inside a mold with high accuracy over a long period of time, and a flow condition evaluation method that enables this method to be performed using a simple measurement system configuration. The purpose is to provide a flow state evaluation device that can be realized.

[Means to solve the problem]

The method for evaluating the flow state inside a continuous casting mold according to the present invention is intended to detect the occurrence of one-sided flow due to an imbalance in the amount of molten metal poured from each pouring port when pouring metal into a continuous casting mold from a plurality of pouring ports. In the method for evaluating the flow state inside the mold, a temperature difference between the inlet and outlet sides of the cooling water supplied to the mold is detected on the downstream side in the flow direction of the poured metal from each of the pouring ports. The flow condition evaluation device according to the present invention, which is characterized in that the evaluation is made based on these comparisons, and which is used to implement this method, is arranged downstream in the flow direction of the molten metal from the plurality of pouring ports, respectively. , a plurality of sets of inlet and outlet thermometers for detecting inlet and outlet temperatures of the cooling water supplied to the mold, and between each set of inlet temperature needle and outlet thermometer; and an evaluation section that mutually compares the calculation results of these temperature difference calculation sections and performs the evaluation based on the comparison results. It is characterized by

[Effect]

In the present invention, on the downstream side in the flow direction of the molten metal from each pouring port, that is, in the case of a slab mold, on both short sides of the mold,
An inlet thermometer and an outlet thermometer are installed to detect the inlet and outlet temperatures of the cooling water supplied to cool the inner wall of the mold, respectively, and the difference between these detected temperatures, that is, the temperature at each pouring port. As a result of cooling the mold on the downstream side in the flow direction of the molten metal, the temperature difference that occurs between the inlet and outlet sides of the cooling water is determined, and by comparing these temperature differences, it is possible to determine the temperature inside the mold. Evaluate flow conditions.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof. FIG. 1 is a schematic diagram showing the implementation state of the method for evaluating the flow state inside a continuous casting mold according to the present invention (hereinafter referred to as the method of the present invention) in continuous slab casting equipment.

In the figure, reference numeral 1 denotes a mold for a slab which has a cylindrical shape with a rectangular cross section and is installed with openings at both ends facing upward and downward, and the cross section along the long side of the rectangle is shown. As shown in the figure, molten metal 3 is injected into the mold 1 through a submerged nozzle 2 extending from the upper opening to the inside, and while the molten metal 3 is staying in the mold 1, the molten metal 3 is poured into the mold 1. The strand 4 is cooled by contact with the water-cooled inner wall of the mold 1, solidifies from the outside as it reaches the bottom, becomes a strand 4 whose outside is covered with a solidified shell 4a, and is directed downward from the lower opening of the mold 1. It is continuously pulled out. The immersion nozzle 2 is equipped at its tip with a pair of pouring ports 2a and 2b that open toward both short sides of the mold 1, respectively, in order to uniformly pour molten metal into the mold 1 having a rectangular cross section as described above. The nozzle is of a two-hole type, and the molten metal 3 flows out from pouring ports 2a and 2b toward both short sides of the mold 1, respectively, as indicated by arrows in the figure. The mold 1 has a cooling water passageway formed around its entire circumference for water cooling the inner wall, and as shown in the figure, the cooling water is passed from the bottom to the top on both short sides of the mold 1. A water passageway 10.11 for flushing water is formed.

In the method of the present invention, in order to evaluate the flow state of the molten metal 3 inside the mold 1 in the continuous slab casting equipment configured as described above, a In the water channels 10 and 11, the temperature difference between the inlet and outlet of the cooling water is used. (referred to as invention device)
As shown in the figure, the temperature measurement results are obtained by the inlet thermometers 12.13 respectively disposed on the inlet side of the water passage 10.11, and the outlet thermometers 14.13 disposed respectively on the outlet side of the passageway 10.11. Using the temperature measurement results of No. 15, the flow state is evaluated as follows. Note that since cooling water is generally supplied to the water passages 10.11 from a common water supply source, a single thermometer placed on the discharge side of the water supply source can be used with two inlet thermometers 12.11. It is also possible to substitute 13.

The temperature measurement results of the inlet side thermometer 12 and the outlet side thermometer 14 of one water passage 10 are given to the first temperature difference calculation section 16, and the temperature difference calculation section 16 calculates the difference between the two temperature values. The temperature measurement results of the inlet side thermometer 13 and outlet side thermometer 15 of the other water passage 11 are given to the second temperature difference calculation section 17, and the temperature difference calculation section 17 is configured to calculate the temperature difference. In section 17, the difference between both temperature measurements is calculated in the same way,
Furthermore, the first. The calculation results of the second temperature difference calculation units 16 and 17 are taken into the evaluation unit 18 at predetermined sampling intervals. With the above configuration, the first. In the second temperature difference calculation unit 16.17, in order to cool the inner wall of the mold 1, the short sides of both sides of the mold 1, that is, the pouring ports 2a, 2b are used.
The temperature difference between the inlet and outlet sides of the cooling water supplied to the downstream portion in the flow direction of the molten metal 3 flowing out from each is calculated, and the evaluation unit 18 calculates the temperature difference thus calculated. The differences are compared, and the flow state of the molten metal 3 is evaluated based on the comparison results.

In order to make this evaluation possible, the present inventors developed the first and second
The amount of cooling water calculated corresponding to each of both short sides of the mold 1 in the temperature difference calculation units 16 and 17.

Temperature difference T between outlet sides 1. Using Tz, an evaluation index H obtained by comparing the two was defined as shown in the following formula.

H=k・(T+Tz)×100(%)
...(11 Note that k in this equation is the temperature difference T+, T
The reciprocal of the average value of t, that is, k=2/ (T, +T,) ... (2
), but it may be an appropriate constant. However, the evaluation index H obtained in this way is a value that is influenced by the relative positional relationship between the submerged nozzle 2 and the mold 1, and in a flow state where the evaluation index H has a large value on average, Since the fluctuation also tends to increase, the evaluation section 18
In the evaluation of the flow state in , the standard deviation σ9 of the evaluation index H obtained within a predetermined time, for example, within the operating time of one charge, or the maximum fluctuation width Hs, x, etc., is used instead of the evaluation index H itself. A value indicating the fluctuation of the index H is used as a degree of one-sided flow indicating the degree of one-sided flow.

FIG. 2 is a diagram showing the results of examining the correlation between the incidence of blistering defects in a cold-rolled galvanized steel sheet and the degree of one-sided flow obtained during the manufacture of the slab that is the raw material for this steel sheet.

In this figure, the evaluation index H is used as the one-sided flow frequency.
The standard deviation σ□ is used, and . and ○ in the figure indicate that the steel types are different. In addition, the incidence of blisters is
It was determined based on the number of blistering defects detected by an ultrasonic flaw detection test conducted within a predetermined area of each steel plate.

As mentioned above, blistering defects on cold-rolled galvanized steel sheets occur due to the inclusion of inclusions due to one-sided flow that occurs inside the mold 1 during continuous casting of slabs used as raw materials.
The rate of occurrence of blisters is considered to be an index indicating the degree of one-sided flow within the mold 1. As shown in Figure 2, there is a clear correlation between the incidence of blisters and the one-sided flow rate σ, and as the one-sided flow rate σ exceeds 3.0, the incidence of blisters increases rapidly. I understand that. In other words, from this result, when the calculation result of the degree of one-sided flow σ8 in the evaluation section 18 exceeds 3.0, it is evaluated that a one-sided flow state has occurred in the mold 1 to the extent that the quality of the product slab is deteriorated during this time. can. This evaluation in the evaluation section 18 is performed at the end of the operation of the 1-charge, and it becomes possible to predict the inclusion of inclusions in the product slab obtained in each charge online based on the above-mentioned evaluation. Depending on the prediction, it is possible to prevent the occurrence of defects in the post-process by taking appropriate measures, such as strengthening quality inspection before sending to the post-process or changing the allocation destination.

FIG. 3 is a diagram showing the results of an investigation into the relationship between the incidence of blistering defects in cold-rolled galvanized steel sheets and the amount of molten metal poured during continuous casting of slabs from which the steel sheets are made. From this figure,
It is clear that the incidence of blistering increases as the amount of poured metal increases. For example, when it is determined that one-sided flow has occurred based on the evaluation result of the evaluation section 18 in a suitable charge, the operation of the next charge At this time, immersion nozzle 2
By reducing the amount of molten metal poured from the molten metal, it is possible to reduce the possibility of inclusions being mixed into the product slab obtained by the charging. That is, the evaluation results by the evaluation section 18 can also be used to prevent inclusions from being mixed into post-charged product slabs.

That is, in the apparatus of the present invention, each pair of inlet sides of the pouring ports 2a and 2b of the immersion nozzle 2 are provided.

Outlet side thermometers 12.14 and 13.15, temperature difference calculation units 16 and 17 that calculate the difference between these temperature measurement results, and an evaluation that mutually compares these calculation results to evaluate the flow state as described above. The flow state can be evaluated with a simple measurement system configuration equipped with the part 18, and the evaluation results can be used to accurately determine the presence or absence of one-sided flow within the mold 1, as shown in FIGS. It can be said that it can be determined by

In this embodiment, a case has been described in which melt is poured into the mold 1 by one submerged nozzle 2 having two pouring ports 2a and 2b. The present invention is also applicable when a plurality of submerged nozzles each having one pouring port are used.

Further, in this embodiment, an example of application to continuous slab casting equipment using a mold 1 having a rectangular cross section has been described, but it goes without saying that the present invention can be applied to other continuous casting equipment as well.

〔effect〕

As detailed above, in the method of the present invention, when pouring metal into a mold for continuous casting from a plurality of pouring ports, the molten metal is supplied from each pouring port downstream in the flow direction to cool the inner wall of the mold. Cooling water people.

By the simple procedure of detecting the temperature difference between the exit sides and comparing them, it is possible to accurately evaluate the flow condition inside the mold, and to prevent inclusions in the product slab due to one-sided flow inside the mold. Contamination and generation of defects in post-processes can be prevented. In addition, the device of the present invention used to carry out this method includes an inlet thermometer and an outlet thermometer for the cooling water, each of which is placed on the downstream side in the flow direction from each pouring port, and a separate thermometer for calculating the difference in detected temperature between these two thermometers. It has a simple configuration that includes a temperature difference calculation section and an evaluation section that evaluates the flow state based on mutual comparison of the calculated temperature differences, and it can achieve the high accuracy mentioned above without requiring maintenance of each part of the measurement system. The present invention has excellent effects such as being able to stably evaluate the flow state over a long period of time.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the state of implementation of the method of the present invention in continuous slab casting equipment, and Figure 2 is the correlation between the frequency of one-sided flow, which is an evaluation criterion in the method of the present invention, and the incidence of blistering caused by one-sided flow. FIG. 3 is a diagram showing the correlation between the amount of molten metal poured into the mold and the incidence of blisters. 1...Mold 2...Immersion nozzle 2a, 2b
... Pouring port 3 ... Molten metal 10.11 ... Water passage
12.13...Inlet side thermometer 14.15...Outlet side thermometer 16.17...Temperature difference calculation section 1B...Evaluation section Patent Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent attorney Kawa No Noboo Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. When pouring metal into a mold for continuous casting from a plurality of pouring ports, the flow state inside the mold is analyzed in order to detect the occurrence of one-sided flow due to imbalance in the amount of metal poured from each pouring port. In the evaluation method, the temperature difference between the inlet and outlet sides of the cooling water supplied to the mold is
A method for evaluating a flow state inside a mold for continuous casting, characterized in that the flow state inside a mold for continuous casting is determined by detecting the flow of the poured metal from each of the pouring ports on the downstream side in the flow direction, and making the evaluation based on a comparison thereof. 2. When pouring metal into a mold for continuous casting from a plurality of pouring ports, a device used to evaluate the flow state inside the mold in order to detect the occurrence of one-sided flow due to imbalance in the amount of metal poured from each pouring port. , a plurality of sets of inlet-side thermometers and outlet-side temperature, which are respectively arranged downstream in the flow direction of the molten metal from the plurality of pouring ports and detect the inlet temperature and outlet temperature of the cooling water supplied to the mold. and separate temperature difference calculation units that calculate the difference in detected temperature between the inlet and outlet thermometers of each set, and mutually compare the calculation results of these temperature difference calculation units. and an evaluation section that performs the evaluation based on the comparison result. A flow condition evaluation device inside a continuous casting mold.