JPH02117750A - Method for detecting molten metal surface level in metal strip continuous casting - Google Patents

Abstract

PURPOSE:To improve the quality of a metal strip by correcting the detected value of molten metal surface level measured with an eddy current sensor and executing casting while accurately grasping molten metal surface level. CONSTITUTION:At the time of pouring the molten metal into pouring basin part 2, the molten metal surface 7 is risen and brought into contact with electrodes 5a, 5b for detection and electric current is conducted between the electrodes 5a and 5b and it is detected that the molten metal surface 7 exists at lower end position of the detecting electrode 5b. This detected value is inputted into a control mechanism 8 to correct the detected value related to the molten metal surface level from the eddy current sensor 6. Further, the pouring is continued and when the molten metal surface 7 is brought into contact with lower end of a detecting electrode 5c, the electric current is conducted between the electrodes 5a and 5c for detection and it is known that the molten metal surface 7 exists at lower end position of the detecting electrode 5c, and this detected value, too, is corrected with the eddy current sensor 6. By taking the detected value of the conductive electrode type sensor 5 into the eddy current sensor 6 as the corrected input, while rejecting circumferential influence to the eddy current sensor 6, the measurement of the molten metal surface level is executed at high accuracy.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention aims to control the surface level of molten metal poured into a sump when continuously casting metal ribbon by rapidly cooling and solidifying molten metal. Concerning how to detect.

(Prior art) When casting molten metal into a thin metal strip close to the final shape,
Since the subsequent hot rolling process, heat treatment process, etc. are simplified, the burden on the equipment is reduced. For example, in a conventional continuous casting machine, a cast slab is hot rolled into a strip, and the strip is conveyed to a cold rolling process. However, if a thin slab (hereinafter referred to as metal ribbon) that can be sent to the cold rolling process is obtained, hot rolling can be omitted, and the strip can be rolled before cold rolling. There is no need for heat treatment.

From this point of view, various continuous casting methods such as single roll method, twin roll method, single belt method, double belt method, and roll-belt method have been proposed as methods for directly manufacturing metal ribbon from molten metal. . In these methods,
In either case, heat is removed from the molten metal poured into the molten metal pool via a cooling roll or belt, and a solidified shell is formed on top of the molten metal. The solidified shell is sent out from the casting space as cooling rolls, belts, etc. rotate or run, and becomes a metal ribbon.

In order to keep the shape, particularly the thickness, of this metal ribbon constant, it is necessary to accurately control the time during which the molten metal contacts the cooling roll or belt and the solidified shell grows. Therefore, in order to always keep the hot water level in the pool constant, it is necessary to detect the hot water level and increase the amount of hot water poured when the hot water level is lower than the set value, and decrease the amount of hot water poured when it is higher. be done.

As a means of accurately measuring the hot water level,
There are measuring instruments that use lasers, X-rays, etc. However, the equipment itself of this measuring instrument is large and complicated, and it is also troublesome to handle. In this regard, an eddy current sensor that focuses on the fact that the molten metal poured into the pool is a conductor can be said to be a measuring device suitable for special conditions.

(Problem to be Solved by the Invention) However, although the eddy current sensor has excellent resolution, it is easily influenced by the surrounding environment. For example, the measurement results will vary greatly depending on the strength of the surrounding magnetic field, the presence or absence of conductors, etc. Therefore, in an environment where metal ribbon is continuously cast, the measurement results will vary from charge to charge, resulting in variations of several millimeters to several millimeters between charges, for example.

If such variations exist, the level of the molten metal poured into the molten metal pool cannot be maintained at an accurate position. This level of the molten metal is a major factor in determining the growth period of the solidified shell, for example in a continuous casting machine using twin rolls of different diameters.

Therefore, if the hot water level deviates from the set value, a metal ribbon having a wall thickness different from the target plate thickness will be manufactured.

Furthermore, since the meniscus fluctuates, foreign matter such as an oxide film floating on the hot water surface is likely to be drawn in.

Therefore, the present invention detects the level of hot water using an eddy current sensor while eliminating the influence of the surroundings for each charge, thereby accurately grasping the state of the hot water pool and casting thin metal strips under stable conditions. The purpose is to

(Means for Solving the Problems) In order to achieve the object, the present invention aims to transfer molten metal poured into a pool section partitioned by cooling rolls and/or belts to the cooling rolls and/or belts. When continuously casting a thin metal strip, an eddy current sensor is placed above the pool, a current-carrying electrode type sensor is placed above the pool, and the current-carrying electrode type sensor is placed above the pool. The method is characterized in that the eddy current sensor detects the level of the molten metal poured into the molten metal pool while correcting the eddy current sensor based on the detected value of the molten metal level detected by the sensor.

(Function) Hereinafter, the features of the present invention will be specifically explained along with its function with reference to the drawings.

FIG. 1 shows a case where the present invention is applied to a continuous casting machine of a twin roll type with different diameters. Note that the present invention is not limited to this different diameter twin roll method, but can be applied to other continuous ribbon casting machines such as other twin roll methods, single roll methods, single belt methods, twin belt methods, roll-belt methods, etc. The same can be applied to.

This continuous casting machine is equipped with a small-diameter upper roll 1a and a large-diameter lower roll 1b that rotate in opposite directions, and a nozzle part of a sump 2 opens between these cooling rolls 1a and 1b. . In the case of FIG. 1, both sides of the water reservoir 2 are partitioned by site weirs facing the surface of the large-diameter cooling roll 1b. Molten metal is injected into this tundish portion 2 from an intermediate container such as a tundish through a pouring nozzle 4.

A current-carrying electrode type sensor 5 is arranged in the water reservoir 2, and an eddy current sensor 6 is arranged above the water reservoir 2. As shown in FIG. 2, the current-carrying electrode type sensor 5
It includes a plurality of detection electrodes 5a, 5b, and 5c. Among these detection electrodes 5a, 5b, and 5C, the long detection electrode 5a is used as a common electrode, and the remaining detection electrodes 5b and 5C have different lengths and detect different hot water levels. On the other hand, the eddy current sensor 6 used is a normal type sensor whose detection value is a change in the magnetic flux density that changes when the magnetic flux generated by the coil passes through the water reservoir 2 .

When molten metal is injected into the pool 2, the level 7 of the molten metal rises and comes into contact with the detection electrodes 5a, 5b. In this state, conduction is established between the detection electrodes 5a and 5b,
It is detected that the hot water level 7 is at the lower end position of the detection electrode 5b. This detected value is input to the control mechanism 8, and the detected value regarding the hot water level from the eddy current sensor 6 is corrected. When pouring continues and the molten metal surface 7 comes into contact with the lower end of the detection electrode 5C, conduction is established between the detection electrodes 5a and 50, and the molten metal surface 7 is at the lower end position of the detection electrode 5C. I understand. This detected value is also input to the control mechanism 8 in the same way,
The value detected by the eddy current sensor 6 is corrected.

The measurement error of the hot water level detected by this energized electrode type sensor 5 is within a range of approximately ±0.5 mm, which is the same as the accuracy of the length setting of the detection molds 8i5a, 5b, and 5C. Then, the detected value of this current-carrying electrode type sensor 5 is taken into the eddy current sensor 6 as a correction input.
The hot water level can be measured with high precision while eliminating the influence of the surroundings on the eddy current sensor 6.

Note that the current-carrying electrode type sensor 5 shown in FIG. 2 is used when the measurement result by the eddy current sensor 6 is corrected in two stages. However, the number of detection electrodes can be varied as necessary without being restricted to this.

The measurement of the hot water level by the energized electrode type sensor 5 is performed with high precision when the hot water level 7 is free of ripples. but,
The actual hot water surface 7 is often undulating, and this effect is likely to appear in the measurement results. Therefore, in order to eliminate the influence of ripples, it is preferable to surround it with a refractory tube 9 as shown in FIG.

The lower end of this refractory tube 9 is cut diagonally, so that molten metal flows into the tube 9 through the lower end opening 9a. The wall of the cylinder 9 blocks waves inside and outside, and prevents ripples occurring in the pool 2 from propagating into the cylinder 9.

Furthermore, if a weir 10 or a filter is provided between the pouring part where the pouring nozzle 4 is arranged and the current-carrying electrode type sensor 5, the turbulent flow 122 occurring in the pouring part will not be received.
The hot water level is detected by the detection electrodes 5a, 5b, and 5C.

The current-carrying electrode type sensor 5 disposed in the water reservoir 2 may be one or more. When a plurality of energized electrode type sensors 5 are installed, for example, when energized Ti top sensors are placed at three locations in the hot water pool 2, one or two or three energized electrode type sensors 5 detect the hot water level 7. Then, the eddy current sensor 6 is corrected. As a result, the hot water reservoir 2
Level measurement of the entire hot water surface 7 is performed.

In this way, when the level of the hot water surface 7 is detected by the eddy current sensor 6 alone, measurement errors are likely to occur due to the influence of the surroundings. It becomes possible to detect the level of In addition, although the measurement is performed using the eddy current sensor 6, the variation for each charge with respect to the absolute level can be suppressed within the range of ±1 mm.

The amount of molten metal poured and the rotational speed of the cooling rolls 1a and 1b are controlled based on the level of the molten metal detected with high precision in this way, so that the cast metal ribbon has stable shape characteristics. It becomes a product that lasts.

(Example) With the equipment configuration shown in Figure 1, stainless steel 5IJS 3
04 composition is poured into the sump 2, and the thickness is 2.0.
A thin metal strip with a plate width of 650 mm was cast. At this time, the level 7 of the molten metal supplied to the pool 2 with the start of pouring was measured by the eddy current sensor 6, and found to have an upward curve as shown in FIG. However, the water level 7
reaches the lower end of the detection electrode 5b, and the detection electrodes 5a and 5b
At time t1 when the eddy current sensor 6 becomes conductive, the eddy current sensor 6
An error of Δh1 occurred in the detected value. Therefore, this error Δh1 was calculated by the control mechanism 8, and the value detected by the eddy current sensor 6 was revised upward.

If pouring continues in this state, the hot water level 7 will rise further,
It came into contact with the lower end of the detection electrode 5C. At this point t2
In this case, an error of Δh2 occurred in the detected value of the eddy current sensor 6. Based on this error Δh2, the value detected by the eddy current sensor 6 was similarly revised upward. Thereafter, molten metal was poured while maintaining the target level, and a metal ribbon was cast.

Since the hot water level in the hot water pool section 2 is maintained accurately,
The obtained metal ribbon had excellent shape characteristics and was free from defects such as poor wall thickness.

(Effects of the Invention) As explained above, in the present invention, the eddy current sensor is based on the fact that the detection electrode of the current-carrying electrode type sensor conducts through the molten metal poured into the pool. The detected value of the measured hot water level is corrected.

Therefore, even though the measurement is performed using an eddy current sensor, the influence of the surroundings is eliminated, the hot water surface level is measured with high precision, and there is no error between the absolute levels measured for each charge. . In this way, casting is performed while accurately grasping the level of the molten metal, making the casting operation more stable and improving the quality of the obtained metal ribbon.

[Brief explanation of the drawing]

Fig. 1 shows the present invention applied to a continuous casting machine with twin rolls of different diameters, Fig. 2 shows an example of a current-carrying electrode type sensor disposed in the sump, and Fig. 3 shows a case where the current-carrying electrode is applied to a continuous casting machine. Another example of the type sensor is shown, and FIG. 4 is a graph specifically expressing the effects of the present invention. 1a, tb, cooling roll 2. Hot water pool part 3, side weir 4. Pouring nozzle 5, current-carrying electrode type sensors 5a to 5c, detection electrode 6. Eddy current sensor 7, hot water level 8. Control mechanism 9, refractory tube
9a, lower end opening 10 of cylinder 9, weir

Claims (1)

[Claims] 1. When continuously casting a metal ribbon by cooling and solidifying the molten metal poured into a pool divided by a cooling roll and/or belt by removing heat through the cooling roll and/or belt, An eddy current sensor is disposed above the hot water pool, a current-carrying electrode type sensor is placed in the hot water pool, and the eddy current sensor is corrected based on a detected value of the hot water level detected by the current-carrying electrode type sensor. A method for detecting a level of molten metal in continuous casting of metal ribbon, characterized in that the eddy current sensor detects the level of molten metal poured into the sump.