JPH02205234A - Method for detecting molten metal surface level in cast strip continuous casting - Google Patents

Abstract

PURPOSE:To produce a uniform continuous cast product having excellent quality by measuring shifting rate of a detecting terminal between the reference point and molten metal surface in pouring basin part and correcting the measured value detected with a vortex current type sensor based on the shifting rate. CONSTITUTION:The molten metal is poured into the pouring basin part 2 sectioned with cooling roll, etc., and cooled and solidified to continuously cast the coast strip. Then, the vortex current type sensor 6 is set at the upper part of the pouring basin part 2. Further, the contact type detecting terminal 9 is set as vertically shiftable. Then, ascendent or descendent shifting rate of the contact type detecting terminal 9 from the reference point A to the position B where the terminal 9 is brought into contact with the molten metal surface 7 in the pouring basin part 2, is measured. Based on this shifting rate, the measured value detected with the vortex current type sensor 6, is corrected. By this method, the molten metal surface level at the casting period can be grasped with the vortex current type sensor at good accuracy.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is aimed at controlling the level of the molten metal poured into the molten metal surface area when continuously casting thin slabs by rapidly cooling and solidifying the molten metal. Concerning how to detect.

(Prior art) When casting thin slabs close to the final shape from molten metal,
Since subsequent steps such as rolling and heat treatment are simplified, the burden on equipment is reduced. For example, in a conventional continuous casting machine, a cast slab was roughly rolled and hot rolled into a strip, and the strip was conveyed to a cold rolling process. but,
If a thin slab is obtained that can be fed directly into the cold rolling process, hot rolling can be omitted and there is no need to heat treat the strip prior to cold rolling.

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 thin slabs from molten metal. There is. In all of these methods, heat is removed from molten metal poured into a sump via a cooling roll or belt, and a solidified shell is formed thereon. The solidified shell is sent out from the casting space as a thin slab while growing as the cooling rolls, belts, etc. rotate and run.

In order to keep the shape, especially the thickness, of the thin slab 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, by detecting the hot water level using an appropriate means and increasing the amount of hot water poured when the hot water level is lower than the set value, and decreasing the amount of hot water poured when it is higher, the hot water level in the pool is always maintained at a constant level. The method will be adopted.

As a measuring device for detecting the level of hot water, 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 suitable measuring device under special conditions. However, although eddy current sensors have excellent resolution, they are easily influenced by the surrounding environment. Therefore, the measurement results will vary greatly depending on the strength of the surrounding magnetic field, the presence or absence of conductors, etc.

Therefore, the present inventors developed a method of detecting the hot water level with high accuracy by using an eddy current sensor and a current-carrying electrode type sensor while eliminating the influence of the surroundings on the eddy current sensor. The application was filed as Application No. 63-268254.

FIG. 4 shows a continuous casting machine with twin rolls of different diameters incorporating this method. 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 3 of a sump part 2 opens between these cooling rolls 1a and lb. . This pool 2 is partitioned on both sides by side weirs (not shown) facing the circumferential surface of the large-diameter lower roll 1b, and molten metal is injected from an intermediate container such as a tundish through a pouring nozzle 4. Ru.

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. The current-carrying electrode type sensor 5 is equipped with a long common electrode and a plurality of counter electrodes of different lengths, and the level of the hot water level 7 can be adjusted in multiple stages depending on the conduction state between the common electrode and the counter electrodes. To detect. On the other hand, as the eddy current type sensor 6, a normal type sensor is used, which detects a change in magnetic flux density as a result of the magnetic flux generated by the coil passing through the water reservoir 2.

When molten metal is poured into the pool 2, the level 7 of the molten metal rises and comes into contact with the electrode of the energized electrode type sensor 5.

As a result, conduction is established between the common electrode and the predetermined counter electrode, and it is detected that the hot water level 7 is at the lower end of the predetermined counter electrode. This detected value is input to the control mechanism 8, and the detected value regarding the hot water level from the eddy current type sensor 6 is corrected. The measurement error of the hot water level detected by this current-carrying 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 electrode. Since the detected value of the energized electrode type sensor 5 is inputted to the control mechanism 8 as a correction input, the hot water level can be measured at high turbulence while eliminating the influence of the surroundings on the eddy current type sensor 6. .

(Problem to be solved by the invention) In the method proposed in the earlier application, the current-carrying electrode type sensor 5
It is assumed that the detection electrode contacts the molten metal and becomes conductive. Therefore, adhesion of molten metal to the detection electrode of the current-carrying electrode type sensor 5 is unavoidable. The adhered molten metal tends to form a bridge between the detection electrodes and solidify, and there is a risk that the detection electrodes may be maintained in a conductive state even if the molten metal level 7 subsequently falls.

In this respect, although the method based on the conduction state of the detection electrode is suitable for detecting the level of the molten metal at the start of casting,
After the molten metal in the pool 2 reaches a steady state, the level of the molten metal cannot be detected with high accuracy. In other words, at the start of pouring, the level of the molten metal tends to rise as the metal pours, and the bridge that makes the detection electrode conductive has not been formed, making it possible to accurately detect whether or not the molten metal has come into contact with the detection electrode. can do.

On the other hand, when the molten metal poured into the molten metal pool 2 reaches a steady state, the output of the eddy current sensor 6
Fluctuations occur due to temperature rise due to radiant heat from the machine, thermal deformation of the jig, etc. At this time, if a bridge is formed between the detection electrodes, the detection electrodes are electrically connected and the current-carrying electrode type sensor 5 cannot detect the hot water level. Moreover, even in a steady state, the molten metal surface 7 moves up and down in response to changes in casting conditions, etc., which tends to affect the thickness and surface properties of the solidified shell formed on the circumferential surfaces of the cooling rolls 1a and 1b. .

Therefore, the present invention obtains correction information to be input to the eddy current sensor from the amount of movement of the contact detection terminal.
Detects the level of molten metal with high accuracy regardless of whether molten metal is attached, and determines the atmospheric conditions for the measurement accuracy of the eddy current sensor.
The purpose is to accurately grasp the condition of the sump while eliminating the influence of thermal conditions, etc., and to cast thin slabs under stable conditions.

(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 thin slabs, an eddy current sensor is placed above the pool, and a contact detection terminal is moved up and down above the pool. possible placement,
The amount of movement of the contact type detection terminal as it descends from a reference point to a position in contact with the hot water surface of the hot water pool, or the amount of movement of the contact type detection terminal as it rises from a position in contact with the hot water surface of the hot water pool. The present invention is characterized in that the measured value detected by the eddy current sensor is corrected based on the amount of movement.

(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 mechanism for directly measuring the hot water level by contact in order to obtain correction information for the eddy current sensor. That is, the contact type detection terminal 9 is arranged above the hot water level 7,
This contact type detection terminal 9 is raised and lowered at a constant speed by a motor such as a stepping motor 10 whose rotation can be accurately measured. The contact type detection terminal 9 is composed of a graphite electrode through which a current flows when its lower end contacts the hot water surface 7, and moves up and down between the reference point A and the contact point B. In order to detect whether or not the contact type detection terminal 9 is present at the reference point A, an optical system consisting of a light emitting element 11a and a light receiving element 11b is provided. For example, the optical path 11c of the laser beam etc. emitted from the light emitting element 11a is connected to the contact detection terminal 9.
, it is determined that the contact type detection terminal 9 is at the reference point A. Note that a detection element such as a limit switch may also be used to detect the contact type detection terminal 9 at the reference point A.

From this state, the contact type detection terminal 9 is lowered to the contact point B by driving the stepping motor 10. At this time, if a graphite electrode is used as the contact type detection terminal 9, a voltage is applied to the contact type detection terminal 9 via a wire. When the contact point B is contacted, a current starts to flow, so the presence or absence of this current is detected to determine whether the contact type detection terminal 9 is present at the contact point B. Conversely, the contact type detection terminal 9 is set at the contact point B, and the contact type detection terminal 9 is raised from this state.
The amount of movement to the reference point A can also be detected.

The amount of movement from the reference point A to the contact point B can be determined by counting the number of steps of the stepping motor 10. Thereby, the level of the hot water surface 7 is actually measured with high accuracy of 10.1 mm or less.

The obtained detected value of the hot water level is input to the control mechanism 8, as in the case of FIG. 4, and is used as information for correcting the measured value from the eddy current sensor 6.

In this method, since the reference point A can be set at a position away from the hot water surface 7, the contact type detection terminal 9 is not exposed to high temperatures due to radiant heat from the hot water surface 7.

Therefore, the hot water level 7 can be measured with high accuracy without being affected by temperature, thermal expansion, etc. In addition, contact type detection terminal 9
Even if molten metal adheres to the tip of the molten metal, there is no method to detect the molten metal level based on the conduction state.
A green contact type detection terminal 9 can be used. Since the contact detection terminal 9 at the contact point B is detected by an optical sensor or the like, it is not affected by attached molten metal or base metal.

Note that when the contact detection terminal 9 is moved up and down, its position may affect the measurement results of the eddy current sensor 6. Therefore, it is preferable to arrange a shield plate 12 around the contact type detection terminal 9. FIG. 2 is a plan view showing that the contact detection terminal 9 and the eddy current sensor 6 are blocked by the shield plate 12.

Further, the molten metal surface 7 during pouring or casting is often rippled, and these ripples tend to affect the measurement results by the contact type detection terminal 9. In this case, if contact-type detection terminals 9 are arranged at multiple locations and the hot water level is determined based on whether one or more contact-type detection terminals 9 come into contact with the hot water surface 7, The effects of ripples are suppressed.

(Example) As a continuous casting machine, one having basically the equipment configuration shown in FIG. 4 was used. However, instead of the current-carrying electrode type sensor 5 shown in FIG. 4, the contact type detection terminal 9 shown in FIG.
Incorporated.

Molten steel having the composition of stainless steel 5US304 was poured into the sump 2, and a thin slab having a wall thickness of 2.0 mm and a plate width of 650 mm was cast. At this time, the level 7 of the molten steel supplied to the pool 2 with the start of pouring had an upward curve as shown in FIG. 3, as measured by the eddy current sensor 6.

However, when the hot water level 7 was actually measured using the contact type detection terminal 9 at time t during pouring, an error of Δh1 had occurred in the detected value of the eddy current type sensor 6. Therefore, this error △h
, was calculated by the control mechanism 8, and the value detected by the eddy current sensor 6 was revised upward.

When pouring was continued in this state, the hot water level 7 in the hot water pool 2 further rose. Therefore, at time t2 when the hot water level 7 reached a steady level, the hot water level 7 was measured again using the contact type detection terminal 9.

At this time, an error Δh2 occurred in the detected value of the eddy current sensor 6. Therefore, similarly, the value detected by the eddy current sensor 6 was revised upward based on the detection error Δh2.

Furthermore, at the stage when the hot water level 7 of the hot water pool portion 2 has reached a steady state,
The hot water level was periodically detected using a contact type detection terminal 9. Then, each detection time point 1, . Based on the errors △h3 and △h4 detected in 14, the eddy current sensor 6
The detected value was revised upward or downward. In this way, molten steel was poured while maintaining the molten metal level 7 at the target level, and a thin slab was cast. The obtained thin-walled slab was cast under stable conditions because the molten metal level 7 was maintained at the target level throughout the casting period, and there were no defects in wall thickness or
It had excellent shape characteristics with no defects such as gas entrainment.

In the above example, a continuous casting machine with different diameter twin rolls was used. However, the present invention is not limited to this, and as long as the poured molten metal is rapidly cooled and solidified to produce a thin slab, other twin roll methods,
Single drum system, single belt system, double belt system, roll
It can be similarly applied to continuous casting machines such as belt type.

(Effects of the Invention) As explained above, in the present invention, the reusable contact type detection terminal is moved between the reference point and the contact point, and the hot water level is actually measured from the amount of movement. There is. Since the detected value of the eddy current type sensor is corrected using this actual measurement value, unlike when using a current-carrying electrode type sensor that detects the hot water level based on the conduction state, the hot water level reaches a steady state. The level can be measured continuously, and the molten metal level during the casting stage can be accurately determined using an eddy current sensor. As a result, reliability in controlling casting conditions is improved, and products of excellent and consistent quality can be manufactured.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the action of the contact type detection terminal used in the present invention, Fig. 2 is a plan view showing the casting space, and Fig. 3 is a diagram specifically showing the effects of the present invention. graph, 4th
The figure shows the main parts of a continuous casting machine equipped with a molten metal level detection mechanism using a current-carrying electrode type sensor previously proposed by the present inventors. 1a: Small diameter upper roll 1b: Large diameter lower roll 2: Pool portion 3: Nozzle portion 4: Pouring nozzle
5: Current-carrying electrode type sensor 6: Eddy current type sensor 7:
Hot water surface 8: Control mechanism 9: Contact type detection terminal 10 Tipping motor 11b = Light receiving element 11a: Light emitting element 12: Shield plate 11C: Optical path A: Reference point
B: Contact point

Claims (1)

[Claims] 1. When continuously casting thin slabs by cooling and solidifying the molten metal poured into a pool section divided by cooling rolls and/or belts by removing heat through the cooling rolls and/or belts, An eddy current type sensor is disposed above the hot water pool, and a contact type detection terminal is placed above the hot water pool so as to be movable up and down, from a reference point to a position where it touches the hot water surface of the hot water pool. the amount of movement of the contact-type detection terminal that descends;
Alternatively, measuring the amount of movement of the contact type detection terminal rising from a position in contact with the hot water surface of the hot water pool to the reference point,
A method for detecting a melt level in continuous casting of thin-walled slabs, characterized in that a measured value detected by the eddy current sensor is corrected based on the amount of movement.