JPH03193244A - Method for continuously casting strip - Google Patents

Abstract

PURPOSE:To stably cast a strip having high quality by controlling rotating velocity of rolls in a twin roll strip continuous casting machine so that surface temp. in width direction of the strip produced from gap between roll pair becomes within the set range. CONSTITUTION:In the roll gap fixed type twin roll strip continuous casting machine, the surface temp. of strip 5 is continuously measured with an infrared thermography instrument 6. The detected output of the thermography instrument 6 is inputted to control circuit 7 and then, the inputted value is compared with the set value, and control signal is outputted to casting operation device so as to become the surface temp. of strip 5 within the range of set value and the rotating velocity of rolls is controlled with a control unit 8 for number of revolution of a motor. By this method, the development of cooling uneven pattern on surface of the strip is prevented and the strip having high quality can be stably produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in a twin-roll continuous sheet casting method for continuously casting thin sheets directly from molten metal.

[Conventional technology]

A pair of internal cooling rolls that rotate in opposite directions are arranged facing each other in parallel with an appropriate gap between them.9 A pool is formed on the circumferential surface of the rolls above this gap (roll gap), and the hot water in this pool is A twin-roll continuous casting machine is known in which a thin plate is continuously cast through a gap between the rolls while being cooled by the circumferential surface of rotating rolls. There has also been a proposal to apply such a twin roll continuous casting machine to continuous casting of steel to directly produce thin steel plates from molten steel. Twin-roll thin plate continuous casting machines can be roughly divided into two types: one is the roll-gap restraint type, which restrains the roll gap, and the other is the roll-gap restraint type, which does not have a mechanism to restrain the roll gap. It is divided into roll gap-free types whose plate thickness is determined by the shell thickness.

[Problem that the invention seeks to solve]

It is inevitable that the shell that solidifies on the circumferential surface of the roll will have some degree of uneven thickness.For this reason, when both shells of the roll pair pass through the roll gap, there will be a portion that is in strong contact with the roll. There are some parts where this is not the case. Additionally, if unevenness occurs on the roll surface due to thermal expansion, etc., the roll gap will not be constant in the width direction and circumferential direction (as the roll rotates), resulting in uneven adhesion between the thin plate being cast and the roll. . Such a difference in adhesion occurs in the width direction or longitudinal direction of the thin plate.

In areas where there is strong contact, the thin plate is strongly cooled by the rolls,
Other parts are slowly cooled. This cooling unevenness appears as a cooling uneven pattern on the surface of the thin plate.

This uneven cooling pattern remains on the surface of the cold-rolled sheet even after the thin sheet undergoes the cold-rolling process, which is a problem.

For example, it is extremely difficult to prevent the occurrence of this uneven cooling pattern in both the fixed roll gap type and the free roll gap type.

Even if we try to measure the force (crimping load) received from the rolls when both shells are crimped in the roll gap and control the casting conditions based on this measured value, the critical crimping load that causes uneven cooling pattern is very small and zero. , it is difficult to control so that uneven cooling patterns do not occur due to problems with the accuracy and noise of the load cell that measures the crimp load. Also.

If casting is carried out at a crimp load close to zero, which reduces uneven cooling patterns, a large amount of unsolidified molten metal remains in the center of the thickness of the thin plate and passes through the roll gap, resulting in a dangerous situation. The present invention is aimed at solving these problems, in which the plate swells or breaks out due to failure to detect the problem.

[Means for solving problems]

A pool of molten metal is formed in contact with the circumferential surfaces of a pair of internal cooling rolls that are arranged opposite to each other with their axes parallel to each other and rotate in opposite directions. In order to solve the above-mentioned problems in a thin plate continuous casting method in which the solidified shell formed on the top is continuously cast into a thin plate through the gap between the pair of rolls, the present invention provides a method for continuously casting a solidified shell formed on the solidified shell into a thin plate through the gap between the pair of rolls. The surface temperature distribution in the width direction of the thin plate is continuously measured at a predetermined position from the gap.

In order for this measured value to fall within a set range, (1) the roll rotation speed is controlled using the measured value as an instruction value;

(2) Controlling the size of the gap using the measured value as an instruction value. (3) controlling the circumferential length of the molten metal in the pool in contact with the roll circumferential surface using the measured value as an instruction value; and (4)
) The magnitude of the compression load of the solidified shell is controlled using the measured value as an instruction value. The present invention provides a continuous thin plate casting method characterized by the following.

That is, the non-uniformity of the degree of adhesion when both solidified shells are pressed together by both rolls in the gap at the closest position between the rolls (hereinafter referred to as the roll gap) is detected by the surface temperature distribution of the thin plate emerging from the gap. The casting operation is performed so that this detected value falls within a preset desired range, and the control operations include the crimping load and roll rotation speed.

The roll gap or the contact length of the molten metal with the roll circumferential surface (circumferential length, and ultimately the molten metal surface level in the pool) is used, and these operations are automatically performed using the detected value of the surface temperature of the thin plate as the indicated value. Open'a (feedback control).

[Effect]

Where the solidified shell is in close contact with the circumferential surface of the roll in the roll gap, the degree of cooling is increased, and the surface temperature of that part immediately after passing through the roll gap is lower than that where it is in weak contact. Therefore, by providing a large number of temperature measurement points in the width direction of the sheet immediately after passing through the roll gap, non-uniformity of adhesion can be determined from the temperature distribution. In this case, non-uniformity in the width direction of the plate can be detected from the temperature distribution between each measurement point, and non-uniformity in the longitudinal direction of the plate can be detected from changes over time at each measurement point. In other words, fluctuations in the two-dimensional temperature distribution of the plate can be read.

If fluctuations in this temperature distribution are detected online and the fluctuations deviate from the set range, the temperature distribution can be returned to normal values by appropriately controlling the casting operation described above. By decreasing the speed, decreasing the roll gap, increasing the contact length of the molten metal with the roll circumferential surface, or increasing the crimping load, you can remove insufficiently cooled areas. If the cooling level is restored to normal, and if the operation is performed in the opposite direction, the strongly cooled areas will be restored to normal cooling level. As a result, uneven cooling is substantially eliminated, and a situation in which unsolidified molten metal abnormally remains inside and leaves the roll gap is avoided.

[Explanation of 11 Examples of the Invention] Figure 1 shows an example in which the method of the present invention is applied to a twin-roll continuous sheet casting machine with a fixed roll gap. A pool 2 of molten metal is formed in contact with the circumferential surfaces of a pair of internal cooling rolls la and lb of the same diameter that rotate in opposite directions, and the molten metal in this pool 2 spreads around the circumference of the pair of rolls 1a and lb. Solidified shells 3a and 3b formed on both circumferential surfaces are continuously cast into a thin plate 5 through a roll gap 4.

In the present invention, the surface temperature of the thin plate 5 is continuously measured by an infrared detection type thermography device 6. That is, at a position not far from the roll gap 4, the surface temperature distribution in the width direction of the thin plate continuously moving at that position is continued to be measured. The detection output of the thermography device 6 is input to a control circuit 7, where the input value is compared with a set value, and if it is determined that the input value exceeds the set value, the casting operation device is instructed to move in a direction that falls within the range of the set value. Outputs a control signal. In the example of FIG. 1, this control signal is transmitted to operate the rotational speed control device 8 of the motor that applies rotational power to the rotating shafts of the roll pair 1a, lb, and the rotational speed of the roll pair 1a, lb is adjusted. Ru. As a result, the solidified shells 3a and 3b are pressed together in the roll gap, and the resulting plate is cast with a predetermined surface temperature distribution both in the width direction and in the casting direction. In other words, uneven cooling.

As a result, the roll rotation speed is automatically controlled to minimize the occurrence of non-uniform adhesion.

Figure 2 shows a sketch of the surface condition of the cast thin plate 5. Figure 2 (a) shows the case where uneven cooling patterns are observed on the plate surface, and the shaded area A is the area where the thin plate and the roll are in strong contact, i.e. Figure 2(b) shows the low-temperature part, and Figure 2(b) shows the surface with a moderate degree of adhesion and a uniform temperature without uneven cooling.
C) shows a case where solidification is insufficient and there is a partial opening containing a large amount of unsolidified molten metal in the center of the plate thickness, and this partial opening becomes an abnormally high temperature area. This abnormally high temperature can cause swelling or breakouts. This (→, b> and (
Condition C) both occurs even when the crimping load is at a level of approximately zero. Therefore, it cannot be determined by measuring the force applied to the plate passing through the roll gap, but by observing with the thermography device 6, these three states can be easily distinguished. The present invention utilizes this to directly determine the uneven cooling of the thin plate 5 that has come out of the roll gap by measuring the surface temperature of the thin plate. In other words, the temperature is low in the parts of the thin plate surface that are in close contact with the rolls, and relatively high in other parts, and if there is a large amount of unsolidified molten metal in the center of the thickness, that part will be abnormally high. The surface temperature will be high. Therefore, if the measured thin plate surface temperature is lower than the standard value, the casting operation factors should be manipulated in the direction of weakening the adhesion between the roll and the thin plate. As shown in Figure 1, the fixed roll gap type In this case, the roll rotation speed is increased to reduce the time during which the molten metal in the pool 2 contacts the roll circumferential surface (the solidification time of the molten metal), thereby reducing the shell thickness when passing through the roll gap.
The ratio of the shell thickness to the roll gap is then reduced to weaken the adhesion between the roll and the thin plate. On the other hand, if the measured surface temperature of the thin plate is higher than the reference value.

Repeat the operation in reverse to the above to strengthen the adhesion between the roll and the thin plate.

As a means of measuring the surface temperature of the thin plate, a normal two-color thermometer or an infrared temperature needle may be used, but since the temperature can only be measured in a limited area by scratching, a two-color thermometer such as a thermography device 1 may be used.
A device that can capture dimensional surface temperature distribution is more convenient. The measured temperature data may use an average value or a weighted average value in the board width direction at each point in time as a representative value, or may further average values within an arbitrary time period and use it as a representative value. Moreover, the maximum value and minimum value of temperature may be managed for temperature unevenness that exists two-dimensionally on the surface of the thin plate. Furthermore, in order to reduce temperature unevenness, the difference between the highest value and the lowest value may be managed, and the above combination or data further processed may be used. Alternatively, these data outputs, such as 0 or more, which may be determined based on brightness or the like without being converted into temperature, are fed back to the casting operation through an appropriate logic circuit.

FIG. 3 shows the roll gap expansion/contraction mechanism 9a from the control circuit 7.
For a twin-roll continuous casting machine with t9b, the system is the same as the example in FIG. 1, except that the control circuit 7 outputs a control operation signal to the expansion/contraction operation parts 1o of the expansion/contraction mechanisms 9a, 9b. It shows. Even in the roll gap restraint type, expansion and contraction mechanisms 9a and 9b adjust the degree of restraint.
In this example, the roll gap is automatically controlled by the expansion/contraction operation section 10. In this case, automatic control is also carried out so that the measured value by the surface thermometer 6 falls within the set range even if the thickness of the solidified shells/1z3a, 3b that pass through the roll gap fluctuates or becomes non-uniform for some reason. It can be done. In other words, if the measured surface temperature of the thin plate is lower than the reference value, the operation is performed in the direction of weakening the adhesion between the roll and the thin plate, that is, in the direction of widening the roll gap. If it is high, the thin plate surface temperature can be kept within the predetermined set value range by performing the opposite operation to the above to strengthen the adhesion between the roll and the thin plate, that is, to reduce the roll gap. .

FIG. 4 shows a control method similar to that in FIG. 1, except that the contact lengths 11a and 11b at which the molten metal in the pool 2 contacts the circumferential surface of the roll are controlled. Increasing or decreasing the contact lengths 11a and llb in contact with the circumferential surface increases or decreases the thickness of the solidified shells 3a and 3b passing through the roll gap, so by manipulating this, the degree of adhesion between the roll and the thin plate can be controlled in the same way as described above. . The contact lengths 11a and 11b, that is, the height of the molten metal sump 2 can be controlled by controlling the injection speed of the molten metal supplied to the sump 2. An example is shown in which a control operation signal is sent from the control circuit 7 to the operation section I5 of the flow rate adjustment valve 14 when injecting molten metal using the injection nozzle 13 having an interposed one. In this case as well, even if the thickness of the solidified shells 3a, 3b passing through the roll gap fluctuates or becomes non-uniform for some reason, automatic control can be performed so that the measured value by the surface thermometer 6 falls within the set range. That is, if the measured surface temperature of the thin plate is lower than the reference value, the flow rate adjustment valve 14 is operated in a direction to weaken the adhesion between the first hole and the thin plate, that is, to reduce the contact length 11a, llb. On the other hand, if the measured surface temperature of the thin plate is higher than the reference value, the thin plate surface temperature can be adjusted to a predetermined set value by operating in the direction of strengthening the adhesion between the roll and the thin plate, that is, in the direction of opening the flow rate adjustment valve 14. It can be kept within the range.

FIG. 5 shows the application of the present invention to a roll gap-free type in which the roll gap changes depending on the thickness of the solidified shells 3a and 3b formed on the circumferential surfaces of the rolls la and lb as they pass through the roll gap 4. In this case, one roll 1a is pressed against the other roll 1b via the roll pressing mechanism 16 under a predetermined pressure load. This crimp load is applied by a hydraulic cylinder, an air cylinder, a spring, etc., and is the same as the previous example except that a control operation signal is outputted from the control circuit 7 to the operation section 17 of this crimp load. Even in such a case, automatic control can be performed so that the measured value by the surface thermometer 6 falls within the set range. That is, if the measured thin plate surface temperature is lower than the reference value, the roll pressing mechanism 16 is operated in a direction that weakens the adhesion between the roll and the thin plate, that is, in a direction that increases the pressure bonding load, and on the other hand, the measured thin plate surface If the temperature is higher than the reference value, the roll pressing mechanism 16 is operated in a direction that strengthens the adhesion between the roll and the thin plate, that is, in a direction that reduces the crimping load, so that the thin plate surface temperature falls within a predetermined set value range. be able to. In addition, in the example shown in FIG. 5, the rolls 1B and 1b with different diameters are arranged in upper and lower stages, and the water reservoir 2 is provided on the side, but as shown in FIG.
The present invention can be applied even when the rollers a and lb are arranged in the horizontal direction, as long as the pressure bonding load can be controlled by the roll pressing mechanism.

[Example] 500 kg of 5IJS304 molten steel was cast using a twin roll thin plate continuous caster as shown in FIG.

The thickness of the cast plate is 3mm and the average casting speed is 20m/s+i
It was n.

At 500 mm beyond the roll gap, the surface temperature of the plate during casting was measured using a thermography device.

As the control criteria for the surface temperature, it was decided that both the maximum temperature in the board width direction at each time point be 1410°C or less, and the average temperature be within 1370°C±20°C. However, in case of conflict, the former condition shall take precedence. In addition, the liquidus temperature of 5US304 is 1454
°C, and the solidus temperature is 1428 °C.In order to satisfy the standard of 0 or more, an operation command is output to increase or decrease the voltage of the motor that provides rotational power to the roll through the control circuit. The rotation speed was controlled.

As a result, a thin plate with a uniform surface condition was obtained, without any uneven cooling pattern, and without any plate formation or breakout due to non-solidification.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent the occurrence of uneven cooling patterns on the surface of the yi plate, and it is also possible to manufacture a thin plate with a uniform surface without swollen plates without the risk of breakout. , can stably cast high-quality thin plates. The uneven cooling pattern is caused by polishing or heat treatment.

It is difficult to erase even by cold rolling, and is particularly effective in continuous thin plate casting of stainless steel, where surface quality is important.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view showing the operating state of a roll gap restrained thin plate continuous caster to which the method of the present invention is applied, Figure 2 is a plan view illustrating various surface conditions of the cast thin plate, and Figure 3 is a roll A schematic sectional view showing the operating state of another example in which the method of the present invention is applied to a gap restraint type thin plate continuous casting machine, and Fig. 4 is a schematic sectional view showing the operating state of another example in which the method of the present invention is applied to a roll gap restraint type continuous thin plate caster. FIG. 5 is a schematic cross-sectional view showing an operating state in which the method of the present invention is applied to a roll gap-free continuous sheet casting machine. la, lb...internal cooling roll, 2...hot water pool. 3a, 3b... solidified shell, 4... roll gap 5... thin plate to be cast, 6... surface temperature measuring meter 7...
・Control circuit, 8...Motor rotation speed control device 9a, 9
b...Roll gap expansion/contraction mechanism. 10... Expansion/contraction operation section of the expansion/contraction mechanisms 9a, 9b. l2...Intermediate container, 13...Injection nozzle. 14: Flow rate adjustment valve, 15: Flow rate adjustment valve operation unit 116: Roll pressing mechanism, 17: Crimp load operation unit. Figure 2

Claims (4)

[Claims] (1) A pool of molten metal is formed in contact with the circumferential surface of a pair of internal cooling rolls that are arranged opposite to each other with their axes parallel to each other and rotate in opposite directions. In a continuous thin plate casting method in which a solidified shell formed on a circumferential surface is continuously cast into a thin plate through the gap between the pair of rolls, the surface temperature distribution in the width direction of the thin plate that continuously emerges from the gap between the pair of rolls is A thin plate continuous casting method, characterized in that measurement is continued at a predetermined position from the gap, and the roll rotation speed is controlled using the measured value as an instruction value so that the measured value falls within a set range. (2) A pool of molten metal is formed in contact with the circumferential surfaces of a pair of internal cooling rolls that are arranged opposite to each other with their axes parallel to each other and rotate in opposite directions. In a continuous thin plate casting method in which a solidified shell formed on a circumferential surface is continuously cast into a thin plate through the gap between the pair of rolls, the surface temperature distribution in the width direction of the thin plate that continuously emerges from the gap between the pair of rolls is A thin plate continuous casting method characterized by continuing to measure at a predetermined position from the gap, and controlling the size of the gap using the measured value as an instruction value so that the measured value falls within a set range. (3) A pool of molten metal is formed in contact with the circumferential surfaces of a pair of internal cooling rolls that are arranged opposite to each other with their axes parallel to each other and rotate in opposite directions. In a continuous thin plate casting method in which a solidified shell formed on a circumferential surface is continuously cast into a thin plate through the gap between the pair of rolls, the surface temperature distribution in the width direction of the thin plate that continuously emerges from the gap between the pair of rolls is Continuing to measure at a predetermined position from the gap, and controlling the circumferential length of the molten metal in the pool in contact with the roll circumferential surface using the measured value as an indication so that the measured value falls within a set range. A thin plate continuous casting method characterized by: (4) A pool of molten metal is formed in contact with the circumferential surfaces of a pair of internal cooling rolls that are arranged opposite to each other with their axes parallel to each other and rotate in opposite directions, and the molten metal in the pool is transferred to the pair of rolls. In a continuous thin plate casting method in which a solidified shell formed on a circumferential surface is continuously cast into a thin plate through the gap between the pair of rolls, the surface temperature distribution in the width direction of the thin plate that continuously emerges from the gap between the pair of rolls is A thin plate continuous casting method characterized by continuing to measure at a predetermined position from the gap, and controlling the magnitude of the crimp load of the solidified shell using the measured value as an indication value so that the measured value falls within a set range. .