JP2020171943A - Method of detecting a crater-end position in continuous casting - Google Patents

Abstract

To provide a method of detecting a crater-end position in continuous casting allowing for detecting a crater-end position at required accuracy during continuous casting.SOLUTION: A method of detecting a crater-end position includes roll-reducing a cast slab 10 under continuous casting by a reducing roll pair 6, measuring a rolling reduction of the cast slab, and determining a solidification completion position (crater-end position 41) of the cast slab. A reducing roll 1 constituting the reducing roll pair 6 has a roll outer periphery shape in a section including a roll-rotation axis configuring a convex shape protruding outward in a region including a widthwise center position 13 of the cast slab. The convex shape has a curve profile protruding outward and not having a corner, in a range of totally a length 0.40×W of from a widthwise center position 13 to both sides in a roll-width direction (convex shape-defining range 14). This makes it possible to accurately detect a crater-end position by increasing the change amount of rolling reduction corresponding to the variation of the crater-end position.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for detecting a crater end position in continuous casting.

In continuous casting of molten metal, initial solidification is performed in a mold to form a solidified shell, the initially solidified slab is pulled downward, and solidification is completed while supporting the slab with a support roll to form a slab. .. The final support roll position in the casting direction is called the "machine edge". The distance from the position of the molten metal in the mold to the end of the machine along the slab is called the "machine length" of the continuous casting machine (see Non-Patent Document 1, page 434).

When continuous casting is performed in a steady state, the thickness of the solidified shell increases as the distance from the molten metal surface position increases in the casting direction. A solid-liquid coexisting layer is formed on the side of the solidified shell in contact with the liquid phase. The ratio of the solid phase in the central part of the thickness of the slab is called the "central solid phase ratio". The distance in the casting direction from the position of the molten metal is called the "casting length". The central solid phase ratio is 0 from the position of the molten metal to the predetermined casting length range, and when the solid-liquid coexisting layer of the solidified shell reaches the center of the thickness, the central solid phase ratio increases in response to the increase in casting length. It becomes a finite value and gradually increases, and the central solid phase ratio reaches 1 at the position where it is completely solidified to the center of the thickness. The completely solidified position is referred to as the "crater end position" here. On the downstream side of the crater end position, the central solid phase ratio is constant at 1.

In continuous casting, the crater end position needs to be located upstream of the final support roll position (machine end). This is because if the crater end position is on the downstream side of the final support roll, bulging of the slab due to static pressure of molten steel cannot be suppressed, resulting in bulging deformation. Therefore, it is necessary to hold the crater end position on the upstream side of the machine end of the continuous casting machine.

The crater end position varies depending on the continuous casting conditions. The faster the casting speed, the weaker the spray strength in the secondary cooling zone, and the higher the casting temperature, the lower the crater end position is on the downstream side of the casting (see Non-Patent Document 1, p. 426).

In order to improve the productivity of the continuous casting machine, it is effective to increase the casting speed of the slab. As mentioned above, the crater end position moves downstream as the casting speed increases. On the other hand, it is necessary to maintain the crater end position on the upstream side of the machine edge. Therefore, in order to maximize the casting speed, it is effective to set the crater end position on the upstream side of the machine edge and to make it as close to the machine edge as possible.

As mentioned above, the crater end position is known to be affected by the casting speed, the spray strength of the secondary cooling zone, and the casting temperature, but even if the casting speed, spray strength, and casting temperature are the same, the crater It is known that the end position varies. Therefore, even when the casting speed is increased and the crater end position is extended to the very limit of the machine edge, the position on the upstream side of the machine edge must be set as the crater end position in consideration of the variation in the crater end position. Absent. Normally, the maximum casting speed is selected so that the expected crater end position is located about 2 m upstream from the machine end.

In particular, there is a big problem in the unsteady part where the casting speed fluctuates rapidly. For example, the casting speed may be reduced when casting different steel grades in succession or upon receiving an alarm from a breakout prediction device, and the crater end position recedes upstream during low-speed casting. After that, when the speed is increased to a steady casting speed, in order to secure productivity, it is necessary to rapidly advance the crater end position that has receded to the upstream side to the very edge of the machine edge. Unless it is accurately grasped, the casting speed cannot be rapidly increased.

If the crater end position can be actually measured at a position close to the machine edge of continuous casting, the crater end position can be accurately known, and the crater end position can be closer to the machine end than before. It is preferable because it can improve the property. Even when the casting speed is changed from low speed to high speed, if the crater end position can be measured, it will be possible to drastically increase the speed.

In Patent Document 1, the crater end position is estimated based on the surface temperature and heat transfer calculation. Although a certain degree of accuracy can be expected in the stationary part, it is easily affected by changes in casting speed and surface temperature measurement variations, and is less sensitive to crater end position fluctuations.

Patent Document 2 is continuous, characterized in that the crater end position (central solid phase ratio = 1.0) of the slab is detected by transmitting electromagnetic ultrasonic waves through the slab cast by the continuous casting machine. This is a method for determining the quality of cast slabs. However, in addition to the need to introduce new equipment, the accuracy remains questionable when the slab thickness is large.

Patent Document 3 describes a solidification completion detection method in which a reduction cylinder is provided on the final roll of the final segment, and the presence or absence of solidification of the slab is detected based on the reduction amount of the slab when the reduction is performed by a predetermined reduction force. It is disclosed. In addition, an invention is also disclosed in which a reduction cylinder is provided on the entry side roll of the final segment. The relationship between the unsolidified thickness of the slab and the reduction amount when the reduction is performed with a predetermined reduction force is grasped, and the completion of solidification is detected from the measured reduction amount. According to the same document, the reduction amount is 0.02 mm when the reduction roll position coincides with the complete solidification position, and the reduction amount is smaller when the complete solidification position is on the upstream side of the reduction roll. When measuring the reduction amount by the reduction roll during continuous casting, the measurement accuracy of the reduction amount is at most 0.4 mm, and when the complete solidification position is on the upstream side of the reduction roll, the reduction amount on the reduction roll is used. It is difficult to detect the complete solidification position based on this.

Japanese Patent No. 5954043 Japanese Patent No. 4241137 JP-A-2007-245168 Japanese Unexamined Patent Publication No. 2003-94154

5th Edition Steel Handbook Volume 1 Ironmaking / Steelmaking Vol. 426, 434

An object of the present invention is to provide a method for detecting a crater end position in continuous casting, which can detect a crater end position with a required accuracy during continuous casting.

[1] The slab during continuous casting is reduced by a pair of reduction rolls (hereinafter referred to as "reduction roll pair"), the reduction amount of the slab by the reduction roll pair is measured, and the reduction amount is based on the reduction amount. , A crater end position detection method for determining the solidification completion position of a slab (hereinafter referred to as "crater end position"), where the width of the slab to be cast is W (mm).
For at least one of the reduced rolls constituting the reduced roll pair, the outer peripheral shape of the roll in the cross section including the roll rotation axis is a region including the center position in the width direction of the slab (hereinafter referred to as “width center position”). A convex shape protruding outward is formed, and the convex shape has a total length of 0.40 × W on both sides in the roll width direction from the width center position (hereinafter referred to as “convex shape defined range”). Either a curved shape that is convex outward and has no corners, or a shape that is a combination of a curve that is convex outward and a straight line with a length of 0.25 × W or less and has no corners. A method for detecting a crater end position in continuous casting, wherein the reduction roll radius at the width center position is 9 mm or more larger than the reduction roll radius at both ends of the convex shape specified range.
[2] The continuation according to [1], wherein the crater end position is determined based on the reduction amount of the slab having at least two or more reduction roll pairs and measuring the reduction amount of the slab by each reduction roll pair. Crater end position detection method in casting.

According to the present invention, by using a convex curved roll as the reduction roll shape for detecting the crater end position, the amount of change in the reduction amount corresponding to the fluctuation of the crater end position becomes large, and the crater end position can be detected with high accuracy. Is possible.

It is a figure explaining the crater end position detection method of this invention, (A) is a partial side view of a continuous casting apparatus, (B) is a sectional view showing a reduction roll and a slab, and (C) is a convex curved roll. It is a partial view which shows the shape. It is a partial view which shows the shape of a convex curve roll. It is a partial view which shows the shape of a convex disc roll. It is a figure which shows the relationship between the reduction position and the crater end position, and the reduction-crater end distance is negative in (A), 0 in (B), and positive in (C). It is a figure which shows the relationship between the reduction-crater end distance and the reduction amount when the convex curve roll is used. It is a figure which shows the relationship between the reduction-crater end distance and the reduction amount when the convex disc roll is used. It is a figure which shows the relationship between the numerical analysis result and the actual casting result about the relationship between the reduction-crater end distance and the reduction amount when a convex curved roll is used. It is a figure which shows the 2nd Embodiment, (A) is the cross-sectional shape of the reduction roll, (B) is the reduction amount and the reduction roll shape (the length of a straight line 17) obtained by the deformation analysis of the finite element method. It is a figure which shows the relationship of.

Before and after solidification is completed during continuous casting, when trying to reduce the slab using a reduction roll, both short sides of the slab have already completed solidification and the temperature has dropped, so it is accompanied by reduction. The deformation resistance is large, and the amount of reduction is small even when a predetermined reduction force is applied. On the other hand, instead of using a roll whose roll diameter is constant in the roll width direction (hereinafter referred to as "flat roll"), as shown in FIG. 3, the roll diameter of the portion corresponding to the central portion of the slab width is used. Both short sides where solidification of the slab is completed using a roll having a large shape and a roll diameter of a portion corresponding to both sides of the slab width smaller than that of the central portion of the width (hereinafter referred to as "convex roll 3"). A technique is known in which the side is not reduced and only the central portion of the slab width is reduced. In Patent Document 4, a convex crown (flat surface) roll having a width of 200 mm to 240 mm on a convex plane is used, and a reduction of 0.5 mm to 10.0 mm per stage is obtained by applying reduction to a slab in an unsolidified state. It is written that it can be done. As the convex roll 3, a horizontal portion 20 is provided at the center position in the width direction (width center position 13) of the slab, and inclined portions 21 are provided on both sides of the horizontal portion 20 in the width direction, and the horizontal portion 20 and the inclined portion 21 A roll was used for the joining position of the above, so as to form the corner portion 15. Hereinafter, a roll having such a shape will be referred to as a "convex disc roll 5".

In adopting the convex roll 3 as the reduction roll 1 for reducing the slab, the present inventor does not use the roll (convex disc roll 5) forming the horizontal portion 20-corner portion 15-inclined portion 21 described above. , When the roll outer peripheral shape in the cross section including the roll rotation axis is a curved shape that is convex outward and has no corners as shown in FIGS. 1 and 2, when the roll is reduced by a predetermined reducing force. I came up with the idea that the amount of reduction could be increased. Hereinafter, the convex roll 3 forming a curved shape that is convex outward and has no corners is referred to as a “convex curved roll 4”.

FIG. 4 shows a cross section during continuous casting including the vicinity of the reduction roll pair 6. The reduction roll 1 and the reduction roll 2 form a reduction roll pair 6. The slab 10 during casting is supported from both sides by the support roll 40. The reduction roll pair 6 is arranged in a part of the support roll band. In each of FIGS. 4A to 4C, the region of the solid phase 47 increases and the region of the liquid phase 49 decreases toward the downstream side 44 in the casting direction 45. A solid-liquid coexisting layer 48 is formed between the solid phase 47 and the liquid phase 49. The crater end position 41 is the position where the entire thickness direction of the slab 10 becomes the solid phase 47. The crater end position 41 is located on the upstream side 43 of the reduction position 42 in FIG. 4 (A), exactly on the reduction position 42 in FIG. 4 (B), and on the downstream side 44 of the reduction position 42 in FIG. 4 (C). The distance from the reduction position 42 to the crater end position 41 in the casting direction 45 is referred to as "reduction-crater end distance L". When the crater end position 41 is on the downstream side 44 when viewed from the reduction position 42 (when the reduction position 42 is on the upstream side 43 when viewed from the crater end position 41) (see FIG. 4C), the reduction-crater end distance. L takes a positive value, and when the crater end position 41 is on the upstream side 43 when viewed from the reduction position 42 (when the reduction position 42 is on the downstream side 44 when viewed from the crater end position 41) (FIG. 4 (A)). (See), the reduction-crater end distance L takes a negative value.

First, by deformation analysis using the finite element method, using each of the convex disc roll 5 and the convex curved roll 4, the same reduction is applied to the slab being cast with a predetermined reduction-crater end distance L. The deformation behavior was determined to determine how much reduction amount could be obtained when the slab during continuous casting was reduced by force. The slab to be continuously cast is high carbon steel having a C content of 0.40% by mass, and the width W of the slab is 550 mm and the thickness is 400 mm. As shown in FIG. 3, the convex disc roll 5 has a horizontal portion 20 having a width of 200 mm at the center of the width, and inclined portions 21 having an inclination of 17 ° are provided on both sides of the horizontal portion 20. As shown in FIGS. 1B and 2, the convex curved roll 4 has a roll outer peripheral shape 11 in a cross section passing through the roll rotation shaft 12 and an arc shape 18 having an arc radius R ₁ of 400 mm. In both convex rolls 3, the roll radius r _{C at the} width center position 13 is 200 mm. The convex disc roll 5 is in contact with the slab only by the horizontal portion 20 and the inclined portion 21 up to a reduction amount of 10 mm. The convex curved roll 4 is in contact with the slab 10 with only 18 arcuate parts up to a reduction amount of 10 mm. As shown in FIG. 1, among the reduction roll pairs, the reduction roll 2 on the F side (lower side) is a flat roll, and each convex roll 3 is used for the reduction roll 1 on the L side (upper side).

In the deformation analysis by the finite element method, the convex disc roll 5 and the convex curve roll 4 are used as the reduction rolls, and the reduction force is 100 tons and 140 tons (the convex curve roll 4 has an additional 160 tons). The amount of reduction by the roll was evaluated. Regarding the reduction-crater end distance L defined above, distances of 6 points were set in the section from -4 m to + 5 m, and analysis was performed for the case where reduction was performed at each distance, and the reduction amount was calculated. FIG. 5 shows the result when the convex curve roll 4 is used, and FIG. 6 shows the result when the convex disc roll 5 is used, where the horizontal axis is the reduction-crater end distance L and the vertical axis is the reduction amount. In both the convex curve roll 4 and the convex disc roll 5, the reduction amount increases as the reduction-crater end distance L increases, that is, as the crater end position 41 is located downstream of the reduction position 42. Further, the larger the rolling force, the larger the rolling force.

First, for example, at the same reduction-crater end distance L = 0 m and a reduction force of 140 tons, the reduction amount was 2.5 mm for the convex disc roll 5, whereas it was 6.5 mm for the convex curved roll 4. It was confirmed that the convex curved roll 4 had about 2.5 times the sensitivity of the convex disc roll 5 as compared with the convex disc roll 5.

Secondly, looking at the amount of change in the amount of reduction when the reduction-crater end distance L is 0 m and 2 m, it is about 0.5 mm when the convex disc roll 5 is used at the same reduction force of 140 tons. On the other hand, when the convex curved roll 4 is used, the change in the rolling reduction amount is about 1 mm, and it can be confirmed that the convex curved roll 4 has about twice the sensitivity as compared with the convex disc roll 5. It was.

Next, in continuous casting using an actual continuous casting apparatus, the slab 10 is reduced by using the convex curved roll 4 as the reduction roll 1, and the reduction-crater end distance L is variously changed to measure the reduction amount. went. The slab size and composition to be cast are the same as in the above finite element method analysis, and the slab is a high carbon steel having a width W of 550 mm, a thickness of 400 mm, and a C content of 0.40% by mass. The shape of the convex curved roll 4 is the same as that of the above-mentioned finite element method analysis, and as shown in FIG. 2, the roll outer peripheral shape 11 in the cross section passing through the roll rotation axis 12 is an arc shape 18 having an arc radius R ₁ of 400 mm. There is. The roll radius r _{C at the} width center position 13 is 200 mm.

As shown in FIG. 1, a magnetostriction sensor for measuring the distance between the upper and lower roll support mechanisms is installed on both the reduction roll pair 6 and the roll pair 7 adjacent to the upstream side of the reduction roll pair 6 to measure the roll interval. The roll interval was set to 8 and the roll interval between the upper and lower rolls was measured. Regarding the reduction roll pair 6 in which the convex curved roll 4 is used as the reduction roll 1 on the upper surface side, the vertical roll interval in the center of the width is adopted as the roll interval. The difference between the roll interval of the adjacent rolls 7 on the upstream side and the roll interval of the reduction rolls 6 is defined as the reduction amount by the reduction rolls.

The rolling force of the rolling roll was set to 140 tons, and the casting speed was increased from a constant 0.40 m / min casting to a speed of 0.50 m / min by increasing the casting speed. At this time, the crater end position moves from the upstream side to the downstream side with the passage of time. The crater end position 41 for each elapsed time was calculated as an estimated position of the solidification position determined by heat transfer calculation reflecting the change history of the casting speed, and the reduction-crater end distance L was calculated. The timing from the reduction-crater end distance L to 5 m at a pitch of 0.5 m was calculated, and the reduction amount was obtained by averaging the measurement results of 0.25 m before and after each timing. The horizontal axis represents the reduction-crater end distance L, and the vertical axis represents the reduction amount, which are indicated by the ◆ marks in FIG. At the same time, the results of the finite element method analysis are indicated by ◇ in the figure. As is clear from FIG. 7, when the convex curved roll 4 is used as the reduction roll, the relationship between the reduction-crater end distance L and the reduction amount is the result of the finite element method analysis and the actual measurement result in the actual continuous casting. It can be seen that the agreement is very good.

In both the continuous casting actual measurement result and the finite element method analysis result, the reduction amount changes by 0.5 mm for every 1 m change in the reduction-crater end distance L in the range of about -2 m to + 3 m. In an actual continuous casting apparatus, the accuracy when measuring the change in the reduction amount is about 0.4 mm. Therefore, by measuring the reduction amount using a convex curved roll as the reduction roll, it is possible to measure the reduction-crater end distance within a range of ± 1.0 m.

Next, the requirements to be satisfied by the convex curved roll 4 which is the reduction roll used in the crater end position detection method of the present invention will be described below in the order of the first embodiment and the second embodiment.

The first embodiment of the present invention will be described with reference to FIGS. 1 and 2. In the reduction roll 1, the roll outer peripheral shape 11 in the cross section passing through the roll rotation shaft 12 has the following shape. First, the roll outer peripheral shape 11 constitutes a convex shape that projects outward in a region including the width direction center position (width center position 13) of the slab. The outside is a direction in which the outer circumference of the roll moves away from the roll rotation shaft 12. By constructing such a shape, the roll radius r _C becomes maximum at the width center position 13, and when the slab 10 is reduced, the amount of reduction on the slab surface becomes maximum at the width center position 13. Next, a predetermined length range from the width center position 13 on both sides in the roll width direction is defined as a "convex shape defined range 14". Under the reduction of the slab using the convex roll 3, the width both ends of the slab 10 have a large deformation resistance, so that the reduction is not performed. If the slab 10 is reduced in the convex shape defined range 14 or a width narrower than this, the reduction force required for reduction can be suppressed low while ensuring the required reduction amount. Therefore, if the convex shape of the reduction roll 1 is determined within the convex shape regulation range 14, the good reduction of the present invention can be performed. The convex shape within the convex shape defined range 14 is a curved shape that is convex outward and has no corners. The outward convex means that it is convex in the direction away from the roll rotation axis 12. As the roll radius r _{C at the} center of the width increases with respect to the reduction roll radius r _{E at} both ends of the convex shape specified range 14, the maximum reduction while keeping the reduction roll range in contact with the slab during reduction within the convex shape specified range. The amount can be increased. If the reduction roll radius at the width center position is 9 mm or more larger than the reduction roll radius at both ends of the convex shape specified range, it is possible to secure a sufficient reduction amount when used as the reduction roll of the present invention.

As the simplest and most effective shape among the convex shapes within the convex shape defined range 14, the arc shape 18 having a single arc radius R ₁ can be used as shown in FIG. At this time, the roll outer peripheral shape 11 in the convex shape defined range 14 constitutes an arch shape in which the length portion of the convex shape defined range 14 is the string 31. The length of the convex shape specified range 14 (the length of the chord 31) is s, the radius of the bow shape is R, and the height of the arc 32 of the bow shape (reduced roll radius r _{E at} both ends of the convex shape specified range and the roll radius at the width center position). When h (difference from r _C ) is h (convex shape margin), the following relationship is established. Let the central angle of the bow be 2θ.
h = R (1-cosθ) (Equation 2)
s = 2R · sinθ (Equation 3)
From these equations, the following equations are derived.
cos θ = (s ² -4h ² ) / (s ² + 4h ² ) (Equation 4)

Therefore, first, the convex shape defining range (s) and the convex shape margin (h) are determined, and when R that satisfies this condition is determined, θ is determined by substituting s and h into the above (Equation 4). Further, R can be determined by substituting θ into (Equation 2) or (Equation 3). For example, when s = 150 mm and h = 9 mm are targeted, R = 316 mm can be derived by substituting into the above equation. On the other hand, when R is determined in advance, the larger the convex shape defined range (s), the larger the convex shape margin (h). For example, when R = 400 mm is adopted in continuous casting with a slab width W = 550 mm, the convex shape defined range (s) is 0.4 × W = by the calculation using the above (Equation 3) and (Equation 4). If it is 220 mm, the convex shape margin (h) is 15.6 mm, and if the convex shape specified range (s) is 0.8 × W = 440 mm, the convex shape margin (h) is 66 mm.

As described above, when the convex shape defined range 14 (s) is 0.4 × W, when the radius R of the arc shape 18 is set to a suitable value of about 400 mm, the rolling radius at both ends of the convex shape defined range is reduced. The difference h (convex shape margin) between r _E and the roll radius r _C at the center of the width can be 9 mm or more, and a sufficient reduction margin can be secured when used as the reduction roll 1. Therefore, in the present invention, the convex shape defined range 14 is defined as 0.4 × W.

Convex shapes include the arc shape 18 having a single arc radius R ₁ , a parabolic shape, an elliptical shape, a hyperbolic shape, and a shape in which arcs having different radii depending on the location are smoothly connected. Can be selected arbitrarily from. In a curved shape having no corners, which constitutes a convex shape, the radius of curvature of the curve is preferably at least 1 × h or more. As a result, the effect of the present invention due to the convex shape being a curved line can be fully exhibited. The minimum radius of curvature of the curve is the same in the second embodiment described later.

The roll outer peripheral shape 11 on the outer side of the convex shape defined range 14 of the rolling roll and on the end side in the width direction is not particularly specified. Preferably, the outer peripheral shape is a straight line or a curved shape having no corners. When the roll shape at both ends in the width direction is a cylindrical shape 22, the outer peripheral shape of the roll is a combination of smooth straight lines and curves from the convex shape defined range 14 to the position of the cylindrical shape 22 and has corners. It is preferable to have a shape that does not. Immediately before connecting to the cylindrical shape 22, it is preferable to make an outwardly concave curve.

As the simplest and most effective shape of the roll outer circumference of the rolling roll, as shown in FIG. 2, a single convex shape defined range 14 and a predetermined range (radius R ₁ range 23) on both sides thereof are single. The arc shape 18 has an arc radius R ₁ , and the radius R ₂ range 24 on both sides thereof is a single arc shape 19 with an arc radius R ₂ and a concave shape is smoothly connected to the outside, and finally. A shape that smoothly connects to the straight line of the cylindrical shape 22 of the flat roll can be adopted. Since there are no corners in any part of the outer peripheral shape of the roll, the roll reduction amount in the reduction roll increases, the reduction range in the roll in the width direction exceeds the convex shape regulation range 14, and the cylindrical shape of the flat roll. Even when the reduction is performed until the 22 parts come into contact with the slab 10, any portion of the surface of the slab after the reduction can have a smooth surface without forming corners. As a result, it is possible to prevent rolling defects caused by the concave shape of the slab generated by rolling with the convex roll in the hot rolling in the post-process following the continuous casting.

As a requirement to be satisfied by the convex curved roll 4 which is the reduction roll of the present invention, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the reduction roll has the following shape as the outer peripheral shape of the roll in the cross section including the roll rotation axis. That is, in the first embodiment, the convex shape within the specified convex shape range is defined as a curved shape that is convex outward and has no corners. On the other hand, in the second embodiment, the convex shape within the specified convex shape is a combination of the outwardly convex curve 16 and the straight line 17 having a length of 0.25 × W or less, and the corner portion is formed. It is defined as a shape that does not have. The grounds for this determination will be described below.

The effectiveness of the second embodiment was also confirmed by deformation analysis using the finite element method. As the roll outer peripheral shape 11, as shown in FIG. 8A, for the combination of the convex curve 16 and the straight line 17, the convex curve has an arc shape 18 having an arc radius R ₁ of 0.8 × W, and the straight line 17 Provided a straight line portion of an arbitrary length parallel to the roll axis with the width center position 13 as the center, and smoothly connected the arc shape 18 and the straight line 17. After setting various lengths of the straight line 17, the casting conditions are adjusted so that the reduction-crater end distance L is 0 mm, the reduction force is set to 140 tons, and the reduction force is applied, and the deformation analysis is performed by the finite element method. The amount of reduction was calculated with. The result is shown in FIG. 8 (B). The length D of the straight line 17 is indicated by D / W in the figure. As the D / W becomes larger, that is, as the length D of the straight line 17 becomes longer, the reduction amount gradually decreases, but if the length D of the straight line 17 is in the range of 0.25 × W or less, the convex disc roll 5 It was found that a larger reduction amount can be achieved. Therefore, the second embodiment is also defined as the shape of the reduction roll of the present invention.

As described in detail above, as shown in FIG. 1 in the present invention, a pair of reduction roll pairs 6 is provided in the continuous casting apparatus, and at least one of the reduction rolls constituting the reduction roll pair 6 is a convex curved roll. By measuring the amount of reduction when the pressure is reduced by a predetermined reduction force, the distance between the reduction position 42 and the crater end position 41 when the crater end position 41 exists in the vicinity of the reduction roll pair 6. (Compression-crater end distance L) can be evaluated. However, in order to evaluate the crater end position 41 with high accuracy, the crater end is in the range where the reduction-crater end distance L is in the range of -2 m to + 3 m, which is a region where the change in the reduction amount is large with respect to the change in the reduction-crater end distance. There must be position 41. For example, when the reduction roll pair 6 is arranged at a position 2 m from the machine end 46 of the continuous casting apparatus to the upstream side 43, the existing area of the crater end position 41 is located 5 m to the upstream side from the machine end 46 to the machine end 46 position. When it is within the range, the crater end position 41 can be measured accurately, but when the crater end position 41 exists at a position 5 m or more away from the machine end 46 on the upstream side 43, the crater end position 41 is accurately measured. I can't evaluate it well.

In the present invention, by arranging the reduction roll pairs 6 provided with the convex curved roll 4 as the reduction roll 1 at at least two positions in the casting direction 45, the casting direction range in which the crater end position 41 can be evaluated accurately is expanded. can do. For example, the first reduction roll pair is arranged at a position 4 m upstream from the machine edge, and the second reduction roll pair is arranged 2 m upstream from the machine edge. If the crater end position is 6 m to 4 m upstream from the machine edge, it can be evaluated by the first reduction roll pair, and if it is 4 m to 2 m, it can be evaluated by both the first and second reduction roll pairs. ~ If it is the machine edge, it can be evaluated by the second reduction roll pair. At this time, in particular, in the range of the crater end position of 4 m to 2 m, the position can be estimated based on the two pairs of roll reduction amounts. The index S / N ratio = [signal strength] / [background noise] indicating the measurement sensitivity is proportional to √N times the number of times of data integration N. Therefore, if the reduction roll pair is a two-pair roll, the estimation accuracy is √2 times that of the pair roll. From this, it can be expected that the crater end position will be stabilized by more precise casting speed control. For example, it is effective when the crater end is short and there is a risk of overrun in position estimation using only a pair of rolls, such as low coal steel grades.

Using a curved bloom continuous casting device with a machine length of 30 m, which casts bloom with a slab shape of width: 550 mm and thickness: 400 mm, the component content is mass%, C: 0.4%, Si: The present invention was applied when casting high carbon steel having 0.5%, Mn: 1.4%, P: 0.03%, and S: 0.05%.

In the example of the present invention, as shown in FIG. 1, a reduction roll pair 6 in which the F-plane roll is a flat roll and the L-plane roll is a convex curved roll 4 is prepared at a position 26.5 m upstream from the machine edge. In both the reduction roll pair 6 and the roll pair 7 adjacent to the upstream side of the reduction roll pair, a magnetostrictive sensor for measuring the distance between the upper and lower roll support mechanisms is installed to form a roll interval measuring device 8, and a roll between the upper and lower rolls is used. The interval was measured and the reduction amount was evaluated. The rolling force was 140 tons.
As shown in FIG. 2, the convex curved roll 4 of the present invention includes a convex shape defined range 14 (a range of a total length of 0.40 × W = 220 mm on both sides in the roll width direction from the width center position). A roll having an arc shape 18 having a constant radius of 430 mm and a roll radius r _{C at the} width center position 13 larger than the reduction roll radius r _{E at} both ends of the convex shape defined range 14 was used. The roll radius r _{C at the} width center position 13 is 400 mm. The arc shape 18 in the convex shape defined range 14 continues to the outside of the convex shape defined range 14 (radius R ₁ range 23), and the radius R ₁ range 23 is 440 mm. After that, it is smoothly connected to the outwardly concave arc shape 19 (radius R ₂ range 24) with an arc radius R ₂ = 100 mm, and finally to a flat roll portion having a cylindrical shape 22 having a roll radius r _F 340 mm. are doing.

In the comparative example, when predicting the crater end position, the position was determined from the heat transfer calculation measured by the slab surface temperature measurement result with a radiation thermometer without using a reduction roll.

In both the examples of the present invention and the comparative examples, casting was performed at the maximum casting speed within a range in which the crater end position during casting was not on the downstream side of the machine edge. It was confirmed that the crater end position is on the upstream side of the machine edge because of the presence of internal cracks that occur at the solid-liquid interface under overpressure.

In the comparative example, it was necessary to set the target of the crater end position 41 at a position of 5.0 m from the machine end 46 to the upstream side 43.
On the other hand, in the example of the present invention, the reduction amount by the reduction roll pair 6 was constantly measured, and the casting speed was adjusted so that the reduction amount did not exceed 6 mm. As a result, the target of the crater end position 41 can be set to a position of 3.0 m from the machine end 46 to the upstream side 43. Due to the fact that the crater end position target could be changed from 5.0 m in the comparative example to 3.0 m in the example of the present invention, the average casting speed could be improved by 8%, and the productivity of the continuous casting apparatus could be increased. I was able to realize it.

1 Reduced roll 2 Reduced roll 3 Convex roll 4 Convex curved roll 5 Convex disc roll 6 Reduced roll vs 7 Adjacent roll 8 Roll interval measuring device 10 Slab 11 Roll outer circumference shape 12 Roll rotation shaft 13 Width center position 14 Convex shape Specified range 15 Square part 16 Curve 17 Straight line 18 Arc shape 19 Arc shape 20 Horizontal part 21 Inclined part 22 Cylindrical shape 23 Radius R ₁ Range 24 Radius R ₂ Range 31 String 32 Arc 40 Support roll 41 Crater end position 42 Reduction position 43 Upstream side 44 Downstream side 45 Casting direction 46 Machine end 47 Solid phase 48 Solid-liquid coexistence layer 49 Liquid phase L Reduction-crater end distance W Slab width r _C Width center position reduction roll radius r _F width End reduction roll Radius r _E Convex shape Specified range Reduction roll radius at both ends R ₁ Arc radius R ₂ Arc radius h Bow-shaped arc height s Bow-shaped string length θ Half of the center angle of the bow-shaped bow-shaped radius

Claims (2)

The slabs during continuous casting are reduced by a pair of reduction rolls (hereinafter referred to as "reduction roll pairs"), the reduction amount of the slabs by the reduction roll pair is measured, and the slabs are based on the reduction amount. This is a crater end position detection method for determining the solidification completion position (hereinafter referred to as "crater end position"), and the width of the slab to be cast is W (mm).
For at least one of the reduced rolls constituting the reduced roll pair, the outer peripheral shape of the roll in the cross section including the roll rotation axis is a region including the center position in the width direction of the slab (hereinafter referred to as “width center position”). A convex shape protruding outward is formed, and the convex shape has a total length of 0.40 × W on both sides in the roll width direction from the width center position (hereinafter referred to as “convex shape defined range”). Either a curved shape that is convex outward and has no corners, or a shape that is a combination of a curve that is convex outward and a straight line with a length of 0.25 × W or less and has no corners. A method for detecting a crater end position in continuous casting, wherein the reduction roll radius at the width center position is 9 mm or more larger than the reduction roll radius at both ends of the convex shape specified range. The crater in continuous casting according to claim 1, wherein the crater has at least two pairs of reduced rolls, the amount of reduction of the slab by each pair of reduced rolls is measured, and the crater end position is obtained based on the reduced amount. End position detection method.

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