JP2012030269A - Roll stand for continuous casting machine for performing partial high rolling-reduction of slab - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the porosity while reducing the reaction force from a cast slab, and to easily reduce the face-to-face distance between upper and lower rolls toward downstream side of the casting direction.SOLUTION: A roll stand installed on a horizontal path part of a continuous casting machine has an upper frame 11a, a lower frame 11b, and six pairs of roll pairs. Projecting parts 43b, 43d, 43f are mounted on rolls 412, 414, 416 mounted on the upper frame 11a. Two projecting parts are mounted on each of the rolls 412, 414, 416. The projecting parts 43b, 43d, 43f are each provided at the positions of ≥130 mm from ends at one side, of the rolls 412, 414, 416. The outside diameters of the projecting parts 43b, 43d, 43f are larger in this order.

Description

  The present invention relates to a roll stand installed in a horizontal portion of a continuous casting machine for slabs.

  In the continuous casting process of steel, the porosity generated inside the slab is reduced by reducing the slab in the casting direction at the end of solidification of the molten steel. At this time, when the slab is squeezed over the entire width direction, a large reaction force is received from the end of the slab width that quickly solidifies due to secondary cooling or the like, so that a load is applied to the roll and the bearing. As a result, it is necessary to increase the strength of rolls and bearings. In consideration of such points, in Patent Document 1, a width region (region disposed near the center of the slab) having a solid phase ratio of 0.7 or less so that only a necessary region can be preferentially reduced. The slab is squeezed down using a roll having a diameter of the roll body larger than the diameter of the roll body disposed at both ends in the width direction of the slab. Further, the porosity is gradually reduced by arranging the rolls in parallel in the casting direction from the position where the solid phase ratio of the slab becomes 0.3 or more to the complete solidification position.

  Patent Documents 2 and 3 do not aim to reduce porosity, but disclose techniques for locally reducing the slab for the purpose of reducing center segregation.

  The method disclosed in Patent Document 2 is a roll cylinder for the purpose of pressure-bonding both ends of the slab width at the solidification interface separated in the thickness direction of the slab after bulging the slab including the unsolidified portion. This is a method using a roll in which the roll diameter in the vicinity of both ends of the section is larger than the roll diameter in the center of the roll body. Before using the roll, the solidified interface at the center of the slab width is pressure-bonded using a flat roll having a constant roll diameter of the roll body, but the roll diameter in the vicinity of both ends of the roll body is at the center. Rolling with a roll larger than the roll diameter is to press both ends of the slab width at the solidification interface, which could not be crimped with a flat roll, and to concentrate the molten steel existing between the solidification interfaces on both sides in the casting direction. Since it aims at discharging | emitting downstream, this roll is arrange | positioned only at the last part before completion of solidification of molten steel.

  In the method disclosed in Patent Document 3, the quarter width position of the slab where the reduction amount is insufficient and 3 in the final solidification part of the continuous casting process so that the same reduction amount can be applied in the slab width direction. This is a method of rolling down the slab using a pair of rolls having a roll having a large diameter portion formed at a position corresponding to the slab end side from the / 4 width position.

Japanese Patent Application Laid-Open No. 08-257715 JP 2001-334353 A Japanese Patent Laid-Open No. 06-218510

  At the end of solidification of molten steel, the volume (thickness) of the slab decreases as the slab solidifies, so it is necessary to shorten the distance between the surfaces of the upper and lower rolls constituting the roll pair as it progresses downstream in the casting direction. It becomes. When all the rolls arranged in parallel in the casting direction have the same roll diameter, it is necessary to adjust the distance between the upper and lower rolls for each roll pair. When a plurality of pairs of rolls are provided together on one roll stand, it is necessary to adjust the distance between the upper and lower rolls by tilting the upper and lower stands that hold the upper and lower rolls. However, the adjustment of the distance between the surfaces of the upper and lower rolls requires a very complicated adjustment.

  In patent document 1, it is disclosed that the roll which made the diameter of the center vicinity of a roll trunk | drum larger than the diameter of both ends is arranged in parallel by the casting direction. However, the rolls arranged side by side are adjusted so that the diameter of the roll body corresponding to the width region (center part of the slab) having a solid phase ratio of 0.7 or less is larger than the diameters at both ends in the width direction. Therefore, it is considered that the plurality of rows of rolls (roll diameter) arranged in parallel in the casting direction are all the same roll (roll diameter). Therefore, in the method disclosed in Patent Document 1, in order to reduce the distance between the upper and lower rolls as the process proceeds downstream in the casting direction, the distance between the roll faces is adjusted for each roll pair, and the upper and lower rolls holding the upper and lower rolls are adjusted. It may be necessary to tilt the stand.

  Moreover, in patent document 2, the roll whose roll diameter near the both ends of a roll trunk | drum is larger than the roll diameter of the center part of a roll trunk | drum is arrange | positioned downstream of the flat roll in which the roll diameter of a roll trunk | drum is constant. Is disclosed. However, since only one of the above-mentioned rolls arranged downstream of the flat rolls has to be arranged at the final position before the solidification of the slab is completed, in Patent Document 2, the above-described rolls are excluded. Then, it is considered that flat rolls are juxtaposed in the casting direction. Moreover, in patent document 2, since it is not paying attention about the roll diameter of this flat roll, it is thought that all the flat rolls arranged in parallel by the casting direction are rolls of the same diameter.

  Furthermore, in patent document 3, although the roll which has arrange | positioned the large diameter part in the slab width position where the amount of reduction is insufficient is used, it is disclosed that this roll should be used only for a pair of rolls to the last. Has been. Therefore, in patent document 3, it is thought that the flat roll of the same diameter is arranged in parallel by the casting direction except the roll in which the above-mentioned large diameter part was formed. Moreover, even if the roll in which the above-mentioned large diameter part was formed was arranged in parallel by the casting direction, these rolls are considered to be a roll of the same outer diameter.

  From the above, also in Patent Documents 2 and 3, since it is considered that rolls with the same outer diameter are arranged in parallel in the casting direction, in order to shorten the distance between the upper and lower rolls as the process proceeds downstream in the casting direction. The complicated distance adjustment which adjusts the distance between the surfaces of the upper and lower rolls itself or tilts the upper and lower frames is required.

  Therefore, the object of the present invention is to reduce the porosity while reducing the reaction force received from the slab, and to move up and down as it goes downstream in the casting direction without performing complicated adjustment of the distance between the upper and lower rolls. It is an object of the present invention to provide a roll stand for a slab continuous casting machine that can easily shorten the distance between roll surfaces.

The present invention is a roll stand installed in a horizontal part of a continuous casting machine for slabs, and two or more pairs of rolls composed of an upper roll and a lower roll facing each other are juxtaposed in the casting direction. The upper roll and the lower roll are divided into 2 to 4 in the axial direction of the roll. Further, at least one of the upper roll and the lower roll is provided with a large-diameter convex portion having an outer diameter larger than that of the upper roll and the lower roll. Two or more large-diameter convex portions are provided apart from each other in the width direction of the slab in one row of rolls divided into 2 to 4 in the axial direction of the roll, and 2 to 4 in the axial direction of the roll. Of the two or more large-diameter convex portions provided on the divided one-row roll, the large-diameter convex portion provided on the outermost side in the width direction of the slab is closest to the large-diameter convex portion. It is arranged away from one end of the roll by a distance X that satisfies the following expression (1).
130 mm ≦ X (1)
Further, the center line in the width direction of the slab of the upstream large-diameter convex portion provided on the upstream roll and the casting of the downstream large-diameter convex portion provided on the downstream roll located downstream from the upstream roll. The center lines in the width direction of the pieces coincide with each other, and the outer diameter of the upstream large-diameter convex portion is smaller than the outer diameter of the downstream large-diameter convex portion.

According to the present invention, the large-diameter convex portions are arranged at a plurality of locations at positions where the porosity is likely to occur, in other words, at a width position separated by 130 mm or more from each of the width ends of the slab toward the width center. It is possible to effectively reduce the width position of the slab where porosity is likely to occur. Thereby, a porosity can be reduced. Further, the large-diameter convex portion is not disposed at a position in the width direction of the slab where the slab is rapidly solidified and has almost no porosity. Therefore, since the position is not reduced, the reaction force received from the slab at the time of reduction can be reduced.
Moreover, since the outer diameter of the upstream large-diameter convex portion is smaller than the outer diameter of the downstream large-diameter convex portion, the distance between the surfaces of the upper roll and the lower roll facing each other can be simplified as it proceeds downstream in the casting direction. Can be shortened.
Furthermore, since the upstream large-diameter convex portion and the downstream large-diameter convex portion are arranged so that the center lines in the width direction of the slab coincide with each other, the reduction position by the large-diameter convex portion is the width of the slab. Meandering in the direction can be prevented. Moreover, since the large diameter convex part is provided in the division | segmentation roll, the distance from the end of a large diameter convex part to the end of a division | segmentation roll can be shortened. As a result, it is possible to reduce the load applied to the bearing and the roll during the reduction.

Further, in the present invention, the large-diameter convex portion has a flat portion parallel to a roll body portion which is a portion where the large-diameter convex portion is not provided among the rolls provided with the large-diameter convex portion. The width of the flat portion of the upstream large-diameter convex portion is larger than the width of the flat portion of the downstream large-diameter convex portion, and the upstream large-diameter convex portion. the width W _i of the flat portion of the width W _{i + 1} of the flat part of the downstream large-径凸portion arranged in the immediate vicinity of the upstream large径凸portion preferably satisfies the following formula (2).
W _i −W _{i + 1} ≧ 10 mm (where i is a natural number) (2)

Since the slab located downstream is more solidified than the slab located upstream, the necessary rolling force increases as it progresses downstream. According to the above configuration, the surface area of the flat portion of the downstream large-diameter convex portion that reduces the slab is smaller than the surface area of the flat portion of the upstream large-diameter convex portion. It can be made larger than the rolling pressure by the upstream large-diameter convex portion. Therefore, the reduction pressure can be increased as it goes downstream.
Further, a depression is formed on the surface of the slab by the reduction of the large-diameter protrusion, and the amount of reduction can be measured by this depression. According to the above configuration, the width W _i of the flat portion of the upstream large-diameter convex portion is different from the width W _{i + 1 of} the downstream large-diameter flat portion disposed in the immediate vicinity of the upstream large-diameter convex portion by 10 mm or more. The amount of reduction by each large-diameter convex portion can be accurately determined. Thereby, it is possible to predict the cause of under-rolling and under-rolling by each large-diameter convex portion, and as a result, it is possible to quickly deal with such products.

  According to the present invention, since the large-diameter convex portion is arranged at a position where the porosity is likely to occur, the width position of the slab where the porosity is likely to be generated can be surely reduced and the porosity can be reduced. Since the large-diameter convex portion is not disposed at the slab width position where the slab is rapidly solidified and has almost no porosity, the reaction force that the roll receives from the slab during rolling can be reduced. Also, since the outer diameter of the upstream large-diameter convex portion is smaller than the outer diameter of the downstream large-diameter convex portion in one roll stand, the surfaces of the upper roll and the lower roll that face each other as they go downstream in the casting direction The distance can be shortened easily.

It is the whole continuous casting machine schematic. It is a figure which shows the structure of a roll stand. It is a figure which shows the structure of the roll of the anti-reference | standard side provided in the roll stand. It is a figure which shows the structure of a pair of roll provided in the roll stand. (A) is an enlarged view of the roll one end part shown in FIG. (B) is the elements on larger scale of the convex part shown to (a). It is sectional drawing of a slab. It is a figure which shows the UT defect occurrence ratio with respect to the distance from the end about the width direction of slab. It is a figure which shows the conditions used in the Example. It is a figure which shows the conditions used in the Example. (A)-(c) is a figure which shows the result of an Example.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(Continuous casting machine)
As shown in FIG. 1, the continuous casting machine 100 for slabs cools the tundish 1 and the molten steel poured from the tundish 1 through the immersion nozzle 2 to form a solidified shell (solidified shell) having a predetermined shape. A casting mold 3 to be formed and a plurality of roll pairs 4 provided in the secondary cooling zone are provided. The roll pair 4 is juxtaposed along the casting path Q from directly below the mold 3, and is provided on a roll stand (not shown).

  The roll pair 4 is composed of rolls 41 and 42 arranged to face each other across the casting path Q. The roll (upper roll) 41 is disposed on the opposite side of the casting path Q (the side corresponding to the upper side of the continuously cast slab). Further, the roll (lower roll) 42 is disposed on the reference side (the side corresponding to the lower side of the continuously cast slab). Each of the rolls 41 and 42 is divided into 2 to 4 in the axial direction of the roll (the width direction of the slab). In addition, about 4 to 8 rows of rolls 41 and 42 are juxtaposed in the casting direction on one roll stand. A plurality of roll stands are arranged in parallel along the casting path Q from directly below the mold 3. Cooling sprays 5 are provided between two rows of rolls 41 adjacent in the casting direction and between two rows of rolls 42 adjacent in the casting direction, respectively. The cooling spray 5 sprays a predetermined amount of cooling water onto the solidified shell (solidified shell transported through the casting path Q) pulled out from the mold 3.

  The casting path Q includes a vertical path portion extending in a substantially vertical direction, an arc path portion extending in an arc shape from the vertical path portion to the downstream side, and provided in the downstream of the arc path portion and extending in the horizontal direction. A horizontal path part (horizontal part) that exists, and a correction path part that smoothly connects the arc path part and the horizontal path part.

  Molten steel held in the tundish 1 is poured into the mold 3 through the immersion nozzle 2 and then cooled in the mold 3. Thereby, in the casting_mold | template 3, while a solidified shell is formed, the slab which has an unsolidified part inside is formed. The slab in the mold 3 passes through the casting path Q and is sent to the downstream side while being sandwiched between the plurality of roll pairs 4 and being cooled by the cooling water sprayed from the cooling spray 5. The solidified shell gradually solidifies and grows toward the inside of the slab, and finally, a slab that is completely solidified to the inside is formed.

  According to the continuous casting machine according to this embodiment, for example, a slab slab having a width of 2400 mm or less and a thickness of 230 to 400 mm can be cast. The steel type of the slab is not particularly limited. In this embodiment, FIG. 1 shows a vertical bending type continuous casting machine 100. However, the type of the continuous casting machine is not limited to the vertical bending type, and a bending type continuous casting machine may be used. Good.

  In the continuous casting machine 100, solidification of the molten steel is completed in the horizontal path portion of the casting path Q. The object of the present invention is to reduce the porosity existing in the slab by the reduction in the horizontal path portion, and in the horizontal path portion, the distance between the surfaces of the pair of rolls 41 and 42 as it goes downstream in the casting direction. Therefore, the configuration of a roll stand for achieving this object will be described below.

(Roll stand installed in horizontal path part (horizontal part) of casting path Q)
FIG. 2 shows a side view of a roll stand (hereinafter also referred to as “roll stand”) provided in the horizontal path portion of the casting path Q. FIG. 3 shows the configuration of a roll on the anti-reference side (a roll disposed on the side corresponding to the upper side of the cast slab to be cast) provided on the roll stand shown in FIG. FIG. 4 shows the configuration of a pair of rolls provided on the roll stand shown in FIG. 2 to 4 show one roll stand among the plurality of roll stands provided in the horizontal path portion of the casting path Q, the plurality of rolls provided in the horizontal path portion of the casting path Q. Since the stand has substantially the same configuration as the roll stand shown in FIGS.

  As shown in FIG. 2, the roll stand 10 includes six pairs of an upper frame 11a and a lower frame 11b that are arranged so as to face each other across a cast piece (horizontal path portion), and arranged in parallel in the casting direction. Has roll pairs. The upper frame 11a is disposed on the upper side (anti-reference side) of the horizontal path portion, and the lower frame 11b is disposed on the lower side (reference side) of the horizontal path portion. Six rows of anti-reference-side rolls 411, 412, 413, 414, 415, 416 (corresponding to the roll 41 shown in FIG. 1) arranged at a predetermined pitch in the casting direction are attached to the upper frame 11 a. . The lower frame 11b is provided with six rows of reference-side rolls 421, 422, 423, 424, 425, and 426 (corresponding to the roll 42 shown in FIG. 1) arranged at a predetermined pitch in the casting direction. Yes.

  2 to 4, six rows of reference-side rolls 41 installed on the upper frame 11a are designated as rolls 411, 412,..., 416 in order from the upstream, and six rows of rolls installed on the lower frame 11b. 42 are assumed to be rolls 421, 422,..., 426 in order from the upstream, and a pair of roll pairs is constituted by the rolls 411, 421, rolls 412, 422,. Further, as described above, the rolls 411,..., 416, 412,..., 416 are divided into 2 to 4 in the axial direction of the roll (width direction of the slab). In this embodiment, the divided rolls constituting the rolls 411, 412, ..., 416, 421, 422, ..., 426 are respectively directed from one end to the other end in the axial direction of the roll (in FIG. The three rolls in the same row are shown as follows in order (from the left end to the right end). The divided rolls constituting the roll 411 are divided rolls 411a, 411b, 411c, the divided rolls constituting the roll 412 are divided rolls 412a, 412b, 412c, and the divided rolls constituting the roll 413 are divided rolls 413a, 413b, 413c. .., And the divided rolls constituting the roll 422 are represented as divided rolls 422a, 422b, and 422c (hereinafter, omitted) (see FIGS. 3 and 4).

  As shown in FIG. 2, the rolls 411, 412, 413, 414, 415, and 416 on the anti-reference side are attached to the upper frame 11a via the axle box 12a. The reference-side rolls 421, 422, 423, 424, 425, and 426 are attached to the lower frame 11b via the axle box 12b. Bearings (not shown) are accommodated in the axle boxes 12a and 12b. The upper frame 11 a and the lower frame 11 b are disposed so as to be substantially parallel to each other and are fastened via four hydraulic cylinders 13. By injecting the drive oil into the hydraulic cylinder 13, the upper frame 11a can be raised or lowered. Note that the lower frame 11b does not move but is fixed. In addition, two convex portions (large-diameter convex portions) 43b, 43d, and 43f are attached to the anti-reference-side rolls 412, 414, and 416, respectively (see FIG. 3).

  During continuous casting of the slab (when the slab is squeezed down in the horizontal path portion), the same amount of drive oil is injected into each of the four hydraulic cylinders 13 to bring the upper frame 11a into the lower frame 11b. It is lowered while maintaining a substantially parallel state. In the present embodiment, as will be described later, since the outer diameters of the convex portions 43b, 43d, and 43f attached to the rolls 412, 414, and 416 are different from each other, the upper frame 11a is substantially parallel to the lower frame 11b. The distance between the surfaces of the reference-side roll and the non-reference-side roll facing each other can be easily shortened as it goes downstream in the casting direction.

(roll)
, 416 and rolls 421, 422,..., 426 are divided into 2 to 4 in the axial direction (the width direction of the slab). And the axial box 12a is each provided in the both ends of the division | segmentation roll (refer FIG. 3). By using the split roll, it is possible to prevent the roll from bending or to reduce the load on the bearing.

  As shown in FIG. 3, the rolls 412, 414, 416 (divided rolls 412a, 412c, 414a, 414c, 416a, 416b) are provided with convex portions 43b, 43d, 43f, respectively. Since the distance from one end of the convex portion to one end of the roll provided with the convex portion can be shortened by using a split roll for the roll on which the convex portions 43b, 43d, and 43f are provided, the load on the bearing at the time of rolling down Can be reduced.

  Although the number of divisions of the rolls 41 and 42 is not particularly limited, it is preferably 3 to 4 divisions from the relationship between the width of the slab slab and the position where the slab needs to be reduced (position where the convex portion is provided). . Moreover, in this Embodiment, the roll 41 and 42 whose length regarding the axial direction of the roll 41 is substantially the same length as the width | variety of a slab (slab) is used.

(Convex part (large diameter convex part))
As shown in FIG. 3, the roll 412 is provided with two convex portions 43 b separated in the width direction of the slab (see FIG. 4). Also, the roll 414 is provided with two convex portions 43d separated in the width direction of the slab. Also, the roll 416 is provided with two convex portions 43f separated in the width direction of the slab. Two convex portions 43b are respectively arranged at a distance from both ends of the roll 412 by a distance X _i. In other words, the convex portion 43 b, at the same one end of the nearest roll 412 are separated by a distance _{X i.} Further, the two convex portions 43d are disposed at positions separated from both ends of the roll 414 by a distance X _{i + 1} , respectively. Further, the two convex portions 43f are arranged at positions separated from both ends of the roll 416 by a distance X _{i + 2} . As for the convex portions 43d and 43f, similarly to the convex portion 43b, the convex portions 43b and 43f and one end of the rolls 414 and 416 closest thereto are separated by distances X _{i + 1} and X _{i + 2} , respectively.

  The convex portions 43b, 43d, and 43f have outer diameters larger than the outer diameters of the rolls 412, 414, and 416, respectively, and are short lengths in which hollows having substantially the same outer diameter as the roll 41 (412, 414, 416) are formed. It is a cylindrical member. Further, as shown in FIG. 2, the outer diameters of the convex portions 43b, 43d, and 43f are increased in this order, and the outer diameter of the convex portion attached to the roll positioned downstream is the roll positioned upstream. It is larger than the outer diameter of the convex part attached to. The outer diameters of the convex portions 43b, 43d, and 43f are based on the distance between the surfaces of a pair of rolls (a reference-side roll and an anti-reference-side roll that face each other) provided on the roll stand 10. Adjusted.

Further, as shown in FIG. 3, when the convex portions 43b, 43d, 43f are attached to the rolls 412, 414, 416, respectively, the trunk portions of the rolls 412, 414, 416 (the trunks of the rolls 412, 414, 416). And flat portions 44b, 44d, and 44f that are parallel to the portions to which the convex portions 43b, 43d, and 43f are not attached) (see FIGS. 3 and 4). In Figure 3, the width direction of the slab, the width of the flat portion of the convex portion 43b indicated as _{W i,} the width of the flat portion of the convex portion 43d shows a _{W i + 1,} the width of the flat portion of the protrusion 43f _{W i + 2} It is shown. These widths are W _i > W _{i + 1} > W _{i + 2} . In the present embodiment, the difference between W _i and W _{i + 1} and the difference between W _{i + 1} and W _{i + 2} are each 10 mm or more. Thus, the outer diameters and widths of the convex portions 43b, 43d, and 43f are different from each other.

  The convex portions 43b, 43d, and 43f are arranged at substantially the same position in the width direction of the slab. And the convex part 43b, 43d, 43f arrange | positioned in the substantially same position is arrange | positioned so that the center (dashed line shown in FIG. 3) regarding the width direction of each slab may correspond to a casting direction.

Next, the shape of a convex part is demonstrated using FIG. FIG. 5A is an enlarged schematic diagram of a region surrounded by a dotted line in FIG. 4, and FIG. 5B is an enlarged schematic diagram of a region surrounded by a dotted line shown in FIG. 5A and 5B, only the roll 412 and the convex portion 43b are shown, and the convex portions 43d and 43f are omitted. As shown to Fig.5 (a), the edge part 45b is formed in the both ends of the flat part 44b of the convex part 43b. Further, as shown in FIG. 5B, each of the edge portions 45b is subjected to smooth R processing (curvature radius: R) and a notch (notch angle: θ). . By forming R processing and a notch in the edge part 45b, it is possible to prevent wrinkles from being generated on the surface of the slab when the slab is being reduced. In FIG. 5, “W”, “R”, and “θ” indicate the following.
W: Width of the flat portion of the convex portion in the width direction of the slab R: Radius of curvature of R processing applied to the edge portion θ: Notch angle of the edge portion

  In the present embodiment, the radius of curvature R of R processing applied to the edge portion 45d is 10 mm or more and 25 mm or less, and the notch angle is 30 ° or more.

  Since the convex portions 43b, 43d, and 43f directly reduce the cast slab, the convex portions 43b, 43d, and 43f are preferably made of a material having substantially the same strength and hardness as the rolls 41 and 42.

  In FIG. 5, only the enlarged view of the convex portion 43b is shown, and the enlarged view of the convex portions 43d and 43f is omitted, but the edge portion 45b of the convex portion 43b is also connected to the edge portions of the convex portions 43d and 43f. Similarly, R processing is performed and a notch is formed.

  Then, the position where a convex part is arrange | positioned, the outer diameter of a convex part, and the edge part of a convex part are demonstrated in detail.

(Position (1) where the convex part is arranged)
An object of the present invention is to arrange a convex portion at a position where porosity is likely to occur in the width direction of the slab, and to reduce the porosity by reduction by the convex portion. Therefore, in the following, the position where the convex portion in the width direction of the slab is arranged will be described.

  In continuous casting, the solidification rate of the molten steel is not uniform in the width direction of the slab, and porosity is generated at a site where the solidification of the molten steel is slow. The reason why the solidification speed of the molten steel is not uniform in the width direction of the slab is mainly due to the discharge flow of the molten steel discharged from the immersion nozzle to the mold and the interference due to cooling of the solidified shell.

  The reason will be described in detail with reference to FIG. 6A and 6B are cross-sectional views of the slab in the mold. In the continuous casting of the slab, as described above, molten steel is poured from the immersion nozzle to the mold, and the molten steel is drawn downstream while forming a solidified shell having a predetermined shape in the mold. Since the molten steel flow discharged from the immersion nozzle to the mold collides with a specific part of the solidified shell in the mold, solidification of the molten steel is delayed at the collision part. For example, a two-hole immersion nozzle is generally used in a slab continuous casting machine. The immersion nozzle has a bottomed cylindrical shape, and a pair of opposed discharge holes are formed slightly above the inner bottom of the immersion nozzle. When this immersion nozzle is used, the molten steel flow discharged from the two discharge holes of the immersion nozzle each impinges on two specific portions of the solidified shell formed in the mold. Thereby, as shown to Fig.6 (a), solidification of molten steel becomes slow in two area | regions A inside a slab.

  In the mold, unsolidified molten steel is bulged by the static pressure. Thereby, in the width direction of the slab, the vicinity of the center of the unsolidified portion (region b shown in FIG. 6B) is in good contact with the mold and is easily cooled, but both ends of the unsolidified portion (FIG. 6). In the region a) shown in (b), the contact with the mold is not sufficient. Therefore, the solidification of the molten steel is slower at both ends (region a) of the unsolidified portion than near the center (region b) of the unsolidified portion (slab). Such non-uniform solidification of the molten steel in the mold is further promoted by the non-uniform solidification of the molten steel in the width direction of the slab in the secondary cooling zone.

  And the edge part (area | region shown in FIG.6 (b)) of the said non-solidified part corresponded with the collision location (area | region A shown in FIG.6 (a)) of the molten steel flow discharged from the immersion nozzle mentioned above. In this case, at the position in the width direction of the slab, since the solidification of the molten steel becomes very slow, the amount of generated porosity increases.

  It should be noted that both end portions in the width direction of the slab (region C shown in FIG. 6 (a), region c shown in FIG. 6 (b)), specifically, the thickness of the slab from both ends in the width direction of the slab. In the range of ½, solidification of the molten steel proceeds inward from the upper surface, the lower surface and the side surface. On the other hand, in the region excluding ½ width of the slab thickness from both ends of the slab, the solidification of the molten steel proceeds from the upper surface and the lower surface only to the inside. Therefore, at both ends in the width direction of the slab (region C shown in FIG. 6A, region c shown in FIG. 6B), the solidification of the molten steel is fast and there is almost no porosity.

  Further, for the reasons described above, it is presumed that the porosity is likely to occur on opposite sides (laterally symmetrical positions around the width center) across the center in the width direction of the slab.

  Considering the above points, the flow rate and amount of molten steel discharged from the immersion nozzle to the mold, the thickness and width of the slab, and the secondary cooling conditions (the amount of cooling water from the cooling spray, the solidification rate, etc. ) And the like, a position where solidification of the molten steel is delayed in the width direction of the slab, in other words, a position where porosity is likely to occur in the width direction of the slab can be estimated.

  As described above, since the solidification of the molten steel is completed in the horizontal path portion of the casting path Q, the solidification of the molten steel proceeds in advance. There is almost no porosity at the location where the solidification of the molten steel has progressed, and if this location is reduced, the reaction force received from the slab increases the load on the rolls and bearings. Therefore, if the convex portion is disposed only in the position in the width direction of the slab where the solidification of the molten steel is slow, in other words, the position where the porosity exists, the porosity can be effectively reduced, and It is possible to reduce the reaction force received.

  Next, an example showing the relationship between the position in the width direction where the porosity of the cast slab slab is generated and the amount of the generated slab slab will be described with reference to FIG.

  FIG. 7 shows the relationship between the distance from one end of the slab width (distance from one end to the other end in the width direction of the slab) and the UT defect occurrence ratio. A UT defect (UT defect) is a defect generated in a product obtained by rolling a cast slab (hereinafter referred to as a final product), and is caused by the porosity remaining in the cast slab. It will occur. Therefore, a large UT defect occurrence ratio indicates that the amount of porosity remaining in the cast slab is large. Further, in a part where the UT defect occurrence ratio exceeds 1%, there is a practical problem in the quality of the final product in that part. Therefore, it is preferable that the UT defect occurrence ratio in all width directions of the slab is 1% or less.

  The conditions for continuous casting of the slab cast obtained in the example shown in FIG. 7 will be described below. In this example, a slab slab having a thickness of 280 mm and a width of 2100 mm was cast. In the continuous casting machine used for this continuous casting, the roll stand installed in the horizontal path portion has an upper frame, a lower frame, and a plurality of pairs of rolls arranged in parallel in the casting direction. The rolls constituting the roll pair were flat rolls having a constant outer diameter of the roll body. Moreover, all the rolls provided in the roll stand were rolls having the same outer diameter. Therefore, when rolling down the slab, by tilting at least one of the upper frame and the lower frame, the rolls on the reference side (rolls attached to the upper frame) that face each other as they go downstream in the casting direction Adjustment was made so that the distance between the surface and the roll on the opposite side (the roll attached to the lower frame) was short. In addition, since the other structure of the continuous casting machine used by this example is substantially the same as the structure of the continuous casting machine of this embodiment, description is abbreviate | omitted.

  From FIG. 7, in this example, from one end in the width direction of the slab, the region is 180 mm or more and 400 mm or less (width 220 mm), the region is 740 mm or more and 800 mm or less (width 60 mm), and is 1100 mm or more and 1180 mm or less. The UT defect occurrence ratio exceeded 1% in the four width regions of the region (width 80 mm) and the region (width 200 mm) that was 1740 mm or more and 1940 mm or less. On the other hand, it can be seen that almost no porosity is generated in the width region of the slab excluding the above four regions. Further, from FIG. 7, the reason why the UT defect occurrence ratio exceeds 1% in the above-mentioned width region is affected by the above-described interference caused by the discharge flow of molten steel discharged from the immersion nozzle and the cooling of the solidified shell. I guess that.

  Therefore, in the above example, in the roll stand installed in the horizontal path portion, if the convex portions are arranged in the regions in the width direction of the four slabs, the porosity generated in those regions can be reduced. Therefore, it becomes possible to make the UT defect occurrence ratio 1% or less in all the width directions of the slab.

  In detail, the convex part whose width | variety of a flat part is 240 mm is arrange | positioned in the position 170 mm away from the end regarding the axial direction of a slab. Moreover, the convex part whose width | variety of a flat part is 80 mm is arrange | positioned in the position away 720 mm from the end regarding the axial direction of a slab. Moreover, the convex part whose width | variety of a flat part is 100 mm is arrange | positioned in the position 1100 mm away from the end regarding the axial direction of a slab. Moreover, the convex part whose width | variety of a flat part is 220 mm is arrange | positioned in the position 1720 mm away from the end regarding the axial direction of a slab. Thereby, the porosity which generate | occur | produced in the said area | region can be reduced reliably. Moreover, it is possible to reduce the reaction force from the slab that is received during the rolling by not arranging the convex portion in the width region of the slab excluding the above-described region, in other words, in the portion where solidification of the molten steel has progressed. As described above, the position where the amount of generated porosity is large is assumed to be positions opposite to each other across the center in the width direction of the slab (symmetrical with respect to the width center). In this example, the convex part having a flat part width of 240 mm is disposed at a position 170 mm away from both ends in the axial direction of the slab, and the convex part having a flat part width of 80 mm is disposed on the axis of the slab. It was also generated in the above-mentioned region by disposing a convex portion having a flat portion width of 100 mm at a position distant from one end with respect to the direction at a distance of 1100 mm from one end with respect to the axial direction of the slab. The porosity can be surely reduced, and the reaction force from the slab received during rolling can be reduced.

  From the reasons and examples described above, the convex portions are positions separated by 130 mm or more from the both ends in the width direction of the slab toward the center of the width, respectively, and from both ends in the width direction of the slab toward the center of the width. At a position within 600 mm. Positions in the above range are susceptible to the influence of interference caused by cooling of the molten steel discharged from the immersion nozzle and the solidified shell, so that solidification of the molten steel is slow and porosity is likely to occur. Therefore, the porosity can be effectively reduced by arranging the convex portions at positions in the width direction of the slab in this range.

  Note that, as described above, the solidification of the molten steel is performed in the regions less than 130 mm from both ends in the width direction of the slab, in other words, in the regions from both ends in the width direction of the slab to each half of the thickness of the slab. However, since it progresses from the upper surface, the lower surface and the side surface to the inside, solidification of the molten steel is fast. Therefore, since there is almost no porosity in this region, the necessity for reduction is low. Further, in this region, since the solidification of the molten steel proceeds, the reaction force received from the slab when the range is reduced is large. Therefore, it is possible to reduce the load applied to the roll and the bearing by not arranging the convex portion in this region.

  Also, solidification of the molten steel relatively progresses in a region exceeding 600 mm from both ends in the width direction of the slab toward the center of the width, in other words, in the vicinity of the center in the width direction of the slab. This is because, as described above, the unsolidified molten steel bulges in the mold, so that the vicinity of the center in the width direction of the slab is in good contact with the mold, and the solidification of the molten steel proceeds rapidly. is there. Therefore, in this region, since the amount of porosity generated is relatively small, the necessity for reduction is relatively low. Further, in this region, since the solidification of the molten steel is relatively advanced, the reaction force received from the slab when the range is reduced is large. Therefore, it is possible to reduce the load applied to the roll and the bearing by not arranging the convex portion in this region.

  Since the width of the slab and the length in the axial direction of the roll are substantially the same length, the convex portions are respectively positioned 130 mm or more away from the both ends in the axial direction of the roll toward the center. The above-mentioned effect is acquired by arrange | positioning and arrange | positioning in the distance within 600 mm toward the center from the both ends about the axial direction of a roll, respectively.

Therefore, when attaching the convex part to the roll, the distance X (X _i , X _{i + 1} , X _{i + 2} shown in FIG. 3) between the convex part and one end of the roll closest to the convex part is separated by a distance that satisfies the following formula: , Arrange the convex part.
130 mm ≦ X ≦ 600 mm (1)
Since porosity is estimated to occur at positions opposite to each other with respect to the center of the slab in the width direction (symmetrical with respect to the center of the width), X is X ≦ (casting 1/2) of the width of the piece.

In the present embodiment, the convex portions are arranged so that the distances X _i , X _{i + 1} , and X _{i + 2} shown in FIG. 3 satisfy the above expression (1).

  The number of projections provided on one roll is the position where porosity occurs, in other words, the amount of molten steel discharged from the immersion nozzle to the mold and its flow rate, the thickness and width of the slab, and Depending on the secondary cooling conditions (the amount of cooling water from the cooling spray, the solidification rate, etc.), as described above, the porosity is on the opposite side (width) across the width center of the slab. Since it is estimated that a large number of positions occur symmetrically with respect to the center, two or more convex portions are provided on one roll and the convex portions are arranged in the axial direction of the roll (the width direction of the slab). ) Separated.

(Width of convex part (1))
As described above, by arranging the convex portion in the width region of the slab where porosity is generated, the porosity can be surely reduced, but in order to reduce the reaction force from the slab that is received during rolling In this case, it is only necessary to arrange the convex portions only in the region where the amount of porosity is large. Therefore, by adjusting the width W of the flat portion of the convex portion so as to correspond to the width of the region where the amount of generated porosity is large, the reaction force from the slab received during rolling can be surely reduced. . As described above, the width region of the slab where porosity is likely to occur is the discharge rate and flow rate of molten steel from the immersion nozzle to the mold, the thickness and width of the slab, and the secondary cooling conditions (from the cooling spray). In consideration of these conditions and the example shown in FIG. 7, the width of the region where the amount of generated porosity is large is about 80 mm or more and within about 400 mm. Presumed to be. Therefore, the width W of the flat portion of the convex portion is 80 mm or more and 400 mm or more. Thereby, while being able to reduce a porosity reliably, it becomes possible to reduce the reaction force received from a slab reliably.

In the present embodiment, the width W _i of the convex portion 43b, the width W _{i + 1} of the convex portion 43d, and the width W _{i + 2} of the convex portion 43f shown in FIG. 3 are 80 mm or more and 400 mm or more.

(Position where the convex part is arranged (2))
As shown in FIG. 3, the centers (the alternate long and short dash lines shown in FIG. 3) of the convex portions 43b, 43d, and 43f in the width direction of the slab coincide with the casting direction. When the centers of the convex portions of the slabs provided on the rolls in different rows do not coincide with the casting direction, the rolling position meanders in the width direction of the slabs, so that the load on the bearing increases. Therefore, as shown in FIG. 3, the center in the width direction of the convex slabs provided on the rolls in different rows, in other words, in the width direction of the convex slab provided in the upstream roll. If the center and the center in the width direction of the slab of the convex portion provided on the roll located on the downstream side are substantially coincided with the casting direction, the reduction position does not meander in the width direction of the slab. The applied load can be reduced.

(Position where the convex part is arranged (3))
In the roll stand shown in FIG. 3, the slab is pressed down by the convex portion. Accordingly, when the convex portions are concentrated and arranged at a specific location such as the upstream side or the downstream side within the roll stand, the specific roll, the specific bearing, and the specific hydraulic pressure within the roll stand during the reduction. The load is concentrated on the cylinder. For example, in the roll stand shown in FIG. 3, when the convex portions are arranged on the rolls 411, 412, and 413 on the upstream side in the casting direction, the rolls 411 and 412 arranged on the upstream side in the casting direction on the roll stand. , 413, the bearing, and the load are concentrated on the hydraulic cylinder. Therefore, in order to prevent this, it is preferable to arrange the convex portions uniformly in the casting direction. In addition, by arranging the projections uniformly in the casting direction, the reaction force received by the upper and lower frames can be distributed throughout the upper and lower frames when the slab is being reduced. Can be reduced. For example, as shown in FIG. 3, the protrusions are arranged on the rolls 412, 414, and 416 in the second, fourth, and sixth rows provided on the roll stand 10, respectively. 43b, 43d, 43f are provided. In the roll stand 10, all the rolls 411, 412, 413, 414, 415, 416 are provided with convex portions, or the rolls 411, 413, 415 in the first, third and fifth rows are provided with convex portions. The projections can be evenly arranged in the casting direction.

(Diameter of convex part)
As the solidification of the molten steel proceeds, the volume (thickness) of the slab decreases. Therefore, in the horizontal path portion of the casting path Q, which is the final stage of solidification of the molten steel, as the downstream of the casting direction proceeds, It is necessary to shorten the distance between the roll 41 and the reference roll 42 (see FIG. 1). As a method of adjusting the distance between the surfaces of the rolls facing each other, for example, there is a method of inclining at least one of the upper frame and the lower frame constituting the roll stand. This method requires very complicated adjustment. . In the present embodiment, as shown in FIG. 2, the outer diameters of the convex portions 43b, 43d, and 43f attached to the rolls 412, 414, and 416 are increased in this order. Accordingly, by lowering the upper frame 11a while maintaining a state substantially parallel to the lower frame 11b, the distance between the surfaces of the reference-side roll and the anti-reference-side roll facing each other is reduced in the downstream in the casting direction. It can be shortened easily as it goes to. Therefore, complicated adjustment of inclining at least one of the upper frame 11a and the lower frame 11b becomes unnecessary.

Specifically, in the plurality of convex portions arranged in the casting direction, the outer diameter of the convex portion attached to the roll arranged on the upstream side is d _i , and the convex portion attached to the roll arranged downstream from the roll Is expressed as d _{i + 1} , and the outer diameter of the convex portion attached to the roll arranged downstream from the roll arranged downstream is d _{i + 2} ,.
d _i <d _{i + 1} <d _{i + 2} <... (where i is a natural number)

  In the present embodiment, as shown in FIG. 2, the outer diameter of the convex portion 43b <the outer diameter of the convex portion 43d <the outer diameter of the convex portion 43f. Therefore, by simply lowering the upper frame 11a while maintaining a state substantially parallel to the lower frame 11b, the distance between the surfaces of the rolls can be easily shortened as it proceeds downstream in the casting direction. The outer diameters of the protrusions 43b, 43d, and 43f are not particularly limited as long as the above requirements are satisfied, and the outer diameter appropriate for those skilled in the art depends on the shape of the slab (such as width and thickness), the steel type, and the operating conditions. The diameter can be set.

(Width of the flat part of the convex part)
In the horizontal path portion of the casting path Q, which is the final stage of solidification of the molten steel, the solidification of the molten steel progresses as it progresses downstream in the casting direction, so it is necessary to increase the rolling force. In this embodiment, since the slab is rolled down by the convex portions 43b, 43d, and 43f, the rolling pressure can be adjusted by adjusting the surface area of the convex portions 43b, 43d, and 43f. Specifically, by reducing the width of the flat portions 44b, 44d, and 44f of the convex portions 43b, 43d, and 43f, the surface areas of the flat portions 44b, 44d, and 44f of the convex portions 43b, 43d, and 43f are reduced. The pressure can be increased.

  The widths of the convex portions 43b, 43d, and 43f can be determined based on the minimum required reduction force downstream in the casting direction. In addition, although the width | variety of the convex part attached to the roll located downstream and the width | variety of the convex part attached to the roll arrange | positioned upstream may be the same width, as mentioned above, on the downstream side, Since the solidification of the molten steel is proceeding more than the upstream side, a larger rolling pressure than that of the upstream side is required. Then, the width of the convex part attached to the roll arrange | positioned downstream is made smaller than the width | variety of the convex part attached to the roll arrange | positioned upstream.

From the above, in the plurality of convex portions arranged in the casting direction, the width of the convex portion attached to the roll arranged on the upstream side is W _i (where i is a natural number), and the roll arranged downstream of the roll. When the width of the convex portion attached to is W _{i + 1} and the width of the convex portion W _{i + 2} attached to the roll arranged on the downstream side of the roll arranged downstream thereof,.
W _i > W _{i + 1} > W _{i + 2} >...

  Moreover, a concave shape is formed on the surface of the slab by the reduction of the convex portion. The amount of reduction can be measured from this concave shape. If the width of the convex part arranged upstream is different from the width of the convex part arranged downstream, the difference in concave shape due to each convex part arranged in the casting direction will be clarified, so the position where the reduction amount is insufficient In addition, it becomes easy to determine the cause of the under-rolling, and it is possible to quickly cope with the product due to the under-rolling.

In consideration of the above points, the width W _{i of the} convex portion disposed on the upstream roll and the width W _{i + 1} of the convex portion disposed on the downstream downstream roll satisfy the following expression. It is preferable.
W _i −W _{i + 1} ≧ 10 mm (where i is a natural number, i = 1, 2, 3,...)

In the present embodiment, the width of the convex portion 43b (W _i shown in FIG. 3), the width of the convex portion 43d (W _{i + 1} shown in FIG. 3), and the width of the convex portion 43f (W _{i + 2} shown in FIG. 3) are convex. The width of the portion 43b> the width of the convex portion 43d> the width of the convex portion 43f.
Further, the width of the convex portion 43b−the width of the convex portion 43d ≧ 10 mm, and the width of the convex portion 43d−the width of the convex portion 43f ≧ 10 mm.

(Edge of convex part)
As described above, since the concave shape is formed on the surface of the slab by the convex portion after the reduction, if the edge portion of the convex portion is pointed, the surface defects due to the concave shape remain in the final product. There is. Therefore, the surface flaw of the slab is reduced by subjecting the edge portion of the convex portion to R processing or forming a notch. On the other hand, the R-processed part and the notched part of the edge part receive a reaction force from the slab at the time of rolling, as in the flat part of the convex part. The reaction force received from the slab with respect to the R portion is increased, and when the notch angle θ is too small, the reaction force received from the slab with respect to the notch surface is increased. Therefore, it is preferable that the curvature radius R in the R processing is 10 mm or more and less than 25 mm. Further, the notch angle θ is preferably 30 ° or more.

As described above, the continuous casting machine 100 according to this embodiment has the following effects. The two convex portions 43b are arranged at positions where porosity is likely to be generated, in other words, at positions separated by distance X _i from the both ends of the roll 412 toward the center of the width. Further, the two convex portions 43d are arranged at positions separated from each of the both ends of the roll 414 by a distance X _{i + 1} toward the center of the width. Further, the two convex portions 43f are arranged at positions separated from each of both ends of the roll 416 by a distance X _{i + 2} toward the center of the width. Therefore, the position in the width direction of the slab where the porosity exists can be effectively reduced by the convex portions 43b, 43d, and 43f. Thereby, a porosity can be reduced. Further, since the large-diameter convex portion is not disposed at the position in the width direction of the slab where the slab is rapidly solidified and has almost no porosity, the position is not reduced. Therefore, the reaction force received from the slab at the time of rolling down can be reduced.

In addition, the widths W _i , W _{i + 1} , and Wi _{+ 2} of the flat portions 44b, 44d, and 44f of the convex portions 43b, 43d, and 43f are formed to have a size corresponding to the width of the region where the amount of porosity is large. Therefore, the porosity can be surely reduced and the reaction force received from the slab can be surely reduced.

  Furthermore, in one roll stand 10, since the outer diameter of the convex portion 43b> the outer diameter of the convex portion 43d> the outer diameter of the convex portion 43f, the upper frame 11a is substantially parallel to the lower frame 11b. By descending while maintaining the state, the process proceeds downstream in the casting direction. Therefore, the distance between the surfaces of the reference-side roll and the semi-reference-side roll facing each other can be easily shortened.

  And since convex part 43b, 43d, 43f arrange | positioned in the same width position of slab is arrange | positioned so that those centerlines may correspond, the reduction position by convex part 43b, 43d, 43f is slab. Do not meander in the width direction. Thereby, the load concerning bearing 12a, 12b, roll 412,414,416, etc. can be reduced. Moreover, since convex part 43b, 43d, 43f is provided in the division | segmentation roll 412a, 412c, 414a, 414c, 416a, 416c, the distance from the end of a convex part to the end of a division | segmentation roll can be shortened. Thereby, it is possible to reduce a load applied to the bearing and the roll when the slab is being reduced.

Further, since the widths W _i , W _{i + 1} , and Wi _{+ 2} of the flat portions 44b, 44d, and 44f of the convex portions 43b, 43d, and 43f are W _i > W _{i + 1} > W _{i + 2} , the flat portions 44b, 44d, and 44f are in this order. , Their surface area is getting smaller. As a result, the rolling force can be increased as it proceeds downstream.

Furthermore, to meet the width _{W i} of the flat portion 44b, the width _{W i + 1} of the flat portion 44d, and a width _{W i + 2} of the flat portion 44f _{is, W i -W i + 1 ≧} 10mm and _{W i + 1 -W i + 2} ≧ 10mm, The amount of reduction by each of the convex portions 43b, 43d, and 43f can be accurately determined. Thereby, it is possible to predict the cause of under-rolling and under-rolling caused by each of the convex portions 43b, 43d, and 43f, and thus it is possible to quickly deal with such products.

  Next, examples according to the present invention will be described.

  Based on the boundary conditions shown in Tables 1 and 2 and the physical property values shown in FIGS. The roll reaction force with respect to the notch angle θ of the edge portion of the convex portion and the roll reaction force with respect to the radius of curvature (R) of the edge portion of the convex portion were obtained. The configuration of the continuous casting machine according to the present embodiment is the same as that of the above-described embodiment except for the boundary conditions shown in Tables 1 and 2, the position where the convex portion is disposed, the notch angle θ and the radius of curvature (R). Since it is a continuous casting machine of the structure substantially the same as this continuous casting machine, description is abbreviate | omitted.

<Analysis method>
(Procedure 1)
Various heat transfer boundary conditions for slabs shown in Table 1, solid phase density, liquid phase density and solidification latent heat of medium carbon steel shown in Table 2, and conditions shown in FIGS. 8A and 8B ("industrial furnace design manual" ”, Nippon Steel Forging Association, P. 71), and conducted heat transfer and solidification analysis. For heat transfer and solidification calculations, “CASTEM” (“Kobe Steel Technical Report”, 1987, Vol. 37, No. 4, P. 99-100, and “Kobe Steel Technical Report” , 1985, Vol. 35, No. 2, P. 75). Based on the above analysis, the temperature distribution (relationship between solid phase ratio and temperature) shown in FIG. 8C was calculated.

The heat transfer coefficient (α) of the secondary cooling was calculated using the following Mitsuka-Hoogendome formula (Japan Iron and Steel Institute Special Report, No. 29, forced cooling of steel, p. 19).
log α = 2.358 + 0.663 log W−0.00147θS
Here, W is the water density (l / m ² · min), and θs is the slab surface temperature (° C.). As the water density W, a value obtained by dividing the amount of water distributed to each part of the continuous casting machine by the number of nozzles was used.

(Procedure 2)
Next, using the temperature distribution shown in FIG. 8 (c), the conditions shown in FIGS. 9 (a) and 9 (b), and the various heat transfer boundary conditions shown in Table 1, an elasto-plastic analysis is performed. The reaction force received from one piece (hereinafter referred to as roll reaction force) was determined. For analysis, “ABAQUS”, which is widely used, was used. The results are shown in FIGS. 10 (a) to (c).

In the elasto-plastic analysis, the slab slab was calculated by a ½ model that was symmetric about the center in the width direction. Further, it was assumed that a spherical porosity with a diameter of 3 mm was present at the center of the slab before the horizontal path portion was reduced. Further, the roll installed on the roll stand was made of a rigid body, and analysis was performed in consideration of the movement and rotation of the roll. The conditions for the heat transfer solidification analysis and the bullet composition analysis are shown below.
<Conditions for heat transfer solidification analysis and bullet composition analysis>
-Number of roll rows installed on one roll stand: 6 rows-Roll pitch (distance between adjacent rolls arranged side by side in the casting direction): 270 mm
-Arrangement of convex portions: In one roll stand, the convex portions were placed on the rolls in the second, fourth, and sixth rows from the upstream to the downstream in the casting direction. Two convex portions were attached to each roll in the second, fourth, and sixth rows. The two convex portions attached to one row of rolls were provided apart in the width direction of the slab.
・ Cross section in the casting direction of the slab slab: (thickness) 250 to 400 mm × (width) 1000 to 2400 mm

  FIG. 10A shows the roll reaction force with respect to the distance from one end of the roll to the convex portion. FIG. 10B shows the roll reaction force with respect to the notch angle (θ) of the edge portion of the convex portion. FIG.10 (c) has shown the roll reaction force with respect to the curvature radius (R) of the edge part of a convex part.

Moreover, each analysis condition of Fig.10 (a)-(c) is shown below.
(Fig. 10 (a))
FIG. 10A shows the result of analysis when R processing is performed on both edge portions of the convex portion (when notches are not formed). In the following analysis conditions, the amount of reduction indicates the difference between the “outer diameter of the convex portion” and the “outer diameter of the roll”.
<Analysis conditions>
・ Slab width: 2100mm
-Rolling amount: 18mm
-Width W of the flat part of the convex part: 100 mm
-Curvature radius (R) of the convex edge: 10 mm
(Fig. 10 (b))
FIG. 10 (b) shows the result of analysis when both edges of the convex portion are subjected to R machining and a notch is formed.
<Analysis conditions>
・ Slab width: 2100mm
-Rolling amount: 18mm
-Width W of the flat part of the convex part: 100 mm
-Curvature radius (R) of the convex edge: 10 mm
・ Cut width of edge part: 5mm / one side (10mm / both sides)
-Distance from one end of the roll to the center in the width direction of the convex slab: 215 mm
(Fig. 10 (c))
FIG. 10 (c) shows the result of analysis when both edges of the convex portion are R-processed and notches are formed.
<Analysis conditions>
・ Slab width: 2100mm
-Rolling amount: 18mm
-Width W of the flat part of the convex part: 100 mm
・ Notch angle (θ): 30 °
・ Cut width of edge part: 5mm / one side (10mm / both sides)
-Distance from one end of the roll to the center in the width direction of the convex slab: 215 mm

  The basic static radial load rating (Cor) of a bearing (24024 type (outer diameter 180 mm × inner diameter 120 mm × width 60 mm)) generally used in a continuous casting machine is 70 tonf. If the upper limit of the total load that does not damage the bearing is 70 kgf and the roll reaction force exceeds 70 kgf, it is assumed that the bearing cannot withstand the roll reaction force (load) and is damaged. If the load is applied equally to each other, the safety factor is 2. Therefore, in this case, if the roll reaction force is 70 kgf, the load applied to one bearing (bearing provided at one end of the roll) is 35 kgf. Become.

<Analysis result>
From FIG. 10 (a), when the distance from one end of the roll to the convex portion is less than 130 mm, the roll reaction force exceeds 70 kgf, so that it is estimated that the bearing is damaged. For this reason, damage to a bearing can be prevented by making the distance from a roll one end to a convex part 130 mm or more.

  From FIG. 10 (b), when the notch angle of the edge portion of the convex portion is less than 30 °, it is estimated that the bearing is damaged because the roll reaction force exceeds 70 kgf. For this reason, damage of a bearing can be prevented by making the notch angle of the edge part of a convex part into 30 degrees or more.

  From FIG.10 (c), when the curvature radius (R) of the edge part of a convex part exceeds 25 mm, since a roll reaction force exceeds 70 kgf, it is estimated that a bearing is damaged. For this reason, damage of a bearing can be prevented by making the curvature radius (R) of the edge part of a convex part into less than 25 mm.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments and examples, and various modifications can be made as long as they are described in the claims. is there. For example, in the above-described embodiment, the convex portions 43b, 43d, and 43f are provided on the anti-reference-side rolls 412, 414, and 416, but the reference-side roll is also provided with a convex portion, A convex portion may be provided only on the side roll.

  Moreover, in this Embodiment, although the roll of 6 rows was provided in one roll stand, the roll provided in one roll stand is not restricted to a roll of 6 rows, For example, also as a roll of 2-8 rows Good. In accordance with this, the number of roll rows in which the convex portions are provided is not limited to 3 rows as shown in the present embodiment, and may be 2 to 8 rows, for example.

  The present invention is applied to a roll stand constituting a continuous casting machine for slabs.

DESCRIPTION OF SYMBOLS 1 Tundish 2 Immersion nozzle 3 Mold 10 Roll stand 11a Upper frame 11b Lower frame 12a, 12b Shaft box 13 Hydraulic cylinder 43b, 43d, 43f Convex part (large-diameter convex part)
44b, 44d, 44f Flat part 45b, 45d, 45f Edge part 41, 411, 412, 413, 414, 415, 416 Roll (upper roll)
42,421,422,423,424,425,426 roll (lower roll)
411a, 411b, 411c, 412a, 412b, 412c, 413a, 413b, 413c, 414a, 414c, 416a, 416b Split roll 100 Continuous casting machine

Claims (2)

A roll stand installed on the horizontal part of a continuous casting machine of a slab,
In the roll stand, two or more pairs of rolls composed of an upper roll and a lower roll facing each other are juxtaposed in the casting direction,
The upper roll and the lower roll are divided into 2 to 4 in the axial direction of the roll,
At least one of the upper roll and the lower roll is provided with a large-diameter convex portion having an outer diameter larger than that of the upper roll and the lower roll,
Two or more large-diameter convex portions are provided apart from each other in the width direction of the slab in one row of rolls divided into 2 to 4 in the axial direction of the roll,
Among the two or more large-diameter convex portions provided in one row of rolls divided into 2 to 4 in the axial direction of the roll, the large-diameter convex portion provided on the outermost side in the width direction of the slab , The one end of the roll closest to the large-diameter convex portion is disposed away by a distance X satisfying the following expression (1),
130 mm ≦ X (1)
A center line in the width direction of the slab of the upstream large-diameter convex portion provided on the upstream roll, and a slab of the downstream large-diameter convex portion provided on the downstream roll located downstream from the upstream roll. The center line in the width direction matches each other,
A roll stand for a continuous casting machine for performing partial large reduction of a slab, characterized in that the outer diameter of the upstream large-diameter convex portion is smaller than the outer diameter of the downstream large-diameter convex portion. The large-diameter convex portion has a flat portion parallel to a roll body portion which is a portion where the large-diameter convex portion is not provided among the rolls provided with the large-diameter convex portion,
About the width W in the width direction of the slab of the flat portion, the width of the flat portion of the upstream large-diameter convex portion is larger than the width of the flat portion of the downstream large-diameter convex portion,
The width W _i of the flat portion of the upstream large-diameter convex portion and the width W _{i + 1} of the flat portion of the downstream large-diameter convex portion arranged in the immediate vicinity of the upstream large-diameter convex portion satisfy the following expression (2). The roll stand for a continuous casting machine for performing partial large reduction of the slab according to claim 1.
W _i −W _{i + 1} ≧ 10 mm (where i is a natural number) (2)

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