WO2009082095A2

WO2009082095A2 - Side rolling roller and rolling method using the same

Info

Publication number: WO2009082095A2
Application number: PCT/KR2008/007084
Authority: WO
Inventors: Myung-Sik Chun; Yong-Min Kim; Byeong-Seong Woo; Yong-Kwon Kim
Original assignee: Posco
Priority date: 2007-12-24
Filing date: 2008-12-01
Publication date: 2009-07-02
Also published as: KR101482257B1; WO2009082095A3; CN101909772B; CN101909772A; KR20090068606A

Abstract

There is provided a side rolling roller and a rolling method using the same. A side rolling roller according to an aspect of the invention may include: at least one inclined rolling unit performing a rolling process to form an inclined portion on a side of the slab; and at least one curved rolling unit performing a rolling process to form a depressed portion in connection with the inclined portion. Accordingly, the size of a defective region generated in the widthwise ends of a slab can be reduced in a rolling process, the slab can be prevented from being lifted, skewed, and/or separated by the side rolling roller to thereby reduce the size of the defective region generated in the widthwise ends of the slab, and defects occurring at the end of the slab caused by bulging and dog-bone deformation in the rolling process can be reduced.

Description

SIDE ROLLING ROLLER AND ROLLING METHOD USING

THE SAME

Technical Field

[1] The present invention relates to a rolling roller and a rolling method using the same that reduces defects generated on the edges of slabs during a rolling process. Background Art

[2] In general, a rolling process consisting of five to seven passes is performed on slabs to obtain the thickness and width of the slabs corresponding to reference dimensions of products.

[3] As shown in FIG. 1, a rolling system that has been used in a rolling process according to the related art includes a side rolling roller 2 that performs a rolling process on a slab 20 to reduce its width and a thickness rolling roller 3 that performs a rolling process of the slab 20 to reduce its thickness. The rolling system 10 may also include a finishing rolling roller 4 to smooth the surface of the slab 20 subjected to the rolling process such that a finishing rolling process is performed to obtain a final product thickness. Furthermore, tension reels 5 may be provided before and after the rolling roller 4 (at both ends thereof). The rolling system 10 is designed to accurately determine the thickness and width of the slab 20 subjected to the rolling process so that products can be manufactured according to predetermined specifications.

[4] Here, the side rolling roller 2, which is used to perform the rolling process of the slab along the width direction thereof, may generally include a side roller called a vertical roll or an edger roll. When the rolling system 10 includes the finishing rolling roller 4, the rolling roller 3, which is used to perform the rolling process of the width of the slab 20, may be formed of a roughing mill. The slab 20 having predetermined specifications is subjected to the rolling process so as to be reduced to the required product thickness by the rolling system 10 according to the related art.

[5] As shown in FIG. 2, a linear defective region 20a of approximately 15mm is generated on the width wise edges of the slab 20 rolled by the rolling system 10 according to the related art. The linear detective region 20a has a width of approximately 30mm over the entire width of the slab 20 (that is, including both edges thereof).

[6] As the end of the slab 20 bulges by lateral rolling and the side of the slab 20 bulges by width-direction rolling, a side region 21 of the edge of the slab 20 is transferred (moved) to upper and lower regions 22a and 22b of the edge. The linear defective region 20a is generated. The bulging may also cause defects in the rolled slab 20. For example, the rolled slab 20 may be shaped like a dog bone in which the upper and lower portions 22a and 22b of the edge of the slab 20 are thicker than the central region thereof.

[7] The defective region 20a of the edge of the slab 20 may be called an edge seam or a slab edge. The larger the defective region 20a that is formed on the edge of the slab 20, the wider the edge of the slab 20 needs to be cut. Therefore, when the width of the final product is designed, allowance (tolerance) needs to be increased in consideration of the dimensions of the slab 20 that needs to be cut. That is, the increase in size of the defective region 20a causes lower product yield.

[8] To solve this problem, the rolling system 10, according to the related art, has been proposed in which a rolling unit 2a, provided at the center of guide units 2b of the side rolling roller 2, has inclined surfaces. The proposed side rolling roller 2 has the rolling unit 2a that is inclined downwards toward the inner center of the rolling unit 2a as shown in FIG. 3A.

[9] As shown in FIG. 3B, when the edge of the slab 20 is rolled, the side region 21 of the slab 20, which contacts the rolling unit 2a, is pressed toward the lower part of the rolling unit 2a by the rolling unit 2a of the rolling roller 2 inclined downward, thereby performing the rolling process of the slab 20.

[10] As shown in FIG. 3B, however, the bulge, that is, the increase in thickness occurring when the side region 21 of the slab 20 is transferred to the upper and lower regions 22a and 22b of the edge of the slab 20 is not reduced as expected. That is, since a width A of the upper region 22a of the edge of the slab 20 rolled by the inclined surface of the rolling unit 20a is greater than that of the lower region 22b, a position at which the upper region 22a bulges is closer to the central area of the slab 20 than a position at which the lower region 22b bulges. As a result, the defective region 20a is not significantly reduced. The edge of the slab 20 is also shaped like a dog bone to increase the edge thickness.

[11] That is, when the slab 20 is rolled along the width direction by the side rolling roller

2 according to the related art, it may be impossible to reduce the size of the defective region 20a formed due to bulging.

[12] Even when the rolling process is performed using the side rolling roller 2 having the improved rolling unit 2a, which is inclined downward, the defective region 20a generated in the widthwise end of the slab 20 cannot be reduced because the upper and lower regions 22a and 22b of the edge of the slab 20 get thicker, and the bulging creates asymmetry between the upper and lower regions 22a and 22b.

[13] In order to solve this problem, a method using a sizing press has been proposed to reduce the size of the defective region of the widthwise edge of the slab. With the sizing press, an anvil surface contacting the side surface of the slab is protruded to reduce the amount of the side region of the slab that is transferred (moved) to front and rear surfaces (upper and lower regions of the edge of the slab) thereof.

[14] Also, as a method of heavy width reduction of a hot-rolled slab, there has been proposed a method that reduces the width reduction amount of a general edger mill (side roller), which is arranged in a roughing rolling line, to 20mm or less to maintain a bulging amount of 5mm or less during horizontal rolling, and reversely conveys the slab toward the sizing press during a roughing rolling process to thereby perform a sizing process by a large width reduction amount.

[15] When the above-described sizing press for the heavy reduction width is used, the anvil shape is locally modified to be convex so as to make the edge of the slab concave, thereby preventing bulging. However, the sizing press needs to have an anvil for general steel to be subjected to heavy width reduction rolling and stainless steel to be subjected to light width reduction rolling. Furthermore, this method can be performed only when the anvils of the sizing press for the upper general steel and the lower stainless steel can be conveyed along a vertical direction according to processing conditions.

Disclosure of Invention Technical Problem

[16] The present invention has been made to solve at least one of the foregoing requirements or problems with the related art, which occur from a conventional side rolling roller and a rolling method using the same

[17] One aspect of the present invention is to reduce the size of a defective region generated on the ends on a slab along the width direction in a process of rolling the slab along the width direction.

[18] Another aspect of the invention is to reduce the amount of a side region of a slab being transferred to upper and/or lower regions of the end of the slab in a process of rolling the slab along the width direction.

[19] Another aspect of the invention is to reduce defects occurring when a side region of a slab that is transferred to upper and/or lower region of the end of the slab by reducing bulging in a process of rolling the slab along a width direction.

[20] Another aspect of the invention is to prevent a widthwise cross-section of a slab from being shaped like a dog bone due to bulging.

[21] Another aspect of the invention is to prevent a slab from being lifted by a side rolling roller in a process of rolling the slab along the width direction.

[22] Another aspect of the invention is to prevent a slab from being skewed by pres- surization of a side rolling roller in a process of rolling the slab in the width direction.

[23] Another aspect of the invention is to prevent a slab from being separated from a conveying axis by pressurization using a side rolling roller in a process of rolling the slab in the width direction. Technical Solution

[24] A side rolling roller and a rolling method using the same in connection with an exemplary embodiment of the invention may include the following characteristics.

[25] The present invention is basically designed to reduce the size of a defective region of a widthwise end of a slab by preventing bulging occurring in a process of rolling the slab and/or preventing distortion in shape like a dog bone.

[26] According to an aspect of the invention, the invention provides a side rolling roller including: at least one inclined rolling unit performing a rolling process to form an inclined portion on a side of the slab; and at least one curved rolling unit performing a rolling process to form a depressed portion in connection with the inclined portion.

[27] The inclined rolling unit may be disposed to perform a rolling process on an upper part of the side of the slab, and the curved rolling unit may be disposed to perform a rolling process on a lower part of the side of the slab.

[28] The inclined rolling unit may have an inclination angle of 0.1 to 2 degrees to prevent the slab from being lifted, skewed, or separated due to compressive force applied by lateral rolling. A central portion of the curved rolling unit may have a greater diameter than the end thereof by 2 to 6mm. The maximum diameter of the end of the inclined rolling unit may be equal to or greater than that of the curved rolling unit.

[29] The inclined rolling unit may be disposed to perform a rolling process on the upper and lower parts of the side of the slab, and the curved rolling unit may be disposed to perform a rolling process of a central part of the side of the slab. The inclined rolling unit may include upper and lower inclined rolling units, the upper inclined rolling unit having an inclination angle greater than the lower inclined rolling unit.

[30] According to an aspect of the invention, the invention provides a rolling method including: performing a rolling process on a slab along a width direction; and performing a rolling process on the slab along a thickness direction, wherein the rolling process on the slab along the width direction is performed to form at least one inclined portion on the side of the slab and a depressed portion in connection with the inclined portion.

[31] The rolling of the slab may include, in combination: performing width-direction rolling and thickness-direction rolling; and performing thickness-direction rolling.

[32] The rolling of the slab may be performed using one side rolling roller and one thickness rolling roller by conveying the slab in a forward direction and a backward direction.

[33] The rolling of the slab may include, in combination: performing width-direction rolling and thickness-direction rolling of the slab conveyed in a forward direction; performing thickness-direction rolling of the slab conveyed in a backward direction; and performing thickness-direction rolling on the slab conveyed in a forward direction.

[34] The rolling of the slab may include: performing both width-direction rolling and thickness-direction rolling of a slab moving in a forward direction to a first pass; performing only thickness-direction rolling of the slab conveyed in a backward direction to a second pass; performing both width-direction rolling and thickness- direction rolling of the slab conveyed in the forward direction in a third pass; performing only thickness-direction rolling of the slab conveyed in the backward direction in a fourth pass; performing only thickness-direction rolling of the slab conveyed in the forward direction in a fifth pass; performing only thickness-direction rolling of the slab conveyed in the backward direction in a sixth pass; and performing both thickness-direction rolling and width-direction rolling of the slab to reduce the width of the slab conveyed in the forward direction in a seventh pass to reduce the thickness of the slab by 0 to 5mm.

[35] The maximum width-direction rolling may be performed in the first pass and the third pass.

Advantageous Effects

[36] According to the exemplary embodiment of the invention, the size of a defective region generated in the widthwise ends of a slab during a rolling process on the slab can be reduced. [37] According to the exemplary embodiment, in a process of rolling the side of the slab, the amount of the side of the slab that is transferred to an upper and/or lower region of the end of the slab can be reduced. [38] According to the exemplary embodiment, bulging occurring when rolling the side of the slab is prevented to reduce defects generated when the side of the slab is transferred to the upper and/or lower region of the end of the slab. [39] According to the exemplary embodiment, a cross-section of the slab along the width direction can be prevented from being shaped like a dog bone due to bulging. [40] According to the exemplary embodiment, in the process of rolling the side of the slab along the width direction, the slab can be prevented from being lifted upward by using the side rolling roller, thereby reducing the size of the defective region generated in the end of the slab along the width direction. [41] According to the exemplary embodiment, in the process of rolling the side of the slab along the width direction, the slab can be prevented from being skewed by the side rolling roller, thereby reducing the size of the defective region generated in the end of the slab along the width direction. [42] According to the exemplary embodiment, in the process of rolling the side of the slab along the width direction, the slab can be prevented from being separated from a conveying axis by the side rolling roller, thereby reducing the defective region generated in the end of the slab along the width direction. Brief Description of Drawings

[43] FIG. 1 is a view illustrating a rolling process according to the related art.

[44] FIG. 2 is a view showing a state in which a detective region is generated along the width direction in the ends of a slab subjected to a rolling process according to the related art.

[45] FIG. 3 is a view illustrating an improved configuration of a side rolling roller used in the rolling process according to the related art and a state in which a defective region is generated along the width direction in the ends of a slab rolled using the side rolling roller.

[46] FIG. 4 is a view illustrating a schematic configuration of a side rolling roller according to an exemplary embodiment of the invention and a state in which a detective region of a slab rolled using the side rolling roller is reduced.

[47] FIG. 5 is a view illustrating a schematic configuration of a side rolling roller according to another exemplary embodiment of the invention and a state in which a detective region of a slab rolled using the side rolling roller is reduced.

[48] FIG. 6 is a schematic view illustrating a rolling process according to an exemplary embodiment of the invention.

[49] FIG. 7 is a view illustrating a rolling method according to an exemplary embodiment of the invention.

[50] FIG. 8 is a graph illustrating the difference in defects generated in the end of a slab along the width direction between when a rolling process according to the related art is performed and when a rolling process according to an exemplary embodiment of the invention is performed. Mode for the Invention

[51] A side rolling roller and a rolling method using the same according to exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[52] The invention will be described in connection with preferred embodiments to illustrate the technical characteristics of the invention. However, the technical characteristics of the invention should not be construed as limited to the embodiments set forth herein. The invention can be exemplified by the embodiments set forth herein. Therefore, the present invention may be embodied in many different forms as disclosed in the following exemplary embodiments, which fall within the scope of the invention.

[53] In the drawings, the same or similar reference numerals will be used throughout to designate the same or like components.

[54] The exemplary embodiments according to the present invention are basically designed to reduce the size of a defective region generated in the widthwise ends of a slab by preventing bulging caused by rolling the slab and distortion in shape such as dog bone.

[55] Referring to FIG. 4, a side rolling roller 120 according to an exemplary embodiment of the invention may have the following configuration.

[56] As shown in FIG. 4A, the side rolling roller 120 may include a rolling unit 121 that is located at the center between guide units 122 to prevent separation of a slab 20. When a rolling process is performed on the side of the slab 20, the rolling unit 121 may be configured to prevent a front end of the slab 20 from being lifted as a widthwise end of the slab 20 is pressed downward. For this configuration, the rolling unit 121 may include an inclined rolling portion 121a. In order to reduce bulging that causes the transferral of a side region 21 of the slab 20 to the upper and lower regions of the end of the slab 20, the rolling unit 121 may further include a curved rolling portion 121b.

[57] With this configuration, when the slab 20 is rolled in the width direction, the inclined rolling portion 121a exerts compressive force along the width direction on the side region 21 of the slab 20, and at the same time, a force to press the side region 21 of the slab 20 downwards.

[58] For example, as shown in FIGS. 4A and 4C, when the inclined rolling portion 121a contacts an upper part of the side region of the slab 20, an inclined portion 21a is formed on the upper part of the side region of the slab 20 by the inclined rolling portion 121a, and at the same time, force is supplied to press the slab 20 downwards.

[59] On the contrary, when the inclined rolling portion 121a contacts a lower part of the side region of the slab 20, the inclined portion 21a is formed on the lower part of the side region of the slab 20 by the inclined rolling portion 121a, and at the same time, the inclined rolling portion 121a exerts a force to lift the slab 20 upwards.

[60] The exerted force allows the slab 20 to be conveyed in a stable position, that is, at a predetermined position (upper or low part) at all times during the rolling process along the lateral direction. In this way, one end portion of the slab 20 along the width direction can be prevented from being located at a relatively lower or higher position than another end portion along the width direction. That is, the skewing of the slab 20 can be prevented.

[61] As such, the slab 20 may be conveyed while the widthwise end of the slab 20 is pressed toward the upper or low part of the rolling unit 121 by the inclined rolling portion 121a. Here, when the side region 21 of the slab 20 is rolled, a defective region 20a generated in the widthwise end of the slab 20 can be constantly generated at the same position of the side region. Therefore, after the rolling process, the defective region 20a that is to be cut during a cutting process can be cut at a constant region (width).

[62] That is, the slab 20 can be prevented from being separated from a predetermined conveying path by the inclined rolling portion 121a, the defective region 20a, generated in the end of the slab 20, can be of a constant area (size), and the optimum design of the defective region 20a that needs to be cut can be obtained.

[63] That is, when the rolling unit 121 of the side rolling roller 120 has the inclined rolling portion 121a, the slab 20 can be stably conveyed.

[64] The rolling unit 121 of the side rolling roller 120 may have the rolling portion 121b as well as the inclined rolling portion 121a. The curved rolling portion 121b is provided to prevent bulging that causes the transferral of the side region 21 of the slab 20 to the upper and/or lower part of the end of the slab 20. The reduction in bulges can prevent or reduce cross-section defects such as a dog-bone shape after the slab 20 is rolled in the thickness direction by the thickness rolling roller 130.

[65] In other words, as the curved rolling portion 121b forms a depressed portion 21b in the side region 21 of the slab 20, if the slab 20 is rolled along the thickness direction during the thickness rolling roller 130, bulging that causes the transferral of the side region 21 to the upper or lower surface of the end of the slab 20 during the thickness- direction rolling can be prevented while the end of the slab becomes thicker after the lateral rolling process. That is, the upper and/or lower region of the side of the slab 20 can be prevented from being transferred to the upper and/or lower surfaces of the end of the slab 20 as the central region of the side region 21 bulges more than the upper and lower regions thereof in the rolling process in the thickness direction.

[66] That is, the rolling unit 121 of the side rolling roller 120 allows the slab 20 to be stably conveyed by the inclined rolling portion 121a and the curved rolling portion 121b, and reduces the bulging amount that causes transferring of the upper and/or lower region of the side surface of the slab 20 to the upper and/or lower surfaces of the end of the slab 20 as the central region of the side region 21 of the slab 20 bulges. As a result, the size of the defective region 20a formed in the widthwise ends of the slab 20 can be reduced.

[67] Meanwhile, the inclined rolling portion 121a may be located at the upper part of the rolling unit 121 of the side rolling roller 120, and the curved rolling portion 121b may be located at the lower part of the rolling unit 121 of the side rolling roller 120. Here, the slab 20 is guided by the guide unit 122 that is located at the upper part of the side rolling roller 120. Further, as the width-direction rolling and a downwards pressing force are applied to the side surface of the slab 20 by the inclined rolling portion 121a, the inclined portion 21a is formed on the side surface of the slab 20, and the slab 20 is stably (constantly) conveyed.

[68] In addition, compressive force is supplied to the slab 20 along the lateral direction by the curved rolling portion 121b to form the depressed portion 21b on the slab 20. When the slab 20 is rolled along the thickness direction by the thickness rolling roller 130 while the depressed portion 21b is formed, bulging occurs mostly in the depressed portion 21b (particularly, the central area of the depressed portion).

[69] For example, the depressed portion 21b rolled to a thickness B bulges mostly when the width-direction rolling is performed. Therefore, only a very small part of the inclined portion 21a may be transferred to the upper surface of the slab 20.

[70] As such, when the width-direction rolling is performed after the lateral rolling of the slab 20, bulging occurring in the widthwise ends of the slab 20 can be reduced. In addition, the side region 21 of the slab 20 can be prevented from being transferred to the upper or lower surface due to the bulging end of the slab 20.

[71] The inclined rolling portion 121a of the rolling unit 121 may be inclined at an angle of approximately 0.1 to 2 degrees with respect to the perpendicular direction. That is, the inclined rolling portion 121a may be inclined downwards toward the inside (center) of the rolling unit 121 from the guide unit 122 located on the upper part of the side rolling roller 120. The inclination angle may be determined so that a force is exerted to press the slab 20 down.

[72] The curved rolling portion 121b may have a central protruding portion 121d that is thicker than both end portions thereof, that is, one end portion contacting the inclined rolling portion 121a and the other end contacting the guide unit 122 by approximately 2 to 6mm. The difference in thickness determines how deep the depressed portion 21b is formed in the side of the slab 20. The thickness of the central protruding portion 12 Id of the curved rolling portion 121b may vary according to the specifications of the slab 20 subjected to the rolling process.

[73] The maximum diameter of the curved rolling portion 121b may be the same as that of the inclined rolling portion 121a according to the specifications of the rolled slab 20. On the other hand, the maximum diameter of the inclined rolling portion 121a may be greater than that of the curved rolling portion 121b. That is, the diameter of the end portion of the inclined rolling portion 121a adjacent to the guide unit 122 constituting the rolling roller 120 may be equal to or greater than that of the central protruding portion 12 Id of the curved rolling portion 121b.

[74] In the case of the configuration shown in FIG. 4, the slab 20 may be subjected to a lateral rolling process while the slab 20 is obliquely pressed down by the inclined rolling portion 121a.

[75] In the repetitive rolling process, when the width-direction rolling process is performed again with respect to the side region 21 of the slab 20, the inclined portion 21a and the depressed portion 21b (lower end) of the slab 20 are supported by one recessed portion 121c formed at the interface between the inclined rolling portion 121a and the curved rolling portion 121b and another recessed portion 121e formed at the interface between the curved rolling portion 121b and the lower guide unit 122, thereby performing a lateral rolling process. Here, force exerted by the inclined rolling portion 121a may be also supplied.

[76] Therefore, even when the slab 20 gets thinner during the repetitive rolling process, downwards force is sufficiently exerted on the slab 20 by the inclined rolling portion 121a. Therefore, as the slab 20 is stably conveyed, the rolling process on the widthwise ends of the slab 20 can be stably performed. That is, the defective region 20a generated at the end of the slab 20 is formed at a predetermined area, and a process of cutting the defective region 20a of the slab 20 after the rolling process can be easily designed.

[77] As shown in FIG. 5A, the side rolling roller 120 may have another configuration.

That is, the rolling unit 121 of the side rolling roller 120 may have an inclined rolling unit 121 that is different from the example illustrated in FIG. 4A. In the inclined rolling unit 121, a curved rolling portion 121b may be disposed at the center thereof, and inclined rolling portions 121a and 12 If may be disposed at the upper and lower parts of the curved rolling portion 121b.

[78] Here, the inclined rolling portion 121a provided at the upper part of the curved rolling portion 121b may have a greater inclination angle than the inclined rolling portion 121f provided at the lower part of the curved rolling portion 121b. As the upper circumference of the slab 20 that gets thinner by the repetitive rolling process receives sufficient force from the inclined rolling portion 121a provided at the upper part of the curved rolling portion 121b, the slab 20 can be subjected to a lateral rolling process while being stably conveyed.

[79] The side region 21 of the slab 20 can be subjected to the lateral rolling process by the inclined rolling portions 121a and 12 If that are disposed at both sides (upper and lower parts in the drawing) of the curved rolling portion 121b while the side region 21 is obliquely pressed in an up and down direction. As a result of this rolling process using the curved rolling portion 121b, a depressed portion 21b is formed at the center of the side region 21 of the slab 20. Further, inclined rolling portions 21a and 2 If may be formed on both sides (upper and lower parts in the drawing) of the depressed portion 21b by the inclined rolling portions 121a and 12 If during the rolling process.

[80] Bulging occurs mostly at the depressed portion 21b rolled to a width C when the thickness-direction rolling process is performed. Therefore, only a very small portion of the inclined rolling portions 21a and 2 If may be transferred to the upper surface of the slab 20. [81] Meanwhile, the rolling operation by the curved rolling portion 121b and the inclined rolling portions 121a and 12 If can be easily understood by a person skilled in the art from the above-described embodiments illustrated with reference to FIG. 4. Thus, a description thereof will be omitted.

[82] FIG. 6 is a view illustrating a rolling system 100 that has the rolling roller 120 according to any one of the exemplary embodiments of the invention. The rolling system 100 includes the side rolling roller 120 that performs a rolling process on the slab 20 along the width direction and the thickness rolling roller 130 that performs the rolling process on the slab 20 along the thickness direction. The finishing rolling roller 140 may be additionally provided to smooth the surface of the slab 20 subjected to the rolling process. The tension reels 150 may be provided before and after (both ends of) the finishing rolling roller 140. A winding reel 160 may be additionally provided so that the rolled slab is wound to a roll.

[83] The rolling system 100 may have the same configuration as a general rolling system.

Here, the side rolling roller that performs the lateral rolling process may have the same configuration illustrated in the above-described embodiments. Thus, a detailed description thereof will be omitted.

[84] A rolling method according to another exemplary embodiment of the invention will now be described with reference to FIG. 7.

[85] A rolling method using the rolling system 100 may include repetitive reversing and non-reversing rolling processes. Here, the rolling process on the slab 20 is performed by repeating the process of rolling the slab 20 along the width direction using the side rolling roller 120 and the process of rolling the slab 20 along the thickness direction using the thickness rolling roller 130.

[86] The width-direction rolling of the slab 20 may be performed so that at least one inclined portion 21a is formed at the side of the slab 20 by the side rolling roller 120 and the depressed portion 21b is formed in connection with the inclined portion 21a.

[87] In this rolling method, when width-direction rolling of the slab 20 is performed by the side rolling roller 120, the side (the edge) of the slab 20 bulges along the thickness direction. That is, the side of the slab 20 is shaped like a dog bone so that both ends of the slab 20 are thicker than the central portion thereof. The increase in thickness due to the dog bone profile may cause an increase in width of the slab 20 and a decrease in thickness thereof when the width-direction rolling of the slab 20 is performed using the thickness rolling roller 130.

[88] Here, the difference in deformation between a contact surface of the thickness rolling roller 130 and the slab 20 and the center of the thickness of slab 20 causes bulging at the widthwise ends of the slab 20. The bulging spreads to the front and rear surfaces of the side of the slab 20 (upper and lower surfaces of the slab) as the rolling reduction increases, which may cause a discrete or continuous linear defect in the widthwise ends of the slab 20. The defective region generated in the widthwise ends of the slab increases as the rolling reduction along the thickness direction and the width direction increases. The defective region may be most likely formed in the circumference of the slab 20 where the temperature falls.

[89] Therefore, the process of rolling the slab 20 may include a combination of a process of rolling the slab 20 both along the thickness direction and the width direction and a process of rolling the slab 20 only along the thickness direction. Here, in the process of rolling the slab 20 along the thickness direction and the width direction, width- direction rolling to form the depressed portion 21b in the side of the slab 20 by the side rolling roller 120 and thickness-direction rolling to cause the depressed portion 21b to bulge mostly may be performed. In the process of rolling the slab 20 only along the thickness direction, the width-direction rolling of the slab 20 may be only performed.

[90] The rolling process may be performed by a single side rolling roller 120 and a single thickness rolling roller 130 or a combination of the plurality of side rolling rollers 120 and thickness rolling rollers 130.

[91] One example of a rolling method using a combination of the lateral rolling and the thickness rolling may consist of a method of rolling a slab as follows. The rolling method may include reverse rolling in which a rolling process is performed by forward conveyance and backward conveyance. Alternatively, the rolling process may be performed only by forward conveyance using a combination of the plurality of side rolling rollers 120 and the plurality of thickness rolling rollers 130.

[92] In a case of the reversing rolling, the side of the slab 20 may not be rolled during the rolling process by backward conveyance. During the rolling process by the forward conveyance, the side of the slab 20 may only be rolled in selected passes. Further, when the side of the slab 20 is rolled by the forward conveyance, the rolling process may be performed according to different rolling reductions.

[93] One example of the rolling method based on the reversing rolling will be described.

The entire rolling process may include seven passes. Here, the rolling may be performed by forward conveyance in the first, third, fifth, and seventh passes, and the rolling process may be performed by backward conveyance in the second, fourth, and sixth passes.

[94] In this rolling method, both the width-direction rolling and the thickness-direction rolling of the slab 20 may be performed in the first and third passes where the rolling process is performed by the forward conveyance. Further, the thickness-direction rolling of the slab 20 may only be performed by the backward conveyance in the second, fourth, fifth, sixth and seventh passes.

[95] Here, different rolling reductions during the lateral rolling process on the side of the slab may be applied in the early first and third passes. That is, vertical (thickness) rolling and horizontal (width) rolling of the slab are repeated according to a reversing rolling process to thereby manufacture a bar having a predetermined thickness. Further, in the rolling pass having an inlet thickness smaller than a barrel length of the side rolling roller 120 having the curved rolling portion 121b, the defective region 20a of the front and rear surfaces (upper and lower surfaces of the slab) is increased by asymmetric rolling. Therefore, in this case, the rolling of the sides of the slab is not performed, and thickness-direction rolling only may be performed.

[96] For example, a slab having a thickness of 200mm is generally being manufactured and is subjected to a rolling process. Here, the side of the slab has a double bulging profile in cross-section since an aspect ratio (contact length between side rolling roller and slab side/mean thickness of slab at inlet and outlet) is 0.83 or less in the first and second passes. Then, the side of the slab may be deformed into a single bulging shape at an aspect ratio of 0.83 or more after the third pass.

[97] The double bulging leads to the formation of the depressed portion, and has a smaller bulging amount than the single bulging. Therefore, the size of the defective region 20a of the slab can be reduced by forming the depressed portion 21 in the third pass where rolling reduction is great and single bulging is caused.

[98] Therefore, the bulging amount during the thickness-direction rolling in the first and second passes can be reduced by previously forming the depressed portion 21b corresponding to the inlet thickness of the slab. Furthermore, the amount of bulging during the thickness-direction rolling in the third to seventh passes can be reduced by the depressed portion 21b formed in the third pass.

[99] Here, during the width rolling in the fifth pass, lateral rolling is not performed.

During the lateral rolling of the slab in the seventh pass, a weak rolling process causing a deformation of 5mm or less may be performed to maintain the right-angle end (edge part) of the slab.

[100] In another example, each of the passes may include a selective lateral rolling process on the side of the slab in order to reduce the amount of bulging occurring at the side of the slab. Here, the rolling reduction may be selectively adjusted. The rolling process along the lateral direction and the rolling reduction may vary according to the material and/or the specifications of the slab.

[101] As shown in FIG. 8, as a result of performing the rolling process according to the embodiment of the invention, when a rolling method according to the related art is performed on a slab using the side rolling roller according to the embodiment of the invention, the size of a defective region formed on the slab is shown to be reduced. Further, when the rolling method according to the embodiment of the invention is performed on a slab using the side rolling roller, the size of a defective region formed in the slab is shown to be even further reduced. That is, when the side rolling roller according to the embodiment of the invention is used, the defective region is reduced from 30mm to 27.2 mm on average. When the rolling method proposed in the invention is used, the defective width of the slab is reduced to 25.3 mm on average. Thus, production yield is increased by 4.7 mm. The above-described side rolling roller and the rolling method using the same are not limited to the exemplary embodiments disclosed, but all or part of the exemplary embodiments can be selectively combined to form modifications and variations.

Claims

[1] A side rolling roller comprising: at least one inclined rolling unit performing a rolling process to form an inclined portion on a side of the slab; and at least one curved rolling unit performing a rolling process to form a depressed portion in connection with the inclined portion. [2] The side rolling roller according to claim 1, wherein the inclined rolling unit is disposed to perform a rolling process of an upper part of the side of the slab, and the curved rolling unit is disposed to perform a rolling process of a lower part of the side of the slab. [3] The side rolling roller according to claim 1, wherein the inclined rolling unit has an inclination angle of 0.1 to 2 degrees to prevent the slab from being lifted, skewed, or separated due to compressive force applied by lateral rolling. [4] The side rolling roller according to claim 1, wherein a central portion of the curved rolling unit has a greater diameter than the end thereof by 2 to 6mm. [5] The side rolling roller according to claim 1, wherein the maximum diameter of the end of the inclined rolling unit is equal to or greater than that of the curved rolling unit. [6] The side rolling roller according to claim 1, wherein the inclined rolling unit is disposed to perform a rolling process on the upper and lower parts of the side of the slab, and the curved rolling unit is disposed to perform a rolling process of a central part of the side of the slab. [7] The side rolling roller according to claim 6, wherein the inclined rolling unit comprises upper and lower inclined rolling units, the upper inclined rolling unit having an inclination angle greater than the lower inclined rolling unit. [8] A rolling method comprising: performing a rolling process on a slab along a width direction; and performing a rolling process on the slab along a thickness direction, wherein the rolling process on the slab along the width direction is performed to form at least one inclined portion on the side of the slab and a depressed portion in connection with the inclined portion. [9] The method according to claim of 8, wherein the rolling the slab comprises, in combination: performing width-direction rolling and thickness- direction rolling; and performing thickness-direction rolling. [10] The method according to claim 9, wherein the rolling is performed using one side rolling roller and one thickness rolling roller by conveying the slab in a forward direction and a backward direction. [11] The method according to claim 8, wherein the rolling the slab comprises, in co mbination: performing width-direction rolling and thickness- direction rolling of the slab conveyed in a forward direction; performing thickness-direction rolling of the slab conveyed in a backward direction; and performing thickness-direction rolling on the slab conveyed in a forward direction. [12] The method according to claim 8, wherein the rolling of the slab comprises: performing both width-direction rolling and thickness- direction rolling of a slab moving in a forward direction to a first pass; performing only thickness-direction rolling of the slab conveyed in a backward direction to a second pass; performing both width-direction rolling and thickness-direction rolling of the slab conveyed in the forward direction in a third pass; performing only thickness-direction rolling of the slab conveyed in the backward direction in a fourth pass; performing only thickness-direction rolling of the slab conveyed in the forward direction in a fifth pass; performing only thickness-direction rolling of the slab conveyed in the backward direction in a sixth pass; and performing both thickness-direction rolling and width-direction rolling of the slab to reduce the width of the slab conveyed in the forward direction in a seventh pass to reduce the thickness of the slab by 0 to 5mm. [13] The method according to claim 12, wherein the maximum width-direction rolling is performed in the first pass and the third pass.