The present disclosure relates to a continuous casting machine including a mold and segments guiding a strand, and more particularly, to a continuous casting machine in which the number and distance of rolls of outer frames are set to be different from those of rolls of inner frames for producing slabs having improved quality.

Generally, in a continuous casting process, molten steel is continuously supplied to a mold having a predetermined shape, and a slab semi-solidified in the mold is continuously drawn from a lower side of the mold.

FIG. 1 is a schematic view illustrating the structure and segments of a general continuous casting machine.

The continuous casting machine includes: ladles 10 in which molten steel refined through a steel making process is poured; a turndish 20 temporarily storing the molten steel supplied from the ladles 10 through a nozzle; a mold 30 receiving the molten steel from the turndish 20 for primarily solidifying the molten steel to have a predetermined shape; and a strand guide 40 including a plurality of segments 50 arranged below the mold 30 to guide and cool a slab not fully solidified.

The segments 50 are arranged in such a manner that a plurality of rolls 52 and 54 face each other. Each of the segments 50 includes: upper and lower frames 51 and 53 spaced apart from each other in a vertical direction; a plurality of tie rods (not shown) vertically connecting the upper and lower frames 51 and 53; and a plurality of hydraulic cylinders (not shown) using the tie rods as pistons to control gaps between the upper and lower frames 51 and 53 for applying depressive force to a slab 1.

In the continuous casting machine, molten metal contained in the mold 30 has to be maintained at a constant level during a casting process. However, if the rate of casting is increased, the level of molten metal contained in the mold 30 may be markedly varied. In this case, the rate of casting may not be further increased. Furthermore, a slab having a high temperature may periodically swell between the rolls 52 and 54 of the segments 50 due to pressure, and thus mold level hunting may occur.

An aspect of the present disclosure may provide a continuous casting machine configured to reduce mold level hunting caused by periodic pressure-induced swelling of a high-temperature slab passing between rolls during a high-speed casting process.

An aspect of the present disclosure may also provide a continuous casting machine for producing slabs having improved quality by reducing mold level hunting caused by periodic swelling of the slabs.

The present disclosure provides segments and a continuous casting machine as described below.

According to an aspect of the present disclosure, a continuous casting machine may include: a mold providing a slab; and a plurality of segments configured to guide the slab through a strand guide and cool the slab, wherein each of the segments may include an inner frame, an outer frame spaced apart from the inner frame, and a plurality of rolls disposed on the inner and outer frames through roll supports, and the number N_fixed of the rolls disposed on the outer frame may be set to be different from the number N_loosed of the rolls disposed the inner frame so as to reduce mold level hunting caused by a slab shape.

The outer frame may have an average roll pitch P_avg,fixed different from an average roll pitch P_avg,loosed of the inner frame.

The inner frame and the outer frame may have the same segment length so as to be disposed in a horizontal or vertical zone of the strand guide.

The outer frame may have a segment length greater than that of the inner frame, and the outer and inner frames may be disposed in a bow zone of the strand guide, wherein the average roll pitch P_avg,fixed of the outer frame and the average roll pitch P_avg,loosed of the inner frame may satisfy the following formula: $$\frac{P_{\mathit{avg},\mathit{loosed}}}{P_{\mathit{avg},\mathit{fixed}}}=\left(1-\frac{t_{\mathit{slab}}}{r}\right)*\frac{N_{\mathit{fixed}}}{N_{\mathit{loosed}}}$$
where t_slab refers to a slab thickness, and r refers a curvature of radius of the strand guide.

The number N_loosed of the rolls disposed the inner frame may be greater than the number N_fixed of the rolls disposed on the outer frame (N_fixed<N_loosed).

The inner frame and the outer frame may include pinch rolls, respectively, so as to draw the slab passing therebetween, and centers of the pinches of the inner frame and the outer frame are not aligned.

The outer frame may be a fixed frame, and the inner frame may be a loosed frame that is movable.

Even in a high-speed casting process, the segments of the present disclosure may prevent mold level hunting caused by periodic pressure-induced swelling of a high-temperature slab passing between rolls.

In addition, the continuous casting machine of the present disclosure may produce slabs having improved quality by reducing mold level hunting caused by periodic swelling of the slabs.

• FIG. 1 is a schematic view illustrating a continuous casting machine of the related art.
• FIG. 2 is a view illustrating a slab welling at segments of the continuous casting machine of the related art.
• FIG. 3 is a schematic view illustrating a segment configured to be used in a horizontal zone according to an embodiment of the present disclosure.
• FIG. 4 is a schematic view illustrating a segment configured to be used in a bow zone according to an embodiment of the present disclosure.
• FIG. 5 is a schematic view illustrating a continuous casting machine including segments according to an embodiment of the present disclosure.

Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

FIG. 3 is a schematic view illustrating a segment 150 used in a horizontal or vertical zone of a strand guide, according to an embodiment of the present disclosure.

In the embodiment, the segment 150 includes: a loosed frame 151, an inner frame loosely and movably disposed on an upper side and facing the center of curvature of the strand guide; and a fixed frame 154, an outer frame fixed to a lower side to face outward in a radial direction of the strand guide. A plurality of rolls 152 and 154 are arranged on the loosed frame 151 and the fixed frame 154. The rolls 152 and 154 include a pair of pinch rolls 153 and 156.

The rolls 152 are arranged at regular intervals along an overall segment length l_seg,loosed of the loosed frame 151, and the number of the rolls 152 is N_loosed. The rolls 152 are arranged on the loosed frame 151 with a constant pitch P_loosed. Although the pinch roll 153 has a diameter slightly different from that of the rolls 152, gaps l_loosed between the rolls 152 are substantially equal.

Similarly, the rolls 155 are arranged at regular intervals on an overall segment length l_seg,fixed of the fixed frame 154, and the number of the rolls 155 is N_fixed. The rolls 155 are arranged on the loosed frame 151 with a constant pitch P_fixed. Although the pinch roll 156 has a diameter slightly different from that of the rolls 155, gaps l_fixed between the rolls 156 are substantially equal.

In the segment 150 showing in FIG. 3, the number of the rolls 155 of the fixed frame 154 is greater than the number of the rolls 152 of the loosed frame 151. Therefore, the centers of the rolls 152 of the loosed frame 151 are located between the centers of the rolls 155 of the fixed frame 154.

In the embodiment shown in FIG. 3, the segment length l_seg,loosed of the loosed frame 151 and the segment length l_seg,fixed of the fixed frame 154 are equal so that the segment 150 may be disposed on a horizontal or vertical zone. An average pitch P_avg may be calculated by dividing an overall segment length l_seg by the number N of rolls as shown in Formula 1 below. $${\mathit{P}}_{\mathit{avg}}=\frac{{\mathit{l}}_{\mathit{seg}}}{\mathit{N}}$$

Since the overall segment length l_seg,loosed of the loosed frame 151 and the overall segment length l_seg,fixed of the fixed frame 154 are equal (l_{seg, loosed}=l_{seg, fixed}) and the number N_loosed of the rolls 152 of the loosed frame 151 is different from the number N_fixed of the rolls 155 of the fixed frame 154, according to Formula 1, the P_avg,loosed of the loosed frame 151 is greater than the P_avg,fixed of the fixed frame 154 (P_avg,loosed>P_avg,fixed).

As described above, since the P_avg,loosed of the loosed frame 151 is different from the P_avg,fixed of the fixed frame 154, gaps between the rolls 152 and 155 are different. Therefore, a distance that a slab travels from one roll to the next roll of the rolls 152 and 155 of the loosed and fixed frames 151 and 154 is different from the next distance that the slab travels, thereby preventing mold level hunting that occurs when a slab makes contact with rolls constantly and repeatedly as in the case of the related art.

The pinch rolls 153 and 156 of the rolls 152 and 155 used to draw a slab passing through the segment 150 may not be aligned at centers thereof. The reason for this is as follows: in a high-speed casting process, the influence of shearing caused by misaligned centers of the pinch rolls 153 and 156 is low, but mold level hunting is severe if the pinch rolls 153 and 155 are aligned to periodically correspond to each other. Herein, high-speed casting refers to casting having a rate of 400 mm•m/min or greater (for example, a slab weighing 80 metric tons is produced at a rate of 5 m/min or greater).

FIG. 4 illustrates a segment 160 configured to be used in a bow zone of a strand guide 140.

Referring to FIG. 4, the segment 160 includes: a loosed frame 161 loosely and movably disposed to face the center of the vow zone; and a fixed frame 164 disposed at a side opposite to the loosed frame 161. A plurality of rolls 162 and 164 are arranged on the loosed frame 161 and the fixed frame 164, and the rolls 162 and 164 include a pair of pinch rolls 163 and 166.

Like in the embodiment shown in FIG. 3, in the segment 160 shown in FIG. 4, the rolls 161 are arranged at regular intervals on the overall segment length l_seg,loosed of the loosed frame 161, and the number of the rolls 162 is N_loosed. The rolls 152 are arranged on the loosed frame 151 with a constant pitch P_loosed. Although the pinch roll 163 has a diameter slightly larger than that of the rolls 162, gaps l_loosed between the rolls 152 are substantially equal.

The rolls 165 are arranged at regular intervals on the overall segment length l_seg,fixed of the fixed frame 164, and the number of the rolls 165 is N_fixed. The rolls 165 are arranged on the loosed frame 161 with a constant pitch P_fixed. Although the pinch roll 166 has a diameter slightly larger than that of the rolls 165, gaps l_fixed between the rolls 165 are substantially equal.

The segment 160 of the embodiment shown in FIG. 4 is used in a bow zone. In a continuous casting machine 100 (refer to FIG. 5), the bow zone of the strand guide 140 (refer to FIG. 5) is curved with a curvature of radius (r), and the segment length l_seg,loosed of the loosed frame 161 is different from the segment length l_seg,fixed of the fixed frame 164 disposed at a side opposite to the loosed frame 161.

In detail, the segment length l_seg,loosed of the loosed frame 161 and the segment length l_seg,fixed of the fixed frame 164 are set to satisfy l_seg,loosed : l_seg,fixed = r : r-t_slab, where t_slab refers to the thickness of a slab. Since the thickness of the slab has a positive value, the segment length l_seg,loosed of the loosed frame 161 is shorter than the segment length l_seg,fixed of the fixed frame 164.

Like in the previous embodiment shown in FIG. 3, in the current embodiment, the numbers N_loosed and N_fixed of the rolls 162 and 165 of the loosed and fixed frame 161 and 164 are different. Thus, average pitches P_avg satisfy Formula 2 below. $$\frac{P_{\mathit{avg},\mathit{loosed}}}{P_{\mathit{avg},\mathit{fixed}}}=\left(1-\frac{t_{\mathit{slab}}}{r}\right)*\frac{N_{\mathit{fixed}}}{N_{\mathit{loosed}}}$$

As the difference between the average pitch of the rolls 162 of the loosed frame 161 and the average pitch of the rolls 165 of the fixed frame 164 is increased, mold level hunting may be suppressed. Particularly, in the embodiment shown in FIG. 4, the segment length l_seg,loosed of the loosed frame 161 is shorter than the segment length l_seg,fixed of the fixed frame 164. Therefore, if the number N_fixed of the rolls 165 of the fixed frame 164 is greater than the number N_fixed of the rolls 162 of the loosed frame 161, the difference between the average pitches may be increased, and thus mold level hunting caused by the shape of a slab may be effectively prevented.

FIG. 5 illustrates the continuous casting machine 100 including a plurality the segments 150 and 160 according to an embodiment of the present disclosure. The continuous casting machine 100 includes: ladles 110 in which molten steel refined through a steel making process is poured; a turndish 120 temporarily storing the molten steel supplied from the ladles 110 through a nozzle; a mold 130 receiving the molten steel from the turndish 20 for primarily solidifying the molten steel to have a predetermined shape; and the cooling line 140 including the segments 150 and 160 arranged below the mold 30 to perform a series of forming processes on a slab not fully solidified while cooling the slab.

In the segments 150 and 160 included in the strand guide 140 of the continuous casting machine 100, the number N_loosed of the rolls 152 and 162 of the loosed frames 151 and 161 is greater than the number N_fixed of the rolls 155 and 165 of the fixed frames 154 and 164 (N_loosed > N_fixed), and thus the average pitch of the rolls 155 and 165 of the fixed frames 154 and 164 is greater than the average pitch of the rolls 152 and 162 of the loosed frames 151 and 161 (P_{avg, loosed}<P_{avg, fixed}).

Therefore, when a high-speed continuous casting process is performed using the continuous casting machine 100 of the embodiment of the present disclosure, mold level hunting caused by the shape of a slab may be reduced, and thus the quality of the slab may be improved.

In the embodiment shown in FIG. 5, the number N_loosed of the rolls 152 and 162 of the loosed frames 151 and 161 of the segments 150 and 160 is greater than the number N_fixed of the rolls 155 and 165 of the fixed frames 154 and 164 of the segments 150 and 160 (N_loosed > N_fixed) in both bow and horizontal zones 141 and 142 of the strand guide 140. However, the segments 150 and 160 arranged in the bow zone of the strand guide 140 may be configured such that the number N_loosed of the rolls 152 and 162 of the loosed frames 151 and 161 is greater than the number N_fixed of the rolls 155 and 165 of the fixed frames 154 and 164 (N_loosed > N_fixed), and the segments 150 and 160 arranged in the horizontal zone of the strand guide 140 may be configured such that the number N_loosed of the rolls 152 and 162 of the loosed frames 151 and 161 is smaller than the number N_fixed of the rolls 155 and 165 of the fixed frames 154 and 164 (N_loosed < N_fixed).