KR100674617B1 - Casting roll for twin-roll strip caster - Google Patents

Abstract

A casting roll for twin-roll strip caster which can manufacture a cast strip with improved quality by preventing solidification delay on edge parts of a casting roll and uniformly maintaining cooling capability along a width direction of the casting roll is provided. A casting roll for twin-roll strip caster comprises: a shaft in which a main cooling water line is formed; a sleeve(12) for surrounding an outer peripheral surface of the shaft; a cooling water channel(16) which is disposed in the sleeve along a circumferential direction of the sleeve with being spaced from the circumference of the sleeve, which extends in a width direction of the sleeve, and which is in communication with the main cooling water line through connection lines connected to both ends thereof; and a metal layer(20) which is disposed to cover an inner wall of a width direction of the cooling water channel, and which has lower thermal conductivity than the sleeve. The casting roll for twin-roll strip caster further comprises a Ni-plating layer(17) plated on a surface of the sleeve.

Description

Casting roll for twin-roll strip caster

1 is a schematic view of a typical twin roll sheet metal casting machine.

Figure 2 is a schematic diagram showing an initial portion of the molten steel in contact with the casting roll to form a solidified shell in a typical twin roll casting machine.

3 is a longitudinal sectional view of a casting roll of a twin-roll thin-plate casting machine according to an embodiment of the present invention.

4 is an enlarged cross-sectional view of the coolant channel area illustrated in FIG. 3.

5 is a graph showing the total heat transfer coefficient value of the casting roll according to the thickness of the nickel plating layer.

6 is a graph showing the overall heat transfer coefficient value of the casting roll according to the thickness of the metal layer formed in the cooling water channel.

7A and 7B are photographs showing edge portions of a stainless steel sheet wound and cast by one embodiment and a comparative example of the present invention.

Description of the main parts of the drawing

11: shaft 12: sleeve

13: Main coolant line 15: Connection line

16: coolant channel 20: metal layer

The present invention relates to a casting roll of a twin-roll type sheet casting machine, and more particularly, to a casting roll width by forming a metal layer having a different thermal conductivity from a sleeve on which a cooling water channel is formed, on the inner wall of the cooling water channel through which cooling water is circulated and supplied to cool the casting roll. The present invention relates to a casting roll of a twin-roll thin plate casting machine that can improve the quality of a casting piece by adjusting the cooling ability in the direction.

Twin roll type sheet casting process is a technology that can manufacture the plate directly from molten steel instead of making slab or thin slab in the conventional casting process and then rolling it. This is a breakthrough technology that can omit the whole hot rolling process. .

1 is a schematic view of a typical twin roll sheet metal casting machine.

Referring to FIG. 1, a twin roll type sheet casting machine 100 used in a twin roll type sheet casting process arranges a molten steel of a tundish 5 on a pair of casting rolls 1 and both sides thereof through a molten steel supply nozzle 3. The molten steel pool 4 is formed between the edge dams 2 formed therein, and the casting roll 1 is rotated in the opposite direction to rapidly melt the molten steel by heat leakage into the roll through contact between the roll and the molten steel. It is an apparatus which manufactures the casting piece 6 by solidifying. Therefore, in order to produce a casting piece of good quality, uniform solidification and shape must be secured over the entire width of the casting piece, which is highly dependent on the widthwise cooling ability of the casting roll 1.

Figure 2 is a schematic diagram showing the initial portion of the molten steel in contact with the casting roll to form a solidified shell in a typical twin roll casting machine.

Referring to FIG. 2, when the solidification shell 6 starts to be formed at the boundary between the casting roll 1 and the molten steel, which is cooled by water, the solidification shell 6 of the roll edge part contracts toward the center portion of the roll. At both roll edges of 1), the gas gap 7 between the casting piece and the roll becomes larger than the roll center portion. In this case, the difference in size of the gas gap 7 formed in the roll edge portion and the center portion is only a few μm, but there is a big difference in the heat transfer coefficient value between the casting piece and the roll, which affects the cooling ability. The phenomenon of molten steel coagulation is delayed compared to the roll center part.

If the solidification delay at the roll edge becomes worse, the edge of the casting piece may fall off or bulging may occur. In this case, not only the casting error rate decreases but also the edge diameter of the casting piece is continuously increased, thereby rewinding. Various problems occur, such as wave generation. In order to solve this problem, it is essential to control the casting roll widthwise cooling ability, and various techniques have been proposed for this purpose.

Japanese Patent Laid-Open No. 9-327753 discloses a method of adjusting the cooling ability by changing the roughness of the roll surface along the width direction of the casting roll. Further, Japanese Patent Laid-Open No. 9-271905 discloses a method of adjusting the cooling ability by forming a plating layer having a low thermal conductivity so as to have a different thickness along the width direction on the surface of the casting roll. However, according to Japanese Patent Laid-Open No. 9-327753, the roughness shape of the roll surface is transferred to the surface of the casting piece, so that the glossiness of the casting piece may be uneven in the width direction. In addition, in Japanese Unexamined Patent Application Publication No. 9-271905, a crown is provided by applying a deep crown to the surface of the roll and repeating the plating process so that the center portion of the roll is thickened and the edge portion is thinly processed. The plating process procedure becomes complicated, and there may be the need to repeat the process of removing and forming the plating layer during the casting roll maintenance.

The technical problem to be achieved by the present invention is to provide a casting roll of a twin-roll type sheet casting machine that can prevent the solidification delay of the casting roll edge portion, and to uniformly cool the cooling roll along the casting roll width direction to produce a casting piece having improved quality There is.

In order to achieve the above technical problem, the present invention provides a casting roll of a twin roll thin plate casting machine having a metal layer formed on at least a portion of an inner wall of a cooling water channel. The casting roll has a shaft having a main cooling water line formed therein. A sleeve is disposed to surround the outer circumferential surface of the shaft. Cooling water channels extending in the width direction of the sleeve and communicating with the main cooling water line through connecting lines connected to both ends thereof are disposed to be spaced apart at regular intervals along the circumferential direction of the sleeve. A metal layer having a thermal conductivity different from that of the sleeve is disposed to cover the inner wall of at least a partial region in the width direction of the cooling water channel.

In some embodiments, the metal layer has a lower thermal conductivity than the sleeve, and at the center of the casting roll so as to offset the difference in cooling capability in the casting roll edge portion of the low cooling capacity and the central portion of the high cooling casting roll during casting The corresponding inner wall of the central portion of the cooling water channel may be covered.

In other embodiments, the metal layer has a lower thermal conductivity than the sleeve and is disposed to cover the entire inner wall of the cooling water channel, wherein the casting layer has a lower cooling capacity in casting and a cooling center in a high cooling casting roll. It may have a greater thickness at the center portion of the coolant channel corresponding to the casting roll center portion, the edge portion of the coolant channel corresponding to the casting roll edge portion so as to offset the performance difference.

In this case, the metal layer may be made of a babbit metal or solder.

In still other embodiments, the casting roll of the twin-roll sheet caster may further include a nickel plating layer plated on the surface of the sleeve.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed subject matter is thorough and complete, and that the scope of the invention to those skilled in the art will fully convey. Like numbers refer to like elements throughout.

3 is a longitudinal sectional view of a casting roll of a twin-roll thin-plate casting machine according to an embodiment of the present invention.

Referring to FIG. 3, the casting roll 10 includes a shaft 11 and a sleeve 12 surrounding an outer circumferential surface of the shaft 11. The shaft 11 may be made of general steel or alloy steel, which is relatively inexpensive. In addition, the sleeve 12 may be made of copper or copper alloy having excellent thermal conductivity, and may be formed to surround the outer circumferential surface of the shaft 11 by a shrink fit process. On the outer circumferential surface of the sleeve 12, a nickel (Ni) plating layer 17 having excellent mechanical properties such as wear resistance may be formed.

In the central portion of the shaft 11 is formed a main coolant line 13 which serves as a main passage of the coolant, and inside the main coolant line 13 a hollow cylindrical tube 14 for partitioning the inlet and outlet passages of the coolant. ) Is placed. The coolant channel 16 having a length extending in the width direction X of the sleeve 12 is disposed in the sleeve 12. In addition, the cooling water channels 16 are arranged to be spaced apart from each other along the circumferential direction of the sleeve 12. Although not shown in FIG. 2, the inner wall of the at least some region in the width direction of the cooling water channel 16 has a thermal conductivity different from that of the sleeve 12, more preferably, than the sleeve 12, as described in detail below. A metal layer with low thermal conductivity is disposed.

 The coolant channel 16 is in communication with the main coolant line 13 by connecting lines 15 connected at both ends thereof. Each of the connection lines 15 has a first connection line 15a extending radially from the main cooling water line 13 and one end of the first connection line 15a and the cooling water channel 16. It may include a second connecting line 15b interposed therebetween to communicate with each other.

4 is an enlarged cross-sectional view of the coolant channel 16 region illustrated in FIG. 3.

As shown in FIG. 4, according to the present invention, a metal layer 20 having a different thermal conductivity from the sleeve 12 is formed in at least a portion of the cooling water channel 16 in the width direction of the cooling water channel 16. The inner wall of the coolant channel 16 is disposed to cover the inner wall. In this case, the metal layer 20 may be formed on the inner wall of the cooling water channel 16 by various methods such as plating, shrinkage, babbitting or soldering.

In general, in a casting piece manufacturing process using a twin-roll type sheet casting machine, at the edge portion of the casting roll due to the shrinkage of the casting piece, the gas gap becomes larger than the central portion of the casting roll, a solidification delay phenomenon occurs. Therefore, in order to prevent the solidification nonuniformity of the casting roll width direction, it is necessary to improve the cooling ability of a casting roll edge part, or to reduce the cooling ability of the casting roll center part.

Therefore, according to an embodiment of the present invention, the inner wall of the central portion of the cooling water channel 16 corresponding to the central portion RC of the casting roll 10 has a metal layer 20 having a lower thermal conductivity than the sleeve 12. It is formed to surround the, by reducing the cooling ability of the center portion (RC) of the casting roll can eliminate the uneven cooling capability of the center portion (RC) and the edge portion (RE) of the casting roll (10). Alternatively, the metal layer 20 may be formed to cover the entire inner wall of the cooling water channel 16. In this case, the metal layer 20 may have a greater thickness at the center of the coolant channel corresponding to the center of the casting roll RC and at the edge of the coolant channel corresponding to the casting roll edge RE. By being formed, it is possible to adjust the uneven cooling capability of the casting roll center portion RC and the casting roll edge portion RE.

On the other hand, as an item for displaying the cooling capacity of the casting roll 10, the overall heat transfer coefficient value represented by Equation 1 below is used, which means that the heat transfer is good when the overall heat transfer coefficient value is large.

[Where H: overall heat transfer coefficient value (W / m ² K),

h _c : Heat transfer coefficient of the coolant channel (W / m ² K),

d ₁ : metal layer thickness (m) in the coolant channel,

d ₂ : depth from the sleeve surface to the coolant channel (m)

d ₃ : Thickness of the sleeve surface plating layer (m)

C _k : Thermal conductivity (W / mK) of the metal layer in the coolant channel

S _k : Thermal conductivity of the sleeve (W / mK)

C _k ´: Thermal conductivity of sleeve surface plating layer (W / mK)]

As in the present invention, when the metal layer 20 is formed in the cooling water channel 16, d ₁ / C _{k in} Equation 1 The term changes and the diameter of the coolant line changes, so 1 / h _c changes. Therefore, when the metal layer 20 is selectively formed in at least a portion of the cooling water channel 16 or the thickness of the metal layer 20 is changed, the above two terms can be changed, thereby casting casting 10 The overall heat transfer coefficient value according to the width direction of the) can be adjusted, and finally the cooling ability of the width direction of the casting roll 10 can be adjusted.

Further, in Equation 1, the heat transfer coefficient value h _c of the cooling water channel 16 may be calculated from Equation 2 below.

[Where k: thermal conductivity of the cooling water (= 0.611 W / mK),

D: coolant channel diameter

Nu _D: number neosel (Nusselt) in the cooling water channel ^{_{(= 0.023Re D 0 .8 Pr 0}} .4)

Re _D : Reynolds number in the coolant channel

Pr: Prandtle number of cooling water (= 5.9)]

Experimental Examples

In order to determine the effect of the casting roll according to an embodiment of the present invention, the following experiments were performed.

5 is a graph showing the total heat transfer coefficient value of the casting roll according to the thickness of the nickel plated layer, Figure 6 is a graph showing the total heat transfer coefficient value of the casting roll according to the thickness of the metal layer 20 formed in the cooling water channel (16). . 5 and 6 are calculated by assuming that a coolant channel 16 having a diameter of 11 mm is formed in a sleeve made of copper. In this case, the heat transfer coefficient of the coolant channel is expressed by Equation 2 Calculated from> 36,000W / m ² k.

5 shows that when the nickel plating layer is changed from 1 mm to 2 mm on the surface of the sleeve without forming a metal layer in the cooling water channel, the equation except for the metal layer related term (d ₁ / C _k ) in Equation _{1 is} obtained. It shows the change of the total heat transfer coefficient value of the casting roll calculated from. On the other hand, the result of Figure 6 is to form a nickel plating layer of 1mm on the surface of the sleeve for comparison, instead of changing the thickness of the nickel plating layer, when changing the metal layer in the cooling water channel to a thickness of 0mm ~ 2mm above <Equation 1> It shows the change of the total heat transfer coefficient value of the casting roll calculated from. In this case, a babbit metal having a thermal conductivity of 24 W / mK was used as the metal layer formed in the cooling water channel.

5 and 6, when the thickness of the nickel plating layer is changed from 1 mm to 2 mm, the total heat transfer coefficient of the casting roll is changed from 9,042 W / m ² K to 8,124 W / m ² K It was reduced by 10%. On the other hand, as shown in FIG. 6, when the Babbitt metal was formed to have a thickness of 1 mm, the total heat transfer coefficient of the casting roll was changed from 9,042 W / m ² K to 6,957 W / m ² K, which was reduced by about 23%. .

The result is that rather than varying the thickness of the nickel plating layer formed on the sleeve surface in the casting roll width direction to control the widthwise cooling ability of the casting roll, the metal layer 20 in the cooling water channel 16 as in the present invention. Forming selectively indicates that it is possible to more effectively control the overall heat transfer coefficient value of the casting roll, thereby ultimately preventing the nonuniformity in the cooling direction of the casting roll in the width direction.

7A and 7B are photographs showing edge portions of a stainless steel sheet wound and cast by one embodiment and a comparative example of the present invention.

The stainless steel sheet shown in Figs. 7A and 7B was cast using a large twin roll type sheet casting machine in which the diameter and width of the casting roll were 1250 mm and 1300 mm, respectively. FIG. 7A is a photograph showing a result of casting and forming a Babbitt metal on an inner wall of a central part of a coolant channel corresponding to a center of a casting roll such that the overall heat transfer coefficient of the center of the casting roll is 20% lower than that of the casting roll edge, and FIG. 7B is a cooling water channel. This picture shows the result when no metal layer is formed on the inner wall.

When no metal layer was formed in the coolant channel, edge buildup occurred as shown in FIG. 7B. On the other hand, in the case where the metal layer, i.e., the Babbitt metal, is formed on the inner wall of the central portion of the cooling water channel to reduce the cooling ability of the center portion of the casting roll width direction, as shown in FIG. It was possible to produce a stainless steel sheet having excellent edge quality without build up.

As described above, according to the present invention, by forming a metal layer having a thermal conductivity different from that of the sleeve in at least a portion of the width direction on the inner wall of the cooling water channel formed in the sleeve of the casting roll, thereby adjusting the widthwise cooling ability of the casting roll, It is possible to prevent deterioration of the quality of the casting pieces such as edge build-up phenomenon of the casting pieces due to uneven cooling ability and to improve the operation stability.

Claims (5)

A shaft having a main coolant line formed therein; A sleeve surrounding an outer circumferential surface of the shaft; A coolant channel disposed to be spaced apart from each other along the circumferential direction of the sleeve and extending in the width direction of the sleeve and communicating with the main coolant line through connection lines connected to both ends thereof; And The casting roll of the twin-roll type sheet casting machine comprising a metal layer having a lower thermal conductivity than the sleeve while being disposed to cover the inner wall in the width direction of the cooling water channel. The method of claim 1, The inner wall of the metal layer is a casting roll of a twin-roll thin plate casting machine, characterized in that formed in the central portion of the cooling water channel corresponding to the central portion of the casting roll. The method of claim 1, The inner wall of the metal layer is disposed to cover the entire inner wall of the cooling water channel, wherein the central portion of the cooling water channel corresponding to the center of the casting roll has a thickness larger than the edge of the cooling water channel corresponding to the casting roll edge portion A casting roll of a twin roll sheet metal casting machine characterized by the above-mentioned. The method of claim 2 or 3, The metal layer is a cast roll of a twin-roll thin plate casting machine, characterized in that consisting of a babbit metal or solder (solder). The method of claim 1, Casting roll of a twin-roll thin plate casting machine, characterized in that it further comprises a nickel plated layer plated on the surface of the sleeve.

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