Patent Application
20190262895
The present disclosure relates to casting equipment and a casting method using same, and more particularly, to casting equipment capable of effectively removing inclusions in molten steel and restricting reoxidation of the molten steel, and a casting method using same.
Continuous casting equipment receives molten steel from steel manufacturing equipment to manufacture a slab. The continuous casting equipment includes: a ladle transporting molten steel; a tundish that receives the molten steel from the ladle to temporarily store the received molten steel; a mold that continuously receives the molten steel from the tundish and primarily coagulates the molten steel into a slab; and a cooling zone performing a series of molding works while secondarily cooling the slab, which is continuously drawn from the mold.
While the molten steel is accommodated in the tundish and remained for a predetermined time, inclusions float to be separated, slag is stabilized, and reoxidation is prevented. Thereafter, the molten steel is supplied to the mold to form an initial coagulated layer as a shape of the slab. Here, a surface quality of the slab is determined.
A degree of the surface quality of the slab in the mold is determined according to cleanliness of the molten steel with respect to inclusions. For example, when the cleanliness of the molten steel with respect to inclusions is poor, a defect may be generated on a surface of the slab due to the inclusion itself, and, as a submerged nozzle is clogged by the inclusions, a flow of the molten steel may become abnormal to degrade the surface quality of the slab.
The cleanliness of the molten steel with respect to inclusions may be greatly varied according to a degree of floating and separation of the inclusions while the molten steel remains for a predetermined time in the tundish, and the degree of floating and separation of the inclusions may be proportional to a time in which the molten steel remains in the tundish.
Thus, a residence time of the molten steel is typically adjusted by controlling a flow of the molten steel by building a dam or a weir in the tundish as a method for extending the residence time of the molten steel in the tundish. However, when each of the inclusions mixed to the molten steel has a size of 30 μm or less, a time in which the inclusions float to be separated is greater than the residence time of the molten steel. Due to this reason, the inclusions each having a size of 30 μm or less may be hardly removed by using the dam and the weir of the tundish.
Japanese Registered Patent No. 4096635
Japanese Registered Patent No. 3654181
The present disclosure provides casting equipment capable of restricting a nozzle clogging phenomenon during casting by effectively removing inclusions in molten steel and a casting method using same.
The present disclosure also provides casting equipment capable of securing cleanliness by restricting reoxidation of molten steel and a casting method using same.
In accordance with an exemplary embodiment, casting equipment includes: a cover member installed on a tundish to define a space in at least a portion of an upper portion of a melting surface of molten steel accommodated in the tundish; a vacuum pump connected to the cover member to form vacuum in the space; and a control unit configured to control an operation of the vacuum pump.
The cover member may include: a vertical part having a hollow shape in which upper and lower portions are opened and vertically provided so that at least a portion is submerged into the molten steel; and a horizontal part connected to an upper portion of the vertical part to define a space between the vertical part and the horizontal part. Here, an exhaust hole may be defined in the horizontal part for connection with the vacuum pump.
The horizontal part may cover only the upper portion of the vertical part.
The horizontal part may be seated on an upper portion of the tundish.
A structure and an induction member may be provided in the tundish. Here, the structure may cross an inside of the tundish while being spaced apart from a bottom surface of the tundish in order to form a flow of molten steel, and the induction member may be disposed at each of both sides of the structure in parallel to the structure while being spaced apart from the bottom surface of the tundish.
The induction member may have a top surface higher in position than a top surface of the structure.
A nozzle may be provided to supply a gas to the tundish, and the nozzle may be provided at one side of the structure between the induction members.
The casting equipment may further include a detection unit configured to measure a level of the melting surface of the molten steel in the space.
The detection unit may include at least one of a distance sensor and a temperature sensor.
In accordance with another exemplary embodiment, a casting method includes: preparing a tundish; injecting molten steel to the tundish; installing a vacuum forming member on an upper portion of the tundish to form vacuum in at least a partial area of an upper portion of a melting surface of molten steel accommodated in the tundish; forming a rotational flow by blowing a gas into the molten steel; and forming vacuum in at least a partial area of the upper portion of the melting surface of the molten steel.
The preparing of the tundish may include forming an induction member configured to define an area for forming vacuum. Here, the induction member may be formed at each of both sides of a structure, which crosses an inside of the tundish while being spaced apart from a bottom surface of the tundish, in parallel to the structure.
The installing of the vacuum forming member may include: installing a cover member between the induction members; forming a space, which is spaced apart from the melting surface of the molten steel, in the cover member by submerging at least a portion of the cover member into the molten steel; and connecting a vacuum pump to the cover member.
The forming of the rotational flow may include blowing a gas to one side of the structure.
The forming of the vacuum may include suctioning the space by operating the vacuum pump.
The forming of the vacuum may be performed when at least a portion of the cover member is submerged into the molten steel.
The forming of the vacuum may include measuring variation in level of the melting surface of the molten steel in the space, and a degree of vacuum of the space may be adjusted according to the variation in level of the melting surface of the molten steel.
According to the casting equipment and the casting method using same in accordance with the exemplary embodiment, the rotational flow may be continuously formed in the molten steel regardless of the variation of the melting surface of the molten steel to effectively remove the inclusions in the molten steel. That is, as the space is formed in at least a portion of the upper portion of the melting surface of the molten steel accommodated in the tundish, and the inside of the space is suctioned to form vacuum, the level of the melting surface of the molten steel may be constantly maintained at all times. Thus, as the level of the melting surface of the molten steel is constantly maintained by forming the vacuum in the space regardless of the variation of the melting surface of the molten steel outside the space, the residence time of the molten steel in the tundish may increase to effectively remove the inclusions in the molten steel.
Also, since the gas injected to form the rotational flow is discharged to the outside through the space in which vacuum is formed, the exposed molten steel generated by the gas discharge may be prevented from contacting the atmosphere to restrict or prevent the reoxidation of the molten steel.
Also, as the cleanliness of the molten steel is maintained, the nozzle clogging or the slab defect, which may be generated during the casting, may be restricted or prevented.
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Like reference numerals in the drawings denote like elements.
Referring to
Referring to
One steel outlet hole 21 may be provided to each of both sides in a longitudinal direction of the tundish 20, and as a shroud nozzle 12 is disposed at a center in the longitudinal direction of the tundish 20, the molten steel accommodated in the ladle 10 may be injected to the tundish 20.
Through the above-described constitution, the molten steel injected through the nozzle 12 may move through a passage defined by the weir 24 and the dam 23 in the tundish 20 and be discharged through the steel outlet hole 21. As described above, as a residence time of the molten steel in the tundish 20 increases by forming a flow of the molten steel in the tundish 20, inclusions in the molten steel may be collected by a slag S disposed on the molten steel.
However, since the molten steel injected from the shroud nozzle 12 forms a flow that simply passes the passage defined by the weir 24 and the dam 23 in the above-described structure of the tundish 20, the inclusions in the molten steel may not be sufficiently removed. Thus, a rotational flow of the molten steel may be formed in the tundish by installing a nozzle 26 at a lower portion of the tundish 20 and blowing a gas, e.g., inert gas, into the tundish 20. Here, the nozzle 26 may be provided to one side of the weir 24, e.g., a portion adjacent to the shroud nozzle 12. As a result, the molten steel may form the rotational flow flowing by the gas supplied from the nozzle 26 while surrounding the weir 24, and the residence time of the molten steel in the tundish 20 may further increase.
However, in this case, since while the gas injected into the tundish is discharged, the slag moves to form naked molten steel, the molten steel contacts the atmosphere and is reoxidized. Also, since the level of the melting surface of the molten steel in the tundish 20 decreases when the ladle is replaced, the rotational flow of the molten steel in the tundish 20 is not smoothly generated.
Thus, in accordance with an exemplary embodiment, as a vacuum forming member 100 capable of forming vacuum in at least a portion of the tundish 20 is installed to continuously generate a rotational flow regardless of variation in level of the melting surface of the molten steel, the inclusions in the molten steel may be effectively removed, and the reoxidation, which is caused by contact between the molten steel and the atmosphere, may be restricted.
An induction member 25 that defines an area for constantly maintaining the level of the melting surface of the molten steel in the tundish 20, i.e., an area for forming the rotational flow, may be provided to install the vacuum forming member 100. In case of forming vacuum in a predetermined area in the tundish 20 by using the vacuum forming member 100, since a vacuum state is hardly maintained when the level of the melting surface of the molten steel is lower than an upper portion of the weir 24, an area for installing the vacuum forming member 100, i.e., an area for forming the rotational flow, may be prepared in advance by providing the induction member 25 to the tundish 20. For example, while vacuum may be formed by using the vacuum forming member 100 when the level of the melting surface of the molten steel is higher than the upper portion of the weir 24, the vacuum may be released when the level of the melting surface of the molten steel is lower than the upper portion of the weir 24 because a space is formed between the vacuum forming member 100 and the melting surface of the molten steel.
The induction member 25 may cross the inside of the tundish 20 while being spaced apart from the bottom surface of the tundish 20, and be disposed at each of both sides of the weir while being parallel to the weir 24. Here, the induction members 25 may be provided at an upper side, at which the nozzle 26 is defined, to form the rotational flow of the molten steel therebetween. Also, the weir 24 may be disposed between the induction members 25, and the rotational flow may be formed by the molten steel moving along the weir 24 between the induction members 25 by a gas supplied through the nozzle 26. Here, a guide member 25a may be provided to at least one side surface of the induction member 25 to smoothly generate the rotational flow of the molten steel. The guide member 25a may control a movement direction of the molten steel by forming an inclined surface on one side surface of the induction member 25. Although the inclined surface 25a is provided to the induction member 25 disposed at one side of the weir 24 at which a downward flow is formed in the drawing, the inclined surface may be provided to the induction member 25 disposed at the other side of the weir 24 at which an upward flow is formed. Here, directions of the inclined surfaces provided to the side at which the upward flow is formed and the side at which the downward flow is formed may be different from each other.
The induction member 25 may have a lower portion disposed lower than the upper portion of the weir 24 and an upper portion disposed higher than the upper portion of the weir 24. Thus, even when the level of the melting surface of the molten steel decreases, e.g., when the ladle is replaced, the molten steel may smoothly generate the rotational flow while maintaining the level of the melting surface to be higher than the upper portion of the weir 24.
Referring to
The cover member 110 may be disposed along a width direction of the tundish 20 and have an opened lower portion and a hollow upper portion in which an exhaust hole 114 is defined. The cover member 110 may include a vertical part 111 extending in a vertical direction and a horizontal part 112 connected to an upper portion of the vertical part 111. Here, the exhaust hole 114 may be defined in the horizontal part 112 and connected to the vacuum pump 120 through a separate exhaust pipe.
As the vertical part 111 is inserted between the induction members 25, a lower portion of the vertical part 111 may be submerged into the molten steel, and the vertical part 111 may have a length to define the space (a) upward from the melting surface of the molten steel in the cover member 110 while being submerged into the molten steel. Through the above-described constitution, the cover member 110 may have at least a portion, e.g., a lower portion, submerged into the molten steel to define the space (a) therein at an upper portion of the tundish 20.
Also, the horizontal part 112 may connect upper portions of the vertical parts 111 to define the space (a) between the horizontal part 112 and the vertical part 111. The horizontal part 112 may have an area corresponding to an area defined inside the vertical part 111 to cover only the upper portion of the vertical part 111. Alternatively, as illustrated in
Also, the cover member 110a may include a detection unit 130 for measuring the level of the melting surface of the molten steel in the space (a). As illustrated in (a) of
The vacuum pump 120 may be connected to the cover member 110 to suction the space (a) in the cover member 110, thereby forming vacuum in the space (a). Thus, as an inner pressure of the cover member 110, i.e., a pressure of the space (a), is less than a surrounding pressure, the level of the melting surface of the molten steel inside the cover member 110 is greater than surroundings, i.e., that of the melting surface of the molten steel outside the cover member 110.
The control unit may receive a result measured from the detection unit 130 and control an operation of the vacuum pump 120 according to the level of the melting surface of the molten steel, thereby constantly controlling the level of the melting surface of the molten steel in the space (a). For example, when the molten steel is continuously injected to the tundish 20 from the ladle 10, the rotational flow may be smoothly formed by the gas blown through the nozzle 26. However, when the supply of the molten steel is temporarily stopped for replacing the ladle 10, the level of the melting surface of the molten steel in the tundish 20 may be lowered. Thus, the level of the melting surface of the molten steel in the cover member 110 may be constantly maintained by appropriately adjusting the pressure of the space (a) through controlling of the operation of the vacuum pump 120 according to variation in level of the melting surface of the molten steel inside the cover member 110.
Hereinafter, a casting method in accordance with an exemplary embodiment will be described.
First, the molten steel, which has undergone refining, is inserted to the ladle 10, and then the ladle 10 moves to continuous casting equipment and is seated on a ladle turret. When the ladle is seated on the ladle turret, a nozzle unit (not shown) including the shroud nozzle 12 is connected to the steel outlet hole at a lower portion of the ladle 10.
When the nozzle unit is connected to the ladle 10, the vacuum forming member 100 is installed at an upper portion of the tundish 20, and the steel outlet hole at the lower portion of the ladle 10 is opened to inject the molten steel to the tundish 20.
When the molten steel is injected to the tundish, and the level of the melting surface of the molten steel injected to the tundish 20 reaches to form the rotational flow, e.g., reaches to an upper portion of the weir 24, a gas is blown to the molten steel through the nozzle 26. Here, the gas blown into the tundish 20 may include an inert gas such as argon (Ar). When the gas is supplied to the tundish 20, as illustrated in (a) of
When the level of the melting surface of the molten steel increases by injecting the molten steel to the tundish 20, a lower portion of the cover member 110 installed on the tundish 20, i.e., a portion of the vertical part 111, may be submerged into the molten steel, and the space (a) may be formed at the upper portion of the melting surface of the molten steel inside the cover member 110.
When the vertical part 111 is submerged into the molten steel to form the space (a) inside the cover member 110, the control unit may operate the vacuum pump 120 to suction the inside of the cover member 110, thereby forming vacuum. Here, since air may be introduced into the tundish 20 when the vacuum pump 120 suctions the inside of the cover member 110 before the vertical part 111 is submerged, vacuum is preferably formed by suctioning the inside of the cover member 110 after the vertical part 111 of the cover member 110 is submerged into the molten steel.
Whether the vertical part 111 is submerged into the molten steel may be measured through the detection unit 130. As illustrated in (a) of
Also, as illustrated in (b) of
A slab may be manufactured by injecting the molten steel to the mold 30 through the submerged nozzle 32 connected to communicate with the steel outlet hole 21 at the lower portion of the tundish 20 by opening the steel outlet hole 21.
During casting of the slab, the rotational flow of the molten steel may be formed by continuously injecting a gas into the tundish 20, and the vacuum state may be maintained by suctioning the inside of the cover member 110 through the vacuum pump 120. Thus, the rotational flow may be continuously formed in the tundish 20 during the casting. Also, since the gas generating the rotational flow is discharged to an area at which the vacuum is formed, the molten steel may be prevented from contacting the atmosphere.
On the other hand, the supply of the molten steel to the tundish 20 may be temporarily stopped while the ladle is replaced. In this case, as illustrated in (b) of
As described above, the rotational flow of the molten steel, which is formed between the induction members 25, i.e., the lower portion of the cover member 110, may be continuously maintained regardless of the variation in level of the melting surface of the molten steel in the tundish 20. As the rotational flow of the molten steel is continuously formed in the tundish 20 during the casting of the slab, the residence time of the molten steel in the tundish 20 may increase to effectively remove the inclusions in the molten steel. Also, the molten steel may be prevented from contacting the atmosphere in the area at which the rotational flow of the molten steel is formed to prevent the reoxidation of the molten steel.
Although the specific embodiments are described and illustrated by using specific terms, the terms are merely examples for clearly explaining the embodiments, and thus, it is obvious to those skilled in the art that the embodiments and technical terms can be carried out in other specific forms and changes without changing the technical idea or essential features. Therefore, it should be understood that simple modifications according to the embodiments of the present invention may belong to the technical spirit of the present invention.
The casting equipment and the casting method using same in accordance with the exemplary embodiment may effectively remove the inclusions in the molten steel to maintain the cleanliness of the molten steel. Thus, the nozzle clogging or the slab defect, which are generated during casting, may be restricted or prevented, and, through this, the process efficiency and the productivity may be enhanced.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2016-0148865 | Nov 2016 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2017/012308 | 11/2/2017 | WO | 00 |
