The present invention relates to a hybrid cooling nozzle apparatus equipped in a segment of a continuous casting machine and, more particularly, to a hybrid cooling nozzle apparatus capable of selecting a spraying manner and performing a spraying action accordingly based on the speed of a metal strip passing through segments of a continuous casting machine, and a method of controlling a cooling nozzle of the continuous casting machine using the same.

Generally, a continuous casting process is a process that continuously solidifies molten steel into a solid product in a specified form. Here, a plurality of nozzles are provided on each of the segments of a continuous casting machine in order to cool a metal strip during the continuous casting process.

FIG. 1 is a view showing a conventional continuous casting process.

In the continuous casting process, refined molten steel is poured from a ladle 30 into a tundish 40 through a long nozzle, the molten steel being temporarily stored in the tundish 40 is transferred into a mold 50 through a delivery system between the tundish 40 and the mold 50, and the molten steel is primarily cooled in the mold and then secondarily cooled and solidified below the mold 50, thereby producing a metal strip 60 such as billet, bloom, slab or the like.

After primarily cooled in the mold 50, molten steel being discharged from the mold 50 is introduced between an upper frame 22 and a lower frame 23 of each of the segments 20 of the continuous casting machine in a state of the outer surface thereof being slightly solidified, where the molten steel is continuously and quickly solidified into a product in the form of a metal strip to be fabricated by spraying cooling water thereon via a plurality of nozzles 24.

FIG. 2 is a view showing the segment onto which the nozzles used in continuous casting are mounted.

As shown in FIG. 2, the segment 20 is provided with both a plurality of guide rolls 21 generally consisting of 5 to 10 rolls on upper and lower frames, respectively, and the plurality of nozzles 24, which sprays cooling water for quick solidification of the molten steel.

Here, if the cooling water is not uniformly sprayed via the nozzles 24, a bulging phenomenon occurs in a region where the cooling water is not sprayed, due to delayed solidification, so that the metal strip expands between the guide rolls owing to a widthwise ferro-static pressure. Such a bulging phenomenon causes internal defects or central segregation of the metal strip so that relatively high density molten steel in a solidification-interface layer propagates towards the center of the molten steel in a compressed state, being segregated. Upon the occurrence of such segregation, since relatively low density molten metal is supplied after the high density molten steel is compressed, defects which accompany with not-segregated regions are generated, adversely affecting quality of a final product.

On the one hand, if cooling water is excessively sprayed from the nozzles 24, or otherwise casting speed is low in the continuous casting process, the metal strip passing through the segments may have a defect such as edge cracks due to decreased temperature. Defects such as cracks degrade surface quality of a metal strip, which must be removed in a further process. Such a further process problematically causes further costs.

In order to solve the above problem, an apparatus and method for preventing edge cracks of a metal strip in continuous casting by controlling cooling of the metal strip using an air mist spray nozzle is known in the art (Korean Unexamined Patent Publication No. 10-2012-0074744).

However, the conventional technique does not solve a problem of delayed solidification, because, upon high speed continuous casting, it does not effectively cool the metal strip passing through the segments.

Further, a problem arises in that, when the pressure of cooling water is increased, the cooling water flows backward into an air inlet of the air mist spray nozzle.

The present invention is directed to a hybrid cooling nozzle apparatus capable of selecting a spraying mode and performing a spraying action based on the speed of a metal strip passing through segments of a continuous casting machine, thereby preventing a bulging phenomenon due to delayed solidification and edge cracks due to subcooling of the metal strip, and a method of controlling a cooling nozzle of the continuous casting machine using the same.

Further, the present invention is directed to a hybrid cooling nozzle apparatus which is provided, in an air line for supplying air to a hybrid nozzle, with a shut-off valve for preventing a backflow of cooling water, thereby increasing a turn down ratio.

In an aspect of the present invention, there is provided a cooling nozzle apparatus including: a plurality of hybrid nozzles provided in a segment of a continuous casting machine and configured to spray cooling water in a mist-spraying mode or a water-jet spraying mode onto a metal strip passing through the segment; at least one speed sensor installed in the segment and configured to detect the speed of the metal strip passing through the segment; a cooling water supply configured to supply cooling water to the hybrid nozzles; an air supply configured to supply air to the hybrid nozzles, and a controller configured to receive the speed of the metal strip detected by the speed sensor, and to select the spraying mode of the hybrid nozzles depending on the received speed of the metal strip, and control a pressure and a flow rate of the cooling water and air, respectively, to be supplied to the hybrid nozzles by controlling the cooling water supply and the air supply.

The cooling water supply may include a cooling water line through which the cooling water is supplied to the hybrid nozzle and a cooling water valve installed in the cooling water line to control the pressure of the cooling water being supplied to the hybrid nozzle; the air supply may include an air line through which air is supplied to the hybrid nozzle, an air valve installed in the air line to control a flow rate of air being supplied to the hybrid nozzle, and a shut-off valve configured to prevent a backflow of the cooling water; and the controller may control the cooling water valve and the air valve depending on the spraying mode of the hybrid nozzle.

The controller may be configured to close the shut-off valve so as to prevent the cooling water from being introduced into the air line, when the pressure of the cooling water being supplied to the hybrid nozzle is 8 bars or more.

In another aspect of the present invention, there is provided a method of controlling a plurality of hybrid nozzles provided in a segment of a continuous casting machine so as to spray cooling water on a metal strip, the method including: detecting a kind and a speed of the metal strip passing through the segment; selecting a spraying mode of the hybrid nozzles depending on the detected speed of the metal strip; and controlling a pressure and a flow rate of the cooling water and air, respectively, to be supplied to the hybrid nozzles depending on the selected spraying mode of the hybrid nozzles.

The spraying mode may be selected from a mist-spraying mode or a water-jet spraying mode depending on the kind and speed of the metal strip passing through the segment.

When the water-jet spraying mode is selected, the pressure of the cooling water may be controlled to be 8 bars or more, and when the mist-spraying mode is selected, the pressure of the cooling water may be controlled to be below 8 bars.

According to the present invention, the hybrid cooling nozzle apparatus is capable of selecting a spraying mode and performing a spraying action based on the speed of a metal strip passing through segments of a continuous casting machine, thereby preventing a bulging phenomenon due to delayed solidification and edge cracks due to subcooling of the metal strip.

Further, edge cracks of the metal strip are prevented, thereby reducing additional processes and costs for removing such cracks.

Further, the flow rate of air and the pressure of the cooling water are controlled depending on the speed of the metal strip, thereby preventing a waste of air and cooling water and reducing the process costs.

Furthermore, a shut-off valve is installed in the air line for supplying air to the hybrid nozzle to prevent a backflow of cooling water, thereby increasing a turn down ratio.

• FIG. 1 is a view showing a conventional continuous casting process;
• FIG. 2 is a view showing a segment having spray nozzles used in the conventional continuous casting process;
• FIG. 3 is a view showing a hybrid cooling nozzle apparatus according to an embodiment of the present invention being installed;
• FIG. 4 is a diagram showing correlation between an air flow rate and a pressure of cooling water according to a spraying mode of a hybrid spray nozzle according to an embodiment of the present invention;
• FIG. 5 is a graph showing cooling performance with the adaptation of the hybrid spray nozzle according to the embodiment of the present invention; and
• FIG. 6 is a flow chart showing a method of controlling a cooling nozzle of a continuous casting machine according to an embodiment of the present invention.

A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. However, the present invention is not restricted or limited to the embodiment. For reference, like numerals substantially refer to like elements throughout the drawings so they can be cited from other drawings in the following description, and contents that are determined to be apparent to those skilled in the art or are repeated can be omitted.

FIG. 3 is a view showing a hybrid cooling nozzle apparatus according to an embodiment of the present invention being installed, FIG. 4 is a diagram showing correlation between an air flow rate and a pressure of cooling water according to a spraying mode of a hybrid spray nozzle according to an embodiment of the present invention, and FIG. 5 is a graph showing cooling performance with the adaptation of the hybrid spray nozzle according to the embodiment of the present invention.

As shown in the drawings, a hybrid cooling nozzle apparatus 10 includes: a plurality of hybrid nozzles 100 provided in a segment 20 of a continuous casting machine and configured to spray cooling water in a mist-spraying mode or a water-jet spraying mode onto a metal strip 60 passing through the segment 20; at least one speed sensor 200 installed on one side of the segment 20 and configured to detect the speed of the metal strip 60 passing through the segment 20; a cooling water supply 300 configured to supply cooling water to the hybrid nozzles 100; an air supply 400 configured to supply air to the hybrid nozzles 100, and a controller 500 configured to receive the speed of the metal strip 60 detected by the speed sensor 200, and to select the spraying mode of the hybrid nozzles 100 depending on the received speed of the metal strip, and control a pressure and a flow rate of the cooling water and air, respectively, being supplied to the hybrid nozzles 100.

The hybrid nozzle 100 cools the metal strip 60 passing through the segment 20 in a mist-spraying mode, in which the cooling water is discharged together with air and thus is sprayed in a mist form, or a water-jet spraying mode, in which only the cooling water is sprayed.

The speed sensor 200 detects the speed of the metal strip 60 passing through the segment 20, and sends the detected speed to the controller 500.

The speed of the metal strip 60 passing through the segment 20 is directly measured, or otherwise is indirectly measured by measuring a rotary speed of guide rolls 21 provided in the segment 20 so as to guide the metal strip 60.

Here, the speed sensor 200 may be a magnetic sensor, a tacho-generator, a stroboscope-type sensor, or the like, for example. The speed sensor 200 may not be limited to those described in the above embodiment, but may be selected from various kinds of speed sensors capable of detecting the speed of the metal strip 60 or the rotary speed of the guide roll 21.

The cooling water supply 300 includes a cooling water line 310 which is connected with the hybrid nozzles 100 so as to supply cooling water, and a cooling water valve 320 which is installed to the cooling water line 310 so as to control a pressure of the cooling water being supplied to the hybrid nozzles 100. Here, the cooling water valve 320 is controlled by the controller 500 depending on a kind of the metal strip 60 and the speed of the metal strip detected by the speed sensor 200.

The cooling water valve 320 may include, for example, a relief valve, a pressure-reducing valve, a safety valve, or the like. The cooling water valve 320 may not be limited to those described in the above embodiment, but may be selected from various kinds of valves capable of regulating the pressure of the cooling water being supplied to the hybrid nozzles 100.

The air supply 400 includes an air line 410, which is connected with the hybrid nozzles 100 so as to supply air, an air valve 420, which is installed to the air line 410 so as to regulate a flow rate of air being supplied to the hybrid nozzles 100, and a shut-off valve 430, which is installed between the air valve 420 and the hybrid nozzle 100 so as to prevent the cooling water from flowing backward into the air line 420 connected with the hybrid nozzles 100 when the spraying mode of the hybrid nozzle 100 is the water-jet spraying mode in which only the cooling water is sprayed. When the spraying mode of the hybrid nozzle 100 is the mist-spraying mode, air is supplied through the air line, together with the cooling water, so that the cooling water is sprayed in a mist form.

The air valve 420 and the shut-off valve 430 are controlled by the controller 500 depending on a kind of the metal strip 60 and the speed of the metal strip detected by the speed sensor 200.

Here, the air valve 420 may include, for example, a relief valve, a pressure-reducing valve, a safety valve, or the like. The air valve 420 may not be limited to those described in the above embodiment, but may be selected from various kinds of valves capable of regulating the flow rate of air being supplied to the hybrid nozzles 100.

The shut-off valve 430 is configured to close the air line 410 in the water-jet spraying mode of the hybrid nozzle 100 depending on the kind and speed of the metal strip 60, thereby preventing the high-pressure cooling water from flowing backward into the air line 410.

While the shut-off valve 430 is used to prevent a backflow of the cooling water into the air line 410 in the above embodiment, the shut-off valve 430 is not limited to those described, but may be selected from various kinds of valves such as a check valve capable of preventing a backflow of the cooling water into the air line 410.

The controller 500 is configured such that a kind of the metal strip and a reference speed of the metal strip 60 according to the kind are previously input thereto. The controller 500 performs a control action such that, when the detected speed of the metal strip 60 is higher than the reference speed, the shut-off valve is closed so as to close the air line 410, and the cooling water valve 320 is controlled to allow the cooling water to be supplied to the hybrid nozzle 100 in a water-jet spraying mode with a pressure of 8 to 25 bars.

Further, when the detected speed of the metal strip 60 is lower than the reference speed, the controller controls the hybrid nozzles 100 to be operated in a mist-spraying mode in order to prevent edge cracks of the metal strip 60 from occurring due to decreased temperature of the metal strip 60. Here, the controller 500 opens the shut-off valve 430 and controls the air valve 420 so that the flow rate of air being supplied to the hybrid nozzle 100 ranges from zero to 15 Nm³/hr, and also controls the cooling water valve 320 so that the pressure of the cooling water being supplied to the hybrid nozzle 100 ranges zero to 8 bars, thereby allowing the cooling water to be sprayed in a mist form.

A method of controlling a cooling nozzle of a continuous casting machine using the above-mentioned hybrid cooling nozzle apparatus 10 will now be described with reference to the drawings.

FIG. 6 is a flow chart showing the control method for the cooling nozzle of the continuous casting machine according to an embodiment of the present invention.

As shown in the drawing, the control method using the hybrid cooling nozzle apparatus 10 includes detecting a kind and a speed of the metal strip 60 passing through the segment 20, selecting a spraying mode of the hybrid nozzles 100 depending on the detected speed of the metal strip 60, and controlling a pressure and a flow rate of the cooling water and air, respectively, to be supplied to the hybrid nozzle 100 depending on the selected spraying mode of the hybrid nozzle 100.

The kind and speed of the metal strip are detected with respect to the metal strip introduced into the segment 20 from via the mold 50 are sent to the controller 500. The speed of the metal strip 60 is measured by the speed sensor 200.

The spraying mode of the hybrid nozzle 100 is selected such that, when receiving a kind and a speed of the metal strip 60 and comparing the measured speed with a reference speed, which is previously input to the controller depending on a kind of the metal strip 60, if the speed of the metal strip sensed by the speed sensor 200 is determined to be higher than the reference speed, a water-jet spraying mode is selected as the spraying mode of the hybrid nozzles 100, and if the measured speed is determined to be lower than the reference speed, a mist-spraying mode is selected as the spraying mode of the hybrid nozzles 100.

The cooling water and air being supplied to the hybrid nozzles 100 are regulated with respect to a pressure of the cooling water and a flow rate of air depending on the spraying mode of the hybrid nozzles 100.

FIG. 4 shows the correlation between the flow rate of air and the pressure of the cooling water depending on the spraying mode of the hybrid nozzle according to an embodiment of the present invention.

As shown in FIG. 4, when the speed of the metal strip 60 is relatively high, a water-jet spraying mode is selected as the spraying mode of the hybrid nozzles 100, and the controller 500 closes the air valve 420 so as to prevent air from being supplied to the hybrid nozzles 100, closes the shut-off valve 430 so as to prevent the cooling water from flowing backward into the air line 410, and at the same time, controls the cooling water valve 320 so that the cooling water being supplied to the hybrid nozzles 100 has a pressure of 8 to 25 bars depending on the measured speed.

Further, when the speed of the metal strip 60 is relatively low, a mist-spraying mode is selected as the spraying mode of the hybrid nozzles 100, and the controller 500 opens the shut-off valve 430 to control the air valve 420 to supply air to the hybrid nozzle at a flow rate of zero to 15 Nm³/hr depending on the measured speed, and at the same time, controls the cooling water valve 320 so that the cooling water being supplied to the hybrid nozzles 100 has a pressure of zero to 8 bars.

Here, when the pressure of the cooling water being supplied to the hybrid nozzles 100 is 8 bars or more, the controller 500 controls the cooling water valve 320, the air valve 420, and the shut-off valve 430 such that the spraying mode of the hybrid nozzles 100 selects the water-jet spraying mode. Further, when the pressure of the cooling water being supplied to the hybrid nozzles 100 is below 8 bars, the controller 500 controls the cooling water valve 320, the air valve 420, and the shut-off valve 430 such that the spraying mode of the hybrid nozzles 100 selects the mist-spraying mode.

While the present invention has been described with reference to the preferred embodiment, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.