JP2018015781A - Secondary cooling method and secondary cooling device of continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cope with acceleration of casting speed by improving cooling capacity of secondary cooling in a continuous casting machine without increasing the quantity of water or without elongating a machine length of the continuous casting machine.SOLUTION: In a secondary cooling method of continuous casting, a cooling device 31 is provided in a clearance between each support roll 10 for conveying a cast slab H. The cooling device 31 includes a coolant guide plate 32 installed approximately in parallel to the cast slab H with a clearance 34 for forming a coolant passage between itself and the surface of the cast slab H, and a refrigerant pipe (water supply pipe 33) for supplying the coolant into the clearance 34, to thereby achieve cooling so that the coolant has a contact with the cast slab H in a non-boiling or nuclear-boiling region.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a secondary cooling method and a secondary cooling device when performing continuous casting of a slab with a continuous casting machine.

  In the continuous casting of the steel industry, spray-type cooling has been widely performed as a method for secondary cooling of a slab. In this secondary cooling method, a spray nozzle is disposed between support rolls that convey a slab, and cooling water is sprayed onto the surface of the slab to cool it.

  However, in the case of the spray method, water is scattered by spraying water onto a high-temperature slab, and the sprayed water is not efficiently used, so that the cooling capacity is limited. Therefore, in order to increase the casting speed and improve the productivity in the future, it is necessary to increase the amount of water supply significantly or extend the length of the continuous casting machine to increase the secondary cooling section. That is, the current continuous casting machine cannot cope with it, and in order to increase the speed of continuous casting, a significant improvement in the heat transfer coefficient in secondary cooling is desired.

  Conventionally, for example, Patent Document 1 discloses a secondary cooling method in which a slab surface temperature is maintained in a film boiling region in order to reduce temperature unevenness in secondary cooling and perform uniform cooling. Describes that a cooling plate is ejected by arranging a perforated plate.

  Moreover, as a method for improving the cooling capacity of secondary cooling, for example, Patent Document 2 discloses a cooling grid facility using a wear plate.

  Patent Document 3 discloses a secondary cooling method for a continuous slab that uses a water film flow to cool the slab and enhances the cooling capacity.

Japanese Patent No. 5146006 Japanese Patent No. 4453562 JP 2002-086253 A

  However, in the case of Patent Document 1, since cooling water is injected from a plurality of ejection holes arranged in the longitudinal direction of the slab, interference between the cooling waters and the accompanying retention of the cooling water easily occur, and uniform cooling cannot be performed. . Further, Patent Document 1 is for cooling in the region of film boiling so as not to overcool, and a significant improvement in cooling capacity cannot be expected.

  In the case of Patent Document 2, since the wear plate is in contact with the slab, wrinkles are generated on the surface of the slab, resulting in a quality problem.

  Further, in the case of Patent Document 3, each water film forming plate is moved in the gap between the water film forming plate and the slab that is continuously moved in the direction opposite to the drawing direction of the slab, for example, driven by a caterpillar. A secondary cooling method for continuous casting in which water is supplied from a provided water supply port to form a water film flow having a thickness of 0.1 to 2.5 mm is disclosed, but from a plurality of water supply ports arranged in the longitudinal direction. Since the cooling water is supplied, interference between the cooling waters and the stagnation of the cooling water accompanying this easily occur, and uniform cooling cannot be performed.

  Therefore, the present invention improves the cooling capacity of the secondary cooling in the continuous casting machine, can cope with a higher casting speed without significantly increasing the amount of water or extending the length of the continuous casting machine. An object of the present invention is to provide a secondary cooling method and secondary cooling device for casting.

  In order to solve the above-mentioned problem, the present invention is a secondary cooling method for continuous casting, in which a cooling device is provided in a gap between support rolls that convey a slab, and the cooling device is connected to a surface of the slab. A refrigerant guide plate that is installed substantially parallel to the slab with a gap for forming a refrigerant flow path therebetween, and a refrigerant pipe that supplies the refrigerant to the gap, and is supplied to the gap Provided is a secondary cooling method for continuous casting, wherein the slab is cooled by contacting the slab in a region where the refrigerant is non-boiling or nucleate boiling. Note that non-boiling or nucleate boiling refers to a state in which at least a part of the refrigerant contacts the slab surface in a liquid state to cool the slab.

The gap may be greater than 0.5 mm and not more than d ₀ mm satisfying the following formula (1).
d ₀ = 3.838 × 10 ⁻⁴ × W ^0.48 × (T + 273) ^0.80 (1)
here,
d ₀ (mm): Channel gap interval W (L / min.m ² ) at which the heat transfer coefficients of water film cooling and spray cooling are equivalent: Water density T (° C.): Evaluation temperature In addition, what is water film cooling? It is cooling using the cooling device of the present invention, and spray cooling is cooling using a refrigerant sprayed in a spray form.

  The refrigerant is supplied to the gap through a supply port formed in the refrigerant guide plate, and the supply port has a plurality of holes arranged in a line in the width direction of the slab, or the width of the slab. It may be a slit whose direction is the longitudinal direction.

Further, the present invention is a cooling device that performs secondary cooling of continuous casting, and is provided in a gap between support rolls that convey a slab, and forms a coolant channel between the surfaces of the slab. And a refrigerant guide plate installed substantially parallel to the slab with a gap for the purpose, and a refrigerant pipe for supplying the refrigerant to the gap. The gap exceeds 0.5 mm, and the following formula (1) D ₀ mm or less that satisfies the above condition, and the coolant supplied to the gap contacts the slab in the non-boiling or nucleate boiling region to cool the slab, and the secondary cooling of continuous casting Providing equipment.
d ₀ = 3.838 × 10 ⁻⁴ × W ^0.48 × (T + 273) ^0.80 (1)
here,
d ₀ (mm): Channel gap interval W (L / min.m ² ) at which the heat transfer coefficients of water film cooling and spray cooling are equivalent: Water density T (° C.): Evaluation temperature

  A supply port for supplying the refrigerant to the gap is formed in the refrigerant guide plate, and the supply port extends in a plurality of holes arranged in a line in the width direction of the slab or in the width direction of the slab. The slit may be a direction.

  According to the present invention, since the cooling efficiency of the secondary cooling of continuous casting can be greatly improved, the casting speed can be increased without increasing the amount of cooling water.

It is a side view which shows the outline | summary of the continuous casting machine concerning embodiment of this invention. It is sectional drawing which shows the outline of the experimental apparatus which tests the cooling capacity of spray cooling. It is the graph which showed the heat transfer coefficient of the spray cooling measured by the experimental apparatus of FIG. 2 with respect to the water density when the slab temperature is 900 ° C. and 600 ° C. It is sectional drawing which shows the outline of the experimental apparatus which tests the cooling capacity of water film cooling. It is a figure explaining the change of the state of the water which contacts a slab in water film cooling. When the slab temperature is 900 ° C., the water film cooling heat transfer coefficient measured by the experimental apparatus of FIG. 4 is compared with the heat transfer coefficient of spray cooling measured by the experimental apparatus of FIG. It is the graph shown with respect to. When the slab temperature is 600 ° C., the heat transfer coefficient of water film cooling measured by the experimental apparatus of FIG. 4 is compared with the heat transfer coefficient of spray cooling measured by the experimental apparatus of FIG. It is the graph shown with respect to. It is a side view which shows a part of continuous casting machine provided with the cooling device concerning embodiment of this invention. It is the figure which looked at FIG. 8 in front of the slab surface. It is a side view which shows a part of continuous casting machine provided with the cooling device concerning other embodiment of this invention. It is the figure which looked at FIG. 10 in front of a slab surface.

  Embodiments of the present invention will be described below. FIG. 1 is an explanatory diagram showing an outline of the configuration of a continuous casting machine 1 according to the present embodiment.

  As shown in FIG. 1, the continuous casting machine 1 includes a tundish 2 for temporarily storing molten steel, an immersion nozzle 4 for injecting molten steel into the mold 3 from the bottom of the tundish 2, and a slab H pulled out from the mold 3. A slab passage 5 to be passed, and a pair of roll groups 6 and 7 arranged to face each other with the slab passage 5 interposed therebetween are provided.

A pair of rolls 6 and 7, so as to guide the slab H in the casting direction D ₁ along the slab passage 5, are provided on both surfaces of the slab passage 5. The inner peripheral roll group 6 includes a plurality of support rolls 10 that guide the inner peripheral side of the slab H in the slab passage 5. Each supporting roll 10, the center axis thereof so as to face in the width direction of the slab H, are arranged in a row along the casting direction D _1. Further, the outer peripheral side roll group 7 has a plurality of support rolls 11 for guiding the outer peripheral side of the slab H in the slab passage 5. Each supporting roll 11 has its central axis so as to face in the width direction of the slab H, are arranged in a row along the casting direction D _1.

  Molten steel in the tundish 2 is injected from the upper side of the mold 3 through the immersion nozzle 4 and is primarily cooled by the mold 3 to form a solidified shell on the contact surface with the mold 3. Further, the slab H having the solidified shell as the outer shell and having the unsolidified molten steel inside is continuously cooled by the secondary cooling water in the state sandwiched between the support rolls 10 and 11 below the mold 3. The slab H that has been drawn out and is finally solidified to the center is produced.

  FIG. 2 shows an experimental apparatus for measuring the cooling capacity of the spray nozzle 15 generally used in the current continuous casting machine. Cooling water was sprayed onto the surface of the steel slab using various nozzles from above the center of the steel slab 16 preheated to a temperature equal to or higher than a predetermined evaluation temperature, thereby cooling the steel slab 16. The temperature transition of the steel slab 16 during cooling was measured, and the measurement result was used to obtain the heat transfer coefficient of the steel slab surface. At this time, the temperature transition of a portion of the steel slab surface where the spray jet 17 of the cooling water from the spray nozzle 15 does not directly collide is also measured, and the spray jet 17 of the cooling water discharged from the spray nozzle 15 becomes the steel slab. A value averaged over a rectangular range in which an ellipse formed by colliding with the surface is an inscribed circle was calculated as a heat transfer coefficient when the spray nozzle 15 was used. The temperature measurement of the steel slab 16 was performed by embedding a thermocouple at a position 2 mm inside from the cooling surface of the steel slab 16 in the thickness direction.

  Table 1 shows the measured values of the heat transfer coefficient when the evaluation temperature is 900 ° C. FIG. 3 is a plot of heat transfer coefficient versus water density. Here, the water amount density is obtained by dividing the amount of cooling water sprayed from the spray nozzle by the rectangular area on the steel piece.

  It can be seen from Table 1 and FIG. 3 that the heat transfer coefficient improves as the water density increases.

  Table 2 shows the measured values of the heat transfer coefficient when the evaluation temperature is 600 ° C. It can be seen that the heat transfer coefficient improves as the water density increases even at the evaluation temperature of 600 ° C. The measured value at 600 ° C. is also shown in FIG.

  Next, the cooling effect of water film cooling was tested. FIG. 4 shows an outline of a model device 21 for testing the cooling capacity of water film cooling. A coolant guide plate 23 was provided at an appropriate interval from the surface of the steel piece 22, and water was supplied from the water supply nozzle 24 toward the gap 25 between the steel piece 22 and the coolant guide plate 23. The gap 25 becomes a water flow path, a water film is formed on the surface of the steel piece 22, and the steel piece 22 is cooled. The temperature of the steel slab 22 according to the distance from the water supply nozzle 24 in the direction in which water flows (X direction) was measured, and the cooling capacity was examined. The temperature of the steel slab 22 was measured by embedding a thermocouple at a position 1.5 mm inside in the thickness direction (Z direction) from the cooling surface of the steel slab 22.

  Tables 3 and 4 show the measured values of the heat transfer coefficient by water film cooling when the evaluation temperatures are 900 ° C. and 600 ° C., respectively. In the water film cooling experiment, the area in which the water film was formed on the surface of the steel slab was taken as the evaluation target area. From Tables 3 and 4, it was found that increasing the water density increases the heat transfer coefficient, and even at the same water density, the heat transfer coefficient can be improved by reducing the channel gap interval. This is considered to be because, when the gap between the flow paths is reduced, the flow rate of the water film flowing between the steel piece and the refrigerant guide plate is increased, and the formation of the vapor film on the steel piece surface is suppressed. The definition of the water amount density is obtained by dividing the amount of cooling water supplied from the water supply port to form a water film flow by the area of the steel slab.

  When water film cooling is performed, it is conceivable that the cooling capacity for the slab H varies greatly depending on the state of water in contact with the slab H. That is, as shown in FIG. 5, water comes into contact with the hot slab H at the water supply point, and in sequence, non-boiling (section A), nucleate boiling (section B), film boiling (section C), and anhydrous (section D). ) State. The cooling effect is large in the sections A to B, and the cooling effect is reduced from the section C in which the film is in a boiling state. When water film cooling is performed, a high heat transfer coefficient can be exhibited by keeping the cooling water in contact with the slab H in a non-boiling or nucleate boiling state.

  As shown in Table 3 and Table 4, it is impossible to cool the steel slab at the level where the refrigerant guide plate and the steel slab are close to each other until the gap between the channels is 0.5 mm, and the heat transfer coefficient is measured. I couldn't. This is presumably because the flow path of the cooling water is blocked by the scale generated on the surface of the steel slab by cooling or the bending of the steel slab generated by cooling.

As shown in Tables 3 and 4, the maximum value of the water density in the water film cooling experiment was 1000 L / min. It was m ^2. This is because the maximum supply capacity of the cooling water pump in the existing continuous casting machine is 1000 L / min. This is because when it is about m ² and attempts to supply more cooling water than this, a new cooling water pump is required, so that the amount of capital investment becomes excessive, which is not realistic.

  Moreover, the space | interval of the support roll in continuous casting is about 200 mm-250 mm, and when installing the coolant guide board for water film cooling between support rolls, the length of the said cooling guide board is about 200 mm at maximum. As will be described later, it was assumed that water was supplied from the center of the refrigerant guide plate, and half of the supplied cooling water flowed upward (on the mold side) and the other half downward. For this reason, in this test, the length of the water film flow was set to 100 mm.

FIG. 6 is a plot of the heat transfer coefficient by water film cooling when the evaluation temperature is 900 ° C. with the water density plotted on the horizontal axis. The numerical value indicated on the shoulder of each plot indicates the interval of the channel gap of each condition. Moreover, the continuous line shown in FIG. 6 is the measured value of the heat transfer coefficient by spray cooling implemented at the evaluation temperature of 900 degreeC. From FIG. 6, for example, the water density is 600 L / min. From the plot of m ² , it can be seen that a very large heat transfer coefficient can be obtained when the gap distance between the channels is 0.6 mm. From this, it can be seen that the heat transfer coefficient decreases as the flow path gap interval increases, and the same heat transfer coefficient as spray cooling is obtained when the flow path gap interval is 2.3 mm. That is, in this respect, the same heat transfer coefficient is obtained by spray cooling and water film cooling. Furthermore, at the level where the gap between the channels is increased to 4.0 mm, the measured heat transfer coefficient is lower than the spray cooling value. Even if water film cooling is introduced, the heat transfer coefficient is smaller than that of spray cooling. Indicates that there is no improvement. This is because when the gap between the channels is enlarged, the flow rate of the water film flowing between the steel slab and the refrigerant guide plate is reduced, and the effect of suppressing the formation of the vapor film on the steel slab surface, which is the effect of water film cooling, is lost. it is conceivable that. From the above, the evaluation temperature is 900 ° C., the water density is 600 L / min. In the case of m ² , it can be read that the channel gap interval of the water film cooling should be set in the range of 0.6 mm to 2.3 mm.

  FIG. 7 plots the heat transfer coefficient by cooling the water film when the evaluation temperature is 600 ° C., similarly to FIG. 6, with the water density plotted on the horizontal axis. By conducting the same study on the other plots in FIG. 6 and the plots in FIG. 7, it is possible to read the channel gap interval of the water film cooling that is effective in each condition.

  In other words, when the part where the slab is actually secondary cooled by the spray nozzle is replaced with water film cooling, there is an upper limit to the water film thickness that can be set in order to obtain a larger heat transfer coefficient than spray cooling. I understood.

  In addition, at any of the evaluation temperatures of 900 ° C. and 600 ° C., the cooling water in the water film estimated from the measured heat transfer coefficient value is non-boiling that provides a heat transfer coefficient larger than spray cooling. Or it is thought that it is in the state of nucleate boiling.

  The above results were examined for the experimental results at all levels listed in Tables 3 and 4, and “○” was marked as the condition level where the heat transfer coefficient for water film cooling was equal to or greater than the heat transfer coefficient for spray cooling. The heat transfer coefficient is smaller than that of spray cooling, or “×” is marked in the table as a preferential condition for water film cooling at the level of conditions where cooling by water film cooling is impossible.

The inventors analyzed the experimental results at different evaluation temperatures and water density for the measurement results of the heat transfer coefficients of water film cooling and spray cooling. As a result, a mathematical formula for obtaining the channel gap interval has been derived. Here, the channel gap interval where the heat transfer coefficients of water film cooling and spray cooling are equivalent is defined as d ₀ (mm), the water density is defined as W (L / min.m ² ), and the evaluation temperature is defined as T (° C.). Then, d ₀ can be expressed by the following formula (1).
d ₀ = 3.838 × 10 ⁻⁴ × W ^0.48 × (T + 273) ^0.80 Expression (1)
here,
d ₀ (mm): Channel gap interval W (L / min.m ² ) at which the heat transfer coefficients of water film cooling and spray cooling are equivalent: Water density T (° C.): Evaluation temperature

In deriving the above equation (1), the channel gap interval d _{0 at} which the heat transfer coefficients of the water film cooling and spray cooling are equivalent is set to the power of the water density W and the evaluation temperature T as shown in the following equation (2). It is assumed that it is obtained by the product of The water density W is divided by the length of 100 mm through which water flows, and the evaluation temperature T is divided by 873 K (600 ° C.) after being converted to an absolute temperature. Then, from the measurement results shown in Tables 3 and 4, the coefficient A and the multipliers B and C were obtained, and the above formula (1) was derived. In addition, the inventors have confirmed that the above formula (1) is established in the evaluation temperature range of 600 ° C to 900 ° C.
d ₀ = A × (W / 100) ^B × {(T + 273) / 873} ^C (2)

(Embodiment 1)
8 and 9 show an embodiment of the present invention, and show a part of a continuous casting machine 1 provided with a cooling device 31 that performs water film cooling. As shown in FIGS. 8 and 9, a cooling device 31 is provided in the gap between the support rolls 10 that convey the slab H. The cooling device 31 has a refrigerant guide plate 32 whose longitudinal direction is the width direction of the slab H and a water supply pipe 33 as a refrigerant pipe, and is supported by a support mechanism (not shown). The refrigerant guide plate 32 is installed substantially parallel to the surface of the slab H with a gap 34 for forming a flow path of cooling water between the surface of the slab H and the thickness of the gap 34 can be adjusted. It is attached as follows. Further, the coolant guide plate 32 is formed with a water supply port 35 that is a supply port into the gap 34 of the cooling water supplied from the water supply pipe 33. For example, as shown in FIG. 9, the water supply port 35 may be a plurality of round holes of about φ5 mm arranged in a line in the width direction of the slab H, or one slit whose longitudinal direction is the width direction of the slab H Alternatively, a plurality of slits arranged in a line in the width direction may be used.

  The water supplied from the water supply pipe 33 to the gap 34 becomes a water film flow in the gap 34, cools the surface of the slab H, flows through the gap 34, and then is discharged from the end of the refrigerant guide plate 32. .

(Embodiment 2)
Next, another embodiment of the present invention will be described. 10 and 11 show a part of a continuous casting machine 1 including a cooling device 31 according to another embodiment. The cooling device 31 includes a refrigerant guide plate 32 and a water supply pipe 33 as in the above embodiment. In the cooling device 31, water is supplied from the central portion of the refrigerant guide plate 32 through the water supply pipe 33, and half of the supplied cooling water flows upward (mold side) and the other half flows downward. In the illustrated example, the cooling device 31 is provided in the vertical portion or the curved portion of the continuous casting machine 1, but the cooling device 31 is provided in the horizontal portion as shown in FIGS. May be.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  The present invention can be applied to a method and an apparatus for cooling a slab or a steel plate with a refrigerant.

DESCRIPTION OF SYMBOLS 1 Continuous casting machine 2 Tundish 3 Mold 4 Immersion nozzle 5 Slab passage 6, 7 Roll group 10, 11 Support roll 15 Spray nozzle 16 Steel slab 17 Cooling water spray jet 21 Model apparatus 22 Steel slab 23 Refrigerant guide plate 24 Water supply Nozzle 25 Crevice 31 Cooling device 32 Refrigerant guide plate 33 Water supply pipe 34 Crevice 35 Water supply port H Slab

Claims (5)

A secondary cooling method for continuous casting,
A cooling device is provided in the gap between the support rolls that convey the slab,
The cooling device supplies a refrigerant guide plate installed substantially parallel to the slab with a gap for forming a refrigerant flow path between the slab and the surface of the slab, and supplies the refrigerant to the gap. With a refrigerant pipe,
A secondary cooling method for continuous casting, wherein the coolant supplied to the gap contacts the slab in a non-boiling or nucleate boiling region to cool the slab. The secondary cooling method for continuous casting according to claim 1, wherein the gap is 0.5 mm or more and d ₀ mm or less satisfying the following formula (1).
d ₀ = 3.838 × 10 ⁻⁴ × W ^0.48 × (T + 273) ^0.80 (1)
here,
d ₀ (mm): Channel gap interval W (L / min.m ² ) at which the heat transfer coefficients of water film cooling and spray cooling are equivalent: Water density T (° C.): Evaluation temperature The refrigerant is supplied to the gap through a supply port formed in the refrigerant guide plate.
3. The supply port according to claim 1, wherein the supply port is a plurality of holes arranged in a line in the width direction of the slab, or a slit whose longitudinal direction is the width direction of the slab. The secondary cooling method for continuous casting according to one item. A cooling device for performing secondary cooling of continuous casting,
A refrigerant guide plate provided in a gap between support rolls for conveying the slab, and provided substantially parallel to the slab with a gap for forming a refrigerant flow path between the slab and the surface of the slab A refrigerant pipe for supplying the refrigerant to the gap,
The gap exceeds 0.5 mm and is equal to or less than d ₀ mm satisfying the following formula (1), and the coolant supplied to the gap comes into contact with the slab in a non-boiling or nucleate boiling region, and the casting A secondary cooling device for continuous casting, characterized by cooling a piece.
d ₀ = 3.838 × 10 ⁻⁴ × W ^0.48 × (T + 273) ^0.80 (1)
here,
d ₀ (mm): Channel gap interval W (L / min.m ² ) at which the heat transfer coefficients of water film cooling and spray cooling are equivalent: Water density T (° C.): Evaluation temperature A supply port for supplying the refrigerant to the gap is formed in the refrigerant guide plate,
5. The continuous casting according to claim 4, wherein the supply port is a plurality of holes arranged in a line in the width direction of the slab, or a slit whose longitudinal direction is the width direction of the slab. Secondary cooling device.

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