KR20140017182A - Cooling method of mold for continuous casting - Google Patents

Abstract

The present invention relates to a cooling method of a mold for continuous casting which controls the amount of cooling water sprayed from just below the mold by predicting the thickness of a solidified shell, the cooling method comprising: a step of calculating a predicted thickness (S) of a solidified shell on the outlet of the mold based on a casting speed and a heat rejection rate inside the mold, when the continuous casting is performed; a step of comparing the predicted thickness (S) of a solidified shell with a predetermined critical thickness (Sc); a step of controlling the thickness of the solid shell of a continuously casted slab manufactured by increasing the quantity (Q) of cooling water sprayed from a nozzle positioned directly under the molt, in case the predicted thickness (S) is less than the critical thickness (Sc) based on the comparison between the predicted thickness (S) and the critical thickness (Sc). [Reference numerals] (AA) START; (BB) END; (S10) Calculate thickness of a solidified shell; (S20) Compare the predicted thickness of a solidified shell with a predetermined critical thickness; (S30) Control the thickness of the solid shell by increasing the quantity of cooling water sprayed from a nozzle positioned directly under the mold, in case the predicted thickness is less than the critical thickness

Description

Cooling method of continuous casting mold {COOLING METHOD OF MOLD FOR CONTINUOUS CASTING}

The present invention relates to a method for cooling a continuous casting mold, and more particularly, to a method for cooling a continuous casting mold for predicting a solidification shell thickness in a mold and controlling the amount of cooling water sprayed directly under the mold.

In general, a continuous casting machine is a facility for producing cast steel of a certain size by receiving a molten steel produced in a steelmaking furnace and transferred to a ladle (Tundish) and then supplied to a continuous casting machine mold.

The continuous casting machine includes a ladle for storing molten steel, a casting mold for forming a tundish and a molten steel that is guided in the tundish first to form a cast slab having a predetermined shape, and a casting member connected to the mold, A plurality of pinch rolls and the like. The molten steel introduced from the ladle and the tundish is formed into a cast slab having a predetermined width, thickness and shape in the mold and is transported through the pinch roll. The slab transported through the pinch roll is cut by a cutter to have a predetermined shape Slabs, blooms, billets, and the like.

In the mold of the continuous casting machine, solidification of molten steel starts, and solidification starts from the molten steel surface in the mold to form a solidification shell. The solidified shell formed as described above is thickened as the solidified shell is cooled by the cooling water sprayed onto the surface of the cast piece while the pinch roll passes through the mold, and finally is manufactured in the form of one slab.

Related prior art is Korean Patent Publication No. 2011-0034470 (published: April 5, 2011, the title of the invention: secondary cooling method of continuous casting).

The present invention is to provide a cooling method of a continuous casting mold that can predict the thickness of the solidified shell in the mold and thus can effectively adjust the amount of cooling water directly under the mold.

The technical objects to be achieved by the present invention are not limited to the above-mentioned technical problems.

The method for cooling the continuous casting mold of the present invention for achieving the above object is the step of calculating the solidification shell predicted thickness (S) of the mold exit side through the casting speed and the amount of heat transfer in the mold during continuous casting, and the calculation above Comparing the solidified shell predicted thickness S with a predetermined threshold thickness Sc and when the predicted thickness S is less than or equal to the threshold thickness Sc by the comparison, the amount of cooling water sprayed from a nozzle located directly under a mold It may include the step of adjusting the thickness of the solidified shell of the cast cast produced by increasing (Q).

Specifically, in the step of adjusting the thickness of the solidification shell, the cooling water amount (Q) by the comparison of the predicted thickness (S) and the critical head (Sc) can be adjusted by the following equation (1).

Relationship 1

However, Sc is the critical thickness, S is the solidified shell prediction thickness, Q1 is the initial cooling water amount, Q2 is the increased amount of cooling water, S <Sc may be assumed in the present invention.

In the calculating step, the solidified shell prediction thickness (S) may be calculated by the following equation (2).

Relation 2

S = 18.3-7.58 × VC + 5.50 × HF

However, VC is the casting speed (n / min), HF may be the heat transfer amount in the mold (MW / m ² ).

The threshold thickness can be set in the range of 10 ~ 12mm.

As described above, the present invention has an effect of predicting the thickness of the solidified shell in the mold and thus effectively controlling the amount of cooling water directly under the mold, thereby preventing the cast slab bursting during the continuous casting.

In addition, by precisely controlling the amount of cooling water directly under the mold, the solidification shell of the cast steel that has passed through the mold can be maintained at an appropriate level without being excessively thickened or thinned to enable high-quality slab production.

1 is a conceptual diagram showing a continuous casting machine according to an embodiment of the present invention mainly on the flow of molten steel.
Fig. 2 is a conceptual diagram showing the distribution of the molten steel M in the mold and its adjacent portion in Fig. 1. Fig.
3 is a flowchart illustrating a cooling method of a continuous casting mold according to an embodiment of the present invention in order.
4 is a view schematically showing a position directly under a mold during continuous casting according to the present invention.
5 is a graph showing embodiments of the cooling water increase amount due to the difference in the solidification shell prediction thickness and the critical thickness according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components are denoted by the same reference symbols whenever possible. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

1 is a conceptual diagram showing a continuous casting machine according to an embodiment of the present invention mainly on the molten steel flow. Continuous casting is a casting process in which a molten metal is continuously cast into a bottomless mold while continuously drawing a steel ingot or steel ingot. Continuous casting is used to make long products of simple cross-section, such as square, rectangular or round, and mainly slabs, blooms or billets, which are materials for rolling.

The continuous casting machine may include a ladle 10 and a tundish 20, a mold 30, secondary cooling bands 60 and 65, a pinch roll 70, and a cutter 90, as shown .

The tundish 20 is a container that receives the molten metal from the ladle 10 and supplies the molten metal to the mold 30. Ladle 10 is provided in a pair, alternately receives molten steel to supply to the tundish 20. In the tundish 20, the supply rate of the molten metal flowing into the mold 30 is controlled, the molten metal is distributed to each mold 30, the molten metal is stored, and the slag and the nonmetallic inclusions are separated.

The mold 30 is typically made of water-cooled copper and allows the molten steel to be primary cooled. The mold 30 has a pair of structurally opposed faces open to form a hollow portion for receiving molten steel. In the case of manufacturing the slab, the mold 30 includes a pair of barriers and a pair of end walls connecting the barriers. Here, the end wall has a smaller area than the barrier. The walls of the mold 30, mainly short walls, may be rotated away from or close to each other to have a certain level of taper.

The mold 30 serves to form a strong solidification angle or solidified shell 81 so that the cast steel drawn from the mold maintains a certain shape and a molten metal which is still less solidified does not flow out. Do it. The water-cooling structure includes a method using a copper tube, a method of water-cooling the copper block, and a method of assembling a copper tube having a water-cooling groove. The mold 30 is oscillated to prevent the molten steel from adhering to the wall of the mold, and powder to prevent burning and to reduce friction between the mold 30 and the solidification shell 81 during oscillation. Lubricants such as Powder are used. The powder is added to the molten metal in the mold to become slag, as well as the lubrication of the mold 30 and the solidified shell, as well as to prevent oxidative nitriding and thermal insulation of the molten metal in the mold, and to absorb non-metallic inclusions on the surface of the molten metal. .

The secondary cooling zones 60 and 65 further cool the molten steel primarily cooled in the mold 30. The primary cooled molten steel is directly cooled by the spraying means 65 for spraying water while being maintained by the support roll 60 so that the coagulation angle is not deformed. The solidification of the cast steel is mostly made by the secondary cooling.

The drawing device adopts a multidrive method using a pair of pinch rolls 70 and the like so as to pull out the cast pieces without slipping. The pinch roll 70 pulls the solidified tip of the molten steel in the casting direction, thereby allowing the molten steel passing through the mold 30 to continuously move in the casting direction. Continuously produced cast pieces are cut to a certain size by a predetermined cutter (not shown).

The shape of the molten steel M in the mold 30 and the adjacent portion thereof will be described with reference to FIG. 2. FIG. 2 is a conceptual view illustrating a distribution form of molten steel M in the mold 30 and adjacent portions of FIG. 1.

Referring to FIG. 2, a pair of discharge ports 25a are typically formed at the left and right ends of the immersion nozzle 25 on the left and right sides of the drawing. The shapes of the mold 30 and the immersion nozzle 25 are assumed to be symmetrical with respect to the center line C, and thus only the left side is shown in this drawing.

The molten steel M discharged together with the argon (Ar) gas from the discharge port 25a draws a trajectory flowing in the upward direction A1 and downward direction A2 as indicated by arrows A1 and A2. do.

The powder layer 51 is formed on the upper part of the mold 30 by the powder supplied from the powder feeder 50 (see FIG. 1). The powder layer 51 may include a layer existing in a form in which the powder is supplied and a layer sintered by the heat of the molten steel M (sintered layer is formed closer to the unsolidified molten steel 82). Below the powder layer 51, a slag layer or a liquid fluidized layer 52 formed by melting powder by molten steel M is present. The liquid fluidized bed 52 maintains the temperature of the molten steel M in the mold 30 and blocks the penetration of foreign matter. A portion of the powder layer 51 solidifies at the wall surface of the mold 30 to form the lubrication layer 53. The lubrication layer 53 functions to lubricate the solidified shell 81 so as not to stick to the mold 30.

The thickness of the solidification shell 81 becomes thicker as it progresses along the casting direction. The portion of the solidification shell 81 located in the mold 30 is thin, and an oscillation mark 87 may be formed by oscillation of the mold 30. The solidification shell 81 is supported by the support roll 60, the thickness thereof is thickened by the spray means 65 for spraying water. The solidification shell 81 may be thickened and a bulging region 88 may be formed in which a portion protrudes convexly.

3 is a flowchart illustrating a cooling method of a continuous casting mold according to an embodiment of the present invention in order. First, in the present invention, a molten steel tapped from a tundish during solid casting is formed by solidifying in a mold. Begin by calculating the thickness (S10).

In general, during continuous casting, productivity is controlled by adjusting the speed of injecting molten steel into the mold, that is, casting speed. If the casting speed is too fast, the molten steel has a short residence time in the mold, so that the solidification shell thickness is thin and the iron static pressure at the mold exit is maintained. Failure to win will result in a breakout in which the solidification shell bursts and the molten steel bursts outward. If breakout occurs like this, the produced cast steel will be defective. This should be prevented. In actual operation, the solidification shell thickness at the exit of the mold cannot be measured or observed. It is impossible to judge whether or not.

Therefore, the present invention calculates the solidification shell prediction thickness (S) generated in the mold through the casting speed and the heat transfer in the mold during continuous casting, wherein the solidification shell prediction thickness (S) means the solidification shell thickness at the mold exit It can be calculated as shown in the following relation 1.

Relationship 1

S = 18.3-7.58 × VC + 5.50 × HF

In relation 1, VC is the casting speed (n / min) and HF is the heat transfer amount in the mold (MW / m ² ). Equation 1 is the result of regression analysis based on the data obtained through repetitive experiments confirming that the solidification shell in the mold is affected by the casting speed and the heat transfer amount in the mold during continuous casting operation. The regression equation has a correlation of 92.3% with the coagulation shell prediction thickness (ie, the coefficient of determination R ² = 0.923).

The solidified shell prediction thickness S calculated as described above is compared with a predetermined threshold thickness Sc (S20). The critical thickness in the present invention can be set in accordance with the operating environment in the range of 10 ~ 12mm. If the critical thickness is less than the lower limit, the solidification shell thickness may be so thin that breakout may occur in the cast steel. In addition, when the critical thickness exceeds the upper limit, the solidification shell thickness may be too thick, so it is necessary to select appropriately within the above range.

The present invention compares the predicted thickness of the solidification shell at the exit of the mold with a predetermined threshold thickness to increase the amount of coolant sprayed to the cast steel that has passed through the mold when the predicted thickness is smaller than the threshold thickness, thereby controlling the thickness of the solidified shell. Its feature is to prevent outs.

When the predicted thickness S is equal to or less than the critical thickness Sc by the comparison, the solidification shell thickness of the cast piece manufactured is increased by increasing the amount of cooling water Q injected from the nozzle located directly below the mold (S30).

In the present invention, when the predicted thickness is smaller than the critical thickness, by increasing the amount of cooling water injected from the injection nozzle installed directly below the mold shown in Figure 4 to cool the surface of the cast casting cast more quickly to increase the thickness of the solidified shell To prevent breakout. That is, the present invention assumes that the prediction thickness is less than or equal to the threshold thickness.

In this case, the adjustment of the amount of cooling water Q by the comparison of the predicted thickness S and the threshold head Sc may be determined by Equation 2 below. The solidified shell predicted thickness was measured several times through the casting speed and the amount of heat in the mold measured during the operation, and then the casting cast was manufactured while changing the increase of cooling water. It was confirmed that there is a relationship as shown in the following relation between the thickness and the initial amount of cooling water and the amount of cooling water increase.

At this time, the relationship between the predicted thickness and the critical thickness of the solidified shell and the initial coolant amount and the coolant increase amount is the same as the exponential graph. The following relation 2 was derived.

Relation 2

In the present invention, since A is 0 <A≤1 as a constant, B is 0 <B≤1 as a constant, and the threshold thickness is always larger than the predicted thickness, the difference between the predicted thickness and the threshold thickness is always positive. The percentage (%) is derived by multiplying the difference between the predicted thickness and the critical thickness by 100. In addition, the cooling water increase amount directly under the mold also always has a positive number, and the cooling water increase rate (%) directly under the mold is a value expressed as a percentage by multiplying the cooling water increase amount under the mold by 100.

If the relation 1 is described in more detail as shown in the following relation 3.

Relation 3

At this time, Sc-S / S (△ S) of the left side means the difference between the solidification shell prediction thickness and the critical thickness with respect to the solidification shell prediction thickness, and accordingly Q2-Q1 / Q1 (△ Q ) Represents the relationship increased by the exponential function, and the overall interpretation of Equation 2 can be defined as S ∝ Q ⁿ . In relation 3, Q2-Q1, that is, ΔQ is about how much coolant to increase further to the initial coolant amount, and means an increase in coolant with respect to the initial coolant amount.

As described above, in order to derive Equation 3, the present invention measures the solidification shell predicted thickness through the casting speed and the amount of heat in the mold measured during the operation, and then manufactures the cast pieces while varying the increase in the amount of cooling water. This relationship was regressed and the results are shown in FIG. 5.

5 shows a regression graph for various values, wherein the regression equation derived by Example 1 is as shown in Equation 4 below.

Relationship 4

In relation 4, Sc is a critical thickness, S is a solidified shell prediction thickness, Q1 is the initial cooling water amount, Q2 is an increased amount of cooling water, and S <Sc in the present invention.

Equation 4 is an embodiment of the method of the present invention according to Equation 2, and when operating according to Equation 4, the amount of cooling water is adjusted by the solidification shell predicted thickness and the critical thickness difference ratio along the blue line shown in FIG. shall.

For example, a 3% difference between the predicted thickness and the critical thickness of the shell can increase the cooling water by about 23%, and it can be derived from the graph. In addition, when the difference between the predicted thickness and the critical thickness is 5% occurs, it can be derived from the graph that the cooling water of about 60% can be increased and sprayed directly under the mold.

If the variables such as casting speed and the amount of heat transfer in the mold are changed during operation, another type of graph is derived according to the definition of Equation 2, and accordingly, the amount of cooling water according to the difference between the predicted solidification shell thickness and the critical thickness difference calculated during the operation. The increase in will be derived differently.

As described above, the present invention has an effect of predicting the thickness of the solidified shell in the mold and thus effectively controlling the amount of cooling water directly under the mold, thereby preventing the cast slab bursting during the continuous casting. In addition, by accurately controlling the amount of cooling water directly under the mold through the present invention, the solidification shell of the cast steel that has passed through the mold can be maintained to maintain a proper level without being excessively thickened or thinned, thereby helping to produce high quality slabs.

The cooling method of the continuous casting mold as described above is not limited to the configuration and operation of the embodiments described above. The above embodiments may be configured such that various modifications may be made by selectively combining all or part of the embodiments.

10: Ladle 20: Tundish
30: mold 51: powder layer
52: liquid fluidized bed 53: lubricating layer
60: Support roll 65: Spray means
80: playing piece 81: solidification shell
82: unsolidified molten steel 83: tip
85: solidification completion point 87: oscillation marks
88: bulging region 90: cutter
91: Cutting point

Claims (4)

Calculating the solidification shell prediction thickness S at the exit of the mold through the casting speed and the amount of heat in the mold during continuous casting;
Comparing the solidified shell prediction thickness S calculated above with a predetermined threshold thickness Sc; And
If the prediction thickness (S) is less than the critical thickness (Sc) by the comparison, adjusting the solidification shell thickness of the cast pieces produced by increasing the amount of cooling water (Q) injected from the nozzle located directly below the mold; Cooling method of the continuous casting mold.
The method according to claim 1,
In the step of adjusting the solidification shell thickness,
The cooling method of the continuous casting mold for adjusting the amount of cooling water (Q) by the following relation 1 by comparing the predicted thickness (S) and the critical sclerometer (Sc).
Relationship 1

(Where A is 0 <A≤1 as a constant, B is 0 <B≤1 as a constant and the threshold thickness is always larger than the predicted thickness)
The method according to claim 1,
In the calculating step,
The solidification shell prediction thickness (S) is a cooling method of the continuous casting mold is calculated by the following equation (2).
Relation 2
S = 18.3-7.58 × VC + 5.50 × HF
(However, VC is the casting speed (n / min), HF is the heat transfer amount in the mold (MW / m ² ))
The method according to claim 1,
The critical thickness of the cooling method of the continuous casting mold is set in the range 10 ~ 12mm.

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