KR101443585B1 - Method for estimating clogging degree of submerged entry nozzle - Google Patents

Abstract

The present invention is continuously cast starting initial, the initial flow rate of the molten steel is transferred to the mold from a tundish (D ₀₎ and the turn and measuring the initial height (H ₀₎ of the inside stopper dish, the initial flow rate (D ₀₎ and the Calculating a theoretical height Hs of the stopper with respect to the discharge amount D of molten steel delivered through the immersion nozzle in the steady state in the tundish by substituting the initial height H ₀ of the stopper into the following relationship, Measuring the operating height Hw which is the height of the stopper when the molten steel discharge amount D is discharged and calculating a clogging index IDc (IDc) of the immersion nozzle by using the theoretical height Hs and the operating height Hw, , And comparing the clogging index (IDc) with a preset reference value to estimate the clogging degree of the immersion nozzle.

Description

METHOD FOR ESTIMATING CLOGGING DEGREE OF SUBMERGED ENTRY NOZZLE [0002]

The present invention relates to a method for estimating the degree of clogging of an immersion nozzle in continuous casting.

In general, a continuous casting machine is a facility for producing a slab of a predetermined size by receiving molten steel produced in a steelmaking furnace and transferred to a ladle in a turndish and supplying it to a mold for a continuous casting machine.

The continuous casting machine includes a ladle for storing molten steel, a tundish, and a continuous casting machine mold for initially cooling the molten steel to be cast from the tundish to form a casting having a predetermined shape, and a casting mold connected to the casting mold, And a plurality of pinch rollers for moving the pinch rollers.

In other words, the molten steel introduced in the ladle and the tundish is formed into a casting such as a slab or a bloom, a billet or the like having a predetermined width and thickness in the mold, and is conveyed through the pinch roller.

Related Prior Art Korean Patent Laid-Open Publication No. 2009-71221 (published on Jul. 1, 2009, entitled "Method and apparatus for predicting clogging of an immersion nozzle") is available.

An object of the present invention is to provide a method for estimating the degree of clogging of the immersion nozzle by using the amount of molten steel discharged from the tundish through the immersion nozzle and the height of the stopper in the tundish in continuous casting.

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

Immersion nozzle clogging degree estimation method of the present invention for realizing the above-described problems is the initial height (H ₀₎ of the initial discharge amount (D ₀₎ and the tundish within the stopper of the molten steel is transferred to the mold from the start of continuous casting initially tundish measuring a stopper for the initial flow rate (D ₀₎ and the flow rate (D) of molten steel by applying to the initial height (H ₀₎ the relation of the stopper, which is conveyed through the immersion nozzle in a normal state in the tundish Measuring a working height Hw which is a height of a stopper when the molten steel discharge amount D is discharged during continuous casting; and calculating the working height Hs by comparing the theoretical height Hs with the operating height Hs Obtaining a clogging index IDc of the immersion nozzle by using the measured clogging index Hc and Hw and comparing the clogging index IDc with a predetermined reference value to estimate the degree of clogging of the immersion nozzle .

Relation

Specifically, the clogging index IDc can be obtained by the following relational expression.

Relation

Here, Hs is the theoretical height (mm) of the stopper, and Hw is the operating height (mm) of the stopper.

The reference value may be 0.70.

The step of estimating the degree of clogging of the immersion nozzle may determine that the immersion nozzle is clogged when the clogging index (IDc) exceeds the reference value.

As described above, according to the immersion nozzle clogging degree estimation method of the present invention, in the continuous casting, the degree of clogging of the immersion nozzle for discharging molten steel from the tundish to the mold in the stopper system is estimated, and when the immersion nozzle clogging occurs, So that productivity can be improved.

1 is a side view showing a continuous casting machine according to one embodiment of the present invention.
Fig. 2 is a conceptual diagram for explaining the continuous casting machine of Fig. 1 centered on the flow of molten steel M. Fig.
3 is a graph showing the discharge amount and the height of the stopper in the steady-state immersion nozzle.
4 is a graph showing a rough comparison of the operating heights (Hw) of the stoppers according to the continuous casting time of the embodiments of the present invention.
FIG. 5 is a graph showing a rough comparison of the clogging indexes according to the continuous casting time of the embodiments related to the present invention. FIG.
FIG. 6 is a flowchart illustrating an immersion nozzle clogging degree estimation method 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 side view showing a continuous casting machine according to an embodiment of the present invention.

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 manufacture slabs, blooms and billets, which are mainly rolled materials, and long products of simple cross-section such as square, rectangle, and circle.

The shape of a continuous casting machine is classified into a vertical type and a vertical bending type. In Figs. 1 and 2, a vertical bending-like shape is illustrated.

1, the continuous casting machine may include a ladle 10 and a tundish 20, a mold 30, a secondary cooling stand 60 and 65, a pinch roll 70, and a cutter 90 have.

A tundish 20 is a container for receiving molten metal from a ladle 10 and supplying molten metal to a mold 30. The ladles 10 are provided in pairs to alternately receive molten steel and supply the molten steel 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.

Mold 30 is typically made of water-cooled copper and allows the molten steel taken to be first 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, mainly the walls, of the mold 30 can be rotated to be away from or close to each other to have a certain level of taper. This taper is set to compensate for the shrinkage due to the solidification of the molten steel M in the mold 30. The degree of solidification of the molten steel (M) varies depending on the carbon content according to the steel type, the kind of the powder (strong cold type Vs and cold type), the casting speed and the like.

The mold 30 is formed of a solidified shell 81 or a solidified shell 81 that retains the shape of the casting 80 pulled out of the mold 30, And the like. 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 by the oscillator 40 to prevent the molten steel from sticking to the wall surface of the mold 30. A lubricant is used to reduce the friction between the mold 30 and the solidification shell 81 during oscillation and to prevent burning. As the lubricant, there is oil to be sprayed and powder added to the molten metal surface in the mold 30. The powder is added to the molten metal in the mold 30 to become slag so that not only the lubrication of the mold 30 and the solidification shell 81 but also the prevention and oxidation of the molten metal in the mold 30, It also functions to absorb the emerging nonmetallic inclusions. A powder feeder 50 is installed to feed the powder into the mold 30. The portion of the powder feeder 50 for discharging the powder is directed to the inlet of the mold 30.

The secondary cooling bands 60 and 65 further cool the molten steel that has been primarily cooled in the mold 30. The primary cooled molten steel is directly cooled by the spray 65 spraying water, while the coagulation angle is kept unchanged by the support roll 60. Most of the solidification of the cast slab 80 is achieved by the secondary cooling.

The pulling device employs a multi-drive type or the like which uses several pairs of pinch rolls 70 so that the casting piece 80 can be pulled out without slipping. The pinch roll 70 pulls the solidified tip portion 83 of the molten steel in the casting direction so that molten steel passing through the mold 30 can be continuously moved in the casting direction.

The cutter 90 is formed so as to cut the continuous casting piece 80 continuously produced to a predetermined size. As the cutter 90, a gas torch or an oil pressure shearing machine may be employed.

Fig. 2 is a conceptual diagram for explaining the continuous casting machine of Fig. 1 centered on the flow of molten steel M. Fig.

Referring to this figure, the molten steel M flows into the tundish 20 while being accommodated in the ladle 10. For this flow, the ladle 10 is provided with a shroud nozzle 15 extending toward the tundish 20. The shroud nozzle 15 extends into the molten steel in the tundish 20 so that the molten steel M is not exposed to the air to be oxidized and nitrided. The case where the molten steel M is exposed to air due to breakage of the shroud nozzle 15 or the like is referred to as open casting.

The molten steel M in the tundish 20 is caused to flow into the mold 30 by the submerged entry nozzle 25 extending into the mold 30. The immersion nozzle 25 is disposed at the center of the mold 30 so that the flow of the molten steel M discharged from both the discharge ports of the immersion nozzle 25 can be made symmetrical. The start, discharge speed and interruption of the discharge of the molten steel M through the immersion nozzle 25 are determined by a stopper 21 provided on the tundish 20 in correspondence with the immersion nozzle 25. [ Specifically, the stopper 21 can be vertically moved along the same line as that of the immersion nozzle 25 so as to open and close the inlet of the immersion nozzle 25.

Molten steel (M) in the mold (30) starts to solidify from a portion in contact with the wall surface of the mold (30). This is because the periphery of the molten steel M is liable to lose heat by the water-cooled mold 30. The rear portion along the casting direction of the cast slab 80 is formed into a shape in which the non-solidified molten steel 82 is wrapped in the solidifying shell 81 by the method in which the peripheral portion first coagulates.

The non-solidified molten steel 82 moves together with the solidifying shell 81 in the casting direction as the pinch roll 70 (Fig. 1) pulls the tip end portion 83 of the fully-solidified cast slab 80. The non-solidified molten steel (82) is cooled by the spray (65) spraying the cooling water in the course of the above movement. This causes the thickness of the non-solidified molten steel (82) to gradually decrease in the cast steel (80). When the cast steel 80 reaches one point 85, the cast steel 80 is filled with the solidified shell 81 as a whole. The solidification casting 80 having been solidified is cut to a predetermined size at the cutting point 91 and is divided into a slab P such as a slab or the like.

1, the apparatus including the support roll 60, the spray 65, and the pinch roll 70 is also referred to as a strand.

Here, the discharge of molten steel from the tundish 20 to the mold 30 is determined by the amount of molten steel discharged as the height of the stopper increases. However, when the molten steel is Ca-untreated steel, fused materials such as alumina adhere to the inner wall of the immersion nozzle 25, and clogging occurs in the immersion nozzle 25 due to the adhesion. When the immersion nozzle 25 is clogged, the height of the stopper must be increased to inject a certain amount of molten steel into the mold 30.

By using this principle, the reference height of the stopper, that is, the discharge amount of molten steel discharged from the steady-state immersion nozzle 25 and the actual operating height Hw of the stopper for discharging the molten steel of the reference amount, Can be estimated.

Fig. 3 is a graph relating to the amount of discharge and the height of the stopper in the steady-state immersion nozzle 25 during continuous casting under the preferable operating conditions. The vertical axis is the height of the stopper, and the horizontal axis is the discharge rate per minute of molten steel. As shown in the figure, the height of the stopper and the discharge amount of the molten steel have a linear function relationship, specifically, the following relational expression (1).

Relationship 1

Here, Hs is the stopper height (mm) in the immersion nozzle 25 in the steady state and the discharge amount D is the discharge amount per minute (ton / min) of the molten steel transferred from the tundish 20 to the mold 30.

However, in actual continuous casting, the stopper is heated to a high temperature and is inflated or the verticality of the stopper is poor, so that the above relational expression 1 can not be followed and the value of the initial height of the stopper in the steady state of the immersion nozzle as shown in FIG. When the initial height of the stopper is changed, as shown in FIG. 5, the clogging index is calculated as a value exceeding 0 even though nozzle clogging does not occur, and it is difficult to accurately estimate the degree of clogging of the immersion nozzle by using the relational expression 1.

Therefore, it is possible to more accurately estimate the degree of clogging of the immersion nozzle during continuous casting in actual continuous casting by measuring the initial discharge amount of molten steel and the initial height of the stopper at an arbitrary point in the initial stage of continuous casting and correcting relational expression 1 with the measured value . Specifically, as shown in the following relational expression 2, the initial discharge amount D ₀ is subtracted from the discharge amount D, and then the coefficient value 7.01 is multiplied. The initial height H _{0 of} the stopper is added to the thus obtained value, (Hs) is obtained.

Relation 2

Here, Hs is the theoretical height of the stopper, and the extrusion rate (D) is based on the discharge amount of molten steel to be discharged at the time of continuous casting, the initial flow rate (D ₀₎ is the discharge amount of molten steel from the initial time of continuous casting, H ₀ is the initial continuous casting The height of the stopper at the time point.

In general, when the continuous casting is performed, the tundish 20 is discharged from the tundish 20 with a predetermined reference discharge amount. When the nozzle clogging occurs under a constant molten steel discharge amount, the height of the stopper . In consideration of such a phenomenon, the nozzle clogging index IDc is determined by the relationship (3).

Relation 3

Here, IDc is the nozzle clogging index, Hs is the theoretical height (mm) of the steady state stopper, and Hw is the operating height (mm) of the clogged state stopper.

On the other hand, if the immersion nozzle clogging index IDc is 0.70, it is judged that the immersion nozzle is clogged. That is, when the immersion nozzle clogging index IDc is 0.70, the nozzles are clogged to a large extent and high productivity can not be maintained.

FIG. 6 is a flowchart illustrating an immersion nozzle clogging degree estimation method according to an embodiment of the present invention.

Referring to the flowchart, first, measures the tundish initial discharge rate of the molten steel is transferred to a mold (30) from (20) (D ₀₎ and the tundish 20, the initial height of the stopper (H _0). (S10 ) These initial values can be measured at the beginning of the continuous casting start.

The initial amount of molten steel discharge can be obtained by determining the degree of decrease in the height of the molten steel bath surface in the tundish so that the amount of molten steel discharged from the tundish to the mold is inverted. In order to measure the initial discharge amount of molten steel in this way, a sensor (not shown) or a measuring device (not shown) may be further provided.

The initial height of the stopper in the tundish can be obtained by subtracting the length of the stopper inserted into the tundish from the inner depth of the entire tundish to the height from the opening formed in the lower portion of the tundish to the bottom of the tundish for discharging the molten steel . In order to measure the height of the stopper in the tundish in this way, a sensor (not shown) or a measuring device (not shown) may be additionally provided.

Next, the theoretical height Hs of the stopper with respect to the discharge amount D of molten steel fed through the immersion nozzle in the steady state is calculated in the tundish 20 (S20). Here, the theoretical height Hs of the stopper The initial discharge amount D ₀ of the molten steel and the initial height H ₀ of the stopper measured in advance are substituted into the following relational expression 2 and the discharge amount D of the molten steel delivered through the immersion nozzle at the current measurement time is further substituted Respectively. At this time, the discharge amount (D) of molten steel at the present measurement time is adjusted to a constant amount to keep the continuous casting speed constant. In addition, since the casting speed varies depending on the type of the cast steel, the discharge amount D of the molten steel is set to be different depending on the type of the cast steel.

Relation 2

Here, Hs is the theoretical height (Hs) of the stopper, and the extrusion rate (D) is a molten steel discharge amount in the current measurement time point, the initial flow rate (D ₀₎ is the flow rate of molten steel from the initial time of continuous casting, H ₀ is continuous The height of the stopper at the initial stage of casting.

Then, while the continuous casting process is actually being carried out, the operating height Hw, which is the height of the stopper for discharging the same amount of molten steel as the discharge amount D, is measured in a state where the immersion nozzle is clogged during the actual continuous casting process. (S30) At this time, the method of measuring the operating height Hw of the stopper is the same as the method of measuring the initial height of the stopper described above.

Then, the clogging index IDc of the immersion nozzle is obtained using the theoretical height Hs of the stopper and the operating height Hw of the stopper. (S40) At this time, the clogging index IDc of the immersion nozzle is Is determined by the following equation (3). In addition, the degree of clogging of the immersion nozzle can be estimated based on the clogging index.

Relation 3

Here, IDc is the nozzle clogging index IDc, Hs is the theoretical height (mm) of the steady state stopper, and Hw is the operating height (mm) of the clogged state stopper.

On the other hand, if the immersion nozzle clogging index IDc is 0.70 as described above, it is judged that the immersion nozzle is clogged. That is, when the immersion nozzle clogging index IDc is 0.70, the nozzles are clogged to a large extent and high productivity can not be maintained.

As described above, according to the immersion nozzle clogging degree estimation method of the present invention, when the molten steel is discharged into the mold by the stopper method in the continuous casting, the degree of clogging of the immersion nozzle can be estimated in advance, have.

Also, since the nozzle clogging time can be predicted, it is possible to determine whether or not the next ladle is taken, thereby preventing the casting from being stopped due to nozzle clogging.

The method of estimating the degree of clogging of the immersion nozzle is not limited to the construction and the operation of the embodiments described above. The embodiments may be configured so that all or some of the embodiments may be selectively combined so that various modifications may be made.

10: Ladle 15: Shroud nozzle
20: tundish 25: immersion nozzle
30: Mold 40: Mold oscillator
50: Powder feeder
60: Support roll 65: Spray
70: pinch roll 80: performance cast
81: Solidification shell 82: Non-solidified molten steel
83: tip portion 85: solidified point
90: Cutter 91: Cutting point

Claims (4)

The method comprising the initial start of the continuous casting, measuring the initial flow rate (D ₀₎ and the tundish initial height (H ₀₎ of the stopper within the liquid steel is transferred to the mold from the tundish;
Theoretical height of the stopper with respect to the initial flow rate (D ₀₎ and the flow rate (D) of molten steel by applying to the initial height (H ₀₎ the relation of the stopper, which is conveyed through the immersion nozzle in the normal state from the tundish (Hs );
Measuring a working height (Hw) which is a height of a stopper when the molten steel discharge amount (D) is discharged during continuous casting;
Obtaining a clogging index IDc of the immersion nozzle using the theoretical height Hs and the operating height Hw; And
And comparing the clogging index (IDc) with a preset reference value to estimate the clogging degree of the immersion nozzle.
Relationship 1

Relation 2

Here, Hs is the theoretical height (mm) of the stopper, and Hw is the operating height (mm) of the stopper.
delete The method according to claim 1,
Wherein the reference value is 0.70.
The method according to claim 1,
Wherein the step of estimating the degree of clogging of the immersion nozzle comprises:
And determining that the immersion nozzle is clogged when the clogging index (IDc) is greater than a reference value.

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