KR20130013742A - Device for monitoring crack using frictional force in mold and method therefor - Google Patents

Abstract

PURPOSE: A crack monitoring device using a frictional force inside a mold and a method thereof are provided to monitor the existence of the generation of surface cracks by sensing the continuous increase or decrease of the frictional force between a mold and a solidification shell in a strand casting process, thereby dealing properly with a manufactured cast strands. CONSTITUTION: A crack monitoring device using a frictional force inside a mold(30) comprises a vibration detecting sensor(110) and a central processing unit(160). The vibration detecting sensor is mounted on an outer side of the mold or a mold carriage, thereby detecting the vibration width of the mold. The central processing unit calculates the frictional force between the mold and a solidification shell using the detected vibration width and determines whether the calculated frictional force is consecutively increased or decreased during a preset reference period, thereby predicting the existence of the generation surface cracks of the cast strands. [Reference numerals] (120) Central processing unit; (130) Memory; (140) Display unit; (150) Input unit; (160) Central processing unit; (161) Frictional force calculating unit; (163) Change rate calculating unit; (165) Crack generation calculating unit; (170) Alarm signal generating unit; (21) Stopper; (50) Powder feeder; (70) Pinch roll

Description

Crack monitoring device using friction force in mold and its method {DEVICE FOR MONITORING CRACK USING FRICTIONAL FORCE IN MOLD AND METHOD THEREFOR}

The present invention relates to crack monitoring using a friction force, and more particularly, to a crack monitoring apparatus and a method using a friction force in the mold for monitoring the occurrence of cracks through the friction between the mold and the solidification shell in the continuous casting process.

In general, the continuous casting machine is a facility for producing slabs of a constant size by receiving a molten steel produced in a steelmaking furnace and transferred to a ladle in a tundish and then supplying it to a mold for continuous casting.

The continuous casting machine includes a ladle for storing molten steel, a continuous casting machine mold for cooling the tundish and the molten steel exiting from the tundish into a casting having a predetermined shape, and a casting formed in the mold connected to the mold. It includes a plurality of pinch rolls to move.

In other words, the molten steel injected into the mold is gradually cooled to form a casting in the lower part of the mold, where the casting existing in the lower part of the mold has its epidermis solidified and inside of the molten steel. Becomes When the molten steel injected into the mold reaches a predetermined level, the mold starts oscillating width up and down, and the drawing of the casting by the pinch roll starts at the bottom of the mold, and simultaneously the casting is cooled by the cooling water by the coolant spray device. To produce a completely cooled casting to the epidermis and its interior.

Related prior art is Korean Patent Publication No. 2004-59505 (published 2004.07.06).

An object of the present invention is to provide a crack monitoring device using a friction force in a mold and a method for monitoring crack occurrence through continuous increase or decrease of friction force between a mold and a solidification shell in a continuous casting process.

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

In the mold crack monitoring apparatus of the present invention for achieving the above object is a vibration detection sensor for detecting the vibration width is applied to the outside of the mold or the mold carriage; And a central processing unit for calculating a friction force between the mold and the solidification shell by using the vibration width detected by the vibration detection sensor, and determining whether the calculated friction force is continuously increased or decreased for a predetermined reference time to predict the occurrence of cracking of the cast steel piece. It can include;

Specifically, the central processing unit calculates the instantaneous change between the calculated frictional force and the previous frictional force, and then monitors whether the instantaneous change is continuously greater than '0' or less than '0' for the set reference time, and whether the crack of the playing cast is generated. Can be determined.

The reference time set in the central processing unit may be at least 14 seconds.

In the mold crack monitoring method of the present invention for achieving the above object, detecting the vibration width according to the vibration of the mold; Calculating a frictional force using the detected vibration width; Calculating an instantaneous change in friction force by subtracting a previous friction force from the friction force calculated above; And predicting whether or not a crack occurs in the playing cast by determining whether the friction force is continuously increased or decreased during a predetermined reference time, based on the calculated instantaneous change in friction force.

In the step of predicting whether the crack has occurred, it is possible to predict whether the crack of the playing cast by determining whether the instantaneous amount of change in frictional force is continuously greater than '0' or less than '0' during the set reference time.

As described above, the present invention monitors the occurrence of surface cracks by continuously increasing or decreasing the friction force between the mold and the solidification shell in the continuous casting process, thereby taking appropriate measures for the manufactured cast steel and There is an advantage that it is possible to predict in advance before failure occurs.

In addition, by predicting the occurrence of surface cracks and breakage of the cast pieces in advance to take appropriate measures, there is an advantage that can improve the quality and productivity of the cast.

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 view illustrating a distribution form of molten steel M in the mold of FIG. 1 and a portion adjacent thereto.
3 is a view showing an in-mold crack monitoring apparatus according to an embodiment of the present invention.
4 is a flowchart illustrating a crack monitoring process in a mold according to an embodiment of the present invention.
5 and 6 is a view showing a change in friction force according to the type and steel type and circumferential speed of the mold powder.
7 is a view illustrating a crack monitoring method according to the friction force and the amount of change thereof.
FIG. 8 is a view illustrating a surface crack of a slab according to the result of FIG. 7.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like elements in the figures are denoted by the same reference numerals wherever 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 flow of molten steel.

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 type of continuous casting machine is classified into vertical type and vertical curved type. In Fig. 1, a vertical bending type is illustrated.

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

The tundish 20 is a container that receives the molten metal from the ladle 10 and supplies the molten metal to the mold 30. 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 a slab, the mold 30 includes a pair of barriers and a pair of end walls connecting the barriers. Here, the short 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. This taper is set to compensate for shrinkage due to solidification of the molten steel M in the mold. The degree of solidification of the molten steel (M) will vary depending on the carbon content, the type of powder (steel cold Vs slow cooling), casting speed and the like depending on the steel type.

The mold 30 is formed such that a solidified shell or a solidified shell 81 is formed so as to maintain the shape of the casting pluck pulled out from the mold 30 and to prevent the molten metal from being hardly outflowed from flowing out. . The water-cooled structure includes a method of using a copper pipe, a method of drilling a water cooling groove in the copper block, and a method of assembling a copper pipe having a water cooling groove.

The mold 30 is oscillated by the oscillator 40 to prevent the molten steel from sticking to the wall of the mold. Lubricant is used to reduce friction between the mold 30 and the solidification shell 81 and prevent burning during oscillation. Lubricants include flat oil sprayed and powder added to the molten metal surface in the mold. 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 solidification shell 81, as well as the prevention of oxidative and nitrification of the molten metal in the mold, the insulation, and the absorption of nonmetallic inclusions on the surface of the molten metal. It also functions. In order to inject the powder into the mold 30, a powder feeder 50 is installed. The part for discharging the powder of the powder feeder 50 faces the inlet of the mold 30.

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 spray means 65 for spraying water while maintaining the solidification angle by the support roll 60 not to be 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.

The continuous casting machine configured as described above allows the molten steel M accommodated in the ladle 10 to flow into the tundish 20. 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 molten steel M in the tundish 20 flows into the mold by a submerged entry nozzle 25 extending into the mold. The immersion nozzle 25 is disposed in the center of the mold 30 so that the flow of molten steel M discharged from both discharge ports of the immersion nozzle 25 can be symmetrical. The start, discharge speed, and stop of the discharge of the molten steel M through the immersion nozzle 25 are determined by a stopper 21 installed in the tundish 20 corresponding to the immersion nozzle 25. Specifically, the stopper 21 may be vertically moved along the same line as the immersion nozzle 25 to open and close the inlet of the immersion nozzle 25. Control of the flow of the molten steel M through the immersion nozzle 25 may use a slide gate method, which is different from the stopper method. The slide gate controls the discharge flow rate of the molten steel M through the immersion nozzle 25 while the sheet material slides in the horizontal direction in the tundish 20.

The molten steel M in the mold starts to solidify from the part in contact with the wall surface of the mold 30. This is because heat is more likely to be lost by the mold 30 in which the periphery is cooled rather than the center of the molten steel M. By the way that the periphery is first solidified, the back portion along the casting direction of the casting cast piece 80 forms a shape in which the non-solidified molten steel 82 is wrapped in the solidified shell 81.

As the pinch roll 70 (FIG. 1) pulls the tip portion 83 of the completely cast solid cast piece 80, the unsolidified molten steel 82 moves together with the solidified shell 81 in the casting direction. The uncondensed molten steel 82 is cooled by the spray means 65 for spraying the cooling water in the above movement process. This causes the thickness of the non-solidified molten steel 82 in the playing cast 80 to gradually decrease. When the cast steel 80 reaches one point 85, the cast steel 80 is filled with the solidification shell 81 of the entire thickness. The solidified cast piece 80 is cut to a certain size at the cutting point 91 is divided into slabs (P) such as slabs.

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 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 and blocks the ingress 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 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 view showing a crack monitoring device in a mold according to an embodiment of the present invention, the crack monitoring device 100 is a vibration detection sensor 110, a signal conversion unit 120, a memory 130, a display unit 140 , An input unit 150, and a central processing unit 160 are configured.

The vibration detection sensor 110 is mounted on at least one outside of the mold 30 or the carriage of the mold 30 to detect the vibration width and the vibration speed of the mold 30. The vibration detection sensor 110 may be a load cell for detecting a deformation amount of pressure applied to the mold 30 or a vibration sensor for generating a signal according to the vibration width of the mold 30.

The signal converter 120 amplifies and converts the vibration width of the mold 30 detected by the vibration detection sensor 110 into a signal, for example, a digital signal, which can be processed at a later stage.

The memory 130 stores a cycle for detecting a friction force of the mold 30, a reference time for determining an abnormality of the friction force of the mold 30, and friction force data according to the detected vibration width.

The display unit 140 displays the measured values of the friction force of the mold 30 and the instantaneous change amount of the friction force in a text or graph on the time axis.

The input unit 150 is configured to receive various commands or reference values from the outside and transmit them to the central processing unit 160.

The central processing unit 160 calculates a friction force between the mold 30 and the solidification shell 81 by using the vibration width detected by the vibration detection sensor 110 and determines whether the calculated friction force is continuously increased or decreased during the set reference time. By judging and predicting the occurrence of cracks in the cast piece 80, if the cracks are generated appropriate control according to the abnormal signs. Here, the central processing unit 160 may include a friction force calculation unit 161, a change amount calculation unit 163 and a crack generation prediction unit 165.

The friction force calculator 161 calculates a friction force by using the vibration width detected by the vibration detection sensor 110.

The change calculator 163 calculates the instantaneous change by subtracting the previous friction force from the friction force calculated by the friction force calculator 161 and stores the calculated instantaneous change in the memory 130. Here, when the instantaneous change amount is greater than '0', it means that the friction force is increased, and when the instantaneous change amount is less than '0', it means that the friction force is decreased. Here, in the case where the increase and decrease of the friction force is alternately repeated, the instantaneous change amount for the friction force repeatedly has a positive value (+) and a negative value (−). If the frictional force continues to increase or decrease, the calculated instantaneous change amount will have a positive value (+) or a negative value (-) continuously.

The crack generation prediction unit 165 monitors the instantaneous changes of the frictional force stored in the memory 130 to determine whether the frictional force is increased or decreased during the set reference time, and if the frictional force is increased or decreased for at least the set reference time, the cast steel 80 It is estimated that the crack has occurred in the). That is, the crack generation prediction unit 165 diagnoses that a crack is generated in the cast steel 80 when the instantaneous changes are continuously greater than '0' or less than '0' during the set reference time.

In addition, the crack generation prediction unit 165 increases the amount of powder supplied to the mold 30 by controlling the powder feeder 50 when predicting crack occurrence, or by controlling the pinch roll 70 to decrease the casting speed. The amount of molten steel introduced into the mold 30 may be reduced by controlling the stopper 21. Of course, the cracks generated cast piece 80 can be removed from the crack formed on the surface of the slab through the scarfing process of the rear end.

In addition, the crack generation prediction unit 165 through the alarm generation unit 170 is predicted that the cracking force between the mold 30 and the solidification shell 81 may increase the fracture or breakage of the cast piece 80 A warning light or alarm sound may also be generated.

Thus, in the present invention, instead of monitoring whether the friction force is out of the reference range (for example, W 500 N / sec), the friction force falls within the reference range by determining whether the friction force has continuously increased or decreased during the set reference time. Even if there is a feature that can predict whether or not the performance cast (80).

4 is a flowchart illustrating a process for monitoring frictional force in a mold according to the present invention, which will be described with reference to the accompanying drawings.

First, at least one vibration detection sensor 110 mounted on the outside of the mold 30 or the mold 30 carriage detects the vibration width of the mold 30 and transmits the vibration width to the signal conversion unit 120 (S1). The signal converter 120 amplifies and converts the vibration width of the mold 30 detected by the vibration detection sensor 110 into a signal, for example, a digital signal, which can be processed at a later stage, and transmits the signal to the central processing unit 160.

The friction force calculating unit 161 of the central processing unit 160 calculates the friction force by using the vibration width data input through the signal converting unit 120 (S2).

In general, the frictional force during casting fluctuates in a certain period and width due to the vibration effect of the mold 30. Therefore, if the instantaneous change of the friction force is calculated and monitored, it is maintained within a certain range regardless of operating conditions such as steel grade and circumferential speed during normal operation. However, when an abnormality occurs in the mold, the frictional force increases or decreases rapidly, and thus the change is out of a certain range at a specific point in time. When sticking of a part of the solidification shell 81 with the mold 30 occurs, the friction force can only increase, and an air gap between the solidification shell 81 and the mold 30 is generated. When much is produced, the frictional force can only continue to decrease. Here, the frictional force may vary depending on the type of powder or the type of steel (low carbon steel, medium carbon steel), casting speed and molten steel temperature as shown in FIGS. 5 and 6. Currently, friction force exists between the mold 30 and the solidification shell 81 interface in the mold, and is measured and monitored in real time through the vibration detection sensor 110 attached to the mold 30 carriage. Since these frictional forces tend to vary depending on the steel grade, powder type, casting speed, molten steel temperature, etc., it is not easy to monitor the frictional force based on a certain value.

During the continuous casting process, the vibration width of the mold 30 may be, for example, about 2.7 mm. When the friction force between the mold 30 and the solidification shell 81 increases, the vibration width gradually decreases. The reason why the oscillation width is reduced is that the friction force between the mold 30 and the solidification shell 81 is increased to hinder the oscillation width of the mold 30.

Subsequently, the change calculation unit 163 of the central processing unit 160 calculates the instantaneous change amount (deviation) between the calculated friction force and the previous friction force, and stores the calculated instantaneous change amount DFn in the memory 130 (S3). ). In this case, when the increase and decrease of the frictional force are alternately repeated, the instantaneous change amount DFn repeatedly has a positive value (+) and a negative value (−) in Equation 1 below.

Equation 1

Here, DFn (Deviation of Friction) is the change of the friction force moment of time n seconds after the casting, Fn is the frictional force (Friction Force) of n second time after casting.

If the frictional force increases or decreases for a predetermined time, the instantaneous change amount DFn in Equation 1 will have a positive value (+) or a negative value (-) continuously. Here, when the instantaneous change amount DFn is greater than '0', it means that the friction force is increased, and when the instantaneous change amount DFn is less than '0', it means that the friction force is decreased.

The crack generation prediction unit 165 monitors the instantaneous changes of the friction force stored in the memory 130 to determine whether the friction force is increased or decreased during the set reference time (S4), and if the friction force is increased or decreased at least during the set reference time. It is predicted that cracks have occurred in the performance cast piece 80 (S5, S6). That is, the crack generation prediction unit 165 diagnoses that a crack is generated in the cast steel 80 when the instantaneous changes are continuously greater than '0' or less than '0' during the set reference time. The reference time set above may be at least 14 seconds. In 14 seconds or less, the reliability of the result may be inferior, which is not preferable. When the frictional force is collected at one second intervals, the crack generation prediction unit 165 may have at least 13 or more consecutive values of the instantaneous change amount stored in the memory 130 that are greater than '0' or smaller than '0'. If present, it can be determined that the friction force has increased or decreased for 14 seconds.

The friction force calculator 161 and the variation calculator 163 may display the calculated friction force and the variation of friction through the display unit 140 as shown in FIG. 7. If the momentary change of frictional force is calculated and monitored, during normal operation, it remains within a certain reference range (DFref; e.g., 500 N / sec) regardless of operating conditions such as steel grade, circumferential speed, etc. Since the frictional force increases or decreases rapidly, it may show a change out of a certain range at a specific point in time. However, even when the frictional force continuously increases (ⓐ section) or decreases (ⓑ section) for a predetermined time even within a certain reference range DFref as shown in FIG. 7, the surface of the cast steel 80 as shown in FIG. 8. Cracks (©) may occur.

The central processing unit 160 determines that a crack is generated on the surface of the cast steel 80 when the friction force is continuously increased or decreased during the set reference time (which may include the number of times). At least one or more controls may be performed to reduce. As a control method for reducing the frictional force in the mold 30, for example, by controlling the powder feeder 50 to increase the amount of powder supplied to the mold 30 or to control the pinch roll 70 to increase the casting speed By reducing or controlling the stopper 21 to reduce the amount of molten steel introduced into the mold 30 or by controlling the current value supplied to an electromagnetic coil (not shown) attached to the outside of the mold 30. The flow of molten steel can be operated in low speed mode.

In addition, the central processing unit 160 generates a warning light or an alarm sound through the alarm generator 170 when it is predicted that the friction force between the mold 30 and the solidification shell 81 may increase and crack or slab breakage may occur. So that the administrator can easily check and cope with it (S7).

According to the present invention as described above, by measuring the vibration width of the mold 30, by calculating the amount of change in friction between the mold 30 and the solidification shell 81 to predict abnormal signs, regardless of the type of steel or powder There is an advantage to monitor and predict abnormal symptoms through certain criteria.

In addition, the central processing unit 160 may display an abnormality in the mold even when the instantaneous change amount or the accumulated value of the instantaneous change amount repeatedly goes out of the set reference range (eg, 500 N / sec) during the set reference time (including the number of times). May be determined to have occurred. Such a method may be practiced in parallel with the method of the present invention.

The crack prediction method using the friction force 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 15: shroud nozzle
20: Tundish 25: Immersion Nozzle
30: mold 40: mold oscillator
50: powder feeder 51: powder layer
52: liquid fluidized bed 53: lubricating layer
60: support roll 65: spray
70: pinch roll 80: performance cast
81: solidified shell 82: unsolidified molten steel
83: tip 85: solidification completion point
87: Oscillation mark 91: Cutting point
100: crack monitoring device 110: vibration detection sensor
120: signal processor 130: memory
140: display unit 150: input unit
160: central processing unit 161: frictional force calculation unit
163: variation comparison unit 165: crack generation prediction unit
170: alarm signal generator

Claims (7)

A vibration detection sensor mounted on an outside of the mold or the mold carriage to detect a vibration width of the mold; And
A central processing unit for calculating a friction force between the mold and the solidification shell by using the vibration width detected by the vibration detection sensor, and determining whether the calculated frictional force is continuously increased or decreased for a predetermined reference time and predicting the crack of the playing cast; Crack monitoring device using a friction force in the mold comprising a.
The method according to claim 1,
The central processing unit calculates the instantaneous change amount between the calculated friction force and the previous friction force, and then monitors whether the instantaneous change amount is larger than '0' or smaller than '0' continuously for a predetermined reference time to determine whether cracks of the cast steel are generated. Crack monitoring device using the frictional force in the mold.
The method according to claim 1,
And a reference time set in the central processor is at least 14 seconds.
The method according to claim 1,
And a display unit configured to display, on a time axis, an instantaneous change amount of the friction force or the frictional force of the mold measured under the control of the central processing unit.
Detecting a vibration width according to vibration of the mold;
Calculating a frictional force using the detected vibration width;
Calculating an instantaneous change in friction force by subtracting a previous friction force from the friction force calculated above; And
And predicting whether or not a crack occurs in the cast steel piece by determining whether the friction force is continuously increased or decreased during a predetermined reference time, based on the calculated instantaneous change in friction force.
The method according to claim 5,
In the step of predicting whether or not the crack occurs, the crack using the frictional force in the mold for predicting the occurrence of cracks of the cast cast by determining whether the instantaneous change of frictional force is continuously greater than '0' or less than '0' during the set reference time Surveillance Method.
The method according to claim 5,
And predicting whether the crack has occurred, wherein the set reference time is at least 14 seconds.

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