KR100889290B1 - A Method for Calculating the Roll Life in a Continuous Casting - Google Patents

Abstract

The roll life prediction method of the continuous casting machine according to the present invention measures the flow rate of the coolant flow and the flow rate of the roll attached to the segment of the continuous casting machine used in the continuous casting process of steel mills, and the accurate life of the roll using the cast temperature and the solidification pattern The present invention relates to a method for predicting roll life of a continuous casting machine for timely maintenance and replacement in units of segments. To this end, in a plurality of roll life prediction method attached to each of a plurality of segments installed in a continuous casting machine for continuous casting of cast steel, it is removed by the cooling water flowing into the i-th roll and circulated inside the roll and discharged A first step of calculating calorie Qi per unit area of the roll; A second step of calculating a positional temperature of the cast steel using the Qi and obtaining a solidification pattern of the cast steel using the temperature; A third step of calculating the temperature, deformation amount and stress of the roll in contact with the cast steel; A fourth step of calculating the shear strain energy Ud1 and the maximum shear strain energy Ud2 which is a failure condition of the roll; Calculating a roll life of the roll; Calculating a maximum average temperature value (T2max) of the roll cooling water at a maximum average temperature value (T1max) of the roll cooling water and a set time interval; And a seventh step of checking the roll when the Ud1? Ud2, the Lroll? N (set roll life) and | T1max-T2max |?? (Tolerance) are simultaneously satisfied.

Continuous Casting Machine, Roll, Coolant, Segment, Cast

Description

A method for calculating the roll life in a continuous casting

1 is a perspective view schematically showing a continuous casting machine of a steel mill in general.

Figure 2 (a) is a block diagram according to an embodiment of a segment measuring device applied to the present invention.

Fig. 2 (b) is an internal sectional view of one segment 5 shown in Fig. 2 (a).

3 is a detailed block diagram of a segment measuring device according to the present invention.

Figure 4 is a flow chart showing a process for predicting the roll life by using a secondary cooling formula model for roll prediction in accordance with the present invention.

5 is a schematic view of a slab for calculating slab temperature and solidification pattern.

Figure 6 is the cast slab temperature distribution calculated according to an embodiment of the present invention and the measured temperature of the roll cooling water discharge side.

 Explanation of symbols on the main parts of the drawings

1: molten steel 2: ladle

3: tundish 4: mold

5: segment 6: casting direction

7 cast steel 8: segment junction

10: control unit 11: roll                 

12,13: specific signal line 14: segment frame

15,17 U-shaped piping 17: Roll-in insertion piping

18: cooling water inflow direction 19; Cooling water discharge direction

21: thermometer 22: flow meter

The present invention relates to a method for predicting roll life of a continuous casting machine. More specifically, the present invention relates to a cooling water inflow temperature and a flow rate variation of a roll attached to a segment of a continuous casting machine used in a continuous casting process of a steel mill. The present invention relates to a method for predicting the roll life of a continuous casting machine for timely maintenance and replacement of the roll unit by predicting the accurate life of the roll.

In general, the continuous casting process is a process of shaping the molten steel that has been refined in the steelmaking process of the steel mill to the size and quality required by the demand, and the quality of the slab depending on how to cool the heat of the molten steel. And productivity depend.

1 is a perspective view schematically showing a continuous casting machine generally used in steel mills. As shown in FIG. 1, the continuous casting machine includes a ladle 2 containing molten steel 1, a tundish 3 having a molten steel storage function and an inclusion separation function between the ladle 2 and the mold 4. It consists of a mold 4 which solidifies the slab 7 in the required shape and size and a secondary cooling stand 5 which is composed of a plurality of segments 5. The secondary cooling stand 5 performs cooling by the nozzle and pressing down by the roll 11 so that the slab 7 passing through the cooling stand 5 maintains a solidified shell of a constant thickness at an arbitrary position. .

The method of calculating the cooling pattern of the cast steel 7 in the continuous casting operation in the continuous casting machine is mainly based on a one-dimensional mathematical model that considers only the thermal conduction phenomenon of the cast steel 7. In general, the cooling pattern of the cast steel is the temperature of the cast steel by the secondary cooling consisting of primary cooling in the mold (4), roll 11 in the strand (strand), spray by the nozzle, mechanical cooling, etc. It decreases linearly and appears differently depending on the steel grade and operating conditions of the cast (7). This secondary cooling can be regarded as consisting of radiation to the atmosphere by the hot slab 7 called the heat transfer mode, contact heat transfer by the support roll 11, convection cooling by the nozzle, and the like. Therefore, when the solidification pattern of the cast steel is calculated by the mathematical model, an accurate mathematical model based on the conduction, convection, and radiation heat transfer phenomena in the heat transfer mode is required.

However, the exact mathematical model for temperature prediction of cast steel has not been established yet, and in the past, only the approximate numerical model has been relied on. In particular, the current site has undergone many trials and errors, and introduced the correction coefficient of the concept of average heat transfer coefficient, and it is now possible to estimate the temperature prediction or the completion of solidification by strand position within normal error during normal casting operation. However, there was a problem that the accuracy of the mathematical model was very poor in abnormal casting, i.e., at the beginning and the end of the casting, and the replacement of the roll 11 was only about three months based on experience regardless of deformation or breakage of the roll 11. Since the situation is sent to the maintenance shop in units of segments (5) to check for abnormalities, systematic facility management was not carried out and there was a problem of causing an increase in working costs. In particular, there was a problem that the deformation and breaking of the roll could not be predicted in advance and the quality of the cast steel was lowered.

As such, the conventional strand mathematical model simply has a problem of low degree of casting at the beginning and end of the casting process because it mainly depends on the initial operating conditions of continuous casting, and casting conditions (for example, circumferential speed, secondary cooling pattern or seasonal) Inevitably, many trials and errors must be passed to derive the correction factor.

When predicting and determining the life of a roll, theoretically, it is common to calculate a stress based on a thermoelastic relationship. However, in the related art, a thermal history for this purpose is collected online to construct a life prediction system of the roll 11. It is not. Therefore, while maintaining the mechanical and metallurgical state of the roll in each casting in real time, there is a need for an improved formula model for improving the accuracy of the electrothermal modification model by the contact of the roll, as well as a separate method for predicting the life of the equipment. .

As the present invention has been proposed to solve the above problems, the present invention, continuous casting machine for formulating the roll replacement time by detecting the coolant temperature passing through the roll in real time and accurately predicting the life of the roll using the cast temperature and cooling pattern The purpose of the present invention is to provide a method for predicting roll life.

In the present invention for achieving the above object, in a plurality of roll life prediction method attached to each of a plurality of segments provided in a continuous casting machine for continuously casting the cast steel,

A first step of calculating a calorific value Qi per unit area of the roll introduced into the i th roll and removed by cooling water discharged after circulating the inside of the roll; A second step of calculating a positional temperature of the cast steel using the Qi and obtaining a solidification pattern of the cast steel using the temperature; A third step of calculating the temperature, deformation amount and stress of the roll in contact with the cast steel; A fourth step of calculating a shear strain energy Ud1 of the roll and a maximum shear strain energy Ud2 which is a break condition of the roll; Calculating a roll life of the roll; Calculating a maximum average temperature value (T2max) of the roll cooling water at a maximum average temperature value (T1max) of the roll cooling water and a set time interval; And a seventh step of checking the roll when the Ud1? Ud2, the Lroll? N (set roll life) and | T1max-T2max |?? (Tolerance) are simultaneously satisfied.

SUMMARY OF THE INVENTION The present invention provides a method for monitoring cast lifespans in a strand and for predicting roll life, which is measured in real time by measuring the cooling water inflow and outflow temperatures of the rolls 11 attached to the segments 5 of the continuous casting machine in a continuous casting operation. The present invention relates to a method for more accurately outputting the temperature and solidification pattern of the guide slab to be guided, as well as predicting the life of the roll to be maintained and replaced by the segment.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail the present invention.

Figure 2 (a) is a block diagram according to an embodiment of a segment measuring device applied to the present invention and Figure 2 (b) is an internal cross-sectional view of one segment 5 shown in Figure 2 (a). As shown in the figure, the segment measuring device according to the present invention is provided with a plurality of rolls 11 (generally four to six pairs of upper and lower portions per segment 5) attached to a plurality of segments 5. Segment junctions 8 are provided for joining a plurality of electrical lines 12, 13 connected to a thermometer and a flow meter (shown in FIG. 3) to measure the temperature and flow rate of the cooling water passing through and to connect the electrical lines 12, 13 The temperature and flow rate measurement signals of the coolant measured through the input to the control unit 10 and the control unit 10 converts into the corresponding coolant temperature and flow rate measurement values using the measurement signal. The controller 10 calculates the heat transfer and solidification pattern of the cast steel 7 by using the temperature and flow rate measured values of the cooling water.

The structure of the thermometer 21 and the flow meter 22 according to the present invention in segments for explaining the coolant flow in the roll 11 and the temperature and flow rate measurement of the coolant in detail is shown in FIG. 3. . 3 is a detailed block diagram of a segment measuring device according to the present invention. Referring first to FIG. 3 (a), the cast piece 7 moves between a plurality of rolls 11 belonging to one segment 5, and the reference numeral 6 denotes the moving direction of the cast piece 7. Among the plurality of rolls 11, there are a pinch roll that serves to move the cast piece 7 and a guide roll that serves as a guide of the moved cast piece 7. Therefore, what constitutes one segment 5 is a guide roll for supporting the cast piece 7 up and down, and a pinch roll for drawing the cast piece 7 in the casting direction 6. Reference numerals 12 and 13 denote electric lines for moving the temperature and flow rate measurement signals for the coolant flowing between the rolls 11 to the controller 10, and reference numeral 8 denotes the joining of the plurality of electric lines 12 and 13. Segment junction for making it. An apparatus for cooling water flow inside the roll 11 is shown in FIGS. 3 (b) and 3 (c). 3 (b) and 3 (c), two first and second U-shaped pipes 15 and 17 connected to the segment frame 14 are provided, and the respective U-shaped pipes 15, 17 are each connected to another pipe 16, which is inserted into the roll 11 as shown in FIG. 3 (b). These integrated pipes are located one each on the left and right sides of the roll 11. However, the other pipe 16 inserted into the roll 11 may be made to pass through the roll 11 as one.

Generally, the temperature of the roll 11 is about 900 to 1,300 ° C. under the influence of the temperature of the slab 7 in contact with the roll 11, which greatly affects the life of the roll 11. Therefore, it is important to cool the roll 11, such that the coolant of the roll 11 is introduced into the first U-shaped pipe 15 from a cooling water mother pipe (not shown) installed inside the segment frame 14, It is discharged through the second U-shaped pipe 17 again through another pipe 16 inserted into the roll 11. Here, reference numerals 18 and 19 denote inflow and outflow directions of the cooling water, respectively.

As shown in FIG. 3 (b), the flow meter 22 installed in the segment measuring device according to the present invention is installed at the inflow side of the first U-shaped pipe 15 through which coolant flows into the roll 11. The thermometer 21 is installed on the discharge side of the second U-shaped pipe 17 discharged after the cooling water circulates through the roll 11. Here, it is assumed that the temperature of the cooling water flowing into the roll 11 is known in advance. This may be possible by installing another thermometer. The temperature and flow rate measurement signals of the coolant generated by the plurality of thermometers 21 and the flowmeters 22 provided for each of the rolls 11 are controlled by the control unit 10 via the segment junction 8 through the electric lines 12 and 13. Are converted into temperature and flow measurement values, respectively.

4 is a flowchart illustrating a process of predicting roll life by using a quadratic formula model for roll prediction according to the present invention. Referring to FIG. 4, the accuracy improvement of the mathematical model using the variation in the physical quantity of the roll cooling water and the life prediction method of the roll 11 are described as follows. First, operating conditions and boundary conditions are given, including information on the steel grade to be cast, its components, casting speed, initial temperature, cooling pattern during secondary cooling, and the amount of heat removed from the slab 7 in contact with the roll 11. 2 and 3, each unique number of the plurality of thermometers 21 and the flow meter 22 installed on the plurality of rolls 11 is Ni (i = 1, 2, 3,. n), Nj (j = 1,2,3, ... n), and the heat quantity Qi per unit area removed by the cooling water at the number i of the roll 11 is calculated as in Equation 1 below. (S402).

[Equation 1]

는 상기 유량계(12)에서 검출된 시간당 냉각수 변동량이고, 상기 Cp는 냉각수의 정압비열이고, 상기 △Ti는 i 번째의 롤(11)에서 검출된 온도의 입출측 편차이며, 상기 Ar은 상기 롤의 표면적이다.
Where

Is the amount of change in the cooling water per hour detected by the flowmeter 12, Cp is the constant pressure specific heat of the cooling water, ΔTi is the deviation on the entry and exit side of the temperature detected by the ith roll 11, Ar is the Surface area.

Next, the principle of calculating the temperature of the slab 7 will be described. The operation parameters and the boundary conditions of calculation given in the step S401 are read as input data, and as shown in FIG. In order to find an abnormal solution in the y-axis direction, which is the casting direction (6), taking the cross section of the calculation area A into consideration and considering only the heat transfer gradient in the x-axis direction, the following energy equations are finitely differentiated to obtain the abnormal solution in the casting direction. The coordinate y to (6) is divided by a finite number, and each position is defined as y _K (k = 1, 2, 3, ... n), and the center, surface, and Using the temperature between the center and the surface and the temperature of the cast steel 7 at each position, the solidification pattern such as the solidification thickness of the cast steel 7 is calculated using the following boundary condition equations (2, 3, 4 and 5): S403).

[Formula 2]

[Equation 3]

when x = 0,

[Equation 4]

when x = x _L ,

[Equation 5]

............. 주형 영역

............. Mold area

............. 2차 냉각 영역

............. 2nd cooling zone

............. 기계냉각(복사) 영역

Machine Cooling (Copy) Area

Where Keff is the effective thermal conductivity coefficient, H (T) is the temperature-dependent enthalpy, T is the slab temperature, ρ is the slab density, h _m is the average convective heat transfer coefficient between the mold copper plate and the surface of the slab in the mold region, and hi is the cooling region i The average heat transfer coefficient at, Ta is the ambient temperature, σ is the Stefan-Boltzmann constant, ε is the radiant emissivity, q is the heat flux, and the heat flux flows out per unit area, Qi is the roll (10, 11) and the slab (7) The amount of heat removal per unit area due to contact.

In addition, in the method of calculating the life of the roll 11 from the coolant temperature and the flow rate measurement signal detected from the thermometer 21 and the flow meter 22, the electrothermal analysis of the roll 11 also uses the same energy as in Equation 2 above. Formula 6 is formulated by finite element equation, and the following equation 6 is numerically analyzed for stress analysis. Here, the temperature of the roll 11 in contact with the slab 7 by using the temperature of the slab 7 and the solidification pattern, the amount of deformation of the roll 11 due to the temperature roll and the stress of the slab 11 It is calculated using Equations 7 and 8 below (S404).

[Equation 6]

[Formula 7]

Calculate roll deformation

는 롤의 최대처짐량, P는 롤의 위치에서 가해지는 철정력, l은 롤의 길이, v는 프와송비, a,b는 분할롤의 각각의 길이, E는 롤 재료의 탄성 계수이다.here,

Is the maximum deflection of the roll, P is the iron tension applied at the position of the roll, l is the length of the roll, v is Poisson's ratio, a and b is the length of each of the split rolls, and E is the elastic modulus of the roll material.

Equation 8                     

Roll stress calculation

는 롤 반경방향의 응력,

는 원주방향의 응력을 말하며, E는 롤 재료의 탄성계수, v는 프와송비, α는 열탄성계수, T는 롤의 온도,

는 원주방향의 변형율,

는 반경방향의 변형율이다.
here,

Is the radial stress in the roll,

Is the stress in the circumferential direction, E is the elastic modulus of the roll material, v is the Poisson's ratio, α is the thermoelastic coefficient, T is the roll temperature,

Is the strain rate in the circumferential direction,

Is the radial strain rate.

On the other hand, the criterion that the roll 11 is broken is that the yield elasticity calculated from the thermal stress of the roll 11 is equal to the value of the pure shear elastic energy when the yield point is reached at the yield point at the uniaxial tensile strength of the material. The safety condition of the material of the roll 11 is determined by using the maximum shear strain energy theory, which is considered to be started, and the relation is expressed by Equations 9 and 10. Using the above equations, the shear strain energy Ud1 and the energy Ud2 serving as a failure condition are calculated (S405 and S406).

[Equation 9]

Shear strain energy

Equation 10

Energy that breaks down

는 단축인장 주응력, v는 프와송비, E는 탄성계수이다.
here,

Is the uniaxial tensile stress, v is Poisson's ratio, and E is the modulus of elasticity.

In addition, the roll 11 is not considered that the deformation or breakage is proportional to the load or the stress, and ultimately, the geometric size (radius, length, split form, etc.) and the use conditions, that is, the yield of the cast steel 7, the roll ( 11) Since it can be expressed as a function of the wear coefficient and the history of cast stagnation, the life prediction calculation formula shown in Equation 11 is used (S407).

[Equation 11]

Where Lroll is the actual roll life (hours), A is the proportional constant, L is the roll length, w is the roll wear factor, Sn is the number of monthly stagnations of the cast, n is the number of segments removed, Pmy is monthly, and annual cast production (ton), r is the diameter of a roll.

In addition, in the case of the temperature detected by the thermometer 21, the maximum average temperature T1max before 1 hour at any time and the maximum average temperature at any time is calculated T2max (S408). Subsequently, it is determined whether the following conditions 1,2 and 3 are simultaneously satisfied using the calculated values of Ud1, Ud2, Lroll, T1max and T2max (S409).

[Condition 1]

Ud1 ≥Ud2

[Condition 2]

Lroll ≥N hours

[Condition 3]

T1max-T2max

Here, N is a preset roll life (time), and β is an error value defined by the mathematical model, which is set according to the resolution and noise of the controller 10.

Subsequently, when the three conditions are satisfied at the same time as a result of the determination in step S409, an alarm is generated to detect that the corresponding roll 11 has reached the end of life or is defective and check it (S410). On the contrary, if any one of the three conditions is not satisfied, the process returns to the step S401 and the processes are repeated.

5 is a schematic diagram of a slab for calculating slab temperature and solidification pattern. In the case of the slab 7 shown in Fig. 5, the two-dimensional cross section inside and outside the slab 7 used for the calculation is indicated by oblique lines, and only the oblique part is selected in consideration of the symmetry condition in order to reduce the calculation capacity. . That is, the coordinate origin of x, y is the part where liquid molten steel is initially injected, and the temperature and the solidification shell thickness inside and outside of the cast slab change as the cooling conditions of boundary conditions change over time. It is possible by numerically solving the above-described formula (2).

As described above, the cooling water temperature value detected from the thermometer 21 mounted on the roll 11 of the segment 5 and the cooling water flow rate detected from the flow meter 22 in the continuous casting machine for continuously casting the cast 7. After analyzing the fluctuation amount, the heat removal amount by the roll 11 is calculated by using the temperature value and the flow rate fluctuation amount measured according to the real time operation, the roll life and the equipment defect are predicted, and the roll 11 cooling water By setting the heat removal amount as a new input value of the equation model, it is possible to output cast solidification pattern and to monitor the life expectancy and defect monitoring of the continuous casting roll 11 which is maintained and replaced by the segment (5). have.

Figure 6 is the cast steel temperature distribution calculated in accordance with an embodiment of the present invention and the measured temperature of the roll cooling water discharge side. In order to confirm the usefulness of the present invention, the solidification pattern analysis of the cast steel 7 in consideration of cooling of the roll 11 was carried out to calculate and graph the center and the surface temperature of the cast steel 7. Referring to FIG. 6 (a), due to the cooling effect and the recuperative phenomenon caused by the roll 11, the temperature type is different from that of the conventional mathematical model using the average heat transfer coefficient.

In addition, as a result of examining the temperature change of the cooling water for detecting the heat removal amount of the roll 11 according to the casting time, as shown in FIG. 6 (b), the detection value of the thermometer 21 proposed in the present invention is shown. By using the and the mathematical model, a higher mathematical model and roll life prediction are possible.

The foregoing detailed description and contents of the drawings illustrate one embodiment of the invention and do not limit the invention. In particular, the segment measuring device according to an embodiment of the present invention may be manufactured and implemented in various ways without departing from the technical spirit of the present invention. Accordingly, the scope of the present invention should be determined by the appended claims.

According to the present invention, by introducing a mean heat transfer coefficient to the formula model of the continuous cast slab that has been used previously, by constructing a new formula model for additional collection and analysis of the heat history data of the roll to improve the degree of the mathematical model as well In addition, the maintenance of roll equipment and the quality of cast steels are also improved, and the systematic maintenance management of the rolls is enabled, which has a great effect on process improvement.

Claims (5)

In the multiple roll life prediction method attached to each of a plurality of segments installed in a continuous casting machine for continuously casting the cast piece, A first step of calculating a calorific value Qi per unit area of the roll introduced into the i th roll and removed by cooling water discharged after circulating the inside of the roll; A second step of calculating a positional temperature of the cast steel using the Qi and obtaining a solidification pattern of the cast steel using the temperature; A third step of calculating the temperature, deformation amount and stress of the roll in contact with the cast steel; A fourth step of calculating the shear strain energy Ud1 and the maximum shear strain energy Ud2 which is a failure condition of the roll; Calculating a roll life of the roll; Calculating a maximum average temperature value (T2max) of the roll cooling water at a maximum average temperature value (T1max) of the roll cooling water and a set time interval; And A seventh step of checking the roll when the Ud1? Ud2, the Lroll? N (set roll life) and | T1max-T2max |?? (Tolerance) are simultaneously satisfied; Roll life prediction method of a continuous casting machine comprising a. The method of claim 1, wherein the heat quantity Qi per unit area of the roll is calculated based on the following equation 1. [Calculation 1]

(here,

Is the amount of variation in the cooling water flow rate per hour, Cp is the static pressure specific heat of the cooling water, ΔTi is the deviation of the cooling water temperature at the i-th roll, Ar is the surface area of the roll) The method of claim 2, And measuring the flow rate of the cooling water flowing into the roll, and measuring the temperature of the cooling water discharged from the roll after circulating the roll. The method of claim 1, wherein the roll life (Lroll) is calculated by the following equation (2). [Calculation 2]

Where A is the proportional constant, L is the roll length, w is the roll wear factor, Sn is the number of monthly stagnations of the slab, n is the number of segments removed, Pmy is monthly, annual cast production (ton), and r is the diameter of the roll. ) The method of claim 1, The shear strain energy (Ud1) and the maximum shear strain energy (Ud2) is calculated by the following equation using the maximum shear strain energy theory, characterized in that the roll life prediction method of the continuous casting machine. [Calculation 3]

(here,

Is shortened tensile stress, v is Poisson's ratio, E is modulus of elasticity,

Yield stress)

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