JP3188148B2 - Continuous casting machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a steel continuous casting machine, and relates to an alarm system for predicting in advance the danger of breakout.

[0002]

2. Description of the Related Art In a continuous steel casting machine, prediction of a so-called breakout (hereinafter referred to as "BO") accident in which a thin portion of a solidified shell is broken in a mold and establishment of a technology for preventing the accident are eternal issues. is there. Particularly in recent continuous casting machines for billets, there is an increasing demand for high-speed casting for the purpose of high productivity. However, as the casting speed increases, the thickness of the solidified shell formed in the mold decreases, and B.I. Since the risk of O generation increases, B.I. It is necessary to predict and prevent O accidents.

Conventionally, in a continuous caster for blooms and slabs which performs powder casting, a B.I. For O, various B.O.s by measuring the temperature distribution in the mold. O prediction and alarm technology has been developed and is in the stage of practical use. However, in a continuous casting machine for billets mainly using oil lubrication, a restricted B.I.
O rarely occurs, and most B.O. O is caused by a vertical crack in a corner portion generated immediately below the mold due to uneven solidification in the mold. Moreover, this type of B. O, the higher the casting speed, the smaller the average solidified shell thickness formed in the mold. The risk of O generation has tended to increase, which has limited the casting speed in billet continuous casting machines.

[0004] Therefore, in the billet continuous casting machine, B.I. O. Prediction technology has been developed, and non-uniform solidification occurring in the mold is related to rhombic deformation of the slab, and the degree of rhombic deformation is detected. A method of predicting the danger of O and measuring the temperature distribution of the slab surface immediately below the mold to detect an abnormally thin portion of the solidified shell. Methods for predicting O have been devised, but none of them has been put to practical use.

[0005]

SUMMARY OF THE INVENTION In the billet continuous casting machine, B.I. O is almost always caused by the thin corner portion of the solidified shell being broken immediately below the mold due to uneven solidification in the mold. Therefore, if the change in the thickness of the solidified shell in the mold during casting can be measured every moment, B.I. It is thought that prediction of O is also possible. But,
It is very difficult to directly measure the thickness of the solidified shell of the slab just below the mold, and it is considered impossible with the current technology.

[0006] The thickness of the solidified shell formed in the mold varies depending on the temperature of molten steel, the heat removal capability of the mold, the casting speed, and the like. The corner part is separated from the mold wall at an early stage, an air gap is formed, and the solidified shell at the corner part is destined to be unevenly solidified, and the thickness of the solidified shell immediately below the mold is expected to change. Even it was considered difficult.

[0007]

[MEANS FOR SOLVING THE PROBLEMS]
Ming's continuous caster configuration is designed to continuously cast molten steel in a mold.
In the continuous casting machine to be manufactured, the cooling water amount of the above mold
(F), inlet cooling water temperature (T ₁), Outlet cooling water temperature (T
_Two) And the drawing speed (V) of the slab are constantly measured and sent to a computer.
In addition to the input, the casting dimensions such as the casting dimensions and steel type
Based on the coefficient (K) calculated in advance from the
And the equation da = F (T_Two-T₁) / K · V
The average solidified shell thickness (da) formed in the mold
Calculated, and the minimum solidified shell thickness
Determined from once, limit solidification shell thickness at which breakout occurs
By comparing with the
The risk of breakout increases when the thickness is below the well thickness
Means for issuing a warning.

That is, since the heat removal ability of the mold changes in accordance with the casting conditions of continuous casting and the change in the cooling efficiency of the mold, the heat removal amount in the mold is calculated as the product of the mold cooling water amount and the temperature rise of the cooling water. From the actual measurement data, the change in the average solidified shell thickness formed in the mold can be estimated and calculated from the casting conditions corresponding to the constantly changing heat removal amount, based on the measured data. On the other hand, from the experience of many operations, the unevenness of the solidified shell thickness (minimum thickness /
Average thickness) is generally from 0.6 to 0.7; It is also known that the critical solidified shell thickness in which O is not generated is 5 to 6 mm.

By applying the above to a computer control system adopted in a recent continuous caster, the average of the direct under the mold can be obtained from changes in equipment, casting conditions and operating conditions input to the computer. Calculate the solidified shell thickness, constantly monitor the change, specify the minimum solidified shell thickness,
B. B. Compared with the O-thick solidified shell thickness. A system for issuing an alarm by determining the risk of occurrence of O is established.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a continuous casting machine, it is important to form a solidified shell having sufficient strength in a mold, and if the solidified shell is insufficiently formed, various external forces are imposed upon leaving the mold. The thinned portion of the solidified shell, which is exposed to heat and heat stress, has a low strength due to a high shell temperature, so that portion is broken, and B.I. It is said that O occurs. In this case, B. It is said that the critical solidified shell thickness at which O does not occur is theoretically about 5 to 6 mm.

However, as shown in the sectional view of the slab just below the mold in FIG. 2, the solidified shell 13 forming the outer shell of the slab 14 The occurrence of an air gap in the corner portion due to shrinkage delays the progress of solidification in the corner portion, resulting in a state in which so-called uneven solidification has occurred. The non-uniform solidification in the mold is fatal, and varies somewhat depending on the design conditions of the mold body. However, the degree of non-uniformity is represented by dmin / (minimum solidified thickness dmin / average solidified shell thickness da). da = 0.6 to 0.7.

Next, the relationship between equipment conditions, casting conditions and operating conditions and the average solidified shell thickness formed in the mold (assuming that solidification has progressed uniformly) will be considered. First, as casting conditions, the physical properties of the steel, the specific gravity γ (kg / m ³ ) of the solidified shell, the specific heat C _P (kcal / kg ° C.), Give latent heat H (kcal / kg). next,
Operating conditions include casting speed V (m / min) and casting temperature T
_S (℃) Mold cooling water volume F (l / min), cooling water temperature rise Δ
T (° C.), the slab surface temperature T _SU (° C.) immediately below the mold.
Assuming that the average solidified shell thickness da (m) formed in the mold, the heat removal Q (kcal / min) in the mold and the heat required for forming the solidified shell are considered to be equal, and the following equation is established.

[0013]

(Equation 1)

Therefore, by giving necessary information, the average solidified shell thickness (da) can be calculated by the above equation (2).

Therefore, an actual calculation control system will be described with reference to the drawings. FIG. 1 is a system configuration diagram as an embodiment of the present invention, and FIG. 3 is a flowchart of the present system. In these drawings, reference numeral 1 denotes a mold, 2
Is a drawing drive roll, 3 is a drawing pinch roll, 4 is a driving motor, 5 is a cooling water supply, 6 is a tachometer, 7 is a flow meter, 8, 9 cooling water thermometer, 10 is a computer, and 11 is a monitor. A screen, 12 is molten steel, 13 is a solidified shell, and 14 is a slab. 1 and 3, this continuous casting machine is typically constituted by a mold 1 and drawing pinch rolls 2 and 3. The molten steel 12 is continuously supplied from above the mold 1, is strongly cooled by contacting the water cooling wall of the mold 1, solidifies to form a solidified shell 13, and a slab 14 having a predetermined sectional shape is manufactured. And the product billet is continuously drawn and corrected by the pinch rolls 2 and 3 at a predetermined drawing speed 15.
Produced in.

Here, the mold 1 has a structure in which a large amount of cooling water 5 is supplied from below and forcedly cooled, and drained from the upper portion 5a, and cooled by a flow meter 7 and thermometers 8 and 9. Signals of the water amount F, the inlet cooling temperature T ₁ , and the outlet cooling temperature T ₂ are constantly input to the computer 10.

On the other hand, in the drawing pinch rolls 2 and 3, the driving roll 2 is driven by a motor 4 via a speed reducer, and a signal of a drawing speed V is input to a computer 10 from a tachometer 6 directly connected to the motor. I do.

In the computer 10, from the casting conditions and the physical properties of the steel given in advance and the operation data (F, T ₁ , T ₂ , V) which are always inputted, the above equation (2) is used. To calculate the average solidified shell thickness da, and the change is displayed on the monitor screen 11.

Simultaneously with the calculation of the average solidified shell thickness da,
The minimum solidified shell thickness dmin is also calculated from the assumed nonuniformity, compared with the limit solidified shell thickness (set empirically at 5 to 6 mm), and an alarm is issued when the limit value is approached. Configure a system to

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below, but the present invention is not limited thereto.

As an example, a 150 mm square billet, S
A case where the present invention is applied to D casting will be described. As casting conditions, casting dimensions A = 0.15 m, B = 0.15 m, and casting temperature T _S =
1550 ° C., slab surface temperature T _SU = 1100 ° C., and physical properties of steel (γ = 7400 kg / m ³ , H = 65 kcal / kg, C _P
= 0.21 kcal / kg ° C), K = 4.98 × 10 ⁵ , and equation (2) gives da = F (T ₂ −T ₁ ) /4.98×10 ⁵
× V.

In actual operation, the casting temperature and the slab surface temperature are not used as input data because continuous measurement is difficult. Believe that there is no big error. The cooling water flow rate of the mold was F = 300 l / min and the operation was almost constant.However, the heat removal capacity of the mold changed significantly due to the degree of contact between the mold and the slab and the decrease in cooling efficiency due to scale deposition. Therefore, the heat removal amount is ΔT = T ₂ −T ₁ =
The temperature ranged from 8 to 13 ° C.

On the other hand, the casting speed is V = 2.2 to 3.2 m /
The average solidified shell thickness calculated by a computer after operating over a wide range of min changes to a range of da = 8 to 16 mm,
B. O limit shell thickness has been approached, O
An alarm was issued. B. above. When the O alarm is issued, the casting speed is reduced and the operation is continued. O Prevent accidents.

[0024]

As described above, as described above, the B.I. of the corner portion due to the undeveloped solidified shell immediately below the mold has been conventionally used. It is considered that the O accident was caused by an abnormal decrease in the mold heat removal capability and an inappropriate casting speed. Although the cause was often noticed after the occurrence of the O accident, in the present invention, the formation amount of the solidified shell was constantly monitored. A warning is issued to increase the risk of O occurrence,
B. by changing casting conditions, etc. O-prevention measures can be implemented, which is very practical. In recent continuous casters, many computer control systems using computers have been adopted, and it is easy to apply the system of the present invention, which greatly contributes to high productivity in high speed casting of the continuous caster.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram as an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a slab showing a formation state of a solidified shell immediately below a mold.

FIG. 3 is a flowchart of the present system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 pull-out drive roll 3 pull-out pinch roll 4 drive motor 5 cooling water supply water 5a cooling water drainage 6 rotation speed meter 7 flow meter 8,9 cooling water thermometer 10 computer 11 monitor screen 12 molten steel 13 solidified shell 14 cast slab

Continuation of the front page (72) Inventor Tadashi Nishimura 1-20-24 Kanon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Inside Rishige Steel Engineering Co., Ltd. (56) References JP-A-6-320245 (JP, A) JP-A Sho 63-115660 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 11/16

Claims (1)

(57) [Claims] 1. A continuous casting machine for continuously casting molten steel in a mold, comprising: a cooling water amount (F) of the mold, an inlet cooling water temperature (T ₁ ),
The outlet cooling water temperature (T ₂ ) and the slab drawing speed (V) are constantly measured and input to a computer. From the above casting dimensions, casting conditions such as steel type, and physical properties of the steel,
Based on the coefficient (K) calculated in advance, the equation da = F
The average solidified shell thickness (da) formed in the mold is calculated by (T ₂ −T ₁ ) / K · V, and the minimum solidified shell thickness is calculated from the nonuniformity. A continuous casting machine comprising means for issuing an alarm for increasing the risk of occurrence of breakout when the thickness of the solidified shell becomes equal to or less than a breakout occurrence limit thickness by comparing with the solidified shell thickness.