JP3096232B2 - Continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a continuous casting method. In particular, by detecting the solidification state in the mold,
The present invention relates to a continuous casting method for preventing molten steel from flowing out of a machine due to breakout.

[0002]

2. Description of the Related Art A conventional continuous casting method will be described with reference to FIG.

In the continuous casting method, as shown in FIG. 1, molten steel 11 is injected into a mold 1 from a tundish 4 in which molten steel is injected from a ladle, through a nozzle 2 made of refractory material, and vibrated vertically ( A solidified shell (shell) 10 is formed in a mold to be oscillated, and a pinch roll 9 is formed.
To continuously produce cast slabs. Mold 1
, In a water-cooled box to quickly solidify the molten steel 11,
Using a plate made of copper or copper alloy with high thermal conductivity, using powder 3 as a lubricant, the copper plate has a function of solidifying molten steel poured into the mold by cooling the back surface with water. ing. However, if the solidification by this mold is insufficient, the strength of the shell leaving the mold is weak, and the solidified shell is broken by losing the molten steel static pressure,
This causes a problem called breakout, in which molten steel flows out of the machine, and a phenomenon occurs in which casting is stopped.

[0004] Normally, by operating at a casting speed that does not cause this breakout, the solidified shell thickness is ensured,
This trouble is avoided. However, since an excessive decrease in the casting speed causes a decrease in productivity, various operation methods have been proposed that actually ensure both productivity and avoid trouble.

For example, Japanese Patent Application Laid-Open No. 63-183763 proposes a method of embedding a thermocouple in a mold copper plate, estimating the solidification state of the mold from its temperature information, and preventing breakout. However, since this method is an indirect evaluation method of embedding in a mold, estimation accuracy is poor, and it is impossible to completely prevent breakout. The cause is that the powder is in contact with the mold at the upper end of the mold, and an air gap (non-contact portion with the mold) is generated at the lower end of the mold due to solidification shrinkage, and these thermal resistances are extremely large. This is because it is difficult to accurately estimate the solidification state of the entire mold with a thermocouple in the mold.

As described above, although the thickness of the solidified shell immediately below the mold is very important in preventing breakout, there has been no method for accurately estimating the thickness.

[0007]

SUMMARY OF THE INVENTION According to the present invention, it is possible to accurately estimate the thickness of a solidified shell immediately below a mold and appropriately control a casting speed based on the estimated information, thereby ensuring productivity and avoiding trouble. It is an object of the present invention to provide a continuous casting method that achieves both.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a slab immediately below a continuous casting mold is monitored by an optical device, and a video thereof is subjected to luminance analysis by an image analysis device. This is a continuous casting method that ensures both productivity and avoids troubles by determining the shell thickness and controlling the casting speed necessary to prevent breakout.

That is, according to the present invention, when a slab is inspected by an optical device, the casting speed is controlled from the luminance based on the finding that there is an inversely proportional correlation between the luminance of the slab and the solidified shell thickness. This is a highly productive continuous casting method that secures an appropriate solidified shell thickness and prevents breakout.

[0010] The solidification state of the slab in the mold during continuous casting is usually selected at a casting speed such that the thickness of the solidified shell at the lower end of the mold is at least 10 mm by cooling by the mold. However, as can be seen from the actually broken-out slab, the mold speed is selected so as to achieve the above, and even when the operation is performed at a constant mold speed, the solidified shell has an uneven thickness. Now, there is a case where the shell is abnormally thin such that the shell thickness at the lower end of the mold is 5 mm or less in some cases. The cause of this phenomenon is that the powder used as the lubricant has a great effect on the heat transfer form in the mold. That is, a powder is interposed as a lubricant between the mold and the solidified shell, and has a form of heat transfer through the powder.However, although it is desirable that the powder always flows with a constant viscosity during casting, it is actually By adsorbing the alumina present in the molten steel, the components are altered and the viscosity is also greatly changed. Therefore, during the actual casting, there is a case where the air flows excessively, or conversely, a phenomenon in which air is drawn in without flowing. In this case, the shell becomes unusually thin, and the slab surface temperature increases accordingly. As a result, the brightness of the cast slab immediately below the mold is in a halation (white brilliant) state, and can be detected by the optical device disposed immediately below the mold. The present invention further performs a brightness analysis on the image detected by the optical device, accurately converts the thickness into a shell thickness, and controls the casting speed based on the result to constantly break out the solidified shell thickness immediately below the mold. The present inventors have found that it is possible to control the thickness to be appropriate for prevention, and completed the present invention.

The optical device used in the present invention is, as an image pickup device, a vidicon utilizing a photoelectric effect, an image pickup tube type represented by a SIT tube utilizing a photoelectron emission effect, or a CCD / MOS / CID. A solid-state imaging type, a fiber sensor, or the like is used.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an outline of a continuous casting apparatus for carrying out the method of the present invention. FIG. 2 is a diagram showing the relationship between the slab brightness and the shell thickness obtained when the imaging conditions of the optical device are fixed in advance.

Equation (1) is an equation for producing a solidification coefficient K at the time of operation at a local point using the shell thickness obtained from the brightness of the slab, and equation (2) is equation (1). Is a formula for producing a casting speed for securing a solidified shell to a required thickness immediately below the mold using the K value obtained in the above. Note that the brightness used here represents the absolute brightness at the time of shooting under predetermined shooting conditions in 255 gradations, but is not limited to this.

[0015]

(Equation 1) In the above formula (1), K: solidification coefficient (-), L: mold length (m), _Vc : casting speed during operation (m / min),
And l ₁ : solidified shell thickness (mm) in the current operation.

[0016]

(Equation 2) In the above formula (2), V _c ′: target casting speed (m / min) for preventing breakout, K: solidification coefficient (−), L: mold length (m), and l ₂ : mold Shows the required lower shell thickness (mm).

As shown in FIG. 1, molten steel 11 is injected into a mold 1 from a tundish 4 in which molten steel is injected from a ladle, through a nozzle 2 made of refractory material, and is oscillated in a vertical direction (oscillation). , A solidified shell (shell) 10 is formed, continuously extracted with a pinch roll 9, and an operation of continuously casting a slab is performed. In the continuous casting operation, an image of the slab is detected by the optical device 5 installed immediately below the mold, and the output thereof is subjected to luminance analysis by the image analysis device 6 to calculate the slab surface luminance. From this information, based on the relationship between the brightness and the solidified shell thickness shown in FIG. 2, which has been verified in advance, the current solidified shell thickness 10 at the lower end of the mold is obtained, and the solidified shell thickness at the local point is obtained from the solidified shell thickness calculation formula (1). The coefficient K value is calculated, and using this solidification coefficient K value, the casting speed is determined by an arithmetic expression (2) so that the solidified shell thickness at the lower end of the mold does not break out. This calculation is performed by the calculation controller 7 for the coagulation coefficient and the required speed. Then, based on the calculation result, the casting speed control is performed by the casting speed adjuster 8. According to this operation method, it is possible to efficiently secure the productivity of continuous casting without breakout.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG.
Using a continuous casting machine in which the image analysis device 6, the arithmetic and control unit 7 and the speed regulator 8 were installed, two operations were carried out: an operation for casting without controlling the casting speed and an operation for controlling the casting speed. .

In order to make the two operating conditions comparable, the casting is started not only with regard to the used powder 3, the shape of the immersion nozzle 2, the amount of secondary cooling water after passing through the mold 1, the casting width, but also the casting speed. 2.0m / after 10min
The operation was carried out under the same conditions as much as possible, such as casting in min. The imaging conditions of the optical system are as follows: aperture value f = 2.
5. Photographing is performed at a shutter speed of 1/200 second, and FIG. 2 is a correlation diagram under the actual photographing conditions.

FIG. 3 shows a casting speed (m / min) with respect to a casting time (min) obtained when the casting was continued without using the installed apparatus and without controlling the casting speed.
It is a figure which shows the result of a brightness | luminance, solidification shell thickness (mm), and solidification constant (-). FIG. 4 shows the use of the above-described device.
The casting time (mi) obtained when the casting speed was controlled
It is a figure which shows the result of casting speed (m / min), brightness | luminance, solidification shell thickness (mm), and solidification constant (-) with respect to n).

As shown in FIG. 3, when the casting speed control was not performed, the brightness of the slab at the lower end of the mold started to increase gradually after 30 minutes from the start of casting, and further increased after 32 minutes. 35 minutes after all
Later, a breakout occurred. Looking at this phenomenon with a shell thickness 10 calculated based on FIG.
The operation to secure a shell thickness of 10 mm or more was carried out until in, but the shell thickness became 10 mm or less due to the increase in luminance after 30 min, and eventually a breakout occurred when the shell thickness became 5 mm after 35 min. I understand.

When the casting speed control shown in FIG. 4 was carried out, an increase in luminance which was considered to be caused by the deterioration of the powder 3 was observed 25 minutes after the start of casting, as in FIG. The control by the arithmetic and control unit 7 and the speed adjuster 8 based on the equation (2) reduces the casting speed so as to secure the solidified shell thickness at the lower end of the mold of 10 mm, so that the breakout as in the case of FIG. 3 does not occur. Was. Furthermore, the operation was continued as it was,
Later, on the contrary, the brightness gradually decreased (the deterioration of the powder was recovered), so the casting speed returned to the casting speed before the decrease again, and such a situation was repeated several times for 300 mi.
The stable operation was continued until the end of n, and the casting was completed.

[0023]

As described above, according to the present invention, the continuous casting operation can be efficiently performed without breaking out, and the productivity can be secured.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a continuous casting apparatus.

FIG. 2 is a diagram showing a relationship between a slab luminance and a solidified shell thickness obtained when imaging conditions of an optical system are fixed.

FIG. 3 is a diagram showing a result obtained when continuous casting is continued without controlling the casting speed.

FIG. 4 is a diagram showing a result obtained when a casting speed is controlled.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 immersion nozzle 3 powder 4 tundish 5 optical device 6 image analysis device 7 arithmetic controller 8 speed controller 9 pinch roll 10 solidified shell 11 molten steel

Continuing on the front page (72) Inventor Yasuhiro Sakamoto 5-3 Tokai-cho, Tokai-shi Nippon Steel Corporation Nagoya Works (72) Inventor Hideaki Sakurai 5-3 Tokai-cho, Tokai-shi Nippon Steel Corporation Nagoya Works (56) References JP-A-48-80430 (JP, A) JP-A-57-97857 (JP, A) JP-A-57-171555 (JP, A) JP-A-53-37532 (JP, A) JP-A-52-156728 (JP, A) JP-A-58-135758 (JP, A) JP-A-63-183763 (JP, A) JP-A-8-90185 (JP, A) 8-90184 (JP, A) JP-A-59-94024 (JP, A) JP-A-63-132758 (JP, A) JP-A-1-254362 (JP, A) JP-A-57-17359 (JP, A) A) JP-A-52-123650 (JP, A) JP-B-40-10561 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/16 104 B22D 11/16 B22D 11/20 G01B 11/06 101

Claims (1)

(57) [Claims] 1. A slab immediately below a continuous casting mold is monitored by an optical device, and an image thereof is subjected to luminance analysis by an image analyzer to obtain a solidified shell thickness immediately below the mold from the value of the luminance. A continuous casting method characterized by controlling a casting speed necessary to prevent out-flow.