JPS6171162A - Method for controlling surface temperature of ingot in continuous casting machine - Google Patents

Abstract

PURPOSE:To improve the accuracy of control by determining the heat conductivity of the ingot for each of water spraying segments by taking the previous spraying segments into consideration and calculating the temp. decreasing pattern in accordance with such heat conductivity. CONSTITUTION:The ingot formed to a predetermined shape by a mold 2 is conducted by guide rolls 3 and enters the secondary cooling zone 5. The zone 5 is segmented to water spraying segments (a), (b), (c), (d), (e) and finally a recuperating part (f) is provided thereto. Ingot surface thermometers 6a-6e and water spraying nozzles 7a-7e are respectively disposed to the cooling parts (a)-(e). The water is sprayed by the nozzle 7a in the cooling part (a) and the temp. measured with the thermometer 6a is fed to a control device. This temp. is compared with the temp. decreasing pattern and the nozzle 7a is so controlled as to adjust the water spraying rate in the next cooling part (b) in the control device. The temp. decreasing patterns are successively calculated by taking the previous water spraying segments into consideration in the respective cooling parts, by which the accuracy of control is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control method for controlling the surface temperature of a slab in a continuous casting machine.

[Prior Art] A continuous casting machine cools a slab to a predetermined temperature according to a predetermined β degree drop pattern while maintaining a predetermined casting speed. Particularly in a curved continuous casting machine, if the temperature at the so-called straightening point is not within a predetermined range, there is a high risk that internal defects and surface defects will occur in the slab.

By the way, cooling of slabs in a continuous casting machine is carried out in a so-called secondary cooling zone. The cooling of the slab in the secondary cooling zone is thought to include (1) cooling by cooling water, (2) heat transfer to guide rolls, and (3) radiation. Control is performed for each watering category.

However, in the conventional control of the surface temperature of the slab, there is a significant difference between the water spraying and the actually measured temperature drop pattern, and there is a problem in that accurate temperature control cannot be performed.

[Object of the Invention] An object of the present invention is to provide a surface temperature control method that can accurately control the surface temperature of a slab according to a predetermined temperature pattern.

[Structure of the Invention] According to the present invention, there is provided a control method for controlling in two water spraying sections divided into a plurality of watering sections, wherein the heat transfer coefficient of the slab in each of the above watering sections is equal to the water spraying in the previous stage of the watering section. There is obtained a method for controlling the surface temperature of a slab in a continuous casting machine, characterized in that the temperature drop pattern is determined in consideration of the classification, and the temperature drop pattern is calculated based on the heat transfer coefficient.

[Embodiments of the invention] The present invention will be described above based on embodiments.

First, referring to FIG. 1, the molten steel from the kundish 1 is injected into the mold 2, and this rs! 12!
is cooled to a predetermined temperature in mold 2 (-secondary cooling).

A slab 4 formed into a predetermined shape with a mold 2
is guided by guide rolls 3 and enters secondary cooling zone 5.

This secondary cooling zone 5 has z, b, c,
It is divided into watering sections d and e and area f (hereinafter referred to as a).
, b, c, d, e are the cooling section, r
This section is called the recuperation section. ), each cooling section a, b,
As shown in the figure, c, d, and e respectively have slab surface thermometers 6a, 6b, 6c, 6cl, and 6e and water spray nozzles 7a, 7b, 7c, and 7d.

7e, are arranged respectively. The slab 4 pulled out from the mold 2 is cooled in a secondary cooling zone 5 according to a preset surface temperature drop pattern of the slab.

That is, first, in the cooling section a, a predetermined amount of cooling water is sprayed from the spray nozzle 7a, thereby cooling the slab 4.
The surface temperature is measured by a surface thermometer 6a and sent to the control device. The control device compares the preset temperature drop pattern described above with the measured surface temperature of the slab, and for example, if the surface temperature of the slab 4 in cooling section a is higher than the temperature drop pattern, all cooling sections are The spray nozzle 7b is controlled so that the amount of water sprayed at is greater than the set amount, and the surface temperature of the slab 4 is brought close to the set temperature drop pattern. On the other hand, if the surface temperature of the slab 4 in the cooling section a is lower than the temperature drop pattern, the spray nozzle 7a is controlled so that the amount of water sprayed in the cooling section is less than the set amount.

Similarly, in the cooling sections c, d, and e,
The spray nozzles 7c, 7d, and 7e are controlled so that the slab 4 is sequentially cooled according to a predetermined temperature drop pattern. The slab 4 coming out of the cooling section e is naturally cooled in the recuperation section f and is straightened by the straightening rolls 8.

As shown in FIG. 2, in addition to the slab surface temperature signal from the above-mentioned surface thermometer 6, the control device 10 of the continuous casting machine receives the casting speed signal measured by the slab speed measuring device 11 manually. be done. In addition, the control device 10 has melting! Ijlil! ! temperature, mold cooling water volume, mold cooling water temperature, and spray cooling water temperature are measured manually, and information such as steel type (physical constants), slab size, etc. is entered in advance from the operation table, and as described above, the optimum cooling water volume is determined. The amount of water is determined and the amount of water is set, and the operation status is monitored on a display (not shown) or the like.

By the way, in cooling the slab in the secondary cooling zone, as described above, the slab is cooled by (1) cooling by cooling water, (2) heat transfer to the guide rolls, (3) radiation, etc. Therefore, the heat transfer coefficient (h) in the secondary cooling zone is the first
It is shown by the formula.

h= hw+ h r o l l + h rad-
・・・---(1) However, hW: Heat transfer coefficient due to cooling water hroll: Heat transfer coefficient to fJ idle hrad: Heat transfer coefficient due to radiation In the first equation, it has a decisive effect on cooling the slab The first term on the right side is the heat transfer coefficient (hW) due to the cooling water. Therefore, the first equation is
It becomes like the expression. Cooling water and heat transfer coefficient h = αhw (2) is shown.
'hwi=f (T, wi)...
...(3) However, T: surface temperature of slab W: water flow density (amount of cooling water sprinkled on unit area) i: i-th cooling section However, using the second and third equations, Perform thermal calculations,
When the surface temperature drop pattern of the slab is determined, it is extremely different from the actually measured temperature drop pattern. The reason for this is 2
For example, in the i-th cooling zone in the next cooling zone, 1 to (i-
1) The cooling water used in step 1 may drip onto the slab, cool the guide rolls, or cause damage to the guide a-
This is thought to be because water accumulates between the steel plate and the slab, cooling the slab indirectly. Therefore, the water density Wi at the i-th position is set as shown in the fourth equation, taking into consideration the 1st to (i-1)th cooling sections. Wi=a1wl+a2w2+・=−・・+aiw;= in the fourth equation
2: hjvvj------------(4) σ:l The coefficient aj is measured (Fig. 3 shows each cooling section'Ll b,
c.

Actual measurements of heat transfer coefficient in d and e are shown. ), Wi is obtained from the relationship between the heat transfer coefficient and water density obtained by solving a -dimensional heat transfer equation (not shown), and aj that fits this Wi is determined recursively.

Applying the above-mentioned formula 4 to the continuous casting machine shown in Fig. 1, aj is determined from the measured heat transfer rate shown in Fig. 3, and the water volume density ( W
i) was determined as follows.

W1=wl (cooling section a)
W2=0.15w1+w2 (cooling section b) W3:=0. hl+0.30w2+w3=0.3
0w2+w3 (Cooling part C) W4=0.0wl +0
．． Div2+0.05v3+w4=0.05w3+w4
(Cooling part d) W5=0.0wl+O, Ow2÷0. Ow3÷0. Ow
4+w5=w5 (cooling section e) The result of heat transfer calculation using W1 to W5 (℃)
, the horizontal axis indicates the distance from the meniscus 9 shown in FIG.

In the figure, the 0 mark and the mark indicate the surface temperature of the slab measured using a two-color double meter and a handy thermometer, respectively (Casting method If (
vc) = 1.05 m/min). In addition, the △ mark and the mu mark indicate the surface temperature of the slab when measured using a two-color thermometer and a handy thermometer, respectively (Pouring speed (vc) = 1.1
5 m/min). Here, in order to compare the surface temperature drop pattern according to the present invention and the surface temperature drop pattern according to the conventional method, FIG. 5 shows the surface temperature drop pattern according to the conventional method. In Figure 5-5, the vertical axis does not indicate the surface temperature of the slab actually measured with a handy thermometer (casting speed (vc
) = 1.05 m/min).

Comparing FIG. 4 and FIG. 5, it can be seen that the surface temperature drop pattern according to the present invention matches the actually measured value with high accuracy.

Further, FIGS. 6(a) and 6(b) respectively show variations in the amount of cooling water in cooling sections S and C when the method for controlling the surface temperature of a slab according to the present invention is used. In addition, Fig. 6 (a
) and (b), the vertical axis is the degree, and the horizontal axis is the cooling water amount C1
Z minutes). Here, the variations in the amount of cooling water in cooling sections S and C when the conventional surface temperature control method is used are shown in FIGS. 7(a) and 7(b), respectively. In addition, Fig. 6 (a
) and (b), and the casting speed is constant in both cases of FIGS. 7(a) and (b). Figures 6(a) and (b), Figure 7(
As is clear from a) and (b), the surface temperature control method according to the present invention has little variation. This is shown in Figures 6(a) and (b) and Figure 7(a) and (b).
This is also clear from the table below which shows the standard deviation calculated from .

Table [Effects of the Invention] As explained above, according to the present invention, the surface temperature of the slab can be accurately controlled based on the temperature drop pattern preset in the control device, which is extremely useful for quality control of the slab. It is.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the casting process of a slab in a continuous casting plate, Fig. 2 is a diagram showing the control according to the present invention, and Fig. 3 is a diagram showing the control according to the present invention.
The figure is a diagram showing the actually measured heat transfer coefficient of the slab in each water sprinkling section (cooling section) of the secondary cooling zone, and Figure 4 is a diagram showing the temperature drop pattern when using the present invention. Figure 5 is a diagram to show the conventional temperature drop pattern, Figure 6 (a
) and (b) are diagrams showing variations in the set amount of water according to the present invention, and FIGS. 7(a) and (b) are diagrams showing variations in the conventional set amount of water. 1... evening/ditshu, 2... mold. 3... Guide roll, 4... Slab, 5...
・Secondary cooling zone, 6...Surface thermometer, 7...
spray nozzle. 8... Straightening roll, 9... Meniscan 10...
・Control device, 11...Speed measuring device agent (58=il') Patent Attorney Ueto 1) Diagram 1 (α) Frequency (b)

Claims (1)

[Claims] 1. A control method for controlling the surface temperature of a slab cast in a predetermined temperature drop pattern by a continuous casting machine having a secondary cooling zone divided into a plurality of water sprinkling sections, the method comprising: The surface temperature of the slab, characterized in that the heat transfer coefficient of the slab for each section is determined by taking into consideration the watering section preceding the watering section, and the temperature drop pattern is calculated from the heat transfer coefficient. Control method.