JPH0475751A - Horizontal continuous casting method and nozzle for horizontal continuous casting apparatus - Google Patents

Abstract

PURPOSE:To prevent breakout, fine crack and pit and to improve the casting quality and the yield by selecting the suitable size of a nozzle connecting a tundish and a mold in a horizontal continuous casting apparatus. CONSTITUTION:In the horizontal continuous casting for intermittently drawing a cast billet by connecting the tundish 11 and the mold 21 through the nozzle and fitting a brake ring 18 at the inlet side of the mold 21, the nozzle size is selected so that sum SIGMA(L1/A1) of ratio of nozzle length L1 to cross sectional areas A1 of the nozzle and drawing acceleration velocity aO in the cast billet satisfies the inequality. In the inequality, DELTAPa (acceleration): permissible pressure variation Pa in the mold at the time of accelerating, DELTAPa (deceleration): permissible pressure variation Pa in the mold at the time of deceleration, rho: density (kg/cm<3>) of molten metal, AO: cross sectional area (M<2>) of the mold, aO: drawing acceleration velocity (m/s<2>) of the cast billet.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a nozzle for supplying molten metal from a tundish to a mold in a horizontal continuous casting method and a horizontal continuous casting apparatus.

This invention is utilized for horizontal continuous casting of carbon steel, stainless steel, and other metal fillets.

[Conventional technology] Horizontal continuous casting equipment requires less equipment cost and installation area than vertical continuous casting equipment, and there is no stress caused by bending of slabs, and the internal pressure of slabs is low, so pulsing does not occur. few. In particular, it is economically efficient for small-capacity casting equipment. Therefore, in recent years, horizontal continuous casting equipment has been put into practical use for casting fillets and the like.

FIG. 1 shows a vertical cross-section of a connecting portion between a tundish (1) and a mold (2I) in a general horizontal continuous casting apparatus. As shown in the drawings, in the horizontal continuous casting apparatus, the tundish II and the mold 21 are in communication via a tundish nozzle 12, a sliding nozzle 14, and a foot nozzle 16. The tundish 11, tundish nozzle 12, sliding nozzle 14, and feed nozzle 16 are made of a refractory material with relatively low thermal conductivity. The mold I" 21 is generally made of a metal material with relatively high thermal conductivity, and is cooled by cooling water W. A break ring 18 is attached to the entrance side of the mold. The break link 18 is made of a heat-resistant material. In many cases, the sliding nozzle 14 is not provided with the sliding nozzle 14, depending on the device.

The molten metal M supplied into the mold 21 is cooled by the inner peripheral surface of the mold to form a solidified shell S. Formation of the solidified shell S is started from the break ring 18.

The break ring 18 prevents the solidified shell S from growing in the opposite direction, that is, toward the feed nozzle 16 side. A slab formed by solidifying the molten metal M is intermittently pulled out from the exit side of the mold 21 by a pulling device (not shown) such as a pinch roll. By this operation, a gap is created between the break link 18 and the tip of the solidified shell S, and a new molten metal M flows into this gap, forming a new solidified shell S.

The surface of the solidified shell S produced through this process may have dents. If this dent is large, the amount of grinding required to grind the surface of the slab in the subsequent process will increase, leading to a decrease in yield. The inventors believe that this dent is caused by pressure fluctuations within the mold, and that if this pressure fluctuation is large, breakout may occur, making it impossible to cast. We have discovered that by appropriately designing the nozzle that connects the mold, it is possible to suppress this pressure fluctuation within the mold and prevent dents.

As for the conventional technology regarding the molten metal flow path (nozzle) between the tundish and the tundish, JP-A-52-'1
There are horizontal continuous casting devices disclosed in 368.37 and Japanese Patent Application Laid-Open No. 63-14050, but neither of them takes into account the pressure fluctuations of the molten metal in the mold, and neither of them takes into account the pressure fluctuations in the mold. There is also no mention of the length of the molten metal flow path, which is an essential element. For this reason, the conventional techniques have not been able to exhibit the above-mentioned effects.

[Problems to be Solved by the Invention] The present invention provides a horizontal continuous casting method and a horizontal continuous casting apparatus that can produce high-quality slabs without dents and that are capable of stable operation with less breakout. It provides a nozzle.

[Means for Solving the Problems] The present invention provides a horizontal continuous casting method in which a tundish and a mold communicate with each other via a nozzle, and a break ring is attached to the entrance side of the mold to intermittently pull out a slab. Cross-sectional area A of the nozzle.

A horizontal continuous casting method characterized in that the sum Σ(L1/A,) of the ratio of the length Ll of the nozzle to the length Ll of the nozzle and the pulling acceleration a0 of the slab satisfy the following formula.

≦Δpa (deceleration) Here, ΔP, (acceleration), allowable pressure variation in the mold during acceleration [P
6] Allowable pressure fluctuation in the mold at the time of second deceleration (ΔP deceleration) [P,
] ρ: Density of molten metal [kg/mJIAo
=Mold cross-sectional area [m21ao: Pulling acceleration of slab [m/s2] Also, the tundish and mold are connected through a nozzle, and a break link is attached to Kutsukuda 1 of the drying route, and stainless steel is intermittently In the horizontal continuous casting method, the sum of the ratios of the cross-sectional area A of the nozzle to the length L of the nozzle is Σ(1-).

/A, ) and the drawing acceleration ao of the slab satisfy the following formula.

Here, p, density of molten metal [kg#n3] AO drying route cross-sectional area [m2] ao = drawing acceleration of slab [m/s2] Furthermore, the tundish and the drying route are connected via a nozzle. Then, take the break link on the entrance side of Chi-ruto and now 1
Then, the length L4 of the nozzle with respect to the cross-sectional area A1 of the nozzle is set in a horizontal continuous casting machine that draws out stainless steel intermittently. This is a nozzle for a horizontal continuous casting apparatus, characterized in that the sum of the ratios Σ(L, /A,) does not satisfy the following formula.

Here, ρ′ Density of stainless steel molten steel [kg/m3] Ao
:Mold cross-sectional area [m2] First, the invention of claim 1 of the present invention will be explained.

When the slab is withdrawn intermittently, it includes acceleration and deceleration steps. The slab is drawn out according to one drawing speed pattern as shown in FIG. 4, for example. In the figure, part a is an acceleration process, part b is a constant speed drawing process, and part C is a deceleration process, and the slab is withdrawn by a certain amount through these processes. Portions d and h are stopping steps, and in this step, the molten metal that has flowed into the gap between the break ring 18 in FIG. 1 and the tip of the solidified shell S is solidified. e, f, and g are push-back steps, which are provided to compensate for the shrinkage of the newly generated solidified shell as it solidifies. Also during the push-back process, an acceleration process e,
Although there is a deceleration step g, the magnitude of its acceleration is very small compared to steps a and e, so its effect as a factor in the mold pressure fluctuation described below is small. Therefore, the push-back step will be omitted from the following description.

When the cast slab is accelerated or decelerated in the above process, the molten metal in each nozzle connecting the tundish and the mold is also accelerated and decelerated accordingly. This acceleration and deceleration of the molten metal is caused by the difference between the pressure inside the tundish and the pressure inside the mold. That is, when the drawing is accelerated, the pressure inside the mold decreases in order to accelerate the molten metal in each nozzle, and conversely, when the drawing is decelerated, the pressure inside the mold increases in order to decelerate the molten metal in each nozzle. Here, it is assumed that the capacity of the tundish is sufficiently large, and pressure fluctuations due to acceleration and deceleration of the molten metal in the tundish can be ignored.

We derive an equation that shows the relationship between this pressure fluctuation and the nozzle shape.

As shown in Fig. 2, when the tundish +1 and the mold 21 are connected through one nozzle (cross-sectional area: A, length = 1.), the pressure difference between both ends of the nozzle (the internal pressure of the tundish) (positive when the mold internal pressure is high) is ΔP
Then, the force acting on the molten metal in the nozzle is -ΔP-A. The mass of the molten metal in the nozzle is m, the acceleration of the molten metal is a, and -ΔP=□...(
1) Furthermore, if ρ is the density of the molten metal, Ao is the cross-sectional area of the mold, and ao is the acceleration of slab drawing, then from the continuity relationship, the relationship between a and ao is a = (AO/A)・aQ. Therefore, Equation (1) becomes 6. The right-hand side of Equation (2) +: Since both variables can be known in advance, this equation can be used to calculate the pressure fluctuation ΔP due to acceleration and deceleration of withdrawal. I can do what I want.

The above was a case of one nozzle. If there are multiple nozzles, calculate the pressure fluctuation ΔP for each nozzle element using equation (2).
and then add these together, using the following formula (3
) can be obtained.

ΔPn　”　　9Ao　aoΣ−−7−(:l)A.

The nozzles include a tundish nozzle, a slate ink nozzle, and a foot nozzle, and the suffix 1 is used to distinguish and indicate these nozzles. Nozzles with the same cross-sectional area may be treated as -1 nozzles.

As is clear from equation (3), in order to reduce the pressure fluctuation, it is sufficient to shorten the length Ll of each nozzle and increase the cross-sectional area A1 of each nozzle. Molten metal density ρ, mold cross section HA. Since it is determined by manufacturing conditions, there is no way to change it. Also, it is possible to reduce the pressure fluctuation by reducing the drawing acceleration ao. This means that when the casting speed is considered constant, the time required for the drawing process shown in Fig. 1 becomes longer. It is known that when such a drawing speed is used, the surface defects (cold shut marks, hot tears) of the slab deteriorate, so in reality, the drawing acceleration is approximately 0.7 m/s'. I can only get lower.

Note that slag and solidified shells actually adhere to the inner surface of the nozzle, reducing the effective nozzle cross-sectional area. Furthermore, when the nozzle diameter changes stepwise or rapidly, the effective cross-sectional area decreases because the molten metal does not flow smoothly. Therefore, the pressure fluctuation is (
3) It is expected that the value is even larger than the value given by Eq.

In order to bring the pressure fluctuation close to the value of equation (3), it is necessary to take measures such as insulating the nozzles and connecting each nozzle smoothly.

From the above, the special allowable pressure fluctuation Δp, which is characterized by the permissible pressure fluctuation to prevent denting or breakout of the slab, is determined by (rise) respectively, it is necessary to satisfy formula (4).

ΔP, (acceleration) ≦-pA, ao X''-A.

≦ΔPa (deceleration) Here, ΔPa (acceleration), allowable pressure variation in the mold during acceleration [P
a] ΔP, (deceleration) allowable pressure fluctuation in the mold at two or more speeds [
P, ρ: Density of molten metal [kg/m3] Ao
- Mold cross-sectional area [m21ao = slab drawing acceleration [m/s2].

Next, the invention of claim 2 of the present invention will be explained.

Figure 5 shows the results of actually controlling the stiffness of stainless steel horizontal continuous casting equipment. The pressure drop during acceleration is -20kPa (-0,20kg/cm2) or less, or the pressure rise during deceleration is 30kPa (0,30kg/cm2) or less.
m2) or more, breakout occurred and casting was impossible. Also. The pressure drop during acceleration is -8kPa (-0
,08kg/cm2) to -20kPa (-0,20
kg/cm2) per m' of slab surface.
Only 3 to 15 dents occurred. Also, the pressure increase during deceleration is 20 kPa (0.20 kg/cm2) to 30 kP.
a (0.30 kg/cm2), minute cracks occur on the surface of the slab due to the pressure increase, and these cracks seep into the molten steel or the surface of the slab, and even if it does not lead to breakout, the slab may deteriorate. The quality has deteriorated significantly. Pressure fluctuations due to acceleration/deceleration are reduced to -8kPa (-0.08kg/cm") ~20
When the pressure was kept to kPa (-0.20 kg/cm'), it was possible to cast slabs with good surface quality without any problems.

From the above, when performing horizontal continuous casting of stainless steel, the allowable pressure fluctuation ΔPa is -8kPa" (
-0.08kg/cm2), 20 kPa during deceleration
(0.20 kg/cm2), and equation (5) must be fully satisfied.

-8,. oo≦-pAOaoXL-≦20.000...
・(5) In 22, ρ・Density of molten metal [kg/m3] Ao: Mold cross-sectional area [m2] a,: Pulling acceleration of 9f [m/S2] Note that the allowable pressure fluctuation ΔP1 during deceleration is Since the stiffness for acceleration is large, the pulling acceleration during deceleration of the pulling pattern can be set to be larger than the pulling acceleration during acceleration.

Next, the invention of claim 3 of the present invention will be explained.

Now, the magnitude of the acceleration and deceleration of slab drawing is 0.7.
17 m/s', in order to prevent breakouts, dents on the slab surface, minute cracks, etc. in the drawing pattern that Tsutomi is known for.
Conditions regarding the shape of the nozzle are derived. Applying 2 to equation (5) for the condition ao20.7m during acceleration, the condition for preventing breakout and denting of the slab surface is...(6) Similarly, the condition during deceleration is Since ao≦-0.7 m/s2, this is a condition to prevent breakouts and fine cracks on the slab surface from occurring. Then, −...(7) can be obtained.

In order to avoid problems with casting letters, use formula 4 (6)
, (7).Since t-1,ll''λ must satisfy both, it is necessary to satisfy equation (8).

(ε)) Here, two nozzles are designed and sealed so as to satisfy the following equation (8): Density of ρ stainless steel molten steel [J/m Ao, mold cross-sectional area [m']. Problems such as iron breakouts and micro-cracks are avoided by producing slabs using a conventional drawing pattern. −;
It is possible.

When the above-mentioned allowable pressure fluctuation ΔP8 is not satisfied and the nozzle is to be installed, it is desirable to make the nozzle length Ll as small as possible and the nozzle cross-sectional area A1 as large as possible, as is clear from equation (4). However, the total length of the nozzle Σ1−
1. Due to the configuration of the equipment, it is limited to the sum of the N values of the tandidge refractory, iron shell, and foot nozzle. When a slide ink nozzle is provided, the length of the nozzle becomes considerably longer.

The total nozzle length ΣL should be within 300 mm if no striped ink nozzle is provided, and within 500 mm if a striped ink nozzle is provided. Furthermore, increasing the cross-sectional area A5 of the nozzle increases the size of the nozzle, resulting in poor furnace construction workability and an increase in cost. The cross-sectional area of tandate nozzle Table 5 and the slip ink nozzle is usually 0.5"1.5 of the mold cross-sectional area.
It is desirable to double the amount.

It is used for fixing the foot nozzle blade and the bullnaught ring, so as it is clear from Figure 1, its cross-sectional area is smaller than the mold cross-sectional area, or the mold cross-sectional area is 0.4 mm. 42 or 5 would be preferable, making it more than -1.

When determining the shape of the nozzle, combine the first and second nozzles and suppress the pressure fluctuation within the allowable pressure fluctuation ΔP7 with f-.
Please take into consideration electric vehicles and heavy electrical equipment.

[Example Figure 3 (a)-1c) shows the dimensions of the 41 nostle, the drawing speed pattern ↓; and the pressure fluctuation during drying. ″
There is.

Figure 3 (aL) (b) is the 1-conventional 2 nozzle shown in (c) that has been improved according to the invention. Table 1 shows the pressure fluctuation ΔP1 in the fidget nozzle (3) The results of the calculation using the formula I7 are shown below.ΔP4 is (5
) expression can be directly evaluated. No. 5, in Figure 3, the pressure fluctuation is calculated based on the static pressure of the molten steel in the tundish, which is 70 kPa (0.7 J/cm) in addition to the pressure fluctuation. The results were shown.

Although the drawing speed pattern is always the same, the pressure fluctuation in the case of the present invention is considerably smaller than that of the conventional one. In other words, when accelerating, conventional -1 (
1,4kPa (-0,104kg/c+++2), or -3,6kPa (-0,104kg/c+++2) in Example (a).
036kg/cm2), -6.6k in Example (b)
Pa (-0,066 kg/cm 5.1
There are 1. During deceleration, the conventional pressure was 259kPa (0,259
kg/c+n'J, or 9 in Example (a)
．． OkPa (0.09 kg/cm2), Example (b)
T has been improved to 16.4 kPa (0.164 kg/cm). ↓5. From Table 1, it is clear that Example (C) does not satisfy the condition of formula (5).

Example (c): 0.3 to 15 per m2 of slab surface
Microscopic cracks were formed on the surface of the slab, and molten steel seeped into the surface of the slab through these cracks, resulting in a significant deterioration in the quality of the slab. In Examples (a) and (b), it was possible to cast slabs with good surface properties.

Table 1 (calculation conditions) p -7000kg/+m3, A o
=0. ]5x O, ]5= 0.0225 m2 Pull-out acceleration at acceleration ao= 1. Drawing acceleration of Om/s2m/hour ao--2.5m/s2U Effects of the Invention In this invention, pressure fluctuations in the molten metal in the mold can be suppressed by selecting appropriate nozzle dimensions. As a result, breakouts, microcracks, and dents on the surface of the slab are prevented, so the quality and yield of the slab can be improved, and it is possible to omit the scratch removal work.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a connecting portion between a tundish and a mold in a general horizontal continuous casting apparatus. Second
The figure is a schematic diagram of a single nozzle and mold showing specifications for pressure fluctuation calculation. Figure 3 (a), (b),
(c) shows the nozzle dimension diagram, drawing speed pattern diagram, and pressure fluctuation graph together, and the third
Figures (a) and (b) show this invention, and Figure 3 (
C) is conventional. FIG. 4 is a diagram showing a general drawing pattern, and FIG. 5 is a diagram showing an allowable pressure fluctuation range. 11...Tundish, 12...Tundish nozzle, 14...Sly tink nozzle, I6...
Feet nozzle, 18...Break ring, 21...
・Mold, 22... Mold side wall M... Molten metal, S
... solidified shell, W... cooling water.

Claims (1)

[Claims] 1. In a horizontal continuous casting method in which the tundish and the mold communicate through a nozzle, a break ring is attached to the entrance side of the mold, and the slab is intermittently pulled out, the cross-sectional area A_i of the nozzle is The sum Σ(L_i/A_i) of the ratio of the nozzle length L_i to
A horizontal continuous casting method characterized in that satisfies the following formula. ΔP_a (acceleration)≦−ρA_oa_oΣL_i/A_i
≦ΔP_a (deceleration) where, ΔP_a (acceleration): Allowable pressure variation in the mold during acceleration [
P_a] ΔP_a (deceleration): Allowable pressure fluctuation in the mold during deceleration [
P_a] ρ: Density of molten metal [kg/m^3] A_o: Mold cross-sectional area [m^2] a_o: Pulling acceleration of slab [m/s^2] 2. Connect the tundish and mold through the nozzle. In a horizontal continuous casting method in which stainless steel is intermittently pulled out by attaching a break ring to the entrance side of the mold, the length L_ of the nozzle relative to the cross-sectional area A_i of the nozzle is
A method for horizontal continuous casting of stainless steel slabs, characterized in that the sum of the ratios of i (L_i/A_i) and the withdrawal acceleration a_o of the slab satisfy the following formula. −8,000≦−ρA_oa_oΣL_i/A_i≦2
0,000 where, ρ: Density of molten metal [kg/m^3
] A_o: Mold cross-sectional area [m^2] a_o: Pulling acceleration of slab [m/s^2] 3. Connect the tundish and the mold via a nozzle, and attach a break ring to the entrance side of the mold. In a horizontal continuous casting device that draws stainless steel intermittently, the nozzle length L_ with respect to the nozzle cross-sectional area A_i
A nozzle for a horizontal continuous casting apparatus, characterized in that the sum of the ratios of i (Σ(L_i/A_i)) satisfies the following formula. ρA_oΣL_i/A_i≦11,400 Here, ρ: Density of molten stainless steel [kg/m^3]A
＿o: Mold cross-sectional area [m^2]