JPS5987957A - Casting mold in continuous casting - Google Patents

Abstract

PURPOSE:To form the section of a billet to a prescribed size and shape and to economize energy in the succeeding stage in a curved type continuous casting wherein the unsolidified billet is unbent and set by forming a casting mold into the shape wherein the relation among the thickness and radius of curvature of the billet as well as the width on the top and bottom surfaces of the casting mold is specified. CONSTITUTION:The shape of a casting mold with which the equations ( I ), (II) hold is selected with respect to the width sizes Lu, Ll on the top and bottom surfaces of the mold and the average LM of Lu and Lu where the average width size on the top and bottom surfaces of a straight billet at an ordinary temp. is designated as lMC, the thickness of the billet as (t) and the radius of curvature of the mold as R. The specified sectional size and shape of the straight billet are thus obtd. by such casting and therefore the efficiency in the succeeding stage is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mold for a continuous casting machine.

Figure 1 is an explanatory diagram of a curved continuous casting machine with a curved casting shaft.The outer shell of the slab is made in the mold (1), and the slab falls on a curved track (Tl). The slab is cooled while descending, and solidification progresses gradually toward the inside, and it solidifies completely after traveling on the horizontal track (10) for a while. At the correction point U in this solidification and conveyance process, the curved slab is bent. It is straightened and straightened and moves on a horizontal track.Since the slab is bent in an unsolidified state, it is deformed during straightening, resulting in a slab with a different cross-sectional shape and dimensions than when it was made in the mold. That is, the Q piece drawn from the mold with a rectangular cross section as shown in Fig. 2 has a trapezoidal cross section as shown in Japanese Patent Application Laid-Open No. 56-5760. In order to manufacture a slab having a rectangular cross-sectional shape, the above-mentioned Japanese Patent Application Laid-Open No. 56-57
As described in Japanese Patent No. 60, it is necessary to use a mold having a trapezoidal cross section as shown in FIG.

In addition, the above-mentioned Japanese Patent Application Laid-Open No. 56-5760 discloses that a mold with a trapezoidal cross section (trapezoidal mold) is used in which the ratio of the upper surface width dimension (Lu) and the lower surface width dimension (Lc) of the mold satisfies the following relationship. It is disclosed that a slab with a rectangular cross section can be obtained after straightening the warp.

However, t: @ piece thickness 几; radius of curvature of the mold a pi 0.2 Also, in Japanese Patent Publication No. 44-8481, 几 = 60
00.4000.2000 m, it is disclosed that a slab with a rectangular cross section can be obtained by using molds with a trapezoidal cross section with tl of 1.5, 2.0, and 2.5%, respectively.

However, these known trapezoidal molds with a bottom width dimension are extremely insufficient to produce slabs with a rectangular cross section after straightening, and molds based on these formulas do not necessarily yield slabs with a rectangular cross section. I can't do it. This is due to the aspect ratio (IJ M/t) of the slab during straightening. This is because the rate of change between L rotation and lower surface d] is different, and the amount of dimensional change in the soil and lower surface during straightening also changes depending on the respective temperatures of the upper and lower surfaces.

On the other hand, the dimensional changes of the upper and lower surfaces 1 during conventional correction are as follows:
It is assumed that deformation occurs symmetrically on the top and bottom surfaces, so there is no change in the average of the top and bottom surfaces of the slab, and the average width of the mold is determined by considering only the shrinkage formula due to heat shrinkage. However, in reality, the restraint of the surface of the slab due to the vertical pressing force at the straightening point is not equal, so the width of the top surface does not become narrower as the width of the bottom surface becomes wider, and the upper and lower surfaces deform asymmetrically, causing the upper and lower surfaces to become narrower. The average rlJ changes.

Furthermore, as shown in Japanese Patent Application Laid-Open No. 52-52126.55-5115, as a means to prevent internal cracking, when the temperature of the lower surface is raised and the temperature of the lower surface is raised, The deformation rate in the casting direction becomes significantly asymmetrical, and along with this, the dimensional changes in the upper and lower blood vessels also become significantly asymmetrical.
The upper and lower average values change.

Therefore, with a trapezoidal mold in which the average width is determined by considering only the shrinkage formula due to heat shrinkage without considering the change in the average of the upper and lower surfaces, a slab with the desired average width cannot be obtained.

Therefore, the present invention aims to correct the changes in the cross-sectional shape and dimensions caused by unbending and straightening the unsolidified slab by adjusting the upper and lower surfaces of the mold to appropriate dimensions. The object of the present invention is to provide a mold for continuous casting that can obtain slabs of 1.

The mold for continuous casting of the present invention is used for the continuous casting of the unsolidified slab for straightening the bending process.
When the average width of the lower surface is LMo%, the thickness of the slab is t, and the radius of curvature of the mold is R, the upper and lower width dimensions of the mold are Lu,
Regarding the average TJM of LL and Lu and LL, -= 1+(1-γ)Xt/2几...Mountain...
- (1) A mold for continuous casting characterized by having upper and lower surface width dimensions having the relationship of t.

However, (11, [0.0'6X('Lu+LA)/2t<r<(1,1
X(T, u+L2)/2t0.4〈β〈08+Δ'I
'/100 α=0.035 (thermal contraction rate of slab) Δ=TL−Tu Tu: Top surface temperature TL at straightening point; Upper surface temperature at straightening point.

The overculm until reaching the mold of the present invention will be explained in detail below.

4 and 5 show cross sections of the cast slab at the B-'B and O-0 positions in FIG. 1. FIG. 6 shows a cross section of the slab at room temperature.

In the following description, Lu: Upper (inner) middle dimension of the mold L; Lower (outer) width of the mold LM: Average width of the upper and lower surfaces of the mold tu: Upper surface width of the slab before straightening t: Straightened Lower surface width of slab before straightening t'u: Lower surface width of slab immediately after straightening t2; Lower surface width of slab immediately after straightening A'uc; Upper surface width of slab at room temperature after straightening L'L
c: Medium dimension of the bottom surface of the slab at room temperature after straightening, tM: Average width dimension of the top and bottom surfaces of the slab before straightening Z/M; Average middle dimension of the top and bottom surfaces of the slab immediately after straightening tMO: Top and bottom surfaces of the slab at room temperature Average width dimension.

First, when bending back a rectangular cross-section slab, it is assumed that there is no restraint on the short side and that the upper and lower surfaces are deformed to 1-. In this case, the dimensions of the upper and lower surfaces before and after unbending are expressed by equations (41, (51) from the viewpoint of simple plastic deformation.

tu　　　　　　　R Here, ν is Poisson's ratio, which is considered to be at most 0.5.

In the case of a rectangular cross-section mold, tI+=mu, and since R is generally extremely large compared to t (41, (from formula 51, ρ・
Equation (6) approximately holds true.

L'u R Next, assuming that the deformation is completely restrained on the short side, the dimensions of the top and bottom surfaces will remain unchanged within the restrained area, so that the slab will have a rectangular cross section. When restrained, the following equation (7) is established L'u. Therefore, it can be easily inferred that the ratio of the width dimensions of the upper and lower surfaces after correction falls within the range of equation (8).

However, research has shown that the actual change in width depends on the ratio of the slab thickness 1) and the width dimensions of the top and bottom surfaces of the slab, and that it is almost accurately expressed by equation (9). ,results of the experiment,
known.

Note that γ' is a numerical value within the range expressed by formula 01.

212, in the casting process, the temperature of the top and bottom surfaces are almost equal and the difference in heat shrinkage is almost negligible, so the following θ11
, +12 formula holds true.

1’ u L’ut.

nLu Therefore, if you set the upper and lower surface width dimensions of the mold to the upper and lower surface width ratio shown in formula 03 (corresponding to formula (I)) in advance, you can obtain slabs that hardly become trapezoidal.9■JL t
L However, r is a numerical value within the range defined by formula 04.

Here, the basis defined by the γt-(14) formula is shown in Table 1.
This will be explained using FIG.

[Table-1] Examples 1 and 2.3 of [Table-1] are examples of molds with R=3000 (7) rectangular cross section, and Example 4 is the mold of the above-mentioned JP-A-56-567.
11 shown in Publication No. 0. This is an example of a mold with a rectangular cross section of =10500. And (l-γ′) in [Table-1]
The numerical value in the column is expressed as (9) using tte'j of [Table-1],
It was obtained by substituting tucl, t, and R. FIG. 7 illustrates these results.

r' iti calculated from this (γ calculated from equation 11
If it is within the range of ', it is clear that formula 11 is well established.

Next, when the slab is straightened and bent back horizontally, if the restraint by the suppressing force of the upper and lower rolls is equal and the deformation rate of the upper and lower changes is symmetrical, then the upper and lower surfaces of the slab before and after straightening will be Regarding the average dimensions J, M, and t/M (41, (from formula 51, formula 09 holds true.

In a rectangular cross-section mold, Lu=■ is -11M, so 09
The formula is simplified to formula 00.

However, in reality, it does not become as shown in equation 11, and t M / becomes wider than TJMj.

Therefore, assuming that the width Lu on the upper surface side does not change at all before and after correction, the following 0η, θne formula% formula% r')Xt/2
nl OS is derived, and formula 1 can be derived using this formula 00.

t/2R)) = 1+(1-r') t/4R(+101 formula indicates the theoretical maximum value; in reality, instead of 01 formula, (
b) Use the formula.

Here, how to obtain β in the above equation will be explained.

The 3-dimensional equation shows the change in the width of the slab before and after unbending and straightening, but it can actually be measured only when the slab is at room temperature, and considering the thermal contraction during that time, from equation (A), the following el) Formula ((2
) corresponds to the expression. ) will be guided.

LMO(3,+a)=l'M=LM(1+β(1-r)
t/4rL) oJ)C! α in the η equation is the thermal shrinkage rate of the slab.

From the test results when t is changed, β can be found by eliminating α in the formula (2η. In other words, in the same mold, tl,
If the average width of the upper and lower surfaces at room temperature e L c1 * t (2) of slabs manufactured with two thicknesses of t2, then the formula Q
From 1), aa, formula (c) can be obtained.

t(+(1+α)=LM(1+β・(l r'+)tt
/4n) Cl2tC2(l+α)=T, M(1+β・
(1-γ'2) t2/4R) (2) and C+a,
By eliminating α from equation (c), equation (goods) can be derived.

Q4) To find β according to the formula, change t [Table 2]
The test was conducted under the conditions shown below.

ΔT in [Table 2] above is the upper surface temperature Tu at the correction location.
('C) and the bottom surface temperature Tt(C), and is defined by equation (c).

Δ'l' = 'I'4- T u
'2', +1 Note that the above bottom surface temperature 'r't = one of the test conditions when obtaining the various data in [Table 2].
s o ~ 1000C°C).

[Table 2] shows that when there is no temperature difference between the upper and lower surfaces, the value of β is smaller than the theoretical upper limit (β-1), and when there is a temperature difference, it is smaller than the theoretical upper limit. It shows that the value increases, and also shows that α is 0.035.

The relationship between ΔT and jMo and the relationship between ΔT and β in Table C-2) are shown in FIGS. 8 and 9.

From FIG. 9, the value of β can be approximately limited to the range of equation (c).

0.4〈β〈0.8+ΔT/100
By setting the formulas that determine the range of (1-r') in Figure 7 and the range of β in Figure 9, the dimensions of the mold are limited to those in the range of formulas (1) and (2) in the present invention. We were able to.

Next, the dimensions are determined based on the casting results using an example of the mold of the present invention that satisfies formulas (11 and +21) and the conventional concept disclosed in Japanese Patent Publication No. 44-8481 and Japanese Patent Application Laid-open No. 56-5760. An example of casting results using conventional molds (1) and (2) is shown in [Table 3].

[Table-3] f, M, IJLI of the mold of the present invention in [Table-3]
+T and L were calculated as follows.

By substituting r'=r, tMO='1050, and t=250 into this equation, l-γ)-0·70 is determined. Q [β from formula 9
=0.8, (l-γ)=0.70. β=0.8,
jMO=1050, α=O-035, t=250. R1
=3000'e Substitute into formula (21), LM=1076f
3: I asked for it.

In both formulas, TJu+TJL=2LM, TIM=1076
, (1-γ)=()・70. t=250, 几=3000
By substituting , Lu=1092, T, z=1060 were obtained.

Conventional molds in [Table 3] (11 TJMs,
J.U.

T, 9 was determined as follows based on the conventional method disclosed in Japanese Patent Publication No. 44-8481, and does not change in the average of the upper and lower surfaces of the slab before and after straightening, that is, β
=O, so the Ql) formula is LMo(1+α)=LM
Then, the point tMc = 1. o 50, α=0
．． By substituting 035, T, )(=Io87 is determined.

When n = 4000.2000, the dimensional difference (Tlg - Lu) between the upper surface 11 of the mold and the lower surface is set to the 2nd, 2nd, and 5th ratio of the average upper and lower surface middle dimension TJM, and the difference in dimension is Adjust the top width dimension TJLI evenly to the mold TJ”
, bottom width dimension T, /, so R-3000
So, W −Lu = O−0225LM and Ll −
Lu-25, Lu = 1087 + 12-5 = 1099-
5, T...! ! =1087-'12・5=1
074.5. Note that t = 250, n =
The TIM of conventional mold (2) in [Table 3] is calculated by substituting 3000.
I and 11°Ll were determined as follows based on the concept of Japanese Patent Application Laid-Open No. 56-5760.

There is no change in the average of the top and bottom surfaces of the slab before and after straightening, that is, /
= O, so the conventional mold (TJM = 108 as in 11)
It becomes 7. Lu, 1. J! - For Jull
In both equations of L, n=O-2, LM=1087. t=250, [
Substitute L=3000 and get T, f=1078, Lu
-1096.

[Table 3] Conventional molds (11, (21) have target tMC
On the other hand, L2ms is wider and molds (11 and (21) have trapezoidal differences of 5*x and 10+u between the middle and upper surfaces of the lower surface, respectively, but the slabs using the mold of the present invention have an average It's only 2-Ova wide inside, and there's not much left in the trapezoid shape.

The difference between the width of the conventional mold and the width of the mold of the present invention is more than 1%.
By using the mold of the present invention, it becomes possible to prevent yield loss. In addition, the obtained slab is usually width-reduced in the next rolling process, but at that time, the billboard does not curl due to the conventional mold, and only a few passes and reductions are required, which significantly reduces energy loss and wear of the rolls in the rolling process. is obtained, with extremely useful effects.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a curved continuous casting machine, FIG. 2 is a cross-sectional view of a rectangular mold, FIG. 3 is a cross-sectional view of a trapezoidal mold (corresponding to the A-A cross section in FIG. 1), and FIG. 4. m5 figure ui1 figure 17) B-B, 0-OK er fJ,
s'Pr cross-sectional view, Figure 6 is a cross-sectional view of the slab at room temperature, Figure 7 is a chart showing the chilameter (i-γ') indicating the degree of trapezoidization depending on the aspect ratio of the slab, Fig. 8 is a diagram showing that the upper and lower average dimensions of the slab change by 75 mm due to the temperature difference between the upper and lower surfaces at the straightening point, and Fig. 9 shows the change in the upper and lower average dimensions of the slab due to the temperature difference between the upper and lower surfaces at the straightening point a. It is a chart showing a parameter β indicating the degree of change in the average width of the two lower surfaces of . (1)...Mold, (■)...Curved trajectory, (■)...
・Horizontal Orbit Agent Patent Attorney: Masa Akizawa, 2 Mitsugai

Claims (1)

[Claims] (1) The average width of the upper and lower surfaces of the room-temperature slab in the bowl-type continuous casting process for straightening the unsolidified slab is tMo,
When the slab thickness is t% and the radius of curvature of the mold is R, the upper and lower middle dimensions of the mold are Lu, LZ, and IJLI and LL.
IJLI −=1+(1−γ)xt/2R・・・・・・・・・・・・−
・(1)■□E(11, +21 formula and a mold for continuous casting characterized by having the lower surface width dimension. However, (11, +21 formula is 2 and 0.06X (IJLILA)/ 2t<γ<0.10X(
Lu+LL)/2tO14<β<0.8+ΔT/100 α−0,035 (thermal contraction rate of slab) ΔT=Te −Tu Tu: Upper surface temperature at the straightening point TL: Upper surface temperature at the straightening point.