JP3020538B2 - Width expansion method during continuous casting - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for enlarging width during continuous casting, and more particularly, to changing a width of a billet by moving a short side of a mold during continuous casting. The present invention relates to a method for expanding a width at the time of continuous casting to improve a time rate.

2. Description of the Related Art In recent years, in continuous casting of steel, a continuous casting method of changing a slab width of a continuous mold without stopping casting has been practiced in order to improve an operation rate and a slab yield. Above all, since a method of directly connecting the continuous casting step and the rolling step has been put to practical use, it is desired to change the slab width during continuous casting according to the product sheet width.

When changing the slab width without stopping the operation of the continuous casting machine in this way, shorten the width change time as much as possible, make the width change portion of the slab as short as possible, and immediately change to the required width. is important. When such conditions are satisfied, the capacity of the width changing equipment of the continuous casting machine can be utilized,
The width change time can be reduced.

A commonly used continuous caster width changing device is the fourth type.
As shown in the figure.

The width changing device shown in FIG. 4 is of a type in which the long side of the mold is fixed and the short side is moved.

That is, a pair of short sides 1a and 1b are sandwiched between long sides 2a and 2b fixed to a mold vibration table (not shown),
Driven by two electric or hydraulic drive devices 3a, 3b mounted on 1a, 1b, the width of the cast slab 4 to be cast is changed without stopping casting. When the width is changed by such an apparatus, if the speed is increased, the driving force on the short side is increased and a slab defect is generated, which hinders speeding up of the width change.

Conventionally, as a width changing method, (1), JP-A-60-68
As described in Japanese Patent Publication No. 137, the width reduction section of the short side is divided into forward inclination, parallel movement, and backward inclination, and the slab width is changed by changing the short side movement speed between the upper and lower sides of the short side in each period. How to reduce,
(2) As described in JP-A-61-115656, the narrow section of the short side is divided into forward tilt and backward tilt, and the horizontal moving speed of the upper and lower ends of the short side in each period is increased. The speed ratio α is determined as a parameter of the allowable shell change resistance, and the speed difference between the upper and lower ends of the short side is determined by a certain mathematical formula.
And a method of changing the width while maintaining the speed difference ΔV constant. (3) As described in JP-A-61-137659, an error caused by a difference in taper between the start and end of the width change is inclined forward. (4) a method of absorbing with a parallel period between
As described in JP-A-61-144255, the maximum allowable moving speed Vmax of the short side is set according to the rolling conditions and / or the constraints of the short side driving device, and the short side of the short side in the forward or backward inclination of the width change is set. When the upper end speed V exceeds the maximum allowable moving speed Vmax, a method has been proposed in which the short side is moved in parallel with the moving speed Vp in a specific range between the first half and the second half of the width change.

However, these width changing methods are effective for changing the width of the slab, but have sufficient conditions such as the width changing time, the length of the width changing portion of the slab, and the width changing speed. Neither can it take full advantage of the capabilities of the width changing equipment.

Problem to be Solved by the Invention The object of the present invention is to solve the above problems, specifically, in changing the slab width during continuous casting, when moving the slab short side to expand the width, the meniscus portion of the short side Therefore, it is an object of the present invention to propose a method of increasing the width at the time of continuous casting that shortens the width changing time at the time of casting, and further maximizes the capacity of the width changing equipment at the time of casting.

Means for Solving the Problems and the Function thereof That is, the present invention relates to a method for changing the width by moving the short side of the mold during continuous casting, and changing the width by the meniscus portion of the short side, the short side moving speed Satisfies the following expressions (1) and (2); When adjusting the taper between the short side and the slab formed at this time to the target taper, the moving speed of the short side satisfies the following equations (3) and (4). However, the symbols in the equations (1), (2), (3) and (4) indicate the following.

 Vu (t): moving speed V at the meniscus portion on the short side (T): moving speed at the lower end of the short side Vc: casting speed m: length from the meniscus part of the mold to the lower end T (t): taper length of the short side θ₁, Θ_Two: Distortion tolerance φ, ψ: Meniscus deformation allowance t: Time.

Hereinafter, the configuration as the means of the present invention and its operation will be described in detail as follows.

First, looking at the deformation behavior of the slab during the width change during continuous casting, the meniscus portion is easier to deform, and the slab to be cast is deformed by the molten steel static pressure.

If such deformation of the meniscus portion and deformation due to the molten steel static pressure are effectively used, it is preferable in terms of equipment capacity and the time required for width change.

From such a point, the moving speed of the short side can be determined based on the equations (1) and (2) in which the parameters φ and θ are substituted in consideration of such a point. There is no air gap between the short side of the mold and the slab, and the short side can be quickly moved to achieve the width direction under the condition that the deformation of the slab is within the allowable strain.

That is, the moving speed V (ε,
t) is expressed by equation (5).

In equation (5), ξ is a variable in the short side length direction, ξ = 0 is a meniscus portion, ξ = m is a lower end of the mold, V
(Ξ, t) indicates the short side moving speed at に お け る, t.
When the equation (5) is divided into two, the left-hand side term is a condition without air gap, the right-hand side term is a condition indicating a state within allowable slab deformation, and the short side moving speed deviates from these conditions. Then, an air gap is generated at the time of the width movement, and the deformation of the cast slab is out of the allowable distortion range. However, according to the present invention, even if the moving speed of the short side is not determined under the condition of the expression (5), the moving speed of the short side is adjusted to the upper limit by adding the parameter φ considering the deformation of the meniscus portion to the upper limit. We learned that it could be raised, and it was established from this point.

 The following is a description of Equation (5).

Assuming that the short side moving speed when moving the short side from the state shown in FIG. 1 (a) to the state shown in FIG. 1 (b) is V (ξ, t), V (ξ, t) is as follows. It is.

In other words, the triangle indicated by the hatched portion in FIG. 1B has a similar relationship to the triangle surrounded by the line indicating the short side, the line indicating the depth of the rectangular side, and the line of the meniscus portion shown in FIG. Using this triangle Then, the moving speed in the horizontal direction is obtained. Assuming that this is at the time Δt, the short-side velocity V (ξ, t) × Δt in the triangle of the hatched portion is Can be expressed as If this is removed from the concept of Δt, And the expression on the left side of equation (5).

Equation (5) is obtained by exchanging T (t) and Vc. Or 'm means that the error is small even if it is almost equal to m, unless the short side angle becomes large. Is used, but if this is accurately expressed, it becomes' m.

Also, the short side moving speed expressed by V (ξ, t) is If an air gap is exceeded, an inequality sign is given to keep the condition without air gap. When the allowable deformation of the solidified shell of the slab is added to this expression, the right side is established, and Expression (5) is obtained.

In terms of units, these symbols are as follows: Vc: casting speed (mm / min) m: distance from meniscus to lower end (mm) T (t): short side taper between meniscus portion and lower end of short side It indicates the amount (mm), and the right side of the equation (5) is expressed by the moving speed.

If the equation (5) is divided into steps of width change, the short side of the mold is more rigid than the slab, so the conditions of the meniscus portion and the lower end of the shorter side of the mold may be suppressed. In the meniscus part, Each equation is obtained. In the formulas (1) 'to (4)', the following condition is added: Vc = constant (6) θ ₁ = θ ₂ = θ (7) Then, the equal signs of (1) 'to (4)' are adopted, To obtain each expression.

 Therefore, (1) "-(2)" and (3) "-
When (4) ″ is calculated, ΔV≡Vu (t) −V (T) = θ (8), and consequently, as described in JP-A-61-115656.
ΔV = α · L / Uc (= const) (9) ΔV: Speed difference between the upper and lower ends of the short side (= const) α: The speed increase rate of the upper and lower ends of the short side (= const) L: Mold Short side length (= const) Uc: Casting speed (= const) is obtained. (= Const) in equation (9) is
It is assumed.

However generally a continuous casting operation Vc = constant is necessarily not, also, the meniscus portion distortion tolerance theta ₂ and lower strain tolerance θ ₁ θ _{1 =} θ not _2, the thin meniscus solidifying shell at elevated temperatures The part and the solidified shell thicker than the part, the meniscus part is also easily deformed in the cooled lower part, θ
_2> is a theta ₁ (meniscus portion is easily deformed).

Therefore, even when only the fact that θ ₂ > θ ₁ is used, the taper amount is moved more quickly than when the width is changed by the constraint of the expression (9) (speed is given by (1) ″ to (4) ″). You can do it. This is because when deriving (1) ″ to (4) ″, it is necessary to assume θ ₁ = θ ₂ , but in the above technique, although θ ₂ > θ ₁ , whichever is smaller, That is because must adopt the value of theta _1. Although a △ V = theta (8) above, in the present invention is a portion that can be adopted theta ₂ △ V
= Θ _{2, which} is free from the constraint of the expression (9) and can be operated at high speed.

Furthermore, when the present inventors confirmed by experiments,
It has been found that a parameter φ can be further added to the right side of equation (1) ′. Equation (1) 'is an equation expressing a condition that does not cause an air gap between the short side of the mold and the slab.

Here, as a condition for preventing the occurrence of the air gap, the short side of the mold is moved according to the casting speed of the slab so that the deformed portion of the slab and the short side of the mold due to the width change always adhere to each other without an air gap. It comes to take speed.

However, as observed in continuous casting, the slab tends to be accompanied by bulging, and the meniscus portion bulges even with a slight static pressure. Therefore, the condition of no air gap can be formed in addition to the bulging. By taking this parameter as φ, the following equation can be obtained.

The high-speed width changing condition using the deformation due to the bulging is set by the above equation. Similarly, for the equations (3) ′ and (4) ′, the parameter ψ of the equation (4) ′ can be added in consideration of bulging using the static iron pressure at the lower end of the short side.

 Therefore, the following equation is obtained.

Here, the high-speed width changing condition is set similarly.

The parameters φ and ψ are parameters indicating the speed at which the solidified shell bulges due to bulging, and are proportional to the static iron pressure and may be experimentally determined in advance depending on the type of steel and casting conditions.

In order to change the width at the fastest, it is necessary to satisfy the expressions (1) to (4), and the following expression is obtained.

 That is, so that the expressions (1) to (4) are always satisfied.
Vu (t), V (T) needs to be determined. Fig. 2
And the horizontal component force P 'of the molten steel pressure isIs required.

Since φ in equation (1) is proportional to P ′ (E is a constant).

 Now, the time derivative of the short side taper T (t)Represents the speed at which the taper changes, which is
Since the side can be assumed to be a rigid body, the short side upper end velocity Vu (t)
And the lower edge speed V (T).

That is, Using equations (1) and (2), Get.

By solving this differential equation, the movement of the short side taper for performing the width change below the deformation resistance without the air gap is obtained.

 From equations (1) to (2) and (14),
Vu, V Is found, Can be obtained.

Therefore, in the period (I) in which the width is changed using the meniscus portion (hereinafter referred to as the I-th period), the moving speed can be considered by the expressions (15) and (16).

Similarly, From equation (17) Then From equations (3) and (4) (19) (Note, T ₂₀ is the value of the taper when transitioning to late half.) (Hereinafter referred to as Stage II) the period to match the taper on the target value
Then, the moving speed is obtained by the equations (20) and (21).

As explained above, the moving speed of each period in the width expansion is In Phase II Is given as the basic expression of (15), (16), (20),
(21) To make the formula easier to see, When determining the moving speed of the short side by the formulas (22) to (25),
When the width change amount ΔW is given, the short side moving speed pattern at which the fastest width change is performed is fixed. That is, Phase I,
The required time for Phase II is represented by t ₁ and t ₂ , respectively, the width change amount is 2 △ W ₁ , 2 △ W ₂ , and the total width change amount is 2
Assuming that ΔW, ΔW = ΔW ₁ + ΔW ₂ .

Here, since △ W ₁ and △ W ₂ are the time integrals of the short side moving speed, respectively. Becomes Similarly, Becomes Here, the T ₂₀ is defined, the taper amount when transitioning from stage I to stage II, i.e., a tapered amount of time period the I ends. this is, Integrated Can be more demanded, Get.

When the taper returns to the initial state after the width change is completed, since T (t) = 0 at t = t ₂ , from the equation (19), (29), t ₂ is determined once the t ₁ from the equation (30). Thus, also, (26), (27), t ₁ from equation will be determined to a unique (28). t ₁ and t ₂ can be solved by iterative calculation. Therefore, all parameters are determined and △
If W is given, t ₁ and t ₂ are obtained, and the width change amounts of the _first and _second periods are obtained.

Even if the taper at the end of the width change is different from the initial state, the speed pattern is given by the method shown here, the taper and the width are monitored near the end of the width change, and only the movement above or below the short side is performed. Should be stopped.

For example, when the width is changed under the following conditions, the result is as follows.

FIG. 3 is a graph showing the relationship between the width change time and the short side moving speed in this case.

△ W = 100 mm (both short side width changes 200mm in) θ _{1 =} 30mm / min theta _{2 =} 50 mm / min A = 3 mm / min A '= 1.5 mm / min m = 900mm Vc = 1.5m / min = 1500 mm / min (26) when obtaining ~ the required time t ₁ and t ₂ of the second stage I and stage II, by performing repeated calculation using the formula (30), respectively, t ₁ = 1.72 min, t ₂ = 1.17 min Become. Using this (27), when the determined width change amount of the stage I and stage first II △ W ₁ and △ W ₂ each from (28), △ W ₁ = 99 mm,
△ W ₂ = 1mm is obtained.

<Effects of the Invention> As described in detail above, the present invention relates to a method of changing the width of a slab by moving the short side of a mold during continuous casting,
When expanding the casting width, there is a period in which the moving speed of the short side is changed according to the moving speed of the meniscus part of the short side, and furthermore, so as not to generate an air gap at various places between the short side and the slab. In addition, it is characterized in that the deformation of the slab is maintained within an allowable strain range.

Therefore, according to the present invention, the moving speed of the short side is changed according to the moving speed of the meniscus portion under specific conditions, so that the required width can be immediately shifted, and the width changing time is reduced as much as possible. The length of the width changing portion of the piece can be shortened, and the capacity of the width changing equipment can be maximized.

[Brief description of the drawings]

1 (a) and 1 (b) are diagrams for explaining a horizontal moving speed of an upper portion of a short side at the time of width change according to the present invention, and FIG. 2 is molten steel static at the time of width change according to the present invention. FIG. 3 is a graph for explaining a horizontal component force of iron pressure, FIG. 3 is a graph showing a relationship between a width change time and a short side moving time of an example of the embodiment of the present invention, and FIG. It is explanatory drawing which shows an example of a width | variety changing apparatus notionally.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-60-33855 (JP, A) JP-A-62-263857 (JP, A) JP-A-62-192245 (JP, A) JP-A 61-263245 9956 (JP, A) JP-A-2-59158 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/16 106

Claims (1)

(57) [Claims] 1. The width of a mold is changed by moving a short side of a mold during continuous casting.
Method, the width is changed by the meniscus on the short side.
When changing, the short side moving speed is the following (1) and
Satisfying the expression (2), The taper between the short side formed at this time and the slab is set to the target taper.
When matching, the moving speed of the short side is
Satisfy expression (4) However, the symbols in the formulas (1), (2), (3) and (4)
Indicates the following: Vu (t): moving speed V at the meniscus portion on the short side (T): moving speed at the lower end of the short side Vc: casting speed m: length from the meniscus part of the mold to the lower end T (t): taper length of the short side θ₁, Θ_Two: Allowable strain φ, ：: Deformation allowance of meniscus portion t: Time: A width expansion method at the time of continuous casting characterized by: