JPS6340621B2 - - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] The present invention reduces the air gap, reduces the moving thrust of the short piece, and accurately adjusts the inclination angle when changing the inclination angle of the mold short piece when changing the width during continuous casting. The purpose is to provide a method for stably and quickly changing the width.

[Prior art]

Techniques for changing mold width during continuous casting include:
It is known to carry out this by fixing the long sides of the mold and moving the short pieces. FIG. 1 shows an example of a well-known variable width mold in which the short piece is configured to be movable. It is configured to move forward or backward. In this movement of the short piece, for example, as shown in FIG. 2 (when the width is reduced) and FIG. 3 (when the width is expanded), at the beginning of the movement, the lower part of the short piece, for example, the joint 10b between the cylinder device 32 and the short piece 1, is used as a rotation fulcrum. After turning the short piece and making the inclination angle α′ of the short piece stronger (m ₁ ) than the predetermined angle α during normal operation, the short piece is moved in parallel (m ₂ ), and at the end of the movement, the upper part of the short piece is
For example, the joint 10 between the cylinder device 31 and the short piece 1
a as a rotational fulcrum, and the predetermined angle α
(m ₃ ) methods are also known. FIG. 4 shows the movement of the short piece using a velocity diagram of the top surface 1a and bottom surface 1b of the short piece, taking width reduction as an example. In FIG. 4, first, the upper surface 1a of the short piece 1 is
The slab 2 is moved in the width reduction direction at a speed of Vm ₁ to make the inclination angle α' of the short piece 1 stronger than the predetermined angle α.
Next, the short piece 1 is moved in parallel at a speed of Vm ₂ , and at the end of the movement when the upper surface 1a of the short piece reaches a predetermined width, the lower surface 1b of the short piece 1 is moved at a speed of Vm ₃ , and the inclination angle α' of the short piece 1 is changed to the predetermined angle. Width reduction is performed by returning to α. The amount of change in inclination ΔT to obtain the inclination angle α′ during the above-mentioned parallel movement is the short piece parallel movement speed
It is generally determined by the following formula using Vm ₂ and casting speed Vc.

ΔT=k・l・Vm ₂ /Vc ΔT: Inclination change amount, Vm ₂ : Short piece parallel movement speed k: Inclination change system, Vc: Casting speed l: Effective short piece length, Therefore, in order to implement high-speed width variation If the short piece moving speed Vm ₂ is increased, the amount of change in inclination _ΔT will be _increased . a monosolidified shell,
The gap between the short wall of the mold (hereinafter referred to as an air gap) becomes large, causing breakouts, etc. On the other hand, the moving speed Vm ₁ when changing the inclination angle,
Increasing Vm ₃ increases the deformation resistance of the solidified slab shell, and the deformation resistance becomes extremely large at the end of the change in inclination angle. Therefore, the resistance exceeds the above resistance.
A thrust force is required to move the short piece, and equipment for moving the short piece becomes expensive. Also, the movement speed when changing the inclination angle
If Vm ₁ and Vm ₃ are increased, it becomes difficult to ensure stopping accuracy when stopping to change the inclination angle. The poor accuracy of this inclination angle has a large negative effect on deterioration of slab quality and breakout.

As described above, if the inclination angle changing speeds Vm ₁ and Vm ₃ are constant, there is a drawback that no matter how fast or slow the inclination angle changing speeds are, they have an adverse effect on the slab.

[Structure and operation of the invention]

The present invention is a variable width continuous casting method in which the long sides of the mold are fixed and the short pieces are moved.The inclination angle of the short pieces is strengthened by turning the lower part of the short piece as a rotational fulcrum, and then moved in parallel, and at the end of the movement, the upper part of the short piece is moved. In this method, the speed of the upper part of the short piece is reduced in stages when changing the inclination angle at the beginning of movement, and the speed of the lower part of the short piece is reduced in stages when changing the inclination angle at the end of movement. It is characterized by this. FIG. 5 shows an example of speed change based on the present invention, and is a speed diagram representing the short piece movement when the width is reduced.

In this example, first, the upper part of the short piece is moved at a high speed Vm ₁ to increase the inclination angle of the short piece 1. When changing the inclination angle at the beginning of movement to increase this inclination angle, when the short piece upper part leaves only ΔT ₁ ' of the inclination change amount ΔT ₁ , the short piece upper part movement speed is reduced to Vm ₁ ' and the set inclination angle α during parallel movement is changed. ’. During this time, the lower part of the short piece remains stationary and its speed is zero. Then, the upper and lower parts of the short pieces are moved in parallel at a speed of Vm ₂ to change the width of the mold. When the upper part of the short piece reaches the set width, while the upper part of the short piece is stopped, the lower part of the short piece is moved at a speed of Vm ₃ to weaken the inclination angle α' and return it to the predetermined angle α. When returning to the predetermined inclination angle α at the end of this movement, the inclination movement amount ΔT ₂ ′ remains,
Reduce the short piece lower travel speed to Vm ₃ ' to complete the change of inclination angle.

By the way, when changing the inclination angle, the timing of increasing the inclination angle and then shifting to parallel movement and the timing of returning the inclination angle to a predetermined angle α and stopping the movement of the lower part of the short piece are determined by, for example, the cylinder devices 31 and 32 shown in FIG. It is determined by detecting the stroke of the short piece 1 or by detecting the positions of the upper and lower surfaces 1a and 1b of the short piece 1. Based on the detected value, parallel movement start commands and stop commands are issued to drive devices such as the cylinder devices 31 and 32. For this reason, when the above-mentioned parallel movement start or stop operation is performed directly from a high-speed movement state as in the conventional method, there is a delay between detecting that the above-mentioned upper and lower surface positions have reached the set positions and actually starting or stopping the parallel movement. This resulted in a large error in the position of the upper and lower surfaces relative to the set position due to the time difference.
Therefore, the inclination angle α' during parallel movement and the predetermined angle α after returning to normal operation do not match the preset optimal angle, causing breakouts and surface flaws.

On the other hand, when carrying out width reduction, if the lower part of the short piece with the thicker solidified shell is moved at high speed, the thrust will become larger. Figure 6 shows how the thrust acting on the short piece changes when the short piece is moved (in the direction of width reduction) under a conventional high-speed condition, and in particular increases rapidly when returning to the predetermined angle α at the end of the movement. I know that there is. As described above, the present invention reduces the speed of the upper and lower parts of the short piece in stages when changing the inclination angle at the beginning and end of the short piece movement, thereby minimizing the amount of movement (including deviation) during the time difference as described above. This makes it possible to change the inclination angle of the short piece with high precision. In addition, the seventh
As shown in the figure, the speed decreases at the end of the inclination angle change when the thrust of the short piece increases rapidly, so the thrust can be greatly reduced. There is no longer any need to make it larger.

_{Now ,} in _{the example of FIG .}
The relationship between Vm ₃ ′ is the short piece moving speed (Vm ₁ , Vm ₂ ,
Vm ₃ ), short piece effective length l, casting speed Vc, etc., but according to the experience of the present inventors, ΔT ₁ ′/ΔT ₁ ≦0.5, ΔT ₂ ′/ΔT ₂ ≦0.5, and 0.3≦Vm ₁ ′
/Vm ₁ ≦0.7, 0.3≦Vm ₃ '/Vm ₃ ≦0.7.

Furthermore, in the above example, the movement speed was reduced only once when changing the inclination angle, but the width variable speed Vm ₂
When the amount of slope change ΔT becomes very large, the effect of the present invention described above can be obtained even if it is reduced multiple times or continuously.
Also, in the case of width expansion, short piece movement can be performed in the same manner as in the example of width reduction. FIG. 8 is a diagram showing the speed of the upper and lower surfaces 1a and 1b of the short piece when the width is expanded.

As described above, according to the present invention, it is possible to increase the moving speeds V ₁ and Vm ₃ when changing the inclination angle,
This makes it possible to shorten the time for changing the inclination angle, allowing the mold short side to fully follow the solidified slab shell, reducing the air gap, and reducing the short piece moving speed to Vm ₁ ' and Vm ₃ ' at the end of the inclination angle change. As a result, it has become possible to reduce the deformation resistance of the solidified slab shell and to improve the accuracy of stopping against the target when changing the inclination angle.

〔Example〕

The present invention was carried out when a cast slab with a width of 1000 mm and a thickness of 250 mm was reduced to a width of 900 mm during continuous casting.

In this example, as shown in FIG. 7, the casting speed Vc
=1.6m/min Vm ₁ =Vm ₃ =48mm/min, Vm ₁ ′=
Width reduction was performed at Vm ₃ ′ = 24 mm/min and Vm ₂ = 32 mm/min. At this time, ΔT ₁ and ΔT ₂ were determined from the following formulas.

ΔT=ΔT ₁ =ΔT ₂ = k·l·Vm ₂ /Vc=0.7×772×32/1600=10.8 [mm] Incidentally, the inclination change coefficient k was 0.7, and the effective short piece length l was 772 mm. Therefore, ΔT ₁ ′ and ΔT ₂ ′ are smaller than 0.5, and ΔT ₁ ′/ΔT ₁ and ΔT ₂ ′/ΔT ₂ described above are smaller than 0.5.
Also, consider the amount of misalignment (approximately 3 mm when Vm ₁ = Vm ₃ = 48 mm/min) when changing the inclination angle from high speed (Vm ₁ , Vm ₃ ) to low speed (Vm ₁ ', Vm ₃ '). and set it to 4mm.

As a result, in this example, compared to the conventional case of moving at a constant speed of Vm ₁ = Vm ₃ = 24 mm/min in order to reduce the deformation resistance force of the slab shell when changing the inclination angle and improve the accuracy of stopping the inclination angle. The time required to change the tilt angle has been shortened by approximately 2/3, and the air gap when changing the tilt has been reduced from the previous maximum of 1.5 mm.
The size has been reduced to MAX 0.8mm. In addition, the deformation resistance of the slab solidified shell and the accuracy of stopping the inclination angle at the final stage of changing the inclination angle were maintained at the same level as before.

As described above, according to the present invention, when changing the inclination angle when changing the width, it is possible to reduce the air gap, reduce the movement thrust of the short piece, and change the inclination angle with high accuracy.

〔Effect of the invention〕

With the present invention, when changing the inclination angle, by reducing the air gap and short piece moving thrust and improving the inclination angle stopping accuracy, high-speed width changes during continuous casting can be stably performed, and breakout can be prevented while maintaining good slab quality. This makes it possible to carry out variable width continuous casting without any trouble, and the effect is very large.

[Brief explanation of the drawing]

Figures 1 to 4 show conventionally well-known embodiments; Figure 1 is a cross-sectional structural diagram of a variable width mold;
The figure shows a width reduction method, Figure 3 is a structural diagram showing an example of a width expansion method, Figure 4 is a velocity diagram of the upper and lower surfaces of the short piece during width reduction, Figures 5, 8, and 9. is a velocity diagram of the upper and lower surfaces of the short piece based on the present invention, and FIGS. 6 and 7 are diagrams showing changes in the thrust generated in the short piece when the width is reduced. This is based on the Inventions Act. In the figure, 1 is a mold short piece, 2 is a slab, and 31 and 32 are cylinder devices.

Claims (1)

[Claims] 1 A variable width continuous casting method in which the long side of the mold is fixed and the short piece is moved, and the inclination angle of the short piece is strengthened by rotating the bottom of the short piece as a rotation fulcrum, then moved in parallel, and at the end of the movement, the top of the short piece is rotated. In the method of turning the tilt angle as a fulcrum and returning the inclination angle to a predetermined angle,
A variable width continuous casting method characterized in that the speed at the top of the short piece is gradually reduced at the beginning of the movement, and the speed at the bottom of the short piece is gradually reduced at the end of the movement.