JPH0847757A - Divided roll with groove and device for guiding cast slab and method for guiding cast slab - Google Patents

Abstract

PURPOSE:To provide a support roll which can make a crator end shape nearly uniform in the width direction of a cast slab and has excellent effect for further increasing the rolling reduction effect near the crator end. CONSTITUTION:The support roll for guiding the continuously cast slab of a steel adopts a divided roll with grooves satisfying the following conditional expressions I, II. P/L<=0.1... expression I, 2mm<D... expression II. Wherein, P is pitch of projections on the roll (mm), L is the roll length (mm) and D is the depth of recesses (mm).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of the crater end shape of a slab for improving the center segregation and center porosity of the slab in continuous casting of steel.

[0002]

2. Description of the Related Art Conventionally, when a slab crater end is subjected to reduction in order to improve segregation of a slab, for example, Japanese Patent Publication No. 59-16.
862, as seen in JP-A-62-259647,
When performing light reduction with multiple roll pressures, or when trying to apply a reduction amount commensurate with solidification contraction and heat contraction with the walking bar method, to prevent bulging on the support rolls in the secondary cooling zone after the mold, It uses split rolls. In this split roll support method, in the cast piece, there is an unsupported portion between the split rolls, that portion is overcooled, and the temperature distribution in the cast piece width direction greatly varies,
For this reason, the crater end had a fishtail shape and the peaks and valleys were deep.

Since the crater end positions are different in the width direction as described above, it is unavoidable that the light rolling reduction effect is reduced and the segregation and center porosity improving effects become insufficient. With split rolls like this,
Since there is a part where the solidification is fast and a part where the solidification is slow in the width direction of the slab, there is a difference in the segregation level in the width direction when a reduction is applied at the crater end, and the improvement of segregation due to the reduction must be incomplete. There wasn't.

[0004]

As described above, in the split support rolls used in the secondary cooling zone, since the connecting portion between the split rolls has a concave shape, The roll does not come into contact with the slab and a large amount of cooling water flows, resulting in strong cooling, which causes center segregation in the width direction of the slab and uneven center porosity, resulting in center segregation.
When roll reduction or surface reduction is applied to improve the center porosity, the effect may not be fully exerted.

[0005]

The present invention has been made to solve the above problems, and the gist thereof is a support roll for guiding a continuously cast slab of steel, which roll is in contact with the slab. There is a grooved division roll characterized by providing a large number of irregularities on the surface, and among the support rolls for guiding the continuously cast slab of steel, at least immediately below the mold foot roll, a plurality of the grooved division rolls. Individually arranged, and in the slab guide equipment characterized by arranging a rolling down device for rolling down the slab crater end in the downstream, further in the support roll for guiding the continuous cast slab of steel , At least the roll just below the mold foot roll is guided by the plurality of grooved split rolls, and the crater end vicinity of the cast slab is provided at the downstream thereof with a reduction roll device or a surface pressure reduction device. In in the slab guidance method which is characterized in that pressure.

[0006]

As described above, in the split roll used in the conventional cast slab support roll, the roll chock portion between the split rolls 1a and 1b has a concave shape 2 as shown in FIG. Since it is not in contact with the slab 3, a large amount of cooling water in the secondary cold zone flows through this portion. FIG. 4 shows the water amount density ratio distribution in the width direction of the slab, which supports this fact. Therefore, the cooling of this portion is excessively higher than that of the other portions, and the solidification of the slab is further enhanced.
Therefore, as described above, the crater end shape largely changes due to the nonuniform cooling in the width direction of the slab, and deep ridges and valleys are formed.

According to the present invention, in order to improve the shape of the crater end, grooves (recesses) having a size sufficient to allow cooling water to pass through are provided on the surface of the divided rolls of the support roll. Must be satisfied. P / L ≦ 0.1 (1) 2 mm <D (2) P: pitch of roll irregularities (mm) L: roll length (mm) D: depth of roll irregularities (mm) )

Here, the reason for limiting the mathematical formula will be described.
In the formula (1), it has been experimentally revealed that when the pitch of the groove exceeds 10% of the roll length, the center segregation and the center porosity are adversely affected. The condition was 10% or less. As the lower limit is smaller (the number of grooves is larger), the effect of meeting the object of the present invention can be obtained. When the formula (2) satisfies the formula (1), the depth of the unevenness of the roll needs to be larger than the bulging amount of the slab, and the cooling water flow is improved to contribute to uniform cooling. From the condition of the minimum required depth, the depth of the unevenness of the roll was set to 2 mm or more.

In the present invention, the above-mentioned grooved division rolls are used as the support rolls for guiding continuously cast slabs of steel. FIG. 1 shows an example of a grooved division roll according to the present invention. Grooves 4 are provided on the surfaces of the division rolls 1a and 1b based on the above formula (1). Fig. 3 shows the distribution of the water content density ratio in the width direction of the cast on this roll.
As shown in Table 1, it can be seen that a substantially uniform water amount distribution is obtained. In the present invention, such a grooved division roll is arranged as a support roll for guiding a cast piece drawn from a continuous casting mold in a steel continuous casting machine having a crater end reduction device.

FIG. 7 shows an overall view of the slab guide equipment of the present invention. The slab 3 drawn from the mold 11 passes through a foot roll 12 immediately below the mold, and a support roll provided with a grooved split roll. It is supported and guided by 13. further,
The vicinity of the crater end is reduced by a reduction device 14 (for example, a roll reduction device) to improve the center folding and the like. The location of the grooved split rolls is, of course, on the upstream side of the slab reduction device, and immediately below the mold foot rolls, where there are many molten steel unsolidified portions of the slab, are preferable in terms of its effect, and the total number of support rolls You may install over.

[0011]

Example In a steel continuous casting machine equipped with a device for rolling down the vicinity of the crater end, a split roll with a groove under the following conditions was incorporated into a support roll directly below a mold foot roll to guide a slab. P: pitch of unevenness of roll (mm) = 15 mm, 30 m
m L: Roll length (mm) = 2480 mm D: Depth of roll irregularity (mm) = 3 mm Number of rolls: 26 rolls in total (total of F and L surfaces) Tacking in the width direction of the slab and measurement of surface temperature The nonuniform length of solidification was estimated by the temperature. The result is shown in FIG. In FIG. 5, the ● marks are the estimated values from the tacking results, and the Δ marks are the estimated values from the temperature measurement results. The conventional non-grooved split roll shown in FIG. 5a had a solidification non-uniform length of about 1.2 m.
It was improved to m.

Similarly, FIG. 6 shows a comparison of the segregation rating results of the cast pieces under each condition. FIG. 6a is an example of a grooved split roll, FIG. 6b is an example of a grooved split roll outside the scope of the present invention, and FIG. 6c is an example of a grooved split roll of the present invention.
As is clear from the figure, in the case of the split roll, the segregation score is deteriorated in the portion where the water amount density is large, and when the formula (1) of the present invention is not satisfied, the improvement effect is small. Than this,
The segregation level in the width direction can be made uniform and reduced by the grooved dividing roll having the irregularities satisfying the expression (1).

[0013]

EFFECTS OF THE INVENTION According to the present invention, by using a split roll with a groove under specific conditions as a slab guide support roll, it is possible to make the crater end shape substantially uniform in the slab width direction, and in the vicinity of the crater end. It has an excellent effect of further increasing the rolling reduction effect.

[Brief description of drawings]

FIG. 1 is a view showing an example of a grooved division roll of the present invention.

FIG. 2 is a view showing a slab support state in a conventional split roll.

FIG. 3 is a view showing a water quantity density distribution in a width direction of a cast piece by a grooved split roll of the present invention.

FIG. 4 is a view showing a water content density distribution in a width direction of a cast product by a conventional split roll.

FIG. 5 is a diagram showing a crater end shape improving effect.

FIG. 6 is a diagram showing a segregation level improving effect.

FIG. 7 is a diagram showing an example of the equipment of the present invention.

[Explanation of symbols]

 1a, 1b Split roll 2 Recessed portion 3 Cast piece 4 Groove portion 11 Mold 12 Foot roll 13 Support roll 14 Rolling down device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ken Seki, Oita City, Oita City, 1st Nishinosu, Nippon Steel Co., Ltd. Inside the Oita Steel Works, Ltd. (72) Inventor, Yasuhiko Kawada, Oita City, Oita Prefecture, 1st Nishinosu, New Japan Oita Steel Works, Ltd.

Claims (3)

[Claims] 1. A support roll for guiding a continuously cast slab of steel, which satisfies the following conditional expression, and is a grooved division roll. P / L ≦ 0.1 (1) 2 mm <D (2) P: pitch of roll irregularities (mm) L: roll length (mm) D: depth of roll irregularities (mm) ) 2. A plurality of rolls according to claim 1 are provided at least directly under a mold foot roll among support rolls for guiding a continuously cast slab of steel, and the slab crater end vicinity reduction is provided downstream thereof. A slab guide facility characterized by arranging a rolling down device. 3. Among the support rolls for guiding the continuously cast slab of steel, at least the roll just below the mold foot roll is guided by the plurality of rolls according to claim 1, and the crater of the slab is downstream thereof. A slab guide method characterized in that the vicinity of the end is reduced by a reduction roll device or a surface reduction device.