JPH09150249A - Roll for secondary cooling zone in continuous caster and continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roll for secondary cooling zone having low cooling capacity and long service life by arranging plural annular grooves extended in the peripheral direction on the peripheral surface of the roll at the interval in the axial direction of the roll and limiting the contacting zone of the roll with a cast slab. SOLUTION: Plural annular grooves 6 extended in the peripheral direction on the peripheral surface of the roll 5 for secondary cooling are arranged at the interval in the axial direction of the roll and the peripheral surfaces of the roll interposed with the annular grooves 6 are the contacting zone 7 with the cast slab 1. The length in the axial direction of the roll in this contacting zone 7 is set to 0.25-0.70 times of the cast slab width. It is desirable that the flow passage of cooling water is formed by arranging annular grooves or slit grooves on the inner part of the roll 5 to execute the cooling in the inner part. Further, it is effective to inject mists from the outside of the roll barrel part. The rolls 5 in the secondary cooling zone are parallel lined in the drawing direction of the cast slab 1 and provided to a continuous casting. At this time, it is profitable to execute the continuous casting under condition of arrangement alternately arranging the annular grooves 6 and the contacting zones 7 in the drawing direction.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a roll used for secondary cooling of a continuous casting machine and a continuous casting method in which the roll is applied to a secondary cooling zone. For example, when continuously casting a high-grade wire rod or bar material or a steel sheet that requires excellent surface properties, that is, a so-called surface crack sensitive steel type,
In order to prevent surface cracks in the slab, it is advantageous to carry out dry casting, in which the secondary cooling water of the continuous casting machine is extremely reduced.

That is, in the secondary cooling zone of continuous casting shown in FIG. 1, the casting slab 1 after cooling is cooled by the secondary cooling zone roll 2, the secondary cooling water 3a from the nozzle 3 and the secondary cooling water 3a. This is performed by utilizing heat conduction due to contact with the pooled water 4 in the vicinity of the cooling water roll 2 and heat radiation to the atmosphere. In normal continuous casting, the influence of this secondary cooling water is great, but in dry casting, conversely, it is essential to suppress the secondary cooling water as much as possible. Specifically, first, it is difficult to reduce or stop the supply of the secondary cooling water, while controlling the heat radiation to the atmosphere.
It is necessary to control the cooling of the slab. Therefore, 2
It is customary to employ an internal cooling structure having a low cooling capacity for the rolls arranged in the next cooling zone.

[0003]

However, this type of roll naturally has a low cooling ability against the heat load from the slab, so that the cooling of the roll itself is insufficient and the roll life is shortened. A structure has been proposed that enhances the cooling capacity of the roll without increasing the cooling capacity.

That is, Japanese Patent Application Laid-Open No. 59-50963 discloses that
An internally cooled roll having a spiral cooling passage and an internally cooled roll having an annular cooling passage are proposed in Japanese Patent Publication No. 53-12447. The former roll is expected to improve the roll life because of its high cooling effect, but it has a disadvantage that it requires complicated processing for forming the cooling passage and thus increases production costs. On the other hand, the latter roll does not increase the manufacturing cost, but has a problem in that it has a poor cooling effect. Further, since these rolls have a high roll cooling ability as compared with the conventional ones, it is unavoidable that the cooling ability for the slab becomes relatively high, and it is difficult to apply them to the above-mentioned dry casting.

[0005]

SUMMARY OF THE INVENTION Therefore, the present invention provides a roll for a secondary cooling zone, which has a low cooling ability for cast slabs that is applicable to dry casting and has a long roll life. It is an object of the present invention to propose an advantageous continuous casting method using this secondary cooling zone roll.

[0006]

SUMMARY OF THE INVENTION The present invention is a roll for secondary cooling of a continuous casting machine, wherein a plurality of annular grooves extending in the circumferential direction are provided on the circumferential surface of the roll at intervals in the axial direction of the roll. 2 of the continuous casting machine in which the length in the axial direction of the roll in the contact area with the slab of the roll is limited to 0.25 to 0.70 times the width of the slab.
It is a roll for the next cooling zone. This secondary cooling zone roll is
Having a passage for cooling water inside the roll cylinder, or having a means for spraying mist outside the roll cylinder,
Effective in improving roll life.

Further, according to the present invention, when the above-mentioned secondary cooling zone rolls are arranged in parallel in the slab drawing direction to perform continuous casting, the annular groove and the slab contact area of the adjacent secondary cooling zone rolls are It is a continuous casting method characterized in that it is arranged alternately in the drawing direction.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The secondary cooling zone roll according to the present invention will be described in detail with reference to FIG. The roll 5
Has a plurality of annular grooves 6 extending in the circumferential direction on the circumferential surface thereof at intervals in the axial direction of the roll, and the circumferential surfaces of the rolls sandwiched by the annular grooves 6 serve as contact areas 7 with the slab. is there.
Reference numeral 8 is a roll bearing. Here, it is important that the roll 5 is provided by providing the annular groove 6.
Is to adjust the contact area with the slab 1 to reduce the amount of heat removed from the slab 1. Therefore, it is necessary to limit the length of the contact area 7 of the roll 5 with the slab 1.

That is, in order to reduce the amount of heat removed from the slab, it is advantageous to shorten the contact length between the roll and the slab, but if the contact length is too short, the annular groove portion increases. However, since the contact pressure with the slab increases, part of the slab is pushed into the annular groove and streaky indentations remain on the slab, so a contact length that does not cause these indentations is required. .

The length of the contact portion between the roll and the slab is b, the width of the slab is B, and the contact ratio is b / B. With b / B as a parameter, FIG. 9 shows the relationship between b / B and the cast heat removal amount Q, the indentation depth d of the cast, the roll surface temperature t _s , and the roll life L as data obtained from casting results. . The casting conditions are as follows. Steel type: Normal steel to low alloy steel (C = 0.1 to 1.0%) Slab size: 400 x 600 mm Casting speed: 0.4 to 0.6 m / min Specific water volume: 0.1 to 0.4 l / kg

From the results shown in the figure, the lower limit of the proper range of b / B is determined by the indentation depth d. If the normal scale-off margin of 0.3 mm is exceeded, there are problems in surface quality and yield. The value is usually b / B> 0.25. Also, in terms of the heat removal amount Q and the life L, the effect is small when b / B <0.25, and b / B = 0.25 is the lower limit practically. on the other hand,
The upper limit is b, considering the effects on the heat removal amount Q and life L.
When /B>0.7, the effect of forming an annular groove is small. Therefore,
Practically, the proper range is 0.25 ≦ b / B ≦ 0.7.

Therefore, the length of the roll in the axial direction in the contact area with the cast piece is set to be 0.25 to 0.70 times the width of the cast piece. Because, if the contact area is less than 0.25 times the width of the slab, the width required for supporting the slab cannot be ensured and the indentation due to the annular groove remains, while if it exceeds 0.70 times, the amount of heat removed from the slab is Since it becomes too large to achieve dry casting, the contact area with the slab of the roll is 0.25 to 0.70 of the slab width.
Set to double.

From the viewpoint of the strength and life of the roll itself, it is desirable to cool the roll to ensure heat resistance. For the cooling of the roll, an external water cooling method that is performed by spraying water is effective, but the slab is also cooled by splashing water,
Therefore, it is not suitable for dry casting because of the fear. Therefore, as shown in FIG. 5, the cooling water 9 consisting of an annular groove or a slit-shaped groove along the circumferential surface inside the roll
It is preferable to form the flow path 10 to perform internal cooling.
Incidentally, reference numeral 11 in the drawing is a rotary joint. Although there are various types of internal water-cooled structures, the structure shown in FIG. 5 is recommended in view of the cooling capacity that affects the roll surface temperature and the roll manufacturing cost. If the cooling capacity is too strong, it impedes dry casting. Therefore, it is preferable to limit the cooling load to a range where the heat load on the roll can be reduced.

As another cooling means, shown in FIG.
It is also effective to spray the mist onto the roll from the mist nozzle 12 installed outside the roll cylinder. The cooling by the mist can reduce the cooling to the slab by adjusting the air-water ratio of the mist to cool the roll, so that unlike the case of spraying water, there is no risk of cooling the slab. Note that, as shown in FIG. 6, it is convenient for the mist to be sprayed in a direction inclined with respect to the roll axis in order to avoid cooling the cast slab.

Now, the above-mentioned secondary cooling zone roll has two
In the roller apron that constitutes the next cooling zone, a plurality of slabs are arranged in the drawing direction of the slab for continuous casting. Here, as shown in FIG. 7, the annular groove 6 or the contact area 7 is drawn between the adjacent rolls. The annular groove 6 and the contact area 7 do not line up in the direction.
It is preferable that the and are arranged alternately in the drawing direction. That is, if the annular groove 6 or the contact area 7 is continuous in the drawing direction, a locally cooled portion and a locally rolled portion are generated in the slab to deteriorate the quality of the slab. It is advantageous to carry out continuous casting under an arrangement in which 7 and 7 are arranged alternately in the drawing direction.

In practice, as shown in FIG. 7, the annular groove 6
When rolls having different forming positions are arranged adjacent to each other, or when rolls having the same annular groove 6 forming positions are adjacent to each other, one of the rolls is shifted in the roll axial direction and the annular groove 6 is not continuous in the drawing direction. Realize the placement.

[0017]

[Example] Using high carbon steel containing C: 1 wt%, size at a casting speed of 0.9 m / min and a specific water amount of 0.15 l / kg
In continuously casting a slab of 300 × 400 mm, the roll having the structure shown in FIG. 5 was arranged in the secondary cooling zone of the continuous casting machine according to the place shown in FIG. 7, and continuous casting was carried out. The rolls for the secondary cooling zone are made of chromium, molybdenum steel (SC
Made of (M 435 equivalent), roll diameter (diameter of contact area 7): 250 mm
Under the basic structure in which a roll having an axial length of 600 mm is provided with annular grooves 6 having a depth of 3 mm at intervals of 5 mm in the axial direction, as shown in FIG. In order to prevent this, a plurality of types of rolls in which the formation position of the annular groove 6 differs in the axial direction were prepared.

For comparison, a conventional roll having a similar size and no annular groove was placed in the secondary cooling zone, and continuous casting was similarly performed. As shown in FIG. 8, the structure of this conventional roll has a cooling water passage 13 spirally extending along the circumferential surface inside the roll.

Table 1 shows the results of investigations on the surface temperature of the slab, surface cracking of the slab, and roll life in each of the above continuous castings. Here, the slab surface temperature indicates a measured value at the end point of the slab support region by the roll. In the roll of the invention example, the surface temperature of the slab has increased by 50 ° C., and the effect of slow cooling of the roll is recognized. The defective rate due to surface cracking of the cast piece indicates the defective rate due to surface cracking after rolling the cast piece. Although the defective rate is almost halved, this is considered to be the effect of increasing the surface temperature of the slab and avoiding the brittle temperature range in the bending straightening range. And roll life increased by 10%. This is considered to be the effect of relaxing the thermal stress on the roll surface and reducing the generation amount of cracks due to the thermal stress on the roll surface by grooving.

[0020]

[Table 1]

[0021]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a secondary cooling zone roll having an extremely low cooling ability for a cast slab and a long heat-resistant life and having optimum performance for dry casting. Moreover, since an appropriate means for applying this roll to the secondary cooling zone is provided, advantageous continuous casting in which slab surface cracking is suppressed is realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a heat removal amount in secondary cooling.

FIG. 2 is an explanatory view showing a roll for a secondary cooling zone of the present invention.

FIG. 3 is a diagram showing a force acting on a roll in a secondary cooling zone.

FIG. 4 is a diagram showing a force acting on a roll in a secondary cooling zone.

FIG. 5 is an explanatory view showing a cooling means in the roll for a secondary cooling zone of the present invention.

FIG. 6 is an explanatory view showing a cooling means in the roll for the secondary cooling zone of the present invention.

FIG. 7 is a diagram showing an arrangement of rolls in a secondary cooling zone.

FIG. 8 is a view showing a roll for a conventional secondary cooling zone.

FIG. 9 is a graph showing the influence of Q, t _s , L, and d on the contact rate with the cast slab.

[Explanation of symbols]

 1 cast slab 2 roll 3 nozzle 3a secondary cooling water 4 pooled water 5 secondary cooling zone roll 6 annular groove 7 contact area 8 bearing 9 cooling water 10 flow path 11 rotary joint 12 mist nozzle

Claims (4)

[Claims] 1. A roll used for secondary cooling of a continuous casting machine, wherein a plurality of annular grooves extending in the circumferential direction are provided on the circumferential surface of the roll at intervals in the axial direction of the roll, and the roll has a contact area with a cast piece. The roll for the secondary cooling zone of the continuous casting machine, in which the length in the axial direction of the roll is limited to 0.25 to 0.70 times the width of the slab. 2. The roll for a secondary cooling zone of a continuous casting machine according to claim 1, wherein a cooling water passage is provided inside the roll cylinder. 3. The roll for a secondary cooling zone of a continuous casting machine according to claim 1, further comprising a mist spraying means provided outside the roll cylinder. 4. When the secondary cooling zone rolls according to claim 1 are arranged in parallel in the direction of drawing of the slab for continuous casting, an annular groove and a slab contact area of adjacent secondary cooling zone rolls are provided. The continuous casting method is characterized in that the two are arranged alternately in the drawing direction.