JPH0829401B2 - Continuous casting method for thin slabs - Google Patents

Description

TECHNICAL FIELD The present invention relates to a continuous casting method for thin-wall cast slabs, and more particularly to a twin-drum type continuous casting method.

The twin-drum type (or “twin roll type”) continuous casting method is a continuous casting method in which a molten metal is injected between a pair of rotating cooling drums and a slab having a thickness corresponding to the interval between the cooling drums is cast. It is particularly suitable for casting thin-walled slabs having a thickness close to the product thickness.

In the mold composed of the cooling drum and the side weir, the injected molten metal forms a pool, and the molten metal in the pool is cooled on the outer peripheral surface of the cooling drum to form a solidified shell, The solidified shells that grew on the outer peripheral surfaces of both cooling drums due to rotation coalesce near the closest contact points (so-called “kissing points”) of both drums to complete solidification, and become cast pieces that are drawn out between the cooling drums. Be done.

[Conventional technology]

In the twin-drum type continuous casting method, in order to prevent lateral cracking of the slab, a method of making the deposit thickness uniform on the outer peripheral surface of the cooling drum has already been proposed (for example, JP-A-60-184449, JP-A-62-176650). The deposits are generated due to oxides caused by volatile components in the molten metal, scum floating on the surface of the pool, etc. It becomes uneven. As a result, solidified shell formation on the outer peripheral surface of the cooling drum
Growth also becomes non-uniform and lateral slab cracks occur. Therefore,
In the above-mentioned conventional method, the outer circumferential surface of the cooling drum is cleaned with a rotating brush to make the thickness of the deposit uniform, thereby preventing lateral cracking of the slab.

However, in these conventional methods, even if lateral cracks can be prevented by making the deposit thickness uniform, the deposit thickness gradually increases during casting, and the slab thickness decreases accordingly. There is a problem that a thick slab cannot be obtained stably.

[Problems to be Solved by the Invention]

The present invention solves the problems inherent in the conventional method, prevents lateral cracking of the slab, and stably casts a slab of a predetermined thickness by keeping the deposit thickness constant. It is an object of the present invention to provide a continuous casting method for possible thin-walled slabs.

[Means for solving the problem]

According to the present invention, the above-mentioned problem is obtained by injecting a molten metal between a pair of rotary cooling drums and casting a slab having a thickness corresponding to the distance between the cooling drums in a continuous casting method for thin-walled slabs. A rotating brush for finishing and a rotating brush for finishing grinding are arranged in this order in accordance with the cooling drum rotating method, and at least one rotating brush for rough grinding and one rotating for finish grinding are provided on the free outer peripheral surface of the cooling drum. Start the casting by pressing the brush, and continuously measure the thickness of the deposit on the free outer peripheral surface of the cooling drum during casting, and according to the measured value, the number of pressings, the number of rotations and the pressing force of the rotating brush This is achieved by a continuous casting method for thin-walled slabs, characterized in that the thickness of the deposit is kept constant by adjusting the priorities as required.

[Action]

In the method of the present invention, during casting, an increase in the thickness of deposits is removed by a rotating brush for rough grinding having a large removal ability, and the rough grinding surface is prevented from lateral cracking by a rotating brush for finish grinding. Since it can be smoothed to the extent possible, it is possible to simultaneously prevent the reduction of the thickness of the slab and lateral cracking.

Hereinafter, the present invention will be described in more detail by way of examples with reference to the accompanying drawings.

[Examples] FIG. 1 shows an example of a continuous casting method in which a rotating brush is arranged according to the present invention.

Molten metal is poured between a pair of cooling drums 1 rotating in the direction of arrow R to form a pool 2, and solidification is completed near the kissing point K to cast a slab 3.

The thickness of the slab 3 is set by the casting speed, the amount of heat removed by the cooling drum 1, the level of the molten metal in the pool 2, the pressing force of the cooling drum 1, and the like.

For each cooling drum 1, two rough-grinding rotating brushes 11 and one finishing-grinding rotating brush 12 are arranged in the order shown in the range indicated by the arrow S on the free outer peripheral surface of the cooling drum 1, that is, the outer peripheral surface 4. It is located at. Further, the thickness of the deposit on the outer peripheral surface 4 of the cooling drum 1 can be continuously measured by the infrared imaging device 13 at the position of the point P on the free outer peripheral surface 4.

The measured value is output as an electronic signal from the infrared imaging device 13 and compared with a predetermined deposit thickness by a comparator (not shown), and the use condition of the rotating brushes 11 and 12 is determined by the number of pressing (use) according to the comparison result. , The number of rotations, and the pressing force are set and adjusted by a control device (not shown).

Rotating brush 11 for rough grinding and rotating brush 12 for finish grinding
Is a fine-grained grinding tool suitable for smoothing that can prevent lateral cracks by setting the former as a brush with a high ability to remove deposits by appropriately setting the material, thickness, length, and density of the brush wire. Create as a brush. For example, when casting thin stainless steel slabs, it was evaporated from the molten steel.
The oxides of Mn occupy most of the deposits, and for removing them by grinding, a very high hardness high carbon steel wire is suitable as a wire of the rotating brush 11 for rough grinding, and a rotating brush 12 for finish grinding is used. SUS304 stainless steel wire, which is softer than the former and suitable for smoothing, is desirable as the wire.

The rough-grinding rotary brush 11 and the finish-grinding rotary brush 12 are arranged such that the former is on the upstream side of the latter in the rotational direction R of the cooling drum 1. Further, the infrared imaging device 13 is arranged on the downstream side of the rotating brush 12. Such relative positions can, of course, be arranged other than the illustrated arrangement. It may be arranged at a position where the necessary removal effect can be easily obtained, depending on the temperature of the deposits on the free outer peripheral surface 4 of the cooling drum 1 or the like.

The number of brushes arranged is one or more, and is set according to the effect of removing deposits, the tolerance of equipment, and the like. By arranging a plurality of brushes for each, and pressing or separating them from the outer peripheral surface 4 of the cooling drum 1,
Be prepared to be able to adjust the number to be used appropriately.

The thickness of the deposit is measured by the infrared imaging device 13 according to the principle disclosed in Japanese Patent Application No. 2-8461 by the present inventor. That is, the infrared intensity of the outer peripheral surface 4 of the cooling drum 1 after contacting the molten metal is measured, the emissivity of the outer peripheral surface 4 is calculated from the measured value and the temperature of the outer peripheral surface 4, and the calculated emissivity is calculated based on the calculated value. Find the kimono thickness.

Then, using the apparatus shown in FIG. 1 having the characteristics as described above, a thin slab of SUS304 stainless steel having a thickness of 3.8 mm was cast according to the present invention. The casting conditions and rotary brush conditions at this time were as follows.

Cooling drum; (diameter) 1.200mmφ, (width) 800mm Level of molten metal (indicated by angle θ in Fig. 1); 40 ° Casting speed; 40m / min Rotating brush for rough grinding; (Material) Hard steel wire, (Diameter ) 0.25 mm, (length) 50 mm (rpm) customary 100～1.600Rpm, standard 600 rpm (pressing force ^*) conventional 0.5~2.5kg / cm ^2, a standard 1.5 kg / cm ² fine grinding rotary brush; (material) SUS304, (diameter) 0.15 mm, (length) 50 mm (rpm) customary 100～1.600Rpm, standard 600 rpm (pressing force ^*) conventional 0.5~2.5kg / cm ^2, Note standard 1.5 kg / cm ^2, pressing force ( ^* ) Indicates the pressure displayed on the air cylinder used.

Therefore, a specific method for controlling the thickness of the deposit will be described below.

First of all, one of the rough grinding rotary brushes and the finish grinding rotary brush were rotated at a rotation speed of 600 rpm and a pressing force of 1.5 k.
Pressing against the cooling drum 1 at g / cm ² started casting.

After that, when the casting was almost stabilized, that is, 3 minutes after the start of casting, the thickness of the deposit was measured by the infrared imaging device 13. The measurement value obtained first serves as a reference value for controlling the thickness of the deposit. The control procedure thereafter is as follows.

(1) After 10 seconds (this value can be set arbitrarily), measure the thickness of the deposit and check whether the amount of increase in thickness exceeds the allowable range of 0.25 μm (this value can also be set arbitrarily). Weigh whether or not.

(2) If it exceeds -0.25 μm, proceed to (3).

If the thickness is within −0.25 μm or the thickness is reduced, return to (1).

(3) Increase the number of rotating brushes used for rough grinding by one. The rotation speed and pressing force are the same as those already in use.

(4) After the elapse of 10 seconds, the thickness of the deposit is measured, and it is comparatively examined whether the amount of increase or decrease of the thickness with respect to the reference value is within the allowable range of 0.25 μm.

(5) -If the increase exceeds 0.25 μm, (6)
Move to.

-If the increase or decrease is within 0.25 μm,
Return to (4).

-If the reduction amount exceeds 0.25 μm, proceed to (7).

(6) Increase the number of rotations of the rough grinding rotary brush by 50 rpm (this value can be set arbitrarily) and return to (4).

(7) Reduce the number of rotating brushes for rough grinding by one,
Move to (8).

(8) Increase the rotation speed of the rough grinding rotary brush by 50 rpm,
Move to (9). If the rotation speed is the upper limit of the normal rotation speed 1.60
If it exceeds 0 rpm, reset it to 600 rpm and return to (3).

(9) After the lapse of 10 seconds, the thickness of the deposit is measured, and it is comparatively examined whether or not the amount of increase or decrease of the thickness with respect to the reference value is within the allowable range of 0.25 μm.

(10) -If the increase exceeds 0.25 μm, (8)
Return to.

-If the increase or decrease is within 0.25 μm,
Return to (9).

-If the reduction exceeds 0.25 μm, proceed to (11).

(11) Reduce the rotation speed of the rotating brush for rough grinding by 50 rpm,
Go to 2).

(12) Increase the pressing force of the rotating brush for rough grinding by 0.1kg / cm ² (this value can be set arbitrarily), and move to (13). if,
When the pressing force exceeds the upper limit value 2.5 kg / cm ² conventional pressing force is re-set to 1.5 kg / cm ^2, the flow returns to (8).

(13) After 10 seconds have elapsed, the thickness of the deposit is measured, and it is comparatively examined whether or not the amount of increase or decrease of the thickness with respect to the reference value is within the allowable range of 0.25 μm.

(14) -If the increment exceeds 0.25 μm, (12)
Return to.

-If the increase is within 0.25 μm or if the thickness is reduced, return to (13).

By performing control based on the above procedure, the thickness of the deposit on the cooling drum 1 becomes constant.

In addition, in this example, the measurement interval of the deposit thickness is
10 seconds, permissible range of increase in deposit thickness is 0.25 μm, rotational speed increase range of rough grinding rotary brush is 50 rpm, and pressing force increase range of rough grinding rotary brush is 0.1 kg / cm ² . Set. The finer these values are, the higher the control accuracy is. However, if there is a large disturbance, the control may be lost, so it is necessary to select appropriate values for each device.

FIGS. 2 (a) and 2 (b) show changes in the deposit thickness and the corresponding slab thickness when the casting according to the present invention was carried out. It can be seen that the one-sided thickness is also constant.

In addition, for comparison, in the apparatus of FIG. 1, only the rotary brush 12 for finish grinding was used, and only the grinding removal was performed to prevent lateral cracking as in the conventional case. The changes are shown in FIGS. 3 (a) and 3 (b).

In the conventional method, the thickness of the deposit is 1 to 500 m during the casting length of 500 m.
The slab thickness continues to increase linearly up to about 1.5 μm, and the slab thickness linearly decreases from the prescribed value of 3.8 mm to 3.5 mm.

On the other hand, in the method of the present invention, the deposit thickness increased to about 0.4 μm by the casting length of about 120 m is kept constant thereafter, and the cast piece thickness becomes stable at the predetermined value of 3.8 mm. Have been secured.

In each case, no lateral cracking of the cast slab was observed.

〔The invention's effect〕

As described above, according to the present invention, it is possible to prevent lateral cracking and stably cast a thin cast piece having a predetermined thickness.

[Brief description of drawings]

FIG. 1 is a view showing a state in which a rotating brush is arranged according to the present invention and casting is carried out, and FIGS. 2 (a) and 2 (b) show the casting length when casting a thin cast piece according to the present invention ( (a) Graph showing changes in deposit thickness and (b) changes in slab thickness, and FIGS. 3 (a) and 3 (b) are casting lengths when casting thin slabs by a conventional method. 3 is a graph showing changes in the thickness of the deposit (a) and changes in the thickness of the slab (b) with respect to FIG. DESCRIPTION OF SYMBOLS 1 ... Cooling drum, 2 ... Hot water pool, 3 ... Cast piece, 4 ... Free outer peripheral surface of the cooling drum 1, 11 ... Rough grinding rotary brush, 12 ... Finish grinding rotary brush, 13 ... Infrared imager, K ... Kissing -Point, R ... Rotation direction of cooling drum 1, θ ... Level of molten metal (angle).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuyasu Sakanashi 1-1-1 Emitsu, Hachimanto-ku, Kitakyushu, Kitakyushu, Fukuoka Inside the Engineering Department, Nippon Steel Corporation (72) Takashi Yamane Nishi-ku, Hiroshima-shi, Hiroshima Kannon Shinmachi 4-6-22 Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (56) Reference Japanese Patent Laid-Open No. 63-90343 (JP, A) Tokuheihei 2-503170 (JP, A)

Claims (1)

[Claims] 1. A method for continuously casting thin-walled cast pieces, in which a molten metal is poured between a pair of rotary cooling drums to cast a cast piece having a thickness corresponding to the interval between the cooling drums, a rotary brush for rough grinding and finish grinding. And a rotary brush for use in the cooling drum are arranged in this order along the rotating direction of the cooling drum, and at least one rotary brush for rough grinding and one rotary brush for finish grinding are pressed against the free outer peripheral surface of the cooling drum to perform casting. Start and continuously measure the thickness of the deposit on the free outer peripheral surface of the cooling drum during casting, and adjust as needed according to the obtained measurement value in the order of priority of the number of rotating brushes, rotation speed, and pressing force. The continuous casting method for a thin cast slab, characterized in that the thickness of the deposit is kept constant by doing so.