JPH09262643A - Method for continuously casting thin cast strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the development of wearing of recessed parts and surface crack on a thin cast strip in a method for casting the thin cast strip by using a twin roll type continuous casting apparatus machining the recessed parts on the peripheral surface of the cooling roll. SOLUTION: On the peripheral surfaces of one pair of the cooling rolls 2, 3, plating is applied and many recessed parts are machined on this plated surface. Molten metal is supplied and solidified on the peripheral surfaces of one pair of the cooling rolls 2, 3 and solidified shells 12, 12 are continuously cast to the thin cast strip 13 while adding the pushing force of <=7×10<4> N/m of the width of roll at the steady time with the cooling rolls 2, 3 rotation-driving mutually to reverse direction. At this time, this pushing force is controlled so as to become <=25×10<4> N/m of the width of roll at the unsteady time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to continuous casting of strip cast using a twin-drum type continuous casting apparatus.
In particular, the present invention relates to a method for obtaining a strip slab having excellent surface quality.

[0002]

2. Description of the Related Art A twin-drum type continuous casting apparatus comprises a pair of cooling drums which are rotationally driven in opposite directions, and side weirs which are pressed against both end faces of the cooling drum. When the molten metal is supplied to the molten metal pool 3 formed by the weir, the molten metal forms a solidified shell on the peripheral surface of the cooling drum, and the solidified shell is pressure-bonded between the pair of cooling drums to continuously cast thin strip slabs. can do.

Since the thin strip cast produced by using the twin drum type continuous casting apparatus has a thin plate thickness of about 1 to 7 mm, the surface condition thereof is significantly affected by the formation state of the solidified shell, and particularly solidified. Due to the non-uniformity of the shell thickness in the plate width direction, defects such as surface cracks are likely to occur on the slab.

In order to solve such a problem, a method of providing a large number of dot-shaped depressions on the peripheral surface of the cooling drum is known, for example, from Japanese Patent Application Laid-Open No. 60-184449. A gas gap, which serves as a heat insulating layer, is formed between the cooling drum and the solidification shell by this depression, and the amount of heat removed from the cooling drum is reduced to allow slow cooling of the molten metal, and at the same time, the convex transfer due to the depression is formed on the surface of the strip slab. Is formed and coagulation is started from the peripheral portion of the convex transfer, so that the coagulated shell thickness is made uniform in the plate width direction.

However, even when a thin strip cast is cast using a cooling drum having such a recess processed, surface cracks may occur in the obtained strip cast. For example,
Although a slab without surface cracks can be obtained in a portion corresponding to the initial stage of casting, surface cracks tend to occur as the casting progresses, and in some cases surface cracks may occur from the initial stage of casting.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for casting a strip cast using a twin-drum type continuous casting machine in which a depression is formed on the peripheral surface of a cooling drum. The challenge is to prevent it.

[0007]

Means for Solving the Problems In order to clarify the cause of surface cracking of a strip cast, the present inventor investigated the depressions on the peripheral surface of the cooling drum after casting, and found that the cast had surface cracks. When it was done, the dent was heavily worn. Further, as a result of detailed investigation of the shape of the worn dent, the dent had a crushed form.

In this case, if the pressing force of the cooling drum is reduced, it is considered that the wear of the depression is reduced, but in the conventional twin-drum type continuous casting, the pressing force per drum width is 10 to 30 in a steady state. × 10 ⁴ N / m or so, as 10~50 × 10 ⁴ N / m in the unsteady such at the start of casting, by crimping strongly solidified shell between the drum, the crystal structure as well as preventing breakout and bulging Was being made uniform.

However, the present inventor considers that when a depression is provided on the peripheral surface of the cooling drum, the conventional pressing force is excessive, and as a result of performing casting while changing the drum pressing force variously, the pressing force is higher than the conventional one. It has been found that the above problem does not occur even if it is made smaller. Further, there is a close relationship between the drum pressing force and the wear amount of the depression, and the cause of wear of the depression is due to the drum pressing force itself, and if the drum pushing force is adjusted to a predetermined value, wear of the depression is caused. It turned out that the amount can be reduced.

Therefore, according to the present invention, when the casting is started, or when the continuous casting is unsteady in which the pushing force of the drum becomes large due to the involvement of the metal,
It controls the drum pressing force by dividing it into regular and
Pushing force per drum width during continuous casting is 7 ×
Controlled below 10 ⁴ N / m, the pressing force per drum width during non-stationary and controls below 25 × 10 ⁴ N / m. If the pressing force per drum width is less than 0.1 × 10 ⁴ N / m in the steady state and unsteady state, it is difficult to form a slab due to insufficient drum pressing force. Is 0.1 × 10 ⁴ N / m.

The non-steady state in the present invention is defined as follows. In twin-drum type continuous casting, until the cooling drum starts about one revolution after the cooling drum is activated, both the molten metal level and the drum rotation speed are increasing, solidification unevenness is likely to occur, and the solidification shell is partially abnormally thick. The part is easy to form, the pressing force of the drum is large, and the depression is crushed.

At the end of casting, after all the molten metal in the tundish is supplied to the pool, the level of the molten metal in the pool starts to decrease, so that metal is generated in the pool. The solidified shell is abnormally thickened due to the inclusion of the metal and the drum pressing force is increased to crush the depression.

Further, in addition to the above, when the metal is rolled up due to the disturbance of the operation or the like, and the metal is rolled up, the solidified shell becomes abnormally thick, the pressing force of the drum becomes large, and the depression is pushed. Crushed. At this time, in any case, when the pressing force per drum width exceeds 25 × 10 ⁴ N / m, the depression is crushed.

Therefore, the non-steady state means that the level of the molten metal in the tundish is maintained after the cooling drum is activated and makes one revolution, and after all the molten metal in the tundish is supplied to the molten metal. When the drum pressure exceeds the fluctuation range during the steady state and when the drum pressing force rises beyond the fluctuation range during the steady state due to the occurrence of metal inclusion.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a twin-drum type continuous casting apparatus 1 for carrying out the present invention. A pair of cooling drums 2 and 3, which are the main components of the twin-drum type continuous casting apparatus, are made of copper having a good thermal conductivity. It is made of copper alloy, is cooled by cooling water circulating inside, and is rotationally driven in opposite directions (directions of arrows) at the same rotational speed by a drive mechanism (not shown).

The entire area of the peripheral surfaces of the cooling drums 2 and 3 is plated with Ni or cobalt or an alloy thereof having a low thermal conductivity and excellent mechanical durability, and the plated surface is shot blasted or photo-coated. Many depressions are processed by etching, laser processing, or the like. The conditions of the depression differ depending on the type of cast steel and the like. For example, in the case of stainless steel, the average depth is 50 to 60 μm or more, the maximum depth is 100 μm or less, and the area ratio of the depression is 30% or more. In this case, the average depth is 60 to 70 μm or more,
The maximum depth is 200 μm or less, and the area ratio of the depressions is 30% or more.

In order to increase the wear allowance of the depression, it is desirable that the depression be deep, but if the depression depth exceeds the above value, high convex transfer corresponding to the depression occurs on the surface of the slab and the product has uneven gloss. Occurs, or flaws occur on the surface of the product after cold rolling. In addition, as a method of measuring the depression depth, for example, a replica is taken from the peripheral surface of the cooling drum, and the roughness is measured based on the replica.

The twin-drum type continuous casting apparatus 1 includes a pair of bearings 6, 6 and 7, 7 for rotatably supporting both ends of the shafts 4 and 5 of the cooling drums 2 and 3 (in FIG. 1, shafts 4 and 5 are shown). Shows only the bearings 6 and 7 on one end side of the above.
And a common frame 8 (shown in phantom) for supporting these bearings 6, 6 and 7, 7.
And the bearings 7 and 7 provided between the frame 7 and the frame 8, respectively.
And hydraulic cylinders 9 and 9 that respectively determine the positions with respect to the shafts 4 and 4, and a load detector (load cell) 10 that detects the load (reaction force) acting on the bearings 6 and 6, that is, the pressing force N / m per drum width. I have it.

The gap between the cooling drums 2 and 3 is determined by the positions of the bearings 7 and 7 defined by the hydraulic cylinders 9 and 9, and the main factor that determines the thickness of the thin strip 13 to be continuously cast. Becomes A pair of side dams (not shown) are pressed against both end faces of the cooling drums 2 and 3, and a hot water pool 11 is formed above the gap between the cooling drums 2 and 3.

The tundish 14 is provided in the hot water pool 11.
The molten metal pouring nozzle 15 is extended, and molten metal (generally, molten metal) is supplied to the molten metal pool portion 11 by the molten metal pouring nozzle 15. The molten steel supplied to the molten metal pool 11 is cooled on the peripheral surfaces of the cooling drums 2 and 3 to form a solidified shell 12,
When the cooling drums 2 and 3 are driven to rotate in the directions of the arrows, the solidified shell 12 passes through the drum closest point and receives a rolling-down force to become a thin strip slab 13, which is continuously fed downward.

When the continuous casting is performed, the cooling drum 3 is pressed toward the cooling drum 2 by the hydraulic cylinders 9, 9 so that the thin strip cast piece 13 (solidified shell 12) is formed.
A pressing force acts on the load detectors 10, 10 as a reaction force of a magnitude corresponding to the pressing force per drum width N / m.
Is detected by

The hydraulic system illustrated in FIG. 2 determines the position of the cooling drum 3 described above and, in order to apply the necessary rolling force to the strip casting 13, the hydraulic cylinders 9 mounted on the bearings 7, 7. It is composed of a hydraulic circuit for supplying pressure oil to 9. When the first chamber 20 and the second chamber 21 before and after the piston of the hydraulic cylinder 9 are connected to the hydraulic pump 25 via the servo valve 22 and the electromagnetic switching valve 24, and the electromagnetic switching valve 24 opens. In addition, the servo valve 22 adjusts the pressing force N / m per drum width in a steady state to receive the supply of pressure oil.

The first chamber 20 and the second chamber 2 of the hydraulic cylinder 9
1 is communicated when the electromagnetic switching valve 26 is opened. The second chamber 21 can release the pressure oil to the reserve tank 29 via the electromagnetic switching valve 27 and the pressure reducing relief valve 28, so that the second chamber 21 can be maintained at the set hydraulic pressure. The servo valve 22 and the electromagnetic switching valves 24, 26 and 27 are all controlled by a controller (not shown).

A second hydraulic pressure supply path 32 including an accumulator 31 is provided in parallel with the path 30 in addition to the first hydraulic pressure supply path 30 for supplying pressure oil via the electromagnetic switching valve 24 and the servo valve 22. ing. Second hydraulic pressure supply path 32
Is connected in series with the electromagnetic switching valve 33 and the electromagnetic switching valve 34 to connect the hydraulic pump 25 and the first chamber 20 of the hydraulic cylinder 9 to reduce the pressure between the electromagnetic switching valve 33 and the electromagnetic switching valve 34. The relief valve 23 and the accumulator 31 are connected.

The accumulator 31 compresses an air chamber or an elastic body formed inside the accumulator 31, and has a pressure accumulating function of temporarily accumulating the pressure oil acting on the second hydraulic pressure supply path 32, thereby rapidly increasing the pressure oil. With a buffer function to relieve
It is also called a shock absorber,
The capacity is 2 times the pushing force per drum width
It is set to be 5 × 10 ⁴ N / m or less. The pressure reducing relief valve 23 includes a switching valve that sets the hydraulic pressure between the pressure reducing relief valve 23 and the hydraulic cylinder 9. The electromagnetic switching valves 33 and 34 are controlled to open and close by a control device (not shown).

The hydraulic cylinder 9 is a bearing 7 for the cooling drum,
There are also 2 hydraulic circuits provided in each of the 7
Although each hydraulic cylinder 9 is provided, for example, the hydraulic pump 25 or the like can be shared between the two hydraulic circuits.

Next, the operation of this apparatus will be described. Of the casting of thin strip cast using twin drum continuous casting equipment,
In a constant state, in order to suppress the wedge amount of the thin strip slab to a low level, a pair of hydraulic cylinders 9 that support both ends of the shaft 5 of the cooling drum via bearings 7 move in unison, and the cooling drums 2 and 3 move. By maintaining the parallel state, the pressing force per width of the cooling drum is controlled to 0.1 to 7 × 10 ⁴ N / m so that the thickness of the thin strip slab has the same value in the width direction.

That is, the control device opens the electromagnetic switching valve 24 and at the same time closes the electromagnetic switching valves 26, 27, 33 and 34 so that the accumulator 31 in the second hydraulic pressure supply path 32 is supplied. The communication is cut off and the first hydraulic pressure supply passage 30 is connected. In this state, the control device controls the servo valve 22 to control the first chamber 20 of the hydraulic cylinder 9.
The pressure oil in the second chamber 21 is adjusted, and the thickness of the strip slab 13 is adjusted by moving it back and forth while keeping the position of the cooling drum 3 parallel to the cooling drum 2 via the bearing 7. .

Among the continuous casting of thin strip slabs using the twin drum type continuous strip casting apparatus, the operation is carried out as follows in the unsteady state. In the non-steady state, the weight scale (not shown) detects that the molten drum in the tundish 14 has run out until the cooling drum is activated and makes one revolution, and then the molten metal level in the molten metal pool 11 is detected. It is assumed that the fluctuation range during steady casting is reduced and the pushing force per drum width detected by the load detector rises beyond the fluctuation range during steady state.

The electromagnetic switching valve 24 is activated until the cooling drum starts up and makes one revolution, and when the non-steady state is detected as described above.
And the electromagnetic switching valve 27 is closed (OFF), the relief circuit by the first hydraulic pressure supply path 30 and the relief valve 28 is cut off, and the electromagnetic switching valves 33 and 34 are opened (ON).
The pressure oil of the hydraulic pump 25 is supplied to the second hydraulic pressure supply path 3
2 is supplied to the first chamber 20 of the hydraulic cylinder 9.

At this time, when the electromagnetic switching valve 26 is also opened, the first chamber 20 and the second chamber 21 of the hydraulic cylinder 9 are communicated with each other, and the pressurized oil is simultaneously supplied to the second chamber 21. The effective area of the front and back of the piston 35 of No. 9 is the first chamber 20 is the second chamber 21 by the cross-sectional area of the piston rod 36.
The bearing 7 and the shaft 5 are pressed to the left in FIG. 2 by the relatively small force generated by the difference in their areas.

When the metal or the like passes through the gap between the cooling drums 2 and 3, the reaction force acting on each bearing and the corresponding hydraulic pressure in the second hydraulic pressure supply path 32 also try to rise rapidly, but the cooling drum 3 In addition to the relatively small force for pressing the valve toward 2, as described above, since the pressure reducing relief valve 23 and the accumulator 31 are provided in the second hydraulic pressure supply path 32, the metal is cooled. The sudden increase in hydraulic pressure that occurs when passing through the gap between the drums 2 and 3 is absorbed by the accumulator 31. As a result, the gap between the cooling drums 2 and 3 opens without great resistance, allowing the metal to pass easily. Therefore, it is possible to reliably prevent damage to the peripheral surface of the cooling drum caused by the passing of the metal or the like through the gap between the cooling drums 2 and 3.

FIG. 3 shows a load detector 10 when 500 ton strip casting of SUS304 stainless steel strip having a plate thickness of 3.5 mm is continuously cast using the twin drum type continuous casting apparatus shown in FIGS. 1 and 2. 3 shows the relationship between the pressing force per drum width (N / m) detected in the steady state and the non-steady state and the corresponding wear amount of the depression. In FIG. 3, the pressing force per drum width in the steady state is 7 × 10 ⁴ N /
If it exceeds m, the drum pressing force during non-steady state is 25 × 1
When it exceeds 0 ⁴ N / m, the depth of the depression is drastically reduced, and the depression does not perform its function. Therefore, it is necessary that the drum pressing force in the steady state is 7 × 10 ⁴ N / m or less and the drum pressing force in the non-steady state is 25 × 10 ⁴ N / m or less.

In the above description, the cast steel type is SUS3.
Although 04 stainless steel was used, the present invention can be applied to other steel types such as ordinary steel.

[0035]

EXAMPLE A SUS304 stainless steel strip cast having a plate thickness of 3.5 mm was cast by the twin-drum type continuous casting apparatus shown in FIGS. 1 and 2, and then cold rolled to obtain a sheet having a plate thickness of 0.5 mm. Manufactured the product. Width 1000 when manufacturing thin strip
mm, the peripheral surface of a cooling drum having a diameter of 1200 mm was processed by shot blasting to form recesses having an average depth of 65 μm or 70 μm.

Table 1 shows the casting conditions other than the above and the surface properties of the obtained strip casting. In addition, the occurrence of thin strip slab cracking in Table 1 was judged again by visual observation after pickling the obtained thin strip plate and further by visual observation after cold rolling. Further, FIGS. 4, 5, 6 and 7 show typical changes with time of the drum pressing force and the crack generation amount of the thin strip cast. Fig. 4 shows the experimental example No. 1,
Fig. 5 shows the experimental example No. 7 and FIG. 8 and FIG. 10 is an example.

[0037]

[Table 1]

In Table 1, when the drum pressing force in the steady state is set to more than 7 × 10 ⁴ N / m, the recess on the drum peripheral surface after the casting wears beyond the lower limit value (50 μm),
Along with that, cracks occurred on the surface of the slab corresponding to the latter half of casting. Also, the drum pushing force is 25 × at the start of casting.
When it exceeds 10 ⁴ N / m, surface cracking occurs in the entire length of the slab, and when it exceeds 25 × 10 ⁴ N / m after the start of casting, the slabs cast after that Cracks occurred on the surface.

[0039]

According to the present invention, in a strip cast using a twin-drum type continuous casting apparatus, surface damage of the strip cast can be prevented by preventing damage to the depression provided on the peripheral surface of the cooling drum. Since this can be prevented, the life of the drum can be extended and a slab with good surface quality can be manufactured.

[Brief description of drawings]

FIG. 1 is a partial sectional side view showing a main part of a twin-drum type continuous casting apparatus for carrying out the present invention.

2 is a circuit diagram of a hydraulic system provided in the device shown in FIG.

FIG. 3 is a diagram showing a relationship between a pressing force per drum width and a wear amount of a dent in the drum in a steady state and a non-steady state.

FIG. 4 is a diagram showing a drum pressing force (A) and a slab surface crack generation amount (B) corresponding to a casting length in a comparative example.

FIG. 5 is a diagram showing a drum pressing force (A) and a slab surface crack generation amount (B) with respect to a casting length in another comparative example.

FIG. 6 is a view showing a drum pressing force (A) and a cast slab surface crack generation amount (B) with respect to a casting length in another comparative example.

FIG. 7 is a diagram showing a drum pressing force (A) and a slab surface crack generation amount (B) with respect to a casting length on the present invention side.

[Explanation of symbols]

 1 ... Twin-drum type continuous casting device 2, 3 ... Cooling drum 4, 5 ... Cooling drum shaft 6, 7 ... Bearing 8 ... Frame 9 ... Hydraulic cylinder 10 ... Load detector 11 ... Melt pool 12 ... Solidification shell 13 ... Thin strip slab 14 ... Tundish 15 ... Pouring nozzle 20 ... First chamber of hydraulic cylinder 21 ... Second chamber of hydraulic cylinder 22 ... Servo valve 23, 28 ... Decompression relief valve 24, 26, 27, 33, 34 ... Electromagnetic switching valve 25 ... hydraulic pump 29 ... reservoir tank 30 ... first hydraulic pressure supply path 31 ... accumulator 32 ... second hydraulic pressure supply path 35 ... piston

Claims (1)

[Claims] 1. A molten metal is supplied to the peripheral surfaces of a pair of cooling drums, the peripheral surfaces of which are plated and a large number of depressions are formed on the surface of the plating, and the molten metal is solidified on the peripheral surface of the cooling drum. In a method of continuously producing a solidified shell and continuously applying a pressing force to the solidified shell by the pair of cooling drums to form a thin strip slab, the pressing force per drum width in the steady state of the continuous casting is 7 × 10. Control to ⁴ N / m or less,
Pressing force per drum width at non-steady state is 25 × 10 ⁴
A continuous casting method for thin strip castings, which is controlled to N / m or less.