JPH0551386B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention rotates twin rolls, which are arranged parallel to each other and appropriately spaced apart, in directions facing each other, and pours molten steel into a pool on the twin rolls. This relates to a twin-roll continuous casting method in which steel sheets are continuously cast between rolls while cooling the steel.

[Prior art] In the twin-roll continuous casting method, a molten metal pool is formed on two cooling rolls placed in parallel with each other at an appropriate interval, molten steel is supplied to the molten metal pool, and the molten steel is poured into the molten steel in the molten metal pool. The molten steel is cooled on the surface of the cooling roll that is in contact with the steel, forming a solidified shell on the surface, and both solidified shells are combined and discharged from the gap between the rolls to continuously cast steel plates of constant thickness. be.

By the way, conventionally, when forming a molten metal pool on twin rolls, it is formed into a substantially rectangular shape with side seal plates that cover both end faces of the rolls and a barrel weir extending in the axial direction at the top of the rolls, and the molten steel in the molten metal pool is We are ensuring that there is sufficient quantity. If you form a pool of water with the side seal plate and barrel weir like this,
A constant solidified shell is always formed on the surface of the cooling roll up to the barrel weir and the roll gap, and by appropriately replenishing the molten steel into the molten metal pool, it becomes possible to cast a plate of approximately constant thickness.

However, if the amount of molten steel is large, the amount of heat of the molten steel will be large, and the cooling rate will not be constant, which will adversely affect the growth of the solidified shell. In addition, coagulated substances tend to accumulate and grow in the contact area between the barrel weir and the rolls, and when this is combined with the solidified shell and discharged, a problem arises in that it has an adverse effect on the plate thickness.

[Problems to be Solved by the Invention] Therefore, as shown in FIG. A molten steel pool 3 is formed on the surface of the roll 1, and molten steel 4 is poured into the pool 3, and while it is cooled by the twin rolls 1 and 1, the rolls 1 are moved in directions facing each other as shown by the arrows in the figure. A method has been proposed in which the steel plate 6 is continuously discharged from the roll gap 5 between the rolls 1 and cast.

The casting method shown in FIG. 1 has the advantage of eliminating the above-mentioned conventional problems since there is no barrel weir.

However, the molten steel 4 accommodated in the molten pool 3
As the capacity of the plate decreases, the liquid level fluctuates widely, making it difficult to control the plate thickness.

If the rolling force and roll rotation speed of the cooling roll 1 are constant, the thickness of the steel plate to be cast is mainly determined by the height of the liquid level of the molten steel 4 in the molten metal pool 3. In other words, if the liquid level is high, the solidified shell becomes longer and the contact time between the molten steel 4 and the cooling roll 1 increases, resulting in a thicker steel plate being cast.If the liquid level is low, the solidified shell becomes longer. becomes shorter, the contact time between the molten steel 4 and the cooling roll 1 becomes shorter, the cooling rate becomes slower, and the thickness becomes thinner.

Conventionally, in order to pour molten steel into a tundish, the molten steel in a ladle is first received in a tundish, and then poured from the tundish into the tundish. This pouring is not done continuously but at intervals.

In this case, if the volume of the molten pool is made large as in the past, changes in the plate thickness will have no effect on fluctuations in the liquid level, but as shown in Figure 1, the volume of the molten pool 3 is small and the molten steel is As the liquid level increases or decreases, the length of the solidified shell that is formed changes, which directly results in changes in the plate thickness. For this reason, it is conceivable to pour the metal continuously so that the liquid level is always constant, but it is difficult to control the liquid level to be constant.

SUMMARY OF THE INVENTION An object of the present invention is to provide a twin-roll continuous casting method that can always cast a steel plate with a uniform thickness even if the height of the molten steel in the pool changes.

[Problems to be Solved by the Invention] The present invention provides side seal plates on both end surfaces of both rolls that are rotatably provided parallel to each other while being appropriately spaced apart, and a pool is formed by the side seal plates and the roll surfaces. Then, pour molten steel into the pool,
In this method, a solidified shell is formed on the roll surface from the liquid level of the molten steel to the roll gap, and both solidified shells are joined and discharged from the roll gap to continuously cast a steel plate. Determine the height h from the center of the roll to the liquid surface, determine the cooling angle θ at which the solidified shell is formed from the height h, and determine the appropriate rotational speed N of the roll from that cooling angle.
is determined, and the rotational speed of the twin rolls is controlled so that the appropriate rotational speed N is obtained according to the height h.

[Effect]

According to the above configuration, the height h of the liquid level of molten steel is detected by, for example, ultrasonic waves, the appropriate rotational speed N at the liquid level height h is determined, and the twin rolls are rotated so that the appropriate rotational speed N is achieved. By controlling the rotation, i.e., increasing the rotation speed of the roll when the liquid level height h is high and slowing the rotation speed of the roll when the liquid level height is low, the thickness of the steel plate cast from the roll gap can be increased. can be controlled so that it is always uniform.

[Example] A preferred example of the twin-roll continuous casting method according to the present invention will be described below with reference to the accompanying drawings.

In FIG. 2, cooling rolls 1 are provided parallel to each other with a roll gap 5, and a rotating device (not shown) for rotating the rolls 1 in directions facing each other is connected to the cooling rolls 1. .
This rotation is configured such that the rotation speed of the device roll 1 can be variably adjusted. A cooling device (not shown) is provided inside the cooling roll 1 to cool the surface of the cooling roll 1.
is provided.

Side seal plates 2, 2 are provided on both end surfaces of the twin rolls 1, 1, and a pool 3 of molten steel 4 is formed on the opposing surfaces of the twin rolls 1, 1.

The height of the liquid level in the pool 3 is detected by a height detector 7 using ultrasonic waves, etc., and the detection signal is transmitted to a computing device (not shown), which then transmits it to the rotating device to rotate the roll 1. Speed is controlled.

The relationship between the liquid level height of the molten steel 4 and the rotational speed of the roll 1 will be explained in more detail.

As shown in Figure 2, molten steel 4
is poured, the molten steel 4 is cooled by the cooling roll 1, forms a solidified shell 8 on the surface of the cooling roll 1, and both solidified shells 8 are joined and discharged from the roll gap 5 as a cast steel plate 6. Ru. In this case, the thickness of the solidified shell 7 gradually increases from a point 9 where it contacts the cooling roll 1 on the surface of the molten steel 4 to a tight point 10 where both solidified shells 8 are joined to each other. Now, if the rolling force of the cooling roll 1 is constant and is the minimum value that allows both solidified shells 8 to be joined, the tight point 10 is on the line connecting the center O of the cooling roll 1,
That is, it is formed at the position of the roll gap 5 and is kept in that position during casting. Therefore, since the line connecting the tight point 10 and the center O of the cooling roll 1 coincides, the height h of the liquid level of the molten steel 4 can be expressed as the distance from the center O of the roll 1 to the liquid level, and The effective cooling length of the cooling roll 1 that cools the molten steel 4 is from the point 9 where solidification begins to the line connecting the center O (Kitus point 10). Therefore, the cooling angle θ from this point 9 to the line connecting the center O is expressed by the following equation, where D is the diameter of the roll 1.

θ=sin ^-1 (2h/D)...(1) Also, if the rotational speed of the roll 1 is N [rpm] and the thickness of the solidified shell 8 at the hard point 10 is δ, then the rotational speed N and the solidified thickness δ are The relationship is expressed by the following equation.

N=θA ² /6δ ² …(2) However, in the above equation (2), A is the coagulation coefficient [mm/
sec ^1/2 ].

Now, if the thickness of the steel plate 6 to be cast is t, the solidification thickness δ at the kitsu point 10 and the plate thickness t are δ=t/2
Therefore, by substituting this into equation (2), we get N=θA ² /3t ² ...(3).

In other words, from equation (3), if the rotation speed N of the roll 1 is constant, as the cooling angle θ decreases, the thickness t of the steel plate 6 also decreases, that is, as can be seen from the equation, the height h of the liquid level of the molten steel 4 As the height h of the liquid level increases, the plate thickness t decreases.
It can be seen that it also becomes larger.

Therefore, the above (1) and (3) are applied to the arithmetic device (not shown) in advance.
The formula is input in advance, the height of the liquid level of the molten steel 4 is detected by the height detector 7, the detection signal is input to the above-mentioned calculation device, the calculation device calculates the appropriate rotational speed N, and then The calculation output is transmitted to the rotating device for the twin rolls 1, 1, and the roll 1 is adjusted to an appropriate rotational speed N.

As described above, the steel plate 6 cast and discharged from between the rolls 1 can always have a constant thickness despite changes in the liquid level of the molten steel 4.

Also, a tight point 10 where the solidified shells 8 are joined to each other.
A part of the solidified shell 8 protrudes above and receives the heat of the molten steel 4 to form a so-called pine phase 11 which becomes a semi-solid body. As the solidified thickness δ increases above the Kitsu point 10, the growth of the Matushi phase 11 is promoted and becomes gigantic. Since the cooling roll 1 itself has a lower rigidity than a reduction roll or the like, when the above-mentioned pine phase 11 becomes large, it gets caught in the roll gap 5 and is ejected, and the cross section of the cast steel plate 6 is shaped like a snake. A steel plate with an abnormally thick part that looks like an egg has been swallowed will be cast, but since the rotational speed of the roll 1 is controlled according to the liquid level of the molten steel 4 as described above, the hardness point 10 In this way, the solidification thickness can be controlled, the growth of the pine phase can be prevented, and the problem of casting a steel plate with an abnormally thick part can be solved at the same time.

[Effects of the Invention] As is clear from the detailed description above, the present invention exhibits the following excellent effects.

(1) By forming a pool of molten steel between the side seal plate and the roll surface and controlling the rotational speed of the roll according to the height of the molten steel level in the pool, changes in the thickness of the steel plate due to changes in the liquid level can be prevented. It is possible to always cast steel plates with a constant thickness.

(2) Since the rotation speed of the roll can be controlled, it is possible to suppress the growth of the pine phase at the point where the solidified shells on the surface of the roll intersect with each other, and it is possible to prevent the occurrence of abnormal plate thickness due to the pine phase encroachment. .

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a twin-roll continuous casting apparatus, and FIG. 2 is a front sectional view showing an embodiment of the apparatus for carrying out the twin-roll continuous casting method according to the present invention. In the figure, 1 is a roll, 2 is a side seal plate, 3 is a molten metal pool, 4 is molten steel, 6 is a roll gap, and 7 is a height detector.

Claims (1)

[Claims] 1 Side seal plates are provided on both end surfaces of twin rolls that are rotatably provided parallel to each other while being appropriately spaced apart, a molten metal pool is formed between the side seal plates and the roll surfaces, and molten steel is poured into the molten metal pool. In this method, a solidified shell is formed on the roll surface from the liquid level of the molten steel to the roll gap, and both solidified shells are joined and discharged from the roll gap to continuously cast a steel plate. Find the height h from the center of the roll to the liquid level, and from that height h,
The cooling angle θ at which the solidified shell is formed is determined, the appropriate rotational speed N of the rolls is determined from the cooling angle, and the rotational speed of the twin rolls is controlled so as to reach the appropriate rotational speed N according to the height h. Twin roll continuous casting method.