KR100977781B1 - Initial casting method for stable casting in twin roll strip casting - Google Patents

Abstract

The present invention relates to an initial casting stable operation method of a twin-roll sheet casting machine, In the initial casting stable operation method of a twin-roll sheet casting machine; The direction in which the thickness is increased from thinner than the target thickness by increasing the ratio of the molten steel height reaching time than the casting speed reaching time until the speed of the initial casting roll and the molten steel height reach the target value and are cast in the normal state. It provides a stable initial casting operation method of the twin-roll sheet caster, characterized in that the casting to be controlled while controlling.

According to the present invention, by intentionally adjusting the movement of the initial casting roll to prevent the skull formed in the edge dam is easily dropped, thereby preventing the mixing in the cast steel, thereby improving the quality of the cast steel as well as achieving the stabilization of the casting initial equipment To provide the effect.

Initial casting, stabilization, edge scull, edge dam, casting roll, mixing

Description

INITIAL CASTING METHOD FOR STABLE CASTING IN TWIN ROLL STRIP CASTING}

The present invention relates to an initial casting stable operation method of a twin-roll sheet caster, and more specifically, to control the casting speed and the molten steel height to adjust the flow direction of the casting roll to prevent the mixing of scum into the initial cast slab edge portion of the initial casting The present invention relates to a method of stable initial casting of a twin roll sheet casting machine to ensure stability.

In general, a twin-roll thin sheet casting process supplies molten steel through a molten steel supply nozzle between a pair of casting rolls being cooled to rotate the casting rolls in a direction facing the casting rolls while maintaining a constant height of the molten steel pool. The shell is coalesced at near points between the casting rolls to form a cast steel, for example, a process of continuously producing thin sheets directly from molten steel.

For example, as shown in FIG. 1, edge dams 12 for preventing the outflow of the molten steel 14 are installed at both sides of the pair of casting rolls 10, and the casting rolls 10 are provided through the molten steel supply nozzles 16. The molten steel 14 supplied therebetween is cooled while being in contact with the casting roll 10 which is water-cooled, and the edge dam 12 is also cooled while being in contact with the casting roll 10, so that heat loss of the molten steel occurs at these contacts. This makes molten steel easy to solidify.

However, as shown in FIG. 2, the edge scull 20 is generated during the solidification of the molten steel at the movable surface of the edge dam 12, and grows on the surface of the edge dam 12. Locally dissolved and reduced in size or completely dissolved and removed, however, the skull formed at the beginning of casting is large in size and is not easily melted, so that if the skull is incorporated into the edge of the slab 18, the casting roll 10 is pressed down. The force is sharply increased to open the roll gap, and in severe cases, the edge dam 12 does not come into contact with the casting roll 10, thereby causing casting instability.

As a solution to this problem, Japanese Patent Laid-Open No. 2001-150106 discloses that a metal tube is installed at the lower end of the edge dam to prevent solidification of molten steel by injecting an inert gas from the lower end of the edge dam through the tube.

However, this method still has the disadvantage of suppressing edge scull in the steady state after the start of casting, but it still has the disadvantage that it is virtually impossible to completely suppress the scull formed by contact with molten steel at the initial temperature reduction of the casting edge dam.

That is, in the initial casting time, the casting roll speed continues to increase to the target speed, and the casting thickness is continuously changed until the supplied molten steel reaches the target height.

Here, the casting thickness is determined by the contact time between the casting roll and the molten steel. In this transitional state, the casting thickness is not constant, so most of the parts have no value as a product, so the casting speed and the molten steel height are preferably maintained to maintain a steady state. It should rise quickly.

However, if the casting parameters of the initial casting speed and the molten steel height are determined only in terms of fast securing to a steady state, serious problems may arise due to the mixing of the skull formed in the edge dam.

For example, if the target molten metal height is 20 seconds and the target casting speed is 15 seconds, after 15 seconds, only the molten steel height is increased while the casting speed is constant, so the contact time between the casting roll and the molten steel is between 15 seconds and 20 seconds. Since the casting thickness is increased to increase the casting roll 10 as shown in Figure 4 flows in the opening direction.

On the other hand, the target molten steel height reaching time is 20 seconds and if the target casting speed reaching time is 30 seconds, the casting speed is continuously increased while the molten steel height is constant between 20 seconds and 30 seconds, so the contact time between the casting roll and the molten steel is increased. Since the casting thickness is shortened to reduce the casting roll 10, the casting roll 10 flows in a direction in which the roll gap is narrowed as shown in FIG. 3.

That is, in the case of FIG. 4, the casting roll 10 is moved in the direction opposite to the edge skull which is already formed, and in the case of FIG. 3, the casting roll 10 is moved toward the edge scull. Due to the physical impact on the edge skull will cause a problem of mixing due to the dropping of the skull.

The present invention has been made in view of the above-mentioned problems in the prior art, and has been created to solve this problem. By adjusting the initial casting steel height and casting speed appropriately, the initial casting variable is increased in the direction of increasing the contact time between the casting roll and the molten steel. Initial control operation method of twin roll type sheet casting machine to improve the instability of the initial casting operation by preventing falling of the edge skull attached to the edge dam generated at the beginning of casting by preventing the mixing into the cast steel. There is a major challenge in providing it.

The present invention as a means for achieving the above object, in the initial casting stable operation method of the twin-roll sheet caster; The direction in which the thickness is increased from thinner than the target thickness by increasing the ratio of the molten steel height reaching time than the casting speed reaching time until the speed of the initial casting roll and the molten steel height reach the target value and are cast in the normal state. It provides a stable initial casting operation method of the twin-roll sheet caster, characterized in that the casting to be controlled while controlling.

At this time, the ratio of the casting speed reaching time and the molten steel height reaching time is also characterized in that 1: 1.2-1.3.

According to the present invention, by intentionally adjusting the movement of the initial casting roll to prevent the skull formed in the edge dam is easily dropped, thereby preventing the mixing in the cast steel, thereby improving the quality of the cast steel as well as achieving the stabilization of the casting initial equipment To provide the effect.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment according to the present invention.

4 is an exemplary principal cross-sectional view showing the movement of the casting roll by the method according to the invention.

As shown in Figure 4, the present invention is to adjust the contact time between the casting roll and the molten steel in the direction of increasing the casting time until the initial casting roll 10 speed and the molten steel height reaches a steady state.

That is, in FIG. 4, the casting roll 10 moves away from the initial casting to the steady state in the direction of the arrow with respect to the center of the edge dam 12, that is, the casting roll 10 is minutely flowed in the opening direction. To control it.

In this case, the casting speed of the casting roll 10 to be considered is determined by the ability of the motor to rotate it, and it is common to increase the casting pressure drop for the purpose of stable bonding of the initial casting strip and the cast steel, but a lot of torque Since is required, there is a limit in maintaining the casting rate increase rate of the casting roll higher than a certain level.

In addition, if the speed gradient of the casting roll 10 is too fast, the difficulty of the discharge operation of the rear end of the casting roll 10 for drawing the casting material is also increased, making the casting operation very difficult.

Therefore, the casting speed of the casting roll 10 is preferably adjusted as quickly as possible within the range that does not harm it in consideration of securing the performance of the motor and the stability of the discharge operation.

In other words, the molten steel height is slowly increased relative to the speed of the initial casting roll 10 to operate in the direction of increasing the contact time between the molten steel and the casting roll 10, and the preferred ratio is a target casting speed reaching time: It is particularly preferable that the ratio of the target molten metal height reaching time is in the ratio of 1: 1.2 to 1.3.

The reason for limiting such a ratio is because, as described above, the contact time between the casting roll 10 and the molten steel can be increased while fully considering the aspects of motor performance and securing stability of discharge operation. This is because the phenomenon shown in FIG. 4 can be induced only within the ratio.

In particular, if the ratio exceeds the roll gap between the casting rolls 10 is rapidly increased, the initial casting is difficult, if it is maintained below the interest rate, the present invention can not achieve the desired object.

Hereinafter, an Example is described.

In order to confirm the effect when the method according to the present invention is applied, cast roll diameter 1250mm, cast roll width 1300mm, and the material of the sleeve is copper alloy and the surface of the cast roll are plated with 1-2mm nickel to confirm the effect when applying the method according to the present invention. Was used.

In addition, the molten steel height of the steady state was 450mm, the casting speed was 40m / min, 132m / min.

Thus, the average of the values tested several times is shown in Table 1, and the casting failure rate due to the mixing of the initial casting edge scull according to the height adjustment of the molten steel and the rate of rise of the casting roll during the casting are calculated. As shown in Fig. 1, the casting failure rate was calculated as the rate at which the casting was not completed at the time of 100 ton casting by the initial casting of the edge skull.

division Target casting speed 40m / min Target casting speed 132m / min Molten steel height
Time to reach Target speed
Time to reach casting
Disability rate Molten steel height
Time to reach Target speed
Time to reach casting
Disability rate Conventional example 18 seconds 7 sec 1.1% 18 seconds 40 seconds 30.4% Inventive Example 18 seconds 7 sec 1.1% 45 sec 40 seconds 1.8%

(At this time, the conventional example is an example according to the constant casting speed increase rate and the molten steel height control irrespective of the target casting speed, the invention example is an example of slowly increasing the molten steel height in the scope of the present invention, unlike the prior art in the case of high-speed casting)

As shown in Table 1, in the case of low speed casting, there is no significant difference in the conventional example or the invention example, but in the case of high speed casting, it was found that the casting failure rate was remarkably different, and thus the method of the present invention was confirmed to be very effective. It was.

1 is a perspective view showing a main part showing a thin plate casting example using a general thin cast machine,

2 is a schematic diagram showing a process of forming the initial edge skull around the edge dam in accordance with the prior art,

Figure 3 is an exemplary cross-sectional view showing the movement of the initial casting roll casting according to the prior art,

Figure 4 is an exemplary principal cross-sectional view showing the movement of the casting roll by the method according to the present invention.

♧ description of the symbols for the main parts of the drawing ♧

10..Casting Roll 12 .... Edge Dam

20 .... Escal

Claims (2)

In the initial casting stable operation method of the twin-roll sheet casting machine; The direction in which the thickness is increased from thinner than the target thickness by increasing the ratio of the molten steel height reaching time than the casting speed reaching time until the speed of the initial casting roll and the molten steel height reach the target value and are cast in the normal state. To be controlled while casting, The ratio of the casting speed reaching time and the molten steel height reaching time is 1: 1.2 ~ 1.3 casting initial stable operation method of the twin-roll sheet casting machine. delete

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