JPS63188464A - Method for controlling casting velocity in continuous casting - Google Patents

Abstract

PURPOSE:To improve the productivity by assuming a roll alignment by finding drawing resistance of a cast slab from load of pinch roll driving motor and finding the limited casting velocity based on relation between the steel component and the casting velocity. CONSTITUTION:Load meters 7 of each ammeter, etc., are arranged to each driving motor 6 of the pinch rolls 5 and connected to a casting velocity control device 8. Further, the casting velocity detector 10 is arranged to the pinch roll 5 and this output signal is inputted in the control device 8. The control device 8 operates the cast slab drawing resistance F based on the signals from the load meter 7 and the detector 10. The roll alignment is assumed corresponding to change of drawing resistance F and the velocity of the pinch rolls 5 is controlled so as not to exceed the limited casting velocity obtd. by the relation between the steel component and the casting velocity. Safety operation is secured and as sufficient measure can be executed to a sudden accident, the productivity of casting is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a casting speed control method in continuous casting.

[Conventional technology]

In a continuous casting machine, the solidified shell is supported by pinch rolls in order to pull out the slab during solidification, thereby suppressing the occurrence of bulging due to static pressure. For this reason, the roll spacing is usually arranged in advance to prevent bulging strain from occurring, taking into account the allowance for solidification and shrinkage of the slab.

However, after many years of use or unexpectedly during operation, rolls may bend or fall due to damage to the support bearings, resulting in roll alignment irregularities, and when this happens, bulging distortion in that area becomes large. This mainly causes internal cracking of the slab and the inability to pull it out.

Therefore, conventionally, in order to avoid such unstable operation and to obtain the required quality, the limit of the casting speed has been set in consideration of the safety factor.

Moreover, as mentioned above, since it is important to manage roll alignment, roll alignment has been measured using a dedicated measuring machine or jig when the operation is stopped.

[Problem that the invention seeks to solve]

However, in the conventional method described above, measuring the roll alignment when the operation is stopped and operating the casting speed while considering the safety factor based on this results in a reduction in the safety factor and the casting speed, which improves productivity. inferior to

Furthermore, even if the casting speed is set with a safety factor in mind, if a sudden accident during operation causes major alignment irregularities, the safety factor will be exceeded and unexpected troubles will occur. .

Therefore, the main object of the present invention is to provide a casting speed control method that allows operation at the highest possible casting speed, thereby improving productivity, and that can sufficiently cope with unexpected accidents during casting. There is a particular thing.

[Means for solving problems]

In order to solve the above-mentioned problems and achieve the above-mentioned objects, the present invention calculates the pull-out resistance of the slab from the load of the pinch roll drive motor of the continuous casting machine, estimates the roll alignment of the pinch rolls from this value, Based on this estimated alignment and the casting safety determined by the relationship between the casting speed and steel composition determined in advance, a critical casting speed that ensures casting safety is determined, and this critical casting speed is not exceeded. The present invention is characterized in that the speed of the pinch roll is controlled in such a manner.

[For production]

According to the findings of the present inventors, it has been found that the load (current) of the pinch roll does not have an exact one-to-one correspondence with the roll alignment, but is substantially proportional to the roll alignment. Therefore, if you know the load on the pinch roll, you can know the roll alignment.

On the other hand, bulging strain 8. are molten steel static pressure P, Young's modulus E,
Casting distance, solidification coefficient K, roll pitch! , casting speed■
. However, except for Young's modulus E and casting speed ■ゎ, the other parameters are uniquely determined by the continuous casting equipment, so it can be seen that there are only two essential parameters. Therefore, the relationship εboqVc/H holds true. Young's modulus E is determined by the molten steel temperature Tc and the surface temperature T.
5 and can be expressed as an E (TL, T, ) function.

In order to prevent the bulging strain εb from exceeding the slab internal crack limit value εcri, it is necessary to satisfy εb≦εC+′iL. If ε, = εCr1L, the maximum casting speed V erit is Vcrtt (X: εcrrt
' satisfies the relationship E. Here, since eCrit is a constant, it satisfies the relationship VerttOCE, and V IFi
L is governed by two parameters. Therefore, ■ to prevent internal cracks. Since it is sufficient to satisfy ≦V Cr i L, the casting speed V can be determined based on the parameters TL and T.

In this way, the casting speed can be determined by knowing T and T, but the basis for such matters is the known roll alignment, roll spacing, and roll pitch. It is assumed that it remains unchanged.

However, such roll alignment can be determined by knowing the load on the pinch rolls according to the above-mentioned knowledge.

On the other hand, the slab internal cracking limit value εC18 is determined by the molten steel composition (C,
Since it is determined from the Si, Mn, S) values,
It can be known in advance before continuous casting based on the component analysis values in the converter, and can be regarded as a constant.

Therefore, by primarily monitoring the load on the pinch roll drive motor and the steel composition, operation at maximum casting speed is possible.

〔Example〕

The present invention will be explained in more detail below with reference to Examples.

Figure 1 shows the equipment for carrying out the method of the present invention, in which molten steel from a ladle 1 is poured into a tundish 2 and then into a mold 3, and a slab 4 passing through a cooling zone is transferred to pinch rolls. 5. It is extracted by 5...

In the present invention, a load meter 7 such as an ammeter is installed in order to know the load on the drive motor 6 of each pinch roll, and the signals thereof are taken into the casting speed control device 8.

In addition to the above-mentioned information such as molten steel static pressure and pouring distance, the pouring speed control device 8 stores molten steel composition analysis values (C.

External information 9 such as Si, Mn, S, P) is given.

Furthermore, in order to know the current casting speed, the pinch roll is provided with a casting speed detector 10, and its signal is input to the casting speed control device 8.

In such equipment, the casting speed control device 8 determines the slab pull-out resistance F according to equation (11) based on the signals from the load meter 7 and the casting speed detector IO.

Here, PM: Motor load, ■c: Casting speed, K:
It is a constant.

If such slab pull-out resistance F is known, the roll alignment can be evaluated because there is a 1:1 correspondence between the amount of roll alignment irregularity and the pull-out resistance increment as shown in FIG.

Note that the roll misalignment amount is a deviation of the roll surface position from the reference roll surface position. Furthermore, when there are multiple pairs of pinch rolls, the roll alignment may be evaluated using the sum of the pull-out resistances.

During continuous casting, the casting control device 8 determines in advance the slab internal cracking limit value εcrit based on the component analysis values (C, Si, Mn, S, P) from the converter. Limit value ε
criL is generally determined by the following formula.

εcrtt=2.26X10-' (Ceq5)-”
” (S) −”” ・−・(tlIdanshiCeq5=(
C%) + (Si%)/7+(Mn%) 15 (% is weight %).

That is, the limit value is greatly influenced by the component value, especially (S).

Figure 2 shows the safety range in which internal cracking of the slab or inability to pull out occurs based on the relationship between the component analysis value [S] in particular and the casting speed VC (provided that [C]≦0. 08%).

As is clear from the figure, the safety margin varies depending on the amount of roll misalignment. Changes in this safety margin can be understood through the alignment evaluation described above.

Therefore, based mainly on the roll alignment and the molten steel composition values, it is possible to operate at a casting speed close to the limit value that allows stable operation.

In addition, in the case of following the example in FIG. 2, the line X is the casting speed curve conventionally determined taking into account the safety factor.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to operate at a casting speed close to the limit of safe operation, and therefore productivity is improved, and even if an unexpected accident occurs during casting, it can be sufficiently coped with.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an example of equipment for carrying out the method of the present invention, and Figure 2 shows that the safety margin is determined by the relationship between steel composition (susceptibility, which is an indicator of internal cracking) and casting speed, depending on the degree of roll irregularity. FIG. 3 is a diagram showing the relationship between roll misalignment and pull-out resistance. 5... Pinch roll, 6... Drive motor, 7...
Load meter, 8... Casting speed control device, 9... External information (molten steel composition value, etc.), lO... Casting speed detector. Imaginary diagram 1

Claims (1)

[Claims] (1) Determine the withdrawal resistance of the slab from the load of the pinch roll drive motor of the continuous casting machine, estimate the roll alignment of the pinch rolls from this value, and combine this estimated alignment with the predetermined casting speed and steel composition. Continuous casting characterized in that a critical casting speed at which casting safety is ensured is determined based on the casting safety determined by the relationship between Casting speed control method.