JPS60162559A - Method for controlling electromagnetic stirring in continuous casting machine - Google Patents

Abstract

PURPOSE:To permit easy formation of an equiaxed crystal rate and to improve the quality of a billet by using adequately and selectively rotational stirring and translational stirring according to the flattening ratio in the unsolidified part of the billet and the thickness of the unsolidified part. CONSTITUTION:The magnetic field directions 4 of electromagnetic stirrers 3, 3' facing each other are made the same and translational stirring is executed in the case of >=2 the flattening ratio n=(B-2d)/(A-2d) in the unsolidified part of a billet on the front face of the electromagnetic stirrers (where, A: the width on the short side of the billet, B: the width on the long side of the billet, d: the thickness of the shell) and <150mm. the thickness (a) in the unsolidified part. The magnetic field directions are reversed in other cases except said case and rotational stirring is executed. The equiaxed crystal rate is thus easily formed and the quality of the billet is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of application in M industry) The present invention relates to an electromagnetic stirring method in continuous casting and casting using a linear motor type electromagnetic stirring device.

(Prior art) The electromagnetic stirring method of the continuous @ machine is mainly applied to pieces with a small aspect ratio (long side length / short side length), such as blooms, by generating a rotational flow in the unsolidified part to prevent center segregation. There is a rotational agitation method that aims to improve this, and a translational agitation method that is applied to slabs with a high aspect ratio of the diagonal profile.

In the case of a slab with a large aspect ratio, the cross-sectional shape of the unsolidified part of the slab becomes more round as solidification progresses.
Rotary stirring cannot provide smooth rotational flow. or,
When the thickness of the unsolidified area becomes thinner as solidification progresses, in rotary stirring, the moving directions of the magnetic poles of the electromagnetic stirring devices that face each other across the pieces are opposite, so the thickness of the unsolidified area becomes thinner in the center of the unsolidified area. When the flows of molten copper come into contact with each other, a shearing force acts on the boundary that hinders the flow of each other, and the agitation flow may not be sufficiently absorbed.

In addition, even when translational stirring is applied to a bloom with a small aspect ratio, there are six points in which the agitation is not sufficient. I'm sorting it out. However, at present, stirring methods are simply used depending on the shape of slabs, blooms, etc. each year.

There are various prior art related to these, such as the one shown in Japanese Patent Publication No. 52-2367. That is, regarding conventional stirring using an electromagnetic stirring device, there are descriptions of translational stirring and rotational stirring, respectively. However, there is no description of the aspect ratio of the slab, the unsolidified thickness, and the specifics of translational and rotational stirring. The same applies to other known techniques.

(Objective of the Invention) In view of the above-mentioned circumstances, the object of the present invention is to always perform stirring most centrally segregated rX% by optimally using rotational stirring and translational stirring.

(Structure and operation of the invention) The present invention gradually changes the surface shape of the unsolidified heir of the previous electromagnetic stirring device, has an unsolidified aspect ratio of 2.0 or more, and has an unsolidified thickness of 1. Translational stirring was performed when the pressure was less than 150W1+1, and rotational stirring was performed under other conditions. Yes, A is the width of the short side of the slab, B is the width of the long side of the slab, d
is the shell thickness. Here, A and B are intertwined with @-type dimensions, and d is a known means, for example, γm? There is an estimation method based on calculations based on process information.

As an example of calculation, There is a method to approximate it by a(t) = KJτ.

Also, K is the cooling water current density (-3, 2 times), and t
is the elapsed time ta] (see) after casting.

From the short side width A, long side width B, and shell thickness d obtained in this way, the unsolidified part aspect ratio n and the solidified thickness a can be calculated by the following formula:
It is determined by a-A-2d.

The relationship between this unsolidified aspect ratio n, the stirring method (rotation, translation), the quality index of the candy pieces, and the solid thickness a is shown in Figure 2 as a result of various tests. A samurai is a samurai.

That is, the horizontal axis represents the aspect ratio n of the unsolidified portion, and the vertical axis represents the equiaxed crystallinity ratio m, and the comparison is made for each unsolidified thickness.

Here, the equiaxed crystallinity ratio m is It is expressed as

When the equiaxed crystal ratio mlJ''=1.0, there is no difference in the generation of equiaxed crystal ratio . It is easy to obtain crystallinity, and m
When the ratio is 0, it is easier to obtain a higher equiaxed crystal ratio by rotary stirring.

As is clear from Fig. 2, when the unsolidified aspect ratio n exceeds 2.0 and the unsolidified thickness a is less than 150 mm, translational stirring is performed (・, for other conditions, rotational stirring is performed. By doing this, it is possible to obtain a more vortex equiaxed crystallinity.

FIG. 3 is an explanatory diagram of rotary stirring. By setting the magnetic field directions 4 of electromagnetic stirring devices 3 and 3' installed before and after the slab in opposite directions, a rotary stirring flow 5 is applied to the unsolidified portion 2. bring about

FIG. 4 is an explanatory diagram of translational stirring, and shows the electromagnetic stirring device 3.
By making the directions 4 of the magnetic fields 3' the same, a translational stirring flow 5 is generated.

(Example) While casting a slab with C: 0.20% and slab size: 247 x 330, translational stirring was performed using an electromagnetic stirring device in the manner shown in FIG. 4 at a point where the shell thickness d=90 m.

The aspect ratio n of the unsolidified part was , and the thickness a of the unsolidified part was 67 va. The equiaxed crystal ratio at this time was 36%, and a high equiaxed crystal ratio was obtained.

(Comparative example) A slab of C: 0.20%, slab size: 247 x 330 was rotary stirred at the shell thickness d: 9 Q during casting using the method shown in Figure 3 using an electromagnetic stirring device. . The aspect ratio n of the unsolidified portion was n = 2.23, the unsolidified thickness a = 57 rran, and the equiaxed crystal ratio formed was 26%.

(Effects of the Invention) As an effect of implementing the present invention, rotational stirring and translational stirring can be appropriately used depending on the aspect ratio of the unsolidified part of the slab and the thickness of the unsolidified part, and the generation of equiaxed crystallinity can be improved. Make it easy,
This contributes to improving the quality of slabs.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the slab, Figure 2 is a chart showing the relationship between the aspect ratio of the unsolidified part and the equiaxed crystallinity ratio for each unsolidified thickness.
The figure is an explanatory diagram of rotational agitation, and FIG. 4 is an explanatory diagram of translational agitation. 1: Coagulated area 2: Unsolidified area 3.3': Electromagnetic stirrer 4: Magnetic field direction 5: Stirring flow Figure 1 4Ja hand ratio (n) of unsolidified area

Claims (1)

[Claims] In continuous casting using an electromagnetic stirring device, the unsolidified part aspect ratio n of the section in front of the electromagnetic stirring device is 2.0 or more,
If the unsolidified thickness a is less than 150 mm, translational stirring is performed with the magnetic poles of the opposing electromagnetic stirring devices moving in the same direction; otherwise, the moving direction of the magnetic poles of the opposing electromagnetic stirring devices is the same. An electromagnetic stirring method in a continuous casting machine characterized by performing rotational stirring in the opposite direction.