JPS6072652A - Electromagnetic stirrer - Google Patents

Abstract

PURPOSE:To obtain a casting body having a good surface by making the distance between the iron cores of an electromagnetic stirrers disposed on the outside of the side wall of a casting mold and the molten steel in the mold gradually larger from the upstream side to the downstream side of the molten metal thereby weakening stirring in the part where waving arises and stirring thoroughly the other part. CONSTITUTION:When electric current is passe to a coil 15, stirring force is generated by a moving magnetic field and molten steel 16 flows but as the distance between iron cores 14 and the molten steel 16 increases gradually from the upstream side of the molten steel toward the downstream side and therefore the magnetic flux density attenuates exponential-functionally and the stirring force in the corner parts 18 where the molten steel 16 changes the direction of flow as shown by the lengths of arrows 17 is made smaller than the stirring force in other places. The flow rate in said parts decreases and therefore waving does not arise. The stirring force is made optionally adjustable by adding a mechanism to vary the distance between the iron cores 14 and the mold to obtain a higher effect.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides an electromagnetic stirrer for stirring m@ in a mold by electromagnetic force, reducing the presence of non-metallic substances inside the slab, and improving the quality of the surface of the slab. Regarding.

[Technical background of the invention]

In recent years, continuous casting has become common in the steel manufacturing industry, and as a result, electromagnetic stirrers are increasingly being used. For example, there is a structure as shown in FIGS. 1 and 2 as a means for stirring molten steel in a mold having a rectangular cross section.

That is, the mold 1 is surrounded by a copper plate 2, a backup grate 3'f is attached to the side wall in the longitudinal direction of the copper plate 2, and an iron plate 4 is installed at a certain distance outside all of the backup grate 3. An electromagnetic stirrer 6 consisting of a coil 5 wound around the iron core 4 is provided, and by passing a current through the coil 5, a moving magnetic field is generated as shown by the arrow 7, and the moving magnetic field stirs the molten steel 8. Stirring is performed by flowing in the direction of a moving magnetic field.

[Problems with background technology]

In the above-mentioned electromagnetic stirring, if the stirring force is increased, the nonmetallic inclusions inside the slab can be reduced, the quality of the slab surface can be improved, and the stirring time can be shortened.

Here, the stirring force for the molten steel 8 is generally proportional to the square of the magnetic flux density, the flow rate of the molten steel 8 is proportional to the square root of the stirring force, and the magnetic flux density varies with the distance from the iron core 4, as shown in Figure 3. It increases or decreases exponentially depending on the amount. (Although Figure 3 shows the increase/decrease in magnetic flux density according to the distance from the iron core surface for one electromagnetic stirrer, a pair of electromagnetic stirrers were arranged to face each other on both sides of the mold.) The same thing can be said if we consider each unit individually.] L fr knee 7% In order to increase the stirring force by increasing the current flowing downstream of the coil, or by increasing the distance between the iron core and the molten steel. Just make it smaller.

However, if the stirring force is simply increased to increase the flow rate of the molten steel, the flow direction of the molten steel will suddenly change at the corner 9 of the mold, causing a waving phenomenon of the molten steel. When the waving phenomenon occurs, scratches occur on the surface of the slab, or slag floating on the surface of the molten steel gets caught up in the molten steel in the mold, leading to an increase in the number of nonmetallic inclusions inside the slab. As a result, the provision of the electromagnetic stirrer actually has the opposite effect.

In order to eliminate this drawback, the length of the moving magnetic field generated by the electromagnetic stirrer is made shorter than the slug width, thereby reducing the magnetic flux density at the corners of the mold and reducing the flow velocity of the molten steel colliding with the mold wall. Conceivable.

However, when applying such a method to a continuous casting machine that allows the slab dimensions to be changed, an electromagnetic stirrer is installed in advance according to the maximum slag width, and a switching means such as a tap is used to Depending on the slab size, the moving magnetic field generation length 4
It needs to change.

Therefore, the tap switching device tX requires a space for taking out the tag, and furthermore, the moving magnetic field generation length is predetermined by the tap position, making it inflexible.

In addition, if the length of the electromagnetic stirrer is increased, the range of influence of the moving magnetic field will be narrowed, making it sufficient for the stirrup. The agitation force in the area where IA agitation force is desired is weak, which is a problem especially when applying tap switching to small slug widths, and the drawback is that the electric capacity must be increased. be.

[Purpose of the invention]

The present invention has been made to improve the above-mentioned conventional drawbacks, and its purpose is to increase the stirring force in areas that require sufficient stirring, and to increase the stirring power in areas where undulation is likely to occur. The object of the present invention is to provide an electromagnetic stirrer that can reduce the amount of non-metallic material involved and produce a cast product with a good surface by reducing the stirring force.

[Summary of the invention]

In order to achieve the above object, the present invention provides an electromagnetic stirrer disposed outside the side wall of the mold, and a distance between the iron core of one electromagnetic stirrer and the molten steel in the mold from the upstream of the flow of the molten steel. The outline is that it gradually increases in size as it goes downstream.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

FIG. 4 shows a plan cross section of the casting machine, and the outer wall of the mold 1o, which has a rectangular cross section, is composed of a copper plate 11.
Backup grates 12 are attached to the outer surfaces of the left and right side walls of the mold 10 in the longitudinal direction. A pair of left and right electromagnetic stirrers 13, 13 are arranged apart from these backup grates 12, 12.◎ These electromagnetic stirrers 13 consist of an iron core 14 and a coil 15 wound around this iron core 14. The left and right electromagnetic stirrers 13, 13 are arranged so that the stirring directions are opposite to each other, in other words, the moving magnetic fields are generated in opposite directions.
has been done. The length of the iron core 14 is approximately equal to the length of the side wall, and the distance between the iron core 14 and the molten steel 16 in the mold 10 becomes smaller in the upstream part of the molten steel made to flow by the moving magnetic field, and in the downstream part. As a result, the 14 cores are arranged at an angle with respect to the backup grate 12.

In the above, when the current k ptr is applied to the coil 15, stirring force is generated by the moving magnetic field, which causes the molten steel 16 to flow, but as the molten steel flows from upstream to downstream,
As the iron core 14 and the molten steel gradually separate, the magnetic flux density decays exponentially as described above, and as can be seen from the length of the arrow 17, the stirring force at the corner 18 where the molten steel 16 changes its flow direction increases. It is smaller than other parts and the flow velocity is lower, so waving does not occur.

Incidentally, the above is an example of the implementation of the present invention, and the present invention is not limited to the above. For example, in the illustrated example, two agitators are installed so that the stirring directions are opposite, but the number of agitators may be arbitrary, and if multiple agitators are installed, the stirring directions may be the same. is also possible.

Further, in the embodiment, a type in which the iron core 14 is fixed to the mold is shown, but a mechanism for controlling the distance between the iron core 14 and the mold (copper plate) may be added. This method is more effective because the stirring force can be adjusted as desired.

〔Effect of the invention〕

As explained above, according to the present invention, in an electromagnetic stirrer for stirring molten steel in a mold having a rectangular cross section, the distance between the iron core of the electromagnetic stirrer and the molten steel in the mold is made equal to the distance between the iron core of the electromagnetic stirrer and the molten steel in the mold, so that the molten steel flows. It is possible to prevent the occurrence of waving by reducing the flow velocity of the molten steel only at corners where the molten steel suddenly changes, and sufficient stirring can be performed at other locations without reducing the flow velocity of the molten steel. Therefore, it is possible to obtain a cast product with less inclusion of non-metallic inclusions and an extremely good surface.

In addition, only the relative distance between the iron core and the molten steel ((therefore, stirring chips can be controlled), the structure is simple and highly flexible, and it can be applied to various fA persimmons, making it possible to change the slab dimensions. It exhibits many effects such as being extremely suitable for continuous casting machines.

[Brief explanation of drawings]

Fig. 1 is a longitudinal side view of a casting machine using a conventional electromagnetic stirrer, Fig. 2 is a plan sectional view of the same casting machine, and Fig. 3 is a graph showing the relationship between the distance from the iron core surface and magnetic flux density. FIG. 4 is a plan cross-sectional view of a casting machine to which the 'itja stirrer of the present invention is applied. 1.10... Mold, 2.11... Copper plate, 3.12.
... Punk up slate, 4.14 ... Iron core, 5.
15... Coil, 6.13... Electromagnetic stirrer, 8.1
6... Molten steel. Applicant's agent Kiyoshi Inomata

Claims (1)

[Claims] 1. In an electromagnetic stirrer consisting of an iron core disposed outside the side wall of a mold having a rectangular cross-section and a coil wound around the iron core, molten steel flows along the inner surface of the side wall. The distance between the molten steel and the iron core is gradually varied along the flow direction of the molten steel so that the distance between the molten steel and the iron core in the downstream part is larger than the distance between the molten steel and the iron core in the upstream part. Electromagnetic stirrer. 2. The electromagnetic stirrer according to claim 1, wherein the iron cores are respectively disposed on the outside of both side walls of the mold.